Document:

<PAGE>
NOTE: Information in this document marked with an "[*]" has been omitted and
filed separately with the Commission. Confidential treatment has been requested
with respect to the omitted portions.

                                   VIRRX, INC.

                   SERIES A PREFERRED STOCK PURCHASE AGREEMENT

                                  March 7, 2002

<PAGE>

                                TABLE OF CONTENTS

<Table>
<Caption>
                                                                                                                    PAGE
                                                                                                                    ----
<S>                                                                                                                 <C>
1.       Purchase and Sale of Stock...................................................................................1

         1.1      Sale and Issuance of Series A Preferred Stock.......................................................1
         1.2      Closings............................................................................................2
         1.3      Use of Proceeds.....................................................................................3
         1.4      Sales of Investor Common Stock......................................................................3

2.       Representations and Warranties of the Company Applicable to each Closing.....................................3

         2.1      Organization; Good Standing; Qualification..........................................................3
         2.2      Corporate Power.....................................................................................3
         2.3      Authorization.......................................................................................4
         2.4      Valid Issuance of Series A Preferred Stock..........................................................4
         2.5      Capitalization and Voting Rights....................................................................4
         2.6      Subsidiaries........................................................................................5
         2.7      Compliance with Other Instruments...................................................................5
         2.8      Governmental Consent, etc...........................................................................5
         2.9      Offering............................................................................................6
         2.10     Agreements; Action..................................................................................6
         2.11     Obligations to Related Parties......................................................................6
         2.12     Title to Properties and Assets......................................................................7
         2.13     Intellectual Property...............................................................................7
         2.14     Employees; Employee Benefit Plans...................................................................7
         2.15     Proprietary Information and Inventions Assignment Agreement.........................................8
         2.16     Litigation..........................................................................................8
         2.17     Insurance...........................................................................................8
         2.18     Registration Rights.................................................................................8
         2.19     Brokers or Finders; Other Offers....................................................................8
         2.20     Permits.............................................................................................9
         2.21     Financial Statements................................................................................9
         2.22     Tax Returns, Payments and Elections.................................................................9
         2.23     Corporate Documents.................................................................................9
         2.24     Minute Books.......................................................................................10
         2.25     Section 83(b) Elections............................................................................10
         2.26     Qualified Small Business Stock.....................................................................10
         2.27     Environmental and Safety Laws......................................................................10
         2.28     Disclosure.........................................................................................10

3.       Representations and Warranties of the Company Applicable to Milestone Investment Closings...................10

         3.1      Purchase Entirely for Own Account..................................................................10
         3.2      Reliance upon Company's Representations............................................................11
         3.3      Disclosure of Information..........................................................................11
</Table>

                                      -i-

<PAGE>

                                TABLE OF CONTENTS
                                   (CONTINUED)

<Table>
<Caption>
                                                                                                                    PAGE
<S>                                                                                                                 <C>
         3.4      Investment Experience; Economic Risk...............................................................11
         3.5      Residency..........................................................................................11
         3.6      Restricted Securities..............................................................................11
         3.7      Brokers or Finders.................................................................................12
         3.8      Further Limitations on Disposition.................................................................12
         3.9      Legends............................................................................................12

4.       Representations, Warranties and Covenants of the Investor...................................................12

         4.1      Power; Authorization...............................................................................12
         4.2      Purchase Entirely for Own Account..................................................................13
         4.3      Reliance upon Investor's Representations...........................................................13
         4.4      Disclosure of Information..........................................................................13
         4.5      Investment Experience; Economic Risk...............................................................13
         4.6      Accredited Investor Status.........................................................................13
         4.7      Residency..........................................................................................14
         4.8      Restricted Securities..............................................................................14
         4.9      Brokers or Finders.................................................................................14
         4.10     Further Limitations on Disposition.................................................................14
         4.11     Legends............................................................................................14

5.       Conditions to Closing of the Investor.......................................................................15

         5.1      Conditions Applicable to All Closings..............................................................15
         5.2      Conditions Applicable to the Closing of the Initial Investment.....................................16
         5.3      Conditions Applicable to the Closing of each Quarterly Investment..................................17
         5.4      Conditions Applicable to the Closing of the First Milestone Investment.............................17
         5.5      Conditions Applicable to the Closing of each Second Milestone Investment...........................17
         5.6      Conditions Applicable to the Closing of each Third Milestone Investment............................18

6.       Conditions to Closing of Company............................................................................18

         6.1      Conditions Applicable to All Closings..............................................................18
         6.2      Conditions Applicable to the Closing of the Initial Investment.....................................18

7.       Investor's Purchase Right...................................................................................19

         7.1      Purchase Option....................................................................................19
         7.2      Acquisition Agreement..............................................................................20
         7.3      Assignment of Option...............................................................................21
         7.4      Further Agreements.................................................................................21
         7.5      Stockholder Execution of this Agreement............................................................21

8.       Miscellaneous...............................................................................................21

         8.1      Governing Law......................................................................................21
         8.2      Survival of Warranties.............................................................................21
</Table>

                                      -ii-

<PAGE>

                                TABLE OF CONTENTS
                                   (CONTINUED)

<Table>
<Caption>
                                                                                                                    PAGE
<S>                                                                                                                 <C>
         8.3      Successors and Assigns.............................................................................21
         8.4      Entire Agreement...................................................................................22
         8.5      Amendment..........................................................................................22
         8.6      Notices............................................................................................22
         8.7      Delays or Omissions................................................................................22
         8.8      Finder's Fees......................................................................................22
         8.9      Expenses...........................................................................................23
         8.10     Attorney's Fees....................................................................................23
         8.11     Severability.......................................................................................23
         8.12     Interpretation.....................................................................................23
         8.13     Counterparts.......................................................................................23
         8.14     Telecopy Execution and Delivery....................................................................23
         8.15     Adjustments........................................................................................23
</Table>

Schedules:

A        -        Schedule of Stockholders

Exhibits:

A        -        Amended and Restated Certificate of Incorporation

B        -        Schedule of Exceptions

C        -        Investors' Rights Agreement

D        -        Right of First Refusal and Co-Sale Agreement

E        -        Form of Proprietary Information and Inventions Assignment
                  Agreement

F        -        Opinion of Company Counsel

G        -        Repurchase Option Agreement

                                     -iii-

<PAGE>
NOTE: Information in this document marked with an "[*]" has been omitted and
filed separately with the Commission. Confidential treatment has been requested
with respect to the omitted portions.

                   SERIES A PREFERRED STOCK PURCHASE AGREEMENT

         This Series A Preferred Stock Purchase Agreement (this "Agreement") is
made as of March 7, 2002 (the "Effective Date") by and among VirRx, Inc., a
Delaware corporation (the "Company"), Introgen Therapeutics, Inc., a Delaware
corporation (the "Investor"), and the individuals and entities listed on
Schedule A hereto (each a "Stockholder" and, collectively, the "Stockholders").

         1. Purchase and Sale of Stock.

                  1.1 Sale and Issuance of Series A Preferred Stock.

                           (a) The Company shall adopt and file with the
Delaware Secretary of State on or before the Closing (as defined in Section
1.2(f)) of the Initial Investment (as defined in Section 1.2(a)) the Amended and
Restated Certificate of Incorporation in the form attached to this Agreement as
Exhibit A (the "Restated Certificate").

                           (b) The Company has authorized the sale and issuance
of up to [*] shares (the "Series A Shares") of its Series A Preferred Stock, par
value $0.01 per share (the "Series A Preferred Stock"), pursuant to this
Agreement.

                           (c) Subject to the terms and conditions of this
Agreement, the Investor agrees to purchase at each Closing (as defined in
Section 1.2(f)) and the Company agrees to sell and issue to the Investor at each
Closing that number of shares of the Company's Series A Preferred Stock to be
sold in the applicable Closing at a purchase price of [*] per share of Series A
Preferred Stock. The purchase price per share of Series A Preferred Stock shall
be paid by the Investor in cash at each Closing other than the Closings of the
Milestone Investments (as defined in Section 1.2(e)). The purchase price per
share of Series A Preferred Stock at each Closing of a Milestone Investment
shall be paid by, and at the sole discretion of, the Investor in either cash or
by issuing shares of the Investor's Common Stock, par value $0.001 per share
("Investor Common Stock"), valued at the Fair Market Value (as defined below)
thereof. The shares of Series A Preferred Stock to be sold to the Investor
hereunder are hereinafter referred to as the "Shares".

                           (d) The "Fair Market Value" of Investor Common Stock
means, with respect to the date of any Closing:

                                    (i) if the Investor Common Stock is then
traded on a national securities exchange or the Nasdaq Stock Market (or a
similar national quotation system), then the Fair Market Value of the Investor
Common Stock shall be deemed to be the average of the closing prices of the
Investor Common Stock on such exchange or system over the thirty (30) day
trading period ending three (3) trading days prior to the date of the applicable
Closing;

                                    (ii) if the Investor Common Stock is then
actively traded over-the-counter, then the Fair Market Value of the Investor
Common Stock shall be deemed to be the average of the closing bid prices of the
Investor Common Stock over the thirty (30) day trading period ending three (3)
trading days prior to the date of the applicable Closing; and

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  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

<PAGE>
                                    (iii) otherwise, the Fair Market Value of
the Investor Common Stock shall be the fair market value of the Investor Common
Stock as of the date of the applicable Closing, as determined in good faith by
the Investor's Board of Directors.

                  1.2 Closings.

                           (a) The initial purchase and sale of the Shares shall
take place on the date of this Agreement, at which time the Investor shall
purchase [*] Shares (the "Initial Investment").

                           (b) Beginning on April 1, 2002, and upon each July 1,
October 1, January 1 and April 1 thereafter through January 1, 2006, the
Investor will purchase, and the Company will sell to the Investor, [*] Shares
(the "Quarterly Investments").

                           (c) Upon a date mutually agreed to by the Company and
the Investor, but in any event no later than [*] after [*] first completion of a
Phase I clinical study of the first Licensed Product (as defined in the
Collaboration and License Agreement) by the Company, the Investor will purchase,
and the Company will sell to the Investor, [*] Shares (the "First Milestone
Investment"). It is understood that the First Milestone Investment shall be made
[*], and that the total investment under this Section 1.2(c) shall not exceed
[*] Shares.

                           (d) Upon a date mutually agreed to by the Company and
the Investor, but in any event no later than [*] after [*] first completion
of a Phase II clinical study of the first Licensed Product (as defined in the
Collaboration and License Agreement) for each of the [*] defined in the
Collaboration and License Agreement) by the Company, the Investor will purchase,
and the Company will sell to the Investor, [*] Shares (the "Second Milestone
Investments"), subject to the limitations of the Collaboration and License
Agreement. It is understood that a Second Milestone Investment shall be made
only [*] and that the total investment under this Section 1.2(d) shall not
exceed [*] Shares.

                           (e) Upon a date mutually agreed to by the Company and
the Investor, but in any event no later than [*] after [*] first completion of a
Phase III clinical study of the first Licensed Product (as defined in the
Collaboration and License Agreement) for each of the [*] (as defined in the
Collaboration and License Agreement) by the Company, the Investor will purchase,
and the Company will sell to the Investor, [*] Shares (the "Third Milestone
Investments"), subject to the limitations of the Collaboration and License
Agreement. It is understood that a Third Milestone Investment shall be made only
[*], and that the total investment under this Section 1.2(e) shall not exceed

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  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

                                      -2-
<PAGE>

[*] shares. (Collectively, the First Milestone Investment, Second Milestone
Investments and Third Milestone Investments are referred to in this Agreement as
the "Milestone Investments.")

                           (f) The closing of the Initial Investment, each
Quarterly Investment and each Milestone Investment (each a "Closing," and,
collectively, the "Closings") shall take place at the offices of Wilson Sonsini
Goodrich & Rosati, Professional Corporation, located at 8911 Capital of Texas
Highway N., Westech 360, Suite 3350, Austin, Texas 78759-7247, at 4:00 PM local
time, on the date of the applicable Closing.

                           (g) At each Closing, the Company shall deliver to the
Investor a certificate representing the Shares that the Investor is purchasing
against payment of the purchase price therefor by check, wire transfer, shares
of Investor Common Stock (if the Closing is of a Milestone Investment), or any
combination thereof.

                  1.3 Use of Proceeds. The Company agrees that it shall use the
proceeds it receives from the sale of the Shares at each Closing, or from the
sale of any Investor Common Stock received pursuant to this Agreement, solely
for the purpose of conducting (a) the Research Program (as defined in the
Collaboration and License Agreement (as defined in Section 5.2(g) below)) to be
conducted pursuant to the Collaboration and License Agreement or (b) Other
Funded Research (as defined in, and only to the extent permitted under, the
Collaboration and License Agreement).

                  1.4 Sales of Investor Common Stock. If the Company proposes to
sell any Investor Common Stock received by the Company at a Milestone Closing,
then, at least 10 calendar days prior to the date of such proposed sale, the
Company shall notify the Investor of such proposed sale. The Company agrees to
consult with the Investor regarding the terms, conditions and timing of any such
proposed sale in order to facilitate the orderly sale of the Investor Common
Stock proposed to be sold. The Investor agrees to use its commercially
reasonable efforts to facilitate the proposed sale, including providing access
to (a) the Investor's investment bankers and (b) institutional investors whom
the Investor knows desire to purchase Investor Common Stock in a block
transaction.

         2. Representations and Warranties of the Company Applicable to each
Closing.

         Except as set forth on the Schedule of Exceptions attached to this
Agreement as Exhibit B (the "Schedule of Exceptions"), the Company represents
and warrants to the Investor as of the date of each Closing, as follows:

                  2.1 Organization; Good Standing; Qualification. The Company is
a corporation duly organized and validly existing and in good standing under the
laws of the State of Delaware. The Company is duly qualified and is authorized
to transact business and is in good standing as a foreign corporation in the
State of Missouri and in each jurisdiction in which the failure to so qualify
would have a material adverse effect on the Company's business, properties or
financial condition.

                  2.2 Corporate Power. The Company has all requisite legal and
corporate power and authority (i) to own and operate its properties and assets
and to carry on its business as presently

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  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

                                      -3-
<PAGE>

conducted, (ii) to execute and deliver this Agreement, the Investors' Rights
Agreement in the form attached hereto as Exhibit C (the "Investors' Rights
Agreement") and the Right of First Refusal and Co-Sale Agreement in the form
attached hereto as Exhibit D (the "Co-Sale Agreement") (collectively, other than
this Agreement, the "Ancillary Agreements"), (iii) to sell and issue the Shares
and the Common Stock issuable upon conversion thereof and (iv) to carry out and
perform the provisions of this Agreement and the Ancillary Agreements.

                  2.3 Authorization. All corporate action on the part of the
Company, its officers, directors and stockholders necessary for the
authorization, execution, delivery of this Agreement and the Ancillary
Agreements, the performance of all obligations of the Company hereunder and
thereunder, and the authorization, issuance (or reservation for issuance), sale
and delivery of the Shares and the Common Stock issuable upon conversion thereof
has been taken or will be taken prior to the Closing of the Initial Investment.
This Agreement and the Ancillary Agreements, when executed and delivered by the
Company, will constitute valid and binding obligations of the Company,
enforceable in accordance with their respective terms, except (i) as limited by
applicable bankruptcy, insolvency, reorganization, moratorium and other laws of
general application affecting enforcement of creditors' rights generally, (ii)
as limited by laws relating to the availability of specific performance,
injunctive relief or other equitable remedies and (iii) to the extent the
indemnification provisions contained in the Investors' Rights Agreement may be
limited by applicable laws and principles of public policy.

                  2.4 Valid Issuance of Series A Preferred Stock. The Shares,
when issued, sold and delivered in accordance with the terms of this Agreement
for the consideration expressed herein, will be duly authorized, validly issued,
fully paid and nonassessable, and will be free of restrictions on transfer other
than restrictions on transfer under this Agreement and the Ancillary Agreements
and under applicable state and federal securities laws. The Common Stock
issuable upon conversion of the Shares has been duly authorized, validly
reserved for issuance and, upon issuance in accordance with the terms of the
Restated Certificate, will be validly issued, fully paid and nonassessable, and
will be free of restrictions on transfer other than restrictions on transfer
under this Agreement and the Ancillary Agreements and under applicable state and
federal securities laws.

                  2.5 Capitalization and Voting Rights. The authorized capital
of the Company consists, or will consist immediately prior to the Closing of the
Initial Investment, of:

                           (a) Preferred Stock. [*] shares of Preferred Stock,
par value $0.01, of which [*] shares have been designated Series A Preferred
Stock, none of which are issued and outstanding. The relative rights, privileges
and preferences of each authorized series of Preferred Stock will be as stated
in the Restated Certificate.

                           (b) Common Stock. [*] shares of Common Stock, par
value $0.01 ("Common Stock"), [*] of which shares are issued and outstanding.

                           (c) The outstanding shares of Common Stock have been
duly authorized and validly issued, are fully paid and nonassessable, and were
issued in accordance with the

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  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

                                      -4-
<PAGE>

registration or qualification provisions of the Securities Act of 1933, as
amended (the "Securities Act"), and any applicable state securities laws or
pursuant to valid exemptions therefrom.

                           (d) Except for (i) the conversion privileges of the
Series A Preferred Stock, (ii) the rights provided in the Investors' Rights
Agreement and (iii) outstanding options to purchase up to [*] shares of Common
Stock under the VirRx Incentive Stock Plan (the "Stock Plan"), there are no
outstanding options, warrants, rights (including conversion or preemptive
rights) or agreements for the purchase or acquisition from the Company of any of
its securities. The Company has reserved a total of [*] shares of its Common
Stock for options and stock purchase rights granted under the Stock Plan. No
stock plan, stock purchase, stock option or other agreement or understanding
between the Company and any holder of any of the Company's equity securities or
rights to purchase the Company's equity securities provides for acceleration or
other changes in the vesting provisions or other terms of such securities, as
the result of any merger, sale of stock or assets, change in control or other
similar transaction by the Company. The Company is not a party or subject to any
agreement or understanding, and, to the Company's knowledge, there is no
agreement or understanding between any persons that affects or relates to the
voting or giving of written consents with respect to any security or the voting
by a director of the Company.

                  2.6 Subsidiaries. The Company does not own or control,
directly or indirectly, any interest in any corporation, partnership, limited
liability company, association or other business entity. The Company is not a
participant in any joint venture, partnership or similar arrangement, other than
with the Investor.

                  2.7 Compliance with Other Instruments. The Company is not in
violation or default of any provision of its charter or bylaws (both as amended
to date) or of any provision of any mortgage, indenture, agreement, instrument
or contract to which it is a party or by which it is bound or, to the best of
its knowledge, of any federal or state judgment, order, writ, decree, statute,
rule or regulation applicable to the Company. The execution, delivery and
performance by the Company of this Agreement and the Ancillary Agreements, and
the consummation of the transactions contemplated hereby and thereby, will not
result in any such violation or be in conflict with or constitute, with or
without the passage of time or giving of notice, either a default under any such
provision or an event that results in the creation of any lien, charge or
encumbrance upon any assets of the Company or the suspension, revocation,
impairment, forfeiture or nonrenewal of any material permit, license,
authorization or approval applicable to the Company, its business or operations
or any of its assets or properties.

                  2.8 Governmental Consent, etc. No consent, approval,
qualification, order or authorization of, or filing with, any federal, state or
local governmental authority on the part of the Company is required in
connection with the Company's execution, delivery or performance of this
Agreement, the offer, sale or issuance of the Shares or the issuance of the
Common Stock issuable upon conversion of the Shares, except (i) filing of the
Restated Certificate with the Delaware Secretary of State and (ii) such filings
as have been made prior to the Closing, except any notices of sale required to
be filed with the Securities and Exchange Commission under Regulation D of the
Securities Act, or such post-Closing filings as may be required under applicable
state securities laws, which will be timely filed with the applicable periods
therefor.

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  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

                                      -5-
<PAGE>

                  2.9 Offering. Subject in part to the truth and accuracy of the
Investor's representations set forth in Section 4 of this Agreement, the offer,
sale and issuance of the Shares as contemplated by this Agreement are exempt
from the registration requirements of Section 5 of the Securities Act, and all
applicable state securities laws, and neither the Company nor any authorized
agent acting on its behalf will take any action hereafter that would cause the
loss of such exemption.

                  2.10 Agreements; Action.

                           (a) Except for agreements explicitly contemplated by
this Agreement or the Ancillary Agreements, there are no agreements,
understandings or proposed transactions between the Company and any of its
officers, directors, affiliates, or any affiliate thereof.

                           (b) There are no contracts, agreements, instruments,
leases, commitments, understandings, proposed transactions, judgments, orders,
writs or decrees to which the Company is a party or by which it is bound that
may involve (i) obligations (contingent or otherwise) of, or payments to the
Company in excess of, $5,000 or (ii) provisions restricting or affecting the
development, manufacture or distribution of the Company's products or services
or (iii) indemnification by the Company with respect to infringements of
proprietary rights.

                           (c) The Company has not (i) declared or paid any
dividends or authorized or made any distribution upon or with respect to any
class or series of its capital stock, (ii) incurred any indebtedness for money
borrowed or any other liabilities individually in excess of $5,000 or, in the
case of indebtedness and/or liabilities individually less than $5,000, in excess
of $15,000 in the aggregate, (iii) made any loans or advances to any person,
other than ordinary advances for travel expenses, or (iv) sold, exchanged or
otherwise disposed of any of its assets or rights, other than the sale of its
products or services in the ordinary course of business.

                           (d) For the purposes of subsections (b) and (c)
above, all indebtedness, liabilities, agreements, understandings, instruments,
contracts and proposed transactions involving the same person or entity
(including persons or entities the Company has reason to believe are affiliated
therewith) shall be aggregated for the purpose of meeting the individual minimum
dollar amounts of such subsections.

                  2.11 Obligations to Related Parties. No employee, officer,
director or stockholder of the Company or member of his or her immediate family
is indebted to the Company, nor is the Company indebted (or committed to make
loans or extend or guarantee credit) to any of them other than (i) for payment
of salary for services rendered, (ii) reimbursement for reasonable expenses
incurred on behalf of the Company and (iii) for other standard employee benefits
made generally available to all employees (including stock option agreements
outstanding under any stock option plan approved by the Company's Board of
Directors and stock purchase agreements approved by the Company's Board of
Directors). None of such persons has any direct or indirect ownership interest
in any firm or corporation with which the Company is affiliated or with which
the Company has a business relationship, or any firm or corporation that
competes with the Company, except that employees, officers, directors or
stockholders of the Company and members of their immediate families may own
stock in publicly traded companies that may compete with the Company. No

                                      -6-
<PAGE>

employee, officer, director or stockholder, or any member of their immediate
families, is, directly or indirectly, interested in any material contract with
the Company (other than such contracts as relate to any such person's ownership
of capital stock or other securities of the Company).

                  2.12 Title to Properties and Assets. The Company owns its
property and assets free and clear of all mortgages, liens, claims, and
encumbrances other than (i) for liens for current taxes not yet delinquent, (ii)
for liens imposed by law and incurred in the ordinary course of business for
obligations not past due to carriers, warehousemen, laborers, materialmen and
the like, (iii) for liens in respect of pledges or deposits under workers'
compensation laws or similar legislation or (iv) for minor defects in title,
none of which, individually or in the aggregate, materially interferes with the
use of such property. With respect to the property and assets it leases, the
Company is in compliance with such leases and, holds a valid leasehold interest
free of any liens, claims, or encumbrances, subject to clauses (i)-(iv) above.

                  2.13 Intellectual Property. The Company owns or possesses
sufficient legal rights to all patents, trademarks, service marks, trade names,
copyrights, trade secrets, licenses, information, and proprietary rights and
processes (collectively, "Intellectual Property") necessary for its business as
now conducted and as presently proposed to be conducted, and, to the best of its
knowledge, without any conflict with or infringement of the rights of others.
The Schedule of Exceptions contains a complete list of the Company's patents and
pending patent applications. There are no outstanding options, licenses, or
agreements of any kind relating to the Company's Intellectual Property, nor is
the Company bound by or a party to any options, licenses or agreements of any
kind with respect to the Intellectual Property of any other person or entity
with the exception of shrink-wrap, click-wrap or similar widely-available
commercial end-user software licenses. The Company has not received any
communications alleging that the Company has violated or, by conducting its
business as presently proposed, would violate any of the Intellectual Property
of any other person or entity. The Company is not aware that any of its
employees is obligated under any contract (including licenses, covenants or
commitments of any nature) or other agreement, or subject to any judgment,
decree or order of any court or administrative agency, that would interfere with
the use of his or her best efforts to promote the interests of the Company or
that would conflict with the Company's business as presently proposed to be
conducted. Neither the execution nor delivery of this Agreement or the Ancillary
Agreements, nor the carrying on of the Company's business by the employees of
the Company, nor the conduct of the Company's business as presently proposed,
will, to the Company's knowledge, conflict with or result in a breach of the
terms, conditions or provisions of, or constitute a default under, any contract,
covenant or instrument under which any of such employees is now obligated. The
Company does not believe it is or will be necessary to utilize any inventions of
any of its employees (or people it currently intends to hire) made prior to
their employment by the Company.

                  2.14 Employees; Employee Benefit Plans. To the Company's
knowledge, there is no strike, labor dispute or union organization activities
pending or threatened between it and its employees. None of the Company's
employees belongs to any union or collective bargaining unit. The Company has
complied in all material respects with all applicable state and federal equal
opportunity and other laws related to employment. To the Company's knowledge, no
employee of the Company is or will be in violation of any judgment, decree, or
order, or any term of any

                                      -7-

<PAGE>

employment contract, patent disclosure agreement, or other contract or agreement
relating to the relationship of any such employee with the Company, or any other
party because of the nature of the business presently conducted or presently
proposed to be conducted by the Company. The Company does not have any Employee
Benefit Plan as defined in the Employee Retirement Income Security Act of 1974,
as amended. The Company is not aware that any officer or key employee, or that
any group of key employees, intends to terminate their employment with the
Company, nor does the Company have a present intention to terminate the
employment of any of the foregoing. Subject to general principles related to
wrongful termination of employees, the employment of each officer and employee
of the Company is terminable at the will of the Company.

                  2.15 Proprietary Information and Inventions Assignment
Agreement. Each current or former consultant of the Company that assists or
assisted with the development of the Company's Intellectual Property or has or
had access to the Company's Intellectual Property and each current and former
employee and officer of the Company has executed a proprietary information and
inventions assignment agreement in the form or forms attached hereto as Exhibit
E. The Company, after reasonable investigation, is not aware that any of its
employees, officers or consultants are in violation thereof. No current or
former employee or officer has excluded works or inventions made prior to his or
her employment with the Company from his or her assignment of inventions
pursuant to such employee's proprietary information and inventions assignment
agreement.

                  2.16 Litigation. There is no action, suit, proceeding or
investigation pending or, to the Company's knowledge, currently threatened
against the Company, nor, to the Company's knowledge is there any reasonable
basis therefor. The foregoing includes, without limitation, any action, suit,
proceeding or investigation pending or, to the Company's knowledge, currently
threatened involving the prior employment of any of the Company's employees,
their use in connection with the Company's business of any information or
techniques allegedly proprietary to any of their former employers or their
obligations under any agreement with their former employers. The Company is not
a party to or, to its knowledge, named in or subject to any order, writ,
injunction, judgment or decree of any court, government agency or
instrumentality. There is no action, suit, proceeding or investigation by the
Company currently pending or that the Company currently intends to initiate.

                  2.17 Insurance. The Company has in full force and effect fire
and casualty insurance policies, with extended coverage, sufficient in amount
(subject to reasonable deductibles) to allow it to replace any of its properties
that might be damaged or destroyed.

                  2.18 Registration Rights. Except as set forth in the
Investors' Rights Agreement, the Company is presently not under any obligation
and has not granted any rights to register under the Securities Act any of its
presently outstanding securities or any of its securities that may hereafter be
issued.

                  2.19 Brokers or Finders; Other Offers. The Company has not
incurred, and will not incur, directly or indirectly, as a result of any action
taken by the Company, any liability for brokerage or finders' fees or agents'
commissions or any similar charges in connection with this Agreement.

                                      -8-
<PAGE>

                  2.20 Permits. The Company has all franchises, permits,
licenses and any similar authority necessary for the conduct of its business as
presently conducted by it, the lack of which could result in a material adverse
effect on the Company's business, properties or financial condition, and the
Company believes it can obtain, without undue burden or expense, any similar
authority for the conduct of its business as presently proposed to be conducted.
The Company is not in default in any material respect under any of such
franchises, permits, licenses or other similar authority.

                  2.21 Financial Statements. The Company has delivered to the
Investor its unaudited financial statements (balance sheet and profit and loss
statement) as at and for the period from the Company's inception through
December 31, 2001 and as at and for the one-month period ended January 31, 2002
(the "Financial Statements"). The Financial Statements fairly present the
financial condition and operating results of the Company as of the dates, and
for the periods, indicated therein. Except as set forth in the Financial
Statements, the Company has no material liabilities, contingent or otherwise,
other than liabilities incurred in the ordinary course of business subsequent to
January 31, 2002, which individually or in the aggregate are not material to the
financial condition or operating results of the Company. The Company is not a
guarantor or indemnitor of any indebtedness of any other person, firm or
corporation. The Company maintains and will continue to maintain a standard
system of accounting established and administered in accordance with generally
accepted accounting principles.

                  2.22 Tax Returns, Payments and Elections. The Company has
filed all tax returns and reports as required by law. These returns and reports
are true and correct in all material respects. The Company has paid all taxes
and other assessments due, except those contested by it in good faith that are
listed in the Schedule of Exceptions. The provision for taxes of the Company as
shown in the Financial Statements is adequate for taxes due or accrued as of the
date thereof. The Company has not elected pursuant to the Internal Revenue Code
of 1986, as amended (the "Code"), to be treated as a Subchapter S corporation or
a collapsible corporation pursuant to Section 1362(a) or Section 341(f) of the
Code, nor has it made any other elections pursuant to the Code (other than
elections that relate solely to methods of accounting, depreciation or
amortization) that would have a material effect on the Company's business,
properties or financial condition. The Company has never had any tax deficiency
proposed or assessed against it and has not executed any waiver of any statute
of limitations on the assessment or collection of any tax or governmental
charge. None of the Company's federal income tax returns and none of its state
income or franchise tax or sales or use tax returns has ever been audited by
governmental authorities. Since the date of the Financial Statements, the
Company has made adequate provisions on its books of account for all taxes,
assessments and governmental charges with respect to its business, properties
and operations for such period. The Company has withheld or collected from each
payment made to each of its employees, the amount of all taxes (including, but
not limited to, federal income taxes, Federal Insurance Contribution Act taxes
and Federal Unemployment Tax Act taxes) required to be withheld or collected
therefrom, and has paid the same to the proper tax receiving officers or
authorized depositaries.

                  2.23 Corporate Documents. Except for amendments necessary to
satisfy representations and warranties or conditions contained herein (the form
of which amendments has

                                      -9-
<PAGE>

been approved by the Investor), the Company's charter and bylaws are in the form
previously provided to special counsel for the Investor.

                  2.24 Minute Books. The copy of the Company's minute books
provided to the Investor's special counsel contains minutes of all meetings of
directors and stockholders and all actions by written consent without a meeting
by the directors and stockholders since the date of incorporation and accurately
reflects all actions by the directors and stockholders with respect to all
transactions referred to in such minutes in all material respects.

                  2.25 Section 83(b) Elections. To its knowledge, all
individuals who have purchased shares of the Company's Common Stock under
agreements that provide for the vesting of such shares have timely filed
elections under Section 83(b) of the Code and any analogous provisions of
applicable state tax laws.

                  2.26 Qualified Small Business Stock. As of the date of this
Agreement, the Shares constitute "qualified small business stock" within the
meaning of Section 1202 of the Code. The Company will use its reasonable best
efforts to comply with any applicable filing or reporting requirements of
Section 1202 and any regulations promulgated thereunder.

                  2.27 Environmental and Safety Laws. To its knowledge, the
Company is not in violation of any applicable statute, law or regulation
relating to the environment or occupational health and safety, and to its
knowledge, no material expenditures are or will be required in order to comply
with any such existing statute, law or regulation.

                  2.28 Disclosure. The Company has provided the Investor with
all the information reasonably available to it without undue expense that the
Investor has requested for deciding whether to purchase the Shares and all
information that the Company believes is reasonably necessary to enable the
Investor to make such decision. Neither this Agreement, the Ancillary
Agreements, nor any other written statements or certificates made or delivered
in connection herewith, when taken as a whole, contains any untrue statement of
a material fact or omits to state a material fact necessary to make the
statements contained herein or therein not misleading in light of the
circumstances under which they were made.

         3. Representations and Warranties of the Company Applicable to
Milestone Investment Closings.

         The Company represents and warrants to the Investor as of the date of
the Closing of each Milestone Investment at which the Company receives Investor
Common Stock pursuant to Section 1.1(c), as follows:

                  3.1 Purchase Entirely for Own Account. The Company hereby
agrees that the Investor Common Stock will be acquired for investment for the
Company's own account, not as a nominee or agent, and not with a view to the
resale or distribution of any part thereof, and the Company further agrees that
it has no present intention of selling, granting any participation in, or

                                      -10-
<PAGE>

otherwise distributing the same. By executing this Agreement, the Company
further represents that the Company does not have any contract, undertaking,
agreement or arrangement with any person to sell, transfer or grant
participations to the person or to any third person with respect to any of the
Investor Common Stock.

                  3.2 Reliance upon Company's Representations. The Company
understands that the Investor Common Stock is not registered under the
Securities Act on the ground that the sale provided for in this Agreement and
the issuance of the Investor Common Stock hereunder is exempt from registration
under the Securities Act pursuant to Section 4(2) thereof, and that the
Investor's reliance on such exemption is predicated on the Company's
representations set forth herein.

                  3.3 Disclosure of Information. The Company believes it has
received all the information the Company considers necessary or appropriate for
deciding whether to purchase the Investor Common Stock. The Company has had an
opportunity to ask questions and receive answers from the Investor regarding the
terms and conditions of the offering of the Investor Common Stock and the
Investor's business, properties, prospects and financial condition and to obtain
additional information (to the extent the Investor possessed such information or
could acquire it without unreasonable effort or expense) necessary to verify the
accuracy of any information furnished to the Company or to which the Company had
access.

                  3.4 Investment Experience; Economic Risk. The Company
understands that an investment in the Investor involves substantial risks. The
Company is experienced in evaluating and investing in private placement
transactions of securities of companies in a similar stage of development to
that of the Investor and acknowledges that the Company is able to fend for
itself. The Company has such knowledge and experience in financial and business
matters that the Company is capable of evaluating the merits and risks of the
investment in the Investor Common Stock. The Company can bear the economic risk
of the Company's investment and is able, without impairing the Company's
financial condition, to hold the Investor Common Stock for an indefinite period
of time and to suffer a complete loss of the Company's investment.

                  3.5 Residency. The state of the Company's principal place of
business is Missouri.

                  3.6 Restricted Securities. The Company understands that the
Investor Common Stock is characterized as "restricted securities" under the
federal securities laws inasmuch as they are being acquired from the Investor in
a transaction not involving a public offering and that under such federal
securities laws and applicable regulations such Investor Common Stock may be
resold without registration under the Securities Act only in certain limited
circumstances. In this connection, the Company represents that it is aware of
the provisions of Rule 144 promulgated under the Securities Act which permit
limited resale of shares purchased in a private placement subject to the
satisfaction of certain conditions, including, among other things, the existence
of a public market for the shares, the availability of certain current public
information about the Investor, the resale occurring not less than one year
after a party has purchased and paid for the security to be sold, the sale being
effected through a "broker's transaction" or in transactions directly with a
"market maker"

                                      -11-
<PAGE>

and the number of shares being sold during any three-month period not exceeding
specified limitations.

                  3.7 Brokers or Finders. The Investor has not, and will not,
incur, directly or indirectly, as a result of any action taken by the Company,
any liability for brokerage or finders' fees or agents' commissions or any
similar charges in connection with this Agreement.

                  3.8 Further Limitations on Disposition. Without in any way
limiting the representations set forth above, the Company further agrees not to
make any disposition of all or any portion of the Investor Common Stock unless
and until (X) there is then in effect a registration statement under the
Securities Act covering such proposed disposition and such disposition is made
in accordance with such registration statement or (Y) the Company shall have
notified the Investor of the proposed disposition and shall have furnished the
Investor with a detailed statement of the circumstances surrounding the proposed
disposition, and if reasonably requested by the Investor, the Company shall have
furnished the Investor with an opinion of counsel, reasonably satisfactory to
the Investor, that such disposition will be exempt from registration under the
Securities Act. Notwithstanding the foregoing, no such registration statement or
opinion of counsel shall be necessary for a transfer by the Investor to any
person that directly, or indirectly through one or more intermediaries, controls
or is controlled by, or is under common control with, the Investor; provided,
however, that, in such case, the transferee agrees in writing to be subject to
the terms of this Agreement to the same extent as if it were the Company
hereunder.

                  3.9 Legends. The Company understands and agrees that the
certificates evidencing the Investor Common Stock shall bear the following
legend (in addition to any legend required under applicable state securities
laws):

         "THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR THE SECURITIES LAWS OF ANY
STATE, AND MAY NOT BE SOLD, TRANSFERRED, ASSIGNED, PLEDGED OR HYPOTHECATED
UNLESS AND UNTIL REGISTERED UNDER SUCH ACT AND/OR APPLICABLE STATE SECURITIES
LAWS, OR UNLESS THE CORPORATION HAS RECEIVED AN OPINION OF COUNSEL OR OTHER
EVIDENCE, REASONABLY SATISFACTORY TO THE CORPORATION AND ITS COUNSEL, THAT SUCH
REGISTRATION IS NOT REQUIRED."

         4. Representations, Warranties and Covenants of the Investor. The
Investor hereby represents, warrants and covenants to the Company as follows:

                  4.1 Power; Authorization. The Investor has all requisite power
and authority to execute and deliver this Agreement and the Ancillary
Agreements. This Agreement and the Ancillary Agreements, when executed and
delivered by the Investor, will constitute valid and legally binding obligations
of the Investor, enforceable in accordance with their respective terms, except
(i) as limited by applicable bankruptcy, insolvency, reorganization, moratorium
and other laws of general application affecting enforcement of creditors' rights
generally, (ii) as limited by laws relating to the availability of specific
performance, injunctive relief or other equitable remedies and

                                      -12-
<PAGE>

(iii) to the extent the indemnification provisions contained in the Investors'
Rights Agreement may be limited by applicable laws and principles of public
policy.

                  4.2 Purchase Entirely for Own Account. This Agreement is made
with the Investor in reliance upon the Investor's representation to the Company,
which by the Investor's execution of this Agreement the Investor hereby
confirms, that the Shares and the Common Stock issuable upon conversion thereof
will be acquired for investment for the Investor's own account, not as a nominee
or agent, and not with a view to the resale or distribution of any part thereof,
and that the Investor has no present intention of selling, granting any
participation in, or otherwise distributing the same. By executing this
Agreement, the Investor further represents that the Investor does not have any
contract, undertaking, agreement or arrangement with any person to sell,
transfer or grant participations to the person or to any third person with
respect to any of the Shares and the Common Stock issuable upon conversion
thereof.

                  4.3 Reliance upon Investor's Representations. The Investor
understands that the Shares are not, and any Common Stock acquired on conversion
thereof at the time of issuance may not be, registered under the Securities Act
on the ground that the sale provided for in this Agreement and the issuance of
the Shares hereunder is exempt from registration under the Securities Act
pursuant to Section 4(2) thereof, and that the Company's reliance on such
exemption is predicated on the Investor's representations set forth herein.

                  4.4 Disclosure of Information. The Investor believes it has
received all the information the Investor considers necessary or appropriate for
deciding whether to purchase the Shares. The Investor has had an opportunity to
ask questions and receive answers from the Company regarding the terms and
conditions of the offering of the Shares and the Company's business, properties,
prospects and financial condition and to obtain additional information (to the
extent the Company possessed such information or could acquire it without
unreasonable effort or expense) necessary to verify the accuracy of any
information furnished to the Investor or to which the Investor had access. The
foregoing, however, does not limit or modify the representations and warranties
of the Company in Section 2 of this Agreement or the right of the Investor to
rely thereon.

                  4.5 Investment Experience; Economic Risk. The Investor
understands that the Company has a limited financial and operating history and
that an investment in the Company involves substantial risks. The Investor is
experienced in evaluating and investing in private placement transactions of
securities of companies in a similar stage of development to that of the Company
and acknowledges that the Investor is able to fend for himself, herself or
itself. The Investor has such knowledge and experience in financial and business
matters that the Investor is capable of evaluating the merits and risks of the
investment in the Shares. The Investor can bear the economic risk of the
Investor's investment and is able, without impairing the Investor's financial
condition, to hold the Shares and the Common Stock issuable upon conversion
thereof for an indefinite period of time and to suffer a complete loss of the
Investor's investment.

                  4.6 Accredited Investor Status. The Investor is an Accredited
Investor, as such term is defined in Regulation D promulgated under the
Securities Act.

                                      -13-
<PAGE>

                  4.7 Residency. The state of the Investor's principal place of
business is Texas.

                  4.8 Restricted Securities. The Investor understands that the
Shares and the Common Stock issuable upon conversion thereof are characterized
as "restricted securities" under the federal securities laws inasmuch as they
are being acquired from the Company in a transaction not involving a public
offering and that under such federal securities laws and applicable regulations
such Shares and the Common Stock issuable upon conversion thereof may be resold
without registration under the Securities Act only in certain limited
circumstances. In this connection, the Investor represents that it is aware of
the provisions of Rule 144 promulgated under the Securities Act which permit
limited resale of shares purchased in a private placement subject to the
satisfaction of certain conditions, including, among other things, the existence
of a public market for the shares, the availability of certain current public
information about the Company, the resale occurring not less than one year after
a party has purchased and paid for the security to be sold, the sale being
effected through a "broker's transaction" or in transactions directly with a
"market maker" and the number of shares being sold during any three-month period
not exceeding specified limitations.

                  4.9 Brokers or Finders. The Company has not, and will not,
incur, directly or indirectly, as a result of any action taken by the Investor,
any liability for brokerage or finders' fees or agents' commissions or any
similar charges in connection with this Agreement.

                  4.10 Further Limitations on Disposition. Without in any way
limiting the representations set forth above, the Investor further agrees not to
make any disposition of all or any portion of the Shares and the Common Stock
issuable upon conversion thereof unless and until (X) there is then in effect a
registration statement under the Securities Act covering such proposed
disposition and such disposition is made in accordance with such registration
statement or (Y) the Investor shall have notified the Company of the proposed
disposition and shall have furnished the Company with a detailed statement of
the circumstances surrounding the proposed disposition, and if reasonably
requested by the Company, the Investor shall have furnished the Company with an
opinion of counsel, reasonably satisfactory to the Company, that such
disposition will be exempt from registration under the Securities Act.
Notwithstanding the foregoing, no such registration statement or opinion of
counsel shall be necessary for a transfer by the Investor to any person that
directly, or indirectly through one or more intermediaries, controls or is
controlled by, or is under common control with, the Investor; provided, however,
that, in such case, the transferee agrees in writing to be subject to the terms
of this Agreement to the same extent as if it were the original Investor
hereunder.

                  4.11 Legends. The Investor understands and agrees that the
certificates evidencing the Shares and any Common Stock issuable upon conversion
thereof shall bear the following legend (in addition to any legend required by
the Ancillary Agreements or under applicable state securities laws):

                  "THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN
                  REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR
                  THE SECURITIES LAWS OF ANY STATE, AND MAY NOT BE SOLD,
                  TRANSFERRED, ASSIGNED,

                                      -14-
<PAGE>

                  PLEDGED OR HYPOTHECATED UNLESS AND UNTIL REGISTERED UNDER SUCH
                  ACT AND/OR APPLICABLE STATE SECURITIES LAWS, OR UNLESS THE
                  CORPORATION HAS RECEIVED AN OPINION OF COUNSEL OR OTHER
                  EVIDENCE, REASONABLY SATISFACTORY TO THE CORPORATION AND ITS
                  COUNSEL, THAT SUCH REGISTRATION IS NOT REQUIRED."

         5. Conditions to Closing of the Investor.

                  5.1 Conditions Applicable to All Closings. The obligations of
the Investor under Section 1.2 of this Agreement upon the date of any Closing
are subject to the fulfillment on or before the applicable Closing of each of
the following conditions:

                           (a) Representations and Warranties Correct. The
representations and warranties of the Company contained in Section 2, as
modified or qualified by the Company in an updated Schedule of Exceptions, which
updated Schedule of Exceptions shall be delivered at least two (2) business days
prior to the date of the applicable Closing, shall be true and correct in all
material respects on and as of the applicable Closing with the same effect as
though such representations and warranties had been made on and as of the date
of the Closing. The representations and warranties of the Company contained in
the Collaboration and License Agreement, as modified or qualified by the terms
of that agreement, shall be true and correct in all material respects on and as
of the applicable Closing with the same effect as though such representations
and warranties had been made on and as of the date of the Closing.

                           (b) Covenants. All covenants, agreements and
conditions contained in this Agreement to be performed by the Company on or
prior to the applicable Closing shall have been performed or complied with in
all material respects.

                           (c) Compliance Certificate. The Company's President
or Chief Executive Officer shall deliver to the Investor at the applicable
Closing a certificate certifying that the conditions specified in Sections
5.1(a), (b) and (f) and, if applicable, Section 5.4(b), 5.5(b) or 5.6(b), have
been fulfilled.

                           (d) Qualifications. The Company shall have obtained
all necessary Blue Sky law permits and qualifications, or have the availability
of exemptions therefrom, required by any state for the offer and sale of the
Shares and the Common Stock issuable upon conversion thereof.

                           (e) Proceedings and Documents. All corporate and
other proceedings in connection with the transactions contemplated at the
Closing and all documents incident thereto shall be reasonably satisfactory in
form and substance to the Investor's special counsel, which shall have received
all such counterpart original and certified or other copies of such documents as
it may reasonably request.

                                      -15-
<PAGE>

                           (f) Material Adverse Change. Since the date of the
immediately preceding Closing (or since the date of this Agreement, in the case
of the Closing of the Initial Investment), there shall not have occurred any
event, change or effect that is materially adverse to the condition (financial
or otherwise), properties, assets or operations of the Company, taken as a
whole.

                  5.2 Conditions Applicable to the Closing of the Initial
Investment. The obligations of the Investor under Section 1.2(a) of this
Agreement are subject to the fulfillment on or before the date of the Closing of
the Initial Investment of each of the following conditions (in addition to those
set forth in Section 5.1):

                           (a) Secretary's Certificate. The Company shall have
delivered to the Investor a certificate of the Company executed by the Company's
Secretary, dated as of the Closing, certifying to the truth and correctness of
the Restated Certificate, the Bylaws and the board and stockholder resolutions
adopted in connection with the transactions contemplated by this Agreement.

                           (b) Restated Certificate. The Restated Certificate
shall have been filed with and certified by the Delaware Secretary of State.

                           (c) Investors' Rights Agreement. The Company shall
have executed and delivered the Investors' Rights Agreement.

                           (d) Co-Sale Agreement. The Company and the Executives
(as defined in the Co-Sale Agreement) shall have executed and delivered the
Co-Sale Agreement.

                           (e) Opinion of Company Counsel. The Investor shall
have received from Armstrong Teasdale LLP, the Company's corporate counsel, an
opinion, dated the date of the Closing of the Initial Investment, in the form
attached to this Agreement as Exhibit F.

                           (f) Collaboration and License Agreement. The Company
and the Investor shall have entered into a Collaboration and License Agreement
(the "Collaboration and License Agreement") satisfactory in form and substance
to the Investor (as determined in the Investor's sole discretion), and the
Investor shall have received all such counterpart original and certified or
other copies of such Collaboration and License Agreement, and any related
documents, as it may reasonably request.

                           (g) Agreement with [*] University. The Company
shall have entered into an agreement with [*] University satisfactory in
form and substance to the Investor.

                           (h) Agreement with [*] University. The Company
shall have entered into a license agreement with [*] University
satisfactory in form and substance to the Investor.

                           (i) The Company shall have entered into a Repurchase
Option Agreement, in the form attached to this Agreement as Exhibit G, with [*].

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  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

                                      -16-
<PAGE>

                  5.3 Conditions Applicable to the Closing of each Quarterly
Investment. The obligations of the Investor under Section 1.2(b) of this
Agreement are subject to the fulfillment on or before the date of the Closing of
the applicable Quarterly Investment of each of the following conditions (in
addition to those set forth in Section 5.1):

                           (a) Collaboration and License Agreement. The
Collaboration and License Agreement shall be in full force and effect as of the
date of the applicable Closing, and the Investor shall not have received notice
of termination of the Collaboration and License Agreement on or prior to the
date of the applicable Closing.

                           (b) Research Program. The Research Program (as
defined in the Collaboration and License Agreement) shall not have been
terminated by either party as of the date of the applicable Closing, and the
Investor shall not have received notice of termination of the Research Program
on or prior to the date of the applicable Closing.

                           (c) Agreement with [*] University. The agreement with
[*] University described in Section 5.2(h) shall be in full force and effect as
of the date of the applicable Closing, and the Company shall not have received
or given notice of termination of that agreement on or prior to the date of the
applicable Closing.

                           (d) Agreement with [*] University. The license
agreement with [*] University described in Section 5.2(i) shall be in full force
and effect as of the date of the applicable Closing, and the Company shall not
have received or given notice of termination of that agreement on or prior to
the date of the applicable Closing..

                  5.4 Conditions Applicable to the Closing of the First
Milestone Investment. The obligations of the Investor under Section 1.2(c) of
this Agreement are subject to the fulfillment on or before the date of the
Closing of the First Milestone Investment of the following conditions (in
addition to those set forth in Sections 5.1 and 5.3):

                           (a) The final study report upon first completion of a
Phase I clinical study of the first Licensed Product by the Company shall have
been completed.

                           (b) In the event that the Company is receiving
Investor Common Stock at such Closing pursuant to Section 1.1(c), the
representations and warranties of the Company contained in Section 3 shall be
true and correct on and as of the Closing of the First Milestone Investment with
the same effect as though such representations and warranties had been made on
and as of the date of such Closing.

                  5.5 Conditions Applicable to the Closing of each Second
Milestone Investment. The obligations of the Investor under Section 1.2(d) of
this Agreement are subject to the fulfillment on or before the date of the
Closing of each Second Milestone Investment of the following conditions (in
addition to those set forth in Sections 5.1 and 5.3):

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  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

                                      -17-
<PAGE>

                           (a) The final study report upon first completion of a
Phase II clinical study of the first Licensed Product of one of the first three
Distinct [*] Vectors by the Company shall have been completed.

                           (b) In the event that the Company is receiving
Investor Common Stock at such Closing pursuant to Section 1.1(c), the
representations and warranties of the Company contained in Section 3 shall be
true and correct on and as of the Closing of the applicable Second Milestone
Investment with the same effect as though such representations and warranties
had been made on and as of the date of such Closing.

                  5.6 Conditions Applicable to the Closing of each Third
Milestone Investment. The obligations of the Investor under Section 1.2(e) of
this Agreement are subject to the fulfillment on or before the date of the
Closing of each Third Milestone Investment of the following conditions (in
addition to those set forth in Sections 5.1 and 5.3):

                           (a) The final study report upon first completion of a
Phase III clinical study of the first Licensed Product of one of the first three
Distinct [*] Vectors by the Company shall have been completed.

                           (b) In the event that the Company is receiving
Investor Common Stock at such Closing pursuant to Section 1.1(c), the
representations and warranties of the Company contained in Section 3 shall be
true and correct on and as of the Closing of the applicable Third Milestone
Investment with the same effect as though such representations and warranties
had been made on and as of the date of such Closing.

         6. Conditions to Closing of Company.

                  6.1 Conditions Applicable to All Closings. The obligations of
the Company to the Investor under this Agreement upon the date of any Closing
are subject to the fulfillment on or before the applicable Closing of each of
the following conditions by the Investor:

                           (a) Representations. The representations and
warranties of the Investor contained in Section 4 shall be true on and as of the
Closing with the same effect as though such representations and warranties had
been made on and as of the date of the Closing.

                           (b) Blue Sky. The Company shall have obtained all
necessary Blue Sky law permits and qualifications, or have the availability of
exemptions therefrom, required by any state for the offer and sale of the Shares
and the Common Stock issuable upon conversion thereof.

                  6.2 Conditions Applicable to the Closing of the Initial
Investment. The obligations of the Company under Section 1.2(a) of this
Agreement are subject to the fulfillment on or before the date of the Closing of
the Initial Investment of each of the following conditions (in addition to those
set forth in Section 6.1):

                           (a) Restated Certificate. The Restated Certificate
shall have been filed with and certified by the Delaware Secretary of State.

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  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

                                      -18-
<PAGE>

                           (b) Investors' Rights Agreement. The Investor shall
have executed and delivered the Investors' Rights Agreement.

                           (c) Co-Sale Agreement. The Investor shall have
executed and delivered the Co-Sale Agreement.

         7. Investor's Purchase Right.

                  7.1 Purchase Option. The Company and the Stockholders hereby
agree that the Investor shall have the right (the "Option") to acquire all of
the issued and outstanding securities of the Company not then held by the
Investor, including all outstanding options (whether vested or unvested),
warrants and other securities convertible into or exchangeable or exercisable
for Company capital stock (collectively, the "Non-Investor Shares") at any time
on or prior to the fifth anniversary of the Effective Date (the "Purchase
Period"), on the following terms:

                           (a) Purchase. Upon the exercise of the Option by the
Investor, the price per share paid by the Investor for each Non-Investor Share
(assuming the exercise, exchange or conversion of all securities exercisable or
exchangeable for or convertible into Company capital stock) shall be the
applicable Per Share Purchase Price (as defined below); provided, however, if
the aggregate consideration paid by the Investor for all of the Non-Investor
Shares would otherwise exceed the applicable Maximum Purchase Price (as defined
below), the applicable Per Share Purchase Price shall be [*]; provided, further,
however, that in the event that after the Effective Date the Company grants
options pursuant to the Stock Plan to purchase its Common Stock to its employees
or consultants who were not employees or consultants of the Company as of the
Effective Date, the Maximum Purchase Price shall be [*] (as defined below).

                           (b) Certain Definitions. For the purposes of this
Section 7, the "Per Share Purchase Price," "Maximum Purchase Price" and "Maximum
Option Purchase Price" shall be determined based on the date that the Investor
is deemed to deliver notice of the exercise of the Option to the Company, as set
forth in the following table:

<Table>
<Caption>
DATE NOTICE OF EXERCISE IS
DEEMED DELIVERED                 PER SHARE PURCHASE PRICE      MAXIMUM PURCHASE PRICE        MAXIMUM OPTION PURCHASE PRICE
--------------------------       ------------------------      ----------------------        -----------------------------
<S>                              <C>                           <C>                           <C>
[*]                              [*]                           [*]                           [*]
</Table>

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  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

                                      -19-
<PAGE>

<Table>
<Caption>
DATE NOTICE OF EXERCISE IS
DEEMED DELIVERED                 PER SHARE PURCHASE PRICE      MAXIMUM PURCHASE PRICE        MAXIMUM OPTION PURCHASE PRICE
--------------------------       ------------------------      ----------------------        -----------------------------
<S>                              <C>                           <C>                           <C>
[*]                              [*]                           [*]                           [*]
</Table>

                           (c) Exercise; Acceleration Upon IPO.

                                    (i) In the event that the Company
contemplates an initial public offering of its securities (the "IPO"), the
Company shall provide notice (the "IPO Notice") to the Investor of such IPO at
least thirty (30) days prior to the date of filing (the "IPO Filing Date") of
the Company's registration statement for the IPO with the Securities and
Exchange Commission.

                                    (ii) If the IPO Notice is timely given by
the Company and the Option is not exercised by the Investor prior to the IPO
Filing Date (as set forth in the IPO Notice), then the Option shall expire as of
the IPO Filing Date and shall not be exercisable on or after the IPO Filing
Date; provided, however, that in the event that after giving the IPO Notice the
Company does not consummate the IPO on or prior to the day that is one hundred
fifty (150) days after the IPO Filing Date, the Option shall be reinstated and
shall be again exercisable by the Investor as otherwise set forth in this
Section 7.

                                    (iii) Other than as set forth in Section
7.1(c)(ii), the Option may be exercised by the Investor at any time during the
Purchase Period through the delivery of written notice of exercise to the
Company.

                  7.2 Acquisition Agreement. Upon the exercise of the Option by
the Investor, the Company and the Investor shall in good faith negotiate and
execute a definitive acquisition agreement containing customary terms and
conditions, including standard representations and warranties, indemnification
of the Investor and its affiliates by the Company's stockholders, an escrow fund
for indemnification claims and providing for the purchase price to be payable in
shares of Investor's common stock (valued at the then fair market value
thereof), cash, or any combination thereof, as determined by the Investor in its
sole discretion.

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  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

                                      -20-
<PAGE>

                  7.3 Assignment of Option. The Investor may assign the Option
to any person by providing notice of such assignment to the Company. Such
assignment by the Investor shall not require the consent of the Company or the
Stockholders. For the purposes of this Section 7, the term "Investor" shall
include any assignee of the Option.

                  7.4 Further Agreements. If the Option is exercised by the
Investor, each of the parties to this Agreement agrees to use its best efforts
to take, or cause to be taken, all actions and to do or cause to be done all
things necessary, proper or advisable under applicable laws and regulations to
consummate and make effective the transactions contemplated by the Option,
including, but not limited to, obtaining any necessary stockholder, governmental
or third party approvals. Except as required by the federal securities laws,
statues, rules or regulations, no party to this Agreement shall publicly
disclose the existence of the Option without the written consent of the
nondisclosing party. The Company covenants and agrees, while the Option is in
effect, not to sell, lease, license or otherwise transfer any of the Company's
assets or any interest in the Company's assets to any third party (including,
without limitation, any parent, subsidiary or affiliate of the Company), or take
any other action the effect of which would be to reduce the value of the Company
or the Option, except in the ordinary course of business and consistent with
past practice or with the prior written consent of the Investor.

                  7.5 Stockholder Execution of this Agreement. The Company
agrees to use its best efforts to cause all current and future holders of
capital stock of the Company, including all outstanding options (whether vested
or unvested), warrants and other securities convertible into or exchangeable or
exercisable for Company capital stock, to execute and become a party to this
Agreement. Upon the execution of this Agreement by any such person, such person
shall become a party to this Agreement as a "Stockholder" and shall be listed on
Schedule A hereto.

         8. Miscellaneous.

                  8.1 Governing Law. THIS AGREEMENT SHALL BE GOVERNED IN ALL
RESPECTS BY THE INTERNAL LAWS OF THE STATE OF DELAWARE AS APPLIED TO AGREEMENTS
ENTERED INTO AMONG DELAWARE RESIDENTS TO BE PERFORMED ENTIRELY WITHIN DELAWARE,
WITHOUT REGARD TO CONFLICT OF LAWS RULES.

                  8.2 Survival of Warranties. The representations, warranties
and covenants of the Company and the Investor contained herein or made pursuant
to this Agreement shall survive for two years from the date of the applicable
Closing.

                  8.3 Successors and Assigns. Except as otherwise provided
herein, the provisions of this Agreement shall inure to the benefit of, and be
binding upon, the respective successors, assigns, heirs, executors and
administrators of the parties to this Agreement. Nothing in this Agreement,
express or implied, is intended to confer upon any party other than the parties
to this Agreement or their respective successors and assigns any rights,
remedies, obligations or liabilities under or by reason of this Agreement,
except as expressly provided in this Agreement.

                                      -21-
<PAGE>

                  8.4 Entire Agreement. This Agreement, including the exhibits
attached to this Agreement, and the other documents delivered pursuant to this
Agreement constitute the full and entire understanding and agreement among the
parties with regard to the subject matter hereof and thereof, and no party shall
be liable or bound to any other party in any manner by any warranties,
representations or covenants except as specifically set forth herein or therein.

                  8.5 Amendment. Except as expressly provided herein, neither
this Agreement nor any term of this Agreement may be amended, waived, discharged
or terminated other than by a written instrument signed by the party against
whom enforcement of any such amendment, waiver, discharge or termination is
sought.

                  8.6 Notices. All notices and other communications required or
permitted under this Agreement shall be in writing and shall be delivered
personally by hand or by courier, mailed by United States first-class mail,
postage prepaid, sent by facsimile or sent by electronic mail directed (a) if to
the Investor, at the Investor's address, facsimile number or electronic mail
address set forth on the Investor's signature page to this Agreement, or at such
other address, facsimile number or electronic mail address as the Investor may
designate by ten (10) days' advance written notice to the Company, (b) if to the
Company, to its address or facsimile number set forth on its signature page to
this Agreement and directed to the attention of the President, or at such other
address or facsimile number as the Company may designate by ten (10) days'
advance written notice to the Investor and (c) if to a Stockholder, at such
Stockholder's address, facsimile number or electronic mail address set forth in
the Company's records (which information the Company shall promptly provide to
the Investor upon request). All such notices and other communications shall be
deemed given upon personal delivery, on the date of mailing, upon confirmation
of facsimile transfer or when directed to the appropriate electronic mail
address.

                  8.7 Delays or Omissions. Except as expressly provided herein,
no delay or omission to exercise any right, power or remedy accruing to the
Investor, upon any breach or default of the Company under this Agreement, shall
impair any such right, power or remedy of the Investor nor shall it be construed
to be a waiver of any such breach or default, or an acquiescence therein, or of
any similar breach or default thereafter occurring; nor shall any waiver of any
single breach or default be deemed a waiver of any other breach or default
theretofore or thereafter occurring. Any waiver, permit, consent or approval of
any kind or character on the part of the Investor of any breach or default under
this Agreement, or any waiver on the part of the Investor of any provisions or
conditions of this Agreement, must be in writing and shall be effective only to
the extent specifically set forth in such writing. All remedies, either under
this Agreement or by law or otherwise afforded to the Investor, shall be
cumulative and not alternative.

                  8.8 Finder's Fees. With respect to any finder's fees arising
out of the purchase of the Shares pursuant to this Agreement:

                           (a) The Company hereby agrees to indemnify and to
hold the Investor harmless of and from any liability for any commission or
compensation in the nature of a finder's fee to any broker or other person or
firm (and the costs and expenses of defending against such

                                      -22-
<PAGE>

liability or asserted liability) for which the Company or any of its employees
or representatives are responsible.

                           (b) The Investor hereby agrees to indemnify and to
hold the Company harmless of and from any liability for any commission or
compensation in the nature of a finder's fee to any broker or other person or
firm (and the costs and expenses of defending against such liability or asserted
liability) for which the Investor or any of its employees or representatives,
are responsible.

                  8.9 Expenses. Each party shall pay all costs and expenses that
such party incurs with respect to the negotiation, execution, delivery and
performance of this Agreement.

                  8.10 Attorney's Fees. If any action at law or in equity is
necessary to enforce or interpret the terms of this Agreement, the Ancillary
Agreements or the Restated Certificate, the prevailing party shall be entitled
to reasonable attorney's fees, costs and necessary disbursements in addition to
any other relief to which such party may be entitled.

                  8.11 Severability. In the event that any provision of this
Agreement becomes or is declared by a court of competent jurisdiction to be
illegal, unenforceable or void, this Agreement shall continue in full force and
effect without said provision; provided that no such severability shall be
effective if it materially changes the economic benefit of this Agreement to any
party.

                  8.12 Interpretation. The words "include," "includes" and
"including" when used herein shall be deemed in each case to be followed by the
words "without limitation." The titles and subtitles used in this Agreement are
used for convenience only and are not considered in construing or interpreting
this Agreement.

                  8.13 Counterparts. This Agreement may be executed in any
number of counterparts, each of which shall be enforceable, and all of which
together shall constitute one instrument.

                  8.14 Telecopy Execution and Delivery. A facsimile, telecopy or
other reproduction of this Agreement may be executed by one or more parties to
this Agreement, and an executed copy of this Agreement may be delivered by one
or more parties to this Agreement by facsimile or similar electronic
transmission device pursuant to which the signature of or on behalf of such
party can be seen, and such execution and delivery shall be considered valid,
binding and effective for all purposes. At the request of any party to this
Agreement, all parties to this Agreement agree to execute an original of this
Agreement as well as any facsimile, telecopy or other reproduction of this
Agreement.

                  8.15 Adjustments. In the event that after the Effective Date
the Company shall effect a stock dividend, stock split, combination,
reorganization, recapitalization, reclassification or other similar event with
respect to its any class or series of its capital stock, then the "Per Share
Purchase Price" and any share or option numbers referenced in Section 7 hereof
shall be adjusted as appropriate to effect the intent of the parties hereto;
provided, however, that the "Maximum Purchase

                                      -23-
<PAGE>

Price" and "Maximum Option Purchase Price" shall not be subject to any such
adjustment. In the event that after the Effective Date the Company shall effect
a stock dividend, stock split, combination, reorganization, recapitalization,
reclassification or other similar event with respect to the Series A Preferred
Stock, then the number of Shares purchased by the Investor at each Closing
thereafter and the price per Share paid by the Investor at each Closing
thereafter shall be adjusted as appropriate to effect the intent of the parties
hereto.

                                      -24-
<PAGE>

         IN WITNESS WHEREOF, the parties have executed this Agreement on the
day, month and year first set forth above.

                                    "COMPANY"

                                    VirRx, Inc.

                                    By: /s/ WILLIAM WOLD
                                       ----------------------------------------
                                                William Wold, President

                                    Address:

                                    1609 Adgers Wharf Drive
                                    St. Louis, Missouri 63017
                                    Facsimile #: 314-773-3403
                                    [*]

                                   VIRRX, INC.
                   SERIES A PREFERRED STOCK PURCHASE AGREEMENT
                                 SIGNATURE PAGE

------------
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  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.
<PAGE>

                                    "INVESTOR"

                                    Introgen Therapeutics, Inc.

                                    By: /s/ DAVID NANCE
                                       ----------------------------------------
                                    Name:  David Nance
                                         --------------------------------------
                                    Title: President and CEO
                                          -------------------------------------

                                    Address:

                                    301 Congress Avenue, Suite 1850
                                    Austin, Texas 78701
                                    Facsimile: (512) 708-9311

                                   [*]

                                   VIRRX, INC.
                   SERIES A PREFERRED STOCK PURCHASE AGREEMENT
                                 SIGNATURE PAGE

     ----------
     * Certain information on this page has been omitted and filed separately
       with the Commission. Confidential treatment has been requested with
       respect to the omitted portions.
<PAGE>

                                    "STOCKHOLDER"+

                                      [*]
                                    -------------------------------------------
                                    (Signature)

                                      [*]
                                    -------------------------------------------
                                    (Print Name of Stockholder)

                                    -------------------------------------------
                                    (Title, if signing on behalf of an entity)

                                    +Executes this Agreement solely for the
                                    purposes of Section 7 hereof.

                                   VIRRX, INC.
                   SERIES A PREFERRED STOCK PURCHASE AGREEMENT
                                 SIGNATURE PAGE

     ----------
     * Certain information on this page has been omitted and filed separately
       with the Commission. Confidential treatment has been requested with
       respect to the omitted portions.
<PAGE>

                                    "STOCKHOLDER"+

                                      [*]
                                    -------------------------------------------
                                    (Signature)

                                      [*]
                                    -------------------------------------------
                                    (Print Name of Stockholder)

                                    -------------------------------------------
                                    (Title, if signing on behalf of an entity)

                                    +Executes this Agreement solely for the
                                    purposes of Section 7 hereof.

                                   VIRRX, INC.
                   SERIES A PREFERRED STOCK PURCHASE AGREEMENT
                                 SIGNATURE PAGE

     ----------
     * Certain information on this page has been omitted and filed separately
       with the Commission. Confidential treatment has been requested with
       respect to the omitted portions.
<PAGE>

                                    "STOCKHOLDER"+

                                      [*]
                                    -------------------------------------------
                                    (Signature)

                                      [*]
                                    -------------------------------------------
                                    (Print Name of Stockholder)

                                    -------------------------------------------
                                    (Title, if signing on behalf of an entity)

                                    +Executes this Agreement solely for the
                                    purposes of Section 7 hereof.

                                   VIRRX, INC.
                   SERIES A PREFERRED STOCK PURCHASE AGREEMENT
                                 SIGNATURE PAGE

     ----------
     * Certain information on this page has been omitted and filed separately
       with the Commission. Confidential treatment has been requested with
       respect to the omitted portions.
<PAGE>

                                    "STOCKHOLDER"+

                                      [*]
                                    -------------------------------------------
                                    (Signature)

                                      [*]
                                    -------------------------------------------
                                    (Print Name of Stockholder)

                                    -------------------------------------------
                                    (Title, if signing on behalf of an entity)

                                    +Executes this Agreement solely for the
                                    purposes of Section 7 hereof.

                                   VIRRX, INC.
                   SERIES A PREFERRED STOCK PURCHASE AGREEMENT
                                 SIGNATURE PAGE

     ----------
     * Certain information on this page has been omitted and filed separately
       with the Commission. Confidential treatment has been requested with
       respect to the omitted portions.
<PAGE>

                                    "STOCKHOLDER"+
                                      [*]
                                    -------------------------------------------
                                    (Signature)

                                      [*]
                                    -------------------------------------------
                                    (Print Name of Stockholder)

                                    -------------------------------------------
                                    (Title, if signing on behalf of an entity)

                                    +Executes this Agreement solely for the
                                    purposes of Section 7 hereof.

                                   VIRRX, INC.
                   SERIES A PREFERRED STOCK PURCHASE AGREEMENT
                                 SIGNATURE PAGE

     ----------
     * Certain information on this page has been omitted and filed separately
       with the Commission. Confidential treatment has been requested with
       respect to the omitted portions.
<PAGE>

                                    "STOCKHOLDER"+

                                      [*]
                                    -------------------------------------------
                                    (Signature)

                                      [*]
                                    -------------------------------------------
                                    (Print Name of Stockholder)

                                    -------------------------------------------
                                    (Title, if signing on behalf of an entity)

                                    +Executes this Agreement solely for the
                                    purposes of Section 7 hereof.

                                   VIRRX, INC.
                   SERIES A PREFERRED STOCK PURCHASE AGREEMENT
                                 SIGNATURE PAGE

     ----------
     * Certain information on this page has been omitted and filed separately
       with the Commission. Confidential treatment has been requested with
       respect to the omitted portions.
<PAGE>

                                   SCHEDULE A

                            Schedule of Stockholders

     [*]

     ----------
     * Certain information on this page has been omitted and filed separately
       with the Commission. Confidential treatment has been requested with
       respect to the omitted portions.

                                      S-1

<PAGE>

                                    EXHIBIT A

            Form of Amended and Restated Certificate of Incorporation

                                      E-1
<PAGE>

                                   VIRRX, INC.

                AMENDED AND RESTATED CERTIFICATE OF INCORPORATION
                                  -----------

         VirRx, Inc., a corporation organized and existing under the laws of the
State of Delaware (the "Corporation"), hereby certifies as follows:

         A. The name of the Corporation is VirRx, Inc. The Corporation filed its
original Certificate of Incorporation with the Delaware Secretary of State on
May 8, 2001.

         B. This Amended and Restated Certificate of Incorporation (the
"Restated Certificate") was duly adopted by the Corporation's directors and
stockholders in accordance with the applicable provisions of Sections 228, 242
and 245 of the Delaware General Corporation Law (the "DGCL").

         C. This Restated Certificate restates, integrates and amends the
provisions of the Certificate of Incorporation of this Corporation, as
heretofore amended.

         D. The text of the Certificate of Incorporation, as heretofore amended,
is hereby amended and restated in its entirety to read as follows:

                                   ARTICLE I

         The name of this Corporation is VirRx, Inc.

                                   ARTICLE II

         The purpose of the Corporation is to engage in any lawful act or
activity for which corporations may be organized under the DGCL.

                                  ARTICLE III

         The address of the Corporation's registered office in the State of
Delaware is 1209 Orange Street, in the City of Wilmington, County of New Castle.
The name of its registered agent at such address is The Corporation Trust
Company.

                                   ARTICLE IV

         This Corporation is authorized to issue two classes of stock to be
designated, respectively, "Common Stock" and "Preferred Stock." The total number
of shares of capital stock that this Corporation shall have authority to issue
is 25,300,000. The total number of shares of Common Stock this Corporation shall
have authority to issue is 15,300,000 with a par value of $0.01 per share. The
total number of shares of Preferred Stock this Corporation shall have authority
to issue is 8,700,000 with a par value of $0.01 per share, of which 10,000,000
shall be designated Series A Preferred Stock.

<PAGE>

         The relative rights, preferences, privileges, limitations and
restrictions granted to or imposed on the respective classes and series of the
shares of capital stock or the holders thereof are as follows:

         4.1 Dividends. The holders of the Series A Preferred Stock shall be
entitled to receive dividends when, as and if declared by the Corporation's
Board of Directors, out of any assets legally available therefor, prior and in
preference to any declaration or payment of any dividend (payable other than in
Common Stock or other securities or rights convertible into, or entitling the
holder thereof to receive directly or indirectly, additional shares of Common
Stock ("Common Stock Equivalents")) on the Corporation's Common Stock at the
rate of $0.07 per share (as adjusted for any stock dividend, stock split,
combination, reorganization, recapitalization, reclassification or other similar
event with respect to such share) per annum. The right to receive dividends on
shares of any series of Preferred Stock shall not be cumulative, and no right to
such dividends shall accrue to holders of any series of Preferred Stock by
reason of the fact that dividends on such shares are not declared or paid in any
year. Upon conversion of any share of any series of Preferred Stock pursuant to
subsection (A) or (B) of Section 4.3, all dividends declared but unpaid on such
share shall be paid in shares of Common Stock at the then fair market value
thereof, as determined in good faith by the Corporation's Board of Directors. No
dividends shall be paid or declared, and no distribution shall be made, on any
shares of Common Stock (payable other than in Common Stock or Common Stock
Equivalents) unless (x) all dividends declared but unpaid on any series of
Preferred Stock have been paid or set apart for payment and (y) a dividend
(including the amount of any dividend paid pursuant to the first sentence of
this Section 4.1) is paid with respect to all outstanding shares of Series A
Preferred Stock in an amount for each such share of Series A Preferred Stock
equal to or greater than the aggregate amount of such dividends for all shares
of Common Stock into which each such share of Series A Preferred Stock could
then be converted.

         4.2 Liquidation Preference.

             (A) Preferred Stock Preference. In the event of any liquidation,
dissolution or winding up of the Corporation, either voluntary or involuntary,
the holders of the Series A Preferred Stock shall be entitled to receive, prior
and in preference to any distribution of any of the Corporation's assets or
surplus funds to the holders of the Corporation's Common Stock by reason of
their ownership thereof, an amount equal to $0.70 per share (as adjusted for any
stock dividend, stock split, combination, reorganization, recapitalization,
reclassification or other similar event with respect to such share) plus an
additional amount equal to any dividends declared but unpaid on each such share.
If, upon such liquidation, dissolution or winding up, the assets and funds
distributed are insufficient to permit the payment to each holder of Series A
Preferred Stock the full aforesaid preferential amounts, the entire assets and
funds legally available for distribution shall be distributed ratably to such
holders in proportion to the preferential amount each such holder is otherwise
entitled to receive.

             (B) Remaining Assets. Upon the completion of the distribution
required by subsection (A) of this Section 4.2, the Corporation's remaining
assets or funds available for distribution to stockholders shall be distributed
ratably to the holders of Series A Preferred Stock and Common Stock based on the
number of shares of Common Stock held by each such holder (assuming full
conversion of the Series A Preferred Stock) until, with respect to the holders
of

                                      -2-

<PAGE>

Series A Preferred Stock, such holders shall have received an aggregate of $2.10
per share (as adjusted for any stock dividend, stock split, combination,
reorganization, recapitalization, reclassification or other similar event with
respect to such share and including amounts paid pursuant to subsection (A) of
this Section 4.2); thereafter, if assets or funds remain in this Corporation,
all of such remaining assets or funds shall be distributed ratably to the
holders of Common Stock based on the number of shares of Common Stock held by
each such holder.

             (C) (1) Unless otherwise determined by the holders of at least a
majority of the Preferred Stock then outstanding, for the purposes of this
Section 4.2, a liquidation, dissolution or winding up of the Corporation shall
be deemed to include (X) the acquisition of the Corporation by another entity by
means of any transaction or series of related transactions (including, without
limitation, any merger, consolidation or other form of reorganization in which
outstanding shares of the Corporation are exchanged for securities or other
consideration issued, or caused to be issued, by the acquiring entity or its
subsidiary, but excluding any transaction effected primarily for the purpose of
changing the Corporation's jurisdiction of incorporation) that results in the
transfer or acquisition of at least a majority of the Corporation's voting power
or (Y) a sale of all or substantially all of the assets of the Corporation.

                 (2) If any assets of the Corporation distributed to
stockholders in connection with any liquidation, dissolution or winding up of
the Corporation are other than cash, then the value of such assets shall be
their fair market value as mutually determined by the Corporation's Board of
Directors and the holders of at least a majority of the voting power of all then
outstanding shares of Preferred Stock

                 (3) In the event the requirements of this subsection (C) are
not complied with, the Corporation shall forthwith either:

                     (a) cause such closing to be postponed until such time as
the requirements of this Section 4.2 have been complied with, or

                     (b) cancel such transaction, in which event the rights,
preferences, privileges and restrictions of the holders of the Preferred Stock
shall revert to and be the same as such rights, preferences, privileges and
restrictions existing immediately prior to the date of the first notice referred
to in subsection (C)(4).

                 (4) The Corporation shall give each holder of record of
Preferred Stock written notice of a transaction described in subsection (C)(1)
not later than twenty (20) days prior to the stockholders' meeting called to
approve such transaction, or twenty (20) days prior to the closing of such
transaction, whichever is earlier, and shall also notify such holders in writing
of the final approval of such transaction. The first of such notices shall
describe the material terms and conditions of the impending transaction and the
provisions of this Section 4.2, and the Corporation shall thereafter give such
holders prompt notice of any material changes. The transaction shall in no event
take place sooner than twenty (20) days after the Corporation has given the
first notice provided for herein or sooner than ten (10) days after the
Corporation has given notice of any material changes provided for herein;
provided, however, that such periods may be shortened upon

                                      -3-
<PAGE>

the written consent of the holders of at least a majority of the shares of
Preferred Stock then outstanding.

         4.3 Conversion. The holders of the Preferred Stock have conversion
rights as follows:

             (A) Right to Convert. Each share of each series of Preferred Stock
shall be convertible, at the option of the holder thereof, at any time after the
date of issuance of such share, at the office of the Corporation or any transfer
agent for the Preferred Stock, into such number of fully paid and nonassessable
shares of Common Stock as is determined by dividing the Conversion Value for
such series of Preferred Stock by the Conversion Price for such series of
Preferred Stock, determined as hereinafter provided, in effect at the time of
the conversion (the "Conversion Rate"). The "Conversion Value" per share for the
Series A Preferred Stock shall be $0.70. The initial "Conversion Price" per
share for the Series A Preferred Stock shall be $0.70. Such initial Conversion
Price for each series of Preferred Stock shall be subject to adjustment as
provided in subsection (D) of this Section 4.3.

             (B) Automatic Conversion. Each share of each series of Preferred
Stock shall automatically be converted into fully paid and nonassessable shares
of Common Stock at its then effective Conversion Rate upon the earlier of (i)
immediately prior to the closing of a firm commitment underwritten public
offering pursuant to an effective registration statement on Form S-1 under the
Securities Act of 1933, as amended (the "1933 Act"), covering the offer and sale
of Common Stock to the public for the account of the Corporation in which the
public offering price (prior to underwriter's discounts or commissions and
offering expenses) exceeds $5.00 per share (subject to adjustment for any stock
dividend, stock split, combination, reorganization, recapitalization,
reclassification or other similar event) and the aggregate gross proceeds raised
equals or exceeds $15,000,000 (a "Qualified IPO") or (ii) the date specified by
written consent or agreement of the holders of at least a majority of the then
outstanding shares of Preferred Stock.

             (C) Mechanics of Conversion.

                 (1) Before any holder of Preferred Stock shall be entitled to
convert the same into shares of Common Stock, such holder shall surrender the
certificate or certificates therefor, duly endorsed, at the office of the
Corporation or of any transfer agent for such Preferred Stock, and shall give
written notice to the Corporation at such office that such holder elects to
convert the same and shall state therein the name or names in which such holder
wishes the certificate or certificates for shares of Common Stock to be issued.
The Corporation shall, as soon as practicable thereafter, issue and deliver at
such office to such holder of Preferred Stock, a certificate or certificates for
the number of shares of Common Stock to which such holder shall be entitled as
aforesaid. Such conversion shall be deemed to have been made immediately prior
to the close of business on the date of surrender of the shares of Preferred
Stock to be converted, and the person or persons entitled to receive the shares
of Common Stock issuable upon such conversion shall be treated for all purposes
as the record holder or holders of such shares of Common Stock on such date;
provided, however, that in the event of an automatic conversion in connection
with a Qualified IPO, the outstanding shares of Preferred Stock shall be
converted automatically without any further action by the holders of such shares
and whether or not the certificates representing such shares are surrendered to
the Corporation or its transfer agent; provided further, however, that the

                                      -4-
<PAGE>

Corporation shall not be obligated to issue certificates evidencing the shares
of Common Stock issuable upon such automatic conversion unless the certificates
evidencing such shares of Preferred Stock are either delivered to the
Corporation or its transfer agent as provided above.

                 (2) If the conversion is in connection with an underwritten
offering of securities pursuant to the 1933 Act, the conversion may, at the
option of any holder tendering shares of Preferred Stock for conversion, be
conditioned upon the closing with the underwriters of the sale of securities
pursuant to such offering, in which event the person(s) entitled to receive the
Common Stock upon conversion of the Preferred Stock shall not be deemed to have
converted such Preferred Stock until immediately prior to the closing of such
sale of securities.

             (D) Adjustment of Conversion Price. The Conversion Price for each
series of Preferred Stock shall be subject to adjustment from time to time as
follows:

                 (1) (a) If the Corporation shall issue, after the date of
filing of this Restated Certificate, any Additional Stock (as defined in
subsection (D)(2)) without consideration or for a consideration per share less
than the Conversion Price for any series of Preferred Stock in effect
immediately prior to the issuance of such Additional Stock, the Conversion Price
for such series in effect immediately prior to each such issuance of Additional
Stock shall forthwith (except as otherwise provided in this subsection (D)) be
adjusted to a price equal to the price paid per share for such Additional Stock.

                     (b) No adjustment in the Conversion Price for any series of
Preferred Stock need be made if such adjustment would result in a change in the
Conversion Price of less than $0.01. Any adjustment of less than $0.01 which is
not made shall be carried forward and shall be made at the time of and together
with any subsequent adjustment that, on a cumulative basis, amounts to an
adjustment of $0.01 or more in the Conversion Price. Except to the limited
extent provided for in subsections (D)(1)(e)(iii) or (iv), no adjustment of the
Conversion Price for any series of Preferred Stock pursuant to this subsection
(D)(1) shall have the effect of increasing any such Conversion Price above the
Conversion Price in effect immediately prior to such adjustment.

                     (c) In the case of the issuance of Common Stock for cash,
the consideration shall be deemed to be the amount of cash paid therefor before
deducting any discounts, commissions or other expenses allowed, paid or incurred
by the Corporation for any underwriting or otherwise in connection with the
issuance and sale thereof.

                     (d) In the case of the issuance of Common Stock for a
consideration in whole or in part other than cash, the consideration other than
cash shall be deemed to be the fair value thereof as determined in good faith by
the Corporation's Board of Directors irrespective of any accounting treatment.

                     (e) In the case of the issuance (whether before, on or
after the date of filing of this Restated Certificate) of (i) options to
purchase or rights to subscribe for Common Stock, (ii) securities by their terms
convertible into or exchangeable for Common Stock or (iii) options to purchase
or rights to subscribe for securities by their terms convertible into or

                                      -5-
<PAGE>

exchangeable for Common Stock, the following provisions shall apply for all
purposes of subsections (D)(1) and (2):

                         (i) The aggregate maximum number of shares of Common
Stock deliverable upon exercise (assuming the satisfaction of any conditions to
exercisability, including without limitation, the passage of time, but without
taking into account potential antidilution adjustments) of such options to
purchase or rights to subscribe for Common Stock shall be deemed to have been
issued at the time such options or rights were issued and for a consideration
equal to the consideration (determined in the manner provided in subsections
(D)(1)(c) and (D)(1)(d)), if any, received by the Corporation upon the issuance
of such options or rights plus the minimum exercise price provided in such
options or rights (without taking into account potential antidilution
adjustments) for the Common Stock covered thereby.

                         (ii) The aggregate maximum number of shares of Common
Stock deliverable upon conversion of or in exchange (assuming the satisfaction
of any conditions to convertibility or exchangeability, including without
limitation, the passage of time, but without taking into account potential
antidilution adjustments) for any such convertible or exchangeable securities or
upon the exercise of options to purchase or rights to subscribe for such
convertible or exchangeable securities and subsequent conversion or exchange
thereof shall be deemed to have been issued at the time such securities were
issued or such options or rights were issued and for a consideration equal to
the consideration, if any, received by the Corporation for any such securities
and related options or rights (excluding any cash received on account of accrued
interest or accrued dividends), plus the minimum additional consideration, if
any, to be received by the Corporation (without taking into account potential
antidilution adjustments) upon the conversion or exchange of such securities or
the exercise of any related options or rights (the consideration in each case to
be determined in the manner provided in subsections (D)(1)(c) and (D)(1)(d)).

                         (iii) In the event of any change in the number of
shares of Common Stock deliverable or in the consideration payable to this
Corporation upon exercise of such options or rights or upon conversion of or
exchange for such convertible or exchangeable securities, including, but not
limited to, a change resulting from the antidilution provisions thereof, the
Conversion Price for each series of Preferred Stock, to the extent in any way
affected by or computed using such options, rights or securities, shall be
recomputed to reflect such change, but no further adjustment shall be made for
the actual issuance of Common Stock or any payment of such consideration upon
the exercise of any such options or rights or the conversion or exchange of such
securities.

                         (iv) Upon the expiration of any such options or rights,
the termination of any such rights to convert or exchange or the expiration of
any options or rights related to such convertible or exchangeable securities,
the Conversion Price for each series of Preferred Stock, to the extent in any
way affected by or computed using such options, rights or securities or option
or rights related to such securities, shall be recomputed to reflect the
issuance of only the number of shares of Common Stock (and convertible or
exchangeable securities that remain in effect) actually issued upon the exercise
of such options or rights, upon the conversion or exchange of such securities or
upon the exercise of the options or rights related to such securities.

                                      -6-
<PAGE>

                         (v) The number of shares of Common Stock deemed issued
and the consideration deemed paid therefor pursuant to subsections (D)(1)(e)(i)
and (ii) shall be appropriately adjusted to reflect any change, termination or
expiration of the type described in either subsection (D)(1)(e)(iii) or (iv).

                 (2) "Additional Stock" shall mean any shares of Common Stock
issued (or deemed to have been issued pursuant to subsection (D)(1)(e) of this
Section 4.3) by this Corporation after the date of filing of this Restated
Certificate other than:

                     (a) shares of Common Stock issued pursuant to an event or
transaction described in subsection (D)(3) of this Section 4.3;

                     (b) shares of Common Stock issued or issuable upon
conversion of the any series of Preferred Stock;

                     (c) up to 1,000,000 shares (net of any cancellations,
expirations or repurchases) of Common Stock, warrants, options or other rights
to purchase Common Stock or other securities issued to the Corporation's
employees, officers, directors, consultants, advisors or service providers
pursuant to any plan, agreement or similar arrangement, provided such plan,
agreement or arrangement is approved by the Corporation's Board of Directors;

                     (d) shares of Common Stock, warrants, options or other
rights to purchase Common Stock or other securities issued to banks or equipment
lessors, provided such issuance is approved by the Corporation's Board of
Directors (including the director elected by the holders of Series A Preferred
Stock);

                     (e) shares of Common Stock, warrants, options or other
rights to purchase Common Stock or other securities issued in connection with
sponsored research, collaboration, technology license, development, OEM,
marketing or other similar agreements or strategic partnerships, provided such
issuance is approved by the Corporation's Board of Directors (including the
director elected by the holders of Series A Preferred Stock);

                     (f) shares of Common Stock or other securities issued in
connection with a bona fide business acquisition of or by the Corporation
(whether by merger, consolidation, sale of assets, sale or exchange of stock or
otherwise), provided such acquisition is approved by the Corporation's Board of
Directors (including the director elected by the holders of Series A Preferred
Stock);

                     (g) shares of Common Stock issued in a firm commitment
underwritten public offering pursuant to an effective registration statement
under the 1933 Act pursuant to which all outstanding shares of each series of
Preferred Stock are converted to Common Stock; or

                     (h) on a cumulative basis, up to 100,000 shares (net of any
cancellations, expirations or repurchases) of Common Stock, warrants, options or
other rights to purchase Common Stock or other securities issued for any
purpose, provided such issuance is unanimously approved by the Corporation's
Board of Directors.

                                      -7-
<PAGE>

                 (3) Subdivision, etc. In the event this Corporation should at
any time or from time to time after the date of filing of this Restated
Certificate, fix a record date for the effectuation of a split or subdivision of
the outstanding shares of Common Stock or the determination of holders of Common
Stock entitled to receive a dividend or other distribution payable in additional
shares of Common Stock or Common Stock Equivalents without payment of any
consideration by such holder for the additional shares of Common Stock or the
Common Stock Equivalents (including the additional shares of Common Stock
issuable upon conversion or exercise thereof), then, as of such record date (or
the date of such dividend distribution, split or subdivision if no record date
is fixed), the Conversion Price for each series of Preferred Stock shall be
appropriately decreased so that the number of shares of Common Stock issuable on
conversion of each share of such series shall be increased in proportion to such
increase of the aggregate of shares of Common Stock outstanding and those
issuable with respect to such Common Stock Equivalents.

                 (4) Combination. If the number of shares of Common Stock
outstanding at any time after the date of filing of this Restated Certificate is
decreased by a combination of the outstanding shares of Common Stock, then, on
the effective date of such combination, the Conversion Price for each series of
Preferred Stock shall be appropriately increased so that the number of shares of
Common Stock issuable on conversion of any shares of Preferred Stock shall be
decreased in proportion to such decrease in outstanding shares.

             (E) Other Distributions. In the event the Corporation shall declare
a distribution payable in securities of other persons, evidences of indebtedness
issued by this Corporation or other persons, assets (excluding cash dividends)
or options or rights not referred to in subsection (D)(3) of this Section 4.3,
then, in each such case for the purpose of this subsection (E), the holders of
Preferred Stock shall be entitled to a proportionate share of any such
distribution as though they were the holders of the number of shares of Common
Stock of the Corporation into which their respective shares of Preferred Stock
are convertible as of the record date fixed for the determination of the holders
of Common Stock of the Corporation entitled to receive such distribution.

             (F) Recapitalizations. If, at any time or from time to time after
the date of filing of this Restated Certificate, there shall be a
recapitalization of the Corporation's Common Stock (other than (x) a subdivision
or combination provided for elsewhere in this Section 4.3 or (y) a merger or
sale of assets referred to in Section 4.2(C)) provision shall be made so that
the holders of each series of Preferred Stock shall thereafter be entitled to
receive upon conversion of each such series of Preferred Stock the number of
shares of stock or other securities or property of the Corporation or otherwise,
to which a holder of Common Stock deliverable upon conversion of such series of
Preferred Stock would have been entitled on such recapitalization. In any such
case, appropriate adjustment shall be made in the application of the provisions
of this Section 4.3 with respect to the rights of the holders of each series of
Preferred Stock after the recapitalization to the end that the provisions of
this Section 4.3 (including adjustment of the Conversion Price then in effect
and the number of shares issuable upon conversion of each series of Preferred
Stock) shall be applicable after that event as nearly equivalent as prior to
that event as may be practicable.

             (G) No Impairment. The Corporation will not, by amendment of its
Certificate of Incorporation or through any reorganization, recapitalization,
transfer of assets, consolidation, merger, dissolution, issue or sale of
securities or any other voluntary action, avoid or seek to avoid

                                      -8-
<PAGE>

the observance or performance of any of the terms to be observed or performed
hereunder by the Corporation, but will at all times in good faith assist in the
carrying out of all the provisions of this Section 4.3 and in the taking of all
such action as may be necessary or appropriate in order to protect the
conversion rights of the holders of each series of Preferred Stock set forth in
this Section 4.3 against impairment. This provision shall not restrict the
Corporation's right to amend its Certificate of Incorporation with the requisite
stockholder consent.

             (H) No Fractional Shares and Certificate as to Adjustment.

                 (1) No fractional shares shall be issued upon the conversion of
any share of any series of Preferred Stock and, in lieu of any fractional shares
to which any holder of any series of Preferred Stock would otherwise be
entitled, the Corporation shall pay cash equal to such fraction multiplied by
the then effective Conversion Price for the applicable series of Preferred
Stock. Whether or not fractional shares are issuable upon such conversion shall
be determined on the basis of the total number of shares of the applicable
series of Preferred Stock of each holder at the time converting into Common
Stock and the number of shares of Common Stock issuable upon such aggregate
conversion.

                 (2) Upon the occurrence of each adjustment or readjustment of
the Conversion Rate for any series of Preferred Stock pursuant to this Section
4.3, the Corporation, at its expense, shall promptly compute such adjustment or
readjustment in accordance with the terms hereof and prepare and furnish to each
holder of such series of Preferred Stock a certificate setting forth such
adjustment or readjustment and showing in detail the facts upon which such
adjustment or readjustment is based. The Corporation shall, upon written request
at any time of any holder of any series of Preferred Stock, furnish or cause to
be furnished to such holder a like certificate setting forth (i) all such
adjustments and readjustments, (ii) the Conversion Rate at the time in effect,
and (iii) the number of shares of Common Stock and the amount, if any, of other
property that at the time would be received upon the conversion of such holder's
shares of Preferred Stock.

             (I) Notices of Record Date. In the event of any taking by the
Corporation of a record of the holders of any class of securities for the
purpose of determining the holders thereof who are entitled to receive any
dividend (other than a cash dividend) or other distribution, any right to
subscribe for, purchase or otherwise acquire any shares of stock of any class or
any other securities or property or to receive any other right, the Corporation
shall mail to each holder of Preferred Stock at least twenty (20) days prior to
such record date, a notice specifying the date on which any such record is to be
taken for the purpose of such dividend or distribution or right, and the amount
and character of such dividend, distribution or right.

             (J) Reservation of Stock Issuable Upon Conversion. The Corporation
shall at all times reserve and keep available out of its authorized but unissued
shares of Common Stock solely for the purpose of effecting the conversion of the
shares of Preferred Stock such number of its shares of Common Stock as shall
from time to time be sufficient to effect the conversion of all outstanding
shares of Preferred Stock; and if at any time the number of authorized but
unissued shares of Common Stock shall not be sufficient to effect the conversion
of all then outstanding shares of Preferred Stock, the Corporation will take
such corporate action as may, in the opinion of its counsel, be necessary to
increase its authorized but unissued shares of Common Stock to such

                                      -9-
<PAGE>

number of shares as shall be sufficient for such purpose, including, without
limitation, engaging its best efforts to obtain the requisite stockholder
approval for any necessary amendment to this Restated Certificate.

         4.4 Voting.

             (A) General. Each holder of each share of Series A Preferred Stock
(i) shall be entitled to the number of votes equal to the number of shares of
Common Stock into which such share of Series A Preferred Stock could be
converted at the record date for determination of the stockholders entitled to
vote, or, if no such record date is established, at the date such vote is taken
or any written consent of stockholders is solicited, (ii) shall have voting
rights and powers equal to the voting rights and powers of the Common Stock
(except as otherwise provided herein or as required by law, voting together with
the Common Stock as a single class) and (iii) shall be entitled to notice of any
stockholders' meeting in accordance with the Corporation's Bylaws. Fractional
votes shall not, however, be permitted and any fractional voting resulting from
the above formula (after aggregating all shares into which shares of Series A
Preferred Stock held by each holder could be converted) shall be rounded to the
nearest whole number (with one-half being rounded upward). Each holder of each
share of Common Stock shall be entitled to one vote.

             (B) Election of Directors.

                 (1) The Board of Directors shall consist of three members. The
holders of Common Stock, voting as a single class, shall be entitled to elect
one (1) member of the Corporation's Board of Directors at each meeting or
pursuant to each consent of the Corporation's stockholders for the election of
directors. The holders of Series A Preferred Stock, voting as a single class,
shall be entitled to elect one (1) member of the Corporation's Board of
Directors at each meeting or pursuant to each consent of the Corporation's
stockholders for the election of directors. The holders of Common Stock and
Series A Preferred Stock, voting together as a single class and on an
as-converted basis, shall be entitled to elect the remaining members of the
Corporation's Board of Directors at each meeting or pursuant to each consent of
the Corporation's stockholders for the election of directors.

                 (2) Vacancies in the Board of Directors may be filled by at
least a majority of the remaining directors originally elected by the class or
classes of stock or series thereof that elected the member who created the
vacancy (or the remaining director so elected if there is but one, or if there
is no such director remaining, by the affirmative vote of the holders of at
least a majority of the shares of that class or classes or series).

                 (3) Any director who was elected by a specified class or
classes of stock or series thereof may be removed during his or her term of
office, either for or without cause, by, and only by, the affirmative vote of
the holders of at least a majority of the shares of the class or classes of
stock or series thereof that initially elected such director.

             4.5 Preferred Stock Protective Provisions. The Corporation shall
not, without first obtaining the approval (by vote or written consent) of the
holders of at least a majority of the shares of Series A Preferred Stock then
outstanding:

                                      -10-
<PAGE>

                 (A) take any action that would alter or change materially and
adversely the rights, preferences or privileges of any series of Preferred Stock
then outstanding;

                 (B) authorize or issue any new class or series of equity
securities having any preference or priority as to voting, dividends, or
distribution of assets upon liquidation, merger or otherwise which is superior
to or on a parity with any such preference or priority of any series of
Preferred Stock then outstanding;

                 (C) sell all or substantially all of its assets, or merge into
or consolidate with any other entity (other than a wholly-owned subsidiary of
the Corporation), or effect any transaction or series of related transactions in
which at least a majority of the Corporation's voting power is disposed of;

                 (D) increase or decrease (other than by conversion) the number
of authorized shares of any class or series of equity securities;

                 (E) effect an exchange, reclassification or cancellation of
shares of any class or series of Stock;

                 (F) increase the number of authorized directors of the
Corporation's Board of Directors to more than three (unless unanimously approved
by the Corporation's Board of Directors);

                 (G) pay or declare a dividend on any shares of Common Stock
(payable other than in Common Stock or Common Stock Equivalents); or

                 (H) do any act which would result in taxation under Section 305
of the Internal Revenue Code of 1986, as amended.

The provisions of this Section 4.5 shall not limit or restrict any rights which
any holder of Preferred Stock may have under the DGCL.

             4.6 Status of Converted Stock. In the event any shares of any
series of Preferred Stock are converted pursuant to Section 4.3, the Corporation
shall never again issue the shares so converted and all such shares so converted
shall, upon such conversion, cease to be a part of the Corporation's authorized
stock. The Corporation's Certificate of Incorporation shall be appropriately
amended to effect the corresponding reduction in the Corporation's authorized
stock.

             4.7 Notices. Any notice required by the provisions of Sections 4.2
or 4.3 to be given to the holders of shares of any series of Preferred Stock
shall be in writing and shall be delivered personally by hand or by courier,
mailed by United States first-class mail, postage prepaid, sent by facsimile
directed to each holder of record at such holder's address, facsimile number
appearing on the Corporation's books. Any such notice shall be deemed given upon
personal delivery, on the date of mailing, upon confirmation of facsimile
transfer.

                                      -11-
<PAGE>

                                    ARTICLE V

         Except as may otherwise be provided in this Restated Certificate, in
furtherance and not in limitation of the powers conferred by the laws of the
state of Delaware, the Corporation's Board of Directors is expressly authorized
to make, alter, amend or repeal the Corporation's Bylaws.

                                   ARTICLE VI

         Election of directors need not be by written ballot.

                                   ARTICLE VII

         7.1 Limitation of Director's Liability. To the fullest extent permitted
by the DGCL, as the same exists or may hereafter be amended, a director of this
Corporation shall not be personally liable to this Corporation or its
stockholders for monetary damages for breach of fiduciary duty as a director.

         7.2 Indemnification of Directors and Officers. To the fullest extent
permitted by applicable law, this Corporation is authorized to provide
indemnification of, and advancement of expenses to, directors, officers,
employees and other agents of this Corporation and any other persons to which
the DGCL permits this Corporation to provide indemnification.

         7.3 Repeal or Modification. Any repeal or modification of this
ARTICLE VII, by amendment of this ARTICLE VII or by operation of law, shall not
adversely affect any right or protection of a director, officer, employee or
other agent of this Corporation existing at the time of, or increase the
liability of any such person with respect to any acts or omissions in their
capacity as a director, officer, employee, or other agent of the corporation
occurring prior to, such repeal or modification.

                                  ARTICLE VIII

         Subject to Section 4.5 of ARTICLE IV, the Corporation reserves the
right to amend, alter, change or repeal any provision contained in this
Certificate of Incorporation, in the manner now or hereafter prescribed by
statute, and all rights conferred upon stockholders herein are granted subject
to this reservation.

                                  -----------

                                      -12-

<PAGE>

         IN WITNESS WHEREOF, the Corporation has caused this Amended and
Restated Certificate of Incorporation to be signed by its President on February
___, 2002.

                                         VirRx, Inc.

                                         ---------------------------------------
                                         William Wold, President

                                      -13-
<PAGE>

                                    EXHIBIT B

                             Schedule of Exceptions

                                      [*]

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* Certain information on this page has been omitted and filed separately with
  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

                                      E-2

<PAGE>

                                    EXHIBIT C

                       Form of Investors' Rights Agreement

                                      [*]

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* Certain information on this page has been omitted and filed separately with
  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

                                      E-3

<PAGE>

                                    EXHIBIT D

              Form of Right of First Refusal and Co-Sale Agreement

                                      [*]

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* Certain information on this page has been omitted and filed separately with
  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

                                      E-4

<PAGE>

                                    EXHIBIT E

       Form of Proprietary Information and Inventions Assignment Agreement

                                      [*]

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* Certain information on this page has been omitted and filed separately with
  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

                                      E-5

<PAGE>

                                   EXHIBIT F

                       Form of Opinion of Company Counsel

                                      [*]

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* Certain information on this page has been omitted and filed separately with
  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

                                      E-6

<PAGE>

                                    EXHIBIT G

                       Form of Repurchase Option Agreement

                                      [*]

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* Certain information on this page has been omitted and filed separately with
  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

                                      E-7<PAGE>
NOTE: Information in this document marked with an "[*]" has been omitted and
filed separately with the Commission. Confidential treatment has been requested
with respect to the omitted portions.

                       COLLABORATION AND LICENSE AGREEMENT

         This Collaboration and License Agreement ("AGREEMENT") is made as of
March 7, 2002 (the "EFFECTIVE DATE") by and between the VirRx, Inc., a Delaware
corporation, having a place of business at 1609 Adgers Wharf Drive, St. Louis,
Missouri 63017 ("VIRRX") and Introgen Therapeutics, Inc., a Delaware corporation
having a place of business at 301 Congress Avenue, Suite 1850, Austin, Texas
78701 ("INTROGEN"). Each of VirRx and Introgen are referred to in this Agreement
as a "PARTY" and collectively as "PARTIES."

                                    RECITALS:

A.       VirRx owns or controls certain technology related to [*] Vectors (as
         defined below), and desires to conduct further research relating to
         such [*] Vectors and other matters;

B.       Introgen is willing, for the purposes of enabling such research, to
         make an equity investment in VirRx under the terms of the Stock
         Purchase Agreement between the Parties dated as of the Effective Date
         (the "STOCK PURCHASE AGREEMENT"); and

C.       As a benefit of Introgen's funding of VirRx's research, Introgen
         desires to obtain an exclusive license from VirRx to the Licensed
         Subject Matter (as defined below), all on the terms and conditions set
         forth below.

NOW, THEREFORE, in consideration of the mutual covenants and promises herein
contained, the Parties hereto agree as follows:

                                   ARTICLE I

                                   DEFINITIONS

         As used in this Agreement, the following terms shall have the meanings
indicated:

         1.1 "[*] Vector" means any composition comprising both: (i) [*].

         1.2 "Affiliate" means any entity that controls, is controlled by or is
under common control with Introgen. An entity shall be regarded as in control of
another entity for purposes of this definition if it owns or controls more than
fifty percent (50%) of the shares of the subject entity entitled to vote in the
election of directors (or, in the case of an entity that is not a corporation,
for the election of the corresponding managing authority).

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* Certain information on this page has been omitted and filed separately with
  the Commission. Confidential treatment has been requested with respect to the
  omitted portions.

<PAGE>

         1.3 "BLA Approval" means approval from the United States Food and Drug
Administration (or its equivalent in a Major Market Country outside the United
States) of a BLA filed by or on behalf of Introgen, to market a Licensed
Product. For such purposes a "BLA" means a Biological License Application, as
defined in the United States Food, Drug and Cosmetic Act and the regulations
promulgated thereunder, or an equivalent foreign application for marketing
approval in Major Market Country outside the United States.

         1.4 "Collaboration Technologies" means any data, invention, material or
other subject matter conceived or first reduced to practice by VirRx personnel
(including persons or entities working on VirRx's behalf) arising out of or in
connection with the Research Program during the Research Term or the one-year
period immediately thereafter, or derived by VirRx personnel (including persons
or entities working on VirRx's behalf) from Introgen Confidential Information.

         1.5 "Contract Year" means a year of 365 days (or 366 days in a leap
year) beginning on the Effective Date and ending one (1) year thereafter and so
on year-by-year.

         1.6 "Control" means, with respect to particular subject matter, a
Party's possession of the ability to grant a license or sublicense in such
subject matter under this Agreement without violating the terms of any agreement
or other arrangement, if any, under which the Party first acquired rights in
such subject matter from a third party.

         1.7 "Distinct [*] Vectors" means [*] Vectors differing in one or more
distinct substantive functions that result in materially different therapeutic
effects as to safety and/or efficacy and/or to materially different types of
cancer that can be treated.

         1.8 "Existing Third-Party Agreements" means that certain License and
Exclusive License Option Agreement between VirRx and [*] University
dated March 1, 2002, and that Materials Transfer Agreement between VirRx and
[*] University dated January 17, 2002.

         1.9 "Funded Expenses" means, with respect to the Research Program or
Other Funded Research, respectively: (i) direct salary expense for VirRx
employees conducting such Research Program or Other Funded Research, plus direct
employee benefit costs of such personnel (not including any amount associated
with equity incentive plans), on a percentage-of-time basis, (ii) amounts paid
to third parties for their performance of the Research Program or Other Funded
Activities, (iii) administrative expenses, and (iv) other direct costs incurred
by VirRx in performing the Research Program or Other Funded Research. For
purposes of clause (iii), "administrative expenses" shall mean the reasonable
and customary costs of supporting and maintaining the Research Program and the
Other Funded Research, respectively (e.g. legal, payroll and accounting
expenses), and for purposes of clause (iv), "other direct costs" shall mean the
costs of facilities, equipment and materials used by VirRx directly in the
Research Program or Other Funded Activities, respectively, provided that: (x)
such administrative expenses and other direct costs are allocated to the
Research Program and Other Funded Research on a reasonable basis, in the same
manner and on a consistent basis for all such activities and other activities of
VirRx outside the Research Program and the Other Funded Research, and (y) in no
event shall the sum of such administrative expenses and such other direct costs
for the Research Program or the Other Funded Research, respectively, exceed
[*] of the respective costs described in (i) for the

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Research Program or such Other Funded Research. In addition, in no event shall
such administrative expenses and other direct costs include costs of capital, or
the costs of capacity not required or not utilized for the conduct of the
Research Program.

         1.10 "IND" means an Investigational New Drug Application for a product,
as defined in the U.S. Food, Drug and Cosmetic Act and the regulations
promulgated at 21 C.F.R. Section 312 et seq., and any other regulatory filing in
any country other than the United States made for the purpose of proceeding with
clinical testing.

         1.11 "JRC" has the meaning set forth in Section 2.2.

         1.12 "Licensed Product" means (i) a product, composition or material
the manufacture, sale or use of which would, but for the license granted herein,
directly infringe a Valid Claim in the country for which such product,
composition or material is sold, or (ii) solely for the purposes of Introgen's
royalty obligations under Section 5.4, a commercial product within the Licensed
Subject Matter comprising an [*] Vector, as provided by VirRx to Introgen under
this Agreement.

         1.13 "Licensed Subject Matter" means the Collaboration Technologies,
the Patent Rights, and, to the extent owned or Controlled by VirRx, any
inventions, discoveries and other subject matter covered by or relating to the
Patent Rights including, without limitation, the Related Materials.

         1.14 "Major Market Country" means any one of the United States, United
Kingdom, France, Germany, Italy, Spain or Japan.

         1.15 "Net Sales" means sales to third parties of Licensed Products by
Introgen, its Affiliates, or Sublicensees, for which royalties are due under
ARTICLE V below. Net Sales shall be equal to net sales as determined in
accordance with generally accepted accounting principles minus, to the extent
not already considered in determining net sales in accordance with generally
accepted accounting principles: (i) trade, cash and quantity credits, discounts,
refunds or government rebates; (ii) amounts for claims, allowances or credits
for returns, retroactive price reductions, or chargebacks; (iii) shipping costs,
including packaging, handling fees and freight; (iv) sales taxes, value-added
taxes, duties and other governmental charges; and (v) provisions for
uncollectible accounts. For the removal of doubt, Net Sales shall not include
sales among Introgen, its Affiliates or Sublicensees, provided that if Introgen
sells a Licensed Product to an Affiliate for resale, Net Sales shall include net
sales by such Affiliate to third parties on the resale of such Licensed Product,
with such net sales determined in the same manner as set forth above for
determining Net Sales by Introgen. In the event that Introgen grants a
sublicense hereunder, and receives payments based upon the Sublicensee's sales
of Licensed Products, Introgen may upon notice to and approval of VirRx, such
approval not to be unreasonably withheld, modify this definition of "Net Sales"
for purposes of calculating royalties payable to VirRx on such Sublicensee's
sales to be the same as the definition of sales on which the Sublicensee's
royalty to Introgen is based.

         1.16 "Other Funded Research" means any activities for which Periodic
Introgen Funding is used, in accordance with Section 5.2.3(b) below.

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         1.17 "Patent Rights" means any and all rights in and to:

                  (a) the patent applications listed in Exhibit 1.17 hereto, any
patents issuing on such patent applications, any foreign counterparts of such
patent applications and patents, and any patent or application anywhere in the
world that claims or otherwise covers subject matter claimed or disclosed in any
of the patent applications in Exhibit 1.17 or the foreign counterparts thereof
(collectively, "Existing Patents");

                  (b) any patent or patent application that claims or otherwise
covers an invention relating to any Collaboration Technology or any invention
owned or Controlled by VirRx relating to any [*] Vector, or the manufacture or
use thereof; and

                  (c) all divisions, continuations, continuations-in-part,
patents of addition, substitutions, registrations, reissues, reexaminations or
extensions of any kind with respect to a patent or patent application described
in Paragraph (a) or (b) above.

         1.18 "Periodic Introgen Funding" means any funds paid to VirRx under
Sections 1.2(a) and (b) of the Stock Purchase Agreement (and as described in
Section 5.1.1 below).

         1.19 "Related Material" means any information, biological materials and
other items that relate to or are useful in connection with subject matter
covered by or within the Patent Rights or the Collaboration Technologies owned
or Controlled by VirRx.

         1.20 "Research Plan and Budget" means the written workplan and budget
for the Research Program to be conducted under this Agreement, as established in
accordance with Section 2.3 hereof.

         1.21 "Research Program" means the research, discovery,
characterization, optimization and pre-clinical development of [*] Vectors,
and/or such other matters as the JRC may approve, conducted by VirRx during the
Research Term.

         1.22 "Research Term" means the period commencing on the Effective Date
and ending on the first to occur of (i) termination of this Agreement or the
Research Program in accordance with ARTICLE XII below; or (ii) four (4) years
after the Effective Date, or if it is extended under Section 2.1(b) below, the
end of such extended period.

         1.23 "Sublicensee" means any non-Affiliate third Party to whom Introgen
has granted the right to manufacture and sell Licensed Products, with respect to
Licensed Products manufactured by such third Party.

         1.24 "Valid Claim" means a claim of an issued and unexpired patent or a
claim of a pending patent application within the Patent Rights which has not
been held unpatentable, invalid or unenforceable by a court or other government
agency of competent jurisdiction and has not been admitted to be invalid or
unenforceable through reissue, re-examination, disclaimer or otherwise;
provided, however, that if the holding of such court or agency is later reversed
by a court or agency with overriding authority, the claim shall be reinstated as
a Valid Claim with respect to Net Sales made after the date of such reversal.
Notwithstanding the foregoing provisions of this Section, if a

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claim of a pending patent application within the Patent Rights has not issued as
a claim of an issued patent within the Patent Rights, within five (5) years
after the filing date from which such claim takes priority, such pending claim
shall not be a Valid Claim for purposes of this Agreement, unless and until a
patent (otherwise meeting the definition of Valid Claim) issues on such
application; from and after such issuance such claim shall be deemed a Valid
Claim with respect to Net Sales made after such issuance.

                                   ARTICLE II

                                RESEARCH PROGRAM

         2.1 Generally.

                  (a) VirRx shall use its reasonable best efforts to conduct,
and shall furnish the facilities and personnel necessary to carry out, the
Research Program in accordance in all respects with the Research Plan and
Budget.

                  (b) The Research Program shall be performed during the
Research Term, which may be extended by written agreement between Introgen and
VirRx. Unless so extended by a written agreement signed by VirRx and Introgen,
the Research Program shall end at the end of the Research Term.

         2.2 The JRC. Promptly after the Effective Date, the Parties shall
establish a Joint Research Committee ("JRC"). The JRC shall have responsibility
to (i) oversee, review and coordinate the Research Program, (ii) expedite the
progress of work being done under the Research Plan and Budget, and (iii) make
such other decisions as are expressly allocated to the JRC under this Agreement.

                  (a) Membership. The JRC shall be comprised of an equal number
of representatives from each of Introgen and VirRx. The exact number of such
representatives shall be two (2) for each of Introgen and VirRx, or such other
number as the Parties may agree. Either Party may replace its respective JRC
representatives at any time, with prior written notice to the other Party.

                  (b) Meetings. The JRC shall meet monthly, or as more or less
often as otherwise agreed by the Parties, at such locations as the Parties
agree. It is understood that such meetings shall be held at least quarterly in
person, otherwise by telephone.

                  (c) Decision Making. Decisions of the JRC shall be made by
majority vote of all JRC members present in person or by other means (e.g.,
teleconference) at any meeting; provided that, if there is not an equal number
of representatives of each Party present at such meeting, then only an equal
number of representatives of each Party shall be entitled to vote at such
meeting. In the event that the votes required to approve a decision cannot be
reached, then either Party may, by written notice to the other, have such issue
referred to the President of Introgen and the President VirRx, for attempted
resolution by good-faith negotiations within thirty (30) days after such notice
is

                                      -5-
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received. Minutes of the JRC meetings shall be taken, and shall, at a minimum,
record all decisions made. Such minutes shall be subject to approval in writing
by both Parties.

                  (d) Coordination. The Parties acknowledge that Introgen may
also conduct activities complementary or related to the research to be performed
by VirRx under the Research Program. To ensure that such activities remain
coordinated, VirRx and the JRC shall meet or consult periodically to establish
and revise priorities for work to be performed under the Research Program,
including the research experiments and other steps to be taken by VirRx in
pursuit of those priorities, all under the provisions of Section 2.1 above.

         2.3 Research Plan and Budget.

                  (a) Priorities. The Research Plan and Budget shall be based on
priorities established by the JRC, taking into account VirRx's and Introgen's
views as to the feasibility of the scope and timing of such research activities
and objectives.

                  (b) Establishment of Research Plan and Budget. The general
plan for the Research Plan and Budget is attached hereto as Exhibit 2.3. As soon
as practicable after the Effective Date, the JRC shall establish and approve a
detailed Research Plan and Budget for the initial Contract Year. By [*] of each
year during the Research Term, the JRC shall establish and approve the detailed
Research Plan and Budget for the next succeeding Contract Year, including a
general plan and budget for the remaining period of the Research Term. The JRC
shall review the Research Plan and Budget on an ongoing basis and may make
changes thereto as the JRC approves in writing.

         2.4 Records. VirRx shall keep accurate financial and scientific records
of its activities under the Research Program and Other Funded Research and will
make such records available to Introgen or Introgen's authorized representative,
during normal business hours, and upon reasonable notice. It is understood that
such records shall include detailed records, including witnessed laboratory
notebooks, sufficient to document inventions made and all Funded Expenses. Upon
request by Introgen and at Introgen's expense, VirRx shall promptly provide
copies of such materials to Introgen, and Introgen hereby acknowledges that such
copies shall be considered Confidential Information (to the extent provided in
Section 9.1 hereof).

         2.5 Information and Reports. VirRx shall disclose to Introgen all
Licensed Subject Matter promptly after the Effective Date. Thereafter, VirRx
shall promptly disclose to Introgen any additional Licensed Subject Matter
developed or acquired after the Effective Date, with significant discoveries or
advances being communicated immediately after such Licensed Subject Matter is
obtained or its significance is appreciated, including in each case biological
or other tangible materials within the Licensed Subject Matter. During the
Research Term, VirRx will provide to Introgen, at least once per quarter, a
written summary of its activities under the Research Program, and the results of
those activities.

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         2.6 Publication and Academic Rights.

                  (a) Publication. Subject to the rights granted to Introgen
pursuant to this Agreement, and the restriction of Paragraph (b) below, VirRx
may publish or otherwise disclose significant scientific results established by
VirRx during the course of the Research Program.

                  (b) Review. VirRx shall submit to the JRC, at least [*] prior
to submission for publication or other disclosure, materials relating to the
Licensed Subject Matter. The JRC shall promptly review the proposed publication
or disclosure and discuss any concerns regarding dissemination of significant
proprietary information. In any case, the proposed publication or disclosure
shall be withheld until the same has been approved by the JRC.

                                  ARTICLE III

                       PATENT RIGHTS AND TECHNOLOGY RIGHTS

         3.1 Ownership.

                  (a) Subject to Sections 3.1(b) and (c), VirRx shall own all
right, title and interest in and to any inventions conceived or reduced to
practice: (i) solely by employees or consultants of VirRx in which said
employees and consultants are not affiliated with or employed by [*] University
with an obligation to assign such rights to [*] University, or (ii) by employees
or consultants of VirRx who do not utilize any [*] University owned and operated
laboratory facilities or receive any research funding which is administered
through [*] University except for research funding provided by VirRx, or (iii)
by third parties retained by VirRx but not [*] University, or, by such employees
and consultants working together, during the term of this Agreement. Subject to
Sections 3.1(b) and (c), inventions within the scope of the Licensed Subject
Matter that are conceived or reduced to practice (x) solely by employees or
consultants of VirRx in which said employees and consultants are affiliated with
or employed by [*] University with an obligation to assign such rights to [*]
University, or (y) by employees or consultants of VirRx who utilize any [*]
University owned and operated laboratory facilities or result from research
funding which is administered through [*] University for research funding
provided to VirRx, or (z) by third parties retained by [*] University, shall be
owned exclusively by [*] University; provided, however, such inventions shall in
each case be Controlled by VirRx pursuant to Existing Third Party Agreements,
included within the Licensed Subject Matter under this Agreement, and licensed
or sublicensed to Introgen under this Agreement without violating the terms of
any Existing Third Party Agreement or any other agreement or arrangement with a
third party.

                  (b) Introgen shall own all right, title and interest in and to
any inventions made by Introgen during the term of this Agreement, to the extent
that Introgen's personnel (including third parties working on behalf of
Introgen) would be an inventor thereof under U.S. patent law.

                  (c) Patent rights to inventions that are made jointly by
employees of VirRx and Introgen shall be owned [*]. For purposes of this Section
3.1, whether an invention is made

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"jointly" shall be determined under principles of inventorship in accordance
with U.S. patent law, [*].

         3.2 Patents. The filing for, prosecution of applications and
maintenance of patents on inventions covered by or within such Collaboration
Technologies shall be handled in accordance with ARTICLE VIII of this Agreement.

         3.3 Assignments. VirRx shall obtain written agreements from all
employees involved in the Research Program who are working for, or at the
request, of VirRx which require that all Collaboration Technologies conceived or
reduced to practice by such VirRx personnel as a result of or in connection with
the Research Program shall be promptly reported and assigned to VirRx. Provided,
however, such requirement to assign shall not apply to Collaboration
Technologies made by employees and consultants that (i) are affiliated with or
employed by [*] University with an obligation to assign such rights to [*]
University, (ii) utilize any [*] University owned and operated laboratory
facilities or result from research funding which is administered through [*]
University except for research funding provided by VirRx.

                                   ARTICLE IV

                                    LICENSES

         4.1 Licensed Subject Matter. VirRx hereby grants to Introgen a
worldwide, exclusive license to make, use, sell, offer to sell, import, export
and otherwise exploit the Licensed Subject Matter; it being understood that:

                  (a) Introgen may have any of the license rights performed on
its behalf by a third Party;

                  (b) Such Licensed Subject matter does not include "Other
Technology" (as defined below); and

                  (c) Introgen may grant and authorize sublicenses within the
scope of the foregoing license, provided that:

                           (i) if this Agreement is terminated for any reason,
any such sublicense shall survive, provided that upon request by VirRx, the
third-party sublicensee promptly agrees in writing to be bound by the applicable
terms of this Agreement; and

                           (ii) Introgen shall provide a copy to VirRx of any
sublicense granted pursuant to this Section 4.1 within five (5) business days of
execution thereof; provided that the terms of an Existing Third-Party Agreement
require VirRx's further disclosure of such sublicense to

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[*] University or [*] University. VirRx shall maintain any such sublicense as
Confidential Information pursuant to ARTICLE IX.

         4.2 Warranties.

                   (a) Licensed Subject Matter. VirRx represents and warrants to
Introgen that: (i) with respect to Licensed Subject Matter existing as of the
Effective Date, VirRx is and shall continue to be during the Term of this
Agreement, the exclusive owner of the entire right, title, and interest in and
to all such Licensed Subject Matter, except as set forth in Sections 4.3 and
13.3; (ii) upon the invention of all other Licensed Subject Matter not described
in clause (i) (or upon VirRx's first acquiring rights in such Licensed Subject
Matter, if such Licensed Subject Matter is not invented by VirRx, its employees,
or others working on VirRx's behalf), VirRx shall be, and shall continue to be
throughout the term of this Agreement, the exclusive owner of the entire right,
title and interest in all such Licensed Subject Matter, except as set forth in
Sections 4.3, 13.3 and/or the written agreement, if any, under which VirRx first
acquires rights in such Licensed Subject Matter from a third party; (iii) VirRx
has the full right to enter into this Agreement and perform its obligations
hereunder; (iv) VirRx has not previously granted and will not grant any rights
in the Licensed Subject Matter that are inconsistent with the rights and
licenses granted to Introgen herein; (v) to VirRx's knowledge, there are no
claims of any third parties that would call into question the rights of VirRx to
grant to Introgen the rights and licenses contemplated hereunder; and (vi)
except for the Patent Rights, and the Related Materials, as of the Effective
Date, VirRx does not own or Control rights to any patent, patent application,
invention or other subject matter pertaining to [*] Vectors or claims of which
would dominate any practice of the Licensed Subject Matter; (vii) VirRx is not
aware of any prior art that is not cited in the Patent Rights existing as of the
Effective Date that could render unpatentable any invention within a pending
patent application, or render invalid or unenforceable any issued patent, within
such Patent Rights, and (viii) VirRx has disclosed to Introgen all information
of which VirRx is aware relating to VirRx or the Licensed Subject Matter that,
in the reasonable opinion of VirRx as of the Effective Date, would materially
impact Introgen's decision to enter into this Agreement and the transactions
contemplated hereby.

         4.3 Third-Party Rights. The Parties understand and acknowledge that
with respect to particular [*] Vectors, VirRx's rights in and to all or part of
the Licensed Subject Matter may derive from the Existing Third-Party Agreement
(the "In-Licensed Rights"). VirRx represents and warrants to Introgen that (a)
VirRx has the right, under the Existing Third-Party Agreement, to fully include
the In-Licensed Rights within the Licensed Subject Matter under this Agreement,
and to grant to Introgen under this Agreement the same rights with respect to
the In-Licensed Rights as are granted to Introgen with respect to Licensed
Subject Matter owned by VirRx, including the right for Introgen to grant and
authorize sublicenses; and (b) to the extent it obtains or has obtained such
rights under the Existing Third-Party Agreement, such Existing Third-Party
Agreement shall not terminate, expire, or in any way be limited at any time in
any manner that would affect Introgen's rights under this Agreement as a direct
result of any act or failure to act by VirRx, or as a direct result of the
breach of any covenant, representation or warranty made by VirRx under the
Existing Third Party Agreement. If, despite the representations and warranties
set forth in this Section 4.3, an Existing Third-Party Agreement terminates,
expires or is otherwise limited in a manner that affects Introgen's rights under
this Agreement, Introgen may at its option and without limiting any other rights
and remedies available to it, become a direct licensee under the Existing
Third-Party

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Agreement with respect to the rights VirRx obtained under that Agreement;
provided that (i) Introgen is in full compliance with the terms hereof, (ii) all
payments owed under such Existing Third-Party Agreement resulting from the
activity hereunder are paid in full; and (iii) Introgen agrees to assume all
duties of VirRx under such Existing Third-Party Agreement. In addition, except
as set forth in the preceding sentence, it is understood that VirRx is solely
responsible for payments that are or may become due under the Existing
Third-Party Agreement.

         4.4 Disclaimer. EXCEPT AS PROVIDED IN THIS ARTICLE IV, NEITHER PARTY
MAKES ANY WARRANTIES OR CONDITIONS (EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE)
WITH RESPECT TO THE SUBJECT MATTER HEREOF, AND VIRRX SPECIFICALLY DISCLAIMS ANY
AND ALL IMPLIED WARRANTIES OR CONDITIONS OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE (WHETHER OR NOT VIRRX KNOWS, HAS REASON TO KNOW, HAS BEEN
ADVISED, OR IS OTHERWISE IN FACT AWARE OF ANY SUCH PURPOSE) AND ALL WARRANTIES
AND CONDITIONS OF THE VALIDITY OF THE PATENT RIGHTS OR NONINFRINGEMENT OF THIRD
PARTY INTELLECTUAL PROPERTY RIGHTS.

                                   ARTICLE V

                              PAYMENTS AND REPORTS

         5.1 Equity Investment. In consideration for VirRx's performance of its
obligations under this Agreement, Introgen and VirRx shall enter into the Stock
Purchase Agreement under which Introgen will purchase up to [*] of VirRx
Preferred Stock, as described below (but in all cases, subject to the terms and
conditions of the Stock Purchase Agreement).

                  5.1.1 Periodic Funding. Under Sections 1.2(a) and (b) of the
Stock Purchase Agreement, Introgen will make periodic investments in VirRx of up
to an aggregate of Two Million Four Hundred and Seventy Five Thousand Dollars
(US $2,475,000) during the Research Term.

                  5.1.2 Milestone-Based Funding. In addition, under Sections
1.2(c), (d) and (e) of the Stock Purchase Agreement, Introgen will make the
following investments in VirRx upon achievement of the corresponding milestones:

                           (i) Two Hundred Thousand Dollars (US $200,000) upon
[*] upon completion of the first Phase I clinical study of the [*], it being
understood that the foregoing investment shall be made only [*] and that the
total investment under this clause (i) shall not exceed $200,000;

                           (ii) Four Hundred Thousand Dollars (US $400,000) upon
[*] upon completion of the first Phase II clinical study for [*] it being
understood that: (1) the foregoing investments described in this clause (ii)
shall be made only [*]

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with respect to each such Distinct [*] Vector); (2) the total investment under
this clause (ii) shall not exceed $1,200,000; (3) Introgen shall receive a
credit equal to fifty percent (50%) of the investment made under this clause
(ii) in the form of immediately available funds toward the amount, if any, that
may thereafter be due and payable under Section 5.3 below; and (4) Introgen
shall have [*] with respect to any Distinct [*] Vector if Introgen previously
made an investment [*] (for purposes of this clause (ii) [*], and

                           (iii) One Million Dollars (US $1,000,000) upon [*]
upon completion of the first Phase III clinical study of [*] it being understood
that: (1) the foregoing investments described in this clause (iii) shall be made
only [*] with respect to each such Distinct [*] Vector); (2) the total
investment under this clause (iii) shall not exceed $3,000,000; (3) Introgen
shall receive a credit equal to twenty- five percent (25%) of the amounts
invested under this clause (iii) in the form of immediately available funds
toward the amount, if any, that may thereafter be due and payable under Section
5.3 below; and (4) Introgen shall have [*] with respect to any Distinct [*]
Vector if Introgen previously made an investment [*] (for purposes of this
clause (iii), [*].

                  5.1.3 Stock Purchase Agreement Controls. Notwithstanding
Sections 5.1.1 and 5.1.2, it is understood that Introgen's obligations to make
any investment in VirRx shall be solely in accordance with the terms and
conditions of the Stock Purchase Agreement. In the event of any conflict or
inconsistency between the Stock Purchase Agreement and Section 5.1.1 or 5.1.2
above, the terms and conditions of the Stock Purchase Agreement shall control.

         5.2 Use of Proceeds for Research Program. VirRx shall use the Periodic
Introgen Funding solely for the In-License Expenses and the Funded Expenses that
VirRx incurs in performing the Research Program and/or Other Funded Research, as
further described in Sections 5.2.1, 5.2.2 and 5.2.3 below.

                  5.2.1 In-License Expenses. VirRx may use up to [*] of the
Periodic Introgen Funding to pay In-License Expenses for any Contract Year
during the Research Term. As used in this Agreement, "In-License Expenses" means
license fees payable by VirRx to [*] University and [*] University under the
terms of an Existing Third-Party Agreement in consideration of all or a portion
of the In-Licensed Rights.

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                  5.2.2 Research Program. After the payment of the In-License
Expenses authorized under Section 5.2.1, at least [*] of the
Periodic Introgen Funding (on a rolling, six-month basis) shall be used solely
for Funded Expenses that VirRx incurs in performing the Research Program in
accordance with the Research Plan and Budget approved by the JRC.

                  5.2.3 Other Funded Research. After the payment of the
In-License Expenses authorized under Section 5.2.1, VirRx may use up to [*] of
the Periodic Introgen Funding to pay up to an additional [*] in In-License
Expenses (beyond that authorized under Section 5.2.1) and for Funded Expenses of
Other Funded Research in accordance with this Section 5.2.3.

                           (a) From time to time, VirRx may propose to the JRC a
plan for research activities to be supported with Periodic Introgen Funding
outside the Research Program, together with information to enable the JRC to
understand the background, rationale and prospects for such activities. Promptly
following receipt of such a proposal, the JRC will discuss whether the proposed
activities should be included under the Research Program. To the extent that
VirRx and Introgen mutually agree to do so, the Research Plan and Budget may be
modified to include such activities within the Research Program (i.e. in
addition to or in lieu of other activities, then within the Research Program).

                           (b) In the event VirRx and Introgen do not agree to
include the proposed activities within the Research Program in accordance with
paragraph (a) above, then subject to paragraph (c) below, VirRx shall have the
right to pursue such activities outside the Research Program ("Other Funded
Research") and to utilize a portion of the Periodic Introgen Funding for such
Other Funded Research. VirRx agrees that the only costs outside the Research
Plan and Budget that can be funded with Periodic Introgen Funding are the Funded
Expenses of Other Funded Research described in this Section 5.2.3(b). VirRx also
agrees that the Other Funded Research will only include bona fide scientific
research initiatives directed toward the discovery or development of
pharmaceutical products or technologies useful for pharmaceutical research.

                           (c) In consideration for its support of Other Funded
Research, VirRx agrees to provide Introgen a right of first offer with respect
to the grant of any rights by VirRx or its Affiliates with respect to any
product or technology arising out of such Other Funded Research ("OTHER
TECHNOLOGY"). VirRx shall notify Introgen in writing of any such proposed grant
of rights to Other Technology, and upon request by Introgen (the "NEGOTIATION
REQUEST") within thirty (30) days after Introgen's receipt of such notice from
VirRx, the parties shall negotiate toward the grant to Introgen of rights to
such Other Technology on reasonable terms and conditions. Such negotiations
shall continue for a period of [*] after the Negotiation Request (such period
being referred to as the "NEGOTIATION PERIOD"). If the Parties do not agree on
the terms of such a grant to Introgen by the end of the Negotiation Period, such
rights may be granted to a third party. It is understood that if Introgen does
not provide a Negotiation Request within the above-described 30-day period,
VirRx will be free to grant to a third party rights to that Other Technology on
such terms as VirRx considers appropriate.

         5.3 Milestone Payment. In further consideration of the rights and
licenses granted by VirRx to Introgen under this Agreement, and in addition to
the amounts described in Section 5.1

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above, Introgen shall pay to VirRx an amount equal to Five Million Dollars
($5,000,000) within thirty (30) days following the first achievement by
Introgen, its Affiliates or Sublicensees, as the case may be, of the first BLA
Approval of the first Licensed Product. It is understood that such payment shall
be made only one time, in no event shall more than one payment be due under this
Section 5.3, and that Introgen shall receive credit toward the payment of such
amount as provided in Section 5.1.2 above.

         5.4 Royalties.

                  (a) Base Royalty. In consideration of the rights and licenses
granted by VirRx to Introgen under this Agreement, subject to the terms and
conditions of this Section 5.4, Introgen agrees to pay to VirRx the following
royalties based on Net Sales by Introgen, its Affiliates or Sublicensees of
Licensed Products:

                           (i) [*] of such Net Sales with respect to Licensed
Products that consist of an [*] Vector developed by VirRx that are not
materially modified by Introgen (or by a third party under the authority of
Introgen); or

                           (ii) [*] of such Net Sales with respect to Licensed
Products other than those described in (i) above. It is understood that Licensed
Products for which the royalty will be as set forth in this Section 5.4(a)(ii)
will include those comprising an [*] Vector materially modified by Introgen (or
by a third Party under authority of Introgen), which modifications may include,
but shall not be limited to, bona fide modification of the coding region or
delivery of the [*] Vector, or incorporation into the [*] Vector of other
subject matter. It is understood that a modification to an [*] Vector made
solely for the purpose of reducing the royalties payable to VirRx shall not be
deemed a "material modification" for the purposes of this Section 5.4(a)(ii).

The base royalties calculated under this Section 5.4(a) shall be reduced by [*]
with respect to Net Sales of Licensed Products if the sale or use of such
Licensed Products would not, but for the license granted herein, directly
infringe a Valid Claim in the country for which such Licensed Products are sold.

                  (b) Royalty Term. The obligation of Introgen to pay royalties
under this Section 5.4 shall continue for each Licensed Product on a
country-by-country basis, until such time as neither the manufacture, sale nor
use of such Licensed Product would infringe a Valid Claim in such country.

                  (c) Multiple Royalties. If Introgen, its Affiliate or
Sublicensee is required to pay to non-Affiliate third parties amounts with
respect to a Licensed Product under agreements for patent rights or other
technologies that Introgen, its Affiliate or Sublicensee in-licenses or acquires
with respect to such Licensed Product, Introgen may deduct [*] of the amount
owing such non-Affiliate third parties (prior to any reductions) from the
royalty owing to VirRx for the sale of such Licensed Product pursuant to Section
5.4(a) above. Notwithstanding the foregoing provisions of this Section 5.4(c),
(i) Introgen may deduct [*] of amounts owing to third parties with respect to a
patent or patent application if Introgen concludes that the manufacture, sale,
offer

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 for sale, use, import, export or other exploitation of the Licensed Product
could infringe such patent or patent application in any country, but (ii) in no
event shall the royalties due to VirRx pursuant to Section 5.4(a) above be
reduced under this Section 5.4(c) to less than [*] of the amount that would
otherwise be due to VirRx hereunder.

                  (d) Credit for Milestone Payment. If Introgen is required to
make a milestone payment to VirRx under Section 5.3 of this Agreement, Introgen
may deduct [*] of the amount of that payment from any royalties then owing, or
that may later become owing, to VirRx pursuant to Section 5.4(a) above for sales
of Licensed Product; provided that such credit shall not reduce by more than [*]
the amount of any such royalty payment. To the extent any milestone payment
under Section 5.3 of this Agreement is paid to VirRx in Introgen common stock,
for the purpose of calculating the credit amount available to Introgen under
this Section 5.4(d), the amount of such milestone payment paid in Introgen
common stock shall be determined by multiplying the number of shares of Introgen
common stock transferred to VirRx by the lesser of (i) the price per share at
the time of the milestone payment or (ii) the then current price per share at
the time the credit is taken; provided that if VirRx previously sold (or
otherwise transferred) all or a portion of such Introgen common stock shares,
the amount of the milestone payment attributable to those shares shall in no
event be less than the amount determined by multiplying the number of the shares
by the per-share price at which VirRx sold them.

              (e) Credit for Distinct [*] Vectors Dropped from the Program. If
Introgen ceases at any time diligent research, development or marketing of any
Distinct [*] Vectors for which Introgen has made a milestone-based investment in
VirRx as described in Section 5.1(iii), then, with respect to each such Distinct
[*] Vectors, Introgen may deduct [*] of the amount of that milestone-based
investment from any royalties then owing, or that may later become owing, to
VirRx pursuant to Section 5.4(a) above for sales of Licensed Product; provided
that such credit shall not reduce by more than [*] the amount of any such
royalty payment. To the extent any milestone payment under Section 5.1(iii) of
this Agreement is paid to VirRx in Introgen common stock, for the purpose of
calculating the credit amount available to Introgen under this Section 5.4(e),
the amount of such milestone payment paid in Introgen common stock shall be
determined by multiplying the number of shares of Introgen common stock
transferred to VirRx by the lesser of (i) the price per share at the time of the
milestone payment or (ii) the then current price per share at the time the
credit is taken; provided that if VirRx previously sold (or otherwise
transferred) all or a portion of such Introgen common stock shares, the amount
of the milestone payment attributable to those shares shall in no event be less
than the amount determined by multiplying the number of the shares by the
per-share price at which VirRx sold them.

                  (f) Single Royalty; Non-Royalty Sales. In the event that more
than one Valid Claim within the Patent Rights is applicable to any Licensed
Product subject to royalties under this Section 5.4, then only one royalty shall
be paid to VirRx with respect to such Licensed Product. It is understood that
royalties shall only be payable under this Section 5.4 with respect to Licensed
Products whose manufacture, sale or use would infringe a Valid Claim in the
country for which such Licensed Product is sold. In no event shall more than one
royalty be due hereunder with respect to any Licensed Product unit; nor shall a
royalty be payable under Section 5.4(a) with respect to sales of Licensed
Products for use in research and/or development, in clinical trials or as
samples. Notwithstanding Section 5.4(a) above, no royalty shall be due hereunder
with respect to transfers of

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Licensed Products for use in clinical trials, development or other transactions
that are not a full commercial sale.

                  (g) Combination Products. In the event that a Licensed Product
is sold in combination for a single price with another product, component or
service, or if a Licensed Product incorporates an active ingredient, for which
no royalty would be due hereunder if sold separately, Net Sales from such
combination sales for purposes of calculating the amounts due under this Section
5.4 shall be as reasonably allocated by Introgen between such Licensed Product
and such other product, component and/or service.

                  (h) Competition. If, despite the exclusive license granted to
Introgen under the Patent Rights hereunder, there is substantial competition
from sales of competing products in a particular country during a calendar
quarter, the royalties otherwise payable under this Section 5.4 with respect to
sales of Licensed Products in such quarter in such country shall be reduced by
[*]. For such purposes, "substantial competition" means that sales by dollars or
units of a competing product by a third party that is not an Affiliate exceed
[*] of the corresponding sales of Licensed Products; and "competing product"
means a product or service that comprises an [*] Vector and is directed against
the same indications as a Licensed Product.

                  (i) Royalty Reports and Payments. After the first commercial
sale by Introgen, its Affiliates or Sublicensees of a Licensed Product for which
royalties are payable under this Section 5.4, Introgen shall make quarterly
written reports to VirRx within forty-five (45) days after the end of each
calendar quarter, stating in each such report the number, description, and
aggregate Net Sales of such Licensed Product sold during the calendar quarter.
Simultaneously with the delivery of each such report, Introgen shall pay to
VirRx the total royalties, if any, due to VirRx for the period of such report.
If no royalties are due, Introgen shall so report. VirRx shall not provide to
third parties any information contained in reports provided to VirRx pursuant to
this Section 5.4(i), except as required by any VirRx licensor or as otherwise
permitted hereunder. For the purposes of this Section 5.4(i), commercial sales
by Introgen's Affiliates and Sublicensees shall be considered made during the
calendar quarter in which the Affiliate or Sublicensee reports the sale to
Introgen.

                  (j) Currency Conversion. If any currency conversion shall be
required in connection with the calculation of royalties under this Section 5.4,
such conversion shall be made using the selling exchange rate for conversion of
the foreign currency into U.S. Dollars, quoted for current transactions reported
in The Wall Street Journal for the last business day of the calendar quarter to
which such payment pertains.

                  (k) Records; Inspection. Introgen shall keep complete, true
and accurate books of account and records for the purpose of determining the
royalty amounts payable under this Section 5.4. Such books and records shall be
kept reasonably accessible for at least [*] following the end of the calendar
quarter to which they pertain. Such records will be open for inspection during
such [*] period by a representative or agent of VirRx for the purpose of
verifying the royalty statements. Such inspections may be made no more than once
each calendar year, at reasonable times mutually agreed by Introgen and VirRx.
The VirRx's representative or agent will be obliged to execute a reasonable
confidentiality agreement prior to commencing any such

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inspection. VirRx shall bear the costs and expenses of inspections conducted
under this Section 5.4(k), unless a variation or error producing an underpayment
in royalties payable exceeding [*] of the amount paid for the period covered by
the inspection is established in the course of any such inspection, whereupon
all costs relating to the inspection and any unpaid amounts that are discovered
will be paid by Introgen, together with interest on such unpaid amounts at the
rate specified in Section 5.7 below.

                  (l) Conversion. Effective upon written notice to VirRx,
Introgen may convert the license granted to Introgen under Section 4.1 to be
non-exclusive. In such event, or in the event such license becomes non-exclusive
under ARTICLE VI below, the royalties payable to VirRx under this Section 5.4
following such notice after any adjustment shall be [*].

         5.5 License Fee. In further consideration of the rights and licenses
granted by VirRx to Introgen under this Agreement, Introgen agrees to pay to
VirRx an annual license maintenance fee equal in amount to [*] plus any annual
license fees due and payable by VirRx to [*] University, which shall be due and
payable within thirty (30) days after each yearly anniversary following the end
of the Research Term (i.e., so that the first such payment shall be due thirty
(30) days after the first anniversary of the end of the Research Term);
provided, however, that:

                  (a) If Introgen converts the license granted to it under
Section 4.1 to a non-exclusive license, or such license otherwise becomes
non-exclusive under ARTICLE VI below, the license maintenance fee payable to
VirRx under this Section 5.5 following such notice and after any adjustment
under Section 5.5(b), shall be reduced by [*]; and

                  (b) If, in any year after the end of the Research Term,
Introgen is required to pay royalties to VirRx in an amount greater than [*]
under Section 5.4 above for Net Sales of Licensed Products made during such
year, by Introgen, its Affiliates or Sublicensees, Introgen may deduct the
amount by which those royalty payments exceed [*] from the license maintenance
fee payable by Introgen to VirRx under this Section 5.5 for such year.

         5.6 Patent Expenses. Introgen shall reimburse VirRx for reasonable
documented out-of-pocket expenses of filing, prosecuting and maintaining the
patents and patent applications within the Patent Rights prior to the Effective
Date, up to a maximum of [*]. Such amount shall be reimbursed within thirty (30)
days after the Effective Date. Expenses for prosecution of the Patent Rights
after the Effective Date are covered by ARTICLE VIII below.

         5.7 Payment Method. Except to the extent the milestone-based
investments contemplated by Section 5.1.2 of this Agreement may be made (under
the terms of the Stock Purchase Agreement) in Introgen common stock, all amounts
payable under this Agreement shall be made by bank wire transfer in immediately
available funds to an account designated by VirRx. All payments hereunder shall
be made in U.S. dollars. Any payments or portions thereof due under this ARTICLE
V which are not paid on the date such payments are due under this Agreement
shall bear interest equal to the prime rate as reported by Citibank, New York,
New York, plus two percent (2%), on the date such payment is due, calculated on
the number of days such payment is delinquent.

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                                   ARTICLE VI

                                  DUE DILIGENCE

         6.1 Introgen agrees to use its commercially reasonable efforts to
develop one or more Licensed Product(s) in the United States as soon as
practical, consistent with Introgen's normal business practices and judgments.
In any event, however, Introgen shall be deemed to have satisfied its
obligations under this Section 6.1 if Introgen has an ongoing research and/or
development program with respect to such Licensed Products involving
expenditures of at least [*] per year. Any efforts of Introgen's sublicensees
shall be considered efforts of Introgen for the purpose of determining
Introgen's compliance with its obligation under this Section 6.1.

         6.2 After the first year from the Effective Date, VirRx shall have the
right, no more often than once per year upon sixty (60) days written notice to
Introgen, to require Introgen to report to VirRx in writing on its efforts in
complying with Section 6.1 above.

         6.3 If Introgen fails to fulfill its obligations under Section 6.1 and
VirRx so notifies Introgen in writing, Introgen shall have [*] from the date of
VirRx's notice to undertake the required efforts. If after the [*] period,
Introgen is continuing not to make the required efforts, Introgen shall not be
deemed to be in breach of this Agreement, but the exclusive license granted by
VirRx to Introgen under Section 4.1 shall become non-exclusive and the license
maintenance fee payable by Introgen shall increase to an amount equal to [*].

                                  ARTICLE VII

                           INFRINGEMENT BY THIRD PARTY

         7.1 Enforcement.

                  (a) By Introgen. As between the Parties to this Agreement,
Introgen (itself or through others) shall have the initial right to control the
enforcement of the Licensed Subject Matter or defend any declaratory judgment
action with respect thereto (each for the purposes of this ARTICLE VII, an
"ENFORCEMENT ACTION").

                  (b) By VirRx. In the event that Introgen does not initiate an
Enforcement Action to enforce the Licensed Subject Matter against infringement
or misappropriation by a third party in a country, within [*] days of a request
by VirRx to initiate such Enforcement Action, VirRx may initiate an Enforcement
Action against such infringement or misappropriation at its own expense.
Notwithstanding the foregoing, Introgen shall have the exclusive right to
sublicense any alleged infringer consistent with the requirements of Section 4.1
above and subject to the notice and approval obligations under the Existing
Third-Party Agreement. In the event VirRx initiates an Enforcement Action
against infringement or misappropriation by a third party and

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Introgen or an Affiliate enters into a sublicense or settlement agreement with
such third party, any license fees, settlements, royalties and other payments to
Introgen by such third party shall first go to VirRx to the extent VirRx has
incurred any out of pocket costs and expenses related to such Enforcement
Action.

         7.2 Cooperation. The non-controlling Party shall, at the controlling
Party's reasonable request, fully cooperate with the Party controlling any
Enforcement Action, including but not limited to, joining as a Party-plaintiff,
using best efforts to cause its employees to testify at such an action and to
make available relevant records, papers, information, samples, specimens and the
like. The Party controlling the Enforcement Action shall keep the
non-controlling Party reasonably informed of the progress of such action, and
the non-controlling Party shall have the right to participate in such
Enforcement Action with counsel of its own choice at its own expense.

         7.3 Division of Recoveries. All court-awarded judgments recovered in an
Enforcement Action shall be first applied to reimburse the controlling Party and
then the non-controlling Party's unreimbursed expenses, including without
limitation, reasonable attorneys' fees and court costs. Any remainder shall be
divided with [*] of the remainder being paid to the controlling Party, and [*]
of the remainder being paid to the non-controlling Party.

         7.4 Defense. Introgen may notify VirRx if Introgen obtains knowledge,
or reasonably believes, that Introgen, its Affiliate or Sublicensee, distributor
or other customer has or may be sued by a third Party charging infringement of
patent rights that dominate a claim of patents within the Patent Rights, or
cover the development, manufacture, importation, use, distribution or sale of a
Licensed Product. In such case, as between Introgen and VirRx, Introgen shall be
entitled to control the defense in any such action(s), and Introgen may, in
addition to its rights under Section 5.4(c), [*] of the amounts otherwise
payable by Introgen to VirRx under Section 5.3 or 5.4 above, as a reserve to [*]
of the legal defense costs, attorneys' fees and liability incurred in
preparation, defense and/or settlement of such a claim pending the final
resolution such a claim or action. Notwithstanding, Introgen shall withhold only
that portion of such amounts as may reasonably be necessary to reimburse amounts
in accordance with this Section 7.4. In addition, if Introgen is required to pay
a royalty or other amount to a third Party to develop, make, import, use
distribute or sell a Licensed Product as a result of a final judgment or
settlement, Introgen may, consistent with Section 5.4(c), deduct [*] of such
amounts from the royalties otherwise payable to VirRx under this Agreement;
provided that such royalties shall not be reduced by more than [*].

                                  ARTICLE VIII

                         INVENTIONS/ PATENT PROSECUTION

         8.1 Prosecution by VirRx. Subject to Section 8.2 below, VirRx shall
have the right, at its option, to control the filing for, prosecution and
maintenance of the patents within the Patent Rights; provided however that VirRx
shall first consult with Introgen as to the filing, prosecution and maintenance
of such patents and patent applications, shall keep Introgen fully informed in
relation

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thereto, and shall furnish to Introgen copies of documents relevant to any such
filing, prosecution and maintenance. For purposes of this ARTICLE VIII,
"prosecution and maintenance" of patents and patent applications shall be deemed
to include, without limitation, the conduct of interferences or oppositions,
and/or requests for re-examinations, reissues or extensions of patent terms;
provided, however, that VirRx shall initiate an interference, opposition,
re-examination, reissue or other similar procedure only as mutually agreed by
VirRx and Introgen. Introgen shall reimburse VirRx for all reasonable
out-of-pocket expenses incurred by VirRx after the Effective Date for the filing
for, prosecution and maintenance of patents within the Patent Rights. Such
payments shall be due thirty (30) days following receipt of invoice by Introgen
for such expenses. If Introgen elects to no longer pay the expenses of a patent
or patent application within the Patent Rights in any country (an "Excluded
Country"), Introgen shall notify VirRx not less than thirty (30) days prior to
such action; in such event Introgen shall no longer be obligated to reimburse
such expenses incurred after the date of Introgen's notice, provided that the
license granted to Introgen hereunder with respect to such patent or patent
application shall terminate (with respect to Excluded Countries that are Major
Market Countries) or become non-exclusive (with respect to Excluded Countries
that are not Major Market Countries).

         8.2 Prosecution by Introgen. If VirRx elects not to file, prosecute or
maintain any patent application or patent within the Patent Rights, or pay any
fee related thereto, in any country other than an Excluded Country, VirRx shall
promptly notify Introgen of such election, but in no case later than sixty (60)
days prior to any required action relating to the filing, prosecution or
maintenance of such patent application or patent. In such event, or if Introgen
elects to take over the filing, prosecution and/or maintenance of one or more
patents or applications within the Patent Rights, then in any such case upon
notice to VirRx Introgen shall have the right, at its option, to control the
filing, prosecution and/or maintenance of any such patent applications or
patents within the Patent Rights at its own expense. In the event that Introgen
takes over the filing, prosecution and/or maintenance of a patent or application
within the Patent Rights, Introgen shall keep VirRx reasonably informed on
matters regarding such filing, prosecution and maintenance.

                                   ARTICLE IX

                                 CONFIDENTIALITY

         9.1 Confidential Information. The Parties may, from time to time, in
connection with this Agreement, disclose to each other Confidential Information.
"Confidential Information" shall mean any information disclosed in writing by
Introgen or VirRx to the other, and marked by the disclosing Party with the
legend "CONFIDENTIAL" or other similar legend sufficient to identify such
information as confidential proprietary information of the disclosing Party.
Neither Party shall use Confidential Information of the other Party except as
expressly authorized in this Agreement, and each Party will use diligent efforts
to prevent the disclosure of the other Party's Confidential Information to third
parties. Notwithstanding the foregoing, the recipient Party's obligations under
this ARTICLE IX shall not apply to Confidential Information that:

                  (a) is disclosed orally; provided, however, that the recipient
Party's obligations under this ARTICLE IX shall apply to information disclosed
orally if such information is reduced to

                                      -19-
<PAGE>

writing and marked with the legend "CONFIDENTIAL" by the disclosing Party within
thirty (30) days after disclosure thereof or if such information is disclosed
orally during any meeting of the JRC or board of directors of VirRx;

                  (b) is in the recipient Party's possession at the time of
disclosure thereof as demonstrated by documentary evidence;

                  (c) is or later becomes part of the public domain through no
fault of the recipient Party;

                  (d) is received from a third Party having no obligations of
confidentiality to the disclosing Party; or

                  (e) is developed independently by the recipient Party without
access to the disclosing Party's Confidential Information;

         9.2 Compelled Disclosures. Notwithstanding the provisions of Section
9.1:

                  (a) The recipient Party may disclose the other Party's
Confidential Information to the extent the recipient party is required to do so
by law or regulation; provided, however, that the recipient Party: (i) asserts
the confidential nature of the Confidential Information to the court or agency;
(ii) provides prompt written notice to the other Party to enable such other
Party to seek a protective order or otherwise prevent disclosure of such
Confidential Information; and (iii) reasonably cooperates with the other Party
(at the other Party's expense) in protecting against the disclosure or in
obtaining a protective order narrowing the scope of the compelled disclosure;
and

                  (b) VirRx may disclose to [*] University or [*] University (as
applicable) the terms of any sublicense provided to it by Introgen pursuant to
Section 4.1; provided, however, that: (i) such disclosure is limited to that
which is required by the terms of an Existing Third-Party Agreement then in
effect; and (ii) before the disclosure, [*] University or [*] University (as
applicable) enters into a confidentiality agreement with Introgen that is at
least as protective of Introgen's Confidential Information as the terms of this
Agreement are.

         9.3 Licensed Subject Matter.

                  (a) Notwithstanding the provisions of Section 9.1, Introgen
may use and disclose Confidential Information comprising the Licensed Subject
Matter: (a) to the extent necessary or useful in connection with the exercise of
Introgen's rights (including commercialization and/or sublicensing of Licensed
Subject Matter), or performance of Introgen's obligations or duties under this
Agreement, or to investors, advisors and others on a need-to-know basis under
reasonable conditions of confidentiality; and (b) as required by law.

                  (b) VirRx shall not disclose or provide the information
comprising the Licensed Subject Matter to any third party except: (a) as
required to file for, prosecute and maintain patents within the Licensed Subject
Matter under Section 8.1; (b) as required by an Existing Third-Party Agreement;
(c) as required by the patent disclosure policy of [*] University; or (d) as
required by law.

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         9.4 Survival. The obligations of the Parties pursuant to this ARTICLE
IX with respect to Confidential Information of the other Party shall continue in
full force and effect for a period of five (5) years after expiration or
termination of this Agreement.

                                   ARTICLE X

                                 INDEMNIFICATION

         10.1 Indemnification of VirRx. Introgen shall hold VirRx, its
successors and assigns, the directors, officers, consultants and employees of
any of the foregoing, and [*] University and its [*] (collectively, the "VIRRX
INDEMNITEES") harmless against any loss, cost, liability and expense (including
settlement costs, court costs, and the reasonable fees of attorneys and other
professionals) arising out of or resulting from, any and all claims brought by
third parties alleging personal injury or property damage in conjunction with,
or arising out of the design, manufacture, distribution or use of Licensed
Products and other products embodying the Licensed Subject Matter by Introgen,
its Affiliates or Sublicensees.

         10.2 Indemnification of Introgen. VirRx shall hold Introgen, its
Affiliates and Sublicensees, the successors and assigns of each, and the
directors, officers and employees of any of the foregoing (collectively, the
"INTROGEN INDEMNITEES") harmless against any loss, cost, liability and expense
(including settlement costs, court costs, and the reasonable fees of attorneys
and other professionals) arising out of or resulting from, any claimed breach of
the representations and warranties made by VirRx under this Agreement.

         10.3 Procedure. Notwithstanding the foregoing, a party under this
Agreement ("INDEMNIFYING PARTY") shall have no obligation to hold an Indemnitee
of the other party harmless under this ARTICLE X unless the Indemnitee seeking
indemnification hereunder (i) promptly notifies the Indemnifying Party of such
claim (ii) gives the Indemnifying Party sole control of the defense or
settlement of such claim, and (iii) provides the Indemnifying Party, at the
Indemnifying Party's expense, with reasonable assistance and full information
with respect to such claim. Notwithstanding the foregoing, the Indemnifying
Party shall have no obligations for any claim if the Indemnitee seeking
indemnification makes any admission, settlement or other communication regarding
such claim without the prior written consent of the Indemnifying Party, which
consent shall not be unreasonably withheld.

                                   ARTICLE XI

                                  USE OF NAMES

         11.1 Party Names. Except as required by law, neither Introgen nor VirRx
shall issue any press release or other public statements in connection with this
Agreement intended for use in the public media in a manner suggesting any
endorsement by the other of Introgen or VirRx, respectively, without the
approval of such other Party, which approval shall not be unreasonably withheld.

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                                  ARTICLE XII

                              TERM AND TERMINATION

         12.1 Term. Unless terminated earlier pursuant to this ARTICLE XII, the
term of this Agreement shall commence on the Effective Date and continue in full
force and effect until the later of: (a) the expiration, revocation or
invalidation of the last patent within the Patent Rights; or (b) the abandonment
of the last patent application within the Patent Rights. Introgen's license
under Section 4.1 shall survive the expiration, (but not an earlier termination,
except as provided in Section 12.4 below) of this Agreement.

         12.2 Termination for Breach. In the event of a material breach of this
Agreement, the nonbreaching Party shall be entitled to terminate this Agreement
by written notice to the breaching Party, if such breach is not cured within
sixty (60) days after written notice is given by the nonbreaching Party to the
breaching Party specifying the breach. However, if the Party alleged to be in
breach of this Agreement disputes such breach within such sixty (60) day period,
the nonbreaching Party shall not have the right to terminate this Agreement
unless it has been determined by a mutually agreed process of binding
arbitration that this Agreement was materially breached, and the breaching Party
fails to comply with its obligations hereunder within thirty (30) days after
such determination.

         12.3 Certain Terminations Upon Notice.

                  (a)      Any provision herein notwithstanding, Introgen may
                           terminate this Agreement in its entirety, at any time
                           by giving VirRx written notice. Upon termination of
                           this Agreement in its entirety under this Section
                           12.3(a), all rights and obligations of the Parties
                           shall terminate, except as provided in Section 12.4
                           below.

                  (b)      Any provision herein notwithstanding, Introgen may
                           terminate its rights and obligations as to any
                           particular patent or patent application within the
                           Patent Rights, or as to any particular Licensed
                           Product, at any time by giving VirRx at least thirty
                           (30) days prior written notice. From and after the
                           effective date of such termination under this Section
                           12.3(b) with respect to a particular patent or patent
                           application, such patent(s) and application(s) in the
                           particular country shall cease to be within the
                           Patent Rights for all purposes of this Agreement, and
                           all rights and obligations of Introgen with respect
                           to such patent(s) and patent application(s) shall
                           terminate. From and after the effective date of a
                           termination under this Section 12.3(b) with respect
                           to particular Licensed Product, the license granted
                           to Introgen under Section 4.1 shall terminate with
                           respect to such Licensed Product.

                  (c)      Any provision herein notwithstanding, Introgen may
                           terminate the Research Program, effective any time
                           after the one-year anniversary of the Effective Date
                           by giving VirRx at least ninety (90) days prior
                           written notice. Upon

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                                      -22-
<PAGE>

                           termination of the Research Program under this
                           Section 12.3(c): (i) all rights and obligations of
                           the Parties under Sections 2.1, 2.2 and 2.3 shall
                           terminate, except those rights and obligations
                           accrued prior to termination; and (ii) the exclusive
                           license granted by VirRx to Introgen under Section
                           4.1 shall become non-exclusive, except that the
                           license shall remain exclusive with respect to any
                           Licensed Subject Matter that relates to any Distinct
                           [*] Vectors (and the manufacture and use thereof) for
                           which, at the time of the Research Program's
                           termination, an IND has been filed.

         12.4 Survival.

                  (a) Termination of this Agreement for any reason shall not
release either Party hereto from any liability which at the time of such
termination has already accrued to the other Party.

                  (b) In the event this Agreement is terminated for any reason,
Introgen and its Affiliates shall have the right to sell or otherwise dispose of
the stock of any Licensed Products then on hand, all subject to the payment to
VirRx of fees and royalties pursuant to ARTICLE V hereof. Upon termination of
this Agreement for any reason, any sublicense to a third Party granted by
Introgen hereunder shall survive, provided that upon request by VirRx, such
third Party promptly agrees in writing to be bound by the applicable terms of
this Agreement.

                  (c) Articles 3, 4, 7, 8, 9, 10, 11 and 13, and Section 5.2,
shall survive the expiration and any termination of this Agreement; provided
that upon a termination by Introgen under Section 12.3(a) above, or under
Section 12.2 by reason of a breach by Introgen, the provisions of Articles 4, 7
and 8 shall terminate and not survive. Except as otherwise provided in this
Section 12.4, all rights and obligations of the Parties under this Agreement
shall terminate upon the expiration or termination of this Agreement.

                                  ARTICLE XIII

                                     GENERAL

         13.1 Governing Law. This Agreement shall be governed by, and construed
and interpreted in accordance with, the laws of Texas, without regard to
conflicts-of-laws principles.

         13.2 Independent Contractors. The relationship of Introgen and VirRx
established by this Agreement is that of independent contractors. Nothing in
this Agreement shall be construed to create any other relationship between
Introgen and VirRx. Neither Party shall have any right, power or authority to
assume, create or incur any expense, liability or obligation, express or
implied, on behalf of the other.

         13.3 Assignment. This Agreement may not be assigned by either Party
without the prior written consent of the other, except that either Party may
assign its rights and obligations under this Agreement to a third Party that
succeeds to all or substantially all of the business or assets of the assigning
Party relating to this Agreement whether by sale, merger, operation of law or
otherwise;

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                                      -23-
<PAGE>

provided that such assignee or transferee agrees in writing to be bound by the
terms and conditions of this Agreement. In addition, Introgen may assign this
Agreement to an entity that is an Affiliate of Introgen at the time of the
assignment, provided, that VirRx consents to such assignment, such consent shall
not be unreasonably withheld.

         13.4 Limitation of Liability. NEITHER PARTY SHALL BE LIABLE TO THE
OTHER PARTY OR ANY THIRD PARTY FOR ANY SPECIAL, CONSEQUENTIAL, EXEMPLARY OR
INCIDENTAL DAMAGES (INCLUDING LOST OR ANTICIPATED REVENUES OR PROFITS RELATING
TO THE SAME), ARISING FROM ANY CLAIM RELATING TO THIS AGREEMENT, WHETHER SUCH
CLAIM IS BASED ON CONTRACT, TORT (INCLUDING NEGLIGENCE) OR OTHERWISE, EVEN IF AN
AUTHORIZED REPRESENTATIVE OF SUCH PARTY IS ADVISED OF THE POSSIBILITY OR
LIKELIHOOD OF SAME.

         13.5 No Implied Obligations. Introgen's sole obligation to exploit the
Licensed Subject Matter is as set forth in ARTICLE VI. Nothing in this Agreement
shall be deemed to require Introgen to otherwise exploit the Licensed Subject
Matter nor prevent Introgen from commercializing products similar to or
competitive with a Licensed Product.

         13.6 Force Majeure. In the event either Party hereto is prevented from
or delayed in the performance of any of its obligations hereunder by reason of
acts of God, war, strikes, riots, storms, fires, or any other cause whatsoever
beyond the reasonable control of the Party, the Party so prevented or delayed
shall be excused from the performance of any such obligation to the extent and
during the period of such prevention or delay.

         13.7 Notices. Any notice or other communication required by this
Agreement shall be made in writing and given by prepaid, first class, certified
mail, return receipt requested, and shall be deemed to have been served on the
date received by the addressee at the following address or such other address as
may from time to time be designated to the other Party in writing:

         If to VirRx:              VirRx, Inc.
                                   1609 Adgers Wharf Drive
                                   St. Louis, Missouri 63017
                                   Attn:  William Wold

         With copy to:             Armstrong Teasdale, LLP
                                   One Metropolitan Square, Suite 2600
                                   St. Louis, Missouri, 63102
                                   Attn: Andrew T. Hoyne, Esq.

         If to Introgen:           Introgen Therapeutics, Inc.
                                   301 Congress Avenue, Suite 1850
                                   Austin, Texas 78701
                                   Attn:  President

         With a copy to:           Wilson Sonsini Goodrich & Rosati
                                   650 Page Mill Road
                                   Palo Alto, California 94304-1050
                                   Attn:  Kenneth A. Clark

                                      -24-
<PAGE>

         And with a copy of all financial reports to:

                                   Introgen Therapeutics, Inc.
                                   301 Congress Avenue, Suite 1850
                                   Austin, Texas 78701
                                   Attn:  Chief Financial Officer

         13.8 Compliance with Law. Each of the Parties shall comply with all
applicable federal, state and local laws and regulations in connection with its
activities pursuant to this Agreement.

         13.9 Modification; Waiver. This Agreement may not be altered, amended
or modified in any way except by a writing signed by both Parties. The failure
of a Party to enforce any provision of this Agreement shall not be construed to
be a waiver of the right of such Party to thereafter enforce that provision or
any other provision or right.

         13.10 Headings. Headings included herein are for convenience only, do
not form a part of this Agreement and shall not be used in any way to construe
or interpret this Agreement.

         13.11 Severability. If any provision of this Agreement shall be found
by a court to be void, invalid or unenforceable, the same shall be reformed to
comply with applicable law or stricken if not so conformable, so as not to
affect the validity or enforceability of the remainder of this Agreement.

         13.12 Entire Agreement. The Parties hereto acknowledge that this
Agreement and its Exhibits set forth the entire agreement and understanding of
the Parties hereto as to the subject matter hereof, and supersedes all prior
discussions, agreements and writings in respect hereto.

         13.13 Counterparts. This Agreement may be executed in counterparts,
each of which shall be deemed an original, but both of which together shall
constitute one and the same instrument.

         IN WITNESS WHEREOF, the Parties hereto have caused their duly
authorized representatives to execute this Agreement.

VIRRX, INC.                                     INTROGEN THERAPEUTICS, INC.
("VirRx")                                       ("Introgen")

By:  /s/ WILLIAM WOLD                           By: /s/ DAVID G. NANCE
   ----------------------------                    ----------------------------

Name:  William Wold                             Name: David G. Nance
     --------------------------                      --------------------------

Title: President                                Title: President & CEO
      -------------------------                       -------------------------

                                      -25-
<PAGE>
                                  EXHIBIT 1.17
                                  ------------
                                EXISTING PATENTS

<TABLE>
<Caption>
Tech. Disclosure #/        Appln Serial #/           Date           Title
VirRx I.D. No.             Issued Patent #
<S>                        <C>                       <C>            <C>
[*]
</TABLE>

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<PAGE>
                                  EXHIBIT 2.3
                                  -----------
                   GENERAL PLANS FOR RESEARCH PLAN AND BUDGET

     [*]

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