CLDX Celldex Therapeutics Inc

Table of Contents

Filed Pursuant to Rule 424(b)(5)
Registration No. 333- 214882

PROSPECTUS SUPPLEMENT

(To Prospectus Dated February 13, 2017)

Up to $75,000,000

Common Stock

In accordance with the terms of the Controlled Equity Offering SM  sales agreement, dated May 19, 2016, we entered into with Cantor Fitzgerald & Co., or Cantor Fitzgerald, we may offer and sell shares of our common stock having an aggregate offering price of up to an additional $75.0 million from time to time through Cantor Fitzgerald, acting as sales agent.

Our common stock is traded on the Nasdaq Global Market, or Nasdaq, under the symbol “CLDX”. On November 7, 2017, the last reported sales price of our common stock on Nasdaq was $2.62 per share.

Sales of our common stock, if any, under this prospectus supplement and the accompanying prospectus may be made in sales deemed to be an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended, or the Securities Act, including sales made directly on or through Nasdaq or any other existing trading market for our common stock. Cantor Fitzgerald is not required to sell any specific number or dollar amount of securities, but will act as a sales agent using commercially reasonable efforts consistent with its normal trading and sales practices, on mutually agreed terms between Cantor Fitzgerald and us. There is no arrangement for funds to be received in any escrow, trust or similar arrangement.

Cantor Fitzgerald will be entitled to compensation at a fixed commission rate equal to 3.0% of the gross sales price per share sold. In connection with the sale of our common stock on our behalf, Cantor Fitzgerald will be deemed to be an “underwriter” within the meaning of the Securities Act and the compensation of Cantor Fitzgerald will be deemed to be underwriting commissions or discounts.

Investing in our common stock involves risks. Before buying any shares, you should read the discussion of material risks of investing in our common stock in “Risk Factors” beginning on page S-5 of this prospectus supplement, and in the risks discussed under similar headings in the documents incorporated by reference in this prospectus supplement and accompanying prospectus, as they may be amended, updated or modified periodically in our reports filed with the Securities and Exchange Commission.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement and accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus supplement is November 9, 2017.

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 and other cancer-targeting biologics. Our drug candidates, including antibodies, antibody-drug conjugates and other protein-based therapeutics, are derived from a broad set of complementary technologies which have the ability to engage the human immune system and/or directly inhibit tumors 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 cancer. We established proof of principle in a Phase 1 study with varlilumab, which supported the initiation of combination studies in various indications. We also have a number of earlier stage drug candidates in clinical development, including CDX-3379, a human monoclonal antibody designed to block the activity of ErbB3 (HER3) in solid tumors; CDX-014, an antibody-drug conjugate targeting renal and ovarian cancers; CDX-1401, a targeted immunotherapeutic aimed at antigen presenting cells, or APCs, for cancer indications; and, CDX-301, an immune cell mobilizing agent and dendritic cell growth factor. 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 Celldex-sponsored clinical studies that we are actively pursuing at this time. All programs are currently fully owned by Celldex.

1 checkpoint inhibitor; 2 BMS collaboration; 3 expected to initiate by year-end 2017

We also routinely work with external parties, such as government agencies, to collaboratively advance our drug candidates. The following pipeline reflects clinical trials of our drug candidates being actively pursued by outside organizations. In addition to the studies listed below, we also have an Investigator Initiated Research (IIR) program with seven studies ongoing with our drug candidates and additional studies currently under consideration.

S- 2

Table of Contents

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- 3

Table of Contents

Table of Contents

Table of Contents

could issue and sell additional shares of our common stock in the public markets. We cannot predict the effect that future sales of our common stock would have on the market price of our common stock .

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 2015 through September 30, 2017, the market price of our common stock has fluctuated from a high of $32.82 per share in the first quarter of 2015, to a low of $2.20 per share in the second quarter of 2017. 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.

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- 6

Table of Contents

Table of Contents

·                   our ability to protect our intellectual property rights, including the ability to successfully defend patent oppositions filed against a European patent related to technology we use in varlilumab, and our ability to avoid intellectual property litigation, which can be costly and divert management time and attention.

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 for the year ended December 31, 2016, 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- 8

Table of Contents

Table of Contents

Table of Contents

Table of Contents

Table of Contents

Table of Contents

Perryville III Building, 53 Frontage Road, Suite 220,

Hampton, New Jersey 08827
(908) 200-7500

Any statement contained in this prospectus supplement or in a document incorporated or deemed to be incorporated by reference into this prospectus supplement will be deemed to be modified or superseded for purposes of this prospectus supplement to the extent that a statement contained in this prospectus supplement or any other subsequently filed document that is deemed to be incorporated by reference into this prospectus supplement modifies or supersedes the statement.  Any statement so modified or superseded will not be deemed, except as so modified or superseded, to constitute a part of this prospectus supplement.

You should rely only on information contained in, or incorporated by reference into, this prospectus supplement and the accompanying prospectus.  We have not authorized anyone to provide you with information different from that contained in this prospectus supplement and the accompanying prospectus or incorporated by reference in this prospectus supplement and the accompanying prospectus.  We are not making offers to sell the securities in any jurisdiction in which such an offer or solicitation is not authorized or in which the person making such offer or solicitation is not qualified to do so or to anyone to whom it is unlawful to make such offer or solicitation.

S- 14

Table of Contents

PROSPECTUS

CELLDEX THERAPEUTICS, INC.

$250,000,000

Common Stock
Preferred Stock
Warrants
Depositary Shares
Units

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

up to a maximum aggregate offering price of $250,000,000.

This prospectus provides a general description of the securities we may offer.  Each time we sell securities, we will provide specific terms of the securities offered in a supplement to this prospectus (which includes an at-the-market offering 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 February 8, 2017, the last reported sale price of our common stock on the NASDAQ Global Market was $3.42 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 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 decision, you should carefully review the information contained in this prospectus under the heading “Risk Factors” beginning on page 3 of this prospectus.

Table of Contents

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 February 13, 2017.

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 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 may offer. Each time we sell securities pursuant to this prospectus, we will provide a prospectus supplement (which term includes, as applicable, the at-the-market offering prospectus filed with the registration statement of which this prospectus forms a part) containing specific information about the terms of a particular offering by us. 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 or any prospectus supplement. 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.”

PROSPECTUS SUMMARY

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

1

Table of Contents

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.  As discussed below, we recently acquired Kolltan Pharmaceuticals, Inc. thereby expanding our pipeline of drug candidates.

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.

Recent Developments

On November 29, 2016, we consummated the transactions contemplated by that certain Agreement and Plan of Merger dated as of November 1, 2016 by and among Celldex, Kolltan Pharmaceuticals, Inc., a Delaware corporation, Connemara Merger Sub 1 Inc. a Delaware corporation and a wholly-owned subsidiary of Celldex  and Connemara Merger Sub 2 LLC., a Delaware limited liability company and a wholly-owned subsidiary of Celldex. Upon consummation of the transactions, Kolltan became a wholly-owned subsidiary of Celldex.

Prior to the merger, Kolltan was a privately-held clinical-stage company focused on the discovery and development of novel, antibody-based drug candidates targeting reception tyrosine kinases, or RTKs. Kolltan’s programs include: (i) KTN0158, a humanized monoclonal antibody that is a potent inhibitor of KIT activation and receptor dimerization in tumor cells and mast cells, which is currently in a Phase 1 dose escalation study in refractory gastrointestinal stromal tumors (GIST); (ii) KTN3379, a human monoclonal antibody designed to block the activity of ErbB3 (HER3), which recently completed a Phase 1b study with combination cohorts where meaningful responses and stable disease were observed in cetuximab (Erbitux ® ) refractory patients in head and neck squamous cell carcinoma and in BRAF-mutant non-small cell lung cancer (NSCLC); and (iii) a multi-faceted TAM program, a broad antibody discovery effort underway to generate antibodies that modulate the TAM family of RTKs, comprised of Tyro3, AXL and MerTK, which are expressed on tumor-infiltrating macrophages, dendritic cells and some tumors. Research supports TAMs having broad application and potential across immuno-oncology and inflammatory diseases.

Under the terms of the Merger Agreement, upon consummation of the transactions contemplated by the Merger Agreement, Kolltan’s investors received, in exchange for their share and debt interests in Kolltan, an aggregate of 18,257,996 shares of Celldex’s common stock with a calculated value of $62.5 million, based on the average closing price of Celldex’s stock for the five trading day period ending on October 28, 2016, the third calendar day prior to the date of the Merger Agreement, as adjusted downward pursuant to the terms of the Merger Agreement. The Merger Agreement provides that the number of shares that can be issued at the closing can be increased or decreased by no more than 5% in either direction based on the comparable average closing prices over the five trading days prior to the closing date.  Therefore, because the average closing price of Celldex’s stock over the five trading days prior to the closing date was higher than the comparable average closing prices over the five trading days prior to the date of the Merger Agreement, there was a full 5% downward adjustment in the number of shares issued at closing.  In addition, following closing, certain officers of Kolltan will receive an aggregate of 437,901 shares of Celldex’s common stock in lieu of cash severance obligations owed to them by Kolltan.  In addition, in the event that certain specified preclinical and clinical development milestones related to Kolltan’s development programs and/or Celldex’s development programs and certain commercial milestones related to Kolltan’s product candidates are achieved, Celldex will be required to pay Kolltan’s stockholders milestone payments of up to $172.5 million, which milestone payments may be made, at Celldex’s sole election, in cash, in shares of Celldex’s common stock or a combination of both, subject to NASDAQ listing requirements and provisions of the Merger Agreement.  The number of shares of Celldex common stock issued in connection with a milestone payment, if any, will be determined based on the average closing price per share of Celldex common stock for the five trading day period ending three calendar days prior to the achievement of such milestone. Pursuant to applicable NASDAQ listing rules, we are required to obtain stockholder approval of such issuances of our common stock to the extent that such issuances exceed 19.9% of our common stock outstanding prior to the merger.  If we do not obtain stockholder approval of such common stock issuances, we may elect to pay the milestone consideration in cash to maintain compliance with applicable NASDAQ listing standards.  We may still decide to pay cash even if we obtain stockholder approval.

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.

2

Table of Contents

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.

Table of Contents

Ratios of Combined Fixed Charges and Preferred Stock Dividends to Earnings

(1)  Due to our losses from continuing operations for the nine months ended September 30, 2016 and for the years ended December 31, 2015, 2014, 2013, 2012 and 2011 earnings were insufficient to cover fixed charges by $98.1 million, $129.5 million, $122.4 million, $81.4 million, $58.1 million, and $43.3 million, respectively.  For this reason, no ratios are provided.

Table of Contents

Dividends

The Board of Directors may, out of funds legally available, at any regular or special meeting, declare dividends to the holders of shares of our common stock as and when they deem expedient, subject to the rights of holders of the preferred stock, if any.

Voting

Each share of common stock entitles the holders to one vote per share on all matters requiring a vote of the stockholders, including the election of directors. No holders of shares of common stock shall have the right to vote such shares cumulatively in any election for the board of directors.

Rights Upon Liquidation

In the event of our voluntary or involuntary liquidation, dissolution, or winding up, the holders of our common stock will be entitled to share equally in our assets available for distribution after payment in full of all debts and after the holders of preferred stock, if any, have received their liquidation preferences in full.

Miscellaneous

No holders of shares of our common stock shall have any preemptive rights to subscribe for, purchase or receive any shares of any class, whether now or hereafter authorized, or any options or warrants to purchase any such shares, or any securities convertible into or exchanged for any such shares, which may at any time be issued, sold or offered for sale by Celldex.

Anti-Takeover Provisions

Certain provisions in our third restated certificate of incorporation, as amended, and applicable Delaware corporate, as well as our shareholder rights agreement, may have the effect of discouraging a change of control of Celldex, even if such a transaction is favored by some of our stockholders and could result in stockholders receiving a substantial premium over the current market price of our shares. The primary purpose of these provisions is to encourage negotiations with our management by persons interested in acquiring control of our corporation. These provisions may also tend to perpetuate present management and make it difficult for stockholders owning less than a majority of the shares to be able to elect even a single director.

Computershare Trust Company, N.A. is presently the transfer agent and registrar for our common stock.

Table of Contents

With respect to each series of our Class C Preferred Stock, our board of directors has the authority to fix the following terms:

·                   the designation of the series;

·                   the number of shares within the series;

·                   whether dividends are cumulative and, if cumulative, the dates from which dividends are cumulative;

·                   the rate of any dividends, any conditions upon which dividends are payable, and the dates of payment of dividends;

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

·                   whether the shares are redeemable, the redemption price and the terms of redemption;

·                   the amount payable to you for each share you own if we dissolve or liquidate;

·                   whether the shares are convertible or exchangeable, the price or rate of conversion or exchange, and the applicable terms and conditions;

·                   any restrictions on issuance of shares in the same series or any other series;

·                   voting rights applicable to the series of preferred stock; and

·                   any other rights, priorities, preferences, restrictions or limitations of such series.

The rights with respect to any shares of our Class C Preferred Stock will be subordinate to the rights of our general creditors. Shares of our Class C Preferred Stock that we issue in accordance with their terms will be fully paid and nonassessable, and will not be entitled to preemptive rights unless specified in the applicable prospectus supplement.

Our ability to issue preferred stock, or rights to purchase such shares, could discourage an unsolicited acquisition proposal. For example, we could impede a business combination by issuing a series of preferred stock containing class voting rights that would enable the holders of such preferred stock to block a business combination transaction. Alternatively, we could facilitate a business combination transaction by issuing a series of preferred stock having sufficient voting rights to provide a required percentage vote of the stockholders. Additionally, under certain circumstances, our issuance of preferred stock could adversely affect the voting power of the holders of our common stock. Although our board of directors is required to make any determination to issue any preferred stock based on its judgment as to the best interests of our stockholders, our board of directors could act in a manner that would discourage an acquisition attempt or other transaction that some, or a majority, of our stockholders might believe to be in their best interests or in which stockholders might receive a premium for their stock over prevailing market prices of such stock. Our board of directors does not at present intend to seek stockholder approval prior to any issuance of currently authorized stock, unless otherwise required by law or applicable stock exchange requirements.

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

6

Table of Contents

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 other terms of the warrants, including terms, procedures and limitations relating to the exchange and exercise of the warrants;

·                   the date on which the right to exercise the warrants shall commence and the date on which the right shall expire;

·                   if applicable, the maximum or minimum number of warrants which may be exercised at any time;

·                   the identity of the warrant agent;

·                   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 the warrant certificate properly completed and duly executed at the corporate trust office of the warrant agent or any other office indicated in the applicable prospectus supplement, 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;

9

Table of Contents

·                   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

·                   whether the units will be issued in fully registered global form.

This summary of certain general terms of units and any summary description of units in the applicable prospectus supplement do not purport to be complete and are qualified in their entirety by reference to all provisions of the applicable unit agreement and, if applicable, collateral arrangements and depositary arrangements relating to such units. The forms of the unit agreements and other documents relating to a particular issue of units will be filed with the SEC each time we issue units, and you should read those documents for provisions that may be important to you.

PLAN OF DISTRIBUTION

We may sell the securities covered hereby from time to time pursuant to underwritten public offerings, direct sales to the public, negotiated transactions, block trades or a combination of these methods. A distribution of the securities offered by this prospectus may also be effected through the issuance of derivative securities, including without limitation, warrants and subscriptions. We may sell the securities to or through underwriters or dealers, through agents, or directly to one or more purchasers. We may distribute securities from time to time in one or more transactions:

·                   at a fixed price or prices, which may be changed;

·                   at market prices prevailing at the time of sale;

·                   at prices related to such prevailing market prices;

·                   at varying prices determined at the time of sale; or

·                   at negotiated prices.

·                   A prospectus supplement or supplements will describe the terms of the offering of the securities, including:

·                   the name or names of the underwriters, dealers or agents participating in the offering, if any;

·                   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

11

Table of Contents

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 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 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 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 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, New York, New York. If the validity of the securities offered hereby in connection with offerings made pursuant to this prospectus are passed upon by counsel for the

12

Table of Contents

underwriters, dealers or agents, 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 the Annual Report on Form 10-K/A for the year ended December 31, 2015 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.

The financial statements of Kolltan Pharmaceuticals, Inc., incorporated in this prospectus by reference to Celldex Therapeutics, Inc.’s Current Report on Form 8-K/A dated February 7, 2017, have been so incorporated in reliance upon the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in accounting and auditing.

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” into this prospectus the information we have filed with the SEC, which means that we can disclose important information to you by referring you to those documents. Any information that we file subsequently with the SEC will automatically update this prospectus. We incorporate by reference into this prospectus the information contained in the documents listed below, which is considered to be a part of this prospectus:

·       Our Annual Report on Form 10-K for the fiscal year ended December 31, 2015, filed with the SEC on February 23, 2016;

·                   Our Annual Report on Form 10-K/A for the fiscal year ended December 31, 2015, filed with the SEC on February 25, 2016;

·                   Our Quarterly Reports on Form 10-Q for the fiscal quarters ended March 31, 2016, June 30, 2016 and September 30, 2016, filed on May 5, 2016, August 8, 2016 and November 7, 2016, respectively;

·                   Our Current Reports on Form 8-K or 8-K/A filed with the SEC on February 23, 2016, March 7, 2016, May 19, 2016, June 9, 2016, August 11, 2016, November 1, 2016, November 29, 2016, as amended by Form 8-K/A filed on February 7, 2017, December 5, 2016, and December 14, 2016 (in each case, not including any information furnished under Items 2.02 or 7.01 of Form 8-K, including the related exhibits, which information is not incorporated by reference herein);

13

Table of Contents

·                   Our Definitive Proxy Statement on Schedule 14A, filed with the SEC on April 21, 2016 (other than the portions thereof which are furnished and not filed); and

·                   The description of our common stock contained in our Registration Statement on Form 8-A, filed on November 8, 2004, as amended by Form 8-A/A filed on October 22, 2007 and March 7, 2008.

We also incorporate by reference all documents we file under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act (a) after the initial filing date of the registration statement of which this prospectus is a part and before the effectiveness of the registration statement and (b) after the effectiveness of the registration statement and before the filing of a post-effective amendment that indicates that the securities offered by this prospectus have been sold or that deregisters the securities covered by this prospectus then remaining unsold. The most recent information that we file with the SEC automatically updates and supersedes older information. The information contained in any such filing will be deemed to be a part of this prospectus, commencing on the date on which the document is filed.

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:

Corporate Secretary

Celldex Therapeutics, Inc.

Perryville III Building, 53 Frontage Road, Suite 220,

Hampton, New Jersey 08827

(908) 200-7500

14

Table of Contents

Celldex Therapeutics, Inc.

Up to $75,000,000

Common Stock

PROSPECTUS SUPPLEMENT

November 9, 2017