CLDX Celldex Therapeutics Inc

Table of Contents

Filed Pursuant to Rule 424(b)(5)
Registration No. 333-192640

Table of Contents

Table of Contents

Table of Contents

PROSPECTUS SUPPLEMENT SUMMARY

The following summary of our business highlights some of the information contained elsewhere in or incorporated by reference into this prospectus supplement.  Because this is only a summary, however, it does not contain all of the information that may be important to you.  You should carefully read this prospectus supplement and the accompanying prospectus, including the documents incorporated by reference, which are described under “Incorporation of Documents by Reference” and “Where You Can Find More Information” in this prospectus supplement.  You should also carefully consider the matters discussed in the section titled “Risk Factors” in this prospectus supplement and in the accompanying prospectus and in other periodic reports incorporated by reference herein.

Our Company

We are a biopharmaceutical company focused on the development and commercialization of several immunotherapy technologies for the treatment of cancer and other difficult-to-treat diseases. Our drug candidates are derived from a broad set of complementary technologies which have the ability to utilize the human immune system and enable the creation of therapeutic agents. We are using these technologies to develop targeted immunotherapeutics comprised of protein-based molecules such as vaccines, antibodies and antibody-drug conjugates that are used to treat specific types of cancer or other diseases.

Our latest stage drug candidate, glembatumumab vedotin (also referred to as CDX-011) is a targeted antibody-drug conjugate in a randomized, Phase 2b study for the treatment of triple negative breast cancer and a Phase 2 study for the treatment of metastatic melanoma. Varlilumab (also referred to as CDX-1127) is an immune modulating antibody that is designed to enhance a patient’s immune response against their cancer. We established proof of concept in a Phase 1 study with varlilumab, which has allowed several combination studies to begin in various indications. We also have a number of earlier stage drug candidates in clinical development, including CDX-1401, a targeted immunotherapeutic aimed at antigen presenting cells, or APCs, for cancer indications, CDX-301, an immune cell mobilizing agent and dendritic cell growth factor, and CDX-014, an antibody drug conjugate targeting TIM-1. Our drug candidates address market opportunities for which we believe current therapies are inadequate or non-existent.

We are building a fully integrated, commercial-stage biopharmaceutical company that develops important therapies for patients with unmet medical needs. Our program assets provide us with the strategic options to either retain full economic rights to our innovative therapies or seek favorable economic terms through advantageous commercial 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.

The following table reflects our current clinical pipeline.

Glembatumumab Vedotin

Glembatumumab vedotin is an antibody-drug conjugate, or ADC, that consists of a fully human monoclonal antibody, CR011, linked to a potent cell-killing drug, monomethyl-auristatin E, or MMAE. The CR011 antibody specifically targets glycoprotein NMB, referred to as gpNMB, that is over-expressed in a variety of cancers including breast cancer, melanoma, non-small cell lung cancer, uveal melanoma and osteosarcoma, among others. The ADC technology, comprised of MMAE and a stable linker system for attaching it to CR011, was licensed from Seattle Genetics, Inc. and is the same as that used in the marketed product Adcetris ®. The ADC is designed to be stable in the bloodstream. Following intravenous administration, glembatumumab vedotin targets and binds to gpNMB, and upon internalization into the targeted cell, glembatumumab vedotin is designed to release MMAE from CR011 to produce a cell-killing effect. The FDA has granted Fast Track designation to glembatumumab vedotin for the treatment of advanced, refractory/resistant gpNMB-expressing breast cancer. A companion diagnostic is in development for certain indications and we expect that, if necessary, such a companion diagnostic must be approved by the FDA or certain other foreign regulatory agencies before glembatumumab vedotin may be commercialized in those indications.

S- 2

Table of Contents

Treatment of Metastatic Breast Cancer:   The Phase 1/2 study of glembatumumab vedotin administered intravenously once every three weeks evaluated patients with locally advanced or metastatic breast cancer who had received prior therapy (median of seven prior regimens). Results were published in the  Journal of Clinical Oncology  in September 2014. The study began with a bridging phase to confirm the maximum tolerated dose, or MTD, and then expanded into a Phase 2 open-label, multi-center study. The study confirmed the safety of glembatumumab vedotin at the pre-defined maximum dose level (1.88 mg/kg) in 6 patients. An additional 28 patients were enrolled in an expanded Phase 2 cohort (for a total of 34 treated patients at 1.88 mg/kg, the Phase 2 dose) to evaluate the progression-free survival (PFS) rate at 12 weeks. The 1.88 mg/kg dose was well tolerated in this patient population with the most common adverse events of rash, neuropathy 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 27 (33%) evaluable patients were progression-free at 12 weeks. For all patients treated at the maximum dose level, 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, 12-week PFS rate was 60% (6/10), 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 EMERGE study was a randomized, multi-center Phase 2b study of glembatumumab vedotin in 124 patients with heavily pre-treated, advanced, gpNMB-positive breast cancer. Results from EMERGE were published in the  Journal of Clinical Oncology  in April 2015. Patients were randomized (2:1) to receive either glembatumumab vedotin or single-agent Investigator’s Choice, or IC, chemotherapy. Patients randomized to receive IC were allowed to cross over to receive glembatumumab vedotin following disease progression. Activity endpoints included response rate, PFS and overall survival (OS). The final results, as shown below, suggested that glembatumumab vedotin induces significant response rates compared to currently available therapies in patient subsets with advanced, refractory breast cancers with high gpNMB expression (expression in at least 25% of tumor cells) and in patients with triple negative breast cancer. The OS and PFS of patients treated with glembatumumab vedotin was also observed to be greatest in patients with triple negative breast cancer who also have high gpNMB expression and all patients with high gpNMB expression.

EMERGE: Overall Response Rate and Disease Control Data (Intent-to-Treat Population)

In December 2013, we initiated METRIC, a randomized, controlled Phase 2b study of glembatumumab vedotin in patients with triple negative breast cancer that over-express gpNMB. Clinical trial sites are open to enrollment across the U.S., Canada, Australia and the European Union. The METRIC protocol was amended in late 2014 based on feedback from clinical investigators conducting the study that the eligibility criteria for study entry were limiting their ability to enroll patients they felt were clinically appropriate. In addition, we had spoken to country-specific members of the European Medicines Agency, or EMA, and believed a significant opportunity existed to expand the study into the EU. The amendment expanded patient entry criteria to position it for full marketing approval with global regulators, including the EMA, and to support improved enrollment in the study. The primary endpoint of the study is PFS as PFS is an established endpoint for full approval registration studies in this patient population in both the U.S. and the EU. The sample size (n=300) and the secondary endpoint of OS remained unchanged. We implemented these changes in parallel to regulatory discussions to maintain momentum at open clinical trial sites. Since implementation, both the FDA and central European regulatory

S- 3

Table of Contents

authorities have reviewed the protocol design, and we believe the METRIC study could support marketing approval in both the U.S. and Europe dependent upon data review. Our goal is to complete enrollment by year end 2016.

Treatment of Metastatic Melanoma:   The Phase 1/2 open-label, multi-center, dose escalation study evaluated the safety, tolerability and pharmacokinetics of glembatumumab vedotin in 117 patients with unresectable stage III or IV melanoma who had failed no more than one prior line of cytotoxic therapy. The MTD was determined to be 1.88 mg/kg administered intravenously once every three weeks. The study achieved its primary activity objective with an overall response rate (ORR) in the Phase 2 cohort of 15% (5/34). Median PFS was 3.3 months for patients treated with the Phase 2 MTD. Glembatumumab vedotin was generally well tolerated, with the most frequent treatment-related adverse events being rash, fatigue, alopecia, pruritus, diarrhea and nausea. A nonsignificant trend toward prolonged PFS was seen for patients with tumors expressing higher levels of gpNMB. The development of rash, which may be associated with the presence of gpNMB in the skin, also seemed to correlate with greater PFS.

In December 2014, we initiated a single arm, single-agent, open label Phase 2 study of glembatumumab vedotin in patients with unresectable stage III or IV melanoma (n=60) and enrollment has been completed. The Company is currently amending the protocol to add a second cohort of patients to a glembatumumab vedotin and varlilumab combination arm to assess the potential clinical benefit of the combination and to explore varlilumab’s potential biologic and immunologic effect when combined with an antibody drug conjugate. The primary endpoint of each cohort is ORR. Secondary endpoints include analyses of PFS, duration of response, OS, retrospective investigation of whether the anticancer activity of glembatumumab vedotin is dependent upon the degree of gpNMB expression in tumor tissue and safety of both the monotherapy and combination regimen. The Company expects to present data from the single-agent cohort at an appropriate medical meeting in the second half of 2016.

Treatment of Other Indications:   We have entered into a collaborative relationship with PrECOG, LLC, which represents a research network established by the Eastern Cooperative Oncology Group (ECOG), under which PrECOG, LLC, is conducting an open-label Phase 1/2 study in patients with unresectable stage IIIB or IV, gpNMB-expressing, advanced or metastatic squamous cell cancer (SCC) of the lung, who have progressed on prior platinum-based chemotherapy. This study opened to enrollment in April 2016. The study will include a dose-escalation phase followed by a two-stage Phase 2 portion (Simon two-stage design). The Phase 1, dose-escalation portion of the study will assess the safety and tolerability of glembatumumab vedotin at the current dose of 1.9 mg/kg and then 2.2 mg/kg in order to determine whether higher dosing is feasible in this population. The first stage of the Phase 2 portion will enroll approximately 20 patients, and if at least two patients achieve a partial response or complete response, a second stage may enroll an additional 15 patients. The primary objective of the Phase 2 portion of the study is to assess the anti-tumor efficacy of glembatumumab vedotin in squamous cell lung cancer as measured by ORR. Secondary objectives of the study include analyses of safety and tolerability and further assessment of anti-tumor activity across a broad range of endpoints.

We have also entered into a Cooperative Research and Development Agreement, or CRADA, with the National Cancer Institute, or NCI, under which NCI is sponsoring two studies of glembatumumab vedotin—one in uveal melanoma and one in pediatric osteosarcoma. Both studies are currently open to enrollment. The uveal melanoma study is a single arm, open label study in patients with locally recurrent or metastatic uveal melanoma. The primary outcome measure is ORR. Secondary outcome measures include change in gpNMB expression on tumor tissue via immunohistochemistry, safety, OS and PFS. The osteosarcoma study is a single arm, open label, evaluation of adolescent and adult patients with recurrent or refractory osteosarcoma. The co-primary objectives are to determine whether glembatumumab vedotin therapy either increases the disease control rate at 4 months in patients with recurrent measurable osteosarcoma as compared to historical experience and/or whether glembatumumab vedotin therapy produces an objective response rate greater than 20% in patients without previous eribulin (eribulin mesylate) treatment. Secondary outcome measures include safety, pharmacokinetics and the relation of gpNMB expression as measured by immunohistochemistry to clinical response.

Varlilumab

Varlilumab, a fully human monoclonal agonist antibody, binds and activates CD27, a critical co-stimulatory molecule in the immune activation cascade, primarily by stimulating T cells to attack cancer cells. Restricted expression and regulation of CD27 enables varlilumab specifically to activate T cells, resulting in an enhanced immune response with a favorable safety profile. Varlilumab has also been shown to directly kill or inhibit the growth of CD27 expressing lymphomas and leukemias  in vitro  and  in vivo . We have entered into license agreements with the University of Southampton, UK for intellectual property to use anti-CD27 antibodies and with Medarex (now a subsidiary of the Bristol-Myers Squibb Company, or BMS) for access to the UltiMab technology to develop and commercialize human antibodies to CD27.

Patient treatment is complete in the open label Phase 1 study of varlilumab in patients with selected malignant solid tumors or hematologic cancers at multiple clinical sites in the U.S. Initial dose escalation cohorts were conducted to determine an optimal dose for future study, and no maximum tolerated dose was reached. The lymphoid malignancies dose escalation arm completed enrollment (n=24), and a new cohort was added to include evaluation of T cell malignancies. An expansion cohort was also added at 0.3 mg/kg dosed once every three weeks in patients with Hodgkin lymphoma (n= up to 15). The solid tumor arm, which included patients with various solid tumors, completed dose escalation in 2013. Two expansion cohorts were subsequently added at 3 mg/kg dosed weekly in

S- 4

Table of Contents

metastatic melanoma (n=16) and renal cell carcinoma, or RCC, (n=15) to better characterize clinical activity and further define the safety profile in preparation for combination studies.

We presented updated data from this Phase 1 study in November 2014. Varlilumab was very well tolerated and induced immunologic activity in patients that is consistent with both its mechanism of action and preclinical models. A total of 90 patients have been dosed in the study. 56 patients have been dosed in dose escalation cohorts (various solid and hematologic B-cell tumors), and 34 patients have been dosed in the expansion cohorts (melanoma and RCC) at 3 mg/kg. In both the solid tumor and hematologic dose-escalations, the pre-specified maximum dose level (10 mg/kg) was reached without identification of a maximum tolerated dose. The majority of adverse events, or AEs, related to treatment have been mild to moderate (Grade 1/2) in severity, with only three serious AEs related to treatment reported. No significant immune-mediated adverse events (colitis, hepatitis, etc.) typically associated with checkpoint blockade have been observed. Two patients experienced significant objective responses including a complete response in Hodgkin lymphoma (continues at 33.1+ months) and a partial response in renal cell carcinoma of 24.7+ months. Thirteen patients experienced stable disease with a range of 3-41.4+ months (as of April 2016) to-date. Based on the results observed in hematologic malignancies, an expansion cohort in up to 15 patients with Hodgkin lymphoma, and an abbreviated dose escalation in T cell hematologic malignancies were added and are now closed to enrollment. Any incremental data updates from this study will be included in future scientific presentations/publications.

In May 2014, we entered into a clinical trial collaboration with Bristol-Myers Squibb to evaluate the safety, tolerability and preliminary efficacy of varlilumab and Opdivo ®, Bristol-Myers Squibb’s PD-1 immune checkpoint inhibitor, in a Phase 1/2 study. Under the terms of this clinical trial collaboration, Bristol-Myers Squibb made a one-time payment to us of $5.0 million, and the companies amended the terms of our existing license agreement with Medarex (a subsidiary of Bristol-Myers Squibb) related to our CD27 program whereby certain future milestone payments were waived and future royalty rates were reduced that may have been due from us to Medarex. In return, Bristol-Myers Squibb was granted a time-limited right of first negotiation if we wish to out-license varlilumab. The companies also agreed to work exclusively with each other to explore anti-PD-1 antagonist antibody and anti-CD27 agonist antibody combination regimens. The clinical trial collaboration provides that the companies will share development costs and that we will be responsible for conducting the Phase 1/2 study.

The Phase 1/2 study was initiated in January 2015 and is being conducted in adult patients with multiple solid tumors to assess the safety and tolerability of varlilumab at varying doses when administered with Opdivo followed by a Phase 2 expansion to evaluate the activity of the combination in disease specific cohorts. The Phase 1 dose escalation portion of the study, conducted in patients with solid tumors, has completed enrollment (n=36) and primarily enrolled patients with colorectal and ovarian cancer.

Data was presented from the Phase 1 portion of the varlilumab and nivolumab study in a poster at the American Association for Cancer Research (AACR) Annual Meeting 2016 in April. The primary objective of the Phase 1 portion of the study was to evaluate the safety and tolerability of the combination. The combination showed acceptable tolerability and safety across all dose levels without any evidence of increased autoimmunity or inappropriate immune activation. Marked changes in the tumor microenvironment including increased infiltrating CD8+ T cells and increased PD-L1 expression, which have been shown to correlate with a greater magnitude of treatment effect from checkpoint inhibitors in other clinical studies were observed. Additional favorable immune biomarkers, such as increase in inflammatory chemokines and decrease in T regulatory cells, were also noted. In a subset of patients (n=17) on study who had both pre- and post-tumor biopsies available, preliminary evidence suggest a correlation between biomarker data and stable disease or better in seven of these patients (4 ovarian cancer, 2 colorectal cancer, 1 squamous cell carcinoma of the head and neck). All dose levels of the combination therapy showed acceptable tolerability and safety, without identification of a maximum tolerated dose. In the Phase 2 portion of the study, varlilumab will be administered at 3 mg/kg, which is based upon cumulative data across multiple studies.

The Phase 2 portion of the study opened to enrollment in April 2016 and includes cohorts in advanced non-small cell lung cancer (n=35), colorectal cancer (n=18), ovarian cancer (n=18), head and neck squamous cell carcinoma (n=18), renal cell carcinoma (n=25) and glioblastoma (n=20). The primary objective of the Phase 2 cohorts will be ORR, except glioblastoma, where the primary objective is the rate of 12-month overall survival. Secondary objectives include pharmacokinetics assessments, determining the immunogenicity of varlilumab when given in combination with Opdivo and further assessing the anti-tumor activity of combination treatment.

In March 2015, we entered into a clinical trial collaboration with Roche to evaluate the safety, tolerability and preliminary efficacy of varlilumab and atezolizumab (anti-PDL1), Roche’s investigational cancer immunotherapy, in a Phase 1/2 study. The Phase 1 portion of the study is being conducted in multiple tumor types, and the primary outcome is safety and tolerability. The Phase 2 portion of the study will be conducted in RCC, and the primary outcome is ORR. Secondary outcome measures include safety and tolerability, pharmacokinetics, immunogenicity and further assessment of anti-tumor activity across a broad range of endpoints. Under the terms of this agreement, Roche will provide study drug, and we will be responsible for conducting and funding the study, which opened to enrollment in December 2015.

In April 2015, we initiated a Phase 1/2 safety pilot and expansion study examining the combination of varlilumab and Yervoy ®  in patients with stage III or IV metastatic melanoma. In the Phase 2 portion of the study, patients with tumors that express NY-ESO-1

S- 5

Table of Contents

will also receive CDX-1401. The Phase 1 portion of the study will assess the safety and tolerability of varlilumab at varying doses when administered with Yervoy to identify a recommended dose for the Phase 2 portion of the study. The Phase 2 study will include two cohorts—one comprised of patients who are NY-ESO-1 positive and one comprised of patients who are NY-ESO-1 negative. Patients who are NY-ESO-1 positive will also receive CDX-1401 (with poly-ICLC at 2 mg given as an adjuvant) in addition to varlilumab and Yervoy. The primary objective for both cohorts is objective response rate up to 24 weeks. Secondary objectives for the Phase 2 study include safety and tolerability, immunogenicity, pharmacokinetics and further assessment of anti-tumor activity across a broad range of endpoints.

In May 2015, we initiated a Phase 1/2 safety and tolerability study examining the combination of varlilumab and sunitinib (Sutent ® ) in patients with metastatic clear cell renal cell carcinoma. The Phase 1 portion of the study will assess the safety and tolerability of varlilumab at varying doses when administered with sunitinib to identify a recommended dose for the Phase 2 portion of the study. The primary objective of the Phase 2 portion of the study is to assess the preliminary anti-tumor efficacy of the varlilumab/sunitinib combination measured by the overall response rate. Secondary objectives include safety and tolerability, pharmacokinetics, immunogenicity and further assessment of anti-tumor activity across a broad range of endpoints.

In addition to our sponsored studies and clinical trial collaborations, we anticipate that varlilumab’s potential activity will also be explored in investigator sponsored studies at various academic institutions.

Rintega ®

On March 7, 2016, we announced that our Phase 3 study of Rintega ® in patients with newly diagnosed EGFRvIII-positive glioblastoma was being discontinued. This decision was made based on the outcome of a preplanned interim analysis conducted by an independent Data Safety and Monitoring Board (DSMB). The DSMB determined that continuation of the study would not result in reaching statistical significance for the primary endpoint of the study, overall survival in patients with minimal residual disease, as both the Rintega arm and the control arm were performing on par with each other. In the ACT IV study, Rintega performed consistently with prior Phase 2 studies but the control arm significantly outperformed expectations (Hazard ratio = 0.99; median OS: Rintega 20.4 months vs. control 21.1 months). Based on this recommendation, we discontinued the study and do not anticipate incurring substantial additional costs related to Rintega at this time. All patients on the Rintega arm of the ACT IV study, prior Phase 2 studies and existing compassionate use recipients were offered ongoing access to Rintega on a compassionate use basis. We are in the process of conducting a thorough analysis of the data. It is our goal to share this information either through scientific publication or at a medical meeting in the future.

Corporate Information

We are a Delaware corporation organized in 1983.  Our principal executive offices are located at Perryville III Building, 53 Frontage Road, Suite 220, Hampton, New Jersey 08827 and our telephone number is (908) 200-7500.  Our corporate website is www.celldex.com .  The information on our website is not incorporated by reference into this prospectus.

S- 6

Table of Contents

Table of Contents

Table of Contents

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.

Because we do not intend to declare cash dividends on our shares of common stock in the foreseeable future, stockholders must rely on appreciation of the value of our common stock for any return on their investment.

We have never declared or paid cash dividends on our common stock. We currently anticipate that we will retain future earnings for the development, operation and expansion of our business and do not anticipate declaring or paying any cash dividends in the foreseeable future. In addition, the terms of any existing or future debt agreements may preclude us from paying dividends. As a result, we expect that only appreciation of the price of our common stock, if any, will provide a return to investors in this offering for the foreseeable future.

S- 9

Table of Contents

Table of Contents

You should also consider carefully the statements set forth in the section entitled “Risk Factors” in this prospectus supplement and in our Annual Report on Form 10-K/A for the year ended December 31, 2015, respectively, as updated by any other document that we subsequently filed with the Securities and Exchange Commission and that is incorporated by reference into this prospectus supplement, which address various factors that could cause results or events to differ from those described in the forward-looking statements.  All subsequent written and oral forward-looking statements attributable to us or to persons acting on our behalf are expressly qualified in their entirety by the applicable cautionary statements.  We have no plans to update these forward-looking statements.

S- 11

Table of Contents

Table of Contents

Table of Contents

Table of Contents

Table of Contents

Table of Contents

PROSPECTUS

CELLDEX THERAPEUTICS, INC.

Common Stock

Preferred Stock

Warrants

Depositary Shares

Units

Celldex Therapeutics, Inc. or any selling securityholders may offer, issue and sell from time to time, together or separately, in one or more offerings, any combination of:

·                   our common stock,

·                   our preferred stock, which we may issue in one or more series,

·                   warrants,

·                   depositary shares, and

·                   units.

This prospectus provides a general description of the securities we may offer.  Each time we or any selling securityholders sell securities, we will provide specific terms of the securities offered in a supplement to this prospectus.  The prospectus supplement may also add, update or change information contained in this prospectus.  You should read this prospectus and the accompanying prospectus supplement, as well as the documents incorporated or deemed incorporated by reference in this prospectus, carefully before you make your investment decision.  Our common stock is traded on the NASDAQ Global Market under the symbol “CLDX.” On November 29, 2013, the last reported sale price of our common stock on the NASDAQ Global Market was $27.76 per share.  You are urged to obtain current market quotations of the common stock.  Each prospectus supplement will indicate if the securities offered thereby will be listed on any securities exchange.

This prospectus may not be used to sell securities unless accompanied by a prospectus supplement.

We or any selling securityholders may offer to sell these securities on a continuous or delayed basis, through agents, dealers or underwriters, or directly to purchasers.  The prospectus supplement for each offering of securities will describe in detail the plan of distribution for that offering.  If our agents or any dealers or underwriters are involved in the sale of the securities, the applicable prospectus supplement will set forth the names of the agents, dealers or underwriters and any applicable commissions or discounts.  Our net proceeds from the sale of securities will also be set forth in the applicable prospectus supplement.  For general information about the distribution of securities offered, please see “Plan of Distribution” in this prospectus.

Investing in our securities involves risks.  Before making an investment decisions, you should carefully review the information contained in this prospectus under the heading “Risk Factors” beginning on page 6 of this prospectus.

NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES COMMISSION OR REGULATORY BODY HAS APPROVED OR DISAPPROVED OF THESE SECURITIES OR DETERMINED IF THIS PROSPECTUS IS TRUTHFUL OR COMPLETE.  ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

The date of this prospectus is December 3, 2013.

Table of Contents

Table of Contents

ABOUT THIS PROSPECTUS

This prospectus is a part of a registration statement that we filed with the Securities and Exchange Commission, or the SEC, utilizing a “shelf” registration process.  Under this shelf registration process, we or any selling securityholders may, from time to time, sell any combination of the securities described in this prospectus in one or more offerings.

The registration statement containing this prospectus, including the exhibits to the registration statement, provides additional information about us and the securities offered under this prospectus.  You should read the registration statement and the accompanying exhibits for further information.  The registration statement, including the exhibits and the documents incorporated or deemed incorporated herein by reference, can be read and are available to the public over the Internet at the SEC’s website at http://www.sec.gov as described under the heading “Where You Can Find More Information.”

This prospectus provides you with a general description of the securities we or any selling securityholders may offer.  Each time we or any selling securityholders sell securities pursuant to this prospectus, we will provide a prospectus supplement containing specific information about the terms of a particular offering by us or any selling securityholders.  That prospectus supplement may include a discussion of any risk factors or other special considerations that apply to those securities.  The prospectus supplement may add, update or change information in this prospectus.  If the information in the prospectus is inconsistent with a prospectus supplement, you should rely on the information in that prospectus supplement.  You should read both this prospectus and, if applicable, any prospectus supplement.  See “Where You Can Find More Information” for more information.

You should rely only on the information incorporated by reference or provided in this prospectus.  We have not authorized any dealer, salesman or other person to give any information or to make any representation other than those contained or incorporated by reference in this prospectus or any prospectus supplement.  You must not rely upon any information or representation not contained or incorporated by reference in this prospectus or any prospectus supplement.  This prospectus and any prospectus supplement do not constitute an offer to sell or the solicitation of an offer to buy any securities other than the registered securities to which they relate, nor do this prospectus and any prospectus supplement constitute an offer to sell or the solicitation of an offer to buy securities in any jurisdiction to any person to whom it is unlawful to make such offer or solicitation in such jurisdiction.  You should not assume that the information contained in this prospectus or any prospectus supplement is accurate on any date subsequent to the date set forth on the front of such document or that any information we have incorporated by reference is correct on any date subsequent to the date of the document incorporated by reference, even though this prospectus and any prospectus supplement is delivered or securities are sold on a later date.

Unless this prospectus indicates otherwise or the context otherwise requires, the terms “we,” “our,” “us,” “Celldex” or the “Company” as used in this prospectus refer to Celldex Therapeutics, Inc. and its subsidiaries, except that such terms refer to only Celldex Therapeutics, Inc. and not its subsidiaries in the sections entitled “Description of Common Stock,” “Description of Preferred Stock,” “Description of Warrants,” “Description of Depositary Shares,” and “Description of Units.”

1

Table of Contents

PROSPECTUS SUMMARY

Company Overview

We are a biopharmaceutical company focused on the development and commercialization of several immunotherapy technologies for the treatment of cancer and other difficult-to-treat diseases.  Our lead drug candidates include rindopepimut (CDX-110), an immunotherapeutic vaccine in a pivotal Phase 3 study for the treatment of front-line glioblastoma and a Phase 2 study for the treatment of recurrent glioblastoma, and CDX-011, an antibody-drug conjugate for which we initiated an accelerated approval study in December 2013 for the treatment of advanced breast cancer.  We also have a number of earlier stage candidates in clinical development, including CDX-1127, a therapeutic fully human monoclonal antibody in a Phase 1 study for cancer indications, CDX-1135, a molecule that inhibits a part of the immune system called the complement system, CDX-301, an immune cell mobilizing agent and dendritic cell growth factor and CDX-1401, an APC Targeting Technology™ program in a Phase 1 study for cancer indications.  Our drug candidates address market opportunities for which we believe current therapies are inadequate or non-existent.

We are building a fully integrated, commercial-stage biopharmaceutical company that develops important therapies for patients with unmet medical needs.  Our program assets provide us with the strategic options to either retain full economic rights to our innovative therapies or seek favorable economic terms through advantageous commercial 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.

Rindopepimut (CDX-110)

Rindopepimut is an experimental immunotherapeutic drug that targets the tumor-specific molecule, epidermal growth factor receptor variant III, or EGFRvIII.  EGFRvIII is a mutated form of the epidermal growth factor receptor, or EGFR, that is only expressed in cancer cells and not in normal tissue and can directly contribute to cancer cell growth.  EGFRvIII is expressed in approximately 30% of glioblastoma, or GB, tumors, the most common and aggressive form of brain cancer.  The rindopepimut vaccine is composed of the EGFRvIII peptide linked to a carrier protein called Keyhole Limpet Hemocyanin, or KLH, and administered together with the adjuvant GM-CSF.  The Food and Drug Administration, or FDA, and the European Medicines Agency, or EMA, have both granted orphan drug designation for rindopepimut for the treatment of EGFRvIII expressing GB and the FDA has also granted Fast Track designation.

Glembatumumab Vedotin (CDX-011)

CDX-011 is an antibody-drug conjugate, or ADC, for the treatment of patients with glycoprotein NMB, or gpNMB, expressing advanced, refractory breast cancer.  CDX-011 consists of a fully-human monoclonal antibody, CR011, linked to a potent cell-killing drug, monomethyl-auristatin E, or MMAE.  CDX-011 targets the protein gpNMB, which is over-expressed in a variety of 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 FDA has granted Fast Track designation to CDX-011 for the treatment of advanced, refractory/resistant gpNMB-expressing breast cancer.

In connection with our acquisition of CuraGen Corporation, we assumed the license agreement between CuraGen and Seattle Genetics, whereby CuraGen acquired the rights to proprietary ADC technology, with the right to sublicense, for use with its proprietary antibodies for the potential treatment of cancer.  Under the terms of the agreement, we have the responsibility of using commercially reasonable efforts to develop, commercialize and market such treatment.  In furtherance of these responsibilities, technical assistance from Seattle Genetics is available to us as necessary.  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, including our CDX-011 program.  The term of the agreement varies country to country and may be until the later of the expiration of the last relevant patent or the 10 th  anniversary of the first commercial sale.  The agreement allows us to terminate with prior written notice, with both parties being able to terminate the agreement for an uncured material breach or insolvency of the other party.

The patent rights licensed from Seattle Genetics include issued patents and pending applications in Australia, Canada, Europe, the U.S. and Japan which include composition of matter claims relating to the toxin and conjugation technology.  If maintained to full term in due course, the main Seattle Genetics patent rights would have estimated patent expiry dates ranging from 2023 in Europe to 2026 in the U.S.

CDX-1127

CDX-1127 is a human monoclonal antibody that targets CD27, a potentially important target for immunotherapy of various cancers.  CD27 acts downstream from CD40 and may provide a novel way to regulate the immune responses.  CD27 is a co-stimulatory molecule on T cells and is over-expressed in certain lymphomas and leukemias.  CDX-1127 is an agonist antibody designed to have two potential therapeutic mechanisms.  CDX-1127 has been shown to activate immune cells that can target and eliminate cancerous

2

Table of Contents

cells in tumor-bearing mice and to directly kill or inhibit the growth of CD27-expressing lymphomas and leukemias in vitro and in vivo.  Both mechanisms have been seen even at low doses in preclinical models.

CDX-1135

CDX-1135 is a molecule that inhibits a part of the human 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 has been shown to inhibit the activation of the complement cascade in animal models and in human clinical trials.  In preclinical studies, CDX-1135 has been shown to inhibit both the classical and alternative pathways of complement activation.  Our initial experience under an investigator sponsored IND indicated that CDX-1135 limits complement abnormalities in Dense Deposit Disease, or DDD, which is a rare and devastating disease that is caused by uncontrolled activation of the alternative pathway of complement activation and leads to progressive kidney damage in children.  There is currently no treatment for patients with DDD and about half progress to end-stage renal disease within 10 years.  Because DDD recurs in virtually all patients who receive a kidney transplant, transplantation is not a viable option for these patients.  In animal models of DDD, CDX-1135 treatment showed evidence of reversal of kidney damage.

Corporate Information

We are a Delaware corporation organized in 1983.  On October 1, 2009, a wholly-owned subsidiary of Celldex merged with and into CuraGen Corporation.  On December 31, 2009, CuraGen Corporation was merged with and into Celldex and the separate existence of CuraGen ceased.

Our principal executive offices are located at 119 Fourth Avenue, Needham, Massachusetts 02494 and our telephone number is (781) 433-0771.  Our corporate website is www.celldextherapeutics.com.  The information on our website is not incorporated by reference into this prospectus.

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus, including the documents that we incorporate by reference, contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act.  Any statements about our expectations, beliefs, plans, objectives, assumptions or future events or performance are not historical facts and may be forward-looking.  These statements are often, but not always, made through the use of words or phrases such as “anticipate,” “estimate,” “plans,” “projects,” “continuing,” “ongoing,” “expects,” “management believes,” “we believe,” “we intend” and similar words or phrases.  Accordingly, these statements involve estimates, assumptions and uncertainties, which could cause actual results to differ materially from those expressed in them.  Any forward-looking statements are qualified in their entirety by reference to the risk factors discussed in this prospectus or discussed in documents incorporated by reference in this prospectus.

Forward-looking statements are subject to known and unknown risks and uncertainties, which change over time, and are based on management’s expectations and assumptions at the time the statements are made, and are not guarantees of future results.  Our actual results may differ materially from those expressed or anticipated in the forward-looking statements for many reasons including the factors described in the section entitled “Risk Factors” in this prospectus and in any risk factors described in a supplement to this prospectus or in other filings.

You are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date on which they were made.  We undertake no obligation to publicly revise any forward-looking statement to reflect circumstances or events after the date of this prospectus or to reflect the occurrence of unanticipated events.  You should, however, review the factors and risks we describe in the reports we file from time to time with the SEC after the date of this prospectus.  We undertake no obligation to revise or update the forward-looking statements contained in this prospectus at any time.  All forward-looking statements are qualified in their entirety by this cautionary statement.

3

Table of Contents

Table of Contents

prospectus supplement differ from any of the terms described herein, then the terms described herein will be deemed superseded by the terms set forth in that prospectus supplement.

We may issue securities in book-entry form through one or more depositaries, such as The Depository Trust Company, Euroclear or Clearstream, named in the applicable prospectus supplement.  Each sale of a security in book-entry form will settle in immediately available funds through the applicable depositary, unless otherwise stated.  We will issue the securities only in registered form, without coupons, although we may issue the securities in bearer form if so specified in the applicable prospectus supplement.  If any securities are to be listed or quoted on a securities exchange or quotation system, the applicable prospectus supplement will say so.

Table of Contents

Table of Contents

Terms of the Preferred Stock That We May Offer and Sell to You

We summarize below some of the provisions that will apply to the preferred stock that we may offer to you unless the applicable prospectus supplement provides otherwise.  This summary may not contain all information that is important to you.  You should read the prospectus supplement, which will contain additional information and which may update or change some of the information below.  Prior to the issuance of a new series of preferred stock, we will further amend our third restated certificate of incorporation, as amended, designating the stock of that series and the terms of that series.  We will file a copy of the certificate of designation that contains the terms of each new series of preferred stock with the SEC each time we issue a new series of preferred stock.  Each certificate of designation will establish the number of shares included in a designated series and fix the designation, powers, privileges, preferences and rights of the shares of each series as well as any applicable qualifications, limitations or restrictions.  You should refer to the applicable certificate of designation as well as our third restated certificate of incorporation, as amended, before deciding to buy shares of our preferred stock as described in the applicable prospectus supplement.

Our board of directors has the authority, without further action by the stockholders, to issue preferred stock in one or more series and to fix the number of shares, dividend rights, conversion rights, voting rights, redemption rights, liquidation preferences, sinking funds, and any other rights, preferences, privileges and restrictions applicable to each such series of preferred stock.

The issuance of any preferred stock could adversely affect the rights of the holders of common stock and, therefore, reduce the value of the common stock.  The ability of our board of directors to issue preferred stock could discourage, delay or prevent a takeover or other corporate action.

The terms of any particular series of preferred stock will be described in the prospectus supplement relating to that particular series of preferred stock, including, where applicable:

·                   the designation, stated value and liquidation preference of such preferred stock;

·                   the number of shares within the series;

·                   the offering price;

·                   the dividend rate or rates (or method of calculation), the date or dates from which dividends shall accrue, and whether such dividends shall be cumulative or noncumulative and, if cumulative, the dates from which dividends shall commence to cumulate;

·                   whether interests in the shares of preferred stock will be represented by depositary shares as more fully described below under “Description of Depositary Shares”;

·                   any redemption or sinking fund provisions;

·                   the amount that shares of such series shall be entitled to receive in the event of our liquidation, dissolution or winding-up;

·                   the terms and conditions, if any, on which shares of such series shall be convertible or exchangeable for shares of our stock of any other class or classes, or other series of the same class;

·                   the voting rights, if any, of shares of such series; the status as to reissuance or sale of shares of such series redeemed, purchased or otherwise reacquired, or surrendered to us on conversion or exchange;

·                   the conditions and restrictions, if any, on the payment of dividends or on the making of other distributions on, or the purchase, redemption or other acquisition by us or any subsidiary, of the common stock or of any other class of our shares ranking junior to the shares of such series as to dividends or upon liquidation;

·                   the conditions and restrictions, if any, on the creation of indebtedness by us or by any subsidiary, or on the issuance of any additional stock ranking on a parity with or prior to the shares of such series as to dividends or upon liquidation; and

·                   any additional dividend, liquidation, redemption, sinking or retirement fund and other rights, preferences, privileges, limitations and restrictions of such preferred stock.

7

Table of Contents

The description of the terms of a particular series of preferred stock in the applicable prospectus supplement will not be complete.  You should refer to the applicable amendment to our third restated certificate of incorporation, as amended, for complete information regarding a series of preferred stock.

The preferred stock will, when issued against payment of the consideration payable therefor, be fully paid and nonassessable.  Unless otherwise specified in the applicable prospectus supplement, each series of preferred stock will, upon issuance, rank senior to the common stock and on a parity in all respects with each other outstanding series of preferred stock.  The rights of the holders of our preferred stock will be subordinate to that of our general creditors.

Table of Contents

·                   any mandatory or optional redemption provision;

·                   whether the warrants are to be issued in registered or bearer form;

·                   whether the warrants are extendible and the period or periods of such extendibility;

·                   information with respect to book-entry procedures, if any; and

·                   any other terms of the warrants.

Before exercising their warrants, holders of warrants will not have any of the rights of holders of the securities purchasable upon such exercise, including the right to receive dividends, if any, or payments upon our liquidation, dissolution or winding-up or to exercise voting rights, if any.

Exercise of Warrants

Each warrant will entitle the holder thereof to purchase such number of shares of common stock or preferred stock or other securities at the exercise price as will in each case be set forth in, or be determinable as set forth in, the applicable prospectus supplement.  Warrants may be exercised at any time up to the close of business on the expiration date set forth in the applicable prospectus supplement.  After the close of business on the expiration date, unexercised warrants will become void.  Warrants may be exercised as set forth in the applicable prospectus supplement relating to the warrants offered thereby.  Upon receipt of payment and proper completion and due execution at the corporate trust office of the warrant agent or any other office indicated in the applicable prospectus supplement of the warrant certificate, we will, as soon as practicable, forward the purchased securities.  If less than all of the warrants represented by the warrant certificate are exercised, a new warrant certificate will be issued for the remaining warrants.

Enforceability of Rights of Holders of Warrants

Each warrant agent will act solely as our agent under the applicable warrant agreement and will not assume any obligation or relationship of agency or trust with any holder of any warrant.  A single bank or trust company may act as warrant agent for more than one issue of warrants.  A warrant agent will have no duty or responsibility in case of any default by us under the applicable warrant agreement or warrant, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us.  Any holder of a warrant may, without the consent of the related warrant agent or the holder of any other warrant, enforce by appropriate legal action its right to exercise, and receive the securities purchasable upon exercise of, that holder’s warrant(s).

Modification of the Warrant Agreement

The warrant agreement will permit us and the warrant agent, without the consent of the warrant holders, to supplement or amend the agreement in the following circumstances:

·                   to cure any ambiguity;

·                   to correct or supplement any provision which may be defective or inconsistent with any other provisions; or

·                   to add new provisions regarding matters or questions that we and the warrant agent may deem necessary or desirable and which do not adversely affect the interests of the warrant holders.

Table of Contents

The shares of common stock or any class or series of preferred stock represented by depositary shares will be deposited under a deposit agreement among us, a depositary selected by us, and the holders of the depositary receipts.  The depositary will be a bank or trust company having its principal office in the United States and having a combined capital and surplus of at least $50,000,000.  Subject to the terms of the deposit agreement, each owner of a depositary share will be entitled, in proportion to the applicable fraction of a share of common stock or preferred stock represented by such depositary share, to all the rights and preferences of the shares of common stock or preferred stock represented by the depositary share, including dividend, voting, redemption and liquidation rights.

The depositary shares will be evidenced by depositary receipts issued pursuant to the deposit agreement.  Depositary receipts will be distributed to those persons purchasing the fractional shares of common stock or the related class or series of preferred shares in accordance with the terms of the offering described in the related prospectus supplement.

Table of Contents

·                   the purchase price of the securities sold by us to any underwriter or dealer and the net proceeds we expect to receive from the offering;

·                   any over-allotment options under which underwriters may purchase additional securities from us;

·                   any agency fees or underwriting discounts or commissions and other items constituting agents’ or underwriters’ compensation;

·                   any securities exchange or market on which the securities may be listed.

Only underwriters named in the prospectus supplement will be underwriters of the securities offered by the prospectus supplement.

If underwriters are used in the sale, they will acquire the securities for their own account and may resell the securities from time to time in one or more transactions at a fixed public offering price or at varying prices determined at the time of sale.  The obligations of the underwriters to purchase the securities will be subject to the conditions set forth in the applicable underwriting agreement.  We may offer the securities to the public through underwriting syndicates represented by managing underwriters or by underwriters without a syndicate.  Subject to certain conditions, the underwriters will be obligated to purchase all of the securities offered by the prospectus supplement, other than securities covered by any over-allotment option.  Any public offering price and any discounts or commissions or concessions allowed or reallowed or paid to dealers may change from time to time.  We may use underwriters with whom we have a material relationship.  We will describe in the prospectus supplement, naming the underwriter, the nature of any such relationship.

We or any selling securityholders may sell securities directly or through agents we designate from time to time.  We will name any agent involved in the offering and sale of securities and we will describe any commissions and other compensation we will pay the agent in the prospectus supplement.  Unless the prospectus supplement states otherwise, our agent will act on a best-efforts basis for the period of its appointment.

We or any selling securityholders may authorize agents or underwriters to solicit offers by certain types of institutional investors to purchase securities from us at the public offering price set forth in the prospectus supplement pursuant to delayed delivery contracts providing for payment and delivery on a specified date in the future.  We will describe the conditions to these contracts and the commissions we must pay for solicitation of these contracts in the prospectus supplement.

We may provide agents and underwriters with indemnification against civil liabilities related to this offering, including liabilities under the Securities Act, or contribution with respect to payments that the agents or underwriters may make with respect to these liabilities.  Agents and underwriters may engage in transactions with, or perform services for, us in the ordinary course of business.

All securities we may offer, other than common stock, will be new issues of securities with no established trading market.  Any agents or underwriters may make a market in these securities, but will not be obligated to do so and may discontinue any market making at any time without notice.  We cannot guarantee the liquidity of the trading markets for any securities.  There is currently no market for any of the offered securities, other than our common stock which is listed on the NASDAQ Global Market.  We have no current plans for listing of the preferred stock, warrants or subscription rights on any securities exchange or quotation system; any such listing with respect to any particular preferred stock, warrants or subscription rights will be described in the applicable prospectus supplement or other offering materials, as the case may be.

Any underwriter may engage in overallotment, stabilizing transactions, short covering transactions and penalty bids in accordance with Regulation M under the Exchange Act.  Overallotment involves sales in excess of the offering size, which create a short position.  Stabilizing transactions permit bids to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum.  Short covering transactions involve purchases of the securities in the open market after the distribution is completed to cover short positions.  Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the securities originally sold by the dealer are purchased in a stabilizing or short covering transaction to cover short positions.  Those activities may cause the price of the securities to be higher than it would otherwise be.  If commenced, the underwriters may discontinue any of the activities at any time.

Any agents and underwriters who are qualified market makers on the NASDAQ Global Market may engage in passive market making transactions in the securities on the NASDAQ Global Market in accordance with Regulation M, during the business day prior to the pricing of the offering, before the commencement of offers or sales of the securities.  Passive market makers must comply with

11

Table of Contents

applicable volume and price limitations and must be identified as passive market makers.  In general, a passive market maker must display its bid at a price not in excess of the highest independent bid for such security; if all independent bids are lowered below the passive market maker’s bid, however, the passive market maker’s bid must then be lowered when certain purchase limits are exceeded.  Passive market making may stabilize the market price of the securities at a level above that which might otherwise prevail in the open market and, if commenced, may be discontinued at any time.

LEGAL MATTERS

Unless otherwise indicated in the applicable prospectus supplement, the validity of the securities offered hereby will be passed upon for us by Lowenstein Sandler LLP, Roseland, New Jersey.  If the validity of the securities offered hereby in connection with offerings made pursuant to this prospectus are passed upon by counsel for the underwriters, dealers, agents or selling securityholders, if any, such counsel will be named in the prospectus supplement relating to such offering.

EXPERTS

The financial statements and management’s assessment of the effectiveness of internal control over financial reporting (which is included in Management’s Report on Internal Control over Financial Reporting) incorporated in this prospectus by reference to our Annual Report on Form 10-K for the year ended December 31, 2012 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

WHERE YOU CAN FIND MORE INFORMATION

We have filed with the SEC a registration statement on Form S-3, including exhibits, under the Securities Act of which this prospectus forms a part.  This prospectus does not contain all of the information set forth in the registration statement.  This prospectus contains descriptions of certain agreements or documents that are exhibits to the registration statement.  The statements as to the contents of such exhibits, however, are brief descriptions and are not necessarily complete, and each statement is qualified in all respects by reference to such agreement or document.  For further information about us, please refer to the registration statement and the documents incorporated by reference in this prospectus.

We file annual, quarterly and current reports, proxy statements and other information with the SEC.  Our SEC filings are available to the public over the Internet at the SEC’s website at http://www.sec.gov.  The SEC’s website contains reports, proxy statements and other information regarding issuers, such as Celldex Therapeutics, Inc., that file electronically with the SEC.  You may also read and copy any document we file with the SEC at the SEC’s Public Reference Room, located at 100 F Street, N.E., Washington, D.C. 20549.  Please call the SEC at 1-800-SEC-0330 for further information on the operation of its Public Reference Room.  We make available free of charge through our web site our Annual Report on Form 10-K, Quarterly Reports on Form 10-Q, Current Reports on Form 8-K, Proxy Statements on Schedule 14A and all amendments to those reports as soon as reasonably practicable after such material is electronically filed with or furnished to the SEC.  Our website address is http://www.celldextherapeutics.com.  Please note that our website address is provided as an inactive textual reference only.  Information contained on or accessible through our website is not part of this prospectus or the prospectus supplement, and is therefore not incorporated by reference unless such information is otherwise specifically referenced elsewhere in this prospectus or the prospectus supplement.

INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

The SEC allows us to incorporate by reference in this prospectus much of the information we file with the SEC, which means that we can disclose important information to you by referring you to those publicly available documents.  The information that we incorporate by reference in this prospectus is considered to be part of this prospectus.  Because we are incorporating by reference future filings with the SEC, this prospectus is continually updated and those future filings may modify or supersede some of the information included or incorporated in this prospectus.  This means that you must look at all of the SEC filings that we incorporate by reference to determine if any of the statements in this prospectus or in any document previously incorporated by reference have been modified or superseded.  This prospectus incorporates by reference the documents listed below (File No. 000-15006) and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934, as amended, or the Exchange Act (in each case, other than those documents or the portions of those documents not deemed to be filed) until the offering of the securities under the registration statement is terminated or completed:

·                   Our Annual Report on Form 10-K for the fiscal year ended December 31, 2012, filed with the SEC on March 8, 2013 (including the portions of our Proxy Statement on Schedule 14A, filed with the SEC on April 23, 2013, incorporated by reference therein);

12

Table of Contents

·                   Our Quarterly Reports on Form 10-Q for the fiscal quarters ended March 31, 2013, June 30, 2013 and September 30, 2013, filed on May 3, 2013, August 6, 2013 and November 8, 2013, respectively;

·                   Our Current Reports on Form 8-K filed with the SEC on February 4, 2013, February 6, 2013, March 7, 2013 (with respect to Item 8.01 only), May 20, 2013 and June 13, 2013;

·                   The description of our Common Stock contained in our registration statement on Form 8-A, filed with the SEC on September 22, 1986 under Section 12 of the Securities Exchange Act, and any amendments or reports filed for the purpose of updating such description; and

·                   The description of the rights to purchase our Series C-1 Junior Participating Cumulative Preferred Stock contained in our registration statement on Form S-4, filed with the SEC on December 21, 2007, our registration statement on Form 8-A filed with the SEC on November 8, 2004, our registration statement on Form 8-A/A filed with the SEC on October 22, 2007, our registration statement on Form 8-A/A filed with the SEC on March 7, 2008, and any amendment or report filed with the SEC for the purposes of updating such descriptions.

Nothing in this prospectus shall be deemed to incorporate information furnished but not filed with the SEC pursuant to Item 2.02 or 7.01 of Form 8-K.

We will furnish without charge to each person, including any beneficial owner, to whom this prospectus is delivered, upon written or oral request, a copy of any documents incorporated by reference other than exhibits to those documents.  Requests should be addressed to:

Celldex Therapeutics, Inc.
Attention: Investor Relations
119 Fourth Avenue
Needham, Massachusetts 02494
Telephone number: (781) 433-0771

13

Table of Contents

Celldex Therapeutics, Inc.

Up to $60,000,000

Common Stock

PROSPECTUS SUPPLEMENT

May 19, 2016