Exhibit 10.50

***Text Omitted and Filed Separately
Confidential Treatment Requested
Under 17 C.F.R. §§ 200.80(b)(4) and
240.24b-2(b)(1)
     AMENDMENT No. 1 (this “Amendment”), dated as of December 30, 2005, to the
Asset Purchase Agreement dated as of November 23, 2005 (the “Agreement”), by and
between IDM PHARMA, INC., a Delaware corporation (the “Seller”), and PHARMEXA
INC., a Delaware corporation (the “Buyer”). Capitalized terms used but not
defined herein shall have the meanings assigned to such terms in the Agreement.
RECITALS:
     A. The Seller and the Buyer have entered into the Agreement; and
     B. The Seller and the Buyer have agreed to enter into this Amendment.
     NOW, THEREFORE, in consideration of the foregoing and the rights and
obligations contained herein, and intending to be legally bound hereby, the
Seller and the Buyer hereby agree as follows:
          Section 1. Section 3.15. Section 3.15 shall be added to the Agreement
as follows:
“3.15 Transfer to [. . . *** . . .]. On the Closing Date, Buyer shall sell,
assign, transfer and convey to [. . . *** . . .] (a) the equipment and
(b) Buyer’s interest in the agreements, in each case listed on Schedule 3.15, in
exchange for aggregate consideration of [. ***.], to be paid by [. . . *** . .
.], and shall issue a Bill of Sale to [. . . *** . . .] evidencing such
transfer.”
          Section 2. Schedule 3.15. Schedule 3.15, attached hereto as Exhibit A,
shall be added to the Agreement.
          Section 3. Schedule 4.5(a). Schedule 4.5(a) of the Agreement shall be
deleted and replaced in its entirety by the schedule attached hereto as
Exhibit B.
          Section 4. Schedule 6.6. Schedule 6.6 of the Agreement shall be
deleted and replaced in its entirety by the schedule attached hereto as
Exhibit C.
          Section 5. Entire Agreement. The Agreement, as amended by this
Amendment, constitutes the entire agreement of the parties with respect to the
subject matter hereof and supersedes all prior agreements and undertakings, both
written and oral, between the parties. Except as amended by this Amendment, the
Agreement shall continue in full force and effect in accordance with its terms.
          Section 6. Severability. If any term or other provision of this
Amendment is invalid, illegal or incapable of being enforced by any rule of law,
or public policy, all other conditions and provisions of this Amendment shall
nevertheless remain in full force and effect so long as the economic or legal
substance of the transactions contemplated by this Amendment is not affected in
any manner materially adverse to any party. Upon such determination that any
term or other provision is invalid, illegal or incapable of being enforced, the
parties hereto shall

     
 
  *Confidential Treatment Requested
   under 17 C.F.R. §§ 200.80(b)(4) and
   240.24b-2(b)(1)

 

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negotiate in good faith to modify this Amendment so as to effect the original
intent of the parties as closely as possible in a mutually acceptable manner in
order that the transactions be consummated as originally contemplated by the
Agreement as amended by this Amendment to the fullest extent possible.
          Section 7. Counterparts. This Amendment may be executed and delivered
(including by facsimile transmission) in one or more counterparts, and by the
different parties hereto in separate counterparts, each of which when executed
shall be deemed to be an original but all of which taken together shall
constitute one and the same agreement.
          Section 8. Governing Law.
          (a) This Agreement shall be construed and enforced in accordance with
the laws of the State of California without giving effect to the principles of
conflicts of laws.
          (b) The parties irrevocably agree that any dispute, controversy or
claim arising out of or relating to this Amendment or the transactions
contemplated thereby, or the breach, termination or invalidity thereof, shall be
settled by arbitration in accordance with Section 11.7 of the Agreement.
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2

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     IN WITNESS WHEREOF, the Seller and the Buyer have executed, or have caused
to be executed by their respective officers thereunto duly authorized, this
Amendment as of the date first written above.

                  IDM PHARMA, INC.    
 
           
 
  By:  /s/ Emile Loria    
 
           
 
   Name:   Emile Loria    
 
   Title:   President and Chief Business Officer    
 
                PHARMEXA INC.    
 
           
 
  By:  /s/ Marc Hertz    
 
           
 
   Name:   Marc Hertz, Ph.D.    
 
   Title:   Chief Executive Officer    

 

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Exhibit A
Schedule 3.15. Equipment and Agreements to be Transferred to [. . . *** . . .].
(a) Equipment:
[. . . *** . . .]
(b) Agreements:
[. . . *** . . .]

     
 
  *Confidential Treatment Requested
   under 17 C.F.R. §§ 200.80(b)(4) and
   240.24b-2(b)(1)

 

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Exhibit B
Schedule 4.5(a). Material Contracts and Required Consents for Material
Contracts.
Material Contracts Not Requiring Consent:
[. . . *** . . .]

     
 
  *Confidential Treatment Requested
   under 17 C.F.R. §§ 200.80(b)(4) and
   240.24b-2(b)(1)

 

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[. . . *** . . .]
Material Contracts Requiring Consent:
[. . . *** . . .]

     
 
  *Confidential Treatment Requested
   under 17 C.F.R. §§ 200.80(b)(4) and
   240.24b-2(b)(1)

 

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[. . . *** . . .]

     
 
  *Confidential Treatment Requested
   under 17 C.F.R. §§ 200.80(b)(4) and
   240.24b-2(b)(1)

 

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Exhibit C
Schedule 6.6. Consents Required to Close.
[. . . *** . . .]

     
 
  *Confidential Treatment Requested
   under 17 C.F.R. §§ 200.80(b)(4) and
   240.24b-2(b)(1)