ANTIGENICS INC WARRANT

Exhibit 4.1

NEITHER THESE SECURITIES NOR THE SECURITIES FOR WHICH THESE SECURITIES ARE EXERCISABLE HAVE BEEN REGISTERED WITH THE SECURITIES AND EXCHANGE COMMISSION OR THE SECURITIES COMMISSION OF ANY STATE IN RELIANCE UPON AN EXEMPTION FROM REGISTRATION UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), AND, ACCORDINGLY, MAY NOT BE OFFERED OR SOLD EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT OR PURSUANT TO AN AVAILABLE EXEMPTION FROM, OR IN A TRANSACTION NOT SUBJECT TO, THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT AND IN ACCORDANCE WITH APPLICABLE STATE SECURITIES LAWS. THESE SECURITIES AND THE SECURITIES ISSUABLE UPON EXERCISE OF THESE SECURITIES MAY BE PLEDGED IN CONNECTION WITH A BONA FIDE MARGIN ACCOUNT OR OTHER LOAN SECURED BY SUCH SECURITIES.

ANTIGENICS INC

WARRANT

Antigenics Inc., a Delaware corporation (the “ Company ”), hereby certifies that, for value received,              or its registered assigns (including permitted transferees, the “ Holder ”), as registered owner of this warrant (the “ Warrant ”), is entitled to purchase from the Company up to a total of              shares (as adjusted from time to time as provided in Section 9 ) of Common Stock (as defined below), at an exercise price equal to $3.75 per share (as adjusted from time to time as provided in Section 9 , the “ Exercise Price ”), at any time and from time to time from and after October10, 2008 (the “ Initial Exercise Date ”) to and including April 9, 2013 (the “ Expiration Date ”), and subject to the following terms and conditions.

1. Definitions . The capitalized terms used herein and not otherwise defined shall have the meanings set forth below:

“ Affiliate ” of any specified Person means any other person or entity directly or indirectly controlling, controlled by or under direct or indirect common control with such specified Person. For purposes of this definition, “ control ” means the power to direct the management and policies of such Person or firm, directly or indirectly, whether through the ownership of voting securities, by contract or otherwise.

“ Commission ” means the United States Securities and Exchange Commission.

“ Common Stock ” means the common stock of the Company, $0.01 par value per share.

“ Eligible Market ” means any of the New York Stock Exchange, the American Stock Exchange or Nasdaq (as defined below), and any successor markets thereto.

“ Exchange Act ” means the Securities Exchange Act of 1934, as amended

“ Market Price ” shall mean (i) if the principal trading market for such securities is an exchange, the average of the last reported sale prices per share for the last ten previous Trading Days in which a sale was reported, as officially reported on any consolidated tape, (ii) if clause (i) is not applicable, the average of the closing bid price per share for the last ten previous Trading Days as set forth by Nasdaq or (iii) if clauses (i) and (ii) are not applicable, the average of the closing bid price per share for the last ten previous Trading Days as set forth in the National Quotation Bureau sheet listing for such securities. Notwithstanding the foregoing, if there is no reported sales price or closing bid price, as the case may be, on any of the ten Trading Days preceding the event requiring a determination of Market Price hereunder, then the Market Price shall be determined in good faith after reasonable investigation by resolution of the Board of Directors of the Company.

“ Nasdaq ” means the Nasdaq Global Market or Nasdaq Capital Market, and any successor markets thereto.

“ Other Securities ” refers to any capital stock (other than Common Stock) and other securities of the Company or any other Person which the Holder of this Warrant at any time shall be entitled to receive, or shall have received, pursuant to the terms hereof upon the exercise of this Warrant, in lieu of or in addition to Common Stock.

“ Person ” means any court or other federal, state, local or other governmental authority or other individual or corporation, partnership, trust, incorporated or unincorporated association, joint venture, limited liability company, joint stock company, government (or an agency or subdivision thereof) or other entity of any kind.

“ Trading Day ” means (a) any day on which the Common Stock is listed or quoted and traded on any Eligible Market or (b) if the Common Stock is not then quoted and traded on any Eligible Market, then a day on which trading occurs on the Nasdaq Global Market (or any successor thereto).

“ Warrant Shares ” shall initially mean shares of Common Stock and in addition may include Other Securities and Substituted Property (as defined in Section 9(e)(x) ) issued or issuable from time to time upon exercise of this Warrant.

2. Registration of Warrant . The Company shall register this Warrant, upon records to be maintained by the Company for that purpose (the “ Warrant Register ”), in the name of the record Holder hereof from time to time. The Company may deem and treat the registered Holder of this Warrant as the absolute owner hereof for the purpose of any exercise hereof or any distribution to the Holder, and for all other purposes.

-2-

3. Registration of Transfers . The Company shall register the transfer of any portion of this Warrant in the Warrant Register, upon surrender of this Warrant, with the Form of Assignment attached hereto as Appendix A duly completed and signed, to the Company at its address specified herein. Upon any such registration and transfer, a new warrant in substantially the form of a Warrant (any such new warrant, a “ New Warrant ”), evidencing the portion of this Warrant so transferred shall be issued to the transferee and a New Warrant evidencing the remaining portion of this Warrant not so transferred, if any, shall be issued to the transferring Holder. The acceptance of the New Warrant by the transferee thereof shall be deemed the acceptance by such transferee of all of the rights and obligations of a holder of a Warrant.

4. Exercise and Duration of Warrant .

(a) This Warrant shall be exercisable, either in its entirety or for a portion of the number of Warrant Shares, by the registered Holder at any time and from time to time from and after the Initial Exercise Date to and including the Expiration Date. At 5:00 P.M. New York City time on the Expiration Date, the portion of this Warrant not exercised prior thereto shall be and become void and of no value, and the Holder hereof shall have no right to purchase any additional Warrant Shares hereunder.

(b) A Holder may exercise this Warrant by delivering to the Company, in accordance with Section 13 , this Warrant, together with (i) an exercise notice, in the form attached hereto as Appendix B (the “ Exercise Notice ”), appropriately completed and duly signed, and (ii) (A) payment of the Exercise Price for the number of Warrant Shares as to which this Warrant is being exercised pursuant to a Cash Exercise (as set forth in Section 4(c) below) or (B) if available pursuant to Section 4(d) below, by notifying the Company that this Warrant is being exercised pursuant to a Cashless Exercise (as set forth in Section 4(d) below), and the date such items are received by the Company is an “ Exercise Date .” Execution and delivery of an Exercise Notice in respect of less than all of the Warrant Shares issuable upon exercise of this Warrant shall result in the cancellation of the original Warrant and issuance of a New Warrant evidencing the right to purchase the remaining number of Warrant Shares.

(c) Cash Exercise . In the event the Holder has elected to pay the Exercise Price in cash, it shall pay the Exercise Price by certified bank check payable to the order of the Company or by wire transfer of immediately available funds in accordance with the Company’s instructions (a “ Cash Exercise ”).

(d) Cashless Exercise . Notwithstanding anything contained herein to the contrary, if, at any time a registration statement covering the resale of the Warrant Shares that are the subject of the Exercise Notice by the Holder pursuant to the Securities Act (the “ Unavailable Warrant Shares ”) is not available for the resale of such Unavailable Warrant Shares, and the Company is otherwise obligated to have a resale registration statement available for such resale, the Holder may, in its sole discretion, exercise this Warrant in whole or in part and, in lieu of making the cash payment otherwise contemplated to be made to the Company upon such exercise in payment of the Exercise Price, elect instead to receive upon such exercise the “Net Number” of shares of Common Stock determined according to the following formula (a “ Cashless Exercise ”):

-3-

For purposes of the foregoing formula,

A = the total number of shares with respect to which this Warrant is then being exercised.

B = the weighted average price per share of the Common Stock (as reported by Bloomberg) on the Trading Day immediately preceding the date of the Exercise Notice.

C = the Exercise Price then in effect for the applicable Warrant Shares at the time of such exercise.

Notwithstanding anything to the contrary herein or in the Securities Purchase Agreement dated April 9, 2008 between the Company, the Holder, and other parties named therein (the “ Securities Purchase Agreement ”), the Holder agrees that the Holder’s ability to elect a Cashless Exercise if there is not an effective registration statement covering the Warrant Shares represents the sole and exclusive monetary remedy of the Holder for a registration default with respect to the Warrant Shares, and in no event shall the Company be required to satisfy the Warrants through net cash settlement.

(e) Except as otherwise provided for herein, this Warrant shall not entitle the Holder to any voting rights or other rights as a stockholder of the Company by virtue of the ownership hereof.

5. Delivery of Warrant Shares .

(a) Upon exercise of this Warrant, the Company shall promptly (but in no event later than three Trading Days after the Exercise Date) issue or cause to be issued and deliver or cause to be delivered to the Holder, in such name or names as the Holder may designate, a certificate for the Warrant Shares issuable upon such exercise (the “ Certificate ”) bearing no restrictive legends. The Holder, or any Person so designated by the Holder to receive the Warrant Shares, shall be deemed to have become holder of record of such Warrant Shares as of the Exercise Date.

(b) Neither these securities nor the securities for which these securities are exercisable have been registered with the Commission or the securities commission of any state in reliance upon an exemption from registration under the Securities Act, and, accordingly, may not be offered or sold except pursuant to an effective registration statement under the Securities Act or pursuant to an available exemption from, or in a transaction not subject to, the registration requirements of the Securities Act and in accordance with applicable state securities laws. The Holder acknowledges and agrees that the Warrant may be sold only pursuant to an applicable exemption from the registration requirements of the Securities Act and that the Warrant Shares may only be sold pursuant to an effective registration statement under the Securities Act or in accordance with any applicable exemption from the registration requirements of the Securities Act.

-4-

(c) This Warrant is exercisable, either in its entirety or, from time to time, for a portion of the number of Warrant Shares. Upon surrender of this Warrant following one or more partial exercises, the Company shall issue or cause to be issued, at its expense, a New Warrant evidencing the right to purchase the remaining number of Warrant Shares.

(d) To the extent permitted by law, the Company’s obligations to issue and deliver Warrant Shares in accordance with the terms hereof are absolute and unconditional, irrespective of any action or inaction by the Holder to enforce the same, any waiver or consent with respect to any provision hereof, the recovery of any judgment against any Person or any action to enforce the same, or any setoff, counterclaim, recoupment, limitation or termination, or any breach or alleged breach by the Holder or any other Person of any obligation to the Company or any violation or alleged violation of law by the Holder or any other Person, and irrespective of any other circumstance which might otherwise limit such obligation of the Company to the Holder in connection with the issuance of Warrant Shares. Nothing herein shall limit the Holder’s right to pursue any other remedies available to it hereunder, in equity including, without limitation, a decree of specific performance and/or injunctive relief with respect to the Company’s failure to timely deliver Common Stock upon exercise of this Warrant as required pursuant to the terms hereof.

6. Charges, Taxes and Expenses . Issuance and delivery of certificates for shares of Common Stock upon exercise of this Warrant shall be made without charge to the Holder for any issue or transfer tax, withholding tax, transfer agent fee or other incidental tax or expense in respect of the issuance of such certificates, all of which taxes and expenses shall be paid by the Company; provided , however , that the Company shall not be required to pay any tax which may be payable in respect of any transfer involved in the issue, delivery or registration of any certificates for Warrant Shares or Warrant in a name other than that of the Holder and that the Holder will be required to pay any tax with respect to cash received in lieu of fractional shares. The Holder shall be responsible for all other tax liability of the Holder that may arise as a result of holding or transferring this Warrant or receiving Warrant Shares upon exercise hereof.

7. Replacement of Warrant . If this Warrant is mutilated, lost, stolen or destroyed, the Company, at the sole expense of the Holder (such expenses, if any imposed by the Company to be reasonable), shall issue or cause to be issued in exchange and substitution for and upon cancellation hereof, or in lieu of and in substitution for this Warrant, a New Warrant, but only upon receipt of evidence reasonably satisfactory to the Company of such loss, theft or destruction and customary and reasonable indemnity, if requested by the Company.

8. Reservation of Warrant Shares . The Company covenants that it will at all times reserve and keep available out of the aggregate of its authorized but unissued and otherwise unreserved Common Stock, solely for the purpose of enabling it to issue Warrant Shares upon exercise of this Warrant as herein provided, the number of Warrant Shares which are then issuable and deliverable upon the exercise of this entire Warrant, free from all taxes, liens, claims, encumbrances with respect to the issuance of such Warrant Shares and will not be subject to any pre-emptive rights or similar rights (taking into account the adjustments and

-5-

restrictions of Section 9 hereof). The Company covenants that all Warrant Shares so issuable and deliverable shall, upon issuance and the payment of the applicable Exercise Price in accordance with the terms hereof, be duly and validly authorized, issued, fully paid and nonassessable. The Company will take all such action as may be necessary to assure that such shares of Common Stock may be issued as provided herein without violation of any applicable law or regulation, or of any requirements of any securities exchange or automated quotation system upon which the Common Stock may be listed or quoted, as the case may be.

9. Certain Adjustments . The Exercise Price and number of Warrant Shares issuable upon exercise of this Warrant are subject to adjustment from time to time as set forth in this Section 9.

(a) Stock Dividends . If the Company, at any time while this Warrant is outstanding, pays a dividend on its Common Stock payable in additional shares of Common Stock or otherwise makes a distribution on any class of capital stock that is payable in shares of Common Stock, then in each such case the Exercise Price shall be multiplied by a fraction, (A) the numerator of which shall be the number of shares of Common Stock outstanding immediately prior to the opening of business on the day after the record date for the determination of stockholders entitled to receive such dividend or distribution and (B) the denominator of which shall be the number of shares of Common Stock outstanding immediately after the distribution date of such dividend or distribution. Any adjustment made pursuant to this Section 9(a) shall become effective immediately after the record date for the determination of stockholders entitled to receive such dividend or distribution; provided, however , that if following such record date the Company rescinds or modifies such dividend or distribution, the Exercise Price shall be appropriately adjusted (as of the date that the Company effectively rescinds or modifies such dividend or distribution) to take into account the effect of such rescinded or modified dividend or distribution on the Exercise Price pursuant to this Section 9(a) .

(b) Stock Splits . If the Company, at any time while this Warrant is outstanding, (i) subdivides outstanding shares of Common Stock into a larger number of shares, or (ii) combines outstanding shares of Common Stock into a smaller number of shares, then in each such case the Exercise Price shall be multiplied by a fraction, (A) the numerator of which shall be the number of shares of Common Stock outstanding immediately before such event and (B) the denominator of which shall be the number of shares of Common Stock outstanding immediately after such event. Any adjustment pursuant to this Section 9(b) shall become effective immediately after the effective date of such subdivision or combination.

(c) Reclassifications . A reclassification of the Common Stock (other than any such reclassification in connection with a merger or consolidation to which Section 9(e) applies) into shares of any other class of stock shall be deemed:

(i) a distribution by the Company to the holders of its Common Stock of such shares of such other class of stock for the purposes and within the meaning of this Section 9 ; and

(ii) if the outstanding shares of Common Stock shall be changed into a larger or smaller number of shares of Common Stock as part of such reclassification, such change shall be deemed a subdivision or combination, as the case may be, of the outstanding shares of Common Stock for the purposes and within the meaning of Section 9(b) .

-6-

(d) Other Distributions . If the Company, at any time while this Warrant is outstanding, distributes to holders of Common Stock (i) evidences of its indebtedness, (ii) shares of any class of capital stock, (iii) rights or warrants to subscribe for or purchase any shares of any class of capital stock or (iv) any other asset, other than a distribution of Common Stock covered by Section 9(a) , (in each case, “ Distributed Property ”), then in each such case the Exercise Price in effect immediately prior to the record date fixed for determination of stockholders entitled to receive such distribution (and the Exercise Price thereafter applicable) shall be adjusted (effective on and after such record date) to equal the product of such Exercise Price multiplied by a fraction, (A) the numerator of which shall be Market Price on such record date less the then fair market value of the Distributed Property distributed in respect of one outstanding share of Common Stock, which, if the Distributed Property is other than cash or marketable securities, shall be as reasonably determined in good faith by the Board of Directors of the Company whose determination shall be described in a board resolution, and (B) the denominator of which shall be the Market Price on such record date; provided, however , that if following the record date for such distribution the Company rescinds or