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                                                                    EXHIBIT 10.3

                           INTROGEN THERAPEUTICS INC.

                             2000 STOCK OPTION PLAN

     1. Purposes of the Plan. The purposes of this 2000 Stock Option Plan are:

        o   to attract and retain the best available personnel for positions of
            substantial responsibility,

        o   to provide additional incentive to Employees, Directors and
            Consultants, and

        o   to promote the success of the Company's business.

        Options granted under the Plan may be Incentive Stock Options or
Nonstatutory Stock Options, as determined by the Administrator at the time of
grant. Stock Purchase Rights may also be granted under the Plan.

     2. Definitions. As used herein, the following definitions shall apply:

        (a) "Administrator" means the Board or any of its Committees as shall be
administering the Plan, in accordance with Section 4 of the Plan.

        (b) "Applicable Laws" means the requirements relating to the
administration of stock option plans under U. S. state corporate laws, U.S.
federal and state securities laws, the Code, any stock exchange or quotation
system on which the Common Stock is listed or quoted and the applicable laws of
any foreign country or jurisdiction where Options or Stock Purchase Rights are,
or will be, granted under the Plan.

        (c) "Board" means the Board of Directors of the Company.

        (d) "Code" means the Internal Revenue Code of 1986, as amended.

        (e) "Committee" means a committee of Directors appointed by the Board in
accordance with Section 4 of the Plan.

        (f) "Common Stock" means the common stock of the Company.

        (g) "Company" means Introgen Therapeutics Inc., a Delaware corporation.

        (h) "Consultant" means any person, including an advisor, engaged by the
Company or a Parent or Subsidiary to render services to such entity.

        (i) "Director" means a member of the Board.

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        (j) "Disability" means total and permanent disability as defined in
Section 22(e)(3) of the Code.

        (k) "Employee" means any person, including Officers and Directors,
employed by the Company or any Parent or Subsidiary of the Company. A Service
Provider shall not cease to be an Employee in the case of (i) any leave of
absence approved by the Company or (ii) transfers between locations of the
Company or between the Company, its Parent, any Subsidiary, or any successor.
For purposes of Incentive Stock Options, no such leave may exceed ninety days,
unless reemployment upon expiration of such leave is guaranteed by statute or
contract. If reemployment upon expiration of a leave of absence approved by the
Company is not so guaranteed, on the 181st day of such leave any Incentive Stock
Option held by the Optionee shall cease to be treated as an Incentive Stock
Option and shall be treated for tax purposes as a Nonstatutory Stock Option.
Neither service as a Director nor payment of a director's fee by the Company
shall be sufficient to constitute "employment" by the Company.

        (l) "Exchange Act" means the Securities Exchange Act of 1934, as
amended.

        (m) "Fair Market Value" means, as of any date, the value of Common Stock
determined as follows:

            (i) If the Common Stock is listed on any established stock exchange
or a national market system, including without limitation the Nasdaq National
Market or The Nasdaq SmallCap Market of The Nasdaq Stock Market, its Fair Market
Value shall be the closing sales price for such stock (or the closing bid, if no
sales were reported) as quoted on such exchange or system for the last market
trading day prior to the time of determination, as reported in The Wall Street
Journal or such other source as the Administrator deems reliable;

            (ii) If the Common Stock is regularly quoted by a recognized
securities dealer but selling prices are not reported, the Fair Market Value of
a Share of Common Stock shall be the mean between the high bid and low asked
prices for the Common Stock on the last market trading day prior to the day of
determination, as reported in The Wall Street Journal or such other source as
the Administrator deems reliable; or

            (iii) In the absence of an established market for the Common Stock,
the Fair Market Value shall be determined in good faith by the Administrator.

        (n) "Incentive Stock Option" means an Option intended to qualify as an
incentive stock option within the meaning of Section 422 of the Code and the
regulations promulgated thereunder.

        (o) "Nonstatutory Stock Option" means an Option not intended to qualify
as an Incentive Stock Option.

        (p) "Notice of Grant" means a written or electronic notice evidencing
certain terms and conditions of an individual Option or Stock Purchase Right
grant. The Notice of Grant is part of the Option Agreement.

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        (q) "Officer" means a person who is an officer of the Company within the
meaning of Section 16 of the Exchange Act and the rules and regulations
promulgated thereunder.

        (r) "Option" means a stock option granted pursuant to the Plan.

        (s) "Option Agreement" means an agreement between the Company and an
Optionee evidencing the terms and conditions of an individual Option grant. The
Option Agreement is subject to the terms and conditions of the Plan.

        (t) "Option Exchange Program" means a program whereby outstanding
Options are surrendered in exchange for Options with a lower exercise price.

        (u) "Optioned Stock" means the Common Stock subject to an Option or
Stock Purchase Right.

        (v) "Optionee" means the holder of an outstanding Option or Stock
Purchase Right granted under the Plan.

        (w) "Parent" means a "parent corporation," whether now or hereafter
existing, as defined in Section 424(e) of the Code.

        (x) "Plan" means this 2000 Stock Option Plan.

        (y) "Restricted Stock" means shares of Common Stock acquired pursuant to
a grant of Stock Purchase Rights under Section 11 of the Plan.

        (z) "Restricted Stock Purchase Agreement" means a written agreement
between the Company and the Optionee evidencing the terms and restrictions
applying to stock purchased under a Stock Purchase Right. The Restricted Stock
Purchase Agreement is subject to the terms and conditions of the Plan and the
Notice of Grant.

        (aa) "Rule 16b-3" means Rule 16b-3 of the Exchange Act or any successor
to Rule 16b-3, as in effect when discretion is being exercised with respect to
the Plan.

        (bb) "Section 16(b) " means Section 16(b) of the Exchange Act.

        (cc) "Service Provider" means an Employee, Director or Consultant.

        (dd) "Share" means a share of the Common Stock, as adjusted in
accordance with Section 13 of the Plan.

        (ee) "Stock Purchase Right" means the right to purchase Common Stock
pursuant to Section 11 of the Plan, as evidenced by a Notice of Grant.

        (ff) "Subsidiary" means a "subsidiary corporation", whether now or
hereafter existing, as defined in Section 424(f) of the Code.

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     3. Stock Subject to the Plan. Subject to the provisions of Section 13 of
the Plan, the maximum aggregate number of Shares that may be optioned and sold
under the Plan is 3,000,000 Shares, plus an annual increased to be added on the
first day of the Company's fiscal year beginning in 2001 equal to the lesser of
(i) 1,000,000 shares, (ii) 5% of the outstanding shares on such date, or (iii) a
lesser amount determined by the Board. The Shares may be authorized, but
unissued, or reacquired Common Stock.

        If an Option or Stock Purchase Right expires or becomes unexercisable
without having been exercised in full, or is surrendered pursuant to an Option
Exchange Program, the unpurchased Shares which were subject thereto shall become
available for future grant or sale under the Plan (unless the Plan has
terminated); provided, however, that Shares that have actually been issued under
the Plan, whether upon exercise of an Option or Right, shall not be returned to
the Plan and shall not become available for future distribution under the Plan,
except that if Shares of Restricted Stock are repurchased by the Company at
their original purchase price, such Shares shall become available for future
grant under the Plan.

     4. Administration of the Plan.

        (a) Procedure.

            (i) Multiple Administrative Bodies. Different Committees with
respect to different groups of Service Providers may administer the Plan.

            (ii) Section 162(m). To the extent that the Administrator determines
it to be desirable to qualify Options granted hereunder as "performance-based
compensation" within the meaning of Section 162(m) of the Code, the Plan shall
be administered by a Committee of two or more "outside directors" within the
meaning of Section 162(m) of the Code.

            (iii) Rule 16b-3. To the extent desirable to qualify transactions
hereunder as exempt under Rule 16b-3, the transactions contemplated hereunder
shall be structured to satisfy the requirements for exemption under Rule 16b-3.

            (iv) Other Administration. Other than as provided above, the Plan
shall be administered by (A) the Board or (B) a Committee, which committee shall
be constituted to satisfy Applicable Laws.

        (b) Powers of the Administrator. Subject to the provisions of the Plan,
and in the case of a Committee, subject to the specific duties delegated by the
Board to such Committee, the Administrator shall have the authority, in its
discretion:

            (i) to determine the Fair Market Value;

            (ii) to select the Service Providers to whom Options and Stock
Purchase Rights may be granted hereunder;

            (iii) to determine the number of shares of Common Stock to be
covered by each Option and Stock Purchase Right granted hereunder;

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            (iv) to approve forms of agreement for use under the Plan;

            (v) to determine the terms and conditions, not inconsistent with the
terms of the Plan, of any Option or Stock Purchase Right granted hereunder. Such
terms and conditions include, but are not limited to, the exercise price, the
time or times when Options or Stock Purchase Rights may be exercised (which may
be based on performance criteria), any vesting acceleration or waiver of
forfeiture restrictions, and any restriction or limitation regarding any Option
or Stock Purchase Right or the shares of Common Stock relating thereto, based in
each case on such factors as the Administrator, in its sole discretion, shall
determine;

            (vi) to reduce the exercise price of any Option or Stock Purchase
Right to the then current Fair Market Value if the Fair Market Value of the
Common Stock covered by such Option or Stock Purchase Right shall have declined
since the date the Option or Stock Purchase Right was granted;

            (vii) to institute an Option Exchange Program;

            (viii) to construe and interpret the terms of the Plan and awards
granted pursuant to the Plan;

            (ix) to prescribe, amend and rescind rules and regulations relating
to the Plan, including rules and regulations relating to sub-plans established
for the purpose of qualifying for preferred tax treatment under foreign tax
laws;

            (x) to modify or amend each Option or Stock Purchase Right (subject
to Section 15(c) of the Plan), including the discretionary authority to extend
the post-termination exercisability period of Options longer than is otherwise
provided for in the Plan;

            (xi) to allow Optionees to satisfy withholding tax obligations by
electing to have the Company withhold from the Shares to be issued upon exercise
of an Option or Stock Purchase Right that number of Shares having a Fair Market
Value equal to the amount required to be withheld. The Fair Market Value of the
Shares to be withheld shall be determined on the date that the amount of tax to
be withheld is to be determined. All elections by an Optionee to have Shares
withheld for this purpose shall be made in such form and under such conditions
as the Administrator may deem necessary or advisable;

            (xii) to authorize any person to execute on behalf of the Company
any instrument required to effect the grant of an Option or Stock Purchase Right
previously granted by the Administrator;

            (xiii) to make all other determinations deemed necessary or
advisable for administering the Plan.

        (c) Effect of Administrator's Decision. The Administrator's decisions,
determinations and interpretations shall be final and binding on all Optionees
and any other holders of Options or Stock Purchase Rights.

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     5. Eligibility. Nonstatutory Stock Options and Stock Purchase Rights may be
granted to Service Providers. Incentive Stock Options may be granted only to
Employees.

     6. Limitations.

        (a) Each Option shall be designated in the Option Agreement as either an
Incentive Stock Option or a Nonstatutory Stock Option. However, notwithstanding
such designation, to the extent that the aggregate Fair Market Value of the
Shares with respect to which Incentive Stock Options are exercisable for the
first time by the Optionee during any calendar year (under all plans of the
Company and any Parent or Subsidiary) exceeds $100,000, such Options shall be
treated as Nonstatutory Stock Options. For purposes of this Section 6(a),
Incentive Stock Options shall be taken into account in the order in which they
were granted. The Fair Market Value of the Shares shall be determined as of the
time the Option with respect to such Shares is granted.

        (b) Neither the Plan nor any Option or Stock Purchase Right shall confer
upon an Optionee any right with respect to continuing the Optionee's
relationship as a Service Provider with the Company, nor shall they interfere in
any way with the Optionee's right or the Company's right to terminate such
relationship at any time, with or without cause.

        (c) The following limitations shall apply to grants of Options:

            (i) No Service Provider shall be granted, in any fiscal year of the
Company, Options to purchase more than 1,000,000 Shares.

            (ii) In connection with his or her initial service, a Service
Provider may be granted Options to purchase up to an additional 1,000,000
Shares, which shall not count against the limit set forth in subsection (i)
above.

            (iii) The foregoing limitations shall be adjusted proportionately in
connection with any change in the Company's capitalization as described in
Section 13.

            (iv) If an Option is cancelled in the same fiscal year of the
Company in which it was granted (other than in connection with a transaction
described in Section 13), the cancelled Option will be counted against the
limits set forth in subsections (i) and (ii) above. For this purpose, if the
exercise price of an Option is reduced, the transaction will be treated as a
cancellation of the Option and the grant of a new Option.

     7. Term of Plan. Subject to Section 19 of the Plan, the Plan shall become
effective upon its adoption by the Board. It shall continue in effect for a term
of ten (10) years unless terminated earlier under Section 15 of the Plan.

     8. Term of Option. The term of each Option shall be stated in the Option
Agreement. In the case of an Incentive Stock Option, the term shall be ten (10)
years from the date of grant or such shorter term as may be provided in the
Option Agreement. Moreover, in the case of an Incentive Stock Option granted to
an Optionee who, at the time the Incentive Stock Option is granted, owns stock
representing more than ten percent (10%) of the total combined voting power of
all classes of stock of the Company or any Parent or Subsidiary, the term of the
Incentive Stock

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Option shall be five (5) years from the date of grant or such shorter term as
may be provided in the Option Agreement.

     9. Option Exercise Price and Consideration.

        (a) Exercise Price. The per share exercise price for the Shares to be
issued pursuant to exercise of an Option shall be determined by the
Administrator, subject to the following:

            (i) In the case of an Incentive Stock Option

                (A) granted to an Employee who, at the time the Incentive Stock
Option is granted, owns stock representing more than ten percent (10%) of the
voting power of all classes of stock of the Company or any Parent or Subsidiary,
the per Share exercise price shall be no less than 110% of the Fair Market Value
per Share on the date of grant.

                (B) granted to any Employee other than an Employee described in
paragraph (A) immediately above, the per Share exercise price shall be no less
than 100% of the Fair Market Value per Share on the date of grant.

            (ii) In the case of a Nonstatutory Stock Option, the per Share
exercise price shall be determined by the Administrator. In the case of a
Nonstatutory Stock Option intended to qualify as "performance-based
compensation" within the meaning of Section 162(m) of the Code, the per Share
exercise price shall be no less than 100% of the Fair Market Value per Share on
the date of grant.

            (iii) Notwithstanding the foregoing, Options may be granted with a
per Share exercise price of less than 100% of the Fair Market Value per Share on
the date of grant pursuant to a merger or other corporate transaction.

        (b) Waiting Period and Exercise Dates. At the time an Option is granted,
the Administrator shall fix the period within which the Option may be exercised
and shall determine any conditions that must be satisfied before the Option may
be exercised.

        (c) Form of Consideration. The Administrator shall determine the
acceptable form of consideration for exercising an Option, including the method
of payment. In the case of an Incentive Stock Option, the Administrator shall
determine the acceptable form of consideration at the time of grant. Such
consideration may consist entirely of:

            (i) cash;

            (ii) check;

            (iii) promissory note;

            (iv) other Shares which (A) in the case of Shares acquired upon
exercise of an option, have been owned by the Optionee for more than six months
on the date of surrender, and

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(B) have a Fair Market Value on the date of surrender equal to the aggregate
exercise price of the Shares as to which said Option shall be exercised;

            (v) consideration received by the Company under a cashless exercise
program implemented by the Company in connection with the Plan;

            (vi) a reduction in the amount of any Company liability to the
Optionee, including any liability attributable to the Optionee's participation
in any Company-sponsored deferred compensation program or arrangement;

            (vii) any combination of the foregoing methods of payment; or

            (viii) such other consideration and method of payment for the
issuance of Shares to the extent permitted by Applicable Laws.

     10. Exercise of Option.

        (a) Procedure for Exercise; Rights as a Shareholder. Any Option granted
hereunder shall be exercisable according to the terms of the Plan and at such
times and under such conditions as determined by the Administrator and set forth
in the Option Agreement. Unless the Administrator provides otherwise, vesting of
Options granted hereunder shall be tolled during any unpaid leave of absence. An
Option may not be exercised for a fraction of a Share.

            An Option shall be deemed exercised when the Company receives: (i)
written or electronic notice of exercise (in accordance with the Option
Agreement) from the person entitled to exercise the Option, and (ii) full
payment for the Shares with respect to which the Option is exercised. Full
payment may consist of any consideration and method of payment authorized by the
Administrator and permitted by the Option Agreement and the Plan. Shares issued
upon exercise of an Option shall be issued in the name of the Optionee or, if
requested by the Optionee, in the name of the Optionee and his or her spouse.
Until the Shares are issued (as evidenced by the appropriate entry on the books
of the Company or of a duly authorized transfer agent of the Company), no right
to vote or receive dividends or any other rights as a shareholder shall exist
with respect to the Optioned Stock, notwithstanding the exercise of the Option.
The Company shall issue (or cause to be issued) such Shares promptly after the
Option is exercised. No adjustment will be made for a dividend or other right
for which the record date is prior to the date the Shares are issued, except as
provided in Section 13 of the Plan.

            Exercising an Option in any manner shall decrease the number of
Shares thereafter available, both for purposes of the Plan and for sale under
the Option, by the number of Shares as to which the Option is exercised.

        (b) Termination of Relationship as a Service Provider. If an Optionee
ceases to be a Service Provider, other than upon the Optionee's death or
Disability, the Optionee may exercise his or her Option within such period of
time as is specified in the Option Agreement to the extent that the Option is
vested on the date of termination (but in no event later than the expiration of
the term of such Option as set forth in the Option Agreement). In the absence of
a specified time in the Option Agreement, the Option shall remain exercisable
for three (3) months following the

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Optionee's termination. If, on the date of termination, the Optionee is not
vested as to his or her entire Option, the Shares covered by the unvested
portion of the Option shall revert to the Plan. If, after termination, the
Optionee does not exercise his or her Option within the time specified by the
Administrator, the Option shall terminate, and the Shares covered by such Option
shall revert to the Plan.

        (c) Disability of Optionee. If an Optionee ceases to be a Service
Provider as a result of the Optionee's Disability, the Optionee may exercise his
or her Option within such period of time as is specified in the Option Agreement
to the extent the Option is vested on the date of termination (but in no event
later than the expiration of the term of such Option as set forth in the Option
Agreement). In the absence of a specified time in the Option Agreement, the
Option shall remain exercisable for twelve (12) months following the Optionee's
termination. If, on the date of termination, the Optionee is not vested as to
his or her entire Option, the Shares covered by the unvested portion of the
Option shall revert to the Plan. If, after termination, the Optionee does not
exercise his or her Option within the time specified herein, the Option shall
terminate, and the Shares covered by such Option shall revert to the Plan.

        (d) Death of Optionee. If an Optionee dies while a Service Provider, the
Option may be exercised within such period of time as is specified in the Option
Agreement (but in no event later than the expiration of the term of such Option
as set forth in the Notice of Grant), by the Optionee's estate or by a person
who acquires the right to exercise the Option by bequest or inheritance, but
only to the extent that the Option is vested on the date of death. In the
absence of a specified time in the Option Agreement, the Option shall remain
exercisable for twelve (12) months following the Optionee's termination. If, at
the time of death, the Optionee is not vested as to his or her entire Option,
the Shares covered by the unvested portion of the Option shall immediately
revert to the Plan. The Option may be exercised by the executor or administrator
of the Optionee's estate or, if none, by the person(s) entitled to exercise the
Option under the Optionee's will or the laws of descent or distribution. If the
Option is not so exercised within the time specified herein, the Option shall
terminate, and the Shares covered by such Option shall revert to the Plan.

        (e) Buyout Provisions. The Administrator may at any time offer to buy
out for a payment in cash or Shares an Option previously granted based on such
terms and conditions as the Administrator shall establish and communicate to the
Optionee at the time that such offer is made.

     11. Stock Purchase Rights.

        (a) Rights to Purchase. Stock Purchase Rights may be issued either
alone, in addition to, or in tandem with other awards granted under the Plan
and/or cash awards made outside of the Plan. After the Administrator determines
that it will offer Stock Purchase Rights under the Plan, it shall advise the
offeree in writing or electronically, by means of a Notice of Grant, of the
terms, conditions and restrictions related to the offer, including the number of
Shares that the offeree shall be entitled to purchase, the price to be paid, and
the time within which the offeree must accept such offer. The offer shall be
accepted by execution of a Restricted Stock Purchase Agreement in the form
determined by the Administrator.

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        (b) Repurchase Option. Unless the Administrator determines otherwise,
the Restricted Stock Purchase Agreement shall grant the Company a repurchase
option exercisable upon the voluntary or involuntary termination of the
purchaser's service with the Company for any reason (including death or
Disability). The purchase price for Shares repurchased pursuant to the
Restricted Stock Purchase Agreement shall be the original price paid by the
purchaser and may be paid by cancellation of any indebtedness of the purchaser
to the Company. The repurchase option shall lapse at a rate determined by the
Administrator.

        (c) Other Provisions. The Restricted Stock Purchase Agreement shall
contain such other terms, provisions and conditions not inconsistent with the
Plan as may be determined by the Administrator in its sole discretion.

        (d) Rights as a Shareholder. Once the Stock Purchase Right is exercised,
the purchaser shall have the rights equivalent to those of a shareholder, and
shall be a shareholder when his or her purchase is entered upon the records of
the duly authorized transfer agent of the Company. No adjustment will be made
for a dividend or other right for which the record date is prior to the date the
Stock Purchase Right is exercised, except as provided in Section 13 of the Plan.

     12. Non-Transferability of Options and Stock Purchase Rights. Unless
determined otherwise by the Administrator, an Option or Stock Purchase Right may
not be sold, pledged, assigned, hypothecated, transferred, or disposed of in any
manner other than by will or by the laws of descent or distribution and may be
exercised, during the lifetime of the Optionee, only by the Optionee. If the
Administrator makes an Option or Stock Purchase Right transferable, such Option
or Stock Purchase Right shall contain such additional terms and conditions as
the Administrator deems appropriate.

     13. Adjustments Upon Changes in Capitalization, Dissolution, Merger or
Asset Sale.

        (a) Changes in Capitalization. Subject to any required action by the
shareholders of the Company, the number of shares of Common Stock covered by
each outstanding Option and Stock Purchase Right, and the number of shares of
Common Stock which have been authorized for issuance under the Plan but as to
which no Options or Stock Purchase Rights have yet been granted or which have
been returned to the Plan upon cancellation or expiration of an Option or Stock
Purchase Right, as well as the price per share of Common Stock covered by each
such outstanding Option or Stock Purchase Right, shall be proportionately
adjusted for any increase or decrease in the number of issued shares of Common
Stock resulting from a stock split, reverse stock split, stock dividend,
combination or reclassification of the Common Stock, or any other increase or
decrease in the number of issued shares of Common Stock effected without receipt
of consideration by the Company; provided, however, that conversion of any
convertible securities of the Company shall not be deemed to have been "effected
without receipt of consideration." Such adjustment shall be made by the Board,
whose determination in that respect shall be final, binding and conclusive.
Except as expressly provided herein, no issuance by the Company of shares of
stock of any class, or securities convertible into shares of stock of any class,
shall affect, and no adjustment by reason thereof shall be made with respect to,
the number or price of shares of Common Stock subject to an Option or Stock
Purchase Right.

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        (b) Dissolution or Liquidation. In the event of the proposed dissolution
or liquidation of the Company, the Administrator shall notify each Optionee as
soon as practicable prior to the effective date of such proposed transaction.
The Administrator in its discretion may provide for an Optionee to have the
right to exercise his or her Option until ten (10) days prior to such
transaction as to all of the Optioned Stock covered thereby, including Shares as
to which the Option would not otherwise be exercisable. In addition, the
Administrator may provide that any Company repurchase option applicable to any
Shares purchased upon exercise of an Option or Stock Purchase Right shall lapse
as to all such Shares, provided the proposed dissolution or liquidation takes
place at the time and in the manner contemplated. To the extent it has not been
previously exercised, an Option or Stock Purchase Right will terminate
immediately prior to the consummation of such proposed action.

        (c) Merger or Asset Sale. In the event of a merger of the Company with
or into another corporation, or the sale of substantially all of the assets of
the Company, each outstanding Option and Stock Purchase Right shall be assumed
or an equivalent option or right substituted by the successor corporation or a
Parent or Subsidiary of the successor corporation. In the event that the
successor corporation refuses to assume or substitute for the Option or Stock
Purchase Right, the Optionee shall fully vest in and have the right to exercise
the Option or Stock Purchase Right as to all of the Optioned Stock, including
Shares as to which it would not otherwise be vested or exercisable. If an Option
or Stock Purchase Right becomes fully vested and exercisable in lieu of
assumption or substitution in the event of a merger or sale of assets, the
Administrator shall notify the Optionee in writing or electronically that the
Option or Stock Purchase Right shall be fully vested and exercisable for a
period of fifteen (15) days from the date of such notice, and the Option or
Stock Purchase Right shall terminate upon the expiration of such period. For the
purposes of this paragraph, the Option or Stock Purchase Right shall be
considered assumed if, following the merger or sale of assets, the option or
right confers the right to purchase or receive, for each Share of Optioned Stock
subject to the Option or Stock Purchase Right immediately prior to the merger or
sale of assets, the consideration (whether stock, cash, or other securities or
property) received in the merger or sale of assets by holders of Common Stock
for each Share held on the effective date of the transaction (and if holders
were offered a choice of consideration, the type of consideration chosen by the
holders of a majority of the outstanding Shares); provided, however, that if
such consideration received in the merger or sale of assets is not solely common
stock of the successor corporation or its Parent, the Administrator may, with
the consent of the successor corporation, provide for the consideration to be
received upon the exercise of the Option or Stock Purchase Right, for each Share
of Optioned Stock subject to the Option or Stock Purchase Right, to be solely
common stock of the successor corporation or its Parent equal in fair market
value to the per share consideration received by holders of Common Stock in the
merger or sale of assets.

     14. Date of Grant. The date of grant of an Option or Stock Purchase Right
shall be, for all purposes, the date on which the Administrator makes the
determination granting such Option or Stock Purchase Right, or such other later
date as is determined by the Administrator. Notice of the determination shall be
provided to each Optionee within a reasonable time after the date of such grant.

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     15. Amendment and Termination of the Plan.

        (a) Amendment and Termination. The Board may at any time amend, alter,
suspend or terminate the Plan.

        (b) Shareholder Approval. The Company shall obtain shareholder approval
of any Plan amendment to the extent necessary and desirable to comply with
Applicable Laws.

        (c) Effect of Amendment or Termination. No amendment, alteration,
suspension or termination of the Plan shall impair the rights of any Optionee,
unless mutually agreed otherwise between the Optionee and the Administrator,
which agreement must be in writing and signed by the Optionee and the Company.
Termination of the Plan shall not affect the Administrator's ability to exercise
the powers granted to it hereunder with respect to Options granted under the
Plan prior to the date of such termination.

     16. Conditions Upon Issuance of Shares.

        (a) Legal Compliance. Shares shall not be issued pursuant to the
exercise of an Option or Stock Purchase Right unless the exercise of such Option
or Stock Purchase Right and the issuance and delivery of such Shares shall
comply with Applicable Laws and shall be further subject to the approval of
counsel for the Company with respect to such compliance.

        (b) Investment Representations. As a condition to the exercise of an
Option or Stock Purchase Right, the Company may require the person exercising
such Option or Stock Purchase Right to represent and warrant at the time of any
such exercise that the Shares are being purchased only for investment and
without any present intention to sell or distribute such Shares if, in the
opinion of counsel for the Company, such a representation is required.

     17. Inability to Obtain Authority. The inability of the Company to obtain
authority from any regulatory body having jurisdiction, which authority is
deemed by the Company's counsel to be necessary to the lawful issuance and sale
of any Shares hereunder, shall relieve the Company of any liability in respect
of the failure to issue or sell such Shares as to which such requisite authority
shall not have been obtained.

     18. Reservation of Shares. The Company, during the term of this Plan, will
at all times reserve and keep available such number of Shares as shall be
sufficient to satisfy the requirements of the Plan.

     19. Shareholder Approval. The Plan shall be subject to approval by the
shareholders of the Company within twelve (12) months after the date the Plan is
adopted. Such shareholder approval shall be obtained in the manner and to the
degree required under Applicable Laws.

                                     - 12 -

<PAGE>   13

                           INTROGEN THERAPEUTICS INC.

                             2000 STOCK OPTION PLAN

                             STOCK OPTION AGREEMENT

         Unless otherwise defined herein, the terms defined in the Plan shall
have the same defined meanings in this Option Agreement.

I.       NOTICE OF STOCK OPTION GRANT

         [Optionee's Name and Address]

         You have been granted an option to purchase Common Stock of the
Company, subject to the terms and conditions of the Plan and this Option
Agreement, as follows:

         Grant Number
                                             -----------------------------------
         Date of Grant
                                             -----------------------------------
         Vesting Commencement Date
                                             -----------------------------------
         Exercise Price per Share            $
                                             -----------------------------------
         Total Number of Shares Granted
                                             -----------------------------------
         Total Exercise Price                $
                                             -----------------------------------
         Type of Option:                         Incentive Stock Option
                                             ----
                                                 Nonstatutory Stock Option
                                             ----
         Term/Expiration Date:
                                             -----------------------------------

         Vesting Schedule:

         Subject to accelerated vesting as set forth below, this Option may be
exercised, in whole or in part, in accordance with the following schedule:

         [25% OF THE SHARES SUBJECT TO THE OPTION SHALL VEST TWELVE MONTHS AFTER
THE VESTING COMMENCEMENT DATE, AND 1/48 OF THE SHARES SUBJECT TO THE OPTION
SHALL VEST EACH MONTH THEREAFTER, SUBJECT TO THE OPTIONEE CONTINUING TO BE A
SERVICE PROVIDER ON SUCH DATES].

<PAGE>   14

         Termination Period:

         This Option may be exercised for three months after Optionee ceases to
be a Service Provider. Upon the death or Disability of the Optionee, this Option
may be exercised for twelve months after Optionee ceases to be a Service
Provider. In no event shall this Option be exercised later than the
Term/Expiration Date as provided above.

II. AGREEMENT

     A. Grant of Option.

        The Plan Administrator of the Company hereby grants to the Optionee
named in the Notice of Grant attached as Part I of this Agreement (the
"Optionee") an option (the "Option") to purchase the number of Shares, as set
forth in the Notice of Grant, at the exercise price per share set forth in the
Notice of Grant (the "Exercise Price"), subject to the terms and conditions of
the Plan, which is incorporated herein by reference. Subject to Section 15(c) of
the Plan, in the event of a conflict between the terms and conditions of the
Plan and the terms and conditions of this Option Agreement, the terms and
conditions of the Plan shall prevail.

        If designated in the Notice of Grant as an Incentive Stock Option
("ISO"), this Option is intended to qualify as an Incentive Stock Option under
Section 422 of the Code. However, if this Option is intended to be an Incentive
Stock Option, to the extent that it exceeds the $100,000 rule of Code Section
422(d) it shall be treated as a Nonstatutory Stock Option ("NSO").

     B. Exercise of Option.

        (a) Right to Exercise. This Option is exercisable during its term in
accordance with the Vesting Schedule set out in the Notice of Grant and the
applicable provisions of the Plan and this Option Agreement.

        (b) Method of Exercise. This Option is exercisable by delivery of an
exercise notice, in the form attached as Exhibit A (the "Exercise Notice"),
which shall state the election to exercise the Option, the number of Shares in
respect of which the Option is being exercised (the "Exercised Shares"), and
such other representations and agreements as may be required by the Company
pursuant to the provisions of the Plan. The Exercise Notice shall be completed
by the Optionee and delivered to [TITLE] of the Company. The Exercise Notice
shall be accompanied by payment of the aggregate Exercise Price as to all
Exercised Shares. This Option shall be deemed to be exercised upon receipt by
the Company of such fully executed Exercise Notice accompanied by such aggregate
Exercise Price.

              No Shares shall be issued pursuant to the exercise of this Option
unless such issuance and exercise complies with Applicable Laws. Assuming such
compliance, for income tax purposes the Exercised Shares shall be considered
transferred to the Optionee on the date the Option is exercised with respect to
such Exercised Shares.

                                      -2-
<PAGE>   15

        C. Method of Payment.

           Payment of the aggregate Exercise Price shall be by any of the
following, or a combination thereof, at the election of the Optionee:

           1. cash; or

           2. check[; OR

           3. CONSIDERATION RECEIVED BY THE COMPANY UNDER A CASHLESS EXERCISE
PROGRAM IMPLEMENTED BY THE COMPANY IN CONNECTION WITH THE PLAN][; OR

           4. SURRENDER OF OTHER SHARES WHICH (i) IN THE CASE OF SHARES ACQUIRED
UPON EXERCISE OF AN OPTION, HAVE BEEN OWNED BY THE OPTIONEE FOR MORE THAN SIX
(6) MONTHS ON THE DATE OF SURRENDER, AND (ii) HAVE A FAIR MARKET VALUE ON THE
DATE OF SURRENDER EQUAL TO THE AGGREGATE EXERCISE PRICE OF THE EXERCISED
SHARES[; OR

           5. WITH THE ADMINISTRATOR'S CONSENT, DELIVERY OF OPTIONEE'S
PROMISSORY NOTE (THE "NOTE") IN THE FORM ATTACHED HERETO AS EXHIBIT C, IN THE
AMOUNT OF THE AGGREGATE EXERCISE PRICE OF THE EXERCISED SHARES TOGETHER WITH THE
EXECUTION AND DELIVERY BY THE OPTIONEE OF THE SECURITY AGREEMENT ATTACHED HERETO
AS EXHIBIT B. THE NOTE SHALL BEAR INTEREST AT THE "APPLICABLE FEDERAL RATE"
PRESCRIBED UNDER THE CODE AND ITS REGULATIONS AT TIME OF PURCHASE, AND SHALL BE
SECURED BY A PLEDGE OF THE SHARES PURCHASED BY THE NOTE PURSUANT TO THE SECURITY
AGREEMENT][; OR

           6. TO THE EXTENT PERMITTED BY THE ADMINISTRATOR, DELIVERY OF A
PROPERLY EXECUTED EXERCISE NOTICE TOGETHER WITH SUCH OTHER DOCUMENTATION AS THE
ADMINISTRATOR AND THE BROKER, IF APPLICABLE, SHALL REQUIRE TO EFFECT AN EXERCISE
OF THE OPTION AND DELIVERY TO THE COMPANY OF THE SALE PROCEEDS REQUIRED TO PAY
THE EXERCISE PRICE.]

        D. Non-Transferability of Option.

           This Option may not be transferred in any manner otherwise than by
will or by the laws of descent or distribution and may be exercised during the
lifetime of Optionee only by the Optionee. The terms of the Plan and this Option
Agreement shall be binding upon the executors, administrators, heirs, successors
and assigns of the Optionee.

        E. Term of Option.

           This Option may be exercised only within the term set out in the
Notice of Grant, and may be exercised during such term only in accordance with
the Plan and the terms of this Option Agreement.

        F. Tax Consequences.

           Some of the federal tax consequences relating to this Option, as of
the date of this Option, are set forth below. THIS SUMMARY IS NECESSARILY
INCOMPLETE, AND THE TAX LAWS AND REGULATIONS ARE SUBJECT TO CHANGE. THE OPTIONEE
SHOULD

                                      -3-
<PAGE>   16

CONSULT A TAX ADVISER BEFORE EXERCISING THIS OPTION OR DISPOSING OF THE
SHARES.

        G. Exercising the Option.

           1. Nonstatutory Stock Option. The Optionee may incur regular federal
income tax liability upon exercise of a NSO. The Optionee will be treated as
having received compensation income (taxable at ordinary income tax rates) equal
to the excess, if any, of the Fair Market Value of the Exercised Shares on the
date of exercise over their aggregate Exercise Price. If the Optionee is an
Employee or a former Employee, the Company will be required to withhold from his
or her compensation or collect from Optionee and pay to the applicable taxing
authorities an amount in cash equal to a percentage of this compensation income
at the time of exercise, and may refuse to honor the exercise and refuse to
deliver Shares if such withholding amounts are not delivered at the time of
exercise.

           2. Incentive Stock Option. If this Option qualifies as an ISO, the
Optionee will have no regular federal income tax liability upon its exercise,
although the excess, if any, of the Fair Market Value of the Exercised Shares on
the date of exercise over their aggregate Exercise Price will be treated as an
adjustment to alternative minimum taxable income for federal tax purposes and
may subject the Optionee to alternative minimum tax in the year of exercise. In
the event that the Optionee ceases to be an Employee but remains a Service
Provider, any Incentive Stock Option of the Optionee that remains unexercised
shall cease to qualify as an Incentive Stock Option and will be treated for tax
purposes as a Nonstatutory Stock Option on the date three (3) months and one (1)
day following such change of status.

           3. Disposition of Shares.

              (a) NSO. If the Optionee holds NSO Shares for at least one year,
any gain realized on disposition of the Shares will be treated as long-term
capital gain for federal income tax purposes.

              (b) ISO. If the Optionee holds ISO Shares for at least one year
after exercise and two years after the grant date, any gain realized on
disposition of the Shares will be treated as long-term capital gain for federal
income tax purposes. If the Optionee disposes of ISO Shares within one year
after exercise or two years after the grant date, any gain realized on such
disposition will be treated as compensation income (taxable at ordinary income
rates) to the extent of the excess, if any, of the lesser of (A) the difference
between the Fair Market Value of the Shares acquired on the date of exercise and
the aggregate Exercise Price, or (B) the difference between the sale price of
such Shares and the aggregate Exercise Price. Any additional gain will be taxed
as capital gain, short-term or long-term depending on the period that the ISO
Shares were held.

              (c) Notice of Disqualifying Disposition of ISO Shares. If the
Optionee sells or otherwise disposes of any of the Shares acquired pursuant to
an ISO on or before the later of (i) two years after the grant date, or (ii) one
year after the exercise date, the Optionee shall immediately notify the Company
in writing of such disposition. The Optionee agrees that he or she may be
subject to income tax withholding by the Company on the compensation income
recognized from such early disposition of ISO Shares by payment in cash or out
of the current earnings paid to the Optionee.

                                      -4-

<PAGE>   17

        H. Entire Agreement; Governing Law.

           The Plan is incorporated herein by reference. The Plan and this
Option Agreement constitute the entire agreement of the parties with respect to
the subject matter hereof and supersede in their entirety all prior undertakings
and agreements of the Company and Optionee with respect to the subject matter
hereof, and may not be modified adversely to the Optionee's interest except by
means of a writing signed by the Company and Optionee. This agreement is
governed by the internal substantive laws, but not the choice of law rules, of
Texas.

        I. NO GUARANTEE OF CONTINUED SERVICE.

           OPTIONEE ACKNOWLEDGES AND AGREES THAT THE VESTING OF SHARES PURSUANT
TO THE VESTING SCHEDULE HEREOF IS EARNED ONLY BY CONTINUING AS A SERVICE
PROVIDER AT THE WILL OF THE COMPANY (AND NOT THROUGH THE ACT OF BEING HIRED,
BEING GRANTED AN OPTION OR PURCHASING SHARES HEREUNDER). OPTIONEE FURTHER
ACKNOWLEDGES AND AGREES THAT THIS AGREEMENT, THE TRANSACTIONS CONTEMPLATED
HEREUNDER AND THE VESTING SCHEDULE SET FORTH HEREIN DO NOT CONSTITUTE AN EXPRESS
OR IMPLIED PROMISE OF CONTINUED ENGAGEMENT AS A SERVICE PROVIDER FOR THE VESTING
PERIOD, FOR ANY PERIOD, OR AT ALL, AND SHALL NOT INTERFERE WITH OPTIONEE'S RIGHT
OR THE COMPANY'S RIGHT TO TERMINATE OPTIONEE'S RELATIONSHIP AS A SERVICE
PROVIDER AT ANY TIME, WITH OR WITHOUT CAUSE.

           By your signature and the signature of the Company's representative
below, you and the Company agree that this Option is granted under and governed
by the terms and conditions of the Plan and this Option Agreement. Optionee has
reviewed the Plan and this Option Agreement in their entirety, has had an
opportunity to obtain the advice of counsel prior to executing this Option
Agreement and fully understands all provisions of the Plan and Option Agreement.
Optionee hereby agrees to accept as binding, conclusive and final all decisions
or interpretations of the Administrator upon any questions relating to the Plan
and Option Agreement. Optionee further agrees to notify the Company upon any
change in the residence address indicated below.

OPTIONEE:                                           INTROGEN THERAPEUTICS INC.

---------------------------                         ---------------------------
Signature                                           By

---------------------------                         ---------------------------
Print Name                                          Title

---------------------------
Residence Address

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

                                      -5-
<PAGE>   18

                                CONSENT OF SPOUSE

           The undersigned spouse of Optionee has read and hereby approves the
terms and conditions of the Plan and this Option Agreement. In consideration of
the Company's granting his or her spouse the right to purchase Shares as set
forth in the Plan and this Option Agreement, the undersigned hereby agrees to be
irrevocably bound by the terms and conditions of the Plan and this Option
Agreement and further agrees that any community property interest shall be
similarly bound. The undersigned hereby appoints the undersigned's spouse as
attorney-in-fact for the undersigned with respect to any amendment or exercise
of rights under the Plan or this Option Agreement.

                                                      -------------------------
                                                      Spouse of Optionee

<PAGE>   19

                                    EXHIBIT A
                                    ---------

                           INTROGEN THERAPEUTICS INC.

                             2000 STOCK OPTION PLAN

                                 EXERCISE NOTICE

Introgen Therapeutics Inc.
301 Congress Avenue, Suite 1850
Austin, Texas 78701

Attention:  [Title]

           1. Exercise of Option. Effective as of today, ________________,
_____, the undersigned ("Purchaser") hereby elects to purchase ______________
shares (the "Shares") of the Common Stock of Introgen Therapeutics Inc. (the
"Company") under and pursuant to the 2000 Stock Option Plan (the "Plan") and the
Stock Option Agreement dated, _____ (the "Option Agreement"). The purchase price
for the Shares shall be $_____, as required by the Option Agreement.

           2. Delivery of Payment. Purchaser herewith delivers to the Company
the full purchase price for the Shares.

           3. Representations of Purchaser. Purchaser acknowledges that
Purchaser has received, read and understood the Plan and the Option Agreement
and agrees to abide by and be bound by their terms and conditions.

           4. Rights as Shareholder. Until the issuance (as evidenced by the
appropriate entry on the books of the Company or of a duly authorized transfer
agent of the Company) of the Shares, no right to vote or receive dividends or
any other rights as a shareholder shall exist with respect to the Optioned
Stock, notwithstanding the exercise of the Option. The Shares so acquired shall
be issued to the Optionee as soon as practicable after exercise of the Option.
No adjustment will be made for a dividend or other right for which the record
date is prior to the date of issuance, except as provided in Section 13 of the
Plan.

           5. Tax Consultation. Purchaser understands that Purchaser may suffer
adverse tax consequences as a result of Purchaser's purchase or disposition of
the Shares. Purchaser represents that Purchaser has consulted with any tax
consultants Purchaser deems advisable in connection with the purchase or
disposition of the Shares and that Purchaser is not relying on the Company for
any tax advice.

<PAGE>   20

           6. Entire Agreement; Governing Law. The Plan and Option Agreement are
incorporated herein by reference. This Agreement, the Plan and the Option
Agreement constitute the entire agreement of the parties with respect to the
subject matter hereof and supersede in their entirety all prior undertakings and
agreements of the Company and Purchaser with respect to the subject matter
hereof, and may not be modified adversely to the Purchaser's interest except by
means of a writing signed by the Company and Purchaser. This agreement is
governed by the internal substantive laws, but not the choice of law rules, of
Texas.

Submitted by:                                   Accepted by:

PURCHASER:                                      INTROGEN THERAPEUTICS INC.

---------------------------                     -------------------------------
Signature                                       By

---------------------------                     -------------------------------
Print Name     Its

Address:                                        Address:
-------                                         -------

                                                INTROGEN THERAPEUTICS INC.
---------------------------
                                                301 Congress Avenue, Suite 1850
---------------------------
                                                Austin, Texas 78701
---------------------------

                                                -------------------------------
                                                Date Received

                                      -2-
<PAGE>   21

                                    EXHIBIT B

                               SECURITY AGREEMENT

           This Security Agreement is made as of __________, _____ between
Introgen Therapeutics Inc., a Delaware corporation ("Pledgee"), and
_________________________ ("Pledgor").

                                    Recitals

           Pursuant to Pledgor's election to purchase Shares under the Option
Agreement dated ________ (the "Option"), between Pledgor and Pledgee under
Pledgee's 2000 Stock Option Plan, and Pledgor's election under the terms of the
Option to pay for such shares with his promissory note (the "Note"), Pledgor has
purchased _________ shares of Pledgee's Common Stock (the "Shares") at a price
of $________ per share, for a total purchase price of $__________. The Note and
the obligations thereunder are as set forth in Exhibit C to the Option.

           NOW, THEREFORE, it is agreed as follows:

           1. Creation and Description of Security Interest. In consideration of
the transfer of the Shares to Pledgor under the Option Agreement, Pledgor,
pursuant to the Texas Commercial Code, hereby pledges all of such Shares (herein
sometimes referred to as the "Collateral") represented by certificate number
______, duly endorsed in blank or with executed stock powers, and herewith
delivers said certificate to the Secretary of Pledgee ("Pledgeholder"), who
shall hold said certificate subject to the terms and conditions of this Security
Agreement.

         The pledged stock (together with an executed blank stock assignment for
use in transferring all or a portion of the Shares to Pledgee if, as and when
required pursuant to this Security Agreement) shall be held by the Pledgeholder
as security for the repayment of the Note, and any extensions or renewals
thereof, to be executed by Pledgor pursuant to the terms of the Option, and the
Pledgeholder shall not encumber or dispose of such Shares except in accordance
with the provisions of this Security Agreement.

         2. Pledgor's Representations and Covenants. To induce Pledgee to enter
into this Security Agreement, Pledgor represents and covenants to Pledgee, its
successors Iand assigns, as follows:

               (a) Payment of Indebtedness. Pledgor will pay the principal sum
of the Note secured hereby, together with interest thereon, at the time and in
the manner provided in the Note.

               (b) Encumbrances. The Shares are free of all other encumbrances,
defenses and liens, and Pledgor will not further encumber the Shares without the
prior written consent of Pledgee.

<PAGE>   22

               (c) Margin Regulations. In the event that Pledgee's Common Stock
is now or later becomes margin-listed by the Federal Reserve Board and Pledgee
is classified as a "lender" within the meaning of the regulations under Part 207
of Title 12 of the Code of Federal Regulations ("Regulation G"), Pledgor agrees
to cooperate with Pledgee in making any amendments to the Note or providing any
additional collateral as may be necessary to comply with such regulations.

         3. Voting Rights. During the term of this pledge and so long as all
payments of principal and interest are made as they become due under the terms
of the Note, Pledgor shall have the right to vote all of the Shares pledged
hereunder.

         4. Stock Adjustments. In the event that during the term of the pledge
any stock dividend, reclassification, readjustment or other changes are declared
or made in the capital structure of Pledgee, all new, substituted and additional
shares or other securities issued by reason of any such change shall be
delivered to and held by the Pledgee under the terms of this Security Agreement
in the same manner as the Shares originally pledged hereunder. In the event of
substitution of such securities, Pledgor, Pledgee and Pledgeholder shall
cooperate and execute such documents as are reasonable so as to provide for the
substitution of such Collateral and, upon such substitution, references to
"Shares" in this Security Agreement shall include the substituted shares of
capital stock of Pledgor as a result thereof.

         5. Options and Rights. In the event that, during the term of this
pledge, subscription Options or other rights or options shall be issued in
connection with the pledged Shares, such rights, Options and options shall be
the property of Pledgor and, if exercised by Pledgor, all new stock or other
securities so acquired by Pledgor as it relates to the pledged Shares then held
by Pledgeholder shall be immediately delivered to Pledgeholder, to be held under
the terms of this Security Agreement in the same manner as the Shares pledged.

         6. Default. Pledgor shall be deemed to be in default of the Note and of
this Security Agreement in the event:

               (a) Payment of principal or interest on the Note shall be
delinquent for a period of 10 days or more; or

               (b) Pledgor fails to perform any of the covenants set forth in
the Option or contained in this Security Agreement for a period of 10 days after
written notice thereof from Pledgee.

               In the case of an event of Default, as set forth above, Pledgee
shall have the right to accelerate payment of the Note upon notice to Pledgor,
and Pledgee shall thereafter be entitled to pursue its remedies under the Texas
Commercial Code.

         7. Release of Collateral. Subject to any applicable contrary rules
under Regulation G, there shall be released from this pledge a portion of the
pledged Shares held by Pledgeholder hereunder upon payments of the principal of
the Note. The number of the pledged Shares which shall be released shall be that
number of full Shares which bears the same proportion to the initial number of

                                      -2-
<PAGE>   23

Shares pledged hereunder as the payment of principal bears to the initial full
principal amount of the Note.

         8. Withdrawal or Substitution of Collateral. Pledgor shall not sell,
withdraw, pledge, substitute or otherwise dispose of all or any part of the
Collateral without the prior written consent of Pledgee.

         9. Term. The within pledge of Shares shall continue until the payment
of all indebtedness secured hereby, at which time the remaining pledged stock
shall be promptly delivered to Pledgor, subject to the provisions for prior
release of a portion of the Collateral as provided in paragraph 7 above.

         10. Insolvency. Pledgor agrees that if a bankruptcy or insolvency
proceeding is instituted by or against it, or if a receiver is appointed for the
property of Pledgor, or if Pledgor makes an assignment for the benefit of
creditors, the entire amount unpaid on the Note shall become immediately due and
payable, and Pledgee may proceed as provided in the case of default.

         11. Pledgeholder Liability. In the absence of willful or gross
negligence, Pledgeholder shall not be liable to any party for any of his acts,
or omissions to act, as Pledgeholder.

         12. Invalidity of Particular Provisions. Pledgor and Pledgee agree that
the enforceability or invalidity of any provision or provisions of this Security
Agreement shall not render any other provision or provisions herein contained
unenforceable or invalid.

         13. Successors or Assigns. Pledgor and Pledgee agree that all of the
terms of this Security Agreement shall be binding on their respective successors
and assigns, and that the term "Pledgor" and the term "Pledgee" as used herein
shall be deemed to include, for all purposes, the respective designees,
successors, assigns, heirs, executors and administrators.

         14. Governing Law. This Security Agreement shall be interpreted and
governed under the internal substantive laws, but not the choice of law rules,
of Texas.

                                      -3-
<PAGE>   24

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

"PLEDGOR"                               ---------------------------------------
                                        Signature

                                        ---------------------------------------
                                        Print Name

                                        Address:
                                                -------------------------------

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

"PLEDGEE"                               INTROGEN THERAPEUTICS INC.
                                        a Delaware corporation

                                        ---------------------------------------
                                        Signature

                                        ---------------------------------------
                                        Print Name

                                        ---------------------------------------
                                        Title

"PLEDGEHOLDER"
                                        ---------------------------------------
                                        Secretary of Introgen Therapeutics Inc.

                                      -4-
<PAGE>   25

                                    EXHIBIT C

                                      NOTE

$                                                              [City,State]
-------------------------
                                                       ------------------,-----

         FOR VALUE RECEIVED, _____________________ promises to pay to Introgen
Therapeutics Inc., a Delaware corporation (the "Company"), or order, the
principal sum of _______________________ ($_____________), together with
interest on the unpaid principal hereof from the date hereof at the rate of
_______________ percent (____%) per annum, compounded semiannually.

         Principal and interest shall be due and payable on _______________,
_____. Payment of principal and interest shall be made in lawful money of the
United States of America.

         The undersigned may at any time prepay all or any portion of the
principal or interest owing hereunder.

         This Note is subject to the terms of the Option, dated as of
________________. This Note is secured in part by a pledge of the Company's
Common Stock under the terms of a Security Agreement of even date herewith and
is subject to all the provisions thereof.

         The holder of this Note shall have full recourse against the
undersigned, and shall not be required to proceed against the collateral
securing this Note in the event of default.

         In the event the undersigned shall cease to be an employee, director or
consultant of the Company for any reason, this Note shall, at the option of the
Company, be accelerated, and the whole unpaid balance on this Note of principal
and accrued interest shall be immediately due and payable.

         Should any action be instituted for the collection of this Note, the
reasonable costs and attorneys' fees therein of the holder shall be paid by the
undersigned.

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

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

<PAGE>   26

                           INTROGEN THERAPEUTICS INC.

                             2000 STOCK OPTION PLAN

                             STOCK OPTION AGREEMENT

         Unless otherwise defined herein, the terms defined in the Plan shall
have the same defined meanings in this Option Agreement.

I.       NOTICE OF STOCK OPTION GRANT

         [Optionee's Name and Address]

         You have been granted an option to purchase Common Stock of the
Company, subject to the terms and conditions of the Plan and this Option
Agreement, as follows:

<TABLE>
<S>                                        <C>
         Grant Number                      _____________________________________

         Date of Grant                     _____________________________________

         Vesting Commencement Date         _____________________________________

         Exercise Price per Share          $____________________________________

         Total Number of Shares Granted    _____________________________________

         Total Exercise Price              $____________________________________

         Type of Option:                   ___ Incentive Stock Option

                                           ___ Nonstatutory Stock Option

         Term/Expiration Date:             _____________________________________
</TABLE>

         Vesting Schedule:

         Subject to accelerated vesting as set forth below, this Option may be
exercised, in whole or in part, in accordance with the following schedule:

         [25% OF THE SHARES SUBJECT TO THE OPTION SHALL VEST TWELVE MONTHS AFTER
THE VESTING COMMENCEMENT DATE, AND 1/48 OF THE SHARES SUBJECT TO THE OPTION
SHALL VEST EACH MONTH THEREAFTER, SUBJECT TO THE OPTIONEE CONTINUING TO BE A
SERVICE PROVIDER ON SUCH DATES]. [NOTWITHSTANDING THE FOREGOING OR ANYTHING TO
THE CONTRARY IN THE PLAN, 100% OF THE SHARES SUBJECT TO THE OPTION SHALL
IMMEDIATELY VEST AND BECOME EXERCISABLE IN THE EVENT OF (i) THE MERGER OR
REORGANIZATION OF THE COMPANY WITH OR INTO ANOTHER CORPORATION, ENTITY, OR
PERSON, (ii) THE SALE OF ALL OR SUBSTANTIALLY ALL OF THE COMPANY'S ASSETS TO
ANOTHER CORPORATION, ENTITY, OR

<PAGE>   27

PERSON, OR (iii) ANY CHANGE IN OWNERSHIP OF THE COMPANY'S VOTING STOCK RESULTING
IN OWNERSHIP OF MORE THAN 50% OF THE COMPANY'S VOTING STOCK BY ONE OR MORE
PERSONS ACTING IN CONCERT WHO DID NOT PRIOR TO THE DATE OF GRANT OWN MORE THAN
50% OF THE COMPANY'S VOTING STOCK.]

         Termination Period:

         This Option may be exercised for three months after Optionee ceases to
be a Service Provider. Upon the death or Disability of the Optionee, this Option
may be exercised for twelve months after Optionee ceases to be a Service
Provider. In no event shall this Option be exercised later than the
Term/Expiration Date as provided above.

II.      AGREEMENT

         A.       Grant of Option.

                  The Plan Administrator of the Company hereby grants to the
Optionee named in the Notice of Grant attached as Part I of this Agreement (the
"Optionee") an option (the "Option") to purchase the number of Shares, as set
forth in the Notice of Grant, at the exercise price per share set forth in the
Notice of Grant (the "Exercise Price"), subject to the terms and conditions of
the Plan, which is incorporated herein by reference. Subject to Section 15(c) of
the Plan, in the event of a conflict between the terms and conditions of the
Plan and the terms and conditions of this Option Agreement, the terms and
conditions of the Plan shall prevail.

                  If designated in the Notice of Grant as an Incentive Stock
Option ("ISO"), this Option is intended to qualify as an Incentive Stock Option
under Section 422 of the Code. However, if this Option is intended to be an
Incentive Stock Option, to the extent that it exceeds the $100,000 rule of Code
Section 422(d) it shall be treated as a Nonstatutory Stock Option ("NSO").

         B.       Exercise of Option.

                  (a)      Right to Exercise. This Option is exercisable during
its term in accordance with the Vesting Schedule set out in the Notice of Grant
and the applicable provisions of the Plan and this Option Agreement.

                  (b)      Method of Exercise. This Option is exercisable by
delivery of an exercise notice, in the form attached as Exhibit A (the "Exercise
Notice"), which shall state the election to exercise the Option, the number of
Shares in respect of which the Option is being exercised (the "Exercised
Shares"), and such other representations and agreements as may be required by
the Company pursuant to the provisions of the Plan. The Exercise Notice shall be
completed by the Optionee and delivered to [TITLE] of the Company. The Exercise
Notice shall be accompanied by payment of the aggregate Exercise Price as to all
Exercised Shares. This Option shall be deemed to be exercised upon receipt by
the Company of such fully executed Exercise Notice accompanied by such aggregate
Exercise Price.

                           No Shares shall be issued pursuant to the exercise of
this Option unless such issuance and exercise complies with Applicable Laws.
Assuming such compliance, for income tax purposes the Exercised Shares shall be
considered transferred to the Optionee on the date the Option is exercised with
respect to such Exercised Shares.

                                      -2-
<PAGE>   28

         C.       Method of Payment.

                  Payment of the aggregate Exercise Price shall be by any of the
following, or a combination thereof, at the election of the Optionee:

                  1.       cash; or

                  2.       check[; OR

                  3.       CONSIDERATION RECEIVED BY THE COMPANY UNDER A
CASHLESS EXERCISE PROGRAM IMPLEMENTED BY THE COMPANY IN CONNECTION WITH THE
PLAN][; OR

                  4.       SURRENDER OF OTHER SHARES WHICH (i) IN THE CASE OF
SHARES ACQUIRED UPON EXERCISE OF AN OPTION, HAVE BEEN OWNED BY THE OPTIONEE FOR
MORE THAN SIX (6) MONTHS ON THE DATE OF SURRENDER, AND (ii) HAVE A FAIR MARKET
VALUE ON THE DATE OF SURRENDER EQUAL TO THE AGGREGATE EXERCISE PRICE OF THE
EXERCISED SHARES[; OR

                  5.       WITH THE ADMINISTRATOR'S CONSENT, DELIVERY OF
OPTIONEE'S PROMISSORY NOTE (THE "NOTE") IN THE FORM ATTACHED HERETO AS EXHIBIT
C, IN THE AMOUNT OF THE AGGREGATE EXERCISE PRICE OF THE EXERCISED SHARES
TOGETHER WITH THE EXECUTION AND DELIVERY BY THE OPTIONEE OF THE SECURITY
AGREEMENT ATTACHED HERETO AS EXHIBIT B. THE NOTE SHALL BEAR INTEREST AT THE
"APPLICABLE FEDERAL RATE" PRESCRIBED UNDER THE CODE AND ITS REGULATIONS AT TIME
OF PURCHASE, AND SHALL BE SECURED BY A PLEDGE OF THE SHARES PURCHASED BY THE
NOTE PURSUANT TO THE SECURITY AGREEMENT][; OR

                  6.       TO THE EXTENT PERMITTED BY THE ADMINISTRATOR,
DELIVERY OF A PROPERLY EXECUTED EXERCISE NOTICE TOGETHER WITH SUCH OTHER
DOCUMENTATION AS THE ADMINISTRATOR AND THE BROKER, IF APPLICABLE, SHALL REQUIRE
TO EFFECT AN EXERCISE OF THE OPTION AND DELIVERY TO THE COMPANY OF THE SALE
PROCEEDS REQUIRED TO PAY THE EXERCISE PRICE.]

         D.       Non-Transferability of Option.

                  This Option may not be transferred in any manner otherwise
than by will or by the laws of descent or distribution and may be exercised
during the lifetime of Optionee only by the Optionee. The terms of the Plan and
this Option Agreement shall be binding upon the executors, administrators,
heirs, successors and assigns of the Optionee.

         E.       Term of Option.

                  This Option may be exercised only within the term set out in
the Notice of Grant, and may be exercised during such term only in accordance
with the Plan and the terms of this Option Agreement.

         F.       Tax Consequences.

                  Some of the federal tax consequences relating to this Option,
as of the date of this Option, are set forth below. THIS SUMMARY IS NECESSARILY
INCOMPLETE, AND THE TAX LAWS AND REGULATIONS ARE SUBJECT TO CHANGE. THE OPTIONEE
SHOULD

                                      -3-
<PAGE>   29

CONSULT A TAX ADVISER BEFORE EXERCISING THIS OPTION OR DISPOSING OF THE SHARES.

         G.       Exercising the Option.

                  1.       Nonstatutory Stock Option. The Optionee may incur
regular federal income tax liability upon exercise of a NSO. The Optionee will
be treated as having received compensation income (taxable at ordinary income
tax rates) equal to the excess, if any, of the Fair Market Value of the
Exercised Shares on the date of exercise over their aggregate Exercise Price. If
the Optionee is an Employee or a former Employee, the Company will be required
to withhold from his or her compensation or collect from Optionee and pay to the
applicable taxing authorities an amount in cash equal to a percentage of this
compensation income at the time of exercise, and may refuse to honor the
exercise and refuse to deliver Shares if such withholding amounts are not
delivered at the time of exercise.

                  2.       Incentive Stock Option. If this Option qualifies as
an ISO, the Optionee will have no regular federal income tax liability upon its
exercise, although the excess, if any, of the Fair Market Value of the Exercised
Shares on the date of exercise over their aggregate Exercise Price will be
treated as an adjustment to alternative minimum taxable income for federal tax
purposes and may subject the Optionee to alternative minimum tax in the year of
exercise. In the event that the Optionee ceases to be an Employee but remains a
Service Provider, any Incentive Stock Option of the Optionee that remains
unexercised shall cease to qualify as an Incentive Stock Option and will be
treated for tax purposes as a Nonstatutory Stock Option on the date three (3)
months and one (1) day following such change of status.

                  3.       Disposition of Shares.

                           (a)      NSO. If the Optionee holds NSO Shares for at
least one year, any gain realized on disposition of the Shares will be treated
as long-term capital gain for federal income tax purposes.

                           (b)      ISO. If the Optionee holds ISO Shares for at
least one year after exercise and two years after the grant date, any gain
realized on disposition of the Shares will be treated as long-term capital gain
for federal income tax purposes. If the Optionee disposes of ISO Shares within
one year after exercise or two years after the grant date, any gain realized on
such disposition will be treated as compensation income (taxable at ordinary
income rates) to the extent of the excess, if any, of the lesser of (A) the
difference between the Fair Market Value of the Shares acquired on the date of
exercise and the aggregate Exercise Price, or (B) the difference between the
sale price of such Shares and the aggregate Exercise Price. Any additional gain
will be taxed as capital gain, short-term or long-term depending on the period
that the ISO Shares were held.

                           (c)      Notice of Disqualifying Disposition of ISO
Shares. If the Optionee sells or otherwise disposes of any of the Shares
acquired pursuant to an ISO on or before the later of (i) two years after the
grant date, or (ii) one year after the exercise date, the Optionee shall
immediately notify the Company in writing of such disposition. The Optionee
agrees that he or she may be subject to income tax withholding by the Company on
the compensation income recognized from such early disposition of ISO Shares by
payment in cash or out of the current earnings paid to the Optionee.

                                      -4-
<PAGE>   30

         H.       Entire Agreement; Governing Law.

                  The Plan is incorporated herein by reference. The Plan and
this Option Agreement constitute the entire agreement of the parties with
respect to the subject matter hereof and supersede in their entirety all prior
undertakings and agreements of the Company and Optionee with respect to the
subject matter hereof, and may not be modified adversely to the Optionee's
interest except by means of a writing signed by the Company and Optionee. This
agreement is governed by the internal substantive laws, but not the choice of
law rules, of Texas.

         I.       NO GUARANTEE OF CONTINUED SERVICE.

                  OPTIONEE ACKNOWLEDGES AND AGREES THAT THE VESTING OF SHARES
PURSUANT TO THE VESTING SCHEDULE HEREOF IS EARNED ONLY BY CONTINUING AS A
SERVICE PROVIDER AT THE WILL OF THE COMPANY (AND NOT THROUGH THE ACT OF BEING
HIRED, BEING GRANTED AN OPTION OR PURCHASING SHARES HEREUNDER). OPTIONEE FURTHER
ACKNOWLEDGES AND AGREES THAT THIS AGREEMENT, THE TRANSACTIONS CONTEMPLATED
HEREUNDER AND THE VESTING SCHEDULE SET FORTH HEREIN DO NOT CONSTITUTE AN EXPRESS
OR IMPLIED PROMISE OF CONTINUED ENGAGEMENT AS A SERVICE PROVIDER FOR THE VESTING
PERIOD, FOR ANY PERIOD, OR AT ALL, AND SHALL NOT INTERFERE WITH OPTIONEE'S RIGHT
OR THE COMPANY'S RIGHT TO TERMINATE OPTIONEE'S RELATIONSHIP AS A SERVICE
PROVIDER AT ANY TIME, WITH OR WITHOUT CAUSE.

         By your signature and the signature of the Company's representative
below, you and the Company agree that this Option is granted under and governed
by the terms and conditions of the Plan and this Option Agreement. Optionee has
reviewed the Plan and this Option Agreement in their entirety, has had an
opportunity to obtain the advice of counsel prior to executing this Option
Agreement and fully understands all provisions of the Plan and Option Agreement.
Optionee hereby agrees to accept as binding, conclusive and final all decisions
or interpretations of the Administrator upon any questions relating to the Plan
and Option Agreement. Optionee further agrees to notify the Company upon any
change in the residence address indicated below.

OPTIONEE:                                 INTROGEN THERAPEUTICS INC.

-------------------------------------     --------------------------------------
Signature                                 By

-------------------------------------     --------------------------------------
Print Name                                Title

-------------------------------------
Residence Address

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

                                      -5-
<PAGE>   31

                                CONSENT OF SPOUSE

         The undersigned spouse of Optionee has read and hereby approves the
terms and conditions of the Plan and this Option Agreement. In consideration of
the Company's granting his or her spouse the right to purchase Shares as set
forth in the Plan and this Option Agreement, the undersigned hereby agrees to be
irrevocably bound by the terms and conditions of the Plan and this Option
Agreement and further agrees that any community property interest shall be
similarly bound. The undersigned hereby appoints the undersigned's spouse as
attorney-in-fact for the undersigned with respect to any amendment or exercise
of rights under the Plan or this Option Agreement.

                                             -----------------------------------
                                             Spouse of Optionee

<PAGE>   32

                                    EXHIBIT A

                           INTROGEN THERAPEUTICS INC.

                             2000 STOCK OPTION PLAN

                                 EXERCISE NOTICE

Introgen Therapeutics Inc.
301 Congress Avenue, Suite 1850
Austin, Texas 78701

Attention:  [Title]

         1.       Exercise of Option. Effective as of today, ________________,
_____, the undersigned ("Purchaser") hereby elects to purchase ______________
shares (the "Shares") of the Common Stock of Introgen Therapeutics Inc. (the
"Company") under and pursuant to the 2000 Stock Option Plan (the "Plan") and the
Stock Option Agreement dated, _____ (the "Option Agreement"). The purchase price
for the Shares shall be $_____, as required by the Option Agreement.

         2.       Delivery of Payment. Purchaser herewith delivers to the
Company the full purchase price for the Shares.

         3.       Representations of Purchaser. Purchaser acknowledges that
Purchaser has received, read and understood the Plan and the Option Agreement
and agrees to abide by and be bound by their terms and conditions.

         4.       Rights as Shareholder. Until the issuance (as evidenced by the
appropriate entry on the books of the Company or of a duly authorized transfer
agent of the Company) of the Shares, no right to vote or receive dividends or
any other rights as a shareholder shall exist with respect to the Optioned
Stock, notwithstanding the exercise of the Option. The Shares so acquired shall
be issued to the Optionee as soon as practicable after exercise of the Option.
No adjustment will be made for a dividend or other right for which the record
date is prior to the date of issuance, except as provided in Section 13 of the
Plan.

         5.       Tax Consultation. Purchaser understands that Purchaser may
suffer adverse tax consequences as a result of Purchaser's purchase or
disposition of the Shares. Purchaser represents that Purchaser has consulted
with any tax consultants Purchaser deems advisable in connection with the
purchase or disposition of the Shares and that Purchaser is not relying on the
Company for any tax advice.

<PAGE>   33

         6.       Entire Agreement; Governing Law. The Plan and Option Agreement
are incorporated herein by reference. This Agreement, the Plan and the Option
Agreement constitute the entire agreement of the parties with respect to the
subject matter hereof and supersede in their entirety all prior undertakings and
agreements of the Company and Purchaser with respect to the subject matter
hereof, and may not be modified adversely to the Purchaser's interest except by
means of a writing signed by the Company and Purchaser. This agreement is
governed by the internal substantive laws, but not the choice of law rules, of
Texas.

Submitted by:                           Accepted by:

PURCHASER:                              INTROGEN THERAPEUTICS INC.

----------------------------------      ----------------------------------------
Signature                               By

----------------------------------      ----------------------------------------
Print Name      Its

Address:                                Address:

----------------------------------      INTROGEN THERAPEUTICS INC.
----------------------------------      301 Congress Avenue, Suite 1850
----------------------------------      Austin, Texas 78701

                                        ----------------------------------------
                                        Date Received

                                      -2-
<PAGE>   34

                                    EXHIBIT B

                               SECURITY AGREEMENT

         This Security Agreement is made as of __________, _____ between
Introgen Therapeutics Inc., a Delaware corporation ("Pledgee"), and
_________________________ ("Pledgor").

                                    Recitals

         Pursuant to Pledgor's election to purchase Shares under the Option
Agreement dated ________ (the "Option"), between Pledgor and Pledgee under
Pledgee's 2000 Stock Option Plan, and Pledgor's election under the terms of the
Option to pay for such shares with his promissory note (the "Note"), Pledgor has
purchased _________ shares of Pledgee's Common Stock (the "Shares") at a price
of $________ per share, for a total purchase price of $__________. The Note and
the obligations thereunder are as set forth in Exhibit C to the Option.

         NOW, THEREFORE, it is agreed as follows:

         1.       Creation and Description of Security Interest. In
consideration of the transfer of the Shares to Pledgor under the Option
Agreement, Pledgor, pursuant to the Texas Commercial Code, hereby pledges all of
such Shares (herein sometimes referred to as the "Collateral") represented by
certificate number ______, duly endorsed in blank or with executed stock powers,
and herewith delivers said certificate to the Secretary of Pledgee
("Pledgeholder"), who shall hold said certificate subject to the terms and
conditions of this Security Agreement.

         The pledged stock (together with an executed blank stock assignment for
use in transferring all or a portion of the Shares to Pledgee if, as and when
required pursuant to this Security Agreement) shall be held by the Pledgeholder
as security for the repayment of the Note, and any extensions or renewals
thereof, to be executed by Pledgor pursuant to the terms of the Option, and the
Pledgeholder shall not encumber or dispose of such Shares except in accordance
with the provisions of this Security Agreement.

         2.       Pledgor's Representations and Covenants. To induce Pledgee to
enter into this Security Agreement, Pledgor represents and covenants to Pledgee,
its successors and assigns, as follows:

                  (a)      Payment of Indebtedness. Pledgor will pay the
principal sum of the Note secured hereby, together with interest thereon, at the
time and in the manner provided in the Note.

                  (b)      Encumbrances. The Shares are free of all other
encumbrances, defenses and liens, and Pledgor will not further encumber the
Shares without the prior written consent of Pledgee.

<PAGE>   35

                  (c)      Margin Regulations. In the event that Pledgee's
Common Stock is now or later becomes margin-listed by the Federal Reserve Board
and Pledgee is classified as a "lender" within the meaning of the regulations
under Part 207 of Title 12 of the Code of Federal Regulations ("Regulation G"),
Pledgor agrees to cooperate with Pledgee in making any amendments to the Note or
providing any additional collateral as may be necessary to comply with such
regulations.

         3.       Voting Rights. During the term of this pledge and so long as
all payments of principal and interest are made as they become due under the
terms of the Note, Pledgor shall have the right to vote all of the Shares
pledged hereunder.

         4.       Stock Adjustments. In the event that during the term of the
pledge any stock dividend, reclassification, readjustment or other changes are
declared or made in the capital structure of Pledgee, all new, substituted and
additional shares or other securities issued by reason of any such change shall
be delivered to and held by the Pledgee under the terms of this Security
Agreement in the same manner as the Shares originally pledged hereunder. In the
event of substitution of such securities, Pledgor, Pledgee and Pledgeholder
shall cooperate and execute such documents as are reasonable so as to provide
for the substitution of such Collateral and, upon such substitution, references
to "Shares" in this Security Agreement shall include the substituted shares of
capital stock of Pledgor as a result thereof.

         5.       Options and Rights. In the event that, during the term of this
pledge, subscription Options or other rights or options shall be issued in
connection with the pledged Shares, such rights, Options and options shall be
the property of Pledgor and, if exercised by Pledgor, all new stock or other
securities so acquired by Pledgor as it relates to the pledged Shares then held
by Pledgeholder shall be immediately delivered to Pledgeholder, to be held under
the terms of this Security Agreement in the same manner as the Shares pledged.

         6.       Default. Pledgor shall be deemed to be in default of the Note
and of this Security Agreement in the event:

                  (a)      Payment of principal or interest on the Note shall be
delinquent for a period of 10 days or more; or

                  (b)      Pledgor fails to perform any of the covenants set
forth in the Option or contained in this Security Agreement for a period of 10
days after written notice thereof from Pledgee.

         In the case of an event of Default, as set forth above, Pledgee shall
have the right to accelerate payment of the Note upon notice to Pledgor, and
Pledgee shall thereafter be entitled to pursue its remedies under the Texas
Commercial Code.

         7.       Release of Collateral. Subject to any applicable contrary
rules under Regulation G, there shall be released from this pledge a portion of
the pledged Shares held by Pledgeholder hereunder upon payments of the principal
of the Note. The number of the pledged Shares which shall be released shall be
that number of full Shares which bears the same proportion to the initial number
of

                                      -2-
<PAGE>   36

Shares pledged hereunder as the payment of principal bears to the initial full
principal amount of the Note.

         8.       Withdrawal or Substitution of Collateral. Pledgor shall not
sell, withdraw, pledge, substitute or otherwise dispose of all or any part of
the Collateral without the prior written consent of Pledgee.

         9.       Term. The within pledge of Shares shall continue until the
payment of all indebtedness secured hereby, at which time the remaining pledged
stock shall be promptly delivered to Pledgor, subject to the provisions for
prior release of a portion of the Collateral as provided in paragraph 7 above.

         10.      Insolvency. Pledgor agrees that if a bankruptcy or insolvency
proceeding is instituted by or against it, or if a receiver is appointed for the
property of Pledgor, or if Pledgor makes an assignment for the benefit of
creditors, the entire amount unpaid on the Note shall become immediately due and
payable, and Pledgee may proceed as provided in the case of default.

         11.      Pledgeholder Liability. In the absence of willful or gross
negligence, Pledgeholder shall not be liable to any party for any of his acts,
or omissions to act, as Pledgeholder.

         12.      Invalidity of Particular Provisions. Pledgor and Pledgee agree
that the enforceability or invalidity of any provision or provisions of this
Security Agreement shall not render any other provision or provisions herein
contained unenforceable or invalid.

         13.      Successors or Assigns. Pledgor and Pledgee agree that all of
the terms of this Security Agreement shall be binding on their respective
successors and assigns, and that the term "Pledgor" and the term "Pledgee" as
used herein shall be deemed to include, for all purposes, the respective
designees, successors, assigns, heirs, executors and administrators.

         14.      Governing Law. This Security Agreement shall be interpreted
and governed under the internal substantive laws, but not the choice of law
rules, of Texas.

                                      -3-
<PAGE>   37

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

"PLEDGOR"
                                   ---------------------------------------------
                                   Signature

                                   ---------------------------------------------
                                   Print Name

                                   Address:
                                            ------------------------------------

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

"PLEDGEE"                          INTROGEN THERAPEUTICS INC.
                                   a Delaware corporation

                                   ---------------------------------------------
                                   Signature

                                   ---------------------------------------------
                                   Print Name

                                   ---------------------------------------------
                                   Title

"PLEDGEHOLDER"
                                   ---------------------------------------------
                                   Secretary of Introgen Therapeutics Inc.

                                      -4-
<PAGE>   38

                                    EXHIBIT C

                                      NOTE

$__________________________                                        [City, State]

                                                       __________________, _____

         FOR VALUE RECEIVED, _____________________ promises to pay to Introgen
Therapeutics Inc., a Delaware corporation (the "Company"), or order, the
principal sum of _______________________ ($_____________), together with
interest on the unpaid principal hereof from the date hereof at the rate of
_______________ percent (____%) per annum, compounded semiannually.

         Principal and interest shall be due and payable on _______________,
_____. Payment of principal and interest shall be made in lawful money of the
United States of America.

         The undersigned may at any time prepay all or any portion of the
principal or interest owing hereunder.

         This Note is subject to the terms of the Option, dated as of
________________. This Note is secured in part by a pledge of the Company's
Common Stock under the terms of a Security Agreement of even date herewith and
is subject to all the provisions thereof.

         The holder of this Note shall have full recourse against the
undersigned, and shall not be required to proceed against the collateral
securing this Note in the event of default.

         In the event the undersigned shall cease to be an employee, director or
consultant of the Company for any reason, this Note shall, at the option of the
Company, be accelerated, and the whole unpaid balance on this Note of principal
and accrued interest shall be immediately due and payable.

         Should any action be instituted for the collection of this Note, the
reasonable costs and attorneys' fees therein of the holder shall be paid by the
undersigned.

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

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

<PAGE>   39
                           INTROGEN THERAPEUTICS INC.

                             2000 STOCK OPTION PLAN

                     NOTICE OF GRANT OF STOCK PURCHASE RIGHT

         Unless otherwise defined herein, the terms defined in the Plan shall
have the same defined meanings in this Notice of Grant.

         [Grantee's Name and Address]

         You have been granted the right to purchase Common Stock of the
Company, subject to the Company's Repurchase Option and your ongoing status as a
Service Provider (as described in the Plan and the attached Restricted Stock
Purchase Agreement), as follows:

<TABLE>
<S>                                                <C>

         Grant Number
                                                     ---------------------------

         Date of Grant
                                                     ---------------------------

         Price Per Share                             $
                                                     ---------------------------

         Total Number of Shares Subject
           to This Stock Purchase Right
                                                     ---------------------------

         Expiration Date:
                                                     ---------------------------
</TABLE>

         YOU MUST EXERCISE THIS STOCK PURCHASE RIGHT BEFORE THE EXPIRATION DATE
OR IT WILL TERMINATE AND YOU WILL HAVE NO FURTHER RIGHT TO PURCHASE THE SHARES.
By your signature and the signature of the Company's representative below, you
and the Company agree that this Stock Purchase Right is granted under and
governed by the terms and conditions of the 2000 Stock Option Plan and the
Restricted Stock Purchase Agreement, attached hereto as Exhibit A-1, both of
which are made a part of this document. You further agree to execute the
attached Restricted Stock Purchase Agreement as a condition to purchasing any
shares under this Stock Purchase Right.

GRANTEE:                                 INTROGEN THERAPEUTICS INC.

--------------------------------         -------------------------------------
Signature                                By

--------------------------------         -------------------------------------
Print Name                               Title

<PAGE>   40

                                   EXHIBIT A-1

                           INTROGEN THERAPEUTICS INC.

                             2000 STOCK OPTION PLAN

                       RESTRICTED STOCK PURCHASE AGREEMENT

         Unless otherwise defined herein, the terms defined in the Plan shall
have the same defined meanings in this Restricted Stock Purchase Agreement.

         WHEREAS the Purchaser named in the Notice of Grant, (the "Purchaser")
is a Service Provider, and the Purchaser's continued participation is considered
by the Company to be important for the Company's continued growth; and

         WHEREAS in order to give the Purchaser an opportunity to acquire an
equity interest in the Company as an incentive for the Purchaser to participate
in the affairs of the Company, the Administrator has granted to the Purchaser a
Stock Purchase Right subject to the terms and conditions of the Plan and the
Notice of Grant, which are incorporated herein by reference, and pursuant to
this Restricted Stock Purchase Agreement (the "Agreement").

         NOW THEREFORE, the parties agree as follows:

         1. Sale of Stock. The Company hereby agrees to sell to the Purchaser
and the Purchaser hereby agrees to purchase shares of the Company's Common Stock
(the "Shares"), at the per Share purchase price and as otherwise described in
the Notice of Grant.

         2. Payment of Purchase Price. The purchase price for the Shares may be
paid by delivery to the Company at the time of execution of this Agreement of
cash, a check, or some combination thereof.

         3. Repurchase Option.

            (a) In the event the Purchaser ceases to be a Service Provider for
any or no reason (including death or disability) before all of the Shares are
released from the Company's Repurchase Option (see Section 4), the Company
shall, upon the date of such termination (as reasonably fixed and determined by
the Company) have an irrevocable, exclusive option (the "Repurchase Option") for
a period of sixty (60) days from such date to repurchase up to that number of
shares which constitute the Unreleased Shares (as defined in Section 4) at the
original purchase price per share (the "Repurchase Price"). The Repurchase
Option shall be exercised by the Company by delivering written notice to the
Purchaser or the Purchaser's executor (with a copy to the Escrow Holder) AND, at
the Company's option, (i) by delivering to the Purchaser or the Purchaser's
executor a check in the amount of the aggregate Repurchase Price, or (ii) by
canceling an amount of the Purchaser's

<PAGE>   41

indebtedness to the Company equal to the aggregate Repurchase Price, or (iii) by
a combination of (i) and (ii) so that the combined payment and cancellation of
indebtedness equals the aggregate Repurchase Price. Upon delivery of such notice
and the payment of the aggregate Repurchase Price, the Company shall become the
legal and beneficial owner of the Shares being repurchased and all rights and
interests therein or relating thereto, and the Company shall have the right to
retain and transfer to its own name the number of Shares being repurchased by
the Company.

            (b) Whenever the Company shall have the right to repurchase Shares
hereunder, the Company may designate and assign one or more employees, officers,
directors or shareholders of the Company or other persons or organizations to
exercise all or a part of the Company's purchase rights under this Agreement and
purchase all or a part of such Shares. If the Fair Market Value of the Shares to
be repurchased on the date of such designation or assignment (the "Repurchase
FMV") exceeds the aggregate Repurchase Price of such Shares, then each such
designee or assignee shall pay the Company cash equal to the difference between
the Repurchase FMV and the aggregate Repurchase Price of such Shares.

         4. Release of Shares From Repurchase Option.

            (a) _______________________ percent (______%) of the Shares shall be
released from the Company's Repurchase Option [one year] after the Date of Grant
and __________________ percent (______%) of the Shares [at the end of each month
thereafter], provided that the Purchaser does not cease to be a Service Provider
prior to the date of any such release.

            (b) Any of the Shares that have not yet been released from the
Repurchase Option are referred to herein as "Unreleased Shares."

            (c) The Shares that have been released from the Repurchase Option
shall be delivered to the Purchaser at the Purchaser's request (see Section 6).

         5. Restriction on Transfer. Except for the escrow described in Section
6 or the transfer of the Shares to the Company or its assignees contemplated by
this Agreement, none of the Shares or any beneficial interest therein shall be
transferred, encumbered or otherwise disposed of in any way until such Shares
are released from the Company's Repurchase Option in accordance with the
provisions of this Agreement, other than by will or the laws of descent and
distribution.

         6. Escrow of Shares.

            (a) To ensure the availability for delivery of the Purchaser's
Unreleased Shares upon repurchase by the Company pursuant to the Repurchase
Option, the Purchaser shall, upon execution of this Agreement, deliver and
deposit with an escrow holder designated by the Company (the "Escrow Holder")
the share certificates representing the Unreleased Shares, together with the
stock assignment duly endorsed in blank, attached hereto as Exhibit A-2. The
Unreleased Shares and stock assignment shall be held by the Escrow Holder,
pursuant to the Joint Escrow Instructions of the Company and Purchaser attached
hereto as Exhibit A-3, until such time as the Company's

                                      -2-
<PAGE>   42

Repurchase Option expires. As a further condition to the Company's obligations
under this Agreement, the Company may require the spouse of Purchaser, if any,
to execute and deliver to the Company the Consent of Spouse attached hereto as
Exhibit A-4.

            (b) The Escrow Holder shall not be liable for any act it may do or
omit to do with respect to holding the Unreleased Shares in escrow while acting
in good faith and in the exercise of its judgment.

            (c) If the Company or any assignee exercises the Repurchase Option
hereunder, the Escrow Holder, upon receipt of written notice of such exercise
from the proposed transferee, shall take all steps necessary to accomplish such
transfer.

            (d) When the Repurchase Option has been exercised or expires
unexercised or a portion of the Shares has been released from the Repurchase
Option, upon request the Escrow Holder shall promptly cause a new certificate to
be issued for the released Shares and shall deliver the certificate to the
Company or the Purchaser, as the case may be.

            (e) Subject to the terms hereof, the Purchaser shall have all the
rights of a shareholder with respect to the Shares while they are held in
escrow, including without limitation, the right to vote the Shares and to
receive any cash dividends declared thereon. If, from time to time during the
term of the Repurchase Option, there is (i) any stock dividend, stock split or
other change in the Shares, or (ii) any merger or sale of all or substantially
all of the assets or other acquisition of the Company, any and all new,
substituted or additional securities to which the Purchaser is entitled by
reason of the Purchaser's ownership of the Shares shall be immediately subject
to this escrow, deposited with the Escrow Holder and included thereafter as
"Shares" for purposes of this Agreement and the Repurchase Option.

         7. Legends. The share certificate evidencing the Shares, if any, issued
hereunder shall be endorsed with the following legend (in addition to any legend
required under applicable state securities laws):

         THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO CERTAIN
RESTRICTIONS UPON TRANSFER AND RIGHTS OF REPURCHASE AS SET FORTH IN AN AGREEMENT
BETWEEN THE COMPANY AND THE SHAREHOLDER, A COPY OF WHICH IS ON FILE WITH THE
SECRETARY OF THE COMPANY.

         8. Adjustment for Stock Split. All references to the number of Shares
and the purchase price of the Shares in this Agreement shall be appropriately
adjusted to reflect any stock split, stock dividend or other change in the
Shares that may be made by the Company after the date of this Agreement.

         9. Tax Consequences. The Purchaser has reviewed with the Purchaser's
own tax advisors the federal, state, local and foreign tax consequences of this
investment and the transactions contemplated by this Agreement. The Purchaser is
relying solely on such advisors and not on any statements or representations of
the Company or any of its agents. The Purchaser understands that

                                      -3-
<PAGE>   43

the Purchaser (and not the Company) shall be responsible for the Purchaser's own
tax liability that may arise as a result of the transactions contemplated by
this Agreement. The Purchaser understands that Section 83 of the Internal
Revenue Code of 1986, as amended (the "Code"), taxes as ordinary income the
difference between the purchase price for the Shares and the Fair Market Value
of the Shares as of the date any restrictions on the Shares lapse. In this
context, "restriction" includes the right of the Company to buy back the Shares
pursuant to the Repurchase Option. The Purchaser understands that the Purchaser
may elect to be taxed at the time the Shares are purchased rather than when and
as the Repurchase Option expires by filing an election under Section 83(b) of
the Code with the IRS within 30 days from the date of purchase. The form for
making this election is attached as Exhibit A-5 hereto.

         THE PURCHASER ACKNOWLEDGES THAT IT IS THE PURCHASER'S SOLE
RESPONSIBILITY AND NOT THE COMPANY'S TO FILE TIMELY THE ELECTION UNDER SECTION
83(b), EVEN IF THE PURCHASER REQUESTS THE COMPANY OR ITS REPRESENTATIVES TO MAKE
THIS FILING ON THE PURCHASER'S BEHALF.

         10. General Provisions.

            (a) This Agreement shall be governed by the internal substantive
laws, but not the choice of law rules of Texas. This Agreement, subject to the
terms and conditions of the Plan and the Notice of Grant, represents the entire
agreement between the parties with respect to the purchase of the Shares by the
Purchaser. Subject to Section 15(c) of the Plan, in the event of a conflict
between the terms and conditions of the Plan and the terms and conditions of
this Agreement, the terms and conditions of the Plan shall prevail. Unless
otherwise defined herein, the terms defined in the Plan shall have the same
defined meanings in this Agreement.

            (b) Any notice, demand or request required or permitted to be given
by either the Company or the Purchaser pursuant to the terms of this Agreement
shall be in writing and shall be deemed given when delivered personally or
deposited in the U.S. mail, First Class with postage prepaid, and addressed to
the parties at the addresses of the parties set forth at the end of this
Agreement or such other address as a party may request by notifying the other in
writing.

                Any notice to the Escrow Holder shall be sent to the Company's
address with a copy to the other party hereto.

            (c) The rights of the Company under this Agreement shall be
transferable to any one or more persons or entities, and all covenants and
agreements hereunder shall inure to the benefit of, and be enforceable by the
Company's successors and assigns. The rights and obligations of the Purchaser
under this Agreement may only be assigned with the prior written consent of the
Company.

            (d) Either party's failure to enforce any provision of this
Agreement shall not in any way be construed as a waiver of any such provision,
nor prevent that party from thereafter enforcing any other provision of this
Agreement. The rights granted both parties hereunder are

                                      -4-
<PAGE>   44

cumulative and shall not constitute a waiver of either party's right to assert
any other legal remedy available to it.

            (e) The Purchaser agrees upon request to execute any further
documents or instruments necessary or desirable to carry out the purposes or
intent of this Agreement.

            (f) PURCHASER ACKNOWLEDGES AND AGREES THAT THE VESTING OF SHARES
PURSUANT TO SECTION 4 HEREOF IS EARNED ONLY BY CONTINUING SERVICE AS A SERVICE
PROVIDER AT THE WILL OF THE COMPANY (AND NOT THROUGH THE ACT OF BEING HIRED OR
PURCHASING SHARES HEREUNDER). PURCHASER FURTHER ACKNOWLEDGES AND AGREES THAT
THIS AGREEMENT, THE TRANSACTIONS CONTEMPLATED HEREUNDER AND THE VESTING SCHEDULE
SET FORTH HEREIN DO NOT CONSTITUTE AN EXPRESS OR IMPLIED PROMISE OF CONTINUED
ENGAGEMENT AS A SERVICE PROVIDER FOR THE VESTING PERIOD, FOR ANY PERIOD, OR AT
ALL, AND SHALL NOT INTERFERE WITH PURCHASER'S RIGHT OR THE COMPANY'S RIGHT TO
TERMINATE PURCHASER'S RELATIONSHIP AS A SERVICE PROVIDER AT ANY TIME, WITH OR
WITHOUT CAUSE.

         By Purchaser's signature below, Purchaser represents that he or she is
familiar with the terms and provisions of the Plan, and hereby accepts this
Agreement subject to all of the terms and provisions thereof. Purchaser has
reviewed the Plan and this Agreement in their entirety, has had an opportunity
to obtain the advice of counsel prior to executing this Agreement and fully
understands all provisions of this Agreement. Purchaser agrees to accept as
binding, conclusive and final all decisions or interpretations of the
Administrator upon any questions arising under the Plan or this Agreement.
Purchaser further agrees to notify the Company upon any change in the residence
indicated in the Notice of Grant.

DATED:
          -------------------------

PURCHASER:                                  INTROGEN THERAPEUTICS INC.

-----------------------------------         ----------------------------------
Signature                                   By

-----------------------------------         ----------------------------------
Print Name                                  Title

                                      -5-
<PAGE>   45

                                   EXHIBIT A-2

                      ASSIGNMENT SEPARATE FROM CERTIFICATE

         FOR VALUE RECEIVED I, _______________________________, hereby sell,
assign and transfer unto ____________ (__________) shares of the Common Stock of
Introgen Therapeutics Inc., standing in my name of the books of said corporation
represented by Certificate No. _____ herewith and do hereby irrevocably
constitute and appoint ____________ to transfer the said stock on the books of
the within named corporation with full power of substitution in the premises.

         This Stock Assignment may be used only in accordance with the
Restricted Stock Purchase Agreement (the "Agreement")
between________________________ and the undersigned dated ________________,
_______.

Dated: _______________, _____

                                        Signature:____________________________

         INSTRUCTIONS: Please do not fill in any blanks other than the signature
line. The purpose of this assignment is to enable the Company to exercise the
Repurchase Option, as set forth in the Agreement, without requiring additional
signatures on the part of the Purchaser.

<PAGE>   46

                                   EXHIBIT A-3

                            JOINT ESCROW INSTRUCTIONS

                                                                       ,
                                                     ------------------  ----

Corporate Secretary
Introgen Therapeutics Inc.
301 Congress Avenue, Suite 1850
Austin, Texas 78701

Dear           :
     ----------

         As Escrow Agent for both Introgen Therapeutics Inc., a Delaware
corporation (the "Company"), and the undersigned purchaser of stock of the
Company (the "Purchaser"), you are hereby authorized and directed to hold the
documents delivered to you pursuant to the terms of that certain Restricted
Stock Purchase Agreement ("Agreement") between the Company and the undersigned,
in accordance with the following instructions:

         1. In the event the Company and/or any assignee of the Company
(referred to collectively as the "Company") exercises the Company's Repurchase
Option set forth in the Agreement, the Company shall give to Purchaser and you a
written notice specifying the number of shares of stock to be purchased, the
purchase price, and the time for a closing hereunder at the principal office of
the Company. Purchaser and the Company hereby irrevocably authorize and direct
you to close the transaction contemplated by such notice in accordance with the
terms of said notice.

         2. At the closing, you are directed (a) to date the stock assignments
necessary for the transfer in question, (b) to fill in the number of shares
being transferred, and (c) to deliver same, together with the certificate
evidencing the shares of stock to be transferred, to the Company or its
assignee, against the simultaneous delivery to you of the purchase price (by
cash, a check, or some combination thereof) for the number of shares of stock
being purchased pursuant to the exercise of the Company's Repurchase Option.

         3. Purchaser irrevocably authorizes the Company to deposit with you any
certificates evidencing shares of stock to be held by you hereunder and any
additions and substitutions to said shares as defined in the Agreement.
Purchaser does hereby irrevocably constitute and appoint you as Purchaser's
attorney-in-fact and agent for the term of this escrow to execute with respect
to such securities all documents necessary or appropriate to make such
securities negotiable and to complete any transaction herein contemplated,
including but not limited to the filing with any applicable state blue sky
authority of any required applications for consent to, or notice of transfer of,
the securities.

<PAGE>   47

Subject to the provisions of this paragraph 3, Purchaser shall exercise all
rights and privileges of a shareholder of the Company while the stock is held by
you.

         4. Upon written request of the Purchaser, but no more than once per
calendar year, unless the Company's Repurchase Option has been exercised, you
shall deliver to Purchaser a certificate or certificates representing so many
shares of stock as are not then subject to the Company's Repurchase Option.
Within 90 days after Purchaser ceases to be a Service Provider, you shall
deliver to Purchaser a certificate or certificates representing the aggregate
number of shares held or issued pursuant to the Agreement and not purchased by
the Company or its assignees pursuant to exercise of the Company's Repurchase
Option.

         5. If at the time of termination of this escrow you should have in your
possession any documents, securities, or other property belonging to Purchaser,
you shall deliver all of the same to Purchaser and shall be discharged of all
further obligations hereunder.

         6. Your duties hereunder may be altered, amended, modified or revoked
only by a writing signed by all of the parties hereto.

         7. You shall be obligated only for the performance of such duties as
are specifically set forth herein and may rely and shall be protected in relying
or refraining from acting on any instrument reasonably believed by you to be
genuine and to have been signed or presented by the proper party or parties. You
shall not be personally liable for any act you may do or omit to do hereunder as
Escrow Agent or as attorney-in-fact for Purchaser while acting in good faith,
and any act done or omitted by you pursuant to the advice of your own attorneys
shall be conclusive evidence of such good faith.

         8. You are hereby expressly authorized to disregard any and all
warnings given by any of the parties hereto or by any other person or
corporation, excepting only orders or process of courts of law, and are hereby
expressly authorized to comply with and obey orders, judgments or decrees of any
court. In case you obey or comply with any such order, judgment or decree, you
shall not be liable to any of the parties hereto or to any other person, firm or
corporation by reason of such compliance, notwithstanding any such order,
judgment or decree being subsequently reversed, modified, annulled, set aside,
vacated or found to have been entered without jurisdiction.

         9. You shall not be liable in any respect on account of the identity,
authorities or rights of the parties executing or delivering or purporting to
execute or deliver the Agreement or any documents or papers deposited or called
for hereunder.

         10. You shall not be liable for the outlawing of any rights under the
statute of limitations with respect to these Joint Escrow Instructions or any
documents deposited with you.

         11. You shall be entitled to employ such legal counsel and other
experts as you may deem necessary properly to advise you in connection with your
obligations hereunder, may rely upon the advice of such counsel, and may pay
such counsel reasonable compensation therefor.

                                      -2-
<PAGE>   48

         12. Your responsibilities as Escrow Agent hereunder shall terminate if
you shall cease to be an officer or agent of the Company or if you shall resign
by written notice to each party. In the event of any such termination, the
Company shall appoint a successor Escrow Agent.

         13. If you reasonably require other or further instruments in
connection with these Joint Escrow Instructions or obligations in respect
hereto, the necessary parties hereto shall join in furnishing such instruments.

         14. It is understood and agreed that should any dispute arise with
respect to the delivery and/or ownership or right of possession of the
securities held by you hereunder, you are authorized and directed to retain in
your possession without liability to anyone all or any part of said securities
until such disputes shall have been settled either by mutual written agreement
of the parties concerned or by a final order, decree or judgment of a court of
competent jurisdiction after the time for appeal has expired and no appeal has
been perfected, but you shall be under no duty whatsoever to institute or defend
any such proceedings.

         15. Any notice required or permitted hereunder shall be given in
writing and shall be deemed effectively given upon personal delivery or upon
deposit in the United States Post Office, by registered or certified mail with
postage and fees prepaid, addressed to each of the other parties thereunto
entitled at the following addresses or at such other addresses as a party may
designate by ten days' advance written notice to each of the other parties
hereto.

             COMPANY:           Introgen Therapeutics Inc.
                                301 Congress Avenue, Suite 1850
                                Austin, Texas 78701

             PURCHASER:
                                -----------------------------------------

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

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

             ESCROW AGENT:      Corporate Secretary
                                Introgen Therapeutics Inc.
                                301 Congress Avenue, Suite 1850
                                Austin, Texas 78701

         16. By signing these Joint Escrow Instructions, you become a party
hereto only for the purpose of said Joint Escrow Instructions; you do not become
a party to the Agreement.

         17. This instrument shall be binding upon and inure to the benefit of
the parties hereto, and their respective successors and permitted assigns.

                                      -3-
<PAGE>   49

         18. These Joint Escrow Instructions shall be governed by, and construed
and enforced in accordance with, the internal substantive laws, but not the
choice of law rules, of Texas.

                                       Very truly yours,

                                       INTROGEN THERAPEUTICS INC.

                                       -------------------------------------
                                       By

                                       -------------------------------------
                                       Title

                                       PURCHASER:

                                       -------------------------------------
                                       Signature

                                       -------------------------------------
                                       Print Name

ESCROW AGENT:

-------------------------------------
Corporate Secretary

                                      -4-
<PAGE>   50

                                   EXHIBIT A-4

                                CONSENT OF SPOUSE

         I, _________________________, spouse of ________________________, have
read and approve the foregoing Restricted Stock Purchase Agreement (the
"Agreement"). In consideration of the Company's grant to my spouse of the right
to purchase shares of Introgen Therapeutics Inc., as set forth in the Agreement,
I hereby appoint my spouse as my attorney-in-fact in respect to the exercise of
any rights under the Agreement and agree to be bound by the provisions of the
Agreement insofar as I may have any rights in said Agreement or any shares
issued pursuant thereto under the community property laws or similar laws
relating to marital property in effect in the state of our residence as of the
date of the signing of the foregoing Agreement.

Dated: ____________________, _____

                                      _________________________________________
                                      Signature of Spouse

<PAGE>   51

                                   EXHIBIT A-5

                          ELECTION UNDER SECTION 83(b)

                      OF THE INTERNAL REVENUE CODE OF 1986

The undersigned taxpayer hereby elects, pursuant to Section 83(b) of the
Internal Revenue Code of 1986, as amended, to include in taxpayer's gross income
for the current taxable year the amount of any compensation taxable to taxpayer
in connection with his or her receipt of the property described below:

1.      The name, address, taxpayer identification number and taxable year of
        the undersigned are as follows:

<TABLE>
<S>                                 <C>                                         <C>
         NAME:                      TAXPAYER:                                   SPOUSE:

         ADDRESS:

         IDENTIFICATION NO.:        TAXPAYER:                                   SPOUSE:

         TAXABLE YEAR:
</TABLE>

2.      The property with respect to which the election is made is described as
        follows: ___ shares (the "Shares") of the Common Stock of Introgen
        Therapeutics Inc. (the "Company").

3.      The date on which the property was transferred is: ___________________,
        ______.

4.      The property is subject to the following restrictions:

        The Shares may be repurchased by the Company, or its assignee, upon
        certain events. This right lapses with regard to a portion of the
        Shares based on the continued performance of services by the taxpayer
        over time.

5.      The fair market value at the time of transfer, determined without regard
        to any restriction other than a restriction which by its terms will
        never lapse, of such property is: $__________.

6.      The amount (if any) paid for such property is:  $___________.

The undersigned has submitted a copy of this statement to the person for whom
the services were performed in connection with the undersigned's receipt of the
above-described property. The transferee of such property is the person
performing the services in connection with the transfer of said property.

The undersigned understands that the foregoing election may not be revoked
except with the consent of the Commissioner.

Dated:                   ,
       ------------------  -------         -------------------------------------
                                           Taxpayer

The undersigned spouse of taxpayer joins in this election.

Dated:                   ,
       ------------------  -------         -------------------------------------
                                           Spouse of Taxpayer<PAGE>   1
                                                             Exhibit 10.4
                           INTROGEN THERAPEUTICS INC.

                        2000 EMPLOYEE STOCK PURCHASE PLAN

     1. Purpose. The purpose of the Plan is to provide employees of the Company
and its Designated Subsidiaries with an opportunity to purchase Common Stock of
the Company through accumulated payroll deductions. It is the intention of the
Company to have the Plan qualify as an "Employee Stock Purchase Plan" under
Section 423 of the Internal Revenue Code of 1986, as amended. The provisions of
the Plan, accordingly, shall be construed so as to extend and limit
participation in a manner consistent with the requirements of that section of
the Code.

     2. Definitions.

          (a) "Board" shall mean the Board of Directors of the Company.

          (b) "Code" shall mean the Internal Revenue Code of 1986, as amended.

          (c) "Common Stock" shall mean the Common Stock of the Company.

          (d) "Company" shall mean Introgen Therapeutics Inc., a Delaware
corporation, and any Designated Subsidiary of the Company.

          (e) "Compensation" shall mean all base straight time gross earnings
and commissions, exclusive of payments for overtime, shift premium, incentive
compensation, incentive payments, bonuses and other compensation.

          (f) "Designated Subsidiary" shall mean any Subsidiary that has been
designated by the Board from time to time in its sole discretion as eligible to
participate in the Plan.

          (g) "Employee" shall mean any individual who is an Employee of the
Company for tax purposes whose customary employment with the Company is at least
twenty (20) hours per week and more than five (5) months in any calendar year
and who has been employed by the Company for at least sixty (60) consecutive
calendar days prior to the first day of an Offering Period. For purposes of the
Plan, the employment relationship shall be treated as continuing intact while
the individual is on sick leave or other leave of absence approved by the
Company. Where the period of leave exceeds 90 days and the individual's right to
reemployment is not guaranteed either by statute or by contract, the employment
relationship shall be deemed to have terminated on the 91st day of such leave.

          (h) "Enrollment Date" shall mean the first day of each Offering
Period.

          (i) "Exercise Date" shall mean the last day of each Offering Period.

<PAGE>   2

          (j) "Fair Market Value" shall mean, as of any date, the value of
Common Stock determined as follows:

               (1) If the Common Stock is listed on any established stock
exchange or a national market system, including without limitation the Nasdaq
National Market or The Nasdaq SmallCap Market of The Nasdaq Stock Market, its
Fair Market Value shall be the closing sales price for such stock (or the
closing bid, if no sales were reported) as quoted on such exchange or system for
the last market trading day on the date of such determination, as reported in
The Wall Street Journal or such other source as the Board deems reliable, or;

               (2) If the Common Stock is regularly quoted by a recognized
securities dealer but selling prices are not reported, its Fair Market Value
shall be the mean of the closing bid and asked prices for the Common Stock on
the date of such determination, as reported in The Wall Street Journal or such
other source as the Board deems reliable, or;

               (3) In the absence of an established market for the Common Stock,
the Fair Market Value thereof shall be determined in good faith by the Board; or

               (4) For purposes of the Enrollment Date of the first Offering
Period under the Plan, the Fair Market Value shall be the initial price to the
public as set forth in the final prospectus included within the registration
statement in Form S-1 filed with the Securities and Exchange Commission for the
initial public offering of the Company's Common Stock (the "Registration
Statement").

          (k) "Offering Period" shall mean a period of approximately six (6)
months during which an option granted pursuant to the Plan may be exercised,
commencing on the first Trading Day on or after May 1 and terminating on the
last Trading Day in the period ending the following October 31, or commencing on
the first Trading Day on or after November 1 and terminating on the last Trading
Day in the period ending the following April 30; provided, however, that the
first Offering Period under the Plan shall commence with the first Trading Day
on or after the date on which the Securities and Exchange Commission declares
the Company's Registration Statement effective and ending on the last Trading
Day on or before October 31, 2000. The duration of Offering Periods may be
changed pursuant to Section 4 of this Plan.

          (l) "Plan" shall mean this 2000 Employee Stock Purchase Plan.

          (m) "Purchase Price" shall mean an amount equal to 85% of the Fair
Market Value of a share of Common Stock on the Enrollment Date or on the
Exercise Date, whichever is lower; provided, however, that the Purchase Price
may be adjusted by the Board pursuant to Section 20.

          (n) "Reserves" shall mean the number of shares of Common Stock covered
by each option under the Plan which have not yet been exercised and the number
of shares of Common Stock which have been authorized for issuance under the Plan
but not yet placed under option.

          (o) "Subsidiary" shall mean a corporation, domestic or foreign, of
which not less than 50% of the voting shares are held by the Company or a
Subsidiary, whether or not such corporation now exists or is hereafter organized
or acquired by the Company or a Subsidiary.

                                     - 2 -
<PAGE>   3

          (p) "Trading Day" shall mean a day on which national stock exchanges
and the Nasdaq System are open for trading.

     3. Eligibility.

          (a) Any Employee who shall be employed by the Company on a given
Enrollment Date shall be eligible to participate in the Plan.

          (b) Any provisions of the Plan to the contrary notwithstanding, no
Employee shall be granted an option under the Plan (i) to the extent that,
immediately after the grant, such Employee (or any other person whose stock
would be attributed to such Employee pursuant to Section 424(d) of the Code)
would own capital stock of the Company and/or hold outstanding options to
purchase such stock possessing five percent (5%) or more of the total combined
voting power or value of all classes of the capital stock of the Company or of
any Subsidiary, or (ii) to the extent that his or her rights to purchase stock
under all employee stock purchase plans of the Company and its subsidiaries
accrues at a rate which exceeds Twenty-Five Thousand Dollars ($25,000) worth of
stock (determined at the fair market value of the shares at the time such option
is granted) for each calendar year in which such option is outstanding at any
time.

     4. Offering Periods. The Plan shall be implemented by consecutive Offering
Periods with a new Offering Period commencing on the first Trading Day on or
after May 1 and November 1 each year, or on such other date as the Board shall
determine, and continuing thereafter until terminated in accordance with Section
20 hereof; provided, however, that the first Offering Period under the Plan
shall commence with the first Trading Day on or after the date on which the
Securities and Exchange Commission declares the Company's Registration Statement
effective and ending on the last Trading Day on or before October 31, 2000. The
Board shall have the power to change the duration of Offering Periods (including
the commencement dates thereof) with respect to future offerings without
stockholder approval if such change is announced prior to the scheduled
beginning of the first Offering Period to be affected thereafter.

     5. Participation.

          (a) An eligible Employee may become a participant in the Plan by
completing a subscription agreement authorizing payroll deductions in the form
of Exhibit A to this Plan and filing it with the Company's payroll office prior
to the applicable Enrollment Date.

          (b) Payroll deductions for a participant shall commence on the first
payroll following the Enrollment Date and shall end on the last payroll in the
Offering Period to which such authorization is applicable, unless sooner
terminated by the participant as provided in Section 10 hereof.

     6. Payroll Deductions.

          (a) At the time a participant files his or her subscription agreement,
he or she shall elect to have payroll deductions made on each pay day during the
Offering Period in an amount not exceeding ten percent (10%) of the Compensation
which he or she receives on each pay day during the Offering Period.

                                     - 3 -
<PAGE>   4

          (b) All payroll deductions made for a participant shall be credited to
his or her account under the Plan and shall be withheld in whole percentages
only. A participant may not make any additional payments into such account.

          (c) A participant may discontinue his or her participation in the Plan
as provided in Section 10 hereof, or may increase or decrease the rate of his or
her payroll deductions during the Offering Period by completing or filing with
the Company a new subscription agreement authorizing a change in payroll
deduction rate. The Board may, in its discretion, limit the number of
participation rate changes during any Offering Period. The change in rate shall
be effective with the first full payroll period following five (5) business days
after the Company's receipt of the new subscription agreement unless the Company
elects to process a given change in participation more quickly. A participant's
subscription agreement shall remain in effect for successive Offering Periods
unless terminated as provided in Section 10 hereof.

          (d) Notwithstanding the foregoing, to the extent necessary to comply
with Section 423(b)(8) of the Code and Section 3(b) hereof, a participant's
payroll deductions may be decreased to zero percent (0%) at any time during an
Offering Period. Payroll deductions shall recommence at the rate provided in
such participant's subscription agreement at the beginning of the first Offering
Period which is scheduled to end in the following calendar year, unless
terminated by the participant as provided in Section 10 hereof.

          (e) At the time the option is exercised, in whole or in part, or at
the time some or all of the Company's Common Stock issued under the Plan is
disposed of, the participant must make adequate provision for the Company's
federal, state, or other tax withholding obligations, if any, which arise upon
the exercise of the option or the disposition of the Common Stock. At any time,
the Company may, but shall not be obligated to, withhold from the participant's
compensation the amount necessary for the Company to meet applicable withholding
obligations, including any withholding required to make available to the Company
any tax deductions or benefits attributable to sale or early disposition of
Common Stock by the Employee.

     7. Grant of Option. On the Enrollment Date of each Offering Period, each
eligible Employee participating in such Offering Period shall be granted an
option to purchase on the Exercise Date of such Offering Period (at the
applicable Purchase Price) up to a number of shares of the Company's Common
Stock determined by dividing such Employee's payroll deductions accumulated
prior to such Exercise Date and retained in the Participant's account as of the
Exercise Date by the applicable Purchase Price; provided that in no event shall
an Employee be permitted to purchase during each Offering Period more than
10,000 shares (subject to any adjustment pursuant to Section 19), and provided
further that such purchase shall be subject to the limitations set forth in
Sections 3(b) and 12 hereof. Exercise of the option shall occur as provided in
Section 8 hereof, unless the participant has withdrawn pursuant to Section 10
hereof. The Option shall expire on the last day of the Offering Period.

     8. Exercise of Option. Unless a participant withdraws from the Plan as
provided in Section 10 hereof, his or her option for the purchase of shares
shall be exercised automatically on the Exercise Date, and the maximum number of
full shares subject to option shall be purchased for such participant at the
applicable Purchase Price with the accumulated payroll deductions in his or her

                                     - 4 -
<PAGE>   5

account. No fractional shares shall be purchased; any payroll deductions
accumulated in a participant's account which are not sufficient to purchase a
full share shall be retained in the participant's account for the subsequent
Offering Period, subject to earlier withdrawal by the participant as provided in
Section 10 hereof. Any other monies left over in a participant's account after
the Exercise Date shall be returned to the participant. During a participant's
lifetime, a participant's option to purchase shares hereunder is exercisable
only by him or her.

     9. Delivery. As promptly as practicable after each Exercise Date on which a
purchase of shares occurs, the Company shall arrange the delivery to each
participant, as appropriate, the shares purchased upon exercise of his or her
option.

     10. Withdrawal.

          (a) A participant may withdraw all but not less than all the payroll
deductions credited to his or her account and not yet used to exercise his or
her option under the Plan at any time by giving written notice to the Company in
the form of Exhibit B to this Plan. All of the participant's payroll deductions
credited to his or her account shall be paid to such participant promptly after
receipt of notice of withdrawal and such participant's option for the Offering
Period shall be automatically terminated, and no further payroll deductions for
the purchase of shares shall be made for such Offering Period. If a participant
withdraws from an Offering Period, payroll deductions shall not resume at the
beginning of the succeeding Offering Period unless the participant delivers to
the Company a new subscription agreement.

          (b) A participant's withdrawal from an Offering Period shall not have
any effect upon his or her eligibility to participate in any similar plan which
may hereafter be adopted by the Company or in succeeding Offering Periods which
commence after the termination of the Offering Period from which the participant
withdraws.

     11. Termination of Employment. Upon a participant's ceasing to be an
Employee for any reason, he or she shall be deemed to have elected to withdraw
from the Plan and the payroll deductions credited to such participant's account
during the Offering Period but not yet used to exercise the option shall be
returned to such participant or, in the case of his or her death, to the person
or persons entitled thereto under Section 15 hereof, and such participant's
option shall be automatically terminated. The preceding sentence
notwithstanding, a participant who receives payment in lieu of notice of
termination of employment shall be treated as continuing to be an Employee for
the participant's customary number of hours per week of employment during the
period in which the participant is subject to such payment in lieu of notice.

     12. Interest. No interest shall accrue on the payroll deductions of a
participant in the Plan.

     13. Stock.

          (a) Subject to adjustment upon changes in capitalization of the
Company as provided in Section 19 hereof, the maximum number of shares of the
Company's Common Stock which shall be made available for sale under the Plan
shall be three hundred thousand (300,000) shares, plus an annual increase to be
added on the first day of the Company's fiscal year beginning in 2001 equal to
the lesser of (i) 300,000 shares, (ii) 1.5% of the outstanding shares on such
date, or (iii) a lesser

                                     - 5 -
<PAGE>   6

amount determined by the Board. If, on a given Exercise Date, the number of
shares with respect to which options are to be exercised exceeds the number of
shares then available under the Plan, the Company shall make a pro rata
allocation of the shares remaining available for purchase in as uniform a manner
as shall be practicable and as it shall determine to be equitable.

          (b) The participant shall have no interest or voting right in shares
covered by his option until such option has been exercised.

          (c) Shares to be delivered to a participant under the Plan shall be
registered in the name of the participant or in the name of the participant and
his or her spouse.

     14. Administration. The Plan shall be administered by the Board or a
committee of members of the Board appointed by the Board. The Board or its
committee shall have full and exclusive discretionary authority to construe,
interpret and apply the terms of the Plan, to determine eligibility and to
adjudicate all disputed claims filed under the Plan. Every finding, decision and
determination made by the Board or its committee shall, to the full extent
permitted by law, be final and binding upon all parties.

     15. Designation of Beneficiary.

          (a) A participant may file a written designation of a beneficiary who
is to receive any shares and cash, if any, from the participant's account under
the Plan in the event of such participant's death subsequent to an Exercise Date
on which the option is exercised but prior to delivery to such participant of
such shares and cash. In addition, a participant may file a written designation
of a beneficiary who is to receive any cash from the participant's account under
the Plan in the event of such participant's death prior to exercise of the
option. If a participant is married and the designated beneficiary is not the
spouse, spousal consent shall be required for such designation to be effective.

          (b) Such designation of beneficiary may be changed by the participant
at any time by written notice. In the event of the death of a participant and in
the absence of a beneficiary validly designated under the Plan who is living at
the time of such participant's death, the Company shall deliver such shares
and/or cash to the executor or administrator of the estate of the participant,
or if no such executor or administrator has been appointed (to the knowledge of
the Company), the Company, in its discretion, may deliver such shares and/or
cash to the spouse or to any one or more dependents or relatives of the
participant, or if no spouse, dependent or relative is known to the Company,
then to such other person as the Company may designate.

     16. Transferability. Neither payroll deductions credited to a participant's
account nor any rights with regard to the exercise of an option or to receive
shares under the Plan may be assigned, transferred, pledged or otherwise
disposed of in any way (other than by will, the laws of descent and distribution
or as provided in Section 15 hereof) by the participant. Any such attempt at
assignment, transfer, pledge or other disposition shall be without effect,
except that the Company may treat such act as an election to withdraw funds from
an Offering Period in accordance with Section 10 hereof.

                                     - 6 -
<PAGE>   7

     17. Use of Funds. All payroll deductions received or held by the Company
under the Plan may be used by the Company for any corporate purpose, and the
Company shall not be obligated to segregate such payroll deductions.

     18. Reports. Individual accounts shall be maintained for each participant
in the Plan. Statements of account shall be given to participating Employees at
least annually, which statements shall set forth the amounts of payroll
deductions, the Purchase Price, the number of shares purchased and the remaining
cash balance, if any.

     19. Adjustments Upon Changes in Capitalization, Dissolution, Liquidation,
Merger or Asset Sale.

          (a) Changes in Capitalization. Subject to any required action by the
stockholders of the Company, the Reserves, the maximum number of shares each
participant may purchase per Offering Period (pursuant to Section 7), as well as
the price per share and the number of shares of Common Stock covered by each
option under the Plan which has not yet been exercised shall be proportionately
adjusted for any increase or decrease in the number of issued shares of Common
Stock resulting from a stock split, reverse stock split, stock dividend,
combination or reclassification of the Common Stock, or any other increase or
decrease in the number of shares of Common Stock effected without receipt of
consideration by the Company; provided, however, that conversion of any
convertible securities of the Company shall not be deemed to have been "effected
without receipt of consideration." Such adjustment shall be made by the Board,
whose determination in that respect shall be final, binding and conclusive.
Except as expressly provided herein, no issuance by the Company of shares of
stock of any class, or securities convertible into shares of stock of any class,
shall affect, and no adjustment by reason thereof shall be made with respect to,
the number or price of shares of Common Stock subject to an option.

          (b) Dissolution or Liquidation. In the event of the proposed
dissolution or liquidation of the Company, the Offering Period then in progress
shall be shortened by setting a new Exercise Date (the "New Exercise Date"), and
shall terminate immediately prior to the consummation of such proposed
dissolution or liquidation, unless provided otherwise by the Board. The New
Exercise Date shall be before the date of the Company's proposed dissolution or
liquidation. The Board shall notify each participant in writing, at least ten
(10) business days prior to the New Exercise Date, that the Exercise Date for
the participant's option has been changed to the New Exercise Date and that the
participant's option shall be exercised automatically on the New Exercise Date,
unless prior to such date the participant has withdrawn from the Offering Period
as provided in Section 10 hereof.

          (c) Merger or Asset Sale. In the event of a proposed sale of all or
substantially all of the assets of the Company, or the merger of the Company
with or into another corporation, each outstanding option shall be assumed or an
equivalent option substituted by the successor corporation or a Parent or
Subsidiary of the successor corporation. In the event that the successor
corporation refuses to assume or substitute for the option, the Offering Period
then in progress shall be shortened by setting a new Exercise Date (the "New
Exercise Date"). The New Exercise Date shall be before the date of the Company's
proposed sale or merger. The Board shall notify each participant in writing, at
least ten (10) business days prior to the New Exercise Date, that the Exercise
Date for the participant's option has been changed to the New Exercise Date and
that the participant's option shall

                                     - 7 -
<PAGE>   8

be exercised automatically on the New Exercise Date, unless prior to such date
the participant has withdrawn from the Offering Period as provided in Section 10
hereof.

     20. Amendment or Termination.

          (a) The Board of Directors of the Company may at any time and for any
reason terminate or amend the Plan. Except as provided in Section 19 hereof, no
such termination can affect options previously granted, provided that an
Offering Period may be terminated by the Board of Directors on any Exercise Date
if the Board determines that the termination of the Offering Period or the Plan
is in the best interests of the Company and its stockholders. Except as provided
in Section 19 and Section 20 hereof, no amendment may make any change in any
option theretofore granted which adversely affects the rights of any
participant. To the extent necessary to comply with Section 423 of the Code (or
any other applicable law, regulation or stock exchange rule), the Company shall
obtain shareholder approval in such a manner and to such a degree as required.

          (b) Without stockholder consent and without regard to whether any
participant rights may be considered to have been "adversely affected," the
Board (or its committee) shall be entitled to change the Offering Periods, limit
the frequency and/or number of changes in the amount withheld during an Offering
Period, establish the exchange ratio applicable to amounts withheld in a
currency other than U.S. dollars, permit payroll withholding in excess of the
amount designated by a participant in order to adjust for delays or mistakes in
the Company's processing of properly completed withholding elections, establish
reasonable waiting and adjustment periods and/or accounting and crediting
procedures to ensure that amounts applied toward the purchase of Common Stock
for each participant properly correspond with amounts withheld from the
participant's Compensation, and establish such other limitations or procedures
as the Board (or its committee) determines in its sole discretion advisable
which are consistent with the Plan.

          (c) In the event the Board determines that the ongoing operation of
the Plan may result in unfavorable financial accounting consequences, the Board
may, in its discretion and, to the extent necessary or desirable, modify or
amend the Plan to reduce or eliminate such accounting consequence including, but
not limited to:

               (1) altering the Purchase Price for any Offering Period including
an Offering Period underway at the time of the change in Purchase Price;

               (2) shortening any Offering Period so that Offering Period ends
on a new Exercise Date, including an Offering Period underway at the time of the
Board action; and

               (3) allocating shares.

     Such modifications or amendments shall not require stockholder approval or
the consent of any Plan participants.

     21. Notices. All notices or other communications by a participant to the
Company under or in connection with the Plan shall be deemed to have been duly
given when received in the form specified by the Company at the location, or by
the person, designated by the Company for the receipt thereof.

                                     - 8 -
<PAGE>   9

     22. Conditions Upon Issuance of Shares. Shares shall not be issued with
respect to an option unless the exercise of such option and the issuance and
delivery of such shares pursuant thereto shall comply with all applicable
provisions of law, domestic or foreign, including, without limitation, the
Securities Act of 1933, as amended, the Securities Exchange Act of 1934, as
amended, the rules and regulations promulgated thereunder, and the requirements
of any stock exchange upon which the shares may then be listed, and shall be
further subject to the approval of counsel for the Company with respect to such
compliance.

     As a condition to the exercise of an option, the Company may require the
person exercising such option to represent and warrant at the time of any such
exercise that the shares are being purchased only for investment and without any
present intention to sell or distribute such shares if, in the opinion of
counsel for the Company, such a representation is required by any of the
aforementioned applicable provisions of law.

     23. Term of Plan. The Plan shall become effective upon the earlier to occur
of its adoption by the Board of Directors or its approval by the stockholders of
the Company. It shall continue in effect for a term of ten (10) years unless
sooner terminated under Section 20 hereof.

                                     - 9 -
<PAGE>   10

                                    EXHIBIT A

                           INTROGEN THERAPEUTICS INC.

                        2000 EMPLOYEE STOCK PURCHASE PLAN

                             SUBSCRIPTION AGREEMENT

          Original Application                      Enrollment Date:
---------                                                           ------------
          Change in Payroll Deduction Rate
---------
          Change of Beneficiary(ies)
---------

1.   _____________________________________ hereby elects to participate in the
     Introgen Therapeutics Inc. 2000 Employee Stock Purchase Plan (the "Employee
     Stock Purchase Plan") and subscribes to purchase shares of the Company's
     Common Stock in accordance with this Subscription Agreement and the
     Employee Stock Purchase Plan.

2.   I hereby authorize payroll deductions from each paycheck in the amount of
     ____% of my Compensation on each payday (from 0 to 10%) during the Offering
     Period in accordance with the Employee Stock Purchase Plan. (Please note
     that no fractional percentages are permitted.)

3.   I understand that said payroll deductions shall be accumulated for the
     purchase of shares of Common Stock at the applicable Purchase Price
     determined in accordance with the Employee Stock Purchase Plan. I
     understand that if I do not withdraw from an Offering Period, any
     accumulated payroll deductions will be used to automatically exercise my
     option.

4.   I have received a copy of the complete Employee Stock Purchase Plan. I
     understand that my participation in the Employee Stock Purchase Plan is in
     all respects subject to the terms of the Plan. I understand that my ability
     to exercise the option under this Subscription Agreement is subject to
     stockholder approval of the Employee Stock Purchase Plan.

5.   Shares purchased for me under the Employee Stock Purchase Plan should be
     issued in the name(s) of (Employee or Employee and Spouse only):
     ______________________________.

6.   I understand that if I dispose of any shares received by me pursuant to the
     Plan within 2 years after the Enrollment Date (the first day of the
     Offering Period during which I purchased such shares), I will be treated
     for federal income tax purposes as having received ordinary income at the
     time of such disposition in an amount equal to the excess of the fair
     market value of the shares at the time such shares were purchased by me
     over the price which I paid for the shares. I hereby agree to notify the
     Company in writing within 30 days after the date of any disposition of
     shares and I will make adequate provision for Federal, state or other tax
     withholding obligations, if any, which arise upon the disposition of the
     Common Stock. The Company may, but will not be obligated to, withhold from
     my compensation the amount necessary to meet any applicable withholding
     obligation including any withholding necessary

<PAGE>   11

     to make available to the Company any tax deductions or benefits
     attributable to sale or early disposition of Common Stock by me. If I
     dispose of such shares at any time after the expiration of the 2-year
     holding period, I understand that I will be treated for federal income tax
     purposes as having received income only at the time of such disposition,
     and that such income will be taxed as ordinary income only to the extent of
     an amount equal to the lesser of (1) the excess of the fair market value of
     the shares at the time of such disposition over the purchase price which I
     paid for the shares, or (2) 15% of the fair market value of the shares on
     the first day of the Offering Period. The remainder of the gain, if any,
     recognized on such disposition will be taxed as capital gain.

7.   I hereby agree to be bound by the terms of the Employee Stock Purchase
     Plan. The effectiveness of this Subscription Agreement is dependent upon my
     eligibility to participate in the Employee Stock Purchase Plan.

8.   In the event of my death, I hereby designate the following as my
     beneficiary(ies) to receive all payments and shares due me under the
     Employee Stock Purchase Plan:

         NAME:  (Please print)          ----------------------------------------
                                        (First)        (Middle)       (Last)

         --------------------------     ----------------------------------------
         Relationship

                                        ----------------------------------------
                                                     (Address)

         Employee's Social
         Security Number:               ----------------------------------------

         Employee's Address:            ----------------------------------------

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

                                      - 2 -
<PAGE>   12

I UNDERSTAND THAT THIS SUBSCRIPTION AGREEMENT SHALL REMAIN IN EFFECT THROUGHOUT
SUCCESSIVE OFFERING PERIODS UNLESS TERMINATED BY ME.

Dated:
       -------------------

                           -----------------------------------------------------
                           Signature of Employee

                           -----------------------------------------------------
                           Spouse's Signature (If beneficiary other than spouse)

                                      - 3 -
<PAGE>   13

                                    EXHIBIT B

                           INTROGEN THERAPEUTICS INC.

                        2000 EMPLOYEE STOCK PURCHASE PLAN

                              NOTICE OF WITHDRAWAL

     The undersigned participant in the Offering Period of the Introgen
Therapeutics Inc. 2000 Employee Stock Purchase Plan which began on ___________,
______ (the "Enrollment Date") hereby notifies the Company that he or she hereby
withdraws from the Offering Period. He or she hereby directs the Company to pay
to the undersigned as promptly as practicable all the payroll deductions
credited to his or her account with respect to such Offering Period. The
undersigned understands and agrees that his or her option for such Offering
Period will be automatically terminated. The undersigned understands further
that no further payroll deductions will be made for the purchase of shares in
the current Offering Period and the undersigned shall be eligible to participate
in succeeding Offering Periods only by delivering to the Company a new
Subscription Agreement.

                                          Name and Address of Participant:

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

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

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

                                          Signature:

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

                                          Date:
                                                --------------------------------

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