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                                                                EXHIBIT 10.18(c)

                    AMENDMENT #2 TO THE EMPLOYMENT AGREEMENT
                                    BETWEEN
                          INTROGEN THERAPEUTICS, INC.
                                      AND
                                 DAVID G. NANCE

         Introgen Therapeutics, Inc. ("Company") and David G. Nance ("Employee")
hereby agree to the following amendments to the Employment Agreement
("Employment Agreement") dated August 1, 1996, between Company and Employee,
which Employment Agreement was previously amended by Amendment #1 effective as
of August 1, 1998:

         Paragraph 2, providing the term of the Agreement ("Term") is amended
as follows:

         The date "July 31, 1999," set forth in the first sentence of Paragraph
         2, is changed to "July 31, 2003." The remainder of Paragraph 2 shall
         remain in full force and effect.

         Paragraph 3 is deleted and replaced with the following new paragraph 3:

         "3. COMPENSATION. Employee shall receive an aggregate base salary at
         the rate of $275,000 per annum until July 31, 2000. Employee's base
         salary will be raised by 10% effective August 1, 2000, by an
         additional 10% effective August 1, 20001, and by an additional 10%
         effective August 1, 2002. Employee will be granted options to purchase
         50,000 shares of the Corporation's common stock pursuant to the
         Company's 2000 Stock Plan on August 1, 2000, August 1, 2001, and
         August 1, 2002 (for a total of 150,000 shares). Such options will be
         exercisable at a price determined by the Plan Administrator, but no
         greater than the fair market value of the underlying shares on the
         date of each grant, and will vest in full when granted. Installments
         of base salary shall be paid not less often than bi-weekly. Employee
         may be paid bonuses (in stock, cash or other consideration) from
         time-to-time as determined by the Board of Directors or the
         Compensation Committee."

         This Amendment #2 is conditioned upon and shall become effective upon
closing for an Initial Public Offering of the Company's securities.

         Except as amended herein, the Employment Agreement shall continue in
full force and effect.

         Signed this 15th day of February, 2000.

                                      COMPANY:

                                      INTROGEN THERAPEUTICS, INC.

                                      By: /s/ JAMES W. ALBRECHT, JR.
                                          --------------------------------------
                                          James W. Albrecht, Jr., Vice President
                                          and Chief Financial Officer

                                      EMPLOYEE:

                                      /s/ DAVID G. NANCE
                                      ------------------------------------------
                                      David G. Nance<PAGE>   1
                                                                 EXHIBIT 10.19

                                SERVICE AGREEMENT

         This Service Agreement ("Agreement") is entered into by and between
Intron Therapeutics, Inc., a Delaware corporation, ("Intron") and Domecq
Technologies, Inc., a Texas corporation ("Domecq").

         1. Term of Service. Intron hereby employs Domecq and Domecq hereby
accepts retainer with Intron beginning on July 1, 1994, the ("Commencement
Date") and ending on the earlier of the third anniversary of the Commencement
Date or termination of this agreement as provided in Section 6 hereof. This
Agreement shall be automatically renewed for an additional one year term upon
the third anniversary and each subsequent anniversary hereof, unless either
party gives notice of termination before such anniversary.

         2. Duties and Responsibilities. During the term hereof, Domecq shall be
retained to provide services by and for the benefit of Intron. Domecq agrees to
provide the services of David G. Nance ("Nance") to serve Intron as president
and chief executive officer, or in such other capacity as designated by Intron's
board of directors. Nance shall devote such time and attention as Nance
determines may in good faith be required by Intron for the performance of those
duties designated by Intron from time to time, which duties shall initially
include managing and operating the corporation. Intron recognizes that Nance is
engaged in other business activities, including, but not limited to, serving as
managing partner of Texas Biomedical Development Partners, as officer and
director of Technology Capital Corporation, President of Domecq Technologies,
Inc., and as an officer, director, partner or trustee of other entities. Nance
shall be permitted to continue these activities.

         3. Compensation. Domecq shall receive and Intron shall pay to Domecq
during the term of this Agreement the amount of $175,000 per calendar year,
payable in semi-monthly installments. Upon mutual agreement by Intron and
Domecq, all or part of said compensation may be paid in Intron's stock or
options for such stock, at such valuation as may be agreed by the parties.
Failure of Intron to pay any amount due hereunder shall not be deemed a waiver
of such payment, which amount shall accrue and continue as a liability of Intron
to Domecq.

         4. Business Expenses. Domecq or Nance shall be reimbursed for
reasonable business expenses incurred in the performance of services hereunder
at such times and in such amounts as shall be determined to be reasonable by
Intron. Domecq or Nance shall keep accurate records and receipts reflecting
expenses so incurred and shall furnish Intron with any and all supporting
documentation of such expenses at the request of Intron.

         5. Vacations and Sick Leave. During the term of this Agreement, Nance
shall be entitled to reasonable periods of vacation and sick leave with full
payment as determined by Intron from time to time.

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         6. Termination of Agreement.

            a . This Agreement and Domecq's retainer with Intron shall terminate
            upon the occurrence of any of the following events:

                 (i)   Termination by Intron for a cause;

                (ii)   Death of Nance; or

               (iii)   Permanent Disability (as defined herein) of Nance.

            b. For purposes of this Section 6, termination "for cause" shall
            include:

                 (i)   Willful misconduct or breach of his fiduciary duties to
                       Intron established by clear and convincing evidence;

                (ii)   intentional failure to perform stated duties;

               (iii)   willful and knowing violation of any law, rule, or
                       regulation involving moral turpitude; or

                (iv)   A material and intentional breach of any provision of
                       this Agreement.

            c. For purposes of this Section 6, "Permanent Disability" shall mean
when the Intron in its reasonable discretion shall find, on the basis of clear
and convincing medical evidence, that Nance, because of a mental or physical
condition, is unable to carry out the duties of his employment with Intron and
that such condition will in reasonable medical probability continue during the
remainder of Nance's life.

         7. Non-Disclosure Agreement. Domecq and Nance hereby expressly
acknowledge that pursuant to this Service Agreement, Domecq or Nance may obtain
or be given access to certain information, documents and records of a
confidential or proprietary nature with respect to the Intron and its business,
prospects, licensors, customers, agents competitors and suppliers. Domecq and
Nance further acknowledge that the unauthorized use or disclosure of any such
information both during and after the term of this Agreement could seriously
damage and interfere with Intron's business and business prospects. Accordingly,
Domecq and Nance hereby expressly covenant and agree with Intron, that Domecq
and Nance are in a fiduciary relationship with Intron, and as such, shall treat
all information, records and confidences, including but not limited to prospect
and customer lists, computer software and programs, contracts (including this
Agreement) patent applications, patents and all other written documents
pertaining to any business of Intron, and any other agreements between Intron
and its respective employees, agents, or contractors, all support data related
to or used in conjunction with the business of Intron, and any other information
which Intron has provided to or which Domecq or Nance may obtain or generate or
may have already obtained or generated in organizing and starting Intron or in
fulfilling Domecq's services under this

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Agreement as CONFIDENT AND PROPRIETARY in nature. Domecq and Nance further
covenant and agree not to copy, reproduce, disclose or distribute any such
materials or information at any time without Intron's prior written consent,
which consent may be withdrawn at any time. Domecq further agrees that upon
termination of this Agreement Domecq and Nance will not at any time disclose to
any third party any of the information described above. Domecq agrees that all
of the aforementioned information and materials are the exclusive property of
Intron and agrees not to use or disclose such confidential information at any
time either prior to or after the termination of this Agreement except as
specifically provided for herein. Domecq agrees that Intron shall be entitled to
an injunction to restrain Domecq and Nance from the commission of any of the
acts prohibited by this paragraph; provided, however, that nothing herein shall
be construed as prohibiting Intron from pursuing any other remedies available to
it for any breach or any threatened breach by Domecq of the provisions of this
paragraph and the fiduciary relationship described herein. This covenant shall
be effective immediately upon execution hereof, and shall be applicable to all
such documents and information given or disclosed to Domecq prior to or after
the date of execution hereof.

         8. Indemnity. Should any claim or cause of action be asserted against
Domecq arising out of or in connection with any act or omission of Domecq or
Nance which occurs during or as a result of performance by Domecq or Nance of
duties and provided that the act or omission occurred or is alleged to have
occurred while Domecq or Nance were acting in good faith within the scope of
service to Intron, and not contrary to any instructions or policy of Intron,
Intron will indemnify and hold harmless Domecq and Nance from all reasonable
costs and expenses incurred in connection with such claim, including, but not
limited to, attorney's fees and costs of court.

         9. Entire Agreement. This Agreement supersedes any and all other
agreements, either oral or written, between the parties hereto with respect to
the subject matter hereof and contains all of the covenants and agreements
between the parties with respect hereto.

         10. Modification. No change or modification of this Agreement shall be
valid or binding upon the parties hereto, nor shall any waiver of any term or
condition in the future be so binding, unless such change or modification or
waiver shall be in writing and signed by the parties hereto.

         11. Governing Law. This Agreement and the rights and obligations of the
parties hereto, shall be governed by and construed in accordance with the laws
of the State of Texas shall be performable in Travis County, Texas.

         12. Counterparts. This Agreement may be executed in counterparts, each
of which shall constitute an original, but all of which shall constitute one in
the same document.

         13. Costs. If any action at law or in equity is necessary to enforce or
interpret the terms of this Agreement, the prevailing party shall be entitled to
reasonable attorney's fees, costs and necessary disbursements in addition to any
other relief to which he or it may be entitled.

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         14. Estate. If Nance dies prior to the expiration of the term of
employment, any moneys or corporate shares that may be due him from the Intron
under this Agreement as of the date of his death shall be paid to Domecq.

         15. Assignment. Intron shall have the right to assign this Agreement to
its successors or assigns, provided that all covenants and agreements contained
herein shall be enforceable against Intron's successors or assigns. The terms
"successors" and "assigns" shall include any person, corporation, partnership or
other entity that buys all or substantially all of Intron's assets or all of its
stock, or with which Intron merges or consolidates. The rights, duties and
benefits to Domecq hereunder are personal to Domecq, and no such right or
benefit may be assigned by Domecq.

         16. Binding Effect. This Agreement shall be binding upon the parties
hereto, together with their respective executors, administrators, successors,
personal representatives, heirs and assigns.

         17. Waiver of Breach. The waiver by a party of a breach of any
provision of this Agreement shall not operate or be construed as a waiver of any
subsequent breach.

         IN WITNESS WHEREOF, the parties hereto have executed this Agreement to
be effective July 1, 1994, (the "Commencement Date").

                                         INTRON THERAPEUTICS, INC.

                                         By: /s/ JOHN N. KAPOOR
                                             -----------------------------------
                                                 John N. Kapoor, Director

                                         DOMECQ TECHNOLOGIES, INC.

                                         By: /s/ DAVID G. NANCE
                                             -----------------------------------
                                                 David G. Nance, President

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