1 Exhibit 10.33 SmithKline Beecham Pharmaceuticals Jean Stephenne Senior Vice President and General Manager December 23, 1997 Dr. Steven Gillis President, Chief Executive Officer Corixa Corporation 1124 Columbia Street Suite 200 Seattle, WA 98104...

   1
                                  Exhibit 10.33


                       XxxxxXxxxx Xxxxxxx Pharmaceuticals
                                 Xxxx Xxxxxxxxx
                    Senior Vice President and General Manager


                                December 23, 1997




Xx. Xxxxxx Xxxxxx
President, Chief Executive Officer
Corixa Corporation
0000 Xxxxxxxx Xxxxxx
Xxxxx 000
Xxxxxxx, XX  00000

        OPTION AGREEMENT DATED MARCH 1, 1997

Dear Xxxxx:

        This is to inform you of SB's intention to extend the [xxx] Option
Period for one additional eighteen month period pursuant to Section 3(c) of the
Option Agreement dated March 1, 1997.

        The Option Extension Fee of $2,000,000 defined in Section 3(d) of said
Option Agreement will be transferred to you by wire transfer.

Yours Sincerely,


/s/ Xxxx Xxxxxxxxx
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Xxxx Xxxxxxxxx