<PAGE>

                                                                   EXHIBIT 10.21


                                LICENSE AGREEMENT

 This Agreement is made and entered into between President and Fellows of
 Harvard College (hereinafter HARVARD) having offices at the Office for
 Technology and Trademark Licensing, 124 Mt. Auburn Street, Suite 410 South,
 Cambridge, MA 02138 and Virus Research Institute (hereinafter LICENSEE), a
 corporation of Massachusetts, having offices at 61 Moulton Street, Cambridge,
 MA 02139.

 Whereas HARVARD is the owner by assignment of the entire right, title and
 interest in a patent application [*] in the foreign patent applications
 corresponding, thereto, and in the inventions described and claimed therein and
 any patents issuing thereon:

 Whereas HARVARD is committed to a policy that ideas or creative works produced
 at HARVARD should be used for the greatest possible public benefit; and

 Whereas HARVARD accordingly believes that every reasonable incentive should be
 provided for the prompt introduction of such ideas into public use, all in a
 manner consistent with the public interest; and

 Whereas LICENSEE is desirous of obtaining, an exclusive worldwide license in
 order to practice the above-referenced invention covered by PATENT RIGHTS in
 the United States and in certain foreign countries, and to manufacture, use and
 sell in the commercial market the products made in accordance therewith; and

 Whereas HARVARD is desirous of granting a license to LICENSEE in accordance
 with the terms of this Agreement.

 Now therefore, in consideration of the foregoing premises, the parties agree as
 follows:

                                    ARTICLE I

                                   DEFINITIONS

1.1      PATENT RIGHTS shall mean any and all patents or patent applications
         attached hereto in Appendix A, the inventions described and claimed
         therein, and any divisions, continuations, continuations-in-part
         directed to subject matter specifically described in the applications
         and patents listed in Appendix A, patents issuing thereon, foreign
         counterparts thereof or reissues or reexaminations thereof, which will


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<PAGE>

         be automatically incorporated in and added to this Agreement and shall
         periodically be added to Appendix A and made a part thereof.

1.2      LICENSED PRODUCTS shall mean products which in the country where sold
         or manufactured are covered by (i) an issued, unexpired claim contained
         in PATENT RIGHTS which has not been declared invalid or unenforceable
         by a court of competent jurisdiction or administrative agency or (ii) a
         claim of a pending patent application of PATENT RIGHTS which
         application has been pending for a period of no more than five years
         including the pendency of any parent application in which the claim is
         supported. The period of pendency of a United States provisional
         application shall not be considered in determining such five (5) year
         period.

1.3      LICENSED PROCESSES shall mean processes which in the country where used
         are covered by (i) an issued, unexpired claim contained in PATENT
         RIGHTS which has not been declared invalid or unenforceable by a court
         of competent JURISDICTION OR administrative agency or (ii) a claim of a
         pending patent application of PATENT RIGHTS which application has been
         pending for a period of no more THAN FIVE YEARS including the pendency
         of any parent application in which the claim is supported. The period
         of pendency of a United States provisional application shall not be
         CONSIDERED IN determining such five (5) year period.

1.4      NET SALES means the total received by LICENSEE from sale of LICENSED
         PRODUCTS less transportation charges and insurance, sales taxes, use
         TAXES, EXCISE taxes, value added taxes, customs duties or other
         imports, to the extent itemized on invoice, normal and customary
         quantity and cash discounts (to THE EXTENT ALLOWED), allowances and
         credits on account of rejection or return of LICENSED PRODUCTS and
         rebates including but not limited to those REQUIRED BY A GOVERNMENT OR
         AGENCY THEREOF. In the event that a LICENSED PRODUCT includes, a
         component which has therapeutic and/or prophylactic activity ("Active
         Component(s)") covered by a PATENT RIGHT (Patented Component(s)) and
         Active Components not covered by a PATENT RIGHT (Unpatented
         Component(s)) (such PRODUCT being a Combined Product), then NET SALES
         shall be the amount which is normally received by LICENSEE FROM A SALE
         OF THE PATENTED Component(s) when sold separately in an arm's length
         transaction with an unaffiliated third party. If the Patented
         Component(s) are not sold SEPARATELY, THEN NET SALES upon which royalty
         is paid shall be the NET SALES of the Combined Produce multiplied by a
         fraction, the numerator of which is the cost for producing the Patented
         Components and the denominator of which is the cost for PRODUCING THE
         COMBINED Product.

1.5      AFFILIATES shall mean any company, corporation, or business (i) in
         which LICENSEE directly or indirectly owns or controls at least fifty
         percent (50%) of the VOTING STOCK, or (ii) which directly or indirectly
         owns or controls at least fifty percent (50%) of the voting stock of
         LICENSEE or (iii) the majority ownership of which is DIRECTLY or
         indirectly under common control with LICENSEE.


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1.6      BIOLOGICAL MATERIAL shall mean the materials supplied by HARVARD
         (identified in Appendix B).

1.7      TECHNOLOGY shall mean any and all information or PATENT RIGHTS, or
         BIOLOGICAL MATERIAL supplied by HARVARD to LICENSEE.

1.8      The term "SUBLICENSEE" shall mean any non-AFFILIATE third party
         licensed by LICENSEE to make, have made, use or sell any product or use
         any process under PATENT RIGHTS.

1.9      NON-ROYALTY SUBLICENSE INCOME shall mean sublicense issue fees,
         sublicense maintenance fees, sublicense milestone payments other than
         those listed in Article 3.6, and similar lump-sum royalty payments
         made by SUBLICENSEES to LICENSEE on account of sublicenses pursuant to
         this Agreement but excluding any payments by SUBLICENSEES constituting
         (i) bona fide product research and development expenses and (ii) loans.

1.10     IMPROVEMENT INVENTIONS shall mean any inventions or discoveries that
         ENHANCE, substitute for, or are useful with the products, procedures or
         processes described in PATENT RIGHTS (and which are not included in
         PATENT RIGHTS) to the extent they are (i) dominated by any claims of a
         pending and/or issued patent or patent application which is then
         included in the PATENT RIGHTS, and HARVARD'S OWNERSHIP INTEREST in any
         United States or foreign patents and patent application thereon, and
         (ii) made (i.e., conceived and reduced to practice) by Dr. John Collier
         and/or Michael Starnbach solely or jointly with others directly
         supervised in their laboratories at Harvard Medical School.


                                   ARTICLE II

                                      GRANT

2.1      For the term of this Agreement, HARVARD hereby grants to LICENSEE and
         LICENSEE accepts, subject to the terms and conditions hereof, a
         worldwide license under PATENT RIGHTS and a worldwide license to use
         the BIOLOGICAL MATERIAL, to make and have made, to use and have used,
         to sell and have sold the LICENSED PRODUCTS, and to practice the
         LICENSED PROCESSES. SUCH LICENSE shall include the right to grant
         sublicenses. HARVARD agrees it will not grant licenses to others except
         as required or as permitted in paragraph 2.2 (b). To the extent
         required by an agreement with a government agency that funded research
         which LED TO PATENT RIGHTS, LICENSEE agrees during the period of
         exclusivity of this license in the United States that any LICENSED
         PRODUCT produced for sale in the United States will be manufactured
         substantially in the United States.


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<PAGE>

2.2      The granting and acceptance of this license is subject to the following
         conditions:

         (a) HARVARD's "Statement of Policy in Regard to Inventions, Patents and
         Copyrights" dated March 17, 1986, Public Law 96-517, Public Law 98-620.
         Any right granted in this Agreement greater than that permitted under
         Public Law 96-517 or Public Law 98-620 shall be subject to modification
         as may be required to conform to the provisions of that statute.

         (b) HARVARD's right to make and to use and to grant non-exclusive
         licenses to make and to use, for academic research purposes only and
         not for any commercial purpose, the subject matter described and
         claimed in PATENT RIGHTS, or the BIOLOGICAL MATERIAL.

2.3      HARVARD hereby grants to LICENSEE the right to extend the licenses
         granted or to be granted in paragraph 2.1 to an AFFILIATE subject to
         the terms and conditions hereof.

2.4      All rights reserved to the United States Government and others under
         Public Law 96-517 and 98-620 shall remain and shall in no way be
         affected by this Agreement.

2.5      LICENSEE has provided HARVARD with a development plan for developing
         and obtaining regulatory approval of the LICENSED PRODUCT selected BY
         LICENSEE, which development plan includes milestones.

         LICENSEE shall exert reasonable efforts under THE CIRCUMSTANCES TO
         ACHIEVE SUCH milestones. In the event LICENSEE subsequently indicates
         in writing to HARVARD that such milestones cannot be met or fails to
         meet such milestones, LICENSEE shall promptly notify HARVARD, and
         LICENSEE and HARVARD shall promptly ENTER INTO good faith negotiations
         to reconsider such milestones. In the event that the parties cannot
         agree to the milestones within sixty (60) days after beginning good
         FAITH NEGOTIATIONS, THE matter shall be submitted to arbitration to
         determine the milestones and the time period therefor which should be
         met pursuant to this Section. THE ARBITRATOR IN SETTING AND determining
         milestones shall consider the state of technology; the efforts exerted
         by LICENSEE, the business circumstances of LICENSEE and the public
         INTEREST OBJECTIVES to HARVARD'S licensing program; and technical and
         regulatory problems. Thereafter, LICENSEE shall exert reasonable
         efforts to achieve such milestones.

         In the event that LICENSEE cannot meet the milestones set by
         arbitration because of technological or regulatory problems, HARVARD
         shall not unreasonably deny an extension of time to meet the
         milestones, upon a showing by LICENSEE that it has made good faith
         reasonable efforts to meet the milestones.

         If LICENSEE (i) fails to meet the milestones established by agreement
         of the parties and (ii) fails to obtain extensions of such milestones
         established by arbitration and (iii)


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<PAGE>

         LICENSEE has not exerted good faith reasonable efforts to meet such
         milestones, as its sole and exclusive remedy HARVARD shall have the
         right to terminate or convert the licenses to non exclusive licenses by
         providing to LICENSEE sixty (60) days prior written notice.

         LICENSEE shall ensure that for any PRODUCT being developed or
         commercialized by a SUBLICENSEE, such SUBLICENSEE shall assume the
         obligations imposed on LICENSEE under this paragraph.

         The efforts of an AFFILIATE, SUBLICENSEE or collaborator of LICENSEE
         shall be considered as efforts of LICENSEE.

2.6      The above licenses to sell any LICENSED PRODUCT include the right of
         LICENSEE, its AFFILIATES, and SUBLICENSEES to grant to the purchaser
         thereof the right to use or resell such purchased LICENSED PRODUCT
         without payment of a further royalty.

2.7      HARVARD hereby grants to LICENSEE an exclusive option to negotiate an
         exclusive license to IMPROVEMENT INVENTIONS. It is the intent of the
         parties that such license shall be under substantially the same terms
         and conditions as this LICENSE AND THAT LICENSEE shall only be required
         to pay one royalty for each LICENSED PRODUCT. HARVARD shall notify
         LICENSEE promptly, in writing, of any IMPROVEMENT INVENTION, and
         LICENSEE shall notify HARVARD, in writing, within thirty (30) days
         after receipt of the written notification from HARVARD as to whether or
         not LICENSEE is exercising the option. If the option is not exercised
         within such thirty (30) day period, LICENSEE shall no longer have ANY
         RIGHTS TO THE IMPROVEMENT INVENTION as to which notice was received. If
         the option is exercised, the parties shall negotiate a license in
         accordance with this PARAGRAPH 2.7, in good faith, and if an agreement
         is not reached within six (6) months thereafter, the rights granted
         under this paragraph 2.7 with respect to SUCH IMPROVEMENT INVENTION
         shall terminate. If during such thirty (30) days or six month period,
         HARVARD desires to file a patent application with respect TO THE
         IMPROVEMENT INVENTION, LICENSEE shall bear the cost of filing thereof
         if LICENSEE still desires a license thereunder, provided that the
         filing of such patent APPLICATION IS NECESSITATED BY A BAR DATE or the
         parties have reached final agreement as to the financial terms of the
         license or LICENSEE has requested such filing.


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<PAGE>

                                                         CONFIDENTIAL TREATMENT


                                   ARTICLE III

                                    ROYALTIES

3.1      LICENSEE shall pay to HARVARD a non-refundable license fee as follows:
         [*]

3.2      (a) LICENSEE shall pay HARVARD, during the term of the license granted
         in Section 2.1, (i) a running royalty of [*], and (ii) [*] of running
         royalties [*] received by LICENSEE or its AFFILIATES from a SUBLICENSEE
         for LICENSED PRODUCTS sold by a SUBLICENSEE.

         (b) In the event that a sublicense agreement does not require a
         SUBLICENSEE to pay running royalties, LICENSEE shall pay HARVARD [*].

3.3      Beginning in calendar year 2005 and each calendar year thereafter,
         HARVARD shall have the right to terminate or render non-exclusive this
         license IN THE EVENT that LICENSEE does not pay to HARVARD at least
         [*] in ROYALTIES.

         In the event that actual royalties are not at least equal to the above
         amounts for a specified calendar year, LICENSEE shall have the right to
         pay any DIFFERENCE BETWEEN such minimum amounts and the actual
         royalties paid in satisfaction of its obligations under this Agreement,
         which shall be due and payable within sixty (60) days of the end of the
         applicable calendar year.

3.4      In the event that LICENSEE is required to pay royalties to one or more
         third parties under patents other than PATENT RIGHTS COVERING LICENSED
         PRODUCTS OR LICENSED PROCESSES, LICENSEE shall be entitled to a credit
         against royalties due HARVARD in an amount equal to [*].

3.5      LICENSEE shall pay HARVARD the following amounts within sixty (60) DAYS
         AFTER THE following milestone is achieved by LICENSEE or its
         SUBLICENSEE for each LICENSED PRODUCT:

         (i)      [*]


         (ii)     [*]





/*/ Confidential material omitted and filed separately with the Securities and
    Exchange Commission.



                                       6

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                                                         CONFIDENTIAL TREATMENT


         (iii) [*]

3.6      Only one royalty shall be due and payable for a LICENSED PRODUCT and
         use thereof irrespective of the number of patents included within
         PATENT RIGHTS which are applicable to such LICENSED PRODUCT and use.

3.7      Unless this agreement is earlier terminated, the initial payment under
         paragraph 3.1 and the payments due under paragraph 6.1 shall be due and
         payable on the earlier of (i) six (6) months after the effective date
         of this agreement or (ii) the date on which LICENSEE is granted a
         license under U.S. Patent No. [*] by the UNITED STATES Government.



                                   ARTICLE IV

                                    REPORTING

4.1      LICENSEE shall provide written annual reports within sixty (60) days
         after JUNE 30 of each calendar year which shall include but not be
         limited to: reports of PROGRESS on research and development, regulatory
         approvals, manufacturing, sublicensing, marketing and sales during the
         preceding twelve (12) months.

4.2      LICENSEE shall report to HARVARD the date of first sale of LICENSED
         PRODUCTS in each country within thirty (30) days of occurrence.

4.3      Commencing with the calendar year half in which NET SALES first occur,
         LICENSEE agrees to submit to HARVARD within sixty (60) days after the
         calendar half years ending June 30 and December 31, reports setting
         forth for the preceding six (6) month period the amount of the LICENSED
         PRODUCTS sold by LICENSEE, its AFFILIATES and SUBLICENSEES in each
         country, the NET SALES thereof, and the amount of royalty due thereon
         and with each such report pay the amount of royalty due. Such report
         shall be certified as correct by an officer of LICENSEE and SHALL
         INCLUDE a detailed listing of all deductions from NET SALES, or from
         royalties as specified herein. Such report shall also specify which
         PATENT RIGHTS are used in or by each LICENSED PRODUCT generating
         royalty income. If no royalties ARE DUE to HARVARD for any reporting
         period, the written report shall so state. If ROYALTIES FOR any
         calendar year do not equal or exceed the minimum royalties established
         in paragraph 3.3, LICENSEE shall include the balance of the minimum
         royalty with the PAYMENT for the half year ending December 31. All
         royalties due hereunder shall be PAYABLE in United States dollars and
         shall be made payable to President and Fellows of Harvard College.
         Conversion of foreign currency to U.S. dollars shall be made at the
         CONVERSION rate existing in the United States on the last business day
         in the reporting period as reported in the Wall Street Journal. All
         such reports shall be maintained in CONFIDENCE by HARVARD, except as
         required by law, including Public Law 96-517 and 98-620.





/*/ Confidential material omitted and filed separately with the Securities and
    Exchange Commission.



                                       7

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4.4      If by law, regulation, or fiscal policy of a particular country,
         conversion into United States dollars or transfer of funds of a
         convertible currency to the United States is restricted or forbidden,
         LICENSEE shall give HARVARD prompt notice in writing and shall pay the
         royalty and other amounts due through such means or methods as are
         lawful in such country as HARVARD may reasonably designate. Failing the
         designation by HARVARD of such lawful means or methods within thirty
         (30) days after such notice is given to HARVARD, LICENSEE shall deposit
         such royalty payment in local currency to the credit of HARVARD in a
         recognized banking institution designated by HARVARD, or if none is
         designated by HARVARD within the thirty (30) day period described
         above, in a recognized banking institution selected by LICENSEE and
         identified in a written notice to HARVARD by LICENSEE, and such deposit
         shall fulfill all obligations of LICENSEE to HARVARD with respect to
         such royalties.

4.5      Any tax required to be withheld by LICENSEE under the laws of any
         FOREIGN COUNTRY for the account of HARVARD, shall be promptly paid by
         LICENSEE for and on behalf of HARVARD to the appropriate governmental
         authority, and LICENSEE shall use its best efforts to furnish HARVARD
         with proof of payment of such tax. Payments to HARVARD shall be net of
         any such payments of taxes.


                                    ARTICLE V

                                 RECORD KEEPING

5.1      LICENSEE shall keep, and shall require its AFFILIATES AND SUBLICENSEES
         TO KEEP accurate and correct records of LICENSED PRODUCTS made, used or
         sold under this Agreement, appropriate to determine the AMOUNT OF
         ROYALTIES DUE HEREUNDER to HARVARD. Such records shall be retained for
         at least three (3) years following a given reporting period. They shall
         be available during normal business hours FOR INSPECTION at the expense
         of HARVARD by HARVARD's Internal Audit Department or by a Certified
         Public Accountant selected by HARVARD and approved by LICENSEE for the
         sole purpose of verifying reports and payments hereunder. Such
         accountant shall not disclose to HARVARD any information other than
         information relating to accuracy of reports and payments made under
         this Agreement. In THE EVENT THAT ANY SUCH INSPECTION shows an under
         reporting and underpayment in excess of five percent (5%) for any
         twelve (12) month period, then LICENSEE shall pay the cost of such
         EXAMINATION.


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                                   ARTICLE VI

                       DOMESTIC AND FOREIGN PATENT FILING
                                 AND MAINTENANCE

6.1      LICENSEE shall reimburse HARVARD for all reasonable expenses HARVARD
         has incurred and shall incur for the preparation, filing, prosecution
         and maintenance of PATENT RIGHTS for which HARVARD has not been, and is
         not eligible to be reimbursed by any third party. HARVARD shall take
         responsibility for the preparation, filing, prosecution and maintenance
         of any and all patent applications and patents included in PATENT
         RIGHTS using patent counsel reasonably acceptable to LICENSEE, provided
         however that HARVARD shall first consult with LICENSEE as to the
         preparation, filing, prosecution and maintenance of such patent
         applications and patents and shall furnish to LICENSEE copies of
         documents relevant to any such preparation, filing, prosecution or
         maintenance.

6.2      HARVARD and LICENSEE shall cooperate fully in the preparation, filing,
         prosecution and maintenance of PATENT RIGHTS and of all patents and
         patent applications licensed to LICENSEE hereunder, executing all
         papers and instruments or requiring members of HARVARD to execute such
         papers and instruments so as to enable HARVARD to apply for, to
         prosecute and to maintain patent applications and patents in HARVARD's
         name in any country. Each party shall provide to the other prompt
         notice as to all matters which come to its attention and which may
         affect the preparation filing, prosecution or maintenance of any such
         patent applications or patents.

6.3      If LICENSEE elects not to pay the expenses OF A PATENT APPLICATION OR
         PATENT INCLUDED within PATENT RIGHTS in a particular country, LICENSEE
         shall notify HARVARD not less than sixty (60) days prior to such action
         and shall thereby surrender its rights under such patent or patent
         application in such country.

6.4      HARVARD agrees not to allow any PATENT RIGHT to become abandoned or to
         lapse without the written permission of LICENSEE.


                                   ARTICLE VII

                                  INFRINGEMENT

7.1      With respect to any PATENT RIGHTS under which LICENSEE is exclusively
         licensed pursuant to this Agreement, LICENSEE or its SUBLICENSEE shall
         have the right to prosecute in its own name and at its own expense any
         infringement of such patent, so long as such license is exclusive at
         the time of the commencement of such action. HARVARD agrees to notify
         LICENSEE promptly of each infringement of such patents of which HARVARD
         is or becomes aware. Before LICENSEE or its SUBLICENSEES


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<PAGE>

                                                         CONFIDENTIAL TREATMENT



         commences an action with respect to any infringement of such patents,
         LICENSEE shall give careful consideration to the views of HARVARD and
         to potential effects on the public interest in making its decision
         whether or not to sue and in the case of a SUBLICENSE, shall report
         such views to the SUBLICENSEE.

7.2      (a) If LICENSEE or its SUBLICENSEE elects to commence an action
         described above and HARVARD is a legally indispensable party to such
         action, HARVARD shall join the action as a co-plaintiff. Upon doing so,
         LICENSEE shall reimburse HARVARD for reasonable legal expenses and
         other out-of-pocket costs incurred by HARVARD for its participation in
         such action as a nominal plaintiff.

         (b) To the extent permitted by law, HARVARD shall have the right to
         intervene in any such action, and if HARVARD elects to do so, HARVARD
         shall jointly control such action with LICENSEE.

7.3      If LICENSEE or its SUBLICENSEE elects to commence an action as
         described above, LICENSEE may reduce, by [*], the royalty due to
         HARVARD EARNED UNDER THE patent subject to suit by the amount of the
         expenses and costs of such action, including reasonable attorney fees.
         In the event that such expenses and costs exceed the amount of
         royalties withheld by LICENSEE for any calendar YEAR, LICENSEE MAY TO
         THAT extent reduce the royalties due to HARVARD from LICENSEE in
         succeeding calendar years, but never by [*].

7.4      Recoveries or reimbursements from such action shall first be APPLIED TO
         REIMBURSE LICENSEE and HARVARD for litigation costs not paid from
         royalties (if any) and then to reimburse HARVARD for royalties
         withheld. Any REMAINING RECOVERIES or reimbursements shall be
         distributed as follows:

         (i) If the amount is lost profits, LICENSEE shall RECEIVE AN AMOUNT
         EQUAL TO THE damages the court determines LICENSEE has suffered as a
         result OF THE INFRINGEMENT less the amount of any royalties that would
         have been due HARVARD ON SALES of LICENSED PRODUCTS lost by LICENSEE as
         a result of THE INFRINGEMENT HAD LICENSEE made such sales and HARVARD
         shall receive an amount equal to the royalties they would have received
         if such sales had been made by LICENSEE; OR

         (ii) As to awards other than lost profits, 80% to LICENSEE and 20% to
         HARVARD.

7.5      In the event that LICENSEE and its SUBLICENSEE, if any, elect not to
         exercise their right to prosecute an infringement of the PATENT RIGHTS
         pursuant to the above paragraphs, or does not do so within sixty (60)
         days after written NOTICE FROM HARVARD, HARVARD may do so at its own
         expense, controlling such action and retaining all recoveries
         therefrom, and LICENSEE shall cooperate with HARVARD with respect
         thereto.




/*/ Confidential material omitted and filed separately with the Securities and
    Exchange Commission.



                                       10

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                                  ARTICLE VIII

                            TERMINATION OF AGREEMENT

8.1      This Agreement, unless extended or terminated as provided herein, shall
         remain in effect for the life of the last to expire of PATENT RIGHTS
         licensed hereunder, at which time LICENSEE shall have a fully paid up
         license.

8.2      In the event that one party to this Agreement shall be in default in
         the performance of any obligations under this Agreement, and if the
         default has not been remedied within ninety (90) days after the date of
         notice in writing of such default, the party giving such notice may
         terminate this Agreement by written notice.

8.3      In the event that LICENSEE shall cease to carry on its business,
         HARVARD SHALL HAVE the right to terminate this entire Agreement by
         giving LICENSEE written notice of such termination.

8.4      In the event that the licenses granted to LICENSEE under this Agreement
         are terminated, any granted sub-licenses shall remain in full force and
         effect as a direct license from HARVARD to the SUBLICENSEE, provided
         that the SUBLICENSEE is not then in breach of its sub-license agreement
         and the SUBLICENSEE agrees to be BOUND (as a licensee) to HARVARD (as a
         licensor) under the terms and conditions of THE SUB-LICENSE agreement.

8.5      LICENSEE shall have the right to terminate this Agreement or its
         LICENSE UNDER ANY PATENT RIGHT in any country by giving thirty (30)
         days advance written notice to HARVARD to that effect. Upon
         termination, a formal report shall be submitted and any royalty
         payments and unreimbursed patent expenses due to HARVARD become
         immediately payable.

8.6      Sections 8.4, 8.6, 9.2, 9.3 and 9.4 of this Agreement shall survive
         termination.

8.7      In the event that LICENSEE disputes the termination of this Agreement
         or any license granted hereunder and initiates legal proceedings in
         this respect, then this Agreement or any such license shall not be
         terminated until there is a final decision from WHICH no appeal has
         been or can be taken.


                                   ARTICLE IX

                                     GENERAL

 9.1     HARVARD represents and warrants that the entire right, title, and
         interest in the patent applications or patents comprising the PATENT
         RIGHTS have been or will be assigned


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<PAGE>

         to it and that HARVARD has the authority to issue the licenses under
         said PATENT RIGHTS set forth herein and that there are and will be no
         rights and/or licenses inconsistent with the rights and licenses
         granted to LICENSEE under this Agreement. HARVARD does not warrant the
         validity of the PATENT RIGHTS licensed hereunder and makes no
         representations whatsoever with regard to the scope of the licensed
         PATENT RIGHTS or that such PATENT RIGHTS may be exploited by LICENSEE,
         an AFFILIATE, or sublicensee without infringing other patents.

9.2      EXCEPT AS PROVIDED IN SECTION 9.1, HARVARD EXPRESSLY DISCLAIMS ANY AND
         ALL IMPLIED OR EXPRESS WARRANTIES AND MAKES NO EXPRESS OR IMPLIED
         WARRANTIES OF MERCHANTABILITY OR FITNESS OF THE TECHNOLOGY, LICENSED
         PROCESSES OR LICENSED PRODUCTS CONTEMPLATED BY THIS AGREEMENT.

9.3      (a) LICENSEE shall indemnify, defend and hold harmless HARVARD and its
         directors, governing board members, trustees, officers, faculty,
         medical and professional staff, employees, students, and agents and
         their respective successors, heirs and assigns (the "Indemnitees"),
         against any liability, damage, loss or expenses (including REASONABLE
         attorneys' fees and expenses of litigation) incurred by or imposed upon
         the Indemnitees or any one of them in connection with any claims,
         suits, actions, demands or judgments arising out of any theory of
         product liability (including, but not limited to, ACTIONS IN THE form
         of tort, warranty, or strict liability) concerning any product, process
         or service used or sold pursuant to any right or license granted UNDER
         THIS AGREEMENT.

         (b) LICENSEE'S indemnification under (a) above shall not apply to any
         liability, damage, loss or expense t the extent to apply to any
         liability, damage, loss OR EXPENSE to the extent that it is
         attributable to the negligent activities or willful misconduct of the
         Indemnitees.

         (c) HARVARD shall notify LICENSEE promptly of any claim OR THREATENED
         CLAIM under this Paragraph 9.3 and shall fully cooperate with all
         REASONABLE REQUESTS OF LICENSEE with respect thereto.

         (d) LICENSEE agrees, at its own expense, to provide attorneys
         reasonably acceptable to HARVARD to defend against any actions brought
         or filed against any party indemnified hereunder with respect to the
         indemnity contained HEREIN, WHETHER OR NOT such actions are rightfully
         brought and LICENSEE shall have the right to control the defense,
         settlement or compromise of any such claim or action.

         (e) At such time as any LICENSED PRODUCT is being commercially
         DISTRIBUTED or sold (other than for research purposes or for the
         purpose of obtaining regulatory approvals) by LICENSEE, or by an
         AFFILIATE, SUBLICENSEE or agent of LICENSEE (hereunder "Other Seller"),
         LICENSEE shall itself or in the ALTERNATIVE SHALL ensure that Other
         Seller either (i) at its sole cost and expense, procure(s) and
         maintain(s)


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<PAGE>

         comprehensive general liability insurance in amounts not less than
         $2,000,000 per incident and $2,000,000 annual aggregate and naming the
         Indemnitees as additional insureds or (ii) pay(s) for the procurement
         and maintenance by HARVARD of insurance in the amounts and in the form
         set forth in this paragraph. Such comprehensive general liability
         insurance shall provide (i) product liability coverage and (ii) broad
         form contractual liability coverage for LICENSEE'S indemnification
         under Paragraph 9.3(a) of this Agreement. LICENSEE shall ensure that if
         LICENSEE or the Other Seller elects to self-insure all or part of the
         limits described above (including deductibles or retentions which are
         in excess of $250,000 annual aggregate) such self-insurance program
         must be acceptable to HARVARD and the Risk Management Foundation. The
         minimum amounts of insurance coverage required under this Paragraph
         9.3(c) shall not be construed to create a limit of LICENSEE'S liability
         with respect to its indemnification under Paragraph 9.3(a) of this
         Agreement. At such time, or at any time, LICENSEE can request that
         HARVARD ascertain whether Risk Management Foundation has in effect
         Uniform Indemnification and Insurance Provisions more favorable than
         those of this Agreement, in which event LICENSEE and HARVARD shall
         amend this AGREEMENT TO include such more favorable provisions.

         (f) LICENSEE shall provide HARVARD with written evidence of such
         INSURANCE upon request of HARVARD. LICENSEE shall provide HARVARD with
         written notice of at least thirty (30) days prior to the cancellation,
         non-renewal or MATERIAL CHANGE IN such insurance; if LICENSEE does not
         obtain replacement insurance providing comparable coverage within such
         thirty (30) days period, HARVARD SHALL HAVE THE RIGHT to terminate this
         Agreement effective at the end of such thirty (30) day period by
         written notice to LICENSEE.

         (g) LICENSEE shall itself maintain, or shall ENSURE THAT OTHER SELLER
         MAINTAINS OR that payments are made for the maintenance by HARVARD of,
         as the case may be, such comprehensive general liability insurance
         beyond the expiration or termination of this Agreement during (i) the
         period that any LICENSED PRODUCT is being COMMERCIALLY distributed or
         sold (other than for research purposes or the purpose of obtaining
         regulatory approvals) by Other Seller and (ii) a reasonable period
         after period referred to in (g) (i) above which shall in no event be
         less than ten (10) years. The obligations of (g) (ii) above can be
         satisfied by the purchase of insurance by LICENSEE or a third party
         which covers claims resulting from occurrences during such period of
         (g)(ii) above for LICENSED PRODUCT commercially distributed or sold by
         LICENSEE or Other Seller during the period referred to in (g) (i)
         above.

9.4      LICENSEE shall not use HARVARD's name or any adaptation of it in any
         ADVERTISING, promotional or sales literature without the prior written
         assent of HARVARD.

9.5      Without the prior written approval of HARVARD, the entire license
         GRANTED PURSUANT to this Agreement shall not be transferred by LICENSEE
         to any party other than to a successor to the business interest of
         LICENSEE relating to the PATENT RIGHTS with


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<PAGE>

         such transfer including but not being limited to mergers,
         consolidations, and transfer or sale of assets. This Agreement shall be
         binding upon the successors, legal representatives and assignees of
         HARVARD and LICENSEE.

9.6      The interpretation and application of the provisions of this Agreement
         shall be governed by the laws of the Commonwealth of Massachusetts.

9.7      LICENSEE agrees to comply with all applicable laws and regulations. In
         particular, it is understood and acknowledged that the transfer of
         certain commodities and technical data is subject to United States laws
         and regulations controlling the export of such commodities and
         technical data, including all Export Administration Regulations of the
         United States Department of Commerce. These laws and regulations, among
         other things, prohibit or require a license for the export of certain
         types of technical data to certain specified countries. LICENSEE hereby
         agrees and gives written assurance that it will comply with all United
         States laws and regulations controlling the export of commodities and
         technical data, that it will be solely responsible for any violation of
         such by LICENSEE or its AFFILIATES or sublicensees, and that it will
         defend and hold HARVARD harmless in the event of any legal action of
         any nature occasioned by such violation.

9.8      Written notices required to be given under this Agreement shall be
         addressed as follows:

         If to HARVARD:        Office of Technology and
                               Trademark Licensing
                               Harvard University
                               124 Mt. Auburn Street
                               Suite 410 South
                               Cambridge, MA 02138

         CC:                   Office of Technology Licensing
                               and Industry Sponsored Research
                               Harvard Medical School
                               333 Longwood Ave.
                               Boston, MA 02115

         If to LICENSEE:       Virus Research Institute
                               61 Moulton Street
                               Cambridge, MA 02139
                               Attn: President

 or such other address as either party may request in writing.


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<PAGE>

9.9      Should a court of competent jurisdiction later consider any provision
         of this Agreement to be invalid, illegal, or unenforceable, it shall be
         considered severed from this Agreement. All other provisions, rights
         and obligations shall continue without regard to the severed provision,
         provided that the remaining provisions of this Agreement are in
         accordance with the intention of the parties.

9.10     Any matter under Section 2.3 of this Agreement which is to be resolved
         by arbitration shall be submitted to a mutually-selected single
         arbitrator to so decide any such matter or disagreement. The arbitrator
         shall conduct the arbitration in accordance with the then applicable
         Rules of the American Arbitration Association, unless the parties agree
         otherwise. If the parties are unable to mutually select an arbitrator,
         the arbitrator shall be selected in accordance with the procedures of
         the American Arbitration Association. The decision and award rendered
         by the arbitrator shall be final and binding. Judgment upon the award
         may be entered pursuant to this section and arbitration shall be held
         in Boston, MA, or such other place as may be mutually agreed upon in
         writing by the PARTIES.

9.11     This Agreement constitutes the entire understanding between the parties
         and neither party shall be obligated by any condition or representation
         other than those expressly stated herein or as may be subsequently
         agreed to by the parties hereto in writing.

 IN WITNESS WHEREOF, the parties hereto have caused this Agreement TO BE
 EXECUTED BY their duly authorized representatives.

 The effective date of this Agreement is March 28, 1997.

 PRESIDENT AND FELLOWS OF HARVARD COLLEGE

 By:  /s/ JOYCE BRINTON
      ----------------------
 Name and Title: Joyce Brinton, Director



 Virus Research Institute:

 By:   /s/  WILLIAM A. PACKER
       ----------------------------
 Name and Title: William A. Packer, President


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<PAGE>

                                                         CONFIDENTIAL TREATMENT


 Appendix A

 The following comprise PATENT RIGHTS:

[*]









/*/ Confidential material omitted and filed separately with the Securities and
    Exchange Commission.




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