Exhibit 10.1

ANTIGENICS INC.

1999 EQUITY INCENTIVE PLAN, AS AMENDED

SECTION 1. Purpose

The purpose of the Antigenics Inc. 1999 Equity Incentive Plan (the “Plan”) is to
attract and retain directors, key employees and consultants of the Company and
its Affiliates, to provide an incentive for them to achieve long-range
performance goals, and to enable them to participate in the long-term growth of
the Company.

SECTION 2. Definitions

“Affiliate” means any business entity that directly, or indirectly through one
or more intermediaries, controls, is controlled by or is under common control
with the Company. For purposes hereof, “Control” (and with correlative meanings,
the terms “controlled by” and “under common control with”) shall mean the
possession of the power to direct or cause the direction of the management and
policies of the Company, whether through the ownership of voting stock, by
contract or otherwise. In the case of a corporation “control” shall mean, among
other things, the direct or indirect ownership of more than fifty percent
(50%) of its outstanding voting stock.

“Award” means any Option, Stock Appreciation Right, Restricted Stock or
Unrestricted Stock awarded under the Plan.

“Board” means the Board of Directors of the Company.

“Code” means the Internal Revenue Code of 1986, as amended from time to time,
and any successor to such Code.

“Committee” means a committee of not less than two members of the Board
appointed by the Board to administer the Plan. If a Committee is authorized to
grant Options to a Reporting Person or a “covered employee” within the meaning
of Section 162(m) of the Code, each member shall be a “non-employee director” or
the equivalent within the meaning of Rule 16b-3 under the Securities Exchange
Act of 1934, as amended from time to time, or any successor law, and an “outside
director” or the equivalent within the meaning of Section 162(m) of the Code,
respectively. Until such committee is appointed, “Committee” means the Board.

“Common Stock” or “Stock” means the Common Stock, $0.01 par value, of the
Company.

“Company” means Antigenics Inc.

“Designated Beneficiary” means the beneficiary designated by a Participant, in a
manner determined by the Committee, to receive amounts due or exercise rights of
the Participant in the event of the Participant’s death. In the absence of an
effective designation by a Participant, “Designated Beneficiary” shall mean the
Participant’s estate.

“Effective Date” means November 15, 1999.

“Fair Market Value” means, with respect to Common Stock or any other property,
the fair market value of such property as determined by the Committee in good
faith or in the manner established by the Committee from time to time.

“Incentive Stock Option” means an option to purchase shares of Common Stock
awarded to a Participant under Section 6 that is intended to meet the
requirements of Section 422 of the Code or any successor provision.

“Nonstatutory Stock Option” means an option to purchase shares of Common Stock
awarded to a Participant under Section 6 that is not intended to be an Incentive
Stock Option.

“Option” means an Incentive Stock Option or a Nonstatutory Stock Option.

“Participant” means a person selected by the Committee to receive an Award under
the Plan.

“Reporting Person” means a person subject to Section 16 of the Securities
Exchange Act of 1934 or any successor provision.

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“Restricted Period” means the period of time selected by the Committee during
which an Award may be forfeited to the Company pursuant to the terms and
conditions of such Award.

“Restricted Stock” means shares of Common Stock subject to forfeiture awarded to
a Participant under Section 8.

“Stock Appreciation Right” or “SAR” means a right to receive any excess in value
of shares of Common Stock over the exercise price awarded to a Participant under
Section 7.

“Unrestricted Stock” means Stock not subject to any restrictions under the terms
of the Award.

SECTION 3. Administration

The Plan shall be administered by the Committee. The Committee shall have
authority to adopt, alter and repeal such administrative rules, guidelines and
practices governing the operation of the Plan as it shall from time to time
consider advisable, and to interpret the provisions of the Plan. The Committee’s
decisions shall be final and binding. To the extent permitted by applicable law,
the Committee may delegate to one or more executive officers of the Company the
power to make Awards to Participants who are not Reporting Persons or covered
employees and all determinations under the Plan with respect thereto, provided
that the Committee shall fix the maximum amount of such Awards for all such
Participants and a maximum for any one Participant.

SECTION 4. Eligibility

All employees, directors and consultants of the Company or any Affiliate capable
of contributing significantly to the successful performance of the Company,
other than a person who has irrevocably elected not to be eligible, are eligible
to be Participants in the Plan. Incentive Stock Options may be granted only to
persons eligible to receive such Options under the Code.

SECTION 5. Stock Available for Awards

(a) Subject to adjustment under subsection (b), Awards may be made under the
Plan for up to 10,000,000 shares of Common Stock. If any Award in respect of
shares of Common Stock expires or is terminated unexercised or is forfeited
without the Participant having had the benefits of ownership (other than voting
rights), the shares subject to such Award, to the extent of such expiration,
termination or forfeiture, shall again be available for award under the Plan.
Common Stock issued through the assumption or substitution of outstanding grants
from an acquired company shall not reduce the shares available for Awards under
the Plan. Shares issued under the Plan may consist in whole or in part of
authorized but unissued shares or treasury shares.

(b) In the event that the Committee determines that any stock dividend,
extraordinary cash dividend, creation of a class of equity securities,
recapitalization, reorganization, merger, consolidation, split-up, spin-off,
combination, exchange of shares, warrants or rights offering to purchase Common
Stock at a price substantially below fair market value, or other similar
transaction affects the Common Stock such that an adjustment is required in
order to preserve the benefits or potential benefits intended to be made
available under the Plan, then the Committee (subject, in the case of Incentive
Stock Options, to any limitation required under the Code) shall equitably adjust
any or all of (i) the number and kind of shares in respect of which Awards may
be made under the Plan, (ii) the number and kind of shares subject to
outstanding Awards, and (iii) the award, exercise or conversion price with
respect to any of the foregoing, and if considered appropriate, the Committee
may make provision for a cash payment with respect to an outstanding Award,
provided that the number of shares subject to any Award shall always be a whole
number.

(c) Subject to adjustment under Subsection (b): (i) the maximum number of shares
of Common Stock with respect to which Options and Stock Appreciation Rights may
be granted to any Participant in the aggregate in any calendar year shall not
exceed 1,000,000 shares, and (ii) the maximum number of shares of Common Stock
that may be granted as Restricted Stock, with respect to which performance goals
apply, to any Participant in the aggregate in any calendar year shall not exceed
1,000,000 shares.

SECTION 6. Stock Options

(a) Subject to the provisions of the Plan, the Committee may award Incentive
Stock Options and Nonstatutory Stock Options and determine the number of shares
to be covered by each Option, the option price therefor and the conditions and
limitations applicable to the exercise of the Option. The terms and conditions
of Incentive Stock Options shall be subject to and comply with Section 422 of
the Code or any successor provision and any regulations thereunder, and no
Incentive Stock Option may be granted hereunder more than ten years after the
Effective Date.

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(b) The Committee shall establish the option price at the time each Option is
awarded, which price shall not be less than 100% of the Fair Market Value of the
Common Stock on the date of award with respect to Incentive Stock Options.
Nonstatutory Stock Options may be granted at such prices as the Committee may
determine.

(c) Each Option shall be exercisable at such times and subject to such terms and
conditions as the Committee may specify in the applicable Award or thereafter.
The Committee may impose such conditions with respect to the exercise of
Options, including conditions relating to applicable federal or state securities
laws, as it considers necessary or advisable.

(d) No shares shall be delivered pursuant to any exercise of an Option until
payment in full of the option price therefor is received by the Company. Such
payment may be made in whole or in part in cash or, to the extent permitted by
the Committee at or after the award of the Option, by delivery of a note or
shares of Common Stock owned by the optionee, including Restricted Stock, or by
retaining shares otherwise issuable pursuant to the Option, in each case valued
at their Fair Market Value on the date of delivery or retention, or such other
lawful consideration as the Committee may determine.

SECTION 7. Stock Appreciation Rights

(a) Subject to the provisions of the Plan, the Committee may award SARs in
tandem with an Option (at or after the award of the Option), or alone and
unrelated to an Option. SARs in tandem with an Option shall terminate to the
extent that the related Option is exercised, and the related Option shall
terminate to the extent that the tandem SARs are exercised.

(b) The Committee shall fix the exercise price of each SAR or specify the manner
in which the price shall be determined. SARs granted in tandem with Options
shall have an exercise price not less than the exercise price of the related
Option. SARs granted alone and unrelated to an Option may be granted at such
exercise prices as the Committee may determine.

SECTION 8. Stock

(a) Subject to the provisions of the Plan, the Committee may award shares of
Restricted Stock and determine the duration of the Restricted Period during
which, and the conditions under which, the shares may be forfeited to the
Company and the other terms and conditions of such Awards. The Committee may
establish Performance goals for the granting or lapse of risk of forfeiture of
Restricted Stock. Such performance goals may be based on earnings per share,
revenues, sales or expense targets of the Company or any subsidiary, division or
product line thereof, stock price or such other business criteria as the
Committee may determine. Shares of Restricted Stock may be issued for no cash
consideration or such minimum consideration as may be required by applicable
law.

(b) Shares of Restricted Stock may not be sold, assigned, transferred, pledged
or otherwise encumbered, except as permitted by the Committee, during the
Restricted Period. Shares of Restricted Stock shall be evidenced in such manner
as the Committee may determine. Any certificates issued in respect of shares of
Restricted Stock shall be registered in the name of the Participant and unless
otherwise determined by the Committee, deposited by the Participant, together
with a stock power endorsed in blank, with the Company. At the expiration of the
Restricted Period, the Company shall deliver such certificates to the
Participant or if the Participant has died, to the Participant’s Designated
Beneficiary.

(c) Subject to the provisions of the Plan, the Committee may award shares of
Unrestricted Stock.

SECTION 9. General Provisions Applicable to Awards

(a) Documentation. Each Award under the Plan shall be evidenced by a writing
delivered to the Participant or agreement executed by the Participant specifying
the terms and conditions thereof and containing such other terms and conditions
not inconsistent with the provisions of the Plan as the Committee considers
necessary or advisable to achieve the purposes of the Plan or to comply with
applicable tax and regulatory laws and accounting principles.

(b) Committee Discretion. Each type of Award may be made alone, in addition to
or in relation to any other type of Award. The terms of each type of Award need
not be identical, and the Committee need not treat Participants uniformly.
Except as otherwise provided by the Plan or a particular Award, any
determination with respect to an Award may be made by the Committee at the time
of award or at any time thereafter.

(c) Settlement. The Committee shall determine whether Awards are settled in
whole or in part in cash, Common Stock, other securities of the Company, Awards
or other property. The Committee may permit a Participant to defer all or any
portion of a payment under the Plan, including the crediting of interest on
deferred amounts denominated in cash and dividend equivalents on amounts
denominated in Common Stock.

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(d) Dividends and Cash Awards. In the discretion of the Committee, any Award
under the Plan may provide the Participant with (i) dividends or dividend
equivalents payable currently or deferred with or without interest, and
(ii) cash payments in lieu of or in addition to an Award.

(e) Termination of Employment or Service on the Board. The Committee shall
determine the effect on an Award of the disability, death, retirement or other
termination of employment or service on the Board of a Participant and the
extent to which, and the period during which, the Participant’s legal
representative, guardian or Designated Beneficiary may receive payment of an
Award or exercise rights thereunder.

(f) Change in Control. In order to preserve a Participant’s rights under an
Award in the event of a change in control of the Company (as defined by the
Committee), the Committee in its discretion may, at the time an Award is made or
at any time thereafter, take one or more of the following actions: (i) provide
for the acceleration of any time period relating to the exercise or realization
of the Award, (ii) provide for the purchase of the Award upon the Participant’s
request for an amount of cash or other property that could have been received
upon the exercise or realization of the Award had the Award been currently
exercisable or payable, (iii) adjust the terms of the Award in a manner
determined by the Committee to reflect the change in control, (iv) cause the
Award to be assumed, or new rights substituted therefor, by another entity, or
(v) make such other provision as the Committee may consider equitable to
Participants and in the best interests of the Company.

(g) Loans. The Committee may authorize the making of loans or cash payments to
Participants in connection with any Award under the Plan, which loans may be
secured by any security, including Common Stock, underlying or related to such
Award (provided that such Loan shall not exceed the Fair Market Value of the
security subject to such Award), and which may be forgiven upon such terms and
conditions as the Committee may establish at the time of such loan or at any
time thereafter.

(h) Withholding Taxes. The Participant shall pay to the Company, or make
provision satisfactory to the Committee for payment of, any taxes required by
law to be withheld in respect of Awards under the Plan no later than the date of
the event creating the tax liability. In the Committee’s discretion, the minimum
tax obligations required by law to be withheld in respect of Awards may be paid
in whole or in part in shares of Common Stock, including shares retained from
the Award creating the tax obligation, valued at their Fair Market Value on the
date of retention or delivery. The Company and its Affiliates may, to the extent
permitted by law, deduct any such tax obligations from any payment of any kind
otherwise due to the Participant.

(i) Foreign Nationals. Awards may be made to Participants who are foreign
nationals or employed outside the United States on such terms and conditions
different from those specified in the Plan as the Committee considers necessary
or advisable to achieve the purposes of the Plan or to comply with applicable
laws.

(j) Amendment of Award. The Committee may amend, modify or terminate any
outstanding Award, including substituting therefor another Award of the same or
a different type, changing the date of exercise or realization and converting an
Incentive Stock Option to a Nonstatutory Stock Option, provided that the
Participant’s consent to such action shall be required unless the Committee
determines that the action, taking into account any related action, would not
materially and adversely affect the Participant.

(k) Transferability. In the discretion of the Committee, any Award may be made
transferable upon such terms and conditions and to such extent as the Committee
determines, provided that Incentive Stock Options may be transferable only to
the extent permitted by the Code. The Committee may in its discretion waive any
restriction on transferability.

SECTION 10. Miscellaneous

(a) No Right To Employment or Service on the Board. No person shall have any
claim or right to be granted an Award, and the grant of an Award shall not be
construed as giving a Participant the right to continued employment or service
on the Board. The Company expressly reserves the right at any time to dismiss a
Participant free from any liability or claim under the Plan, except as expressly
provided in the applicable Award.

(b) No Rights As Stockholder. Subject to the provisions of the applicable Award,
no Participant or Designated Beneficiary shall have any rights as a stockholder
with respect to any shares of Common Stock to be distributed under the Plan
until he or she becomes the holder thereof. A Participant to whom Common Stock
is awarded shall be considered the holder of the Stock at the time of the Award
except as otherwise provided in the applicable Award.

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(c) Effective Date. Subject to the approval of the stockholders of the Company,
the Plan shall be effective on the Effective Date. Before such approval, Awards
may be made under the Plan expressly subject to such approval.

(d) Amendment of Plan. The Board may amend, suspend or terminate the Plan or any
portion thereof at any time, subject to any stockholder approval that the Board
determines to be necessary or advisable.

(e) Governing Law. The provisions of the Plan shall be governed by and
interpreted in accordance with the laws of Delaware.

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This Plan was approved by the Board of Directors on November 15, 1999.

This Plan was approved by the Stockholders on May 18, 2000.

Amendment No. 1 to this Plan was approved by the Board of Directors on March 28,
2003.

Amendment No. 1 to this Plan was approved by the Stockholders on June 10, 2003.

Amendment No. 2 to this Plan was approved by the Board of Directors on April 8,
2004.

Amendment No. 2 to this Plan was approved by the Stockholders on May 26, 2004.

Amendment No. 3 to this plan was approved by the Board of Directors on March 16,
2006.

Amendment No. 3 to this plan was approved by the Stockholders on June 14, 2006.