Document:

<PAGE>

                                                                   Exhibit 10.28

                                AMENDMENT No. 12

                                       to

              THE DEVELOPMENT AND MANUFACTURING SERVICES AGREEMENT

                              Dated 08 January 2004

                                     Between

                               LONZA BIOLOGICS ***

                                       and

                          TRUBION PHARMACEUTICALS, INC.

<PAGE>

THIS AMENDMENT No. 12 ("Twelfth Amendment") is made the 31st day of March 2006

BETWEEN

LONZA BIOLOGICS *** of *** (hereinafter referred to as "LB"), and

TRUBION PHARMACEUTICALS, INC, of 2401 4th Avenue, Suite 1050, Seattle, WA 98121,
USA (herein after referred to as the "Customer")

WHEREAS

A. LB and the Customer entered into a development and manufacturing services
agreement ("the Agreement") dated 08 January 2004, pursuant to which LB agreed
to provide Services to the Customer, and,

B. The Customer now wishes LB to perform additional services under the
Agreement, and,

C. LB is willing to perform such additional services on the terms set out in the
Agreement, and,

D. The parties wish to amend the Agreement in accordance with Clause 13.5
thereto.

NOW THEREFORE IT IS HEREBY AGREED as follows:

1.   SCHEDULE 1 OF THE AGREEMENT SHALL BE AMENDED TO INCLUDE THE FOLLOWING:

(A)  ***

     Inserted into Agreement by Amendment 11.

(B)  ***

<PAGE>

<TABLE>
<CAPTION>
                                   METHOD
    TEST NO.      CRITERION   (LB SOP NUMBER)   SPECIFICATION
---------------   ---------   ---------------   -------------
<S>               <C>         <C>               <C>
Characteristics
***               ***         ***               ***
***               ***         ***               ***
***               ***         ***               ***
***               ***         ***               ***
***               ***         ***               ***
***
***               ***         ***               ***
***
***               ***         ***               ***
                  ***         ***               ***
                                                ***
                  ***         ***               ***
                                                ***
***               ***         ***               ***
***
***               ***         ***               ***
***               ***         ***               ***
***               ***         ***               ***
                  ***         ***               ***
                  ***         ***               ***
***               ***         ***               ***
***               ***         ***               ***
***
***               ***         ***               ***
***               ***         ***               ***
***
***               ***         ***               ***
                                                ***
***               ***         ***               ***
***               ***         ***               ***
***               ***         ***               ***
</TABLE>

     Storage and shipping information

     Final Formulation Buffer: *** (Pharmaceutical Grade)

     Bottling of Bulk Product:

          Primary containers: ***

                                       -2-

<PAGE>

          Denominations:

               ***

               Any remaining Product will be filled into ***. If this is not
               filled with a tolerance of ***, this will be labelled as a
               Customer Sample and will not be released for clinical use.

               For the calculation of the total fill volume it is assumed that
               1g of liquid ~ 1ml.

     Product Storage Conditions: ***(0)C

     Shipment Temperature: ***(0)C

     Customer samples (removed during the middle of dispensing):

          To be agreed by LB and Customer.

     Shipment Temperature: ***

2.   SCHEDULE 2 OF THE AGREEMENT SHALL BE AMENDED TO ADD STAGES 36 AND 37 TO
     READ AS FOLLOWS:

     36   "STAGE 36 - ***

          36.1 OBJECTIVE

               ***

          36.2 ACTIVITIES

               ***

          36.3 TIMESCALE

               This Stage may commence when the cell bank *** is available for
               use, the Process development activities are complete and cGMP
               documents are approved.

               This Stage shall be complete upon disposition of Product by LB's
               Quality department. It is estimated that Product will be
               delivered *** from commencement of this Stage. ***. It is
               estimated that this shipment could occur *** from commencement of
               this Stage.

                                       -3-

<PAGE>

          37   STAGE 37 - ***

               37.1 OBJECTIVE

                    ***

               37.2 ACTIVITIES

                    ***

               37.3 TIMESCALE

                    This Stage may commence when the cell bank *** is available
                    for use, the Process development activities are complete and
                    cGMP documents are approved.

                    This Stage shall be complete upon disposition of Product by
                    LB's Quality department. It is estimated that Product will
                    be delivered *** from commencement of this Stage ***. It is
                    estimated that this shipment could occur *** from
                    commencement of this Stage.

                                       -4-

<PAGE>

SCHEDULE 3 TO THE AGREEMENT SHALL BE AMENDED TO INCLUDE PROVISION FOR PAYMENT
FOR THE ABOVE MENTIONED ADDITIONAL SERVICES, AS SET OUT BELOW HERETO. INVOICES
FOR THESE ADDITIONAL SERVICES SHALL BE ISSUED, AND CUSTOMER PAYMENTS SHALL BE
MADE, IN ***:

     "1.  PRICE

          ***

     2.   PAYMENT

          FOR STAGE 36

          *** upon removal of an ampoule out of freeze.

          *** upon completion of Stage 36.

          ***

          FOR STAGE 37

          *** upon removal of an ampoule out of freeze.

          *** upon completion of Stage 37.

          *** will be invoiced separately

                                       -5-

<PAGE>

                                                                    (LONZA LOGO)

SAVE AS HEREIN PROVIDED ALL OTHER TERMS AND CONDITIONS OF THE AGREEMENT SHALL
REMAIN IN FULL FORCE AND EFFECT.

AS WITNESS the hands of the duly authorised representatives of the parties
hereto the day and year first above written.

Signed for and on behalf of
LONZA BIOLOGICS ***                     ***
                                        ----------------------------------------

                                        ***
                                        ----------------------------------------
                                                                           TITLE

Signed for and on behalf of
TRUBION PHARMACEUTICALS, INC            /s/ Kendall M. Mohler
                                        ----------------------------------------
                                        Senior VP, Research & Development
                                        TITLE<PAGE>

                                                                   EXHIBIT 10.29

                          TRUBION PHARMACEUTICALS, INC.

                                PETER A. THOMPSON

                    AMENDED AND RESTATED EMPLOYMENT AGREEMENT

     This Amended and Restated Employment Agreement is entered into as of March
29, 2006 by and between Trubion Pharmaceuticals, Inc., a Delaware corporation
(the "Company"), and Peter A. Thompson ("Executive").

     WHEREAS, Executive and the Company are parties to an Employment Agreement
dated as of February 1, 2003 (the "Original Agreement").

     WHEREAS, the parties wish to amend and restate the Original Agreement to
reflect the terms set forth herein.

     NOW, THEREFORE, in consideration of the foregoing and the mutual covenants
contained herein, and other good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the Company and Executive hereby
agree as follows:

     1. Duties and Scope of Employment.

          (a) Positions and Duties. Executive will serve as President and Chief
Executive Officer of the Company. Executive will render such business and
professional services in the performance of his duties, consistent with
Executive's position within the Company, as shall reasonably be assigned to him
by the Company's Board of Directors (the "Board"). The period of Executive's
employment under this Agreement is referred to herein as the "Employment Term."

          (b) Obligations. During the Employment Term, Executive will perform
his duties faithfully and to the best of his ability and will, except as
provided below, devote his full business efforts and time to the Company. For
the duration of the Employment Term, Executive agrees not to actively engage in
any other employment, occupation or consulting activity for any direct or
indirect remuneration without the prior written approval of the Board, such
approval not to be unreasonably withheld. It is understood and agreed that
Executive will not be precluded from serving on boards of directors and advisory
boards, provided that such activities do not materially adversely affect
Executive's ability to perform and discharge his duties to the Company and that
Executive does not devote in the aggregate more than twenty-four (24) days per
year to such activities.

     2. At-Will Employment. The parties agree that Executive's employment with
the Company will be "at-will" employment and may be terminated by either party
at any time with or without cause or notice. Executive understands and agrees
that neither his job performance nor promotions, commendations, bonuses or the
like from the Company give rise to or in any way serve as the basis for
modification, amendment, or extension, by implication or otherwise, of his
employment with the Company.

<PAGE>

     3. Compensation.

          (a) Base Salary. From and after January 1, 2006 (the "Effective Date")
and during the Employment Term, the Company will pay Executive as compensation
for his services a base salary at the annualized rate of $345,000.00 (the "Base
Salary"). The Base Salary will be paid periodically in accordance with the
Company's normal payroll practices and be subject to the usual, required
withholding. Executive's Base Salary shall be reviewed annually by the Board or
its Compensation Committee, and any increase will be effective as of the date
determined appropriate by the Board or its Compensation Committee.

          (b) Bonus. During each year of the Employment Term, Executive may be
entitled to receive a performance bonus (in addition to Base Salary) of
$180,000.00 (less applicable withholding taxes) (the "Bonus"), if Executive
meets personal and Company performance milestones to be established and reviewed
at the sole discretion of the Board or its Compensation Committee. The amount of
the Bonus to which the Executive may be entitled shall be subject to annual
review and modification in the sole discretion of the Board or its Compensation
Committee. Any payment to Executive pursuant to this Section 3(b) shall be
payable, at the sole discretion of the Board or its Compensation Committee, in
accordance with the Company's compensation policies.

          (c) Primary Residence. Executive agrees to maintain his primary
residence somewhere within the greater Seattle, Washington area.

          (d) Stock Options. From and after the date hereof, Executive will be
entitled to such new stock options as are determined in the sole discretion of
the Board or its Compensation Committee.

     4. Employee Benefits. During the Employment Term, Executive will be
entitled to participate in the employee benefit plans currently and hereafter
maintained by the Company of general applicability to other senior executives of
the Company, including, without limitation, the Company's group medical, dental,
vision, disability, life insurance, director and officer liability insurance and
flexible-spending account plans. The Company reserves the right to cancel or
change the benefit plans and programs it offers to its employees at any time.

     5. Vacation. Executive will be entitled to paid vacation of three (3) weeks
per year in accordance with the Company's vacation policy, with the timing and
duration of specific vacations mutually and reasonably agreed to by the parties
hereto.

     6. Expenses. The Company will reimburse Executive for reasonable travel,
entertainment or other expenses incurred by Executive in the furtherance of or
in connection with the performance of Executive's duties hereunder, in
accordance with the Company's expense reimbursement policy as in effect from
time to time.

     7. Severance.

          (a) Involuntary Termination. If Executive's employment with the
Company terminates as a result of an "Involuntary Termination" (as defined
herein), and Executive signs and does not revoke a standard release of claims
with the Company, then, subject to Section 10, Executive shall receive (i) a
lump sum payment of severance pay (less applicable withholding taxes)

                                      -2-

<PAGE>

equal to twenty five percent (25%) of Executive's annual Base Salary rate then
in effect; (ii) twelve monthly equal, continuing payments of severance pay (less
applicable withholding taxes) at a rate equal to seventy five percent (75%) of
Executive's Base Salary rate, as then in effect, and (iii) continued benefits
under the Company's then existing benefit plans and policies in accordance with
such plans and policies in effect on the date of termination and in accordance
with applicable law, in each case with respect to subsections 7(a)(ii) and
7(a)(iii) for the lesser of (A) twelve (12) months from the date of such
termination, or (B) until Executive finds full-time employment with a
substantially similar compensation package. Such payments shall be paid
periodically in accordance with the Company's normal payroll policies. In
addition, that portion of any unvested stock options or shares of restricted
stock held by Executive as of the date of Executive's termination of employment
that would otherwise vest through the end of twelve (12) months after the date
of such termination shall be immediately accelerated as of the date of
termination.

          (b) Voluntary Termination; Termination for Cause. If Executive's
employment with the Company terminates voluntarily by Executive or for Cause by
the Company, then (i) all vesting of any unvested stock options or shares of
restricted stock held by Executive as of the date of Executive's termination of
employment will terminate immediately, (ii) all payments of compensation by the
Company to Executive hereunder will terminate immediately (except as to amounts
already earned), and (ii) Executive will only be eligible for severance benefits
in accordance with the Company's established policies as then in effect.

          (c) Termination by Reason of Death or Disability. In the event that
Executive's employment with the Company terminates as a result of Executive's
death or Disability (as defined in Section 8 below), Executive or Executive's
estate or representative will receive all salary accrued (plus any other amounts
payable as determined by the Board in its sole discretion) as of the date of
Executive's death or Disability and any other benefits payable under the
Company's then existing benefit plans and policies in accordance with such plans
and policies in effect on the date of death or Disability and in accordance with
applicable law. In addition, Executive's estate or representative will receive
the amount of Executive's Bonus for the fiscal year in which the death or
Disability occurs to the extent that the Bonus has been earned as of the date of
Executive's death or Disability, as determined by the Board based on the
specific milestones established for such fiscal year.

     8. Definitions.

          (a) Cause. For purposes of this Agreement, "Cause" is defined as (i) a
material violation of a written Company policy that is communicated to Executive
and made by Executive in connection with Executive's responsibilities as an
employee, and that continues uncured for thirty (30) days, (ii) Executive's
conviction of, or plea of nolo contendere to, a felony, or (iii) Executive's
continued substantial violations of his employment duties that continue uncured
for thirty (30) days after Executive has received a written demand for
performance from the Board which specifically sets forth the factual basis for
the Company's belief that Executive has not substantially performed his duties.

          (b) Involuntary Termination. For purposes of this Agreement, an
"Involuntary Termination" shall be deemed to occur if: (i) Executive's
employment with the Company is terminated by the Company for any reason other
than Cause; or (ii) (A) there is (1) a material, adverse and permanent change in
Executive's position as set forth in Section 1(a) of this Agreement

                                      -3-

<PAGE>

causing such position to be of materially reduced stature or responsibility, (2)
a reduction of more than five percent (5%) in Executive's Base Salary (not
including Bonus), other than any such reduction which is a part of, and
generally consistent with, a general reduction of officer or employee salaries,
(3) a material reduction by the Company in the kind or level of employee
benefits (other than Base Salary and Bonus) to which Executive is entitled
immediately prior to such reduction with the result that Executive's overall
benefits package (other than Base Salary and Bonus) is substantially reduced
(other than any such reduction applicable to officers or employees of the
Company generally), (4) any material breach by the Company of any material
provision of this Agreement which continues uncured for thirty (30) days
following notice by Executive thereof, or (5) a refusal by Executive, following
a request by the Company, to relocate to a facility or location more than 40
miles from the Company's current location, and (B) within the ninety (90) day
period immediately following such material change, reduction, expiration of
notice period for breach or refusal, Executive elects to terminate his
employment voluntarily; provided, however, that none of the foregoing shall
constitute Involuntary Termination to the extent that Executive has agreed in
writing to such material change, reduction, breach or refusal.

          (c) Definition of Disability. For purposes of this Agreement,
"Disability" shall mean that Executive has been unable to perform his duties
hereunder as the result of his incapacity due to physical or mental illness, and
such inability, which continues for at least 120 consecutive calendar days or
150 calendar days during any consecutive twelve-month period, is determined to
be total and permanent by a physician selected by the Company and its insurers
and acceptable to Executive or to Executive's legal representative (with such
agreement on acceptability not to be unreasonably withheld).

     9. Confidential Information. Executive agrees that he has entered into the
Company's standard Confidential Information, Invention Assignment,
Non-Competition and Arbitration Agreement (the "Confidential Information
Agreement").

     10. Conditional Nature of Severance Payments.

          (a) Noncompete. Executive agrees and acknowledges that Executive's
right to receive the severance payments set forth in Section 7 (to the extent
Executive is otherwise entitled to such payments) shall be conditioned upon
Executive's continued compliance with Section 8 (Non-Competition) of the
Confidential Information Agreement. Upon any breach of this section, all
severance payments pursuant to this Agreement shall immediately cease.

          (b) Understanding of Covenants. Executive represents that he (i) is
familiar with the covenants set forth in Section 8 of the Confidential
Information Agreement, and (ii) is fully aware of his obligations hereunder,
including, without limitation, the reasonableness of the length of time, scope
and geographic coverage of these covenants.

     11. Assignment. This Agreement will be binding upon and inure to the
benefit of (a) the heirs, executors and legal representatives of Executive upon
Executive's death and (b) any successor of the Company. Any such successor of
the Company will be deemed substituted for the Company under the terms of this
Agreement for all purposes. For this purpose, "successor" means any person,
firm, corporation or other business entity which at any time, whether by
purchase, merger or otherwise, directly or indirectly acquires all or
substantially all of the assets or business of the

                                      -4-

<PAGE>

Company. None of the rights of Executive to receive any form of compensation
payable pursuant to this Agreement may be assigned or transferred except by will
or the laws of descent and distribution. Any other attempted assignment,
transfer, conveyance or other disposition of Executive's right to compensation
or other benefits will be null and void.

     12. Notices. All notices, requests, demands and other communications called
for hereunder shall be in writing and shall be deemed given (i) on the date of
delivery if delivered personally, (ii) one (1) day after being sent by a well
established commercial overnight service, or (iii) four (4) days after being
mailed by registered or certified mail, return receipt requested, prepaid and
addressed to the parties or their successors at the following addresses, or at
such other addresses as the parties may later designate in writing:

          If to the Company:

          Trubion Pharmaceuticals, Inc
          2401 4th Avenue, Suite 1050
          Seattle, Washington 98121
          Attn: Secretary

          If to Executive:

          Peter A. Thompson
          14075 NE 30th Place
          Bellevue, Washington 98007

or to the last residential address known by the Company.

     13. Severability. In the event that any provision hereof becomes or is
declared by a court of competent jurisdiction to be illegal, unenforceable or
void, this Agreement will continue in full force and effect without said
provision.

     14. Arbitration.

          (a) General. In consideration of Executive's service to the Company,
its promise to arbitrate all employment related disputes and Executive's receipt
of the compensation, pay raises and other benefits paid to Executive by the
Company, at present and in the future, Executive agrees that any and all
controversies, claims, or disputes with anyone (including the Company and any
employee, officer, director, shareholder or benefit plan of the Company in their
capacity as such or otherwise) arising out of, relating to, or resulting from
Executive's service to the Company under this Agreement or otherwise or the
termination of Executive's service with the Company, including any breach of
this Agreement, shall be subject to binding arbitration under the Arbitration
Rules set forth in the Revised Code of Washington Chapter 7.04 (the "Rules") and
pursuant to Washington law. Disputes which Executive agrees to arbitrate, and
thereby agrees to waive any right to a trial by jury, include any statutory
claims under state or federal law, including, but not limited to, claims under
Title VII of the Civil Rights Act of 1964, the Americans with Disabilities Act
of 1990, the Age Discrimination in Employment Act of 1967, the Older Workers
Benefit Protection Act, claims of harassment, discrimination or wrongful
termination and any statutory claims. Executive further

                                      -5-

<PAGE>

understands that this Agreement to arbitrate also applies to any disputes that
the Company may have with Executive.

          (b) Procedure. Executive agrees that any arbitration will be
administered by the American Arbitration Association ("AAA") and that a neutral
arbitrator will be selected in a manner consistent with its National Rules for
the Resolution of Employment Disputes. The arbitration proceedings will allow
for discovery according to the rules set forth in the National Rules for the
Resolution of Employment Disputes or the Washington Code of Civil Procedure.
Executive agrees that the arbitrator shall have the power to decide any motions
brought by any party to the arbitration, including motions for summary judgment
and/or adjudication and motions to dismiss and demurrers, prior to any
arbitration hearing. Executive agrees that the arbitrator shall issue a written
decision on the merits with findings of fact and conclusions of law. Executive
also agrees that the arbitrator shall have the power to award any remedies,
including attorneys' fees and costs, available under applicable law. Executive
understands the Company will pay for any administrative or hearing fees charged
by the arbitrator or AAA except that Executive shall pay the first $200.00 of
any filing fees associated with any arbitration Executive initiates. Executive
agrees that the arbitrator shall administer and conduct any arbitration in a
manner consistent with the Rules and that to the extent that the AAA's National
Rules for the Resolution of Employment Disputes conflict with the Rules, the
Rules shall take precedence.

          (c) Remedy. Except as provided by the Rules, arbitration shall be the
sole, exclusive and final remedy for any dispute between Executive and the
Company. Accordingly, except as provided for by the Rules, neither Executive nor
the Company will be permitted to pursue court action regarding claims that are
subject to arbitration. Notwithstanding, the arbitrator will not have the
authority to disregard or refuse to enforce any lawful Company policy, and the
arbitrator shall not order or require the Company to adopt a policy not
otherwise required by law which the Company has not adopted.

          (d) Availability of Injunctive Relief. In addition to the right under
the Rules to petition the court for provisional relief, Executive agrees that
any party may also petition the court for injunctive relief where either party
alleges or claims a violation of this Agreement or the Confidentiality Agreement
or any other agreement regarding trade secrets, confidential information,
non-competition or nonsolicitation. In the event either party seeks injunctive
relief, the prevailing party shall be entitled to recover reasonable costs and
attorneys' fees.

          (e) Administrative Relief. Executive understands that this Agreement
does not prohibit Executive from pursuing an administrative claim with a local,
state or federal administrative body such as the Department of Fair Employment
and Housing, the Equal Employment Opportunity Commission or the workers'
compensation board. This Agreement does, however, preclude Executive from
pursuing court action regarding any such claim.

          (f) Voluntary Nature of Agreement. Executive acknowledges and agrees
that Executive is executing this Agreement voluntarily and without any duress or
undue influence by the Company or any other person. Executive further
acknowledges and agrees that Executive has carefully read this Agreement and
that Executive has asked any questions needed for Executive to understand the
terms, consequences and binding effect of this Agreement and fully understand
it, including that Executive is waiving Executive's right to a jury trial.
Finally, Executive agrees that

                                      -6-

<PAGE>

Executive has been provided an opportunity to seek the advice of an attorney of
Executive's choice before signing this Agreement.

     15. Amendment; Integration. The Original Agreement is amended and restated
in its entirety by this Amended and Restated Employment Agreement. This
Agreement, those certain stock option agreements relating to the stock options
listed in Section 3(d) above and the Confidential Information Agreement
represent the entire agreement and understanding between the parties as to the
subject matter herein and therein, and supersede all prior or contemporaneous
agreements whether written or oral. No waiver, alteration, or modification of
any of the provisions of this Agreement will be binding unless in writing and
signed by duly authorized representatives of the parties hereto.

     16. Tax Withholding. All payments made pursuant to this Agreement will be
subject to withholding of applicable taxes.

     17. Governing Law. This Agreement will be governed by the laws of the State
of Washington, without giving effect to principles of conflict of laws.

                                      -7-

<PAGE>

     IN WITNESS WHEREOF, each of the parties has executed this Agreement, in the
case of the Company by their duly authorized officers, as of the day and year
first above written.

COMPANY:

TRUBION PHARMACEUTICALS, INC.

By: /s/ Michelle Burris                  Date: March 29, 2006
    ----------------------------------
Title: Senior Vice President & CFO

EXECUTIVE:

/s/ Peter A. Thompson                    Date: March 29, 2006
--------------------------------------
Peter A. Thompson, M.D., FACP

                                      -8-

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