Document:

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                                                                   EXHIBIT 10.10

February 1, 2006

Mr. Hans van Houte
TRUBION PHARMACEUTICALS, INC.
2401 Fourth Avenue, Suite 1050
Seattle, Washington 98121

Dear Hans:

Please refer to the Fourth and Battery Office Lease dated April 28, 2003 and all
addenda and amendments thereto (the "Office Lease" or "Lease") for the space
Trubion Pharmaceuticals (hereinafter referred to as "Trubion" or "Lessee")
occupies within the Fourth and Battery building. This letter (this "Amendment")
shall constitute an amendment to the Lease. Capitalized terms used but not
otherwise defined herein shall have the meanings ascribed to such terms in the
Lease.

PREMISES

     Effective as of the Expansion Space Effective Date (defined below), Trubion
     Pharmaceuticals, Inc. agrees to lease the additional space (the "Expansion
     Space") of approximately 15,892 rentable square feet which is the entire
     11th floor of the Fourth and Battery Building, (location attached as
     Exhibit "A") so that, from and after the Expansion Space Effective Date,
     the term "Premises" as defined in Paragraph 1 of your Lease (Description),
     shall be changed from your existing space (10th and 12th floor Premises) of
     31,507 rentable square feet ("Existing Space") to 47,399 rentable square
     feet. The floor plans attached as Exhibit A to the Lease will be
     supplemented by the floor plan of the Expansion Space attached hereto as
     Exhibit A. Lessor shall deliver the Expansion Space to Lessee on the
     Expansion Space Effective Date in the condition described in Section 2 of
     the Lease and the parties agreed that the rights and obligations of Lessee
     and Lessor set forth in Section 2 of the Lease shall apply with respect to
     the Expansion Space.

LEASE TERM

     Lessor shall cause the lease of the current occupant of the Expansion Space
     to terminate as to the Expansion Space, and shall relocate such occupant
     from the Expansion Space, on or prior to May 1, 2006. The term of the Lease
     with

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Mr. Hans van Houte
TRUBION PHARMACEUTICALS, INC.
February 1, 2006
Page 2

     respect to the Expansion Space shall be eighty-four (84) months commencing
     the later of May 1, 2006 and the date Lessor has complied with its
     obligations in the first sentence of this paragraph and delivers to Lessee
     possession of the Expansion Space in the required condition (the "Expansion
     Space Effective Date") and expiring April 30, 2013. The term of the Lease
     for the Existing Space shall be extended so it is coterminous. Lessee and
     Lessee's agents and employees may access the Expansion Space from time to
     time prior to the Expansion Space Effective Date to facilitate Lessee's
     space planning and physical due diligence. If the Expansion Space Effective
     Date is delayed for any reason beyond June 1, 2006, then in addition to
     Lessee's other rights or remedies, Lessee may terminate this Amendment by
     written notice to Lessor, or, at Lessee's election, the date Lessee is
     otherwise obliged to commence payment of rent for the Expansion Space shall
     be delayed by one additional calendar day for each calendar day that the
     Expansion Space Effective Date is delayed beyond such date.

RENT

     The Base Rent per rentable square foot for the Expansion Space shall be at
     the annual rate of $25.00 ($33,108.33 per month) for months 1 through 84.
     The rent for the Existing Space shall remain as is directed in the Office
     Lease and earlier amendment for the full eighty-four (84) months.

     The "base year" for calculating Lessee's proportionate share of Comparison
     Year Costs (if any) with respect to the Expansion Space, shall be the
     calendar year 2006 and Lessee shall have no obligation to pay its
     proportionate share of Operating Services and Real Estate Taxes with
     respect to the Expansion Space until 13 months after the Expansion Space
     Effective Date. The provision of Section 10 of the Lease shall apply with
     respect to the Expansion Space provided however that references therein to
     2004 shall be deemed references to 2006 with respect to the Expansion
     Space. The base year for the Existing Space shall remain as is directed in
     the Office Lease and earlier amendment.

AS-IS, WHERE-IS

     Lessee acknowledges Lessee has fully inspected the Expansion Space and,
     subject to the delivery requirement set forth above, accepts the Expansion
     Space

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Mr. Hans van Houte
TRUBION PHARMACEUTICALS, INC.
February 1, 2006
Page 3

     in an as-is, where-is condition. Lessee shall not call upon Lessor to
     provide any modifications or improvements to the Expansion Space.

PARKING

     Effective as of the Expansion Space Effective Date, Lessee shall have the
     right to lease eleven (11) additional parking spaces inside the building
     garage at the market rate.

PERMITTED ALTERATIONS

     Lessee may construct tenant improvements in the Expansion Space generally
     consistent with the specifications and objectives described in Exhibit "B"
     attached hereto (the "Permitted Improvements") and consistent with the
     terms of Exhibit C to the Office Lease. Lessor acknowledges and agrees that
     Lessee intends to use the North Half of the tenth floor Expansion Space for
     scientific laboratory space and that Lessee shall have the right to install
     certain of the Permitted Improvements on the adjacent roof of the 9th floor
     of the building. The last sentence of Section 47 of the Lease shall apply
     to the Permitted Improvements, and the references therein to "Tenant
     Improvements" shall also include the Permitted Improvements. Lessor shall
     be responsible for the costs described in Section 4 of Exhibit C to the
     Lease to the extent such costs arise in connection with the construction of
     the Permitted Improvements.

RIGHT OF FIRST OFFER

     Subordinate to existing rights of first offer and first refusal, Lessee
     shall have a right of first offer on all space that may become available in
     the Building on the terms set forth in Section 46 of the Lease, and
     references therein to "Expansion Space" hereinafter shall refer to any
     space in the Building that becomes available.

MISCELLANEOUS

     This Amendment (together with the Lease) constitutes the entire agreement
     between Lessor and Lessee regarding the Expansion Space and the subject
     matter contained herein and supersedes any and all prior and/or
     contemporaneous oral or written negotiations, agreements or understandings.

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Mr. Hans van Houte
TRUBION PHARMACEUTICALS, INC.
February 1, 2006
Page 4

     This Amendment shall be binding upon and inure to the benefit of Lessor and
     Lessee and their respective heirs, legal representatives, successors and
     assigns. No subsequent change or addition to this Amendment shall be
     binding unless in writing and duly executed by both Lessor and Lessee.
     Except as specifically amended hereby, all of the terms and conditions of
     the Lease are and shall remain in full force and effect and are hereby
     ratified and confirmed.

Please consider this document, when fully executed, as our agreement for the
amendment of your Office Lease. If you are in agreement with the above, please
sign below where indicated and return all four copies to me for Martin Selig's
signature. Upon Full execution, I will return two copies for your own files.

Thank you Hans, for this lease of additional space. We appreciate your tenancy
with us and look forward to continuing to satisfy your office and lab space
needs.

Very truly yours,

/s/ Theresa Howard
-------------------------------------
Theresa Howard

TRUBION131.06

                              AGREED AND ACCEPTED:

SELIG REAL ESTATE HOLDINGS EIGHT,       TRUBION PHARMACEUTICALS, INC.
LLC

/s/ Martin Selig                        /s/ Hans van Houte
-------------------------------------   ----------------------------------------
By: Martin Selig                        By: Hans van Houte
Its: Managing Member                    Its: VP, Finance

Dated: February 10, 2006                Dated: February 6, 2006

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                                   EXHIBIT B

                            (LAYOUT OF OFFICE SPACE)

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                            (FLOOR PLAN 10th FLOOR)<PAGE>

                                                                   REDACTED COPY

                                                                   Exhibit 10.11

                       COLLABORATION AND LICENSE AGREEMENT

                                 by and between

                                      WYETH

                acting through its Wyeth Pharmaceuticals Division

                                       and

                          TRUBION PHARMACEUTICALS, INC.

                                December 19, 2005

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                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                                       Page
                                                                                                       ----
<S>                                                                                                    <C>
1.   DEFINITIONS....................................................................................     1

2.   LICENSES.......................................................................................    16

     2.1.    Licenses to Wyeth......................................................................    16
             2.1.1.  Exclusive Licenses.............................................................    16
             2.1.2.  Retained Rights of Trubion.....................................................    17

     2.2.    License to Trubion.....................................................................    17

     2.3.    Exclusivity............................................................................    17
             2.3.1.  CD20 Product Exclusivity.......................................................    17
             2.3.2. [***]......................................................Error! Bookmark not defined
             2.3.3.  Limitations....................................................................    18

     2.4.    Sublicensing...........................................................................    18

     2.5.    Direct Licenses to Affiliates..........................................................    19

     2.6.    Right of Reference.....................................................................    20

     2.7.    Section 365(n) of Bankruptcy Code......................................................    20

     2.8.    No Implied Rights......................................................................    21

3.   RESEARCH PROGRAM...............................................................................    21

     3.1.    Scope and Conduct of the Research Program..............................................    21

     3.2.    Designation of Targets.................................................................    22
             3.2.1..................................................................................    22
             3.2.2.  Released Targets...............................................................    23
             3.2.3.  Wyeth Targets..................................................................    23
             3.2.4.  Excluded Targets...............................................................    24

     3.3.    Term and Termination of the Research Program...........................................    27
             3.3.1.  Research Term..................................................................    27
             3.3.2.  Termination of Research Program by Wyeth.......................................    27

     3.4.    Joint Research Committee...............................................................    28
             3.4.1.  Composition....................................................................    28
             3.4.2.  Responsibilities...............................................................    28
             3.4.3.  Meetings.......................................................................    28
             3.4.4.  Voting.........................................................................    28
             3.4.5.  Dispute Resolution.............................................................    28
             3.4.6.  Minutes........................................................................    29

     3.5.    Research Plan..........................................................................    29

     3.6.    Funding of the Research Program........................................................    29
             3.6.1.  Research Funding...............................................................    29
             3.6.2.  Reimbursement Payments.........................................................    30
             3.6.3.  Records and Audits.............................................................    30

     3.7.    Data and Deliverables..................................................................    31
</TABLE>

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<TABLE>
<S>                                                                                                     <C>
     3.8.    Alliance Managers......................................................................    32

4.   PRODUCT DEVELOPMENT, MANUFACTURING, COMMERCIALIZATION AND REGULATORY MATTERS...................    32

     4.1.    Product Development....................................................................    32

     4.2.    Transfer of Product Data and Filings...................................................    33

     4.3.    Regulatory Approvals...................................................................    33

     4.4.    Regulatory Reporting...................................................................    34

     4.5.    Progress Reports.......................................................................    34

     4.6.    CD20 Product Development...............................................................    35

     4.7.    Joint Development Committee............................................................    36

     4.8.    Joint Project Team; Development Plan...................................................    37

     4.9.    Manufacturing..........................................................................    37

     4.10.   Commercialization......................................................................    38

     4.11.   Co-Promotion Option....................................................................    38

     4.12.   Co-Promotion Committee.................................................................    39

     4.13.   Co-Branding............................................................................    39

     4.14.   Marking................................................................................    39

5.   CONSIDERATION..................................................................................    39

     5.1.    Initial Research and Development Expense Payment.......................................    39

     5.2.    Equity.................................................................................    39

     5.3.    Additional Research and Development Expense Payments...................................    39

     5.4.    Royalties..............................................................................    40
             5.4.1.  Licensed Product Royalties.....................................................    40
             5.4.2.  CD20 Product Royalties.........................................................    40
             5.4.3.  [***].....................................................Error! Bookmark not defined
             5.4.4.  Other Product Royalties........................................................    45
             5.4.5.  Expiration of Royalty Period...................................................    46
             5.4.6.  Royalty Adjustments............................................................    46

     5.5.    Reports and Payments...................................................................    47
             5.5.1.  Cumulative Royalties...........................................................    47
             5.5.2.  Royalty Statements and Payments................................................    48
             5.5.3.  Taxes and Withholding..........................................................    48
             5.5.4.  Currency.......................................................................    49
             5.5.5.  Additional Provisions Relating to Royalties....................................    49
             5.5.6.  Interest on Past Due Payments..................................................    49

     5.6.    Maintenance of Records; Audits.........................................................    49
             5.6.1.  Record Keeping.................................................................    49
             5.6.2.  Audits.........................................................................    50
             5.6.3.  Underpayments/Overpayments.....................................................    50
             5.6.4.  Confidentiality................................................................    50

6.   INTELLECTUAL PROPERTY..........................................................................    51

     6.1.    Inventions; Joint Patent Committee.....................................................    51
             6.1.1.  Ownership and Inventorship.....................................................    51
             6.1.2.  SMIP Improvements..............................................................    51
</TABLE>

                                                                              ii

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<TABLE>
<S>                                                                                                     <C>
             6.1.3.  Joint Patent Committee.........................................................    51

     6.2.    Patent Rights..........................................................................    52
             6.2.1.  Filing, Prosecution and Maintenance of Patent Rights...........................    52
             6.2.2.  Enforcement of Patent Rights...................................................    56
             6.2.3.  Infringement and Third Party Licenses..........................................    59
             6.2.4.  Patent Certifications..........................................................    61
             6.2.5.  Patent Term Restoration........................................................    61

     6.3.    Trademarks.............................................................................    61

7.   CONFIDENTIALITY................................................................................    61

     7.1.    Confidentiality........................................................................    62

     7.2.    Authorized Disclosure and Use..........................................................    62
             7.2.1.  Disclosure.....................................................................    62
             7.2.2.  Use............................................................................    63

     7.3.    SEC Filings............................................................................    63

     7.4.    Public Announcements; Publications.....................................................    64
             7.4.1.  Coordination...................................................................    64
             7.4.2.  Announcements..................................................................    64
             7.4.3.  Publications...................................................................    64

8.   REPRESENTATIONS AND WARRANTIES.................................................................    65

     8.1.    Representations and Warranties of Each Party...........................................    66

     8.2.    Additional Representations and Warranties of Trubion...................................    67

     8.3.    Mutual Covenant........................................................................    67

     8.4.    Additional Covenants of Trubion........................................................    67

     8.5.    Representation by Legal Counsel........................................................    67

     8.6.    No Inconsistent Agreements.............................................................    67

     8.7.    Disclaimer.............................................................................    67

9.   GOVERNMENT APPROVALS; TERM AND TERMINATION.....................................................    68

     9.1.    HSR Filing.............................................................................    68

     9.2.    Other Government Approvals.............................................................    68

     9.3.    Term...................................................................................    68

     9.4.    Termination Upon HSR Denial............................................................    68

     9.5.    Material Breach........................................................................    68

     9.6.    Termination by Wyeth...................................................................    69
             9.6.1.  Termination Without Cause......................................................    70
             9.6.2.  Termination for a Material Safety or Regulatory Issue..........................    70

     9.7.    Effects of Termination.................................................................    70
             9.7.1.  Effect of Termination by Wyeth for Cause.......................................    70
             9.7.2.  Effect of Termination by Trubion for Cause.....................................    71
             9.7.3.  Effect of Termination by Wyeth Without Cause...................................    71
             9.7.4.  Effect of Termination by Wyeth for a Material Safety or Regulatory Issue.......    72
             9.7.5.  Post-Termination Rights to Wyeth Technology and Trubion Technology.............    72
             9.7.6.  Post-Termination Licenses to Wyeth Technology..................................    72
</TABLE>

                                                                             iii

<PAGE>

<TABLE>
<S>                                                                                                     <C>
             9.7.7.  Post-Termination Transfer of Product Data and Filings and Existing Trademarks..    72
             9.7.8.  Manufacturing of Licensed Products After Termination...........................    73
             9.7.9.  Post-Termination Disposition of Inventories of Licensed Products...............    74
             9.7.10. Continuation of Rights and Licenses Under Sections 6.1.1 and 6.1.2.............    74
             9.7.11. Continuation of Other Rights and Obligations...................................    74

     9.8.    [***].............................................................Error! Bookmark not defined

     9.9.    Survival of Certain Obligations........................................................    74

     9.10.   Change of Control......................................................................    75
             9.10.1. Definition.....................................................................    75
             9.10.2. Change of Control of Wyeth.....................................................    76
             9.10.3. Change of Control of Trubion...................................................    78

10.  INDEMNIFICATION AND INSURANCE..................................................................    78

     10.1.   Indemnification by Wyeth...............................................................    78

     10.2.   Indemnification by Trubion.............................................................    78

     10.3.   Procedure..............................................................................    79

     10.4.   Insurance..............................................................................    80

11.  DISPUTE RESOLUTION.............................................................................    80

     11.1.   General................................................................................    80

     11.2.   Failure of Executive Officers to Resolve Dispute.......................................    80

     11.3.   Disclaimer of Consequential and Punitive Damages.......................................    80

12.  MISCELLANEOUS..................................................................................    80

     12.1.   Periodic Executive Meetings............................................................    80

     12.2.   Assignment.............................................................................    81

     12.3.   Further Actions........................................................................    81

     12.4.   Force Majeure..........................................................................    81

     12.5.   Non-Solicitation.......................................................................    82

     12.6.   Correspondence and Notices.............................................................    82
             12.6.1. Ordinary Notices...............................................................    82
             12.6.2. Extraordinary Notices..........................................................    82

     12.7.   Amendment..............................................................................    83

     12.8.   Waiver.................................................................................    83

     12.9.   Severability...........................................................................    84

     12.10.  Descriptive Headings...................................................................    84

     12.11.  Governing Law..........................................................................    84

     12.12.  Entire Agreement of the Parties........................................................    84

     12.13.  Independent Contractors................................................................    84

     12.14.  Counterparts...........................................................................    84
</TABLE>

                                                                              iv

<PAGE>

                                    EXHIBITS

Exhibit 1.122 - TRU-015

Exhibit 1.129 - Trubion Patent Rights

Exhibit 1.132 - Trubion Third Party Agreements

Exhibit 3.2.1 - Trubion's "Milestone One"

Exhibit 3.2.4 - Excluded Targets

Exhibit 4.4 - Adverse Event Reporting Procedures

Exhibit 5.2A - Stock Purchase Agreement

Exhibit 5.2B - Amendment to Investor Rights Agreement

Exhibit 5.3 - Additional Research and Development Expense Payments

Exhibit 8.2(d) - Third Party Rights

Exhibit 8.2(e) - Government Funding Agreements

                                                                               v
<PAGE>

                                                                   REDACTED COPY

                       COLLABORATION AND LICENSE AGREEMENT

     This Collaboration and License Agreement (the "Agreement") is entered into
as of December 19, 2005 (the "Signing Date"), by and between Wyeth, together
with its Affiliates (as defined below), acting through its Wyeth Pharmaceuticals
Division, a corporation organized and existing under the laws of the State of
Delaware and having a place of business at 500 Arcola Road, Collegeville,
Pennsylvania 19426 (collectively, "Wyeth") and Trubion Pharmaceuticals, Inc.,
together with its Affiliates (as defined below), a corporation organized and
existing under the laws of the State of Delaware and having a principal place of
business at 2401 4th Avenue, Suite 1050, Seattle, Washington 98121
(collectively, "Trubion"). Wyeth and Trubion may each be referred to herein
individually as a "Party" and collectively as the "Parties".

     WHEREAS, Wyeth is engaged in the research, development and
commercialization of pharmaceutical and health care products;

     WHEREAS, as of the Signing Date, Trubion has developed certain SMIPs (as
defined below) and CD20 Products (as defined below), as well as certain Patent
Rights (as defined below) and Know-How (as defined below) pertaining to
Trubion's SMIP technology platform;

     WHEREAS, Wyeth and Trubion desire to collaborate to discover, research and
develop, and Wyeth desires to research, develop, manufacture and commercialize,
Licensed Products (as defined below) as provided herein; and

     WHEREAS, Wyeth desires to obtain from Trubion, and Trubion desires to grant
to Wyeth, certain exclusive rights so that Wyeth may develop, manufacture and
commercialize such Licensed Products, as provided herein.

     NOW THEREFORE, in consideration of the mutual promises and covenants set
forth below and other good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the Parties hereby agree as
follows:

1.   DEFINITIONS.

     1.1. "ADDITIONAL RESEARCH AND DEVELOPMENT EXPENSE PAYMENT" shall have the
          meaning set forth in Section 5.3 hereof.

     1.2. "ADDITIONAL THIRD PARTY LICENSES" shall have the meaning set forth in
          Section 6.2.3(a) hereof.

     1.3. "AFFILIATE(S)" shall mean, with respect to any Person, any other
          Person which controls, is controlled by or is under common control
          with such Person. A Person shall be regarded as in control of another
          entity if it owns

<PAGE>

          or controls at least fifty percent (50%) of the equity securities of
          the subject entity entitled to vote in the election of directors (or,
          in the case of an entity that is not a corporation, for the election
          of the corresponding managing authority); provided, however, that the
          term "Affiliate" shall not include subsidiaries or other entities in
          which a Party or its Affiliates owns a majority of the ordinary voting
          power necessary to elect a majority of the board of directors or other
          governing board, but is restricted from electing such majority by
          contract or otherwise, until such time as such restrictions are no
          longer in effect.

     1.4. "AGREEMENT" shall have the meaning set forth in the preamble hereof.

     1.5. "BANKRUPTCY CODE" shall have the meaning set forth in Section 2.7
          hereof.

     1.6. "BLA" shall have the meaning set forth in Section 1.100 hereof.

     1.7. "CALENDAR QUARTER" shall mean the respective periods of three (3)
          consecutive calendar months ending on March 31, June 30, September 30
          or December 31, for so long as this Agreement is in effect.

     1.8. "CATEGORY 1 COVERED SMIP IMPROVEMENT" shall have the meaning set forth
          in Section 6.1.3(b) hereof.

     1.9. "CATEGORY 2 COVERED SMIP IMPROVEMENT" shall have the meaning set forth
          in Section 6.1.3(b) hereof.

     1.10. "CD20 ANTIGEN" shall mean the human protein antigen that is known as
          CD20, and identified as a full length CD20 protein antigen in GenBank,
          and identified by [***] or [***], and any other protein that [***] as
          the foregoing.

     1.11. "CD20 EFFECTIVE ROYALTY RATE" shall have the meaning set forth in
          Section 5.4.2(a) hereof.

     1.12. "CD20 PRODUCT" shall mean any TRU-015 Product and/or Follow-On CD20
          Product (as the context requires).

     1.13. "CELL LINES" shall mean the cell lines and any other expression
          systems that produce or express any SMIP.

     1.14. "CHANGE OF CONTROL" shall have the meaning set forth in Section
          9.10.1 hereof.

     1.15. "CLINICAL STUDY SUPPLIES" shall have the meaning set forth in Section
          4.9 hereof.

                                                                               2

<PAGE>

     1.16. "COMBINATION PRODUCT" shall mean any product containing as active
          ingredients both (a) a Product and (b) one or more other
          pharmaceutically active compounds or substances.

     1.17. "COMBINATION SALE" shall have the meaning set forth in Section 1.76
          hereof.

     1.18. "COMMERCIALIZATION" OR "COMMERCIALIZE" shall mean activities directed
          to marketing, promoting, distributing, importing or selling a product.
          Commercialization shall not include any activities related to
          Manufacturing or Development.

     1.19. "COMMERCIALLY REASONABLE EFFORTS" shall mean, with respect to the
          efforts to be expended by any Party with respect to any objective,
          those reasonable, diligent, good faith efforts to accomplish such
          objective as such Party would normally use to accomplish a similar
          objective under similar circumstances. With respect to any objective
          relating to the Development and/or Commercialization of a Licensed
          Product by any Party, "COMMERCIALLY REASONABLE EFFORTS" shall mean
          those efforts and resources normally used by such Party with respect
          to a product owned or controlled by such Party, or to which such Party
          has similar rights, which product is of similar market potential and
          is at a similar stage in its development or life as is such Licensed
          Product, taking into account issues of safety, efficacy, product
          profile, the competitiveness of the marketplace, the proprietary
          position of the Licensed Product, the regulatory structure involved,
          profitability of the Licensed Product and other relevant commercial
          factors. A "COMMERCIALLY REASONABLE" action or decision of a Party
          refers in this Agreement to an action or decision taken or made by
          such Party using its Commercially Reasonable Efforts.

     1.20. "CONFIDENTIAL INFORMATION" of a Party shall mean all Know-How or
          other information, including, without limitation, proprietary
          information and materials (whether or not patentable) regarding such
          Party's technology, products, business information or objectives, that
          is communicated in any way or form by the Disclosing Party to the
          Receiving Party, either prior to or after the Effective Date of this
          Agreement, and whether or not such Know-How or other information is
          identified as confidential at the time of disclosure; provided that,
          information not identified as confidential by the Disclosing Party
          shall be deemed to be Confidential Information of the Disclosing Party
          if the Receiving Party knows, or should have had a reasonable
          expectation, that the information communicated by the Disclosing Party
          is Confidential Information of the Disclosing Party. The terms and
          conditions of this Agreement shall be considered Confidential
          Information of both Parties.

                                                                               3

<PAGE>

     1.21. "CONJUGATE(S)" shall mean SMIP(s) fused genetically or linked, either
          directly or through a linker molecule, with any biological,
          cytostatic, cytotoxic or radioactive agent.

     1.22. "CONTROL" OR "CONTROLLED" shall mean with respect to any (a) item of
          information, including, without limitation, Know-How, or (b)
          intellectual property right, the possession (whether by ownership or
          license, other than pursuant to this Agreement) by a Party of the
          ability to grant to the other Party a license or to extend other
          rights as provided herein, under such item or right without violating
          the terms of any agreement or other arrangements with any Third Party.

     1.23. "CO-PROMOTION" shall mean the joint promotion of a CD20 Product in
          the United States by both Parties and/or their respective Affiliates
          under the same CD20 Product Trademark(s). "CO-PROMOTE," when used as a
          verb, shall mean to engage in such Co-Promotion.

     1.24. "CO-PROMOTION PERIOD" shall have the meaning set forth in Section
          4.11 hereof.

     1.25. "COVERED SMIP IMPROVEMENT" shall have the meaning set forth in
          Section 6.1.2 hereof.

     1.26. "DEPOSITED PROTEIN" shall have the meaning set forth in Section 1.45
          hereof.

     1.27. "DESIGNATED TARGET(S)" shall have the meaning set forth in Section
          9.8 hereof.

     1.28. "DEVELOPMENT" OR "DEVELOP" shall mean non-clinical and clinical drug
          development activities pertaining to a product, including, without
          limitation, toxicology, pharmacology, test method development and
          stability testing, process development, formulation development,
          delivery system development, quality assurance and quality control
          development, statistical analysis, clinical studies (including pre-
          and post-approval studies), regulatory affairs, pharmacovigilance and
          Regulatory Approval and clinical study regulatory activities
          (including regulatory activities directed to obtaining pricing and
          reimbursement approvals).

     1.29. "DEVELOPMENT PLAN" shall mean the written plan for the Development of
          CD20 Products described in Section 4.8 hereof.

     1.30. "DISCLOSING PARTY" shall have the meaning set forth in Section 7.1
          hereof.

     1.31. "EFFECTIVE DATE" shall mean the later to occur of (a) the Signing
          Date and (b) the HSR Clearance Date.

                                                                               4

<PAGE>

     1.32. "EXCHANGE ACT" shall mean the Securities Exchange Act of 1934, as
          amended.

     1.33. "EXCLUDED TARGET(S)" shall mean the Target(s) described in Section
          3.2.4 hereof as Excluded Target(s).

     1.34. "EXCLUSIVITY COVENANTS" shall have the meaning set forth in Section
          9.10.2(c) hereof.

     1.35. "EXECUTIVE OFFICERS" shall mean the President of Wyeth
          Pharmaceuticals (or an executive officer of Wyeth designated by such
          President of Wyeth Pharmaceuticals) and the Chief Executive Officer of
          Trubion (or an executive officer of Trubion designated by such Chief
          Executive Officer).

     1.36. "EXERCISE NOTICE" shall have the meaning set forth in Section
          9.10.2(c) hereof.

     1.37. "EXISTING ACTIVITIES" shall have the meaning set forth in Section
          9.10.2(c) hereof.

     1.38. "EXISTING TRADEMARKS" shall have the meaning set forth in Section
          9.7.1(a).

     1.39. "FDA" shall mean the United States Food and Drug Administration or
          any successor agency thereto.

     1.40. "FD&C ACT" shall mean the United States Federal Food, Drug, and
          Cosmetic Act (21 U.S.C. Section 301 et seq.), as amended, and the
          rules and regulations promulgated thereunder.

     1.41. "FIRST COMMERCIAL SALE" shall mean, with respect to a given Licensed
          Product and any country in the Territory, the first sale or transfer
          for value of such Licensed Product under this Agreement by Wyeth or
          its sublicensees to a Third Party in such country following receipt of
          marketing authorization from the appropriate Regulatory Authority
          permitting commercial sale of such Licensed Product in such country.

     1.42. "FOLLOW-ON CD20 PRODUCT" shall mean any product containing a
          Follow-On CD20 SMIP.

     1.43. "FOLLOW-ON CD20 SMIP" shall mean any SMIP (other than TRU-015)
          directed against the CD20 Antigen or a portion thereof.

     1.44. "FTE" shall mean a full time equivalent scientific person (M.S. or
          Ph.D. level) year, consisting of a minimum of a total of one thousand
          eight hundred eighty (1,880) hours per year of scientific work by an
          employee of Trubion on or directly related to and in support of the
          Research Program.

                                                                               5

<PAGE>

          Work on or directly related to the Research Program can include, but
          is not limited to, experimental preclinical laboratory and research
          work, recording and writing up results, reviewing literature and
          references, holding scientific discussions, managing and leading
          scientific staff and carrying out management duties, in each case
          where such activities are directly related to the Research Program.

     1.45. [***]

     1.46. [***]

     1.47. [***]

     1.48. [***]

     1.49. [***]

     1.50. "HSR ACT" shall mean the Hart-Scott-Rodino Antitrust Improvements Act
          of 1976, as amended, and the rules and regulations promulgated
          thereunder.

     1.51. "HSR FILING" shall mean filings by Wyeth and Trubion with the United
          States Federal Trade Commission and the Antitrust Division of the
          United States Department of Justice of a Notification and Report Form
          for Certain Mergers and Acquisitions (as that term is defined in the
          HSR Act) with respect to the matters set forth in this Agreement,
          together with all required documentary attachments thereto.

     1.52. "HSR CLEARANCE DATE" shall mean the earliest date on which the
          Parties have actual knowledge that all applicable waiting periods
          under the HSR Act with respect to the transactions contemplated
          hereunder have expired or have been terminated.

     1.53. "IND" shall mean an Investigational New Drug Application, as defined
          in the FD&C Act, that is required to be filed with the FDA before
          beginning clinical testing of a Licensed Product in human subjects, or
          an equivalent foreign filing.

     1.54. "INDEMNIFIED PARTY" shall have the meaning set forth in Section 10.3
          hereof.

     1.55. "INDEMNIFYING PARTY" shall have the meaning set forth in Section 10.3
          hereof.

     1.56. "INITIAL TERM" shall have the meaning set forth in Section 3.3.1
          hereof.

     1.57. "JDC" shall have the meaning set forth in Section 4.7 hereof.

                                                                               6

<PAGE>

     1.58. "JOINT INVENTION(S)" shall have the meaning set forth in Section
          6.1.1 hereof.

     1.59. "JOINT KNOW-HOW" shall mean that Know-How related to the Licensed
          Products that is jointly owned by the Parties in accordance with
          Section 6.1.1 of this Agreement.

     1.60. "JOINT PATENT COMMITTEE" shall mean the committee described in
          Section 6.1.3 hereof.

     1.61. "JOINT PATENT RIGHT(S)" shall mean those Patent Right(s) that claim
          Joint Know-How or Joint Invention(s).

     1.62. "JOINT TECHNOLOGY" shall mean the Joint Patent Rights, the Joint
          Inventions and the Joint Know-How.

     1.63. "JPT" shall have the meaning set forth in Section 4.8 hereof.

     1.64. "JRC" shall have the meaning set forth in Section 3.4.1 hereof.

     1.65. "JRC LIAISON" shall mean a JRC member designated by a Party as its
          "JRC Liaison" in accordance with Section 3.4.3 hereof.

     1.66. "KNOW-HOW" shall mean inventions, discoveries, data, information,
          processes, methods, techniques, materials, technology, results or
          other know-how, whether or not patentable.

     1.67. "LIABILITIES" shall have the meaning set forth in Section 10.1
          hereof.

     1.68. "LICENSED PRODUCT(S)" shall mean any Product(s) or Combination
          Product(s).

     1.69. "LICENSED TARGET(S)" shall mean any Trubion Target(s) or Wyeth
          Target(s), so long as they remain the subject of the licenses granted
          to Wyeth under this Agreement.

     1.70. "MAJOR INDICATION(S)" shall mean, with respect to any CD20 Product,
          any indication with a prevalence-based patient population of at least
          [***] patients in the United States, including, without limitation,
          [***].

     1.71. "MAJOR MARKET COUNTRY" shall mean any of the United States, the
          United Kingdom, France, Germany, Italy, Spain or Japan.

     1.72. "MANUFACTURING" or "MANUFACTURE" shall mean activities directed to
          producing, manufacturing, processing, filling, finishing, packaging,
          labeling, quality assurance testing and release, shipping and storage
          of a product.

                                                                               7

<PAGE>

     1.73. "NCBI" shall have the meaning set forth in Section 3.2.1 hereof.

     1.74. "NDA" shall have the meaning set forth in Section 1.100 hereof.

     1.75. "NET COMBINATION SALE AMOUNT" shall have the meaning set forth in
          Section 1.76 hereof.

     1.76. "NET SALES" shall mean the gross amounts charged for sales of
          Licensed Products (on which payments are due under this Agreement) by
          Wyeth or its sublicensees to Third Parties, less the sum of (a) and
          (b) where (a) is a provision, determined under Generally Accepted
          Accounting Principles in the United States and in accordance with
          Wyeth's customary and usual accrual procedures, consistently applied,
          for the accrual of (i) trade, cash, quantity and wholesaler discounts
          or rebates (other than price discounts granted at the time of sale),
          if any, allowed or paid, (ii) credits or allowances given or made for
          rejection or return of, previously sold Licensed Products or for
          retroactive price reductions (including Medicaid, managed care and
          similar types of rebates), (iii) taxes, duties or other governmental
          charges levied on or measured by the billing amount (excluding income
          and franchise taxes), as adjusted for rebates and refunds, and (iv)
          charges for packing, freight, and shipping to the extent included in
          the invoice price and (b) is a periodic adjustment (positive or
          negative, as applicable), determined under Generally Accepted
          Accounting Principles in the United States and in accordance with
          Wyeth's customary and usual adjustment procedures, consistently
          applied, of the provision determined in (a) to reflect amounts
          actually incurred for (i), (ii), (iii) and (iv) based on amounts
          actually invoiced or as separately set forth in agreements with Third
          Parties or as deducted or paid as required by applicable law or
          regulations. (The deductions described in (i), (ii), (iii) and (iv)
          are referred to herein as "Permitted Deductions.") In the case of any
          sale of Licensed Products for consideration other than cash, Net Sales
          shall be calculated on the fair market value of the consideration
          received.

          Notwithstanding the foregoing, if a Licensed Product is sold as a
          Combination Product (a "Combination Sale"), the Net Sales for such
          Combination Product shall be the portion of such Combination Sale
          allocable to the Licensed Product determined as follows:

          Except as provided below, the Net Sales amount for a Combination Sale
          shall equal the gross amount invoiced for the Combination Sale,
          reduced by the Permitted Deductions (the "Net Combination Sale
          Amount"), multiplied by the fraction A/(A+B), where:

               A is the invoice price, in the country where such Combination
               Sale occurs, of the Licensed Product contained in the Combination
               Product, if sold as a separate product in such country by Wyeth
               or

                                                                               8

<PAGE>

               its sublicensees, as the case may be, and B is the aggregate of
               the invoice price or prices, in such country, of products which
               collectively contain as their respective sole active ingredient
               such other pharmaceutically active compounds or substances, as
               the case may be, included in the Combination Product, if sold
               separately in such country by Wyeth or its sublicensees, as
               applicable.

          In the event that Wyeth or its sublicensees sell the Licensed Product
          included in a Combination Product as a separate product in a country,
          but do not separately sell all of the other pharmaceutically active
          compounds or substances, as the case may be, included in such
          Combination Product in such country, the calculation of the Net Sales
          amount for such Combination Sale shall be determined by multiplying
          the Net Combination Sale Amount by the fraction A/C where:

               A is the average wholesale price, in such country, charged by
               Wyeth or its sublicensees, as the case may be, for the Licensed
               Product contained in such Combination Product, when sold as a
               separate product by Wyeth or its sublicensees, as applicable, and
               C is the average wholesale price, in such country, charged by
               Wyeth or its sublicensees, as applicable, for the entire
               Combination Product.

          In the event that Wyeth or its sublicensees do not sell the Licensed
          Product included in a Combination Product as a separate product in a
          country where such Combination Sale occurs, but do separately sell
          products which collectively contain as their respective sole active
          ingredient all of the other pharmaceutically active compounds or
          substances, as the case may be, included in the Combination Product in
          such country, the calculation of Net Sales resulting from such
          Combination Sale shall be determined by multiplying the Net
          Combination Sale Amount by the fraction (C-D)/C, where:

               C is the average wholesale price, in such country, charged by
               Wyeth or its sublicensees, as the case may be, for the entire
               Combination Product, and D is the average wholesale price charged
               by Wyeth or its sublicensees, as the case may be, for the
               products which collectively contain as their sole active
               ingredient such other pharmaceutically active compounds or
               substances, as the case may be, included in the Combination
               Product.

          Where active ingredient portions of a Combination Product are sold
          separately as other products but in different dosage strengths than
          are in the Combination Product, the calculation of the Net Sales
          amount for such Combination Product shall be based on appropriate
          proration of the

                                                                               9

<PAGE>

          amounts of each active ingredient component included therein when
          applying the formulas set forth above.

          Where the calculation of Net Sales resulting from a Combination Sale
          in a country cannot be determined by any of the foregoing methods, the
          calculation of Net Sales for such Combination Sale shall be that
          portion of the Net Combination Sale Amount reasonably determined in
          good faith by the Parties as properly reflecting the value of the
          Licensed Product included in the Combination Product.

          Notwithstanding the foregoing, Net Sales shall not include any
          reimbursement received by Wyeth or its sublicensees in respect of the
          use of a Licensed Product in a country solely as part of a clinical
          trial prior to the receipt of marketing authorization required to
          commence commercial sales of such Licensed Product in such country.

     1.77. "NEW PROTEIN" shall have the meaning set forth in Section 1.45
          hereof.

     1.78. "NICHE INDICATION(S)" shall mean, with respect to any CD20 Product,
          any indication, including, but not limited to, [***], for such CD20
          Product other than a Major Indication.

     1.79. "NOTICE OF BREACH" shall have the meaning set forth in Section 9.5
          hereof.

     1.80. "NOTICE OF MODIFICATION" shall have the meaning set forth in Section
          9.5 hereof.

     1.81. "NOTICE OF TERMINATION" shall have the meaning set forth in Section
          9.5 hereof.

     1.82. "OTHER PRODUCT" shall mean any product containing a SMIP directed
          against a Wyeth Target or a portion thereof.

     1.83. "PART(Y/IES)" shall have the meaning set forth in the preamble
          hereof.

     1.84. "PATENT RIGHTS" shall mean any and all (a) patents, (b) pending
          patent applications, including, without limitation, all provisional
          applications, substitutions, continuations, continuations-in-part,
          divisions, renewals, and all patents granted thereon, (c) all
          patents-of-addition, reissues, reexaminations and extensions or
          restorations by existing or future extension or restoration
          mechanisms, including, without limitation, supplementary protection
          certificates or the equivalent thereof, (d) inventor's certificates,
          and (e) all United States and foreign counterparts of any of the
          foregoing.

     1.85. "PERSON" shall mean an individual, sole proprietorship, partnership,
          limited partnership, limited liability partnership, corporation,
          limited liability

                                                                              10

<PAGE>

          company, business trust, joint stock company, trust, incorporated
          association, joint venture or similar entity or organization,
          including a government or political subdivision, department or agency
          of a government.

     1.86. "PERMITTED DEDUCTION" shall have the meaning set forth in Section
          1.76 hereof.

     1.87. "PHASE I CLINICAL STUDY" shall mean a study of a Licensed Product in
          human subjects with the endpoint of determining initial tolerance,
          safety or pharmacokinetic information in single dose, single ascending
          dose, multiple dose and/or multiple ascending dose regimens.

     1.88. "PHASE II CLINICAL STUDY" shall mean a study of a Licensed Product in
          human patients to determine initial efficacy and dose range finding
          before embarking on Phase III Clinical Studies.

     1.89. "PHASE IIA CLINICAL STUDY" shall mean Trubion's TRU-015 Protocol
          15001.

     1.90. "PHASE IIB CLINICAL STUDY" shall mean Trubion's TRU-015 Protocol
          15002.

     1.91. "PHASE III CLINICAL STUDY" shall mean a pivotal study (whether or not
          denominated a "Phase III" clinical study under applicable regulations)
          in human patients with a defined dose or a set of defined doses of a
          Licensed Product designed to ascertain efficacy and safety of such
          Licensed Product for the purpose of enabling the preparation and
          submission of Regulatory Approval Applications to the competent
          Regulatory Authorities in a country of the Territory.

     1.92. "PREVIOUSLY DEPOSITED PROTEIN" shall have the meaning set forth in
          Section 3.2.4(b) hereof.

     1.93. "PRODUCT" shall mean any CD20 Product, [***], or Other Product, or
          any Conjugate of any CD20 Product, [***], or Other Product.

     1.94. "PRODUCT DATA AND FILINGS" shall mean (a) all clinical protocols,
          studies, clinical data and results used in or resulting from any
          clinical trial of any Licensed Product and (b) all INDs, Regulatory
          Approval Applications and Regulatory Approvals regarding any Licensed
          Product.

     1.95. "PRODUCT LICENSE" shall have the meaning set forth in Section 2.1.1
          hereof.

     1.96. "PRODUCT-RELATED PATENT RIGHTS" shall have the meaning set forth in
          Section 6.2.1(a) hereof.

                                                                              11

<PAGE>

     1.97. "PROVISIONAL EXCLUDED TARGET" shall mean a Target described in
          Section 3.2.4 hereof as a Provisional Excluded Target.

     1.98. "RECEIVING PARTY" shall have the meaning set forth in Section 7.1
          hereof.

     1.99. "RECOMBINANT DNA" shall mean the DNA sequences encoding any SMIP
          including, without limitation, any DNA plasmid expression construct
          encoding any such SMIP.

     1.100. "REGULATORY APPROVAL" shall mean the technical, medical and
          scientific licenses, registrations, authorizations and approvals
          (including, without limitation, approvals of New Drug Applications
          ("NDAs") or Biologic License Applications ("BLAs"), supplements and
          amendments, pre- and post- approvals, pricing approvals, and labeling
          approvals) of any national, supra-national, regional, state or local
          regulatory agency, department, bureau, commission, council or other
          governmental entity, necessary for the commercial Manufacture,
          distribution, marketing, promotion, offer for sale, use, import,
          export and sale of Licensed Product(s) in a regulatory jurisdiction in
          the Territory. For the sake of clarity, Regulatory Approval shall not
          be deemed to have been obtained in a country other than the United
          States until any applicable governmental pricing approvals have also
          been obtained in such country. Regulatory Approval of a Licensed
          Product shall be deemed to have been obtained in the United States
          immediately upon BLA approval for such Licensed Product in the United
          States.

     1.101. "REGULATORY APPROVAL APPLICATION" shall mean an application
          submitted to the appropriate Regulatory Authority seeking Regulatory
          Approval of a Licensed Product for use in one or more therapeutic
          indications in a regulatory jurisdiction within the Territory.

     1.102. "REGULATORY AUTHORIT(Y/IES)" shall mean any national (e.g., the
          FDA), supra-national (e.g., the European Commission, the Council of
          the European Union, or the European Agency for the Evaluation of
          Medicinal Products), regional, state or local regulatory agency,
          department, bureau, commission, council or other governmental entity
          in each country of the Territory involved in the granting of
          Regulatory Approval for a Licensed Product.

     1.103. "RELEASED TARGET" shall have the meaning set forth in Section 3.2.2
          hereof.

     1.104. "REPLACEMENT TARGET" shall have the meaning set forth in Section
          3.2.3 hereof.

     1.105. "RESEARCH BUDGET" shall have the meaning set forth in Section 3.5
          hereof.

                                                                              12

<PAGE>

     1.106. "RESEARCH PLAN" shall mean the written plan for the conduct of the
          Research Program described in Section 3.5 hereof as approved and
          amended by the Parties in accordance with Section 3.5 hereof.

     1.107. "RESEARCH PROGRAM" shall have the meaning set forth in Section 3.1
          hereof.

     1.108. "RESEARCH PROGRAM DATA" shall have the meaning set forth in Section
          3.7 hereof.

     1.109. "RESEARCH TERM" shall have the meaning set forth in Section 3.3.1
          hereof.

     1.110. "ROYALTY PERIOD" shall mean the period of time beginning on the date
          of the First Commercial Sale of a Licensed Product in any country and,
          on a Licensed Product-by-Licensed Product and country-by-country
          basis, extending until the earlier of (a) the termination of this
          Agreement pursuant to Article 9 hereof with respect to such Licensed
          Product in such country or (b) the later of (i) the date on which the
          last Valid Claim included within the Trubion Technology ceases to be a
          Valid Claim, which Valid Claim would be infringed by the composition,
          Manufacture, use, sale, offer for sale or importing of such Licensed
          Product in such country, or (ii)(A) with respect to CD20 Products, the
          [***] anniversary of the First Commercial Sale for the first Major
          Indication of such CD20 Product in such country (provided, however,
          that if such CD20 Product has received Regulatory Approval for a Niche
          Indication in such country but has not received Regulatory Approval
          for a Major Indication in such country, the Royalty Period as defined
          under and for purposes of this clause (ii)(A) for such CD20 Product in
          such country shall be suspended beginning on the [***] anniversary of
          the First Commercial Sale of such CD20 Product in such country until
          such time, if at all, as Regulatory Approval has been obtained
          permitting the marketing of such CD20 Product for a Major Indication
          in such country, at which point such Royalty Period shall commence
          with respect to such CD20 Product for a Major Indication) and (B) with
          respect to each other Licensed Product, the [***] anniversary of the
          First Commercial Sale of such Licensed Product in such country.

     1.111. "SIGNING DATE" shall have the meaning set forth in the preamble
          hereof.

     1.112. "SMIP(S)" or small modular immuno-pharmaceutical(s) shall mean a
          single chain polypeptide that (i) [***] (ii) binds with specificity to
          a target antigen, (iii) has a binding domain, and (iv) may have an
          effector domain which may or may not have effector function, [***].

     1.113. "SMIP IMPROVEMENT" shall mean an invention consisting of any
          modification to the polynucleotide sequence encoding or the amino acid

                                                                              13

<PAGE>

          sequence of a SMIP, if the practice of such invention would infringe
          Patent Rights Controlled by Trubion at the time such invention is
          made.

     1.114. [***].

     1.115. "SUCCESSOR PARTY" shall have the meaning set forth in Section
          9.10.2(a) hereof.

     1.116. "SUED PARTY" shall have the meaning set forth in Section 6.2.3(b)
          hereof.

     1.117. "TARGET" shall mean [***].

     1.118. "TARGET CANDIDATE" [***].

     1.119. "TERRITORY" shall mean the entire world.

     1.120. "THIRD PART(Y/IES)" shall mean any Person(s) other than Wyeth or
          Trubion.

     1.121. "TRADEMARK" shall mean those trademarks used in connection with the
          Commercialization of any Licensed Product by Wyeth or its sublicensees
          hereunder.

     1.122. "TRU-015" shall mean the chimeric SMIP directed against the CD20
          Antigen that is currently designated by Trubion as "TRU-015," as
          further described on Exhibit 1.122 attached hereto.

     1.123. "TRU-015 PRODUCT" shall mean any product containing TRU-015.

     1.124. "TRUBION" shall have the meaning set forth in the preamble hereof.

     1.125. "TRUBION ADDITIONAL THIRD PARTY LICENSE" shall have the meaning set
          forth in Section 6.2.3(a) hereof.

     1.126. "TRUBION INDEMNIFIED PARTY" shall have the meaning set forth in
          Section 10.1 hereof.

     1.127. "TRUBION KNOW-HOW" shall mean any Know-How, other than the Joint
          Know-How, that (a) Trubion Controls as of the Effective Date or that
          comes into the Control of Trubion during the term of this Agreement
          (other than through the grant of a license by Wyeth) and (b) relates
          to any Cell Lines, Conjugates, Licensed Products, Recombinant DNA,
          SMIPs, Licensed Targets, Target Candidates or the Development,
          Manufacture or use of any of the foregoing.

     1.128. "TRUBION LAWYERS" shall have the meaning set forth in Section 3.2.1
          hereof.

                                                                              14
<PAGE>

     1.129. "TRUBION PATENT RIGHTS" shall mean Patent Rights, other than Joint
          Patent Rights, that (a) Trubion Controls as of the Effective Date or
          that come into the Control of Trubion during the term of this
          Agreement and (b) claim any Trubion Know-How. Those Trubion Patent
          Rights known to be existing as of the Signing Date are listed on
          Exhibit 1.129 attached hereto.

     1.130. "TRUBION TARGET" shall mean each of the human CD20 Antigen and/or
          [***], as the context may require.

     1.131. "TRUBION TECHNOLOGY" shall mean Trubion's interest in the Trubion
          Patent Rights, the Trubion Know-How, the Joint Technology and the
          Research Program Data.

     1.132. "TRUBION THIRD PARTY AGREEMENT(S)" shall mean the agreements
          specified on Exhibit 1.132 between Trubion and the indicated Third
          Parties that relate to the research, Development, Manufacture and/or
          Commercialization of Licensed Products under this Agreement.

     1.133. "U.S. WYETH PHARMACEUTICALS" shall have the meaning set forth in
          Section 12.5 hereof.

     1.134. "VALID CLAIM" shall mean a claim that (a) in the case of any
          unexpired United States or foreign patent, shall not have been
          dedicated to the public, disclaimed, nor held invalid or unenforceable
          by a court or government agency of competent jurisdiction in an
          unappealed or unappealable decision, or (b) in the case of any United
          States or foreign patent application, (i) shall not have been
          cancelled, withdrawn or abandoned, without being refiled in another
          application in the applicable jurisdiction, (ii) shall not have been
          finally rejected by an administrative agency or other governmental
          action from which no appeal can be taken and (iii) shall not have been
          pending for more than [***], in either case which claim (if issued)
          would cover the Manufacture, use or sale of any Licensed Product. For
          purposes of this definition, the time period for which a claim is
          pending shall begin on the priority date for such claim, and shall
          continue until such claim is either issued or is no longer deemed to
          be a Valid Claim in accordance with the preceding sentence regardless
          of whether such claim is amended or refiled in another application in
          the applicable jurisdiction. If a claim of a patent application which
          ceased to be a Valid Claim under (b) due to the passage of time later
          issues as part of a patent described within (a) then it shall again be
          considered to be a Valid Claim effective as of the issuance of such
          patent.

     1.135. "WYETH" shall have the meaning set forth in the preamble hereof.

     1.136. "WYETH APPLIED TECHNOLOGY" shall mean, with respect to any Licensed
          Product, that Wyeth Technology which (a) Wyeth had applied to such

                                                                              15

<PAGE>

          Licensed Product prior to any termination of any rights under this
          Agreement with respect to such Licensed Product, provided that such
          Wyeth Technology is necessary or useful for the continued research,
          Development, Manufacture or Commercialization of such Licensed Product
          as it exists at the time of such termination, or (b) Wyeth had
          incorporated into such Licensed Product prior to any termination of
          rights under this Agreement with respect to such Licensed Product;
          provided that Wyeth shall use its Commercially Reasonable Efforts to
          sublicense or otherwise transfer rights under any Third-Party license
          to which the use or exploitation of such Wyeth Applied Technology is
          subject; and further provided, however, that with respect to each of
          clauses (a) and (b) of this Section 1.136, such Wyeth Technology shall
          not include any of Wyeth's conjugation technology.

     1.137. "WYETH INDEMNIFIED PARTY" shall have the meaning set forth in
          Section 10.2 hereof.

     1.138. "WYETH KNOW-HOW" shall mean any Know-How, other than the Joint
          Know-How, that (a) Wyeth Controls as of the Effective Date or that
          comes into the Control of Wyeth (other than as a result of the
          licenses granted by Trubion to Wyeth under Section 2.1 hereof) during
          the term of this Agreement and (b) relates to the Cell Lines,
          Conjugates, Recombinant DNA, Licensed Products, SMIPs, Target
          Candidates or Licensed Targets or the Development, Manufacture, use or
          Commercialization of any of the foregoing.

     1.139. "WYETH PATENT RIGHTS" shall mean Patent Rights, other than the Joint
          Patent Rights, that (a) Wyeth Controls as of the Effective Date or
          that come into the Control of Wyeth (other than as a result of the
          licenses granted by Trubion to Wyeth under Section 2.1 hereof) during
          the term of this Agreement and (b) claim any Wyeth Know-How.

     1.140. "WYETH TARGETS" shall mean the Targets designated by Wyeth under the
          Research Program, as described in Section 3.2 hereof.

     1.141. "WYETH TECHNOLOGY" shall mean Wyeth's interest in the Wyeth Patent
          Rights, the Wyeth Know-How, the Joint Technology and the Research
          Program Data.

2.   LICENSES.

     2.1. LICENSES TO WYETH.

          2.1.1. EXCLUSIVE LICENSES. Subject to the terms and conditions of this
               Agreement, Trubion, effective as of the Effective Date, hereby
               grants to Wyeth an exclusive license (exclusive even as to
               Trubion,

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<PAGE>

               except to the extent necessary for Trubion to perform its
               obligations under this Agreement), with the right to grant
               sublicenses in accordance with the provisions of Section 2.4
               hereof, under the Trubion Technology, to research, Develop, have
               Developed, make, have made, Manufacture, use, have used, import,
               have imported, export, have exported, distribute, have
               distributed, market, have marketed, offer and have offered for
               sale, sell, have sold and Commercialize (subject to Section 4.11)
               Licensed Products in the Territory (the license granted under
               this Section 2.1.1 is sometimes referred to herein as the
               "Product License").

          2.1.2. RETAINED RIGHTS OF TRUBION. For the avoidance of doubt, but
               subject to Sections 2.3 and 3.2 hereof, Trubion shall retain: (a)
               all rights under the Trubion Technology with respect to the
               research, Development, Manufacture, use and Commercialization of
               SMIPs that (i) [***] to Targets that are not Licensed Targets and
               (ii) do not [***] to any Licensed Targets; and (b) the right to
               use SMIPs which [***] to one or more Licensed Targets in in vitro
               studies conducted solely as part of Trubion's internal research
               efforts, provided, however, that Trubion shall not provide any
               such SMIP (that [***] to a Licensed Target) to any Third Party or
               utilize any such SMIP (that [***] to a Licensed Target) in a
               collaboration with any Third Party, except with Wyeth's prior
               written consent.

     2.2. LICENSE TO TRUBION. Wyeth hereby grants to Trubion a royalty-free
          non-exclusive license, with no right to grant sublicenses, under the
          Wyeth Technology, solely for the purpose of, and limited to, Trubion's
          use of the Wyeth Technology in connection with the Trubion Technology
          to research, Develop, have Developed, make, have made, use and have
          used Licensed Products to fulfill its obligations under this
          Agreement. In addition, Wyeth hereby grants to Trubion the
          non-exclusive license under Wyeth's rights to Covered SMIP
          Improvements as set forth in greater detail in Section 6.1.2.

     2.3. EXCLUSIVITY.

          2.3.1. CD20 PRODUCT EXCLUSIVITY. Subject to Section 2.3.3, and except
               for Development of the CD20 Products pursuant to the terms of
               this Agreement, neither Party shall Develop any human therapeutic
               product that contains a protein that [***] to the CD20 Antigen
               during the time period beginning on the Effective Date and ending
               on the earlier of: (a) the First Commercial Sale of any CD20
               Product for a Major Indication in a Major Market Country or (b)
               the termination of the licenses granted by Trubion to Wyeth under
               this Agreement with respect to all CD20 Products.

                                                                              17

<PAGE>

               Subject to Section 2.3.3, and except for Commercialization of the
               CD20 Products pursuant to the terms of this Agreement, neither
               Party shall Commercialize any human therapeutic product that
               contains a protein that [***] to the CD20 Antigen during the time
               period beginning on the Effective Date and ending on the earlier
               of (a) five (5) years after the First Commercial Sale of any CD20
               Product for a Major Indication in a Major Market Country or (b)
               the termination of the licenses granted by Trubion to Wyeth under
               this Agreement with respect to all CD20 Products.

          2.3.2. [***] EXCLUSIVITY. Subject to Section 2.3.3, and except for
               Development of the [***] pursuant to the terms of this Agreement,
               neither Party shall Develop any human therapeutic product that
               contains a protein that [***] to the [***] during the time period
               beginning on the Effective Date and ending on the earlier of: (a)
               the First Commercial Sale of any [***] in any Major Market
               Country or (b) the termination of the licenses granted by Trubion
               to Wyeth under this Agreement with respect to all [***].

               Subject to Section 2.3.3, and except for Commercialization of the
               [***] pursuant to the terms of this Agreement, neither Party
               shall Commercialize any human therapeutic product that contains a
               protein that [***] to the [***] during the time period beginning
               on the Effective Date and ending on the earlier of: (a) five (5)
               years after the First Commercial Sale of any [***] in any Major
               Market Country or (b) the termination of the licenses granted by
               Trubion to Wyeth under this Agreement with respect to all [***].

          2.3.3. LIMITATIONS. The exclusivity provisions of Sections 2.3.1 and
               2.3.2 above (a) shall not apply to Wyeth's Manufacture of any
               product for a Third Party pursuant only to a contract
               manufacturing or supply agreement between Wyeth and such Third
               Party where Wyeth is acting only as a contract manufacturer or
               supplier for such Third Party, (b) shall in no way limit any of
               the licenses granted by Trubion to Wyeth under Section 2.1
               hereof, and (c) shall in no way limit any of the retained rights
               of Trubion set forth in Section 2.1.2 hereof.

     2.4. SUBLICENSING. Wyeth may grant to one or more Third Parties sublicenses
          of the rights granted to it under Section 2.1 hereof at any time;
          provided that Wyeth shall execute a written agreement with each such
          sublicensee and shall comply with the following: Each such sublicense
          (a) shall be subject and subordinate to, and consistent with, the
          terms and conditions of this Agreement, (b) shall not in any way
          diminish, reduce or eliminate any of Wyeth's obligations under this
          Agreement, (c) shall require each such sublicensee to comply with all
          applicable terms of this Agreement,

                                                                              18

<PAGE>

          including to keep books and records, and permit Wyeth to audit (either
          directly or through an independent auditor) such books and records,
          and (d) shall provide that any such sublicensee shall not further
          sublicense except on terms consistent with this Section 2.4. Wyeth
          shall provide Trubion with a copy of each such sublicense agreement
          within thirty (30) days after the execution thereof. Such copy may be
          redacted to exclude confidential, non-Licensed Product-related
          information and financial information (other than such financial
          information that is necessary for assessing the obligations to Trubion
          under this Agreement). Upon Trubion's request and at Trubion's
          expense, Wyeth shall exercise its right to conduct an audit of a
          sublicensee's books and records pertaining to the sale of a Licensed
          Product under any such sublicense agreement at the next time that
          conducting such an audit is permissible under such sublicense
          agreement. Wyeth shall provide Trubion with a copy of the report of
          the findings made in any such audit. If such audit reveals that such
          sublicensee has understated its Net Sales by [***] or more, Wyeth
          shall be responsible for the costs of the audit. Wyeth shall remain
          responsible for its obligations hereunder and for the performance of
          its sublicensees (including, without limitation, making all payments
          due Trubion by reason of any Net Sales of Licensed Products), and
          shall ensure that any such sublicensees comply with all relevant
          provisions of this Agreement. In the event of any uncured material
          breach by any sublicensee under a sublicense agreement that would
          constitute a breach of Wyeth's obligations under this Agreement, Wyeth
          will promptly inform Trubion in writing and shall take such action
          which in Wyeth's reasonable business judgment will address such
          default; provided, however, any such uncured material breach by such
          sublicensee of an obligation that would constitute a breach of Wyeth's
          obligations under this Agreement shall be deemed an uncured material
          breach of Wyeth hereunder unless Wyeth cures such material breach
          within the time provided under Section 9.5 hereof.

     2.5. DIRECT LICENSES TO AFFILIATES. Wyeth may at any time request and
          authorize Trubion to grant licenses within the scope of Section 2.1
          directly to Affiliates of Wyeth by giving written notice designating
          to which Affiliate a direct license is to be granted. Upon receipt of
          any such notice, Trubion shall enter into and sign a separate direct
          license agreement with such designated Affiliate of Wyeth. All such
          direct license agreements shall be consistent with the terms and
          conditions of this Agreement, except for such modifications as may be
          required by the laws and regulations in the country in which the
          direct license will be exercised; provided, however, that Trubion
          shall have no obligation to enter into any such direct license
          agreement if the effect of entering into such agreement (and
          continuing as a Party to this Agreement) would be to increase the
          level of obligations owed by Trubion, decrease the obligations owed to
          Trubion or

                                                                              19
<PAGE>

          the enforceability thereof, or decrease the consideration owed to
          Trubion relative to the obligations owed by or to, or the
          consideration owed to, Trubion under this Agreement, had such direct
          license(s) not been granted. In countries where the validity of such
          direct license agreement requires prior government approval or
          registration, such direct license agreement shall not become binding
          between the parties thereto until such approval or registration is
          granted, which approval or registration shall be obtained by Wyeth.
          All costs of making such direct license agreement(s), including
          Trubion's reasonable attorneys' fees, under this Section 2.5 shall be
          borne solely by Wyeth.

     2.6. RIGHT OF REFERENCE. Trubion hereby grants to Wyeth a "Right of
          Reference," as that term is defined in 21 C.F.R. Section 314.3(b), to
          any data Controlled by Trubion that relates to any CD20 Product (and
          any other Licensed Product, to the extent applicable), and Trubion
          shall provide a signed statement to this effect, if requested by
          Wyeth, in accordance with 21 C.F.R. Section 314.50(g)(3).

     2.7. SECTION 365(N) OF BANKRUPTCY CODE. All rights and licenses now or
          hereafter granted under or pursuant to any Section of this Agreement,
          including Sections 2.1 and 2.5 hereof, are rights to "intellectual
          property" (as defined in Section 101(35A) of Title 11 of the United
          States Code, as amended (such Title 11, the "Bankruptcy Code")). In
          the event this Agreement is rejected under Section 365 of the
          Bankruptcy Code, Trubion hereby grants to Wyeth, subject to Wyeth's
          obligations under Sections 365(n)(2)(A) and (B), a right of access and
          to obtain possession of and to benefit from each of the following
          embodiments to the extent related to Wyeth's exercise of its license
          rights to any Licensed Products or otherwise related to any rights or
          licenses granted under or pursuant to any Section of this Agreement:
          (i) copies of pre-clinical and clinical research data and results,
          (ii) aliquots of laboratory samples, (iii) Licensed Product samples
          and inventory, (iv) Cell Lines expressing Licensed Products, libraries
          encoding Licensed Products or components thereof and sequences
          thereof, (v) copies of laboratory notes and notebooks pertaining to
          Licensed Products, (vi) copies of data and results related to clinical
          trials of Licensed Products, (vii) regulatory filings and approvals of
          Licensed Products, (viii) rights of reference in respect of regulatory
          filings and approvals of Licensed Products, and (ix) plasmid and
          vectors encoding Licensed Product SMIPs, all of which constitute
          "embodiments" of intellectual property pursuant to Section 365(n) of
          the Bankruptcy Code, and (xi) all other embodiments of such
          intellectual property in Trubion's possession or control. Recognizing
          that the embodiments described above may be useful or necessary to
          Trubion in connection with its continued operation of its business,
          and that a Third Party may also have a right of access to such
          embodiment under Section 365(n) of the Bankruptcy Code or applicable
          non-bankruptcy law, where there is a fixed

                                                                              20

<PAGE>

          or limited quantity of any biological material or other tangible item
          of such embodiment described above, Wyeth shall be entitled to a pro
          rata portion thereof. Trubion agrees not to interfere with Wyeth's
          exercise under the Bankruptcy Code of rights and licenses to
          intellectual property licensed hereunder and embodiments thereof in
          accordance with this Agreement and agrees to use Commercially
          Reasonable Efforts (short of any obligation of Trubion to incur
          expenses in connection therewith) to assist Wyeth to obtain such
          intellectual property and embodiments thereof in the possession or
          control of Third Parties as reasonably necessary or useful for Wyeth
          to exercise such rights and licenses in accordance with this
          Agreement; provided, however, that Trubion's Commercially Reasonable
          Efforts for purposes of this Section 2.7 shall not be deemed to
          include an obligation to make payments to Third Parties to obtain such
          intellectual property rights and embodiments thereof. The Parties
          hereto acknowledge and agree that reimbursement payments pursuant to
          Sections 3.6 and 4.6 and all other payments by Wyeth to Trubion
          hereunder other than royalty payments pursuant to Section 5.4 and
          Additional Research and Development Expense Payments under Section 5.3
          do not constitute royalties within the meaning of Bankruptcy Code
          Section 365(n) or relate to licenses of intellectual property
          hereunder.

     2.8. NO IMPLIED RIGHTS. Except as expressly provided in this Agreement,
          neither Party shall be deemed by estoppel or implication to have
          granted the other Party any license or other right with respect to any
          intellectual property of such Party.

3.   RESEARCH PROGRAM.

     3.1. SCOPE AND CONDUCT OF THE RESEARCH PROGRAM. Under the terms and
          conditions set forth herein, Trubion and Wyeth shall collaborate
          through one or more joint project teams in the conduct of a
          pre-clinical research program to identify and evaluate (a) SMIPs
          directed against Licensed Targets and (b) Licensed Products, including
          CD20 Products, [***] and Other Products (collectively, the "Research
          Program"). Such activities shall include, but not be limited to, the
          following:

          [***]

          Subject to and in accordance with the Research Plan and the
          Development Plan (to the extent applicable), the JRC shall determine
          the appropriate activities to be undertaken by Trubion and Wyeth;
          provided, however, that, as of the Signing Date, the Parties
          anticipate that Trubion shall conduct activity (i) above (with input
          from Wyeth), Wyeth shall conduct activities (v), (vi) and (vii) above,
          and Trubion and Wyeth shall jointly conduct activities (ii), (iii) and
          (iv) above. The Research Program shall be conducted in accordance with
          the Research Plan, and each Party shall use its Commercially
          Reasonable Efforts to perform all of its obligations

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<PAGE>

          under the Research Program in accordance with the Research Plan and
          current good laboratory practices.

     3.2. DESIGNATION OF TARGETS..

          3.2.1. DESIGNATION OF TARGETS. Within thirty (30) days after the
               Effective Date, Wyeth shall provide Trubion's Vice President,
               Legal Affairs & Chief Patent Counsel with a list of up to [***]
               Targets (each a "Target Candidate") from which Wyeth shall have
               the exclusive right, until [***], to designate up to [***] Wyeth
               Targets, in accordance with the following provisions (subject to
               Wyeth's right under Section 3.2.3 to designate as Wyeth Targets
               up to [***] Targets (of the [***] Targets that Wyeth may
               designate as Wyeth Targets) that are not Target Candidates at the
               time of selection). In the case of protein Targets that are
               Target Candidates, Wyeth shall designate each such Target
               Candidate on the list by its GenBank accession number provided by
               the National Center for Biotechnology Information ("NCBI")
               (including any nomenclature describing such Target Candidate that
               is provided therewith) or, if an NCBI GenBank accession number is
               not available for such Target Candidate, by its nucleotide and
               amino acid sequences. For the avoidance of doubt, Wyeth may not
               designate as Target Candidates any Targets that are Excluded
               Targets. Subject to the following procedures, Trubion shall not
               undertake any research or Development activities beyond Milestone
               One (as defined on Exhibit 3.2.1 attached hereto) of Trubion's
               internal product development process, or propose to enter into or
               enter into any agreement with any Third Party with respect to any
               SMIP directed against any Target Candidate or with respect to any
               Licensed Product containing such a SMIP, unless and until such
               Target Candidate becomes a Released Target, Excluded Target or
               Provisional Excluded Target. Trubion, through its Legal
               Department, shall maintain a copy of the list of Target
               Candidates in a secure location. Trubion shall take reasonable
               measures and implement reasonable procedures to ensure that only
               its inside attorneys who are employees of its Legal Department
               and its outside patent counsel (collectively, "Trubion Lawyers")
               have knowledge of and access to Wyeth's Target Candidate list.
               The Target Candidate list shall be considered Confidential
               Information of Wyeth, and except as expressly permitted under
               this Section 3.2 or otherwise under this Agreement, Trubion shall
               not use or disclose the Target Candidate list or the information
               set forth therein to any of its Affiliates, to any Third Party,
               or to any employees, officers or agents of Trubion other than
               Trubion Lawyers. For so long as a Target remains a Target
               Candidate, Trubion, through its Legal Department, shall implement
               reasonable

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<PAGE>

               procedures to maintain records of all Third Party inquiries to
               Trubion and Trubion's responses to same, relating to the Target
               Candidate list made pursuant to this Section 3.2. The Trubion
               Legal Department shall also maintain the list of Released
               Targets, Excluded Targets and Provisional Excluded Targets in
               accordance with the provisions of Sections 3.2.2 and 3.2.4. In
               the event of a bona fide dispute arising under this Agreement
               relating to the Target selection process described in this
               Section 3.2, Trubion shall provide to an independent Third Party
               selected by Wyeth and reasonably acceptable to Trubion access to
               the lists of Target Candidates, Released Targets, Excluded
               Targets and Provisional Excluded Targets and records and
               processes related thereto (to the extent relevant to the bona
               fide dispute) maintained by Trubion in accordance with this
               Section 3.2. Such independent Third Party may only communicate to
               Wyeth whether or not the Target selection process was properly
               performed by Trubion's Lawyers.

          3.2.2. RELEASED TARGETS. On or before [***], Wyeth, by written notice
               to Trubion's Vice President, Legal Affairs & Chief Patent
               Counsel, shall identify [***] Target Candidates from the list
               delivered pursuant to Section 3.2.1 (inclusive of any Target
               Candidates that have become Released Targets during such period
               pursuant to Section 3.2.4 hereof), which from the date of such
               identification shall cease to be Target Candidates (each, a
               "Released Target"). At the time that a Target Candidate becomes a
               Released Target, Trubion, subject to Section 2.8, shall be free
               to undertake research and Development activities independent of
               obligations under this Agreement, and to enter into discussions
               or an agreement with a Third Party, with respect to SMIPs
               directed against any such Released Target or any other activities
               in connection with such Released Target. On or before [***],
               Wyeth, by written notice to Trubion, shall identify such
               additional Target Candidates from the list delivered pursuant to
               Section 3.2.1, if any, as additional Released Targets, such that
               there are no more than [***] Target Candidates remaining on the
               list delivered pursuant to Section 3.2.1 (less the number of
               Wyeth Targets that were Target Candidates at the time of
               selection as a Wyeth Target(s) pursuant to Section 3.2.3), which
               from the date of such identification shall cease to be Target
               Candidates and, thereafter each shall also become a Released
               Target. At the end of the Research Term, all remaining Target
               Candidates, if any, shall become Released Targets.

          3.2.3. WYETH TARGETS. Wyeth Targets shall be designated only from
               either (a) Target Candidates that have not become Released
               Targets, or (b) any other Target (including a Released Target
               that

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<PAGE>

               is or becomes available, as described below) that is not then an
               Excluded Target or a Provisional Excluded Target; provided,
               however, that no more than [***] of the Targets designated by
               Wyeth as Wyeth Targets may be Targets that are not Target
               Candidates at the time of selection. Subject to the foregoing
               sentence, Wyeth shall designate: (y) [***] Target Candidates or
               other Targets as Wyeth Targets on or before [***]; and (z) up to
               [***] Target Candidates or other Targets (inclusive of those
               designated as Wyeth Targets during [***] ) as Wyeth Targets on or
               [***]; provided, however, if Wyeth does not designate [***] Wyeth
               Targets on or before such [***], then the lesser number of Wyeth
               Targets so designated shall be the total number of Wyeth Targets
               under this Agreement unless Wyeth extends the Research Program,
               in which case Wyeth may designate, before[***], [***] additional
               Wyeth Targets (up to a cumulative total [***] in the aggregate).
               For the avoidance of doubt and subject to the following sentence,
               Wyeth may designate only up to [***] Wyeth Targets from the
               Effective Date of this Agreement through the end of the Research
               Program (even if extended). During the term of the Research
               Program, Wyeth shall have the right to [***]; provided that [***]
               (a "REPLACEMENT TARGET") must be [***]. In the event that Wyeth
               nominates as a Wyeth Target (whether as a proposed initial
               designation of a Wyeth Target or as a replacement designation as
               a Wyeth Target) a Target that is not then a Target Candidate,
               Trubion's Legal Department, within ten (10) business days after
               receiving written notice of such nomination, shall determine and
               advise Wyeth in writing whether such Target is an Excluded Target
               or a Provisional Excluded Target, as described below (and shall
               indicate whether such Target is an Excluded Target or is a
               Provisional Excluded Target). If such Target is an Excluded
               Target or a Provisional Excluded Target, it shall not be eligible
               to be considered a Wyeth Target. If a proposed Replacement Target
               is not an Excluded Target or a Provisional Excluded Target, then
               the JRC shall either approve or disapprove designation of such
               proposed Replacement Target as a Wyeth Target; provided that the
               original Wyeth Target that Wyeth proposes to replace shall be
               automatically deemed a Released Target upon the JRC's approval of
               the designation of the Replacement Target.

          3.2.4. EXCLUDED TARGETS. Excluded Targets are not eligible to be Wyeth
               Targets for so long as they remain Excluded Targets. The Targets
               deemed "Excluded Targets" as of the Effective Date are set forth
               in Exhibit 3.2.4 attached hereto. Trubion may add additional
               Targets as Excluded Targets or Provisional Excluded Targets

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<PAGE>

               (which may be selected from Released Targets and other Targets,
               but would not include any Wyeth Targets or any Target Candidate
               that has not become a Released Target) in accordance with the
               following procedures:

               (A)  During the period when [***], and upon the written request
                    of a potential Third Party collaborator and/or licensee of
                    Trubion pertaining to the identification, generation and/or
                    Development of SMIPs directed against a Target or Targets,
                    Trubion's Legal Department shall promptly determine whether
                    or not any of such Targets is a Wyeth Target.

               (B)  With respect to any Target newly submitted by a Party to
                    Trubion's Legal Department hereunder, Trubion's Lawyers will
                    determine whether such submitted Target [***] Licensed
                    Targets, Target Candidates, Released Targets, Excluded
                    Targets and Provisional Excluded Targets available to
                    Trubion's Lawyers (each a "Previously Deposited Protein").
                    By way of example only,[***]. Should Wyeth designate a
                    Target that is not a protein, the Parties agree to negotiate
                    in good faith the procedure for identifying and testing
                    whether a subsequent proposed non-protein Target is the
                    "same as" such designated non-protein Target for purposes of
                    this Section 3.2.

               (C)  If Trubion's Legal Department determines, in accordance with
                    Section 3.2.4(b) above, that any such Target is a Wyeth
                    Target, Trubion shall not proceed with such potential Third
                    Party collaboration or license with respect to such Target.
                    If any of such Targets is not a Wyeth Target or a Target
                    Candidate, such Target shall automatically be deemed a
                    "Provisional Excluded Target". If such Target is a Target
                    Candidate, Trubion shall notify Wyeth in writing of
                    Trubion's request that a Target Candidate be recategorized
                    as a Released Target, in order for Trubion to be able to
                    enter substantive negotiations with such Third Party
                    regarding such Target that is a Target Candidate (i.e.,
                    Trubion shall "Put" such Target Candidate to Wyeth). Trubion
                    shall have no obligation to notify Wyeth of the identity of
                    such Third Party or the purpose of the proposed
                    collaboration or license. From the date that Trubion "Puts"
                    such Target Candidate to Wyeth, Wyeth shall have [***] with
                    respect to such Puts made to Wyeth prior to [***], and shall
                    have [***] with respect to such Puts made thereafter, to
                    notify Trubion in writing whether

                                                                              25

<PAGE>

               Wyeth designates such Target Candidate as a Wyeth Target or
               recategorizes such Target Candidate as a Released Target. If
               Wyeth fails to notify Trubion within such [***] period,
               respectively, then such Target Candidate shall automatically be
               deemed a Released Target. Any such Released Targets shall be
               deemed to be Provisional Excluded Targets.

               (D)  If Trubion and such potential Third Party collaborator
                    and/or licensee do not enter into a definitive agreement
                    regarding such Provisional Excluded Target within [***]
                    after the date that such Target is deemed a Provisional
                    Excluded Target (such [***] being subject to a [***]
                    extension by Trubion, if Trubion declares, in writing, to
                    Wyeth that at least one draft definitive agreement has been
                    exchanged between Trubion and such potential Third Party
                    collaborator and/or licensee), thereafter such Provisional
                    Excluded Target would revert to being a Released Target. If
                    Trubion and such potential Third-Party collaborator and/or
                    licensee enter into a definitive agreement within the time
                    period provided above, such Provisional Excluded Target
                    shall be deemed an Excluded Target.

               (E)  During the period when [***], if Trubion itself identifies
                    internally a Target that has progressed to Milestone One (as
                    defined in Exhibit 3.2.1 attached hereto) of Trubion's
                    internal product development process, Trubion's Legal
                    Department shall promptly determine whether or not such
                    Target is a Target Candidate. If such Target is not a Target
                    Candidate, such Target shall be deemed an Excluded Target.
                    If Trubion thereafter abandons work on such Excluded Target,
                    Trubion shall notify Wyeth in writing that Trubion has
                    abandoned work on such Excluded Target and such Excluded
                    Target shall thereafter be deemed a Released Target. If such
                    Target is a Target Candidate, Trubion may Put such Target
                    Candidate to Wyeth. From the date that Trubion Puts such
                    Target Candidate to Wyeth, Wyeth shall have [***] with
                    respect to such Puts made to Wyeth prior to [***], and shall
                    have [***] with respect to such Puts made thereafter, to
                    notify Trubion in writing whether Wyeth designates such
                    Target Candidate as a Wyeth Target or recategorizes such
                    Target Candidate as a Released Target. If Wyeth fails to
                    notify Trubion within such[***], respectively, then such
                    Target Candidate shall automatically be deemed a Released
                    Target. Any such Released Target shall be deemed to be
                    Excluded Target. If

                                                                              26

<PAGE>

                    Trubion thereafter abandons work on any such Excluded
                    Target, Trubion shall notify Wyeth in writing that Trubion
                    has abandoned work on such Excluded Target and such Excluded
                    Target shall thereafter be deemed a Released Target.

               (F)  With respect to the Puts described in (c) and (e) above,
                    Trubion shall not be permitted to Put more than [***] Target
                    Candidates to Wyeth during the first [***] of the Research
                    Program.

     3.3. TERM AND TERMINATION OF THE RESEARCH PROGRAM.

          3.3.1. RESEARCH TERM. The term of the Research Program (the "Research
               Term") shall begin on the Effective Date and shall continue until
               [***] (the "Initial Term"), subject to extension as described
               below. At Wyeth's option (exercisable by providing written notice
               to Trubion no later than [***] prior to the end of the Initial
               Term of the Research Program or any extension year thereof), the
               Research Term may be extended for up to [***] additional [***]
               periods and, thereafter, shall be renewable annually only upon
               mutual written agreement of the Parties.

          3.3.2. TERMINATION OF RESEARCH PROGRAM BY WYETH. Commencing on the
               first anniversary of the Effective Date, Wyeth shall have the
               right to terminate the Research Program, at will, at any time, in
               its entirety, upon one (1) year prior written notice to Trubion;
               provided that Trubion shall have no obligation after the
               effective termination date to complete any Research Program
               activities in connection with any Trubion Target, Wyeth Target,
               SMIP or Licensed Product. Such termination of the Research
               Program shall not constitute termination of this Agreement and
               shall not affect the Parties' rights and obligations under this
               Agreement other than those relating to the Research Program.

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<PAGE>

     3.4. JOINT RESEARCH COMMITTEE.

          3.4.1. COMPOSITION. Within thirty (30) days after the Effective Date,
               the Parties shall establish a Joint Research Committee (the
               "JRC") to oversee the Research Program. The JRC will be in effect
               only during the Research Term. The JRC shall be composed of three
               (3) representatives from each Party. Each Party may replace any
               of its representatives at any time upon written notice to the
               other Party. From time to time, the JRC may establish
               subcommittees to oversee particular projects or activities, and
               such subcommittees shall be constituted as the JRC decides.

          3.4.2. RESPONSIBILITIES. The JRC shall be responsible for
               establishing, reviewing and recommending modifications and
               updates to the Research Plan, including the Research Budget, in
               accordance with Section 3.5 hereof, monitoring and reporting to
               the Parties on activities conducted pursuant to the Research
               Plan, and for such other functions as agreed by the Parties.

          3.4.3. MEETINGS. The JRC shall meet as soon as practicable after it is
               established by the Parties and, thereafter, at such additional
               times as the Parties deem appropriate, not less frequently than
               quarterly. Each Party shall designate one of its JRC members as
               its "JRC Liaison" to co-chair meetings, prepare and circulate JRC
               meeting agendas and JRC meeting minutes. The meetings of the JRC
               shall be held in the United States, and shall alternate between
               the Parties' business locations or as otherwise decided by the
               JRC. JRC meetings may be conducted in person, by telephone or by
               videoconference. Each Party shall use reasonable efforts to cause
               its representatives to attend the meetings of the JRC. If a
               representative of a Party is unable to attend a meeting, such
               Party may designate an alternate member to attend such meeting in
               place of the absent member.

          3.4.4. VOTING. Decisions of the JRC shall be made by unanimous
               consent, with each Party having one vote. The JRC may act without
               a meeting if an action by unanimous written consent is signed by
               each Party's JRC Liaison.

          3.4.5. DISPUTE RESOLUTION. If the JRC is unable to reach agreement on
               a matter, the matter may be referred, at the request of either
               Party, for resolution through good faith discussions between
               Wyeth's Executive Vice President of Discovery Research and
               Trubion's Senior Vice President of Research and Development or
               their respective designees. Notwithstanding the foregoing, in the
               event the JRC cannot promptly resolve a disagreement or a voting

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<PAGE>

               deadlock regarding the Research Program, Wyeth's Executive Vice
               President of Discovery Research shall have the right to cast a
               tie-breaking vote to resolve any such disagreement or voting
               deadlock, such right and tie-breaking authority being subject to
               the terms and conditions of this Agreement.

          3.4.6. MINUTES. The JRC shall keep accurate and complete minutes of
               its meetings that record all proposals and recommendations made,
               and all actions and decisions taken. The JRC minutes shall not be
               effective until approved in writing by each Party's JRC Liaison.
               All records of the JRC shall be available at all times to each
               Party.

     3.5. RESEARCH PLAN. The Parties shall use their Commercially Reasonable
          Efforts to develop and approve a complete Research Plan (including a
          corresponding Research Budget) within sixty (60) days of the Effective
          Date. The Parties shall ensure that the Research Plan is consistent
          with the terms and conditions of this Agreement, and the Research Plan
          shall not impose obligations on either Party that are inconsistent
          with the terms of this Agreement. The Research Plan shall set forth
          generally (a) the activities to be undertaken by the Parties under the
          Research Program consistent with the terms of Section 3.1, (b) the
          utilization of [***] Trubion FTEs in conducting such activities, (c)
          the anticipated schedule on which such activities are to be conducted,
          (d) the desired deliverables to be provided by each Party with respect
          to each Licensed Target that is the subject of the Research Program,
          and (e) the annual budget for non-ordinary expenses (as described in
          Section 3.6.1 below) to be incurred by Trubion under the Research
          Program (the "Research Budget"). The JRC shall review the Research
          Plan, including the Research Budget, on at least an annual basis and
          submit any proposed modifications or updates to the Parties for review
          and approval; any such modifications or updates shall not become
          effective until approved in writing by an authorized officer of each
          of the Parties. The Parties shall review and consider any such
          proposed modifications or updates on an expeditious basis. The Parties
          shall promptly amend the Research Plan from time to time to address
          the performance of the Research Program as it relates to any Licensed
          Targets designated by Wyeth in accordance with Section 3.2 above.

     3.6. FUNDING OF THE RESEARCH PROGRAM.

          3.6.1. RESEARCH FUNDING. During each year of the Research Term (as it
               may be extended), Wyeth shall pay Trubion [***] per year for
               services performed in accordance with the Research Plan. Trubion
               shall commit to the Research Program [***] FTEs per year to

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<PAGE>

               provide services in furtherance of the Research Program in
               accordance with the Research Plan. For the avoidance of doubt,
               Trubion may, at its sole expense and discretion, devote more than
               [***] FTEs from time to time to provide services in furtherance
               of the Research Program. The [***] in research funding described
               above shall be increased automatically once per calendar year by
               the percentage change in the U.S. Consumer Price Index, All Urban
               Consumers over the previous year; provided, however, that no
               increase shall be effective prior to January 1, 2007. [***]
               Trubion shall provide to Wyeth, prior to the first day of each
               Calendar Quarter, a forecast of such expenses (by major expense
               category, on an accrual basis) reimbursable under this Section
               3.6.1 which Trubion expects to incur during such Calendar Quarter
               and the subsequent three Calendar Quarters, in each case shown by
               month. Other than the foregoing amounts and except as otherwise
               expressly provided in this Agreement, each Party shall be solely
               responsible for its costs and expenses incurred in performing its
               obligations under the Research Program.

          3.6.2. REIMBURSEMENT PAYMENTS. Reimbursement to be made to Trubion by
               Wyeth pursuant to Section 3.6.1 will be made pursuant to invoices
               submitted by Trubion to Wyeth no more often than once with
               respect to any Calendar Quarter, within thirty (30) days of the
               end of such Calendar Quarter. Payment shall be due within
               forty-five (45) days after Wyeth receives such an invoice from
               Trubion. Each invoice must be accompanied by supporting
               documentation sufficiently demonstrating the expense so paid on a
               cash basis (such as receipts for out-of-pocket expenses and other
               written documentation reasonably acceptable to Wyeth) and by a
               certificate executed by Trubion's VP, Finance & Administration,
               of the number of FTEs used by Trubion in such Calendar Quarter in
               performing Trubion's obligations under the Research Program.
               Except as approved in writing in advance by Wyeth, Wyeth shall
               not be obligated to reimburse Trubion for amounts in excess of
               the applicable budgeted amounts in the Research Budget.

          3.6.3. RECORDS AND AUDITS. During the Research Term, Trubion shall
               keep books and accounts of record in connection with the expenses
               reimbursable under Section 3.6.1 hereof in accordance with GAAP
               and in sufficient detail to permit accurate determination of all
               figures necessary for verification of costs to be reimbursed
               hereunder. Trubion shall maintain such cost records for a period
               of at least three (3) years after the end of the calendar year in
               which they were generated in order to enable audit of such
               records as set forth below. Upon thirty (30) days prior written
               notice from Wyeth, Trubion shall permit an independent certified
               public

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<PAGE>

               accounting firm of nationally recognized standing selected by
               Wyeth and reasonably acceptable to Trubion, to examine, at
               Wyeth's sole expense, the relevant books and records of Trubion
               as may be reasonably necessary to verify the amount of
               reimbursable out-of-pocket expenses incurred. An examination by
               Wyeth under this Section 3.6.3 shall occur not more than once in
               any calendar year and shall be limited to the pertinent books and
               records for any calendar year ending not more than thirty six
               (36) months before the date of the request. The accounting firm
               shall be provided access to such books and records at Trubion's
               facility(ies) where such books and records are normally kept and
               such examination shall be conducted during Trubion's normal
               business hours. Trubion may require the accounting firm to sign a
               standard non-disclosure agreement before providing the accounting
               firm access to Trubion's facilities or records. The accounting
               firm shall provide both Trubion and Wyeth a written report
               disclosing whether the certificates and invoices submitted by
               Trubion under Section 3.6.2 are correct or incorrect and the
               specific details concerning any discrepancies. No other
               information shall be provided to Wyeth. If the accounting firm
               determines that the aggregate amount of out-of-pocket expenses
               actually incurred by Trubion was less than the amount reimbursed
               by Wyeth during the period covered by the audit, Trubion shall
               refund the excess payments to Wyeth within thirty (30) days of
               its receipt of the auditor's report so concluding (or, if later,
               within fifteen (15) days after resolution of a bona fide
               objection by Trubion to the findings in such report). If the
               amount to be refunded exceeds more than ten percent (10%) of the
               amount that was properly payable, Trubion shall reimburse Wyeth
               for the cost of the audit. All information of Trubion which is
               subject to review under this Section 3.6.3 shall be deemed to be
               Confidential Information of Trubion subject to the provisions of
               Article 7, and such Confidential Information shall not be
               disclosed to any Third Party or used for any purpose other than
               verifying the information provided by Trubion to Wyeth; provided,
               however, that such Confidential Information may be disclosed to
               Third Parties only to the extent necessary to enforce Wyeth's
               rights under this Agreement, as may be necessary for Wyeth to
               exercise its rights under this Agreement, or as otherwise
               expressly permitted under this Agreement.

     3.7. DATA AND DELIVERABLES. During the Research Term, each Party will use
          Commercially Reasonable Efforts to promptly provide to the other Party
          the data or desired deliverables specified in the Research Plan,
          including, without limitation, (a) SMIPs, Recombinant DNA, and Cell
          Lines, to the

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<PAGE>

          extent related to Licensed Targets and/or Licensed Products, (b)
          activity evaluation of the items listed in (a) obtained from in vitro
          or in vivo assays, pharmacology studies, process development data,
          drug product formulation data, toxicology and safety studies, and
          evaluation of chemotherapy conjugates, but only to the extent and in
          the manner that items listed in (a) and (b) are set forth in the
          Research Plan. Each Party shall also disclose to the other Party in
          writing all data, information, inventions, techniques and discoveries
          (whether patentable or not) arising out of the conduct of the Research
          Program. Disclosure of all such aforementioned inventions and
          discoveries shall be delivered to the other Party in a manner mutually
          agreed upon by the Joint Patent Committee. Subject to the terms and
          conditions of this Agreement, each Party shall have the right to use
          any data or information generated under the Research Program for its
          permitted activities under the Research Program and this Agreement
          (collectively, "Research Program Data"). TRUBION MAKES NO
          REPRESENTATION OR WARRANTY, EITHER EXPRESS OR IMPLIED, THAT IT WILL BE
          ABLE TO SUCCESSFULLY DISCOVER, DEVELOP OR DELIVER ANY SMIP DIRECTED
          AGAINST A LICENSED TARGET OR ANY LICENSED PRODUCT.

     3.8. ALLIANCE MANAGERS. Each Party shall designate a single alliance
          manager, who shall perform such duties relating to the day-to-day
          worldwide coordination of the collaboration contemplated by this
          Agreement as are determined by the JRC and the JDC. Such alliance
          managers shall have experience and knowledge appropriate for managers
          with such project management responsibilities. Such alliance managers
          may attend, as non-voting members, any meetings of the committees
          contemplated by this Agreement as deemed fit by such committees. Each
          Party may change its designated alliance manager from time to time
          upon notice to the other Party.

4.   PRODUCT DEVELOPMENT, MANUFACTURING, COMMERCIALIZATION AND REGULATORY
     MATTERS.

     4.1. PRODUCT DEVELOPMENT. Except as otherwise expressly provided in
          Articles 2 and 3 hereof and in this Article 4, Wyeth shall have the
          sole authority, at its expense, for the Development of Licensed
          Products, including the initiation and conduct of clinical trials.
          Wyeth shall be responsible for the Development of and shall use its
          Commercially Reasonable Efforts to Develop Licensed Products
          throughout the Territory where it is Commercially Reasonable to do so
          (it being understood that Wyeth shall have the sole discretion to
          select those countries in which it will conduct clinical studies of
          Licensed Products and, when Commercially Reasonable to do so, to delay
          or discontinue the Development of any Licensed Product directed
          against a particular Licensed Target in favor of pursuing Development
          of another Licensed

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<PAGE>

          Product directed against such Licensed Target). When appropriate based
          on the data obtained during Development, Wyeth shall use its
          Commercially Reasonable Efforts to secure Regulatory Approval for
          Licensed Products in the Territory.

     4.2. TRANSFER OF PRODUCT DATA AND FILINGS. Upon Wyeth's reasonable request
          and in consultation with the JDC from time to time during the term of
          this Agreement and to the extent permitted by applicable law, Trubion
          shall assign and transfer to Wyeth Trubion's entire right, title and
          interest in and to any of the Product Data and Filings pursuant to an
          instrument to such effect in form and substance reasonably
          satisfactory to Wyeth and shall perform all other actions reasonably
          requested by Wyeth to effect and confirm such transfer. The Parties
          shall cooperate through the JDC to ensure that assignment and transfer
          of Trubion's right, title and interest in and to Product Data and
          Filings relating to CD20 Products is made in a manner that does not
          impede Trubion's activities and responsibilities under Section 4.6.
          After receipt of Wyeth's request consistent with the foregoing,
          Trubion shall provide to Wyeth, at Wyeth's expense, within sixty (60)
          days of receipt of such request, complete copies of such Product Data
          and Filings, including, without limitation, relevant clinical data,
          INDs, additional regulatory filings with FDA or other Regulatory
          Authorities, supplements or amendments thereto, all written
          correspondence with FDA or other Regulatory Authorities regarding the
          regulatory filings, and all existing written minutes of meetings and
          memoranda of conversations between Trubion (including, to the extent
          practicable, Trubion's investigators) and FDA or other Regulatory
          Authorities in Trubion's possession (or in the possession of any of
          Trubion's agents and subcontractors, such as contract research
          organizations used by Trubion), to the extent Trubion has the right to
          access and provide to Wyeth such Product Data and Filings, regarding
          such regulatory filings, each to the extent they relate to Licensed
          Products. Within thirty (30) days (or such later date as Wyeth may
          request) after the date of receipt of Wyeth's reasonable request after
          consultation with the JDC, Trubion shall execute and deliver a letter
          to the FDA or other Regulatory Authorities, in a form approved by
          Wyeth, transferring ownership to Wyeth of such regulatory filings, if
          any, filed in the name of Trubion that are related to Licensed
          Products. After such transfer of ownership of regulatory filings
          relating to a Licensed Product, during the term of this Agreement all
          regulatory filings with the FDA or other Regulatory Authorities
          pertaining to such Licensed Product shall be made in the name of
          Wyeth, in accordance with the terms of Section 4.3 below.

     4.3. REGULATORY APPROVALS. Wyeth shall have the sole authority to file, in
          its own name, at its sole expense, all Regulatory Approval
          Applications for Licensed Products. Wyeth shall have the sole
          authority and responsibility for communicating with any Regulatory
          Authority regarding any

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<PAGE>

          Regulatory Approval Application, or any Regulatory Approval once
          granted. To the extent necessary to satisfy applicable regulatory
          requirements with respect to the INDs for the clinical studies of CD20
          Products described in Section 4.6, Wyeth hereby grants to Trubion a
          "Right of Reference," as that term is defined in 21 C.F.R. Section
          314.3(b), to any data Controlled by Wyeth that relates to any CD20
          Products that are the subject of the clinical studies described in
          Section 4.6 hereof, and Wyeth shall provide a signed statement to this
          effect, if requested by Trubion, in accordance with 21 C.F.R. Section
          314.50(g)(3). Copies of all Wyeth regulatory filings that relate to
          Trubion's Development activities under this Agreement will be provided
          by Wyeth to Trubion upon request, subject to reasonable resource and
          time constraints.

     4.4. REGULATORY REPORTING. Wyeth shall be responsible for preparing and
          filing all reports required to be filed in order to maintain any
          Regulatory Approvals granted for Licensed Products in the Territory,
          including, without limitation, adverse drug experience reports. To the
          extent Trubion has or receives any information regarding any adverse
          drug experience which may be related to the use of any Licensed
          Product or to Licensed Product Development, Trubion shall promptly
          provide Wyeth with all such information in accordance with the Adverse
          Event Reporting and pharmacovigilance procedures set forth in Exhibit
          4.4 attached hereto (as may be amended from time to time upon written
          mutual agreement of the Parties). From time to time after the
          Effective Date, representatives from both Parties shall meet to review
          and revise or replace such Adverse Event Reporting and
          pharmacovigilance procedures.

     4.5. PROGRESS REPORTS.

               (a)  Wyeth shall provide Trubion with confidential summary
                    reports of its and its sublicensees' Development activities,
                    on a Licensed Product-by-Licensed Product basis, on a [***],
                    with respect to CD20 Products and [***], and on an [***],
                    with respect to Other Products. The form of the summary
                    reports, and the type of information and the appropriate and
                    reasonable level of detail to be included in such reports,
                    shall be mutually and reasonably agreed by the Parties;
                    provided that the Parties agree that such reports shall
                    include information regarding progress towards and
                    achievement of any event set forth in Exhibit 5.3 attached
                    hereto.

               (b)  Wyeth shall provide Trubion with confidential summary
                    reports of its and its sublicensees' CD20 Product
                    Commercialization activities on a [***] after the First
                    Commercial Sale of a CD20 Product. Beginning [***]

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<PAGE>

                    prior to the anticipated First Commercial Sale of a CD20
                    Product, and thereafter on a [***], Wyeth shall meet with
                    Trubion and provide updates on CD20 Product
                    Commercialization activities.

               (C)  Wyeth shall provide Trubion with confidential summary
                    reports of its and its sublicensees' [***] Commercialization
                    activities on a [***] after the First Commercial Sale of a
                    [***]. Beginning [***] prior to the anticipated First
                    Commercial Sale of a [***], and thereafter on a [***], Wyeth
                    shall meet with Trubion and provide updates on [***]
                    Commercialization activities.

               (D)  Wyeth shall provide Trubion with confidential summary
                    reports of its and its sublicensees' Other Product
                    Commercialization activities on an [***] after the First
                    Commercial Sale of an Other Product. Beginning [***] prior
                    to the anticipated First Commercial Sale of an Other
                    Product, and thereafter on an [***], Wyeth shall meet with
                    Trubion and provide updates on Other Product
                    Commercialization activities.

               (E)  The meetings described in clauses (b) - (d) above shall be
                    coordinated to occur at the same time, to the extent
                    practicable.

     4.6. CD20 PRODUCT DEVELOPMENT. Subject to Section 4.7 hereof, Trubion shall
          use its Commercially Reasonable Efforts to conduct the following
          Development activities for CD20 Products: (a) Trubion shall continue
          the Phase I Clinical Studies and Phase IIa Clinical Studies of TRU-015
          ongoing at the Effective Date for treatment of rheumatoid arthritis
          until completion or termination of such studies, including the
          re-treatment periods of such studies; (b) Trubion shall initiate and
          perform the planned Phase IIb Clinical Study of TRU-015 for treatment
          of rheumatoid arthritis through the completion or termination of such
          study; (c) Trubion shall continue the Phase I Clinical Study ongoing
          at the Effective Date, and shall initiate and perform the planned
          Phase III Clinical Studies (or the appropriate subsequent clinical
          study) of TRU-015 for the treatment of [***] through the completion or
          termination of such studies; (d) Trubion shall have responsibility for
          and shall perform the clinical studies for at least two (2) additional
          Niche Indications selected by the Parties and set forth in the
          Development Plan; and (e) Trubion shall continue to perform the
          ongoing bioprocess development activities, and in each case (a-e) such
          activities and responsibilities of Trubion shall be performed in
          accordance with the Development Plan. None of the clinical studies
          described in this Section 4.6 shall be terminated prior to completion
          before discussion of

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<PAGE>

          such matter by the JDC. Trubion shall keep accurate records of its
          clinical study activities under this Section 4.6 in accordance with
          applicable laws and, upon reasonable request, shall provide Wyeth with
          access to such records. Trubion shall maintain such records for a
          period of at least three (3) years after the end of the calendar year
          in which they were generated. The Development Plan shall provide that
          Trubion is responsible for conducting the clinical trials for
          rheumatoid arthritis, [***] and additional Niche Indications through
          the completion or termination of such clinical studies described above
          and shall contain a budget for such clinical trials. Trubion shall be
          solely responsible for its internal FTE and other internal costs for
          such Development activities, but Wyeth shall reimburse Trubion for all
          out-of-pocket costs incurred by Trubion in connection with the
          foregoing Development activities in accordance with the budget
          contained in the Development Plan (which shall include, without
          limitation, all expenses paid to one or more contract research
          organizations for such Development activities). Trubion shall provide
          to Wyeth, on or before the first day of each Calendar Quarter, a
          forecast of such out-of-pocket costs (by major expense category, on an
          accrual basis) reimbursable under this Section 4.6 that Trubion
          expects to incur during such Calendar Quarter and the subsequent three
          (3) Calendar Quarters, in each case shown by month. Reimbursement to
          be made to Trubion by Wyeth pursuant to this Section 4.6 will be made
          pursuant to invoices submitted by Trubion to Wyeth no more often than
          once with respect to any Calendar Quarter, within forty-five (45) days
          of the end of such Calendar Quarter. Payment shall be due within
          forty-five (45) days after Wyeth receives such an invoice from
          Trubion. Each invoice must be accompanied by supporting documentation
          sufficiently demonstrating the expense so incurred (such as receipts
          for out-of-pocket expenses). The provisions of Section 3.6.3 shall
          apply to the expenses reimbursable by Wyeth under this Section 4.6 in
          the same manner as they apply to expenses reimbursable under Section
          3.6.1.

     4.7. JOINT DEVELOPMENT COMMITTEE. Within thirty (30) days of the Effective
          Date, Wyeth and Trubion shall establish a CD20 Product Joint
          Development Committee (the "JDC"), comprised of appropriate
          representatives of both Parties, to review and provide input to Wyeth
          regarding CD20 Product Development in the Territory, including the
          strategic direction of the overall CD20 Product Development program.
          Wyeth shall consider in good faith any of Trubion JDC members'
          comments and recommendations regarding CD20 Product Development, but
          Wyeth shall have final decision-making authority with respect to how
          the Parties proceed with CD20 Product Development, subject to Wyeth's
          obligations under Section 4.1 in connection therewith. If Trubion
          disagrees with an action or decision by the JDC, Trubion may express
          its concerns through good faith discussions between the Executive
          Officers of Trubion and Wyeth, with Wyeth Research's President having
          the final

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<PAGE>

          decision-making authority with respect to such matter. For the
          avoidance of doubt, the JDC may not impose different or greater CD20
          Product Development obligations on Trubion than those specified in
          Section 4.6.

     4.8. JOINT PROJECT TEAM; DEVELOPMENT PLAN. Trubion and Wyeth shall form a
          Joint Project Team ("JPT") comprised of appropriate representatives of
          both Parties to plan and implement the CD20 Product Development
          activities in accordance with the Development Plan. The JPT shall
          report to the JDC. If the JPT cannot promptly resolve a disagreement
          or a voting deadlock regarding the CD20 Product Development
          activities, the matter shall be brought before the JDC for resolution.
          Wyeth shall prepare the Development Plan with input and advice from
          Trubion through the JPT. The Development Plan will define each Party's
          roles and responsibilities, provide a mechanism to coordinate each
          Party's and/or joint activities, and provide a process for monthly
          meetings of the JPT to monitor and report on all activities of the
          Parties conducted under the Development Plan. The Development Plan
          shall not impose different or greater CD20 Product Development
          obligations on Trubion than those specified in Section 4.6. The
          Development Plan shall be updated annually by the JPT.

     4.9. MANUFACTURING. Wyeth shall have the exclusive right to Manufacture
          Licensed Products itself or through one or more Third Parties selected
          by Wyeth; provided, however, that Trubion shall use its Commercially
          Reasonable Efforts to Manufacture and supply Wyeth with its
          requirements of the TRU-015 Product in accordance with the Development
          Plan under Trubion's existing contract Manufacturing arrangements for
          use in pre-clinical studies and clinical trials ("Clinical Study
          Supplies"); provided that Trubion cannot guarantee as of the Effective
          Date that it will be able to Manufacture and supply such requirements.
          Wyeth shall reimburse Trubion for its direct out-of-pocket cost of
          Clinical Study Supplies, including, without limitation, out-of-pocket
          expenses incurred by Trubion prior to the Effective Date that are
          directly related to the Manufacture, testing and release of Clinical
          Study Supplies to be used after the Effective Date (such pre-Effective
          Date out-of-pocket expenses not to exceed [***]. Reimbursement of such
          pre-Effective Date expenses shall be due within thirty (30) days after
          the first patient is dosed in the first Phase IIb Clinical Study for
          rheumatoid arthritis using such Clinical Study Supplies. Upon Wyeth's
          written request, Trubion shall provide reasonable assistance to Wyeth,
          until the first cGMP batch of TRU-015 Product is Manufactured in a
          Wyeth facility (or the facility of a Third Party designated by Wyeth),
          in support and facilitation of Wyeth's efforts to Manufacture TRU-015
          Products and to secure appropriate TRU-015 Product Manufacturing
          arrangements with Third Parties. Such assistance shall be at no cost
          to Wyeth; provided that Wyeth shall reimburse Trubion for all of its
          reasonable out-of-pocket expenses related thereto. If applicable, upon
          Wyeth's written request,

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<PAGE>

          Trubion shall assign or otherwise transfer to Wyeth (to the extent
          allowable under such agreements) its TRU-015 Product Manufacturing
          agreements with Third Parties.

     4.10. COMMERCIALIZATION. Subject to the terms and conditions of this
          Agreement, Wyeth shall have the sole authority and the exclusive right
          to Commercialize Licensed Products itself or through one or more Third
          Parties selected by Wyeth and shall have sole authority and
          responsibility in all matters relating to the Commercialization of
          Licensed Products. Wyeth shall use Commercially Reasonable Efforts to
          Commercialize Licensed Products in the Territory in each country where
          Wyeth has obtained Regulatory Approval for such Licensed Product(s)
          and for each indication of such Licensed Product(s) for which
          Regulatory Approval has been obtained in such country.

     4.11. CO-PROMOTION OPTION. Subject to the foregoing, in the event of a BLA
          filing with the FDA for Regulatory Approval of a CD20 Product for a
          Niche Indication in the United States, Trubion shall have the option
          to Co-Promote the CD20 Product in the United States for such Niche
          Indication in accordance with Wyeth's marketing plan for up to five
          (5) years after the First Commercial Sale of the first CD20 Product
          for any Niche Indication in the United States (the "Co-Promotion
          Period"). The Trubion Co-Promotion option shall be exercisable by
          Trubion giving written notice to Wyeth no later than [***] after the
          date of the first BLA filing with the FDA for the first Niche
          Indication for the first CD20 Product (or such longer time as the
          Parties may mutually agree). Promptly after Trubion's exercise of such
          option, the Parties shall negotiate, in good faith, a definitive
          Co-Promotion Agreement, which shall require Trubion and Wyeth to use
          Commercially Reasonable Efforts to Co-Promote such CD20 Product. Such
          Co-Promotion Agreement shall contain customary provisions relating to
          relative sales force efforts, responsibility for sales calls, sales
          force training, promotional materials and samples, detailing and the
          number and qualifications of sales force personnel (including medical
          science liaisons) that will be devoted to such Co-Promotion
          activities. The Parties hereby agree, inter alia, that such
          Co-Promotion Agreement, and Wyeth's marketing plan for such CD20
          Product, shall provide (a) Trubion's sales force with a meaningful
          role in the Commercialization of such CD20 Product; (b) that Wyeth
          shall provide CD20 Product-related sales training to Trubion's sales
          force, at no cost to Trubion; and (c) that Trubion's sales force shall
          use CD20 Product promotional materials and samples, to be provided by
          Wyeth at no cost, in connection with their sales efforts. As
          compensation for sales force support provided by Trubion in connection
          with such Co-Promotion, Wyeth shall pay Trubion a fixed fee (to be set
          forth in the definitive Co-Promotion Agreement) for each Product sales
          detail performed by members of Trubion's sales force in accordance
          with Wyeth's marketing

                                                                              38

<PAGE>

          plan for such CD20 Product. Trubion will not have the right to
          contract out for or otherwise delegate to any Third Party any
          responsibility for such sales force support. Trubion's sales force
          activities shall be conducted in accordance with Wyeth's policies and
          the marketing and promotion plan for the CD20 Product.

     4.12. CO-PROMOTION COMMITTEE. If Trubion exercises its Co-Promotion option
          with respect to a CD20 Product in accordance with Section 4.11 hereof,
          a Co-Promotion Committee shall be formed by the Parties within thirty
          (30) days after such exercise. The Co-Promotion Committee shall
          oversee all aspects of Co-Promotion-related activities and reasonably
          relevant aspects of Commercialization of such CD20 Product during the
          Co-Promotion Period, and shall include Trubion's Chief Executive
          Officer and Wyeth's Executive Vice President and General Manager,
          Wyeth BioPharma.

     4.13. CO-BRANDING. To the extent allowed by applicable law, all product
          labeling for CD20 Products shall include both Parties' names, which
          shall be of similar size and prominence to the extent practicable
          (except (i) with respect to labeling of vials or other components of a
          CD20 Product that do not include either Party's name or (ii) with
          respect to labeling of diluent or other components packaged together
          with the CD20 Product that do not customarily contain another Person's
          name).

     4.14. MARKING. All Licensed Products shall be marked with the patent
          numbers of issued patents within Trubion Patent Rights and Wyeth
          Patent Rights that cover such Licensed Products, to the extent
          practicable and permitted by law in countries in which such markings
          have notice value against infringers of patents.

5.   CONSIDERATION.

     5.1. INITIAL RESEARCH AND DEVELOPMENT EXPENSE PAYMENT. In consideration of
          Trubion's agreement to conduct the Research Program and to participate
          on the JRC and JDC, Wyeth shall pay to Trubion Forty Million Dollars
          ($40,000,000.00) within ten (10) days after the Effective Date, which
          payment shall be non-refundable and non-creditable.

     5.2. EQUITY. Wyeth shall purchase from Trubion common stock of Trubion at
          such time, in such amounts and for such price as specified in the
          Stock Purchase Agreement, attached hereto as Exhibit 5.2A. Concurrent
          with the execution of the Stock Purchase Agreement, the Parties shall
          enter into an amendment of Trubion's Amended and Restated Investor
          Rights Agreement, attached hereto as Exhibit 5.2B.

     5.3. ADDITIONAL RESEARCH AND DEVELOPMENT EXPENSE PAYMENTS. In further
          consideration of Trubion's contributions under the Research Program
          and

                                                                              39

<PAGE>

          the Development Program, as provided in Articles 3 and 4 above, Wyeth
          shall pay to Trubion the payments specified in Exhibit 5.3 attached
          hereto (each an "Additional Research and Development Expense Payment")
          in the amounts and at such times as specified in Exhibit 5.3. Wyeth
          shall notify Trubion promptly upon the achievement of each event
          specified in Exhibit 5.3.

     5.4. ROYALTIES.

          5.4.1. LICENSED PRODUCT ROYALTIES. In consideration for the licenses
               granted to Wyeth under Section 2.1 hereof, and in addition to
               those payments required to be made by Wyeth pursuant to Section
               5.1, Section 5.2 and Section 5.3, Wyeth shall pay to Trubion
               royalties during the Royalty Period as set forth in Sections
               5.4.2, 5.4.3 and 5.4.4 below, subject to the adjustments provided
               in Section 5.4.6 below.

          5.4.2. CD20 PRODUCT ROYALTIES.

               (A)  Except as provided in Sections 5.4.2(b) and 5.4.2(c) below,
                    Wyeth shall pay to Trubion royalties in the amount of the
                    Marginal Royalty Rates (set forth below) of the aggregate
                    Net Sales collectively obtained by Wyeth and its
                    sublicensees from the sale of CD20 Products in the Territory
                    during each calendar year in the applicable Royalty Period:

<TABLE>
<CAPTION>
                                  Marginal Royalty Rate
                         (% of the Applicable Portion of Annual
Annual Net Sales Level                 Net Sales)
----------------------   --------------------------------------
<S>                      <C>
Less than [***]                           [***]
From [***]                                [***]
From [***]                                [***]
From [***]                                [***]
Greater than [***]                        [***]
</TABLE>

                    Each Marginal Royalty Rate set forth in the table above
                    shall apply only to that portion of the annual Net Sales
                    that falls within the indicated range. By way of example
                    only,

                                                                              40
<PAGE>

                    if the aggregate Net Sales of CD20 Products during a
                    calendar year equaled [***], the total royalty for CD20
                    Products during such year would equal the specified Marginal
                    Royalty Rate ([***]) of the first [***] of Net Sales, plus
                    the specified Marginal Royalty Rate ([***]) of the next
                    [***] of Net Sales, plus the specified Marginal Royalty Rate
                    ([***]) of the remaining [***] of Net Sales (that is, [***],
                    which would equal [***]).

                    For purposes of this Section 5.4.2, the "CD20 Effective
                    Royalty Rate" for a particular time period shall mean the
                    weighted average, expressed as a percentage, of the Marginal
                    Royalty Rates that would apply under the provisions of this
                    Section 5.4.2(a) to the aggregate CD20 Product Net Sales in
                    the Territory during such time period (without regard, for
                    these purposes, to any adjustments made under Sections
                    5.4.2(b) or 5.4.2(c)). By way of example only, if the
                    aggregate Net Sales of CD20 Products in the Territory during
                    a calendar year equaled [***], the CD20 Effective Royalty
                    Rate for such calendar year would be calculated as follows:
                    (([***] of [***]) plus ([***] of [***]) plus ([***] of
                    [***])) divided by [***], expressed as a percentage, which
                    would equal [***]. By way of further example only, if the
                    aggregate Net Sales of CD20 Products in the Territory during
                    each of the four Calendar Quarters of such calendar year
                    were [***], respectively (for a total of [***]), the CD20
                    Effective Royalty Rates for each of the four Calendar
                    Quarters would be [***], respectively.

               (B)  Subject to the provisions of Section 5.4.2(c) below, in the
                    event that, at any time during the term of the Product
                    License, no issued Valid Claim is included within the
                    Trubion Patent Rights in a country where a CD20 Product is
                    sold (which claim, but for the licenses granted hereunder to
                    Wyeth, would be infringed by Wyeth's or its sublicensees'
                    Manufacture, use, sale, offer for sale or import of such
                    CD20 Product in such country), Wyeth shall pay to Trubion
                    royalties with respect to such CD20 Product in such country
                    during such time period, in lieu of the royalties described
                    in Section 5.4.2(a), equal to the following amount: (i) the
                    CD20 Effective Royalty Rate of the aggregate Net Sales
                    obtained by Wyeth and its sublicensees from the sale of such
                    CD20 Product in such country during such time period minus
                    (ii) [***] of the aggregate Net Sales obtained by Wyeth and
                    its sublicensees from the sale of such CD20 Product in such
                    country during

                                                                              41

<PAGE>

                    such time period. By way of example only, if the aggregate
                    Net Sales of such a CD20 Product in such country during the
                    relevant time period were [***] and the CD20 Effective
                    Royalty Rate (based on Net Sales of CD20 Products throughout
                    the Territory) for such time period were [***], the
                    royalties payable under this Section 5.4.2(b) on Net Sales
                    in such country would equal (i) [***] of [***], (or [***]),
                    minus (ii) [***] of [***], (or [***]), which would equal
                    [***]. By way of further example only, if the aggregate Net
                    Sales of such a CD20 Product in such country during the
                    relevant time period were [***] and the CD20 Effective
                    Royalty Rate (based on Net Sales of CD20 Products throughout
                    the Territory) for such time period were [***], the
                    royalties payable under this Section 5.4.2(b) on Net Sales
                    in such country would equal (i) [***] of [***], (or [***]),
                    minus (ii) [***] of [***], (or [***]), which would equal
                    [***].

               (C)  In the event that at any time during the term of the Product
                    License: (i) no issued Valid Claim is included within the
                    Trubion Patent Rights in a country where a CD20 Product is
                    sold (which claim, but for the licenses granted hereunder to
                    Wyeth, would be infringed by Wyeth's or its sublicensees'
                    Manufacture, use, sale, offer for sale or import of such
                    CD20 Product in such country), (ii) a product is sold by a
                    Third Party in such country, which product would, if sold by
                    such Third Party in the United States, infringe an issued
                    Valid Claim included within the Trubion Patent Rights in the
                    United States, and (iii) such product sold by the Third
                    Party has a [***] or greater unit market share in such
                    country (where the market is defined as the sum of the unit
                    sales of such CD20 Product and of the product described in
                    clause (ii)), Wyeth shall pay to Trubion royalties with
                    respect to such CD20 Product in such country during such
                    time period, in lieu of the royalties described in Section
                    5.4.2(a) and Section 5.4.2(b), equal to the following
                    amount: (i) [***] of (ii) the CD20 Effective Royalty Rate of
                    the aggregate Net Sales obtained by Wyeth and its
                    sublicensees from the sale of such CD20 Product in such
                    country during such time period. By way of example only, if
                    the aggregate Net Sales of such a CD20 Product in such
                    country during the relevant time period were [***] and the
                    CD20 Effective Royalty Rate for such time period were [***],
                    the royalties payable under this

                                                                              42

<PAGE>

                    Section 5.4.2(c) would equal (i) [***] of (ii) [***] of
                    [***], (or [***]), which would equal [***].

          5.4.3. [***].

               (A)  Except as provided in Sections 5.4.3(b) and 5.4.3(c) below,
                    Wyeth shall pay to Trubion royalties in the amount of the
                    Marginal Royalty Rates (set forth below) of the aggregate
                    Net Sales collectively obtained by Wyeth and its
                    sublicensees from the sale of each [***] in the Territory
                    during each calendar year in the applicable Royalty Period:

<TABLE>
<CAPTION>
                         Marginal Royalty Rate
                         (% of the Applicable
                           Portion of Annual
                              Net Sales)
                         --------------------
<S>                      <C>
Annual Net Sales Level
Less than [***]                  [***]
From [***]                       [***]
From [***]                       [***]
From [***]                       [***]
Greater than [***]               [***]
</TABLE>

                    Each Marginal Royalty Rate set forth in the table above
                    shall apply only to that portion of the annual Net Sales for
                    a particular [***] that falls within the indicated range. By
                    way of example only, if the aggregate Net Sales of a [***]
                    during a calendar year equaled [***], the total royalty for
                    such [***] during such calendar year would equal the
                    specified Marginal Royalty Rate ([***]) of the first [***]
                    of Net Sales, plus the specified Marginal Royalty Rate
                    ([***]) of the next [***] of Net Sales, plus the specified
                    Marginal Royalty Rate ([***]) of the remaining [***] of Net
                    Sales (that is, [***], which would equal [***]).

                    For purposes of this Section 5.4.3, the "[***] Royalty Rate"
                    for a particular time period for a particular [***] shall
                    mean the weighted average, expressed as a percentage, of the
                    Marginal Royalty Rates that would apply under the provisions
                    of this Section 5.4.3(a) to the Net Sales in the Territory
                    of such [***] during such time period (without

                                                                              43

<PAGE>

                    regard, for these purposes, to any adjustments made under
                    Sections 5.4.3(b) or 5.4.3(c)). By way of example only, if
                    the Net Sales of a [***] in the Territory during a calendar
                    year equaled [***], the [***] Royalty Rate for such calendar
                    year for such [***] would be calculated as follows: (([***])
                    plus ([***]) plus ([***])) divided by [***], expressed as a
                    percentage, which would equal [***]. By way of further
                    example only, if the Net Sales of such [***] in the
                    Territory during each of the four Calendar Quarters of such
                    calendar year were [***], and [***], respectively (for a
                    total of [***] in such calendar year), the [***] Royalty
                    Rates for each of the four Calendar Quarters would be [***],
                    respectively.

               (B)  Subject to the provisions of Section 5.4.3(c) below, in the
                    event that, at any time during the term of the Product
                    License, no issued Valid Claim is included within the
                    Trubion Patent Rights in a country where a [***] is sold
                    (which claim, but for the licenses granted hereunder to
                    Wyeth, would be infringed by Wyeth's or its sublicensees'
                    Manufacture, use, sale, offer for sale or import of such
                    [***] in such country), Wyeth shall pay to Trubion
                    royalties with respect to such [***] in such country during
                    such time period, in lieu of the royalties described in
                    Section 5.4.3(a), equal to the following amount: (i) the
                    [***] Royalty Rate for such [***] of the aggregate Net
                    Sales obtained by Wyeth and its sublicensees from the sale
                    of such [***] in such country during such time period minus
                    (ii) [***] of the aggregate Net Sales obtained by Wyeth and
                    its sublicensees from the sale of such [***] in such
                    country during such time period. By way of example only, if
                    the aggregate Net Sales of such a [***] in such country
                    during the relevant time period were [***] and the [***]
                    Royalty Rate (based on Net Sales of such [***] throughout
                    the Territory) for such time period for such [***] were
                    [***], the royalties payable under this Section 5.4.3(b) on
                    Net Sales in such country would equal (i) [***], (or
                    [***]), minus (ii) [***], (or [***]), which would equal
                    [***]. By way of further example only, if the Net Sales of
                    such [***] in such country during the relevant time period
                    were [***] and the [***] Royalty Rate (based on Net Sales
                    of such [***] throughout the Territory) for such time
                    period were [***], the royalties payable under this Section
                    5.4.3(b) on Net Sales in such country would equal (i)
                    [***],

                                                                              44
<PAGE>

                    (or [***]), minus (ii) [***], (or [***]), which would equal
                    [***].

               (C)  In the event that at any time during the term of the Product
                    License: (i) no issued Valid Claim is included within the
                    Trubion Patent Rights in any country where a [***] is sold
                    (which claim, but for the licenses granted hereunder to
                    Wyeth, would be infringed by Wyeth's or its sublicensees'
                    Manufacture, use, sale, offer for sale or import of such
                    [***] in such country), (ii) a product is sold by a Third
                    Party in such country, which product would, if sold by such
                    Third Party in the United States, infringe an issued Valid
                    Claim included within the Trubion Patent Rights in the
                    United States, and (iii) such product sold by a Third Party
                    has a [***] or greater unit market share in such country
                    (where the market is defined as the sum of the unit sales of
                    such [***] and of the product described in clause (ii)),
                    Wyeth shall pay to Trubion royalties with respect to such
                    [***] in such country during such time period, in lieu of
                    the royalties described in Section 5.4.3(a) and Section
                    5.4.3(b), equal to the following amount: (i) [***] of (ii)
                    the [***] Royalty Rate for such [***] of the aggregate Net
                    Sales obtained by Wyeth and its sublicensees from the sale
                    of such [***] in such country during such time period. By
                    way of example only, if the aggregate Net Sales of such a
                    [***] in such country during the relevant time period were
                    [***] and the [***] Royalty Rate for such time period for
                    such [***] were [***], the royalties payable under this
                    Section 5.4.3(c) on Net Sales in such country would equal
                    (i) [***] of (ii) [***] of [***], (or [***]), which would
                    equal [***]. By way of further example only, if the Net
                    Sales of such [***] in such country during the relevant time
                    period were [***] and the [***] Royalty Rate (based on Net
                    Sales of such [***] throughout the Territory) for such time
                    period were [***], the royalties payable under this Section
                    5.4.3(c) on Net Sales in such country would equal (i) [***]
                    multiplied by (ii) [***] of [***], (or [***]), which would
                    equal [***].

          5.4.4. OTHER PRODUCT ROYALTIES.

               (A)  Except as provided in Sections 5.4.4(b) and 5.4.4(c) below,
                    Wyeth shall pay Trubion a royalty of [***] of the aggregate
                    Net Sales obtained by Wyeth and its sublicensees from the
                    sale of each Other Product in the Territory during each
                    calendar year in the applicable Royalty Period.

                                                                              45

<PAGE>

               (B)  Subject to the provisions of Section 5.4.4(c) below, in the
                    event that, at any time during the term of the Product
                    License, no issued Valid Claim is included within the
                    Trubion Patent Rights in a country where an Other Product is
                    sold (which claim, but for the licenses granted hereunder to
                    Wyeth, would be infringed by Wyeth's or its sublicensees'
                    Manufacture, use, sale, offer for sale or import of such
                    Other Product in such country), Wyeth shall pay to Trubion,
                    with respect to such Other Product in such country during
                    such time period, in lieu of the royalty described in
                    Section 5.4.4(a), a royalty of [***] of the aggregate Net
                    Sales obtained by Wyeth and its sublicensees from the sale
                    of such Other Product in such country during such time
                    period.

               (C)  In the event that at any time during the term of the Product
                    License: (i) no issued Valid Claim is included within the
                    Trubion Patent Rights in any country where an Other Product
                    is sold (which claim, but for the licenses granted hereunder
                    to Wyeth, would be infringed by Wyeth's or its sublicensees'
                    Manufacture, use, sale, offer for sale or import of such
                    Other Product in such country), (ii) a product is sold by a
                    Third Party in such country, which product would, if sold by
                    such Third Party in the United States, infringe an issued
                    Valid Claim included within the Trubion Patent Rights in the
                    United States, and (iii) such product sold by a Third Party
                    has a [***] or greater unit market share in such country
                    (where the market is defined as the sum of the unit sales of
                    such Other Product and of the product described in clause
                    (ii)), Wyeth shall pay to Trubion, with respect to such
                    Other Product in such country during such time period, in
                    lieu of the royalties described in Section 5.4.4(a) and
                    Section 5.4.4(b), a royalty of [***] of the aggregate Net
                    Sales obtained by Wyeth and its sublicensees from the sale
                    of such Other Product in such country during such time
                    period.

          5.4.5. EXPIRATION OF ROYALTY PERIOD. After the expiration of the
               Royalty Period for any Licensed Product in any country in the
               Territory, no further royalties shall be payable in respect of
               sales of such Licensed Product in such country and thereafter the
               licenses granted to Wyeth under Section 2.1 [***].

          5.4.6. ROYALTY ADJUSTMENTS.

                                                                              46

<PAGE>

               (A)  CERTAIN THIRD PARTY AGREEMENTS. On a country-by-country
                    basis in a given calendar year, Wyeth shall deduct from CD20
                    Product royalties otherwise payable to Trubion under Section
                    5.4.2 [***] of the aggregate amount of royalties actually
                    paid to Third Parties under Additional Third Party Licenses
                    with respect to the Development, Manufacture or
                    Commercialization of CD20 Products in such country in such
                    calendar year; provided, however, that (i) the amount of
                    such deduction shall not exceed [***] of the amount of the
                    CD20 Product royalties otherwise payable to Trubion under
                    Section 5.4.2 in a given calendar year and (ii) such
                    deduction shall not have the effect, under any
                    circumstances, of reducing the CD20 Product royalties
                    payable under Section 5.4.2 below [***] of the aggregate Net
                    Sales obtained by Wyeth and its sublicensees from the sale
                    of CD20 Products in such country in a given calendar year
                    (before taking into account the operation of Sections
                    5.4.2(b) and 5.4.2(c)). On a country-by-country basis in a
                    given calendar year, Wyeth shall deduct from [***] royalties
                    otherwise payable to Trubion under Section 5.4.3 [***] of
                    the aggregate amount of royalties actually paid to Third
                    Parties under Additional Third Party Licenses with respect
                    to the Development, Manufacture or Commercialization of such
                    [***] in such country in such calendar year; provided,
                    however, that (i) the amount of such deduction shall not
                    exceed [***] of the amount of the [***] royalties otherwise
                    payable to Trubion under Section 5.4.3 in a given calendar
                    year and (ii) such deduction shall not have the effect,
                    under any circumstances, of reducing the [***] royalties
                    payable under Section 5.4.3 below [***] of the aggregate Net
                    Sales obtained by Wyeth and its sublicensees from the sale
                    of such [***] in such country in a given calendar year
                    (before taking into account the operation of Sections
                    5.4.3(b) and 5.4.3(c)). [***]

               (B)  OTHER THIRD PARTY AGREEMENTS. Wyeth shall be solely
                    responsible for all payment obligations related to [***].
                    Trubion shall be solely responsible for all payment
                    obligations related to [***].

     5.5. REPORTS AND PAYMENTS.

          5.5.1. CUMULATIVE ROYALTIES. The obligation to pay royalties under
               Section 5.4 of this Agreement shall be imposed only once with
               respect to a single unit of a Licensed Product, regardless of how
               many Valid Claims included within the Trubion Technology

                                                                              47

<PAGE>

               would, but for this Agreement, be infringed by the Manufacture,
               use, import, offer for sale or sale of such Licensed Product in
               the countr(y)ies of such Manufacture, use or sale. For the
               avoidance of doubt, if a single Licensed Product is both a CD20
               Product and an Other Product, such Licensed Product shall be
               deemed to be a CD20 Product for purposes of the royalty
               obligations under Section 5.4. If a single Licensed Product is
               both a [***] and an Other Product, such Licensed Product shall be
               deemed to be a [***] for purposes of the royalty obligations
               under Section 5.4.

          5.5.2. ROYALTY STATEMENTS AND PAYMENTS. Within [***] after the end of
               each Calendar Quarter, Wyeth shall deliver to Trubion a report
               setting forth for such Calendar Quarter the following
               information, on a Licensed Product-by-Licensed Product and
               country-by-country basis: (a) the gross sales amount (by Wyeth
               and its sublicensees) for each category of Licensed Product sold
               in the United States and the number of units of Licensed Product
               sold in the United States and other countries in the Territory,
               on a country-by-country basis; (b) the Net Sales for each
               Licensed Product; (c) any adjustments (including the basis
               therefor) made pursuant to Sections 5.4.2(b), 5.4.2(c), 5.4.3(b),
               5.4.3(c), 5.4.4(b), 5.4.4(c) or 5.4.6(a) to the royalty amount
               payable for the sale of each Licensed Product, the applicable
               Marginal Royalty Rates and the CD20 Effective Royalty Rate or
               [***] Royalty Rate (as the case may be) payable on the Net Sales,
               and (d) the royalty amount due hereunder for the sale of each
               Licensed Product. No such reports shall be due for any Licensed
               Product before the First Commercial Sale of such Licensed
               Product. The total royalty due for the sale of Licensed Products
               during such Calendar Quarter shall be remitted at the time such
               report is made.

          5.5.3. TAXES AND WITHHOLDING. All payments due Trubion under this
               Agreement will be made without any deduction or withholding for
               or on account of any tax unless such deduction or withholding is
               required by applicable laws or regulations to be assessed against
               Trubion. If Wyeth is so required to deduct or withhold, Wyeth
               will (a) promptly notify Trubion of such requirement, (b) pay to
               the relevant authorities the full amount required to be deducted
               or withheld promptly upon the earlier of determining that such
               deduction or withholding is required or receiving notice that
               such amount has been assessed against Trubion, (c) promptly
               forward to Trubion an official receipt (or certified copy) or
               other documentation reasonably acceptable to Trubion evidencing
               such payment to such authorities, and (d) otherwise reasonably
               cooperate with Trubion in connection with Trubion's attempts to

                                                                              48

<PAGE>

               obtain favorable tax treatment and credit therefor (where
               appropriate) in accordance with applicable laws.

          5.5.4. CURRENCY. All amounts payable and calculations hereunder shall
               be in United States Dollars. As applicable, Net Sales and any
               royalty deductions shall be translated into United States dollars
               in accordance with Wyeth's customary and usual translation
               procedures, consistently applied, which procedures are in
               accordance with Generally Accepted Accounting Principles in the
               United States.

          5.5.5. ADDITIONAL PROVISIONS RELATING TO ROYALTIES. Trubion
               acknowledges and agrees that nothing in this Agreement
               (including, without limitation, any exhibits or attachments
               hereto) shall be construed as representing an estimate or
               projection of either (a) the number of Licensed Products that
               will or may be successfully Developed or Commercialized or (b)
               anticipated sales or the actual value of any Licensed Product and
               that the figures set forth in Section 5.4 or elsewhere in this
               Agreement or that have otherwise been discussed by the Parties
               are merely intended to define Wyeth's royalty obligations to
               Trubion in the event such sales performance is achieved. WYETH
               MAKES NO REPRESENTATION OR WARRANTY, EITHER EXPRESS OR IMPLIED,
               THAT IT WILL BE ABLE TO SUCCESSFULLY DEVELOP OR COMMERCIALIZE ANY
               LICENSED PRODUCT OR, IF COMMERCIALIZED, THAT IT WILL ACHIEVE ANY
               PARTICULAR SALES LEVEL OF SUCH LICENSED PRODUCT(S).

          5.5.6. INTEREST ON PAST DUE PAYMENTS. If either Party fails to pay any
               payment due under this Agreement on or before the date such
               payment is due, as provided in this Agreement, such late payment
               shall bear interest, to the extent permitted by applicable law,
               [***] as reported from time to time in The Wall Street Journal,
               effective for the first date on which payment was delinquent and
               calculated on the number of days such payment is overdue or, if
               such rate is not regularly published, as published in such source
               as the Parties agree.

     5.6. MAINTENANCE OF RECORDS; AUDITS.

          5.6.1. RECORD KEEPING. Wyeth shall keep accurate books and accounts of
               record in connection with the sale of Licensed Products, in
               sufficient detail to permit accurate determination of all figures
               necessary for verification of royalties and other payments to be
               paid to Trubion hereunder. Wyeth shall keep accurate records of

                                                                              49

<PAGE>

               its activities under this Agreement that relate to the events
               with respect to which Additional Research and Development Expense
               Payments may be made under Section 5.3 hereof. Wyeth shall
               maintain such records for a period of at least three (3) years
               after the end of the calendar year in which they were generated.

          5.6.2. AUDITS. Upon thirty (30) days prior written notice from
               Trubion, Wyeth shall permit an independent certified public
               accounting firm of nationally recognized standing selected by
               Trubion and reasonably acceptable to Wyeth, to examine, at
               Trubion's sole expense, the relevant books and records of Wyeth
               as may be reasonably necessary to verify the accuracy of the
               reports submitted by Wyeth in accordance with Section 5.5 and the
               payment of royalties hereunder. An examination by Trubion under
               this Section 5.6.2 shall occur not more than once in any calendar
               year and shall be limited to the pertinent books and records for
               any calendar year ending not more than three (3) years before the
               date of the request. The accounting firm shall be provided access
               to such books and records at Wyeth's facility(ies) where such
               books and records are normally kept and such examination shall be
               conducted during Wyeth's normal business hours. Wyeth may require
               the accounting firm to sign a standard non-disclosure agreement
               before providing the accounting firm access to Wyeth's facilities
               or records. Upon completion of the audit, the accounting firm
               shall provide both Wyeth and Trubion a written report disclosing
               whether the reports submitted by Wyeth are correct or incorrect,
               whether the royalties paid are correct or incorrect, and in each
               case, the specific details concerning any discrepancies. No other
               information shall be provided to Trubion.

          5.6.3. UNDERPAYMENTS/OVERPAYMENTS. If such accounting firm concludes
               that additional royalties were due to Trubion, Wyeth shall pay to
               Trubion the additional royalties within thirty (30) days of the
               date Wyeth receives such accountant's written report so
               concluding. If such royalty underpayment exceeds ten percent
               (10%) of the royalties that were to be paid to Trubion, Wyeth
               also shall reimburse Trubion for the out-of-pocket expenses
               incurred in conducting the audit. If such accounting firm
               concludes that Wyeth overpaid royalties to Trubion, Trubion,
               within thirty (30) days of the date Trubion receives such
               account's report so concluding, will refund such overpayments to
               Wyeth less the reasonable out-of-pocket costs incurred by Trubion
               in conducting the audit.

          5.6.4. CONFIDENTIALITY. All financial information of Wyeth which is
               subject to review under this Section 5.6 shall be deemed to be

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               Wyeth's Confidential Information subject to the provisions of
               Article 7 hereof, and Trubion shall not disclose such
               Confidential Information to any Third Party or use such
               Confidential Information for any purpose other than verifying
               payments to be made by Wyeth to Trubion hereunder; provided,
               however, that such Confidential Information may be disclosed by
               Trubion to Third Parties only to the extent necessary to enforce
               Trubion's rights under this Agreement.

6.   INTELLECTUAL PROPERTY.

     6.1. INVENTIONS; JOINT PATENT COMMITTEE.

          6.1.1. OWNERSHIP AND INVENTORSHIP. A Party shall own all inventions
               and Know-How made solely by employees of such Party, and shall
               jointly own with the other Party any invention, whether or not
               patentable, made jointly by employees of both Parties (a "Joint
               Invention"), all Joint Patent Rights directed thereto, and any
               Know-How made jointly by employees of both Parties ("Joint
               Know-How"). All determinations of inventorship under this
               Agreement shall be made in accordance with United States patent
               law. Each Party shall disclose promptly in writing to the other
               any Joint Inventions and any candidate Joint Inventions of which
               it becomes aware. Subject to (a) the grant of licenses to Wyeth
               under Section 2.1 and to Trubion under Section 2.2, (b) the
               exclusivity provisions of Section 2.3, and (c) the Parties' other
               rights and obligations under this Agreement, each Party shall be
               free to exploit (including to research, Develop, Manufacture,
               Commercialize and enforce), either itself or through the grant of
               licenses to Third Parties (which Third Party licenses are further
               sublicensable), Joint Patent Rights and Joint Know-How throughout
               the world without restriction, without the need to obtain further
               consent from the other Party, and without payment of any
               compensation to the other Party.

          6.1.2. SMIP IMPROVEMENTS. All SMIP Improvements made by Wyeth, whether
               independently or jointly with Trubion, in the course of
               performing Wyeth's obligations under this Agreement during the
               term of the Agreement (each, a "Covered SMIP Improvement") shall
               be promptly disclosed by Wyeth to Trubion. [***]

          6.1.3. JOINT PATENT COMMITTEE.

               (A)  ESTABLISHMENT; MEETINGS; DECISIONS. Within thirty (30) days
                    after the Effective Date, the Parties shall establish a
                    Joint Patent Committee composed of at least one (1)
                    representative from each Party with experience in the
                    prosecution of biotechnology patents. The Joint Patent
                    Committee will have such duties and responsibilities as are
                    expressly assigned to it under this Article 6. The Joint
                    Patent Committee shall meet as soon as practicable after it
                    is established by the Parties and, thereafter, at such

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                    additional times as the Parties deem appropriate, not less
                    frequently than quarterly. The meetings of the Joint Patent
                    Committee shall alternate between the Parties' business
                    locations or as otherwise decided by the Joint Patent
                    Committee; provided that Joint Patent Committee meetings may
                    be conducted in person, by telephone or by videoconference.
                    Each Party shall use reasonable efforts to cause its
                    representative(s) to attend each Joint Patent Committee
                    meeting. Decisions of the Joint Patent Committee shall be
                    made by unanimous consent, with each Party having one vote.
                    The Joint Patent Committee may act without a meeting if an
                    action by unanimous written consent is signed by each
                    committee member. If the Joint Patent Committee is unable to
                    reach agreement on a matter for which it has decision-making
                    authority pursuant to Section 6.1.3(b), 6.2.1(c) or
                    6.2.2(c), the matter may be referred, at the request of
                    either Party, for resolution by outside patent counsel
                    mutually selected by the Parties (wherein such outside
                    patent counsel shall be knowledgeable and experienced in the
                    subject matter of the matter so referred), and such
                    resolution shall be deemed the decision of the Joint Patent
                    Committee. Unless otherwise agreed by the Parties, the
                    patent counsel selected will not have served as primary
                    outside IP counsel to either Party prior to being selected
                    to resolve the Joint Patent Committee disagreement. [***]

               (B)  [***]

     6.2. PATENT RIGHTS.

          6.2.1. FILING, PROSECUTION AND MAINTENANCE OF PATENT RIGHTS.

               (A)  TRUBION PATENT RIGHTS.

                    (I)  TRUBION PATENT RIGHTS. Trubion shall use its
                         Commercially Reasonable Efforts to prepare, file,
                         prosecute and maintain, throughout the Territory, all
                         of the Trubion Patent Rights, using patent counsel of
                         Trubion's choice; provided, however, that Trubion shall
                         give Wyeth before filing a reasonable opportunity to
                         review and comment upon the text of any applications
                         for Trubion Patent Rights to the extent related to any
                         Licensed Product, any SMIPs directed against any
                         Licensed Target, or the Development, Manufacture, use
                         or

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<PAGE>

                         Commercialization thereof (collectively,
                         "Product-Related Patent Rights"); and provided further,
                         however, that patent counsel for patent applications
                         for Product-Related Patent Rights that are prepared or
                         filed on or after the Signing Date and that do not rely
                         on the priority date of a patent or patent application
                         filed before the Signing Date will be mutually agreed
                         upon by the Parties. Trubion shall reasonably consider
                         and address Wyeth's comments on patent applications
                         included in Product-Related Patent Rights. Trubion
                         shall consult with Wyeth with respect to such patent
                         applications, and shall supply Wyeth with a copy of
                         such patent applications as filed, together with notice
                         of each filing date and serial number. Trubion shall
                         also keep Wyeth advised of the status of prosecution of
                         all such patent applications included in the
                         Product-Related Patent Rights, and shall consult with
                         Wyeth and provide Wyeth with a reasonable opportunity
                         to comment on all correspondence received from and all
                         submissions to be made to any government patent office
                         or authority with respect to any such patent
                         application or patent. Trubion shall reasonably
                         consider and address Wyeth's comments on such
                         correspondence and submissions. [***] shall be
                         responsible for [***] of Trubion's [***] incurred in
                         connection with preparing, filing, prosecuting and
                         maintaining such Product-Related Patent Rights
                         throughout the Territory, including, but not limited
                         to, [***]; provided, however, that in the event Trubion
                         grants a license(s) in a given country or countries to
                         one or more Third Parties under any patent application
                         or patent that is included in the Product-Related
                         Patent Rights, Wyeth shall be responsible for a pro
                         rata portion, based on a total number of parties that
                         includes Trubion, Wyeth and all Third Party licensees
                         under such patent application or patent (e.g., if there
                         are two (2) Third Party licensees in addition to Wyeth
                         and Trubion, then Wyeth shall be responsible for
                         twenty-five percent (25%)), of Trubion's [***] incurred
                         in a given country in connection with preparing,
                         filing, prosecuting and maintaining such patent
                         application or patent. (As used in this Article 6,
                         [***] shall be deemed to include, without

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<PAGE>

                         limitation, [***].) Wyeth shall reimburse Trubion on a
                         quarterly basis within [***] of receiving an invoice
                         accompanied by supporting documentation demonstrating
                         the [***] so incurred. On an annual basis, during the
                         last Calendar Quarter of each year, Trubion shall
                         provide Wyeth with a good faith, written estimate of
                         the [***] reimbursable by Wyeth under this Section
                         6.2.1(a) that Trubion expects to incur in the following
                         calendar year. In addition, if Trubion elects not to
                         file a patent application on Trubion Know-How that, if
                         filed, would be a Product-Related Patent Right, or to
                         cease the prosecution and/or maintenance of any
                         Product-Related Patent Rights, (except for abandonment
                         of a patent application in favor of a patent
                         application subsequently filed for purposes of
                         continuing the prosecution of Patent Rights claiming
                         the inventions included in the abandoned patent
                         application), Trubion shall provide Wyeth with written
                         notice immediately upon the decision to not file or
                         continue the prosecution of such patent application or
                         maintenance of such patent. In such event, Trubion
                         shall permit Wyeth, at Wyeth's sole discretion, to file
                         and/or continue prosecution and/or maintenance of such
                         Product-Related Patent Right on Trubion's behalf and at
                         Wyeth's own expense. If Wyeth elects to file or to
                         continue such prosecution or maintenance, it shall
                         notify Trubion in writing of such decision within [***]
                         of receipt of Trubion's written notice, in which case
                         Trubion shall assign to Wyeth such Product-Related
                         Patent Right abandoned by Trubion and shall execute
                         such documents and perform such acts, at Wyeth's
                         expense, as may be reasonably necessary to permit Wyeth
                         to file, prosecute and/or maintain such Product-Related
                         Patent Right. In the event that Wyeth files or
                         continues the prosecution or maintenance of any such
                         Product-Related Patent Right pursuant to this Section
                         6.2.1(a), then Wyeth shall no longer be obligated to
                         pay to Trubion any royalty payments that would be due
                         solely with respect to such Product-Related Patent
                         Right.

               (B)  WYETH PATENT RIGHTS. Subject to Section 6.2.1(d), and except
                    with respect to [***], Wyeth, at its own expense,

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                    shall have the sole right, but not the obligation, to
                    prepare, file, prosecute and maintain, throughout the
                    Territory, all Wyeth Patent Rights, using patent counsel of
                    Wyeth's choice.

               (C)  JOINT PATENT RIGHTS. Subject to Section 6.2.1(d), in the
                    event the Parties make any Joint Invention [***], the Joint
                    Patent Committee shall promptly meet to discuss and
                    determine whether to seek patent protection thereon. If the
                    Joint Patent Committee decides to seek patent protection on
                    such Joint Invention, then [***] shall have the primary
                    obligation to prepare, file, prosecute and maintain any
                    corresponding Joint Patent Rights throughout the Territory
                    using patent counsel mutually agreeable to the Parties, such
                    agreement not to be unreasonably withheld. [***] shall give
                    [***] a reasonable opportunity to review and comment on the
                    text of any patent application with respect to such Joint
                    Patent Right before filing, shall consult with [***] with
                    respect thereto, shall reasonably consider and address any
                    of [***] comments, and shall supply [***] with a copy of
                    each such patent application as filed, together with notice
                    of its filing date and serial number. [***] shall keep [***]
                    advised of the status of the actual and prospective patent
                    filings (including, without limitation, the grant of any
                    Joint Patent Rights), shall provide [***] with a reasonable
                    opportunity to comment on all correspondence received from
                    and all proposed submissions to be made to any government
                    patent office or authority related to the filing,
                    prosecution and maintenance of such patent filings, shall
                    consult with [***] with respect thereto, and shall
                    reasonably consider and address any of [***] comments on
                    such correspondence and submissions. [***] shall reimburse
                    [***] for [***] expenses incurred by [***] in connection
                    with preparing, filing, prosecuting and maintaining such
                    Joint Patent Rights (other than out-of-pocket expenses for
                    inventorship determinations and inventorship disputes),
                    which reimbursement will be made within [***] of receiving
                    invoices, such invoices to be submitted by [***] no more
                    often than once per Calendar Quarter and to be accompanied
                    by supporting documentation demonstrating and detailing the
                    expenses so incurred. On an annual basis, during the last
                    Calendar Quarter of each year, [***] shall provide [***]
                    with a good faith, written estimate of the out-of-pocket
                    expenses reimbursable by [***] under this Section 6.2.1(c)
                    that [***]

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<PAGE>

                    expects to incur in the following calendar year. If [***]
                    elects not to file a patent application on any such Joint
                    Patent Rights, or to cease the prosecution and/or
                    maintenance of any such Joint Patent Rights (except for
                    abandonment of a patent application in favor of a patent
                    application subsequently filed for purposes of continuing
                    the prosecution of Patent Rights claiming the inventions
                    included in the abandoned patent application), [***] shall
                    provide [***] with written notice immediately upon the
                    decision to not file or continue the prosecution of such
                    patent application or maintenance of such patent. In such
                    event, [***] shall permit [***], at [***] sole discretion,
                    to file and/or continue prosecution and/or maintenance of
                    such Joint Patent Rights at [***] own expense. If [***]
                    elects to continue such prosecution or maintenance, it shall
                    notify [***] in writing of such decision within [***] of
                    receipt of [***] written notice, in which case, [***] shall
                    assign to [***] such Joint Patent Rights abandoned by [***]
                    and shall execute such documents and perform such acts, at
                    [***] expense, as may be reasonably necessary to permit
                    [***] to file, prosecute and/or maintain such Joint Patent
                    Rights.

               (D)  [***]

          6.2.2. ENFORCEMENT OF PATENT RIGHTS.

               (A)  NOTICE. If either Wyeth or Trubion becomes aware of any
                    infringement, anywhere in the Territory, of any issued
                    patent within the Trubion Patent Rights (including
                    Product-Related Patent Rights), Wyeth Patent Rights or Joint
                    Patent Rights, which infringing activity adversely affects
                    or is reasonably expected to adversely affect any SMIP or
                    Licensed Product hereunder, it will promptly notify the
                    other Party in writing to that effect and the Parties will
                    consult with each other through the Joint Patent Committee
                    regarding any actions to be taken with respect to such
                    infringing activity; provided, however, that neither Party
                    is obligated to disclose confidential information of a Third
                    Party (other than a sublicensee under this Agreement, to the
                    extent such Party is permitted to do so under the terms of
                    the sublicense).

               (B)  PRODUCT-RELATED PATENT RIGHTS. To the extent permitted under
                    the Trubion Third Party Agreements, if applicable, Wyeth
                    shall have the first right, but not the obligation, to

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<PAGE>

                    take action to obtain a discontinuance of infringement or
                    bring suit against a Third Party infringer of
                    Product-Related Patent Rights under which Wyeth has an
                    exclusive license to make, use and sell Licensed Products
                    under this Agreement, to the extent such infringement
                    involves a product directed against a Licensed Target. Wyeth
                    shall have such first right within three (3) months from the
                    date of notice and the right to join Trubion as a party
                    plaintiff. Wyeth shall be responsible for, and shall bear,
                    all the out-of-pocket expenses of any suit brought by it
                    claiming infringement of any such Product-Related Patent
                    Rights; provided that Trubion shall reimburse Wyeth for
                    [***] of the out-of-pocket expenses incurred in connection
                    therewith. Trubion will cooperate with Wyeth in any such
                    suit and shall have the right to consult with Wyeth and to
                    participate in and be represented by independent counsel in
                    such litigation at its own expense. Wyeth shall incur no
                    liability to Trubion as a consequence of such litigation or
                    any unfavorable decision resulting therefrom, including any
                    decision holding any of the Product-Related Patent Rights
                    invalid or unenforceable. Any recoveries obtained by Wyeth
                    as a result of any proceeding against such Third Party
                    infringer shall be allocated as follows:

                    (I)  Such recovery shall first be used to reimburse each
                         Party for all out-of-pocket litigation expenses in
                         connection with such litigation paid by that Party; and

                    (II) With respect to any remaining recovery, [***].

                    If, after the expiration of the three (3) month period (or,
                    if earlier, the date upon which Wyeth provides written
                    notice that it does not plan to bring suit), Wyeth has not
                    obtained a discontinuance of such infringement of
                    Product-Related Patent Rights or filed suit against any such
                    Third Party infringer hereunder, then Trubion shall have the
                    right, but not the obligation, to bring suit against such
                    Third Party infringer of the Product-Related Patent Rights
                    under which Wyeth has an exclusive license under this
                    Agreement, provided that [***] shall bear [***] of the
                    out-of-pocket expenses of such suit. Wyeth will cooperate
                    with Trubion in any such suit for infringement of such
                    Product-Related Patent Rights brought by Trubion against a
                    Third Party, and shall have the right to consult with
                    Trubion and to participate in and be

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<PAGE>

                    represented by independent counsel in such litigation at its
                    own expense. Trubion shall incur no liability to Wyeth as a
                    consequence of such litigation or any unfavorable decision
                    resulting therefrom, including any decision holding any of
                    the Product-Related Patent Rights invalid or unenforceable.
                    Any recoveries obtained by Trubion as a result of any such
                    proceeding against a Third Party infringer shall be
                    allocated as follows:

                    (III) Such recovery shall first be used to reimburse each
                         Party for all out-of-pocket litigation expenses in
                         connection with such litigation paid by that Party; and

                    (IV) With respect to any remaining recovery, [***].

               (C)  JOINT PATENT RIGHTS. With respect to any notice of a Third
                    Party infringer of the Joint Patent Rights, the Joint Patent
                    Committee shall meet as soon as reasonably practicable to
                    discuss such infringement and determine an appropriate
                    course of action. Wyeth shall have the first right but not
                    the obligation to bring an action against such Third Party
                    infringer or otherwise address such alleged infringement
                    within [***] from the date of notice and to control such
                    litigation or other means of addressing such infringement.
                    Wyeth shall be responsible for, and shall bear, all the
                    out-of-pocket expenses of any suit brought by it claiming
                    infringement of any such Joint Patent Rights; provided that
                    Trubion shall reimburse Wyeth for [***] of the out-of-pocket
                    expenses incurred in connection therewith. Trubion shall
                    cooperate with Wyeth, at Wyeth's expense, in any such suit
                    brought by Wyeth and shall have the right to consult with
                    Wyeth and participate in and be represented by independent
                    counsel in such litigation at its own expense. Wyeth shall
                    incur no liability to Trubion as a consequence of such
                    litigation or any unfavorable decision resulting therefrom,
                    including any decision holding any of the Joint Patent
                    Rights invalid or unenforceable. Any recoveries obtained by
                    Wyeth as a result of any proceeding against such Third Party
                    infringer shall be allocated as follows:

                    (I)  Such recovery shall first be used to reimburse each
                         Party for all out-of-pocket litigation expenses in
                         connection with such litigation paid by that Party; and

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<PAGE>

                    (II) With respect to any remaining recovery, [***].

                    If, after the expiration of the three (3) month period (or,
                    if earlier, the date upon which Wyeth provides written
                    notice that it does not plan to bring suit) Wyeth elects not
                    to take action against a Third Party infringer of the Joint
                    Patent Rights and Trubion elects to bring an action, then
                    Wyeth shall cooperate, at Trubion's expense, in such action.
                    Trubion shall incur no liability to Wyeth as a consequence
                    of such litigation or any unfavorable decision resulting
                    therefrom, including any decision holding any of the Joint
                    Patent Rights invalid or unenforceable. Any recoveries
                    obtained by Trubion shall go to Trubion.

          6.2.3. INFRINGEMENT AND THIRD PARTY LICENSES.

               (A)  INFRINGEMENT OF THIRD PARTY PATENTS - COURSE OF ACTION. If
                    the research, Development, Manufacture or Commercialization
                    of any Licensed Product is alleged by a Third Party to
                    infringe a Third Party's patent, the Party becoming aware of
                    such allegation shall promptly notify the other Party.

                    Additionally, if either Party determines (with consultation
                    by the Joint Patent Committee) that, based upon the review
                    of a Third Party's patent or patent application or other
                    intellectual property rights, it may be desirable to obtain
                    a license from such Third Party with respect thereto, such
                    Party shall promptly notify the other Party of such
                    determination. In the event Wyeth determines, after good
                    faith consultation with Trubion through the Joint Patent
                    Committee, that it is necessary or useful to obtain licenses
                    under intellectual property rights from Third Parties
                    ("Additional Third Party Licenses") in order to Develop,
                    Manufacture or Commercialize Licensed Products under this
                    Agreement, Wyeth shall be solely responsible for negotiating
                    and obtaining any such Additional Third Party Licenses, but
                    shall not be obligated to do so. Trubion may elect, in its
                    sole discretion, to obtain one or more Third Party licenses
                    that are applicable to Trubion Technology in general but are
                    not Licensed Product-specific ("Trubion Additional Third
                    Party Licenses"); if Trubion so elects, then Trubion shall
                    be solely responsible for negotiating and obtaining any such
                    licenses, but shall not be obligated to do so.

               (B)  THIRD PARTY INFRINGEMENT SUIT. If a Third Party sues a Party
                    (the "Sued Party") alleging that the Sued Party or its
                    Affiliates' or sublicensees' research, Development,
                    Manufacture or Commercialization of any Licensed

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<PAGE>

                    Product during the term of and pursuant to this Agreement
                    infringes or will infringe said Third Party's patent, then,
                    upon the Sued Party's request and in connection with the
                    Sued Party's defense of any such Third Party infringement
                    suit, the other Party shall provide reasonable assistance to
                    the Sued Party for such defense. If both Wyeth and Trubion
                    are sued by a Third Party, then the Parties shall consult
                    with one another through the Joint Patent Committee. Unless
                    otherwise determined by the Joint Patent Committee, [***]
                    will control the defense of any suit relating to Licensed
                    Products (whether one or both Parties are Sued Parties) and
                    shall select counsel for such suit after consultation
                    through the Joint Patent Committee. [***] shall have the
                    right to participate in and be represented by independent
                    counsel in such litigation at its own expense. If the
                    alleged infringement is of claims related to the [***]
                    utilized by [***] hereunder, [***] shall be responsible for,
                    and shall bear, all the out-of-pocket expenses of such
                    actions; provided that [***] shall reimburse [***] for [***]
                    of the out-of-pocket expenses incurred in connection
                    therewith. In the event [***] is the Party paying such
                    expenses, [***] shall periodically, but no more than once
                    per Calendar Quarter, invoice [***] for its [***] share of
                    expenses incurred. All invoices shall be accompanied by
                    supporting documentation reasonably showing the expenses so
                    incurred. Such invoices shall be paid within [***] of
                    receipt. In the event Wyeth is the Party paying such
                    expenses, Wyeth shall receive a credit in the amount of
                    Trubion's share of such expenses, which credit shall be
                    applied to royalties due to Trubion under Section 5.4, as
                    adjusted under Section 5.4.6; provided that, no such royalty
                    payment to Trubion shall be reduced by more than [***] in
                    any Calendar Quarter as a result of such credit. Any portion
                    of the credit not utilized due to the limitations of the
                    preceding sentence shall be carried over and credited to
                    future royalty payments.

               (C)  INTERFERENCE, OPPOSITION, REVOCATION, AND DECLARATORY
                    JUDGMENT ACTIONS. If the Parties, through the Joint Patent
                    Committee, mutually determine that, based upon the review of
                    a Third Party's patent or patent application or other
                    intellectual property rights, it may be desirable to provoke
                    or institute an interference, opposition, revocation or
                    declaratory judgment action with respect thereto, then the
                    Parties shall consult with one another and shall reasonably

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<PAGE>

                    cooperate in connection with such an action. Unless
                    otherwise determined by the Joint Patent Committee, [***]
                    will control such action and shall select counsel for such
                    action. [***] shall be responsible for, and shall bear, all
                    the out-of-pocket expenses of such action; provided that
                    [***] shall reimburse [***] for [***] of the out-of-pocket
                    expenses incurred in connection therewith. [***] shall
                    submit invoices to [***] for such expenses, such invoices to
                    be accompanied by supporting documentation reasonably
                    showing the expenses so incurred. [***] shall have the right
                    to participate in and be represented by independent counsel
                    in such action at its own expense.

          6.2.4. PATENT CERTIFICATIONS. Each Party shall immediately give
               written notice to the other of any certification of which it
               becomes aware filed pursuant to 21 U.S.C. Section 355(b)(2)(A) or
               Section 355(j)(2)(A)(vii) (or any amendment or successor statute
               thereto), any similar statutory or regulatory requirement enacted
               in the future regarding biologic products, or any similar
               statutory or regulatory requirement in any non-U.S. country in
               the Territory claiming that a Joint Patent Right, Wyeth Patent
               Right or a Trubion Patent Right covering a Licensed Product is
               invalid or that infringement will not arise from the Manufacture,
               use or sale of a product by a Third Party. Upon the giving or
               receipt of such notice, Wyeth shall have the first right, but not
               the obligation, to bring an infringement action against such
               Third Party. In such a case, Wyeth shall notify Trubion at least
               ten (10) days prior to the date set forth by statute or
               regulation of its intent to exercise, or not exercise, this
               right. Any infringement action against a Third Party arising
               under this Section 6.2.4 shall be governed by the provisions of
               Section 6.2.2(b) hereof.

          6.2.5. PATENT TERM RESTORATION. The Parties hereto shall cooperate
               with each other in obtaining patent term restoration, or its
               equivalent anywhere in the Territory, including under 35 U.S.C.
               Section 156 and its foreign counterparts, where applicable to the
               Trubion Patent Rights, Wyeth Patent Rights and Joint Patent
               Rights. If elections with respect to obtaining such patent term
               restoration are to be made, Wyeth shall make such election (after
               consultation with Trubion through the Joint Patent Committee) and
               Trubion shall abide by such election.

     6.3. TRADEMARKS. Wyeth shall, in its sole discretion select and own all
          Licensed Product-related Trademarks, trade dress, logos and copyrights
          and names to be used in connection with the Commercialization of any
          Licensed Product hereunder. Trubion shall neither use nor seek to
          register, anywhere in the Territory, any trademarks which are
          confusingly similar to any Trademark or any other trademarks, trade
          names, trade dress or logos used by or on behalf of Wyeth or its
          sublicensees in connection with any Licensed Product; provided,
          however, that nothing in this Section 6.3 shall be construed to
          prevent Trubion from enforcing its own trademark, trade name, trade
          dress or logo rights or affect the Parties' obligations under Section
          4.13.

7.   CONFIDENTIALITY.

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<PAGE>

     7.1. CONFIDENTIALITY. Except to the extent expressly authorized by this
          Agreement or otherwise agreed in writing, the Parties agree that, for
          the term of this Agreement and for [***] years thereafter, each Party
          (the "Receiving Party"), receiving any Confidential Information of the
          other Party (the "Disclosing Party") hereunder shall keep such
          Confidential Information confidential and shall not publish or
          otherwise disclose or use such Confidential Information for any
          purpose other than as provided for in this Agreement except for
          Confidential Information that the Receiving Party can establish:

               (A)  was already known by the Receiving Party (other than under
                    an obligation of confidentiality), at the time of disclosure
                    by the Disclosing Party and such Receiving Party has
                    documentary evidence to that effect;

               (B)  was generally available to the public or otherwise part of
                    the public domain at the time of its disclosure to the
                    Receiving Party;

               (C)  became generally available to the public or otherwise part
                    of the public domain after its disclosure or development, as
                    the case may be, and other than through any act or omission
                    of a Party in breach of this confidentiality obligation;

               (D)  was disclosed to that Party, other than under an obligation
                    of confidentiality, by a Third Party who had no obligation
                    to the Disclosing Party not to disclose such information to
                    others; or

               (E)  was independently discovered or developed by or on behalf of
                    the Receiving Party without the use of the Confidential
                    Information belonging to the other Party and the Receiving
                    Party has documentary evidence to that effect.

     7.2. AUTHORIZED DISCLOSURE AND USE.

          7.2.1. DISCLOSURE. Notwithstanding the foregoing Section 7.1, each
               Party may disclose Confidential Information belonging to the
               other Party to the extent such disclosure is reasonably necessary
               to:

               (A)  file or prosecute patent applications covering Trubion
                    Know-How, Wyeth Know-How or Joint Know-How as contemplated
                    by this Agreement, in a manner consistent with decisions and
                    recommendations of the Joint Patent Committee under Article
                    6, if the affected Party consents to such disclosure (such
                    consent not to be unreasonably

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                    withheld or delayed); provided that a disclosure of a
                    Party's Confidential Information under this Section 7.2.1(a)
                    shall be treated as a publication under Section 7.4.3, and
                    shall be subject to the requirements of advance notice,
                    review period and opportunity to file patent application(s),
                    as set forth in Section 7.4.3,

               (B)  prosecute or defend litigation,

               (C)  exercise rights hereunder provided such disclosure is
                    covered by terms of confidentiality similar to those set
                    forth herein,

               (D)  facilitate discussions with prospective investors (other
                    than pharmaceutical or biotechnology companies) in
                    connection with financing arrangements (not involving any
                    license, collaboration or other arrangement relating to such
                    Party's technology or products) or a proposed acquisition of
                    such Party, subject to appropriate confidentiality
                    agreements and limiting such disclosure to disclosure of the
                    terms and conditions of this Agreement and Know-How to the
                    extent contained in such Party's patent applications; and

               (E)  comply with applicable governmental laws and regulations.

                    In the event that a Party shall reasonably deem it necessary
                    to disclose, pursuant to this Section 7.2.1, Confidential
                    Information belonging to the other Party, the Disclosing
                    Party shall to the extent possible give reasonable advance
                    notice of such disclosure to the other Party and take
                    reasonable measures to ensure confidential treatment of such
                    information.

          7.2.2. USE. Notwithstanding the foregoing Section 7.1, each Party
               shall have the right to use Confidential Information of the other
               Party in carrying out its responsibilities under this Agreement
               in the research, Development, Manufacture and Commercialization
               of Licensed Products.

     7.3. SEC FILINGS. Either Party may disclose the terms of this Agreement to
          the extent required, in the reasonable opinion of such Party's legal
          counsel, to comply with applicable laws, including, without
          limitation, the rules and regulations promulgated by the United States
          Securities and Exchange Commission. Notwithstanding the foregoing,
          before disclosing this Agreement or any of the terms hereof pursuant
          to this Section 7.3, the Parties will reasonably consult with one
          another on the terms of this

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          Agreement to be redacted in making any such disclosure. If a Party
          discloses this Agreement or any of the terms hereof in accordance with
          this Section 7.3, such Party agrees, at its own expense, to seek
          confidential treatment of portions of this Agreement or such terms, as
          may be reasonably requested by the other Party.

     7.4. PUBLIC ANNOUNCEMENTS; PUBLICATIONS.

          7.4.1. COORDINATION. The Parties agree on the importance of
               coordinating their public announcements respecting this Agreement
               and the subject matter thereof (other than academic, scientific
               or medical publications that are subject to the publication
               provision set forth below). Trubion and Wyeth shall, from time to
               time, and at the request of the other Party, discuss and agree on
               the general information content relating to this Agreement
               (including relating to the Research Program and Development
               Program, and/or to research, Development, Manufacture and/or
               Commercialization of Licensed Products) which may be publicly
               disclosed (including, without limitation, by means of any printed
               publication or oral presentation).

          7.4.2. ANNOUNCEMENTS. Except as may be expressly permitted under
               Section 7.3 or Section 7.4.3 or as may be appropriate for Wyeth
               to make in connection with its Commercialization activities as
               contemplated hereunder, subject to Sections 7.1 and 7.2 hereof,
               neither Party will make any public announcement regarding this
               Agreement, the Research Program or the Development Program,
               and/or the research, Development, Manufacturing or
               Commercialization of Licensed Products without the prior written
               approval of the other Party.

          7.4.3. PUBLICATIONS. During the term of this Agreement, each Party
               will submit to the other Party for review and approval all
               proposed academic, scientific and medical publications and public
               presentations relating to the Research Program, the Development
               Program and/or to the research, Development, Manufacture and/or
               Commercialization of any Licensed Product, or any proposed
               disclosure under Section 7.2.1(a), for review in connection with
               preservation of Patent Rights and/or to determine whether any of
               such other Party's Confidential Information should be modified or
               deleted. Written copies of such proposed publications and
               presentations shall be submitted to the non-publishing Party no
               later than thirty (30) days before submission for publication or
               presentation and the non-publishing Party shall provide its
               comments with respect to such publications and presentations
               within fifteen (15) business days of its receipt of such written
               copy.

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               The review period may be extended for an additional thirty (30)
               days in the event the non-publishing Party can demonstrate
               reasonable need for such extension, including, but not limited
               to, the preparation and filing of patent applications. By mutual
               agreement, this period may be further extended. Wyeth and Trubion
               will each comply with standard academic practice regarding
               authorship of scientific publications and recognition of
               contribution of other parties in any publications relating to the
               Research Program, the Development Program and/or to the research,
               Development, Manufacture and/or Commercialization of any Licensed
               Product.

8.   REPRESENTATIONS AND WARRANTIES.

     8.1. REPRESENTATIONS AND WARRANTIES OF EACH PARTY. Each of Trubion and
          Wyeth hereby represents and warrants to the other Party hereto as
          follows:

               (A)  it is a corporation or entity duly organized and validly
                    existing under the laws of the state or other jurisdiction
                    of its incorporation or formation;

               (B)  the execution, delivery and performance of this Agreement by
                    such Party has been duly authorized by all requisite
                    corporate action and does not require any shareholder action
                    or approval;

               (C)  it has the power and authority to execute and deliver this
                    Agreement and to perform its obligations and to grant the
                    licenses granted by it to the other Party pursuant to this
                    Agreement;

               (D)  the execution, delivery and performance by such Party of
                    this Agreement and its compliance with the terms and
                    provisions hereof does not and will not conflict with or
                    result in a breach of any of the terms and provisions of or
                    constitute a default under (i) any agreement or instrument
                    binding or affecting it or the subject matter of this
                    Agreement; (ii) the provisions of its charter or operative
                    documents or bylaws; or (iii) any order, writ, injunction or
                    decree of any court or governmental authority entered
                    against it or by which any of its property is bound, except
                    where such conflict, breach or default would not materially
                    impact (A) the Party's ability to meet its obligations
                    hereunder or (B) the rights granted to the other Party
                    hereunder; and

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               (E)  it has not granted to any Third Party any right or license
                    which would conflict in any material respect with the rights
                    granted by it to the other Party hereunder.

     8.2. ADDITIONAL REPRESENTATIONS AND WARRANTIES OF TRUBION. In addition to
          the representations and warranties made by Trubion in Section 8.1,
          Trubion, subject to Section 8.7, hereby represents and warrants to
          Wyeth that as of the Signing Date:

               (A)  except as disclosed in Exhibit 8.2(d) attached hereto,
                    Trubion is the sole and exclusive owner of the Trubion
                    Patent Rights and Trubion has not placed, or suffered to be
                    placed, any liens, charges or encumbrances on or against the
                    Trubion Patent Rights;

               (B)  Exhibit 1.129 is a true and complete list of Trubion Patent
                    Rights that pertain to Licensed Products, provided that an
                    inadvertent omission from such list may be cured by amending
                    Exhibit 1.129;

               (C)  the Trubion Patent Rights are existing and, to Trubion's
                    knowledge, no issued or granted patents within the Trubion
                    Patent Rights are invalid or unenforceable;

               (D)  [***]

               (E)  except as set forth in Exhibit 8.2(e) attached hereto, no
                    Trubion Patent Right listed in Exhibit 1.129 attached hereto
                    is subject to any funding agreement with any government or
                    government agency;

               (F)  Trubion has received no written notice alleging infringement
                    of a Third Party Patent Right in connection with its
                    research and Development of SMIPs directed against a Trubion
                    Target, and Trubion has disclosed to Wyeth all material
                    information of which Trubion is aware as to whether the
                    research, Development, Manufacture, use or sale of SMIPs
                    directed against a Trubion Target, in the form that is the
                    subject of the clinical studies ongoing as of the Signing
                    Date, if such SMIPs were researched, Developed,
                    Manufactured, used or sold as of the Signing Date, infringes
                    or would infringe issued or granted patents owned by a Third
                    Party as of the Signing Date;

               (G)  the Trubion Patent Rights are not subject to any litigation,
                    judgments or settlements against or owed by Trubion, nor

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                    has Trubion received written notice of any threats of such
                    litigation;

               (H)  Trubion is in compliance in all material respects with all
                    agreements with Third Parties relating to Licensed Products
                    that are sublicensed to Wyeth hereunder;

               (I)  [***]

               (J)  the Trubion Patent Rights are not the subject of any
                    interference, opposition, reissue or reexamination
                    proceeding in the United States or, to the knowledge of
                    Trubion, any opposition proceeding outside of the United
                    States.

     8.3. MUTUAL COVENANT. Each Party covenants to the other Party that it shall
          at all times comply with all applicable material laws and regulations
          relating to its activities under this Agreement.

     8.4. ADDITIONAL COVENANTS OF TRUBION. During the term of this Agreement,
          Trubion will use diligent efforts not to materially breach any
          agreement between Trubion and a Third Party that provides Trubion
          Patent Rights pertaining to the research, Development, Manufacture or
          Commercialization of any Licensed Product, and it will provide Wyeth
          promptly with notice of any such alleged breach. [***]. During the
          term of this Agreement, Trubion will not knowingly use any Know-How
          misappropriated from a Third Party in connection with any Licensed
          Product being provided for Commercialization under this Agreement.

     8.5. REPRESENTATION BY LEGAL COUNSEL. Each Party hereto represents that it
          has been represented by legal counsel in connection with this
          Agreement and acknowledges that it has participated in the drafting
          hereof. In interpreting and applying the terms and provisions of this
          Agreement, the Parties agree that no presumption shall exist or be
          implied against the Party which drafted such terms and provisions.

     8.6. NO INCONSISTENT AGREEMENTS. Neither Party has in effect and after the
          Signing Date neither Party shall enter into any oral or written
          agreement or arrangement that would be inconsistent with its
          obligations under this Agreement.

     8.7. DISCLAIMER. EXCEPT AS OTHERWISE EXPRESSLY SET FORTH IN SECTIONS 8.1,
          8.2 AND 8.5, THE PARTIES MAKE NO REPRESENTATIONS AND EXTEND NO
          WARRANTIES OF ANY KIND, EITHER EXPRESS OR IMPLIED, AND PARTICULARLY
          THAT LICENSED PRODUCTS WILL BE SUCCESSFULLY

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          DEVELOPED HEREUNDER, AND IF LICENSED PRODUCTS ARE DEVELOPED, WITH
          RESPECT TO SUCH LICENSED PRODUCTS, THE PARTIES DISCLAIM ALL IMPLIED
          WARRANTIES OF TITLE, NON-INFRINGEMENT, MERCHANTABILITY AND FITNESS FOR
          A PARTICULAR PURPOSE.

9.   GOVERNMENT APPROVALS; TERM AND TERMINATION.

     9.1. HSR FILING. Each Party shall be responsible for its own costs,
          expenses, and filing fees associated with any HSR Filing; provided,
          however, that Wyeth shall be solely responsible for any fees (other
          than penalties that may be incurred as a result of actions or
          omissions on the part of Trubion) required to be paid to any
          government agency in connection with making any such HSR Filing.

     9.2. OTHER GOVERNMENT APPROVALS. Trubion and Wyeth will cooperate and use
          respectively all reasonable efforts to make all registrations, filings
          and applications, to give all notices and to obtain as soon as
          practicable all governmental or other consents, transfers, approvals,
          orders, qualifications authorizations, permits and waivers, if any,
          and to do all other things necessary or desirable for the consummation
          of the transactions as contemplated hereby.

     9.3. TERM. The term of this Agreement will commence on the Signing Date and
          shall extend, unless this Agreement is terminated earlier in
          accordance with this Article 9, on a Licensed Product by Licensed
          Product and country by country basis until such time as the Royalty
          Period with respect to the sale of such Licensed Product in such
          country expires.

     9.4. TERMINATION UPON HSR DENIAL. This Agreement shall terminate (a) at
          Wyeth's option, immediately upon written notice to Trubion, in the
          event that the United States Federal Trade Commission and/or the
          United States Department of Justice shall seek a preliminary
          injunction under the HSR Act against Trubion and Wyeth to enjoin the
          transactions contemplated by this Agreement, (b) at the election of
          either Party, immediately upon written notice to the other Party, in
          the event that the United States Federal Trade Commission and/or the
          United States Department of Justice shall obtain a preliminary
          injunction under the HSR Act against Trubion and Wyeth to enjoin the
          transactions contemplated by this Agreement, or (c) at the election of
          either Party, immediately upon written notice to the other Party, in
          the event that the HSR Clearance Date shall not have occurred on or
          prior to [***] days after the effective date of the HSR Filing.

     9.5. MATERIAL BREACH. In the event that either Party commits a material
          breach of its representations, warranties or obligations under this
          Agreement, the other Party may terminate this Agreement (a) on a
          Licensed Target by

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          Licensed Target and country by country basis, to the extent that such
          material breach relates to Licensed Product(s) directed against such
          Licensed Target(s) in such country(ies) or (b) in its entirety only if
          such material breach fundamentally frustrates the objectives or
          transactions contemplated by this Agreement taken as a whole. If a
          Party elects to exercise such right to terminate, it shall do so by
          providing written notice of the alleged breach (the "Notice of
          Breach") to the breaching Party. If such material breach pertains to
          the payment of undisputed amounts payable under this Agreement and
          remains uncured for [***] after the breaching Party's receipt of such
          Notice of Breach or, if such material breach pertains to another
          material breach (other than for non-payment) and remains uncured for
          [***] after the breaching Party's receipt of such Notice of Breach,
          then the non-breaching Party may terminate this Agreement, as and to
          the extent permitted in (a) or (b) above, on [***] days notice by
          giving a written notice of termination ("Notice of Termination") to
          the breaching Party; provided, however, that if such breach (other
          than for non-payment) is not susceptible to cure within the initial
          [***] period and the breaching Party uses continuous, diligent, good
          faith efforts to cure such breach, it shall document such efforts by
          written notice to the non-breaching Party on or before the end of such
          [***] period, and the stated cure period will be extended by an
          additional [***]. This Agreement shall be deemed terminated (as and to
          the extent permitted in (a) or (b) above) [***] after the breaching
          Party's receipt of such Notice of Termination, unless the breaching
          Party has fully cured the breach prior to the expiration of such [***]
          period.

          In the event that Trubion is the breaching Party and fails to cure any
          such material breach within the applicable time period(s) set forth
          above, Wyeth, within [***] after the expiration of the cure period for
          such breach, may elect, in lieu of terminating this Agreement, by
          written notice to Trubion (a "Notice of Modification"), to modify the
          terms of this Agreement, as (and only to the extent) provided in
          Section 9.8, on a Licensed Target-by-Licensed Target and
          country-by-country basis (but only to the extent such material breach
          relates to Licensed Product(s) directed against such Licensed
          Target(s) in such country(ies)), in which event, Wyeth shall be deemed
          to have waived its right to terminate this Agreement under this
          Section 9.5 with respect to such Licensed Target(s) in such
          country(ies) only with respect to the material breach giving rise to
          such action under this Section 9.5. Notwithstanding the foregoing, a
          Party shall not be in breach of its obligations under this Agreement
          to the extent that such breach was caused by the other Party's failure
          to perform its obligations hereunder.

     9.6. TERMINATION BY WYETH.

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          9.6.1. TERMINATION WITHOUT CAUSE. Commencing on the second anniversary
               of the Effective Date, Wyeth shall have the right, exercisable
               upon ninety (90) days prior written notice to Trubion, to
               terminate this Agreement either (a) in its entirety, or (b) on a
               Licensed Target by Licensed Target and country by country basis.
               Wyeth's rights under this Section 9.6.1 are separate from and in
               addition to its rights to terminate the Research Program under
               Section 3.3.2 hereof.

          9.6.2. TERMINATION FOR A MATERIAL SAFETY OR REGULATORY ISSUE. Wyeth
               shall have the right to terminate this Agreement, at any time, on
               a Licensed Target by Licensed Target basis, by giving [***] prior
               written notice to Trubion in the event of any safety or
               regulatory issue that would have a material adverse effect on
               Wyeth's ability to research, Develop, Manufacture or
               Commercialize any Licensed Product directed against such Licensed
               Target, as determined in Wyeth's reasonable judgment and
               according to Wyeth's standard internal procedures for evaluating
               such safety or regulatory issues. Effects of such termination
               shall be as set forth in Section 0.

     9.7. EFFECTS OF TERMINATION.

          9.7.1. EFFECT OF TERMINATION BY WYETH FOR CAUSE.

               (A)  Without limiting any other legal or equitable remedies that
                    Wyeth or Trubion may have, subject to Section 11.3, if this
                    Agreement is terminated in its entirety by Wyeth for cause
                    under Section 9.5, the following provisions shall apply:

                    [***]

               (B)  Without limiting any other legal or equitable remedies that
                    Wyeth or Trubion may have, subject to Section 11.3, if this
                    Agreement is terminated by Wyeth for cause under Section 9.5
                    with respect to a Licensed Target in all countries, but not
                    in its entirety, the following provisions shall apply:

                    [***]

               (C)  Without limiting any other legal or equitable remedies that
                    Wyeth or Trubion may have, subject to Section 11.3, if this
                    Agreement is terminated by Wyeth for cause under Section 9.5
                    with respect to all Licensed Targets in a country, but not
                    in its entirety, the following provisions shall apply:

                    [***]

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          9.7.2. EFFECT OF TERMINATION BY TRUBION FOR CAUSE.

               (A)  Without limiting any other legal or equitable remedies that
                    Trubion or Wyeth may have, subject to Section 11.3, if this
                    Agreement is terminated in its entirety by Trubion for cause
                    under Section 9.5, the following provisions shall apply:

                    [***]

               (B)  Without limiting any other legal or equitable remedies that
                    Trubion or Wyeth may have, subject to Section 11.3, if this
                    Agreement is terminated by Trubion for cause under Section
                    9.5 with respect to a Licensed Target in all countries, but
                    not in its entirety, the following provisions shall apply:

                    [***]

               (C)  Without limiting any other legal or equitable remedies that
                    Trubion or Wyeth may have, subject to Section 11.3, if this
                    Agreement is terminated by Trubion for cause under Section
                    9.5 with respect to all Licensed Targets in a country, but
                    not in its entirety, the following provisions shall apply:

                    [***]

          9.7.3. EFFECT OF TERMINATION BY WYETH WITHOUT CAUSE.

               (A)  If this Agreement is terminated in its entirety by Wyeth
                    under Section 9.6.1, the following provisions shall apply:

                    [***]

               (B)  If this Agreement is terminated by Wyeth under Section 9.6.1
                    with respect to a Licensed Target in all countries, but not
                    in its entirety, the following provisions shall apply:

                    [***]

               (C)  If this Agreement is terminated by Wyeth under Section 9.6.1
                    with respect to all Licensed Targets in a country, but not
                    in its entirety, the following provisions shall apply:

                    [***]

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          9.7.4. EFFECT OF TERMINATION BY WYETH FOR A MATERIAL SAFETY OR
               REGULATORY ISSUE. If this Agreement is terminated with respect to
               a Licensed Target by Wyeth under Section 9.6.2, the following
               provisions shall apply:

               [***]

          9.7.5. POST-TERMINATION RIGHTS TO WYETH TECHNOLOGY AND TRUBION
               TECHNOLOGY. Except as otherwise expressly set forth in this
               Agreement, expiration or termination of this Agreement for any
               reason shall have no effect on Wyeth's rights with respect to the
               Wyeth Technology, and Trubion shall have no right, title or
               interest in or to any of the Wyeth Technology, and such
               expiration or termination shall have no effect on Trubion's
               rights with respect to the Trubion Technology, and Wyeth shall
               have no right, title or interest in or to any of the Trubion
               Technology.

          9.7.6. POST-TERMINATION LICENSES TO WYETH TECHNOLOGY. [***]

          9.7.7. POST-TERMINATION TRANSFER OF PRODUCT DATA AND FILINGS AND
               EXISTING TRADEMARKS. The following provisions shall apply in the
               event of termination by Trubion under Section 9.5 or termination
               by Wyeth under Section 9.6. To the extent permitted by applicable
               law, Wyeth shall assign and transfer to Trubion Wyeth's entire
               right, title and interest in and to Product Data and Filings,
               provide copies of all the Research Program Data, and license or
               otherwise transfer rights to Existing Trademarks that are
               necessary or useful for Trubion to continue to research, Develop,
               Manufacture or Commercialize Licensed Products as constituted at
               the time of termination. To the extent such Research Program
               Data, Product Data and Filings and other rights or items were
               previously transferred from Trubion to Wyeth, Wyeth shall perform
               such transfer at no cost to Trubion. To the extent such Research
               Program Data and Product Data and Filings were not previously
               transferred from Trubion to Wyeth, Trubion shall reimburse Wyeth
               for its reasonable out-of-pocket expenses in connection with such
               transfer, and such transfer shall be pursuant to an instrument in
               form and substance reasonably satisfactory to Trubion. Wyeth
               shall perform all other actions reasonably requested by Trubion
               to effect and confirm such transfer. After receipt of Trubion's
               request consistent with the foregoing, Wyeth shall provide to
               Trubion, within [***] of receipt of such request, complete copies
               of such Product Data and Filings, including,

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               without limitation, relevant clinical data, INDs, additional
               regulatory filings with FDA or other Regulatory Authorities,
               supplements or amendments thereto, all written correspondence
               with FDA or other Regulatory Authorities regarding the regulatory
               filings, and all existing written minutes of meetings and
               memoranda of conversations between Wyeth (including, to the
               extent practicable, Wyeth's investigators) and FDA or other
               Regulatory Authorities in Wyeth's possession (or in the
               possession of any of Wyeth's agents and subcontractors, such as
               contract research organizations used by Wyeth), to the extent
               Wyeth has the right to access and provide to Trubion such Product
               Data and Filings, regarding such regulatory filings, each to the
               extent they relate to Licensed Products. Within thirty (30) days
               (or such later date as Trubion may request) after the date of
               receipt of Trubion's request, Wyeth shall execute and deliver a
               letter to the FDA or other Regulatory Authorities, in a form
               approved by Trubion, transferring ownership to Trubion of such
               regulatory filings, if any, filed in the name of Wyeth that are
               related to Licensed Products.

          9.7.8. MANUFACTURING OF LICENSED PRODUCTS AFTER TERMINATION. If (a)
               with respect to a particular Licensed Target, Trubion terminates
               this Agreement pursuant to Section 9.5 hereof or Wyeth terminates
               this Agreement pursuant to Section 9.6 hereof, and (b) Wyeth is
               engaged in the Manufacturing of a Licensed Product directed
               against such Licensed Target on the date the terminating Party
               gives notice of termination under Section 9.5 or Section 9.6, as
               the case may be, then Wyeth shall Manufacture such Licensed
               Product for Trubion and use Commercially Reasonable Efforts to
               supply Trubion with its entire requirements of such Licensed
               Product until (i) the [***] anniversary of the effective date of
               such termination if at the time of such notice there shall have
               been filed a Regulatory Approval Application for such Licensed
               Product or (ii) the [***] anniversary of the effective date of
               such termination if at the time of such notice there shall not
               have been filed a Regulatory Approval Application for such
               Licensed Product; provided, however, that (w) Wyeth shall not be
               required to conduct any activities to increase the scale on which
               it is then Manufacturing such Licensed Product, (x) Wyeth shall
               not be required to Manufacture or supply such Licensed Product in
               an amount in excess of its available capacity in the
               Manufacturing suite that was used by Wyeth for the Manufacture of
               such Licensed Product (taking into account the other uses Wyeth
               is making of the manufacturing suite as of the date of the Notice
               of Termination) or to change the location of the Manufacturing
               activities, (y) Wyeth shall have no obligation to maintain idle
               capacity in such

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               manufacturing suite for purposes of meeting such Manufacturing
               obligations and (z) Wyeth may at its option assign to Trubion one
               or more of its Licensed Product manufacturing agreements with
               Third Parties, to the extent assignable, in lieu of continuing to
               contract directly with such Third Parties. The purchase price for
               such Licensed Product units actually Manufactured by Wyeth shall
               be at Wyeth's fully absorbed manufacturing cost plus [***], and
               Wyeth's obligations under this Section 9.7.8 shall be subject to
               the execution of a supply agreement and a quality agreement, each
               mutually acceptable to both Parties, which agreements shall
               contain the terms set forth in this Section 9.7.8 and such other
               reasonable terms as mutually agreed by the Parties.

          9.7.9. POST-TERMINATION DISPOSITION OF INVENTORIES OF LICENSED
               PRODUCTS. Following termination of this Agreement with respect to
               one or more Licensed Targets, Wyeth and its sublicensees shall
               have the right to continue to sell their existing inventories of
               Licensed Products directed against such Licensed Targets for a
               period not to exceed [***] after the effective date of such
               termination. Wyeth shall pay royalties and report on such sales,
               and maintain records thereon, in accordance with Sections 5.4,
               5.5 and 5.6, which shall survive termination for such purpose.

          9.7.10. CONTINUATION OF RIGHTS AND LICENSES UNDER SECTIONS 6.1.1 AND
               6.1.2. Notwithstanding anything in this Section 9.7 to the
               contrary, the Parties' rights and licenses set forth in Sections
               6.1.1 and 6.1.2 shall survive any expiration or termination of
               this Agreement.

          9.7.11. CONTINUATION OF OTHER RIGHTS AND OBLIGATIONS. Except as
               expressly provided to the contrary in this Section 9.7, in the
               event that a Party exercises any right that results in the
               termination of some, but not all, of the Parties' rights and
               obligations under this Agreement, all non-terminated rights and
               obligations of the Parties shall continue in full force and
               effect.

     9.8. [***]

     9.9. SURVIVAL OF CERTAIN OBLIGATIONS. Expiration or termination of this
          Agreement shall not relieve the Parties of any obligation accrued or
          accruing before such expiration or termination (including situations
          where it becomes clear only after the time of such expiration or
          termination that such obligation had already accrued). The following
          provisions shall survive the expiration or termination of this
          Agreement: Article 1 (to the extent definitions are embodied in the
          following listed Articles and Sections); Sections 3.6.3, 3.7, 5.6,
          6.1.1, 6.1.2, 9.2, 9.5, 9.6, 9.7, 9.9,

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          9.10.2, 12.3, 12.6, 12.8, 12.9, 12.10, 12.11 and 12.12; and Articles
          7, 10 and 11. Any expiration or early termination of this Agreement
          shall be without prejudice to the rights of either Party against the
          other accrued or accruing under this Agreement before expiration or
          termination, including, without limitation, the obligations (1) to
          provide research funding and reimbursement of expenses for activities
          undertaken prior to such expiration or termination under and in
          accordance with Sections 3.6.1, 3.6.2, 4.6, 4.9, 6.1.3, 6.2.1(a), (c)
          and (d), 6.2.2(b) and (c), and 6.2.3(b) and (c); and (2) to pay
          royalties for Licensed Products sold before such expiration or
          termination, and, to the extent permitted under Section 9.7.9, after
          expiration or termination in accordance with Section 5.4 (and subject
          to the related obligations under Section 5.5); and (3) to pay any
          Additional Research and Development Expense Payments in connection
          with any events specified on Exhibit 5.3 that are achieved prior to
          such expiration or termination, but with respect to which the
          corresponding payments under Exhibit 5.3 were not paid prior to such
          expiration or termination.

     9.10. CHANGE OF CONTROL.

          9.10.1. DEFINITION. With respect to any Party, a "Change of Control"
               means an event in which: (a) any other person or group of persons
               (as the term "person" is used for purposes of Section 13(d) or
               14(d) of the Exchange Act) not then beneficially owning more than
               fifty percent (50%) of the voting power of the outstanding
               securities of such Party acquires or otherwise becomes the
               beneficial owner (within the meaning of Rule 13d-3 promulgated
               under the Exchange Act) of securities of such Party representing
               more than fifty percent (50%) of the voting power of the then
               outstanding securities of such Party with respect to the election
               of directors of such Party; or (b) such Person (i) consummates a
               merger, consolidation or similar transaction with another Person
               where the voting securities of such Party outstanding immediately
               preceding such transaction (or the voting securities issued with
               respect to the voting securities of such Party outstanding
               immediately preceding such transaction) represent less than fifty
               percent (50%) of the voting power of such Party or surviving
               entity, as the case may be, immediately following such
               transaction, (ii) sells or otherwise transfers to any Person(s)
               in one or more related transactions more than fifty percent (50%)
               of its consolidated total assets, or assets from which more than
               fifty percent (50%) of its consolidated operating income for its
               most recent financial year was derived, (iii) disposes by sale,
               assignment, exclusive license or otherwise of all or
               substantially all of its intellectual property rights, except for
               licenses under such intellectual property rights in the ordinary
               course of business and any isolated sale or assignment of
               specific items of intellectual property, or (iv) liquidates,
               dissolves or

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               winds-up; or (c) with respect to Wyeth and with respect to
               Trubion, (at any time following any public offering of voting
               securities by Trubion), any "person" (as the term "person" is
               used for the purposes of Sections 13(d) or 14(d) of the Exchange
               Act) other than Wyeth acquires nineteen and nine-tenths percent
               (19.9%) or more of the voting power of the then-outstanding
               voting securities of such Party.

          9.10.2. CHANGE OF CONTROL OF WYETH.

               (A)  In the event that any transaction results in a Change of
                    Control of Wyeth, Trubion shall be entitled to request
                    further written assurances from the successor in interest to
                    Wyeth (the "Successor Party") re-affirming the commitment of
                    the Successor Party to comply with the terms and conditions
                    of the Agreement. Such further written assurances shall be
                    delivered within [***] of written request by Trubion.
                    Trubion may so request at any time during the [***] period
                    following completion of the subject transaction. Subject to
                    the operation of Section 9.10.2(b) below, the failure of
                    such Successor Party to provide the requested written
                    assurance shall be deemed to be a material breach of the
                    Agreement.

               (B)  In the event that in connection with, or during the [***]
                    period following, a Change of Control of Wyeth, Wyeth or the
                    Successor Party is required, or voluntarily decides, to
                    divest itself of one or more Licensed Products, Wyeth or the
                    Successor Party, subject to any restrictions or limitations
                    imposed by the Federal Trade Commission or other
                    governmental agency on such divestiture, shall offer to
                    Trubion an exclusive opportunity to negotiate the
                    acquisition or license of all rights of Wyeth or such
                    Successor Party, as the case may be, to such Licensed
                    Product(s) on commercially reasonable terms. In the event
                    that Trubion and the Successor Party, after [***] good faith
                    negotiations, are unable to conclude a definitive agreement
                    regarding the acquisition or license of such Licensed
                    Product(s), the Successor Party shall be entitled to divest
                    itself of such Licensed Product(s) to a party other than
                    Trubion; provided, however, no such divestiture to a Third
                    Party shall take place on terms more favorable to such Third
                    Party than those last offered by the Successor Party to
                    Trubion, without first offering such Licensed Product(s) to
                    Trubion on such more favorable terms. Such Third Party shall
                    be required to assume all of the Successor Party's

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<PAGE>

                    obligations owed to Trubion pursuant to this Agreement with
                    respect to the Licensed Product(s) so divested.

               (C)  In the event of a Change of Control of Wyeth, the
                    restrictive covenants set forth in Sections 2.3.1 and 2.3.2
                    (the "Exclusivity Covenants") shall apply to the Successor
                    Party's then-existing Development and Commercialization
                    activities that otherwise would violate the Exclusivity
                    Covenants (the "Existing Activities"). In such event,
                    Trubion shall have the right, exercisable upon written
                    notice given by Trubion (an "Exercise Notice") within [***]
                    after consummation of the Change of Control, to require such
                    Successor Party to engage in good faith discussions
                    regarding the terms and conditions on which such Successor
                    Party would pay reasonable financial consideration to
                    Trubion with respect to such Existing Activities. If Trubion
                    and such Successor Party do not agree on such terms and
                    conditions within [***] after Trubion gives the Exercise
                    Notice (or such longer period as may be agreed to by such
                    parties), or if such Successor Party notifies Trubion in
                    writing during such [***] period that it does not desire to
                    engage in such discussions, Trubion shall have the right,
                    exercisable upon written notice given by Trubion within ten
                    (10) days (i) after the end of such [***] (or such longer
                    period as agreed to by such parties) or (ii) after receipt
                    of such notice from such Successor Party, to require such
                    Successor Party to enter into an agreement to divest to a
                    Third Party either (a) the Existing Activities or (b) the
                    relevant CD20 Products or [***], as the case may be (such
                    Third Party, in the case of a divestiture of the relevant
                    CD20 Products or [***], to be reasonably acceptable to
                    Trubion) within [***] after the date of such notice by
                    Trubion, subject to applicable governmental and regulatory
                    approval. If such Successor Party does not enter into an
                    agreement with a Third Party (such Third Party, in the case
                    of a divestiture of the relevant CD20 Products or [***], to
                    be reasonably acceptable to Trubion) to divest such Existing
                    Activities or such Products within such [***] period (or if
                    such Successor Party does enter into such an agreement but
                    such agreement terminates after such [***] period and such
                    divestiture is not consummated) or if such Successor Party
                    notifies Trubion in writing that it does not intend to
                    divest such Existing Activities or such Products, Trubion
                    shall have the right, exercisable within [***] after the end
                    of such [***] period

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                    (or upon termination of such agreement, if later) to
                    terminate, in its sole discretion, all CD20-related licenses
                    (only where such Existing Activities relate to products
                    directed against the CD20 Antigen which would otherwise
                    violate Wyeth's exclusivity covenants in Section 2.3.1
                    hereof) and/or all [***] (only where such Existing
                    Activities relate to products directed against the [***]
                    which would otherwise violate Wyeth's exclusivity covenants
                    in Section 2.3.2 hereof) granted to Wyeth under the
                    Agreement, on those terms and subject to those conditions
                    that would apply to a termination by Wyeth without cause.

          9.10.3. CHANGE OF CONTROL OF TRUBION. In the event of a Change of
               Control of Trubion where the acquiring party is a top fifteen
               (15) pharmaceutical company (measured by market capitalization),
               Wyeth shall have the right to [***].

10.  INDEMNIFICATION AND INSURANCE.

     10.1. INDEMNIFICATION BY WYETH. Wyeth will indemnify, defend and hold
          harmless Trubion, and each of its respective employees, officers,
          directors and agents (each, a "Trubion Indemnified Party") from and
          against any and all liability, loss, damage, expense (including
          reasonable attorneys' fees and expenses) and cost (collectively,
          "Liabilities") that the Trubion Indemnified Party may be required to
          pay to one or more Third Parties resulting from or arising out of:

               (A)  any claims of any nature pertaining to any act or omission
                    related to performance under this Agreement by, on behalf
                    of, or under the authority of Wyeth (other than by any
                    Trubion Indemnified Party) including, but not limited to,
                    research, Development, Manufacture or Commercialization of
                    Licensed Product(s) or any violation of applicable law, rule
                    or regulation by, on behalf of, or under the authority of
                    Wyeth (other than by any Trubion Indemnified Party); and/or

               (B)  any Wyeth representation or warranty set forth herein being
                    untrue in any material respect when made;

          except in each case, to the extent caused by the negligence or willful
          misconduct of Trubion or any other Trubion Indemnified Party.

     10.2. INDEMNIFICATION BY TRUBION. Trubion will indemnify, defend and hold
          harmless Wyeth and its sublicensees, distributors and each of its and
          their

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          respective employees, officers, directors and agents (each, a "Wyeth
          Indemnified Party") from and against any and all Liabilities that the
          Wyeth Indemnified Party may be required to pay to one or more Third
          Parties resulting from or arising out of:

               (A)  any claims of any nature pertaining to any act or omission
                    related to performance under this Agreement by, on behalf
                    of, or under the authority of Trubion (other than by any
                    Wyeth Indemnified Party) or any violation of applicable law,
                    rule or regulation by, on behalf of, or under the authority
                    of Trubion (other than by any Wyeth Indemnified Party);
                    and/or

               (B)  any Trubion representation or warranty set forth herein
                    being untrue in any material respect when made;

          except in each case, to the extent caused by the negligence or willful
          misconduct of Wyeth or any other Wyeth Indemnified Party.

     10.3. PROCEDURE. Each Party will notify the other in the event it becomes
          aware of a claim for which indemnification may be sought hereunder. In
          case any proceeding (including any governmental investigation) shall
          be instituted involving any Party in respect of which indemnity may be
          sought pursuant to this Article 10, such Party (the "Indemnified
          Party") shall promptly notify the other Party (the "Indemnifying
          Party") in writing within fifteen (15) days and the Indemnifying Party
          and Indemnified Party shall meet to discuss how to respond to any
          claims that are the subject matter of such proceeding. The
          Indemnifying Party, upon request of the Indemnified Party, shall
          retain counsel reasonably satisfactory to the Indemnified Party to
          represent the Indemnified Party and shall pay the fees and expenses of
          such counsel related to such proceeding. The Indemnified Party agrees
          to cooperate fully with the Indemnifying Party in the defense of any
          such claim, action or proceeding, or any litigation resulting from any
          such claim. In any such proceeding, the Indemnified Party shall have
          the right to retain its own counsel, but the fees and expenses of such
          counsel shall be at the expense of the Indemnified Party unless (a)
          the Indemnifying Party and the Indemnified Party shall have mutually
          agreed to the retention of such counsel or (b) the named parties to
          any such proceeding (including any impleaded parties) include both the
          Indemnifying Party and the Indemnified Party and representation of
          both Parties by the same counsel would be inappropriate due to actual
          or potential differing interests between them. All such fees and
          expenses shall be reimbursed as they are incurred. The Indemnifying
          Party shall not be liable for any settlement of any proceeding
          effected without its written consent, but if settled with such consent
          or if there be a final judgment for the plaintiff, the Indemnifying
          Party agrees to indemnify the Indemnified

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<PAGE>

          Party from and against any loss or liability by reason of such
          settlement or judgment. The Indemnifying Party shall not, without the
          written consent of the Indemnified Party, effect any settlement of any
          pending or threatened proceeding in respect of which the Indemnified
          Party is, or arising out of the same set of facts could have been, a
          party and indemnity could have been sought hereunder by the
          Indemnified Party, unless such settlement includes an unconditional
          release of the Indemnified Party from all liability on claims that are
          the subject matter of such proceeding.

     10.4. INSURANCE. Each Party shall use Commercially Reasonable Efforts to
          obtain and maintain, during the term of this Agreement, commercial
          general liability insurance, including products liability insurance,
          with reputable and financially secure insurance carriers to cover its
          indemnification obligations under Sections 10.1 or 10.2, as
          applicable, or self-insurance, in each case with limits of not less
          than [***] per occurrence and in the aggregate. Insurance shall be
          procured with carriers having an A.M. Best Rating of A-VII or better.

11.  DISPUTE RESOLUTION.

     11.1. GENERAL. Any controversy, claim or dispute arising out of or relating
          to this Agreement shall be settled, if possible, through good faith
          negotiations between the Parties. If, however, the Parties are unable
          to settle such dispute after good faith negotiations, the matter shall
          be referred to the Executive Officers to be resolved by negotiation in
          good faith as soon as is practicable but in no event later than thirty
          (30) days after referral. Such resolution, if any, of a referred issue
          shall be final and binding on the Parties.

     11.2. FAILURE OF EXECUTIVE OFFICERS TO RESOLVE DISPUTE. If the Executive
          Officers are unable to settle the dispute after good faith negotiation
          in the manner set forth above, either Party (including its successors
          and permitted assigns but excluding its Affiliates unless an Affiliate
          is a successor or permitted assign) may seek resolution of the dispute
          through any remedies available at law or in equity from any court of
          competent jurisdiction.

     11.3. DISCLAIMER OF CONSEQUENTIAL AND PUNITIVE DAMAGES. Subject to and
          without limiting the indemnification obligations of each Party under
          Article 10, under no circumstances shall either Party be liable to the
          other Party for consequential or punitive damages arising out of or
          relating to this Agreement or any breach thereof. Both Parties hereby
          disclaim such damages.

12.  MISCELLANEOUS.

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<PAGE>

     12.1. PERIODIC EXECUTIVE MEETINGS. The Chief Executive Officer of Trubion,
          the Senior Vice President, Research and Development of Trubion, the
          Executive Vice President and General Manager of the Wyeth
          Pharmaceuticals Biopharma Business Unit and the Executive Vice
          President and Operating Officer of Wyeth's Research Division (and such
          other executive officers of the Parties as may be designated from time
          to time by the Parties) shall meet from time to time during the first
          [***] of the term of this Agreement to review and discuss the Parties'
          activities under this Agreement. Such meetings will be held on a
          quarterly basis or such other periodic basis as such executive
          officers decide, and will take place in locations selected by such
          executive officers. Such meetings may take place by telephone or video
          conference.

     12.2. ASSIGNMENT. Neither this Agreement nor any interest hereunder shall
          be assignable by either Party, without the prior written consent of
          the other Party, which consent shall not be unreasonably withheld or
          delayed, except a Party may make such an assignment without the other
          Party's consent to Affiliates or to a successor to substantially all
          of the business of such Party to which this Agreement relates, whether
          in merger, sale of stock, sale of assets or other transaction. This
          Agreement shall be binding upon the successors and permitted assigns
          of the Parties, and the name of a Party appearing herein shall be
          deemed to include the names of such Party's successors and permitted
          assigns to the extent necessary to carry out the intent of this
          Agreement. In addition to the foregoing, Trubion may assign its right,
          in whole or part, to receive payments under this Agreement; provided,
          however, Trubion shall notify Wyeth of its intention to do so and
          shall provide Wyeth an opportunity for at least [***] days to
          negotiate in good faith the purchase of any such right Trubion intends
          to so assign. Any assignment not in accordance with this Section 12.2
          shall be void.

     12.3. FURTHER ACTIONS. Each Party agrees to execute, acknowledge and
          deliver such further instruments, and to do all such other acts, as
          may be necessary or appropriate in order to carry out the purposes and
          intent of the Agreement.

     12.4. FORCE MAJEURE. Neither Party shall be liable to the other for delay
          or failure in the performance of the obligations on its part contained
          in this Agreement if and to the extent that such failure or delay is
          due to circumstances beyond its control which it could not have
          avoided by the exercise of reasonable diligence. It shall notify the
          other Party promptly should such circumstances arise, giving an
          indication of the likely extent and duration thereof, and shall use
          all Commercially Reasonable Efforts to resume performance of its
          obligations as soon as practicable; provided, however, that neither
          Party shall be required to settle any labor dispute or disturbance.

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<PAGE>

     12.5. NON-SOLICITATION. During the period between the Effective Date and
          the later of (a) the end of [***] or (b) the date [***], but in the
          case of (a) and (b) not later than the [***] of the Effective Date,
          neither Trubion nor the Wyeth pharmaceuticals business operating in
          the United States ("U.S. Wyeth Pharmaceuticals") shall solicit for
          employment any key or technical employee(s) of the other Party who
          become known to U.S. Wyeth Pharmaceuticals or Trubion, as the case may
          be, through the transactions contemplated by this Agreement without
          the other's prior written consent (which consent may be granted or
          denied in the other's sole discretion); provided, however, that
          nothing in this Section 12.5 shall prohibit U.S. Wyeth Pharmaceuticals
          or Trubion, as the case may be, from hiring any employees of the other
          who respond to general employment solicitations not targeted at the
          employees of the other, advertised employment opportunities, or hiring
          by the other by personnel not working on the transactions contemplated
          by this Agreement or who are not otherwise directly or indirectly
          exposed to the personnel working thereon.

     12.6. CORRESPONDENCE AND NOTICES.

          12.6.1. ORDINARY NOTICES. Correspondence, reports, documentation, and
               any other communication in writing between the Parties in the
               course of ordinary implementation of this Agreement shall be
               delivered by hand, sent by facsimile transmission (receipt
               verified), or by airmail to the employee or representative of the
               other Party who is designated by such other Party to receive such
               written communication.

          12.6.2. EXTRAORDINARY NOTICES. Extraordinary notices and other
               communications hereunder (including, without limitation, any
               notice of force majeure, breach, termination, change of address,
               etc.) shall be in writing and shall be deemed given if delivered
               personally or by facsimile transmission (receipt verified),
               mailed by registered or certified mail (return receipt
               requested), postage prepaid, or sent by nationally recognized
               express courier service, to the Parties at the following
               addresses (or at such other address for a Party as shall be
               specified by like notice; provided, however, that notices of a
               change of address shall be effective only upon receipt thereof):

                                                                              82

<PAGE>

               All correspondence to Wyeth shall be addressed as follows:

                    Wyeth Pharmaceuticals
                    500 Arcola Road
                    Collegeville, Pennsylvania 19426
                    Attn: Senior Vice President, Corporate Business Development
                    Fax: (484) 865-6476

               with a copy to:

                    Wyeth
                    5 Giralda Farms
                    Madison, New Jersey 07940
                    Attn: Executive Vice President and General Counsel
                    Fax: (973) 660-7156

               All correspondence to Trubion shall be addressed as follows:

                    Trubion Pharmaceuticals, Inc.
                    2401 4th Avenue
                    Suite 1050
                    Seattle, Washington 98121
                    Attn: President & CEO
                    Fax: (206) 838-0503

               with a copy to:

                    Trubion Pharmaceuticals, Inc.
                    Vice President, Legal Affairs
                    2401 4th Avenue
                    Suite 1050
                    Seattle, Washington 98121
                    Fax: (206) 838-0503

     12.7. AMENDMENT. No amendment, modification or supplement of any provision
          of this Agreement shall be valid or effective unless made in writing
          and signed by a duly authorized officer of each Party.

     12.8. WAIVER. No provision of the Agreement shall be waived by any act,
          omission or knowledge of a Party or its agents or employees except by
          an instrument in writing expressly waiving such provision and signed
          by a duly authorized officer of the waiving Party. The waiver by
          either of the Parties of any breach of any provision hereof by the
          other Party shall not be construed to be a waiver of any succeeding
          breach of such provision or a waiver of the provision itself.

                                                                              83

<PAGE>

     12.9. SEVERABILITY. If any clause or portion thereof in this Agreement is
          for any reason held to be invalid, illegal or unenforceable, the same
          shall not affect any other portion of this Agreement, as it is the
          intent of the Parties that this Agreement shall be construed in such
          fashion as to maintain its existence, validity and enforceability to
          the greatest extent possible. In any such event, this Agreement shall
          be construed as if such clause of portion thereof had never been
          contained in this Agreement, and there shall be deemed substituted
          therefor such provision as will most nearly carry out the intent of
          the Parties as expressed in this Agreement to the fullest extent
          permitted by applicable law.

     12.10. DESCRIPTIVE HEADINGS. The descriptive headings of this Agreement are
          for convenience only, and shall be of no force or effect in construing
          or interpreting any of the provisions of this Agreement.

     12.11. GOVERNING LAW. This Agreement shall be governed by and interpreted
          in accordance with the substantive laws of the State of New York,
          without regard to conflict of law principles thereof.

     12.12. ENTIRE AGREEMENT OF THE PARTIES. This Agreement constitutes and
          contains the complete, final and exclusive understanding and agreement
          of the Parties and cancels and supersedes any and all prior
          negotiations, correspondence, understandings and agreements, whether
          oral or written, among the Parties respecting the subject matter
          hereof and thereof, including, but not limited to, that certain
          Non-Disclosure Agreement of the Parties effective May 27, 2004. For
          the avoidance of doubt, disclosures made under such Confidentiality
          Agreement shall continue to be subject to the terms of this Agreement
          as if first disclosed pursuant hereto. Except as expressly set forth
          in this Agreement, neither Party shall have any other obligations,
          whether by implication or otherwise, with respect to the research,
          Development, Manufacture or Commercialization of Licensed Products.

     12.13. INDEPENDENT CONTRACTORS. Both Parties are independent contractors
          under this Agreement. Nothing herein contained shall be deemed to
          create an employment, agency, joint venture or partnership
          relationship between the Parties hereto or any of their agents or
          employees, or any other legal arrangement that would impose liability
          upon one Party for the act or failure to act of the other Party.
          Neither Party shall have any express or implied power to enter into
          any contracts or commitments or to incur any liabilities in the name
          of, or on behalf of, the other Party, or to bind the other Party in
          any respect whatsoever.

     12.14. COUNTERPARTS. This Agreement may be executed in any number of
          counterparts, each of which need not contain the signature of more
          than one Party but all such counterparts taken together shall
          constitute one and

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<PAGE>

          the same agreement. Facsimile signatures shall be binding upon the
          Parties and shall be treated as if originals.

     IN WITNESS WHEREOF, duly authorized representatives of the Parties have
duly executed this Agreement to be effective as of the Signing Date.

WYETH,                                  TRUBION PHARMACEUTICALS, INC.

ACTING THROUGH ITS

WYETH PHARMACEUTICALS DIVISION

By /s/ William M. Haskel                By Peter A. Thompson, M.D.
   ----------------------------------      -------------------------------------
Name: William M. Haskel                 Name: Peter A. Thompson, M.D.
      -------------------------------   Title: President & CEO
Title: Vice President
       ------------------------------

                                                                              85

<PAGE>

                                  EXHIBIT 1.122

                                     TRU-015

     [***]

     As of the Signing Date, TRU-015 is investigated in the Phase IIa Clinical
Study.

<PAGE>

                                  EXHIBIT 1.129

                              TRUBION PATENT RIGHTS

[***]

<PAGE>

                                  EXHIBIT 1.132

                         TRUBION THIRD PARTY AGREEMENTS

[***]

<PAGE>

                                  EXHIBIT 3.2.1

                            TRUBION'S "MILESTONE ONE"

[***]

<PAGE>

                                  EXHIBIT 3.2.4

                                EXCLUDED TARGETS

                 GENBANK ACCESSION NUMBER (AMINO ACID SEQUENCE)

[***]

<PAGE>

                                   EXHIBIT 4.4

                       ADVERSE EVENT REPORTING PROCEDURES

The terms adverse event or experience (AE) and adverse drug reaction (ADR), used
in this Exhibit 4.4 shall have the meanings set forth in worldwide reporting
regulations. The Parties agree to comply with any and all governmental laws,
regulations and orders that are applicable now and in the future in connection
with product safety collection and reporting.

The Parties agree to meet after the Effective Date to establish a detailed
Safety Agreement outlining the pharmacovigilance responsibilities of each Party
including but not limited to: AE or ADR reporting including literature review
and associated reporting; AE or ADR follow-up reporting; preparation and
submission of all safety reports to the Regulatory Authorities as required by
local laws and/or regulations in the Territory; maintaining the global safety
database; all interactions with health authorities regarding safety; periodic
submissions; labeling modifications; safety monitoring and detection; and safety
measures (e.g., Dear Doctor Letter, restriction on distribution). Wyeth shall
maintain the global safety database for the Licensed Products.

Notwithstanding the foregoing and until such time as the Safety Agreement is
executed, to the extent Trubion has or receives any information regarding any
AE/ADR which may be related to the use of any Licensed Product or to Licensed
Product Development, Trubion shall promptly forward such information as follows:

     -    Fatal or life-threatening serious AE(s)/ADR(s) judged by either the
          investigator and/or sponsor to be reasonably related to the Licensed
          Product(s) Development/protocol shall be transmitted to Wyeth within
          three (3) calendar days from the date received by Trubion.

     -    All other serious AE(s)/ADR(s) not fatal or life-threatening but
          judged by either the investigator and/or sponsor to be reasonably
          related to the Licensed Product(s) Development/protocol shall be
          transmitted to Wyeth within five (5) calendar days from the date
          received by Trubion.

AE/ADR information may be transmitted to Wyeth by:

     a.   Facsimile: 610-989-5544 OR

<PAGE>

     b.   Overnight courier to:

               Global Safety Surveillance & Epidemiology
               Wyeth Research
               GSSE Triage Unit
               Dock E
               500 Arcola Road
               Collegeville, PA 19426

<PAGE>

                                  EXHIBIT 5.2A

                            STOCK PURCHASE AGREEMENT

                          TRUBION PHARMACEUTICALS, INC.

                         COMMON STOCK PURCHASE AGREEMENT

          This Common Stock Purchase Agreement (this "Agreement") is made as of
December __, 2005 by and between Trubion Pharmaceuticals, Inc., a Delaware
corporation (the "Company"), and Wyeth, a Delaware corporation (the
"Purchaser").

                                    RECITALS

          A. The Purchaser and the Company are entering into a collaboration
agreement of even date herewith (the "Collaboration Agreement");

          B. In connection with the Collaboration Agreement, Purchaser desires
to purchase from the Company shares of its Common Stock (the "Common Stock"),
concurrently with and conditioned upon the closing of the Company's initial
public offering, upon the terms and conditions set forth herein;

          C. The Company and the Purchaser wish to set forth the terms and
conditions upon which the Company will sell the Common Stock to the Purchaser;
and

          D. Concurrent with the execution of this Agreement, the Company and
Purchaser are entering into an amendment (the "Rights Agreement Amendment") to
the Company's Amended and Restated Investor Rights Agreement (the "Rights
Agreement") to provide Purchaser with certain rights and obligations thereunder
upon the issuance of the Common Stock hereunder.

          NOW, THEREFORE, in consideration of the premises and mutual covenants
and conditions contained herein, the Company and the Purchaser hereby agree as
follows:

                                    ARTICLE I

                           PURCHASE AND SALE OF SHARES

     1.1 Purchase Price and Closing. Subject solely to the conditions set forth
in Sections 1.2 - 1.5 and Article IV hereof, the Company will issue and sell to
the Purchaser and, subject to the terms and conditions set forth in this
Agreement, the Purchaser will purchase from the Company (the "Sale"), that
number of shares of Common Stock (the "Shares") equal to the quotient obtained
by dividing Twenty-Five Million Dollars ($25,000,000) (the "Investment Amount")
by the per-share price to the public (the "IPO Price") of shares of Common Stock
in the Company's first underwritten, firm commitment public offering (the "IPO")
pursuant to an effective registration statement (the "Registration Statement")
under the Securities Act of 1933, as amended (the "Securities Act"). The per
share price to Purchaser shall be

<PAGE>

the IPO Price. The purchase and sale will take place at a closing (the
"Closing") to be held on the date, at the location and simultaneously with the
closing of the IPO, subject to the satisfaction of all of the conditions to the
Closing specified in Article IV herein. At the Closing the Company will issue
and deliver a certificate evidencing the Shares to the Purchaser against payment
of the full purchase price therefor by wire transfer of immediately available
funds to an account designated by the Company.

     1.2 Maximum Share Number. Notwithstanding Section 1.1 above, in the event
the number of Shares would otherwise constitute more than (i) nineteen and
nine-tenths percent (19.9%) of the Actual Voting Power (as defined in Section
5.1(i)) or (ii) twenty percent (20%) of the number of shares issued in the IPO
(including any shares covered by a related registration statement filed pursuant
to Rule 462(b) of the Securities Act but excluding any shares issued or to be
issued in an overallotment option), then in either case (i) or (ii) above the
Investment Amount (and correspondingly the number of shares purchased by the
Purchaser) shall be reduced by the minimum dollar amount and share amount
necessary to avoid either such event.

     1.3 Restrictions on Transfer. Pursuant to the Rights Agreement Amendment,
Purchaser agrees and acknowledges that the restrictions set forth in Sections
2.1 and 2.12 of the Rights Agreement shall apply to Purchaser and the Shares.

     1.4 HSR Act. Prior to the execution of the Collaboration Agreement and this
Agreement, the parties made certain filings under the Hart-Scott Rodino
Antitrust Improvements Act of 1976, as amended (the "HSR Act"). If either party
concludes in good faith that additional filings or proceedings are necessary or
desirable as a result of the transactions contemplated hereby either as a result
of the signing of this Agreement or in connection with the Closing or otherwise,
the parties agree to promptly file such additional notices, applications and
documents that may be required under the HSR Act, or any other required foreign
or domestic competition law (collectively, the "Competition Laws") and all
applicable additional filings fees associated therewith shall be paid by the
party required to so pay such additional filing fees under the applicable
Competition Law(s). In connection therewith, the Company and Purchaser each
shall use their commercially reasonable efforts to take such actions as may be
required to cause the expiration or early termination of the notice periods
under the Competition Laws as promptly as possible and to resolve such
objections, if any, as may be asserted with respect to the transactions
contemplated by this Agreement under the Competition Laws; provided, however,
that notwithstanding the foregoing, neither party shall agree to any change or
amendment to this Agreement unless such change or amendment is agreed by the
other party in advance. Nothing in this Agreement shall require either party or
any subsidiary or affiliate of either party to sell, hold separate, license or
otherwise dispose of any assets or conduct its business in a specified manner,
or agree or proffer to sell, hold separate, license or otherwise dispose of any
assets or conduct its business in a specified manner, or permit or agree to the
sale, holding separate, licensing or other disposition of any assets of either
party or any subsidiary or affiliate of either party, whether as a condition to
obtaining any approval from, or to avoid potential litigation or administrative
action by, a governmental entity or any other person or for any other reason.

     1.5 Termination of Purchase Right and Obligation. Notwithstanding any
provision of this Agreement to the contrary, Purchaser's right and obligation to
purchase, and the Company's right and obligation to sell, the Shares shall
terminate if the closing of the IPO has not occurred prior to the earliest to
occur of the following:

          (a)  The termination of the Collaboration Agreement; or

                                       2

<PAGE>

     (b) The Company (1) undergoes a Change of Control (as defined in Section
5.1(iv));; provided, however, the following shall be deemed to not be a Change
of Control for purposes of this Section 1.5(b): (i) a transaction effected
exclusively for the purpose of changing the domicile of the Company, or (ii) an
equity financing in which the Company is the surviving corporation, or (2)
engages in a merger, consolidation, reorganization or similar transaction in
which the surviving entity has a class of equity securities registered under
Section 12 of the Exchange Act (as defined below).

                                   ARTICLE II

                  REPRESENTATIONS AND WARRANTIES OF THE COMPANY

     The Company hereby represents and warrants to the Purchaser as follows:

     2.1 Corporate Action. The Company has all necessary corporate power and has
taken all corporate action required to enter into and perform this Agreement and
the Rights Agreement Amendment (collectively, the "Financing Documents"). The
Financing Documents have been duly executed and delivered, and constitute valid,
legal, binding and enforceable obligations of the Company, enforceable in
accordance with their terms, except (i) as limited by applicable bankruptcy,
insolvency, reorganization, moratorium and other laws of general application
affecting enforcement of creditors' rights generally and (ii) as limited by laws
relating to the availability of specific performance, injunctive relief or other
equitable remedies. The issuance, sale and delivery of the Shares in accordance
with this Agreement have been duly authorized by all necessary corporate action
on the part of the Company. The issuance of the Shares is not subject to
preemptive rights or other preferential rights in any present stockholders of
the Company that have not been waived and will not conflict with any provision
of any agreement or instrument to which the Company is a party or by which it or
its property is bound and to which the Company has not obtained appropriate
waivers.

     2.2 No Conflict. The execution and delivery of this Agreement by the
Company does not, and the consummation of the transactions contemplated hereby
will not, conflict with, or result in any violation of, or default under (with
or without notice or lapse of time, or both), or give rise to a right of
termination, cancellation, modification or acceleration of any obligation under
(i) any provision of the Certificate of Incorporation of the Company or Bylaws
of the Company, (ii) any material mortgage, indenture, lease, contract or other
agreement or instrument, permit, concession, or license to which the Company or
any of its properties or assets is subject or (iii) any judgment, order, decree,
applicable to the Company or its properties or assets. To the Company's
knowledge as of the date hereof, no provision of any applicable law, rule or
regulation and no judgment, order, decree or injunction applicable to the
Company or its properties or assets shall prohibit the consummation of the
Closing nor shall the Closing result in any violation of any such law, rule,
regulation, judgment, order, decree or injunction.

     2.3 Status of Shares. The Shares, when issued and delivered in accordance
with the terms hereof and after payment of the purchase price therefor, will be
duly authorized, validly issued, fully-paid and non-assessable, issued in
compliance with applicable state and federal securities laws (subject, in part,
to the representations and warranties of Purchase in Article III hereof) and
free of restrictions on transfer other than restrictions on transfer under the
Financing Documents and applicable state and federal securities laws.

                                       3

<PAGE>

     2.4 Organization, Good Standing and Qualification. The Company is a
corporation duly organized, validly existing and in good standing under the laws
of the State of Delaware and has all requisite corporate power and authority to
carry on its business.

     2.5. Collaboration Agreement. The Collaboration Agreement has been duly
authorized, executed, and delivered by the Company and constitutes a valid and
binding obligation of the Company, enforceable in accordance with its terms,
except (i) as limited by applicable bankruptcy, insolvency, reorganization,
moratorium and other laws of general application affecting enforcement of
creditors' rights generally and (ii) as limited by laws relating to the
availability of specific performance, injunctive relief or other equitable
remedies.

     2.6 Final Prospectus and Registration Statement. The Company, acknowledging
that the Purchaser will be relying on the accuracy and completeness of the
Company's disclosure in connection with the IPO, warrants to the Purchaser that
the Prospectus (as defined below) used in connection with the Company's IPO will
comply, at the time of filing or use, with the requirements of the Securities
Act, and the Prospectus filed or used in connection with the IPO will not, at
such time, contain an untrue statement of a material fact or omit to state a
material fact required to be stated therein or necessary to make the statements
therein, in light of the circumstances under which they were made, not
misleading; the Registration Statement, when it becomes effective, will comply,
in all material respects, with the requirements of the Securities Act; and the
Registration Statement will not, when it becomes effective, contain an untrue
statement of a material fact or omit to state a material fact required to be
stated therein or necessary to make the statements therein; provided, however,
that the Company makes no warranty with respect to any statement contained in
the Registration Statement or a prospectus in reliance upon and in conformity
with information concerning the Purchaser that is furnished by the Purchaser
expressly for use therein. "Prospectus" means the final prospectus (as such term
is defined in Section 2(a)(10) of the Securities Act) as first filed with the
SEC pursuant to paragraph (1) or (4) of Rule 424(b) of the Securities Act.

                                   ARTICLE III

            REPRESENTATIONS AND WARRANTIES AND COVENANTS BY PURCHASER

     The Purchaser represents and warrants and covenants to the Company that:

     3.1 Purchaser is an "accredited investor" as defined in Rule 501(a) under
the Securities Act of 1933, as amended.

     3.2 Purchaser will acquire the Shares for its own account, for the purpose
of investment and not with a view to distribution or resale thereof.

     3.3 Purchaser has all necessary corporate power and has taken all corporate
action required to enter into and perform the Financing Documents. The Financing
Documents have been duly executed and delivered, and constitute valid, legal,
binding and enforceable obligations of Purchaser, enforceable in

                                       4

<PAGE>

accordance with their terms, except (i) as limited by applicable bankruptcy,
insolvency, reorganization, moratorium and other laws of general application
affecting enforcement of creditors' rights generally and (ii) as limited by laws
relating to the availability of specific performance, injunctive relief or other
equitable remedies.

     3.4 Purchaser has taken no action which would give rise to any claim
against the Company by any other person for any brokerage commissions, finders'
fees or the like relating to this Agreement or the transactions contemplated
hereby.

     3.5 Purchaser has had the opportunity to ask questions of and receive
answers from representatives of the Company concerning the terms of the offering
of the Shares and to obtain additional information concerning the Company and
its business.

     3.6 The acquisition by the Purchaser of the Shares shall constitute a
confirmation of these representations and warranties made by the Purchaser as of
the Closing. Purchaser understands that the Shares are "restricted securities"
under the Securities Act and have not been registered under the Securities Act
in reliance upon an exemption for non-public offerings. The Purchaser further
represents that it understands and agrees that, until registered under the
Securities Act or transferred pursuant to the provisions of Rule 144 as
promulgated by the Commission, all certificates evidencing any of the Shares,
whether upon initial issuance or upon any transfer thereof, shall be subject to
the transfer restrictions and bear the legends set forth in Section 2.1 of the
Rights Agreement.

     3.7 To the Purchaser's knowledge as of the date hereof, no provision of any
applicable law, rule or regulation and no judgment, order, decree or injunction
applicable to the Purchaser or its properties or assets shall prohibit the
consummation of the Closing nor shall the Closing result in any violation of any
such law, rule, regulation, judgment, order, decree or injunction.

                                   ARTICLE IV

                              CONDITIONS TO CLOSING

     4.1 Conditions of the Purchaser's Obligation. The obligation of the
Purchaser to purchase and pay for the Shares at the Closing is subject to the
satisfaction of the following conditions:

          (a) Documentation at Closing. The Purchaser shall have received prior
to or at the Closing all of the following documents or instruments, or evidence
of completion thereof, each in form and substance satisfactory to the Purchaser:

               (i) A copy of the Certificate of Incorporation of the Company,
certified by the Secretary of State of the State of Delaware, a copy of the
resolutions of the Board of Directors of the Company evidencing the approval of
this Agreement, the issuance of the Shares and the other matters contemplated
hereby, and a copy of the Bylaws of the Company, all of which shall have been
certified by the Secretary of the Company to be true, complete and correct in
every particular, and certified copies of all documents evidencing other
necessary corporate or other action and governmental approvals, if any, with
respect to this Agreement and the Shares.

               (ii) A customary opinion of counsel to the Company covering the
matters set forth in Exhibit A hereto.

                                       5

<PAGE>

               (iii) A certificate of the Secretary of the Company which shall
certify the names of the officers of the Company authorized to sign this
Agreement, the certificate for the Shares and the other documents, instruments
or certificates to be delivered pursuant to this Agreement by the Company or any
of its officers, together with the true signatures of such officers.

               (iv) A certificate of the President of the Company stating (A)
that the representations and warranties made by the Company in this Agreement
are true and correct in all material respects at the date hereof and as of the
Closing with the same force and effect as though all such representations and
warranties had been made as of the Closing, and (B) that all covenants and
conditions required to be performed prior to or at the Closing have been
performed as of the Closing.

               (v) A Certificate of Good Standing for the Company from the
Secretary of State of the State of Delaware, dated as of a recent date.

          (b) Performance. The Company shall have performed and complied with in
all material respects all agreements, obligations and conditions contained in
this Agreement that are required to be performed or complied with by it on or
before the Closing.

          (c) Consents, Waivers, Etc. The Company shall have obtained all
consents or waivers, if any, necessary to execute and deliver this Agreement,
issue the Shares and to carry out the transactions contemplated hereby and
thereby and the waiting period applicable to this Agreement and the
Collaboration Agreement under the HSR Act (or any other applicable Competition
Laws) shall have expired or terminated early. All corporate and other action and
governmental filings necessary to effect the terms of this Agreement, the
issuance of the Shares and other agreements and instruments executed and
delivered by the Company in connection herewith shall have been made or taken,
except for any post-sale filing that may be required under federal or state
securities laws.

          (d) Rights Agreement Amendment. The Rights Agreement Amendment shall
have been executed by the Company and by the holders of the requisite majority
of Registrable Securities (as such term is defined in the Rights Agreement);
provided, however, the parties acknowledge that subsequent to the date hereof
the Rights Agreement may be further amended in accordance with its terms;
provided, further, however, Purchaser shall be required to consent to such
amendment or be provided substantially equivalent rights in such amendment or
another written agreement with the Company.

          (e) Collaboration Agreement. The Collaboration Agreement shall have
been duly authorized, executed, and delivered by the Company and constitute a
valid and binding obligation of the Company, enforceable in accordance with its
terms, except (i) as limited by applicable bankruptcy, insolvency,
reorganization, moratorium and other laws of general application affecting
enforcement of creditors' rights generally and (ii) as limited by laws relating
to the availability of specific performance, injunctive relief or other
equitable remedies. The Purchaser shall not have the right to terminate the
Collaboration Agreement for cause pursuant to Section 9.5 thereof (provided,
however, if Purchaser's right to so terminate the Collaboration Agreement for
cause is solely dependent on the lapsing on any applicable "cure" period
pursuant to Section 9.5 thereof, solely for purposes of this Section 4.1(e),
Purchaser shall be deemed to have the right to terminate the Collaboration
Agreement for cause notwithstanding the failure of any such cure period to have
lapsed); and the Company shall not have given notice to the Purchaser of its
intent to terminate the Collaboration Agreement.

                                       6

<PAGE>

          (f) Representations and Warranties. The representations and warranties
made by the Company in this Agreement shall have been true and correct in all
material respects at the date hereof and as of the Closing with the same force
and effect as though all such representations and warranties had been made as of
the Closing.

          (g) No Injunctions. No provision of any applicable law, rule or
regulation and no judgment, order, decree or injunction shall prohibit the
consummation of the Closing.

          (h) Listing. The shares of Common Stock sold in the IPO shall be
listed on the New York Stock Exchange ("NYSE") or traded on the Nasdaq National
Market.

          (i) Closing of IPO. The Closing hereunder shall be concurrent with the
closing of the IPO.

     4.2 Conditions of the Company's Obligation. The obligation of the Company
to sell the Shares at the Closing is subject to the satisfaction of the
following conditions:

          (a) Performance. The Purchaser shall have performed and complied with
in all material respects all agreements, obligations and conditions contained in
this Agreement that are required to be performed or complied with by it on or
before the Closing.

          (b) Consents, Waivers, Etc. Any waiting period applicable to this
Agreement and the Collaboration Agreement under the HSR Act (or any other
applicable Competition Laws) shall have expired or terminated early.

          (c) Rights Agreement Amendment. The Rights Agreement Amendment shall
have been executed by the Purchaser.

          (d) Collaboration Agreement. The Collaboration Agreement shall have
been duly authorized, executed and delivered by the Purchaser and constitute a
valid and binding obligation of the Purchaser, enforceable in accordance with
its terms, subject to laws of general application relating to bankruptcy,
insolvency and the relief of debtors and rules of law governing specific
performance, injunctive relief or other equitable remedies. The Company shall
not have the right to terminate the Collaboration Agreement for cause pursuant
to Section 9.5 thereof (provided, however, if the Company's right to so
terminate the Collaboration Agreement for cause is solely dependent on the
lapsing on any applicable "cure" period pursuant to Section 9.5 thereof, solely
for purposes of this Section 4.2(d), the Company shall be deemed to have the
right to terminate the Collaboration Agreement for cause notwithstanding the
failure of any such cure period to have lapsed; and the Purchaser shall not have
given notice to the Company of its intent to terminate the Collaboration
Agreement.

          (e) Representations and Warranties. The representations and warranties
made by the Purchaser in this Agreement shall have been true and correct in all
material respects at the date hereof and as of the Closing with the same force
and effect as though all such representations and warranties had been made as of
the Closing.

          (f) No Injunctions; Applicable Law. No provision of any applicable
law, rule or regulation and no judgment, order, decree or injunction shall
prohibit the consummation of the Closing

                                       7

<PAGE>

nor shall the Closing result in any violation of any such law, rule, regulation,
judgment, order, decree or injunction.

          (g) Listing. The shares of Common Stock sold in the IPO shall be
listed on the NYSE or traded on the Nasdaq National Market.

          (h) Closing of IPO. The Closing hereunder shall be concurrent with the
closing of the IPO.

          (i) Securities Regulations. The sale of the Shares to Purchaser shall
not be prohibited under state and federal securities laws and regulations.

                                    ARTICLE V

                              STANDSTILL AGREEMENT

     5.1. Definitions. For the purposes of this Agreement, the following words
and phrases shall have the following meanings:

          (i) "Actual Voting Power" means, as of the date of determination, the
total number of votes attaching to the outstanding securities entitled to vote
for the election of directors of the Company.

          (ii) "Affiliate" shall have the meaning given it in Rule 12b-2 under
the Securities Exchange Act of 1934, as amended (the "Exchange Act").

          (iii) "Beneficial Ownership" "Beneficial Owner" and "Beneficially Own"
shall have the meanings described to those terms in Rule 13d-1 under the
Exchange Act.

          (iv) "Change of Control" means (1) the acquisition by a Third Party of
more than 50% of the Company's then outstanding Voting Securities or (2) the
consummation of a merger, acquisition, consolidation or reorganization or series
of such related transactions involving the Company, unless immediately after
such transaction or transactions, the Beneficial Owners of the Company
immediately prior to the first such transaction shall Beneficially Own at least
50% of the outstanding Voting Securities of the Company (or, if the Company
would not be the surviving company in such merger, consolidation or
reorganization, the Voting Securities of the surviving corporation issued in
such transaction or transactions in respect of Voting Securities of the Company
shall represent at least 50% of the Voting Securities of such surviving
company).

          (v) "Investor Group" means Purchaser and any member of a 13D Group to
which the Purchaser belongs.

          (vi) "Person" means an individual, corporation, partnership,
association, trust, unincorporated organization or other entity

          (vii) "13D Group" means any group of persons formed for the purpose of
acquiring, holding, voting or disposing of Voting Securities which would be
required under the Exchange Act and the rules and regulations promulgated
thereunder, to file a statement on Schedule 13D with the Securities

                                       8
<PAGE>

and Exchange Commission as a "person" within the meaning of Section 13(d)(3) of
the Exchange Act if such group beneficially owned sufficient securities to
require such a filing under the Exchange Act.

          (viii) "Standstill Period" shall mean the period beginning on the
Closing of the IPO and ending on the date that is one year following the Closing
of the IPO.

          (ix) "Threshold Percentage" means the percentage of Actual Voting
Power owned by the Purchaser immediately following the closing of the IPO and
the sale of Shares hereunder, which in no case shall exceed nineteen and
nine-tenths percent (19.9%) of Actual Voting Power.

          (x) "Third Party" means any Person or two or more Persons acting in
concert, other than the Purchaser and its Affiliates or the Company and its
Affiliates.

          (xii) "Voting Security" means, as of the date of determination, the
Common Stock of the Company, any other security generally entitled to vote for
the election of directors and any outstanding convertible securities, options,
warrants or other rights which are convertible into or exchangeable or
exercisable for securities entitled to vote for the election of directors.

     5.2. Standstill Obligations.

          (a) Limitation. At any time during the Standstill Period, except with
the prior written consent of the Company's Board of Directors, no member of the
Investor Group shall, directly or indirectly:

               (i) acquire any Voting Securities (except by way of stock splits,
stock dividends or other distributions) if the effect of such acquisition or
exercise would be to increase the percentage interest of the Investor Group in
the Actual Voting Power to more than the Threshold Percentage; or

               (ii) publicly propose (on behalf of itself or to or with a Third
Party) any merger, business combination, restructuring, recapitalization or
similar transaction involving the Company or its subsidiaries or the purchase,
sale or other disposition outside the ordinary course of business of any
material portion of the assets of the Company or any of its subsidiaries.

          (b) Repurchases. Notwithstanding Section 5.2(a), no member of the
Investor Group shall be obligated to dispose of any Voting Securities if the
aggregate percentage ownership of the Investor Group is increased as a result of
a repurchase of Voting Securities by the Company.

          (c) Participation. Except with the prior written consent of the
Company's Board of Directors, during the Standstill Period the Investor Group
will not:

               (i) solicit proxies (or powers of attorney or similar rights to
vote) in respect of any Voting Securities;

               (ii) become a "participant" or "participant in a solicitation",
as those terms are defined in Regulation 14A of the General Rules and
Regulations promulgated pursuant to the Exchange Act, in opposition to a
solicitation by the Company; provided, however, that the Investor Group shall
not be deemed to be a "participant" or to have become engaged in a solicitation
hereunder solely by reason of the Company's solicitation of proxies in
connection with any meeting of the stockholders of the Company;

                                        9

<PAGE>

               (iii) seek to advise or intentionally influence any person or
entity with respect to the voting of Voting Securities in connection with any
such solicitation, in opposition to the recommendation of a majority of the
Board of Directors with respect to any matter relating to a Change of Control;

               (iv) initiate, propose or otherwise solicit stockholders for the
approval of any stockholder proposal (as described in Rule 14a-8 under the
Exchange Act or otherwise) with respect to the Company that is opposed by the
Board of Directors;

               (v) form or join any 13D Group for the purpose of voting,
purchasing or disposing of Voting Securities or the acquisition of all or
substantially all of assets of the Company;

               (vi) deposit any Voting Securities in a voting trust or subject
them to a voting agreement or other arrangement of similar effect, except in
order to comply with Competition Laws or other legal requirements;

               (vii) otherwise act, alone or in concert with others, in a manner
designed or having the deliberate effect of circumventing the restrictions
otherwise imposed hereunder, publicly announce any intention, plan or
arrangement inconsistent with the foregoing or finance or agree to finance any
other person in connection with any of the activities prohibited by this
Agreement; or

               (viii) publicly request, propose or otherwise seek any amendment
or waiver of the provisions of this Article 5.

     5.3 Exceptions. The limitations provided in Section 5.2 shall immediately
terminate upon the occurrence of any of the following events:

          (a) the commencement by any Person (other than a member of the
Investor Group or an Affiliate thereof) of a bona fide tender or exchange offer
seeking to acquire Beneficial Ownership of fifty percent (50%) or more of the
outstanding shares of Voting Securities of the Company;

          (b) the execution of an agreement by the Company and any Person which,
if consummated, would result in either (i) a Change of Control of the Company or
(ii) the sale of all or substantially all of the Company's assets; or

          (c) the adoption by the Company of a plan of liquidation or
dissolution with respect to the Company.

     5.4 Exclusion. No action or actions taken by the Purchaser pursuant to the
terms of the Collaboration Agreement or in connection with exercising or
enforcing its rights thereunder shall be deemed to violate the restrictions in
Section 5.2.

                                       10

<PAGE>

                                   ARTICLE VI

                                  MISCELLANEOUS

     6.1 No Waiver. No failure or delay on the part of any party to this
Agreement in exercising any right, power or remedy hereunder shall operate as a
waiver thereof; nor shall any single or partial exercise of any such right,
power or remedy preclude any other or further exercise thereof or the exercise
of any other right, power or remedy hereunder. None of the terms, covenants and
conditions of this Agreement can be waived except by the written consent of the
party waiving compliance.

     6.2 Publicity. The parties may, subject to compliance with the Securities
Act, issue a joint press release announcing this Agreement and the transactions
contemplated hereby following execution of this Agreement. Any proposed
announcement, press release or other public disclosure concerning this Agreement
and/or any of the transactions or relationships contemplated hereby shall be
mutually approved by both parties (which approval shall not be unreasonably
withheld); provided, however, that the restrictions contained in this Section
6.2 do not apply to disclosures required by law, the rules of the NYSE, the NASD
or under U.S. generally accepted accounting principles. The Purchaser agrees and
acknowledges that this Agreement and the transactions contemplated hereby shall
be disclosed in, and filed as an exhibit to, the Registration Statement.

     6.3 Amendments, Waivers and Consents. Any provision in this Agreement to
the contrary notwithstanding, and except as hereinafter provided, changes in or
additions to this Agreement may be made, and compliance with any covenant or
provision set forth herein may be omitted or waived, if the party requesting
such change, addition, omission or waiver shall obtain consent thereto in
writing from the other party. Any waiver or consent may be given subject to
satisfaction of conditions stated therein and any waiver or consent shall be
effective only in the specific instance and for the specific purpose for which
given. Any such amendment or waiver or consent effected in accordance with this
Section 6.3 shall be binding upon the parties and their respective successors
and assigns.

     6.4 Addresses for Notices. Any notice required or permitted by this
Agreement shall be in writing and shall be deemed sufficient upon receipt, when
delivered personally or by courier, overnight delivery service or confirmed
facsimile, or seventy-two (72) hours after being deposited in the regular mail
as certified or registered mail (airmail if sent internationally) with postage
prepaid, if such notice is addressed to the party to be notified at such party's
address or facsimile number as set forth below, or as subsequently modified by
written notice.

     If to the Company:

          Trubion Pharmaceuticals, Inc.
          2401 Fourth Avenue, Suite 1050
          Seattle, WA 98121
          Attn: Chief Executive Officer and General Counsel
          Facsimile Number: (206) 838-0503

     If to the Purchaser:

          Wyeth Pharmaceuticals
          500 Arcola Road

                                       11

<PAGE>

          Collegeville, Pennsylvania 19426
          Attn: Senior Vice President, Corporate Business Development
          Fax: (484) 865-6476

          with a copy to:

          Wyeth
          5 Giralda Farms
          Madison, NJ 07940
          Attn: Executive Vice President and General Counsel
          Facsimile: (973) 660-7156

     6.5 Binding Effect; Assignment. This Agreement may not be assigned by
either party without the prior written consent of the other; provided, however,
that the Purchaser may assign its rights and delegate its duties hereunder to an
Affiliate without the prior written consent of the Company; provided, however,
Purchaser shall remain subject to Section 5 hereof regardless of any such
assignment; and provided further that if the Company undergoes a Change of
Control in which (a) the Company is not the surviving entity and (b) this
Agreement does not terminate pursuant to Section 1.5(b) in connection with such
Change of Control, the surviving entity and the Purchaser shall enter into a
replacement agreement with substantially the same terms as this Agreement.
Subject to the foregoing, the terms and conditions of this Agreement shall inure
to the benefit of and be binding upon the respective successors and assigns of
the parties. Nothing in this Agreement, express or implied, is intended to
confer upon any party other than the parties hereto or their respective
successors and assigns any rights, remedies, obligations, or liabilities under
or by reason of this Agreement, except as expressly provided in this Agreement.

     6.6 Entire Agreement. This Agreement and the documents referred to herein
constitute the entire agreement between the parties and supersede any prior
understandings or agreements concerning the subject matter hereof.

     6.7 Specific Performance. The parties acknowledge and agree that
irreparable damage would occur in the event any of the provisions of Article V
of this Agreement were not performed in accordance with their specific terms or
were otherwise breached. Accordingly, it is agreed that the parties shall be
entitled to an injunction or injunctions to prevent or cure breaches of the
provisions of Article V of this Agreement and to enforce specifically the terms
and provisions of such Article in any court of the United States or any state
thereof having jurisdiction, in addition to any other remedy to which they may
be entitled in law or in equity.

     6.8 Severability. The provisions of this Agreement are severable and, in
the event that any court of competent jurisdiction shall determine that any one
or more of the provisions or part of a provision contained in this Agreement
shall, for any reason, be held to be invalid, illegal or unenforceable in any
respect, such invalidity, illegality or unenforceability shall not affect any
other provision or part of a provision of this Agreement; but this Agreement,
shall be reformed and construed as if such invalid or

                                       12

<PAGE>

illegal or unenforceable provision, or part of a provision, had never been
contained herein, and such provisions or part reformed so that it would be
valid, legal and enforceable to the maximum extent possible.

     6.9 Governing Law. This Agreement shall be governed by, and construed and
enforced in accordance with, the laws of the State of Delaware without reference
to Delaware conflicts of law provisions.

     6.10 Headings. Article, Section and subsection headings in this Agreement
are included herein for convenience of reference only and shall not constitute a
part of this Agreement for any other purpose.

     6.11 Counterparts. This Agreement may be executed in any number of
counterparts, each of which shall be enforceable against the party actually
executing the counterpart, and all of which together shall constitute one
instrument.

                            [Signature page follows.]

                                       13

<PAGE>

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

                                        TRUBION PHARMACEUTICALS, INC.

                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------

                                        WYETH

                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------

<PAGE>

                                                                       EXHIBIT A

                    MATTERS TO BE COVERED BY COMPANY COUNSEL

     1. The Company is a corporation validly existing under Delaware law and in
good standing with the Secretary of the State of Delaware and has the corporate
power to execute and deliver the Agreement and to perform its obligations
thereunder.

     2. The Company has duly authorized, executed and delivered the Agreement,
and the Agreement constitutes the Company's valid and binding agreement
enforceable against the Company in accordance with its terms, except as
enforceability may be limited by bankruptcy, insolvency, reorganization,
moratorium or similar laws relating to or affecting creditors' rights generally
or by general equitable principles.

     3. No consent, approval, authorization or order of, or any filing or
declaration with, any court or governmental agency or body is required in
connection with the execution, delivery and performance of the Agreement by the
Company or in connection with the taking by the Company of any action
contemplated thereby, other than as indicated in the Agreement or such as have
been obtained and made and such as may be required under federal and state
securities laws.

     4. The execution, delivery and performance of the Agreement by the Company,
and the consummation by the Company of the transactions contemplated therein do
not and will not (a) violate the Certificate of Incorporation or By-Laws of the
Company, (b) materially violate any judgment, ruling, decree or order known to
such counsel, (c) materially violate any statute or regulation applicable to the
business or properties of the Company, or (d) result in a material breach or
violation of any of the terms or provisions of, or constitute a default or
result in the acceleration of any obligation under any material contract to
which the Company is a party or bound.

     5. The Shares delivered on the date hereof have been duly authorized and
validly issued and are fully paid and non-assessable shares of the Company.

<PAGE>

                                  EXHIBIT 5.2B

                          TRUBION PHARMACEUTICALS, INC.

                               AMENDMENT NO. 1 TO

                 AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

     This Amendment No. 1 to the Amended and Restated Investor Rights Agreement
(the "RIGHTS AGREEMENT") dated as of July 13, 2004 is entered into as of
________, 2005, by and among Trubion Pharmaceuticals, Inc., a Delaware
corporation (the "COMPANY"), Wyeth, a Delaware corporation ("WYETH"), and the
investors set forth on EXHIBIT A hereto (collectively the "INVESTORS" and each
individually an "INVESTOR").

                                    RECITALS

     A. The Company and the Investors are parties to the Rights Agreement.

     B. The Company and Wyeth have entered into a Common Stock Purchase
Agreement dated as of December __, 2005 (the "PURCHASE AGREEMENT") pursuant to
which the Company will sell to Purchaser and Purchaser will purchase from the
Company shares of the Company's Common Stock concurrent with and conditioned
upon the closing of the Company's initial public offering (the "CLOSING"). A
condition to the Purchaser's obligations under the Purchase Agreement is that
the Rights Agreement be amended in order to provide Purchaser with certain
rights to register shares of the Company's Common Stock.

     C. Pursuant to Section 6.5 of the Rights Agreement, the written consent of
the Company and the Investors holding a majority of the Registrable Securities
(the "REQUISITE HOLDERS") is required to amend the Rights Agreement.

     D. The Company and the Requisite Holders desire to induce Purchaser to
enter into the Purchase Agreement by agreeing to the terms and conditions set
forth herein.

     NOW, THEREFORE, in consideration of the mutual promises, representations,
warranties, covenants and conditions set forth in this Agreement, the parties
hereto agree as follows:

     1. Definitions. Capitalized terms used herein without definition shall have
the meaning ascribed to them in the Rights Agreement.

     2. Addition of Purchaser as a Party to the Rights Agreement. Effective upon
the Closing pursuant to the Purchase Agreement, the parties hereby agree to add
Purchaser as a party to the Rights Agreement and Purchaser shall be deemed a
"Holder" of Registrable Securities for purposes of Sections 1, 2 and 6 of the
Rights Agreement and subject to all of the rights and obligations of such
Sections. For purposes of clarification, Purchaser shall not be entitled to the
rights or subject to the obligations set forth in Sections 3,

<PAGE>

4 and 5 of the Rights Agreement and Purchaser shall not be deemed an "INVESTOR"
for purposes of the Rights Agreement.

     3. Amendment to Section 1.1. The definition of "Registrable Securities" set
forth in Section 1.1 is hereby amended and restated to read in its entirety as
follows:

          "REGISTRABLE SECURITIES" means (a) Common Stock of the Company issued
or issuable upon conversion of the Shares, (b) Common Stock of the Company
issued to Frazier Healthcare Fund ("FRAZIER"), ARCH Venture Fund ("ARCH") and
Scott Minick ("MINICK") pursuant to those certain Common Stock Purchase
Agreements dated November 19, 2002 by and between the Company and each of
Frazier, Arch and Minick, (c) Common Stock of the Company issued to Wyeth
pursuant to the Purchase Agreement, and (d) any Common Stock of the Company
issued as (or issuable upon the conversion or exercise of any warrant, right or
other security which is issued as) a dividend or other distribution with respect
to, or in exchange for or in replacement of, the securities described in (a),
(b) and (c) above; provided, however, the shares referred to in clause (c) above
shall not qualify as Registrable Securities for the purposes of Sections 2.2
hereof until the 15 month anniversary of the Closing. For the avoidance of
doubt, in the event that the Company effects a registration under the Securities
Act pursuant to Section 2.2 hereof prior to the 15 month anniversary of the
Closing, in connection with such registration the Shares referred to in clause
(c) above shall qualify as Registrable Securities for the purposes of Section
2.3. Notwithstanding the foregoing, Registrable Securities shall not include any
securities sold by a person to the public pursuant to a registration statement
or Rule 144 or sold in a private transaction in which the transferor's rights
under SECTION 2 of this Agreement are not assigned.

     4. Amendment to Section 2.1(a)(ii). Section 2.1(a)(ii) is amended effective
immediately following the expiration of the "Market Stand-Off" period set forth
in Section 2.12 hereof, by deleting the last sentence thereof and substituting
therefor the following:

     "Subject to the other terms of this Agreement (including without limitation
     the restrictions on assignment of registration rights set forth in Section
     2.10 and Sections 2.1(b) and (d)), it is agreed that the restrictions
     contained in this Section 2.1(a)(ii) shall not apply to dispositions of
     Shares or Registrable Securities made pursuant to Rule 144 promulgated
     under the Securities Act."

     5. Amendment to Section 6.5. Section 6.5 is hereby amended by adding, after
the final sentence thereof, the following:

          Notwithstanding the foregoing, neither this Agreement nor any term
hereof may be amended, waived, discharged or terminated in any way that
diminishes or eliminates the rights particular to Wyeth hereunder and in a
manner different than the other holders of Registrable Securities, such action
shall require the prior written consent of Wyeth.

     6. Waiver of Right of Participation. Each Investor on behalf of itself and
all other Investors and holders of Registrable Securities hereby waives any
right of participation set forth in Section IV of the Rights Agreement with
respect to the sale and issuance of the shares of Company Common Stock to Wyeth
pursuant to the Purchase Agreement.

                                       -2-

<PAGE>

     7. No Other Amendments. Except as expressly amended or waived as set forth
above, the Rights Agreement shall remain in full force and effect in accordance
with its terms.

     8. Counterparts. This Amendment may be executed in any number of
counterparts, each of which shall be deemed an original and all of which
together shall constitute one document.

                            [Signature pages follow.]

                                       -3-

<PAGE>

IN WITNESS WHEREOF, the parties hereto have executed this AMENDMENT NO. 1 TO THE
RIGHTS AGREEMENT as of the date set forth in the first paragraph hereof.

                                        "COMPANY"

                                        TRUBION PHARMACEUTICALS, INC.
                                        a Delaware corporation

                                        By:
                                            -----------------------------------
                                            Peter Thompson, M.D., FACP
                                            President and
                                            Chief Executive Officer

                      SIGNATURE PAGE TO AMENDMENT NO. 1 TO

                 AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

IN WITNESS WHEREOF, the parties hereto have executed this AMENDMENT NO. 1 TO THE
RIGHTS AGREEMENT as of the date set forth in the first paragraph hereof.

                                        "WYETH"

                                        WYETH

                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Its:
                                             -----------------------------------

                      SIGNATURE PAGE TO AMENDMENT NO. 1 TO

                 AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

IN WITNESS WHEREOF, the parties hereto have executed this AMENDMENT NO. 1 TO THE
RIGHTS AGREEMENT as of the date set forth in the first paragraph hereof.

                                        "INVESTOR"

                                        PROSPECT VENTURE PARTNERS II, L.P.

                                        By: Prospect Management Co. II, LLC
                                        Its General Partner

                                        By:
                                            ------------------------------------
                                        Name: David Schnell
                                        Title: Managing Member

                                        PROSPECT ASSOCIATES II, L.P.

                                        By: Prospect Management Co. II, LLC
                                        Its General Partner

                                        By:
                                            ------------------------------------
                                        Name: David Schnell
                                        Title: Managing Member

                      SIGNATURE PAGE TO AMENDMENT NO. 1 TO

                 AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

IN WITNESS WHEREOF, the parties hereto have executed this AMENDMENT NO. 1 TO THE
RIGHTS AGREEMENT as of the date set forth in the first paragraph hereof.

                                        "INVESTOR"

                                        VENROCK PARTNERS, L.P.
                                           by its General Partner, Venrock
                                           Partners Management, LLC

                                        VENROCK ASSOCIATES IV, L.P.
                                           by its General Partner, Venrock
                                           Management IV, LLC

                                        VENROCK ENTREPRENEURS FUND IV, L.P.
                                           by its General Partner, VEF
                                           Management IV, LLC

                                        By:
                                            ------------------------------------
                                        Name: Anders D. Hove
                                        Title: Member
                                        Address: 30 Rockefeller Plaza
                                                 Room 5508
                                                 New York, NY 10112

                      SIGNATURE PAGE TO AMENDMENT NO. 1 TO

                 AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT
<PAGE>

IN WITNESS WHEREOF, the parties hereto have executed this AMENDMENT NO. 1 TO THE
RIGHTS AGREEMENT as of the date set forth in the first paragraph hereof.

                                        "INVESTOR"

                                        ARCH VENTURE FUND V, L.P.

                                        By: ARCH Venture Partners V, L.P.
                                            Its general partner

                                        By: ARCH Venture Partners V, L.L.C.
                                            Its general partner

                                        By:
                                            ------------------------------------
                                        Title: Managing Director

                                        ARCH V ENTREPRENEURS FUND, L.P.

                                        By: ARCH Venture Partners V, L.P.
                                            Its general partner

                                        By: ARCH Venture Partners V, L.L.C.
                                            Its general partner

                                        By:
                                            ------------------------------------
                                        Title: Managing Director

                                        HEALTHCARE FOCUS FUND, L.P.

                                        By: ARCH Venture Partners V, L.P.
                                            Its general partner

                                        By: ARCH Venture Partners V, L.L.C.
                                            Its general partner

                                        By:
                                            ------------------------------------
                                        Title: Managing Director

8

<PAGE>

IN WITNESS WHEREOF, the parties hereto have executed this AMENDMENT NO. 1 TO THE
RIGHTS AGREEMENT as of the date set forth in the first paragraph hereof.

                                        "INVESTOR"

                                        OXFORD BIOSCIENCE PARTNERS IV L.P.

                                        By: OBP Management IV L.P.

                                        By:
                                            ------------------------------------
                                            Mark P. Carthy - General Partner

                                        MRNA FUND II L.P.

                                        By: OBP Management IV L.P.

                                        By:
                                            ------------------------------------
                                            Mark P. Carthy - General Partner

                      SIGNATURE PAGE TO AMENDMENT NO. 1 TO

                 AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

IN WITNESS WHEREOF, the parties hereto have executed this AMENDMENT NO. 1 TO THE
RIGHTS AGREEMENT as of the date set forth in the first paragraph hereof.

                                        "INVESTOR"

                                        FRAZIER HEALTHCARE IV, L.P.

                                        By FHM IV, LP, its general partner

                                        By FHM IV, LLC, its general partner

                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Its:
                                             -----------------------------------

                                        FRAZIER AFFILIATES IV, L.P.

                                        By FHM IV, LP, its general partner

                                        By FHM IV, LLC, its general partner

                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Its:
                                             -----------------------------------

                                        FRAZIER HEALTHCARE III, L.P.

                                        By FHM III, LLC

                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Its:
                                             -----------------------------------

                                        FRAZIER AFFILIATES III, L.P.

                                        By FHM III, LLC

                      SIGNATURE PAGE TO AMENDMENT NO. 1 TO

                 AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Its:
                                             -----------------------------------

11

<PAGE>

IN WITNESS WHEREOF, the parties hereto have executed this AMENDMENT NO. 1 TO THE
RIGHTS AGREEMENT as of the date set forth in the first paragraph hereof.

                                        "INVESTOR"

                                        ATP CAPITAL, L.P.

                                        By: ATP General Partner LLC
                                            Its General Partner

                                        By:
                                            ------------------------------------
                                            Jonathan Malkin, Manager

                      SIGNATURE PAGE TO AMENDMENT NO. 1 TO

                 AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

IN WITNESS WHEREOF, the parties hereto have executed this AMENDMENT NO. 1 TO THE
RIGHTS AGREEMENT as of the date set forth in the first paragraph hereof.

                                        "INVESTOR"

                                        CASCADE INVESTMENTS, L.L.C.

                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Its:
                                             -----------------------------------

2

<PAGE>

IN WITNESS WHEREOF, the parties hereto have executed this AMENDMENT NO. 1 TO THE
RIGHTS AGREEMENT as of the date set forth in the first paragraph hereof.

                                        "INVESTOR"

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

                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Its:
                                             -----------------------------------

                      SIGNATURE PAGE TO AMENDMENT NO. 1 TO

                 AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

<PAGE>

                                   EXHIBIT 5.3

                       ADDITIONAL RESEARCH AND DEVELOPMENT

                                EXPENSE PAYMENTS

     A. ADDITIONAL RESEARCH AND DEVELOPMENT EXPENSE PAYMENTS FOR CD20 PRODUCTS

[***]

     B. ADDITIONAL RESEARCH AND DEVELOPMENT EXPENSE PAYMENTS FOR [***]

[***]

     C. ADDITIONAL RESEARCH AND DEVELOPMENT EXPENSE PAYMENTS FOR OTHER PRODUCTS

[***]

     D. NO ADDITIONAL PAYMENTS; OTHER APPLICABLE TERMS AND CONDITIONS

[***]

2

<PAGE>

                                 EXHIBIT 8.2(D)

                               THIRD PARTY RIGHTS

                           [INTENTIONALLY LEFT BLANK]

<PAGE>

                                 EXHIBIT 8.2(E)

                          GOVERNMENT FUNDING AGREEMENTS

                            NIH GRANT # 5 R01 CA90143

      PROJECT TITLE: GENE THERAPY WITH MAB DERIVATIVES EXPRESSED ON TUMORS

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