UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10‑K

(Mark One)

☒ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended December 31, 2018.

OR

☐TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from                    to

Commission file number 001‑38650

Y‑mAbs Therapeutics, Inc.

(Exact name of registrant as specified in its charter)

 

Registrant’s telephone number, including area code (646)‑885‑8505

Securities registered pursuant to Section 12(b) of the Act:

 

Securities registered pursuant to Section 12(g) of the Act: None

NONE

(Title of class)

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.

 

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.

 

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.

 

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files).

 

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K (§299.405 of this chapter) is not contained herein, and will not be contained, to the best of the registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10‑K or any amendment to this Form 10‑K. ☒

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non‑accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer”, “accelerated filer”, “smaller reporting company” and “emerging growth company” in Rule 12b‑2 of the Exchange Act.

 

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.    ☒

Indicate by check mark whether the registrant is a shell company (as defined by Rule 12b‑2 of the Exchange Act).

 

The aggregate market value of the common stock held by non-affiliates of the registrant, based on the closing price of a share of common stock on September 21, 2018 as reported by the NASDAQ Global Select Market on such date was approximately $301.6 million. The registrant has elected to use September 21, 2018, which was the initial trading date on the NASDAQ Global Select Market, as the calculation date because on June 30, 2018 (the last business day of the registrant’s most recently completed second fiscal quarter), the registrant was a privately held company. Shares of the registrant’s common stock held by each executive officer, director and holder of 5% or more of the outstanding common stock have been excluded in that such persons may be deemed to be affiliates. This calculation does not reflect a determination that certain persons are affiliates of the registrant for any other purpose. The number of outstanding shares of the registrant’s common stock as of March 14, 2019 was 34,193,666.

Documents Incorporated by Reference:

Portions of the Registrant’s Definitive Proxy Statement relating to the 2019 Annual Meeting of Stockholders, which will be filed with the Securities and Exchange Commission within 120 days after the end of the Registrant’s fiscal year ended December 31, 2018 are incorporated by reference into Part III of this Report.

 

 

 

 

TABLE OF CONTENTS

 

FORWARD LOOKING STATEMENTS.

This Annual Report on Form 10‑K contains forward-looking statements that involve substantial risks and uncertainties. All statements, other than statements of historical facts, contained in this Annual Report on Form 10‑K, including statements regarding our business strategy, future operations and results thereof, future financial position, future revenue, projected costs, prospects, current and prospective products, product approvals, research and development costs, current and prospective collaborations, timing and likelihood of success, plans and objectives of management, expected market growth and future results of current and anticipated products, are forward-looking statements. These statements involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements. The words “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “contemplate,” “intend,” “may,” “might,” “plan,” “potential,” “predict,” “project,” “should,” “target,” “will,” “would” and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words.

 

 

These forward-looking statements include, among other things, statements about:

 

 

We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in the forward-looking statements we make. We have included important factors in the cautionary statements included in this Annual Report on Form 10‑K, particularly in the “Risk Factors” section, that could cause actual results or events to differ materially from the forward-looking statements that we make. Our forward-looking statements do not reflect the potential impact of any future acquisitions, mergers, dispositions, collaborations, joint ventures or investments that we may make or enter into.

The forward-looking statements contained in this Annual Report on Form 10‑K are made as of the date of this Annual Report on Form 10‑K, and we undertake no obligation to publicly update or review any forward-looking statement, whether as a result of new information, future developments or otherwise.

 

PART I

 

ITEM 1.          BUSINESS.

Overview

We are a late‑stage clinical biopharmaceutical company focused on the development and commercialization of novel, antibody‑based therapeutic products for the treatment of cancer. We have a broad and advanced product pipeline, including two pivotal‑stage product candidates—naxitamab and omburtamab—which target tumors that express GD2 and B7‑H3, respectively. We are developing naxitamab for the treatment of pediatric patients with relapsed or refractory, or R/R, high‑risk neuroblastoma, or NB, and radiolabeled omburtamab for the treatment of pediatric patients with central nervous system, or CNS, leptomeningeal metastases, or LM, from NB. NB is a rare and almost exclusively pediatric cancer that develops in the sympathetic nervous system and CNS/LM is a rare and usually fatal complication of NB in which the disease spreads to the membranes, or meninges, surrounding the brain and spinal cord in the CNS.

We expect to submit a BLA for each of our two lead product candidates in 2019, with a goal of receiving approval by the FDA in 2020. We plan to commercialize both of our lead product candidates in the United States as soon as possible after obtaining FDA approval, if such approval occurs. Additionally, we have two omburtamab follow‑on product candidates in pre‑clinical development, omburtamab‑DTPA and huB7‑H3, a humanized version of omburtamab, each targeting indications with large adult patient populations. In addition, we have initiated a Phase I trial with our huGD2 BsAb product candidate for the treatment of refractory GD2 positive adult and pediatric solid tumours, thereby addressing large patient populations. We are also advancing a pipeline of novel BsAbs through late pre‑clinical development, including our huCD33‑BsAb product candidate for the treatment of hematological cancers expressing CD33, a transmembrane receptor expressed on cells of myeloid lineage. We believe that our BsAbs have the potential to result in improved tumor‑binding, longer serum half‑life and significantly greater T‑cell mediated killing of tumor cells without the need for continuous infusion. Our mission is to become the world leader in developing better and safer antibody‑based pediatric oncology products addressing clear unmet medical needs and, as such, have a transformational impact on the lives of patients. We intend to advance and expand our product pipeline into certain adult cancer indications either independently or in collaboration with potential partners.

Naxitamab is a recombinant humanized immunoglobulin G, subtype 1or IgG1κ, monoclonal antibody or mAb that targets ganglioside GD2, which is highly expressed in various neuroectoderm‑derived tumors and sarcomas. Naxitamab is currently being studied in several clinical trials, including pivotal‑stage multicenter development (Study 201) and a Phase 1/2 clinical trial (Study 12‑230) for the treatment of pediatric R/R high‑risk NB, a Phase 2 clinical trial (Study 16‑1643) in front‑line NB, a pilot study (Study 17‑251) of chemoimmunotherapy for high‑risk NB and a Phase 2 clinical trial (Study 15‑096) for relapsed osteosarcoma. We believe that naxitamab has multiple potential advantages over other GD2‑targeting antibody‑based therapies. In particular, its modest toxicity allows for doses two‑and‑a‑half times greater than existing GD2‑targeting antibody‑based therapies. Unlike currently approved GD2‑targeting therapies for NB, which require 10 to 20 hours of infusion and hospitalization for several days, naxitamab is administered in

approximately 30 minutes in an outpatient setting. We believe this significantly shorter administration time is an important advantage considering the overall pain associated with treatment.

In the dose escalation part of Study 12‑230 for naxitamab, which together with Study 201 is expected to form the primary basis of our BLA submission, we achieved an overall response rate, or ORR, of 57% in 23 patients with pediatric R/R high‑risk NB who at study entry had evaluable tumors and no evidence of progression of disease, or PD. Based on our discussions with the FDA, the profile of the non‑PD R/R high‑risk NB pediatric patients in Study 12‑230 is representative of the intended patient population for naxitamab’s target indication. The corresponding ORRs will form the primary objective of our pivotal study (Study 201). Additionally, based on our discussions with the FDA, we believe that naxitamab may qualify for accelerated approval if we can demonstrate a 30% ORR (which is significantly different from a 20% ORR at a 95% confidence interval, or CI) with a duration of response of 12‑weeks or longer. We have proposed to the FDA that, pending comparability between the study population in Study 12‑230 and Study 201, the data from the two studies may be pooled for analysis. Naxitamab has been administered to more than 200 patients to date, who will form the safety portion of our planned BLA submission. In May 2018, we reported topline results from the Phase 2 part of Study 12‑230. The endpoints of this part of the study were complete tumor response (also known as complete remission), or CR, or partial tumor response, or PR. Complete tumor response is the total disappearance of a tumor  and partial tumor response is a decrease in the size of a tumor, or in the extent of cancer in the body, in response to the treatment. This data continued to show response rates at the same levels as in the dose escalation part of the study with 13 of 15 evaluable, or 87% of, primary refractory patients responding and 7 of 23 evaluable, or 30% of, secondary refractory patients responding. We expect to submit the BLA for naxitamab for R/R high‑risk NB in 2019. Currently, there are no FDA‑approved therapies for primary refractory or second‑line pediatric NB patients. Naxitamab has also received orphan drug designation, or ODD, and rare pediatric disease designation, or RPDD, from the FDA for the treatment of NB. In addition, on August 20, 2018, naxitamab received breakthrough therapy designation, or BTD, in combination with GM‑CSF, for the treatment of high‑risk NB refractory to initial therapy or with incomplete response to salvage therapy in patients greater than 12 months of age with persistent, refractory disease limited to bone marrow with or without evidence of concurrent bone involvement. Finally, in November 2018, the European Commission granted orphan medicinal product designation, or (“OMPD”) for naxitamab for the treatment of NB. While our current clinical efforts for naxitamab are focused on rare pediatric cancers, we believe that we can potentially expand its application to the treatment of adults with cancers that express GD2. We estimate that there were more than 200,000 new adult patients diagnosed with GD2‑positive cancers in the United States in 2017.

Omburtamab is a murine monoclonal antibody that targets B7‑H3, an immune checkpoint molecule that is widely expressed in tumor cells of several cancer types. 131I‑omburtamab, which is omburtamab radiolabeled with Iodine‑131, is currently being studied in several clinical trials including pivotal‑stage development (Study 101) and a Phase 1 clinical trial (Study 03‑133) for the treatment of pediatric patients who have CNS/LM from NB. As of August 2017, 93 patients with pediatric CNS/LM from NB had been treated with 131I‑omburtamab in Study 03‑133. An analysis of these 93 patients demonstrated a median overall survival, or OS, of 47 months (including an estimated five‑year OS of approximately 43%), as compared to historical median OS of approximately six months. We have proposed to the FDA that, pending comparability between study population in Study 03‑133 and Study 101, data from both studies may be pooled for analysis for our planned BLA submission. 131I‑omburtamab has received ODD and RPDD from the FDA for the treatment of NB, and BTD for the treatment of pediatric patients who have CNS/LM from NB. In 2019, we expect to submit the BLA for 131I‑omburtamab for CNS/LM from NB.

124I‑omburtamab, which is omburtamab radiolabeled with Iodine‑124, is currently being studied for the treatment of Diffuse Intrinsic Pontine Glioma, or DIPG. 131I‑omburtamab is currently being studied for the treatment of Desmoplastic Small Round Cell Tumors, or DSRCT. Both DIPG and DSRCT are rare, and often fatal, cancers. While our current clinical efforts are focused on rare pediatric cancers, we believe we can potentially expand omburtamab’s application to the treatment of CNS/LM resulting from other adult and pediatric solid tumors expressing B7‑H3 and the underlying solid systemic tumors. We estimate that, in the United States and the EU in 2017, there were more than 30,000 new patients diagnosed with cancer that has metastasized to the CNS/LM, of which the vast majority express B7‑H3.

We have initiated Study 101 and Study 201 to form the primary basis for our planned BLAs, to establish comparability of study population and pharmacokinetics analysis with Study 03‑133 and Study 12‑230, respectively, and

to satisfy the confirmatory study and post‑marketing requirements by the FDA. If the results from Study 101 and Study 201 fail to demonstrate comparability to the satisfaction of the FDA and other comparable regulatory authorities, this may lead to a delay in, or otherwise adversely affect, such clinical trials, including the timing of submission of BLAs.

We have two additional product candidates targeting B7‑H3 in pre‑clinical development, omburtamab‑DTPA (diethylenetriamine pentaacetate), a Lutetium‑177 conjugated antibody, and huB7‑H3, a humanized version of omburtamab, each targeting indications with pediatric and large adult patient populations where we believe there is a significant unmet medical need. We are also advancing a pipeline of novel BsAbs through late pre‑clinical development, including our huCD33‑BsAb product candidate for the treatment of hematological cancers expressing CD33, a transmembrane receptor expressed on cells of myeloid lineage. As of December 10, 2018, FDA cleared the Investigational New Drug (“IND”) application for the humanized bispecific GD2 antibody, and a Phase I trial was initiated with our huGD2‑BsAb product candidate for the treatment of refractory GD2‑positive adult and pediatric solid tumors. In pre‑clinical studies, huGD2‑BsAb has demonstrated the potential for improved tumor‑binding, longer serum half‑life and significantly greater T‑cell mediated killing compared to existing bispecific constructs. 

We currently have four active INDs related to our product candidates. The table below sets forth the product candidate, date of the initial submission of the IND to the FDA, as well as the current sponsor, the subject matter and the current status of each such IND.

 

 

In October 2017, the FDA issued a partial clinical hold on our IND for naxitamab. A partial clinical hold, as opposed to a full clinical hold, is a delay or suspension of only a specific part of the clinical work requested under the IND, which allows otherwise unaffected parts of the clinical work to proceed under the IND. The FDA stated that the proposed acceptance criterion for the ADCC‑CD16, ADCC‑CD32, and CDC assays were too wide to provide sufficient control over these attributes, which are critical for safety and efficacy. ADCC and CDC refer to antibody dependent cell‑mediated cytotoxicity and complement‑dependent cytotoxicity, respectively. We submitted a response to the FDA in March 2018, and met with the FDA in April, 2018. Subsequently, we submitted a complete response to the partial clinical hold to the FDA in May 2018 and the partial clinical hold was removed in June 2018.

We have exclusive rights to MSK’s rights in all of our current product candidates under our 2015 license agreement, or the MSK License, with Memorial Sloan Kettering Cancer Center, or MSK. The MSK License also provides us with non‑exclusive access to technology that involves the creation of a novel human protein tag that can potentially dimerize, or link together, bispecific T‑cell engagers, or BiTEs. We refer to this technology as the MULTI‑TAG technology. We plan to create a broad platform of dimerized BiTEs using the MULTI‑TAG technology and are currently collaborating with MSK on several MULTI‑TAG product candidates. We believe that our strong relationship with MSK, one of the world’s leading cancer treatment centers, and our access to certain of MSK’s

technologies and substantial research capabilities affords us several competitive advantages. In addition, we believe that our relationship with MSK may help us with respect to patient recruitment for clinical trials. Under a separate 2017 CD33 license agreement with MSK, or the MSK CD33 License, we have a worldwide, sub‑licensable license to MSK’s rights in certain patent rights and intellectual property rights related to certain know‑how to develop, make, and commercialize licensed products and to perform services for all therapeutic and diagnostic uses in the field of cancer diagnostics and cancer treatments in connection with certain CD33 antibodies developed in the laboratory of a specific principal investigator at MSK and constructs thereof.

Our management team has substantial public company experience and extensive knowledge in the field of antibody oncology drug development, manufacturing and commercialization. Thomas Gad, our Founder, Chairman, President and Head of Business Development, co‑founded Singad Pharma ApS, a Danish pharmaceutical and distribution company, where, as part of senior management, he gained more than 12 years of experience in the pharmaceutical industry, including in business development, financing and licensing negotiations and manufacturing site qualification. In 2006, Mr. Gad’s then two year old daughter was diagnosed with high‑risk NB and was treated at MSK with the murine version of naxitamab. In 2009, she relapsed with CNS/LM from NB and again was treated at MSK, this time with 131I‑omburtamab. Since then, she has been disease free. Our Chief Executive Officer, Dr. Claus Juan Møller San Pedro, was the co‑founder of Genmab A/S, one of the largest public biotechnology companies in Europe, where he served as Executive Vice President and Chief Operating Officer for approximately 10 years. Our Chief Financial Officer, Bo Kruse, served as Genmab’s Chief Financial Officer and was directly involved in several of Genmab’s financing rounds including Genmab’s initial public offering. Our Senior Vice President and Chief Operating Officer, Joris Wiel Jan Wilms, has extensive industry experience in clinical development, primarily within oncology and hematology indications, and was responsible for overseeing several first‑in‑human studies and pivotal clinical trials, leading to the approval of two monoclonal antibody‑based products while at his previous positions as Vice President—Clinical Trial Services and Pharmacovigilance at KLIFO A/S, and Associate Director of Clinical Development at Genmab. Our Senior Vice President and Head of Technical Operations, Dr. Torben Lund‑Hansen, has substantial experience in antibody process development and manufacturing. Dr. Lund‑Hansen held similar positions at Genmab where he was responsible for sourcing clinical and commercial drug substance and product manufacturing. Our Senior Vice President and Chief Medical Officer, Dr. Steen Lisby, also comes from Genmab where he was Vice President, Medical Lead until July 2017 when he joined our company. Dr. Lisby also has substantial experience in antibody drug development. In addition, since our inception in April 2015, we have raised approximately $230.0 million from our initial public offering and from our founding investors and prominent biotechnology institutional investors, including HBM Healthcare Investments (Cayman) Ltd. and funds advised by or affiliated with Scopia Capital Management LP and Sofinnova Investments, Inc., among others, and as of December 31, 2018, we had cash and cash equivalents of $147.8 million.

Our Pipeline

The following table sets forth our product candidates and their current development stages, estimated development timelines and anticipated milestones.

 

Our Business Strategy

Our mission is to become the world leader in developing better and safer antibody‑based pediatric oncology products addressing clear unmet medical needs and, as such, have a transformational impact on the lives of patients. We intend to advance and expand our product pipeline into certain adult cancer indications either independently or in collaboration with potential partners.

Key elements of our strategy to achieve this goal are:

Current Approaches to the Treatment of Cancer

Cancer Overview

Cancer is a broad group of diseases in which cells divide and grow in an uncontrolled fashion, forming malignancies that can invade other parts of the body. Cancers can subsequently spread throughout the body by processes known as invasion and metastases. Cancer cells that arise in the lymphatic system and bone marrow, or BM, are referred to as hematological malignancies. Cancer cells that arise in other tissues or organs are referred to as solid tumors.

Cancer is a major public health problem in the United States and worldwide. The American Cancer Society, or ACS, estimated that approximately 40% of all men and women in the United States will be diagnosed with cancer during their lifetime (based on 2011‑2013 data). According to the U.S. Centers for Disease Control, cancer is currently the second leading cause of death in the United States, and is expected to surpass heart disease as the leading cause of death in the next several years. Although progress has been made in the diagnosis and treatment of cancer, the ACS estimates that over 1.6 million new cancer cases will be diagnosed in the United States and over 600,000 people will have died from cancer in 2017. Thus, there remains a significant need for novel and improved treatment options for cancer patients.

Cancer treatment has traditionally included chemotherapy, radiation, hormone therapy, surgery or a combination of these approaches. While small molecule chemotherapy agents and cytotoxic agents have demonstrated efficacy in treating certain types of cancers, they can also cause toxicities that may lead to life‑threatening consequences, lower quality of life or untimely termination of treatment. Furthermore, these treatments are only partially effective in solid tumors, in part because the maximal achievable doses are limited by systemic toxicity, which consequently hinders the prospects of long‑term remission in patients. In the last 20 years, cancer research and treatment has shifted to more targeted therapies, such as monoclonal antibodies, and immuno‑oncology, a new field of cancer therapy focused on enhancing antitumor immune responses.

Advances in understanding the immune system’s role in treating cancer have established immunotherapy, or the practice of harnessing immune system functions to combat malignant cell growth, as an important treatment approach. Cancer immunotherapy began with treatments that nonspecifically activated the immune system and had limited efficacy and/or significant toxicity. In contrast, new immunotherapy treatments can activate specific, key immune cells, leading to improved targeting of cancer cells, efficacy, and safety.

Cancer therapies are sometimes characterized as front‑line, second‑line, or third‑line, and the FDA often approves new therapies initially only for third‑line use. When cancer is detected early enough, front‑line therapy is sometimes adequate to effectively treat the cancer or prolong life. Whenever front‑line therapy, usually chemotherapy, radiation therapy, surgery, or a combination of these, proves unsuccessful, second‑line therapy may be administered. Second‑line therapies often consist of more chemotherapy, surgery, antibody drugs, tumor‑targeted therapies such as monoclonal antibodies and small molecule inhibitors, or a combination of these. Third‑line therapies can include bone marrow transplantation, antibody and small molecule targeted therapies, more invasive forms of surgery, and new technologies.

Immune System and Introduction to Antibodies

The immune system is often described as having two main branches—innate (non‑specific) and adaptive (acquired) immunity. It defends against invading pathogens such as viruses, parasites, and bacteria, and provides surveillance against cancers. The innate immune system is the initial response to an infection, and the response is the same every time regardless of prior exposure to the infectious agent. The adaptive immune system includes B‑cells, which secrete antibodies and T‑cells, which can be either helper T‑cells, supressor T‑cells or cytotoxic T‑cells.

An antibody, also known as an IgG, is a large, Y‑shaped protein produced mainly by plasma cells in response to foreign substances, such as viruses or cancer cells. Antibodies circulating in the bloodstream function by binding to the target or antigen they are generated to fight. The binding process involves a lock‑and‑key mechanism in which the

paratope region of the antibody, analogous to a lock, binds to one particular epitope of a specific antigen, analogous to a key. This allows the antibody to bind to a specific antigen with precision, thereby attacking only its intended target.

Different types of antibodies include: (i) Monoclonal Antibodies—laboratory‑made antibodies typically derived from immune cells of mammals that have been immunized with a desired antigen and are all clones of a unique parent; (ii) Humanized/Chimeric Antibodies—antibodies with both mouse and human antibody proteins that are humanized (i.e., engineered to replace mouse components with more human components) to reduce the immune system response against antibodies identified as foreign (i.e., from a different species) in nature; (iii) Naked Monoclonal Antibodies—antibodies without any drug or radioactive material attached and which are the most common type of antibodies in treating cancer; (iv) Antibody Drug Conjugates, or ADCs—monoclonal antibodies that are joined to a chemotherapy drug, a radioactive particle or cancer cell killing agent, in which the monoclonal antibody is used as a homing device to deliver these substances directly to the cancer cell; and (v) Bispecific antibodies comprised of two different monoclonal antibody constructs, which allows the antibody to bind to two specific therapeutic targets at the same time, typically one target on the tumor cell and one target on an immune system cell.

Antibodies may function through multiple mechanisms simultaneously, including binding to cancer cells and flagging for B‑cells and T‑cells to more easily detect the target, or delivering radiation treatment by acting as a vehicle to transfer small radioactive particles directly to the cancer cells and to minimize the effect of radiation on normal cells. Other mechanisms include triggering cell‑membrane destruction, preventing cell growth or blood vessel growth, blocking immune system inhibitors, directly attacking cancer cells and delivering chemotherapy or binding cancer cells and immune cells simultaneously.

Studies have shown that, as a drug class, antibodies have transformed oncology treatment and include some of the best‑selling therapies on the biopharmaceutical market. Drugs derived from antibodies were the fastest growing subsegment of the global biopharmaceutical market in 2016 with $81.9 billion in sales, representing approximately 42% of total biopharmaceutical sales and 10% of the global market for prescription drugs.

Our Product Candidates

We have a broad and advanced product pipeline including two late‑stage and clinically validated product candidates, naxitamab and omburtamab, which target tumors that express GD2 and B7‑H3, respectively. Naxitamab and omburtamab are currently in pivotal stage development for pediatric R/R high‑risk NB and pediatric CNS/LM from NB, respectively, both rare and life‑threatening pediatric cancers for which no FDA approved products currently exist. We expect to submit a BLA for each of our two lead product candidates in 2019, with a goal of receiving approval by the FDA in 2020. We plan to commercialize both of our lead product candidates in the United States as soon as possible after obtaining FDA approval, if such approval occurs. Naxitamab and omburtamab are also in mid‑stage clinical development for additional cancers, and we have initiated clinical development for both product candidates in several other indications. Furthermore, we have two additional B7‑H3 targeting product candidates in pre‑clinical development, omburtamab‑DTPA and huB7‑H3, a humanized version of omburtamab, each targeting indications with large adult cancer patient populations where there is a significant unmet medical need. As of December 10, 2018, FDA cleared the Investigational New Drug (“IND”) application for the humanized bispecific GD2 antibody or huGD2‑BsAb, and we have initiated a Phase I trial with our huGD2‑BsAb product candidate for the treatment of refractory GD2‑positive adult and pediatric solid tumors. In pre‑clinical studies, huGD2‑BsAb has demonstrated the potential for improved tumor‑binding, longer serum half‑life and significantly greater T‑cell mediated killing compared to existing bispecific constructs. We are also advancing a pipeline of novel BsAbs through late pre‑clinical development, including our huCD33‑BsAb product candidate for the treatment of hematological cancers expressing CD33, a transmembrane receptor expressed on cells of myeloid lineage. We have exclusive worldwide commercial rights to all of our current product candidates.

Naxitamab Overview

Naxitamab is a humanized monoclonal antibody being evaluated for the treatment of R/R NB and other GD2‑positive tumors, including osteosarcoma. Naxitamab targets GD2, which, based on our research, is expressed on almost all of NB cancer cells regardless of disease stage and in almost all osteosarcomas. Naxitamab is currently in

pivotal stage development for patients with pediatric R/R high‑risk NB and was granted BTD in this indication in 2018. In November 2018, the European Commission granted orphan medicinal product designation, or OMPD, for naxitamab for the treatment of NB. Naxitamab has also received ODD and RPDD from the FDA for the treatment of NB in 2013 and 2017, respectively. The RPDD qualifies us for receipt of a PRV upon approval of naxitamab for treatment of NB, if such approval occurs. Naxitamab has been administered to more than 200 patients in several clinical trials conducted at MSK since 2011. In the Phase 1 dose escalation part of Study 12‑230, of the 23 patients with pediatric R/R high‑risk NB, with evaluable tumors and who did not have PD at study entry, 13 patients, or 57%, achieved a clinical response. In May 2018, we reported topline results from the Phase 2 part of Study 12‑230. This data continued to show response rates at the same levels as in the dose escalation part of the study with 13 of 15 evaluable, or 87% of, primary refractory patients responding and 7 of 23 evaluable, or 30% of, secondary refractory patients responding.

In pediatric R/R high‑risk NB, we believe that naxitamab has multiple potential advantages over other GD2 targeting antibody‑based therapies. In particular, the modest toxicity it exhibits allows for doses 2.5 times greater than the other GD2 targeting antibody‑based therapies. Naxitamab also has a significantly shorter infusion time (approximately 30 minutes compared to 10 to 20 hours for other GD2 targeting antibody‑based therapies being used in front‑line therapy, which we believe is important given the pain associated with the therapy) and the ability to be administered in an outpatient setting (compared to hospitalization stays of four days or longer for other GD2 targeting antibody‑based therapies).

Based on our discussions with the FDA, the profile of the non‑PD pediatric R/R high‑risk NB patients in Study 12‑230 is representative of the intended patient population for our target indication. The corresponding ORRs will form the primary objective of our pivotal study (Study 201). Additionally, based on our discussions with the FDA, we believe that a 30% ORR (which is significantly different from a 20% ORR at a 95% confidence interval, or CI) with a duration of response of minimum 12 weeks may qualify naxitamab for accelerated approval. We have proposed to the FDA that, pending comparability between the study population in Study 12‑230 and Study 201, the data from the two studies may be pooled for analysis for our planned BLA submission. In addition, naxitamab is currently being evaluated in a Phase 2 clinical study (Study 16‑1643) in front‑line NB, a pilot study (Study 17‑251) of chemoimmunotherapy for high‑risk NB and a Phase 2 clinical study (Study 15‑096) in second‑line relapsed osteosarcoma patients.

GD2 Overview

We believe that monoclonal antibodies such as naxitamab that target ganglioside GD2 are one of the most promising cancer immunotherapy approaches. Gangliosides, including GD2, GM2, GD3, NGcGM3 and OAcGD2, have been shown to be expressed at very high levels in tumor cells of several types of cancers.

As a potential target molecule for anti‑tumor therapy, GD2 has certain advantages when compared to other tumor‑associated gangliosides because it is highly expressed in tumor cells of several types of cancers and is not expressed at all, or expressed at very low levels, in normal cells. The National Cancer Institute pilot program for the prioritization of the most important cancer antigens ranks GD2 as number 12 out of 75 potential targets for cancer therapy based on therapeutic function, immunogenicity, role of the antigen in oncogenicity, specificity, expression level and percent of antigen‑positive cells, stem cell expression, number of patients with antigen‑positive cancers, number of antigenic epitopes, and cellular location of antigen expression. GD2 ranks as number six when compared to antigens that are directly targetable on the cell surface. Antibodies directed against GD2 have been shown to effectively induce cell death through a combination of both apoptosis and tumor cell necrosis in GD2‑positive tumors.

GD2 Expression in Various Cancer Types

Studies have shown that GD2 is highly expressed on neuroectoderm‑derived tumors and sarcomas, including NB, retinoblastoma, melanoma, small cell lung cancer, brain tumors, osteosarcoma, rhabdomyosarcoma, Ewing’s sarcoma in children and adolescents, as well as liposarcoma, fibrosarcoma, leiomyosarcoma and other soft‑tissue sarcomas in adults. These cancers have a high mortality rate ranging from 20‑80% depending on the tumor type.

We believe there is a large market opportunity for the treatment of solid tumors that express GD2. Based on our own research and our review of published research, we believe GD2 expression occurs in approximately 60‑100% of

tumor samples from various cancer types, and in substantially all NB and osteosarcoma tumor samples. We estimate that there were more than 200,000 new patients diagnosed with GD2‑positive cancer in the United States in 2017. While our clinical development efforts for naxitamab are currently focused on rare pediatric cancers, we believe we have the potential to expand naxitamab’s application beyond pediatric cancers to the treatment of adults with cancers that express GD2.

Naxitamab—Mechanism of Action

Our pre‑clinical studies have shown that naxitamab binds to GD2 molecules on tumor cells with high affinity and a slow off‑rate, which indicates naxitamab’s strong binding ability. In mice that have been transplanted with human NB tissue, naxitamab demonstrated dose‑dependent inhibition of tumor growth (i.e., the effect of naxitamab varied with dosage) and generally increased survival. In vitro studies show that when naxitamab binds to tumor cells, it induces tumor cell death through antibody‑dependent cell‑mediated cytotoxicity and complement‑dependent cytotoxicity. Naxitamab may also inhibit tumor cell migration through its inhibitory effect on GD2 molecules, which are involved in tumor cell adhesion and migration. In vitro studies also show that Granulocyte‑Macrophage Colony Stimulating Factor, or GM‑CSF, enhances the activity of naxitamab in a dose‑dependent manner and is therefore generally combined with naxitamab in our clinical trials.

Naxitamab for the Treatment of Pediatric Relapsed or Refractory High‑Risk Neuroblastoma

Naxitamab is currently in pivotal stage development (Study 201) for the treatment of pediatric R/R high‑risk NB and was granted BTD in this indication in 2018. In November 2018, the European Commission granted orphan medicinal product designation, or OMPD, for naxitamab for the treatment of NB. Naxitamab has also received ODD and RPDD from the FDA for the treatment of NB in 2013 and 2017, respectively. The RPDD qualifies us for receipt of a PRV upon approval of naxitamab for treatment of NB by the FDA, if such approval occurs. In the dose escalation part of Study 12‑230, we achieved an ORR of 57% in patients with pediatric R/R high‑risk NB who had evaluable tumors and who did not have PD at study entry. Patients with these characteristics are the intended patient population for our first potential indication for treatment with naxitamab. Based on our discussions with the FDA, we believe that a 30% ORR (which is significantly different from a 20% ORR at a 95% CI) with a duration of response of minimum 12 weeks may qualify for consideration of an expedited approval of naxitamab. We have proposed to the FDA that, pending comparability between the study population in Study 12‑230 and Study 201, the data from the two studies may be pooled for analysis. There would also be a post‑marketing commitment to provide data on progression free survival, or PFS, supporting the efficacy of the product. We believe naxitamab has multiple potential advantages over other GD2 targeting antibodies such as higher doses administered on an outpatient basis.

In our studies to date, naxitamab has demonstrated relatively modest toxicity, which allows for 2.5 times greater dosing as compared to other GD2 targeting antibody‑based therapies. This results in fewer doses per cycle and a significantly shorter infusion time (approximately 30 minutes versus 10 to 20 hours for dinutuximab). Notably, since severe pain is one of the most common side effects of treatment with GD2 targeting antibody‑based therapies, we believe that the ability to reduce infusion time to approximately 30 minutes is very important for patients and may result in a significant reduction in demand for pain medication such as morphine. These factors allow naxitamab to be administered in an outpatient setting whereas other GD2 targeting antibody‑based therapies require hospitalization which usually lasts for four days or more.

Overview of Neuroblastoma

NB is a rare and almost exclusively a pediatric cancer that develops in the sympathetic nervous system, a network of nerves that carries messages from the brain throughout the body. It is the third most common childhood cancer, after leukemia and brain tumors, and is the most common solid extracranial tumor in children. NB is a life‑threatening disease associated with poor long‑term survival. It accounts for approximately six percent of all childhood cancers and approximately 15% of pediatric cancer deaths. Nearly 90% of patients with NB are diagnosed by age five and NB is very rare in people over the age of 10 years. The average age of children when they are diagnosed with NB is one to two years.

The stage of NB, which describes how far the cancer has spread, is based on results of physical exams, imaging tests, and biopsies. The International Neuroblastoma Staging System stages the disease from Stage 1 to Stage 4. Other factors that also affect prognosis of NB include age and amplification of MYCN oncogene.

NB patients can also be placed into different risk groups from low, intermediate to high based on the stage and other prognostic factors. High‑risk NB is defined as MYCN amplified Stage 2, 3, 4S and 4 in patients of any age and MYCN non‑amplified Stage 4 in patients over 18 months of age.

Naxitamab is initially being evaluated for the treatment of pediatric R/R high‑risk NB. There are approximately 700 children diagnosed with high‑risk NB in the United States each year. We believe the European market is at least one and a half times the size of the U.S. market and that there are approximately 1,050 patients diagnosed with high‑risk NB in Europe each year. We believe the current addressable market for naxitamab consists of approximately 960 new front‑line high‑risk NB patients each year and 675 primary or second‑line eligible R/R NB pediatric patients each year, representing approximately 40% of all pediatric patients diagnosed with NB in the United States and Europe, combined. Moreover, based on the protocol we have developed with MSK, between treatment and maintenance therapy, we believe that typically patients will receive five to 10 treatment cycles of naxitamab, each cycle consisting of 3 doses.

Naxitamab for Pediatric Relapsed or Refractory High‑Risk Neuroblastoma—Current Treatment Landscape and Associated Limitations

Currently front‑line treatment for pediatric NB patients usually occurs in three stages: induction, consolidation, and maintenance. During the induction phase, patients receive chemotherapy, radiotherapy and possibly surgery to eliminate as much tumor tissue and as many tumor cells as possible. Commonly used agents for induction treatment include cisplatin, etoposide, doxorubicin, cyclophosphamide, and vincristine. Following surgery and/or radiotherapy, most patients enter into consolidation therapy with the goal of eliminating any residual tumor usually with single dose myeloablative agents (e.g. carboplatin‑etoposide‑melphalan) with stem cell support or an autologous stem cell transplant or repeated transplants with thiotepa‑cyclophosphamide followed by cyclophosphamide, etoposide, and ranimustine. Many treatment centers also use immunotherapy as part of the consolidation stage of treatment.

Relapse is a frequent occurrence after consolidation. Although there are no approved therapies in the United States for R/R NB patients, treatments typically include chemotherapy, radiotherapy and other experimental therapies.

In 2015, the FDA and the European Medicines Agency, or the EMA, approved Unituxin (dinutuximab), a monoclonal GD2 targeting antibody developed by United Therapeutics Corporation, or United Therapeutics, and administered in combination with GM‑CSF, interleukin‑2, or IL‑2, and isotretinoin, also known as 13‑cis‑retinoic acid, for the treatment of pediatric patients with high‑risk NB who achieve at least a partial response, or PR, to prior front‑line multiagent, multimodality therapy. The marketing authorization for Unituxin was voluntarily withdrawn by United Therapeutics in the European Union in 2017. In 2017 the EMA approved Dinutuximab beta Apeiron (also known as dinutuximab beta, ch14.18/CHO, Isqette and currently being commercialized under the name Qarziba® in Europe), a monoclonal GD2 targeting antibody, for the treatment of high‑risk NB in patients aged 12 months and older, who have had some improvement with previous treatments or patients whose NB has not improved with other cancer treatments or has relapsed.

Naxitamab for Pediatric Relapsed or Refractory High‑Risk Neuroblastoma—Clinical Development Program

An earlier murine version of naxitamab was studied in 17 clinical trials at MSK with a total of more than 800 patients over the last 25 years. Naxitamab has been studied in several clinical trials for the treatment of pediatric R/R NB and other diseases, of which Study 201, Study 12‑230, Study 11‑009, Study 15‑096 and Study 16‑1643 are currently ongoing. We expect to receive topline data from our ongoing pivotal trial (Study 201) in pediatric R/R high‑risk NB and submit the BLA in 2019.

Based on our discussion with the FDA, ORR will form the primary objective for our pivotal Study 201. We have proposed to the FDA that, pending comparability analysis between study population in Study 12‑230 and Study

201, the data from the two studies may be pooled to form the primary basis of our BLA. Based on our discussions with the FDA, we believe that a 30% ORR (which is significantly different from a 20% ORR at a 95% confidence interval) with a duration of response of minimum 12 weeks may qualify for accelerated approval. Thirty‑seven patients are expected to be included in Study 201. We expect that the safety portion of our planned BLA submission will be comprised of more than 200 patients treated with naxitamab across multiple indications.

Study 12‑230: Phase 1/2 Study of Combination Therapy of Antibody Naxitamab with Granulocyte‑Macrophage Colony Stimulating Factor (GM‑CSF) in Patients with Relapsed/Refractory High‑Risk Neuroblastoma

Phase 1 Portion of Study 12‑230

Primary Objective

Secondary Objectives

Patient Population

In addition to satisfying certain other criteria, patients must be over one year of age and must have been diagnosed with NB as defined by a) histopathology, or b) BM metastases or Meta‑iodobenzylguanidine, or MIBG, avid lesion(s) plus high urine catecholamine levels.

Patients must have R/R high‑risk NB (including MYCN‑amplified Stage 2, 3, 4, or 4S of any age and MYCN‑non amplified Stage 4 in patients over 18 months of age) resistant to standard therapy. Standard therapy for these types of patients includes intensive induction chemotherapy, followed by a variety of consolidation or salvage therapies, depending on response.

Patients will be mainly children and adolescents.

Treatment Protocol

The Phase 1 portion of Study 12‑230 assessed dose escalation of intravenous, or IV, naxitamab (days one, three, five) in the presence of subcutaneous GM‑CSF (days minus four through five). These three doses of naxitamab and 10 days of GM‑CSF constituted a single treatment cycle. Patients who completed 4 cycles without PD were eligible to continue treatment for up to 24 months. For the Phase II part of study, patient were eligible to continue treatment for up

to 4 cycles after major clinical response was obtained again with a maximum treatment period of 24 months. The diagram below depicts the treatment schedule per cycle in Study 12‑230:

Results of Phase 1 Portion of Study 12‑230

A total of 57 patients were enrolled in the Phase 1 portion of Study 12‑230 between December 2012 and May 2016. A summary of patient characteristics is provided in the table below.

Study 12‑230 patient characteristics (Phase 1)

 

All 57 patients were heavily treated prior to entering the study as indicated by the high number of patients previously receiving 131I‑MIBG (n=17) and anti‑GD2 mAbs (n=47).

Safety Results

MTD was not reached. The maximum dose used was 9.6 mg/kg per cycle. This dose was more than 2.5 times greater than the doses that can be given when using the earlier murine version of naxitamab or dinutuximab, and manageable acute side effects allowed treatment to occur in an outpatient setting. Dose limiting toxicities, or DLTs, occurred in four of 57 patients. These DLTs did not show any consistent pattern, ranging from elevated liver enzymes, anaphylactic reactions, acute renal failure, and hypertension. Thirty‑three patients experienced a total of 150 SAEs, of which 27 SAEs were treatment‑related, and none were fatal. Two patients experienced Grade 4 toxicity that necessitated withdrawal from the study. One patient developed an anaphylactic reaction at cycle 7. Another one patient developed Grade 4 angioedema immediately after completing the second cycle. All 57 patients experienced at least one Treatment Emergent Adverse Event, or TEAE, which is defined as “an event that emerges during treatment, having been absent pretreatment, or worsens relative to the pretreatment state” of any grade. Most frequently observed TEAEs were pain, hypotension, fever, pruritus, and urticaria. Most TEAEs were low‑grade adverse events.

Pharmacokinetic Results

The protocol requires patients to be administered naxitamab at dose levels from 0.3 to 3.6 mg/kg per dose on days one, three, and five of a cycle (0.9 to 10.8 mg/kg per cycle).

Human Anti‑human Antibody (HAHA) Results

Of the 57 patients, 10 patients developed human anti‑human antibody, or HAHA, response. Of the same 57 patients, 47 patients had previously been exposed to anti‑GD2 based therapies, including the earlier murine version of naxitamab.

Efficacy Results

Evidence of anti‑NB activity was observed at all dose levels; however, a dose‑response relationship was not possible due to intra‑patient dose escalation after two cycles as permitted by the protocol.

After excluding two patients with early DLT, 55 of 57 patients were included in the overall analysis of efficacy. Of these 55 patients at study entry, 25 patients had no evidence of disease, or NED, and 30 patients had evaluable disease. Of the 30 patients with evaluable disease, seven patients had PD at study entry.

Of the remaining 23 non‑PD patients with primary or secondary refractory disease, 13 patients achieved either a complete response (also known as complete remission), or CR, or a partial response or PR, which resulted in an ORR of 57% (13/23). Further, one patient had stable disease (cancer that is neither decreasing nor increasing in extent or severity) or SD, another six patients had progressive disease (cancer that is growing, spreading or getting worse) or PD, and two patients were only available for short term follow‑up (long term data not available).

As shown in the table below, eight of 11 primary refractory patients achieved an ORR of approximately 73%, and five of 12 secondary refractory patients achieved an ORR of approximately 42%.

Study 12‑230 efficacy results among non‑PD patients (Phase 1)

 

CR = complete response; PR = partial response.

The scan on the left below shows multiple 123I‑MIBG hot spots (NB lesions) localized to the bone and BM. In the scan on the right below, taken after naxitamab and GM‑CSF treatment, nearly all the metastatic lesions have disappeared. Although not every patient will experience similar results, we believe these scans are indicative of a patient that has responded favorably to naxitamab and GM‑CSF treatment.

Among the 25 patients with NED, it was not possible to classify response by International Neuroblastoma Response Criteria, or INRC criteria, including with 123I‑MIBG. These patients, who had one to five prior relapses and therefore had a poor prognosis, showed an encouraging two‑year event‑free survival, or EFS, of 24%.

Treatment in Study 12‑230 with naxitamab in patients previously exposed to other anti‑GD2 antibodies (dinutuximab or earlier murine version of naxitamab)

A large proportion of the patients (n=47) had previously been treated with anti‑GD2 mAbs. We have also demonstrated that naxitamab has efficacy when used following front‑line treatment with dinutuximab. A survival analysis was completed in all 16 patients with prior exposure to dinutuximab.

Phase 2 Portion of Study 12‑230

The Study 12‑230 protocol was amended in May 2016 to include an expansion Phase 2 portion. In May 2018, topline results from the first 71 patients (including 29 NED patients) in this Phase 2 study were presented, which continued to show response rates at the same levels as in the dose escalation part of the study with 13 of 15 evaluable, or 87% of, primary refractory patients responding and 7 of 23 evaluable, or 30% of, secondary refractory patients responding.

The expansion Phase 2 single‑arm portion of Study 12‑230 was designed to assess the anti‑NB activity of naxitamab and GM‑CSF in patients who presented with lesions that could be objectively measured and/or monitored by 123I‑MIBG scans and who were deemed to have measurable disease and be eligible for response classification by the INRC classification incorporating 123I‑MIBG scans. These patients were classified as having evaluable disease and consisted of patients that were primary refractory patients or secondary refractory patients. Another group of patients included those with NED but with a high risk of relapse.

Patient Population

In addition to satisfying certain other criteria, patients must be over one year of age and will be mainly children and adolescents.

Primary Objectives

Secondary Objectives

Safety Results

HAHA developed in 11 out of 71, or 15% of the patients. Nine out of the 11 HAHA‑positive patients were previously treated with anti‑GD2 antibody.

Treatment was outpatient, without unexpected toxicities.

Efficacy Results

Group 1 included 29 patients 0.9‑to‑17.8 (median 3.3) years post‑diagnosis, 2.2‑to‑24.5 (median 6.3) years old, 25/29 prior‑treated with ≥1 anti‑G_D2 antibody, and status‑post 1 (n=18) or ≥2 (n=11) relapses; 12‑month EFS was 74%.

Group 2 included 17 patients with 15 evaluable for response 5‑to‑19 (median 6.6) months post‑diagnosis, 2.9‑to‑10.9 (median 5.1) years old, and 9/15 with Curie scores 7‑to‑23 plus marrow(+). Thirteen out of 15, or 87% of the, patients achieved CR/PR.

Group 3 included 25 patients 0.9‑to‑10.6 (median 3.5) years post‑diagnosis, 2.6‑to‑23.6 (median 6.5) years old, 23/25 prior‑treated with ≥1 anti‑G_D2 antibody, and status‑post 1 (n=15) or 2‑to‑6 (n=10) relapses; 12‑month PFS was 55%, and seven out of 23, or 30% of the, patients evaluable for response achieved CR/PR.

Study 201: A Phase 2 Trial of Antibody Naxitamab and Granulocyte‑Macrophage Colony Stimulating Factor (GM‑CSF) in High‑Risk Neuroblastoma Patients with Primary or Secondary Refractory Osteomedullary Disease

Study 201 is a single‑arm multi‑center pivotal study using current Good Manufacturing Practices, or cGMP, manufactured naxitamab, which commenced recruitment in the second quarter of 2018. We expect to enroll a total of 37 patients with recruitment ongoing in four sites.

Patient population

In addition to satisfying certain other criteria, patients must have high‑risk NB with primary or secondary refractory osteomedullary disease. Primary refractory disease is defined as no prior relapse but incomplete response to treatment in BM as documented by histology and/or 123I‑MIBG scan. Secondary refractory disease is defined as prior relapse and incomplete response to salvage therapy in BM as documented by histology and/or 123I‑MIBG scan. Patients must be older than one year of age.

Treatment Protocol

Study 201 will follow the same treatment protocol as previously described for Study 12‑230 above.

Primary Objective

Secondary Objectives

We have initiated Study 201 to form the primary basis for our planned BLA, to establish comparability of study population with Study 12‑230 and to satisfy the confirmatory study and post‑marketing requirements by the FDA. If the results from Study 201 fail to demonstrate comparability to the satisfaction of the FDA and other comparable regulatory authorities, this may lead to a delay in, or otherwise adversely affect, such clinical trials, including the timing of submission of the BLA.

In October 2017, the FDA issued a partial clinical hold on our IND for naxitamab. A partial clinical hold, as opposed to a full clinical hold, is a delay or suspension of only a specific part of the clinical work requested under the IND, which allows otherwise unaffected parts of the clinical work to proceed under the IND. The FDA stated that the proposed acceptance criterion for the ADCC‑CD16, ADCC‑CD32, and CDC assays were too wide to provide sufficient control over these attributes, which are critical for safety and efficacy. ADCC and CDC refer to antibody dependent cell‑mediated cytotoxicity and complement‑dependent cytotoxicity, respectively. We submitted a response to the FDA in March 2018, and met with the FDA in April 2018. Subsequently, we submitted a complete response to the partial clinical hold to the FDA in May 2018 and the partial clinical hold was removed in June 2018.

Study 16‑1643: Naxitamab/GM‑CSF Immunotherapy Plus Isotretinoin for Consolidation of First Remission of Patients with High‑Risk Neuroblastoma: A Phase 2 Study

Study 16‑1643 is a Phase 2 single‑arm clinical trial where patients with high‑risk NB in first CR/VGPR undergo consolidation with naxitamab and GM‑CSF for five cycles and isotretinoin for six cycles. The primary objective of the study is to determine relapse‑free survival following treatment with naxitamab combined with GM‑CSF and isotretinoin. As of January 2019, 37 patients had been enrolled in the study.

Patient population

In addition to satisfying certain other criteria, patients must have a diagnosis of NB as defined by a) histopathology, or b) BM metastases or MIBG‑avid lesion(s) plus high urine catecholamine levels. Patients must have high‑risk NB (MYCN‑amplified Stage 2, 3, 4, and 4S of any age and MYCN‑nonamplified Stage 4 in patients above 18 months of age). Patients must be in first CR/VGPR.

Patients will mainly be children and adolescents.

Treatment protocol

The dosing and regimen for naxitamab and GM‑CSF is similar to the protocol in Study 12‑230. Naxitamab and GM‑CSF is given for five cycles and isotretinoin for six cycles. In addition to naxitamab and GM‑CSF, isotretinoin, which has been shown to decrease the risk of relapse in patients treated in CR, is administered at 160mg/m2/d, divided into two doses, for 14 days. This treatment can be repeated after a minimum rest period of 14 days, for a total of six cycles starting after two cycles of naxitamab and GM‑CSF unless HAHA develops and precludes timely administration of cycle 2 of naxitamab and GM‑CSF. The interval between the end of a treatment cycle of naxitamab and GM‑CSF and start of next treatment cycle is two to four weeks through cycle 4, then the interval is up to six to eight weeks until cycle 5.

Primary Objective

Secondary Objective

Safety Results

One patient was reported with an unexpected neuropathic event. The patient suffered from short‑term lower limb paralysis that resolved upon hospitalization treatment. The investigator described the event as myelitis.

Study 11‑009: Phase 1 Study of Naxitamab Monoclonal Antibody in Patients with High‑Risk Neuroblastoma and GD2‑Positive Tumors

Study 11‑009 is a Phase 1 clinical dose escalation study with IV naxitamab given as monotherapy in patients with high‑risk NB or other GD2‑positive tumors. We intend to use the safety data from this study, when available, to support our planned BLA submission for naxitamab in pediatric R/R high‑risk NB. As of January 2019, 68 patients had been enrolled in the study, and we expect to enroll a total of 74 patients. The primary objective of the study is to establish the MTD of naxitamab. The secondary objectives are to study the pharmacokinetics, to assess activity of naxitamab against NB and other GD2‑positive tumors, and to quantitate pain during naxitamab treatment. As of October 2017, a MTD had not been reached in the study. Two patients experienced reversible DLT of elevated liver transaminases.

Study 17‑251: Pilot Study of Naxitamab, Irinotecan/Temozolomide and Sargramostim (HITS) Chemoimmunotherapy for High‑Risk Neuroblastoma

Study 17‑251 is a single arm pilot study in high‑risk R/R NB patients with soft tissue disease. Patients will be treated with naxitamab in combination with irinotecan, temozolomide and sargramostim, or HITS. As of January 2019, 22 patients have been enrolled in the study. If the regimen is found to be acceptable, then we plan to initiate a Phase 2/3 study.

Patient population

In addition to satisfying certain other criteria, the patients must have a diagnosis of NB as defined by international criteria, including histopathology or bone marrow metastases plus high urine catecholamine levels.

High‑risk NB is defined as any of the following:

Patients must have a history of tumor progression or relapse or failure to achieve CR following standard therapy. Patients must also have evaluable disease documented after completion of prior systemic therapy.

Treatment protocol

Each cycle consists of four doses of naxitamab, five doses each of irinotecan and temozolomide and five doses of sargramostim. Irinotecan 50mg/m2/day IV will be administered from day one through five concurrently with temozolomide 150mg/m2/day orally. Naxitamab 2.25mg/kg IV will be administered on days two, four, eight and 10. Sargramostim 250mg/m2/day subcutaneous will be administered from day six through 10. If patients do not experience significant toxicity they will commence a second cycle four to six weeks after the first cycle. If there is no progressive disease and patients do not experience significant toxicity they may receive combination therapy up to two years.

Primary Objective

Secondary Objective

Safety results

Currently, no published safety data is available for this study.

Naxitamab for the Treatment of Relapsed Osteosarcoma

Naxitamab is currently being evaluated in an ongoing Phase 2 clinical study (Study 15‑096) for the treatment of patients with relapsed osteosarcoma that have been rendered surgically free of evident disease. As of January 2019, 25 patients had been enrolled and we expect to enroll a total of 39 patients. The trial is designed to distinguish between 12‑month EFS of 30% versus 50%.

Overview of Osteosarcoma

Osteosarcoma is the most commonly diagnosed primary malignancy of bone, particularly among children and adolescents. It is relatively rare and represents less than one percent of all cancers diagnosed in the United States. According to the ACS, most osteosarcomas occur in children and adolescents between the ages of 10 and 30. In young patients, it most often arises in the metaphyses of long bones, such as the distal femur, proximal tibia, and proximal humerus.

Each year, approximately 1,000 new patients are diagnosed with osteosarcoma in the United States. Assuming similar prevalence as in the United States, we estimate approximately 1,500 patients diagnosed with osteosarcoma per year in Europe. If approved, we would expect to treat approximately 300 patients per year in the United States and Europe, combined.

Naxitamab for Relapsed Osteosarcoma—Current Treatment Landscape and Associated Limitations

Current treatment options for front‑line and relapsed osteosarcoma consist of surgery, chemotherapy, radiotherapy, or a combination of the three. Multimodality treatment is increasingly recognized as an important approach for increasing a patient’s chance of prolonged survival. Approximately 50% to 70% of patients treated with aggressive surgical resection and systemic therapy (combination methotrexate, doxorubicin, and cisplatin chemotherapy) achieve long‑term EFS if they have localized disease at diagnosis. However, as discussed below, the prognosis for patients with metastatic disease at diagnosis or those with relapsed disease is very poor. Over the past three decades, several attempts at improving the prognosis for these patients have achieved little success. Strategies that incorporated dose‑intensification of existing agents or addition of other conventional chemotherapeutic agents as well as biological agents, have not achieved long‑term benefit in patients with relapsed osteosarcoma. We believe that at present, there are no novel compounds that have demonstrated activity in relapsed osteosarcoma and few therapeutic options exist for patients with relapsed disease.

The poor prognosis in relapsed osteosarcoma has been confirmed in several reports. A study from the Cooperative Osteosarcoma Study Group reported that while only one of 205 patients with recurrence survived past five years without surgical resection, the five‑year OS and EFS rates were 32% and 18% for second recurrence, 26% and 0% for third recurrence, 28% and 13% for fourth recurrence, and 53% and 0% for fifth recurrence, respectively, in which a renewed surgical remission was achieved.

Naxitamab for Relapsed Osteosarcoma—Clinical Development Program

Currently, naxitamab is being evaluated in an ongoing Phase 2 clinical trial (Study 15‑096) for the treatment of relapsed osteosarcoma. This Phase 2 clinical trial is designed to assess the efficacy of naxitamab when combined with GM‑CSF in patients with relapsed osteosarcoma who have been rendered surgically free of evident disease. The study commenced in July 2015, and as of January 2019, 25 patients had been enrolled. We expect to recruit a total of 39 patients. This trial is designed to distinguish between a 12‑month EFS of 30% versus 50%.

Study 15‑096: A Phase 2 Study of Monoclonal Antibody Naxitamab with Granulocyte‑Macrophage Colony Stimulating Factor (GM‑CSF) in the Treatment of Recurrent Osteosarcoma

Study 15‑096 is a Phase 2 clinical trial to assess the efficacy of the humanized anti‑GD2 antibody, naxitamab, when combined with GM‑CSF, in patients with recurrent osteosarcoma who have been rendered surgically free of evident disease.

Patient Population

In addition to satisfying certain other criteria, patients must be older than one year and up to 40 years of age. To enroll, patients must have a diagnosis of relapsed osteosarcoma. Patients must also be in or beyond their second CR.

Treatment Protocol

Each cycle of therapy is 10 days. The treatment protocol defined one cycle of treatment with IV naxitamab at a dose of 2.4 mg/kg/dose for three days (days one, three, and five) in the presence of subcutaneous GM‑CSF (administered on day minus four before dose one of naxitamab). These three doses of naxitamab with GM‑CSF administered subcutaneously before dose one of naxitamab constitute a treatment cycle. Cycles can be repeated at two to four week intervals between first days of naxitamab, through five cycles. A maximum of five cycles were administered on protocol. No simultaneous anti‑cancer therapy was permitted while on study.

The primary objective of the study is to evaluate EFS at 12 months and secondary objectives are to evaluate time to recurrence, OS and toxicity associated with naxitamab and GM‑CSF.

Omburtamab Overview

Omburtamab is a novel murine monoclonal antibody currently designed for compartmental immunotherapy, for example in the CNS. Omburtamab targets B7‑H3, an immune checkpoint molecule that is widely expressed in tumor cells of several types of cancers. We have radiolabeled omburtamab with either Iodine‑131 (131I‑omburtamab) or Iodine‑124 (124I‑omburtamab). 131I‑omburtamab is currently in pivotal stage development for the treatment of pediatric CNS/LM from NB, and was granted BTD in this indication in 2017. In 2016, 131I‑omburtamab was granted ODD and RPDD, in each case, for the treatment of NB. The RPDD qualifies us for receipt of a PRV upon approval of omburtamab for treatment of NB, if such approval occurs. An analysis of 93 treated patients treated through August 2017 demonstrated median OS of 47 months (including a five‑year median OS of approximately 43%), as compared to historical median OS of approximately six months. We expect to submit the BLA for 131I‑omburtamab for treatment of patients with R/R NB who have CNS/LM from NB in 2019. In addition, radiolabeled omburtamab is in Phase 1/2 clinical development for two additional rare pediatric cancers, DSRCT and DIPG. The most recent set of DSRCT data was presented in April 2018. We believe that we are well positioned to submit sBLAs in each of these two indications, assuming positive results in these Phase 1/2 clinical trials after approval of our BLA for 131I‑omburtamab for CNS/LM. Further, we believe that omburtamab has the potential to address several other tumors in children and adults that express B7‑H3 such as prostate, ovarian, breast, colon, renal, non‑small cell lung, pancreatic, head and neck cancers, as well as melanoma, glioblastoma, and NB and other small round blue cell tumors of childhood.

B7‑H3 Overview

B7‑H3 is a member of the B7 family of immune‑regulatory ligands. The family includes B7‑1, B7‑2, PD‑L1, PD‑L2, B7‑H3, B7‑H4, B7‑H6 and their ligands on T‑cells PD‑1, CD28, CTLA‑4 and ICOS. B7‑H3 is highly expressed on many solid cancers and displays high tumor‑versus‑normal tissue binding differential. In mice, studies have shown that members of the B7 family have the capability to regulate the immune system through both stimulatory and inhibitory signals. Inhibition of certain members of the B7 family has been shown to have significant anti‑tumor effects in several solid tumor types. As such, we believe that B7‑H3 is a promising target for designing targeted therapeutics with a range of modalities.

B7‑H3 Expression in Various Cancer Types

Studies have shown that B7‑H3 is highly expressed on a variety of solid cancer tumors, including prostate, ovarian, breast, colon, renal, non‑small cell lung, pancreatic, head and neck cancers, as well as melanoma, glioblastoma, and NB and other small round blue cell tumors of childhood. In addition, a high degree of B7‑H3 expression on solid tumors has been correlated with greater disease severity, poor outcomes and worse median OS in a number of these cancer types.

We believe there is a large market opportunity for the treatment of solid tumors that express B7‑H3, with hundreds of thousands of new cases estimated in the United States each year. Based on our review of published research, we believe that B7‑H3 expression occurs in a range of 70% to 100% of tumor samples for various cancer types, which makes B7‑H3 a promising immunotherapy target. Our literature review also revealed that B7‑H3 expression on the systemic tumor is replicated in the metastasized tumor. While our clinical development efforts for omburtamab are currently focused on rare pediatric cancers, we believe we have the potential to expand omburtamab’s application to both the treatment of CNS/LM from solid tumors that express B7‑H3 and the underlying solid systemic tumor. As part of Study 03‑133, we have also treated a small number of adult patients with solid tumors that have metastasized to the CNS/LM compartment with 131I‑omburtamab and preliminary indications potentially suggest promising results.

131I‑omburtamab and 124I‑omburtamab—Mechanism of Action

131I‑omburtamab and 124I‑omburtamab are monoclonal antibodies that are radiolabeled with either Iodine‑131 or Iodine‑124, respectively, and both target B7‑H3. Upon administration, radiolabeled omburtamab binds selectively to B7‑H3 ligand that is expressed on the tumor cell surface. Both Iodine‑131 and Iodine‑124 emit beta radiation, resulting in deoxyribonucleic acid, or DNA, damage and tumor cell death. Beta radiation from both iodine isotopes penetrates 1‑3 mm, affecting not only the antibody bound cell but also the neighboring tumor cells. Iodine‑131 has a half‑life of

eight days while Iodine‑124 has a half‑life of four days. In contrast to Iodine‑131, which emits electrons, Iodine‑124 is a positron‑emitting iodine isotope, enabling measurement of iodine uptake using positron emission tomography, or PET scans. This is important when using radiotherapy in a critical organ such as pons, where overdosing may have serious consequences. Radiolabeling of omburtamab with either Iodine‑124 or Iodine‑131 takes place at qualified radiopharmacies according to a well‑established procedure.

131I‑Omburtamab for the Treatment of Pediatric Central Nervous System/Leptomeningeal Metastases from Neuroblastoma

131I‑omburtamab is currently in pivotal stage development for the treatment of pediatric CNS/LM from NB, and was granted BTD in this indication in 2017. In 2016, 131I‑omburtamab was granted ODD and RPDD, in each case, for the treatment of NB. The RPDD qualifies us for receipt of a PRV upon approval of omburtamab for treatment of NB, if such approval occurs. At our meeting with the FDA in June 2017, we proposed to the FDA that data from Study 03‑133 may be pooled with data from Study 101 and utilized for our planned BLA submission. As of August 2017, 93 patients with pediatric CNS/LM from NB had been treated with 131I‑omburtamab in Study 03‑133. An analysis of these 93 patients demonstrated a median OS of 47 months (including an estimated five‑year OS of approximately 43%), as compared to historical median OS of approximately six months. 131I‑omburtamab can be administered as a push injection in an outpatient setting. We expect to submit a BLA for 131I‑omburtamab in 2019, with a goal of receiving approval from the FDA in 2020. We plan to commercialize 131I‑omburtamab in the United States as soon as possible after obtaining FDA approval, if such approval occurs.

Overview of Central Nervous System/Leptomeningeal Metastases from Neuroblastoma

CNS/LM is a rare and usually fatal complication of NB in which the disease spreads to the membranes, or meninges, surrounding the brain and spinal cord in the CNS. In CNS/LM from NB, the CNS has emerged as a sanctuary site for NB tumor cells leading to relapse with an incidence of CNS/LM from NB of approximately 6% to 10%. It is expected that the incidence of CNS/LM from NB disease will increase concurrently with better treatment options for systemic NB, as more patients achieve longer systemic remissions allowing for more CNS relapses. Relapsed metastatic NB is difficult to treat particularly in patients with R/R NB who have CNS/LM from NB. The median OS after detection of the CNS/LM from NB is approximately six months even with early detection and intervention.

Omburtamab is currently being evaluated for the treatment of CNS/LM from NB. There are approximately 700 children diagnosed with NB in the United States each year. Of these, approximately 50‑60% are high‑risk, and of those at high‑risk who relapse, we believe approximately 20% will suffer from CNS/LM from NB. A published study analyzing frozen sections from tumors with histologically confirmed diagnosis of NB using immunohistochemistry showed 87 out of 90 sections (or approximately 97%) were B7‑H3 positive. We believe the European market is at least one and a half times the size of the U.S. market and that there are approximately 1,050 patients diagnosed with NB in Europe each year. We believe the current addressable market for our product candidate, omburtamab, consists of approximately 200 new patients each year with CNS/LM from NB in the United States and Europe, combined.

131I‑omburtamab for Pediatric Central Nervous System/Leptomeningeal Metastases from Neuroblastoma—Current Treatment Landscape and Associated Limitations

There are currently no approved products for patients with R/R NB who have CNS/LM from NB. A variety of treatments are used alone and in combination with other treatments. It is widely accepted that no effective treatment regimens for CNS/LM from NB are available, and the goals of treatment are generally palliative. For recurrence in the CNS, the therapeutic approach consists primarily of surgery, radiation therapy and/or chemotherapy. These treatments have had very limited success, with median OS of approximately six months. The current standard of care treatment paradigm typically involves the following:

The uniformly poor outcomes associated with these different regimens highlight the significant unmet medical need for treatment of CNS/LM from NB:

131I‑omburtamab for Pediatric Central Nervous System/Leptomeningeal Metastases from Neuroblastoma—Clinical Development Program

Currently, 131I‑omburtamab is in pivotal stage development for the treatment of pediatric CNS/LM from NB as a monotherapy after patients have completed standard of care treatment. At our meeting with the FDA in June 2017, we proposed to the FDA that data from Study 03‑133 may be pooled with data from Study 101 and utilized for our planned BLA submission. As of January 2019, 106 patients with pediatric CNS/LM from NB had been treated with 131I‑omburtamab in Study 03‑133. We are planning to treat an additional 32 patients in a multi‑center pivotal Phase 2 trial (Study 101) with an interim pre-planned after the first 18 patients enrolled for the purposes of pharmacokinetic and dosimetry comparability between study sites using 131I‑omburtamab from our cGMP commercial manufacturer, versus drug product previously produced by MSK. Study 101 has also been designed to satisfy the confirmatory study and post‑marketing requirement by the FDA, and, as a result, we will continue to recruit 14 more patients in addition to the initial 18 patients required for the BLA submission for a total of 32 patients exposed. We expect to submit the BLA for 131I‑omburtamab for treatment of patients with CNS/LM from NB in 2019.

Study 03‑133: Phase 1/2 Study of Intrathecal Radioimmunotherapy using 131I‑omburtamab for Central Nervous System/Leptomeningeal Neoplasms

The trial was originally designed as a Phase 1/2 clinical dose escalation study followed by cohort expansion at the recommended dose. To determine the MTD, patients received up to 70 millicurie, or mCi, 131I‑omburtamab as outpatients. Based on treatment result of the 50 mCi dose to treat neuroblastoma with CNS/LM metastasis and since no DLTs were experienced in the dose escalation part; the 50 mCi dose has been expanded as implemented by a protocol amendment. At our meeting with the FDA in June 2017, we proposed to the FDA that data from Study 03‑133 may be pooled with data from Study 101 and utilized for our planned BLA. As of January 2019, 106 patients with pediatric CNS/LM from NB had been treated with 131I‑omburtamab in Study 03‑133. Of these 106 patients, 94 had been treated with 50 mCi 131I‑omburtamab. We expect that the safety portion of the BLA will be comprised of data from more than 200 patients treated with 131I‑omburtamab or 124I‑omburtamab across multiple indications. Study 03‑133 is held open for recruitment (although enrollment into the NB cohort is put on hold after opening of clinical study 101). Hence, we plan to be able to continue to offer this experimental treatment to patients.

The table below presents a general clinical overview, including safety data, from Study 03‑133 conducted from January 2004 through August 2017. The outlined information in the below table refers to patients treated in Study 03‑133.

Omburtamab—Clinical Overview

Study 03‑133—Patient Profile and AEs (January 2004 - August 2017)

Patient Population

In addition to satisfying certain other criteria, patients must have a histologically confirmed diagnosis of a malignancy known to be reactive to omburtamab, a B7‑H3 binding antibody. Furthermore, patients must have CNS/LM from NB disease which is refractory to conventional therapies or for which no conventional therapy exists, or a relapsed brain tumor with a predilection for LM dissemination (primitive neuroectodermal tumor, rhabdoid tumor, medulloblastoma).

Before enrollment in Study 03‑133, most patients underwent biopsy or debulking surgery to remove brain metastases as much as possible, followed by radiation therapy and chemotherapy. A majority of the patients were also treated with an anti‑GD2 immunotherapy such as naxitamab to control systemic disease after completing the 131I‑omburtamab treatment under Study 03‑133. All patients had an intraventricular device implanted before enrollment in the study.

Approximately 80% of all CNS/LM from NB patients presenting at MSK since the initiation of the study were included in the study and the remaining patients were primarily excluded due to the fact that they had already received the maximum dose of previous radiotherapy to CNS, or had progressive systemic disease.

Treatment Protocol

Patients are treated with up to two cycles (consisting of two treatment and dosimetry doses) of 131I‑omburtamab administered through intrathecal infusion via an Ommaya reservoir by which the drug is distributed at the intrathecal space to the entire CSF, (as shown in the figure on the left below). A treatment cycle with 131I‑omburtamab under Study 03‑133 proceeds as follows:

 

The diagram on the left depicts how our radiolabeled omburtamab can be administered via the Ommaya reservoir and catheter into the deep ventricles of the brain where the CSF is produced. From the ventricles, our radiolabeled omburtamab will flow with the CSF and spread throughout the entire CNS compartment potentially binding and killing B7‑H3 positive cancer cells it may find on its way. The diagram on the right is a PET scan showing the distribution of our radiolabeled omburtamab two hours after administration where it has flowed from the central ventricles throughout the entire CNS compartment.

Primary Objective

Secondary Objective

Safety Results

No MTD was reached in the dose escalation portion of the trial. Although not a DLT, myelosuppression was observed in patients who had received craniospinal radiation and 131I‑omburtamab at dose levels six and seven (60 and 70 mCi, respectively). As a result, a dose of 50 mCi was chosen for the expansion cohort. Among the 93 patients treated with 131I‑omburtamab, a total of 293 injections were administered and myelosuppression was observed in approximately 83 patients.

Long‑term toxicities:  There were no significant long‑term toxicities directly attributed to 131I‑omburtamab. There was no increased risk of radionecrosis; specifically, neurologic deficits secondary to radionecrosis have not been observed in long‑term survivors. However, among long‑term survivors with a history of prior high dose induction chemotherapy, myeloablative regimens, craniospinal radiation therapy and 131I‑omburtamab, observed toxicity included short stature and growth hormone deficiency (n=11), hypothyroidism (n=11), cataracts (n=2), persistence of a seizure disorder since CNS NB onset (n=1), and one patient with both an osteochondroma and meningioma (n=1). Unrelated to omburtamab, there were four long‑term events causing death in patients who were otherwise in remission due to infection (n=1), pulmonary fibrosis (n=1), and treatment related mortality for secondary leukemia (n=2). Cognitive deficits were noted in three infants who received additional tutorial assistance in school.

As of September 2018, 29 % of the patients had an SAE that was considered related to treatment by the investigator. The SAEs considered related by investigator were mainly in the System organ Class: investigations reflecting 131I-mediated  myelosuppression, which were considered related for the majority of the events. Related SAEs of vomiting were reported in five patients (3.4%), headache and meningitis chemical by four patients (2.7%) each.

Efficacy Results

Data reported as of August 2017 indicates that the median OS for the 93 patients with R/R NB who have CNS/LM from NB at relapse treated under Study 03‑133 was 47 months. As of August 2017, of these 93 patients, 51, or approximately 55%, were alive. We believe that the median OS may continue to increase. Based on calculations per the Kaplan‑Meier Plot, the estimated three‑year OS is 56% and the estimated five‑year OS is 43%.

In a previous presentation of ASCO, an analysis of 80 patients showed that 38 patients died. Twenty, or approximately 53%, of these patients were attributed to reasons unrelated to any recurrence of CNS/LM from NB disease. We believe this is further indication of the potential effectiveness of 131I‑omburtamab in treating CNS/LM from NB.

Comparison of Median Overall Survival (Months)

The figure above compares median OS data from Study 03‑133 with historical controls (described previously). Historical patient data extracted from three sources revealed median OS of 8.7 months in the literature, 4.7 months in the German NB Trials, and 5.5 months in the MSK historical cohort prior to the introduction of 131I‑omburtamab treatment. These results further demonstrate the lack of an established, effective therapy for these patients that we believe can potentially be addressed by 131I‑omburtamab.

The chart below shows the historical comparable data and median OS following the introduction of 131I‑omburtamab treatment. This represents 93 treated patients from Study 03‑133 as at August 2017. The estimated three‑year median OS was 56% and the five‑year median OS was 43%. Survivors have been followed for up to 11.1 years, with a current mean duration of follow up of 2.6 years. Fifty‑one, or approximately 55%, of the 93 patients treated with 131I‑omburtamab remained alive at their last follow up.

Study 101: A Multicenter Phase 2/3 Trial of the Efficacy and Safety of Intracerebroventricular Radioimmunotherapy using 131I‑omburtamab for Neuroblastoma Central Nervous System/Leptomeningeal Metastases

Study 101 is a pivotal Phase 2/3 single‑arm, open‑label, non‑randomized, multi‑center efficacy, safety, pharmacokinetics and dosimetry trial of intracerebroventricular 131I‑omburtamab in pediatric patients with R/R NB who have CNS/LM from NB. Patients will receive up to two cycles of 131I‑omburtamab. This study commenced in the second quarter of 2018, and we plan to treat an initial 18 patients for an interim analysis for BLA submission purposes. The purpose of this part of the study is to demonstrate pharmacokinetic and dosimetry comparability between study sites using 131I‑omburtamab from our cGMP commercial manufacturer and drug product previously produced by MSK. Study 101 has also been designed to satisfy the confirmatory study and post‑marketing requirement by the FDA, and as a result, we will continue to recruit at least 14 more patients in addition to the initial 18 patients. We expect to submit the BLA for CNS/LM from NB in pediatric patients and expect to complete this submission in 2019.

As described above an interim analysis will be performed when 18 patients have completed evaluations at week six, at which dosimetry and pharmacokinetics objective and available safety and efficacy data will be assessed. Data from this analysis will also be combined with the data from Study 03‑133 to support a potential accelerated approval for 131I‑omburtamab for the treatment of pediatric patients with high-risk NB who have CNS/LM relapse.

Safety and efficacy data will be investigated with short‑term follow‑up at 26 weeks after treatment and with long‑term follow‑up for up to three years following treatment. Final analysis will be performed when all 32 treated patients have completed long‑term follow‑up (three years or until death).

Median OS at three years and its 95% CI will be estimated using Kaplan‑Meier methods. Efficacy will be achieved if the lower limit of the 95% CI of three‑year median OS exceeds 10%. PFS will also be analyzed using Kaplan‑Meier methods.

Patient Population

In addition to satisfying certain other criteria, patients must be less than 18 years of age at the time of screening. Patients must have a histologically confirmed diagnosis of CNS/LM from NB with relapse.

Treatment Protocol

A single treatment cycle will last five weeks and will include premedication, intracerebroventricular 131I‑omburtamab administration (one dosimetry dose and one treatment dose), an observation period, and post‑treatment evaluations (see figure below).

One 131I‑omburtamab treatment cycle for Study 101

Patients without objective PD are eligible for a second dosing cycle.

Primary Objective

Secondary Objectives

We have initiated Study 101 to form the primary basis for our planned BLA, to establish comparability of study population and pharmacokinetics analysis with Study 03‑133 and to satisfy the confirmatory study and post‑marketing requirements by the FDA. If the results from Study 101 fail to demonstrate comparability to the satisfaction of the FDA and other comparable regulatory authorities, this may lead to a delay in, or otherwise adversely affect, such clinical trials, including the timing of submission of the BLA.

124I‑omburtamab for the Treatment of Diffuse Intrinsic Pontine Glioma

124I‑omburtamab is currently being evaluated in an ongoing Phase 1/2 clinical trial (Study 11‑011) for the treatment of DIPG. In contrast to Iodine‑131, which emits electrons, Iodine‑124 is a positron‑emitting iodine isotope. This enables measurement of iodine uptake using PET scans, which we believe is important when using radiotherapy in a critical organ such as pons, where overdosing may have serious consequences. In 2016, 124I‑omburtamab received RPDD from the FDA for the treatment of DIPG. As of October 2017, we have treated 33 patients with DIPG with 124I‑omburtamab. Interim clinical results from the dose escalation portion of the study, which were reported at the American Society of Clinical Oncology, or ASCO, in June 2017, demonstrated that convection‑enhanced delivery, or CED, of 124I‑omburtamab in the brainstem of children with DIPG appears to be a generally feasible approach for drug delivery, based on an evaluation using distribution and pharmacokinetics. We believe that we may qualify for a sBLA, assuming positive pivotal data.

Overview of Diffuse Intrinsic Pontine Glioma

DIPG is a highly aggressive, malignant and difficult to treat brain tumor that forms from the glial (supportive) cells of the brain. The tumor grows in the area of the brainstem, called the pons, a critical area of the brain. Pons are involved in regulating critical body functions such as respiration and consciousness. They also house cranial nerves that facilitate essential functions such as eye movements, chewing, swallowing, facial expressions, hearing and balance, and assists in the transmission of messages between the various structures of the brain and the spinal cord.

DIPG typically affects children between the ages of five to nine years old and is the most common brainstem tumor in children, representing 75% to 80% of pediatric brainstem tumors. There are an estimated 300 children diagnosed with DIPG per year in the United States. One published research analysis evaluating DIPG specimens using immunohistochemistry demonstrated that 100% (nine out of nine) of the tested specimens were B7‑H3 positive. While DIPG accounts for approximately 10% to 15% of brain tumors in the pediatric population, it constitutes approximately 80% of brain tumor‑related deaths. Assuming similar prevalence as in the United States, we estimate approximately 450 new pediatric patients diagnosed with DIPG per year in Europe. We believe the current addressable market for DIPG consists of approximately 750 new pediatric DIPG patients each year in the United States and Europe, combined.

124I‑omburtamab for Diffuse Intrinsic Pontine Glioma—Current Treatment Landscape and Associated Limitations

DIPG grows diffusely and infiltrates healthy tissue in the critical structures of the brainstem and surgical treatment is not possible. The standard of care for the past three decades for children with newly diagnosed DIPG has been focal radiation therapy. Radiotherapy provides temporary improvement or stabilization of symptoms and extends median OS by an average of approximately three months. Within three to eight months after completion of radiation therapy, most children with DIPG have clinical or radiographic evidence of PD. Due to the strong likelihood of the development of PD in the vast majority of children with DIPG, many receive adjuvant chemotherapy at some point during their disease course in an attempt to improve survival. Despite numerous investigational trials, including those evaluating the efficacy of hyperfractionated radiotherapy and high‑dose chemotherapy, the limited survival of patients with DIPG remains unchanged.

The prognosis for DIPG remains very poor and the median OS of children with DIPG is less than one year from diagnosis and no meaningful improvement in median OS has been realized in more than three decades. The prognosis for children with DIPG is significantly worse than that of other brainstem tumors.

124I‑omburtamab for Diffuse Intrinsic Pontine Glioma—Clinical Development Program

124I‑omburtamab is currently being evaluated in an ongoing Phase 1 clinical study (Study 11‑011) for the treatment of DIPG.

Study 11‑011: A Phase 1 Study of Convection‑Enhanced Delivery of 124I‑omburtamab for Patients with Non‑Progressive Diffuse Pontine Gliomas Previously Treated with External Beam Radiation Therapy

MSK is conducting a Phase 1, dose escalation study of CED of 124I‑omburtamab in children with non‑progressive DIPG previously treated with external beam radiation therapy. The study commenced in December 2011 and as of January 2019, 37 patients had been enrolled. We expect to enroll a total of 64 patients.

Patient Population

In addition to satisfying certain other criteria, patients must be two years of age or older, and 21 years of age or younger. Patients must have non‑PD DIPG previously treated with external beam radiation therapy. At least four weeks but not more than 14 weeks must have elapsed from the completion of radiotherapy.

Treatment Protocol

The intervention is a surgical procedure using interstitial infusion of 124I‑omburtamab into the brainstem tumor. It is performed by stereotactic placement of a small caliber infusion cannula into the tumor followed by a slow infusion CED of 124I‑omburtamab, which was initially administered at doses ranging from 0.25 mCi to 4.0 mCi. Study 11‑011 was subsequently amended for further dose escalation cohorts (using 6, 8, 10 and 12 mCi/injection, respectively).

Primary Objective

Secondary Objectives

Safety Results

As noted above, interim data was presented at the June 2017 annual meeting of ASCO, which demonstrated that CED appears to be a feasible approach for drug delivery in the brainstem of children with DIPG as evaluated using distribution and pharmacokinetics. As of June 2017, 28 patients had been enrolled, of which 25 patients were evaluable. Three patients were not evaluable due to partial dose delivery. Of the 25 evaluable patients, one patient experienced alanine transaminase and aspartate transaminase elevation and one patient experienced Grade 3 hemiparesis.

Multi‑Center Pediatric Brain Tumor Consortium Study

The principal investigator for Study 11‑011, in collaboration with the Pediatric Brain Tumor Consortium, is currently drafting a feasibility study to expand the experiences from Study 11‑011 to other sites. This study will be a non‑randomized, multi‑center, feasibility trial using CED in the brainstem of children with DIPG. Each patient will have previously received external beam radiotherapy to the brainstem and will not have shown clear evidence of tumor

progression following this therapy. Diagnostic and eligibility decisions for patients entering the study will be made by a multidisciplinary pediatric neuro‑oncology team at the treating site. Eligibility and surgical planning will be centrally reviewed. Patients will undergo a single treatment using CED of 124I‑omburtamab. MRI and PET will be used for confirmation of appropriate drug distribution patterns. Perioperative morbidity, device performance (catheter for antibody delivery in pons), and patient tolerance after CED treatment will be monitored. OS and time to recurrence will be monitored. Advanced MR‑based algorithms will be used to monitor for geometric response. Serial liquid biopsies (serum, urine, CSF) will be explored as a correlate of tumor response.

131I‑omburtamab for Treatment of Desmoplastic Small Round Cell Tumor

131I‑omburtamab is currently being evaluated in an ongoing Phase 1 clinical study (Study 09‑090) for the treatment of DSRCT. In the data from 39 out of 41 patients that was presented in April 2018, no DLTs were observed and a MTD was not reached. In addition, there was no significant myelosuppression and stem cell rescue was not required. We believe that we may qualify for a sBLA, assuming positive pivotal data.

Overview of Desmoplastic Small Round Cell Tumor

DSRCT is a rare and aggressive type of a soft tissue cancer (sarcoma) that primarily affects children and young adults and is more common in males. It is formed by small, round cancer cells surrounded by scar‑like tissue and is often found in the peritoneum (the tissue that lines the inside of the abdomen and pelvis). Most patients present with abdominal or pelvic tumors, with subsequent metastases to distant lymph nodes, BM and lungs. Due to the rarity of this neoplasm, no large population based studies exist. Analysis presented in literature suggests there are approximately 100 patients diagnosed with DSRCT per year in the United States. Assuming similar prevalence as in the United States, we estimate approximately 150 patients diagnosed with DSRCT per year in Europe. A published report examining DSRCT samples using immunohistochemistry showed that 44 of 46 (or 96%) of tumor samples were B7‑H3 positive. We believe the current addressable market for DSRCT consists of approximately 160 new DSRCT patients each year, representing approximately 65% of all new patients diagnosed with DSRCT in the United States and Europe, combined.

131I‑omburtamab for Desmoplastic Small Round Cell Tumor—Current Treatment Landscape and Associated Limitations

Patients are typically managed with aggressive multimodal therapy, including neoadjuvant chemotherapy, maximal surgical debulking, intraperitoneal, or IP, chemotherapy in some cases, adjuvant whole abdominopelvic radiation therapy, and stem cell or BM transplant. Studies have shown that use of intense alkylator therapy and gross total resection have been associated with limited improvements in patient survival; thus, there is still a significant unmet clinical need. Because DSRCT most commonly presents as a multicentric abdominal mass, complete upfront resection is not often possible. DSRCTs are chemosensitive, but often recur, necessitating multimodality therapy with radiotherapy, surgery, and/or high dose chemotherapy with stem cell rescue. Additionally, research shows that with a five‑year OS rate of less than 15%, patients almost invariably relapse.

Although many strategies have been attempted, survival in patients with DSRCT remains poor. A review of the published research, including two retrospective studies performed by MSK, suggests that the median OS of DSRCT patients ranges from 17 to 25 months.

131I‑omburtamab for Desmoplastic Small Round Cell Tumor—Clinical Development Program

Currently, 131I‑omburtamab is being evaluated in an ongoing clinical study (Study 09‑090) for the treatment of DSRCT. After completing the BLA submission for CNS/LM from NB, we intend to discuss with the FDA the protocol for the continuation and expansion of this DSRCT study. We believe that we may qualify for a sBLA, assuming positive pivotal data.

Study 09‑090: Phase 1 Study of Intraperitoneal Radioimmunotherapy with 131I‑omburtamab for Patients with Desmoplastic Small Round Cell Tumors and Other Solid Tumors Involving the Peritoneum

MSK is conducting a clinical study of IP 131I‑omburtamab for treatment of patients with DSRCT and other B7‑H3 positive solid tumors metastatic to the peritoneum. The primary purpose of the study is to define the toxicity and the MTD, assess the pharmacokinetics, and assess response of DSRCT and other solid tumors. The study commenced in April 2010 and as of May 2018, 50 patients had been enrolled.

Patient Population

In addition to satisfying certain other criteria, patients must be over one year old and able to cooperate with radiation safety restrictions during therapy period. Patients must have a diagnosis of 131I‑omburtamab reactive DSCRT or solid tumors that involve the peritoneum.

Treatment Protocol

The study was designed as an open‑label single‑arm dose escalation study to evaluate IP 131I‑omburtamab, which was administered at doses ranging from 30 mCi/m2 to 90 mCi/m2. The expansion cohort comprised an additional 10 patients who were dosed at 80 mCi/m2.

Primary Objective

Secondary Objectives

Safety Results

In the data from 41 patients with DSRCT presented in April 2018, no DLTs were observed and a MTD was not reached. In addition, there was no significant myelosuppression and stem cell rescue was not required. Three patients experienced Grade 3 neutropenia, three patients experienced Grade 4 neutropenia, six patients experienced Grade 3 thrombocytopenia, one patient experienced Grade 3 AST elevation and four patients experienced Grade 2 abdominal pain. We believe that the initial data from the first group of patients supports continued investigation of the benefit of 131I‑omburtamab in this patient population.

Non‑Clinical Safety

In non-clinical studies evaluating the pharmacology and toxicology of omburtamab, no significant toxicity was observed in different species, including rats and non-human primates. Omburtamab has preferential affinity for a spectrum of cancerous tissues that express B7-H3, with minimal binding to normal tissues. Omburtamab specifically targets the B7-H3 protein on the surface of cancer cells. B7-H3 expression is restricted to the liver and adrenal glands, and absent in most other human tissues, notably the brain. We believe that the lack of cross reactivity with most normal human tissues, specifically within the brain, and the localized binding of omburtamab to the surface of cancer cells that express B7-H3, makes omburtamab a viable candidate for compartmental targeted radiotherapy.

Omburtamab—DTPA Overview

We intend to leverage our expertise with omburtamab to develop product candidates for the treatment of indications associated with pediatric and large adult patient populations. We believe that our clinical experience with

131I‑omburtamab in 41 patients with tumors such as sarcoma, melanoma and medulloblastoma supports this objective. Our first such product candidate targeted towards larger patient populations is DTPA‑conjugated omburtamab radiolabeled with Lutetium‑177, which is currently in pre‑clinical development for the treatment of B7‑H3 positive LM from solid tumors. Animal toxicity studies of 177Lu‑omburtamab‑DTPA have been completed on current Good Laboratory Practices, or GLP, material and cGMP production has been established. DTPA (diethylenetriamine pentaacetate) is an organic molecule that acts as a chelator of metals such as Lutetium. DTPA can bind to radioactive materials to decrease the amount of time it takes to flush the radioactive material from the body. The resulting product candidate, omburtamab‑DTPA‑Lutetium‑177 conjugate, or 177Lu‑omburtamab‑DTPA, can be distributed directly to hospitals, already conjugated and ready to use. It may then be administered to patients as a single‑step push dose via an Ommaya reservoir, similar to the administration of 131I‑omburtamab in CNS/LM from NB. We believe this is an important advantage because radiopharmacies within hospitals have limited capacity for radiolabeling. Therefore, we believe that a more easily available ready to use radiolabeled antibody such as 177Lu‑omburtamab‑DTPA could be used more frequently, thereby significantly expanding our patient population beyond children. We expect to file an IND for 177Lu‑omburtamab‑DTPA for treatment of B7‑H3 positive LM from solid tumors in 2019.

Overview of B7‑H3 Positive Central Nervous System/Leptomeningeal Metastases from Solid Tumors

As previously described, CNS/LM is a rare and usually fatal complication of cancer in which the disease spreads to the membranes, or meninges, surrounding the brain and spinal cord. Based on autopsy studies, the incidence of metastatic brain tumors is estimated to be 200,000 to 300,000 people per year. Studies have shown that the most common tumors which metastasize to the brain express B7‑H3.

Although any cancer can metastasize to the leptomeninges, breast cancer (12% to 35%), lung cancer (10% to 26%), melanoma (5% to 25%), gastrointestinal malignancies (4% to 14%), and cancers of unknown primary (1% to 7%) are the most common causes of solid‑tumor‑related LM. We believe that the annual incidence of CNS/LM across all tumor types is at least 30,000 patients in the United States and Europe combined.

Despite aggressive treatment, CNS/LM has a poor prognosis with less than 15% of all patients surviving one year following diagnosis. The median OS of untreated patients with CNS/LM is four to six weeks. The median OS of patients with combined treatment (often comprising surgery, radiation and/or chemotherapy) is usually less than eight months.

The incidence of CNS/LM is increasing. An important factor contributing to the increasing incidence of CNS/LM is the availability of more effective systemic therapies. These therapies may increase survival time and could therefore lead to a higher incidence of metastatic disease.

177Lu‑Omburtamab‑DTPA in Central Nervous System/Leptomeningeal Metastases—Current Treatment Landscape and Associated Limitations

Treatment of most patients with CNS/LM requires a combination of surgery, radiation, and/or chemotherapy. However, CNS/LM has been proven difficult to treat due to the localization of the tumor within the CNS compartment making complete removal by surgery difficult. Moreover, the blood‑brain barrier, a membrane that selectively regulates molecules entering the brain from the blood, often inhibits drug delivery to the brain due to the inability of large molecules to cross the blood‑brain barrier. Because the most common tumors that metastasize to the brain express B7‑H3, in contrast with normal brain tissue that lacks B7‑H3 expression, we believe that the incidence of B7‑H3 expression makes omburtamab a viable antibody for targeting metastatic tumors in the CNS.

177Lu‑Omburtamab‑DTPA in Central Nervous System/Leptomeningeal Metastases—Mechanism of Action

We are developing a Lutetium‑177 conjugated omburtamab with DTPA as chelator. 177Lu‑omburtamab‑DTPA will be given as a single‑step push dose administration to patients. The administration for CNS/LM will be intrathecal via an Ommaya reservoir similar to the administration of 131I‑omburtamab in CNS/LM from NB. This form of administration will allow us to bypass the blood brain barrier and gain direct access to the CNS/LM. Lutetium‑177 is a medium‑energy beta‑emitter with a maximal tissue penetration of 2 mm. Its half‑life is approximately 6.7 days.

Lutetium‑177 also emits low‑energy Gamma rays, which allows scintigraphy and subsequent dosimetry with the same therapeutic compound. Lutetium‑177 is bound to omburtamab by DTPA. The resulting product 177Lu‑omburtamab‑DTPA conjugate can be distributed conjugated ready to use. Lutathera, a Lutetium‑177‑DOTA conjugated somatostatin analogue peptide, has already demonstrated significant clinical efficacy in patients with progressive neuro endocrine tumors, or NETs, and is approved by the EMA, and the FDA, in this orphan indication. In a multi‑center, randomized, comparator‑controlled, parallel‑group Phase 3 study that has been the basis for regulatory submission for Lutathera, it demonstrated a significant improvement in PFS in patients with inoperable progressive midgut NETs compared to the general standard of care, with limited acute toxic effects. The beta radiation of Lutetium‑177 is similar to the beta radiation emitted from radioactive iodine, which already has demonstrated efficacy in CNS/LM from NB when conjugated to omburtamab.

We believe Lutetium‑177 may have a number of potential advantages over both Iodine‑131 and Iodine‑124. In particular, the radiolabeling of omburtamab‑DTPA with Lutetium‑177 involves a relatively simple one‑step procedure and can be distributed conjugated ready to use.

Humanized Omburtamab Overview

We are also developing huB7‑H3, a humanized version of omburtamab, for the treatment of B7‑H3 positive adult solid tumors where systemic immunotherapy is needed. We expect that huB7‑H3 will be used as a radio‑conjugated antibody designed to overcome limitations of murine antibodies that may induce HAMA, which may lead to decreased efficacy and increased toxicity when used for systemic immunotherapy.

Bispecific Antibody Program Overview

We are advancing a promising pipeline of novel bivalent tumor targeting BsAbs for the treatment of cancer. We believe that our BsAbs have the potential to overcome limitations associated with existing BsAb constructs. Our first BsAb clinical product candidate, huGD2‑BsAb, is a humanized anti‑GD2 and anti‑CD3 BsAb. The IND for this construct was cleared by the FDA December 2018.

Our second BsAb product candidate, huCD33‑BsAb, is a humanized anti‑CD33 and anti‑CD3 BsAb. We are in pre‑clinical development for our huCD33‑BsAb product candidate for the treatment of huCD33‑positive hermatological cancers.

In addition, the MSK License provides us with non‑exclusive access to MSK’s technology that facilitates the creation of a novel human protein tag that can dimerize, or link together, BiTEs, which we refer to as the MULTI‑TAG technology platform. BiTEs are an important class of BsAbs that has shown significant promise in the treatment of cancer due to their high potency. Based on our pre‑clinical studies, we believe that this novel class of BiTEs has the potential to result in better tumor‑binding, longer serum half‑life and significantly greater T‑cell mediated killing of tumor cells without the need for continuous infusion. We plan to utilize this technology to create a diverse platform of dimerized BiTEs. We are currently working on several MULTI‑TAG candidates with MSK.

Overview of Current Bispecific Antibody Treatment Approaches

BsAbs are engineered proteins capable of simultaneously binding to two different epitopes, on the same or different antigens. Through simultaneous recognition of two different targets, BsAbs can serve as mediators for the redirection of immune effector cells, such as Natural Killer cells, or NK cells, and T‑cells, to tumor cells, in order to enhance tumor cell destruction. In addition, by targeting two different receptors in combination on the same cell, BsAbs can induce modifications of cell signaling, including the inactivation of pathways. BsAbs represent an exciting approach to cancer immunotherapy because, among other factors, they have the potential to overcome the limitations of conventional monoclonal antibody approaches to treating cancers. Moreover, BsAbs can be mass produced without the manufacturing complications and risk of persistent systemic toxicity associated with other new immunotherapy approaches such as CAR‑T therapy.

BsAbs are generally divided into two classes, IgG‑like molecules and non‑IgG‑like molecules. IgG‑like BsAbs retain the traditional monoclonal antibody structure but bind to multiple antigens. Although IgG‑like BsAbs generally demonstrate adequate stability and effector functions, their large size limits tissue penetration.

Non‑IgG‑like BsAbs lack a fragment crystallizable, or Fc, region, consisting instead of chemically linked variable regions and various types of multivalent single‑chain variable fragments, or scFvs. One type of non‑IgG‑like BsAbs are BiTEs. BiTEs are relatively small and have more efficient penetration, however, they exhibit short serum half‑lives. They bind monovalently to tumor targets, which often results in suboptimal tumor binding relative to conventional IgG‑like BsAbs that bind bivalently. Finally, therapeutic dosing of BiTEs is limited by the risk of excessive cytokine release in patients.

The only approved BsAb for treatment of cancer in the United States is blinatumomab, a BiTE, approved for the treatment of acute lymphocytic leukemia.

huGD2‑BsAb Overview

The figure below depicts our first BsAb product candidate, huGD2‑BsAb, a fully humanized IgG‑scFv format antibody, in which the anti‑CD3 scFv is linked to the carboxyl end of the naxitamab IgG1 and the Fc region is mutated to help prevent cytokine release as well as complement‑mediated pain side effects.

Naxitamab (anti‑GD2 and anti‑CD3) Bispecific Antibody

We believe that huGD2‑BsAb may have several potential advantages over other BsAbs, including:

Knockout mice, which lack murine T‑cells, B‑cells and NK cells, were used for human cancer xenograft studies. The picture below demonstrates a study where mice were transplanted with human M14‑Luc melanoma and human peripheral blood mononuclear cells, or PBMC, or activated T‑cells, or ATC, as effector cells. Tumor growth was assessed by luciferin bioluminescence.

Mice, in a control group, treated with saline without effector cells (huGD2‑BsAb only), or effector cells plus ATC+naxitamab‑C825, used as the control BsAb and which does not bind to T‑cells, had equally rapid tumor progression. In contrast, mice treated with huGD2‑BsAb in the presence of human effector cells (ATC+huGD2‑BsAb or PBMC+huGD2‑BsAb) demonstrated nearly total tumor elimination. The picture below is a representative image at day 31.

On December 10, 2018, the FDA cleared the IND application for the humanized bispecific GD2 antibody, and in January 2019, a Phase 1/2 trial with our huGD2 BsAb product candidate for the treatment of refractory GD2 positive adult and pediatric solid tumors was initiated.

Study 18-034: Phase I/II study of humanized 3F8 bispecific antibody (Hu3F8-BsAb) in patients with relapsed/refractory neuroblastoma, osteosarcoma, and other GD2(+) solid tumors

Study 18-034 is a phase I/II single arm, dose escalation clinical trial of the hu3F8 bispecific antibody. Dose escalation to be performed in patients with relapsed/refractory neuroblastoma, osteosarcoma or other GD2-positive tumors. Cohort expansion will be conducted in relapsed/refractory neuroblastoma (group 1) and osteosarcoma (group 2). Up to 30 patients will enroll in Phase I and up to 64 patients will enroll in Phase II. The phase I endpoints include maximum tolerated dose, or MTD , the recommended phase II dose, or RP2D, PK, HAHA, and anti tumor activity. For phase II, the endpoint will for group 1 (RR neuroblastoma) include ORR, duration of CR and OS and for group 2 (R/R Osteosarcoma) include  progression-free survival at four months, ORR, duration of CR and OS. Currently, no published safety data is available for this study.

huCD33‑BsAb Overview

Our second BsAb product candidate, huCD33‑BsAb, is a humanized anti‑CD33 and anti‑CD3 BsAb for the treatment of hematological cancers expressing CD33, a transmembrane receptor expressed on cells of myeloid lineage. Currently we are planning to set up GLP and cGMP production allowing for initiation of formal pre‑clinical toxicology in 2019 and potential IND filing in 2020.

MULTI‑TAG Technology Overview

We believe that our non‑exclusive access to the MULTI‑TAG technology will help us make further advances to our BsAb program by optimizing BiTEs. While there has been significant enthusiasm for BiTEs given their high potency and ability to penetrate more efficiently than conventional IgG‑like BsAbs, their efficacy remains hampered by their size and binding characteristics. BiTEs are relatively small in size, approximately 55kD, resulting in a short serum half‑life given rapid renal clearance. As a result, they require continuous infusion for several weeks in order to achieve a therapeutic response. They also bind monovalently, which often results in suboptimal tumor binding. Further, therapeutic dosing of BiTEs is limited by the risk of excessive cytokine release in patients.

Using the MULTI‑TAG technology, we have designed a novel protein tag of human origin that dimerizes, or links, BiTEs, in a unique conformation, which we believe may result in improved tumor binding, a longer half‑life, and greater T‑cell mediated tumor cell killing. We are using the MULTI‑TAG technology platform to dimerize our BsAbs into proteins of approximately 120kD in size, thereby increasing serum half‑life without the need for continuous infusion. The unique dimerized conformation, while binding bivalently to tumors, also binds monovalently to T‑cells, which we believe, leads to limiting excessive cytokine release. Below is a graphic illustration of the MULTI‑TAG technology, to which, under the MSK License, we have unlimited access to use MSK’s rights in the technology for any target.

MULTI‑TAG—Dimerization technology to enhance potency of T‑cell engaging antibodies

We are currently working on several MULTI‑TAG candidates with MSK.

Manufacturing

Currently, we contract with third party cGMP vendors for the manufacturing of our product candidates for pre‑clinical studies and clinical trials and intend to do so in the future, including for commercialization if our product candidates receive marketing approval. We do not currently own or operate any manufacturing facilities for the production of clinical or commercial quantities of our product candidates. We currently have no plans to build our own clinical or commercial scale manufacturing capabilities. To meet our projected needs for commercial manufacturing, if the need arises, third parties with whom we currently work may need to increase their scale of production or we may need to secure alternate suppliers. Although we rely on our cGMP manufacturers, we have personnel with substantial manufacturing experience to oversee our relationships with such manufacturers.

Manufacturing clinical products is subject to extensive regulations that impose various procedural and documentation requirements, which govern record keeping, manufacturing processes and controls, personnel, quality control and quality assurance. Our vendors are required to comply with cGMP regulations, which are regulatory requirements enforced by the FDA and other regulatory bodies like the EMA to assure proper design, monitoring and control of manufacturing processes and facilities for human pharmaceuticals.

Our current product candidates are mAbs and BsAbs. The manufacturing process for antibodies involves the genetic engineering of a parental host cell line to isolate a cell that produces the antibody. Once the cell or clone (colony of cells derived from a single cell) is isolated, a cell bank is produced under prescribed and documented conditions. The cell bank, preserved frozen, is tested, as required by regulations, to demonstrate that the engineered cell line is free from potentially harmful impurities and contaminants, such as viruses.

The drug substance is an active ingredient that is intended to furnish pharmacological activity or other direct effect in the diagnosis, cure, mitigation, treatment, or prevention of disease or to affect the structure or any function of the human body, but does not include intermediates used in the synthesis of such ingredient while the drug product is a finished dosage form. The manufacturing process for the drug substance begins with the thaw of vials from the cell bank and growth of these cells in established media until sufficient cells are cultured to inoculate a production bioreactor. The cells in the production bioreactor are grown in chemical defined media and under controlled and monitored conditions that stimulate the production of the antibody into the culture media. The production bioreactor is cultured for an established time period and is then harvested by filtration to remove the cells from the culture media.

The antibody solution is purified through a number of steps to remove known process‑ and product‑derived impurities. The technologies employed include ultrafiltration and column and membrane chromatography. Additional steps are performed to inactivate or remove viruses. The final step of the drug substance process adjusts the antibody concentration and produces the final formulation to be used for drug product production. The drug substance is tested to meet pre‑established criteria for purity, potency and safety, and is then periodically tested to demonstrate stability upon storage as required by regulations. The drug substance is stored at prescribed temperatures, typically refrigerated or frozen.

The drug product is produced by sterilization filtration of the drug substance solution, followed by aseptic filling into glass vials and then stoppered. The drug product is subjected to release testing for purity, potency and safety according to pre‑established specifications. Drug product lots are periodically tested to demonstrate stability over the established storage expiry period. The drug product is stored and shipped under temperature‑controlled conditions, typically refrigerated, to sites designated for clinical trial testing, or eventually to commercial pharmaceutical logistics providers.

Naxitamab is a recombinant humanized IgG1κ monoclonal antibody against GD2 expressed in Chinese Hamster Ovary, or CHO, cells. A One mL ampoule from the master or working cell bank is used as seeding for a 1000 L fed batch bioreactor in chemical defined media with no animal derived component. After the growths of the cells are completed the un‑processed bulk from the bioreactor containing the naxitamab drug substance undergoes conditioned clarified harvests, filtration, and subsequent multi‑step product purification.

The naxitamab drug substance is manufactured by Patheon UK Limited in Groningen, The Netherlands and the naxitamab drug product is manufactured at Patheon Manufacturing Services LLC in Greenville, North Carolina, (both part of the Thermo Fisher Scientific Inc., group of companies) collectively Patheon/Thermo Fisher, in compliance with cGMP regulations and no excipients of human or animal origin have been used. The naxitamab drug product is packaged in 10 mL ISO 10R glass vials and frozen.

Omburtamab is a murine IgG1 monoclonal antibody against B7‑H3. The antibody is manufactured in a 200 L bioreactor in chemical defined media with no animal derived components. After harvests, clarification of the fermentation and a multi‑step purification process, the final drug substance is ready for radiolabeling. This non‑radiolabeled omburtamab is packaged in 2 mL ISO 2R glass vials and frozen. The drug substance is manufactured by EMD Millipore Corporation (now part of the Merck KgaA group of companies), or EMD/Merck, in Martillac, France, and the omburtamab drug product is manufactured by Patheon/Thermo Fisher in Ferentino, Italy.

While we believe that Patheon/Thermo Fisher and EMD/Merck are capable of producing sufficient quantities of drug product to support our currently planned clinical trials for naxitamab and omburtamab, we also believe that there are a number of alternative third‑party manufacturers that have similar capabilities that would be capable of providing sufficient quantities of drug product for our planned clinical trials. However, should Patheon/Thermo Fisher and/or EMD/Merck not be able to provide sufficient quantities of drug product for our planned clinical trials, we would be required to seek and then qualify another contract manufacturer to provide this drug product, likely resulting in a delay in such trials.

Commercialization Plan

The sales call points for our late‑stage product candidates in the United States and the European Union are highly concentrated around a few major hospitals and, therefore, can be effectively serviced with a small commercial organization. Both our existing clinical trials at all the relevant sites, as well as our partnership with MSK, have already afforded us the opportunity to identify patients for our product candidates, if approved. We believe these factors position us well for commercialization.

Our management team understands the complexity of rare oncological diseases and we believe we have the necessary expertise to be a true partner to patients, caregivers, and advocacy and healthcare teams leading to shared success. As we advance our product pipeline to address larger patient populations, we intend to establish a specialty sales force and develop an organizational infrastructure to support the network of relevant hospitals, cancer centers, oncologists and other physicians as well as provide support to patients, care‑givers and other healthcare providers. We plan to commercialize our future product candidates in the United States and Europe ourselves, and will evaluate strategic collaborations in select territories in order to maximize the potential of our product candidates.

As additional product candidates advance through our pipeline, our commercial plans may change. The size of the development programs, size of the target market, size of a commercial infrastructure, and manufacturing needs may all influence our strategies in the United States, the European Union and other parts of the world.

Competition

The biotechnology and pharmaceutical industries generally, and the cancer drug sector specifically, are characterized by rapidly advancing technologies, evolving understanding of disease etiology, intense competition and a strong emphasis on intellectual property. While we believe that our product candidates and our knowledge and experience provide us with competitive advantages, we face substantial potential competition from many different sources, including large and specialty pharmaceutical and biotechnology companies, academic research institutions and governmental agencies and public and private research institutions.

In addition to the current standard of care for patients, commercial and academic clinical trials are being pursued by a number of parties in the field of immunotherapy. Early results from these trials have fueled continued interest in immunotherapy, which is being pursued by several biotechnology companies as well as by large pharmaceutical companies. Many of our current or potential competitors, either alone or with their collaboration

partners, have significantly greater financial resources and expertise in research and development, manufacturing, pre‑clinical studies, conducting clinical trials, and marketing approved products than we do. Mergers and acquisitions in the pharmaceutical and biotechnology industries may result in even more resources being concentrated among a smaller number of our competitors. Smaller or early‑stage companies may also prove to be significant competitors, particularly through collaborative arrangements with large and established companies. These competitors also compete with us in recruiting and retaining qualified scientific and management personnel and establishing clinical trial sites and patient registration for clinical trials, as well as in acquiring technologies complementary to, or necessary for, our programs.

Specifically, MacroGenics, Inc. and Daiichi Sankyo Co. are developing antibodies against B7‑H3. United Therapeutics Corporation has commercialized Unituxin (dinutuximab), an antibody against GD2, in the United States. United Therapeutics Corporation has also announced that it is developing a humanized GD2 antibody. In addition, naxitamab may face competition from dinutuximab beta, a similar antibody product against GD2 developed by Apeiron Biologics AG, or Apeiron, that was approved in Europe in May 2017 to treat high‑risk NB and R/R NB. Apeiron has previously announced plans to file for registration of dinutuximab beta in the U.S. in the first quarter of 2019 in R/R NB. In October 2016, EUSA Pharma (UK) Ltd., or EUSA, announced that it had acquired global commercialization rights to dinutuximab beta, which is currently being commercialized under the name Qarziba® in Europe.

Intellectual Property

Patent Portfolio

We strive to protect and enhance the proprietary technology, inventions, and improvements that we believe are commercially important to our business, including seeking, maintaining, and defending patent rights, whether developed internally or licensed from our collaborators or other third parties. Our policy is to seek to protect our proprietary position by, among other methods, filing patent applications in the United States and in jurisdictions outside of the United States related to our proprietary technology, inventions, improvements, and product candidates that are important to the development and implementation of our business. We also rely on trade secrets and know‑how relating to our proprietary technology and product candidates, continuing innovation, and in‑licensing opportunities to develop, strengthen, and maintain our proprietary position in the field of immunotherapy. We additionally rely on data exclusivity, market exclusivity, and patent term extensions when available, and plan to seek and rely on regulatory protection afforded through orphan drug designations. Our commercial success will depend in part on our ability to obtain and maintain patent and other proprietary protection for our technology, inventions, and improvements, whether developed internally or licensed from our collaborators or other third parties; to preserve the confidentiality of our trade secrets; to maintain our licenses to use intellectual property owned by third parties; to defend and enforce our proprietary rights, including our patents; and to operate without infringing on the valid and enforceable patents and other proprietary rights of third parties.

We have in‑licensed numerous patents and patent applications and substantial know‑how relating to the development and commercialization of our immunotherapy product candidates, including related manufacturing processes and technology. In addition, an international patent application has been filed claiming the inventions of investigators at MSK as well as personnel of Y-mAbs Therapeutics.

As of December 31, 2018, our patent portfolio included:

The term of individual patents depends upon the legal term for patents in the countries in which they are granted. In most countries, including the United States, the patent term is generally 20 years from the earliest claimed filing date of a non‑provisional patent application in the applicable country. In the United States, a patent’s term may, in certain cases, be lengthened by patent term adjustment, which compensates a patentee for administrative delays by the United States Patent and Trademark Office, or USPTO, in examining and granting a patent, or may be shortened if a patent is terminally disclaimed over a commonly owned patent or a patent naming a common inventor and having an

earlier expiration date. The Drug Price Competition and Patent Term Restoration Act of 1984, or the Hatch‑Waxman Act, permits a patent term extension of up to five years beyond the expiration date of a U.S. patent as partial compensation for the length of time the drug is under regulatory review while the patent is in force. A patent term extension cannot extend the remaining term of a patent beyond a total of 14 years from the date of product approval, only one patent applicable to each regulatory review period may be extended and only those claims covering the approved drug, a method for using it or a method for manufacturing it may be extended. We cannot provide any assurance that any patent term extension with respect to any U.S. patent will be obtained and, even if obtained, what the duration of such extension may be.

Similar provisions are available in the European Union and certain other non‑U.S. jurisdictions to extend the term of a patent that covers an approved drug. In the future, if and when our product candidates receive approval by the FDA or non‑U.S. regulatory authorities, we expect to apply for patent term extensions on issued patents covering those products, depending upon the length of the clinical trials for each drug and other factors. The expiration dates referred to above are without regard to potential patent term extension or other market exclusivity that may be available to us. However, we cannot provide any assurance that any such patent term extension of a non‑U.S. patent will be obtained and, even if obtained, the duration of such extension.

As for the immunotherapy products and processes we develop and commercialize, in the normal course of business, we intend to pursue, when possible, composition, method of use, dosing and formulation patent protection. We may also pursue patent protection with respect to manufacturing and drug development processes and technology.

Individual patents extend for varying periods of time, depending upon the date of filing of the patent application, the date of patent issuance, and the legal term of patents in the countries in which they are obtained. Generally, patents issued for applications filed in the United States are effective for 20 years from the earliest effective filing date. In addition, in certain instances, a patent term can be extended to recapture a portion of the term effectively lost as a result of the FDA regulatory review period. The restoration period cannot be longer than five years and the total patent term, including the restoration period, must not exceed 14 years following FDA approval. The duration of patents outside of the United States varies in accordance with provisions of applicable local law, but typically is also 20 years from the earliest effective filing date. Generally, as noted above, our in‑licensed issued patents in all jurisdictions will expire on dates ranging from 2021 to 2034. If patents are issued on our pending patent applications, the resulting patents are projected to expire on dates ranging from 2021 to 2038. However, the actual protection afforded by a patent varies on a product‑by‑product basis, from country‑to‑country, and depends upon many factors, including the type of patent, the scope of its coverage, the availability of regulatory‑related extensions, the availability of legal remedies in a particular country, and the validity and enforceability of the patent.

Trademarks

We have obtained USPTO trademark registration of the “Y‑mAbs” mark. Other than Y‑mAbs, we currently rely on our unregistered trademarks, trade names and service marks, as well as our domain names and logos, as appropriate, to market our brands and to build and maintain brand recognition. We are seeking to register and will continue to seek to register and renew, or secure by contract where appropriate, trademarks, trade names and service marks as they are developed and used, and reserve, register and renew domain names as appropriate. However, we have not yet registered any of our trademarks, trade names or service marks with the USPTO other than Y‑mAbs. If we do not secure successfully register trademark registration for our trademarks, we may encounter difficulty in enforcing, or be unable to enforce, our rights in our trademarks, trade names and service marks against third parties.

Trade Secrets

We may also rely, in some circumstances, on trade secrets to protect our technology. However, trade secrets are difficult to protect. We seek to protect our technology and product candidates, in part, by entering into confidentiality agreements with those who have access to our confidential information, including our employees, contractors, consultants, collaborators, and advisors. We also seek to preserve the integrity and confidentiality of our proprietary technology and processes by maintaining physical security of our premises and physical and electronic security of our information technology systems. Although we have confidence in these individuals, organizations, and systems,

agreements or security measures may be breached and we may not have adequate remedies for any breach. In addition, our trade secrets may otherwise become known or may be independently discovered by competitors. To the extent that our employees, contractors, consultants, collaborators, and advisors use intellectual property owned by others in their work for us, disputes may arise as to the rights in related or resulting know‑how and inventions. For this and more comprehensive risks related to our intellectual property and proprietary technology, inventions, improvements and products, please see the section on “Risk Factors—Risks Related to Our Intellectual Property.”

MSK Agreements

On August 20, 2015, we entered into the MSK License, which grants us a worldwide, sub‑licensable license to MSK’s rights in certain patent rights and intellectual property rights related to certain know‑how to develop, make and commercialize licensed products and to perform services for all therapeutic and diagnostic uses in the field of cancer diagnostics and cancer treatments. The MSK License is exclusive with respect to MSK rights in such patent rights and tangible materials within such know‑how, and nonexclusive with respect to MSK’s rights in such know‑how and related intellectual property rights. The patents and patent applications covered by the MSK License are directed, in part, to the naxitamab and omburtamab antibody families, including humanized and chimeric antibodies, as well as MSK’s rights in BsAbs, compositions, and their respective use for immunotherapy. Upon entering into the MSK License in 2015 and in exchange for the licenses thereunder, we paid to MSK an upfront payment of $500,000, issued 1,428,500 shares of our common stock to MSK and agreed to provide certain anti‑dilution rights to MSK as further described below. In addition, we are required to pay to MSK certain royalty and milestone payments. We recorded a total expense of $285,700 for the shares of common stock issued to MSK in 2015 based on the estimated fair value of the shares of common stock of $0.20 per share at issuance date.

Pursuant to the MSK License and the MSK CD33 License, as of December 31, 2018, we have rights to approximately 11 issued U.S. patents, approximately five pending U.S. patent applications, and other patents and patent applications in jurisdictions outside the United States. Upon entering the MSK License, we made an upfront payment to MSK, and we are required to make to MSK certain royalty payments, including minimum annual royalty payments commencing on the fifth anniversary of the MSK License, which are fully creditable against earned royalties.

The MSK License requires us to pay to MSK mid to high single‑digit royalties based on annual net sales of licensed products or the performance of licensed services by us and our affiliates and sublicensees. We are required to pay annual minimum royalties of $80,000 over the royalty term, starting in 2020, which amounts are non‑refundable but are creditable against royalty payments otherwise due thereunder. Total expensed minimum royalty payments under the MSK License were $1,200,000 in 2016, all of which were recorded as long‑term accrued liabilities as of December 31, 2017 and December 31, 2018, respectively, upon determination that the payment of such minimum royalties was probable and the amount was estimable. We are also obligated to pay to MSK certain clinical, regulatory and sales‑based milestone payments under the MSK License, which payments become due upon achievement of the related clinical, regulatory or sales‑based milestones. Certain of these clinical and regulatory milestone payments become due at the earlier of completion of the related milestone activity or the date indicated in the MSK License. Total potential clinical and regulatory milestones potentially due under the MSK License are $2,450,000 and $9,000,000, respectively. There are also sales‑based milestones that become due should we achieve certain amounts of sales of licensed products resulting from the license arrangement with MSK, with total potential sales‑based milestones potentially due of $20,000,000. We have not entered into any sublicenses related to the MSK License. As product candidates progress through clinical development, regulatory approval and commercialization, certain milestone payments will come due either as a result of the milestones having been met or the passage of time even if the milestones have not been met. We will also owe MSK mid to high single digit royalties on commercial sales of our approved products, including an annual fixed minimum royalty of $80,000 over the royalty term starting in 2020 whether or not product sales are ever achieved. In addition, to the extent we enter into sublicense arrangements, we are required to pay to MSK a percentage of certain payments that we receive from sublicensees of the rights licensed to us by MSK, which percentage will be based upon the date we receive such payments or the achievement of certain clinical milestones. Additionally, the terms of the MSK License provide that MSK is entitled to receive 40% - 50% of any income generated from the sale of first such PRV, and 33% of any income generated from the sale of any subsequent PRV or the sale of other comparable incentives provided by any non‑U.S. jurisdiction. Additionally, the terms of the MSK CD33 License provide that MSK is entitled to receive

25% of any income generated from the sale of any PRV or the sale of other comparable incentives provided by any non‑U.S. jurisdiction.

The MSK License will expire, on a country‑by‑country basis, and on a licensed‑product‑by‑licensed‑product or licensed‑service‑by‑licensed‑service basis, on the later of (i) the expiration of the last to expire of the patents and patent applications covering such licensed product or service in such country, (ii) the expiration of any market exclusivity period granted by a regulatory authority for such licensed product or service in such country, or (iii) 15 years from the first commercial sale of such licensed product or service in such country.

MSK may terminate the MSK License upon prior written notice in the event of our uncured material breach, or upon prior written notice if such breach is of a payment obligation. MSK may also terminate the MSK License upon written notice in the event of our bankruptcy or insolvency or our conviction of a felony relating to the licensed products, or if we challenge the validity or enforceability of any licensed patent right. In addition, we have the right to terminate the MSK License in its entirety at will upon prior written notice to MSK, but if we have commenced the commercialization of licensed products and/or licensed services we can only terminate at will if we cease all development and commercialization of such licensed products and/or licensed services.

In connection with the MSK License, on August 20, 2015 we also entered into a letter agreement with MSK pursuant to which we issued to MSK 1,428,500 shares of our common stock and agreed that if in the future we issued any shares of its capital stock, we would issue sufficient shares of common stock to MSK such that at all times prior to us obtaining equity financing equal to or greater than $25,000,000 in the aggregate, MSK shall hold shares of our common stock equal to 12.5% of the issued and outstanding shares of common stock (assuming full conversion or exercise of all outstanding preferred stock and other convertible securities, rights, options and warrants). Following issuances of our common stock in 2016, we issued to MSK an additional 479,328 on May 20, 2016 and 520,601 shares on August 20, 2016 in order for MSK to maintain the 12.5% ownership interest. As of December 31, 2016, MSK no longer had the right to receive additional shares of our common stock under the MSK License. Our failure to meet certain conditions under the MSK License could cause the related license to such licensed product to be canceled and could result in termination of the MSK License by MSK.

On November 10, 2015, we entered into the Sponsored Research Agreement, or the SRA, with MSK pursuant to which we committed to provide aggregate research funding to MSK for a term of five years. The research will be conducted in accordance with a written plan and budget approved by the parties. MSK has granted us a non‑exclusive, non‑commercial, non‑transferable, royalty‑free license to use any inventions or discoveries developed by MSK within the scope of the information resulting from the project, for our internal, non‑commercial research purposes. We have also been granted both a first option to negotiate an exclusive or non‑exclusive commercial license to MSK’s rights in inventions developed by MSK and a first option to negotiate an exclusive license to MSK’s rights in inventions jointly developed by the parties. The term of the SRA shall continue until the earlier of (i) the completion of the activities set forth in each statement of work entered into thereunder or (ii) November 10, 2020. The SRA may be terminated for convenience by either party upon prior written notice. During 2017 and 2018 we incurred research and development expenses of $1,160,000 and $1,192,000, respectively, under the SRA.

On September 20, 2016, we entered into a Master Data Services Agreement, or the MDSA, with MSK pursuant to which we committed to make certain payments to MSK annually in exchange for certain services, including transfer of clinical data and databases, regulatory files and other know‑how to us by employees at MSK who are specifically assigned to assist with such services to us. The MDSA will expire upon the completion of activities set forth in each project description entered into thereunder; however we have the option to extend the term upon written notice to MSK. Either party may terminate the MDSA upon prior written notice in the event of an uncured material breach. During 2017 and 2018, we incurred expenses of $357,000 and $396,000, respectively, under the MDSA.

Also, on June 21, 2017, we entered into the Investigator‑Sponsored Master Clinical Trial Agreement, or the MCTA, as later amended on October 11, 2017, with MSK pursuant to which we committed to provide aggregate funding to MSK up to a certain amount for clinical studies to be conducted at MSK. Each such clinical study will be conducted in accordance with a written plan and budget and protocol approved by the parties. Under the MCTA, we and MSK have granted each other a non‑exclusive, non‑transferable, worldwide, royalty‑free license, without right to sublicense, to use

any inventions or discoveries developed by personnel of each such party, that is within the scope of the information resulting from the relevant study, for the other party’s internal, non‑commercial research purposes until such Invention is commercially available. We have also been granted a first option to negotiate an exclusive or non‑exclusive commercial license to MSK’s rights in inventions or discoveries developed by MSK personnel under this MCTA and a first option to negotiate an exclusive license to MSK’s rights in inventions or discoveries jointly developed by MSK and our personnel under this MCTA. The MCTA will continue in effect through completion of the studies, and may be terminated by either party upon prior written notice. During 2017 and 2018, we incurred research and development expenses of $725,000 and $3,043,000 under the MCTA.

On June 27, 2017, we entered into two separate Core Facility Service Agreements, or CFSAs, with MSK pursuant to which we committed to make certain payments to MSK in exchange for certain laboratory services over the term of the CFSAs. Either party may terminate either of these CFSAs for any reason, or for no reason, upon prior written notice. In the event of termination of either of these CFSAs, we will make full payment to MSK for all work performed on, or expenses related to the project up to the date of termination including all non‑cancelable obligations following receipt from MSK of any completed or in‑process deliverables in connection with the project. During 2017 and 2018, we incurred research and development expenses of $195,000 and $325,000, respectively, under the CFSAs.

On November 13, 2017, we entered into a license agreement, or the MSK CD33 License, with MSK, which grants us a worldwide, sub‑licensable license to MSK’s rights in certain patent rights and intellectual property rights related to certain know‑how to develop, make and commercialize licensed products and to perform services for all therapeutic and diagnostic uses in the field of cancer diagnostics in connection with certain CD33 antibodies generated in a specific principal investigator’s laboratory at MSK and constructs thereof. The MSK CD33 License is exclusive with respect to such patent rights and tangible materials within such know‑how, and nonexclusive with respect to MSK’s rights in such know‑how and related intellectual property rights. As product candidates progress through clinical development, regulatory approval and commercialization, certain milestone payments will come due either as a result of the milestones having been met or the passage of time even if the milestones have not been met. Also, we will owe MSK customary royalties on commercial sales of our approved products, if any. Total potential milestones due under the MSK CD33 License are $550,000, $500,000 and $7,500,000 for clinical, regulatory and sales based milestones, respectively. In addition, the MSK CD33 License contains minimum royalty payments that become due beginning in year 10 of $40,000 per year over the royalty term, increasing to $60,000 once a patent within the licensed rights is issued, subject to increase and creditable against any royalty payments due based on sales in the future. We are required to pay mid to high single digit royalties on sales of licensed products. We also agreed to pay MSK approximately $1,360,000 for research services related to the intellectual property licensed under the MSK CD33 License. The research services are expected to occur over the two year period immediately following the date of the MSK CD33 License.

The MSK CD33 License will expire, on a country‑by‑country basis, and on a licensed product‑by‑licensed‑product or licensed‑service‑by‑licensed‑service basis, on the later of (i) the expiration of the last to expire of the patents and patent applications covering such licensed product or service in such country, (ii) the expiration of any market exclusivity period granted by a regulatory authority for such licensed product or service in such country, or (iii) 15 years from the first commercial sale of such licensed product or service in such country.

MSK may terminate the MSK CD33 License upon prior written notice in the event of our uncured material breach, or upon prior written notice if such breach is of a payment obligation. MSK may also terminate the MSK CD33 License upon written notice in the event of our bankruptcy or insolvency or our conviction of a felony relating to the licensed products, or if we challenge the validity or enforceability of any licensed patent right. In addition, we have the right to terminate the MSK CD33 License in its entirety at will upon prior written notice to MSK, but if we have commenced the commercialization of licensed products and/or licensed services we can only terminate at will if we cease all development and commercialization of such licensed products and/or licensed services.

On November 13, 2017, in connection with the MSK CD33 License, we entered into the Sponsored Research Agreement, or the CD33 SRA, with MSK pursuant to which we committed to provide aggregate research funding to MSK annually for a term of two years. The research will be conducted in accordance with a written plan and budget approved by the parties. MSK has granted us a non‑exclusive, non‑commercial, non‑transferable, royalty‑free license to use any inventions or discoveries developed by MSK within the scope of the information resulting from the research, for

our internal, non‑commercial research purposes. We have also been granted both a first option to negotiate an exclusive or non‑exclusive commercial license to MSK’s rights in inventions developed by MSK personnel and a first option to negotiate an exclusive license to MSK’s rights in inventions jointly developed by the parties and our personnel. The term of the CD33 SRA shall continue until the earlier of (i) the completion of the activities set forth in each statement of work entered into thereunder or (ii) November 13, 2019. The CD33 SRA may be terminated for convenience by either party upon prior written notice. In 2017 and 2018, we incurred research and development expenses of $88,000 and $670,000 under the CD33 SRA.

On July 9, 2018, we entered into the Manufacturing Agreement with MSK’s Radiochemistry and Molecular Imaging Probes Core Facility, or RMIP, pursuant to which RMIP will complete specified manufacturing activities related to 131I‑omburtamab in connection with our pivotal Phase 2 trials for Study 101.

MabVax Sublicense Agreement

On June 27, 2018, we entered into the MabVax Sublicense, pursuant to which MabVax granted us all of the exclusive rights granted to MabVax under the MabVax‑MSK License, for a bi‑valent ganglioside based vaccine intended to treat NB, or the NB vaccine. MSK originally developed the NB vaccine and licensed to MabVax as part of a portfolio of anti‑cancer vaccines. In 2014, MabVax was granted ODD for the vaccine for the treatment of NB. Under the terms of the Mabvax Sublicense, we paid an upfront payment of $700,000, and we will make an additional payment of $600,000 on the first anniversary of the MabVax Sublicense. We will also be responsible for any potential downstream payment obligations to MSK related to the NB vaccine that were specified in the MabVax‑MSK license agreement. This includes the obligation to pay development milestones totaling $1,400,000 and mid single‑digit royalty payments to MSK. In addition, if we obtain FDA approval for the NB vaccine, then we are obligated to file with the FDA for a PRV. If the PRV is granted and subsequently sold, MabVax will receive a percentage of the proceeds from the sale thereof. The MabVax Sublicense will terminate upon the termination or expiration of the MabVax‑MSK License. The MabVax License will expire, on a country‑by‑country basis, on the later of the expiration of (i) 10 years from the first commercial sale of the licensed product in such country or (ii) the last‑to‑expire valid claim covering such licensed product rights at the time of and in the country of sale. MabVax may terminate the MabVax Sublicense upon prior written notice to us in the event of our uncured material breach.

Government Regulation

The FDA and other regulatory authorities at federal, state, and local levels, as well as in foreign countries, extensively regulate, among other things, the research, development, testing, manufacture, quality control, import, export, safety, effectiveness, labeling, packaging, storage, distribution, record keeping, approval, advertising, promotion, marketing, post‑approval monitoring, and post‑approval reporting of biologics such as those we are developing. We, along with third‑party contractors, will be required to navigate the various pre‑clinical, clinical and commercial approval requirements of the governing regulatory agencies of the countries in which we wish to conduct studies or seek approval or licensure of our product candidates. The process of obtaining regulatory approvals and the subsequent compliance with appropriate federal, state, local, and foreign statutes and regulations require the expenditure of substantial time and financial resources.

The process required by the FDA before biologic product candidates may be marketed in the United States generally involves the following:

Prior to beginning the first clinical trial with a product candidate, we must submit an IND to the FDA. An IND is a request for authorization from the FDA to administer an investigational new drug product to humans. The central focus of an IND submission is on the general investigational plan and the protocol(s) for clinical studies. The IND also includes results of animal and in vitro studies assessing the toxicology, pharmacokinetics, pharmacology, and pharmacodynamic characteristics of the product; chemistry, manufacturing, and controls information; and any available human data or literature to support the use of the investigational product. An IND must become effective before human clinical trials may begin. The IND automatically becomes effective 30 days after receipt by the FDA, unless the FDA, within the 30‑day time period, raises safety concerns or questions about the proposed clinical trial. In such a case, the IND may be placed on clinical hold and the IND sponsor and the FDA must resolve any outstanding concerns or questions before the clinical trial can begin. Submission of an IND therefore may or may not result in FDA authorization to begin a clinical trial.

A clinical trial involves the administration of the investigational product to human patients under the supervision of qualified investigators in accordance with cGCPs, which includes the requirement that all research patients provide their informed consent for their participation in any clinical study. Clinical trials are conducted under protocols detailing, among other things, the objectives of the study, the parameters to be used in monitoring safety and the effectiveness criteria to be evaluated. A separate submission to the existing IND must be made for each successive clinical trial conducted during product development and for any subsequent protocol amendments. Furthermore, an IRB for each site proposing to conduct the clinical trial must review and approve the plan for any clinical trial and its informed consent form before the clinical trial begins at that site, and must monitor the study until completed. Regulatory authorities, the IRB or the sponsor may suspend a clinical trial at any time on various grounds, including a finding that the patients are being exposed to an unacceptable health risk or that the trial is unlikely to meet its stated objectives. Some studies also include oversight by an independent group of qualified experts organized by the clinical study sponsor, known as a data safety monitoring board, which provides authorization for whether or not a study may move forward at designated check points based on access to certain data from the study and may halt the clinical trial if it determines that there is an unacceptable safety risk for patients or other grounds, such as no demonstration of efficacy. There are also requirements governing the reporting of ongoing clinical studies and clinical study results to public registries.

For purposes of BLA approval, human clinical trials are typically conducted in three sequential phases that may overlap.

In some cases, the FDA may require, or companies may voluntarily pursue, additional clinical trials after a product is approved to gain more information about the product. These so‑called Phase 4 studies may be made a condition to approval of the BLA.

Phase 1, Phase 2 and Phase 3 testing may not be completed successfully within a specified period, if at all, and there can be no assurance that the data collected will support FDA approval or licensure of the product. Concurrent with clinical trials, companies may complete additional animal studies and develop additional information about the biological characteristics of the product candidate, and must finalize a process for manufacturing the product in commercial quantities in accordance with cGMP requirements. The manufacturing process must be capable of consistently producing quality batches of the product candidate and, among other things, must develop methods for testing the identity, strength, quality and purity of the final product, or for biologics, the safety, purity and potency. Additionally, appropriate packaging must be selected and tested and stability studies must be conducted to demonstrate that the product candidate does not undergo unacceptable deterioration over its shelf life.

BLA Submission and Review by the FDA

Assuming successful completion of all required testing in accordance with all applicable regulatory requirements, the results of product development, non‑clinical studies and clinical trials are submitted to the FDA as part of a BLA requesting approval to market the product for one or more indications. The BLA must include all relevant data available from pertinent pre‑clinical and clinical studies, including negative or ambiguous results as well as positive findings, together with detailed information relating to the product’s chemistry, manufacturing, controls, and proposed labeling, among other things. Data can come from company‑sponsored clinical studies intended to test the safety and effectiveness of a use of the product, or from a number of alternative sources, including studies initiated by investigators. The submission of a BLA requires payment of a substantial User Fee to FDA, and the sponsor of an approved BLA is also subject to annual program fees. These fees are typically increased annually. A waiver of user fees may be obtained under certain limited circumstances.

Once a BLA has been submitted, the FDA’s goal is to review the application within 10 months after it accepts the application for filing, or, if the application relates to an unmet medical need in a serious or life‑threatening indication, six months after the FDA accepts the application for filing. The review process is often significantly extended by FDA requests for additional information or clarification. The FDA reviews a BLA to determine, among other things, whether a product is safe, pure and potent and the facility in which it is manufactured, processed, packed, or held meets standards designed to assure the product’s continued safety, purity and potency. The FDA may convene an advisory committee to provide clinical insight on application review questions. Before approving a BLA, the FDA will typically inspect the facility or facilities where the product is manufactured. The FDA will not approve an application unless it determines that the manufacturing processes and facilities are in compliance with cGMP requirements and adequate to assure consistent production of the product within required specifications. Additionally, before approving a BLA, the FDA will typically inspect one or more clinical sites to assure compliance with cGCP. If the FDA determines that the application, manufacturing process or manufacturing facilities are not acceptable, it will outline the deficiencies in the

submission and often will request additional testing or information. Notwithstanding the submission of any requested additional information, the FDA ultimately may decide that the application does not satisfy the regulatory criteria for approval.

The testing and approval process requires substantial time, effort and financial resources, and each may take several years to complete. The FDA may not grant approval on a timely basis, or at all, and we may encounter difficulties or unanticipated costs in our efforts to secure necessary governmental approvals, which could delay or preclude us from marketing our products. After the FDA evaluates a BLA and conducts inspections of manufacturing facilities where the product will be produced, the FDA may issue an approval letter, or a Complete Response Letter. An approval letter authorizes commercial marketing of the product with specific prescribing information for specific indications. A Complete Response Letter indicates that the review cycle of the application is complete and the application is not ready for approval. A Complete Response Letter may request additional information or clarification. The FDA may delay or refuse approval of a BLA if applicable regulatory criteria are not satisfied, require additional testing or information and/or require post‑marketing testing and surveillance to monitor safety or efficacy of a product.

If regulatory approval of a product is granted, such approval may entail limitations on the indicated uses for which such product may be marketed. For example, the FDA may approve the BLA with a Risk Evaluation and Mitigation Strategy, or REMS, plan to mitigate risks, which could include medication guides, physician communication plans, or elements to assure safe use, such as restricted distribution methods, patient registries and other risk minimization tools. The FDA also may condition approval on, among other things, changes to proposed labeling or the development of adequate controls and specifications. Once approved, the FDA may withdraw the product approval if compliance with pre‑ and post‑marketing regulatory standards is not maintained or if problems occur after the product reaches the marketplace. The FDA may require one or more Phase 4 post‑market studies and surveillance to further assess and monitor the product’s safety and effectiveness after commercialization, and may limit further marketing of the product based on the results of these post‑marketing studies. In addition, new government requirements, including those resulting from new legislation, may be established, or the FDA’s policies may change, which could delay or prevent regulatory approval of our products under development.

A sponsor may seek approval of its product candidate under programs designed to accelerate FDA’s review and approval of new drugs and biological products that meet certain criteria. Specifically, new drugs and biological products are eligible for fast track designation if they are intended to treat a serious or life‑threatening condition and demonstrate the potential to address an unmet medical need for the condition. For a fast track product, the FDA may consider sections of the BLA for review on a rolling basis before the complete application is submitted if relevant criteria are met. A fast track designated product candidate may also qualify for priority review, under which the FDA sets the target date for FDA action on the BLA at six months after the FDA accepts the application for filing. Priority review is granted when there is evidence that the proposed product would be a significant improvement in the safety or effectiveness of the treatment, diagnosis, or prevention of a serious condition. If criteria are not met for priority review, the application is subject to the standard FDA review period of 10 months after FDA accepts the application for filing. Priority review designation does not change the scientific/medical standard for approval or the quality of evidence necessary to support approval.

Under the accelerated approval program, the FDA may approve a BLA on the basis of either a surrogate objective that is reasonably likely to predict clinical benefit, or on a clinical objective that can be measured earlier than irreversible morbidity or mortality, that is reasonably likely to predict an effect on irreversible morbidity or mortality or other clinical benefit, taking into account the severity, rarity, or prevalence of the condition and the availability or lack of alternative treatments. Post‑marketing studies or completion of ongoing studies after marketing approval are generally required to verify the biologic’s clinical benefit in relationship to the surrogate objective or ultimate outcome in relationship to the clinical benefit. In addition, a sponsor may seek FDA designation of its product candidate as a breakthrough therapy if the product candidate is intended, alone or in combination with one or more other drugs or biologics, to treat a serious or life‑threatening disease or condition and preliminary clinical evidence indicates that the therapy may demonstrate substantial improvement over existing therapies on one or more clinically significant objectives, such as substantial treatment effects observed early in clinical development. Sponsors may request the FDA to designate a breakthrough therapy at the time of or any time after the submission of an IND, but ideally before an end‑of‑Phase 2 meeting with FDA. If the FDA designates a breakthrough therapy, it may take actions appropriate to

expedite the development and review of the application, which may include holding meetings with the sponsor and the review team throughout the development of the therapy; providing timely advice to, and interactive communication with, the sponsor regarding the development of the drug to ensure that the development program to gather the non‑clinical and clinical data necessary for approval is as efficient as practicable; involving senior managers and experienced review staff, as appropriate, in a collaborative, cross‑disciplinary review; assigning a cross‑disciplinary project lead for the FDA review team to facilitate an efficient review of the development program and to serve as a scientific liaison between the review team and the sponsor; and considering alternative clinical trial designs when scientifically appropriate, which may result in smaller trials or more efficient trials that require less time to complete and may minimize the number of patients exposed to a potentially less efficacious treatment. Breakthrough designation also allows the sponsor to file sections of the BLA for review on a rolling basis.

Fast Track designation, priority review and BTD do not change the standards for approval but may expedite the development or approval process.

Orphan Drugs

Under the Orphan Drug Act, the FDA may grant orphan designation to a drug or biologic intended to treat a rare disease or condition, defined as a disease or condition with either a patient population of fewer than 200,000 individuals in the United States, or a patient population greater of than 200,000 individuals in the United States when there is no reasonable expectation that the cost of developing and making available the drug or biologic in the United States will be recovered from sales in the United States for that drug or biologic. ODD must be requested before submitting a BLA. After the FDA grants ODD, the generic identify of the therapeutic agent and its potential orphan use are disclosed publicly by the FDA.

If a product that has received ODD and subsequently receives the first FDA approval for a particular active ingredient for the disease for which it has such designation, the product is entitled to orphan product exclusivity, which means that the FDA may not approve any other applications, including a full BLA, to market the same biologic for the same indication for seven years, except in limited circumstances, such as a showing of clinical superiority to the product with orphan drug exclusivity or if FDA finds that the holder of the orphan drug exclusivity has not shown that it can assure the availability of sufficient quantities of the orphan drug to meet the needs of patients with the disease or condition for which the drug was designated. Orphan drug exclusivity does not prevent the FDA from approving a different drug or biologic for the same disease or condition, or the same drug or biologic for a different disease or condition. Among the other benefits of ODD are tax credits for certain research and a waiver of the BLA application user fee.

A designated orphan drug many not receive orphan drug exclusivity if it is approved for a use that is broader than the indication for which it received ODD. In addition, orphan drug exclusive marketing rights in the United States may be lost if the FDA later determines that the request for designation was materially defective or if the manufacturer is unable to assure sufficient quantities of the product to meet the needs of patients with the rare disease or condition.

Rare Pediatric Disease Designation

The Rare Pediatric Disease Priority Review Voucher Program, or the PRV Program, is intended to incentivize pharmaceutical companies to develop drugs for rare pediatric diseases. A company that obtains approval of an IND or a BLA for a designated rare pediatric disease may be eligible for a PRV from the FDA, which may be redeemed to obtain priority review for a subsequent new drug application or BLA by the owner of such PRV. A PRV is fully transferable and can be sold to any company, who in turn can redeem the PRV for priority review of a marketing application in six months, compared to the standard timeframe of approximately ten months. In December 2016, the House of Representatives approved the 21st Century Cures Act, which among other initiatives reauthorizes the PRV Program for rare pediatric diseases until 2020. A drug that receives a RPDD before October 1, 2020 continues to be eligible for a PRV if the drug is approved before October 1, 2022.

Post‑Approval Requirements

Any products manufactured or distributed by us pursuant to FDA approvals are subject to pervasive and continuing regulation by the FDA, including, among other things, requirements relating to record‑keeping, reporting of adverse experiences, periodic reporting, product sampling and distribution, and advertising and promotion of the product. After approval, most changes to the approved product, such as adding new indications or other labeling claims, are subject to prior FDA review and approval. There also are continuing, annual user fee requirements for any marketed products and the establishments at which such products are manufactured, as well as new application fees for supplemental applications with clinical data. Biologic manufacturers and their subcontractors are required to register their establishments with the FDA and certain state agencies, and are subject to periodic unannounced inspections by the FDA and certain state agencies for compliance with cGMP, which impose certain procedural and documentation requirements upon us and our third‑party manufacturers. Changes to the manufacturing process are strictly regulated, and, depending on the significance of the change, may require prior FDA approval before being implemented. FDA regulations also require investigation and correction of any deviations from cGMP and impose reporting requirements upon us and any third‑party manufacturers that we may decide to use. Accordingly, manufacturers must continue to expend time, money and effort in the area of production and quality control to maintain compliance with cGMP and other aspects of regulatory compliance. We cannot be certain that we or our present or future suppliers will be able to comply with the cGMP regulations and other FDA regulatory requirements. If our present or future suppliers are not able to comply with these requirements, the FDA may, among other things, halt our clinical trials, require us to recall a product from distribution, or withdraw approval of the BLA.

We rely, and expect to continue to rely, on third parties for the production of clinical quantities of our product candidates, and expect to rely in the future on third parties for the production of commercial quantities. Future FDA and state inspections may identify compliance issues at our facilities or at the facilities of our contract manufacturers that may disrupt production or distribution, or require substantial resources to correct. In addition, discovery of previously unknown problems with a product or the failure to comply with applicable requirements may result in restrictions on a product, manufacturer or holder of an approved BLA, including withdrawal or recall of the product from the market or other voluntary, FDA‑initiated or judicial action that could delay or prohibit further marketing. The FDA may withdraw approval if compliance with regulatory requirements and standards is not maintained or if problems occur after the product reaches the market. Later discovery of previously unknown problems with a product, including adverse events of unanticipated severity or frequency, or with manufacturing processes, or failure to comply with regulatory requirements, may result in revisions to the approved labeling to add new safety information; imposition of post‑market studies or clinical studies to assess new safety risks; or imposition of distribution restrictions or other restrictions under a REMS program. Other potential consequences include, among other things:

The FDA closely regulates the marketing, labeling, advertising and promotion of biologics. A company can make only those claims relating to safety and efficacy, purity and potency that are approved by the FDA and in accordance with the provisions of the approved label. The FDA and other agencies actively enforce the laws and regulations prohibiting the promotion of off‑label uses. Failure to comply with these requirements can result in, among other things, adverse publicity, warning letters, corrective advertising and potential civil and criminal penalties. Physicians may prescribe legally available products for uses that are not described in the product’s labeling and that differ from those tested by us and approved by the FDA. Such off‑label uses are common across medical specialties.

Physicians may believe that such off‑label uses are the best treatment for many patients in varied circumstances. The FDA does not regulate the behavior of physicians in their choice of treatments. The FDA does, however, restrict manufacturer’s communications on the subject of off‑label use of their products.

Pediatric Studies and Exclusivity

Under the Pediatric Research Equity Act of 2003, a BLA or supplement thereto must contain data that are adequate to assess the safety and effectiveness of the product for the claimed indications in all relevant pediatric subpopulations, and to support dosing and administration for each pediatric subpopulation for which the product is safe and effective. Sponsors must also submit pediatric study plans prior to the assessment data. Those plans must contain an outline of the proposed pediatric study or studies the applicant plans to conduct, including study objectives and design, any deferral or waiver requests and other information required by regulation. The applicant, the FDA, and the FDA’s internal review committee must then review the information submitted, consult with each other and agree upon a final plan. The FDA or the applicant may request an amendment to the plan at any time. For products intended to treat a serious or life‑threatening disease or condition, the FDA must, upon the request of an applicant, meet to discuss preparation of the initial pediatric study plan or to discuss deferral or waiver of pediatric assessments.

The FDA may, on its own initiative or at the request of the applicant, grant deferrals for submission of some or all pediatric data until after approval of the product for use in adults, or full or partial waivers from the pediatric data requirements. Additional requirements and procedures relating to deferral requests and requests for extension of deferrals are contained in FDASIA. Unless otherwise required by regulation, the pediatric data requirements do not apply to products with orphan designation.

The FDA Reauthorization Act of 2017 established new requirements to govern certain molecularly targeted cancer indications. Any company that submits a BLA three years after the date of enactment of that statute must submit pediatric assessments with the BLA if the biologic is intended for the treatment of an adult cancer and is directed at a molecular target that FDA determines to be substantially relevant to the growth or progression of a pediatric cancer. The investigation must be designed to yield clinically meaningful pediatric study data regarding the dosing, safety and preliminary efficacy to inform pediatric labeling for the product.

Pediatric exclusivity is another type of non‑patent marketing exclusivity in the United States and, if granted, provides for the attachment of an additional six months of marketing protection to the term of any existing regulatory exclusivity, including the non‑patent and orphan exclusivity. This six‑month exclusivity may be granted if a BLA sponsor submits pediatric data that fairly respond to a written request from the FDA for such data. The data do not need to show the product to be effective in the pediatric population studied; rather, if the clinical trial is deemed to fairly respond to the FDA’s request, the additional protection is granted. If reports of requested pediatric studies are submitted to and accepted by the FDA within the statutory time limits, whatever statutory or regulatory periods of exclusivity or patent protection cover the product are extended by six months. This is not a patent term extension, but it effectively extends the regulatory period during which the FDA cannot approve another application.

Other Healthcare Laws and Compliance Requirements

Healthcare providers and third‑party payors play a primary role in the recommendation and prescription of drug products that are granted regulatory approval. Arrangements with providers, consultants, third‑party payors and customers are subject to broadly applicable fraud and abuse and other healthcare laws and regulations that may constrain our business and/or financial arrangements. Such restrictions under applicable federal and state healthcare laws and regulations, include the following:

Some state laws require pharmaceutical companies to comply with the pharmaceutical industry’s voluntary compliance guidelines and the relevant compliance guidance promulgated by the federal government in addition to requiring drug manufacturers to report information related to payments to physicians and other health care providers or marketing expenditures. State and foreign laws also govern the privacy and security of health information in some circumstances, many of which differ from each other in significant ways and often are not preempted by HIPAA, thus complicating compliance efforts.

Also, the U.S. Foreign Corrupt Practices Act and similar worldwide anti‑bribery laws generally prohibit companies and their intermediaries from making improper payments to foreign officials for the purpose of obtaining or retaining business. We cannot assure you that our internal control policies and procedures will protect us from reckless or negligent acts committed by our employees, future distributors, partners, collaborators or agents. Violations of these laws, or allegations of such violations, could result in fines, penalties or prosecution and have a negative impact on our business, results of operations and reputation.

Coverage and Reimbursement

Sales of pharmaceutical products depend significantly on the availability of third‑party coverage and reimbursement. Third‑party payors include government health administrative authorities, managed care providers, private health insurers and other organizations. Although we currently believe that third‑party payors will provide coverage and reimbursement for our product candidates, if approved, these third‑party payors are increasingly challenging the price and examining the cost‑effectiveness of medical products and services. In addition, significant uncertainty exists as to the reimbursement status of newly approved healthcare products. We may need to conduct expensive clinical studies to demonstrate the comparative cost‑effectiveness of our products. The product candidates that we develop may not be considered cost‑effective. It is time consuming and expensive for us to seek coverage and

reimbursement from third‑party payors. Moreover, a payor’s decision to provide coverage for a drug product does not imply that an adequate reimbursement rate will be approved. Reimbursement may not be available or sufficient to allow us to sell our products on a competitive and profitable basis.

Review and Approval of Medicinal Products in the European Union

In order to market any product outside of the United States, a company must also comply with numerous and varying regulatory requirements of other countries and jurisdictions regarding quality, safety and efficacy and governing, among other things, clinical trials, marketing authorization, commercial sales and distribution of products. Whether or not it obtains FDA approval for a product, an applicant will need to obtain the necessary approvals by the comparable non‑U.S. regulatory authorities before it can commence clinical trials or marketing of the product in those countries or jurisdictions. Specifically, the process governing approval of medicinal products in the European Union generally follows the same lines as in the United States. It entails satisfactory completion of pre‑clinical studies and adequate and well‑controlled clinical trials to establish the safety and efficacy of the product for each proposed indication. It also requires the submission to the relevant competent authorities of a marketing authorization application, or MAA, and granting of a marketing authorization by these authorities before the product can be marketed and sold in the European Union.

The Clinical Trials Directive 2001/20/EC, the Directive 2005/28/EC on Good Clinical Practice, or GCP, and the related national implementing provisions of the individual EU member states, or EU Member States govern the system for the approval of clinical trials in the European Union. Under this system, an applicant must obtain prior approval from the competent national authority of the EU Member States in which the clinical trial is to be conducted. Furthermore, the applicant may only start a clinical trial at a specific study site after the competent ethics committee has issued a favorable opinion. The clinical trial application must be accompanied by, among other documents, an investigational medicinal product dossier, or the Common Technical Document, with supporting information prescribed by Directive 2001/20/EC, Directive 2005/28/EC, where relevant the implementing national provisions of the individual EU Member States and further detailed in applicable guidance documents.

In April 2014, the new Clinical Trials Regulation, (EU) No 536/2014, or the Clinical Trials Regulation, was adopted, and is anticipated to enter into force in 2019. The Clinical Trials Regulation will be directly applicable in all the EU Member States, repealing the current Clinical Trials Directive 2001/20/EC. Conduct of all clinical trials performed in the European Union will continue to be bound by currently applicable provisions until the new Clinical Trials Regulation becomes applicable. The extent to which on‑going clinical trials will be governed by the Clinical Trials Regulation will depend on when the Clinical Trials Regulation becomes applicable and on the duration of the individual clinical trial. If a clinical trial continues for more than three years from the day on which the Clinical Trials Regulation becomes applicable, the Clinical Trials Regulation will at that time begin to apply to the clinical trial.

The Clinical Trials Regulation aims to simplify and streamline the approval of clinical trials in the European Union. The main characteristics of the regulation include: a streamlined application procedure via a single entry point, the “EU portal”; a single set of documents to be prepared and submitted for the application as well as simplified reporting procedures for clinical trial sponsors; and a harmonized procedure for the assessment of applications for clinical trials, which is divided in two parts. Part I is assessed by the competent authorities of all EU Member States in which an application for authorization of a clinical trial has been submitted (EU Member States concerned). Part II is assessed separately by each EU Member State concerned. Strict deadlines have been established for the assessment of clinical trial applications. The role of the relevant ethics committees in the assessment procedure will continue to be governed by the national law of the concerned EU Member State. However, overall related timelines will be defined by the Clinical Trials Regulation.

To obtain a marketing authorization for a product under European Union regulatory systems, an applicant must submit an MAA either under a centralized procedure administered by the EMA, or one of the procedures administered by competent authorities in the EU Member States (decentralized procedure, national procedure or mutual recognition procedure). A marketing authorization may be granted only to an applicant established in the European Union. Regulation (EC) No 1901/2006 provides that prior to obtaining a marketing authorization in the European Union, applicants have to demonstrate compliance with all measures included in an EMA‑approved Paediatric Investigation

Plan, or PIP, covering all subsets of the pediatric population, unless the EMA has granted (1) a product‑specific waiver, (2) a class waiver or (3) a deferral for one or more of the measures included in the PIP.

The centralized procedure provides for the grant of a single marketing authorization by the European Commission that is valid for all EU Member States and three of the four European Free Trade Association, or EFTA, States, Iceland, Liechtenstein and Norway. Pursuant to Regulation (EC) No 726/2004, the centralized procedure is compulsory for specific products, including for medicines produced by certain biotechnological processes, products designated as orphan medicinal products, advanced therapy products and products with a new active substance indicated for the treatment of certain diseases, including products for the treatment of cancer. For products with a new active substance indicated for the treatment of other diseases and products that are highly innovative or for which a centralized process is in the interest of patients, the centralized procedure may be optional.

Under the centralized procedure, the Committee for Medicinal Products for Human Use, or the CHMP, established at the EMA is responsible for conducting the initial assessment of a product. The CHMP is also responsible for several post‑authorization and maintenance activities, such as the assessment of modifications or extensions to an existing marketing authorization. Under the centralized procedure in the European Union, the maximum timeframe for the evaluation of an MAA is 210 days, excluding clock stops, when additional information or written or oral explanation is to be provided by the applicant in response to questions of the CHMP. Accelerated evaluation might be granted by the CHMP in exceptional cases, when a medicinal product is of major interest from the point of view of public health and in particular from the viewpoint of therapeutic innovation. If the CHMP accepts such request, the time limit of 210 days will be reduced to 150 days but it is possible that the CHMP can revert to the standard time limit for the centralized procedure if it considers that it is no longer appropriate to conduct an accelerated assessment. At the end of this period, the CHMP provides a scientific opinion on whether or not a marketing authorization should be granted in relation to a medicinal product. Within 15 calendar days of receipt of a final opinion from the CHMP, the European Commission must prepare a draft decision concerning an application for marketing authorization. This draft decision must take the opinion and any relevant provisions of EU law into account. Before arriving at a final decision on an application for centralized authorization of a medicinal product the European Commission must consult the Standing Committee on Medicinal Products for Human Use. The Standing Committee is composed of representatives of the EU Member States and chaired by a non‑voting European Commission representative. The European Parliament also has a related “droit de regard”. The European Parliament’s role is to ensure that the European Commission has not exceeded its powers in deciding to grant or refuse to grant a marketing authorization.

Unlike the centralized authorization procedure, the decentralized marketing authorization procedure requires a separate application to, and leads to separate approval by, the competent authorities of each EU Member State in which the product is to be marketed. This application is identical to the application that would be submitted to the EMA for authorization through the centralized procedure. The reference EU Member State prepares a draft assessment and drafts of the related materials within 120 days after receipt of a valid application. The resulting assessment report is submitted to the concerned EU Member States who, within 90 days of receipt, must decide whether to approve the assessment report and related materials. If a concerned EU Member State cannot approve the assessment report and related materials due to concerns relating to a potential serious risk to public health, disputed elements may be referred to the European Commission, whose decision is binding on all EU Member States.

The mutual recognition procedure similarly is based on the acceptance by the competent authorities of the EU Member States of the marketing authorization of a medicinal product by the competent authorities of other EU Member States. The holder of a national marketing authorization may submit an application to the competent authority of an EU Member State requesting that this authority recognize the marketing authorization delivered by the competent authority of another EU Member State.

In the European Union, innovative medicinal products approved on the basis of a complete independent data package qualify for eight years of data exclusivity upon marketing authorization and an additional two years of market exclusivity pursuant to Directive 2001/83/EC. Regulation (EC) No 726/2004 repeats this entitlement for medicinal products authorized in accordance the centralized authorization procedure. Data exclusivity prevents applicants for authorization of generics of these innovative products from referencing the innovator’s data to assess a generic (abbreviated) application for a period of eight years. During an additional two‑year period of market exclusivity, a

generic marketing authorization application can be submitted and authorized, and the innovator’s data may be referenced, but no generic medicinal product can be placed on the European Union market until the expiration of the market exclusivity. The overall 10‑year period will be extended to a maximum of 11 years if, during the first eight years of those 10 years, the marketing authorization holder obtains an authorization for one or more new therapeutic indications which, during the scientific evaluation prior to their authorization, are held to bring a significant clinical benefit in comparison with existing therapies. Even if a compound is considered to be a new chemical entity so that the innovator gains the prescribed period of data exclusivity, another company nevertheless could also market another version of the product if such company obtained marketing authorization based on an MAA with a complete independent data package of pharmaceutical tests, pre‑clinical tests and clinical trials.

A marketing authorization has an initial validity for five years in principle. The marketing authorization may be renewed after five years on the basis of a re‑evaluation of the risk‑benefit balance by the EMA or by the competent authority of the EU Member State. To this end, the marketing authorization holder must provide the EMA or the competent authority with a consolidated version of the file in respect of quality, safety and efficacy, including all variations introduced since the marketing authorization was granted, at least six months before the marketing authorization ceases to be valid. The European Commission or the competent authorities of the EU Member States may decide, on justified grounds relating to pharmacovigilance, to proceed with one further five year period of marketing authorization. Once subsequently definitively renewed, the marketing authorization shall be valid for an unlimited period. Any authorization which is not followed by the actual placing of the medicinal product on the European Union market (in case of centralized procedure) or on the market of the authorizing EU Member State within three years after authorization ceases to be valid (the so‑called sunset clause).

Regulation (EC) No. 141/2000, as implemented by Regulation (EC) No. 847/2000 provides that a drug can be designated as an orphan drug by the European Commission if its sponsor can establish: that the product is intended for the diagnosis, prevention or treatment of (1) a life‑threatening or chronically debilitating condition affecting not more than five in 10,000 persons in the European Union when the application is made, or (2) a life‑threatening, seriously debilitating or serious and chronic condition in the European Union and that without incentives it is unlikely that the marketing of the drug in the European Union would generate sufficient return to justify the necessary investment. For either of these conditions, the applicant must demonstrate that there exists no satisfactory method of diagnosis, prevention or treatment of the condition in question that has been authorized in the European Union or, if such method exists, the drug will be of significant benefit to those affected by that condition.

Once authorized, orphan medicinal products are entitled to 10 years of market exclusivity in all EU Member States and in addition a range of other benefits during the development and regulatory review process including scientific assistance for study protocols, authorization through the centralized marketing authorization procedure covering all member countries and a reduction or elimination of registration and marketing authorization fees. However, marketing authorization may be granted to a similar medicinal product with the same orphan indication during the 10 year period with the consent of the marketing authorization holder for the original orphan medicinal product or if the manufacturer of the original orphan medicinal product is unable to supply sufficient quantities. Marketing authorization may also be granted to a similar medicinal product with the same orphan indication if this product is safer, more effective or otherwise clinically superior to the original orphan medicinal product. The period of market exclusivity may, in addition, be reduced to six years if it can be demonstrated on the basis of available evidence that the original orphan medicinal product is sufficiently profitable not to justify maintenance of market exclusivity.

In case an authorization for a medicinal product in the European Union is obtained, the holder of the marketing authorization is required to comply with a range of requirements applicable to the manufacturing, marketing, promotion and sale of medicinal products. These include:

On June 23, 2016, the electorate in the United Kingdom voted in favor of leaving the European Union (commonly referred to as “Brexit”). Thereafter, on March 29, 2017, the country formally notified the European Union of its intention to withdraw pursuant to Article 50 of the Treaty of Lisbon Amending the Treaty on European Union and the Treaty Establishing the European Community. The withdrawal of the United Kingdom from the European Union will take effect either on the effective date of a withdrawal agreement or, in the absence of agreement, two years after the United Kingdom provides a notice of withdrawal pursuant to the Treaty on European Union (unless such deadline is extended). Since the regulatory framework for pharmaceutical products in the United Kingdom covering quality, safety and efficacy of pharmaceutical products, clinical trials, marketing authorization, commercial sales and distribution of pharmaceutical products is derived from EU directives and regulations, Brexit could materially impact the future regulatory regime which applies to products and the approval of product candidates in the United Kingdom. It remains to be seen how, if at all, Brexit will impact regulatory requirements for product candidates and products in the United Kingdom.

Healthcare Reform

A primary trend in the United States healthcare industry and elsewhere is cost containment. There have been a number of federal and state proposals during the last few years regarding the pricing of pharmaceutical and biopharmaceutical products, limiting coverage and reimbursement for drugs and other medical products, government control and other changes to the healthcare system in the United States.

In March 2010, the U.S. Congress enacted the ACA, which, among other things, includes changes to the coverage and payment for drug products under government health care programs. Among the provisions of the ACA of importance to our potential product candidates are:

Other legislative changes have been proposed and adopted in the United States since the ACA was enacted. In August 2011, the Budget Control Act of 2011, among other things, created measures for spending reductions by Congress. A Joint Select Committee on Deficit Reduction, tasked with recommending a targeted deficit reduction of at least $1.2 trillion for the years 2013 through 2021, was unable to reach required goals, thereby triggering the legislation’s automatic reduction to several government programs. This includes aggregate reductions of Medicare payments to providers up to two percent (2%) per fiscal year, which went into effect in April 2013 and will remain in effect through 2024 unless additional Congressional action is taken.

Since its enactment, there have been numerous legal challenges and Congressional actions to repeal and replace provisions of the ACA. Some of the provisions of the ACA have yet to be implemented, and there have been legal and political challenges to certain aspects of the ACA. Since January 2017, President Trump has signed two executive orders and other directives designed to delay, circumvent, or loosen certain requirements mandated by the ACA. Moreover, the Tax Reform Bill was enacted on December 22, 2017, and includes a provision repealing, effective January 1, 2019, the tax‑based shared responsibility payment imposed by the ACA on certain individuals who fail to maintain qualifying health coverage for all or part of a year that is commonly referred to as the “individual mandate”. Congress may consider other legislation to repeal or replace additional elements of the ACA. We continue to evaluate the effect that the ACA, the repeal of the individual mandate, and any additional repeal and replacement efforts may have on our business but expect that the ACA, as currently enacted or as it may be amended in the future, and other healthcare reform measures that may be adopted in the future could have a material adverse effect on our industry generally and on our ability to maintain or increase sales of our existing products that we successfully commercialize or to successfully commercialize our product candidates, if approved. In addition to the ACA, there will continue to be proposals by legislators at both the federal and state levels, regulators and third party payors to keep healthcare costs down while expanding individual healthcare benefits.

Employees

As of December 31, 2018, we had 32 full time employees. The members of our management team are employed by both our company and Y‑mAbs Therapeutics A/S, our wholly owned Danish subsidiary. As our development and commercialization plans and strategies develop, we intend to continue adding a number of additional managerial, operational, sales, marketing, financial, and other personnel. None of our employees are represented by labor unions or covered by collective bargaining agreements. We consider our relationship with our employees to be good.

Corporate Information

We were incorporated in Delaware on April 30, 2015. Our principal executive offices are located at 230 Park Avenue, Suite 3350, New York, New York 10169, and our telephone number is (646) 885-8505. Our website address is www.ymabs.com. The information contained on, or accessible through, our website is not incorporated by reference into this Form 10-K, and you should not consider any information contained in, or that can be accessed through, our website as part of this 10-K or in deciding whether to purchase our common stock.

 

ITEM 1A.        RISK FACTORS.

Our business is subject to numerous risks. You should carefully consider the risks and uncertainties described below together with all of the other information contained in this Annual Report on Form 10 K, including our financial statements and the related notes, and in our other filings with the SEC. Additional risks and uncertainties that we are unaware of, or that we currently believe are not material, may also become important factors that affect us. If any of the following risks occur, our business, financial condition, results of operations and future growth prospects could be materially and adversely affected. In such event, the trading price of our common stock could decline and you might lose all or part of your investment.

Risks Related to Our Financial Condition and Need for Additional Capital

We have a limited operating history and have incurred significant losses since inception. We have no products approved for commercial sale and we expect to incur significant losses for the foreseeable future. We may never achieve or maintain profitability, which may cause the market value of our common stock to decline significantly.

We are a clinical‑stage biopharmaceutical company with a limited operating history. Since our inception in 2015, we have incurred significant losses. Our net losses were $19.2 million for the year ended December 31, 2017 and $43.3 million for the year ended December 31, 2018. As of December 31, 2018, we had an accumulated deficit of $84.8 million. We have financed our operations principally through private placements and the initial public offering of

our common stock. To date, we have devoted substantially all of our efforts to research and development of our lead product candidates. While our lead product candidates are in pivotal clinical trials, we cannot assure you that we will receive regulatory approval for the sale of these or other product candidates in the near term, if at all. Our other product candidates are in the early stages of clinical development or pre‑clinical research. As a result, we expect that it will be a number of years, if ever, before we have any of these other product candidates approved and ready for commercialization.

We expect to continue to incur significant expenses and increasing operating losses for the foreseeable future. The net losses we incur may fluctuate significantly from quarter to quarter. We have no product candidates approved for commercial sale, have not generated any revenue from product sales, and do not anticipate generating any revenue from product sales until sometime after we receive regulatory approval for the commercial sale of a product candidate. We cannot assure you that we will ever receive regulatory approval for any of our product candidates. Our ability to generate revenue and achieve profitability depends significantly on our success in many factors, including:

Even if one or more of the product candidates that we develop is approved for commercial sale, we anticipate incurring research, development, clinical trial, manufacturing and marketing costs associated with commercializing any approved products. Our expenses could increase beyond expectations if we are required by the FDA or other regulatory agencies, domestic or foreign, to change our manufacturing processes or assays, or to perform clinical, non‑clinical, or other types of studies in addition to those that we currently anticipate. If we are successful in obtaining regulatory approvals to market one or more of our product candidates, our revenue will be dependent, in part, upon the size of the markets in the territories for which we gain regulatory approval, the accepted price for the product, the ability to obtain reimbursement at any price, and whether we own the commercial rights for that territory. If the number of our addressable disease patients is not as significant as we estimate, the indication approved by regulatory authorities is narrower than we expect, or the reasonably expected population for treatment is narrowed by competition, physician choice or treatment guidelines, we may not generate significant revenue from sales of such products, even if approved. If we are not able to generate sufficient revenue from the sale of any approved products, we may never become profitable.

Our limited operating history may make it difficult for you to evaluate the success of our business to date and to assess our future viability.

We were incorporated and began our operations on April 30, 2015. Our operations to date have been limited to organizing and staffing our company, business planning, raising capital, conducting clinical trials of our lead product candidates, conducting pre‑clinical studies of our other product candidates, and identifying additional potential product candidates. We have not yet demonstrated our ability to successfully complete any clinical trials, including large‑scale, pivotal clinical trials, obtain marketing approvals, manufacture a commercial‑scale drug or arrange for a third party to do so on our behalf, or conduct sales and marketing activities necessary for successful drug commercialization. Typically, it takes about six to 10 years to develop a new drug from the time it is in Phase 1 clinical trials to when it is approved for treating patients, but in many cases it may take longer. Consequently, any predictions you make about our future success or viability may not be as accurate as they could be if we had a longer operating history or a history of successfully developing and commercializing pharmaceutical products. In addition, as a business with a limited operating history, we may encounter unforeseen expenses, difficulties, complications, delays and other known and unknown factors as we continue to develop and commercialize our product candidates. As we continue to build our business, we expect our financial condition and operating results to fluctuate significantly from quarter to quarter and year to year due to a variety of factors, many of which are beyond our control. Accordingly, you should not rely upon the results of any particular quarterly or annual periods as indications of future operating performance.

Our payment obligations to MSK may be a drain on our cash resources, or may cause us to incur debt obligations or issue additional equity securities to satisfy such payment obligations, which may adversely affect our financial position and results of operations.

Under the MSK License, we have committed to funding scientific research as well as conducting certain clinical trial activities at MSK through 2020. As licensed product candidates progress through clinical development and commercialization, certain milestone payments will come due, and we will owe MSK customary royalties on commercial sales of our approved products, if any, including, unless such royalties become due earlier, an annual fixed minimum royalty of $80,000 over the royalty term starting in 2020. These milestone payments become due upon achievement of the related clinical, regulatory or sales‑based milestone set forth in the MSK License. Certain of the clinical and regulatory milestone payments become due at the earlier of completion of the related milestone activity or the date indicated in the MSK License, whether or not the milestone activity has been achieved. Total clinical and regulatory milestones potentially due under the MSK License are $2,450,000 and $9,000,000, respectively. There are also sales‑based milestones that become due should we achieve certain amounts of sales of licensed products with total sales‑based milestones potentially due of $20,000,000. Under the MSK CD33 License, we are obligated to make potential payments of $550,000, $500,000 and $7,500,000 for clinical, regulatory and sales based milestones, respectively. In addition, we have committed to acquire certain personnel and laboratory services at MSK under a Master Data Services Agreement, or MDSA, and two separate Core Facility Service Agreements, or CFSAs. We have also entered into an Investigator‑Sponsored Master Clinical Trial Agreement, or MCTA, under which we will provide drug product and funding for certain clinical trials at MSK under separate appendices to be executed. Additionally, we entered into a Sponsored Research Agreement, or the SRA, with MSK pursuant to which we agreed to pay MSK to conduct certain research projects over a period of five years related to the intellectual property licensed under the MSK License. We also entered into a Sponsored Research Agreement, or the CD33 SRA, in connection with the MSK CD33 License, pursuant to which we committed to provide aggregate research funding to MSK annually for a term of two years. We entered into a Manufacturing Agreement with MSK’s Radiochemistry and Molecular Imaging Probes Core Facility, or RMIP, pursuant to which RMIP will complete specified manufacturing activities related to 131I‑omburtamab in connection with our Phase 2 trials for Study 101. Additionally, we entered into a Sublicense Agreement, or the MabVax Sublicense, with MabVax Therapeutics Holdings, Inc., or MabVax, pursuant to which MabVax granted us all of the exclusive rights granted to MabVax under its license agreement with MSK, or the MabVax‑MSK License, for a bi‑valent ganglioside based vaccine intended to treat NB, or the NB vaccine. In addition to the upfront payment of $700,000 that we have made under the terms of MabVax Sublicense, we have agreed to make an additional payment of $600,000 on the first anniversary of the MabVax Sublicense. We will also be responsible for any potential downstream payment obligations to MSK related to the NB vaccine that were specified in the MabVax‑MSK license agreement. This includes the obligation to pay development milestones totaling $1,400,000 and mid single‑digit royalty payments to MSK.

These payments could be significant and in order to satisfy our obligations to MSK, if and when they are triggered, we may use our existing cash, incur debt obligations or issue additional equity securities, which may materially and adversely affect our financial position and results of operations.

We will need substantial additional funding for our product candidates. If we fail to obtain additional funding for our product candidates, we may be forced to delay, reduce or eliminate our research and drug development programs or future commercialization efforts and our license and other agreements may be terminated.

Developing pharmaceutical products, including conducting pre‑clinical studies and clinical trials, is a very time‑consuming, expensive and uncertain process that takes years to complete. We expect our expenses to increase in connection with our ongoing activities, particularly as we conduct clinical trials of, and seek marketing approval for our lead product candidates and our other product candidates. In addition, if we obtain marketing approval for any of our product candidates, we expect to incur commercialization expenses, which may be significant, related to product sales, marketing, manufacturing and distribution to the extent that such sales, marketing, manufacturing and distribution are not the responsibility of any collaborator that we may have at such time for any such product candidate. Furthermore, we expect to incur additional costs associated with operating as a public company. Accordingly, we will need to obtain substantial additional funding in connection with our continuing operations. If we are unable to raise sufficient amounts of additional capital when needed or on attractive terms, we may be forced to delay, reduce or eliminate our research and drug development programs or our future commercialization efforts.

As of December 31, 2018, we had approximately $147.8 million in cash and cash equivalents. We believe that our cash and cash equivalents, will be sufficient to fund our operations through the fourth quarter of 2020. However, changing circumstances may cause us to increase our spending significantly faster than we currently anticipate, and we may need to spend more money than currently expected because of circumstances beyond our control. We will require additional capital for further development and commercialization of our product candidates and may need to raise additional funds earlier if we choose to expand more rapidly than we presently anticipate.

In addition, we cannot be certain that additional funding will be available on acceptable terms, or at all. We have no firmly committed source of additional capital and if we are unable to raise additional capital in sufficient amounts or on terms acceptable to us, we may have to significantly delay, scale back or discontinue the development or commercialization of our product candidates or other research and development initiatives. Our licenses and other agreements may also be terminated if we are unable to meet the payment obligations under the agreements. We could be required to seek collaborators for our product candidates at an earlier stage than otherwise would be desirable or on terms that are less favorable than might otherwise be available or relinquish or license on unfavorable terms our rights to our product candidates in markets where we otherwise would seek to pursue development or commercialization ourselves. Any of the above events could significantly harm our business, prospects, financial condition and results of operations and cause the price of our common stock to decline.

Raising additional capital may cause dilution to our stockholders, restrict our operations or require us to relinquish rights to our product candidates on terms unfavorable to us.

We expect our expenses to increase in connection with our planned operations. Until such time, if ever, as we can generate substantial revenues from the sale of our product candidates, we expect to finance our cash needs through a combination of cash on hand, equity offerings, debt financings, collaborations, strategic alliances and/or licensing arrangements. To the extent that we raise additional capital through the sale of equity or convertible debt securities, your ownership interest will be diluted, and the terms of these securities could include liquidation or other preferences and anti‑dilution protections that could adversely affect your rights as a common stockholder. In addition, debt financing, if available, would result in fixed payment obligations and may involve agreements that include restrictive covenants that limit our ability to take specific actions, such as incurring additional debt, making capital expenditures or acquisitions, limiting our ability to conduct licensing transactions, creating liens, redeeming stock or declaring dividends, that could adversely impact our ability to conduct our business. In addition, securing financing could require a substantial amount of time and attention from our management and may divert a disproportionate amount of their attention away from day‑to‑day activities, which may adversely affect our management’s ability to oversee the development of our product candidates.

If we raise additional funds through collaborations, strategic alliances or licensing arrangements with third parties, we may have to relinquish valuable rights related to our intellectual property, future revenue streams or any of our future product candidates or grant licenses on terms that may not be favorable to us. If we are unable to raise additional funds when needed, we may be required to delay, reduce and/or eliminate our product development or future commercialization efforts or grant rights to develop and market product candidates that we would otherwise prefer to develop and market ourselves.

If we engage in future acquisitions or strategic partnerships, this may increase our capital requirements, dilute our stockholders if we issue equity securities, cause us to incur debt or assume contingent liabilities, and subject us to other risks.

We may evaluate various acquisitions and strategic partnerships, including licensing or acquiring complementary products, intellectual property rights, technologies, or businesses. Any potential acquisition or strategic partnership may entail numerous risks, including:

In addition, if we undertake acquisitions, we may issue dilutive securities, assume or incur debt obligations, incur large one‑time expenses and acquire intangible assets that could result in significant future amortization expense. Moreover, we may not be able to locate suitable acquisition opportunities, which could impair our ability to grow or obtain access to technology or products that may be important to the development of our business.

We may expand our resources to pursue a particular product candidate or indication and fail to capitalize on other product candidates or indications that may be more profitable or for which there is a greater likelihood of success.

We intend to focus our efforts and managerial resources on specific product candidates and on specific indications. As a result, we may forgo or delay pursuit of opportunities with other product candidates or for other indications that may prove to have greater commercial potential. Our resource allocation decisions may cause us to fail to capitalize on viable commercial products or profitable market opportunities. Failure to properly assess potential product candidates for indications could result in focusing on product candidates for indications with lower market potential, which could harm our business and financial condition. Our spending on current and future research and development programs and product candidates for specific indications may not yield any commercially viable product candidates. If we do not accurately evaluate the commercial potential or target market for a particular product candidate, we may relinquish valuable rights to that product candidate through partnering, licensing or other royalty arrangements

in cases in which it would have been more advantageous for us to retain sole development and commercialization rights to such product candidate or product.

It has been determined that we have material weaknesses in our internal control over financial reporting. If our remediation of these material weaknesses is not effective, or if we experience additional material weaknesses or otherwise fail to maintain an effective system of internal controls in the future, we may not be able to accurately or timely report our financial condition or results of operations, which may adversely affect investor confidence in us and, as a result, the value of our common stock. In addition, because of our status as an emerging growth company, our independent registered public accounting firm is not required to provide an attestation report as to our internal control over financial reporting for the foreseeable future.

Our management is responsible for establishing and maintaining adequate internal control over financial reporting. Internal control over financial reporting is a process designed to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements in accordance with generally accepted accounting principles, or GAAP. As a result of being a public company, we will be required, pursuant to Section 404 of the Sarbanes‑Oxley Act, to furnish a report by our management on, among other things, the effectiveness of our internal control over financial reporting beginning with the annual report for our fiscal year 2019. This assessment will need to include disclosures of any material weaknesses identified by our management in our internal control over financial reporting. A “material weakness” is a deficiency, or a combination of deficiencies, in internal control over financial reporting such that there is a reasonable possibility that a material misstatement of our annual or interim financial statements will not be prevented or detected on a timely basis. We are in the very early stages of the costly and challenging process of planning the activities necessary to perform the evaluation needed to comply with Section 404.

In connection with the audit of our financial statements for the year ended December 31, 2017 it was determined that we lack a sufficient number of trained professionals with an appropriate level of accounting knowledge, training and experience to: (a) design and maintain formal accounting policies, procedures and controls over the fair presentation of our financial statements; (b) analyze, record and disclose complex accounting matters timely and accurately, including share‑based compensation arrangements and accounting for license arrangements; and (c) design and maintain controls over the preparation and review of account reconciliations, journal entries and financial statements, including maintaining appropriate segregation of duties.

Each of these control deficiencies could result in a misstatement of these accounts or disclosures that would result in a material misstatement of our annual or interim consolidated financial statements that would not be prevented or detected, and accordingly, it was determined that these control deficiencies constitute material weaknesses.

We have hired finance professionals in 2018 with the plan to help mitigate the identified material weaknesses and are evaluating the implementation of additional procedures to address these material weaknesses. 

We cannot assure you however that these or other measures will fully remediate the material weaknesses described above in a timely manner. We have commenced addressing the material weaknesses identified above by hiring additional finance and accounting personnel and increasing the oversight and review procedures with regard to financial reporting, financial processes and procedures and internal control procedures. Nevertheless, we cannot assure you that we will be able to remedy our current material weaknesses. If we are unable to remediate the material weaknesses, or otherwise maintain effective internal control over financial reporting, we may not be able to report our financial results accurately, prevent fraud or file our periodic reports in a timely manner. If our remediation of these material weaknesses is not effective, or if we experience additional material weaknesses or otherwise fail to maintain an effective system of internal controls in the future, we may not be able to accurately or timely report our financial condition or results of operations, which may adversely affect investor confidence in us and, as a result, the value of our common stock. We cannot assure you that all of our existing material weaknesses have been identified, or that we will not in the future identify additional material weaknesses.

Our independent registered public accounting firm will not be required to formally attest to the effectiveness of our internal control over financial reporting pursuant to Section 404 until the later of the year following the filing of this annual report on Form 10-K with the SEC, or the date we are no longer an “emerging growth company” as defined in the

JOBS Act, if we take advantage (as we expect to do) of the exemptions contained in the JOBS Act. We will remain an “emerging growth company” for up to five years, although if the market value of our common stock that is held by non‑affiliates exceeds $700.0 million as of June 30 of any year before that time, we would cease to be an “emerging growth company” as of December 31 of that year. At such time, our independent registered public accounting firm may issue a report that is adverse in the event it is not satisfied with the level at which our controls are documented, designed or operating. Our remediation efforts may not enable us to avoid material weaknesses in our internal control over financial reporting in the future.

If we are unsuccessful in building an appropriate accounting infrastructure, we may not be able to prepare and disclose, in a timely manner, our financial statements and other required disclosures, or comply with existing or new reporting requirements. Any failure to report our financial results on an accurate and timely basis could result in sanctions, lawsuits, delisting of our shares from the NASDAQ Global Select Market or other adverse consequences that would materially harm our business. If we cannot provide reliable financial reports or prevent fraud, our business and results of operations could be harmed and investors could lose confidence in our reported financial information. Any of the foregoing occurrences, should they come to pass, could negatively impact the public perception of our company, which could have a negative impact on our stock price.

Risks Related to Product Development and Commercialization

Our product candidates and related technologies are novel approaches to cancer treatment that present significant challenges, and our ability to generate product revenue is dependent on the success of one or more of our lead product candidates, which will require additional clinical testing before we can seek regulatory approval and begin commercial sales.

Our product candidates and related technologies represent novel approaches to cancer treatment generally, and developing and commercializing our product candidates subjects us to a number of challenges. We currently generate no revenues from sales of any products, we have never obtained marketing approval for a product candidate and we may never be able to develop a marketable product. Our ability to generate product revenue is highly dependent on our ability to obtain regulatory approval of and successfully commercialize one or more of our lead product candidates, which will require additional clinical and non‑clinical development, regulatory review and approval in each jurisdiction in which we intend to market them, substantial investment, access to sufficient commercial manufacturing capacity, and significant marketing efforts before we can generate any revenue from product sales. We cannot be certain that any of our product candidates will be successful in clinical studies and they may not receive regulatory approval even if they are successful in clinical studies.

The success of our product candidates, including our lead product candidates, will depend on several factors, including the following:

We do not have complete control over many of these factors, including certain aspects of clinical development and the regulatory submission process, potential threats to our intellectual property rights and the manufacturing, marketing, distribution and sales efforts of any future collaborator.

In addition, because our lead product candidates are our most advanced product candidates, and because our other product candidates are based on similar technology, if our lead product candidates encounter safety or efficacy problems, developmental delays, regulatory issues, or other problems, our development plans and business could be significantly harmed. Further, competitors who are developing products with similar technology may experience problems with their products that could identify problems that would potentially harm our business.

Drug development is a lengthy and expensive process, with an uncertain outcome. If clinical trials of our product candidates fail to demonstrate safety and efficacy to the satisfaction of regulatory authorities or do not otherwise produce positive results, we may incur additional costs, experience delays in completing, or ultimately be unable to complete, the development of our product candidates or be unable to obtain marketing approval. We may encounter substantial delays in our clinical trials, or may not be able to conduct our trials on the timelines we expect.

Before obtaining marketing approval from regulatory authorities for the sale of our product candidates, we must complete pre‑clinical development and then conduct extensive clinical trials to demonstrate the safety and efficacy of our product candidates. Clinical testing is expensive, difficult to design and implement, can take many years to complete and is uncertain as to outcome. Failure of one or more clinical trials can occur at any stage of testing. The outcome of pre‑clinical studies and early‑stage clinical trials may not be predictive of the success of later clinical trials, and interim results of a clinical trial, such as the results of our ongoing clinical trials of our lead product candidates, do not necessarily predict final results. Moreover, pre‑clinical and clinical data are often susceptible to varying interpretations and analyses, and many companies that have believed their product candidates performed satisfactorily in pre‑clinical studies and clinical trials have nonetheless failed to obtain marketing approval of their drugs.

We cannot guarantee that any clinical studies will be conducted as planned or completed on schedule, if at all. In addition, we cannot be sure that we will be able to submit INDs for any of our product candidates in the future and we cannot be sure that submission of an IND will result in the FDA allowing clinical trials to begin. Moreover, even if these trials begin, issues may arise that could suspend or terminate such clinical trials. A failure of one or more clinical studies can occur at any stage of testing, and our future clinical studies may not be successful.

The market opportunities for our product candidates may be limited to those patients who are ineligible for or have failed prior treatments and may be small. If we encounter difficulties enrolling patients in our clinical trials, our clinical development activities could be delayed or otherwise adversely affected and it may indicate that the market opportunity for our product candidates is smaller than we expect.

Our current potential patient population is based on our beliefs and estimates regarding the incidence or prevalence of certain types of cancers that may be addressable by our product candidates, which is derived from a variety of sources, including scientific literature, surveys of clinics, patient foundations, or market research. Our projections may prove to be incorrect and the number of potential patients may turn out to be lower than expected. Even if we obtain significant market share for our product candidates, because the potential target populations are small, we may never achieve profitability without obtaining regulatory approval for additional and broader indications, including use of our product candidates for front‑line and second‑line therapy.

We expect to initially seek approval of some of our product candidates as second or third‑line therapies for patients who have failed other approved treatments. Subsequently, for those product candidates that prove to be sufficiently beneficial, if any, we would expect to seek approval as a second‑line therapy and potentially as a front‑line therapy, but there is no guarantee that our product candidates, even if approved for third‑line therapy, would be approved for second‑line or front‑line therapy. In addition, we may have to conduct additional clinical trials prior to gaining approval for second‑line or front‑line therapy.

The timely completion of clinical trials in accordance with their protocols depends, among other things, on our ability to enroll a sufficient number of patients who remain in the trial until its conclusion. We may experience difficulties in patient enrollment in our clinical trials for a variety of reasons, including:

In addition, our clinical trials will compete with other clinical trials for product candidates that are in the same therapeutic areas as our product candidates, and this competition will reduce the number and types of patients available to us, because some patients who might have opted to enroll in our trials may instead opt to enroll in a trial being conducted by one of our competitors. We expect to conduct some of our clinical trials at the same clinical trial sites that some of our competitors use, which will reduce the number of patients who are available for our clinical trials at such clinical trial sites. Moreover, because our product candidates represent a departure from more commonly used methods

for cancer treatment, potential patients and their doctors may be inclined to only use conventional therapies, such as chemotherapy and radiation, rather than enroll patients in any future clinical trial.

Even if we are able to enroll a sufficient number of patients in our clinical trials, delays in patient enrollment may result in increased costs or may affect the timing or outcome of the planned clinical trials, which could prevent completion of these trials and adversely affect our ability to advance the development of our product candidates, submit regulatory filings, obtain marketing approvals and delay the launch of our products, upon approval.

Our product candidates may cause serious adverse events, or SAEs, undesirable side effects or have other properties that could halt their clinical development, prevent, delay, or cause the withdrawal of their regulatory approval, limit their commercial potential, or result in significant negative consequences, including death of patients. If any of our product candidates receives marketing approval and we, or others, later discover that the drug is less effective than previously believed or causes undesirable side effects that were not previously identified, our ability, or that of any potential future collaborators, to market the drug could be compromised.

As with most biological drug products, use of our product candidates could be associated with undesirable side effects or adverse events which can vary in severity from minor reactions to death, and in frequency from infrequent to prevalent. Undesirable side effects or unacceptable toxicities caused by our product candidates could cause us or regulatory authorities to interrupt, delay, or halt clinical trials. To date, there have been no significant long‑term toxicities among patients treated with our lead product candidates.

Treatment‑related undesirable side effects or adverse events could also affect patient recruitment or the ability of enrolled subjects to complete the trial, or could result in potential product liability claims. In addition, these side effects may not be appropriately or timely recognized or managed by the treating medical staff, particularly outside of the research institutions that collaborate with us. We expect to have to educate and train medical personnel using our product candidates to understand their side effect profiles, both for our planned clinical trials and upon any commercialization of any product candidates. Inadequate training in recognizing or managing the potential side effects of our product candidates could result in adverse effects to patients, including death. Any of these occurrences may materially and adversely harm our business, financial condition and prospects.

Clinical trials of our product candidates must be conducted in carefully defined subsets of patients who have agreed to enter into clinical trials. Consequently, it is possible that our clinical trials, or those of any potential future collaborator, may indicate an apparent positive effect of a product candidate that is greater than the actual positive effect, if any, or alternatively fail to identify undesirable side effects. If one or more of our product candidates receives marketing approval and we, or others, discover that the drug is less effective than previously believed or causes undesirable side effects that were not previously identified, including during any long‑term follow‑up observation period recommended or required for patients who receive treatment using our products, a number of potentially significant negative consequences could result, including:

Any of the foregoing could prevent us from achieving or maintaining market acceptance of the particular product candidate, if approved, and could significantly harm our business, results of operations, and prospects, and could adversely impact our financial condition, results of operations, ability to raise additional financing or the market price of our common stock.

The outcome of pre‑clinical studies and early clinical trials may not be predictive of the success of later clinical trials, interim results of a clinical trial do not necessarily predict final results, and the results of our clinical trials may not satisfy the requirements of the FDA or comparable foreign regulatory authorities, and if an adverse safety issue, clinical hold or other adverse finding occurs in one or more of our clinical trials of our lead product candidates, such event could adversely affect our other clinical trials of our lead product candidates.

Success in pre‑clinical studies and early‑stage clinical trials does not mean that future larger registration clinical trials will be successful because product candidates in later‑stage clinical trials may fail to demonstrate sufficient safety and efficacy to the satisfaction of the FDA and non‑U.S. regulatory authorities despite having progressed through pre‑clinical studies and early‑stage clinical trials. Product candidates that have shown promising results in pre‑clinical studies and early‑stage clinical trials may still suffer significant setbacks in subsequent clinical trials. Additionally, the outcome of pre‑clinical studies and early‑stage clinical trials may not be predictive of the success of larger, later‑stage clinical trials.

From time to time, we may publish or report interim or preliminary data from our clinical trials. Interim or preliminary data from clinical trials that we may conduct may not be indicative of the final results of the trial and are subject to the risk that one or more of the clinical outcomes may materially change as patient enrollment continues and more patient data become available. Interim or preliminary data also remain subject to audit and verification procedures that may result in the final data being materially different from the interim or preliminary data. As a result, interim or preliminary data should be viewed with caution until the final data are available.

In addition, the design of a clinical trial can determine whether its results will support approval of a drug and flaws in the design of a clinical trial may not become apparent until the clinical trial is well advanced. We may be unable to design and conduct a clinical trial to support marketing approval. Further, if our product candidates are found to be unsafe or lack efficacy, we will not be able to obtain marketing approval for them and our business would be harmed. A number of companies in the pharmaceutical industry, including those with greater resources and experience than us, have suffered significant setbacks in advanced clinical trials, even after obtaining promising results in pre‑clinical studies and earlier clinical trials.

In some instances, there can be significant variability in safety and efficacy results between different clinical trials of the same product candidate due to numerous factors, including changes in trial protocols, differences in size and type of the patient populations, differences in and adherence to the dosing regimen and other trial protocols and the rate of dropout among clinical trial participants. We do not know whether any clinical trials we may conduct will demonstrate consistent or adequate efficacy and safety sufficient to obtain marketing approval to market our product candidates. We have multiple clinical trials of our lead product candidates currently ongoing. In the event that an adverse safety issue, clinical hold or other adverse finding occurs in one or more of our clinical trials of our lead product candidates, such event could adversely affect our other clinical trials of our lead product candidates.

In October 2017, the FDA issued a partial clinical hold on our IND for naxitamab. A partial clinical hold, as opposed to a full clinical hold, is a delay or suspension of only a specific part of the clinical work requested under the

IND, which allows otherwise unaffected parts of the clinical work to proceed under the IND. The FDA stated that the proposed acceptance criterion for the ADCC‑CD16, ADCC‑CD32, and CDC assays were too wide to provide sufficient control over these attributes, which are critical for safety and efficacy. ADCC and CDC refer to antibody dependent cell‑mediated cytotoxicity and complement‑dependent cytotoxicity, respectively. We submitted a response to the FDA in March 2018, and met with the FDA in April 2018. Subsequently, we submitted a complete response to the partial clinical hold to the FDA in May 2018 and the partial clinical hold was removed in June 2018. One or more clinical trials of our lead product candidates may be subject to additional clinical holds in the future, which may ultimately delay or otherwise adversely affect the clinical development of our lead product candidates.

In addition, we have initiated Study 101 and Study 201 to form the primary basis for our planned BLAs, to establish comparability of study population and phamacokinetics analysis with Study 03‑133 and Study 12‑230, respectively, and to satisfy the confirmatory study and post‑marketing requirements by the FDA. If the results of these studies fail to demonstrate comparability to the satisfaction of the FDA and other comparable regulatory authorities, this may lead to a delay in, or otherwise adversely affect, such clinical trials, including the timing of submission of BLAs.

Further, our product candidates may not be approved even if they achieve their primary endpoints in Phase 3 trials or other pivotal trials. The FDA or non‑U.S. regulatory authorities may disagree with our trial design, our interpretation of data from pre‑clinical studies and clinical trials or conclude that we do not have adequate manufacturing controls or quality systems. In addition, any of these regulatory authorities may change requirements for the approval of a product candidate even after reviewing and providing comments or advice on a protocol for a pivotal clinical trial that has the potential to result in approval by the FDA or another regulatory authority. In addition, any of these regulatory authorities may also approve a product candidate for fewer or more limited indications than we request or may grant approval contingent on the performance of costly post‑marketing clinical trials. The FDA or other non‑U.S. regulatory authorities may not approve the labeling claims that we believe would be necessary or desirable for the successful commercialization of our product candidates.

Before obtaining marketing approvals for the commercial sale of any product candidate for a target indication, we must demonstrate with substantial evidence gathered in pre‑clinical studies and well‑controlled clinical studies, and, with respect to approval in the United States, to the satisfaction of the FDA, that the product candidate is safe and effective for use for that target indication. There is no assurance that the FDA or non‑U.S. regulatory authorities will consider our future clinical trials to be sufficient to serve as the basis for approval of one of our product candidates for any indication. The FDA and non‑U.S. regulatory authorities retain broad discretion in evaluating the results of our clinical trials and in determining whether the results demonstrate that a product candidate is safe and effective. If we are required to conduct additional clinical trials of a product candidate than we expect prior to its approval, we will need substantial additional funds and there is no assurance that the results of any such additional clinical trials will be sufficient for approval.

Research and development of biopharmaceutical products is inherently risky. We may not be successful in our efforts to create a pipeline of product candidates and develop commercially successful products. If we fail to develop additional product candidates, our commercial opportunity will be limited.

The product candidates and related technologies we have licensed have not yet led, and may never lead, to approved or commercially successful products. Even if we are successful in continuing to build our pipeline, obtaining regulatory approvals and commercializing our product candidates will require substantial additional funding beyond our cash and cash equivalents and are prone to the risks of failure inherent in medical product development. Investment in biopharmaceutical product development involves significant risk that any potential product candidate will fail to demonstrate adequate efficacy or an acceptable safety profile, gain regulatory approval, and/or become commercially viable. We cannot provide you any assurance that we will be able to successfully advance any of these additional product candidates through the development process. Our research programs may initially show promise in identifying potential product candidates, yet fail to yield product candidates for clinical development or commercialization for many reasons, including the following:

If any of these events occur, we may be forced to abandon our development efforts for a program or programs, or we may not be able to identify, discover, develop, or commercialize additional product candidates, which would have a material adverse effect on our business and could potentially cause us to cease operations. Even if we receive approval to market our product candidates from the FDA, the EMA, or other regulatory bodies, whether for the treatment of cancers or other diseases, we cannot assure you that any such product candidates will be successfully commercialized, widely accepted in the marketplace or more effective than other commercially available alternatives.

Even if any of our product candidates receive marketing approval, they may fail to achieve the degree of market acceptance by physicians, patients, healthcare payors and others in the medical community necessary for commercial success.

If any of our product candidates receive marketing approval, they may nonetheless fail to gain sufficient market acceptance by physicians, patients, healthcare payors and others in the medical community. For example, current cancer treatments like chemotherapy and radiation therapy are well‑established in the medical community, and doctors may continue to rely on these treatments. If our product candidates do not achieve an adequate level of acceptance, we may not generate significant revenues from sales of drugs and we may not become profitable. The degree of market acceptance of our product candidates, if approved for commercial sale, will depend on a number of factors, including:

We currently have only a limited marketing and sales organization and have only limited experience in marketing products. We may not be successful in commercializing our product candidates if and when they are approved unless we are able to expand our sales and marketing capabilities or enter into agreements with third parties to sell and market such approved products.

We only have a limited sales or marketing infrastructure and have only limited experience in the sale or marketing of pharmaceutical drugs. We are not currently a party to a strategic collaboration that provides us with access to a collaborator’s resources in selling or marketing drugs. To achieve commercial success for any approved drug we must either further develop a sales and marketing organization or outsource these functions to strategic collaborators and other third parties. In the future, we may choose to build a sales and marketing infrastructure to market or co‑promote some of our product candidates if and when they are approved, or enter into collaborations with respect to the sale and marketing of our product candidates.

There are risks involved with both further establishing our own direct sales and marketing capabilities and entering into arrangements with third parties to perform these services. For example, recruiting and training even a small sales force can be expensive and time‑consuming and could delay any commercial launch of a product candidate. If the commercial launch of a product candidate for which we recruit a sales force and establish marketing capabilities is delayed or does not occur for any reason, we would have prematurely or unnecessarily incurred these commercialization expenses. This may be costly, and our investment would be lost if we cannot retain or reposition our sales and marketing personnel.

Factors that may inhibit our efforts to commercialize our drugs on our own after obtaining any regulatory approval to gain market acceptance include:

If we enter into arrangements with third parties to perform sales and marketing services, our revenues from the sale of drugs or the profitability of these revenues to us are likely to be lower than if we were to market and sell any drugs that we develop ourselves. In addition, we may not be successful in entering into arrangements with third parties to sell and market our product candidates or may be unable to do so on terms that are favorable to us. We likely will have little control over such third parties, and any of them may fail to devote the necessary resources and attention to sell and market our drugs effectively. If we do not establish further sales and marketing capabilities successfully, either on our own or in collaboration with third parties, we will not be successful in commercializing our product candidates.

A variety of risks associated with operating our business internationally could materially adversely affect our business.

We plan to seek regulatory approval of our product candidates outside of the United States and, accordingly, we expect that we, and any potential collaborators in those jurisdictions, will be subject to additional risks related to operating in foreign countries, including:

These and other risks associated with our planned international operations may materially adversely affect our ability to attain or maintain profitable operations.

We face significant competition from other biotechnology and pharmaceutical companies, and our operating results will suffer if we fail to compete effectively.

The biopharmaceutical industry, and the market for developing antibody‑based products in particular, is characterized by intense competition and rapid innovation. Our competitors may be able to develop other compounds or drugs that are able to achieve similar or better results. Our potential competitors include major multinational pharmaceutical companies, established biotechnology companies, specialty pharmaceutical companies, universities, and other research institutions. Many of our competitors have substantially greater financial, technical and other resources, such as larger research and development staff and experienced marketing and manufacturing organizations as well as established sales forces. Smaller or early‑stage companies may also prove to be significant competitors, particularly through collaborative arrangements with large, established companies. Mergers and acquisitions in the biotechnology and pharmaceutical industries may result in even more resources being concentrated in our competitors. Competition may increase further as a result of advances in the commercial applicability of technologies and greater availability of capital for investment in these industries. Our competitors, either alone or with collaborative partners, may succeed in developing, acquiring or licensing on an exclusive basis drug or biologic products that are more effective, safer, more easily commercialized, or less costly than our product candidates or may develop proprietary technologies or secure patent protection that we may need for the development of our product candidates and related technologies.

Specifically, MacroGenics, Inc. and Daiichi Sankyo Co. are developing antibodies against B7‑H3. United Therapeutics Corporation has commercialized Unituxin (dinutuximab), an antibody against GD2, in the United States. United Therapeutics Corporation has also announced that it is developing a humanized GD2 antibody. In addition, naxitamab may face competition from dinutuximab beta, a similar antibody product against GD2 developed by Apeiron Biologics AG, or Apeiron, that was approved in Europe in May 2017 to treat high‑risk NB and R/R NB. Apeiron has previously announced plans to file for registration of dinutuximab beta in the U.S. in the first quarter of 2019. In October 2016, EUSA Pharma (UK) Ltd., or EUSA, announced that it had acquired global commercialization rights to dinutuximab beta, which is currently being commercialized under the name Qarziba® in Europe.

Even if we obtain regulatory approval of our product candidates, we may not be the first to market and that may affect the price or demand for our product candidates. Additionally, the availability and price of our competitors’ products could limit the demand and the price we are able to charge for our product candidates. We may not be able to implement our business plan if the acceptance of our product candidates is inhibited by price competition or the reluctance of physicians to switch from existing methods of treatment to our product candidates, or if physicians switch to other new drug or biologic products or choose to reserve our product candidates for use in limited circumstances. Additionally, a competitor could obtain orphan product exclusivity from the FDA with respect to such competitor’s product. If such competitor product is determined to be the same product as one of our product candidates, that may prevent us from obtaining approval from the FDA for such product candidate for the same indication for seven years, except in limited circumstances.

We have entered into several agreements with MSK that are important to our business. We may also form or seek other collaborations or strategic alliances or enter into additional licensing arrangements in the future but may not realize the benefits of such collaborations or strategic alliances. If we are unable to enter into future collaborations, or if such collaborations are not successful, our business could be adversely affected.

We currently have in place several agreements with MSK that are important and we may form or seek strategic alliances, create joint ventures or collaborations, or enter into additional licensing arrangements with third parties that we believe will complement or augment our development and commercialization efforts with respect to our product candidates and any future product candidates that we may develop. Any of these relationships may require us to incur other charges, increase our near and long‑term expenditures, issue securities that dilute our existing stockholders, or disrupt our management and business. In addition, we face significant competition in seeking appropriate strategic partners and the negotiation process is time‑consuming and complex. Moreover, we may not be successful in our efforts to establish a strategic partnership or other alternative arrangements for our product candidates because they may be deemed to be at too early a stage of development for collaborative effort and third parties may not view our product candidates as having the requisite potential to demonstrate safety and efficacy.

Further, arrangements with third parties, such as our arrangement with MSK, or any potential future collaborations we may enter into involving our product candidates, are subject to numerous risks, including the following:

As a result, if we are unable to maintain current arrangements or enter into and maintain future arrangements and collaborations, or if such arrangements or collaborations are not successful, our business could be adversely affected. If we enter into certain arrangements or collaboration agreements and strategic partnerships or license our products or businesses, we may not be able to realize the benefit of such transactions if we are unable to successfully integrate them with our existing operations and company culture, which could delay our timelines or otherwise adversely

affect our business. We also cannot be certain that, following a strategic transaction or license, we will achieve the revenue or specific net income that justifies such transaction. Any delays in entering into new collaborations or strategic partnership agreements related to our product candidates could delay the development and commercialization of our product candidates in certain territories for certain indications, which would harm our business prospects, financial condition, and results of operations.

If we or third parties, such as contract research organizations, or CROs, or contract manufacturing organizations, or CMOs, use hazardous and biological materials in a manner that causes injury or violates applicable law, we may be liable for damages.

Our research and development activities may involve the controlled use of potentially hazardous substances, including chemical and biological materials, by us or third parties, such as CROs and CMOs. The use of Iodine‑131, Iodine‑124 and Lutetium‑177‑labeled antibody treatments involves the inherent risk of exposure from gamma ray emissions, which can alter or harm healthy cells in the body. We and such third parties are subject to federal, state, and local laws and regulations in the United States and Europe governing the use, manufacture, storage, handling, and disposal of medical and hazardous materials. Although we believe that our and such third‑parties’ procedures for using, handling, storing, and disposing of these materials comply with legally prescribed standards, we cannot completely eliminate the risk of contamination or injury resulting from medical or hazardous materials. As a result of any such contamination or injury, we may incur liability or local, city, state, or federal authorities may curtail the use of these materials and interrupt our business operations. In the event of an accident, we could be held liable for damages or penalized with fines, and the liability could exceed our resources. Compliance with applicable environmental laws and regulations is expensive, and current or future environmental regulations may impair our research, development and production efforts, which could harm our business, prospects, financial condition, or results of operations. We currently maintain insurance coverage for injuries resulting from the hazardous materials we use; however, future claims may exceed the amount of our coverage. Also, we do not have insurance coverage for pollution cleanup and removal. Currently the costs of complying with such federal, state, local and foreign environmental regulations are not significant, and consist primarily of waste disposal expenses. However, they could become expensive, and current or future environmental laws or regulations may impair our research, development, production and commercialization efforts.

Our internal computer systems, or those used by our third‑party research institution collaborators, CROs or other contractors or consultants, may fail or suffer security breaches.

Despite the implementation of security measures, our internal computer systems and those of our future CROs and other contractors and consultants are vulnerable to damage from computer viruses and unauthorized access. Although to our knowledge we have not experienced any such material system failure or security breach to date, if such an event were to occur and cause interruptions in our operations, it could result in a material disruption of our development programs and our business operations. For example, the loss of clinical trial data from completed or future clinical trials could result in delays in our regulatory approval efforts and significantly increase our costs to recover or reproduce the data. Likewise, we rely on our third‑party research institution collaborators for research and development of our product candidates and other third parties for the manufacture of our product candidates and to conduct clinical trials, and similar events relating to their computer systems could also have a material adverse effect on our business. To the extent that any disruption or security breach were to result in a loss of, or damage to, our data or applications, or inappropriate disclosure of confidential or proprietary information, we could incur liability and the further development and commercialization of our product candidates could be delayed.

Business disruptions could seriously harm our future revenue and financial condition and increase our costs and expenses.

Our operations, and those of our third‑party research institution collaborators, CROs, CMOs, suppliers, and other contractors and consultants, could be subject to earthquakes, power shortages, telecommunications failures, water shortages, floods, hurricanes, typhoons, fires, extreme weather conditions, medical epidemics, terrorist activities, and other natural or man‑made disasters or business interruptions, for which we are predominantly self‑insured. In addition, we rely on our third‑party research institution collaborators for conducting research and development of our product candidates, and they may be affected by government shutdowns or withdrawn funding. The occurrence of any of these

business disruptions could seriously harm our operations and financial condition and increase our costs and expenses. We rely on third‑party manufacturers to produce and process our product candidates. Our ability to obtain clinical supplies of our product candidates could be disrupted if the operations of these suppliers are affected by a man‑made or natural disaster or other business interruption. Damage or extended periods of interruption to our third‑party collaborators’, including MSK’s, corporate, development or research facilities due to fire, natural disaster, power loss, communications failure, unauthorized entry or other events could cause us to cease or delay development of some or all of our product candidates. Although we intend to maintain property damage and business interruption insurance coverage on these facilities, our insurance might not cover all losses under such circumstances and our business may be seriously harmed by such delays and interruption.

If product liability lawsuits are brought against us, we may incur substantial liabilities and may be required to limit commercialization of our product candidates.

We face an inherent risk of product liability as a result of the clinical testing of our product candidates and will face an even greater risk if we commercialize any products. For example, we may be sued if our product candidates cause or are perceived to cause injury or are found to be otherwise unsuitable during clinical testing, manufacturing, marketing or sale. Any such product liability claims may include allegations of defects in manufacturing, defects in design, a failure to warn of dangers inherent in the product, negligence, strict liability or a breach of warranties. Claims could also be asserted under state consumer protection acts. If we cannot successfully defend ourselves against product liability claims, we may incur substantial liabilities or be required to limit commercialization of our product candidates. Even successful defense would require significant financial and management resources. Regardless of the merits or eventual outcome, liability claims may result in:

Our inability to obtain sufficient product liability insurance at an acceptable cost to protect against potential product liability claims could prevent or inhibit the commercialization of products we develop, alone or with collaborators. We currently carry $5.0 million of clinical trial insurance and expect to take out additional product liability insurance upon marketing approval of any of our product candidates. The amount of our current clinical trial and our future product liability insurance coverage that we may have, may not be adequate, we may be unable to maintain such insurance, or we may not be able to obtain additional or replacement insurance at a reasonable cost, if at all. Our

insurance policies may also have various exclusions, and we may be subject to a product liability claim for which we have no coverage. We may have to pay any amounts awarded by a court or negotiated in a settlement that exceed our coverage limitations or that are not covered by our insurance, and we may not have, or be able to obtain, sufficient capital to pay such amounts. Even if our agreements with any future corporate collaborators entitle us to indemnification against losses, such indemnification may not be available or adequate should any claim arise.

Risks Related to Our Dependence on Third Parties

Third parties have sponsored most clinical trials of our lead product candidates so far, and our ability to influence the design and conduct of such clinical trials has been limited. We have incurred significant expenses and are obligated to make significant payments in the future with respect to such clinical trials. We plan to assume control over the future clinical and regulatory development of such product candidates, including obtaining sponsorship of existing INDs or filing new company‑sponsored INDs, which will entail substantial additional expenses and may be subject to delay. Any failure by a third party to meet its obligations with respect to the clinical and regulatory development of our product candidates may delay or impair our ability to obtain regulatory approval for our product candidates and result in liability for our company.

We have sponsored only a limited number of clinical trials relating to our lead product candidates. Instead, faculty members at our third‑party research institution collaborators, or those institutions themselves, have sponsored most of the clinical trials relating to these product candidates, in each case, under their own INDs. We have incurred significant expenses and are obligated to make significant payments in the future with respect to such clinical trials. To date, we have assumed control of only a limited number of such clinical trials and plan to assume control of the overall clinical and regulatory development of our lead product candidates for future clinical trials and obtain sponsorship of the INDs or file new company‑sponsored INDs, all of which will cause us to incur substantial additional expenses and may be subject to delay. Failure to obtain, or delays in obtaining, sponsorship of INDs or in filing new company‑sponsored INDs for these or any other product candidates we determine to advance could negatively affect the timing of our potential future clinical trials. Such an impact on timing could increase research and development costs and could delay or prevent obtaining regulatory approval for our most advanced product candidates, either of which could have a material adverse effect on our business.

Further, even in the event that the IND sponsorship is obtained for existing and new INDs, we did not control the design or conduct of the previous trials. It is possible that the FDA will not accept these previous trials as providing adequate support for future clinical trials, whether controlled by us or third parties, for any reason, including the safety, purity, and potency of the product candidate, the degree of product characterization, elements of the design or execution of the previous trials or safety concerns, or other trial results. We may also be subject to liabilities arising from any treatment‑related injuries or adverse effects in patients enrolled in these previous trials. As a result, we may be subject to unforeseen third‑party claims and delays in our potential future clinical trials. We may also be required to repeat in whole or in part clinical trials previously conducted by our third‑party research institution collaborators, which will be expensive and delay the submission and licensure or other regulatory approvals with respect to any of our product candidates. Any such delay or liability could have a material adverse effect on our business.

Moreover, we have so far been dependent on contractual arrangements with our third‑party research institution collaborators and will continue to be until we assume control. Such arrangements provide us certain information rights with respect to the previous trials, including access to and the ability to use and reference the data, including for our own regulatory filings, resulting from the previous trials. However, if the data prove to be inadequate compared to the first‑hand knowledge we might have gained had the completed trials been corporate‑sponsored trials, then our ability to design and conduct our planned corporate‑sponsored clinical trials may be adversely affected. Additionally, the FDA may disagree with the sufficiency of our right to reference the pre‑clinical, manufacturing, or clinical data generated by these prior investigator‑sponsored trials, or our interpretation of pre‑clinical, manufacturing, or clinical data from these clinical trials. Moreover, the FDA may require us to obtain and submit additional pre‑clinical, clinical, manufacturing, clinical, toxicology or other in vivo or in vitro datas before we may begin our planned trials and/or may not accept such additional data as adequate to begin our planned trials.

We will rely on third parties to conduct our clinical trials. If these third parties do not successfully carry out their contractual duties or meet expected deadlines or comply with regulatory requirements, we may not be able to obtain regulatory approval of or commercialize our product candidates.

We will rely on third parties to conduct our clinical trials under agreements with MSK, universities, medical institutions, CROs, strategic partners, and others. Nevertheless, we are responsible for ensuring that each of our studies is conducted in accordance with the applicable protocol and legal, regulatory, and scientific standards, and our reliance on third parties does not relieve us of our regulatory responsibilities. We and these third parties are required to comply with current good clinical practices, or cGCPs, which are regulations and guidelines enforced by the FDA and comparable foreign regulatory authorities for product candidates in clinical development. Regulatory authorities enforce these cGCPs through periodic inspections of trial sponsors, principal investigators, and trial sites. If we or any of these third parties fail to comply with applicable cGCP regulations, the clinical data generated in our clinical trials may be deemed unreliable and the FDA or comparable foreign regulatory authorities may require us to perform additional non‑clinical or clinical trials before approving our marketing applications. We cannot be certain that, upon inspection, such regulatory authorities will determine that any of our clinical trials comply with the cGCP regulations. In addition, our clinical trials must be conducted with biologic product produced under cGMP regulations and will require a large number of test patients. Our failure or any failure by these third parties to comply with these regulations or to recruit a sufficient number of patients may require us to repeat clinical trials, which would delay the regulatory approval process. Moreover, our business may be implicated if any of these third parties violates federal or state fraud and abuse or false claims laws and regulations or healthcare privacy and security laws.

If these third parties do not successfully carry out their contractual duties or obligations or meet expected deadlines, if they need to be replaced, or if the quality or accuracy of the clinical data they obtain is compromised due to the failure to adhere to our clinical protocols or regulatory requirements or for other reasons, our clinical trials may be extended, delayed, or terminated and we may not be able to complete development of, obtain regulatory approval of or successfully commercialize our product candidates. We may also rely on investigator‑reported interim data in making business decisions. Independent review of the data could fail to confirm the investigator‑reported interim data, which may lead to revisions in disclosed clinical trial results in the future. Any such revisions that reveal more negative data than previously disclosed investigator‑reported interim data could have an adverse impact on our business prospects and the trading price of our common stock. Such revisions could also reduce investor confidence in investigator‑reported interim data that we disclose in the future.

If any of our relationships with these third‑party CROs terminate, we may not be able to enter into arrangements with alternative CROs or do so on commercially reasonable terms. Switching or adding additional CROs involves additional cost and delays and requires management time and focus. Though we intend to carefully manage our relationships with our CROs, there can be no assurance that we will not encounter similar challenges in the future or that these challenges will not have a material adverse impact on our business, financial condition and prospects.

We will rely on third parties to manufacture our product candidates for our pre‑clinical studies, and in the case of our lead product candidates, our ongoing clinical trials, as well as any additional clinical trials of our other product candidates we may conduct. We also expect to rely on third parties for the manufacturing process of our product candidates, if approved. Our business could be harmed if those third parties fail to provide us with sufficient quantities of product supplies or product candidates, fail to do so at acceptable quality levels or prices, or fail to maintain adequate compliance with CMC guidelines of the FDA.

We do not currently own any facility that may be used as a clinical‑scale manufacturing and processing facility and we intend to rely on outside vendors to manufacture supplies and process our product candidates for pre‑clinical studies and clinical trials under the guidance of our management team. Our lead product candidates have only been manufactured or processed on a limited basis and we may not be able to continue doing so for any of our product candidates. Our manufacturing process may be more difficult or expensive than the approaches currently in use. We may make changes as we work to optimize the manufacturing process, and we cannot be sure that even minor changes in the process will not result in significantly different products that may not be as safe and effective as any product candidates deployed by our third‑party research institution collaborators.

To date, we have obtained the active pharmaceutical ingredient, or API, of our lead product candidates from a limited number of third‑party manufacturers. We have engaged a separate third‑party manufacturer to conduct fill‑and‑finish and labeling services, as well as for the storage and distribution of our lead product candidates to clinical sites. We do not have a long‑term supply agreement with any of these third‑party manufacturers, and we purchase our required drug supplies on a purchase order basis.

We expect to rely on third‑party manufacturers or third‑party collaborators for the manufacture of our product candidates for commercial supply of any of our product candidates for which we or any of our potential future collaborators obtain marketing approval. We may be unable to establish any agreements with third‑party manufacturers or to do so on acceptable terms. Even if we are able to establish agreements with third‑party manufacturers, reliance on third‑party manufacturers entails additional risks, including:

Each of these risks could delay or prevent the completion of our clinical trials, could delay any BLA submissions, and the approval of any of our product candidates by the FDA, result in higher costs or adversely impact commercialization of our product candidates. For example, during 2018 we experienced a shortage in the supply of Iodine‑131, one of the components of our 131I‑omburtamab product candidate, from our single source supplier. We have established a relationship with an additional supplier which we believe will be able to provide us with adequate supplies of Iodine‑131. While we have not yet experienced any delays in the research and development of our 131I‑omburtamab product candidate to date, any such shortages in the supply of such raw materials used in the manufacture of our product candidates could delay or prevent the completion of our clinical trials or the approval of any of our product candidates by the FDA, result in higher costs or adversely impact commercialization of our product candidates. In addition, we will rely on third parties to perform certain specification tests on our product candidates prior to delivery to patients. If these tests are not appropriately done and test data are not reliable, patients could be put at risk of serious harm and the FDA could place significant restrictions on our company until deficiencies are remedied.

The facilities used by our contract manufacturers to manufacture our product candidates must be approved by the FDA pursuant to inspections that will be conducted after we submit our BLA to the FDA. We do not have complete control over all aspects of the manufacturing process of, and are dependent on, our contract manufacturing partners for compliance with cGMP regulations for manufacturing both active drug substances and finished drug products. Any product candidates that we may develop may compete with product candidates of other companies for access to manufacturing facilities. There are a limited number of manufacturers that operate under cGMP regulations and that might be capable of manufacturing for us. Our failure, or the failure of our third‑party manufacturers, to comply with applicable regulations could result in sanctions being imposed on us, including fines, injunctions, civil penalties, delays, suspension or withdrawal of approvals, license revocation, seizures or recalls of product candidates or drugs, operating restrictions and criminal prosecutions, any of which could significantly and adversely affect supplies of our drugs and harm our business and results of operations.

Any performance failure on the part of our existing or future manufacturers could delay clinical development or marketing approval. We do not currently have arrangements in place for redundant supply of our lead product candidates and we only currently use a different single third‑party manufacturer for fill‑and‑finish services for our lead product candidates. If our current contract manufacturers cannot perform as agreed, we may be required to replace those manufacturers. Although we believe that there may be potential alternative manufacturers who could manufacture our product candidates, we may incur added costs and delays in identifying and qualifying any such replacement.

We are and will continue to rely in significant part on outside scientists and their third‑party research institutions for research and development and early clinical testing of our product candidates. These scientists and institutions may have other commitments or conflicts of interest, which could limit our access to their expertise and adversely affect the timing of our IND filings and our ability to conduct future planned clinical trials.

We currently have limited internal research and development capabilities and we have not and are not currently conducting any independent clinical trials. Therefore, we currently rely on third‑party research institutions for both capabilities.

Currently, MSK is conducting clinical trials to address pediatric R/R high‑risk NB and a clinical trial to address relapsed osteosarcoma using our naxitamab product candidate. We are also conducting a clinical trial at MSK for CNS/LM from NB and clinical trials for DIPG and DSRCT for our omburtamab product candidate. Under the terms of the MSK License, we are obligated to pay for the costs associated with these clinical trials.

We have agreed to fund certain research and development costs under both the MSK License and the MSK CD33 License. However, the research we have agreed to fund constitutes only a small portion of the overall research of MSK. Other research being conducted by MSK may receive higher priority than research on the programs we may fund.

The outside scientists who conduct the clinical testing of our current product candidates, and who conduct the research and development upon which our product candidate pipeline depends, are not our employees; rather they serve as either independent contractors or the primary investigators under research and other agreements that we have entered into with MSK. Such scientists and collaborators may have other commitments that would limit their availability to us. Although our scientific advisors generally agree not to do competing work, if an actual or potential conflict of interest between their work for us and their work for MSK or another entity arises, we may lose their services. These factors could adversely affect the timing of our IND filings and our ability to conduct future planned clinical trials. It is also possible that some of our valuable proprietary knowledge may become publicly known through these scientific advisors if they breach their confidentiality agreements with us, which would cause competitive harm to, and have a material adverse effect on, our business.

Our existing agreements with MSK may be subject to termination by MSK upon the occurrence of certain circumstances. If MSK terminates the MSK License, the MSK CD33 License or its other agreements with us, the research and development of the relevant product candidates would be suspended, and we would not be able to research, develop, and license our existing and future product candidates as currently contemplated. We may be required to devote additional resources to the development of our product candidates or seek a new collaboration partner, and the terms of any additional collaborations or other arrangements that we establish may not be favorable to us. Switching or adding third parties to conduct our clinical trial would involve substantial costs and delays and require extensive management time and focus, which can materially impact our ability to meet our desired clinical development timelines.

Our product candidates are biologics and the manufacture of our product candidates is complex. We, or any of our third‑party manufacturers, may encounter difficulties in production, particularly with respect to process development or scaling‑up of our manufacturing capabilities. For some reagents, equipment, and materials, we rely or may rely on sole source vendors or a limited number of vendors. Such difficulties may result in an inadequate supply of our product candidates for clinical trials or our products for patients, if approved, could be delayed or stopped, or we may be unable to maintain a commercially viable cost structure.

Our product candidates are biologics and the process of manufacturing them is complex, highly‑regulated and subject to multiple risks. As a result of the complexities, the cost to manufacture biologics is generally higher than traditional small molecule chemical compounds, and the manufacturing process for biologics is less reliable and is more difficult to reproduce. In addition, manufacturing our product candidates will require many reagents, which are substances used in our manufacturing processes to bring about chemical or biological reactions, and other specialty materials and equipment, some of which are manufactured or supplied by small companies with limited resources and experience to support commercial biologics production. Our manufacturing process may be susceptible to product loss or failure due to interruptions in the manufacturing process variability in product characteristics, quality control, contamination, equipment or reagent failure, improper installation or operation of equipment, product testing, vendor or operator error, availability of qualified personnel, logistics and shipping as well as compliance with strictly enforced federal, state and foreign regulations. Even minor deviations from normal manufacturing processes could result in reduced production yields, product defects, and other supply disruptions. If microbial, viral, or other contaminations are discovered in our product candidates or in the manufacturing facilities in which our product candidates are made, such manufacturing facilities may need to be closed for an extended period of time to investigate and remedy the contamination. We cannot assure you that any stability failures or other issues relating to the manufacture of our product candidates will not occur in the future.

Further, as product candidates are developed through pre‑clinical to late‑stage clinical trials towards approval and commercialization, it is common that various aspects of the development program, such as manufacturing methods, are altered along the way in an effort to optimize processes and results. Such changes carry the risk that they will not achieve these intended objectives, and any of these changes could cause our product candidates to perform differently and affect the results of planned clinical trials or other future clinical trials. Moreover, as we develop and/or scale‑up our manufacturing process, we expect that we will need to obtain rights to and supplies of certain materials and equipment to

be used as part of that process. We may not be able to obtain rights to such materials on commercially reasonable terms, or at all.

In addition, the manufacturing process for any products that we may develop is subject to FDA, EMA and other foreign regulatory authority approval process, and we will need to contract with manufacturers who can meet all applicable FDA, EMA and other foreign regulatory authority requirements on an ongoing basis. If we, or our CMOs, are unable to reliably produce products to specifications acceptable to the FDA, EMA or other foreign regulatory authorities, we may not obtain or maintain the approvals we need to commercialize such products. Even if we obtain regulatory approval for any of our product candidates, there is no assurance that either we or our CMOs will be able to manufacture the approved product to specifications acceptable to the FDA, EMA or other foreign regulatory authorities, to produce it in sufficient quantities to meet the requirements for the potential launch of the product, or to meet potential future demand. Any of these challenges could delay completion of clinical trials, require bridging clinical trials or the repetition of one or more clinical trials, increase clinical trial costs, delay approval of our product candidate, impair commercialization efforts, increase our cost of goods, and have an adverse effect on our business, financial condition, results of operations and growth prospects. Although we are working to develop commercially viable processes, our manufacturing capabilities could be affected by cost‑overruns, unexpected delays, equipment failures, labor shortages, natural disasters, power failures and numerous other factors that could prevent us from realizing the intended benefits of our manufacturing strategy and have a material adverse effect on our business. We may ultimately be unable to, among other things, develop a manufacturing process and distribution network that will, reduce the cost of goods for our product candidates to levels that will allow for an attractive return on investment if and when those product candidates are commercialized.

Although we currently plan to retain all commercial rights to our product candidates, we may enter into strategic collaborations for the development, marketing and commercialization of all or some of our product candidates. If those collaborations are not successful, or if we are unable to establish any such collaborations, we may have to alter or delay our development and commercialization plans.

As we further develop our lead product candidates, we may build a commercial infrastructure with the capability to directly market it to a variety of markets and territories. Although we currently plan to retain all commercial rights to our product candidates, we may enter into strategic collaborations for the development, marketing and commercialization of all or some of our product candidates. Our likely collaborators for any collaboration arrangements include large and mid‑size pharmaceutical companies, regional and national pharmaceutical companies and biotechnology companies. We would face significant competition in seeking appropriate collaborators. Whether we reach a definitive agreement for a collaboration will depend, among other things, upon our assessment of the collaborator’s resources and expertise, the terms and conditions of the proposed collaboration and the proposed collaborator’s evaluation of a number of factors. If we do enter into any such arrangements with any third parties, we will likely have limited control over the amount and timing of resources that our collaborators dedicate to the development, marketing and/or commercialization of our product candidates. Our ability to generate revenues from these arrangements will depend on our collaborators’ abilities to successfully perform the functions assigned to them in these arrangements. In addition, any future collaborators may have the right to abandon research or development projects and terminate applicable agreements, including funding obligations, prior to or upon the expiration of the agreed upon terms.

Collaborations involving our product candidates pose risks to us, including the following:

Collaboration agreements may not lead to development or commercialization of product candidates in the most efficient manner, or at all.

We may not be able to negotiate collaborations on a timely basis, on acceptable terms, or at all, if and when we seek to enter into collaborations. If we are unable to do so, we may have to curtail the development of a product candidate, reduce or delay its development program or one or more of our other development programs, delay its potential commercialization or reduce the scope of any sales or marketing activities, or increase our expenditures and undertake development or commercialization activities at our own expense. If we elect to increase our expenditures to fund development or commercialization activities on our own, we may need to obtain additional capital, which may not be available to us on acceptable terms, or at all. If we do not have sufficient funds, we may not be able to further develop our product candidates or bring them to market and generate revenue from sales of drugs.

Reimbursement decisions by third‑party payors may have an adverse effect on pricing and market acceptance. If there is not sufficient reimbursement for our products, it is less likely that our products will be widely used.

Even if our product candidates are approved for sale by the appropriate regulatory authorities, market acceptance and sales of these products will depend on reimbursement policies and may be affected by future healthcare reform measures. Government authorities and third‑party payors, such as private health insurers and health maintenance organizations, decide which drugs they will reimburse and establish payment levels and, in some cases, utilization management strategies, such as tiered formularies and prior authorization. We cannot be certain that reimbursement will be available for any products that we develop or that the reimbursement level will be adequate to allow us to operate profitably. Also, we cannot be certain that reimbursement policies will not reduce the demand for, or the price paid for, our products. If reimbursement is not available or is available on a limited basis, or if the reimbursement amount is inadequate, we may not be able to successfully commercialize any of our approved products.

Risks Related to Government Regulation; Market Approval and Other Legal Compliance Matters

Even if we complete the necessary pre‑clinical studies and clinical trials, the FDA regulatory approval process is lengthy, time‑consuming, and inherently unpredictable, and we or any of our potential future collaborators may experience significant delays in the clinical development and regulatory approval, if any, for the commercialization of our product candidates. As a result, we cannot predict when or if, and in which territories, we, or any of our potential future collaborators, will obtain marketing approval to commercialize a product candidate.

The research, testing, manufacturing, labeling, approval, selling, import, export, marketing, and distribution of drug products, including biologics, are subject to extensive regulation by the FDA and other regulatory authorities in the United States. Even if we complete the necessary pre‑clinical studies and clinical trials, we will not be permitted to market any biological drug product in the United States until we receive a Biologics License from the FDA. We plan to begin additional clinical trials with our lead product candidates in 2019 and 2020. We intend to conduct each of these clinical trials in the United States and Europe. We intend to discuss with the FDA and EMA submission of BLAs for respective approval of such product candidates as treatments for indications that currently lack FDA‑approved treatments.

The FDA standard for regular approval of a BLA generally requires two well‑controlled Phase 3 studies or one large and robust, well‑controlled Phase 3 study in the patient population being studied that provides substantial evidence that a biologic is safe, pure and potent. Phase 3 clinical studies typically involve hundreds of patients, have significant costs and take years to complete. However, product candidates studied for their safety and effectiveness in treating serious or life‑threatening illnesses and that provide meaningful therapeutic benefit over existing treatments may be eligible for accelerated approval and may be approved on the basis of adequate and well‑controlled clinical trials establishing that the product candidate has an effect on a surrogate endpoint that is reasonably likely to predict clinical benefit, or on a clinical endpoint that can be measured earlier than irreversible morbidity or mortality, that is reasonably likely to predict an effect on irreversible morbidity or mortality or other clinical benefit, taking into account the severity, rarity or prevalence of the condition and the availability or lack of alternative treatments. As a condition of accelerated approval, the FDA may require a sponsor of a drug or biologic receiving accelerated approval to perform post‑marketing studies to verify and describe the predicted effect on irreversible morbidity or mortality or other clinical endpoint, and the drug or biologic may be subject to withdrawal procedures by the FDA that are more accelerated than those available for regular approvals. We believe our accelerated approval strategy is warranted given the currently limited alternative therapies for patients with pediatric relapsed or refractory, or R/R, from neuroblastoma, or NB, but the FDA may not agree. The FDA may ultimately require one or multiple Phase 3 clinical trials prior to approval.

We have not previously submitted a BLA to the FDA, or similar approval filings to comparable foreign authorities. A BLA must include extensive pre‑clinical and clinical data and supporting information to establish that the product candidate is safe, pure, and potent for each desired indication. The BLA must also include significant information regarding the chemistry, manufacturing, and controls for the product, and the manufacturing facilities must complete a successful pre‑license inspection. We expect the novel nature of our product candidates to create further challenges in obtaining regulatory approval from the FDA and other regulatory authorities. The FDA may also require a panel of experts, referred to as an Advisory Committee, to deliberate on the adequacy of the safety and efficacy data to

support licensure. The opinion of the Advisory Committee, although not binding, may have a significant impact on our ability to obtain licensure of the product candidates based on the completed clinical trials. Accordingly, the regulatory approval pathway for our product candidates may be uncertain, complex, expensive, and lengthy, and approval may not be obtained.

The process of obtaining marketing approvals, both in the United States and abroad, is a lengthy, expensive and uncertain process. It may take many years, if approval is obtained at all, and can vary substantially based upon a variety of factors, including the type, complexity and novelty of the product candidates involved. Securing marketing approval requires the submission of extensive pre‑clinical and clinical data and supporting information to regulatory authorities for each therapeutic indication to establish the product candidate’s safety and efficacy. Securing marketing approval also requires the submission of information about the product manufacturing process to, and inspection of manufacturing facilities by, the regulatory authorities. The FDA or other regulatory authorities have substantial discretion and may determine that our product candidates are not safe and effective, only moderately effective or have undesirable or unintended side effects, toxicities or other characteristics that preclude our obtaining marketing approval or prevent or limit commercial use. Any marketing approval we ultimately obtain may be limited or subject to restrictions or post‑approval commitments that render the approved product not commercially viable.

In addition, clinical trials can be delayed or terminated for a variety of reasons, including delays or failures related to:

Patient enrollment is a significant factor in the timing of clinical trials and is affected by many factors. See the risk factor above “—The market opportunities for our product candidates may be limited to those patients who are ineligible for or have failed prior treatments and may be small. If we encounter difficulties enrolling patients in our clinical trials, our clinical development activities could be delayed or otherwise adversely affected.” for additional information on risks related to patient enrollment. Further, a clinical trial may be suspended or terminated by us, the IRBs for the institutions in which such trials are being conducted, the Data Monitoring Committee for such trial, or the FDA or other regulatory authorities due to a number of factors, including failure to conduct the clinical trial in accordance with regulatory requirements or our clinical protocols, inspection of the clinical trial operations or trial site by the FDA or other regulatory authorities resulting in the imposition of a clinical hold, unforeseen safety issues or adverse side effects, failure to demonstrate a benefit from using a product candidate, changes in governmental