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                                                                   EXHIBIT 10.17

          CONFIDENTIAL MATERIALS OMITTED AND FILED SEPARATELY WITH THE
         SECURITIES AND EXCHANGE COMMISSION. ASTERISKS DENOTE OMISSIONS.

                                LICENSE AGREEMENT

This AGREEMENT is made by and between Novirio Pharmaceuticals Limited, a
corporation organized and existing under the laws of the Cayman Islands, having
a principal place of business c/o Walker Secretaries, Walker House, Grand
Cayman, Cayman Islands ("Novirio"), and the Dipartimento di Biologia
Sperimentale "Bernardo Loddo" dell'Universita di Cagliari, having a principal
place of business at Cittadella Universitaria, SS 554 KM 4.5, 09133 Monserrato,
Cagliari, Italy (the "University").

                                  INTRODUCTION

         1.       Novirio SARL, an affiliate of Novirio, and the University are
parties to a certain Cooperative Research Activity Agreement dated as of January
4, 1999 (as amended, the "Research Agreement") pursuant to which Novirio SARL
and the University have agreed to undertake a co-operative activity (the
"Co-operative Activity") in connection with research in the field of antiviral
substances.

         2.       Pursuant to the Research Agreement, the University has granted
to Novirio an exclusive license to use the results obtained within or from the
Co-operative Activity.

         3.       This License Agreement is entered to by Novirio and the
University to further establish and define certain terms and conditions relating
to the license granted to Novirio by the University pursuant to the Research
Agreement.

         In consideration of the mutual covenants and promises contained in this
Agreement and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, Novirio and the University agree
as follows:

                                    ARTICLE 1
                                   DEFINITIONS

         As used in this Agreement, the following terms, whether used in the
singular or plural, shall have the following meanings:

         1.1      "Affiliate" means any corporation, company, partnership, joint
venture, firm and/or entity which controls, is controlled by or is under common
control with a Party. For purposes of this Section 1.1, "control" shall mean (i)
in the case of corporate entities, direct or indirect ownership of at least
thirty percent (30%) of the stock or shares entitled to vote for the election of
directors, and (ii) in the case of non-corporate entities, direct or indirect
ownership of at least thirty percent (30%) of the equity interest with the power
to direct the management and policies of such non-corporate entities.

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         1.2      "Co-operative Activity" has the meaning given to such term in
the Introduction.

         1.3      "Effective Date" means the later of (i) the date on which
Novirio executes this Agreement, or (ii) the date on which the University
executes this Agreement.

         1.4      "FDA" means the United States Food and Drug Administration.

         1.5      "First Commercial Sale" means, with respect to each Licensed
Product, the first commercial sale by Novirio, its Affiliates, Sublicensees
and/or distributors of such Licensed Product, other than for clinical trial
purposes or compassionate use.

         1.6      "IND" means an Investigational New Drug Application filed with
the FDA relating to the Licensed Technology.

         1.7      "Intellectual Property Rights" means (i) the Patent Rights;
(ii) the Licensed Technology; and (iii) any other intellectual property rights
relating to the technology developed within or from the Cooperative Activity.

         1.8      "Licensed Product" means a product which, or the manufacture,
use or sale of which, is covered by a Valid Claim of any of the Patent Rights in
the country where the product is manufactured, used or sold.

         1.9      "Licensed Technology" means all designs, technical
information, know-how, knowledge, data, specifications, test results and other
information, whether or not patented, which is known to the University on the
date of this Agreement or hereafter becomes known to the University and is
useful for the manufacture, use or sale of the Licensed Product.

         1.10     "Net Sales" means the gross amount received by Novirio and/or
its Affiliates, as applicable, from sales or other dispositions of a Licensed
Product to independent third parties, less the following items provided that
such items are included in the amount invoiced and do not exceed reasonable and
customary amounts in the country in which such sale or other disposition occurs:
(i) trade, cash and quantity discounts actually allowed and taken; (ii) excise,
sales, customs taxes or other taxes imposed upon and paid with respect to such
sales (excluding national, state or local taxes based on income); (iii) freight,
insurance and other transportation charges incurred in shipping a Licensed
Product to third parties; (iv) amounts repaid or credited by reason of
rejections, defects, recalls or returns or because of retroactive price
reductions; and (v) rebates paid pursuant to government regulations. Such
amounts shall be determined from the books and records of Novirio and/or its
Affiliates, maintained in accordance with United States generally accepted
accounting principles, consistently applied.

         If a Licensed Product is sold, leased, used or otherwise commercially
disposed of for value (including, without limitation, disposition in connection
with the delivery of other products or services) in a transaction that is not an
outright arm's length sale to an independent third party, the term "Net Sales"
shall mean the average gross selling price paid to Novirio in consideration of
sales of the same quantity of Licensed Product during the six (6) month period
immediately preceding such disposition, without reduction of any kind (other
than as provided in clauses (i) - (v) above). If no disposition of Licensed
Products have occurred in the preceding six (6) months, then sales of comparable
products shall be used in such determination. Net Sales shall not

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include any consideration received by Novirio and/or its Affiliates in respect
of the sale, use or other disposition of a Licensed Product in a country prior
to the receipt of all regulatory approvals required to commence full commercial
sales of such Licensed Product in such country (e.g., sales under "treatment
INDs," "named patient sales," "compassionate use sales," or their equivalents).

         In the event the Licensed Product is sold as part of a Combination
Product (as defined below), the Net Sales from the Combination Product, for the
purposes of determining royalty payments, shall be determined by multiplying the
Net Sales of the Combination Product (as defined in the standard Net Sales
definition), during the applicable royalty reporting period, by the fraction,
A/A+B where A is the average sale price of the Licensed Product when sold
separately in finished form for the same indication as the Combination Product
and B is the average sale price of the other product(s) included in the
Combination Product when sold separately in finished form for the same
indication as the Combination Product, in each case during the applicable
royalty reporting period or, if sales of both the Licensed Product and the other
product(s) did not occur in such period, then in the most recent royalty
reporting period in which sales of both occurred. In the event that such average
sale price cannot be determined for both the Licensed product and all other
product(s) included in the Combination Product, Net Sales for the purposes of
determining royalty payments shall be calculated by multiplying the Net Sales of
the Combination Product by the fraction C/C+D where C is the fair market value
of the Licensed Product and D is the fair market value of all other
pharmaceutical product(s) included in the Combination Product. As used above,
the term "Combination Products" means any pharmaceutical product which
incorporates the Licensed Product and other active compounds and/or ingredients.

         1.11     "Party" means Novirio or the University; "Parties" means
Novirio and the University.

         1.12     "Patent Rights" means all patents and patent applications
listed in attached Exhibit A (which shall be updated as additional patents or
patent applications are added to this Agreement by mutual agreement of the
Parties) throughout the world, including any substitutions, extensions,
reissues, reexaminations, renewals, divisions, continuations or
continuations-in-part, which relate to results obtained within or from the
Co-operative Activity.

         1.13     "Research Agreement" has the meaning given to such term in the
Introduction.

         1.14     "Sublicensee" means any third party other than an Affiliate
granted the right, subject to the terms and conditions of Article 2, to make,
use and sell a Licensed Product, but not including a third party that is not
granted the right to make such Licensed Product but merely purchases such
Licensed Product in finished form for resale.

         1.15     "Sublicense Payments" means sublicense fees, milestone
payments and other cash consideration (excluding royalties) received by Novirio
from a Sublicensee, provided that in no event shall Sublicense Payments include
any funds provided by a Sublicensee to fund research and development, to
reimburse Novirio for research and development expenses or to purchase equity
securities of Novirio.

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         1.16     "Sublicense Royalties" means royalties on sales of a Licensed
Product received by Novirio from a Sublicensee.

         1.17     "Valid Claim" means a claim which (i) in the case of any
unexpired United States or foreign patent, shall not have been donated to the
public, disclaimed, nor held invalid or unenforceable by a court of competent
jurisdiction in an unappealed or unappealable decision, or (ii) in the case of
any United States or foreign patent application, shall not have been cancelled,
withdrawn, abandoned nor been pending for more than five (5) years.

                                    ARTICLE 2
                                  LICENSE GRANT

         2.1      License Grant from the University. Pursuant to the terms of
the Research Agreement, the University has granted to Novirio an exclusive
license, including the right to grant sublicenses pursuant to Section 2.2, under
the Intellectual Property Rights, to make, have made, import, use, have used,
offer to sell, sell and have sold the Licensed Products and practice the
Licensed Technology. The University hereby affirms the grant to Novirio of the
license described in the preceding sentence.

         2.2      Sublicense Rights. Novirio shall have the right to grant
sublicenses under the license granted pursuant to Section 2.1 above to parties
with whom Novirio or its Affiliates has agreed to jointly develop and/or
commercialize Licensed Products; provided that any sublicense granted by Novirio
or its Affiliates under this Agreement shall be subject and subordinate to, and
consistent with, the terms and conditions of this Agreement, and shall provide
that any such Sublicensee shall not further sublicense except on terms
consistent with this Section 2.2. Novino shall provide the University with a
copy of any sublicense granted pursuant to this Section 2.2 within one (1) month
after the execution thereof. Such copy may be redacted to exclude confidential
scientific information and other information required by a Sublicensee to be
kept confidential, provided that all relevant financial terms and information
shall be retained therein.

         2.3      Continued Duties of Novirio. Even if Novirio enters into
sublicenses, Novirio remains primarily liable to the University for all of
Novirio's duties and obligations contained in this Agreement, and in the event
of any act or omission of a Sublicensee that would be a breach of its
sublicense, Novirio shall be liable for the performance of Novirio's duties and
obligations under this Agreement in respect of those matters as to which such
breach by the Sublicensee has occurred.

         2.4      Consideration for Sublicense. Without the prior written
consent of the University, Novirio shall not receive from Sublicensees anything
of value in lieu of cash payments in consideration for any sublicense under this
Agreement.

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                                    ARTICLE 3
                               PAYMENT OBLIGATIONS

         During the period set forth in the next sentence, Novirio shall pay to
the University earned royalties at a rate equal to: [**] percent ([**]%) of Net
Sales or if the Intellectual Property Rights are sublicensed, [**] percent
([**]%) of Sublicense Payments or Royalties [**] of any royalties or other
payments required to be paid for licenses under Intellectual Property Rights of
third parties. Novirio shall be obligated to pay royalties at the rate set forth
in the preceding sentence on a country by country basis, so long as there
continues to be a Valid Claim included in the Patent Rights that covers the
applicable Licensed Product in such country or until the tenth anniversary of
the First Commercial Sale of such Licensed Product in such country, whichever is
longer.

                                    ARTICLE 4
                              REPORTS AND PAYMENTS

         4.1      Royalty Reports and Payments. During the term of this
Agreement and for so long thereafter as Novirio is required to pay royalties
under Article 3 hereof, Novirio shall, within forty-five (45) days after each of
March 31, June 30, September 30 and December 31, deliver to the University a
report indicating:

                  (i)      Net Sales for each Licensed Product, on a country by
country basis, including an accounting of the deductions from Net Sales
permitted by the definition thereof;

                  (ii)     total royalties owed under Article 3;

                  (iii)    total Sublicense Payments received by Novirio; and

                  (iv)     total Sublicense Royalties received by Novirio.

         Simultaneous with the delivery of each such report, Novirio shall pay
to the University the payments due under this Agreement for the period covered
by such report. If no royalties are due, it shall be so reported.

         4.2      Interest. In the event that any royalty payment due under this
Agreement is more than thirty (30) days past due, interest shall accrue on such
overdue amount at a rate equal to two (2) percent above the prime rate set forth
in The Wall Street Journal (US. edition) beginning on the first business day
after the due date.

         4.3      Payment Currency. All amounts due under this Agreement shall
be paid in United States currency by wire transfer. The payments due on sales in
currencies other than United States dollars shall be calculated using the
appropriate exchange rate of such currency quoted in The Wall Street Journal (US
edition) on the close of business on the last business day of the calendar
quarter for which such payment is made.

         4.4      Records; Audit. During the term of the Agreement and for a
period not less than three (3) years thereafter, Novirio shall keep at its
principal place of business, in accordance with United States generally accepted
accounting principles, full, true and accurate books of account

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sufficient to readily and accurately determine the amounts payable pursuant to
Article 3. Under appropriate confidentiality provisions, the University shall
have the right, not more than once during any calendar year, to have, the books
and records of Novirio audited by a qualified independent accounting firm of its
choosing, to ascertain: (i) the accuracy of the reports and royalty payments
hereunder; and (ii) compliance by Novirio, its Affiliates and Sublicensees with
their respective obligations arising under this Agreement. Such audit shall be
preceded by at least thirty (30) days' advance notice and conducted during
normal business hours and in a manner that does not interfere unreasonably with
the business of the entity being audited. Except as otherwise provided herein or
agreed by the Parties, the fees and expenses of performing such audit shall be
borne by the University. If Novirio has underpaid or overbilled an amount due
under this Agreement by more than five percent (5%), Novirio shall promptly pay
or refund the appropriate amount to the University and shall also reimburse the
University for the cost of the audit pursuant to which such underpayment or
overbilling is identified.

                                   ARTICLE 5
                          INTELLECTUAL PROPERTY RIGHTS

         5.1      Prosecution and Maintenance of Patent Rights. Novirio shall be
responsible for prosecution and maintenance of patent applications and patents
constituting a part of the Intellectual Property Rights. The University agrees,
and agrees to cause its trustees, employees, agents and representatives as the
case may be, at the expense of Novirio, to execute and deliver any and all
documents Novirio may reasonably request to effect the filing, prosecution or
maintenance by Novirio of such patents or patent applications. In the event that
Novirio decides not to file, prosecute or maintain in any country, a patent or
patent application included in the Patent Rights, it shall notify the University
of such decision, and the University shall have the right to file, prosecute and
maintain such patent or patent application in such country. Novirio agrees, and
agrees to cause its officers, directors, employees and agents, as the case may
be, at the expense of the University, to execute and deliver any and all
documents the University may reasonably request to effect the filing,
prosecution or maintenance by the University of such patents or patent
applications.

         Novirio, upon ninety (90) days advance written notice to the
University, may discontinue its payment of expenses for filing, prosecuting or
maintaining one or more Patent Rights. At its option, the University may elect
to pay such expenses or permit such Patent Rights to become abandoned or lapsed.

         5.2      Infringement of Licensed Technology. Novirio shall promptly
inform the University and the University shall promptly notify Novirio of any
suspected infringement of any Intellectual Property Rights. During the term of
this Agreement, the University and Novirio shall have the right to institute an
action against a third party for infringement of the Intellectual Property
Rights in accordance with the following:

                           (a)      Novirio may take any and all actions, legal
or otherwise, which are necessary to terminate an infringement of the
Intellectual Property Rights, including without limitation obtaining damages,
injunctive, equitable and all other appropriate relief. The University shall
have the right to be kept informed of the status and progress of all actions
instituted by Novirio pursuant to this Section 5.2(a). Novirio shall bear in
full the costs and

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expenses of all actions which it initiates pursuant to this Section 5.2(a)
(including without limitation attorneys' fees).

                           (b)      If Novirio does not institute an action
within 120 days after receiving notice from the University of an infringement of
the Intellectual Property Rights, then the University may institute an action
with respect thereto. Novirio shall have the right to be kept informed of the
status and progress of all such actions instituted by the University pursuant to
this Section 5.2(b). The University shall bear in full the costs and expenses of
all actions which it initiates pursuant to this Section 5.2(b) (including
without limitation attorneys' fees).

                           (c)      Any recoveries or settlement fees received
from suits or settlements involving an action initiated pursuant to Sections
5.2(a) or (b) above shall be paid to and retained by the Party initiating such
action.

         5.3      Abandonment of Infringement. If Novirio commences an action
under the provisions of this Article 5 and thereafter elects to abandon such
action, Novirio will give timely notice to the University which may continue
prosecution of such action, provided that the sharing of expenses and any
recovery in such suit shall be as agreed upon in advance between the Parties.

         5.4      Use of Name in Suit. Where, in the judgment of the Party
initiating or maintaining an action under Section 5.3 or 5.4 above, it is
necessary to use the other Party's name to prosecute such action, or in the
event the other Party is a legally indispensable Party to such action, the other
Party agrees to allow the initiating or maintaining Party to use its the name;
provided however, that the initiating or maintaining Party agrees to hold the
other Party harmless against costs or damages resulting solely from the use of
the name in the action.

         5.5      No Patent Infringement Suit. To the extent that the rights
have not already been licensed exclusively to a third party, the University
agrees not to sue or take other action against any of Novirio, its Affiliates or
Sublicensee for practicing technology owned by or assigned or licensed to the
University, if the practice of such technology by Novirio, its Affiliates or
Sublicensee is necessary or desirable to make, have made, use, import, offer for
sale, sell or have sold Licensed Products.

                                    ARTICLE 6
                         REPRESENTATIONS AND WARRANTIES

         6.1      Representations and Warranties of the University. The
University represents and warrants to Novirio that:

                           (a)      All action on the part of the University,
its trustees and officers necessary for (i) the authorization, execution and
delivery of this Agreement; and (ii) the performance by the University of its
obligations hereunder has been taken.

                           (b)      This Agreement constitutes a legal and
binding obligation of the University, enforceable against the University in
accordance with its terms.

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                           (c)      The execution of this Agreement and the
performance by the University of the transactions contemplated hereby will not
conflict with or result in a breach of any of the terms, conditions or
provisions of, or constitute a default under, or require any consent which has
not been obtained under its charter documents (as amended or restated to date)
or any agreement or other instrument to which the University is a party or by
which it or any of its property is bound.

                           (d)      The University owns or is licensed to use
the Intellectual Property Rights and has the right to grant to Novirio and its
Affiliates the license to the Intellectual Property Rights. As of the date
hereof, the University is not aware of any claims, threatened or pending, or any
grounds for the assertion of any claim, that (i) the development of the Licensed
Products as contemplated in this Agreement would infringe the proprietary rights
of any third party, or (ii) the University does not have the right to use or
license the Intellectual Property Rights for the development of Licensed
Products as contemplated in this Agreement.

         6.2      Representations and Warranties of Novirio. Novirio represents
and warrants to the University that:

                           (a)      All corporate action on the part of Novirio,
its officers, directors and shareholders necessary for (i) the authorization,
execution and delivery of this Agreement; and (ii) the performance by Novirio of
its obligations hereunder has been taken.

                           (b)      This Agreement constitutes a legal and
binding obligation of Novirio, enforceable against Novirio in accordance with
its terms.

                           (c)      The execution of this Agreement and the
performance by Novirio of the transactions contemplated hereby will not conflict
with or result in a breach of any of the terms, conditions or provisions of, or
constitute a default under, or require any consent which has not been obtained
under either its Memorandum and Articles of Association (as amended or restated
to date) or any agreement or other instrument to which Novirio is a party or by
which it or any of its property is bound.

         6.3      Disclaimer. THE FOREGOING REPRESENTATIONS AND WARRANTIES OF
EACH PARTY ARE IN LIEU OF ALL OTHER REPRESENTATIONS AND WARRANTIES NOT EXPRESSLY
SET FORTH HEREIN. EACH OF THE UNIVERSITY AND NOVIRIO DISCLAIM ALL OTHER
WARRANTIES, WHETHER EXPRESS OR IMPLIED, WITH RESPECT TO THEIR RESPECTIVE
RESEARCH, DEVELOPMENT AND COMMERCIALIZATION EFFORTS HEREUNDER, INCLUDING,
WITHOUT LIMITATION, WHETHER THE LICENSED PRODUCTS CAN BE SUCCESSFULLY DEVELOPED
OR MARKETED, THE ACCURACY, PERFORMANCE, UTILITY, RELIABILITY, TECHNOLOGICAL OR
COMMERCIAL VALUE, COMPREHENSIVENESS, MERCHANTABILITY OR FITNESS FOR ANY
PARTICULAR PURPOSE WHATSOEVER OF THE LICENSED PRODUCTS. IN NO EVENT SHALL EITHER
THE UNIVERSITY OR NOVIRIO BE LIABLE FOR SPECIAL, INDIRECT, INCIDENTAL OR
CONSEQUENTIAL DAMAGES ARISING OUT OF THIS AGREEMENT BASED ON CONTRACT, TORT OR
ANY OTHER LEGAL THEORY.

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                                    ARTICLE 7
                              TERM AND TERMINATION

         7.1      Term. This Agreement shall be effective as of the Effective
Date. Unless earlier terminated by the mutual agreement of the Parties or
otherwise in accordance with the provisions of this Article 8, this Agreement
shall continue in force until the expiration of all royalty payment obligations
under Article 3 hereof.

         7.2      Termination by Novirio. Upon four (4) months' prior written
notice to the University, Novirio may terminate this Agreement. Subsequent to
the termination of this License Agreement, the University may negotiate and
grant to a third party a non-exclusive license relating to the Intellectual
Property Rights covered hereby provided that the prior written consent of
Novirio has been obtained.

         7.3      Survival of Obligations. Notwithstanding any termination of
this Agreement, (a) neither Party shall be relieved of any obligations incurred
prior to such termination, and (b) the obligations of the Parties set forth in
Sections 8.2 and 9.2 and this Section 8.3 as well as any other provisions which
by their nature are intended to survive the termination of this Agreement, shall
survive the termination of this Agreement and continue to be enforceable
notwithstanding the termination of this Agreement.

                                    ARTICLE 8
                                  MISCELLANEOUS

         8.1      Governing Law. This Agreement shall be governed by and
interpreted in accordance with the laws of the France.

         8.2      Dispute Resolution. In the event of a dispute arising out of
or relating to this Agreement, the Parties agree to first pursue amicable
resolution of such dispute. In the event the Parties are unable to resolve the
dispute, the Parties agree that all claims or actions for which judicial
resolution is sought shall be brought in the court in Paris, France.

         8.3      Notices. All notices, instructions and other communications
hereunder or in connection herewith shall be in writing and shall be (a)
delivered personally, (b) sent by registered or certified mail, return receipt
requested, postage prepaid, (c) sent via a reputable nationwide overnight
courier service, or (d) sent by facsimile transmission, in each case to an
address set forth below. Any such notice, instruction or communication shall be
deemed to have been delivered upon receipt if delivered by hand, seven business
days after it is sent by registered or certified mail, return receipt requested,
postage prepaid, two business day after it is sent via a reputable nationwide
overnight courier service, or when transmitted with electronic confirmation of
receipt, if transmitted by facsimile (if such transmission is on a business day;
otherwise, on the next business day following such transmission).

Notices to Novirio shall be addressed to:        Novirio Pharmaceuticals Limited
                                                 c/o Walker Secretaries
                                                 Box 265
                                                 George Town
                                                 Grand Cayman, Cayman Islands

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                                           Tel: (345) 914-4284
                                           Fax: (345) 949-7886

With a copy to:                            Novirio Pharmaceuticals, Inc.
                                           Attention: President
                                           125 Cambridge Park Drive
                                           Cambridge, MA 02140
                                           Tel: (617)250-3100
                                           Fax: (617)250-3101

Notices to the University shall be
addressed to:                              Dipartimento di Biologia Sperimentale
                                           Bernardo Loddo dell'Universita di
                                            Cagliari
                                           Attention: Director
                                           Cittadella Universitaria
                                           SS 554 KM 4.5
                                           09133 Monserrato, Cagliari
                                           Italy
                                           Tel: 39-__________________
                                           Fax: 39-__________________

A Party may change its address by giving notice to the other Party in the manner
herein provided.

         8.4      No Agency. Nothing herein shall be deemed to constitute the
University or Novirio as the agent or representative of the other, or as joint
venturers, employees, employers or partners for any purpose. Neither Party shall
have the authority to assume or create obligations on behalf of or in the name
of the other Party or otherwise bind the other Party to any contract agreement
or undertaking with any third party.

         8.5      Entire Agreement. This Agreement constitutes the full
understanding and entire agreement of the Parties with respect to the subject
matter hereof and supersedes all prior understandings and writings relating
thereto. No waiver, alteration or modification of any of the provisions hereof
shall be binding unless made in writing and signed by the Parties.

         8.6      Headings. The headings contained in this Agreement are for
convenience of reference.

         8.7      Severability. In the event that any provision of this
Agreement is held by a court of competent jurisdiction to be unenforceable
because it is invalid or in conflict with any law of any relevant jurisdiction,
the validity of the remaining provisions shall not be affected, and, to the
extent legally permissible, the Parties shall negotiate a substitute provision
that, to the extent possible, accomplishes the original business purpose. In the
event that any provision essential to the commercial purpose of the Agreement is
determined to be illegal, invalid or unenforceable and can not be replaced by a
valid provision which will implement the commercial purpose of the Agreement,
this Agreement and the rights granted herein shall terminate.

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         8.8      Successors and Assigns. This Agreement shall be binding upon
and inure to the benefit of the Parties hereto and their successors and
permitted assigns.

         8.9      Counterparts. This Agreement may be executed in any number of
counterparts, each of that shall be deemed an original but all of such together
shall constitute one and the same instrument.

         8.10     Place of Execution. This Agreement has been and any subsequent
modifications or amendments hereto shall be deemed to have been executed in
Italy.

IN WITNESS WHEREOF, the Parties hereto have caused this Agreement to be executed
in their names by their properly and duly authorized officers or representatives
as of the date first above written.

                                      NOVIRIO PHARMACEUTICALS LIMITED

                                      By: /s/ Jean-Pierre Sommadossi
                                          --------------------------
                                          Jean-Pierre Sommadossi, Ph.D.
                                          Executive President & Chairman

                                      DIPARIMENTO DI BIOLOGIA SPERIMENTALE
                                      <<BERNARDO LODDO>> DELL'UNIVERSITA DI
                                      CAGLIARI

                                      By: /s/ Illegible
                                          -------------
                                          Title: DIRECTORE DI DIPARTIMENTO

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                                    EXHIBIT A

                                  PATENT RIGHTS

United States Patent Application no.  [**].

United States Patent Application no.  [**].

                                       12<PAGE>

                                                                   EXHIBIT 10.18

          CONFIDENTIAL MATERIALS OMITTED AND FILED SEPARATELY WITH THE
         SECURITIES AND EXCHANGE COMMISSION. ASTERISKS DENOTE OMISSIONS.

                                                                   10 April 2002

                                                        Dipartimento di Biologia
                                                   Sperimentale "Bernardo Loddo"
                                                     dell'Universita di Cagliari
                                                         CittadellaUniversitaria
                                                                   SS 554 KM 4.5
                                                     09133 Monserrato (Cagliari)

Dear Sir:

Co-operative Antiviral Research Activity Agreement

With reference to the Co-operative Antiviral Research Activity Agreement,
entered into on 4th January 1999 by and between Novirio SARL, on behalf and for
the benefit of Novirio Pharmaceutical Limited, and the Dipartimento di Biologia
Sperimentale "Bernardo Loddo" dell'Universita di Cagliari, we have noticed that
no specific reference is made to the Laws that shall govern the agreement at
issue. We would then suggest to explicitly provide within the agreement that it
should be governed and interpreted according to the Laws of Italy (that would,
in any case, be applicable in compliance with the provisions set forth under the
Rome Convention of 1980).

Moreover, as a consequence of the application of the Laws of Italy and also for
your convenience, we would also suggest to amend the agreement by providing that
any settlement of the disputes arising out of the agreement shall fall within
the sole competence of the Milan Court, rather than within the competence of the
Paris Court.

In the light of the above remarks, we therefore propose to amend article 10 of
the agreement at issue as follows:

<PAGE>

"10. APPLICABLE LAWS, LITIGATIONS AND DISPUTES

This agreement shall be governed by and interpreted according to the laws of
Italy.

Parties shall try to settle out of court all litigation and disputes deriving
from the interpretation of this agreement. In case of persistent disagreement
settlement shall fall within the sole and exclusive competence of the Milan
(Italy) Court."

Furthermore, we have also noticed that the agreement is near to expire. We would
then suggest to extend the validity period of the agreement up to 4th January
2006: the agreement would then be for the complex duration of 7 years, that
would facilitate and foster the co-operative activity - which represents the
subject matter of the agreement at issue - and would also become more consistent
with the duration of the Licence Agreement entered into by and between Novirio
Pharmaceutical Limited and the Dipartimento di Biologia Sperimentale "Bernardo
Loddo" dell'Universita di Cagliari.

In consideration of said remarks, we would propose to amend article 11 of the
agreement as follows:

"11. DURATION - TERMINATION

This agreement shall be valid for the duration of 7 years from date of signature
(4th January 1999) and will be renewed for this same period by consent expressed
in writing by the parties at least 30 days prior to the expiration of the
initial term. Each party is entitled to terminate this agreement in case of
non-respect of one or more obligations mentioned in this agreement by the other
party. Termination shall be effective 3 months after reception of a registered
letter sent by the aggrieved party specifying the reason for complaint, unless
the defaulting party has contracted its obligations or proven the fault was a
case of `force majeure' within this time frame.

The possibility of termination shall not exempt the defaulting party from
fulfilling its contracted obligations under this agreement prior to the
effective time of termination. In addition to any other damages suffered by the
non-defaulting party, the defaulting party shall be liable for any harm suffered
by the non-defaulting party due to the early termination of this agreement."

ANNEX 1

Finally, we have observed that the Annex 1 to the agreement at issue (under
"Research Program") only refers to researches concerning antiviral activity
against HIV and HBV. Since other research activities have been carried out on
HCV in the past and research is ongoing, we would suggest to update Annex 1 by
including in Annex 1 also the reference to HCV and ... .

Therefore, we would propose to amend said Annex 1 by adding the reference to HCV
and ... by the reference to HIV and HBV.

                                     * * * *

<PAGE>

License Agreement

With reference to the aforesaid License Agreement - which, as above pointed out
has been entered into by and between Novirio Pharmaceutical Limited and the
Dipartimento di Biologia Sperimentale "Bernardo Loddo" dell'Universita di
Cagliari - we have noticed that no execution date is indicated within the same
agreement. Since this could cause some issues also in consideration of the
provision set forth under article 7 ("Term and Termination"), we would propose
to expressly agree that December 14, 2000 shall represent the execution date of
the License Agreement, and that the amendments herein have an effective date of
your signature on this letter.

Moreover, article 8 ("Miscellaneous") of the License Agreement at issue states
that it shall be governed by the laws of France. Nevertheless, since none of the
parties is from France and also in order to make the License Agreement
provisions compliant with the provisions set forth under the Co-operative
Antiviral Research Activity Agreement, we would propose to provide that the
License Agreement at issue shall be governed and interpreted according to the
Laws of Italy and that any settlement of the disputes arising out of the
agreement shall fall within the sole competence of the Milan Court, rather than
within the competence of the Paris Court.

In the light of the above remarks, we would therefore propose to amend points
8.1 and 8.2 of the agreement at issue as follows:

"8.1 GOVERNING LAW This Agreement shall be governed by and interpreted in
accordance with the laws of Italy".

"8.2. DISPUTE RESOLUTION In the event of a dispute arising out of or relating to
this Agreement, the Parties agree to first pursue amicable resolution of such
dispute. In the event the Parties are unable to resolve the dispute, the Parties
agree that all claims or actions for which judicial resolution is sought shall
be solely and exclusively brought in the court in Milan, Italy".

Finally, Exhibit A to the License Agreement should be updated to include the
recent patent filings U.S.S.N. [**]; U.S.S.N. [**] and U.S.S.N. [**]. A copy of
new Exhibit A is attached.

<PAGE>

We deem that the above mentioned remarks and amendments should facilitate the
interpretation of the aforesaid agreements and the relationships among the
parties. Should these remarks and amendments meet your favour, please return us
a copy of this letter signed for explicit approval.

We thank you in advance for your kind cooperation.

Best regards,

                                                   __ April 2002

                                                        Dipartimento di Biologia
                                                   Sperimentale "Bernardo Loddo"
                                                     dell'Universita di Cagliari

For explicit and extensive approval

 /s/ illegible
----------------------------
                        Name

For specific approval of the amendments to article 10 of the Co-operative
Antiviral Research Activity Agreement:

 /s/ illegible
----------------------------
                        Name

For specific approval of the amendments to article 8 of the License Agreement:

 /s/ illegible
----------------------------
                        Name

<PAGE>

                                    EXHIBIT A

                                  PATENT RIGHTS

United States Patent Application no. [**].

United States Patent Application no. [**].

United States Patent Application no. [**].

United States Patent Application no. [**].

United States Patent Application no. [**].

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