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                                                                Exhibit 10.23(b)
                                                                ----------------

                                 LEUKOSITE, INC.


                                 FIRST AMENDMENT
                                       TO
                   AMENDED AND RESTATED 1993 STOCK OPTION PLAN
                   -------------------------------------------

       This FIRST AMENDMENT (this "Amendment") to the Amended and Restated 1993
Stock Option Plan (the "Plan") of LeukoSite, Inc., a Delaware corporation (the
"Company"), is being adopted by resolution of the Board of Directors at a
meeting held on September 22, 1997 (the "Effective Date"). Effective from and
after the Effective Date, the Plan is hereby amended as follows:

       1. Section 5 of the Plan hereby is amended by adding the following
sentence in the fifteenth (15th) line, following the second sentence: "Subject
to the provisions of the Plan, the Committee shall have complete authority, in
its discretion, to delegate to the President and Chief Executive Officer of the
Company the manner of making the following determinations with respect to each
Awarded Option to be granted by the Company to employees of the Company who are
below the level of Vice President of the Company or to consultants to the
Company, with the same force and effect as if the Committee had made such
determinations itself: (a) the employee or consultant to receive such Awarded
Option; (b) whether the Awarded Option (if granted to an employee) will be an
Incentive Option or Nonstatutory Option; (c) the time of granting the Awarded
Option; (d) the number of Shares subject to the Awarded Option; (e) the Option
Price; (f) the option period; (g) the exercise date or dates or, if the Awarded
Option is immediately exercisable in full on its grant date, the vesting
schedule, if any, applicable to the Shares issuable upon the exercise of the
Awarded Option; (h) the effect of termination of employment, consulting or
association with the Company on the subsequent exercisability of the Awarded
Option; and (i) if the Awarded Option is a Nonstatutory Option, whether such
Nonstatutory Option may be transferred by the Holder to a third party." The
amendment being for the purpose of clarifying that the Committee has the
authority under the Plan to delegate to the President and Chief Executive
Officer of the Company the authority to grant stock options to employees below
the Vice President level and consultants.

       Except to the extent amended hereby, all of the terms, provisions and
conditions set forth in the Plan are hereby ratified and confirmed and shall
remain in full force and effect. The Plan and this Amendment shall be read and
construed together as a single instrument.