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                                                                 EXHIBIT 10.24

   Confidential Materials omitted and filed separately with the Securities and
                Exchange Commission. Asterisks denote omissions.

DATED                        AUGUST 23                             1999
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(1)                           BTG INTERNATIONAL LIMITED


                                     - and -

(2)                               LEUKOSITE, INC.




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                            FURTHER DEED OF VARIATION
                        relating to the Licence Agreement
                           made between the parties on
                                31(st) March 1997

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THIS DEED OF VARIATION made the 23rd day of August 1999 BETWEEN

(1)  BTG INTERNATIONAL LIMITED whose company registration number in England is
     2664412 and whose registered office address is at 10 Fleet Place,
     Limeburner Lane, London, EC4M 7SB ("BTG"); and

(2)  LEOKOSITE INC a Delaware corporation having an address at 215 First Street,
     Cambridge, MA 021142 ("the Licensee")

is supplemental to the Licence Agreement made between the parties on 31st March
1997 (which Licence Agreement, as amended by a Deed of Variation dated 19th May
1998, and a Supplemental Agreement of the same date, is referred to below as
"the Licence Agreement").

WHEREAS:-

(A)  The Licensee's affiliate and sub-licensee L&I Partners L.P. ("L&I) has
     today entered into a Distribution and Development Agreement with Schering
     AG ("Schering") relating to distribution and development of products made
     under the licences granted in the Licence Agreement;

(B)  The parties have agreed to vary certain of the terms of the Licence
     Agreement to reflect the arrangements in the Distribution Agreement.

IT IS AGREED THAT:-

1.   LICENSEE WARRANTIES AND UNDERTAKINGS

1.1  Licensee warrants to BTG that the executed Distribution and Development
Agreement ("the Distribution Agreement") is in the form which is attached as
Appendix A and initialled by both parties and that it is the entire agreement
between L&I and Schering in relation to Campath products.

1.2  The Licensee also undertakes to BTG that the Licensee shall procure that
L&I will not vary or amend the terms of the Distribution Agreement in any way
or assign or charge its rights thereunder without obtaining BTG's prior
written consent. Such consent shall not e unreasonably withheld but BTG shall
be fully entitled to withhold consent where it is of the belief that the
variation or assignment or charge would be to the detriment of or prejudicial
to BTG.

2.   VARIATIONS TO THE LICENCE AGREEMENT

The licence Agreement shall hereafter be read and construed as if:-

2.1  The following clause 2.4 was added:-

     2.4  This Licensee shall make each payment which is to be made under this
          Agreement by telegraphic transfer direct to BTG's US dollars account
          for which the details are:-
<PAGE>

   Confidential Materials omitted and filed separately with the Securities and
                Exchange Commission. Asterisks denote omissions.

                  Account Number:    [**]
                  Account Name:      BTG International Limited
                  Sort Code:         56-00-33
                  Bank Name:         National Westminster Bank plc
                  Branch Name:       Westminster
                  Branch Address:    57 Victoria Street, London, SW1H 0HN

2.2  The following clauses 7.4, 7.5, 7.6 and 7.7 were added after clause 7.3:

               7.4 With respect to the Distribution and Development Agreement by
               and between L&I Partners L.P. ("L&I") and Schering A.G.
               ("Schering") (the "Distributor Agreement") none of the payments,
               loans or other consideration received under the Distribution
               Agreement are subject to clause 7.1, 7.2 or 7.3 hereof other than
               any received under Section 4.2 (b) of the Distribution Agreement
               (re distribution rights to THIRD PARTIES) and any received under
               Section 13.13 of the Distribution Agreement (infringements). For
               the avoidance of doubt it is declared that this clause shall not
               affect or alter any clauses of this Agreement other than said
               clauses 7.1, 7.2 and 7.3.

     7.5  The Licensee shall make the following payments to BTG:

          7.5.1     [**] dollars, U.S. ($[**]) within ten (10) days after L&I
                    receives the [**] dollar, U.S. ($[**]) loan pursuant to
                    Section 9(a) (i) of the Distribution Agreement and [**]
                    dollars, U.S. ($[**]) within ten (10) days after L&I
                    receives the [**] dollar, U.S. ($[**]) loan pursuant to
                    Section 9(a) (iv) of the Distribution Agreement; and

          7.5.2     the greater of:-

                    7.5.2.1   [**] percent ([**]%) of each payment or loan made
                              to L&I pursuant to Section 12.1 (c) (iii) (H) of
                              the Distribution Agreement; and

                    7.5.2.2   [**] percent ([**]%) of any "Excess Payment" with
                              "Excess Payment" calculated on an indication by
                              indication basis and wherein "Excess Payment"
                              means the amount by a payment or loan made under
                              Section 12.1 (c) (iii) (H) of the Distribution
                              Agreement for the relevant indication exceeds the
                              aggregate of the Development Expenses (as defined
                              in the Distribution Agreement) incurred by L&I
                              under the Distribution

<PAGE>

   Confidential Materials omitted and filed separately with the Securities and
                Exchange Commission. Asterisks denote omissions.


                              Agreement for that indication less the amount of
                              Development Expenses that are reimbursed by
                              Schering for that indication and less the amount
                              of Development Expenses for that indication that
                              have been or are credited against any loan made
                              under the Distribution Agreement.

                    Any amount due under clause 7.5.2 is due and payable within
                    thirty (30) days after the relevant payment under Section
                    12.1 (c) (iii) (H) of the Distribution Agreement.

          7.6       To the extent that pursuant to Section 12.1 (c) (iii) (H) of
                    the Distribution Agreement L&I is entitled to receive an
                    additional payment or loan Licensee shall pay BTG a
                    proportionate amount thereof in accordance with clauses
                    7.5.2

          7.7       To the extent that pursuant to Section 12.1 (c) (iii) (H) of
                    the Distribution Agreement L&I actually makes a bona fide
                    refund payment to Schering, the Licensee shall calculate the
                    overpayment to BTG (under clauses 7.5.2) and may then credit
                    such overpayment against royalties payable to BTG under this
                    Agreement provided that the Licensee may not credit the
                    overpayment so that it would amount to more than [**]
                    percent ([**]%) of the royalties otherwise payable in any
                    calendar year (but the Licensee may then carry forward any
                    uncredited part of the overpayment for crediting against
                    royalties in future years).

2.3  The following clause 5.7 is added after clause 5.6:

          5.7       The Licensee has the right to disclose Know-how to a third
                    party in conjunction with the exercise of the rights and
                    licenses granted to Licensee provided that the third party
                    agrees to be bound by the confidentiality obligations of
                    clauses 5.3 and 17.3.1 (but this is without prejudice to any
                    obligations which the Licensee has to WF in relation to
                    confidentiality).

2.4  The following clauses 10.3 and 10.4 were added after clause 10.2:-

          10.3      The Licensee shall procure that L&I permits BTG the same
                    access, information and assistance in relation to L&I's
                    accounts records and documentation as the Licensee is
                    obliged to provide to BTG in respect of the Licensee's
                    accounts records and documentation under clause 10 of the
                    Licence Agreement. This is for the purpose of allowing BTG
                    to verify whether all payments provided for in this
                    Agreement have been properly and fully made to BTG; and

          10.4      If further distribution rights are granted to third parties
                    by L&I, as anticipated by Section 4.2(b) of the Distribution
                    Agreement then the Licensee shall use all reasonable
                    endeavours to procure that BTG is

<PAGE>

                    granted appropriate audit rights in relation to those third
                    parties (to enable BTG to verify royalties)

2.5  The following was added at the end of clause 12:-

     Each of the undertakings above apply to each indication for which the
     Licensee has or has acquired rights hereunder. The word `indication' in
     this clause and the rest of this shall mean `propymphocytic leukaemia and
     chronic lymphocytic leukemia' as one and each of the indications specified
     in the Options, (giving six indications in all).

2.6  The words `subject to clause 16.6' were inserted at the beginning of
     clauses 16.2 and 16.3.

2.7  The cross-reference `16.2' in clause 16.4 was changed to `16.2.2, 16.2.4,
     16.2.5' remedy in the case of 16.2.1 shall be subject to payment of all
     default interest due to BTG under this Agreement and a remedy period
     agreement with BTG'.

2.8  The wording of clause 16.2.3 was changed to `if the Licensee is to breach
     any of the terms or obligations of any of its Agreements with WF and BTG is
     requested by WF to terminate this agreement (such request being made
     pursuant to the agreement made between WF and BTG on 31st March 1997)'.

2.9  The following clause 16.6 was added after clause 16.5:-

     If the Licensee is in breach of any of clauses 12.3, 12.4, 12.5 or 12.6 or
     clause 16.3 applies and (in any such case) BTG serves a notice of
     termination then that notice of termination shall only apply to the
     indication which is the subject of the breach or delay and on any such
     notice becoming effective (forthwith where notice is under clause 16.2 and
     six months after date of service where notice is under clause 16.3) that
     notice shall only apply to the relevant indication. The effect shall then
     be that the Licensee is deemed to lose the rights which it acquired on
     exercise of the relevant Option(s), with no right to re-exercise, or it
     loses rights in respect of propymphocytic leukaemia and chronic lymphocytic
     leukaemia (as appropriate), rather than the Agreement as a whole
     terminating.

2.10 The following was added as a new clause 16.7:-

     BTG shall not exercise any right which it has to terminate its agreement
     with WF dated 31st March 1997 without first obtaining the Licensee's prior
     consent (such consent not to be unreasonably withheld or delayed).

3.   ROYALTIES

For the avoidance of doubt it is declared that arm's length sales of FINAL FORM
PRODUCT (as defined in the Distribution Agreement) by Schering shall be
Chargeable Transactions under the Licence Agreement and shall be the subject of
a royalty under clause 6.1 thereof.
<PAGE>

4.   LAW

     4.1  This Agreement is to be read and construed in accordance with, and
          governed by, English law.

     4.2  The Licensee submits to the jurisdiction of the English Courts and BTG
          submits to the jurisdiction of the Commonwealth of Massachusetts, USA.

IN WITNESS whereof this document has been executed as a Deed the day and year
first above written.

                                     (The COMMON SEAL of
                                     (BTG INTERNATIONAL LIMITED was
                                     (affixed to this Deed in the presence of:-





                                   [ILLEGIBLE]
                          Director/Authorised Signatory

                                   [ILLEGIBLE]
                         Secretary/ Authorized Signatory



The COMMON SEAL of
LEUKOSITE INC was affixed
to this Deed in the presence of:-


                  [ILLEGIBLE]
                  Director

                  [ILLEGIBLE]
                  Authorised Offier