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                                                                     EXHIBIT 4.2

                                 ANTIGENICS INC.

                          REGISTRATION RIGHTS AGREEMENT

January 25, 2005

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                          REGISTRATION RIGHTS AGREEMENT

            THIS REGISTRATION RIGHTS AGREEMENT (the "Agreement") is made and
      entered into as of January 25, 2005, by and among Antigenics Inc., a
      Delaware corporation (the "Company"), UBS Securities LLC, Moors & Cabot,
      Inc. and Brimberg & Co. (collectively, the "Initial Purchasers") pursuant
      to that certain Purchase Agreement, dated January 20, 2005 (the "Purchase
      Agreement"), among the Company and the Initial Purchasers.

            In order to induce the Initial Purchasers to enter into the Purchase
Agreement, the Company has agreed to provide the registration rights set forth
in this Agreement. The execution of this Agreement is a condition to the closing
under the Purchase Agreement. The terms "herein," "hereof," "hereto,"
"hereinafter" and similar terms, as used in this Agreement, shall in each case
refer to this Agreement as a whole and not to any particular section, paragraph,
sentence or other subdivision of this Agreement.

            The Company agrees with the Initial Purchasers (i) for their benefit
as Initial Purchasers and (ii) for the benefit of the beneficial owners
(including the Initial Purchasers) from time to time of the Covered Securities
(as defined herein) (each of the foregoing a "Holder" and, together, the
"Holders"), as follows:

      1. Definitions. Capitalized terms used herein without definition shall
have the respective meanings set forth in the Purchase Agreement. As used in
this Agreement, the following terms shall have the following meanings:

            (a) "Additional Filing Deadline Date" has the meaning set forth in
      Section 2(e) hereof.

            (b) "additional interest" has the meaning set forth in Section 2(e)
      hereof.

            (c) "Additional Interest Accrual Period" has the meaning set forth
      in Section 2(e) hereof.

            (d) "Additional Interest Amount" has the meaning set forth in
      Section 2(e) hereof.

            (e) "Additional Interest Payment Date" means each February 1 and
      August 1 of each year.

            (f) "Affiliate" means, with respect to any specified person, an
      "affiliate," as defined in Rule 144, of such person.

            (g) "Amendment Effectiveness Deadline Date" has the meaning set
      forth in Section 2(d) hereof.

            (h) "Business Day" means each day on which the New York Stock
      Exchange is open for trading.

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            (i) "Claim" has the meaning set forth in Section 9(o) hereof.

            (j) "Common Stock" means the shares of common stock, $0.01 par value
      per share, of the Company and any other shares of capital stock as may
      constitute "Common Stock" for purposes of the Indenture, including the
      Underlying Common Stock.

            (k) "Conversion Rate" has the meaning ascribed to it in the
      Indenture.

            (l) "counsel for the Initial Purchasers" means Dewey Ballantine LLP.

            (m) "Covered Security" has the meaning set forth in Section 1(rr)
      hereof.

            (n) "Designated Counsel" has the meaning set forth in Section 5
      hereof.

            (o) "Effectiveness Deadline Date" has the meaning set forth in
      Section 2(a) hereof.

            (p) "Effectiveness Period" means a period (subject to extension
      pursuant to Section 3(i) hereof) that terminates when there are no
      Registrable Securities outstanding.

            (q) "Event" has the meaning set forth in Section 2(e) hereof.

            (r) "Event Date" has the meaning set forth in Section 2(e) hereof.

            (s) "Exchange Act" means the Securities Exchange Act of 1934, as
      amended, and the rules and regulations of the SEC promulgated thereunder.

            (t) "Filing Deadline Date" has the meaning set forth in Section 2(a)
      hereof.

            (u) "Form S-1" means Form S-1 under the Securities Act.

            (v) "Form S-3" means Form S-3 under the Securities Act.

            (w) "Holder" has the meaning set forth in the preamble hereto.

            (x) "Holder Information" has the meaning set forth in Section 6(b)
      hereof.

            (y) "Indemnified Party" has the meaning set forth in Section 6(c)
      hereof.

            (z) "Indemnifying Party" has the meaning set forth in Section 6(c)
      hereof.

            (aa) "Indenture" means the Indenture, dated as of January 25, 2005,
      between the Company and the Trustee, pursuant to which the Notes are being
      issued.

            (bb) "Initial Purchasers" has the meaning set forth in the preamble
      hereto.

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            (cc) "Initial Shelf Registration Statement" has the meaning set
      forth in Section 2(a) hereof.

            (dd) "Issue Date" means January 25, 2005.

            (ee) "Material Event" has the meaning set forth in Section 3(i)
      hereof.

            (ff) "Notes" means the 5.25% Convertible Senior Notes due 2025 of
      the Company to be purchased pursuant to the Purchase Agreement.

            (gg) "Notice and Questionnaire" means a written questionnaire
      containing substantially the information called for by the Selling
      Securityholder Questionnaire attached as Annex A to the Offering
      Memorandum of the Company, dated January 20, 2005, relating to the Notes
      (the "Offering Memorandum").

            (hh) "Notice Holder" means, on a given date, any Holder that has
      delivered a Notice and Questionnaire to the Company on or prior to such
      date, provided not all of such Holder's Registrable Securities that have
      been registered for resale pursuant to a Notice and Questionnaire have
      been sold in accordance with a Shelf Registration Statement.

            (ii) "Offering Memorandum" has the meaning set forth in Section
      1(gg) hereof.

            (jj) "Option Purchase Date" has the meaning ascribed to it in the
      Indenture.

            (kk) "Proceeding" has the meaning set forth in Section 6(c) hereof.

            (ll) "Prospectus" means the prospectus included in any Shelf
      Registration Statement (including, without limitation, a prospectus that
      discloses information previously omitted from a prospectus filed as part
      of an effective registration statement in reliance upon Rule 415 under the
      Securities Act), as amended or supplemented by any amendment or prospectus
      supplement, including post-effective amendments and any prospectus filed
      with respect to any Shelf Registration Statement pursuant to Rule 424
      under the Securities Act, and all materials incorporated by reference or
      deemed to be incorporated by reference in such Prospectus.

            (mm) "Purchase Agreement" has the meaning set forth in the preamble
      hereof.

            (nn) "Record Date" means, (i) January 15, with respect to an
      Additional Interest Payment Date that occurs on February 1 and (ii) July
      15, with respect to an Additional Interest Payment Date that occurs on
      August 1.

            (oo) "Record Holder" means, with respect to an Additional Interest
      Payment Date relating to a Registrable Security for which any Additional
      Interest Amount has

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      accrued, a Notice Holder that was the holder of record of such Registrable
      Security at the close of business on the Record Date relating to such
      Additional Interest Payment Date.

            (pp) "Redemption" has the meaning ascribed to it in the Indenture.

            (qq) "Redemption Date" has the meaning ascribed to it in the
      Indenture.

            (rr) "Registrable Securities" means the Notes, until such Notes have
      been converted into the Underlying Common Stock, and, at all times, the
      Underlying Common Stock and any securities into or for which such
      Underlying Common Stock has been converted or exchanged, and any security
      issued with respect thereto upon any stock dividend, split or similar
      event (each of the foregoing, a "Covered Security") until, in the case of
      any such security, the earliest of:

                  (i) the date on which such security has been effectively
            registered under the Securities Act and disposed of in accordance
            with the Registration Statement relating thereto;

                  (ii) the date on which such security may be resold without
            restriction pursuant to Rule 144(k) or any successor provision
            thereto;

                  (iii) the date on which such security has been publicly sold
            pursuant to Rule 144 or any successor provision thereto; and

                  (iv) the date that is two (2) years after the later of the
            Issue Date and the latest "additional time of purchase" (as defined
            in the Purchase Agreement).

            (ss) "Registration Expenses" has the meaning set forth in Section 5
      hereof.

            (tt) "Registration Statement" means any registration statement,
      under the Securities Act, of the Company that covers any of the
      Registrable Securities pursuant to this Agreement, including the
      Prospectus forming, or deemed to form, a part of such registration
      statement, any amendments and supplements to such registration statement,
      including post-effective amendments, all exhibits and all materials
      incorporated by reference or deemed to be incorporated by reference in
      such registration statement, Prospectus, amendment or supplement.

            (uu) "Repurchase at Holder's Option" has the meaning ascribed to it
      in the Indenture.

            (vv) "Repurchase Date" has the meaning ascribed to it in the
      Indenture.

            (ww) "Repurchase Upon Repurchase Event" has the meaning ascribed to
      it in the Indenture.

            (xx) "Rule 144" means Rule 144 under the Securities Act, as such
      Rule may be

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      amended from time to time, or any similar rule or regulation hereafter
      adopted by the SEC.

            (yy) "Rule 144A" means Rule 144A under the Securities Act, as such
      Rule may be amended from time to time, or any similar rule or regulation
      hereafter adopted by the SEC.

            (zz) "SEC" means the Securities and Exchange Commission.

            (aaa) "Securities Act" means the Securities Act of 1933, as amended,
      and the rules and regulations promulgated by the SEC thereunder.

            (bbb) "Shelf Registration Statement" means the Initial Shelf
      Registration Statement and any Subsequent Shelf Registration Statement.

            (ccc) "Subsequent Shelf Registration Statement" has the meaning set
      forth in Section 2(b) hereof.

            (ddd) "Subsequent Shelf Registration Statement Effectiveness
      Deadline Date" has the meaning set forth in Section 2(d) hereof.

            (eee) "Suspension Notice" has the meaning set forth in Section 3(i)
      hereof.

            (fff) "Suspension Period" has the meaning set forth in Section 3(i)
      hereof.

            (ggg) "TIA" means the Trust Indenture Act of 1939, as amended.

            (hhh) "Trustee" means HSBC Bank USA, National Association, the
      trustee under the Indenture.

            (iii) "Underlying Common Stock" means the Common Stock issuable upon
      conversion of the Notes.

      2. Shelf Registration.

            (a) The Company shall prepare and file, or cause to be prepared and
      filed, with the SEC, by the date (the "Filing Deadline Date") that is one
      hundred and twenty (120) days after the Issue Date, a Registration
      Statement (the "Initial Shelf Registration Statement") for an offering to
      be made on a delayed or continuous basis pursuant to Rule 415 under the
      Securities Act registering the resale from time to time by Holders thereof
      of all of the Registrable Securities (or, if registration of Registrable
      Securities not held by Notice Holders is not permitted by the rules and
      regulations of the SEC, then registering the resale from time to time by
      Notice Holders of their Registrable Securities). The Initial Shelf
      Registration Statement shall be on Form S-1 or Form S-3 or another
      appropriate form and shall provide for the registration of such
      Registrable Securities for resale by such Holders in accordance with the
      methods of distribution indicated in their

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      Notice and Questionnaires and permitted by the form of Notice and
      Questionnaire included in the Offering Memorandum; provided, however, that
      in no event shall such methods of distribution take the form of an
      underwritten offering of Registrable Securities without the Company's
      prior written consent, which the Company may withhold in its sole
      discretion. The Company shall use its reasonable best efforts to (i) cause
      the Initial Shelf Registration Statement to become effective under the
      Securities Act as promptly as reasonably practicable but in any event by
      the date (the "Effectiveness Deadline Date") that is one hundred eighty
      (180) days after the Issue Date and (ii) (except to the extent permitted
      under Section 3(i) hereof) keep the Initial Shelf Registration Statement
      (and any Subsequent Shelf Registration Statement) continuously effective
      under the Securities Act until the expiration of the Effectiveness Period.
      At the time the Initial Shelf Registration Statement becomes effective
      under the Securities Act, each Holder that became a Notice Holder on or
      before the fifth (5th) Business Day before the date of such effectiveness
      shall be named as a selling securityholder in the Initial Shelf
      Registration Statement and the related Prospectus in a manner that,
      assuming the accuracy of the information in such Notice Holder's Notice
      and Questionnaire, permits such Notice Holder to deliver such Prospectus
      to purchasers of Registrable Securities in accordance with the Securities
      Act.

            (b) If any Shelf Registration Statement ceases to be effective under
      the Securities Act for any reason (except to the extent permitted under
      Section 3(i) hereof) at any time during the Effectiveness Period, the
      Company shall use its reasonable best efforts to promptly cause such Shelf
      Registration Statement to become effective under the Securities Act
      (including obtaining the prompt withdrawal of any order suspending the
      effectiveness of such Shelf Registration Statement), and in any event
      shall, within thirty (30) days of such cessation of effectiveness, (i)
      amend such Shelf Registration Statement in a manner reasonably expected to
      obtain the withdrawal of any order suspending the effectiveness of such
      Shelf Registration Statement or (ii) file an additional Registration
      Statement (a "Subsequent Shelf Registration Statement") for an offering to
      be made on a delayed or continuous basis pursuant to Rule 415 of the
      Securities Act registering the resale from time to time by Holders thereof
      of all securities that are Registrable Securities as of the time of such
      filing (or, if registration of Registrable Securities not held by Notice
      Holders is not permitted by the rules and regulations of the SEC, then
      registering the resale from time to time by Notice Holders of their
      securities that are Registrable Securities as of the time of such filing).
      If a Subsequent Shelf Registration Statement is filed, the Company shall
      use its reasonable best efforts to (A) cause such Subsequent Shelf
      Registration Statement to become effective under the Securities Act as
      promptly as practicable after such filing, but in no event later than the
      Subsequent Shelf Registration Statement Effectiveness Deadline Date and
      (B) except to the extent permitted under Section 3(i) hereof, keep such
      Subsequent Shelf Registration Statement (or another Subsequent Shelf
      Registration Statement) continuously effective until the end of the
      Effectiveness Period. Any such Subsequent Shelf Registration Statement
      shall be on Form S-1 or Form S-3 or another appropriate form and shall
      provide for the registration of such Registrable Securities for resale by
      such Holders in accordance with the methods of distribution indicated in
      their Notice and Questionnaires and permitted by the form of Notice and
      Questionnaire included in the Offering Memorandum; provided, however,

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      that in no event shall such methods of distribution take the form of an
      underwritten offering of Registrable Securities without the Company's
      prior written consent, which the Company may withhold in its sole
      discretion.

            (c) The Company shall supplement and amend any Shelf Registration
      Statement if required by the rules, regulations or instructions applicable
      to the registration form used by the Company for such Shelf Registration
      Statement, if required by the Securities Act or as reasonably requested by
      the Initial Purchasers.

            (d)

                  (i) Each Holder of Registrable Securities agrees that, if such
            Holder wishes to sell Registrable Securities pursuant to a Shelf
            Registration Statement and related Prospectus, it will do so only in
            accordance with this Section 2(d) and Section 3(i). Each Holder of
            Registrable Securities wishing to sell Registrable Securities
            pursuant to a Shelf Registration Statement and related Prospectus
            agrees to deliver a completed and executed Notice and Questionnaire
            to the Company prior to any attempted or actual distribution of
            Registrable Securities under a Shelf Registration Statement. If a
            Holder becomes a Notice Holder after the fifth (5th) Business Day
            before the date the Initial Shelf Registration Statement becomes
            effective under the Securities Act, the Company shall, as promptly
            as reasonably practicable after the date such Holder became a Notice
            Holder, and in any event, subject to clauses (A), (B) and (D) below,
            within five (5) Business Days after such date,

                        (A) if required by applicable law, file with the SEC a
                  supplement to the related Prospectus or a post-effective
                  amendment to the Shelf Registration Statement or file with the
                  SEC a Subsequent Shelf Registration Statement and any
                  necessary supplement or amendment to any document incorporated
                  therein by reference and file any other required document with
                  the SEC so that such Notice Holder is named as a selling
                  securityholder in a Shelf Registration Statement and the
                  related Prospectus in such a manner as to permit such Notice
                  Holder to deliver a Prospectus to purchasers of the
                  Registrable Securities in accordance with the Securities Act;
                  provided, however, that (i) with respect to any Holder that
                  shall become a Notice Holder after the date that is forty five
                  (45) days after the date the Initial Shelf Registration
                  becomes effective under the Securities Act, the Company shall
                  not be required to file more than one (1) such supplement
                  during any thirty (30) day period, and (ii) if a
                  post-effective amendment or a Subsequent Shelf Registration
                  Statement is required by the rules and regulations of the SEC
                  in order to permit resales by such Notice Holder, the Company
                  shall not be required to file more than one (1) post-effective
                  amendment or Subsequent Shelf Registration Statement for such
                  purpose in any ninety (90) day period;

                        (B) if the Company shall have filed a post-effective
                  amendment

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                  to the Shelf Registration Statement or filed a Subsequent
                  Shelf Registration Statement, the Company shall use its
                  reasonable best efforts to cause such post-effective amendment
                  or Subsequent Shelf Registration Statement, as the case may
                  be, to become effective under the Securities Act as promptly
                  as practicable, but in any event by the date (the "Amendment
                  Effectiveness Deadline Date," in the case of a post-effective
                  amendment, and the "Subsequent Shelf Registration Statement
                  Effectiveness Deadline Date," in the case of a Subsequent
                  Shelf Registration Statement) that is forty five (45) days
                  after the date such post-effective amendment or Subsequent
                  Shelf Registration Statement, as the case may be, is required
                  by this Section 2(d) to be filed with the SEC;

                        (C) the Company shall, upon request, provide such Notice
                  Holder a reasonable number of copies of any documents filed
                  pursuant to clause (A) above;

                        (D) if such Holder became a Notice Holder during a
                  Suspension Period, or a Suspension Period is put into effect
                  within five (5) Business Days after the date such Holder
                  became a Notice Holder, the Company shall so inform such
                  Notice Holder and shall, subject to the limitations set forth
                  above in this Section 2(d), take the actions set forth in
                  clauses (A), (B) and (C) above within five (5) Business Days
                  after expiration of such Suspension Period in accordance with
                  Section 3(i);

                        (E) the Company shall notify such Notice Holder as
                  promptly as practicable after the effectiveness under the
                  Securities Act of any post-effective amendment or Subsequent
                  Shelf Registration Statement filed pursuant to clause (A)
                  above; and

                        (F) if, under the Securities Act, the Company has more
                  than one option as to the type or manner of making any such
                  filing, the Company shall make the required filing or filings
                  in the manner or of a type that the Company reasonably expects
                  will result in the earliest availability of a Prospectus for
                  effecting resales of Registrable Securities.

                  (ii) Notwithstanding anything contained herein to the
            contrary, the Company shall be under no obligation to name any
            Holder that is not a Notice Holder as a selling securityholder in
            any Shelf Registration Statement or related Prospectus; provided,
            however, that any Holder that becomes a Notice Holder (regardless of
            when such Holder became a Notice Holder) shall be named as a selling
            securityholder in a Shelf Registration Statement or related
            Prospectus in accordance with the requirements of this Section 2(d)
            or Section 2(a), as applicable.

            (e) The parties hereto agree that the Holders of Registrable
      Securities will suffer damages, and that it would not be feasible to
      ascertain the extent of such damages

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      with precision, if:

                  (i) the Initial Shelf Registration Statement has not been
            filed with the SEC on or prior to the Filing Deadline Date;

                  (ii) the Initial Shelf Registration Statement has not become
            effective under the Securities Act on or prior to the Effectiveness
            Deadline Date;

                  (iii) either a supplement to a Prospectus, a post-effective
            amendment or a Subsequent Shelf Registration Statement is required
            to be filed with the SEC and fails to be filed with the SEC within
            the prescribed period and in the manner set forth in Section 2(d)
            (the date such filing is required to be made being an "Additional
            Filing Deadline Date") or, in the case of a post-effective amendment
            or a Subsequent Shelf Registration Statement, such post-effective
            amendment or Subsequent Registration Statement does not become
            effective under the Securities Act by the Amendment Effectiveness
            Deadline Date or the Subsequent Shelf Registration Statement
            Effectiveness Deadline Date, as the case may be;

                  (iv) the Initial Shelf Registration Statement or any
            Subsequent Registration Statement is filed with the SEC and becomes
            effective under the Securities Act but shall thereafter cease to be
            effective (without being succeeded or replaced by a new Registration
            Statement that has been filed with the SEC, and has become effective
            under the Securities Act, before such cessation) or usable under the
            Securities Act for the offer and sale of Registrable Securities in
            the manner contemplated by this Agreement for a period of time
            (including any Suspension Period) which shall exceed forty five (45)
            days in the aggregate in any three (3) month period or ninety (90)
            days in the aggregate in any twelve (12) month period; or

                  (v) any Registration Statement or amendment thereto, at the
            time it becomes effective under the Securities Act, or any
            Prospectus relating thereto, at the time it is filed with the SEC
            or, if later, at the time the Registration Statement to which such
            Prospectus relates becomes effective under the Securities Act, shall
            fail to name each Holder as a selling securityholder in such a
            manner as to permit such Holder to sell its Registrable Securities
            pursuant to such Registration Statement and Prospectus in accordance
            with the Securities Act, in each case to the extent such Holder was
            entitled, pursuant to the terms of this Agreement, to be so named
            (it being understood that, without limitation, naming such Holder in
            a manner that permits such Holder to sell only a portion of such
            Holder's Registrable Securities referenced in such Holder's Notice
            and Questionnaire shall be deemed to be an "Event" (as defined
            below) for purposes of this clause (v)).

      Each of the events of a type described in any of the foregoing clauses (i)
      through (v) are individually referred to herein as an "Event," and

                  (V) the Filing Deadline Date, in the case of clause (i) above,

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                  (W) the Effectiveness Deadline Date, in the case of clause
            (ii) above,

                  (X) the Additional Filing Deadline Date, the Amendment
            Effectiveness Deadline Date or the Subsequent Shelf Registration
            Statement Effectiveness Deadline Date, as the case may be, in the
            case of clause (iii) above,

                  (Y) the date on which the duration of the ineffectiveness or
            unusability of the Shelf Registration Statement exceeds the number
            of days permitted by clause (iv) above, in the case of clause (iv)
            above, and

                  (Z) the date the applicable Registration Statement or
            amendment thereto shall become effective under the Securities Act,
            or the date the applicable Prospectus is filed with the SEC or, if
            later, the time the Registration Statement to which such Prospectus
            relates becomes effective under the Securities Act, as the case may
            be, in the case of clause (v) above,

      are each herein referred to as an "Event Date." Events shall be deemed to
      continue until the following dates with respect to the respective types of
      Events:

                  (A) the date the Initial Shelf Registration Statement is filed
            with the SEC, in the case of an Event of the type described in
            clause (i) above;

                  (B) the date the Initial Shelf Registration Statement becomes
            effective under the Securities Act, in the case of an Event of the
            type described in clause (ii) above;

                  (C) the date a supplement to a Prospectus, a post-effective
            amendment or a Subsequent Shelf Registration Statement, whichever is
            required, is filed with the SEC (in the case of a supplement) or
            becomes effective under the Securities Act (in the case of a
            post-effective amendment or a Subsequent Shelf Registration
            Statement), in the case of an Event of the type described in clause
            (iii) above;

                  (D) the date the Initial Shelf Registration Statement or the
            Subsequent Shelf Registration Statement, as the case may be, becomes
            effective and usable again, or the date another Subsequent Shelf
            Registration Statement is filed with the SEC pursuant to Section
            2(b) and becomes effective, in the case of an Event of the type
            described in clause (iv) above; or

                  (E) the date a supplement to the Prospectus is filed with the
            SEC, or the date a post-effective amendment to the Registration
            Statement becomes effective under the Securities Act, or the date a
            Subsequent Shelf Registration Statement becomes effective under the
            Securities Act, which supplement, post-effective amendment or
            Subsequent Shelf Registration Statement, as the case may be, names
            as selling securityholders, in such a manner as to permit them to
            deliver such Prospectus supplement, or the Prospectus related to
            such post-effective

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            amendment or Subsequent Shelf Registration Statement, as the case
            may be, to purchasers of Registrable Securities in accordance with
            the Securities Act, all Holders entitled as herein provided to be so
            named, in the case of an Event of the type described in clause (v)
            above.

      Notwithstanding anything herein to the contrary, all Events described in
      clauses (ii), (iii) or (v) of this Section 2(e) shall be deemed to be
      suspended during any Suspension Period, except to the extent the duration
      of such Suspension Period exceeds forty five (45) days in the aggregate in
      any three (3) month period or ninety (90) days in the aggregate in any
      twelve (12) month period.

      Accordingly, commencing on (and including) any Event Date and ending on
      (but excluding) the next date on which there are no Events that have
      occurred and are continuing (an "Additional Interest Accrual Period"), the
      Company agrees to pay, as additional interest ("additional interest") and
      not as a penalty, an amount (the "Additional Interest Amount") at the rate
      described below, payable periodically on each Additional Interest Payment
      Date to Record Holders, to the extent of, for each such Additional
      Interest Payment Date, the unpaid Additional Interest Amount that has
      accrued to (but excluding) such Additional Interest Payment Date (or, if
      the Additional Interest Accrual Period shall have ended prior to such
      Additional Interest Payment Date, to (but excluding) the day immediately
      after the last day of such Additional Interest Accrual Period); provided,
      however, that any unpaid Additional Interest Amount that has accrued with
      respect to any Note, or portion thereof, called for Redemption on a
      Redemption Date, or purchased by the Company pursuant to a Repurchase at
      Holder's Option or Repurchase Upon Repurchase Event on an Option Purchase
      Date or Repurchase Date, as the case may be, that is after the close of
      business on the Record Date relating to such Additional Interest Payment
      Date and before such Additional Interest Payment Date, shall, in each
      case, be instead paid, on such Redemption Date, Option Purchase Date or
      Repurchase Date, as the case may be, to the Holder who submitted such Note
      or portion thereof for Redemption, Repurchase at Holder's Option or
      Repurchase Upon Repurchase Event, as the case may be.

      The Additional Interest Amount shall accrue at a rate per annum equal to
      one quarter of one percent (0.25%) for the ninety (90) day period
      beginning on, and including, the Event Date and thereafter at a rate per
      annum equal to one half of one percent (0.50%) of the aggregate principal
      amount of the Notes of which such Record Holders were holders of record at
      the close of business on the applicable Record Date; provided, however,
      that, notwithstanding the foregoing:

                  (I) except to the extent provided in the final paragraph of
            this Section 2(e), no Additional Interest Amounts shall accrue as to
            any Covered Security from and after the earlier of (x) the date such
            Covered Security is no longer a Registrable Security, (y) in the
            case such Covered Security is a Note, the date, and to the extent,
            such Note is converted into shares of Common Stock in accordance
            with the Indenture and (z) the expiration of the Effectiveness
            Period;

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                  (II) only those Holders (or their subsequent transferees)
            failing to be named as selling securityholders in the manner
            prescribed in Section 2(e)(v) above shall be entitled to receive any
            Additional Interest Amounts that have accrued solely with respect to
            an Event of the type described in Section 2(e)(v) above (it being
            understood that this clause (II) shall not impair any right of any
            Holder to receive Additional Interest Amounts that have accrued with
            respect to an Event other than an Event of the type described in
            Section 2(e)(v) above);

                  (III) only those Holders (or their subsequent transferees)
            whose delivery of a Notice and Questionnaire gave rise to the
            obligation of the Company, pursuant to Section 2(d)(i), to file and,
            if applicable, make effective under the Securities Act the
            supplement, post-effective amendment or Subsequent Shelf
            Registration Statement referred to in Section 2(e)(iii) above shall
            be entitled to receive any Additional Interest Amounts that have
            accrued solely with respect to an Event of the type described in
            Section 2(e)(iii) above (it being understood that this clause (III)
            shall not impair any right of any Holder to receive Additional
            Interest Amounts that have accrued with respect to an Event other
            than an Event of the type described in Section 2(e)(iii) above); and

                  (IV) if a Covered Security ceases to be outstanding during an
            Additional Interest Accrual Period for which an Additional Interest
            Amount would be payable with respect to such Covered Security, then
            the Additional Interest Amount payable hereunder with respect to
            such Covered Security shall be prorated on the basis of the number
            of full days such Covered Security is outstanding during such
            Additional Interest Accrual Period.

      The rate of accrual of the Additional Interest Amount with respect to any
      period shall not exceed the rate provided for in this Section 2(e)
      notwithstanding the occurrence of multiple concurrent Events. Following
      the cure of all Events requiring the payment by the Company of Additional
      Interest Amounts with respect to Registrable Securities pursuant to this
      Section, the accrual of Additional Interest Amounts shall cease (without
      in any way limiting the effect of any subsequent Event requiring the
      payment of Additional Interest Amounts by the Company). All installments
      of Additional Interest shall be paid by wire transfer of immediately
      available funds to the account specified by the Notice Holder or, if no
      such account is specified, by mailing a check to such Notice Holder's
      address shown in the register of the registrar for the Notes or for the
      Underlying Common Stock, as the case may be.

      All of the Company's obligations set forth in this Section 2(e) that are
      outstanding with respect to any Registrable Security at the time such
      Registrable Security ceases to be a Registrable Security shall survive
      until such time as all such obligations with respect to such security have
      been satisfied in full (notwithstanding termination of this Agreement
      pursuant to Section 9(n)).

      The parties hereto agree that the additional interest provided for in this
      Section 2(e) constitutes a reasonable estimate of the damages in respect
      of the Notes that may be

                                      -12-

<PAGE>

      incurred by Holders of the Notes by reason of an Event relating to such
      Notes, including, without limitation, the failure of a Shelf Registration
      Statement to be filed, become effective under the Securities Act, amended
      or replaced to include the names of all Notice Holders or available for
      effecting resales of Registrable Securities in accordance with the
      provisions hereof. Subject to any rights that may arise pursuant to
      Section 6 hereof, the parties hereto also agree that the Company shall
      have no liability to a Holder of Notes for monetary damages with respect
      to an Event relating to such Notes other than the additional interest
      provided for in this Section 2(e); provided, however, that nothing in this
      paragraph shall impair any rights a holder of Underlying Common Stock, to
      the extent such holder holds Underlying Common Stock and not Notes, may
      have with respect to an Event relating to such Underlying Common Stock (it
      being understood that interest that accrues, in accordance with the
      immediately following paragraph, on an Additional Interest Amount with
      respect to an Event that relates to a Note shall be deemed, for purposes
      of this proviso, to be an Event that relates to such Note notwithstanding
      any subsequent conversion of such Note into shares of Underlying Common
      Stock).

      If any Additional Interest Amounts are not paid when due, then, to the
      extent permitted by law, such overdue Additional Interest Amounts, if any,
      shall bear interest, compounded semi-annually, until paid at the rate of
      interest payable with respect to overdue amounts on the Notes pursuant to
      Section 2.12 of the Indenture.

            (f) The Trustee shall be entitled, on behalf of Holders, to seek any
      available remedy for the enforcement of this Agreement, including for the
      payment of any Additional Interest Amount.

      3. Registration Procedures. In connection with the registration
obligations of the Company under Section 2 hereof, the Company shall:

            (a) Prepare and file with the SEC a Shelf Registration Statement or
      Shelf Registration Statements on Form S-1 or Form S-3 or any other
      appropriate form under the Securities Act available for the sale of the
      Registrable Securities by the Holders thereof in accordance with the
      method or methods of distribution described in the Notice and
      Questionnaires, and use its reasonable best efforts to cause each such
      Shelf Registration Statement to become effective under the Securities Act
      and remain effective under the Securities Act as provided herein;
      provided, that, before filing any Shelf Registration Statement or
      Prospectus or any amendments or supplements thereto with the SEC, the
      Company shall furnish to the Initial Purchasers and counsel for the
      Initial Purchasers and, if applicable, Designated Counsel copies of all
      such documents proposed to be filed and shall give reasonable
      consideration to such comments as the Initial Purchasers, counsel for the
      Initial Purchasers or Designated Counsel reasonably shall propose within
      two (2) Business Days of the delivery of such copies to the Initial
      Purchasers and such counsel.

            (b) Prepare and file with the SEC such amendments and post-effective
      amendments to each Shelf Registration Statement as may be necessary,
      except to the

                                      -13-

<PAGE>

      extent permitted under Section 3(i) hereof, to keep such Shelf
      Registration Statement or Subsequent Shelf Registration Statement
      continuously effective until the expiration of the Effectiveness Period;
      cause the related Prospectus to be supplemented by any required Prospectus
      supplement and, as so supplemented, to be filed with the SEC pursuant to
      Rule 424 (or any similar provisions then in force) under the Securities
      Act; and, except to the extent permitted under Section 3(i) hereof, comply
      with the provisions of the Securities Act applicable to it with respect to
      the disposition of all securities covered by each Shelf Registration
      Statement during the Effectiveness Period in accordance with the intended
      methods of disposition by the sellers thereof set forth in such Shelf
      Registration Statement as so amended or such Prospectus as so
      supplemented.

            (c) As promptly as practicable, give notice to the Notice Holders,
      the Initial Purchasers, counsel for the Initial Purchasers and, if
      applicable, Designated Counsel:

                  (i) when any Prospectus, Prospectus supplement, Shelf
            Registration Statement or post-effective amendment to a Shelf
            Registration Statement has been filed with the SEC and, with respect
            to a Shelf Registration Statement or any post-effective amendment,
            when the same has become effective under the Securities Act,

                  (ii) of any request, following the effectiveness of a Shelf
            Registration Statement under the Securities Act, by the SEC or any
            other federal or state governmental authority for amendments or
            supplements to such Shelf Registration Statement or the related
            Prospectus or for additional information,

                  (iii) of the issuance by the SEC or any other federal or state
            governmental authority of any stop order suspending the
            effectiveness of any Shelf Registration Statement or the initiation
            or threatening of any proceedings for that purpose,

                  (iv) of the receipt by the Company or its legal counsel of any
            notification with respect to the suspension of the qualification or
            exemption from qualification of any of the Registrable Securities
            for sale in any jurisdiction or the initiation or threatening of any
            proceeding for such purpose,

                  (v) after the effective date of any Shelf Registration
            Statement filed with the SEC pursuant to this Agreement, of the
            occurrence of (but not the nature of or details concerning) a
            Material Event, and

                  (vi) of the determination by the Company that a post-effective
            amendment to a Shelf Registration Statement or a Subsequent Shelf
            Registration Statement will be filed with the SEC, which notice may,
            at the discretion of the Company (or as required pursuant to Section
            3(i)), state that it constitutes a Suspension Notice, in which event
            the provisions of Section 3(i) shall apply.

            (d) Subject to the terms hereof, use its reasonable best efforts to
      (i) prevent the

                                      -14-

<PAGE>

      issuance of, and, if issued, to obtain the withdrawal of, any order
      suspending the effectiveness of a Shelf Registration Statement and (ii)
      obtain the lifting of any suspension of the qualification (or exemption
      from qualification) of any of the Registrable Securities for sale in any
      jurisdiction in which they have been qualified for sale, in either case at
      the earliest possible moment, and provide prompt notice to each Notice
      Holder and the Initial Purchasers, counsel for the Initial Purchasers and,
      if applicable, Designated Counsel, of the withdrawal or lifting of any
      such order or suspension.

            (e) If requested by the Initial Purchasers or any Notice Holder, as
      promptly as practicable incorporate in a Prospectus supplement or a
      post-effective amendment to a Shelf Registration Statement such
      information as the Initial Purchasers, such Notice Holder or counsel for
      the Initial Purchasers or, if applicable, Designated Counsel shall
      determine to be required to be included therein by the Securities Act and
      make any required filings of such Prospectus supplement or such
      post-effective amendment; provided, however, that the Company shall not be
      required to take any action under this Section 3(e) unless the Company
      receives the opinion of counsel for the party making such request that
      such action is required by the Securities Act.

            (f) As promptly as practicable, furnish, upon request, to each
      Notice Holder and the Initial Purchasers, without charge, at least one (1)
      conformed copy of each Shelf Registration Statement and each amendment
      thereto, including financial statements but excluding schedules, all
      documents incorporated or deemed to be incorporated therein by reference
      and all exhibits (unless requested in writing to the Company by such
      Notice Holder or the Initial Purchasers).

            (g) During the Effectiveness Period, deliver to each Notice Holder,
      in connection with any sale of Registrable Securities pursuant to a Shelf
      Registration Statement, without charge, as many copies of the Prospectus
      or Prospectuses relating to such Registrable Securities and any amendment
      or supplement thereto as such Notice Holder may reasonably request; and
      the Company hereby consents (except during such periods that a Suspension
      Notice is outstanding and has not been revoked) to the use of such
      Prospectus and each amendment or supplement thereto by each Notice Holder,
      in connection with any offering and sale of the Registrable Securities
      covered by such Prospectus or any amendment or supplement thereto in the
      manner set forth therein.

            (h) Prior to any public offering of the Registrable Securities
      pursuant to a Shelf Registration Statement, use its reasonable best
      efforts to register or qualify or cooperate with the Notice Holders in
      connection with the registration or qualification (or exemption from such
      registration or qualification) of such Registrable Securities for offer
      and sale under the securities or Blue Sky laws of such jurisdictions
      within the United States as any Notice Holder reasonably requests in
      writing (which request may be included in the Notice and Questionnaire);
      use its reasonable best efforts to keep each such registration or
      qualification (or exemption therefrom) effective during the Effectiveness
      Period in connection with such Notice Holder's offer and sale of
      Registrable Securities pursuant to such registration or qualification (or
      exemption

                                      -15-

<PAGE>

      therefrom) and do any and all other acts or things reasonably necessary or
      advisable to enable the disposition in such jurisdictions of such
      Registrable Securities in the manner set forth in the relevant Shelf
      Registration Statement and the related Prospectus; provided, however, that
      the Company will not be required to (i) qualify generally to do business
      in any jurisdiction where it is not then so qualified, (ii) take any
      action that would subject it to general service of process in suits, other
      than those arising out of the offering or sale of Registrable Securities
      or arising in connection with this Agreement, in any jurisdiction where it
      is not now so subject, or (iii) take any action that would subject it to
      taxation in any jurisdiction where it is not then so subject.

            (i) Upon: (A) the issuance by the SEC of a stop order suspending the
      effectiveness of any Shelf Registration Statement or the initiation of
      proceedings with respect to any Shelf Registration Statement under Section
      8(d) or 8(e) of the Securities Act; (B) the occurrence of any event or the
      existence of any fact as a result of which any Shelf Registration
      Statement shall contain any untrue statement of a material fact or omit to
      state any material fact required to be stated therein or necessary to make
      the statements therein not misleading, or any Prospectus shall contain any
      untrue statement of a material fact or omit to state any material fact
      necessary in order to make the statements therein, in the light of the
      circumstances under which they were made, not misleading; or (C) the
      occurrence or existence of any pending corporate development (a "Material
      Event") that, in the reasonable discretion of the Company, makes it
      appropriate to suspend the availability of any Shelf Registration
      Statement and the related Prospectus,

                  (i) in the case of clause (B) or (C) above, subject to the
            next sentence, as promptly as practicable, prepare and file, if
            necessary pursuant to the Securities Act, a post-effective amendment
            to such Shelf Registration Statement or a supplement to such
            Prospectus or any document incorporated therein by reference or file
            any other required document that would be incorporated by reference
            into such Shelf Registration Statement and Prospectus so that such
            Shelf Registration Statement does not contain any untrue statement
            of a material fact or omit to state any material fact required to be
            stated therein or necessary to make the statements therein not
            misleading, and so that such Prospectus does not contain any untrue
            statement of a material fact or omit to state any material fact
            necessary in order to make the statements therein, in the light of
            the circumstances under which they were made, not misleading, as
            thereafter delivered to the purchasers of the Registrable Securities
            being sold thereunder (it being understood that the Company may rely
            on information provided by each Notice Holder with respect to such
            Notice Holder), and, in the case of a post-effective amendment to a
            Shelf Registration Statement, subject to the next sentence, use its
            reasonable best efforts to cause it to become effective under the
            Securities Act as promptly as practicable, and

                  (ii) give notice to the Notice Holders, the Initial
            Purchasers, counsel for the Initial Purchasers and, if applicable,
            Designated Counsel that the availability of the Shelf Registration
            Statement is suspended (a "Suspension Notice") (and, upon receipt of
            any Suspension Notice, each Notice Holder agrees

                                      -16-
<PAGE>

            not to sell any Registrable Securities pursuant to such Shelf
            Registration Statement until such Notice Holder's receipt of copies
            of the supplemented or amended Prospectus provided for in clause (i)
            above or until such Notice Holder is advised in writing by the
            Company that the Prospectus may be used).

      The Company will use its reasonable best efforts to ensure that the use of
      the Prospectus may be resumed (x) in the case of clause (A) above, as
      promptly as is practicable, (y) in the case of clause (B) above, as soon
      as, in the reasonable judgment of the Company, the Shelf Registration
      Statement does not contain any untrue statement of a material fact or omit
      to state any material fact required to be stated therein or necessary to
      make the statements therein not misleading and the Prospectus does not
      contain any untrue statement of a material fact or omit to state any
      material fact necessary in order to make the statements therein, in the
      light of the circumstances under which they were made, not misleading, and
      (z) in the case of clause (C) above, as soon as, in the reasonable
      discretion of the Company, such suspension is no longer appropriate. The
      period during which the availability of the Shelf Registration Statement
      and any Prospectus may be suspended (the "Suspension Period") without the
      Company incurring any obligation to pay additional interest pursuant to
      Section 2(e) shall not exceed forty five (45) days in the aggregate in any
      three (3) month period or ninety (90) days in the aggregate in any twelve
      (12) month period. The Effectiveness Period shall be extended by the
      number of days from and including the date of the giving of the Suspension
      Notice to and including the date on which the Notice Holder received
      copies of the supplemented or amended Prospectus provided in clause (i)
      above, or the date on which it is advised in writing by the Company that
      the Prospectus may be used and has received copies of any additional or
      supplemental filings that are incorporated or deemed incorporated by
      reference in such Prospectus.

            (j) Make available for inspection during normal business hours by
      representatives for the Notice Holders and any underwriters participating
      in any disposition pursuant to any Shelf Registration Statement and any
      broker-dealers, attorneys and accountants retained by such Notice Holders
      or any such underwriters, all relevant financial and other records and
      pertinent corporate documents and properties of the Company and its
      subsidiaries, and cause the appropriate officers, directors and employees
      of the Company and its subsidiaries to make available for inspection
      during normal business hours all relevant information reasonably requested
      by such representatives for the Notice Holders, or any such underwriters,
      broker-dealers, attorneys or accountants in connection with such
      disposition, in each case as is customary for similar "due diligence"
      examinations; provided, however, that such persons shall first agree in
      writing with the Company that any information that is confidential at the
      time of delivery of such information shall be kept confidential by such
      persons and shall be used solely for the purposes of exercising rights
      under this Agreement, unless (i) disclosure of such information is
      required by court or administrative order or is necessary to respond to
      inquiries of governmental or regulatory authorities, (ii) disclosure of
      such information is required by law (including any disclosure requirements
      pursuant to federal securities laws in connection with the filing of any
      Shelf Registration Statement or the use of any Prospectus referred to in
      this Agreement) or necessary to defend or prosecute a claim

                                      -17-
<PAGE>

      brought against or by any such persons (e.g., to establish a "due
      diligence" defense), (iii) such information becomes generally available to
      the public other than as a result of a disclosure or failure to safeguard
      by any such person or (iv) such information becomes available to any such
      person from a source other than the Company and such source is not bound
      by a confidentiality agreement or is not otherwise under a duty of trust
      to the Company; provided further, that the foregoing inspection and
      information gathering shall, to the greatest extent possible, be
      coordinated on behalf of all the Notice Holders and the other parties
      entitled thereto by one counsel for such Notice Holders and such other
      parties.

            (k) Comply with all applicable rules and regulations of the SEC that
      are applicable to any Shelf Registration Statement; and make generally
      available to its securityholders earnings statements (which need not be
      audited) satisfying the provisions of Section 11(a) of the Securities Act
      and Rule 158 thereunder (or any similar rule promulgated under the
      Securities Act), which statements shall cover a period of twelve (12)
      months commencing on the first day of the first fiscal quarter of the
      Company commencing after the effective date of each Shelf Registration
      Statement (within the meaning of Rule 158(c) under the Securities Act),
      and which statements shall be so made generally available to the Company's
      securityholders no later than forty (40) days after the end of the
      applicable twelve (12) month period if such period ends on or after
      December 15, 2004 and before December 15, 2006 (or thirty five (35) days
      after the end of the applicable twelve (12) month period if such period
      ends on or after December 15, 2006) (or, if such earnings statement is
      filed with the SEC on Form 10-K under the Exchange Act, (i) seventy five
      (75) days after the end of the applicable twelve (12) month period if such
      period ends before December 15, 2005 or (ii) sixty (60) days after the end
      of the applicable twelve (12) month period if such period ends on or after
      December 15, 2005); provided, however, that, notwithstanding the foregoing
      in this Section 3(k), to the extent any such earnings statement will be
      contained in one report, or any combination of reports, on Form 10-K
      and/or Form 10-Q under the Exchange Act filed by the Company with the SEC
      and the deadline, under the Exchange Act, for the Company to file, with
      the SEC, such report, if such earnings statement is contained in a Form
      10-K, or to file, with the SEC, the last of such reports which together
      constitute such earnings statement, if such earnings statement is
      contained in a combination of reports, is a date that is later than the
      applicable foregoing deadline, then such later date shall apply in place
      of the otherwise applicable foregoing deadline.

            (l) Cooperate with each Notice Holder to facilitate the timely
      preparation and delivery of certificates representing Registrable
      Securities sold pursuant to a Shelf Registration Statement, which
      certificates shall not bear any restrictive legends, and cause such
      Registrable Securities to be in such denominations as are permitted by the
      Indenture and registered in such names as such Notice Holder may request
      in writing at least two (2) Business Days prior to any sale of such
      Registrable Securities.

            (m) Provide a CUSIP number for all Registrable Securities covered by
      a Shelf Registration Statement not later than the effective date of the
      Initial Shelf Registration Statement and provide the Trustee and the
      transfer agent for the Common Stock with

                                      -18-

<PAGE>

      certificates for the Registrable Securities that are in a form eligible
      for deposit with The Depository Trust Company.

            (n) Cooperate and assist in any filings required to be made with the
      National Association of Securities Dealers, Inc.

            (o) Upon the filing of the Initial Shelf Registration Statement, and
      upon the effectiveness under the Securities Act of the Initial Shelf
      Registration Statement, announce the same, in each case by release through
      a reputable national newswire service.

            (p) Cause the Indenture to be qualified under the TIA not later than
      the effective date of the Initial Shelf Registration Statement; and, in
      connection therewith, cooperate with the Trustee to effect such changes to
      the Indenture as may be required for the Indenture to be so qualified in
      accordance with the terms of the TIA and execute, and use its reasonable
      best efforts to cause the Trustee to execute, all documents as may be
      required to effect such changes, and all other forms and documents
      required to be filed with the SEC to enable the Indenture to be so
      qualified in a timely manner.

            (q) Use its reasonable best efforts to cause the Underlying Common
      Stock to be listed on The Nasdaq National Market.

      4. Holder's Obligations. Each Holder agrees, by acquisition of the
Registrable Securities, that no Holder of Registrable Securities shall be
entitled to sell any of such Registrable Securities pursuant to a Shelf
Registration Statement or to receive a Prospectus relating thereto, unless such
Holder has furnished the Company with a Notice and Questionnaire as required
pursuant to Section 2(d) hereof (including the information required to be
included in such Notice and Questionnaire) and the information set forth in the
next sentence. Each Notice Holder agrees promptly to furnish to the Company all
information required to be disclosed in order to make the information previously
furnished to the Company by such Notice Holder not misleading and any other
information regarding such Notice Holder and the distribution of such
Registrable Securities as the Company may from time to time reasonably request.
Any sale of any Registrable Securities by any Holder shall constitute a
representation and warranty by such Holder that the information relating to such
Holder and its plan of distribution is as set forth in the Prospectus delivered
by such Holder in connection with such disposition, that such Prospectus does
not as of the time of such sale contain any untrue statement of a material fact
relating to or provided by such Holder or its plan of distribution and that such
Prospectus does not as of the time of such sale omit to state any material fact
relating to or provided by such Holder or its plan of distribution necessary in
order to make the statements in such Prospectus, in the light of the
circumstances under which they were made, not misleading. Each Holder agrees to
keep confidential the receipt by it of any Suspension Notice and the contents
thereof, except as required pursuant to applicable law.

      5. Registration Expenses. The Company shall bear all fees and expenses
incurred in connection with the performance by the Company of its obligations
under Section 2 and Section 3 of this Agreement whether or not any of the Shelf
Registration Statements are filed or declared

                                      -19-

<PAGE>

effective under the Securities Act. Such fees and expenses ("Registration
Expenses") shall include, without limitation, (i) all registration and filing
fees and expenses (including, without limitation, fees and expenses (x) with
respect to filings required to be made with the National Association of
Securities Dealers, Inc. and (y) of compliance with federal securities laws and
state securities or Blue Sky laws (including, without limitation, reasonable
fees and disbursements of counsel for the Holders in connection with Blue Sky
qualifications of the Registrable Securities under the laws of such
jurisdictions as the Notice Holders of a majority of the Registrable Securities
being sold pursuant to a Shelf Registration Statement may designate), (ii) all
printing expenses (including, without limitation, expenses of printing
certificates for Registrable Securities in a form eligible for deposit with The
Depository Trust Company and printing Prospectuses), (iii) all duplication and
mailing expenses relating to copies of any Shelf Registration Statement or
Prospectus delivered to any Holders hereunder, (iv) all fees and disbursements
of counsel for the Company, (v) the fees and disbursements of one counsel
("Designated Counsel") for the Holders in connection with the Shelf Registration
Statement, which Designated Counsel shall be designated in writing to the
Company by Holders of a majority of the Registrable Securities (provided,
however, that in no event shall the Company be obligated pursuant to this clause
(v) to pay an amount to the extent such amount, in the aggregate with all other
payments theretofore made pursuant to this clause (v), exceeds fifteen thousand
dollars ($15,000)), (vi) all fees and disbursements of the Trustee and its
counsel and of the registrar and transfer agent for the Common Stock, and (vii)
Securities Act liability insurance obtained by the Company in its sole
discretion. In addition, the Company shall pay the internal expenses of the
Company (including, without limitation, all salaries and expenses of officers
and employees performing legal or accounting duties), the expense of any annual
audit or quarterly review, the fees and expenses incurred in connection with the
listing by the Company of the Registrable Securities on any securities exchange
or quotation system on which similar securities of the Company are then listed
and the fees and expenses of any person, including, without limitation, special
experts, retained by the Company. Except as provided above, each Holder shall
pay all brokerage fees and commissions, all transfer taxes, the fees and
expenses of any advisors the Holder engages and all similar fees and costs
relating to such Holder's disposition of Registrable Securities.

      6. Indemnification, Contribution.

            (a) The Company agrees to indemnify, defend and hold harmless each
      Initial Purchaser, each Holder, each person (a "Controlling Person"), if
      any, who controls any Initial Purchaser or Holder within the meaning of
      Section 15 of the Securities Act or Section 20 of the Exchange Act and the
      respective officers, directors, partners, employees, representatives and
      agents of any Initial Purchaser, the Holders or any Controlling Person
      (each, an "Indemnified Party"), from and against any loss, damage,
      expense, liability, claim or any actions in respect thereof (including the
      reasonable cost of investigation) which such Indemnified Party may incur
      or become subject to under the Securities Act, the Exchange Act or
      otherwise, insofar as such loss, damage, expense, liability, claim or
      action arises out of or is based upon any untrue statement or alleged
      untrue statement of a material fact contained in any Shelf Registration
      Statement or Prospectus, including any document incorporated by reference
      therein, or in any amendment or supplement thereto or in any preliminary
      prospectus, or arises out of or is

                                      -20-
<PAGE>

      based upon any omission or alleged omission to state a material fact
      required to be stated in any Shelf Registration Statement or in any
      amendment or supplement thereto or necessary to make the statements
      therein not misleading, or arises out of or is based upon any omission or
      alleged omission to state a material fact necessary in order to make the
      statements made in any Prospectus or in any amendment or supplement
      thereto or in any preliminary prospectus, in the light of the
      circumstances under which such statements were made, not misleading, and
      the Company shall reimburse, as incurred, the Indemnified Parties for any
      legal or other expenses reasonably incurred by them in connection with
      investigating or defending any such loss, damage, expense, liability,
      claim or action in respect thereof; provided, however, that the Company
      shall not be required to provide any indemnification pursuant to this
      Section 6(a) in any such case insofar as any such loss, damage, expense,
      liability, claim or action arises out of or is based upon any untrue
      statement or omission or alleged untrue statement or omission of a
      material fact contained in, or omitted from, and in conformity with
      information furnished in writing by or on behalf of an Initial Purchaser
      or a Holder to the Company expressly for use in, any Shelf Registration
      Statement or any Prospectus, including information provided by such Holder
      in a Notice and Questionnaire; provided further, however, that this
      indemnity agreement will (A) be in addition to any liability which the
      Company may otherwise have to such Indemnified Party and (B) not apply to
      any loss, damage, expense, liability or claim arising from an offer or
      sale, occurring during a Suspension Period, of Registrable Securities by a
      Holder to whom the Company theretofore provided a Suspension Notice in
      accordance with Section 3(i).

            (b) Each Holder, severally and not jointly, agrees to indemnify,
      defend and hold harmless the Company, its directors, officers, employees
      and any person who controls the Company within the meaning of Section 15
      of the Securities Act or Section 20 of the Exchange Act (each, a "Company
      Indemnified Party") from and against any loss, damage, expense, liability,
      claim or any actions in respect thereof (including the reasonable cost of
      investigation) which such Company Indemnified Party may incur or become
      subject to under the Securities Act, the Exchange Act or otherwise,
      insofar as such loss, damage, expense, liability, claim or action arises
      out of or is based upon (A) any untrue statement or alleged untrue
      statement of a material fact contained in, and in conformity with
      information (the "Holder Information") furnished in writing by or on
      behalf of such Holder to the Company expressly for use in, any Shelf
      Registration Statement or Prospectus, or in any amendment or supplement
      thereto, or arises out of or is based upon any omission or alleged
      omission to state a material fact in connection with such Holder
      Information required to be stated in any Shelf Registration Statement or
      Prospectus, or any amendment or supplement thereto, or necessary to make
      such Holder Information not misleading, (B) a sale, by such Holder
      pursuant to a Shelf Registration Statement in or with respect to which
      such Holder is named as a selling security holder, of Registrable
      Securities during a Suspension Period, provided that the Company shall
      have theretofore provided such Holder a Suspension Notice in accordance
      with Section 3(i), or (C) a public sale of Registrable Securities by such
      Holder without delivery, if required by the Securities Act, of the most
      recent applicable Prospectus provided to such Holder by the Company
      pursuant to Section 3(g) or Section 2(d)(i)(C); and, subject to the
      limitation set forth in the immediately preceding clause, each Holder
      shall reimburse, as

                                      -21-

<PAGE>

      incurred, the Company for any legal or other expenses reasonably incurred
      by the Company or any such controlling person in connection with
      investigating or defending any loss, damage, expense, liability, claim or
      action in respect thereof. This indemnity agreement will be in addition to
      any liability which such Holder may otherwise have to the Company or any
      of its controlling persons. In no event shall the liability of any selling
      Holder of Registrable Securities hereunder be greater in amount than the
      dollar amount of the proceeds received by such Holder upon the sale,
      pursuant to the Shelf Registration Statement, of the Registrable
      Securities giving rise to such indemnification obligation.

            (c) If any action, suit or proceeding (each, a "Proceeding") is
      brought against any person in respect of which indemnity may be sought
      pursuant to either Section 6(a) or Section 6(b), such person (the
      "Indemnified Party") shall promptly notify the person against whom such
      indemnity may be sought (the "Indemnifying Party") in writing of the
      institution of such Proceeding and the Indemnifying Party shall assume the
      defense of such Proceeding; provided, however, that the failure to so
      notify such Indemnifying Party shall not relieve such Indemnifying Party
      from any liability which it may have to such Indemnified Party or
      otherwise, except to the extent such failure to notify materially
      prejudices such Indemnifying Party. Such Indemnified Party shall have the
      right to employ its own counsel in any such case, but the fees and
      expenses of such counsel shall be at the expense of such Indemnified Party
      unless the employment of such counsel shall have been authorized in
      writing by such Indemnifying Party in connection with the defense of such
      Proceeding or such Indemnifying Party shall not have employed counsel to
      have charge of the defense of such Proceeding within thirty (30) days of
      the receipt of notice thereof or such Indemnified Party shall have
      reasonably concluded upon the written advice of counsel that there may be
      one or more defenses available to it that are different from, additional
      to or in conflict with those available to such Indemnifying Party (in
      which case such Indemnifying Party shall not have the right to direct that
      portion of the defense of such Proceeding on behalf of the Indemnified
      Party, but such Indemnifying Party may employ counsel and participate in
      the defense thereof but the fees and expenses of such counsel shall be at
      the expense of such Indemnifying Party), in any of which events such
      reasonable fees and expenses shall be borne by such Indemnifying Party and
      paid as incurred (it being understood, however, that such Indemnifying
      Party shall not be liable for the expenses of more than one separate
      counsel in any one Proceeding or series of related Proceedings together
      with reasonably necessary local counsel representing the Indemnified
      Parties who are parties to such action). An Indemnifying Party shall not
      be liable for any settlement of such Proceeding effected without the
      written consent of such Indemnifying Party, but if settled with the
      written consent of such Indemnifying Party, such Indemnifying Party agrees
      to indemnify and hold harmless an Indemnified Party from and against any
      loss or liability by reason of such settlement. Notwithstanding the
      foregoing sentence, if at any time an Indemnified Party shall have
      requested an Indemnifying Party to reimburse such Indemnified Party for
      fees and expenses of counsel as contemplated by the second sentence of
      this paragraph, then such Indemnifying Party agrees that it shall be
      liable for any settlement of any Proceeding effected without its written
      consent if (i) such settlement is entered into more than sixty (60)
      Business Days after receipt by such Indemnifying Party of the aforesaid

                                      -22-

<PAGE>

      request, (ii) such Indemnifying Party shall not have fully reimbursed such
      Indemnified Party in accordance with such request prior to the date of
      such settlement and (iii) such Indemnified Party shall have given such
      Indemnifying Party at least thirty (30) days' prior notice of its
      intention to settle. No Indemnifying Party shall, without the prior
      written consent of any Indemnified Party, effect any settlement of any
      pending or threatened Proceeding in respect of which such Indemnified
      Party is or could have been a party and indemnity could have been sought
      hereunder by such Indemnified Party, unless such settlement includes an
      unconditional release of such Indemnified Party from all liability on
      claims that are the subject matter of such Proceeding and does not include
      an admission of fault or culpability or a failure to act by or on behalf
      of such Indemnified Party.

            (d) If the indemnification provided for in this Section 6 is
      unavailable to an Indemnified Party under Section 6(a) or Section 6(b), or
      insufficient to hold such Indemnified Party harmless, in respect of any
      losses, damages, expenses, liabilities, claims or actions referred to
      therein, then each applicable Indemnifying Party, in lieu of indemnifying
      such Indemnified Party, shall contribute to the amount paid or payable by
      such Indemnified Party as a result of such losses, damages, expenses,
      liabilities, claims or actions (i) in such proportion as is appropriate to
      reflect the relative benefits received by the Company, on the one hand,
      and by the Holders or the Initial Purchasers, on the other hand, from the
      offering of the Registrable Securities or (ii) if the allocation provided
      by clause (i) above is not permitted by applicable law, in such proportion
      as is appropriate to reflect not only the relative benefits referred to in
      clause (i) above but also the relative fault of the Company, on the one
      hand, and of the Holders or the Initial Purchasers, on the other hand, in
      connection with the statements or omissions which resulted in such losses,
      damages, expenses, liabilities, claims or actions, as well as any other
      relevant equitable considerations. The relative fault of the Company, on
      the one hand, and of the Holders or the Initial Purchasers, on the other
      hand, shall be determined by reference to, among other things, whether the
      untrue statement or alleged untrue statement of a material fact or
      omission or alleged omission relates to information supplied by the
      Company or by the Holders or the Initial Purchasers and the parties'
      relative intent, knowledge, access to information and opportunity to
      correct or prevent such statement or omission. The amount paid or payable
      by a party as a result of the losses, damages, expenses, liabilities,
      claims and actions referred to above shall be deemed to include any
      reasonable legal or other fees or expenses reasonably incurred by such
      party in connection with investigating or defending any Proceeding.

            (e) The Company, the Holders and each Initial Purchaser agree that
      it would not be just and equitable if contribution pursuant to this
      Section 6 were determined by pro rata allocation or by any other method of
      allocation which does not take account of the equitable considerations
      referred to in Section 6(d) above. Notwithstanding the provisions of this
      Section 6, no Holder shall be required to contribute any amount in excess
      of the amount by which the total price at which the Registrable Securities
      giving rise to such contribution obligation and sold by such Holder were
      offered to the public exceeds the amount of any damages which it has
      otherwise been required to pay by reason of such untrue or alleged untrue
      statement or omission or alleged omission. No

                                      -23-

<PAGE>

      person guilty of fraudulent misrepresentation (within the meaning of
      Section 11(f) of the Securities Act) shall be entitled to contribution
      from any person who was not guilty of such fraudulent misrepresentation.
      The Holders' respective obligations to contribute pursuant to this Section
      6 are several in proportion to the respective amount of Registrable
      Securities they have sold pursuant to a Shelf Registration Statement, and
      not joint. The remedies provided for in this Section 6 are not exclusive
      and shall not limit any rights or remedies which may otherwise be
      available to any indemnified party at law or in equity.

            (f) The indemnity and contribution provisions contained in this
      Section 6 shall remain operative and in full force and effect regardless
      of (i) any termination of this Agreement, (ii) any investigation made by
      or on behalf of any Holder or any Initial Purchaser or any person
      controlling any Holder or Initial Purchaser, or the Company, or the
      Company's officers or directors or any person controlling the Company and
      (iii) the sale of any Registrable Security by any Holder.

      7. Information Requirements.

            (a) The Company covenants that, if at any time before the end of the
      Effectiveness Period it is not subject to the reporting requirements of
      the Exchange Act, it will cooperate with any Holder of Registrable
      Securities and take such further action as any Holder of Registrable
      Securities may reasonably request in writing (including, without
      limitation, making such representations as any such Holder may reasonably
      request), all to the extent required from time to time to enable such
      Holder to sell Registrable Securities without registration under the
      Securities Act within the limitations of the exemptions provided by Rule
      144, Rule 144A and Regulation S under the Securities Act and customarily
      taken in connection with sales pursuant to such exemptions. Upon the
      written request of any Holder, the Company shall deliver to such Holder a
      written statement as to whether the Company has complied with the
      reporting requirements of the Exchange Act during the preceding twelve
      (12) months, unless such a statement has been included in the Company's
      most recent quarterly or annual report filed with the SEC pursuant to
      Section 13 or Section 15(d) of Exchange Act.

            (b) During the Effectiveness Period, the Company shall use its
      commercially reasonable efforts to (i) file the reports required to be
      filed by it under the Exchange Act during the Effectiveness Period and
      (ii) comply with the registrant requirements set forth in the instructions
      to Form S-3.

      8. Underwritten Registrations. Notwithstanding anything herein to the
contrary, no Registrable Securities covered by a Shelf Registration Statement
may be sold in an underwritten offering pursuant to the Shelf Registration
Statement without the prior written consent of the Company. No person may
participate in any underwritten registration hereunder unless such person (i)
agrees to sell such person's Registrable Securities on the basis reasonably
provided in any underwriting arrangements approved by the persons entitled
hereunder to approve such arrangements and (ii) completes and executes all
questionnaires, powers of attorney, indemnities, underwriting agreements and
other documents reasonably required under the terms of such

                                      -24-

<PAGE>

underwriting arrangements.

      9. Miscellaneous.

            (a) Remedies. The Company acknowledges and agrees that any failure
      by the Company to comply with its obligations under this Agreement may
      result in material irreparable injury to the Initial Purchasers and the
      Holders for which there is no adequate remedy at law, that it will not be
      possible to measure damages for such injuries precisely and that, in the
      event of any such failure, any Initial Purchaser or Holder may obtain such
      relief as may be required to specifically enforce the Company's
      obligations under this Agreement. The Company further agrees to waive the
      defense in any action for specific performance that a remedy at law would
      be adequate. Notwithstanding the foregoing two sentences, this Section
      9(a) shall not apply to the subject matter referred to in and contemplated
      by Section 2(e).

            (b) No Conflicting Agreements. The Company is not, as of the date
      hereof, a party to, nor shall it, on or after the date of this Agreement,
      enter into, any agreement with respect to the Company's securities that
      conflicts with the rights granted to the Holders in this Agreement. The
      Company represents and warrants that the rights granted to the Holders
      hereunder are not in conflict with the rights granted to the holders of
      the Company's securities under any other agreements. The Company
      represents and covenants that it has not granted, and shall not grant, to
      any of its security holders (other than the Holders in such capacity) the
      right to include any of the Company's securities in any Shelf Registration
      Statement filed pursuant to this Agreement.

            (c) Amendments and Waivers. The provisions of this Agreement,
      including the provisions of this sentence, may not be amended, modified or
      supplemented, and waivers or consents to departures from the provisions
      hereof may not be given, unless the Company has obtained the written
      consent of Holders of a majority of outstanding Registrable Securities;
      provided, however, that, no consent is necessary from any of the Holders
      in the event that this Agreement is amended, modified or supplemented for
      the purpose of curing any ambiguity, defect or inconsistency that does not
      adversely affect the rights of any Holders. Notwithstanding the foregoing,
      a waiver or consent to depart from the provisions hereof with respect to a
      matter that relates exclusively to the rights of Holders of Registrable
      Securities whose securities are being sold pursuant to a Shelf
      Registration Statement and that does not directly or indirectly affect the
      rights of other Holders of Registrable Securities may be given by Holders
      of at least a majority of the Registrable Securities being sold by such
      Holders pursuant to such Shelf Registration Statement; provided, however,
      that the provisions of this sentence may not be amended, modified, or
      supplemented except in accordance with the provisions of the immediately
      preceding sentence. Each Holder of Registrable Securities outstanding at
      the time of any such amendment, modification, supplement, waiver or
      consent or thereafter shall be bound by any such amendment, modification,
      supplement, waiver or consent effected pursuant to this Section 9(c),
      whether or not any notice, writing or marking indicating such amendment,
      modification, supplement, waiver or consent appears on the Registrable
      Securities or is delivered to such Holder.

                                      -25-

<PAGE>

            (d) Notices. All notices, documents and other communications
      provided for or permitted hereunder shall be made in writing by hand
      delivery, by telecopier, by courier guaranteeing overnight delivery or by
      first-class mail, return receipt requested, and shall be deemed given (A)
      when made, if made by hand delivery, (B) upon confirmation, if made by
      telecopier, (C) one (1) Business Day after being deposited with such
      courier, if made by overnight courier or (D) on the date indicated on the
      notice of receipt, if made by first-class mail, to the parties as follows:

                  (i) if to a Holder, at the most current address given by such
            Holder to the Company in a Notice and Questionnaire or any amendment
            thereto;

                  (ii) if to the Company, to:

                        Antigenics Inc.
                        630 Fifth Avenue
                        Suite 2100
                        New York, NY 10111
                        Attention: Chief Financial Officer
                        Telecopy No.: (212) 994-8299

                  (iii) if to the Initial Purchasers, to:

                        c/o UBS Securities LLC
                        299 Park Avenue
                        New York, New York 10171
                        Attention: Syndicate Department
                        Telecopy No.: (212) 713-1205

                        with a copy to (for informational purposes only):

                        UBS Securities LLC
                        299 Park Avenue
                        New York, New York 10171
                        Attention: Legal Department
                        Telecopy No.: (212) 821-4042

                              and

                        UBS Securities LLC
                        677 Washington Boulevard
                        Stamford, Connecticut 06901
                        Attention: Syndicate Department
                        Telecopy No.: (203) 719-0683

      or to such other address as such person may have furnished to the other
      persons identified

                                      -26-

<PAGE>

      in this Section 9(d) in writing in accordance herewith.

            (e) Majority of Registrable Securities. For purposes of determining
      what constitutes holders of a majority of Registrable Securities, as
      referred to in this Agreement, a majority shall constitute a majority in
      aggregate principal amount of Registrable Securities, treating each
      relevant holder of shares of Underlying Common Stock of the Notes as a
      holder of the aggregate principal amount of Notes in respect of which such
      Common Stock was issued.

            (f) Approval of Holders. Whenever the consent or approval of Holders
      of a specified percentage of Registrable Securities is required hereunder,
      Registrable Securities held by the Company or its "affiliates" (as such
      term is defined in Rule 405 under the Securities Act) (other than the
      Initial Purchasers or subsequent Holders of Registrable Securities, if the
      Initial Purchasers or such subsequent Holders are deemed to be such
      affiliates solely by reason of their holdings of such Registrable
      Securities) shall not be counted in determining whether such consent or
      approval was given by the Holders of such required percentage.

            (g) Third Party Beneficiaries. The Holders shall be third party
      beneficiaries to the agreements made hereunder between the Company, on the
      one hand, and the Initial Purchasers, on the other hand, and shall have
      the right to enforce such agreements directly to the extent they may deem
      such enforcement necessary or advisable to protect their rights or the
      rights of Holders hereunder. The Trustee shall be entitled to the rights
      granted to it pursuant to this Agreement and shall be bound by the terms
      hereof.

            (h) Successors and Assigns. Any person who purchases any Covered
      Security from any Initial Purchaser or from any Holder shall be deemed,
      for purposes of this Agreement, to be an assignee of such Initial
      Purchaser or such Holder, as the case may be. This Agreement shall inure
      to the benefit of and be binding upon the respective successors and
      assigns of each of the parties hereto and shall inure to the benefit of
      and be binding upon each Holder of any Covered Security.

            (i) Counterparts. This Agreement may be executed in any number of
      counterparts and by the parties hereto in separate counterparts, each of
      which when so executed shall be deemed to be original and all of which
      taken together shall constitute one and the same agreement.

            (j) Headings. The headings in this Agreement are for convenience of
      reference only and shall not limit or otherwise affect the meaning hereof.

            (k) Governing Law. THIS AGREEMENT SHALL BE GOVERNED BY, AND
      CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK, WITHOUT
      REGARD TO CONFLICTS OF LAWS PRINCIPLES THEREOF.

            (l) Severability. If any term, provision, covenant or restriction of
      this

                                      -27-

<PAGE>

      Agreement is held to be invalid, illegal, void or unenforceable, the
      remainder of the terms, provisions, covenants and restrictions set forth
      herein shall remain in full force and effect and shall in no way be
      affected, impaired or invalidated thereby, and the parties hereto shall
      use their reasonable best efforts to find and employ an alternative means
      to achieve the same or substantially the same result as that contemplated
      by such term, provision, covenant or restriction, it being intended that
      all of the rights and privileges of the parties shall be enforceable to
      the fullest extent permitted by law.

            (m) Entire Agreement. This Agreement is intended by the parties
      hereto as a final expression of their agreement and is intended to be a
      complete and exclusive statement of the agreement and understanding of the
      parties hereto in respect of the subject matter contained herein and the
      registration rights granted by the Company with respect to the Registrable
      Securities. Except as provided in the Purchase Agreement, there are no
      restrictions, promises, warranties or undertakings, other than those set
      forth or referred to herein, with respect to the registration rights
      granted by the Company with respect to the Registrable Securities. This
      Agreement supersedes all prior agreements and undertakings among the
      parties with respect to such registration rights. No party hereto shall
      have any rights, duties or obligations other than those specifically set
      forth in this Agreement.

            (n) Termination. This Agreement and the obligations of the parties
      hereunder shall terminate upon the end of the Effectiveness Period, except
      for any liabilities or obligations under Section 4, Section 5 or Section 6
      hereof and the obligations to make payments of and provide for additional
      interest under Section 2(e) hereof to the extent such additional interest
      accrues prior to the end of the Effectiveness Period and to the extent any
      overdue additional interest accrues in accordance with the last paragraph
      of such Section 2(e), each of which shall remain in effect in accordance
      with its terms.

            (o) Submission to Jurisdiction. Except as set forth below, no
      proceeding, claim, counterclaim or dispute of any kind or nature
      whatsoever arising out of or in any way relating to this Agreement
      ("Claim") may be commenced, prosecuted or continued in any court other
      than the courts of the State of New York located in the City and County of
      New York or in the United States District Court for the Southern District
      of New York, which courts shall have jurisdiction over the adjudication of
      such matters, and the Company hereby consents to the jurisdiction of such
      courts and personal service with respect thereto. The Company hereby
      consents to personal jurisdiction, service and venue in any court in which
      any Claim arising out of or in any way relating to this Agreement is
      brought by any third party against any Initial Purchaser. THE COMPANY,
      EACH INITIAL PURCHASER AND EACH HOLDER HEREBY WAIVE ALL RIGHTS TO TRIAL BY
      JURY IN ANY PROCEEDING (WHETHER BASED UPON CONTRACT, TORT OR OTHERWISE) IN
      ANY WAY ARISING OUT OF OR RELATING TO THIS AGREEMENT. The Company, each
      Initial Purchaser and each Holder agree that a final judgment in any such
      Proceeding brought in any such court shall be conclusive and binding upon
      the Company, such Initial Purchaser or such Holder, as applicable, and may
      be enforced in any other courts in the jurisdiction of which the Company,
      such Initial Purchaser or such Holder, as applicable, is or may be
      subject, by

                                      -28-

<PAGE>

      suit upon such judgment.

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                                      -29-

<PAGE>

            IN WITNESS WHEREOF, the parties have executed this Agreement as of
      the date first written above.

                                    Very truly yours,

                                    ANTIGENICS INC.

                                    By: _____________________
                                        Name:
                                        Title:

<PAGE>

Accepted and agreed to as of the date first above written, on behalf of itself
and the other several Initial Purchasers:

UBS SECURITIES LLC

By: _____________________________
    Name:
    Title:

By: _____________________________
    Name:
    Title: