<PAGE>   1
                                                                                
                                                                   EXHIBIT 10.23
  

                                           *** Text Omitted and Filed Separately
                                                Confidential Treatment Requested
                                          Under 17 C.F.R. Sections 200.80(b)(4),
                                                            200.83 and 240.24b-2



                           GRANT OF SECURITY INTEREST
                        (PATENTS AND PATENT APPLICATIONS)


        THIS GRANT OF SECURITY INTEREST (PATENTS AND PATENT APPLICATIONS) is
dated as of October 23, 1998, between COULTER PHARMACEUTICAL, INC., a
corporation formed under the laws of the State of Delaware, having its principal
place of business at 550 California Avenue, Suite 200, Palo Alto, California
94306, USA (the "Assignor"), and SMITHKLINE BEECHAM CORPORATION, with its
principal place of business at One Franklin Plaza, Philadelphia, Pennsylvania
19101, USA ( the "Assignee").

        WHEREAS, pursuant to a certain Loan Agreement dated as of even date
herewith (as the same may be amended, modified, supplemented or restated from
time to time, the "Loan Agreement"), by and between the Assignor and the
Assignee, the Assignee has agreed to make certain advances of money and to
extend certain financial accommodations to Assignee in the amounts and manner
set forth in the Loan Agreement (collectively, the "Loans").

        WHEREAS, pursuant to the terms of a certain Security Agreement dated as
of even date herewith (as the same may be amended, modified, supplemented or
restated, the "Security Agreement"), made by the Assignor in favor of the
Assignee, the Assignor has granted to the Assignee a security interest in all of
the Assignor's right, title and interest, whether presently existing or
hereafter arising or acquired, in, to and under all of the Assignor's
"Collateral," as defined in the Security Agreement.

        WHEREAS, the Assignee is willing to make the Loans to the Assignor, but
only upon the condition, among others, that the Assignor shall grant a security
interest and assign for security purposes (and not as an absolute assignment) in
favor of and to the Assignee, all of its right, title and interest in and to all
Licensed Patents (as defined in the Security Agreement) to secure the
Obligations of the Assignee under the Loan Agreement and the other Loan
Documents.

        NOW, THEREFORE, for good and valuable consideration, receipt of which is
hereby acknowledged, as collateral security for the prompt and complete payment
when due of its Obligations under the Loan Agreement, the Note and the other
Loan Documents, the Assignor hereby represents, warrants, covenants and agrees
as follows:

        1. Unless otherwise defined herein, the terms defined in the Loan
Agreement are used herein as therein defined.

        2. To secure its Obligations, the Assignor does hereby mortgage and
pledge to the Assignee, and grant to the Assignee a security interest in, all of
the Assignor's right, title and interest in, to and under its Licensed Patents,
including, without limitation the patents and patent




                                       1.
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applications listed on Schedule A attached hereto, including, without
limitation, all proceeds thereof.

        The Assignee does hereby further acknowledge and affirm that the rights
and remedies of the Assignor with respect to the assignment of and security
interest in the Collateral made and granted hereby are more fully set forth in
the Security Agreement, the terms and provisions of which are hereby
incorporated herein by reference.

        Following the termination of the Security Agreement in accordance with
its terms, the Licensed Patents, Know-How and any and all financing statements
filed on behalf of the Assignee will be automatically reassigned to the
Assignor, and the Assignee will execute such instruments as may be reasonably
requested to evidence such reassignment.






                                       2.

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        In Witness Whereof, each of the parties have caused this Grant of
Security Interest (Patents and Patent Applications) to be duly executed by its
officers thereunto duly authorized as of the date first written above.

                                           ASSIGNOR:

                                           COULTER PHARMACEUTICAL, INC.,



                                            By:
                                               ---------------------------------
                                            Printed Name:
                                                         -----------------------
                                            Title:
                                                  ------------------------------


                                            ASSIGNEE:

                                            SMITHKLINE BEECHAM CORPORATION



                                            By:
                                               ---------------------------------
                                            Printed Name:
                                                         -----------------------
                                            Title:
                                                  ------------------------------




                                       3.




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                                   SCHEDULE A


                                LICENSED PATENTS



<TABLE>
<CAPTION>
  ATTORNEY                SERIAL NO. /             FILED/
 DOCKET NO.                PATENT NO.               ISSUED               TITLE
-----------               -----------             -----------        -----------
<S>                       <C>                    <C>                <C>
[...***...]               [...***...]             [...***...]        [...***...]
</TABLE>



*                 Claims priority/effective filing date of earlier application

**                ABANDONED in favor of Serial No. [...***...]

                  OWNERSHIP INTERESTS:

[...***...]       Co-owned by Grantor and the Regents of the University of
                  Michigan.

[...***...]       Owned by Grantor, with limited license back to MDS Nordion,
                  Inc.

[...***...]       Owned by the Regents of the University of Michigan, with
                  license to Grantor.









*CONFIDENTIAL TREATMENT REQUESTED



                                   SCHEDULE A
                                  PAGE 1 OF 1