Use these links to rapidly review the document
TABLE OF CONTENTS

Table of Contents

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM 10-K

Commission File Number 0-15006

CELLDEX THERAPEUTICS, INC.
(Exact name of registrant as specified in its charter)

119 Fourth Avenue, Needham, Massachusetts 02494
(Address of principal executive offices) (Zip Code)

Registrant's telephone number, including area code: (781) 433-0771

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

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

         Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes o    No ý

         Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. Yes o    No ý

         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 the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ý    No o

         Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted 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 and post such files). Yes o    No o

         Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K (§229.405 of this Chapter) is not contained herein, and will not be contained, to the best of 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. ý

         Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer or a smaller reporting company. See definitions of "large accelerated filer," "accelerated filer," and "smaller reporting company" in Rule 12b-2 of the Exchange Act. (Check one):

         Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act). Yes o    No ý

         The aggregate market value of the registrant's common stock held by non-affiliates as of June 30, 2010 was $144.7 million. Exclusion of shares held by any person should not be construed to indicate that such person possesses the power, direct or indirect, to direct or cause the actions of the management or policies of the registrant, or that such person is controlled by or under common control with the registrant.

         The number of shares of common stock outstanding at February 28, 2011 was 32,055,382 shares.

DOCUMENTS INCORPORATED BY REFERENCE

         Portions of the definitive Proxy Statement for our 2011 Annual Meeting of Stockholders are incorporated by reference into Part III of this Report.

---

Table of Contents

CELLDEX THERAPEUTICS, INC.
ANNUAL REPORT ON FORM 10-K
YEAR ENDED DECEMBER 31, 2010

TABLE OF CONTENTS

i

---

Table of Contents

        Safe Harbor Statement under the Private Securities Litigation Reform Act of 1995:    This report on Form 10-K contains forward-looking statements made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995 under Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. Forward-looking statements include statements with respect to our beliefs, plans, objectives, goals, expectations, anticipations, assumptions, estimates, intentions and future performance, and involve known and unknown risks, uncertainties and other factors, which may be beyond our control, and which may cause our actual results, performance or achievements to be materially different from future results, performance or achievements expressed or implied by such forward-looking statements. All statements other than statements of historical fact are statements that could be forward-looking statements. You can identify these forward-looking statements through our use of words such as "may," "will," "can," "anticipate," "assume," "should," "indicate," "would," "believe," "contemplate," "expect," "seek," "estimate," "continue," "plan," "point to," "project," "predict," "could," "intend," "target," "potential" and other similar words and expressions of the future.

        There are a number of important factors that could cause the actual results to differ materially from those expressed in any forward-looking statement made by us. These factors include, but are not limited to:

•

our ability to successfully complete product research and further development, including animal, preclinical and clinical studies, and commercialization of rindopepimut, CDX-011, CDX-1307, CDX-1401, CDX-1135, CDX-1127 and other products and the growth of the markets for those product candidates;



•

our ability to raise sufficient capital on terms acceptable to us, or at all;



•

the cost, timing, scope and results of ongoing safety and efficacy trials of rindopepimut, CDX-011, CDX-1307, CDX-1401 and other preclinical and clinical testing;



•

our ability to fund and complete the development and commercialization of rindopepimut internally or to find another strategic partner to fund the development and commercialization of rindopepimut;



•

our ability to adapt our APC Targeting Technology™ to develop new, safe and effective vaccines against oncology and infectious disease indications;



•

the ability to negotiate strategic partnerships or other disposition transactions for our non-core programs;



•

our ability to manage multiple clinical trials for a variety of product candidates at different stages of development;



•

the strategies and business plans of our partners, such as GlaxoSmithKline's plans with respect to Rotarix® and Vaccine Technologies' plans concerning the CholeraGarde® (Peru-15) and ETEC E. coli vaccines, which are not within our control, and our ability to maintain strong, mutually beneficial relationships with those partners;



•

our ability to develop technological capabilities and expand our focus to broader markets for vaccines;



•

the availability, cost, delivery and quality of clinical and commercial grade materials produced by our own manufacturing facility or supplied by contract manufacturers and partners;



•

the timing, cost and uncertainty of obtaining regulatory approvals for our product candidates;



•

our ability to develop and commercialize products before competitors that are superior to the alternatives developed by such competitors;

ii

---

Table of Contents

•

the validity of our patents and our ability to avoid intellectual property litigation, which can be costly and divert management time and attention; and



•

the factors listed under "Risk Factors" in this annual report on Form 10-K.

        All forward-looking statements are expressly qualified in their entirety by this cautionary notice. You are cautioned not to place undue reliance on any forward-looking statements, which speak only as of the date of this report or the date of the document incorporated by reference into this report. We have no obligation, and expressly disclaim any obligation, to update, revise or correct any of the forward-looking statements, whether as a result of new information, future events or otherwise. We have expressed our expectations, beliefs and projections in good faith and we believe they have a reasonable basis. However, we cannot assure you that our expectations, beliefs or projections will result or be achieved or accomplished.

iii

---

Table of Contents

PART I

Item 1.    BUSINESS

General

        As used herein, the terms "we," "us," "our," the "Company", or "Celldex" refer to Celldex Therapeutics, Inc. and its direct and indirect subsidiaries: Celldex Research Corporation ("Celldex Research") and Celldex Therapeutics, Ltd. ("Celldex Ltd."). Our principal activity since our inception has been research and product development conducted on our own behalf, as well as through joint development programs with several pharmaceutical companies and other collaborators.

        We are a biopharmaceutical company currently focusing on the development of several immunotherapy technologies. Our lead programs include rindopepimut (CDX-110), a vaccine that is expected to enter into Phase 3 development for glioblastoma multiforme in the second half of 2011, and CDX-011, an antibody-drug conjugate currently in a randomized Phase 2b trial for treatment of advanced breast cancer. We have additional programs at various stages of clinical and preclinical development, including CDX-1127 a therapeutic human antibody candidate for cancer indications, APC Targeting Technology™ programs, CDX-1307 and CDX-1401, and an immune cell mobilizing agent CDX-301. We are currently resourcing our priority programs and supplement the development of additional programs through external collaborations and funding.

        Our strategy is to develop and demonstrate proof-of-concept for our product candidates before leveraging their value through partnerships or, in appropriate situations, continuing late stage development through commercialization ourselves. Demonstrating proof-of-concept for a product candidate generally involves bringing it through Phase 1 clinical trials and one or more Phase 2 clinical trials so that we are able to demonstrate, based on human trials, good safety data for the product candidate and some data indicating its effectiveness. We thus leverage the value of our technology portfolio through corporate, governmental and non-governmental partnerships. This approach allows us to maximize the overall value of our technology and product portfolio while best ensuring the expeditious development of each individual product. Our current collaborations include the commercialization of an oral human rotavirus vaccine. Our product candidates address market opportunities for which we believe current therapies are inadequate or non-existent.

        Our products are derived from a broad set of complementary technologies which have the ability to utilize the human immune system and enable the creation of preventative and therapeutic agents. We are using these technologies to develop targeted immunotherapeutics comprised of antibodies, adjuvants and monotherapies and antibody-drug conjugates that prevent or treat cancer and other diseases that modify undesirable activity by the body's own proteins or cells. A number of our immunotherapeutic and antibody-drug conjugate product candidates are in various stages of clinical trials. We expect that a large percentage of our research and development expenses will be incurred in support of our current and future clinical trial programs.

1

---

Table of Contents

        The following table includes the programs that we currently believe are material to our business:

        Using our expertise in immunology, we are building business franchises in major disease areas: oncology, inflammatory and infectious diseases. We have pursued some of these opportunities independently in a highly focused manner. In other cases, we have leveraged the financial support and development capabilities of corporate and public sector partners to bring our development projects to fruition. The research we have pursued over the past several years has matured into what we believe is an exciting portfolio of product candidates.

        Our success has depended and will continue to depend upon many factors, including our ability, and that of our licensees and collaborators, to successfully develop, obtain regulatory approval for and commercialize our product candidates. Commercial sales are currently generated by GlaxoSmithKline (GSK), which is marketing Rotarix®. We have had no commercial revenues from sales of our human therapeutic or other human vaccine products and we have had a history of operating losses. It is possible that we may not be able to successfully develop, obtain regulatory approval for or commercialize our product candidates, and we are subject to a number of risks that you should be aware of before investing in us. These risks are described more fully in "Item 1A. Risk Factors."

        We are a Delaware corporation organized in 1983. Our website is located at http://www.celldextherapeutics.com. On our website, investors can obtain a copy of our annual report on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K, and other reports filed or furnished pursuant to Section 13(a) or 15(d) of the Exchange Act of 1934, as amended, as soon as reasonably practicable after we file such material electronically with, or furnishes it to, the Securities and Exchange Commission ("SEC"). None of the information posted on our website is incorporated by reference into this Annual Report.

Clinical Development Programs

Rindopepimut (CDX-110)

        Our lead clinical development program, rindopepimut, is a peptide-based immunotherapy that targets the tumor specific molecule called EGFRvIII, a functional variant of the naturally expressed epidermal growth factor receptor ("EGFR"), a protein which has been well validated as a target for cancer therapy. Unlike EGFR, EGFRvIII is not present in normal tissues, and has been shown to be a transforming oncogene that can directly contribute to the cancer cell growth. EGFRvIII is commonly present in glioblastoma multiforme, or GBM, the most common and aggressive form of brain cancer, and has also been observed in various other cancers such as lung, liver and head and neck cancer. The

2

---

Table of Contents

Food and Drug Administration ("FDA") has granted orphan drug designation for rindopepimut for the treatment of EGFRvIII expressing GBM as well as fast track designation.

        In April 2008, we and Pfizer Inc. ("Pfizer") entered into a License and Development Agreement (the "Pfizer Agreement") under which Pfizer was granted an exclusive worldwide license to rindopepimut. The Pfizer Agreement also gave Pfizer exclusive rights to the use of EGFRvIII vaccines in other potential indications. The Pfizer Agreement also provided for reimbursement by Pfizer of all costs incurred by us in connection with the collaboration since the effective date.

        On September 1, 2010, we received written notice (the "Pfizer Notice") from Pfizer of termination with respect to the Pfizer Agreement. The Pfizer Notice was given under a provision of the Pfizer Agreement which permitted termination at any time and for any reason, upon 60-days' written notice to us. The Pfizer Notice did not state a reason for termination. In November 2010, the Pfizer Agreement was terminated (the "Pfizer Termination") and all rights to rindopepimut were returned to us. Effective with the Pfizer Termination, Pfizer is no longer funding the development of rindopepimut.

        The Phase 1 (VICTORI) and Phase 2a (ACTIVATE) studies of EGFRvIII immunotherapy were led by collaborating investigators at the Brain Center at Duke Comprehensive Cancer Center in Durham, North Carolina and at M.D. Anderson Cancer Center in Houston, Texas and enrolled 14 and 18 evaluable patients, respectively. An extension of the Phase 2a study (ACT II) at the same two institutions evaluated 22 additional GBM patients treated in combination with maintenance temozolomide (TMZ) (the current standard of care).

        We initiated a Phase 2b/3 randomized study (ACT III) of rindopepimut combined with standard of care, TMZ, versus standard of care alone in patients with GBM in over 30 sites throughout the United States. In December 2008, we announced an amendment to convert the ACT III study to a single-arm Phase 2 clinical trial in which all patients were to receive rindopepimut in combination with temozolomide. The decision, which followed the recommendation of the Independent Data Monitoring Committee, was based on the observation that the majority of patients randomized to the control (standard of care) arm withdrew from this open-label study after being randomized to the control arm. Patients participating in the control arm of the study were offered the option to receive treatment with rindopepimut. Under this amendment, the ACT III study provided for a multi-center, non-randomized dataset for rindopepimut in patients with newly diagnosed GBM.

        In November 2010, we announced complete data for the primary endpoint of the 65 patients enrolled to receive rindopepimut in combination with maintenance TMZ in the ACT III study. The data showed that 43 of 65 patients (66%) were progression-free at 5.5 months after entry into the study. Taking into account the 3 to 3.5 months required to complete pre-study chemoradiation and enter into the study, the 5.5 month time point in ACT III corresponds to approximately 8.5 months after diagnosis. The ACTIVATE and ACT II trials, which were conducted in two leading centers, reported progression-free rates at 8.5 months after diagnosis of 70% and 80%, respectively, and similar results were seen in the ACT III trial, which enrolled patients in over 25 centers in the United States.

3

---

Table of Contents

        The following table summarizes the progression free survival ("PFS") and overall survival ("OS") rates from clinical trials of rindopepimut as reported in November 2010 as compared to matched historical controls and the standard of care.

        Importantly, rindopepimut showed a similar benefit in patients whether or not they expressed an active DNA repair gene (MGMT) that has been shown to limit the benefit from TMZ treatment. In ACT III, the number of patients who were expected to be resistant to the TMZ chemotherapy appeared to do better with vaccination than the numbers observed in the historical data. Patients who have an active DNA repair gene, MGMT (unmethylated), generally have a worse outcome, presumably because they do not gain much benefit from TMZ as reported in the literature. Patients with a methylated MGMT promoter in their tumor do not express MGMT and have a more favorable outcome to TMZ treatment. Patients with methylated tumors (n=25) that were treated with the rindopepimut regimen experienced a median PFS of 17.2 months, which compares favorably with the published data from the SOC of radiation plus TMZ (R+TMZ) of 10.3 months. Those with unmethylated tumors (n=40) treated with the rindopepimut regimen experienced a PFS of 11.2 months, which compared favorably to the PFS with SOC of 5.3 months in this patient population. Thus, rindopepimut would appear to benefit both methylated and unmethylated MGMT patients.

        Based on ongoing discussions to date with the FDA, we are currently planning to initiate a pivotal Phase 3 randomized study of rindopepimut in patients with GBM in the second half of 2011.

Glembatumumab Vedotin (CDX-011)

        CDX-011 is an antibody-drug conjugate (ADC) that consists of a fully-human monoclonal antibody, CR011, linked to a potent cell-killing drug, monomethyl-auristatin E (MMAE). The CR011 antibody specifically targets glycoprotein NMB or (GPNMB) that is expressed in a variety of human cancers including breast cancer and melanoma. The ADC technology, comprised of MMAE and a stable linker system for attaching it to CR011, was licensed from Seattle Genetics, Inc. The ADC is designed to be stable in the bloodstream. Following intravenous administration, CDX-011 targets and binds to GPNMB and upon internalization into the targeted cell, CDX-011 is designed to release MMAE from CR011 to produce a cell-killing effect.

        Treatment of Breast Cancer:    In June 2008, an open-label, multi-center Phase 1/2 study was initiated of CDX-011 administered intravenously once every three weeks to patients with locally advanced or metastatic breast cancer who have received prior therapy (median of seven prior

4

---

Table of Contents

regimens). The study began with a bridging phase to confirm the maximum tolerated dose ("MTD") and then expanded into a Phase 2 open-label, multi-center study.

        The study confirmed the safety of CDX-011 at the pre-defined maximum dose level (1.88 mg/kg) in 6 patients. An additional 28 patients were enrolled as an expanded Phase 2 cohort (for a total of 34 treated patients at 1.88 mg/kg, the Phase 2 dose) to evaluate the PFS rate at 12 weeks. As previously seen in melanoma patients, the 1.88 mg/kg dose was well tolerated in this patient population with the most common adverse events of rash, alopecia, and fatigue. The primary activity endpoint, which called for at least 5 of 25 (20%) patients in the Phase 2 study portion to be progression-free at 12 weeks, was met as 9 of 26 (35%) evaluable patients were progression-free at 12 weeks.

        For all patients treated at the maximum dose level, tumor shrinkage was seen in 62% (16/26) and median PFS was 9.1 weeks. A subset of 10 patients had "triple negative disease," a more aggressive breast cancer subtype that carries a high risk of relapse and reduced survival as well as limited therapeutic options due to lack of over-expression of HER2/neu, estrogen and progesterone receptors. In these patients, 78% (7/9) had any tumor shrinkage, 12-week PFS rate was 70% (7/10), and median PFS was 17.9 weeks. Tumor samples from a subset of patients across all dose groups were analyzed for GPNMB expression. The tumor samples from most patients showed evidence of stromal and/or tumor cell expression of GPNMB. The most common treatment-related toxicities were fatigue, rash, nausea, alopecia (hair loss), neutropenia and vomiting.

        In May 2010, the FDA granted Fast Track designation to CDX-011 for the treatment of advanced, refractory/resistant GPNMB-expressing breast cancer.

        In September 2010, we initiated a randomized Phase 2b controlled study in patients with heavily pre-treated, advanced breast cancer whose tumors are confirmed to express GPNMB via a validated, centralized diagnostic assay. We expect that a significant portion of the enrolled patients will have triple-negative disease, since GPNMB is frequently expressed in this patient population. Patients will be randomized (2:1) to receive either CDX-011 or single-agent "Investigator's Choice" chemotherapy. Activity endpoints will include objective response rate ("ORR"), PFS and OS. We expect to complete enrollment of 120 patients at approximately 20-25 clinical sites in the United States in 2011 with preliminary data expected in 2012.

        Treatment of Metastatic Melanoma:    In June 2006, a Phase 1/2 open-label, multi-center, dose escalation study was initiated to evaluate the safety, tolerability and pharmacokinetics of CDX-011 for patients with un-resectable Stage III or Stage IV melanoma who have failed no more than one prior line of cytotoxic therapy. A total of 117 patients were enrolled in this trial. The trial initially evaluated doses of CDX-011 between 0.03 mg/kg to 2.63 mg/kg given once every three weeks. CDX-011 was generally well tolerated, with rash and neutropenia emerging at higher doses. The MTD was determined to be 1.88 mg/kg administered intravenously (IV) once every three weeks.

        The study achieved its primary activity objective with an ORR in the Phase 2 cohort of 15% (5/34). Median PFS was 3.9 months. CDX-011 was found to be active in advanced melanoma patients in the study. The most frequent treatment-related adverse events included rash, fatigue, alopecia (hair loss), pruritus, diarrhea and neuropathy.

        More frequent dosing schedules of CDX-011 were also evaluated, including a weekly and a two out of every three-week regimen, to explore if more frequent administration can provide additional activity in patients with metastatic melanoma. Doses of 1.0 mg/kg given once every week and 1.5 mg/kg given for two out of three weeks were identified as the MTD in each schedule. The response rate was observed to be 20% and 33%, respectively. This increased activity was accompanied by increased toxicity.

        In the subset of patients with tumor biopsies, high levels of tumor expression of GPNMB appeared to correlate with favorable outcome. In the seven patients whose tumors were found to express high

5

---

Table of Contents

amounts of GPNMB, and who were treated at the maximum tolerated doses across all dosing schedules, median PFS was 4.9 months. The development of rash, which may be associated with the presence of GPNMB in the skin also seemed to correlate with greater PFS.

        Melanoma is a difficult disease to work with and, at this point in time, our intention is to first focus our resources on advancing CDX-011 in breast cancer. We intend to conduct additional Phase 2 development of CDX-011 in combination with other therapies in investigator sponsored studies to further develop this product candidate in melanoma.

CDX-1307

        Our lead APC Targeting Technology™ product candidate, CDX-1307, is in development for the treatment of epithelial tumors such as colorectal, pancreatic, bladder, ovarian and breast cancers. CDX-1307 targets the beta chain of human chorionic gonadotropin, known as hCG-Beta, which is an antigen often found in epithelial tumors. The presence of hCG-Beta in these cancers correlates with a poor clinical outcome, suggesting that this molecule may contribute to tumor growth. Normal adult tissues have minimal expression of hCG-Beta; therefore, targeted immune responses are not expected to generate significant side effects.

        The Phase 1 studies are complete. The Phase 1 studies investigated the safety and immunogenicity of CDX-1307 alone and in combination with adjuvants, including GM-CSF (known to increase mannose receptor expression on dendritic cells) and Toll-Like Receptor ("TLR") agonists (poly-ICLC or Hiltonol™ and R848 or resiquimod). Patients with an assortment of different tumor types that are known to express hCG-Beta were enrolled with retrospective analysis for hCG-Beta expression. A regimen of every two week dosing for four doses was utilized with the possibility of retreatment if patients demonstrate tumor regression or stable disease.

        The Phase 1 studies enrolled over 80 patients with heavily pretreated, advanced-stage colorectal, breast, pancreatic, bladder/ureteral, ovarian and testicular cancer. All patient cohorts demonstrated a favorable safety profile with no dose limiting toxicity. The combination of CDX-1307 with TLR agonists significantly enhanced immune responses against hCG-Beta. Immune responses occurred even in the presence of high circulating levels of hCG-Beta, suggesting that the CDX-1307 can overcome antigen tolerance in advanced and heavily pretreated cancers. Nine patients in the studies experienced disease stabilization from 2.3 months to 16 months following the initiation of CDX-1307 vaccination. These data provide the basis for advancing CDX-1307 into a front-line patient population selected for hCG-Beta-expressing cancers.

        In May 2010, we initiated a 60 patient randomized (1:1) Phase 2 controlled study to evaluate the CDX-1307 regimen in both neoadjuvant and adjuvant settings in patients with newly diagnosed muscle-invasive bladder cancers that express hCG-Beta.

CDX-1401

        CDX-1401, also developed from the APC Targeting Technology, is a fusion protein consisting of a fully human monoclonal antibody with specificity for the dendritic cell receptor, DEC-205, linked to the NY-ESO-1 tumor antigen. In humans, NY-ESO-1 has been detected in 20 - 30% of all melanoma, lung, esophageal, liver, gastric, prostate, ovarian and bladder cancers, thus representing a broad opportunity. This product is intended to selectively deliver the NY-ESO-1 antigen to APCs for generating robust immune responses against cancer cells expressing NY-ESO-1. Unlike CDX-1307, which targets the mannose receptor expressing dendritic cells, CDX-1401 is the first APC product targeting DEC-205 expressing dendritic cells. We are developing CDX-1401 for the treatment of malignant melanoma and a variety of solid tumors which express the proprietary cancer antigen NY-ESO-1, which we licensed from the Ludwig Institute for Cancer Research in 2006. We believe that

6

---

Table of Contents

preclinical studies have shown that CDX-1401 is effective for activation of human T-cell responses against NY-ESO-1.

        In September 2009, we initiated enrollment in a dose-escalating Phase 1/2 clinical trial aimed at determining the optimal dose for further development based on the safety, tolerability, and immunogenicity of the CDX-1401 vaccine. The trial will evaluate three different doses of the vaccine in combination with TLR agonists poly-ICLC or Hiltonol™ and/or R848 or resiquimod. We expect to enroll approximately 50 patients with solid tumor cancers at multiple clinical sites in the United States.

        In October 2010, we announced interim data for the first 20 patients enrolled in the study, 35% of whom had confirmed NY-ESO-1 expression. The interim data showed that six patients maintained stable disease and were eligible for multiple cycles of the treatment regimen, including 4 patients who have received 3 or more cycles (6 weeks of treatment followed by a 6 week rest), with stable disease of up to 11.5+ months. The treatment was well tolerated and there were no dose-limiting toxicities. Robust anti-NY-ESO-1 immunity was induced with the majority of the patients developing anti-NY-ESO-1 antibody responses and 39% of the patients having increases in NY-ESO-1 specific T cell responses, including both CD4 and CD8 responses. Importantly, the T cell responses were directed against multiple regions of the NY-ESO-1 antigen.

Preclinical and Other Development Programs

CDX-301

        CDX-301 is a FMS-like tyrosine kinase 3 ligand (Flt3L) that we licensed from Amgen in March 2009. CDX-301 is a growth factor for stem cells and immune cells called dendritic cells. Based on previous experience with this molecule, we believe that CDX-301 has considerable opportunity in various transplant settings as a stem cell mobilizing agent. In addition, CDX-301 is an immune modulating molecule that increases the numbers and activity of specific types of immune cells. We believe CDX-301 has significant opportunity for synergistic development in combination with proprietary molecules in our portfolio. In March 2011, we filed an Investigational New Drug ("IND") application for CDX-301. We are in discussions with collaborators to initiate clinical development with a Phase 1 study in healthy volunteers.

CDX-1127

        We have entered into a License Agreement with the University of Southampton, UK, to develop human antibodies to CD27, a potentially important target for immunotherapy of various cancers. In preclinical models, antibodies to CD27 alone have been shown to mediate anti-tumor effects, and may be particularly effective in combination with other immunotherapy. CD27 is a critical molecule in the activation pathway of lymphocytes. It acts downstream from CD40 and may provide a novel way to regulate the immune responses. In September 2010, we exercised an option under our Research and Commercialization Agreement with Medarex, whereby we have a commercial license to the human antibody technology specifically for our CD27 antibody. Preclinical models with our human monoclonal antibody to CD27 have demonstrated immune cell activation and anti-tumor responses. We expect to file an IND application for a dose escalation Phase 1 study during the fourth quarter of 2011 after completing required preclinical toxicology studies.

CDX-014

        CDX-014 is a fully-human monoclonal ADC that targets TIM-1, an immunomudulatory protein that appears to down regulate immune response to tumors. The antibody, CDX-014, is linked to a potent chemotherapeutic, monomethyl auristatin E (MMAE), using Seattle Genetics' proprietary technology. The ADC is designed to be stable in the bloodstream, but to release MMAE upon

7

---

Table of Contents

internalization into TIM-1-expressing tumor cells, resulting in a targeted cell-killing effect. CDX-014 has shown potent activity in preclinical models of ovarian and renal cancer.

CDX-1135

        CDX-1135 is a molecule that inhibits a part of the immune system called the complement system. The complement system is a series of proteins that are important initiators of the body's acute inflammatory response against disease, infection and injury. Excessive complement activation also plays a role in some persistent inflammatory conditions. CDX-1135 is a soluble form of naturally occurring Complement Receptor 1 that inhibits the activation of the complement cascade in animal models and in human clinical trials. We believe that regulating the complement system could have therapeutic and prophylactic applications in several acute and chronic conditions, including organ transplantation, multiple sclerosis, rheumatoid arthritis, age-related macular degeneration ("AMD"), atypical Hemolytic Uremic Syndrome ("aHUS"), Paroxysmal Nocturnal Hemaglobinuria ("PNH"), Dense Deposit Disease ("DDD") in kidneys, and myasthenia gravis. We are currently defining the most appropriate clinical development path for CDX-1135 and are focusing on rare disease conditions of unregulated complement activation as the fastest route to FDA approval.

Development Strategy

Precision Targeted Immunotherapy Platform:

8

---

Table of Contents

        We believe there is tremendous untapped potential in immunotherapy that can be exploited through the right combination of therapeutic agents. Our industry has traditionally taken biologics that mediate effective cancer regression in mice and expected similar results in humans. There are many explanations why this strategy often does not succeed, but the most important is that immunotherapy has difficulties when following standard drug development. The mechanism of action is complex, activity is generally not dependent on highest tolerated dose, and patient response is highly variable. Our new understanding of the immune system, cancer's effect on immune mediated mechanisms, and the impact of conventional therapies on the immune system provides a new rationale for combining therapies that may lead to significant clinical responses. The concept of Precision Targeted Immunotherapy is to exploit this knowledge and the availability of good products that may not be sufficiently effective to be commercialized as a monotherapy, but which we believe may be very effective in combination approaches. Our goal is to develop products that maximize the efficacy of immunotherapy regimens through combinations of therapeutic agents. This includes:

        Therapeutic Antibody Programs:    These programs are based on the well validated approach to using antibodies that target to cancer and other diseases directly, or through interfering with critical interactions between the patient and the disease. Our antibody programs include antibody-drug conjugates (ADCs) that are designed to deliver potent cytotoxic molecules to cancer cells, and traditional unmodified antibody approaches. Our current programs are based on fully human sequence antibodies to minimize patient reactivity against the drug. In addition, we have access through a Research and Commercialization Agreement with Medarex (now a subsidiary of Bristol-Myers Squibb) to the UltiMAb® Technology for generating fully human monoclonal antibodies. Under this agreement, we can exercise up to ten separate licenses to develop and commercialize therapeutic antibody products, either alone or through collaboration with our licensing partners.

        Our APC Targeting Technology™:    This is a new class of vaccines based on our proprietary antibody-targeted vaccine technology that is used to generate an immune response against cancer or other diseases. Our APC Targeting Technology™ uses human monoclonal antibodies linked to disease associated antigens to efficiently deliver the attached antigens to immune cells known as antigen presenting cells, or APCs. This technology has been designed to allow us to take advantage of many important characteristics of human monoclonal antibodies, including their long circulating half-life, well known safety profile, and standardized manufacturing procedures. We believe that our APC Targeting Technology™ provides significant manufacturing, regulatory and other practical advantages over patient specific and other immune-based treatments and can substantially reduce the dosage and cost currently required in conventional immunotherapies. Preclinical studies have demonstrated that APC Targeting Technology™ is more effective than conventional non-targeted vaccines. We have developed several proprietary monoclonal antibodies that can independently be developed to generate new product opportunities. Our CDX-1307 and CDX-1401 programs are in clinical development with the APC technology.

        Immune System Modulators:    Immune system modulators include drugs that activate or suppress specific parts of the immune system. Currently we are combining our APC technology product candidates with molecules known as Toll-Like Receptor (TLR) agonists that can activate patients' innate and adaptive immunity. We are also developing an immune cell growth factor called FMS-like tyrosine kinase 3 ligand (FLT3-L or CDX-301) designed to expand immune cells and stem cells. In addition, we are investigating the activity of a complement inhibitor (CDX-1135) that suppresses inflammatory reactions. These agents further support our Precision Targeted Immunotherapy Platform.

9

---

Table of Contents

        Antibody-Drug Conjugates (ADC):    ADCs are monoclonal antibodies that are linked to potent cell-killing drugs. Our ADCs utilize fully-human monoclonal antibodies that internalize within target cells after binding to their cell-surface receptors. Enzymes present inside the cell cause the cell-killing drug to be released from the monoclonal antibody, allowing it to have the desired activity. A key component of our ADCs is the linker that attaches the drug to the monoclonal antibody. When the ADC is internalized within the target cell, the drug is released, thereby minimizing toxicity to normal tissues. Our CDX-011 program is in clinical development with the ADC technology.

        Our strategy is to utilize our expertise to design and develop targeted immunotherapeutics that have significant and growing market potential; to establish governmental and corporate alliances to fund development; and to commercialize our products either through corporate partners or, in appropriate circumstances, through our own direct selling efforts. Our goal is to demonstrate clinical proof-of-concept for each product, and then seek partners to help see those products which we cannot develop ourselves through to commercialization. This approach allows us to maximize the overall value of our technology and product portfolios while best ensuring the expeditious development of each individual product.

        Factors that may significantly harm our commercial success, and ultimately the market price of our common stock, include but are not limited to, announcements of technological innovations or new commercial products by our competitors, disclosure of unsuccessful results of clinical testing or regulatory proceedings and governmental approvals, adverse developments in patent or other proprietary rights, public concern about the safety of products developed by us and general economic and market conditions. See "Item 1A. Risk Factors."

Partnerships

        Our strategy is to develop and demonstrate proof-of-concept for our product candidates before leveraging their value through partnerships or, in appropriate situations, continuing late stage development through commercialization ourselves. We have entered into collaborative partnership agreements with pharmaceutical and other companies and organizations that provide financial and other resources, including capabilities in research, development, manufacturing, and sales and marketing, to support our research and development programs. We depend on these relationships and may enter into more of them in the future. Some of our partners have substantial responsibility to commercialize a product and to make decisions about the amount and timing of resources that are devoted to developing and commercializing a product. As a result, we do not have complete control over how resources are used toward some of our products.

        Partnership agreements may terminate without benefit to us if the underlying products are not fully developed. If we fail to meet our obligations under these agreements, they could terminate and we might need to enter into relationships with other collaborators and to spend additional time, money, and other valuable resources in the process.

        We cannot predict whether our collaborators will continue their development efforts or, if they do, whether their efforts will achieve success. Many of our collaborators face the same kinds of risks and uncertainties in their business that we face. A delay or setback to a partner will, at a minimum, delay the commercialization of any affected products, and may ultimately prevent it. Moreover, any partner could breach its agreement with us or otherwise not use best efforts to promote our products. A partner may choose to pursue alternative technologies or products that compete with our technologies or products. In either case, if a partner failed to successfully develop one of our products, we would need to find another partner. Our ability to do so would depend upon our legal right to do so at the time and whether the product remained commercially viable.

10

---

Table of Contents

GlaxoSmithKline plc ("Glaxo") and Paul Royalty Fund II, L.P. ("PRF")

        Rotavirus is a major cause of diarrhea and vomiting in infants and children. In 1997, we licensed our oral rotavirus strain to Glaxo and Glaxo assumed responsibility for all subsequent clinical trials and all other development activities. Glaxo gained approval for its rotavirus vaccine, Rotarix®, in Mexico in July 2004, which represented the first in a series of worldwide approvals and commercial launches for the product leading up to the approval in Europe in 2006 and in the U.S. in 2008. We licensed-in our rotavirus strain in 1995 and owe a license fee of 30% to Cincinnati Children's Hospital Medical Center ("CCH") on net royalties received from Glaxo. We are obligated to maintain a license with CCH with respect to the Glaxo agreement. The term of the Glaxo agreement is through the expiration of the last of the relevant patents covered by the agreement, although Glaxo may terminate the agreement upon 90 days prior written notice. The last relevant patent is scheduled to expire in December 2012. No additional milestone payments are due from Glaxo under the agreement.

        In May 2005, we entered into an agreement whereby an affiliate of PRF purchased a 70% interest in the milestone payments and net royalties that we will receive on the development and worldwide sales of Rotarix®. We have received a total of $60 million in milestone payments under the PRF agreement. No additional milestone payments are due from PRF under the agreement. The PRF agreement terminates on December 12, 2012, unless otherwise extended.

        Royalty rates on Rotarix® escalate from 7% to 10% based on net product sales in countries that have valid patent protection. These royalty rates are discounted by 30% for "non-patent" countries (primarily international markets). In September 2006, we received notice from Glaxo that Glaxo would begin paying royalties on sales of Rotarix® vaccine at the lower of the two royalty rates under their 1997 license agreement. Glaxo's decision to pay the lower royalty rate (which is 70% of the full rate) is based upon Glaxo's assertion that Rotarix® is not covered by the patents Glaxo licensed from us in Australia and certain European countries. We are currently evaluating the basis for Glaxo's action and our potential remedies. If Glaxo's position stands, the royalties to which PRF is entitled will no longer be limited by a $27.5 million annual threshold. With respect to the $27.5 million annual threshold, if worldwide net royalties on sales of Rotarix® exceed $27.5 million in any year, we would retain approximately 65% of all royalties in excess of $27.5 million. Irrespective of Glaxo's position, we will still retain approximately 65% of the royalties on worldwide sales of Rotarix® if PRF receives 2.45 times the aggregate cash payments of $60 million it made to us, though the potential amount of such residual royalties will be lower if Glaxo's position stands.

        In late March 2010, the FDA temporarily suspended the use of Rotarix® in the United States as a precautionary measure following the discovery of PCV-1 DNA material in the vaccine. In May 2010, the FDA determined that healthcare practitioners could resume the use of Rotarix®. Our royalties from sales of Rotarix® were negatively impacted during the year ended December 31, 2010 by the FDA's decision to temporarily suspend the use of Rotarix® from March 2010 through May 2010 and that negative impact from the temporary suspension may extend into the future as well. However, our net loss and cash position were not impacted even though our royalty revenue was impacted because there was an offsetting impact on our royalty expense.

Pfizer Animal Health Agreement

        We entered into a licensing agreement in December 2000 with Pfizer's Animal Health Division whereby Pfizer has licensed our technology for the development of animal health and food safety vaccines. Under the agreement, we may receive additional milestone payments of up to $3 million based upon attainment of specified milestones. We may receive royalty payments on eventual product sales. The term of this agreement is through the expiration of the last of the patents covered by the agreement. We have no obligation to incur any research and development costs in connection with this agreement.

11

---

Table of Contents

Vaccine Technologies, Inc. ("VTI")

        In January 2009, we entered into a license agreement with VTI under which we granted a worldwide exclusive license to VTI to develop and commercialize our CholeraGarde® and ETEC vaccine programs. We may receive milestones payments of up to $0.8 million and royalties in the low to mid teens with respect to development and commercialization of the technology licensed to VTI.

TopoTarget A/S ("TopoTarget")

        Under our April 2008 agreement ("TopoTarget Agreement") with TopoTarget, we could receive up to $6 million in either potential commercial milestone payments related to future net sales of Belinostat or 10% of any sublicense income received by TopoTarget ("TopoTarget Payments"). We have no financial and operational responsibility for the clinical development of Belinostat under the TopoTarget Agreement. In February 2010, TopoTarget entered into a co-development and commercialization agreement for Belinostat with Spectrum Pharmaceuticals, Inc. resulting in our receipt of $3 million of the TopoTarget Payments.

Research Collaboration and License Agreements

        We have entered into license agreements whereby we have received licenses or options to license technology, specified patents and/or patent applications. These license and collaboration agreements generally provide for royalty payments equal to specified percentages of product sales, annual license maintenance fees, continuing patent prosecution costs and potential future milestone payments to third parties upon the achievement of certain development, regulatory and/or commercial milestones.

Medarex, Inc., a subsidiary of Bristol-Myers Squibb ("Medarex")

        We and Medarex, a former related party, have entered into the following agreements, each of which was approved by a majority of its independent directors who did not have an interest in the transaction. These agreements include:

•

An Assignment and License Agreement, as amended, ("Assignment and License Agreement") that provides for the assignment of certain patent and other intellectual property rights and a license to certain Medarex technology related to the Company's APC Targeting Technology™ and an anti-mannose receptor product; and



•

A Research and Commercialization Agreement, as amended, ("Research and Commercialization Agreement") that provides us with certain rights to obtain exclusive commercial licenses to proprietary monoclonal antibodies raised against certain antigens utilizing the Medarex UltiMAb® technology platform for generating antibodies.

        Under the terms of the Assignment and License Agreement, we may be required to pay royalties in the low-single digits on any net product sale of a Licensed Royalty-Bearing Product or Anti-Mannose Product to Medarex until the later of (i) the expiration of the last to expire applicable patent and (ii) the tenth anniversary of the first commercial sale of such licensed product. Under the terms of the Research and Commercialization Agreement, we may be required to pay milestones of up to $7.0 million upon obtaining first approval for commercial sale in a first indication of a product containing a licensed antibody and royalty payments in the low- to mid-single digits on any net product sales to Medarex with respect to the development of any products containing such licensed antibodies until the later of (i) the expiration of the last to expire applicable patent and (ii) the tenth anniversary of the first commercial sale of such licensed product. In September 2010, we exercised an option under our Research and Commercialization Agreement, whereby we have a commercial license to the human antibody technology specifically for CDX-1127, our CD27 antibody.

12

---

Table of Contents

        In October 2007, we and Medarex entered into a settlement and mutual release agreement which settled disputed amounts we owed Medarex. We issued to Medarex 351,692 shares of our common stock equal in value to $3.0 million, based on the per share price of $8.64 set on the second trading day prior to the closing date of the AVANT Merger and exchanged releases. In October 2009, we paid Medarex an additional $3.0 million owed under the Master Services Agreement.

Rockefeller University ("Rockefeller")

        In November 2005, we and Rockefeller entered into a license agreement for the exclusive worldwide rights to human DEC-205 receptor, with the right to sublicense the technology. The license grant is exclusive except that Rockefeller may use and permit other nonprofit organizations to use the human DEC-205 receptor patent rights for educational and research purposes. We may be required to pay milestones of up to $3.9 million upon obtaining first approval for commercial sale in a first indication of a product targeting the licensed receptor and royalty payments in the low- to mid-single digits on any net product sales to Rockefeller with respect to development and commercialization of the human DEC-205 receptor.

Duke University Brain Tumor Cancer Center ("Duke")

        In September 2006, we and Duke entered into a license agreement that gave us access and reference to the clinical data generated by Duke and its collaborators in order for us to generate our own filing with the FDA relating to the CDX-110 product. We may be required to pay milestones of up to $1.0 million upon obtaining first approval for commercial sale in a first indication and royalty payments in the low-single digits on any net product sales to Duke with respect to development and commercialization of the CDX-110 product. In connection with the Pfizer Agreement, we determined that $2.4 million was payable to Duke as a sublicense fee. As provided for under the Duke license, we paid 50% of this amount to Duke in the form of 81,512 shares of our common stock in October 2008.

Ludwig Institute for Cancer Research ("Ludwig")

        In October 2006, we and Ludwig entered into an agreement for the nonexclusive rights to certain cancer tumor targets for use in combination with our APC Targeting Technology. The term of the agreement is for ten years. We may be required to pay milestones of up to $1.0 million upon obtaining first approval for commercial sale in a first indication and royalty payments in the low-single digits on any net product sales to Ludwig with respect to development and commercialization of the technology licensed from Ludwig.

Alteris Therapeutics, Inc. ("Alteris")

        In October 2005, we completed the acquisition of the assets of Alteris, including the EGFRvIII molecule. We may be required to pay Alteris up to $5.0 million upon obtaining the first approval for commercial sale of a product containing EGFRvIII, including CDX-110.

Thomas Jefferson University ("TJU")

        In February 2003, we entered into two exclusive license agreements with TJU. Under these licenses, we may be required to pay milestones of up to $3.0 million upon obtaining first approval for commercial sale in a first indication and royalty payments in the low-single digits on any net product sales to TJU with respect to development and commercialization of the technology licensed from TJU. In connection with the Pfizer Agreement, we amended our licenses with TJU to add additional sublicensing rights and paid $4.5 million in sublicense fees to TJU in 2008.

13

---

Table of Contents

3M Company

        In June 2008, we and 3M Company entered into a license agreement for the exclusive worldwide rights to access 3M Company's proprietary Immune Response Modifier, Resiquimod™, (and additional Toll-Like Receptor 7/8 agonists ("TLR")) for clinical study with our proprietary APC Targeting Technology, for use as vaccine adjuvants, with the right to sublicense the technology. We may be required to pay milestones of up to $3.8 million upon obtaining first approval for commercial sale of each product using this vaccine adjuvant and royalty payments in the low-single digits on any net product sales to 3M Company with respect to development and commercialization of the technology licensed from 3M Company.

University of Southampton, UK ("Southampton")

        In November 2008, we entered into a license agreement with Southampton to develop human antibodies towards CD27, a potentially important target for immunotherapy of various cancers. CD27 is a critical molecule in the activation pathway of lymphocytes, is downstream from CD40, and may provide a novel way to regulate the immune responses. In preclinical models, antibodies to CD27 have been shown to mediate anti-tumor effects alone, and may be particularly effective in combination with our other immunotherapies. We may be required to pay milestones of up to approximately $1.4 million upon obtaining first approval for commercial sale in a first indication and royalty payments in the low-single digits on any net product sales to Southampton with respect to development and commercialization of the technology licensed from Southampton.

Amgen Inc. ("Amgen")

        In March 2009, we entered into a license agreement with Amgen to expand our Precision Targeted Immunotherapy Platform by acquiring exclusive rights to FMS-like tyrosine kinase 3 ligand (Flt3L or CDX-301) and CD40 ligand (CD40L). CDX-301 and CD40L are immune modulating molecules that increase the numbers and activity of immune cells that control immune responses. We may be required to pay milestones of up to $1.3 million upon obtaining first approval for commercial sale in a first indication and royalty payments in the low-single digits on any net product sales to Amgen with respect to development and commercialization of this technology licensed from Amgen.

Amgen Fremont (formerly Abgenix)

        In connection with the CuraGen Merger, we assumed the license agreement between CuraGen and Amgen Fremont (successor in-interest to Abgenix) to develop fully-human monoclonal antibody therapeutics. In May 2009, an amendment to the license agreement ("Amgen Amendment") was entered into related to CuraGen's exclusive rights to develop and commercialize CDX-011 and 11 other licensed antigens. Under the Amgen Amendment, CuraGen and Amgen Fremont agreed to modify the terms of their existing cross-license of antigens whereby the amended license would be fully paid-up and royalty-free (except for any potentially required payments by CuraGen to the original licensor of CDX-011).

Seattle Genetics, Inc. ("Seattle Genetics")

        In connection with the CuraGen Merger, we assumed the license agreement between CuraGen and Seattle Genetics whereby CuraGen acquired the rights to proprietary antibody-drug conjugate ("ADC") technology for use with its proprietary antibodies for the potential treatment of cancer. We may be required to pay milestones of up to $7.5 million upon obtaining first approval for commercial sale in a first indication and royalty payments in the mid-single digits on any net product sales to Seattle Genetics with respect to development and commercialization of the ADC technology.

14

---

Table of Contents

Competition

        The biotechnology and pharmaceutical industries are intensely competitive and subject to rapid and significant technological change. Many of the products that we are attempting to develop and commercialize will be competing with existing therapies. In addition, a number of companies are pursuing the development of pharmaceuticals that target the same diseases and conditions that we are targeting. We face competition from pharmaceutical and biotechnology companies both in the United States and abroad. Our competitors may utilize discovery technologies and techniques or partner with collaborators in order to develop products more rapidly or successfully than us or our collaborators are able to do. Many of our competitors, particularly large pharmaceutical companies, have substantially greater financial, technical and human resources than we do. In addition, academic institutions, government agencies and other public and private organizations conducting research may seek patent protection with respect to potentially competitive products or technologies and may establish exclusive collaborative or licensing relationships with our competitors.

        We face intense competition in our development activities. We face competition from many companies in the United States and abroad, including a number of large pharmaceutical companies, firms specialized in the development and production of vaccines, adjuvants and vaccine and immunotherapeutic delivery systems and major universities and research institutions. The competitors for which we are aware have initiated a Phase 3 study or have obtained marketing approval for a potentially competitive drug include Alexion, Agenus, Baxter, Dendreon, Eli Lilly, GlaxoSmithKline, ImmunoGen, Merck, Northwest Biotherapeutics, Pfizer, Roche, Sanofi-Aventis, Seattle Genetics, and Takeda. We are aware that Dendreon has received marketing approval for Provenge, a therapeutic vaccine for the treatment of prostate cancer which may compete with CDX-1307 and CDX-1401. In addition, companies such as Eli Lilly with its approved product Erbitux™ for the treatment of colorectal cancer, and Roche with its product Herceptin® for the treatment of metastatic breast cancer, have already commercialized antibody-based products that may compete with CDX-1307, CDX-1401 and CDX-011. Various other companies are developing or commercializing products in areas that we have targeted for product development. Some of these products use therapeutic approaches that may compete directly with our product candidates. Many of these companies and institutions, either alone or together with their partners, have substantially greater financial resources and larger research and development staffs than we do. These companies may succeed in obtaining approvals from the FDA and foreign regulatory authorities for their products sooner than we do for our products.

        We are aware of a number of competitive products currently available in the marketplace or under development that are used for the prevention and treatment of the diseases that we have targeted for product development. Various companies are currently marketing or developing biopharmaceutical products that may compete with our product candidates that target colorectal cancer. Product candidates we may develop are also subject to competition in the treatment of colorectal cancer from a number of products already approved and on the market, including the following chemotherapy products: AstraZeneca PLC's Tomudex®, Hoffman-LaRoche's Xeloda® (capecitabine), Immunex Corporation's Leucovorin® calcium, ImClone Systems' Erbitux™, Pfizer, Inc.'s Camptosar® (irinotecan) and Aduracil® (5-FU), Sanofi-Synthelabo Group's Eloxatin™ (oxaliplatin), Genentech's anti-VEGF antibody, Avastin™, GlaxoSmithKline's Eniluracil™, and Titan Pharmaceuticals' CeaVac™, in the treatment of patients with advanced-stage colorectal cancer. In addition, we are aware that other companies such as BioSante, Dendreon and Seattle Genetics may be developing additional cancer vaccines that could potentially compete with some of our other product candidates. We may also face competition from Bristol-Myers Squibb, which is developing a therapeutic vaccine for the treatment of melanoma using its Ipilimumab product candidate. We also face competition from a number of companies working in the fields of anti-angiogenesis and specific active immunotherapy for the treatment of solid tumor cancers. We expect that competition among specific active immunotherapy

15

---

Table of Contents

and anti-angiogenesis products approved for sale will be based on various factors, including product efficacy, safety, reliability, availability, price and patent position.

        We are aware of specific companies that are developing antibody-drug conjugates (ADCs) for use in the treatment of cancer. Trastuzumab-DM1 (T-DM1) is a first-in-class HER2 antibody-drug conjugate comprised of Genentech's (a member of the Roche Group) trastuzumab antibody linked to ImmunoGen's cell-killing agent, DM1. T-DM1 combines anti-HER2 activity and targeted intracellular delivery of the potent anti-microtubule agent, DM1 (a maytansine derivative). A Phase 3 clinical trial evaluating T-DM1 for second-line HER2-positive metastatic breast cancer may be competitive with our developmental program in the breast cancer indication. Other ADCs are in development by our collaborator of the MMAE technology, Seattle Genetics, using monomethylaurastatin derivatives as the cell-killing agent in hematologic cancers and other cancers. Marketed products that are used in the treatment of melanoma include dacarbazine, temozolamide, and interleukin-2. In addition, several other pharmaceutical and biotechnology companies are engaged in research and development for the treatment of melanoma. Many more products are on the market or in development for the treatment of metastatic breast cancer. At this time, it is not clear in what manner CDX-011 will compete with these other commercial and development stage products in metastatic melanoma and breast cancer.

        We also face competition from pharmaceutical and biotechnology companies, academic institutions, government agencies and private research organizations in recruiting and retaining highly qualified scientific personnel and consultants and in the development and acquisition of technologies. Moreover, technology controlled by third parties that may be advantageous to our business may be acquired or licensed by our competitors, thereby preventing us from obtaining technology on commercially reasonable terms, if at all. We will also compete for the services of third parties that may have already developed or acquired internal biotechnology capabilities or made commercial arrangements with other biopharmaceutical companies to target the diseases on which we have focused both in the U.S. and outside of the U.S.

        Our competitive position will also depend upon our ability to attract and retain qualified personnel, obtain patent protection or otherwise develop proprietary products or processes and secure sufficient capital resources for the often lengthy period between technological conception and commercial sales. We will require substantial capital resources to complete development of some or all of our products, obtain the necessary regulatory approvals and successfully manufacture and market our products. In order to secure capital resources, we anticipate having to sell additional capital stock, which would dilute existing stockholders. We may also attempt to obtain funds through research grants and agreements with commercial collaborators. However, these types of fundings are uncertain because they are at the discretion of the organizations and companies that control the funds. As a result, we may not receive any funds from grants or collaborations. Alternatively, we may borrow funds from commercial lenders, likely at high interest rates, which would increase the risk of any investment in us.

Manufacturing

        We have no experience in large scale manufacturing and we have relied upon collaborators or contractors to manufacture some of our proposed products for both clinical and commercial purposes to date. We have established our own manufacturing facility in Fall River, Massachusetts, to produce antibodies, vaccines and other products that we may develop at scale for clinical trials. In 2010, we completed renovations at our Fall River, MA manufacturing facility which increased our capacity by installing a 1000L bioreactor and made the facility European Medicines Agency ("EMEA") compliant. Implementing EMEA requirements along with FDA Good Manufacturing Practices ("GMP") will allow us to distribute potential products to clinical sites in both the US and EU. In order for us to establish a commercial manufacturing facility, we will require substantial additional funds and will be required to hire and retain significant additional personnel and comply with the extensive GMP regulations applicable to such facility. The commercial manufacturing facility would also need to be licensed for

16

---

Table of Contents

the production of antibodies, vaccines and other products by the FDA. We intend to establish manufacturing arrangements with manufacturers that comply with the FDA's requirements and other regulatory standards, although there can be no assurance that we will be able to do so.

        While we believe that there is currently sufficient capacity worldwide for the production of our potential products by our collaborators or through contract manufacturers, establishing long-term relationships with contract manufacturers and securing multiple sources for the necessary quantities of clinical and commercial materials required can be a challenge. Qualifying the initial source of clinical and ultimately commercial material is a time consuming and expensive process due to the highly regulated nature of the pharmaceutical/biotech industry. These costs are hopefully mitigated in the economies of scale realized in commercial manufacture and product sale. The key difficulty in qualifying more than one source for each product is the duplicated time and expense in doing so without the potential to mitigate these costs if the secondary source is never utilized.

        As part of the Pfizer Termination, we acquired rindopepimut drug product that was manufactured by Pfizer which we intend to use in our upcoming Phase 3 clinical trial. We intend to establish a relationship with a contract manufacturer for the future commercial manufacturing of rindopepimut. To date, we have utilized contract manufacturers for the manufacture of clinical trial supplies of CDX-011 and CDX-1135. The two clinical lots of CDX-1307 used in our completed Phase 1 clinical trials of CDX-1307 were manufactured by contract manufacturers. We manufactured additional quantities of CDX-1307 in our Fall River facility to meet our current Phase 2 clinical trial material requirements. We also manufactured in our Fall River facility CDX-1401 clinical materials for our current Phase 1/2 clinical trial and CDX-301 and CDX-1127 clinical materials for our planned Phase 1 clinical trials. Manufacture of the rotavirus vaccine is the responsibility of Glaxo, which has received from us a worldwide exclusive license to commercialize this vaccine.

        The manufacturing processes for our other vaccine and immunotherapeutic delivery systems and vaccines utilize known technologies. We believe that the products we currently have under development can be scaled up to permit manufacture in commercial quantities. However, there can be no assurance that we will not encounter difficulties in scaling up the manufacturing processes.

        Use of third party manufacturers limits our control over and ability to monitor the manufacturing process. As a result, we may not be able to detect a variety of problems that may arise and may face additional costs in the process of interfacing with and monitoring the progress of our contract manufacturers. If third party manufacturers fail to meet our manufacturing needs in an acceptable manner, we would face delays and additional costs while we develop internal manufacturing capabilities or find alternative third party manufacturers. It may not be possible to have multiple third party manufacturers ready to supply us with needed material at all or without incurring significant costs.

Marketing

        Under the terms of existing and future partnership agreements, we rely and expect to continue to rely on the efforts of our collaborators, including Glaxo, for the sale and marketing of our products. There can be no assurance that our collaborators will develop and market vaccine products incorporating our technologies, or, if marketed, that such efforts will be successful. The failure of our collaborators to successfully market products would harm our business.

        We have retained, and in the future intend to retain, marketing rights to some of our product candidates, including vaccine and immunotherapeutic delivery systems and vaccine candidates, in selected geographic areas and for specified indications. We intend to seek marketing and distribution agreements and/or co-promotion agreements for the distribution of our products in these geographic areas and for these indications. We believe that these arrangements could enable us to generate greater financial return than might be obtained from early stage licensing and collaboration agreements. We currently have no marketing and sales staff and limited experience relating to marketing and

17

---

Table of Contents

distribution of commercial products, including vaccines. If we determine in the future to engage in direct marketing of our products, we will be required to recruit an experienced marketing group, develop a supporting distribution capability and incur significant additional expenditures. There can be no assurance that we will be able to establish a successful marketing force. We may choose or find it necessary to enter into strategic partnerships on uncertain, but potentially unfavorable, terms to sell, market and distribute our products. Any delay in the marketing or distribution of our products, whether it results from problems with internal capabilities or with a collaborative relationship, could harm the value of an investment in us.

Patents, Licenses and Proprietary Rights

        In general, our intellectual property strategy is to protect our technology by filing patent applications and obtaining patent rights covering our own technology, both in the United States and in foreign countries that we consider important to our business. In addition, we have acquired and will seek to acquire as needed or desired, exclusive rights of others through assignment or license to complement our portfolio of patent rights. We also rely on trade secrets, unpatented know-how and technological expertise and innovation to develop and maintain our competitive position.

Patents

        The successful development and marketing of products by us will depend in part on our ability to create and maintain intellectual property, including patent rights. We are the owner or exclusive licensee to proprietary patent positions in the areas of vaccine technologies, antibody technologies and complement inhibitor technology. Although we continue to pursue patent protection for our products, no assurance can be given that any pending application will issue as a patent, that any issued patent will have a scope that will be of commercial benefit, or that we will be able to successfully enforce our patent position against infringers. We routinely review our patent portfolio and adjusts its strategies for prosecution and maintenance of individual cases according to a number of factors including program priorities, stage of development, and patent term.

        We own or license rights under more than 400 granted patents and national and regional patent applications around the world covering inventions relating to our business. The key patents owned by us or licensed to us that we consider important to our business include the following (the indicated and estimated patent expiry dates do not include any possible Patent Term Extensions or Supplementary Protection Certificates, if these may be secured in due course):

•

Patents for the technology used in CDX-110 have expiration dates through 2014 in the United States and through 2015 in the United Kingdom, Germany and France. We also have rights under patent applications around the world relating to uses of CDX-110 which are currently pending. If issued and maintained to full term in a form which covers commercial use of CDX-110, the latter filings could potentially provide additional patent protection for the relevant use in the relevant territories to 2026.



•

Our patent portfolio for CDX-011 includes an issued patent in Europe and pending patent applications in the US and Japan. If issued and maintained to full term in due course, these would have estimated patent expiry dates in 2025. In addition, patent rights relating to the toxin and conjugation technology used in CDX-011 have been licensed from Seattle Genetics.



•

US patents and worldwide pending patent applications for the technology used in CDX-1307 have current or estimated expiration dates (subject to issue in the case of pending applications) that range from 2021 to 2024.

18

---

Table of Contents

•

We have a pending international patent application relating to the technology used in CDX-1401 which, if issued in the main designated territories and maintained to full term in due course, would have estimated patent expiry dates in 2028.



•

Patents for the technology used in CDX-301 have current expiration dates that range from 2016 in the major European territories to 2020 in the US.



•

We have licensed pending patent applications in the US, Europe and Japan relating to the technology used in CDX-1127. If issued and maintained to full term in due course, these would have estimated patent expiry dates in 2027. Further filings are also under preparation.



•

Our patent portfolio for CDX-014 includes pending patent applications in the US, Europe and Japan. If issued and maintained to full term in due course, these would have estimated patent expiry dates in 2024.



•

Patents for the technology used in CDX-1135 have expiration dates that range from 2013 to 2016.



•

Patents for the technology used in the cholera and typhoid vaccines expire between 2013 and 2016. Our patent portfolio for ETEC includes pending patent applications around the world which, if issued and maintained to full term in due course, would have estimated patent expiry dates in 2028.



•

Licensed patents for our rotavirus strain that we licensed to Glaxo have expiration dates in 2011 and 2012.

        There can be no assurance that patent applications owned by or licensed to us will result in granted patents or that, if granted, the resultant patents will afford protection against competitors with similar technology. It is also possible that third parties may obtain patents or other proprietary rights that may be necessary or useful to us. In cases where third parties are first to invent a particular product or technology, it is possible that those parties will obtain patents that will be sufficiently broad to prevent us from using important technology or from further developing or commercializing important vaccine and immunotherapeutic systems and vaccine candidates. If licenses from third parties are necessary but cannot be obtained, commercialization of the covered products might be delayed or prevented. Even if these licenses can be obtained, they would probably require us to pay ongoing royalties and other costs, which could be substantial.

        Although a patent has a statutory presumption of validity in the United States, the issuance of a patent is not conclusive as to validity or as to the enforceable scope of the patent claims. The validity or enforceability of a patent after its issuance by the Patent and Trademark Office can be challenged in litigation. As a business that uses a substantial amount of intellectual property, we face a heightened risk of intellectual property litigation. If the outcome of the litigation is adverse to the owner of the patent, third parties may then be able to use the invention covered by the patent without authorization or payment. There can be no assurance that our issued patents or any patents subsequently issued to or licensed by us will not be successfully challenged in the future. In addition, there can be no assurance that our patents will not be infringed or that the coverage of our patents will not be successfully avoided by competitors through design innovation.

        We are aware that others, including universities and companies, have filed patent applications and have been granted patents in the United States and other countries which claim subject matter potentially useful or necessary to the commercialization of our products. The ultimate scope and validity of existing or future patents which have been or may be granted to third parties, and the availability and cost of acquiring rights in those patents necessary to the manufacture, use or sale of our products presently cannot be determined by us.

19

---

Table of Contents

        Third parties may have or may obtain valid and enforceable patents or proprietary rights that could block us from developing products using our technology, including:

•

certain patents and applications in the United States and Europe owned by Sanofi-Aventis, which relate to antibody-antigen conjugates and methods of their use for eliciting an immune response against the antigen;



•

certain patents and applications in the United States and foreign countries covering particular antigens and antigenic fragments targeted by our current vaccine product candidates, including CDX-1307 and CDX-1401;



•

certain patents and pending applications related to particular receptors and other molecules on dendritic cells and macrophages that may be useful for generating monoclonal antibodies and can be employed in our APC Targeting Technology;



•

two United States patents and related foreign patents and applications covering methods of diagnosing gliomas by detecting the presence of the EGFRvIII (tumor specific splice variant) protein;



•

a United States patent relating to certain uses of GM-CSF;



•

a European patent relating to certain tumor antigen splice variants;



•

a United States patent owned by Genentech, Inc., relating to the production of recombinant antibodies in host cells;



•

a United States patent owned by GlaxoSmithKline plc related to methods of culturing cells under certain conditions; and



•

certain patents held by third parties relating to antibody expression in particular types of host cells.

        The CholeraGarde® vaccine candidate and our VibrioVec® vaccine delivery system utilize mutated Vibrio cholerae strains. We are aware of an issued U.S. patent which claims a culture of mutated Vibrio cholerae. We believe that only one claim (the "Claim") of the patent may be pertinent to our CholeraGarde® and VibrioVec® products. The remaining claims of the patent cover other cultures, which we believe are not pertinent to the CholeraGarde® or VibrioVec® products. Our assessment is that the Claim is invalid. While a party challenging the validity of a patent has the burden of proving invalidity, the outcome of any litigation cannot be predicted with certainty. Accordingly, there can be no assurance that, if litigated, a court would conclude that the Claim is invalid.

        In addition to the patents referred to in the previous paragraphs, there may be other patent applications and issued patents belonging to competitors that may require us to alter our vaccine candidates and vaccine and immunotherapeutic delivery systems, pay licensing fees or cease some of our activities. If our product candidates conflict with patents that have been or may be granted to competitors, universities or others, the patent owners could bring legal action against us claiming damages and seeking to enjoin manufacturing and marketing of the patented products. If any of these actions is successful, in addition to any potential liability for damages, we could be required to obtain a license in order to continue to manufacture or market the affected products. There can be no assurance that we would prevail in any such action or that any license required under any such third party patent would be made available on acceptable terms or at all. We believe that there may be significant litigation in the biotechnology and vaccine industries regarding patent and other intellectual property rights. If we become involved in that litigation, we could consume substantial resources.

20

---

Table of Contents

Licenses

        We have entered into several significant license agreements relating to technology that is being developed by us and/or our collaborators. In general, these institutions have granted us an exclusive worldwide license (with right to sublicense) to make, use and sell products embodying the licensed technology, subject to the reservation by the licensor of a non-exclusive right to use the technologies for non-commercial research purposes. Generally, the term of each license is through the expiration of the last of the patents issued with respect to the technologies covered by the license. We have generally agreed to use reasonable efforts to develop and commercialize licensed products and to achieve specified milestones and pay license fees, milestone payments and royalties based on the net sales of the licensed products or to pay a percentage of sublicense income. If we breach our obligations, the licensor has the right to terminate the license, and, in some cases, convert the license to a non-exclusive license. Generally, we control and are responsible for the cost of defending the patent rights of the technologies that we license.

Proprietary Rights

        We also rely on unpatented technology, trade secrets and confidential information, and no assurance can be given that others will not independently develop substantially equivalent information and techniques or otherwise gain access to our know-how and information, or that we can meaningfully protect our rights in such unpatented technology, trade secrets and information. We require each of our employees, consultants and advisors to execute a confidentiality agreement at the commencement of an employment or consulting relationship with us. The agreements generally provide that all inventions conceived by the individual in the course of employment or in providing services to us and all confidential information developed by, or made known to, the individual during the term of the relationship shall be the exclusive property of us and shall be kept confidential and not disclosed to third parties except in limited specified circumstances. There can be no assurance, however, that these agreements will provide meaningful protection for our information in the event of unauthorized use or disclosure of such confidential information.

Government Regulation

        Our activities and products are significantly regulated by a number of governmental entities, including the FDA in the United States and by comparable authorities in other countries. These entities regulate, among other things, the manufacture, testing, safety, effectiveness, labeling, documentation, advertising and sale of our products. We must obtain regulatory approval for a product in all of these areas before we can commercialize the product. Product development within this regulatory framework takes a number of years and involves the expenditure of substantial resources. Many products that initially appear promising ultimately do not reach the market because they are found to be unsafe or ineffective when tested. Our inability to commercialize a product would impair our ability to earn future revenues.

FDA Approval Process

        In the United States, vaccines and immunotherapeutics for human use are subject to FDA approval as "biologics" under the Public Health Service Act and "drugs" under the Federal Food, Drug and Cosmetic Act. The steps required before a new product can be commercialized include: preclinical studies in animals, clinical trials in humans to determine safety and efficacy and FDA approval of the product for commercial sale.

        Data obtained at any stage of testing is susceptible to varying interpretations, which could delay, limit or prevent regulatory approval. Moreover, during the regulatory process, new or changed drug approval policies may cause unanticipated delays or rejection of our product. We may not obtain

21

---

Table of Contents

necessary regulatory approvals within a reasonable period of time, if at all, or avoid delays or other problems in testing our products. Moreover, even if we received regulatory approval for a product, the approval may require limitations on use, which could restrict the size of the potential market for the product.

        The FDA provides that human clinical trials may begin thirty (30) days after receipt and review of an IND application, unless the FDA requests additional information or changes to the study protocol within that period. An IND must be sponsored and filed by us for each of our proposed products. Authorization to conduct a clinical trial in no way assures that the FDA will ultimately approve the product. Clinical trials are usually conducted in three sequential phases. In a Phase 1 trial, the product is given to a small number of healthy volunteers to test for safety (adverse effects). Phase 2 trials are conducted on a limited group of the target patient population; safety, optimal dosage and efficacy are studied. A Phase 3 trial is performed in a large patient population over a wide geographic area to provide evidence for the safety of the product and to prove and confirm efficacy. The FDA has ongoing oversight over all these trials and can order a temporary or permanent discontinuation if warranted. Such an action could materially harm us. Clinical tests are critical to the success of our products but are subject to unforeseen and uncontrollable delay, including delay in enrollment of patients. Any delay in clinical trials could delay our commercialization of a product.

        A product's safety and effectiveness in one test is not necessarily indicative of its safety and effectiveness in another test. Moreover, we may not discover all potential problems with a product even after completing testing on it. Some of our products and technologies have undergone only preclinical testing. As a result, we do not know whether they are safe or effective for humans. Also, regulatory authorities may decide, contrary to our findings, that a product is unsafe or not as effective in actual use as its test results indicated. This could prevent the product's widespread use, require its withdrawal from the market or expose us to liability.

        The results of the clinical trials and all supporting data are submitted to the FDA for approval. A Biologics License Application ("BLA") is submitted for a biologic product; a New Drug Application ("NDA") for a drug product. The interval between IND filing and BLA/NDA filing is usually at least several years due to the length of the clinical trials, and the BLA/NDA review process can take over a year. During this time the FDA may request further testing or additional trials or may turn down the application. Even with approval, the FDA frequently requires post-marketing safety studies (known as Phase 4 trials) to be performed.

        The FDA requires that the manufacturing facility that produces a licensed product meet specified standards, undergo an inspection and obtain an establishment license prior to commercial marketing. Subsequent discovery of previously unknown problems with a product or its manufacturing process may result in restrictions on the product or the manufacturer, including withdrawal of the product from the market. Failure to comply with the applicable regulatory requirements can result in fines, suspensions of regulatory approvals, product recalls, operating restrictions and criminal prosecution.

Expedited Review and Approval

        The FDA has various programs, including fast track, priority review, and accelerated approval, that are intended to expedite or simplify the process for reviewing drugs, and/or provide for approval on the basis of surrogate endpoints. Generally, drugs that may be eligible for these programs are those for serious or life-threatening conditions, those with the potential to address unmet medical needs, and those that offer meaningful benefits over existing treatments, however, these programs do not affect the standards for approval. Fast track designation applies to the combination of the product and the specific indication for which it is being studied. As a condition of approval, the FDA may require that a sponsor of a drug receiving accelerated approval perform post-marketing clinical trials.

22

---

Table of Contents

Orphan Drug

        Under the Orphan Drug Act, the FDA may grant orphan drug designation to drugs intended to treat a rare disease or condition, which is generally a disease or condition that affects fewer than 200,000 individuals in the United States, or more than 200,000 individuals in the United States and for which there is no reasonable expectation that the cost of developing and making available in the United States a drug for this type of disease or condition will be recovered from sales in the United States for that drug. If a product that has orphan drug designation subsequently receives the first FDA approval 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 to market the same drug for the same indication, except in very limited circumstances, for seven years.

        Once an approval is granted, the FDA may withdraw the approval if compliance with regulatory standards is not maintained or if problems occur after the product reaches the market. After approval, some types of changes to the approved product, such as adding new indications, manufacturing changes and additional labeling claims, are subject to further FDA review and approval. In addition, the FDA may require testing and surveillance programs to monitor the effect of approved products that have been commercialized, and the FDA has the power to prevent or limit further marketing of a product based on the results of these post-marketing programs.

Foreign Regulation

        In addition to regulations in the United States, we will be subject to a variety of foreign regulations governing clinical trials and commercial sales and distribution of our products. Whether or not we obtain FDA approval for a product, we must obtain approval of a product by the comparable regulatory authorities of foreign countries before we can commence clinical trials or marketing of the product in those countries. The approval process varies from country to country and the time may be longer or shorter than that required for FDA approval. Approval by the FDA does not ensure approval by the regulatory bodies of other countries.

        Under European Union regulatory systems, we may submit marketing authorization applications either under a centralized or decentralized procedure. The centralized procedure, which is compulsory for medicines produced by biotechnology and optional for those which are highly innovative, provides for the grant of a single marketing authorization that is valid for all European Union member states. The decentralized procedure provides for mutual recognition of national approval decisions. Under the decentralized procedure, the holder of a national marketing authorization may submit an application to the remaining member states. Within 90 days of receiving the applications and assessments report each member state must decide whether to recognize approval. If a member state does not recognize the marketing authorization, the disputed points are eventually referred to the European Commission, whose decision is binding on all member states. As in the United States, we may apply for designation of our products as orphan drug for the treatment of a specific indication in the European Union before the application for marketing authorization is made. Orphan drugs in Europe enjoy economic and marketing benefits, including a 10-year market exclusivity period for the approved indication, but not for the same drug, unless another applicant can show that its product is safer, more effective or otherwise clinically superior to the orphan-designated product.

        Our collaborators are also subject to all of the above-described regulations in connection with the commercialization of products utilizing our technology.

23

---

Table of Contents

Other Regulatory Processes

        We are subject to a variety of financial disclosure and securities trading regulations as a public company in the U.S., including laws relating to the oversight activities of the SEC and the regulations of the NASDAQ Global Market, on which our shares are traded. We are also subject to regulation under other federal laws and regulation under state and local laws, including laws relating to occupational safety, laboratory practices, environmental regulations, and hazardous substance control.

Product Liability

        The risk of product liability claims, product recalls and associated adverse publicity is inherent in the testing, manufacturing, marketing and sale of medical products. If and when we manufacture vaccines that are recommended for routine administration to children, we will be required to participate in the National Vaccine Injury Compensation Program. This program compensates children having adverse reactions to certain routine childhood immunizations with funds collected through an excise tax from the manufacturers of these vaccines.

        Under our license agreements, we are required to maintain clinical trial liability insurance coverage up to $14 million. However, there can be no assurance that such insurance coverage is or will continue to be adequate or available. We may choose or find it necessary under our collaborative agreements to increase our insurance coverage in the future. We may not be able to secure greater or broader product liability insurance coverage on acceptable terms or at reasonable costs when needed. Any liability for mandatory damages could exceed the amount of our coverage. A successful product liability claim against us could require us to pay a substantial monetary award. Moreover, a product recall could generate substantial negative publicity about our products and business and inhibit or prevent commercialization of other product candidates.

Employees

        As of December 31, 2010, we employed 94 full time employees and 6 part time or temporary employees, 13 of whom have Ph.D. and/or M.D. degrees. Of these employees, 83 were engaged in or directly support research and development activities. We believe that our employee relations are good. We believe that our future success will depend in large part on our ability to attract and retain experienced and skilled employees.

Item 1A.    RISK FACTORS

        You should consider carefully these risk factors together with all of the information included or incorporated by reference in this Annual Report in addition to our financial statements and the notes to our financial statements. This section includes forward-looking statements.

        The following is a discussion of the risk factors that we believe are material to us at this time. These risks and uncertainties are not the only ones facing us and there may be additional matters that we are unaware of or that we currently consider immaterial. All of these could adversely affect our business, results of operations, financial condition and cash flows.

Risks Related to our Business

Pfizer's termination of its global development and commercialization agreement with us may cause uncertainty surrounding, as well as delays in and increased costs for, the development of our lead clinical development program, which could adversely affect the value of our common stock, our cash position and results of operations.

        We had licensed our lead clinical development program, rindopepimut, a therapeutic cancer vaccine candidate sometimes referred to as CDX-110, to Pfizer pursuant to the Pfizer Agreement,

24

---

Table of Contents

under which Pfizer was granted an exclusive worldwide license to rindopepimut and Pfizer would have funded all development costs for the program and would have commercialized the product. On September 1, 2010, Pfizer provided a sixty day written notice to terminate the Pfizer Agreement. In November 2010, all rights to the rindopepimut program were returned to us. We are currently evaluating our options with respect to rindopepimut, which may include licensing all or specific portions of the rights to the rindopepimut program to another third party collaborator or retaining the rights and funding the development of the rindopepimut program ourselves. If we retain the rights to the rindopepimut program and are fully responsible for its development and commercialization, we may face delays, difficulties or unanticipated costs in completing the development and commercialization of the product and will need substantial additional financing. Also, our management team does not have significant experience in completing Phase 3 clinical trials and bringing a drug candidate to commercialization. If we elect to enter into an agreement with a new third party collaborator for the licensing, development and commercialization of the product, the process of identifying a new collaborator and negotiating a new collaboration agreement may cause delays and increased costs. In addition, we may not be able to enter into a new collaboration agreement on terms as favorable as the terms in the Pfizer Agreement.

We may be unable to manage one Phase 3 clinical trial or multiple late stage clinical trials for a variety of product candidates simultaneously.

        As our current clinical trials progress, we may need to manage multiple late stage clinical trials simultaneously in order to continue developing all of our current products. The management of late stage clinical trials is more complex and time consuming than early stage trials. Typically early stage trials involve several hundred patients in no more than 10-30 clinical sites. Late stage (Phase 3) trials may involve up to several thousand patients in up to several hundred clinical sites and may require facilities in several countries. Therefore, the project management required to supervise and control such an extensive program is substantially larger than early stage programs. As the need for these resources is not known until some months before the trials begin it is necessary to recruit large numbers of experienced and talented individuals very quickly. If the labor market does not allow this team to be recruited quickly the sponsor is faced with a decision to delay the program or to initiate it with inadequate management resources. This may result in recruitment of inappropriate patients, inadequate monitoring of clinical investigators and inappropriate handling of data or data analysis. Consequently it is possible that conclusions of efficacy or safety may not be acceptable to permit filing of a BLA or NDA for any one of the above reasons or a combination of several.

If we cannot sell capital stock to raise necessary funds, we may be forced to limit our research, development and testing programs.

        We will need to raise more capital from investors to advance our clinical and preclinical products and to fund our operations until we receive final FDA approval and our products begin to generate revenues for us. However, based on our history of losses and the on-going uncertainty of the U.S. capital markets, we may have difficulty raising sufficient capital on terms that are acceptable to us, or at all. As of December 31, 2010, we had cash, cash equivalents and marketable securities of $61.1 million, which, at that time, we believed would support expected operations for more than 12 months.

        We continue to seek partnerships with pharmaceutical and biotech companies and with other organizations to support the clinical development of our programs, in addition to funded research grants. This kind of funding is at the discretion of other organizations and companies which have limited funds and many companies compete with us for those funds. As a result, we may not receive any research grants or funds from collaborators. If we are unable to raise the necessary funds, we may have to delay or discontinue the clinical development of programs, license out programs earlier than

25

---

Table of Contents

expected, raise funds at significant discount or on other unfavorable terms, if at all, or evaluate a sale of all or part of our business.

        Until we begin generating revenue, we may seek funding through the sale of equity, or securities convertible into equity, and further dilution to the then existing stockholders may result. If we raise additional capital through the incurrence of debt, our business may be affected by the amount of leverage it incurs, and its borrowings may subject it to restrictive covenants.

        In January 2011, we entered into a financing facility with Cantor Fitzgerald & Co., providing for the sale of up to 5 million shares of our common stock from time to time into the open market at prevailing prices. As of March 2, 2011, we had not sold any shares under this facility. We may or may not sell shares under this facility, depending on the volume and price of our common stock, as well as our capital needs and potential alternative sources of capital. If we actively sell shares under this facility, a significant number of shares of common stock could be issued in a short period of time, although we would attempt to structure the volume and price thresholds in a way that minimizes market impact. Notwithstanding these control efforts, these sales, or the perceived risk of dilution from potential sales of stock through this facility, may depress our stock price or cause holders of our common stock to sell their shares, or it may encourage short selling by market participants, which could contribute to a decline in our stock price. A decline in our stock price might impede our ability to raise capital through the issuance of additional shares of common stock or other equity securities, and may cause our stockholders to lose part or all of the value of their investment in our stock.

We rely on third parties to plan, conduct and monitor our clinical tests, and their failure to perform as required would interfere with our product development.

        We rely on third parties to conduct a significant portion of our clinical development activities. These activities include clinical patient recruitment and observation, clinical trial monitoring, clinical data management and analysis, safety monitoring and project management. We conduct project management and medical and safety monitoring in-house for some of our programs and rely on third parties for the remainder of our clinical development activities. If any of these third parties fails to perform as we expect or if their work fails to meet regulatory standards, our testing could be delayed, cancelled or rendered ineffective.

We depend greatly on third party collaborators to license, develop and commercialize some of our products, and they may not meet our expectations.

        We have agreements with third party collaborators for the licensing, development and ultimate commercialization of some of our products. Some of those agreements give substantial responsibility over the products to the collaborator. Some collaborators may be unable or unwilling to devote sufficient resources to develop our products as their agreements require. They often face business risks similar to ours, and this could interfere with their efforts. Also, collaborators may choose to devote their resources to products that compete with ours. If a collaborator does not successfully develop any one of our products, we will need to find another collaborator to do so. The success of our search for a new collaborator will depend on our legal right to do so at the time and whether the product remains commercially viable.

        The success of our products depends in great part upon our and our collaborators' success in promoting them as superior to other treatment alternatives. We believe that our products can be proven to offer disease prevention and treatment with notable advantages over drugs in terms of patient compliance and effectiveness. However, there can be no assurance that we will be able to prove these advantages or that the advantages will be sufficient to support the successful commercialization of our products.

26

---

Table of Contents

We may face delays, difficulties or unanticipated costs in establishing sales, distribution and manufacturing capabilities for our commercially ready products.

        We may chose to retain, rather than license to another third party, all rights to rindopepimut, CDX-011 and our APC Targeting Technology programs. If we proceed with this strategy, we will have full responsibility for commercialization of these products if and when they are approved for sale. We currently lack the marketing, sales and distribution capabilities that we will need to carry out this strategy. To market any of our products directly, we must develop a substantial marketing and sales force with technical expertise and a supporting distribution capability. We have little expertise in this area, and we may not succeed. We may find it necessary to enter into strategic partnerships on uncertain but potentially unfavorable terms to sell, market and distribute our products when they are approved for sale.

        Some of our products are difficult to manufacture, especially in large quantities, and we have not yet developed commercial scale manufacturing processes for any of our products. We do not currently plan to develop internal manufacturing capabilities to produce any of our products at commercial scale if they are approved for sale. To the extent that we choose to market and distribute these products ourselves, this strategy will make us dependent on other companies to produce our products in adequate quantities, in compliance with regulatory requirements, and at a competitive cost. We may not find third parties capable of meeting those manufacturing needs.

Our products and product candidates are subject to extensive regulatory scrutiny.

        All of our products and product candidates are at various stages of development and commercialization and our activities, products and product candidates are significantly regulated by a number of governmental entities, including the FDA in the United States and by comparable authorities in other countries. These entities regulate, among other things, the manufacture, testing, safety, effectiveness, labeling, documentation, advertising and sale of our products and product candidates. We or our partners must obtain regulatory approval for a product candidate in all of these areas before we can commercialize the product candidate. Product development within this regulatory framework takes a number of years and involves the expenditure of substantial resources. This process typically requires extensive preclinical and clinical testing, which may take longer or cost more than we anticipate, and may prove unsuccessful due to numerous factors. Many product candidates that initially appear promising ultimately do not reach the market because they are found to be unsafe or ineffective when tested. Companies in the pharmaceutical, biotechnology and vaccines industries have suffered significant setbacks in advanced clinical trials, even after obtaining promising results in earlier trials. Our inability to commercialize a product or product candidate would impair our ability to earn future revenues.

If our products do not pass required tests for safety and effectiveness, we will not be able to derive commercial revenue from them.

        In order to succeed, we will need to derive commercial revenue from the products we have under development. The FDA has not approved our rindopepimut or CDX-011 product candidates or any of our other lead products for sale to date. Our product candidates are in various stages of preclinical and clinical testing. Preclinical tests are performed at an early stage of a product's development and provide information about a product's safety and effectiveness on laboratory animals. Preclinical tests can last years. If a product passes its preclinical tests satisfactorily, and we determine that further development is warranted, we would file an IND application for the product with the FDA, and if the FDA gives its approval we would begin Phase 1 clinical tests. Phase 1 testing generally lasts between 6 and 24 months. If Phase 1 test results are satisfactory and the FDA gives its approval, we can begin Phase 2 clinical tests. Phase 2 testing generally lasts between 6 and 36 months. If Phase 2 test results are satisfactory and the FDA gives its approval, we can begin Phase 3 pivotal studies. Phase 3 studies

27

---

Table of Contents

generally last between 12 and 48 months. Once clinical testing is completed and a new drug application is filed with the FDA, it may take more than a year to receive FDA approval.

        In all cases we must show that a pharmaceutical product is both safe and effective before the FDA, or drug approval agencies of other countries where we intend to sell the product, will approve it for sale. Our research and testing programs must comply with drug approval requirements both in the United States and in other countries, since we are developing our lead products with the intention to, or could later decide to, commercialize them both in the U.S. and abroad. A product may fail for safety or effectiveness at any stage of the testing process. A major risk we face is the possibility that none of our products under development will come through the testing process to final approval for sale, with the result that we cannot derive any commercial revenue from them after investing significant amounts of capital in multiple stages of preclinical and clinical testing.

Product testing is critical to the success of our products but subject to delay or cancellation if we have difficulty enrolling patients.

        As our portfolio of potential products moves from preclinical testing to clinical testing, and then through progressively larger and more complex clinical trials, we will need to enroll an increasing number of patients with the appropriate characteristics. At times we have experienced difficulty enrolling patients and we may experience more difficulty as the scale of our clinical testing program increases. The factors that affect our ability to enroll patients are largely uncontrollable and include principally the following:

•

the nature of the clinical test;



•

the size of the patient population;



•

patients' willingness to receive a placebo or less effective treatment on the control arm of a clinical study;



•

the distance between patients and clinical test sites; and



•

the eligibility criteria for the trial.

        If we cannot enroll patients as needed, our costs may increase or it could force us to delay or terminate testing for a product.

Any delay in obtaining regulatory approval would have an adverse impact on our ability to earn future revenues.

        It is possible that none of the products or product candidates that we develop will obtain the regulatory approvals necessary for us to begin commercializing them. The time required to obtain FDA and other approvals is unpredictable but often can take years following the commencement of clinical trials, depending upon the nature of the product candidate. Any analysis we perform of data from clinical activities is subject to confirmation and interpretation by regulatory authorities, which could delay, limit or prevent regulatory approval. Any delay or failure in obtaining required approvals could have a material adverse effect on our ability to generate revenues from the particular product candidate including, but not limited to, loss of patent term during the approval period. Furthermore, if we, or our partners, do not reach the market with our products before our competitors offer products for the same or similar uses, or if we, or our partners, are not effective in marketing our products, our revenues from product sales, if any, will be reduced.

        We face intense competition in our development activities. We face competition from many companies in the United States and abroad, including a number of large pharmaceutical companies, firms specialized in the development and production of vaccines, adjuvants and vaccine and immunotherapeutic delivery systems and major universities and research institutions. The competitors

28

---

Table of Contents

for which we are aware have initiated a Phase 3 study or have obtained marketing approval for a potentially competitive drug include Alexion, Agenus, Baxter, Dendreon, Eli Lilly, GlaxoSmithKline, ImmunoGen, Merck, Northwest Biotherapeutics, Pfizer, Roche, Sanofi-Aventis, Seattle Genetics, and Takeda. Most of our competitors have substantially greater resources, more extensive experience in conducting preclinical studies and clinical testing and obtaining regulatory approvals for their products, greater operating experience, greater research and development and marketing capabilities and greater production capabilities than those of ours. These companies might succeed in obtaining regulatory approval for competitive products more rapidly than we can for our products, especially if we experience any delay in obtaining required regulatory approvals.

Failure to comply with applicable regulatory requirements would adversely impact our operations.

        Even after receiving regulatory approval, our products would be subject to extensive regulatory requirements, and our failure to comply with applicable regulatory requirements will adversely impact our operations. In the United States, the FDA requires that the manufacturing facility that produces a product meet specified standards, undergo an inspection and obtain an establishment license prior to commercial marketing. Subsequent discovery of previously unknown problems with a product or its manufacturing process may result in restrictions on the product or the manufacturer, including withdrawal of the product from the market. Failure to comply with the applicable regulatory requirements can result in fines, suspensions of regulatory approvals, product recalls, operating restrictions and criminal prosecution.

We depend greatly on the intellectual capabilities and experience of our key executives and scientists and the loss of any of them could affect our ability to develop our products.

        The loss of Anthony S. Marucci, our President and Chief Executive Officer, or other key members of our staff, including Avery W. Catlin, our Chief Financial Officer, Dr. Thomas Davis, our Chief Medical Officer, or Dr. Tibor Keler, our Chief Scientific Officer, could harm us. We entered into employment agreements with Messrs. Marucci, Catlin, Davis and Keler. We also depend on our scientific and clinical collaborators and advisors, all of whom have outside commitments that may limit their availability to us. In addition, we believe that our future success will depend in large part upon our ability to attract and retain highly skilled scientific, managerial and marketing personnel, particularly as we expand our activities in clinical trials, the regulatory approval process and sales and manufacturing. We routinely enter into consulting agreements with our scientific and clinical collaborators and advisors, opinion leaders and heads of academic departments in the ordinary course of our business. We also enter into contractual agreements with physicians and institutions who recruit patients into our clinical trials on our behalf in the ordinary course of our business. Notwithstanding these arrangements, we face significant competition for this type of personnel from other companies, research and academic institutions, government entities and other organizations. We cannot predict our success in hiring or retaining the personnel we require for continued growth.

We rely on contract manufacturers. Should the cost, delivery and quality of clinical and commercial grade materials supplied by contract manufacturers vary to our disadvantage, our business operations could suffer significant harm.

        Although we have small-lot manufacturing capability at our Fall River facility, we rely on sourcing from third-party manufacturers for suitable quantities of some of our clinical and commercial grade materials essential to preclinical and clinical studies currently underway and to planned clinical trials in addition to those currently being conducted by third parties or us. The inability to have suitable quality and quantities of these essential materials produced in a timely manner would result in significant delays in the clinical development and commercialization of products, which could adversely affect our business, financial condition and results of operations. We also rely on collaborators and contract

29

---

Table of Contents

manufacturers to manufacture proposed products in both clinical and commercial quantities in the future. Our leading vaccine candidates require specialized manufacturing capabilities and processes.

        We may face difficulty in securing commitments from U.S. and foreign contract manufacturers as these manufacturers could be unwilling or unable to accommodate our needs. Relying on foreign manufacturers involves peculiar and increased risks, including the risk relating to the difficulty foreign manufacturers may face in complying with GMP requirements as a result of language barriers, lack of familiarity with GMP or the FDA regulatory process or other causes, economic or political instability in or affecting the home countries of our foreign manufacturers, shipping delays, potential changes in foreign regulatory laws governing the sales of our product supplies, fluctuations in foreign currency exchange rates and the imposition or application of trade restrictions.

        There can be no assurances that we will be able to enter into long-term arrangements with third party manufacturers on acceptable terms, or at all. Further, contract manufacturers must also be able to meet our timetable and requirements, and must operate in compliance with GMP; failure to do so could result in, among other things, the disruption of product supplies. As noted above, non-U.S. contract manufacturers may face special challenges in complying with GMP requirements, and although we are not currently dependent on non-U.S. collaborators or contract manufacturers, we may choose or be required to rely on non-U.S. sources in the future as we seek to develop stable supplies of increasing quantities of materials for ongoing clinical trials of larger scale. Our dependence upon third parties for the manufacture of our products may adversely affect our profit margins and our ability to develop and deliver products on a timely and competitive basis.

        The significant third-parties who we currently rely on for sourcing of suitable quantities of some of our clinical and commercial grade materials include:

•

Pfizer, on a transitional basis, Bayer, and Genzyme for rindopepimut;



•

Dalton for Hiltonol which is an integral part of several of our drug products;



•

3M for Resiquimod which is an integral part of several of our drug products; and



•

Piramal for the CDX-011 drug product.

        If we or our third-party manufacturers are unable to produce drug material in suitable quantities of appropriate quality, in a timely manner, and at a feasible cost, our clinical tests will face delays.

Certain factors could negatively affect the demand for and sales and profitability of Rotarix®, which would have a material adverse affect on our revenues.

        We have licensed a rotavirus strain to Glaxo for the purposes of Glaxo developing and commercializing their Rotarix® vaccine worldwide. The term of the Glaxo agreement is through the expiration of the last of the relevant patents covered by the agreement, although Glaxo may terminate the agreement upon 90 days prior written notice. The last relevant patent is scheduled to expire in December 2012. Glaxo gained approval for Rotarix® in Mexico in July 2004, in the European Union in February 2006 and in the United States in April 2008. In May 2005, we entered into an agreement whereby an affiliate of PRF purchased a 70% interest in the net royalties we receive on worldwide sales of Rotarix®. In addition, we retain upside participation in the worldwide net royalties from Rotarix® once, and if, PRF receives an agreed upon return on capital invested (2.45 times PRF's aggregate cash payments to us of $60 million). The PRF agreement terminates on December 12, 2012, unless otherwise extended. The following are potential factors, among others, that may negatively affect the demand for Rotarix®:

30

---

Table of Contents

•

Competitors in the pharmaceuticals, biotechnology and vaccines market have greater financial and management resources, and significantly more experience in bringing products to market, and may develop, manufacture and market products that are more effective or less expensive than Rotarix®;



•

Rotarix® could be replaced by a novel product and may become obsolete;



•

Glaxo may be unable to prevent third parties from infringing upon their proprietary rights related to Rotarix®;



•

Users may not accept such a recently approved product without years of proven history; and



•

We are dependent on Glaxo for the manufacturing, testing, acquisition of regulatory approvals, marketing, distribution and commercialization of Rotarix®.

        Any of these factors could have a material adverse effect on the sales of Rotarix® and our revenues.

Other factors could affect the demand for and sales and profitability of Rotarix® and any other of our current or future products.

        In general, other factors that could affect the demand for and sales and profitability of our products include, but are not limited to:

•

The timing of regulatory approval, if any, of competitive products;



•

Our, Glaxo's, or any other of our partners' pricing decisions, as applicable, including a decision to increase or decrease the price of a product, and the pricing decisions of our competitors;



•

Government and third-party payer reimbursement and coverage decisions that affect the utilization of our products and competing products;



•

Negative safety or efficacy data from new clinical studies conducted either in the U.S. or internationally by any party could cause the sales of our products to decrease or a product to be recalled;



•

The degree of patent protection afforded our products by patents granted to or licensed by us and by the outcome of litigation involving our or any of our licensor's patents;



•

The outcome of litigation involving patents of other companies concerning our products or processes related to production and formulation of those products or uses of those products;



•

The increasing use and development of alternate therapies;



•

The rate of market penetration by competing products; and



•

The termination of, or change in, existing arrangements with our partners.

        Any of these factors could have a material adverse effect on Glaxo's sales of Rotarix® and on any other of our current or future products and results of operations.

We face the risk of product liability claims, which could exceed our insurance coverage, and produce recalls, each of which could deplete our cash resources.

        As a participant in the pharmaceutical, biotechnology and vaccines industries, we are exposed to the risk of product liability claims alleging that use of our products or product candidates caused an injury or harm. These claims can arise at any point in the development, testing, manufacture, marketing or sale of our products or product candidates and may be made directly by patients involved in clinical trials of our products, by consumers or healthcare providers or by individuals, organizations or

31

---

Table of Contents

companies selling our products. Product liability claims can be expensive to defend, even if the product or product candidate did not actually cause the alleged injury or harm.

        Insurance covering product liability claims becomes increasingly expensive as a product candidate moves through the development pipeline to commercialization. Under our license agreements, we are required to maintain clinical trial liability insurance coverage up to $14 million. However, there can be no assurance that such insurance coverage is or will continue to be adequate or available to us at a cost acceptable to us or at all. We may choose or find it necessary under our collaborative agreements to increase our insurance coverage in the future. We may not be able to secure greater or broader product liability insurance coverage on acceptable terms or at reasonable costs when needed. Any liability for damages resulting from a product liability claim could exceed the amount of our coverage, require us to pay a substantial monetary award from our own cash resources and have a material adverse effect on our business, financial condition and results of operations. Moreover, a product recall, if required, could generate substantial negative publicity about our products and business and inhibit or prevent commercialization of other products and product candidates.

        In addition, some of our licensing and other agreements with third parties require or might require us to maintain product liability insurance. If we cannot maintain acceptable amounts of coverage on commercially reasonable terms in accordance with the terms set forth in these agreements, the corresponding agreements would be subject to termination, which could have a material adverse impact on our operations.

Our reliance on third parties requires us to share our trade secrets, which increases the possibility that a competitor will discover them.

        Because we rely on third parties to develop our products, we must share trade secrets with them. We seek to protect our proprietary technology in part by entering into confidentiality agreements and, if applicable, material transfer agreements, collaborative research agreements, consulting agreements or other similar agreements with our collaborators, advisors, employees and consultants prior to beginning research or disclosing proprietary information. These agreements will typically restrict the ability of our collaborators, advisors, employees and consultants to publish data potentially relating to our trade secrets. Our academic collaborators typically have rights to publish data, provided that we are notified in advance and may delay publication for a specified time in order to secure our intellectual property rights arising from the collaboration. In other cases, publication rights are typically controlled exclusively by us, although in some cases we may share these rights with other parties. We also conduct joint research and development programs which may require us to share trade secrets under the terms of research and development partnership or similar agreements. Despite our efforts to protect our trade secrets, our competitors may discover our trade secrets, either through breach of these agreements, independent development or publication of information including our trade secrets in cases where we do not have proprietary or otherwise protected rights at the time of publication. A competitor's discovery of our trade secrets would impair our competitive position.

We may not be able to successfully integrate newly-acquired technology with our existing technology or to modify our technologies to create new vaccines.

        As part of our acquisition of technology assets from entities such as 3M Company and Amgen, we have acquired access to Resiquimod™ (a TLR 7/8 agonist) and Flt3L, which may improve the immunogenicity of our vaccines. If we are able to integrate these licensed assets with our vaccine technologies, we believe these assets will give our vaccines a competitive advantage. However, if we are unable to successfully integrate licensed assets, or other technologies which we have acquired or may acquire in the future, with our existing technologies and potential products currently under development, we may be unable to realize any benefit from our acquisition of these assets, or other

32

---

Table of Contents

technologies which we have acquired or may acquire in the future and may face the loss of our investment of financial resources and time in the integration process.

        We believe that our vaccine technology portfolio may offer opportunities to develop vaccines that treat a variety of oncology, inflammatory and infectious diseases by stimulating a patient's immune system against those disease organisms. If our vaccine technology portfolio cannot be used to create effective vaccines against a variety of disease organisms, we may lose all or portions of our investment in development efforts for new vaccine candidates.

We license technology from other companies to develop products, and those companies could influence research and development or restrict our use of it.

        Companies that license technologies to us that we use in our research and development programs may require us to achieve milestones or devote minimum amounts of resources to develop products using those technologies. They may also require us to make significant royalty and milestone payments, including a percentage of any sublicensing income, as well as payments to reimburse them for patent costs. The number and variety of our research and development programs require us to establish priorities and to allocate available resources among competing programs. From time to time we may choose to slow down or cease our efforts on particular products. If in doing so we fail to fully perform our obligations under a license, the licensor can terminate the licenses or permit our competitors to use the technology. Moreover, we may lose our right to market and sell any products based on the licensed technology.

We have many competitors in our field and they may develop technologies that make ours obsolete.

        Biotechnology, pharmaceuticals and therapeutics are rapidly evolving fields in which scientific and technological developments are expected to continue at a rapid pace. We have many competitors in the U.S. and abroad. The competitors for which we are aware have initiated a Phase 3 study or have obtained marketing approval for a potentially competitive drug include Alexion, Agenus, Baxter, Dendreon, Eli Lilly, GlaxoSmithKline, ImmunoGen, Merck, Northwest Biotherapeutics, Pfizer, Roche, Sanofi-Aventis, Seattle Genetics, and Takeda. Our success depends upon our ability to develop and maintain a competitive position in the product categories and technologies on which we focus. Many of our competitors have greater capabilities, experience and financial resources than we do. Competition is intense and is expected to increase as new products enter the market and new technologies become available. Our competitors may:

•

develop technologies and products that are more effective than ours, making ours obsolete or otherwise noncompetitive;



•

obtain regulatory approval for products more rapidly or effectively than us; and



•

obtain patent protection or other intellectual property rights that would block our ability to develop competitive products.

We rely on patents, patent applications and other intellectual property protections to protect our technology and trade secrets; which are expensive and may not provide sufficient protection.

        Our success depends in part on our ability to obtain and maintain patent protection for technologies that we use. Biotechnology patents involve complex legal, scientific and factual questions and are highly uncertain. To date, there is no consistent policy regarding the breadth of claims allowed in biotechnology patents, particularly in regard to patents for technologies for human uses like those we use in our business. We cannot predict whether the patents we seek will issue. If they do issue, a competitor may challenge them and limit their scope. Moreover, our patents may not afford effective protection against competitors with similar technology. A successful challenge to any one of our patents

33

---

Table of Contents

could result in a third party's ability to use the technology covered by the patent. We also face the risk that others will infringe, avoid or circumvent our patents. Technology that we license from others is subject to similar risks and this could harm our ability to use that technology. If we, or a company that licenses technology to us, were not the first creator of an invention that we use, our use of the underlying product or technology will face restrictions, including elimination.

        If we must defend against suits brought against us or prosecute suits against others involving intellectual property rights, we will incur substantial costs. In addition to any potential liability for significant monetary damages, a decision against us may require us to obtain licenses to patents or other intellectual property rights of others on potentially unfavorable terms. If those licenses from third parties are necessary but we cannot acquire them, we would attempt to design around the relevant technology, which would cause higher development costs and delays, and may ultimately prove impracticable.

Our business requires us to use hazardous materials, which increases our exposure to dangerous and costly accidents.

        Our research and development activities involve the use of hazardous chemicals, biological materials and radioactive compounds. Although we believe that our safety procedures for handling and disposing of hazardous materials comply with the standards prescribed by applicable laws and regulations, we cannot completely eliminate the risk of accidental contamination or injury from these materials. In the event of an accident, an injured party will likely sue us for any resulting damages with potentially significant liability. The ongoing cost of complying with environmental laws and regulations is significant and may increase in the future.

Health care reform and restrictions on reimbursement may limit our returns on potential products.

        Because our strategy ultimately depends on the commercial success of our products, we assume, among other things, that end users of our products will be able to pay for them. In the United States and other countries, in most cases, the volume of sales of products like those we are developing depends on the availability of reimbursement from third-party payors, including national health care agencies, private health insurance plans and health maintenance organizations. Third-party payors increasingly challenge the prices charged for medical products and services. Accordingly, if we succeed in bringing products to market, and reimbursement is not available or is insufficient, we could be prevented from successfully commercializing our potential products.

        The health care industry in the United States and in Europe is undergoing fundamental changes as a result of political, economic and regulatory influences. Reforms proposed from time to time include mandated basic health care benefits, controls on health care spending, the establishment of governmental controls over the cost of therapies, creation of large medical services and products purchasing groups and fundamental changes to the health care delivery system. We anticipate ongoing review and assessment of health care delivery systems and methods of payment in the United States and other countries. We cannot predict whether any particular reform initiatives will result or, if adopted, what their impact on us will be. However, we expect that adoption of any reform proposed will impair our ability to market products at acceptable prices and that uncertainty concerning future government regulation of consumer healthcare purchasing and insurance may result in difficulties for drug development companies, like Celldex, in raising capital.

Changes in laws affecting the health care industry could adversely affect our business.

        In the U.S., there have been numerous proposals considered at the federal and state levels for comprehensive reforms of health care and its cost, and it is likely that federal and state legislatures and health agencies will continue to focus on health care reform in the future. Congress has considered

34

---

Table of Contents

legislation to reform the U.S. health care system by expanding health insurance coverage, reducing health care costs and making other changes. While health care reform may increase the number of patients who have insurance coverage for our products, it may also include cost containment measures that adversely affect reimbursement for our products. Congress has also considered legislation to change the Medicare reimbursement system for outpatient drugs, increase the amount of rebates that manufacturers pay for coverage of their drugs by Medicaid programs and facilitate the importation of lower-cost prescription drugs that are marketed outside the U.S. Some states are also considering legislation that would control the prices of drugs, and state Medicaid programs are increasingly requesting manufacturers to pay supplemental rebates and requiring prior authorization by the state program for use of any drug for which supplemental rebates are not being paid. Managed care organizations continue to seek price discounts and, in some cases, to impose restrictions on the coverage of particular drugs. Government efforts to reduce Medicaid expenses may lead to increased use of managed care organizations by Medicaid programs. This may result in managed care organizations influencing prescription decisions for a larger segment of the population and a corresponding constraint on prices and reimbursement for our products.

        We and our collaborators and partners operate in a highly regulated industry. As a result, governmental actions may adversely affect our business, operations or financial condition, including:

•

new laws, regulations or judicial decisions, or new interpretations of existing laws, regulations or decisions, related to health care availability, method of delivery and payment for health care products and services;



•

changes in the FDA and foreign regulatory approval processes that may delay or prevent the approval of new products and result in lost market opportunity;



•

changes in FDA and foreign regulations that may require additional safety monitoring, labeling changes, restrictions on product distribution or use, or other measures after the introduction of our products to market, which could increase our costs of doing business, adversely affect the future permitted uses of approved products, or otherwise adversely affect the market for our products;



•

new laws, regulations and judicial decisions affecting pricing or marketing practices; and



•

changes in the tax laws relating to our operations.

        The enactment in the U.S. of health care reform, possible legislation which could ease the entry of competing follow-on biologics in the marketplace, new legislation or implementation of existing statutory provisions on importation of lower-cost competing drugs from other jurisdictions, and legislation on comparative effectiveness research are examples of previously enacted and possible future changes in laws that could adversely affect our business. In addition, the Food and Drug Administration Amendments Act of 2007 included new authorization for the FDA to require post-market safety monitoring, along with an expanded clinical trials registry and clinical trials results database, and expanded authority for the FDA to impose civil monetary penalties on companies that fail to meet certain commitments.

If physicians, patients and third-party payors do not accept any future drugs that we may develop, we may be unable to generate significant revenue, if any.

        Even if our drug candidates as well as any drug candidates that we may develop or acquire in the future obtain regulatory approval, they may not gain market acceptance among physicians, patients and health care payors. Physicians may elect not to recommend these drugs for a variety of reasons including:

•

timing of market introduction of competitive drugs;

35

---

Table of Contents

•

lower demonstrated clinical safety and efficacy compared to other drugs;



•

lack of cost-effectiveness;



•

lack of availability of reimbursement from third-party payors;



•

convenience and ease of administration;



•

prevalence and severity of adverse side effects;



•

other potential advantages of alternative treatment methods; and



•

ineffective marketing and distribution support.

        If our approved drugs fail to achieve market acceptance, we would not be able to generate sufficient revenue from product sales to maintain or grow our business.

Risks Related to our Capital Stock

Our history of losses and uncertainty of future profitability make our common stock a highly speculative investment.

        We have had no commercial revenues to date from sales of our human therapeutic or vaccine products and cannot predict when we will. We have an accumulated deficit of $160.2 million as of December 31, 2010. We expect to spend substantial funds to continue the research and development testing of our products that we have in the preclinical and clinical testing stages of development that have not been partnered.

        In anticipation of FDA approval of these products, we will need to make substantial investments to establish sales, marketing, quality control, and regulatory compliance capabilities. These investments will increase if and when any of these products receive FDA approval. We cannot predict how quickly our lead products will progress through the regulatory approval process. As a result, we may continue to lose money for several years.

        We cannot be certain that we will achieve or sustain profitability in the future. Failure to achieve profitability could diminish our ability to sustain operations, pay dividends on our common stock, obtain additional required funds and make required payments on our present or future indebtedness.

Our share price has been and could remain volatile.

        The market price of our common stock has historically experienced and may continue to experience significant volatility. From January 2010 through December 2010, the market price of our common stock has fluctuated from a high of $9.49 per share in the second quarter of 2010, to a low of $2.91 per share in the third quarter of 2010. Our progress in developing and commercializing our products, the impact of government regulations on our products and industry, the potential sale of a large volume of our common stock by stockholders, our quarterly operating results, changes in general conditions in the economy or the financial markets and other developments affecting us or our competitors could cause the market price of our common stock to fluctuate substantially with significant market losses. If our stockholders sell a substantial number of shares of common stock, especially if those sales are made during a short period of time, those sales could adversely affect the market price of our common stock and could impair our ability to raise capital. In addition, in recent years, the stock market has experienced significant price and volume fluctuations. This volatility has affected the market prices of securities issued by many companies for reasons unrelated to their operating performance and may adversely affect the price of our common stock. In addition, we could be subject to a securities class action litigation as a result of volatility in the price of our stock, which could result in substantial costs and diversion of management's attention and resources and could harm our stock price, business, prospects, results of operations and financial condition.

36

---

Table of Contents

The restrictive covenants contained in our credit agreement may limit our activities.

        On December 30, 2010, we entered into a Loan and Security Agreement (the "Loan Agreement") with MidCap Financial, LLC ("MidCap") pursuant to which we borrowed $10 million (the "Term Loan") from MidCap. In March 2011, we amended the Loan Agreement and borrowed an additional $5 million from General Electric Capital Corporation ("GECC") (collectively with MidCap, the "Lenders") to increase the amount owed under the Term Loan to $15 million. Our obligations under the Term Loan are secured by a first priority lien upon and security interest in substantially all of our existing and after-acquired assets, excluding our intellectual property assets (the "Collateral"). Under the Term Loan, we are subject to specified affirmative covenants customary for loans of this type, including but not limited to the obligations to maintain good standing, provide various notices to the Lenders, deliver financial statements to the Lenders, maintain adequate insurance, promptly discharge all taxes, protect our intellectual property and protect the Collateral. The Company is also subject to certain negative covenants customary for loans of this type, including but not limited to prohibitions against certain mergers and consolidations, certain management and ownership changes constituting a "change of control," and the imposition of additional liens on Collateral or other of our assets, as well as prohibitions against additional indebtedness, certain dispositions of property, changes in our business, name or location, payment of dividends, prepayment of certain other indebtedness, certain investments or acquisitions, and certain transactions with affiliates, in each case subject to certain customary exceptions, including exceptions that allow us to enter into non-exclusive and/or exclusive licenses and similar agreements providing for the use of our intellectual property in collaboration with third parties provided certain conditions are met.

        Failure to comply with the restrictive covenants in our Term Loan could accelerate the repayment of any debt outstanding under the Term Loan. Additionally, as a result of these restrictive covenants, we may be at a disadvantage compared to our competitors that have greater operating and financing flexibility than we do.

Our ability to use our net operating loss carryforwards will be subject to limitation and, under certain circumstances, may be eliminated.

        Utilization of our net operating loss ("NOL") and research and development ("R&D") credit carryforwards may be subject to substantial annual limitation due to ownership change limitations that have occurred previously or that could occur in the future provided by Section 382 of the Internal Revenue Code of 1986 ("Section 382"), as well as similar state provisions. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain shareholders or public groups in the stock of a corporation by more than 50 percentage points over a three-year period.

        In October 2007, June 2009 and in December 2009, Celldex Research experienced a change in ownership as defined by Section 382 of the Internal Revenue Code. Celldex Research, since its formation, had raised capital through the issuance of capital stock on several occasions which, combined with shareholders' subsequent disposition of those shares, has resulted in three changes of control, as defined by Section 382. As a result of the ownership change in October 2007, utilization of its Federal NOLs is subject to an annual limitation. Any unused annual limitation may be carried over to later years, and the amount of the limitation may, under certain circumstances, be subject to adjustment if the fair value of the our net assets are determined to be below or in excess of the tax basis of such assets at the time of the ownership change, and such unrealized loss or gain is recognized during the five-year period after the ownership change. Subsequent ownership changes, as defined in Section 382, could further limit the amount of net operating loss carryforwards and research and development credits that can be utilized annually to offset future taxable income.

37

---

Table of Contents

        We have not undertaken a study to assess whether an ownership change or multiple ownership changes has occurred for (i) Celldex Therapeutics, (ii) CuraGen, (iii) Celldex Research on the state level, or (iv) R&D credits. If there has been an ownership change at any time since its formation, utilization of NOL or tax credit carryforwards would be subject to an annual limitation under Section 382.

        Refer to Note 15, "Income Taxes," in the accompanying notes to the consolidated financial statements for additional discussion on income taxes.

Item 1B.    UNRESOLVED STAFF COMMENTS

        None.

Item 2.    PROPERTIES

        Our significant leased properties are described below.

---

(1)

Lease includes two renewal options of five years each.

(2)

Lease includes one renewal option of five years.

(3)

Lease includes one renewal option of three years.

Item 3.    LEGAL PROCEEDINGS

        We are not currently a party to any material legal proceedings.

Item 4.    RESERVED

38

---

Table of Contents

PART II

Item 5.    MARKET FOR REGISTRANT'S COMMON EQUITY, RELATED STOCKHOLDER MATTERS AND ISSUER PURCHASES OF EQUITY SECURITIES

        Our common stock currently trades on The Nasdaq Global Market (the "NASDAQ") under the symbol "CLDX". Effective October 1, 2008, we changed our name from AVANT Immunotherapeutics, Inc. to Celldex Therapeutics, Inc. Prior to October 1, 2008, our common stock traded on NASDAQ under the symbol "AVAN". The following table sets forth for the periods indicated the high and low sale prices per share for our common stock, as reported by NASDAQ.

        As of February 28, 2011, there were approximately 723 shareholders of record of our common stock. On February 28, 2011 the closing price of our common stock, as reported by NASDAQ, was $3.94 per share. We have not paid any dividends on our common stock since our inception and do not intend to pay any dividends in the foreseeable future.

Equity Compensation Plan Information

        The following table provides information as of December 31, 2010 regarding shares of our common stock that may be issued under our existing equity compensation plans, including Celldex's 2008 Stock Option and Incentive Plan (the "2008 Plan") and Celldex's 2004 Employee Stock Purchase Plan (the "2004 Plan").

---

(1)

Does not include any Restricted Stock as such shares are already reflected in our outstanding shares.

(2)

Consists of the 2008 Plan, 2004 Plan, Celldex Research's 2005 Equity Incentive Plan and CuraGen's 2007 Stock Plan.

(3)

Does not include purchase rights accruing under the 2004 Plan because the purchase price (and therefore the number of shares to be purchased) will not be determined until the end of the purchase period.

(4)

Includes shares available for future issuance under the 2008 Plan and the 2004 Plan.

39

---

Table of Contents

CELLDEX THEAPEUTICS, INC., NASDAQ MARKET INDEX—U.S. AND
PEER GROUP INDICES

        The graph below compares the cumulative total stockholder return on the common stock for the period from December 31, 2005 through December 31, 2010, with the cumulative return on (i) NASDAQ Market Index—U.S. Companies and (ii) NASDAQ Pharmaceutical Index. The comparison assumes investment of $100 on December 31, 2005 in our common stock and in each of the indices and, in each case, assumes reinvestment of all dividends. The points on the graph are as of December 31 of the year indicated.

Item 6.    SELECTED FINANCIAL DATA

        The following selected consolidated financial data are derived from our financial statements. The consolidated statement of operations data for the years ended December 31, 2010, 2009 and 2008 and the consolidated balance sheet data as of December 31, 2010 and 2009 have been derived from our audited consolidated financial statements included elsewhere in this Annual Report on Form 10-K. This data should be read in conjunction with our audited consolidated financial statements and related notes which are included elsewhere in this Annual Report on Form 10-K, and "Management's Discussion and Analysis of Financial Condition and Results of Operations" included in Item 7 below.

        On October 1, 2009, the CuraGen Merger became effective. The CuraGen Merger was accounted for using the acquisition method of accounting and was treated as our acquisition of CuraGen. Accordingly, the financial information presented below for periods prior to October 1, 2009 reflects the financial position and the results of operations of us alone, and for periods from October 1, 2009 forward the combined financial position and combined results of operations of us and CuraGen.

        On March 7, 2008, the AVANT Merger became effective. The AVANT Merger was accounted for using the purchase method of accounting and was treated as our acquisition of AVANT. Accordingly, the financial information presented below for periods prior to March 8, 2008 reflects the financial position and the results of operations of us alone, and for periods from March 8, 2008 forward the combined financial position and combined results of operations of us and AVANT. All amounts are in thousands except per share data.

40

---

Table of Contents

CONSOLIDATED STATEMENTS OF OPERATIONS DATA

CONSOLIDATED BALANCE SHEET DATA

41

---

Table of Contents

Item 7.    MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

OVERVIEW

        We are a biopharmaceutical company currently focusing on the development of several immunotherapy technologies. Our lead programs include rindopepimut (CDX-110), a vaccine that is expected to enter into Phase 3 development for glioblastoma multiforme in the second half of 2011, and CDX-011, an antibody-drug conjugate currently in a randomized Phase 2b trial for treatment of advanced breast cancer. We have additional programs at various stages of clinical and preclinical development, including CDX-1127 a therapeutic human antibody candidate for cancer indications, APC Targeting Technology™ programs, CDX-1307 and CDX-1401, and an immune cell mobilizing agent CDX-301. We are currently resourcing our priority programs and supplement the development of additional programs through external collaborations and funding.

        Our strategy is to develop and demonstrate proof-of-concept for our product candidates before leveraging their value through partnerships or, in appropriate situations, continuing late stage development through commercialization ourselves. Demonstrating proof-of-concept for a product candidate generally involves bringing it through Phase 1 clinical trials and one or more Phase 2 clinical trials so that we are able to demonstrate, based on human trials, good safety data for the product candidate and some data indicating its effectiveness. We thus leverage the value of our technology portfolio through corporate, governmental and non-governmental partnerships. This approach allows us to maximize the overall value of our technology and product portfolio while best ensuring the expeditious development of each individual product. Our current collaborations include the commercialization of an oral human rotavirus vaccine. Our product candidates address market opportunities for which we believe current therapies are inadequate or non-existent.

        Our products are derived from a broad set of complementary technologies which have the ability to utilize the human immune system and enable the creation of preventative and therapeutic agents. We are using these technologies to develop targeted immunotherapeutics comprised of antibodies, adjuvants and monotherapies and antibody-drug conjugates that prevent or treat cancer and other diseases that modify undesirable activity by the body's own proteins or cells. A number of our immunotherapeutic and antibody-drug conjugate product candidates are in various stages of clinical trials. We expect that a large percentage of our research and development expenses will be incurred in support of our current and future clinical trial programs.

        The following table includes the programs that we currently believe are material to our business:

42

---

Table of Contents