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"anticipate," "estimate," "plans," "projects," "continuing," "ongoing," "expects," "management believes,” “we" "we believe,” “we intend”" "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’smanagement'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”"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.

RISK FACTORS

Investing in our securities involves significant risks. Before making an investment decision, you should carefully consider the risks and other information we include or incorporate by reference in this prospectus.prospectus and any prospectus supplement. In particular, you should consider the risk factors under the heading “Risk Factors”"Risk Factors" included in our most recent Annual Report on Form 10-K, or 10-K/A, as applicable, as may be revised or supplemented by our subsequent Quarterly Reports on Form 10-Q or Current Reports on Form 8-K, each of which are on file with the SEC and are incorporated herein by reference, and which may be amended, supplemented or superseded from time to time by other reports we file with the SEC in the future. The risks and uncertainties we have described are not the only ones facing our company. Additional risks and uncertainties not currently known to us or that we currently deem immaterial may also affect our business operations. Additional risk factors may be included in a prospectus supplement relating to a particular offering of securities. Our business, financial condition or results of operations could be materially adversely affected by any of these risks. The trading price of our securities could decline due to any of these risks, and you may lose all or part of your investment. This prospectus is qualified in its entirety by these risk factors.

USE OF PROCEEDS

AllUnless otherwise provided in the applicable prospectus supplement to this prospectus used to offer specific securities, we expect to use the net proceeds from any offering of securities by us for general corporate purposes, which may include acquisitions, capital expenditures, investments, payment of milestone payments, and the resalerepayment, redemption or refinancing of all or a portion of any indebtedness or other securities outstanding at a particular time, to fund our operations until we receive FDA approval of our products and are able to commercialize our products and to make

substantial investments to establish sales, marketing, quality control, and regulatory compliance capabilities in anticipation of FDA approval of our products. Pending the application of the net proceeds, we expect to invest the net proceeds in short-term, interest-bearing instruments with a maturity of three months or less at the date of purchase and consist primarily of investments in money market mutual funds with commercial banks and financial institutions or other investment-grade securities. Such investments may include depositing such net proceeds into, and maintaining cash balances with, financial institutions in excess of insured limits.

DESCRIPTIONS OF SECURITIES WE MAY OFFER

This prospectus contains summary descriptions of the common stock, preferred stock, warrants, depositary shares and units that we may offer and sell from time to time. The preferred stock may also be exchangeable for and/or convertible into shares of common stock or another series of preferred stock. When one or more of these securities are offered in the future, a prospectus supplement will explain the particular terms of the securities and the extent to which these general provisions may apply. These summary descriptions and any summary descriptions in the applicable prospectus supplement do not purport to be complete descriptions of the terms and conditions of each security and are qualified in their entirety by reference to our third restated certificate of incorporation, as amended, our by-laws and by applicable Delaware law and any other documents referenced in such summary descriptions and from which such summary descriptions are derived. If any particular terms of a security described in the applicable 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.

DESCRIPTION OF COMMON STOCK

As of June 10, 2020 we are authorized to issue up to 297,000,000 shares of common stock, $0.001 par value per share. As of June 10, 2020, approximately 20,675,269 shares of common stock were outstanding. All outstanding shares of our common stock offered by this prospectus will belongare fully paid and non-assessable. Our common stock is listed on the Nasdaq Capital Market under the symbol "CLDX".

The Board of Directors may, out of funds legally available, at any regular or special meeting, declare dividends to the selling stockholders identified in this prospectus under “Selling Stockholders.” We will not receive any proceeds from the sale or other disposition by the selling stockholdersholders of the shares of our common stock covered by this prospectus.as and when they deem expedient, subject to the rights of holders of the preferred stock, if any.

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.

SELLING STOCKHOLDERS

This prospectus covers an aggregateRights Upon Liquidation

In the event of 18,369,107our 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.

No holders of shares of our common stock thatshall 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 otherwise disposedoffered 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 the sellingsome of our stockholders and their transferees.  Such shares were issuedcould result in stockholders receiving a substantial premium over the current market price of our shares. The primary purpose of these provisions is to the sellingencourage 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 in the transactions described under the caption “Descriptionowning less than a majority of the Merger Transaction” above.shares to be able to elect even a single director.

4Computershare Trust Company, N.A. is presently the transfer agent and registrar for our common stock.

DESCRIPTION OF PREFERRED STOCK

At June 10, 2020, the Company had authorized preferred stock comprised of 3,000,000 shares of Class C Preferred Stock of which 350,000 shares has been designated as Class C-1 Junior Participating Cumulative Preferred Stock, the terms of which are to be determined by our Board of Directors. As of June 10, 2020, there was no preferred stock outstanding.

Class C Preferred Stock

This section describes the general terms and provisions of our Class C Preferred Stock. The following table sets forth certain information with respectapplicable prospectus supplement will describe the specific terms of the shares of preferred stock offered through that prospectus supplement, as well as any general terms described in this section that will not apply to each selling stockholder, including (i)those shares of preferred stock.

Our board of directors has been authorized to provide for the issuance of the 2,650,000 unissued and undesignated shares of our Class C Preferred Stock In general, our third restated certificate of incorporation, as amended, authorizes our board of directors to issue new shares of our common stock beneficially ownedor preferred stock without further stockholder action, provided that there are sufficient authorized shares.

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

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 sellingholders 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 this offering, (ii)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 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 being offered byincluded in a designated series and fix the selling stockholder pursuant to this prospectusdesignation, powers, privileges, preferences and (iii) the selling stockholder’s beneficial ownership after completion of this offering, assuming that allrights of the shares covered hereby are sold.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

The table is based on information available

third restated certificate of incorporation, as amended, before deciding to us as of January 24, 2017, with beneficial ownership and percentage ownership determined in accordance with the rules and regulations of the SEC and include voting or investment power with respect tobuy shares of stock.  This information does not necessarily indicate beneficial ownership for any other purpose.  In computingour 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, beneficially owned by a persondividend 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 percentage ownershiprights of that person, sharesthe holders of common stock subjectand, therefore, reduce the value of the common stock. The ability of our board of directors to any optionsissue preferred stock could discourage, delay or prevent a takeover or other convertible securities held by that person that are convertible or exercisable as of January 24, 2017, or convertible or exercisable within 60 days of January 24, 2017, are deemed outstanding.  Such shares, however, are not deemed outstanding for the purposes of computing the percentage ownership of any other person.  The percentage of beneficial ownership before and after this offering is based on 122,278,437 shares outstanding on January 24, 2017.corporate action.

The registrationterms of these sharesany particular series of commonpreferred stock does not mean that the selling stockholders will sell or otherwise dispose of all or any of those securities.  The selling stockholders may sell or otherwise dispose of all, a portion or none of such shares from time to time. We do not know the number of shares, if any, that will be offereddescribed in the prospectus supplement relating to that particular series of preferred stock, including, where applicable:

The description of the selling stockholders under this prospectus. Furthermore,terms of a particular series of preferred stock in the selling stockholders may have sold, transferred or disposedapplicable prospectus supplement will not be complete. You should refer to the applicable amendment to our third restated certificate of the sharesincorporation, as amended, for complete information regarding a series of common stock covered hereby in transactions exempt from the registration requirements of the Securities Act since the date on which the Company filed this prospectus.

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(1)         These accounts are managed by direct or indirect subsidiaries of FMR LLC.  Abigail P. Johnson is a Director, the Vice Chairman, the Chief Executive Officer and the President of FMR LLC.  Members of the Johnson family, including Abigail P. Johnson, are the predominant owners, directly or through trusts, of Series B voting common shares of FMR LLC, representing 49% of the voting power of FMR LLC. The Johnson family group and all other Series B shareholders have entered into a shareholders’ voting agreement under which all Series B voting common shares will be voted in accordance with the majority vote of Series B voting common shares. Accordingly, through their ownership of voting common shares and the execution of the shareholders’ voting agreement, members of the Johnson family may be deemed, under the Investment Company Act of 1940, to form a controlling group with respect to FMR LLC.  Neither FMR LLC nor Abigail P. Johnson has the sole power to vote or direct the voting of the shares owned directly by the various investment companies registered under the Investment Company Act (“Fidelity Funds”) advised by Fidelity Management & Research Company (“FMR Co”), a wholly owned subsidiary of FMR LLC, which power resides with the Fidelity Funds’ Boards of Trustees. Fidelity Management & Research Company carries out the voting of the shares under written guidelines established by the Fidelity Funds’ Boards of Trustees.

(2)   Elm Street Venture Associates, LLC is the general partner of Elm Street Ventures, LP.  Robert A. Bettigole is the managing partner of Elm Street Venture Associates, LLC and has voting and investment power over the securities held by Elm Street Ventures, LP.

(3)   Frederick C. Goggans is the managing partner of Frederick C. Goggans Family Partnership.

(4)   Thomas H. Glocer is a FINRA member.

(5)   Thomas M. Vertin is the President of VAE, LLC.

(6)   Andrew D. Wingate is the manager of KLP Enterprises, LLC and has the power to vote or dispose of the securities held by KLP Enterprises, LLC.  Each of KLP Enterprises, LLC and Andrew D. Wingate are deemed to beneficially own the securities held by KLP Enterprises, LLC.

(7)   HBM BioCapital Ltd. is the general partner of HBM BioCapital (EUR) L.P. and HBM BioCapital (USD) L.P.

(8)   Deerfield Mgmt, L.P. is the general partner of Deerfield Special Situations Fund, L.P.  Deerfield Management   Company, L.P. is the investment manager of Deerfield Special Situations Fund, L.P.  Mr. James E. Flynn is the sole member of the general partner of each of Deerfield Mgmt, L.P. and Deerfield Management Company, L.P.  Deerfield Mgmt, L.P., Deerfield Management Company, L.P. and James E. Flynn may be deemed to beneficially own the securities held by Deerfield Special Situations Fund, L.P.

(9)   Osage University GP, LP is the general partner of Osage University Partners I, L.P.  Osage Partners, LLC is the general partner of Osage University GP, LP.  William Harrington, Marc Singer and Robert Adelson are the members of Osage Partners, LLC and have shared voting and investment power over the securities held by Osage University Partners I, L.P.

(10) Leerink Swann Co-Investment Fund, LLC is a FINRA member and an affiliate of Leerink Partners LLC, a registered broker-dealer.  Leerink Partners LLC served as a joint book-running manager for underwritten public offerings completed by the Company in 2015 and 2013.

(11) Leerink Holdings LLC is a FINRA member and is the parent company of Leerink Partners LLC, a registered broker-dealer.  Leerink Partners LLC served as a joint book-running manager for underwritten public offerings completed by the Company in 2015 and 2013.

(12) The board of directors of Stanhope Gate Corp., the managing general partner of Beacon Company has the power to vote or dispose of the securities held by Beacon Company.  The board members are Joerg Fischer, Jonathan G. White and Philip J. Le Cornu.

(13) The board of directors of Rosebay Medical Company, Inc., the general partner of Rosebay Medical Company L.P. has the power to vote or dispose of the securities held by Rosebay Medical Company L.P.  The board members are Richard S. Sackler, M.D. and Jonathan D. Sackler.

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PLAN OF DISTRIBUTIONpreferred stock.

The selling stockholders, which as used herein includes anypreferred stock will, when issued against payment of their respective pledgees, donees, transferees, assigneesthe consideration payable therefor, be fully paid and or other successors-in-interest, may, from timenonassessable. Unless otherwise specified in the applicable prospectus supplement, each

series of preferred stock will, upon issuance, rank senior to time, sell any or all of their shares ofthe common stock covered herebyand on a parity in all respects with each other outstanding series of preferred stock. The NASDAQ Global Market or any other stock exchange, market or trading facility on which the securities are traded or in private transactions.  These sales may be at fixed or negotiated prices.  A selling stockholder may use any one or morerights of the following methods when selling securities:holders of our preferred stock will be subordinate to that of our general creditors.

·                                          ordinary brokerage transactions and transactions in which the broker dealer solicits purchasers;DESCRIPTION OF WARRANTS

·                                          block trades in which the broker dealer will attempt to sell the securities as agent but may position and resell a portionWe summarize below some of the block as principalprovisions that will apply to facilitate the transaction;

·                                          purchases by a broker dealer as principal and resale bywarrants unless the broker dealer for its account;

·                                          an exchange distribution in accordance with the rulesapplicable prospectus supplement provides otherwise. This summary may not contain all information that is important to you. The complete terms of the warrants will be contained in the applicable exchange;

·                                          privately negotiated transactions;

·                                          settlement of short sales entered into after the effective date ofwarrant certificate and warrant agreement. These documents have been or will be included or incorporated by reference as exhibits to the registration statement of which this prospectus is a part;part. You should read the warrant certificate and the warrant agreement. You should also read the prospectus supplement, which will contain additional information and which may update or change some of the information below.

·                                          in transactions through broker dealers that agree with the selling stockholders to sell a specified number of such securities at a stipulated price per security;

·                                          through the writingWe may issue, together with other securities or settlement of optionsseparately, warrants to purchase common stock, preferred stock or other hedging transactions, whether through an options exchange or otherwise;

·                                          one or more underwritten offerings on a firm commitment or best efforts basis;

·                                          a combination of any such methods of sale; or

·                                          any other method permitted pursuant to applicable law.

The selling stockholderssecurities. We may also sell securitiesissue the warrants under Rule 144 under the Securities Act, if available, rather than under this prospectus.

Broker dealers engaged by the selling stockholders may arrange for other brokers dealers to participate in sales.  Broker dealers may receive commissions or discounts from the selling stockholders (or, if any broker dealer acts as agent for the purchaser of securities, from the purchaser) in amountswarrant agreements to be negotiated, but, exceptentered into between us and a bank or trust company, as warrant agent, all as set forth in a supplement to this Prospectus,the applicable prospectus supplement. The warrant agent would act solely as our agent in the case of an agency transaction not in excess of a customary brokerage commission in compliance with FINRA Rule 2440; and in the case of a principal transaction a markup or markdown in compliance with FINRA IM-2440.

In connection with the salewarrants of the series being offered and would not assume any obligation or relationship of agency or trust for or with any holders or beneficial owners of warrants.

The applicable prospectus supplement will describe the following terms, where applicable, of warrants in respect of which this prospectus is being delivered:

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 interests therein,payments upon our liquidation, dissolution or winding-up or to exercise voting rights, if any.

Exercise of Warrants

Each warrant will entitle the selling stockholders may enter into hedging transactions with broker-dealersholder thereof to purchase such number of shares of common stock or preferred stock or other financial institutions,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:

DESCRIPTION OF DEPOSITARY SHARES

We summarize below some of the provisions that will apply to depositary shares unless the applicable prospectus supplement provides otherwise. This summary may not contain all information that is important to you. The complete terms of the depositary shares will be contained in the depositary agreement and depositary receipt applicable to any depositary shares. These documents have been or will be included or incorporated by reference as exhibits to the registration statement of which this prospectus is a part. You should read the depositary agreement and the depositary receipt. You should also read the prospectus supplement, which will contain additional information and which may in turn engage in short salesupdate or change some of the securitiesinformation below.

We may, at our option, elect to offer fractional or multiple shares of common stock or preferred stock, rather than single shares of common stock or preferred stock (to be set forth in the courseprospectus supplement relating to such depositary shares). In the event we elect to do so, depositary receipts evidencing depositary shares will be issued to the public.

The shares of hedgingcommon 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 positions they assume.holders of the depositary receipts. The selling stockholdersdepositary 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.

DESCRIPTION OF UNITS

We may also sell securities short and deliver these securities to close out their short positions, or loan or pledge the securities to broker-dealers that in turn may sell these securities.  The selling stockholders may also enter into option or other transactions with broker-dealers or other financial institutions or createissue units comprised of one or more derivativeof the other securities described in this prospectus in any combination. Each unit will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each included security. The unit agreement under which requirea unit is issued may provide that the deliverysecurities included in the unit may not be held or transferred separately, at any time or at any time before a specified date. The applicable prospectus supplement may describe:

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 broker-dealerunits. 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 other financial institutiona combination of these methods. A distribution of the securities offered by this prospectus whichmay also be effected through the issuance of derivative securities, such broker-dealerincluding without limitation, warrants and subscriptions. We may sell the securities to or other financial institutionthrough underwriters or dealers, through agents, or directly to one or more purchasers. We may resell pursuantdistribute securities from time to this prospectus (as supplementedtime in one or amended to reflect such transaction).more transactions:

The selling stockholders and any

Only underwriters broker-dealers or agents that participatenamed in the distributionprospectus supplement will be underwriters of the securities may be deemed to be “underwriters” withinoffered by the meaning of the Securities Act of 1933, and anyprospectus supplement.

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discounts, concessions, commissions or fees received by them and any profit on the resale of the securities sold by them may be deemed to be underwriting discounts and commissions.

The Company is required to pay certain fees and expenses incurred by the Company incident to the registration of the securities.  The Company has agreed to indemnify the selling stockholders against certain losses, claims, damages and liabilities, including liabilities under the Securities Act.

Because selling stockholders may be deemed to be “underwriters” within the meaning of the Securities Act, they will be subject to the prospectus delivery requirements of the Securities Act including Rule 172 thereunder.  In addition, any securities covered by this prospectus which qualify for sale pursuant to Rule 144 under the Securities Act may be sold under Rule 144 rather than under this prospectus. The selling stockholders have advised us that there is no underwriter or coordinating broker acting in connection with the proposed sale of the resale securities by the selling stockholders.

We agreed to keep this prospectus effective until the earlier of (i) the date on which the securities may be resold by the selling stockholders without registration and without regard to any volume or manner-of-sale limitations by reason of Rule 144, without the requirement for the Company to be in compliance with the current public information under Rule 144 under the Securities Act or any other rule of similar effect or (ii) all of the securities have been sold pursuant to this prospectus or Rule 144 under the Securities Act or any other rule of similar effect.  The resale securities will be sold only through registered or licensed brokers or dealers if required under applicable state securities laws. In addition, in certain states, the resale securities covered hereby may not be sold unless they have been registered or qualified for sale in the applicable state or an exemption from the registration or qualification requirement is available and is complied with.

The selling stockholders and other persons participatingIf 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 distributionmore 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 provisionsunderwriting 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 Exchange Actsecurities 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 1934, as amended,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 rulescommissions we must pay for solicitation of these contracts in the prospectus supplement.

We may provide agents and regulations thereunder,underwriters with indemnification against civil liabilities related to this offering, including Regulation M.  This regulationliabilities under the Securities Act, or contribution with respect to payments that the agents or underwriters may limitmake with respect to these liabilities. Agents and underwriters may engage in transactions with, or perform services for, us in the timingordinary course of purchasesbusiness.

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 salesmay 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, byother than our common stock which is listed on the selling stockholdersNasdaq Capital 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 any other person.  The anti-manipulation rulespenalty bids in accordance with Regulation M under the Securities Exchange ActAct. Overallotment involves sales in excess of 1934 may applythe offering size, which create a short position. Stabilizing transactions permit bids to salespurchase 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 and to the activities of the selling stockholders and their affiliates. Furthermore, Regulation M may restrict the ability of any person engaged inafter 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 Capital Market may engage in market-making activitiespassive market making transactions in the securities on the Nasdaq Capital Market in accordance with respectRegulation M, during the business day prior to the particular securities being distributed for a periodpricing of up to five business daysthe offering, before the distribution.  These restrictionscommencement 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 affectstabilize the marketabilitymarket price of the securities at a level above that which might otherwise prevail in the open market and, the ability ofif commenced, may be discontinued at any person or entity to engage in market-making activities with respect to the securities.time.

LEGAL MATTERS

TheUnless otherwise indicated in the applicable prospectus supplement, the validity of the shares of common stocksecurities 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 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 prospectusProspectus by reference to the Annual Report on Form 10-K/A10-K for the year ended December 31, 20152019 have been so incorporated in reliance on the report (which contains an explanatory paragraph relating to the Company’s ability to continue as a going concern as described in Note 1 to the financial statements) 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

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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’sSEC's website athttp://www.sec.gov. The SEC’sSEC'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 ishttp://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"incorporate by reference”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 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, 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);

·                                          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.

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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

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$150,000,000