Document:

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                                                                     Exhibit 4.3

                               [Face of Security]
                                 ANTIGENICS INC.

Certificate No. _______

          [INSERT PRIVATE PLACEMENT LEGEND AND GLOBAL SECURITY LEGEND]

                     5.25% Convertible Senior Note due 2025

                             CUSIP No. ____________

      Antigenics Inc., a Delaware corporation (the "COMPANY"), for value
received, hereby promises to pay to Cede & Co., or its registered assigns, the
principal sum of _____________________ dollars ($__________) on February 1, 2025
and to pay interest thereon, as provided on the reverse hereof, until the
principal and any unpaid and accrued interest are paid or duly provided for.

      Interest Payment Dates: February 1 and August 1, with the first payment to
be made on August 1, 2005.

      Record Dates: January 15 and July 15.

      The provisions on the back of this certificate are incorporated as if set
forth on the face hereof.

      IN WITNESS WHEREOF, Antigenics Inc. has caused this instrument to be duly
signed.

                                                     ANTIGENICS INC.

                                                     By: _______________________
                                                         Name:
                                                         Title:

Dated: _____________________

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TRUSTEE'S CERTIFICATE OF AUTHENTICATION

This is one of the Securities referred to in the within-mentioned Indenture.

HSBC BANK USA, NATIONAL ASSOCIATION, as Trustee

By: _____________________________________
             Authorized Signatory

Dated: _________________________

                                       -2-
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                              [REVERSE OF SECURITY]

                                 ANTIGENICS INC.

                     5.25% CONVERTIBLE SENIOR NOTE DUE 2025

      1.    INTEREST. Antigenics Inc., a Delaware corporation (the "COMPANY"),
promises to pay interest on the principal amount of this Security at the rate
per annum shown above. The Company will pay interest, payable semi-annually in
arrears, on February 1 and August 1 of each year, with the first payment to be
made on August 1, 2005. Interest on the Securities will accrue on the principal
amount from, and including, the most recent date to which interest has been paid
or provided for or, if no interest has been paid or provided for, from, and
including, January 25, 2005, in each case to, but excluding, the next interest
payment date or Maturity Date, as the case may be. Interest will be computed on
the basis of a 360-day year of twelve 30-day months.

      2.    MATURITY. The Securities will mature on February 1, 2025.

      3.    METHOD OF PAYMENT. Except as provided in the Indenture (as defined
below), the Company will pay interest on the Securities to the persons who are
Holders of record of Securities at the close of business on the record date set
forth on the face of this Security next preceding the applicable interest
payment date. Holders must surrender Securities to a Paying Agent to collect the
principal amount, Redemption Price, Option Purchase Price or Fundamental Change
Repurchase Price of the Securities, plus, if applicable, accrued and unpaid
interest, if any, payable as herein provided upon Redemption, Purchase at
Holder's Option or Repurchase Upon Fundamental Change, as the case may be. The
Company will pay, in money of the United States that at the time of payment is
legal tender for payment of public and private debts, all amounts due in cash
with respect to the Securities, which amounts shall be paid (A) in the case this
Security is in global form, by wire transfer of immediately available funds to
the account specified by the Holder hereof; or (B) in the case this Security is
held, other than global form, by a Holder who is the record holder of more than
five million dollars ($5,000,000) aggregate principal amount of Securities, by
wire transfer of immediately available funds to the account specified by such
Holder or, if no such account is specified, or if this Security is held, other
than in global form, by a Holder who is the record holder of five million
dollars ($5,000,000) or less in aggregate principal amount of Securities, by
mailing a check to such Holder's address shown in the register of the Registrar.

      4.    PAYING AGENT, REGISTRAR, CONVERSION AGENT. Initially, HSBC Bank USA,
National Association (the "TRUSTEE"), will act as Paying Agent, Registrar and
Conversion Agent. The Company may change any Paying Agent, Registrar or
Conversion Agent without notice.

      5.    INDENTURE. The Company issued the Securities under an Indenture
dated as of January 25, 2005 (the "INDENTURE") between the Company and the
Trustee. The terms of the Securities include those stated in the Indenture and
those made part of the Indenture by reference to the Trust Indenture Act of 1939
(15 U.S. Code Sections 77aaa-77bbbb) (the "TIA") as amended and in effect from
time to time. The Securities are subject to all such terms, and Holders are
referred to the Indenture and the TIA for a statement of such terms. The
Securities are general unsecured senior obligations of the Company limited to
$50,000,000 aggregate principal amount

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($60,000,000 if the Initial Purchasers have elected to exercise in full the
Option to purchase up to an additional $10,000,000 aggregate principal amount of
the Securities), except as otherwise provided in the Indenture (except for
Securities issued in substitution for destroyed, mutilated, lost or stolen
Securities). Terms used herein without definition and which are defined in the
Indenture have the meanings assigned to them in the Indenture.

      6.    OPTIONAL REDEMPTION.

            The Company shall have the right, at the Company's option, at any
time, and from time to time, on a Redemption Date on or after February 1, 2012,
to redeem all or any part of the Securities at a price payable in cash equal to
one hundred percent (100%) of the principal amount of the Securities to be
redeemed, plus accrued and unpaid interest, if any, to, but excluding, the
Redemption Date.

            Upon surrender to the Paying Agent of a Security subject to
Redemption, such Security shall be paid, to the Holder surrendering such
Security, at the Redemption Price plus accrued and unpaid interest to, but
excluding, the Redemption Date, unless the Redemption Date is an interest
payment date, in which case such accrued and unpaid interest will instead be
paid on such interest payment date to the Holder of record of such Security at
the close of business on the record date for such interest payment. The Company
will make at least fourteen (14) semi-annual interest payments with respect to
the Securities prior to redeeming any Securities under this PARAGRAPH 6.

            If the Paying Agent (other than the Company) holds on a Redemption
Date money sufficient to pay the aggregate Redemption Price with respect to all
Securities to be redeemed, plus accrued and unpaid interest, if any, payable as
provided in the Indenture upon Redemption, then (unless there shall be a Default
in the payment of such aggregate Redemption Price or of such accrued and unpaid
interest) on and after such date such Securities shall be deemed to be no longer
outstanding, interest on such Securities shall cease to accrue, and such
Securities shall be deemed paid whether or not such Securities are delivered to
the Paying Agent. Thereafter, all rights of the Holders of such Securities shall
terminate with respect to such Securities, other than the right to receive the
Redemption Price, plus such accrued and unpaid interest, in accordance with the
Indenture.

      7.    NOTICE OF REDEMPTION. Notice of Redemption will be mailed at least
thirty (30) days but not more than sixty (60) days before the Redemption Date to
each Holder of Securities to be redeemed at its address appearing in the
security register. Securities in denominations larger than $1,000 principal
amount may be redeemed in part but only in integral multiples of $1,000
principal amount.

      8.    PURCHASE BY THE COMPANY AT THE OPTION OF THE HOLDER. Subject to the
terms and conditions of the Indenture, the Company shall become obligated to
purchase, at the option of the Holder, the Securities held by such Holder on
February 1, 2012, February 1, 2015 and February 1, 2020 (each, an "OPTION
PURCHASE DATE") at an Option Purchase Price, payable in cash, equal to one
hundred percent (100%) of the principal amount of the Securities to be
purchased, plus accrued and unpaid interest, if any, to, but excluding, the
applicable Option Purchase Date, upon delivery of a Purchase Notice containing
the information set forth in the

                                       -4-
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Indenture, at any time from 9:00 a.m., New York City time, on the date that is
twenty (20) Business Days prior to the applicable Option Purchase Date until
5:00 p.m., New York City time, on the third (3rd) Business Day immediately
preceding the applicable Option Purchase Date and upon delivery of the
Securities to the Paying Agent by the Holder as set forth in the Indenture.

      Holders have the right to withdraw any Purchase Notice by delivering to
the Paying Agent a written notice of withdrawal in accordance with the
provisions of the Indenture.

      If the Paying Agent (other than the Company) holds on an Option Purchase
Date money sufficient to pay the aggregate Option Purchase Price with respect to
all Securities to be purchased upon Purchase at Holder's Option, plus accrued
and unpaid interest, if any, payable as provided in the Indenture upon Purchase
at Holder's Option, then (unless there shall be a Default in the payment of such
aggregate Option Purchase Price or of such accrued and unpaid interest) on and
after such date such Securities shall be deemed to be no longer outstanding,
interest on such Securities shall cease to accrue, and such Securities shall be
deemed paid whether or not such Securities are delivered to the Paying Agent.
Thereafter, all rights of the Holders of such Securities shall terminate with
respect to such Securities, other than the right to receive the Option Purchase
Price, plus such accrued and unpaid interest, in accordance with the Indenture.

      9.    REPURCHASE AT OPTION OF HOLDER UPON A FUNDAMENTAL CHANGE. Subject to
the terms and conditions of the Indenture, in the event of a Fundamental Change,
each Holder of the Securities shall have the right, at the Holder's option, to
require the Company to repurchase such Holder's Securities including any portion
thereof which is $1,000 in principal amount or any integral multiple thereof on
a date selected by the Company (the "FUNDAMENTAL CHANGE REPURCHASE DATE"), which
date is no later than thirty (30) days after the date on which notice of such
Fundamental Change is mailed in accordance with the Indenture, at a price
payable in cash equal to one hundred percent (100%) of the principal amount of
such Security, plus accrued and unpaid interest to, but excluding, the
Fundamental Change Repurchase Date.

      Within thirty (30) days after the occurrence of the Fundamental Change,
the Company must mail, or cause to be mailed, notice of the occurrence of such
Fundamental Change to each Holder at the address of such Holder appearing in the
register of the Registrar. Such notice shall include, among other things, a
description of the procedure which a Holder must follow to exercise the
Fundamental Change Repurchase Right. To exercise the Fundamental Change
Repurchase Right, a Holder of Securities must, in accordance with the provisions
of the Indenture, (i) deliver, no later than 5:00 p.m., New York City time, on
the third (3rd) Business Day immediately preceding the Fundamental Change
Repurchase Date, a Purchase Notice to the Company (if it is acting as its own
Paying Agent) or to the Paying Agent; and (ii) deliver, at any time after the
delivery of such Purchase Notice, the Securities with respect to which the
Holder is exercising its Fundamental Change Repurchase Right (together with all
necessary endorsements). If the Securities delivered in connection with a
Holder's exercise of its Fundamental Change Repurchase Right are held in
book-entry form through the Depositary, then such Purchase Notice must comply
with applicable procedures of the Depositary.

      10.   CONVERSION.

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      Subject to earlier Redemption, Purchase at Holder's Option or Repurchase
Upon Fundamental Change, Holders may surrender Securities in integral multiples
of $1,000 principal amount for conversion into shares of Common Stock in
accordance with ARTICLE X of the Indenture at any time prior to stated maturity.

      To convert a Security, a Holder must (1) complete and sign the Conversion
Notice, with appropriate signature guarantee, on the back of the Security, (2)
surrender the Security to a Conversion Agent, (3) furnish appropriate
endorsements and transfer documents if required by the Registrar or Conversion
Agent, (4) pay the amount of interest, if any, the Holder must pay in accordance
with the Indenture and (5) pay any tax or duty if required pursuant to the
Indenture. A Holder may convert a portion of a Security if the portion is $1,000
principal amount or an integral multiple of $1,000 principal amount.

      The initial Conversion Rate is 92.9023 shares of Common Stock per $1,000
principal amount of Securities (which results in an effective initial Conversion
Price of approximately $10.76 per share) subject to adjustment in the event of
certain circumstances as specified in the Indenture. The Company will deliver a
check in lieu of any fractional share. Except as other otherwise provided herein
or in the Indenture, on conversion, no payment or adjustment for any unpaid and
accrued interest on, or additional interest with respect to, the Securities will
be made. If a Holder surrenders a Security for conversion after the close of
business on the record date for the payment of an installment of interest and
prior to the related interest payment date, such Security, when surrendered for
conversion, must be accompanied by cash payment of an amount equal to the
interest thereon which the registered Holder at the close of business on such
record date is to receive (other than overdue interest, if any, that has accrued
on such Security), unless such Security has been called for Redemption as
described in the Indenture.

      The Conversion Rate applicable to each Security that is surrendered for
conversion, in accordance with the Securities and ARTICLE X of the Indenture, at
any time from, and including, the date that is fifteen (15) Business Days prior
to the date originally announced by the Company as the anticipated effective
date of a Make-Whole Fundamental Change until, and including, the date that is
fifteen (15) Business Days after the actual effective date of such Make-Whole
Fundamental Change shall be increased to an amount equal to the Conversion Rate
that would, but for SECTION 10.15 of the Indenture, otherwise apply to such
Security pursuant to ARTICLE X of the Indenture, plus an amount equal to the
Make-Whole Conversion Rate Adjustment; provided, however, that such increase to
the Conversion Rate shall not apply if (i) such Make-Whole Fundamental Change
constitutes a Public Acquirer Fundamental with respect to which the Company
shall have duly made, and given full effect to, an election, pursuant to and in
accordance with SECTION 10.15(F) of the Indenture, to make an Acquirer Stock
Conversion Right Adjustment; or (ii) such Make-Whole Fundamental Change is
announced by the Company but shall not be consummated.

      Any shares of Common Stock that are issued upon conversion of a Security
shall bear the Private Placement Legend until after the second anniversary of
the later of the Issue Date and the last date on which the Company or any
Affiliate was the owner of such shares or the Security (or any predecessor
security) from which such shares were converted (or such shorter period of time
as permitted by Rule 144(k) under the Securities Act or any successor provision
thereunder) (or such longer period of time as may be required under the
Securities Act or applicable state

                                       -6-
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securities laws, as set forth in an Opinion of Counsel, unless otherwise agreed
by the Company and the Holder thereof).

      11.   DENOMINATIONS, TRANSFER, EXCHANGE. The Securities are in registered
form, without coupons, in denominations of $1,000 principal amount and integral
multiples of $1,000 principal amount. The transfer of Securities may be
registered and Securities may be exchanged as provided in the Indenture. The
Registrar may require a Holder, among other things, to furnish appropriate
endorsements and transfer documents. No service charge shall be made for any
such registration of transfer or exchange, but the Company may require payment
of a sum sufficient to cover any tax or similar governmental charge that may be
imposed in connection with certain transfers or exchanges. The Company or the
Trustee, as the case may be, shall not be required to register the transfer of
or exchange any Security (i) during a period beginning at the opening of
business fifteen (15) days before the mailing of a notice of redemption of the
Securities selected for Redemption under SECTION 3.04 of the Indenture and
ending at the close of business on the day of such mailing or (ii) for a period
of fifteen (15) days before selecting, pursuant to SECTION 3.03 of the
Indenture, Securities to be redeemed or (iii) that has been selected for
Redemption or for which a Purchase Notice has been delivered, and not withdrawn,
in accordance with the Indenture, except the unredeemed or unrepurchased portion
of Securities being redeemed or repurchased in part.

      12.   PERSONS DEEMED OWNERS. The registered Holder of a Security may be
treated as the owner of such Security for all purposes.

      13.   MERGER OR CONSOLIDATION. Except as provided in the Indenture, the
Company shall not consolidate with, or merge with or into, or sell, transfer,
lease, convey or otherwise dispose of all or substantially all of the property
or assets of the Company to, another person, whether in a single transaction or
series of related transactions, unless (A) either (i) such transaction or series
of transactions shall be a merger or consolidation where the Company shall be
the surviving corporation; or (ii) the surviving, resulting or transferee person
both (a) is a corporation organized and existing under the laws of the United
States, any State thereof or the District of Columbia; and (b) assumes by
supplemental indenture all the obligations of the Company under the Securities
and the Indenture; and (B) immediately after giving effect to such transaction
or series of transactions, no Default or Event of Default shall exist.

      14.   AMENDMENTS, SUPPLEMENTS AND WAIVERS. Subject to certain exceptions,
the Indenture or the Securities may be amended or supplemented with the consent
of the Holders of at least a majority in aggregate principal amount of the
outstanding Securities, and certain existing Defaults or Events of Default may
be waived with the consent of the Holders of a majority in aggregate principal
amount of the Securities then outstanding. In accordance with the terms of the
Indenture, the Company, with the consent of the Trustee, may amend or supplement
this Indenture or the Securities without notice to or the consent of any
Securityholder: (i) to comply with SECTIONS 5.01 and 10.12 of the Indenture and,
in accordance with SECTION 10.15(F) of the Indenture, to give effect to an
election, pursuant to such SECTION 10.15(F), by the Company to make an Acquirer
Stock Conversion Right Adjustment with respect to a Public Acquirer Fundamental
Change; (ii) to make any changes or modifications to the Indenture necessary in
connection with the registration of the Securities under the Securities Act
pursuant to the Registration Rights Agreement or the qualification of the

                                       -7-
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Indenture under the TIA; (iii) to secure the obligations of the Company in
respect of the Securities; (iv) to add to the covenants of the Company described
in the Indenture for the benefit of Securityholders or to surrender any right or
power conferred upon the Company; (v) to make provisions with respect to
adjustments to the Conversion Rate as required by the Indenture or to increase
the Conversion Rate in accordance with the Indenture; (vi) to add additional
events which shall constitute an Event of Default under the Indenture; and (vii)
to provide for a successor Trustee in accordance with the Indenture. In
addition, the Company and the Trustee may enter into a supplemental indenture
without the consent of Holders of the Securities to cure any ambiguity, defect,
omission or inconsistency in the Indenture in a manner that does not
individually or in the aggregate adversely affect the rights of any Holder in
any material respect.

      15.   DEFAULTS AND REMEDIES. Subject to the provisions of the Indenture,
an "EVENT OF DEFAULT" occurs if (i) the Company defaults in the payment of the
principal of, or premium, if any, on, any Security when the same becomes due and
payable, whether at maturity, upon Redemption, on an Option Purchase Date with
respect to a Purchase at Holder's Option, on a Fundamental Change Repurchase
Date with respect to a Repurchase Upon Fundamental Change or otherwise; (ii) the
Company defaults in the payment of an installment of interest or additional
interest, on any Security when due, if such failure continues for thirty (30)
days after the date when due; (iii) the Company fails to satisfy its conversion
obligations upon exercise of a Holder's conversion rights pursuant to the
Indenture; (iv) the Company fails to timely provide a Fundamental Change Notice,
or an Option Purchase Notice, as required by the provisions of the Indenture;
(v) the Company fails to comply with any other term, covenant or agreement set
forth in the Securities or the Indenture and such failure continues for the
period, and after the notice, specified in the Indenture; (vi) the Company or
any of its Subsidiaries defaults in the payment when due, after the expiration
of any applicable grace period, of principal of, or premium, if any, or interest
on, Indebtedness of the Company or any Subsidiary for money borrowed, in the
aggregate principal amount then outstanding of ten million dollars ($10,000,000)
or more, or the acceleration of Indebtedness of the Company or any of its
Subsidiaries for money borrowed in such aggregate principal amount or more so
that it becomes due and payable prior to the date on which it would otherwise
become due and payable and such default is not cured or waived, or such
acceleration is not rescinded, within sixty (60) days after notice to the
Company by the Trustee or to the Company and the Trustee by Holders of at least
twenty five percent (25%) in the aggregate principal amount of the Securities
then outstanding, each in accordance with the Indenture; or (vii) there occur
certain events of bankruptcy or insolvency involving the Company or any of its
Significant Subsidiaries or any group of Subsidiaries that in the aggregate
would constitute a Significant Subsidiary of the Company.

      If an Event of Default (excluding an Event of Default specified in SECTION
6.01(vii) or (viii) of the Indenture with respect to the Company (but including
an Event of Default specified in SECTION 6.01(vii) or (viii) of the Indenture
solely with respect to a Significant Subsidiary of the Company or any group of
Subsidiaries that in the aggregate would constitute a Significant Subsidiary of
the Company)) occurs and is continuing, the Trustee by notice to the Company or
the Holders of at least twenty five percent (25%) in principal amount of the
Securities then outstanding by notice to the Company and the Trustee may declare
the Securities to be due and payable. Upon such declaration, the principal of,
and any premium and accrued and unpaid interest (including any additional
interest) on, all Securities shall be due and payable immediately. If an Event
of Default specified in SECTION 6.01(vii) or (viii) of the Indenture with

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respect to the Company (excluding, for purposes of this sentence, an Event of
Default specified in SECTION 6.01(vii) or (viii) of the Indenture solely with
respect to a Significant Subsidiary of the Company or any group of Subsidiaries
that in the aggregate would constitute a Significant Subsidiary of the Company)
occurs, the principal of, and premium and accrued and unpaid interest (including
any additional interest) on, all the Securities shall ipso facto become and be
immediately due and payable without any declaration or other act on the part of
the Trustee or any Holder. The Holders of a majority in aggregate principal
amount of the Securities then outstanding by written notice to the Trustee may
rescind or annul an acceleration and its consequences if (A) the rescission
would not conflict with any governmental or court order or decree, (B) all
existing Events of Default, except the nonpayment of principal, premium or
interest that has become due solely because of the acceleration, have been cured
or waived and (C) all amounts due to the Trustee under SECTION 7.07 of the
Indenture have been paid.

      Holders may not enforce the Indenture or the Securities except as provided
in the Indenture. The Holders of a majority in aggregate principal amount of the
Securities then outstanding may direct the time, method and place of conducting
any proceeding for any remedy available to the Trustee or exercising any trust
or power conferred on it. However, the Trustee may refuse to follow any
direction that conflicts with law or the Indenture, is unduly prejudicial to the
rights of other Holders or would involve the Trustee in personal liability
unless the Trustee is offered indemnity reasonably satisfactory to it ;
provided, that the Trustee may take any other action deemed proper by the
Trustee which is not inconsistent with such direction.

      If a Default or Event of Default occurs and is continuing as to which the
Trustee has received notice pursuant to the provisions of the Indenture, or as
to which a Responsible Officer of the Trustee shall have actual knowledge, then
the Trustee shall mail to each Holder a notice of the Default or Event of
Default within thirty (30) days after the Trustee has received such notice or
after such Responsible Officer shall have acquired such actual knowledge,
whichever is earlier, unless such Default or Event of Default has been cured or
waived; provided, however, that, except in the case of a Default or Event of
Default in payment of any amounts due with respect to any Security, the Trustee
may withhold such notice if, and so long as it in good faith determines that,
withholding such notice is in the best interests of Holders. The Company must
deliver to the Trustee an annual compliance certificate.

      16.   REGISTRATION RIGHTS. The Holders are entitled to registration rights
as set forth in the Registration Rights Agreement. The Holders shall be entitled
to receive additional interest in certain circumstances, all as set forth in the
Registration Rights Agreement.

      17.   TRUSTEE DEALINGS WITH THE COMPANY. The Trustee under the Indenture,
or any banking institution serving as successor Trustee thereunder, in its
individual or any other capacity, may make loans to, accept deposits from, and
perform services for, the Company or its Affiliates, and may otherwise deal with
the Company or its Affiliates, as if it were not Trustee.

      18.   NO RECOURSE AGAINST OTHERS. No past, present or future director,
officer, employee or stockholder, as such, of the Company shall have any
liability for any obligations of the Company under the Securities or the
Indenture or for any claim based on, in respect of, or by reason of, such
obligations or their creation. Each Holder, by accepting a Security, waives and

                                       -9-
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releases all such liability. The waiver and release are part of the
consideration for the issue of the Securities.

      19.   AUTHENTICATION. This Security shall not be valid until authenticated
by the manual signature of the Trustee or an authenticating agent in accordance
with the Indenture.

      20.   ABBREVIATIONS. Customary abbreviations may be used in the name of a
Holder or an assignee, such as: TEN COM (= tenants in common), TEN ENT (=
tenants by the entirety), JT TEN (= joint tenants with right of survivorship and
not as tenants in common), CUST (= Custodian), and U/G/M/A (Uniform Gifts to
Minors Act).

      THE COMPANY WILL FURNISH TO ANY HOLDER UPON WRITTEN REQUEST AND WITHOUT
CHARGE A COPY OF THE INDENTURE. REQUESTS MAY BE MADE TO:

                                 Antigenics Inc.
                                630 Fifth Avenue
                                   Suite 2100
                               New York, NY 10111

                                      -10-
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                              [FORM OF ASSIGNMENT]

I or we assign to

PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER

_________________________________________________________

________________________________________________________________________________
(please print or type name and address)

________________________________________________________________________________
________________________________________________________________________________

the within Security and all rights thereunder, and hereby irrevocably constitute
and appoint
________________________________________________________________________________

Attorney to transfer the Security on the books of the Company with full power of
substitution in the premises.

Dated: _______________________________   _______________________________________
                                         NOTICE: The signature on this
                                         assignment must correspond with the
                                         name as it appears upon the face of the
                                         within Security in every particular
                                         without alteration or enlargement or
                                         any change whatsoever and be guaranteed
                                         by a guarantor institution
                                         participating in the Securities
                                         Transfer Agents Medallion Program or in
                                         such other guarantee program acceptable
                                         to the Trustee.

Signature Guarantee: ___________________________________________________________

                                      -11-
<PAGE>

In connection with any transfer of this Security occurring prior to the date
which is the earlier of (i) the date of the declaration by the SEC of the
effectiveness of a registration statement under the Securities Act of 1933, as
amended, covering resales of this Security (which effectiveness shall not have
been suspended or terminated at the date of the transfer) and (ii) the Resale
Restriction Termination Date, the undersigned confirms that it is making, and it
has not utilized any general solicitation or general advertising in connection
with, the transfer:

                                   [Check One]

(1)    [ ]        to the Company or any Subsidiary thereof, or

(2)    [ ]        pursuant to, and in compliance with, the exemption from
                  registration provided by Rule 144A under the Securities Act of
                  1933, as amended, or

(3)    [ ]        pursuant to, and in compliance with, the exemption from
                  registration provided by Rule 144 under the Securities Act of
                  1933, as amended, or

(4)    [ ]        pursuant to, and in compliance with, an exemption from
                  registration under the Securities Act of 1933, as amended,
                  other than Rule 144A or Rule 144, or

(5)    [ ]        pursuant to an effective registration statement under the
                  Securities Act of 1933, as amended,

and, unless the box below is checked, the undersigned confirms that this
Security is not being transferred to an "affiliate" of the Company (an
"Affiliate") as defined in Rule 144 under the Securities Act of 1933, as
amended:

      [ ]   The transferee is an Affiliate of the Company. (If the Security is
transferred to an Affiliate, the restrictive legend must remain on the Security
for at least two (2) years following the date of the transfer.)

Unless one of the items (1) through (5) is checked, the Trustee will refuse to
register any of the Securities evidenced by this certificate in the name of any
person other than the registered Holder thereof; provided, however, that if item
(3) or (4) is checked, the Company or the Trustee may require, prior to
registering any such transfer of the Securities, in their sole discretion, such
written legal opinions, certifications and other information as the Trustee or
the Company have reasonably requested to confirm that such transfer is being
made pursuant to an exemption from, or in a transaction not subject to, the
registration requirements of the Securities Act of 1933, as amended. If item (2)
is checked, the purchaser must complete the certification below. If none of the
foregoing items are checked, the Trustee or Registrar shall not be obligated to
register this Security in the name of any person other than the Holder hereof
unless and until the conditions to any such transfer of registration set forth
herein and in the Indenture shall have been satisfied.

Dated: ______________________  Signed: ________________________
                                              (Sign exactly as name appears on
                                              the other side of this Security)

Signature Guarantee: _____________________________________________

                                      -12-
<PAGE>

TO BE COMPLETED BY PURCHASER IF (2) ABOVE IS CHECKED

The undersigned represents and warrants that it is purchasing this Security for
its own account or an account with respect to which it exercises sole investment
discretion and that it and any such account is a "qualified institutional buyer"
within the meaning of Rule 144A under the Securities Act of 1933, as amended,
and is aware that the sale to it is being made in reliance on Rule 144A and
acknowledges that it has received such information regarding the Company as the
undersigned has requested pursuant to Rule 144A and acknowledges that the
transferor is relying upon the undersigned's foregoing representations in order
to claim the exemption from registration provided by Rule 144A.

Dated: ______________________________   ________________________________________
                                        NOTICE: To be executed by an executive
                                        officer

                                      -13-
<PAGE>

                                CONVERSION NOTICE

To convert this Security in accordance with the Indenture, check the box: [ ]

To convert only part of this Security, state the principal amount to be
converted (must be in multiples of $1,000):

                              $ __________________

If you want the stock certificate made out in another person's name, fill in the
form below:

________________________________________________________________________________
(Insert other person's soc. sec. or tax I.D. no.)

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________
(Print or type other person's name, address and zip code)

________________________________________________________________________________

Date:______________    Signature(s): ___________________________________________

                                     ___________________________________________
                                     (Sign exactly as your name(s) appear(s) on
                                     the other side of this Security)

Signature(s) guaranteed by: ____________________________________________________
      (All signatures must be guaranteed by a guarantor institution
      participating in the Securities Transfer Agents Medallion Program or in
      such other guarantee program acceptable to the Trustee.)

                                      -14-
<PAGE>

                                 PURCHASE NOTICE

Certificate No. of Security: ___________

      If you want to elect to have this Security purchased by the Company
pursuant to SECTION 3.08 of the Indenture, check the box: [ ]

      If you want to elect to have this Security purchased by the Company
pursuant to SECTION 3.09 of the Indenture, check the box: [ ]

      If you want to elect to have only part of this Security purchased by the
Company pursuant to SECTIONS 3.08 or 3.09 of the Indenture, as applicable, state
the principal amount to be so purchased by the Company:

                    $ _______________________________________
                       (in an integral multiple of $1,000)

Date: __________________         Signature(s): _________________________________

                                 _______________________________________________
                                 (Sign exactly as your name(s) appear(s) on the
                                 other side of this Security)
Signature(s) guaranteed by:      _______________________________________________
                                 (All signatures must be guaranteed by a
                                 guarantor institution participating in the
                                 Securities Transfer Agents Medallion Program or
                                 in such other guarantee program acceptable to
                                 the Trustee.)

                                      -15-
<PAGE>

                                   SCHEDULE A

          SCHEDULE OF EXCHANGES OF INTERESTS IN THE GLOBAL SECURITY(1)

      The following exchanges of a part of this Global Security for an interest
in another Global Security or for Securities in certificated form, have been
made:

<TABLE>
<CAPTION>
                                                              Principal amount of
                  Amount of decrease                              this Global          Signature or
                  in Principal amount  Amount of Increase in  Security following   authorized signatory
                    of this Global      Principal amount of      such decrease      of Trustee or Note
Date of Exchange       Security        this Global Security       or increase           Custodian
<S>               <C>                  <C>                    <C>                  <C>
</TABLE>

------------------------
(1) This is included in Global Securities only.

                                      -16-
<PAGE>

                                                                     EXHIBIT B-1

                        FORM OF PRIVATE PLACEMENT LEGEND

THIS SECURITY AND THE COMMON STOCK ISSUABLE UPON CONVERSION OF THIS SECURITY
HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE
"SECURITIES ACT") OR ANY STATE SECURITIES LAWS, AND MAY NOT BE OFFERED, SOLD,
PLEDGED OR OTHERWISE TRANSFERRED EXCEPT IN ACCORDANCE WITH THE FOLLOWING
SENTENCE. BY ITS ACQUISITION HEREOF OR OF A BENEFICIAL INTEREST HEREIN, THE
ACQUIRER:

(1)   REPRESENTS THAT IT AND ANY ACCOUNT FOR WHICH IT IS ACTING IS A "QUALIFIED
INSTITUTIONAL BUYER" (WITHIN THE MEANING OF RULE 144A UNDER THE SECURITIES ACT)
AND THAT IT EXERCISES SOLE INVESTMENT DISCRETION WITH RESPECT TO EACH SUCH
ACCOUNT, AND

(2)   AGREES THAT IT WILL NOT DIRECTLY OR INDIRECTLY ENGAGE IN ANY HEDGING
TRANSACTIONS INVOLVING THIS SECURITY OR THE COMMON STOCK ISSUABLE UPON
CONVERSION OF THIS SECURITY UNLESS IN COMPLIANCE WITH THE SECURITIES ACT, AND

(3)   AGREES FOR THE BENEFIT OF THE COMPANY THAT IT WILL NOT OFFER, SELL, PLEDGE
OR OTHERWISE TRANSFER THIS SECURITY OR THE COMMON STOCK ISSUABLE UPON CONVERSION
OF THIS SECURITY, OR ANY BENEFICIAL INTEREST HEREIN OR THEREIN, PRIOR TO THE
DATE THAT IS THE LATER OF (X) TWO YEARS AFTER THE LATER OF THE ORIGINAL ISSUE
DATE HEREOF AND THE LAST DATE ON WHICH THE COMPANY OR ANY AFFILIATE OF THE
COMPANY WAS THE OWNER OF THIS SECURITY (OR ANY PREDECESSOR OF THIS SECURITY) OR
SUCH SHORTER PERIOD OF TIME AS PERMITTED BY RULE 144(K) UNDER THE SECURITIES ACT
OR ANY SUCCESSOR PROVISION THEREUNDER, AND (Y) SUCH LATER DATE, IF ANY, AS MAY
BE REQUIRED BY APPLICABLE LAW, EXCEPT ONLY:

      (A)   TO THE COMPANY OR ANY SUBSIDIARY THEREOF, OR

      (B)   PURSUANT TO A REGISTRATION STATEMENT WHICH HAS BECOME EFFECTIVE
            UNDER THE SECURITIES ACT, OR

      (C)   TO A QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A
            UNDER THE SECURITIES ACT, OR

      (D)   PURSUANT TO AN EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144
            UNDER THE SECURITIES ACT OR ANY OTHER AVAILABLE EXEMPTION FROM THE
            REGISTRATION REQUIREMENTS OF THE SECURITIES ACT.

PRIOR TO THE REGISTRATION OF ANY TRANSFER IN ACCORDANCE WITH (3)(C) ABOVE, A
DULY COMPLETED AND SIGNED CERTIFICATE (THE FORM OF WHICH MAY BE OBTAINED FROM
THE TRUSTEE) MUST BE DELIVERED TO THE TRUSTEE. PRIOR TO THE REGISTRATION OF ANY
TRANSFER IN ACCORDANCE WITH (3)(D) ABOVE, THE COMPANY AND THE TRUSTEE RESERVE
THE RIGHT TO REQUIRE THE DELIVERY OF SUCH LEGAL OPINIONS, CERTIFICATIONS OR
OTHER EVIDENCE AS MAY REASONABLY BE REQUIRED IN ORDER TO DETERMINE THAT THE
PROPOSED TRANSFER IS BEING MADE IN COMPLIANCE WITH THE SECURITIES ACT AND
APPLICABLE STATE SECURITIES LAWS. NO REPRESENTATION IS MADE AS TO THE

                                      -17-
<PAGE>

AVAILABILITY OF ANY EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF THE
SECURITIES ACT.

THIS SECURITY SHALL BE ENTITLED TO THE BENEFITS OF THAT CERTAIN REGISTRATION
RIGHTS AGREEMENT, DATED JANUARY 25, 2005, AMONG ANTIGENICS INC. AND THE OTHER
PARTIES THERETO.

                                      -18-
<PAGE>

                                                                     EXHIBIT B-2

                       FORM OF LEGEND FOR GLOBAL SECURITY

      Any Global Security authenticated and delivered hereunder shall bear a
legend (which would be in addition to any other legends required in the case of
a Restricted Security) in substantially the following form:

            THIS SECURITY IS A GLOBAL SECURITY WITHIN THE MEANING OF THE
      INDENTURE HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF A
      DEPOSITARY OR A NOMINEE OF A DEPOSITARY OR A SUCCESSOR DEPOSITARY. THIS
      SECURITY IS NOT EXCHANGEABLE FOR SECURITIES REGISTERED IN THE NAME OF A
      PERSON OTHER THAN THE DEPOSITARY OR ITS NOMINEE EXCEPT IN THE LIMITED
      CIRCUMSTANCES DESCRIBED IN THE INDENTURE, AND NO TRANSFER OF THIS SECURITY
      (OTHER THAN A TRANSFER OF THIS SECURITY AS A WHOLE BY THE DEPOSITARY TO A
      NOMINEE OF THE DEPOSITARY OR BY A NOMINEE OF THE DEPOSITARY TO THE
      DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY) MAY BE REGISTERED EXCEPT
      IN THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE.

            UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE
      OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), TO THE
      COMPANY OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE, OR PAYMENT,
      AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN
      SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC
      (AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS
      REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE OR
      OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL
      INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST
      HEREIN.

            TRANSFERS OF THIS GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS IN
      WHOLE, BUT NOT IN PART, TO NOMINEES OF CEDE & CO. OR TO A SUCCESSOR
      THEREOF OR SUCH SUCCESSOR'S NOMINEE AND TRANSFERS OF PORTIONS OF THIS
      GLOBAL SECURITY SHALL BE LIMITED TO TRANSFERS MADE IN ACCORDANCE WITH THE
      RESTRICTIONS SET FORTH IN SECTION 2.16 OF THE INDENTURE.

                                      -19-EXHIBIT 10.6.1

                                                  BOARD APPROVAL: MARCH 22, 2005
                                              SHAREHOLDER APPROVAL: MAY 24, 2005

                            CPI AEROSTRUCTURES, INC.
                    AMENDMENT TO PERFORMANCE EQUITY PLAN 2000

     Section 3.1 of the CPI Aerostructures, Inc. Performance Equity Plan 2000
("Plan") is hereby amended to increase the number of shares of common stock
reserved and available for issuance for distribution under the Plan from 830,000
shares of common stock to 1,230,000 shares of common stock.

                                       4

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