Exhibit
10.1
 CONFIDENTIAL
 *
    
    Confidential Treatment has
been requested for the
marked portions of this
exhibit pursuant to Rule
24B-2 of the Securities
Exchange Act of 1934, as
amended.
 WYETH LLC  ACTING THROUGH ITS  WYETH PHARMACEUTICALS DIVISION  500 Arcola Road  Collegeville, Pennsylvania 19426 USA
  th
     *Confidential
Treatment Requested.




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Trubion Pharmaceuticals, Inc.
    
    CONFIDENTIALApril 12, 2010Page 2 of 4
   1.
    
    Amendments to Article 1. Article 1 of the Agreement hereby is amended by
 a.
    
    deleting Sections 1.46 through 1.49 of Article 1 in their entirety;b.
    
    in Section 1.93, deleting the phrase [*] each time it appears within
the definition of Product;c.
    
    replacing Section 1.130 in its entirety with Trubion Targetshall
mean the human CD20 Antigen; andd.
    
    replacing Section 1.140 in its entirety with Wyeth Targetsshall mean the Targets designated
by Wyeth under the Research Program, as described in Section 3.2 hereof. Notwithstanding anything
herein to the contrary, as of April 12, 2010 the Wyeth Targets are [*] (all of which have been
previously designated as Wyeth Targets pursuant to Section 3.2 hereof); any other Targets previously designated by Wyeth as Wyeth Targets pursuant to
Section 3.2 are no longer Wyeth Targets for purposes of the Agreement.
 2.
    
    Amendments to Article 2. Article 2 of the Agreement is hereby amended by
 a.
    
    deleting Section 2.3.2 in its entirety; andb.
    
    in Section 2.3.3 replacing the phrase Sections 2.3.1 and 2.3.2 with
Section 2.3.1.
 3.
    
    Amendments to Article 3. Article 3 of the Agreement is hereby amended by
 a.
    
    in Section 3.1 deleting the phrase [*] from clause (a) thereof.
 4.
    
    Amendments to Article 4. Article 4 of the Agreement is hereby amended by
 a.
    
    in Section 4.5(a), deleting the phrase [*]; andb.
    
    deleting Section 4.5(c) in its entirety.
 *Confidential
Treatment Requested.




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Trubion Pharmaceuticals, Inc.
    
    CONFIDENTIALApril 12, 2010Page 3 of 4
 5.
    
    Amendments to Article 5. Article 5 of the Agreement is hereby amended by
 a.
    
    deleting the reference to Section 5.4.3 from Section 5.4.1.b.
    
    deleting Section 5.4.3 in its entirety;c.
    
    deleting the second sentence of Section 5.4.6(a) in its entirety;d.
    
    deleting the last sentence of Section 5.5.1 in its entirety; ande.
    
    replacing clause (c) of Section 5.5.2 in its entirety with (c) any
adjustments (including the basis therefor) made pursuant to Sections 5.4.2(b),
5.4.2(c), 5.4.4(b), 5.4.4(c) or 5.4.6(a) to the royalty amount payable fore the
sale of each Licensed Product, the applicable Marginal Royalty Rates and the CD20
Effective Royalty Rate (as the case may be) payable on Net Sales, and.
 6.
    
    Amendments to Article 9. Article 9 of the Agreement is hereby amended by
 a.
    
    in the second sentence of Section 9.7.2(a)(ii), deleting the phrase [*]
from each of clauses (B) and (C);b.
    
    in Section 9.8.4(i), deleting the phrase or 2.3.2;c.
    
    in Section 9.10.2(c), replacing the phrase the restrictive covenants
set forth in Sections 2.3.1 and 2.3.2 with the restrictive covenants set forth in
Section 2.3.1, and deleting the phrase [*] each time it appears therein; andd.
    
    also in Section 9.10.2(c), deleting from the third sentence thereof the phrase 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).
 7.
    
    Amendments to Exhibit 5.3. Exhibit 5.3 of the Agreement is hereby amended by
 a.
    
    Deleting Part B of Exhibit 5.3 in its entirety.b.
    
    In subclauses (i) and (iv) of Part D of Exhibit 5.3, replacing
Sections A-C with Sections A and C.c.
    
    In subclause (iv) of Part D of Exhibit 5.3, replacing, in the second
sentence thereof, [*] with the human CD20 Antigen.d.
    
    In subclause (v) of Part D of Exhibit 5.3, deleting, from the first
sentence thereof, the reference to Section B, and replacing, in second sentence
thereof, [*] with CD20 Product each time it appears therein.
  *Confidential
Treatment Requested.




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Trubion Pharmaceuticals, Inc.
    
    CONFIDENTIALApril 12, 2010Page 4 of 4
  Very truly yours,
WYETH LLC, acting through its
WYETH PHARMACEUTICALS DIVISIONBy:
    /s/ ROBERT J. SMITHName:
    Robert J. SmithTitle:
    Senior Vice PresidentACKNOWLEDGED AND AGREED:
TRUBION PHARMACEUTICALS, INC.By:
    /S/ MICHELLE G. BURRISName:
    Michelle G. BurrisTitle:
    SVP, COODate: 14 April 2010