AMENDMENT NO. 4 TO THE DEVELOPMENT AND MANUFACTURING SERVICES AGREEMENT

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                                                                   Exhibit 10.20

                                                                           Lonza

                                 AMENDMENT NO. 4

                                        TO

              THE DEVELOPMENT AND MANUFACTURING SERVICES AGREEMENT

                              DATED 08 JANUARY 2004

                                     BETWEEN

                               LONZA BIOLOGICS ***

                                        AND

                          TRUBION PHARMACEUTICALS, INC.

Re:

Schedule 1

Schedule 2

     Stage 22 ***.

Schedule 3

     Price and Payment

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                                                                           Lonza

THIS AMENDMENT is made the 4th day of January, 2005

BETWEEN

1. LONZA BIOLOGICS ***, the registered office of which is at *** ("LB") and

2. TRUBION PHARMACEUTICALS, INC., 2401 4th Avenue, Suite 1050, Seattle, WA
98121, USA. ("Customer")

WHEREAS

A.    Customer and LB entered into an agreement dated 08 January 2004 as amended
     ("The Agreement"), under which LB is required to perform Services relating
     to the Cell line and Product described, and

B.    Customer would like LB to carry out additional activities under the
     Agreement, and

C.    LB is prepared to perform the additional activities.

NOW THEREFORE it is agreed hereby by the parties to amend the Agreement and
perform additional services