Document:

EXHIBIT 10.19

CERTAIN INFORMATION IN THIS EXHIBIT IS SUBJECT TO A REQUEST FOR CONFIDENTIAL
TREATMENT. IN ACCORDANCE WITH RULE 406 UNDER THE SECURITIES ACT OF 1933, AS
AMENDED, SUCH INFORMATION HAS BEEN OMITTED AND FILED SEPARATELY WITH THE
SECURITIES AND EXCHANGE COMMISSION. THE LOCATION OF SUCH OMITTED INFORMATION HAS
BEEN INDICATED WITH AN ASTERISK(*).

                     [PROTEIN DESIGN LABS, INC. LETTERHEAD]

June 28, 1999

VIA FACSIMILE:                                  713-664-8914

Mr. Eric P. Mirabel
Vice President of Inte11ectual Property
Tanox Inc.
10301 Stella Link
Houston, Texas 77025-5497

        Re: AMENDMENT TO PATENT LICENSE AGREEMENT

Dear Eric:

This letter amendment ("Amendment") sets forth our agreement to amend certain
provisions of the Patent License Agreement dated June 30, 1998 ("Agreement")
between Protein Design Labs, Inc. ("PDL") and Tanox Inc. ("Tanox"). Except as
expressly set forth herein, capitalized terms shall have the meaning and section
references shall refer to those set forth in the Agreement.

                                       *
<PAGE>
Mr. Eric P. Mirabel
June 28, 1999
Page 2

          2. PAYMENT TO PDL. *

          3. ADDITIONAL LICENSES. Through *, Tanox may request that PDL grant a
     nonexclusive worldwide license under the PDL Patent Rights for up to two
     (2) additional antibodies under development by Tanox as of the date hereof.
     The licenses shall be granted under PDL's then current financial terms for
     each license agreement, provided that such financial terms shall in no
     event exceed the following amounts:

          (a) Nonrefundable, noncreditable signing and licensing fee of One:
          Million Seven Hundred Thousand Dollars ($1,700,000);

          (b) Royalties of Three and One Quarter Percent (3.25%) to Three and
          Three Quarters Percent (3.75%), depending on the patents Tanox elects
          to include under the PDL Patent Rights; and

          (c) Annual maintenance fee of One Hundred Fifty Thousand Dollars
          ($150,000) payable on the second (2nd) anniversary of the effective
          date of the license agreement, subject to credit as provided in
          Section 3.05.

          Subject to the foregoing, the form of license agreement for each of
     the two (2) additional antibodies shall be substantially similar to that of
     the Agreement, provided that Sections 2.02, 2.03, 2.04 and 2.05 shall not
     be included as part of such agreements.

          4. LIMITATION. PDL shall have the right to deny Tanox a license
     pursuant to Section 3 of this Amendment for any antibody directed against
     an antigen (a) which is targeted by a product being developed (i.e., in
     which such product is reasonably contemplated to begin a clinical trial
     within twenty-four (24) months or for which a regulatory submission has
     been filed) or marketed by PDL on its own behalf or in
<PAGE>
Mr. Eric P. Mirabel
June 28, 1999
Page 3

     cooperation with a corporate partner, or (b) as to which PDL has granted or
     is in good faith negotiations to grant an exclusive license to a third
     party under PDL Patent Rights.

          5. TERMINATION OF AMENDMENT. This Amendment sets forth the entire
     agreement between the parties with respect to the subject matter hereof.
     Except as expressly provided herein, the Agreement shall remain in full
     force and effect. In any event, this Agreement shall terminate and be of no
     force and effect as of March 1, 2000.

If the foregoing sets forth your understanding of the Amendment, please have a
duly authorized officer of Tanox countersign where noted below.

Sincerely,

/s/ GLEN Y. SATO
Glen Y. Sato
Vice President, Legal
and General Counsel

Acknowledged and agreed by its duly authorized officer.

Tanox, Inc.

By /s/ ILLEGIBLE
Title Sr. VP. OperationsEXHIBIIT 10.22

                 G-CSF RECEPTOR NON-EXCLUSIVE LICENSE AGREEMENT

     THIS G-CSF RECEPTOR NON-EXCLUSIVE LICENSE AGREEMENT is entered into and
made effective this 11th day of January, 2000, by and between IMMUNEX
CORPORATION, a corporation of the state of Washington, having its principle
place of business as 51 University Street, Seattle, Washington 98101
(hereinafter referred to as "Immunex"), and TANOX, INC., a corporation of the
State of Texas, and having a place of business at 10301 Stella Link, Houston,
Texas 77025.

                                   BACKGROUND

          WHEREAS, Immunex is a biopharmaceutical company engaged in the
     research, development, marketing and sale of therapeutics for treating
     human disease. Immunex owns proprietary and confidential information and
     intellectual property relating to G-CSF Receptor ("G-CSF Receptor
     Technology"). Immunex is the sole owner of and has full right to the
     Licensed Patent Rights (as defined below):

          WHEREAS, Licensee (as defined herein) wishes to obtain *

          WHEREAS, the use of G-CSF Receptor Technology is valuable to Licensee
     in the discovery, research and development of Developed Products;
     therefore, Licensee is willing to compensate Immunex for such use by paying
     Immunex *

                                   AGREEMENT

     NOW THEREFORE, in consideration of the premises and mutual covenants and
agreements contained herein, and for good and other valuable consideration, the
receipt and sufficiency of which is hereby acknowledged, Immunex and Licensee,
intending to be legally bound hereby, do hereby agree as follows:
<PAGE>
1.  DEFINITIONS

     1.1  "AFFILIATE" shall mean any corporation, company, partnership, joint
venture, firm or other entity which directly or indirectly owns, is owned by or
is under common ownership with a Party (as defined below) where "owns" or
"ownership" means possession of at least fifty percent (50%) of the equity (or
such lesser percentage which is the maximum allowed to be owned by a foreign
corporation in a particular jurisdiction or such lesser percentage provided the
operational control is held by the Party) having the power to vote on or direct
the affairs of the entity and any person, firm, partnership, corporation or
other entity actually controlled by, controlling or under common control with a
Party.

     1.2  "CALENDAR QUARTER" shall mean each three (3) month period commencing
January 1, April 1, July 1 and October 1 of each year during the Term (as
defined in Section 5.1) of this Agreement.

     1.3  "DEVELOPED PRODUCT" *

     1.4  "EFFECTIVE DATE" shall mean the date this Agreement is effective,
which shall be the date first indicated above.

     1.5  "FIELD" *

     1.6  "FORCE MAJEURE" shall mean any act of God or the public enemy, any
accident, explosion, fire, storm, earthquake, flood, drought, peril of the sea,
riot, embargo, war or foreign, federal, state or municipal order issued by a
court or other authorized official, seizure, requisition or allocation, any
failure or delay of transportation, shortage of or inability to obtain supplies,
equipment, fuel or labor or any other circumstance or event beyond the
reasonable control and without the fault or negligence of the Party relying upon
such circumstance or event.

     1.7  "LICENSED PATENT RIGHTS" *

                                       2
<PAGE>
     1.8  "LICENSEE" shall mean Tanox, Inc. and/or its Affiliates, as
applicable.

     1.9  "NET SALES" *

     1.10  "PARTY" shall mean either Immunex or Licensee, as applicable. The
term "PARTIES" shall mean both Immunex and Licensee.

     1.11  "PHASE III" shall mean, with respect to a Developed Product, the
period of product development commencing with enrollment of the first patient in
a placebo-controlled or otherwise appropriately controlled clinical trial that
is intended to demonstrate efficacy for registration of such Developed Product
and ending upon filing of an NDA, BLA, or foreign equivalent seeking Regulatory
Approval, where the clinical trial is sponsored by a Party or its sublicensees.

     1.12  "REGULATORY AGENCY" shall mean the United States Food and Drug
Administration ("FDA") or any successor agency vested with administrative and
regulatory authority to approve testing and marketing of human pharmaceutical or
biological therapeutic products in the United States and/or any regulatory body
with similar regulatory authority in any other part of the world where any Party
to

                                       3
<PAGE>
this Agreement elects to file an NDA, BLA or foreign equivalent seeking
Regulatory Approval.

     1.13  "REGULATORY APPROVAL" shall mean the receipt by a Party of the
authorization by an appropriate Regulatory Agency to market and sell Developed
Product in a country, including to the extent required, any governmental pricing
approval for such Developed Product in such country.

     1.14  "THIRD PARTY" shall mean any individual, partnership, corporation,
firm, association, unincorporated organization, joint venture, trust or other
entity that is neither a Party nor an Affiliate.

     1.15 *

2.  LICENSE GRANT

     2.1 *

3.  PAYMENTS AND REPORTS

     3.1  LICENSE EXECUTION FEE.  * after the Effective Date, Licensee shall pay
to Immunex *

     3.2  LICENSE MAINTENANCE FEE.  In consideration of maintaining the license
granted to it pursuant to this Agreement. Licensee shall pay to Immunex *

                                       4
<PAGE>
     3.3  MILESTONE FEES.  For each Developed Product, Licensee, or its
Affiliate, shall pay Immunex the following fees upon occurrence of the following
milestone events:

                                       *

     3.4 ROYALTIES. Licensee shall pay Immunex a royalty of * in respect of the
annual Net Sales of all Developed Products * following the last day of each
Calendar Quarter following * Such royalties shall not be returnable in any
event. *

     3.5  ROYALTY REPORTS AND TERM. *

                                       5
<PAGE>
     3.6  CURRENCY CONVERSION.  Royalty and milestone payments by Licensee shall
be made to Immunex in U.S. Dollars. For converting any royalty payments on Net
Sales made in a currency other than U.S. Dollars, Net Sales shall first be
determined in the currency of the country in which they are earned and shall be
converted each Calendar Quarter into an account in U.S. Dollars at the average
of the bid and ask prices reported in the WALL STREET JOURNAL as of the close of
the last business day of such Calendar Quarter in which such royalty is due. If
the last day of such Calendar Quarter is not a business day, then the closest
preceding business day shall be used for such calculation. All such converted
Net Sales shall be consolidated with U.S. Net Sales for each Calendar Quarter
and the applicable royalty payable determined therefrom. If by law, regulation
or fiscal policy of a particular country, remittance of royalties in U.S.
Dollars is restricted or forbidden, notice thereof will be promptly given to
Immunex, and payment of the royalty shall be made by the deposit thereof in
local currency to the credit of Immunex in a recognized banking institution
designated by Licensee. When in any country a law or regulation prohibits both
the transmittal and deposit of royalties on sales in such a country, royalty
payments shall be suspended for as long as such prohibition is in effect and as
soon as such prohibition ceases to be in effect, all royalties that Licensee
would have been under obligation to transmit or deposit but for the prohibition,
shall forthwith be deposited or transmitted promptly to the extent allowable.
The actual currency conversion calculations by Licensee for any country for a
particular Calendar Quarter shall be included in the royalty report provided to
Immunex for such Calendar Quarter under Section 3.5 above.

     3.7  WITHHOLDING TAXES.  All royalty amounts required to be paid to Immunex
pursuant to this Agreement may be paid with deduction for withholding for or on
account of any taxes (other than taxes imposed on or measured by net income) or
similar governmental charge imposed by a jurisdiction other than the United
States ("Withholding Taxes"). At Immunex's request, Licensee shall provide
Immunex a certificate evidencing payment of any Withholding Taxes hereunder and
shall reasonably assist Immunex to obtain the benefit of any applicable tax
treaty, at Immunex's sole cost for providing such reasonable assistance.

4.  RECORDS

     4.1  LICENSEE'S RECORDS.  Licensee shall keep and maintain, and shall
require each Affiliate to keep and maintain, in accordance with generally
acceptable accounting principles, adequate records in sufficient detail to
enable the payments due under Sections 3.3 and 3.4 to be determined. Nothing
herein shall require Licensee or any Affiliate to retain such records longer
than three (3) years after the payments to which they relate are paid.

                                       6
<PAGE>
     4.2  AUDITS.  At Immunex's request and expense. Licensee shall permit such
records under Section 4.1 to be inspected at any time during regular business
hours, but not more than once in any calendar year, by an independent public
accountant, appointed by Immunex for this purpose and reasonably acceptable to
Licensee, who shall report to Immunex only the amount of the royalties due
hereunder. If such independent public accountant reasonably determines that such
royalties, after adjustments in accordance with generally acceptable accounting
principles, have been understated by Licensee, for any calendar year. Licensee
shall pay the amount due for all royalties not properly reported. If it is
determined that Licensee has understated such royalties by an amount equal to or
greater than * Licensee shall pay all reasonable fees and costs
incurred by such independent public accountant in the course of making such
determination.

5.  TERM AND TERMINATION

     5.1  TERM.  *

     5.2  IMMUNEX'S RIGHT TO TERMINATE.  Immunex shall have the right to
terminate this Agreement, including the licenses granted herein, in the event
that any material term or condition of this Agreement is breached by Licensee or
an Affiliate, and such breach is unremedied for a period of * after Licensee's
receipt of Immunex's written notice thereof. If such breach is corrected within
the * period, this Agreement and the rights granted shall continue in force.

     5.3  LICENSEE'S RIGHT TO TERMINATE.  In the event that Licensee determines
that it will no longer carry out or continue drug discovery, research,
development of manufacturing using Licensed Patent Rights or continue
development or sale of Developed Products. Licensee shall notify Immunex in
writing, and this Agreement shall be terminated as of the date Immunex receives
such notice from Licensee.

     5.4  CONTINUING OBLIGATIONS.  Termination of this Agreement shall not
relieve License of any obligations to make payment of any sum due prior to
termination

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<PAGE>
under Article 3, or to keep records and provide written reports with
respect thereto, and to permit inspection thereof in accordance with Section 4.2

6.  WARRANTIES

     6.1  WARRANTIES AND REPRESENTATIONS OF IMMUNEX.  Immunex warrants to
Licensee that:

          6.1.1  Immunex is a corporation duly organized, validly existing and
     in good standing under the laws of the State of Washington and has all
     necessary corporate power to enter into and perform its obligations under
     this Agreement.

          6.1.2  the execution, delivery and performance of this Agreement by
     Immunex have been duly authorized and approved by all necessary corporate
     action, and this Agreement is binding, upon and enforceable against Immunex
     in accordance with its terms (subject to bankruptcy and similar laws
     affecting the rights of creditors generally);

                                        *

     6.2  WARRANTIES AND REPRESENTATION OF LICENSEE.  Licensee represents and
warrants to Immunex that:

          6.2.1  Licensee is a corporation duly organized, validly existing, and
     in good standing, under the laws of the State of Texas and has all
     necessary corporate power to enter into and perform their obligations under
     this Agreement;

          6.2.2  the execution, delivery and performance of this Agreement by
     Licensee, have been duly authorized and approved by all necessary corporate
     action, and this Agreement is binding, upon and enforceable against
     Licensee, in accordance with its terms (subject to bankruptcy and similar
     laws affecting rights of creditors generally); and

          6.2.3  during the Term of this Agreement, Licensee shall not practice
     the Licensed Patent Rights other than as specifically authorized in this
     Agreement.

     6.3  LIMITATION OF LIABILITY.  Immunex has no control over the manner in
which the Licensee intends to use the Developed Products or Licensed Patent
Rights. Immunex shall not be liable to Licensee for any losses, damages, costs
or

                                       8
<PAGE>
expenses of any nature incurred or suffered by Licensee or by a Third Party,
arising, out of any dispute or other claims or proceedings made by or brought
against Licensee, (including, without limitation, product liability claims and
claims by a Third Party alleging infringement of its intellectual property
rights by the use or sale of any Developed Product), nor shall Immunex be
responsible in any way for dealing with any such dispute, claim or proceedings,
except to the extent that any such dispute, claim or proceeding arises from (a)
a breach by Immunex of any warranty set forth in Section 6.1 hereof, or (b) the
gross negligence or willful misconduct by Immunex, its employees, agents or
directors. EXCEPT AS SET FORTH IN SECTION 6.1 OR 6.2 HEREOF, NEITHER PARTY MAKES
ANY PRODUCT WARRANTY, EXPRESS OR IMPLIED, INCLUDING ANY WARRANTY OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. IMMUNEX SHALL NOT BE LIABLE
TO LICENSEE FOR ANY USE OF LICENSED PATENT RIGHTS BY LICENSEE OR FOR ANY LOSS,
CLAIM, DAMAGE, OR LIABILITY, OF ANY KIND OR NATURE, WHICH MAY ARISE FROM OR IN
CONNECTION WITH THIS AGREEMENT. NEITHER PARTY TO THIS AGREEMENT SHALL BE
ENTITLED TO RECOVER FROM THE OTHER ANY SPECIAL INCIDENTAL, CONSEQUENTIAL OR
PUNITIVE DAMAGES. IN ADDITION, THE PARTIES MAKE NO REPRESENTATIONS AND EXTEND NO
WARRANTIES OF ANY KIND, EITHER EXPRESS OR IMPLIED, AND PARTICULARLY THAT
PRODUCTS WILL BE DEVELOPED HEREUNDER, WILL HAVE COMMERCIAL UTILITY OR
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. FURTHERMORE, IMMUNEX MAKES
NO WARRANTY EITHER EXPRESS OR IMPLIED THAT THE COMMERCIALIZATION OF DEVELOPED
PRODUCTS USING THE LICENSED PATENT RIGHTS WILL NOT INFRINGE ANY OTHER
INTELLECTUAL PROPERTY OF A THIRD PARTY.

     6.4  NO CONFLICT.  Each Party represents and warrants that, notwithstanding
anything to the contrary in this Agreement, the execution and delivery of this
Agreement and the performance of its obligations hereunder (a) do not conflict
with or violate any requirements of applicable laws or regulations and (b) do
not and shall not conflict with, violate or breach or constitute a default or
constitute a default or require any consent under, any contractual obligation.

7.  INDEMNIFICATION

     7.1  Licensee shall indemnify and hold harmless each of Immunex, its
successors and assigns, and the officers, employees, agents and counsel thereof
(the "Immunex Indemnities") from and against any and all claims of whatever
kind or nature, including, without limitation, any claim or liability based upon
any theory of negligence, warranty, strict liability, violation of government
regulation or infringement of patent or other proprietary rights, arising from
or occurring as a

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result of (a) the use of Licensed Patent Rights and Developed Products by
Licensee or any agent of Licensee, or (b) any breach of this Agreement by
Licensee, provided:

          7.1.1  Licensee shall not be obligated under this Section to the
     extent that such claim or liability was the result of the breach of any
     warranty of Immunex set forth in Section 6.1 hereof, or gross negligence or
     willful misconduct of any employee or agent of Immunex;

          7.1.2  Licensee shall have no obligation under this Article unless
     Immunex (a) gives Licensee at least thirty (30) days written notice of any
     claim or liability for which it seeks to be indemnified under this
     Agreement, (b) Licensee is granted full authority and control over the
     defense, including settlement, of such claim or liability, and (c) Immunex
     cooperates fully with Licensee and its agents in defense of the claim or
     liability; and

          7.1.3  Immunex shall have the right, at its own expense, to have its
     own counsel participate in the defense of any such claim or liability
     referred to in this Article, provided, however, that Licensee shall have
     full authority and control to handle any such claim or liability, including
     any settlement or other disposition thereof, for which Immunex seeks
     indemnification under this Article and such counsel shall cooperate with
     Licensee.

8.  MISCELLANEOUS

     8.1  NOTICES.  All notices, reports, and other communications to Immunex or
Licensee shall be in writing (including electronic facsimile transmissions),
shall refer specifically to this Agreement and shall be sent by electronic
facsimile transmission or by registered mail or certified mail, return receipt
requested, postage prepaid, by express courier services providing evidence of
delivery, in each case to the respective address specified below (or to such
address as may be specified in writing to the other Party);

If addressed to Licensee:

                            Tanox, Inc.
                            10301 Stella Link
                            Houston, Texas 77025
                            Attention:  Nancy T. Chang, President
                            Fax:  (713) 664-8914

                            with a copy to:
                            Head of Legal Affairs
                            Fax:  (713) 664-8914

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<PAGE>
and if to Immunex shall be sent to:

                            Immunex Corporation
                            51 University Street
                            Seattle, Washington 98101
                            Attn:  General Counsel
                            Fax:  (206) 233-0644

     8.2  FORCE MAJEURE.  Immunex and Licensee shall each be excused for any
failure or delay in performing any of its respective obligations under this
Agreement if such failure or delay is caused by Force Majeure. The Party
affected by the Force Majeure shall use all reasonable efforts to correct the
Force Majeure as quickly as possible and to give the other Party prompt written
notice when it is again fully able to perform its obligations hereunder.

     8.3  ASSIGNABILITY.  Neither this Agreement nor the rights herein granted
may be assigned by either Party to any Third Party without the written consent
of the other, which consent shall not be unreasonably withheld; provided,
however, that either Party may assign this Agreement to any Affiliate, or to any
corporation with which it may merge or consolidate or to which it may transfer
all or substantially all of its assets to which this Agreement relates, without
obtaining the consent of the other Party.

     8.4  AMENDMENTS.  No terms or provisions of this Agreement shall be varied
or modified by any prior or subsequent statement, conduct or act of either of
the Parties, whether oral or written, except that the Parties may amend this
Agreement by written instruments specifically referring to and executed in the
same manner as this Agreement.

     8.5  SEVERABILITY.  If any provision hereof should be held invalid, illegal
or unenforceable in any respect in any jurisdiction, then, to the fullest extent
permitted by law, (a) all other provisions hereof shall remain in full force and
effect in such jurisdiction and shall be liberally construed in order to carry
out the intentions of the parties hereto as nearly as may be possible and (b)
such invalidity, illegality or unenforceability shall not affect the validity,
legality or enforceability of such provision in any other jurisdiction. To the
extent permitted by applicable law, Immunex and Licensee hereby waive any
provision of law that would render any provision hereof prohibited or
unenforceable in any respect. In the event that the terms and conditions of this
Agreement are materially altered as a result of this Section, the parties will
renegotiate the terms and conditions of this Agreement to resolve any
inequities.

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<PAGE>
     8.6  HEADINGS.  Headings used herein are for convenience only and shall not
in any way affect the construction of, or be taken into consideration
interpreting this Agreement.

     8.7  COUNTERPARTS.  This Agreement may be executed in any number of
counterparts, each of which shall be deemed an original, and all of such
counterparts taken together shall constitute one and the same instrument.

     8.8  ENTIRE AGREEMENT.  This Agreement, on and as of the Effective Date
hereof, constitutes the entire agreement between the parties relating to the
subject matter hereof and supersedes all previous or contemporaneous writings
and understanding, whether written or oral.

     8.9  BANKRUPTCY.  Notwithstanding the bankruptcy of Immunex, or the
impairment of performance by Immunex of its obligations under this Agreement as
a result of bankruptcy or insolvency of Immunex, Licensee shall be entitled to
retain the licenses granted herein, subject to Immunex's rights to terminate
this Agreement for reasons other than bankruptcy or insolvency as expressly
provided in this Agreement, and subject to performance by Licensee of its
preexisting obligations under this Agreement.

All rights and licenses granted under or pursuant to this Agreement by Immunex
to Licensee, are, and shall otherwise be deemed to be, for purposes of Section
365(n) of the U.S. Bankruptcy Code, licenses of rights to "intellectual
property" as defined under Section 101(52) of the U.S. Bankruptcy Code. The
parties agree that Licensee, as a license of such rights under this Agreement,
shall retain and may fully exercise all of its rights and elections under the
U.S. Bankruptcy Code, subject to performance by Licensee of its preexisting
obligations under this Agreement. The parties further agree that, in the event
of the commencement of a bankruptcy proceeding by or against Immunex under the
U.S. Bankruptcy Code, Licensee shall be entitled to a complete duplicate of (or
complete access to, as appropriate) any such intellectual property and all
embodiments of such intellectual property, and same, if not already in its
possession, shall be promptly delivered to Licensee (a) upon any such
commencement of a bankruptcy proceeding upon written request therefor by
Licensee, unless Immunex elects to continue to perform all of its obligations
under this Agreement, or (b) if not delivered under (a) above, upon the
rejection of this Agreement by or on behalf of Immunex upon written request
therefor by Licensee, provided, however, that upon Immunex's (or its
successor's) written notification to Licensee that it is again willing and able
to perform all of its obligations under this Agreement. Licensee shall promptly
return all such tangible materials to Immunex, but only to the extent that
Licensee does not require continued access to such materials to enable Licensee
to perform its obligations under this Agreement.

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<PAGE>
     8.10  RELATIONSHIP.  The relationship of employer and employee shall not
exist between Immunex and Licensee under this Agreement. This Agreement shall
not be deemed to establish a joint venture or partnership between Licensee and
Immunex. Nothing contained in this Agreement shall be construed, by implication
or otherwise, as an obligation incurred by Licensee to enter into any further
agreement with Immunex.

     8.11  APPLICABLE LAW.  This Agreement is acknowledged to have been made in
and shall be construed in accordance with the laws of the state of Washington
without reference to any rules govening conflicts of laws.

                      [This space is intentionally left blank.]

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<PAGE>
     8.12  PRESS RELEASE. *

IN WITNESS WHEREOF, the parties have executed the Agreement and have entered the
effective date of the first page hereof.

         IMMUNEX CORPORATION                    TANOX, INC.
         By:  /s/BARRY G. PEA                   By:  /s/NANCY T. CHANG
         Name:  Barry G. Pea                    Name:  Nancy T. Chang
                Vice President and              Title:  President and CEO
         Title: Deputy General Counsel
         Date:  1-12-00                         Date:  1/11/00

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