Document:

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                                                                   EXHIBIT 10.38

                           K-ras ASSIGNMENT AGREEMENT

K-ras ASSIGNMENT AGREEMENT, effective as of July 2, 2001, among Aventis
Pharmaceuticals Products Inc. (formerly Rhone-Poulenc Rorer Pharmaceuticals
Inc.), a Pennsylvania corporation ("APPI"), Aventis Pharma S.A., a company
organized under the laws of France ("APSA" and, together with APPI, the "Aventis
Parties") ("Assignors"), having an office for the transaction of business at
Route 202-206, Bridgewater, NJ, and Introgen Therapeutics Inc., a Delaware
corporation ("Introgen Therapeutics"), ("Assignee"), having an office for the
transaction of business at 301 Congress Avenue, Austin, Texas.

                                   WITNESSETH

WHEREAS, Assignors and Assignee have entered into a Restated p53 and K-ras
Agreement, dated as of June 30, 2001 (the "Restated Agreement"; capitalized
terms used herein and not otherwise defined herein having the respective
meanings given in the Restated Agreement), providing for the restructuring of
the Original p53 Agreement and the Original K-ras Agreement, so that Introgen
Therapeutics takes over from the Aventis Parties the further development and
commercialization of the gene therapy products for the delivery of the p53 and
K-ras inhibition genes, including the INGN 201 product, and that Aventis retain
a potential economic upside in those products by making an additional equity
investment in Introgen Therapeutics; and

WHEREAS, pursuant to Section 4.2.2 of the Restated Agreement, Assignors have
agreed to enter into this Assignment Agreement providing for the assignment of
Assignor of the K-ras Materials and K-ras Documentation ("Assigned Matter")
under Section 4.2.1 of the Restated Agreement;

NOW, THEREFORE, for and in consideration of the mutual consideration provided
for in the Restated Agreement, and for other good and valuable consideration,
the receipt and sufficiency of which is hereby acknowledged, and pursuant to the
terms and conditions of the Restated Agreement, the parties hereto agree as
follows:

1. Assignment of Rights. Each Assignor hereby assigns and relinquishes its
right, title and interest, that any Assignor may have with respect to or in
connection with the K-ras Materials and K-ras Documentation under Section 4.2.2
of the Restated Agreement unless otherwise required to retain such rights and
obligations under a Third Party Agreement or by law and as further limited in
Sections 4.2.1, 7.2 and 7.3 of the Restated Agreement. .

3. Representations and Warranties. The Assignors are not making any
representations or warranties of any nature or kind with respect to the Assigned
Materials, except as expressly made and contained in the Restated Agreement.

4. Conflicts with Restated Agreement. In the event that any provision of this
Agreement is construed to conflict with a provision of the Restated Agreement,
the provision in the Restated Agreement shall be deemed controlling.

5. Governing Law. This Agreement shall be construed and enforced in accordance
with the laws of the State of New York without giving effect to the choice of
law principles thereof which would require the application of the laws of a
jurisdiction other than New York.

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IN WITNESS WHEREOF, each party hereto has caused this Assignment and Assumption
Agreement to be duly executed by its duly authorized officer effective as of the
date indicated above.

INTROGEN  THERAPEUTICS, INC.           AVENTIS PHARMACEUTICALS PRODUCTS INC.

By:      /s/ DAVID NANCE               By:      /s/ THOMAS HOFSTAETTER
   -------------------------------        --------------------------------------

Name:    David Nance                   Name:    Dr. Thomas Hofstaetter
     -----------------------------          ------------------------------------

Title:   CEO                           Title:   Senior Vice President
      ----------------------------           -----------------------------------

                                       AVENTIS PHARMA S.A..

                                       By:     /s/ FRANCOIS MEYER
                                          --------------------------------------

                                       Name:   Francois Meyer
                                            ------------------------------------

                                       Title:  SVP DIA France, Head of Gencell
                                             -----------------------------------

                 [SIGNATURE PAGE TO K-ras ASSIGNMENT AGREEMENT]<PAGE>   1
                                                                   EXHIBIT 10.39

                          REGISTRATION RIGHTS AGREEMENT

         This REGISTRATION RIGHTS AGREEMENT (this "Agreement") is entered into
as of June 30, 2001, by and between Introgen Therapeutics, Inc., a Delaware
corporation (the "Company"), and Aventis Pharmaceuticals Products Inc., a
Pennsylvania corporation ( "APPI"). In addition, Rhone-Poulenc Rorer
International (Holdings), Inc., a Delaware corporation ("RPRIH"), is entering
into this Agreement for the purpose of Section 8.1 only.

                                    RECITALS

         WHEREAS, RPRIH is presently the owner of 3,968,893 shares of the
Company's Common Stock (the "Existing Shares"); and

         WHEREAS, the Company and APPI are parties to that certain Restated p53
and K-ras Agreement of even date herewith, whereby the Company and APPI, among
other things, have agreed to enter into this Agreement; and

         WHEREAS, pursuant to that certain Series A Non-Voting Convertible Stock
Purchase Agreement, of even date herewith, by and among the Company, APPI and
RPRIH (the "Stock Purchase Agreement"), the Company has agreed to sell, and APPI
has agreed to purchase, at the Closing, 100,000 shares of the Company's Series A
Non-Voting Convertible Preferred Stock (the "Series A Shares"); and

         WHEREAS, as an inducement to enter into the Stock Purchase Agreement
and as additional consideration to APPI, the Stock Purchase Agreement
contemplates, among other things, that the Company, APPI and RPRIH enter into
this Agreement and that this Agreement become effective upon the Closing of the
purchase and sale of the Series A Shares under the Stock Purchase Agreement;

                                    AGREEMENT

         NOW, THEREFORE, in consideration of the premises and the mutual
covenants contained herein, and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto,
intending to be legally bound, hereby agree as follows:

         1. CERTAIN DEFINITIONS. As used in this Agreement, the following terms
shall have the following respective meanings:

                  1.1 "Closing" shall have the meaning assigned to such term in
the Stock Purchase Agreement.

                  1.2 "Common Stock" shall mean the common stock of the Company,
par value $0.001 per share.

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                  1.3 "Effective Date" shall mean the date of the Closing of the
purchase and sale of the Series A Shares under the Stock Purchase Agreement.

                  1.4 "Exchange Act" shall mean the United States Securities
Exchange Act of 1934, as amended, and the rules and regulations of the SEC
promulgated thereunder.

                  1.5 "Holder" shall mean APPI and any other person or entity to
whom Registrable Securities and the rights to cause the Company to register the
Registrable Securities hereunder are transferred or assigned in accordance with
Section 9.

                  1.6 "Initiating Holders" means the person or persons who hold
at least a majority of the then outstanding Registrable Securities.

                  1.7 The terms "register," "registered" and "registration"
refer to a registration effected by preparing and filing a registration
statement in compliance with the Securities Act, and the declaration or ordering
of the effectiveness of such registration statement.

                  1.8 "Registrable Securities" shall mean (i) the shares of
Common Stock issuable or issued upon conversion of the Series A Shares and (ii)
any other shares of Common Stock issued as (or issuable upon conversion or
exercise of any warrant, right or other security that is issued as) a dividend
or other distribution with respect to or exchange for or replacement of the
Series A Shares, excluding in all cases, however, any Registrable Securities
sold by a person in a transaction in which a Holder's registration rights under
this Agreement are not assigned; provided, however, that Registrable Securities
shall not include any shares of Common Stock which have been sold to the public
either pursuant to a registration statement or Rule 144 under the Securities
Act.

                  1.9 "Securities Act" shall mean the United States Securities
Act of 1933, as amended, and the rules and regulations of the SEC promulgated
thereunder, all as the same shall be in effect at the time.

                  1.10 "SEC" shall mean the United States Securities and
Exchange Commission or any other federal agency at the time administering the
Securities Act.

         2. PIGGYBACK REGISTRATION RIGHTS.

                  2.1 Registration. If the Company shall determine to register
any of its securities under the Securities Act (including for this purpose a
registration effected by the Company for stockholders other than the Holders,
but excluding any registration requested under Section 7.2 of the Company's
Series C Preferred Stock Purchase Agreement dated as of November 30, 1995 (the
"Series C Agreement") in which any Existing Shares are requested to be
registered), other than (a) a registration relating solely to employee benefit
plans, (b) a registration, including a registration on Form S-4, relating solely
to a transaction subject to Rule 145 promulgated under the Securities Act, or
(c) a registration on any registration form which does not permit secondary
sales or does not include substantially the same information as would be
required to be included in a registration statement covering the sale of
Registrable Securities, the Company will:

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                           (i) promptly give to each Holder written notice
thereof; and

                           (ii) include in such registration, and in any
underwriting involved therein, all of the Registrable Securities specified in a
written request or requests made by any Holder within twenty (20) days after
receipt of the written notice from the Company described in clause (i) above,
except as set forth in Section 2.2 below. Such written request may specify all
or a part of a Holder's Registrable Securities.

                  2.2 Underwriting. If the registration of which the Company
gives notice is for an underwritten offering, the Company shall so advise the
Holders as a part of the written notice given pursuant to Section 2.1. In such
event, the right of any Holder to registration pursuant to this Section 2 shall
be conditioned upon such Holder's participation in such underwriting and the
inclusion of such Holder's Registrable Securities in the underwriting to the
extent provided herein. All Holders proposing to distribute their securities
through such underwriting shall (together with the Company and any other
stockholders proposing to distribute their securities through such underwriting)
enter into an underwriting agreement in customary form with a
nationally-recognized underwriter selected by the Company, subject to the
approval of such Holders, which approval shall not be unreasonably withheld.
Notwithstanding any other provision of this Section 2, if the managing
underwriter in any underwritten offering subject to this Section 2 determines
that marketing factors require a limitation on the number of shares to be
offered in the underwritten offering, the managing underwriter may (subject to
the allocation priority set forth below) exclude from such registration and
underwriting up to all of the Registrable Securities that would otherwise be
underwritten pursuant to this Section 2. The Company shall so advise all holders
of securities requesting registration, and the number of shares of securities
that are entitled to be included in the registration and underwriting under this
Section 2 by persons other than the Company shall be allocated in the following
priority: first, among any stockholders requesting registration pursuant to the
Series C Agreement or the Company's Registration Rights Agreement, dated as of
October 31, 1997 (the "1997 Rights Agreement"); second, among all Holders; and
third, among all other stockholders in proportion, as nearly as practicable, to
the respective amounts of securities that they had requested to be included in
such registration at the time of filing the registration statement. If any
Holder or other stockholder disapproves of the terms of any such underwriting,
such Holder may elect to withdraw therefrom by written notice to the Company and
the managing underwriter. Any Registrable Securities or other securities
excluded or withdrawn from such underwriting shall be withdrawn from such
registration.

                  2.3 Right to Terminate Registration. The Company shall have
the right to terminate or withdraw any registration initiated by the Company
under this Section 2 without liability prior to the effectiveness of such
registration, whether or not any Holder has elected to include securities in
such registration.

                  2.4 Termination of Piggyback Rights. The rights granted
pursuant to this Section 2 shall terminate upon the earliest to occur of (X)
after a Holder has sold any Shares pursuant to a registration under this Section
2 on three (3) occasions; provided, however, that if the number of Shares
requested to be included in an underwritten offering are reduced as a result of
the

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allocation priority in Section 2.2, then such offering pursuant to this Section
2 shall not be counted for purposes of counting the number of registrations
under this clause (X), (Y) as to any Holder, such time at which all Registrable
Securities held by such Holder, together will all Existing Shares held by RPRIH
or any other affiliate of APPI, can be sold in any three-month period without
registration in compliance with Rule 144 of the Securities Act (or any successor
rule thereof), or (Z) four (4) years from the Effective Date of this Agreement;
provided, however, that such four (4) year period shall be extended for the
total number of days of any and all Suspension Periods (as defined in Section
4.1(a)).

         3. DEMAND REGISTRATION.

                  3.1 Request for Registration. If the Company shall receive
from the Initiating Holders, at any time after the one-year anniversary of the
Effective Date, a written request that the Company effect any registration with
respect to any of the then outstanding Registrable Securities which would result
in an aggregate offering of at least $5,000,000 (or any lesser aggregate
offering if such request for registration is with respect to all the Registrable
Securities of such Initiating Holder under this Agreement), the Company will:

                           (a) within 10 days of such request, give written
notice of the proposed registration to all other Holders; and

                           (b) as soon as practicable, and in any event with 60
days of such request, file with the SEC and thereafter use its best efforts to
effect such registration (including, without limitation, the execution of an
undertaking to file post effective amendments, appropriate qualification under
applicable blue sky or other state securities laws and appropriate compliance
with applicable regulations issued under the Securities Act) as may be so
requested and as would permit or facilitate the sale and distribution of all or
such portion of such Registrable Securities as are specified in such request,
together with all or such portion of the Registrable Securities of any Holders
joining in such request as are specified in a written request delivered to the
Company within twenty (20) days after receipt of such written notice from the
Company; provided that the Company shall not be obligated to effect, or to take
any action to effect, any such registration pursuant to this Section 3:

                                    (i) in any particular jurisdiction in which
the Company would be required to execute a general consent to service of process
in effecting such registration, qualification or compliance, unless the Company
is already subject to service in such jurisdiction and except as may be required
by the Securities Act;

                                    (ii) after the Company has effected three
(3) such registrations pursuant to this Section 3.1 and such registrations have
been declared or ordered effective and the sales of such Registrable Securities
have closed; provided, however, that if the effectiveness of any such
registration is not maintained for a period of at least ninety (90) days (or any
lesser period of time in the event the distribution contemplated by the
registration is fully completed), then such registration shall not be counted as
a registration for the purposes of this clause (ii);

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                                    (iii) during the period starting with the
date fifty-five (55) calendar days prior to the Company's good faith estimate of
the date of filing of, and ending on a date one-hundred-fifty (150) calendar
days after the effective date of, any registration statement pertaining to a
public offering of securities for the Company's account; provided that the
Company is actively employing in good faith its reasonable best efforts to cause
such registration statement to be effective; or

                                    (iv) during the period starting with the
date six (6) months prior to the Company's good faith estimate of the effective
date of, and ending on a date six (6) months after the effective date of, any
registration statement pertaining to a public offering of securities for the
account of any stockholder requesting registration pursuant Section 7.2(a) of
the Series C Agreement or pursuant to Section 2 of the 1997 Rights Agreement;
provided that the Company is actively employing in good faith its reasonable
best efforts to cause such registration statement to be effective and provided
further that if the Company has begun to effect a registration pursuant to this
Section 3 and receives a request for registration from a stockholder pursuant
Section 7.2(a) of the Series C Agreement or pursuant to Section 2 of the 1997
Rights Agreement, then the Company shall immediately inform the Holders and
cease and have no further obligation to take any action to effect the
registration begun pursuant to Section 3.1.

         Subject to the foregoing clauses (i) through (iv), the Company shall
file a registration statement covering the Registrable Securities so requested
to be registered as soon as practicable, after receipt of the request or
requests of the Initiating Holders; provided, however, that if the Company shall
furnish to such Holders a certificate signed by the President of the Company (a
"President's Certificate") stating that in the good faith judgment of the Board
of Directors of the Company, it would be seriously detrimental to the Company
and its stockholders for such registration statement to be filed on or before
the time filing would be required and it is therefore essential to defer the
filing of such registration statement, the Company shall have the right to defer
such filing (but not more than once during any twelve-month period) for a period
that the Board of Directors of the Company in its good faith judgment deems
reasonably necessary but in no event shall such period be more than
one-hundred-eighty (180) days after receipt of the request of the Initiating
Holders.

         The registration statement filed pursuant to the request of the
Initiating Holders may, subject to the provisions of Section 3.2 below, include
other securities of the Company that are held by officers or directors of the
Company or that are held by persons who, by virtue of agreements with the
Company, are entitled to include their securities in any such registration.

                  3.2 Underwriting.

                           (a) If the Initiating Holders intend to distribute
the Registrable Securities covered by their request by means of an underwriting,
they shall so advise the Company as a part of their request made pursuant to
this Section 3, and the Company shall include such information in the written
notice referred to in Section 3.1(a). The right of any Holder to registration
pursuant to Section 3 shall be conditioned upon such Holder's participation in
such underwriting and the inclusion of such Holder's Registrable Securities in
the underwriting to the extent provided herein.

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A Holder may elect to include in such underwriting all or a part of such
Holder's Registrable Securities.

                           (b) All Holders proposing to distribute their
securities through an underwritten offering pursuant to this Section 3 shall
enter into an underwriting agreement in customary form with the underwriter or
underwriters. The managing underwriters or underwriters for any such
underwritten offering shall be selected by the Initiating Holder, subject to
approval by the Company, which approval will not be unreasonably withheld.

                           (c) Notwithstanding any other provision of this
Section 3, if the underwriter advises the Initiating Holders that marketing
factors require a limitation on the number of shares to be underwritten, then
the Initiating Holders shall so advise all Holders of Registrable Securities
that would otherwise be underwritten pursuant hereto, and the number of shares
of Registrable Securities that may be included in the underwriting shall be
allocated among all Holders thereof, in proportion (as nearly as practicable) to
the amount of Registrable Securities owned by each Holder; provided, however,
that the number of shares of Registrable Securities to be included in such
underwriting shall not be reduced unless all other shares of Common Stock are
first entirely excluded from such underwriting. If any Holder disapproves of the
terms of any such underwriting, such Holder may elect to withdraw therefrom by
written notice to the Company and the underwriter. Any Registrable Securities
excluded or withdrawn from such underwriting shall be withdrawn from such
registration. If the underwriter has not limited the number of Registrable
Securities or other securities to be underwritten, the Company may include its
securities for its own account in such registration if the underwriter so agrees
and if the number of Registrable Securities and other securities that would
otherwise have been included in such registration and underwriting will not
thereby be limited.

                  3.3 Termination of Demand Rights. The rights granted pursuant
to this Section 3 shall terminate upon the earlier to occur of (X) as to any
Holder, such time at which all Registrable Securities held by such Holder,
together with all Existing Shares held by RPRIH or any other affiliate of APPI,
can be sold in any three-month period without registration in compliance with
Rule 144 of the Securities Act (or any successor rule thereof), or (Y) four (4)
years from the Effective Date of this Agreement; provided, however, that such
four (4) year period shall be extended for the total of (i) any and all
Suspension Periods; (ii) any and all periods that any Holder is prevented from
exercising the rights granted pursuant to this Section 3 by operation of Section
3.1(b)(iii) or Section 3.1(b)(iv); and (iii) any and all periods that any Holder
is prevented from exercising the rights granted pursuant to this Section 3 by
the Company's delivery of a President's Certificate under Section 3.1, unless
any Suspension Period or any limitation on the exercisability of the rights
granted pursuant to this Section 3 by operation of Section 3.1(b)(iv) is caused
by any Holder requesting registration of Existing Shares pursuant to the Series
C Agreement.

         4. REGISTRATION PROCEDURES.

                  4.1 Company Procedures. Whenever required under this Agreement
to effect the registration of any Registrable Securities, the Company shall, as
expeditiously as reasonably possible:

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                           (a) Prepare and file with the SEC a registration
statement with respect to such Registrable Securities and use its best efforts
to cause such registration statement to become effective, and, upon the request
of the Holders of a majority of the Registrable Securities registered
thereunder, keep such registration statement effective for a period of up to
ninety (90) days or any lesser period of time in the event the distribution
described in such registration statement has been fully completed; provided,
however, that the Company shall not be obligated to keep such registration
statement effective if the Company receives a request for registration pursuant
Section 7.2(a) of the Series C Agreement (other than from a Holder) or pursuant
to Section 2 of the 1997 Rights Agreement on or prior to the date that six (6)
months after the effective date of, such registration statement. Any such period
during which the Company is excused by operation of this Section 4.1(a) from
maintaining the effectiveness of the registration statement is referred to as a
"Suspension Period."

                           (b) Prepare and file with the SEC such amendments and
supplements to such registration statement and the prospectus used in connection
with such registration statement as may be necessary to comply with the
provisions of the Securities Act with respect to the disposition of all
securities covered by such registration statement.

                           (c) Furnish to the Holders such numbers of copies of
a prospectus, including a preliminary prospectus, in conformity with the
requirements of the Act, and such other documents as they may reasonably request
in order to facilitate the disposition of Registrable Securities owned by such
Holders.

                           (d) Use its best efforts to register and qualify the
securities covered by such registration statement under such other securities or
Blue Sky laws of such jurisdictions as shall be reasonably requested by the
Holders, provided that the Company shall not be required in connection therewith
or as a condition thereto to qualify to do business or to file a general consent
to service of process in any such states or jurisdictions.

                           (e) In the event of any underwritten public offering,
enter into and perform its obligations under an underwriting agreement, in usual
and customary form, with the managing underwriter of such offering.

                           (f) Notify in writing each Holder of Registrable
Securities covered by such registration statement at any time when a prospectus
relating thereto is required to be delivered under the Securities Act of the
happening of any event as a result of which the prospectus included in such
registration statement, as then in effect, includes an untrue statement of a
material fact or omits to state a material fact required to be stated therein or
necessary to make the statements therein not misleading in the light of the
circumstances then existing.

                           (g) Notify in writing each Holder of Registrable
Securities covered by such registration statement, (a) when such registration
statement or the prospectus included therein or any amendment or supplement or
post-effective amendment has been filed, and, with respect to such registration
statement or any post-effective amendment, when the same has become effective,
(b) of any comments made to the Company or its counsel by the SEC with respect
thereto or any

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request made to the Company or its counsel by the SEC for amendments or
supplements to such registration statement or prospectus or for additional
information (and furnish counsel for the selling Holder(s) copies of such
comment letters and requests), (c) of the issuance by the SEC of any stop order
suspending the effectiveness of such registration statement or the initiation or
threatening of any proceedings for that purpose, (d) of the receipt by the
Company of any notification with respect to the suspension of the qualification
of the Registrable Securities for sale in any jurisdiction or the initiation or
threatening of any proceeding for such purpose.

                           (h) Use its reasonable best efforts to obtain the
withdrawal of any order suspending the effectiveness of such registration
statement or any post-effective amendment thereto at the earliest practicable
date and notify each Holder of Registrable Securities covered by such
registration statement of the withdrawal of any such order.

                           (i) Furnish, at the request of any Holder requesting
registration of Registrable Securities pursuant to this Agreement, on the date
that such Registrable Securities are delivered to the underwriters for sale in
connection with a registration pursuant to this Agreement, if such securities
are being sold through underwriters, or, if such securities are not being sold
through underwriters, on the date that the registration statement with respect
to such securities becomes effective, (i) an opinion, dated such date, of the
counsel representing the Company for the purposes of such registration, in form
and substance as is customarily given to underwriters in an underwritten public
offering, addressed to the underwriters, if any, and to the Holders requesting
registration of Registrable Securities and (ii) a letter dated such date, from
the independent certified public accountants of the Company, in form and
substance as is customarily given by independent certified public accountants to
underwriters in an underwritten public offering, addressed to the underwriters,
if any, and to the Holders requesting registration of Registrable Securities.

                           (j) Make generally available to its securityholders
as soon as practicable but in any event not later than eighteen months after the
effective date of such registration statement, an earning statement (which need
not be audited) complying with Section 11(a) of the Securities Act (including,
at the Company's option, Rule 158 thereunder).

                  4.2 Selling Stockholder Procedures. In connection with a
request for registration of any Registrable Securities pursuant to this
Agreement, any selling Holder shall, as expeditiously as reasonably possible:

                           (a) Furnish to the Company all such information
concerning such Holder necessary for the Company to complete the registration
statement and such Holder will notify the Company promptly if any such
information so furnished is no longer true and correct in all material respects
or if such information so furnished omits any material fact necessary to make
such information not misleading.

                           (b) In the event of any underwritten public offering,
enter into and perform its obligations under an underwriting agreement, in usual
and customary form, with the managing underwriter of such offering.

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                           (c) In the event of any underwritten public offering,
furnish, at the request of the Company, on the date that such Registrable
Securities are delivered to the underwriters, an opinion, dated as of such date,
of the counsel representing the selling Holders in connection with such
registration, in form and substance as is customarily given on behalf of selling
stockholders in an underwritten public offering, addressed to the underwriters
and the Company.

         5. EXPENSES OF REGISTRATION. All expenses (other than underwriting
discounts and commissions and fees and disbursements of a special counsel of a
selling stockholder) incurred in connection with registrations, filings or
qualifications pursuant to Sections 2 and 3, including (without limitation) all
registration, federal and state filing and qualification fees and expenses,
printer's fees, accounting fees and fees and disbursements of counsel for the
Company shall be borne by the Company; provided, however, that the Company shall
not be required to pay for any expenses of any registration begun pursuant to
Section 3 if such registration request is subsequently withdrawn at the request
of the Holders of at least a majority of the Registrable Securities to be
registered (in which case all participating Holders shall bear such expenses),
unless the Holders of at least a majority of the Registrable Securities agree to
forfeit their right to one demand registration pursuant to Section 3; provided
further, however, that if at the time of such withdrawal, the Holders have
learned of a material adverse change in the condition, business, or prospects of
the Company from that known to the Holders at the time of their request and have
withdrawn the request following disclosure by the Company of such material
adverse change, then the Holders shall not be required to pay any of such
expenses and shall not forfeit their right to one demand registration pursuant
to Section 3.

         6. INDEMNIFICATION.

                  6.1 To the extent permitted by law, the Company will indemnify
and hold harmless each Holder, each Holder's officers, directors, employees and
agents, any underwriter (as defined in the Securities Act) for such Holder, and
each person, if any, who controls any such Holder or underwriter within the
meaning of the Securities Act, against any and all claims, losses, damages and
liabilities (joint or several) to which they may become subject under the
Securities Act or other federal or state law, insofar as such claims, losses,
damages or liabilities (or actions in respect thereof) arise out of or are based
on: (i) any untrue statement (or alleged untrue statement) of a material fact
contained in any registration statement, prospectus, offering circular or other
document incident to any such registration, qualification or compliance, (ii)
any omission (or alleged omission) to state therein a material fact required to
be stated therein or necessary to make the statements therein, in light of the
circumstances in which they were made, not misleading or (iii) any violation (or
alleged violation) by the Company of the Securities Act, the Exchange Act, any
state securities law, or any rule or regulation promulgated under the Securities
Act, Exchange Act or any state securities law; and the Company will pay each
such Holder, officer, director, employee, agent, underwriter or controlling
person, as incurred, any legal or other expenses reasonably incurred by them in
connection with investigating and defending any such claim, loss, damage,
liability or action; provided, however, that the indemnity agreement contained
in this Section 6.1 shall not apply to the extent that any such claim, loss,
damage, liability or expense arises out of or is based on any untrue statement
(or alleged untrue statement), omission (or alleged omission) or violation (or

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<PAGE>   10

alleged violation) based upon written information furnished to the Company by
such Holder or underwriter and stated to be specifically for use in any such
registration statement, prospectus, offering circular or other document;
provided further, however, that the indemnity agreement contained in this
Section 6.1 shall not apply to amounts paid in settlement of any such loss,
claim, damage, liability or action if such settlement is effected without the
consent of the Company (which consent shall not be unreasonably withheld).

                  6.2 To the extent permitted by applicable law, each Holder
will, indemnify and hold harmless the Company, each of the Company's officers,
directors employees and agents, each person, if any, who controls the Company
within the meaning of the Securities Act, any underwriter, any other Holder
selling securities pursuant to the registration and any controlling person of
any such underwriter or other Holder, against any and all claims, losses,
damages and liabilities (joint or several) to which they may become subject
under the Securities Act or other federal or state law, insofar as such claims,
losses, damages or liabilities (or actions in respect thereof) arise out of or
are based on: (i) any untrue statement (or alleged untrue statement) of a
material fact contained in any registration statement, prospectus, offering
circular or other document incident to any such registration, qualification or
compliance, (ii) any omission (or alleged omission) to state therein a material
fact required to be stated therein or necessary to make the statements therein,
in light of the circumstances in which they were made, not misleading or (iii)
any violation (or alleged violation) by the Holder of the Securities Act, the
Exchange Act, any state securities law, or any rule or regulation promulgated
under the Securities Act, Exchange Act or any state securities law; and such
Holder will pay the Company, each of the Company's officers, directors employees
and agents, each person controlling the Company, each underwriter, each other
Holder selling securities pursuant to the registration and each person
controlling any such underwriter or other Holder, as incurred, any legal or
other expenses reasonably incurred by them in connection with investigating of
defending any such claim, loss, damage, liability or action, in each case to the
extent (and only to the extent) that such untrue statement (or alleged untrue
statement), omission (or alleged omission) or violation (or alleged violation)
is made in such registration statement, prospectus, offering circular or other
document in reliance upon and in conformity with written information furnished
to the Company by such Holder and stated to be specifically for use therein;
provided, however that the indemnity agreement contained in this Section 6.2
shall not apply to amounts paid in settlement of any such loss, claim, damage,
liability or action if such settlement is effected without the consent of the
Holder (which consent shall not be unreasonably withheld); provided further,
however, that in no event shall the aggregate liability of a Holder for
indemnification under this Section 6.2 exceed the proceeds received by such
Holder from the sale of Registrable Securities in such offering.

                  6.3 Each person entitled to indemnification under this Section
6 (the "Indemnified Party") shall give notice to the party required to provide
indemnification (the "Indemnifying Party") promptly after such Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought and shall
permit the Indemnifying Party to assume the defense of any such claim or any
litigation resulting therefrom, provided that counsel for the Indemnifying
Party, who shall conduct the defense of such claim or any litigation resulting
therefrom, shall be approved by the Indemnified Party (whose approval shall not
unreasonably be withheld), and the Indemnified Party may participate in such
defense at such Indemnified Party's expense, and provided further that the

                                      -10-
<PAGE>   11

failure of any Indemnified Party to give notice as provided herein shall not
relieve the Indemnifying Party of its obligations under this Agreement, except
to the extent that the Indemnified Party is prejudiced thereby. Each Indemnified
Party shall furnish such information regarding itself or the claim in question
as an Indemnifying Party may reasonably request and as shall be reasonably
required in connection with defense of such claim and litigation resulting
therefrom. An Indemnified Party shall have the right to retain its own counsel,
with the fees and expenses to be paid by the Indemnifying Party, if
representation of such Indemnified Party by the counsel retained by the
Indemnifying Party would be inappropriate due to actual or potential differing
interests between such Indemnified Party and any other party represented by such
counsel in such proceeding, provided that in no event shall the Indemnifying
Party be required to pay the fees and expenses of more than one such separate
counsel for each Indemnified Party.

                  6.4 If the indemnification provided for in this Section 6 is
held by a court of competent jurisdiction to be unavailable to an Indemnified
Party with respect to any losses, claims, damages or liabilities referred to
herein, the Indemnifying Party, in lieu of indemnifying such Indemnified Party
thereunder, shall to the extent permitted by applicable law contribute to the
amount paid or payable by such Indemnified Party as the result of such loss,
claim, damage or liability in such proportion as is appropriate to reflect the
relative fault of the Indemnifying Party on the one hand and of the Indemnified
Party on the other in connection with the allegation(s) that resulted in such
loss, claim, damage or liability, as well as any other relevant equitable
considerations. The relative fault of the Indemnifying Party and of the
Indemnified Party shall be determined by a court of law by reference to, among
other things, whether the untrue or alleged untrue statement of a material fact
or the omission to state a material fact relates to information supplied by the
Indemnifying Party or by the Indemnified Party and the parties' relevant intent,
knowledge, access to information and opportunity to correct or prevent such
statement or omission; provided that in no event shall any contribution by a
Holder hereunder exceed the proceeds from the sale of Registrable Securities
received by such Holder.

                  6.5 The obligations of the Company and Holders under this
Section 6 shall survive the completion of any offering of Registrable Securities
in a registration statement and the termination of this Agreement. No
Indemnifying Party, in the defense of any such claim or litigation, shall,
except with the prior written consent of each Indemnified Party (which consent
shall not be unreasonably withheld), consent to the entry of any judgment or
enter into any settlement. Unless waived by the Indemnified Party, all judgments
and settlements must include as an unconditional term thereof the giving by the
claimant or plaintiff to such Indemnified Party of a release from all liability
in respect to such claim or litigation.

         7. RULE 144 REPORTING. With a view to making available the benefits of
certain rules and regulations of the SEC that may permit the sale of the
Registrable Securities to the public without registration, the Company agrees
to:

                  7.1 Make and keep public information available as those terms
are understood and defined in Rule 144 under the Securities Act, at all times;

                                      -11-
<PAGE>   12

                  7.2 File with the SEC in a timely manner all reports and other
documents required of the Company under the Securities Act and the Exchange Act;

                  7.3 Furnish to any Holder, so long as the Holder owns any
Registrable Securities, forthwith upon request (i) a written statement by the
Company that it has complied with the reporting requirements of Rule 144 and of
the Securities Act and the Exchange Act, or that it qualifies as a registrant
whose securities may be resold pursuant to Form S-3; and (ii) such information
as may be reasonably requested in availing any Holder of any rule or regulation
of the SEC (exclusive of Rule 144) that permits the selling of any such
securities without registration or pursuant to such form.

         8. STANDOFF AGREEMENT.

                  8.1 Prior to October 3, 2001, RPRIH shall not, without the
consent of the Company, sell or otherwise transfer or dispose of (other than to
donees who agree to be similarly bound) any Existing Shares.

                  8.2 Notwithstanding anything to the contrary in this
Agreement, prior to July 2, 2002, APPI shall not, without the consent of the
Company, sell or otherwise transfer or dispose of (other than to donees who
agree to be similarly bound) any Registrable Securities.

         9. TRANSFER OR ASSIGNMENT OF REGISTRATION RIGHTS. The rights to cause
the Company to register the Holder's securities granted by the Company under
Sections 2 and 3 hereof may be transferred or assigned by the Holder to a
transferee or assignee of any of the Registrable Securities; provided that (a)
such transfer is only to an "affiliate" of such Holder (as such term is defined
in Rule 12b-2 of the Exchange Act), (b) the Company is given written notice by
such Holder at the time of said transfer or assignment, stating the name and
address of said transferee or assignee and identifying the securities with
respect to which such registration rights are being transferred or assigned, and
(c) the transferee or assignee of such rights assumes the obligations of a
Holder under this Agreement with respect to the Registrable Securities that are
transferred or assigned. To the extent APPI creates a new subsidiary and
transfers any of the Series A Shares to it, or transfers any of the Series A
Shares to any of its subsidiaries or affiliates (as such term is defined in Rule
12b-2 of the Exchange Act), APPI shall cause such transferee to become a
signatory to this Agreement by a duly executed addendum agreement (an "Addendum
Agreement") substantially in the form as that attached hereto as Exhibit A. The
execution of an Addendum Agreement by such transferee shall constitute a
permitted amendment of this Agreement.

         10. MISCELLANEOUS.

                  10.1 Governing Law. This Agreement shall be governed in all
respects by and in accordance with the laws of the State of Delaware, without
regard to the principles of conflicts of law thereof.

                                      -12-
<PAGE>   13

                  10.2 Counterparts. This Agreement may be executed in two or
more counterparts, each of which shall be deemed an original, and all of which
together shall constitute one and the same instrument.

                  10.3 Titles and Subtitles. The titles and subtitles used in
this Agreement are used for convenience only and are not to be considered in
construing or interpreting this Agreement.

                  10.4 Notices. All notices, requests and other communications
required or permitted to be given to a party under this Agreement shall be in
writing and shall be deemed to have been duly given if (i) personally delivered
(by courier service or otherwise) or sent by registered or certified mail
(return receipt requested and postage prepaid), in each case to the respective
address specified below, or such other address as may be specified in writing by
such party to the other parties; or (ii) sent by confirmed telecopier, as
follows:

                                      -13-
<PAGE>   14

         RPRIH and APPI:

                           Aventis Pharmaceuticals Products Inc.
                           Route 202-206
                           Bridgewater, New Jersey 08807-0800
                           Facsimile: (908) 231-3619
                           Attn: Senior Vice President -- Corporate Development

                           and

                           Rhone-Poulenc Rorer International (Holdings), Inc.
                           3711 Kennett Pike, Suite 200
                           Greenville, Delaware 19807
                           Facsimile: (302) 777-7665
                           Attn: Phillip Ridolfi, President

                           with copies to (which shall not constitute notice):

                           Charles D. Dalton
                           Vice President, Legal - Corporate Development
                           Route 202-206
                           Bridgewater, New Jersey 08807-0800
                           Facsimile: (908) 231-4480

                           and

                           Joe S. Poff
                           Baker Botts L.L.P.
                           One Shell Plaza
                           Houston, Texas 77002
                           Facsimile: (713) 229-7710

         Company:

                           Introgen Therapeutics, Inc.
                           301 Congress Ave., Suite 2025
                           Austin, Texas 78701
                           Facsimile: (512) 708-9311
                           Attn: David G. Nance

                           with a copies to (which shall not constitute notice):

                           Rodney Varner, Esq.
                           Wilson & Varner, L.L.P.
                           301 Congress Avenue

                                      -14-
<PAGE>   15

                           Austin, Texas 78701
                           Facsimile: (512) 498-9141

                           and

                           Wilson Sonsini Goodrich & Rosati
                           Professional Corporation
                           8911 Capital of Texas Highway, Suite 3350
                           Austin, Texas 78759
                           Facsimile: (512) 338-5499
                           Attn: Christopher J. Ozburn, Esq.

                  10.5 Amendments. Except as permitted by Section 9, this
Agreement may only be amended with the written consent of the Company and the
holders of at least a majority of the outstanding shares of Registrable
Securities at the time of such amendment. Any amendment effected in accordance
with Section 9 or this Section 10.5 shall be binding upon the Company, the
Holders, each transferee of the Registrable Securities, each future holder of
all such Registrable Securities.

                  10.6 Severability. If any provision of this Agreement should
be held invalid, illegal or unenforceable in any jurisdiction, all other
provisions hereof shall remain in full force and effect in such jurisdiction and
shall be liberally construed in order to carry out the intentions of the parties
as nearly as may be possible. Such invalidity, illegality or unenforceability
shall not affect the validity, legality or enforceability of such provision in
any other jurisdiction.

                  10.7 Successors and Assigns. The provisions of this Agreement
shall be binding on and inure to the benefit of the parties and their respective
successors and permitted assigns.

                  10.8 Delays or Omissions; Waiver. No delay or omission to
exercise any right, power or remedy accruing to any party, upon any breach or
default of this Agreement by another party, shall impair any such right, power
or remedy of the non-breaching party, nor shall it be construed to be a waiver
of any such breach or default, or an acquiescence therein, or of or in 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 any party of any breach or default under
this Agreement or any waiver on the part of any party 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 any holder, shall be
cumulative and not alternative.

                  10.9 Entire Agreement. This Agreement constitutes the entire
agreement among the parties with respect to the subject matter hereof, and
supersedes all prior or contemporaneous agreements and understandings, both
written or oral, among the parties with respect to such subject matter.

                                      -15-
<PAGE>   16

                  10.10 Telecopy Execution and Delivery. A facsimile, telecopy
or other reproduction of this Agreement may be executed by one or more parties,
and an executed copy of this Agreement may be delivered by one or more parties
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 hereto, all parties shall execute an original of this
Agreement as well as any facsimile, telecopy or other reproduction hereof.

                                      -16-
<PAGE>   17

         IN WITNESS WHEREOF, the parties hereto have executed this Registration
Rights Agreement of the day and year first above written.

                                 Introgen Therapeutics, Inc.

                                 By:   /s/ David G. Nance
                                    --------------------------------------------
                                       David G. Nance
                                       President & Chief Executive Officer

                                 Aventis Pharmaceuticals Products Inc.

                                 By: /s/ Thomas Hofstaetter
                                    --------------------------------------------
                                 Name: Dr. Thomas Hofstaetter
                                      ------------------------------------------
                                 Title: Senior Vice President
                                       -----------------------------------------

                                 Rhone-Poulenc Rorer International Holdings Inc.

                                 By: /s/ Phillip R. Ridolfi
                                    --------------------------------------------
                                 Name: Phillip R. Ridolfi
                                      ------------------------------------------
                                 Title: President
                                       -----------------------------------------

                                      -17-

                           INTROGEN THERAPEUTICS, INC.
                          REGISTRATION RIGHTS AGREEMENT
                                 SIGNATURE PAGE

<PAGE>   18

                                    EXHIBIT A

                           FORM OF ADDENDUM AGREEMENT

         This ADDENDUM AGREEMENT (this "Addendum Agreement") made this ___ day
of __________, 200__ by and between _______________ (the "New Holder") and
Introgen Therapeutics, Inc., a Delaware corporation (the "Company"), and
constitutes an amendment of that certain Registration Rights Agreement dated
June 30, 2001 (the "Agreement"), among the Company, Aventis Pharmaceuticals
Products Inc., a Pennsylvania corporation ("APPI") and, solely for the purposes
of Section 8.1 of the Agreement, Rhone-Poulenc Rorer International (Holdings),
Inc., a Delaware corporation ("RPRIH").

                                    RECITALS

         WHEREAS, the Company and APPI entered into the Agreement in order to
impose certain obligations upon the parties thereto with respect to registration
and transfer of certain Registrable Securities; and

         WHEREAS, New Holder is now or will be the holder of certain Registrable
Securities and is or wishes to be entitled to the rights and subject to the
obligations of a Holder under the Agreement; and

         WHEREAS, the Agreement requires that all persons or entitled being
offered Registrable Securities by actions taken subsequent to the date of the
Agreement, must enter into an Addendum Agreement binding the New Holder to the
Agreement to the same extent as if the New Holder were an original party
thereto;

                                    AGREEMENT

         NOW, THEREFORE, in consideration of the premises and mutual covenants
contained herein, and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto, intending to
be legally bound, hereby agree as follows:

         1. Capitalized terms used herein and not otherwise defined shall have
the meanings assigned to such terms in the Agreement.

         2. New Holder shall be bound by, and shall have the benefit of, all the
terms and conditions set out in the Agreement to the same extent as if the New
Holder were a Holder under the Agreement.

         3. This Addendum Agreement constitutes an amendment to the Agreement
shall be attached to and become a part of the Agreement.

<PAGE>   19

         4. Except as modified hereby, New Holder and the Company ratify and
confirm the terms of the Agreement.

                                      EXHIBIT A TO REGISTRATION RIGHTS AGREEMENT

                                       A-2
<PAGE>   20

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

                                        NEW HOLDER

                                        ----------------------------------------
                                        Print Name of New Holder

                                        By:
                                           -------------------------------------
                                             Signature

                                             -----------------------------------
                                             Print Name of Signatory

                                             -----------------------------------
                                             Title (if applicable)

                                        Address for notices under Section 10.4
                                        of the Agreement:

                                        ----------------------------------------

                                        ----------------------------------------

                                        ----------------------------------------

                                        INTROGEN THERAPEUTICS, INC.

                                        By:
                                           -------------------------------------

                                        Name:
                                             -----------------------------------

                                        Title:
                                              ----------------------------------

                                      EXHIBIT A TO REGISTRATION RIGHTS AGREEMENT

                                       A-3

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