<PAGE>

                                                                 EXHIBIT 10.7(f)

      NOTICE OF CONFIDENTIALITY RIGHTS: IF YOU ARE A NATURAL PERSON, YOU MAY
      REMOVE OR STRIKE ANY OF THE FOLLOWING INFORMATION FROM THIS INSTRUMENT
      BEFORE IT IS FILED FOR RECORD IN THE PUBLIC RECORDS: YOUR SOCIAL SECURITY
      NUMBER OR YOUR DRIVER'S LICENSE NUMBER.

                             MODIFICATION AGREEMENT

STATE OF TEXAS

COUNTY OF HARRIS

      WHEREAS, TMX REALTY CORPORATION, a Delaware corporation, whose address is
301 Congress Avenue, Suite 1850, Austin, Texas 78701 ("Maker"), is legally
obligated to pay the unpaid principal balance of that certain Promissory Note
(the "Promissory Note") dated November 23, 1998 in the original principal amount
of SIX MILLION AND NO/100 DOLLARS ($6,000,000.00), executed by Maker and payable
to the order of Riverway Bank (now known as TEXAS STATE BANK) ("Payee"), more
fully described in and secured by the liens created by (1) that certain
Leasehold Deed of Trust (the "Deed of Trust") of even date with the Promissory
Note from Maker to John E. Phillips, Trustee, filed of record under Clerk's File
No. T418083, Official Public Records of Real Property of Harris County, Texas,
and (2) an Assignment of Leases (Space Lease) of even date with the Promissory
Note, executed by Maker in favor of Payee, filed of record under Clerk's File
No. T418084, Official Public Records of Real Property of Harris County, Texas,
the Promissory Note being secured by the liens therein created or mentioned
against the property described in Exhibit "A" attached hereto (the "Property");

      WHEREAS, Maker now desires to increase, modify and renew the Promissory
Note and to extend and carry forward all of the aforementioned liens on the
Property, together with all other liens and security interests, securing the
payment of the Promissory Note (said liens and security interests being
hereinafter collectively referred to as the "Liens");

      WHEREAS, Payee hereby appoints James D. Maclntyre, Trustee, as successor
trustee to John E. Phillips, Trustee, with the said James D. Maclntyre , Trustee
to act instead of and to succeed to all of the rights and powers of the said
John E. Phillips, Trustee;

      WHEREAS, Payee, the legal owner and holder of the Promissory Note and the
Liens, in consideration of the premises and at the request of Maker, has agreed
to modify and renew the Promissory Note (the Promissory Note, as hereinafter
modified and renewed, being referred to as the "Note") as hereinafter provided:

      NOW, THEREFORE, in. consideration of the modification and renewal of the
Promissory Note as hereinafter set forth, Maker hereby renews the Promissory
Note and promises to pay to the order of Payee at its banking house in the City
of Houston, Harris County, Texas, in lawful money of the United States of
America, the sum of SEVEN MILLION EIGHT HUNDRED THOUSAND AND NO/100 DOLLARS
($7,800,000.00), together with interest on the unpaid principal balance hereof
from time to time outstanding until maturity at a rate per annum equal to six
and one quarter percent (6.25%). The rate from time to time in effect on the
Note, including during the Option Period (as hereinafter defined) is herein
referred to as the "Stated Rate". In no event shall interest on the Note ever be
charged or paid at a rate greater than the maximum non-usurious rate permitted
by applicable federal or Texas law from time to time in effect, whichever shall
permit the higher lawful rate (the "Highest Lawful Rate").

      If at any time or times the Stated Rate would exceed the Highest Lawful
Rate but for the limitation set forth above, the rate of interest to accrue on
the unpaid principal balance of the Note during all such times shall be limited
to the Highest Lawful Rate, but any subsequent reduction in the Stated Rate due
to reductions in the rate from time to time applicable to the Note shall not
become effective to reduce the interest rate payable below the Highest

<PAGE>

Lawful Rate until the total amount of interest accrued on the unpaid balance of
the Note equals the total amount of interest which would have accrued if the
Stated Rate had at all times been in effect.

      If, at maturity or final payment of the Note, the total amount of interest
paid or accrued under the foregoing provisions is less than the total amount of
interest which would have accrued if the Stated Rate had at all times been in
effect, then Maker agrees to pay to Payee, to the extent allowed by law, an
amount equal to the difference between (a) the lesser of (i) the amount of
interest which would have accrued on the Note if the Highest Lawful Rate had at
all times been in effect, or (ii) the amount of interest which would have
accrued if the Stated Rate had at all times been in effect, and (b) the amount
of interest accrued in accordance with the other provisions of the Note.

      Interest shall be computed on the basis of the actual number of days
elapsed in a year composed of 360 days; however, if such computation would cause
the Stated Rate to exceed the Highest Lawful Rate, interest shall be computed on
the basis of a year composed of 365 or 366 days, as the case maybe. At all such
times, if any, as Texas law shall establish the Highest Lawful Rate, the Highest
Lawful Rate shall be the "indicated rate ceiling" (as defined in V.T.C.A.,
Finance Code, Chapter 303, as amended) from time to time in effect; provided
that Payee may also rely on alternative maximum rates of interest from time to
time in effect under other applicable laws, if they are higher.

      The Note is payable as follows:

      Principal together with accrued interest shall be due and payable in
monthly installments in the amount of Fifty-Six Thousand Four Hundred and No/100
($56,400.00) each, on the 1st day of each and every calendar month, commencing
June 1, 2004, and continuing regularly and monthly thereafter until the
expiration of two (2) years from the date hereof (the "Final Maturity Date"),
when the entire amount of the Note, both principal and accrued interest then
remaining unpaid, shall be due and payable in full. Payments shall be first
applied to accrued interest with the balance to the reduction of principal.

      Anything in the Note to the contrary notwithstanding, upon the Final
Maturity Date of the Note and so long as an Event of Default (as defined in the
Loan Agreement) does not then exist, Borrower shall have the option to extend
the term of the Note until November 30, 2009 (the "Option Period"), subject to
the following terms and conditions:

      1.    On or before thirty (30) days prior to the Final Maturity Date,
            Borrower shall provide Lender with notice (the "Option Notice") of
            its intent to extend the Final Maturity Date to the Extended
            Maturity Date (as hereinafter defined).

      2.    The Option Period shall commence as of the Final Maturity Date and
            shall expire on November 30, 2009 (the "Extended Maturity Date"). On
            the Extended Maturity Date, the entire balance of the Note,
            principal together with unpaid accrued interest, shall be due and
            payable in full.

      3.    During the Option Period, the Note shall bear interest per annum at
            the rate fixed as of the close of business on the Final Maturity
            Date that is the lesser of (1) the 5 Year Treasury Bond Note as
            published in the Wall Street Journal plus 250 basis points, or (2)
            eight and one-half percent (8.5%).

      4.    During the Option Period principal and interest shall be due and
            payable in equal monthly installments (the "Monthly Payments")
            commencing one (1) month from the Final Maturity Date and continuing
            regularly and monthly thereafter until the Extended Maturity Date.
            The amount of the Monthly Payments shall be fixed as of the Final
            Maturity. The Monthly Payments shall be based on an amortization of
            the principal amount of the Note as of the Final Maturity Date over
            a two hundred twenty-five (225) month period at the interest rate in
            effect on the Final Maturity Date. The Monthly Payments shall be in
            the same amount each month during the Option Period and not subject
            to adjustment.

                                        2

<PAGE>

      The Note may be prepaid in whole or in part at any time without penalty;
provided, however, that all payments received by Payee from Maker upon the Note
shall first be applied to the payment of accrued but unpaid interest, with the
balance thereof to be applied to the reduction of the outstanding principal of
the Note. All prepayments in excess of accrued interest shall be applied to the
outstanding principal balance of the Note in the inverse order of maturity.

      Whenever any payment to be made under the Note shall be stated to be due
on a Saturday, Sunday or legal holiday for commercial banks under the laws of
the State of Texas, then such payment shall be made on the next succeeding
business day.

      In addition to all principal and accrued interest on the Note, Maker
agrees to pay (a) all reasonable costs and expenses incurred by all owners and
holders of the Note in collecting the Note through probate, reorganization,
bankruptcy or any other proceeding, (b) the reasonable attorneys' fees when and
if the Note is placed in the hands of an attorney for collection after default,
and (c) the reasonable attorneys' fees, costs and expenses incurred by Payee in
connection with the preparation and filing of the agreements and documents
contemplated herein.

      Unless as otherwise provided by law, Maker and any and all co-makers,
endorsers, guarantors and sureties severally waive notice (including, but not
limited to, notice of protest, notice of dishonor and notice of intent to
accelerate and notice of acceleration), demand, presentment for payment, protest
and the filing of suit for the purpose of fixing liability and consent that the
time of payment hereof may be extended and re-extended from time to time without
notice to them or any of them, and each agrees that his, her or its liability on
or with respect to the Note shall not be affected by any release of or change in
any security at any time existing or by any failure to perfect or to maintain
perfection of any lien on or security interest in any such security.

      Maker warrants and represents to Payee, and to all other owners and
holders of any indebtedness evidenced hereby, that the loan evidenced by the
Note is and shall be solely for business, commercial or agricultural purposes
and not primarily for personal, family or household use. Maker acknowledges that
the loan evidenced by the Note is specifically exempted under Section 226.3(a)
of Regulation Z issued by the Board of Governors of the Federal Reserve System
and under the Truth-in-Lending Act and that no disclosures are required to be
given under such regulations and federal laws in connection with the Note.

      It is agreed that time is of the essence of this agreement, and that in
the event of default in the payment of any installment of principal or interest
when due, the holder of the Note may declare the unpaid principal balance plus
all accrued but unpaid interest due thereon immediately due and payable without
notice, and failure to exercise said option shall not constitute a waiver on the
part of the holder of the right to exercise the same at any other time.

      In the event of (i) the failure of Maker to make any payment in the Note
provided when due (either of principal and/or interest), or (ii) in the event
the entirety of the unpaid principal balance of the Note plus accrued unpaid
interest thereon is declared due, interest on such past-due indebtedness (either
principal and/or interest) shall accrue at the Highest Lawful Rate.

      All agreements between Maker and Payee, whether now existing or hereafter
arising and whether written or oral, are hereby expressly limited so that in no
event, whether by reason of acceleration of maturity hereof or otherwise, shall
the amount paid or agreed to be paid to Payee for the use, forbearance or
detention of the money to be loaned under the Note or otherwise exceed the
Highest Lawful Rate. If fulfillment of any provision hereof or of any mortgage,
loan agreement or other document evidencing or securing the indebtedness
evidenced by the Note, at the time performance of such provision shall be due,
shall involve transcending the limit of validity prescribed by law, then, ipso
facto, the obligation to be fulfilled shall be reduced to the limit of such
validity; and if Payee shall ever receive anything of value deemed interest
under applicable law which would exceed interest at the Highest Lawful Rate, an
amount equal to any excessive interest shall be applied to the reduction of the
principal amount owing under the Note and not to the payment of interest, or if
such excessive interest exceeds the unpaid balance of principal of the Note,
such excess shall be refunded to Maker. All sums paid or agreed to be paid to
Payee for the use, forbearance or detention of the indebtedness of Maker to
Payee shall, to the extent permitted by applicable law, be amortized, prorated,
allocated and spread throughout the full term of such indebtedness until payment
in full so that the rate of interest on account of such indebtedness is uniform
throughout the term thereof. The provisions of this paragraph shall control all
agreements between Maker and Payee.

                                        3

<PAGE>

      Maker hereby extends the Liens to secure the payment of the Note, until
the same has been fully paid and agrees that the modification, renewal and
extension of the Promissory Note shall in no manner affect or impair the Note or
the Liens securing the same and that the Liens shall not in any manner be
waived, except as otherwise expressly provided herein, the purpose of this
instrument being simply to modify and renew the Promissory Note and to carry
forward or extend the Liens, which are acknowledged by Maker to be valid and
subsisting, and Maker further agrees that all terms and provisions of the
Promissory Note and of the instrument or instruments creating or fixing the
Liens securing the same shall be and remain in full force and effect as therein
written, except as otherwise expressly provided herein.

      None of the rights, titles, liens, interests, securities or equities
existing or to exist under the Deed of Trust in law or in equity are or shall be
in anywise released, diminished, impaired or affected hereby. The Deed of Trust
is recognized to be still in full force and effect insofar as to cover all of
the properties described therein, except for portions of the Property that have
been heretofore released by Payee as evidenced by partial releases filed with
the County Clerk of said County and all rights and liens existing and to exist
under the Deed of Trust as modified hereby are renewed, extended, carried
forward and conveyed by Maker to secure any and all indebtedness of Maker to
Payee.

      Maker expressly covenants, represents and warrants that Maker is the owner
and holder of good and valid title to all of the Property, free and clear of all
liens and encumbrances other than those existing unto and in favor of Payee;
that all costs, expenses and taxes due and owing to date against or with respect
to any and all of the Property have been paid to date and that Maker has the
absolute, unrestricted right and authority to mortgage, assign and convey all of
the Property and any proceeds resulting therefrom to Payee.

      Maker will pay all fees or costs for appraisals that Payee may reasonably
require from time to time, but in no event more than one appraisal annually. In
addition, Maker will pay all recording fees, taxes, abstract fees, attorneys'
fees and all other costs and expenses of every character from time to time
incurred in connection with the making, closing and servicing of the loan
evidenced by the Note, or any renewal, modification, rearrangement or extension
thereof and will pay all reasonable fees and charges made by the Trustee for
services performed under the Deed of Trust and will reimburse Payee and the
Trustee for all expenses incurred by them, respectively, and will indemnify and
hold harmless Payee and the Trustee from and against all claims, demands,
liabilities and causes of action asserted against either of them on account of
any act performed or omitted to be performed hereunder or on account of any
transaction arising out of or in any way connected with the Property or the Deed
of Trust, save and except for their willful misconduct. In the event that Payee
should pay for expenses incurred in way of attorneys' fees in connection with
title examination and legal matters and/or appraisal fees or costs connected
with the making, closing or servicing the Note or any renewal, modification,
rearrangement or extension thereof, or pay any recording or filing fee or fees
incident to recording instruments, Maker shall reimburse Payee for all such sums
upon demand. Any such sums shall become part of the indebtedness secured by the
Deed of Trust and shall bear interest from the date incurred by Payee at the
rate provided in the Note.

      The Note has been executed and delivered in and shall be construed in
accordance with and governed by the laws of the State of Texas and of the United
States of America, except that Chapter 346 of the Texas Finance Code, as amended
(which regulates certain revolving credit loan accounts and revolving tri-party
accounts), shall not apply hereto.

      For purposes of any suit relating to the Note, Maker hereof submits itself
to the jurisdiction of any court sitting in the State of Texas and further
agrees that venue in any suit arising out of the Note or any venue shall be
fixed in Harris County, Texas. Final judgment in any suit shall be conclusive
and may be enforced in any jurisdiction within or without the United States of
America, by suit on the judgment, a certified or exemplified copy of which shall
be conclusive evidence of such liability.

      The Note is given in increase, modification, renewal and extension of the
Promissory Note, and the Liens securing the payment thereof are not extinguished
but are specifically carried forward, ratified in all respects and shall secure
the payment hereof.

      Maker agrees that the unpaid principal balance on the Promissory Note, as
hereby modified, renewed and extended, is $5,584,049.54 as of the date hereof,
prior to funding the amount evidenced by the increase hereof.

                                        4

<PAGE>

      THIS WRITTEN LOAN AGREEMENT REPRESENTS THE FINAL AGREEMENT BETWEEN THE
PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR
SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES.

      THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.

      EXECUTED IN DUPLICATE ORIGINAL COUNTERPARTS, this 29th Day of April, 2004,
EFFECTIVE FOR ALL PURPOSES AS OF APRIL 1, 2004.

                                        TMX REALTY CORPORATION, a Delaware
                                          Corporation

                                        By: /s/ James W. Albrecht, Jr.
                                            ------------------------------------
                                        Name: James W. Albrecht, Jr.
                                        Title: CFO

AGREED TO BY:

TEXAS STATE BANK

By: /s/ Jim D. MacIntyre
    ---------------------------
Name: Jim D. MacIntyre
Title: Executive Vice President

STATE OF TEXAS

COUNTY OF HARRIS

      This instrument was acknowledged before me on the 29th day of April, 2004,
by James W. Albrecht, JR. CFO of TMX Realty Corporation, a Delaware corporation,
on behalf of said corporation.

[SEAL] [VIVIAN SALAZAR NOTARY STAMP]              /S/ Vivian Salazar
                                                  ------------------------------
                                                  Notary Public, State of Texas

STATE OF TEXAS

COUNTY OF HARRIS

      This instrument was acknowledged before me on the 12th day of May 2004, by
Jim D. MacIntyre, EVP of Texas State Bank, on behalf of said bank.

[SEAL] [VIVIAN SALAZAR NOTARY STAMP]              /S/ Vivian Salazar
                                                  ------------------------------
                                                  Notary Public, State of Texas

                                        5

<PAGE>

                                   EXHIBIT "A"

The leasehold interest in and to a tract or parcel containing 2.619 acres
(114,086 square feet) of land situated in the D W C Harris Survey, Abstract
Number 325, Harris County, Texas, and being part of and out of that certain
called 118.831 acres described in deed to the United Stales of America, as
recorded in Volume 1297, Page 87, Deed Records of Harris County, Texas, said
2.619 acre tract being more particularly described as follows (all bearings and
coordinates are based on the Texas State Plane Coordinate System; South Central
Zone; all distances and coordinates are surface and may be converted to grid by
multiplying by a combined scale factor of 0.9998632);

COMMENCING at a 5/8-inch iron rod with plastic cap set marking the intersection
of the south right-of-way (ROW) line of Holcombe Boulevard with the west ROW
line of Almeda Road, and having surface coordinates of X=3,147,967.40;
Y=698,487.10, thence:

      South 14 degrees 53'21" West, with said west ROW line, a distance of
      206.00 feet to a set 5/8-inch iron rod with plastic cap;

      North 75 degrees 06'39" West, a distance of 329.30 feet to a 5/8-inch iron
      rod with plastic cap set marking the POINT OF BEGINNING and northeast
      corner of the herein described tract;

THENCE, SOUTH 14 degrees 53'21" West, a distance of 330.70 feet to a 5/8-inch
iron rod with plastic cap set marking the southeast corner of the herein
described tract;

THENCE, NORTH 75 degrees 06'39" West, a distance of 432.78 feet to a 5/8-inch
iron rod with plastic cap set marking the southwest corner of the herein
described tract;

THENCE, NORTH 41 degrees 44'27" East, a distance of 334.23 feet to a 5/8-inch
iron rod with plastic cap set marking the beginning of a tangent curve;

THENCE, NORTHEASTERLY, with a curve to the left having a radius of 760.00 feet,
a central angle of 03 degrees 35'59", an arc length of 47.75 feet, and a chord
which bears North 39 degrees 56'28" East, 47.74 feet to an "X" in concrete set
marking the most northwesterly corner of the herein described tract;

THENCE, SOUTHEASTERLY, with a non-tangent curve to the left having a radius of
87.50 feet, an arc length of 93.13 feet, a central angle of 60 degrees 59'01",
and a chord which bears South 58 degrees 25'28" East, 88.80 feet to a 5/8-inch
iron rod with plastic cap set marking a point of tangency;

THENCE, SOUTH 88 degrees 54'58" East, a distance of 27.76 feet to a 5/8-inch
iron rod with plastic cap set marking the beginning of a tangent curve;

THENCE, EASTERLY, with a curve to the right having a radius of 281.50 feet, an
arc length of 67.83 feet, a central angle of 13 degrees 48'19", and a chord
which bears South 82 degrees 00'48" East, 67.66 feet to a 5/8-inch iron rod with
plastic cap set marking a point of tangency;

THENCE, SOUTH 75 degrees 06'39" East, a distance of 82.41 feet to the POINT OF
BEGINNING and containing 2.619 acres (114,086 square feet) of land (this
description is based on a Land Title Survey and plat prepared by Terra Surveying
Company, Inc., Project Number 0163-9601-S).

/s/ Beverly B. Kaufman                 ANY PROVISION HERE IN WHICH RESTRICTS
------------------------               THE SALE, RENTAL, OR USE OF THE DESCRIBED
COUNTY  CLERK                          REAL PROPERTY BECAUSE OF COLOR OR RACE
HARRIS COUNTY, TEXAS                   IS INVALID AND UNENFORCEABLE UNDER
                                       FEDERAL LAW.
                                       THE STATE OF TEXAS
                                       COUNTY OF HARRIS

                                       I hereby certify that this instrument was
                                       FILED in File Number Sequence on the date
                                       and at the time stamped hereon by me; and
                                       was duly RECORDED. In the Official Public
                                       Records of Real Property of Harris
                                       County, Texas on

                                                     MAY 13, 2004

                                               /s/ Beverly B. Kaufman
                                               ------------------------
                                               COUNTY  CLERK
                                               HARRIS COUNTY, TEXAS
[HARRIS COUNTY, TEXAS SEAL]
<PAGE>

                          SUBORDINATION, ATTORNMENT AND
                            NON-DISTURBANCE AGREEMENT
                                  (SPACE LEASE)

THE STATE OF TEXAS
                                   KNOW ALL MEN BY THESE PRESENTS THAT:
COUNTY OF HARRIS

      WHEREAS, INTROGEN THERAPEUTICS, INC., a Delaware corporation (herein
called "Introgen") is the Lessee pursuant to that certain Lease Agreement (the
"Lease Agreement) dated November 23, 1998, by and between Introgen, as Lessee
(herein so called) and TMX REALTY CORPORATION, as Lessor ("Landlord") and
covering the Property (herein so called) described therein; and

      WHEREAS, as of November 23, 1998, Landlord executed a leasehold deed of
trust, (the "Mortgage") in favor of Riverway Bank (now known as Texas State
Bank) ("Bank"), thereby creating a lien and security interest upon the ground
subleasehold estate of the Property and all of Landlord's rights, title and
interest in the Lease Agreement, together with a first lien and security
interest on certain fixtures and building components located on the Property for
the purpose of securing the payment of a Promissory Note of even date therewith
in the principal amount of $6,000,000, executed by Landlord, payable to the
order of the Bank (the "Loan"), to which reference is herein made for all
purposes; and

      WHEREAS, as of April_________, 2004, Landlord executed that certain
Modification Agreement (the "Modification Agreement") in the principal amount of
$7,800,000.00 (the "Loan") in favor of the Bank which increased, renewed and
extended the November 23, 1998 Promissory Note and extended the liens created
pursuant to the Mortgage; and

      WHEREAS, the Bank is relying upon the warranties, representations and
agreements contained herein as an inducement to the Bank in making the Loan to
Landlord; and

      WHEREAS, the Landlord agrees to the attornment by and non-disturbance of
the Bank, its successors and assigns, pursuant to the terms and conditions
contained herein.

      NOW, THEREFORE, for and in consideration of the premises and other
valuable consideration, the receipt of which is hereby acknowledged, the
Landlord and Lessee hereby agree, as follows:

      1.    A true, correct and complete copy of the Lease Agreement has been
            delivered to the Bank.

      2.    The Lease Agreement has not been amended or modified. The Lease
            Agreement has been duly authorized and executed by the Landlord and
            Lessee and is in full force and effect and neither the Landlord nor
            Lessee is aware of any default in any respect under the Lease
            Agreement and no notice of default as provided in the Lease
            Agreement is pending or threatened against Lessee.

      3.    Lessee and Landlord have complied fully and completely with all of
            their respective covenants, warranties and other undertakings and
            obligations under the Lease Agreement to this date, with the result
            that Lessee is fully obligated to pay the rent and other charges due
            thereunder upon the Rent Commencement Date (as such term is defined
            in the Lease Agreement), and is fully obligated to perform all of
            the other obligations of Lessee under the Lease Agreement.

      4.    Anything in the Lease Agreement to the contrary notwithstanding, the
            Lessee hereby consents to Landlord executing the Modification
            Agreement in favor of the Bank as part of the security for the Loan
            and recording the same of record thereby creating a lien and

<PAGE>

            security interest on Landlord's leasehold estate in the Property and
            assigning its rights under the Lease Agreement to the Bank.

      5.    Lessee and Landlord agree that as long as the Mortgage as modified
            by the Modification Agreement is in effect, they shall not amend the
            Lease Agreement or terminate it voluntarily (except pursuant to the
            existing terms thereof) prior to the end of its stated term or any
            extended term without Bank's prior written consent, which shall not
            be unreasonably withheld or delayed.

      6.    The Landlord and Lessee represent to Bank that their respective
            interests in the Lease Agreement have not been assigned or conveyed
            and that neither party has agreed to assign or convey the Lease
            Agreement or any interest therein, except pursuant to the Mortgage
            as modified by the Modification Agreement.

      7.    If the interest of Landlord in the Lease Agreement is acquired by
            the Bank by reason of foreclosure of the Mortgage or other
            proceedings brought to enforce the rights of the holder of the
            Mortgage, by assignment in lieu of foreclosure or by any other
            method, the Bank, its successors and assigns shall have the right,
            at its option, to either (a) terminate the Lease Agreement or (b)
            elect to have the Lease Agreement and the rights of the Lessee
            thereunder continue in full force and effect and not be terminated
            or disturbed except pursuant to the Lease Agreement. In the event
            the Bank or its successors and assigns take over Landlord's interest
            in the Lease Agreement and elects to continue same, Lessee shall be
            bound to the Bank, its successors and assigns under all of the
            terms, covenants and conditions of the Lease Agreement for the
            balance of the term thereof remaining, and any extensions or
            renewals thereof which may be effected in accordance with any option
            therefor contained in the Lease Agreement with the same force and
            effect as if the Bank, its successors and assigns, were the Landlord
            under the Lease Agreement. The Lessee agrees that a takeover of
            Landlord's interest under the Lease Agreement by foreclosure,
            assignment or otherwise will not itself constitute a default under
            the Lease Agreement. The Lessee, its successors and assigns do
            hereby attorn to the Bank, said attornment to be effective and
            self-operative without the execution of any other instruments on
            the part of any party hereto or the Bank, its successors or assigns
            immediately upon the Bank, its successors or assigns, succeeding to
            the interest of Landlord under the Lease Agreement, subject to the
            Bank's option to terminate the Loan Agreement as afore said. The
            respective rights and obligations of the Bank, its successors or
            assigns and the Lessee upon such attornment to the extent of the
            then remaining balance of the term of the Lease Agreement and any
            extension or renewal, shall be and are the same as now set forth in
            the Lease Agreement, it being the intention of the parties hereto
            for this purpose to incorporate the Lease Agreement into this
            agreement by reference with the same force and effect as if set
            forth at length herein.

      8.    Landlord hereby subordinates to the Mortgage as modified by the
            Modification Agreement all liens of every kind and character,
            whether contractual, constitutional, statutory or otherwise, which
            Landlord may now have or have acquire against any property of Lessee
            or any subtenant occupying any space on the Property which is now or
            hereafter installed in or located on the Property.

      9.    All notices, requests and communications hereunder shall be in
            writing or by telex or telegram confirmed in writing, and (a) if to
            Landlord shall be sufficient in all respects if delivered or sent by
            registered or certified mail to Landlord at the following address:

                           TMX Realty Corporation
                           301 Congress Avenue, Suite 1850
                           Austin, Texas 78701
                           Attention: James W. Albrecht, Jr.

                                       2
<PAGE>

            and (b) if to the Lessee shall be sufficient in all respects if
            delivered or sent by registered or certified mail to the Lessee at
            the following address:

                           Introgen Therapeutics, Inc.
                           301 Congress Avenue, Suite 1850
                           Austin, Texas 78701
                           Attention: Mr. David G. Nance

            and (c) if to the Bank shall be sufficient in all respects if
            delivered or sent by registered or certified mail to the Bank at the
            following address:

                           Texas State Bank
                           Five Riverway
                           Houston, Texas 77056
                           Attention: Real Estate Department

            Any party may, by proper written notice hereunder to the other
            party, change the address to which notice shall thereafter be sent
            to it.

EXECUTED this _____day of April, 2004.

                                            TMX REALTY CORPORATION, a Delaware
                                            corporation

                                            By: /s/ James W. Albrecht, Jr.
                                                ------------------------------
                                            Name : James W. Albrecht, Jr.
                                            Title: CFO

                                            INTROGEN THERAPEUTICS, INC., a
                                            Delaware corporation

                                            By: /s/ James W. Albrecht, Jr.
                                                ------------------------------
                                            Name: James W. Albrecht, Jr.
                                            Title: CFO

                                            TEXAS STATE BANK

                                            By: ______________________________
                                                James D. MacIntyre
                                                Executive Vice President

                                        3

<PAGE>

THE STATE OF TEXAS

COUNTY OF HARRIS

      This instrument was acknowledged before me on this ________ day of April,
2004, by ____________________, ________________ of TMX REALTY CORPORATION, a
Delaware corporation, for and on behalf of said corporation.

                                                  ______________________________
[SEAL]                                            Notary Public, State of Texas

THE STATE OF TEXAS

COUNTY OF HARRIS

      This instrument was acknowledged before me on this __ day of April, 2004,
by _______________________, __________________ of INTROGEN THERAPEUTICS, INC. a
Delaware corporation, for and on behalf of said corporation.

                                                   _____________________________
[SEAL]                                             Notary Public, State of Texas

THE STATE OF TEXAS

COUNTY OF HARRIS

      This instrument was acknowledged before me on this _____ day of April,
2004, by James D. MacIntyre, Executive Vice President of TEXAS STATE BANK, for
and on behalf of said bank.

                                                   _____________________________
[SEAL]                                             Notary Public, State of Texas

                                        4

<PAGE>

                          SUBORDINATION, ATTORNMENT AND
                            NON-DISTURBANCE AGREEMENT
                                (GROUND SUBLEASE)

THE STATE OF TEXAS
                                     KNOW ALL MEN BY THESE PRESENTS THAT:
COUNTY OF HARRIS

      WHEREAS, INTROGEN THERAPEUTICS, INC., a Delaware corporation (herein
called "Introgen") is the Ground Sublessee pursuant to that certain Ground
Sublease Agreement dated September 24, 1998, as amended and restated by Amended
and Restated Ground Sublease Agreement (the "Lease Agreement") dated effective
September 24, 1998, by and between Introgen, as Ground Sublessee and AMELANG
PARTNERS, INC., as Ground Sublessor ("Landlord") and covering the Property
(herein so called) described therein; and

      WHEREAS, Introgen assigned all of its rights, title and interest as Ground
Sublessee pursuant to the Lease Agreement to TMX Realty Corporation, a Delaware
corporation (herein called "TMX"), pursuant to an Assignment and Assumption of
Lease dated November 23, 1998 (the "TMX Assignment").

      WHEREAS, the Lease Agreement covers a portion of the property described in
that certain Enhanced-Use Lease dated August 25, 1993 by and between Ground
Sublessor as lessee and the United States Department of Veteran Affairs as
lessor.

      WHEREAS, as of November 23, 1998, TMX executed a leasehold deed of trust,
(the "Mortgage") in favor of Riverway Bank (now known as Texas State Bank)
("Bank"), thereby creating a lien and security interest upon the ground
subleasehold estate of the Property and all of TMX's rights, title and interest
in the Lease Agreement, together with a first lien and security interest on
certain fixtures and building components located or to be located on the
Property for the purpose of securing the payment of a Promissory Note of even
date therewith in the principal amount of $6,000,000, executed by TMX, payable
to the order of the Bank, to which reference is herein made for all purposes;
and

      WHEREAS, as of April__________, 2004, Landlord executed that certain
Modification Agreement (the "Modification Agreement") in the principal amount of
$7,800,000.00 (the "Loan") in favor of the Bank which increased, renewed and
extended the November 23, 1998 Promissory Note and extended the liens created
pursuant to the Mortgage; and

      WHEREAS, the Bank is relying upon the warranties, representations and
agreements contained herein as an inducement to the Bank in making the Loan to
TMX; and

      WHEREAS, the Landlord agrees to the attornment by and non-disturbance of
the Bank, its successors and assigns, pursuant to the terms and conditions
contained herein.

      NOW, THEREFORE, for and in consideration of the premises and other
valuable consideration, the receipt of which is hereby acknowledged, Introgen,
the Landlord and TMX hereby agree, as follows:

      1.    A true, correct and complete copy of the Lease Agreement has been
            delivered to the Bank.

      2.    The Lease Agreement has not been amended or modified. The Lease
            Agreement has been duly authorized and executed by the Landlord and
            Introgen and is in full force and effect and neither the Landlord,
            Introgen nor TMX is aware of any default in any respect under the
            Lease Agreement and no notice of default as provided in the Lease
            Agreement is pending or threatened against Introgen or TMX.

<PAGE>

      3.    Introgen, TMX and Landlord have complied fully and completely with
            all of their respective covenants, warranties and other undertakings
            and obligations under the Lease Agreement to this date, with the
            result that Introgen and TMX, jointly and severally, are fully
            obligated to perform all of the obligations of Introgen under the
            Lease Agreement.

      4.    Anything in the Lease Agreement to the contrary notwithstanding, the
            Landlord hereby consents to TMX executing the Modification Agreement
            in favor of the Bank as part of the security for the Loan and
            recording the same of record thereby creating a lien and security
            interest on TMX's subleasehold estate in the Property and
            collaterally assigning its rights under the Lease Agreement to the
            Bank.

      5.    TMX and Landlord agree that as long as the Mortgage as modified by
            the Modification Agreement is in effect, they shall not amend the
            Lease Agreement or terminate it voluntarily (except pursuant to the
            existing terms thereof) prior to the end of its stated term or any
            extended term without Bank's prior written consent, which shall not
            be unreasonably withheld or delayed.

      6.    The Landlord, Introgen and TMX represent to Bank that their
            respective interests in the Lease Agreement have not been assigned
            or conveyed and that neither party has agreed to assign or convey
            the Lease Agreement or any interest therein, except pursuant to the
            Mortgage as modified by the Modification Agreement and the TMX
            Assignment.

      7.    If the interest of TMX in the Lease Agreement is acquired by the
            Bank by reason of foreclosure of the Mortgage or other proceedings
            brought to enforce the rights of the holder of the Mortgage, by
            assignment in lieu of foreclosure or by any other method, it is
            agreed that the Lease Agreement and the rights of the Lessee (as
            defined in the Lease Agreement) thereunder shall continue in full
            force and effect and not be terminated or disturbed except pursuant
            to the Lease Agreement. In the event the Bank or its successors and
            assigns take over TMX's interest in the Lease Agreement, it shall be
            bound to the Landlord under all of the terms, covenants and
            conditions of the Lease Agreement applicable to the Lease Agreement
            for the balance of the term thereof remaining, and any extensions or
            renewals thereof which may be effected in accordance with any option
            therefor contained in the Lease Agreement with the same force and
            effect as if the Bank, its successors and assigns, were the named
            sublessee under the Lease Agreement. The Landlord agrees that a
            takeover of TMX's interest under the Lease Agreement by foreclosure,
            assignment or otherwise will not itself constitute a default under
            the Lease Agreement. The Bank, its successors and assigns do hereby
            attorn to the Landlord, said attornment to be effective and
            self-operative without the execution of any other instruments on the
            part of any party hereto or the Bank, its successors or assigns
            immediately upon the Bank, its successors or assigns, succeeding to
            the interest of TMX under the Lease Agreement. The respective rights
            and obligations of the Bank, its successors or assigns and the
            Landlord upon such attornment to the extent of the then remaining
            balance of the term of the Lease Agreement and any extension or
            renewal, shall be and are the same as now set forth in the Lease
            Agreement as same may hereafter be amended with the consent of the
            Bank, it being the intention of the parties hereto for this purpose
            to incorporate the Lease Agreement into this agreement by reference
            with the same force and effect as if set forth at length herein.

      8.    The Landlord accepts this agreement as the furnishing of Bank's
            address pursuant to Section 27 of the Lease Agreement and Landlord
            agrees to give Bank, as holder of the Mortgage, copies of all
            written notices of any default by TMX pursuant to the Lease
            Agreement and to allow the Bank to cure the same within the time
            periods set forth in Section 27 of the Lease Agreement (herein
            called the "Bank Cure Notice") and in the event Bank, or its
            successor and assign, elects, at its sole option, to cure such
            default and does cure such default within the time periods set forth
            in Section 27, the Landlord shall not exercise any of its rights or
            remedies with respect to such default under the Lease

                                       2

<PAGE>

            Agreement. The Bank Cure Notice shall be given at the same time as
            the original notice of default to TMX. Nothing herein shall be
            construed as an obligation of the Bank to cure any default under the
            Lease Agreement.

      9.    In the event the Bank elects to cure a default referenced in a Bank
            Cure Notice, and in fact cures such default within the time periods
            set forth in Section 27, TMX shall continue, to be in default
            pursuant to the Loan and although an event of default may no longer
            exist pursuant to the Lease Agreement (as a result of the cure
            thereof by the Bank), the Bank may exercise its remedies pursuant to
            the instruments executed in connection with the Loan, including,
            without limitation, foreclosing its lien, security interests and/or
            assignment on TMX's leasehold estate under the Lease Agreement.

      10.   Landlord hereby subordinates to the Mortgage as modified by the
            Modification Agreement all liens of every kind and character,
            whether contractual, constitutional, statutory or otherwise, which
            Landlord may now have or hereafter acquire against any property of
            TMX or any tenant occupying any space on the Property which is now
            or hereafter installed in or located on the Property.

      11.   Landlord hereby acknowledges, pursuant to Section 39 of the Lease
            Agreement, that Introgen, pursuant to the TMX Assignment, assigned
            all of its rights, title and interest as Ground Sublessee pursuant
            to the Lease Agreement to TMX and Landlord consents to such
            assignment and acknowledges that TMX is the "Lessee" as such term is
            defined in the Lease Agreement.

      12.   All notices, requests and communications hereunder shall be in
            writing or by telex or telegram confirmed in writing, and (a) if to
            TMX shall be sufficient in all respects if delivered or sent by
            registered or certified mail to TMX at the following address:

                           TMX Realty Corporation
                           301 Congress Avenue, Suite 1850
                           Austin, Texas 78701
                           Attention: James W. Albrecht, Jr.

            and (b) if to the Landlord shall be sufficient in all respects if
            delivered or sent by registered or certified mail to the Landlord at
            the following address:

                           Amelang Partners, Inc.
                           952 Echo Lane, Suite 100
                           Houston, Texas 77024

            and (c) if to the Bank shall be sufficient in all respects if
            delivered or sent by registered or certified mail to the Bank at the
            following address:

                           Texas State Bank
                           Five Riverway
                           Houston, Texas 77056
                           Attention: Real Estate Department

            And (d) if to Introgen shall be sufficient in all respects if
            delivered or sent by registered or certified mail to Introgen at the
            following address:

                           Introgen Therapeutics, Inc.
                           301 Congress Avenue, Suite 1850
                           Austin, Texas 78701
                           Attention: Mr. David G. Nance

                                       3

<PAGE>

            Any party may, by proper written notice hereunder to the other
            parties, change the address to which notice shall thereafter be sent
            to it.

      EXECUTED this__________day of April, 2004.

                                     TMX REALTY CORPORATION, a Delaware
                                     corporation

                                     By: /s/ James W. Albrecht, Jr.
                                         ---------------------------------------
                                     Name: James W. Albrecht, Jr.
                                     Title: CFO

                                     INTROGEN THERAPEUTICS, INC., a Delaware
                                     corporation

                                     By: /s/ James W. Albrecht, Jr.
                                         ---------------------------------------
                                     Name: James W. Albrecht, Jr.
                                     Title: CFO

                                     AMELANG PARTNERS, INC., a Texas corporation

                                     By:________________________________________
                                     Name:______________________________________
                                     Title:_____________________________________

                                     TEXAS STATE BANK

                                     By:________________________________________
                                          James D. MacIntyre
                                          Executive Vice President

THE STATE OF TEXAS

COUNTY OF HARRIS

      This instrument was acknowledged before me on this __ day of April, 2004,
by ________________, _______________________ of TMX REALTY CORPORATION, a
Delaware corporation, for and on behalf of said corporation.

                                                   _____________________________
[SEAL]                                             Notary Public, State of Texas

                                       4
<PAGE>

THE STATE OF TEXAS

COUNTY OF HARRIS

      This instrument was acknowledged before me on this ________ day of April,
2004, by ________________,_____________________ of INTROGEN THERAPEUTICS, INC. a
Delaware corporation, for and on behalf of said corporation.

                                                   _____________________________
[SEAL]                                             Notary Public, State of Texas

THE STATE OF TEXAS

COUNTY OF HARRIS

      This instrument was acknowledged before me on this ______ day of April,
2004, by ______________,__________________ of AMELANG PARTNERS, INC. a Texas
corporation, for and on behalf of said corporation.

                                                   _____________________________
[SEAL]                                             Notary Public, State of Texas

THE STATE OF TEXAS

COUNTY OF HARRIS

      This instrument was acknowledged before me on this__________day of April,
2004, by James D. MacIntyre, Executive Vice President of TEXAS STATE BANK, for
and on behalf of said bank.

                                                   _____________________________
[SEAL]                                             Notary Public, State of Texas

                                       5

<PAGE>

                              BORROWER'S STATEMENT

DATE: May 6, 2004                                               GFNO: 2711000082

LOAN FROM:  Texas State Bank             TO: TMX Realty Corporation
            1000 Main Street, Suite 100
            Houston, Tax 77002

PROPERTY:   2.619 acres, D.W.C. Harris Survey, Abstract No. 325, Harris County,
            Texas

<TABLE>
<S>                                                                  <C>
CREDITS/FUNDS RECEIVED.............................................
Loan Amount $7,800,000,00 - Amount funded from Texas State Bank....  $   2,203,825.23
            TOTAL..................................................  $   2,203,825.23
LESS: CHARGES/DISBURSEMENTS
LOAN CHARGES to Texas State Bank...................................  $      25,015.00
      Commitment Fee...............................................  $      25,000.00
      Flood Determination Fee......................................  $          15.00
ADDITIONAL SETTLEMENT CHARGES......................................  $      37,180.25
      Lender Attorneys Fees to Porter & Hedges.....................  $       2,679.25
      Broker Fee to States Mortgage Company........................  $      25,000.00
      Appraisal Fee to The Thomas Bearden Company..................  $       9,500.00
      State of Texas Policy Guaranty Fee to Texas Title Insurance
      Guaranty.....................................................  $           1.00
Title Company Charges to LandAmerica Partners Title................  $      34,527.10
      Mortgagee Policy for $7,800,000.00 (less R-8 credit of 30% =
      $2,587.28)...................................................  $      34,214.72
      Tax Certificates.............................................  $         162.38
      Estimated Recording Fees.....................................  $         150.00
LOAN PAYOFF to Compass Bank........................................  $   1,438,652.82
      As of May 12, 2004:..........................................  $   1,438,652.82

            TOTAL CHARGES/DISBURSEMENTS............................  $   1,535,375.17
                  NET AMOUNT DUE TO BORROWER.......................  $     668,450.06
                                                                     ----------------
</TABLE>

Borrower understands the Closing or Escrow Agent has assembled this information
representing the transaction from the best information available from other
sources and cannot guarantee the accuracy thereof. The lender involved may be
furnished a copy of this statement.

The undersigned hereby authorizes LandAmerica Partners Title Company to make
expenditure and disbursements as shown above and approves same for payment. The
undersigned also acknowledges receipt of Loan Funds, if applicable, in the
amount shown above and a receipt of a copy of this Statement

LandAmerica Partners Title Company      TMX Realty Corporation

By ______________________________       /s/  JAMES W. ALBRECHT, JR.
   Reno Hartfiel                        ----------------------------------------
Reno                                    By

                               Compliments of LANDAMERICA PARTNERS TITLE COMPANY