<PAGE>


                                                              EXHIBIT 10.45


                                October 16, 2001


VIA HAND DELIVERY
-----------------

Mr. Walter Ogier
433 Main Street
Winchester, MA 01890

Dear Walter,

     As you know from our meeting on October 11, BioTransplant, Inc.
("BioTransplant" or the "Company") is terminating your employment effective
October 31, 2001. Between today and October 31, 2001, you shall be responsible
primarily for assisting designated Company employees with transitional matters
on an as needed basis. You have agreed to resign as a member of the Company's
Board of Directors on or before October 31, 2001.

     As we discussed, the Company will provide you with the enhanced severance
benefits described below if you sign and return this letter agreement (the
"Agreement") ON OR BEFORE NOVEMBER 7, 2001. By timely signing and returning this
Agreement, you will be agreeing to the terms and conditions set forth in the
numbered sections below, including the release of claims set forth in Section 3.
Therefore, you are advised to consult with an attorney before signing this
Agreement and you may take up to twenty-one (21) days to do so. If you sign this
Agreement, you may change your mind and revoke your assent during the seven (7)
day period after you have signed the Agreement (the "Revocation Period") by
notifying me of your revocation in writing. If you do not revoke your assent to
the Agreement before the expiration of the Revocation Period, this Agreement
will become a binding document between you and the Company. If you choose not to
sign and return this Agreement ON OR BEFORE NOVEMBER 7, 2001, or if you sign the
Agreement but revoke your consent during the Revocation Period, you shall not
receive any enhanced severance benefits from the Company.

     Regardless of signing this Agreement, you may elect to continue receiving
group medical insurance pursuant to the Consolidated Omnibus Budget
Reconciliation Act of 1985 ("COBRA"). If you are eligible for COBRA and elect
COBRA coverage, all group medical insurance premium costs will be paid by you on
a monthly basis for as long as, and to the extent that, you remain covered under
COBRA. You will receive additional information regarding COBRA under separate
cover.

     Also, regardless of signing this Agreement, pursuant to the terms of the
Amendment and Restatement of the Management Equity Incentive Plan of Eligix,
Inc., dated December 8, 2000, as amended by a Letter Agreement by and between
the Company and Eligix dated May 15, 2001 (the "Management Incentive Plan"),
your portion of the Stock Consideration (as defined in the Management Incentive
Plan) shall vest on October 31, 2001. A schedule of the shares that you are
eligible to receive in accordance with the Management Incentive Plan, along with
a listing of your existing Company stock options (together with the relevant
expiration date(s) and exercise price(s)), is attached to this Agreement as
Exhibit 1.


                                  Page 1 of 8

<PAGE>


     The following numbered sections set forth the terms and conditions which
will apply if you sign and return this Agreement ON OR BEFORE NOVEMBER 7, 2001
and do not revoke your consent to the Agreement within the Revocation Period:

1.   TERMINATION DATE - Your effective date of termination as an employee and an
     officer of the Company will be October 31, 2001 (the "Termination Date").
     As of the Termination Date, all salary payments from the Company will cease
     and any benefits you may have under Company-provided benefit plans,
     programs, or practices will terminate, except as required by the terms of
     the Offer Letter and the Management Incentive Plan, by federal or state
     law, or as otherwise described below. In addition, you agree to resign as a
     member of the Company's Board of Directors on or before October 31, 2001.

2.   DESCRIPTION OF ENHANCED SEVERANCE BENEFITS - In return for your timely
     execution and non-revocation of this Agreement, including the release of
     claims in Section 3 below, the Company agrees to provide you with the
     following enhanced severance benefits (collectively, the "Enhanced
     Severance Benefits"):

     (a)  SEVERANCE PAY. Notwithstanding any provisions in the offer letter from
          the Company dated May 15, 2001 to the contrary (the "Offer Letter"),
          the Company agrees to provide you Two Hundred Forty-One Thousand Five
          Hundred Sixty Dollars ($241,560) in severance pay, which equals six
          (6) months of salary at a rate of double your monthly base salary (the
          "Guaranteed Severance Pay"). The Guaranteed Severance Pay will be paid
          to you, less any and all applicable local, state and federal taxes and
          withholdings, in two equal lump sum payments, with the first lump sum
          payment to be made on the tenth - (10th) day following the date that a
          fully executed copy of this Agreement is received by the Chief
          Executive Officer of the Company and the second lump sum payment to be
          made ninety (90) days thereafter (the "Severance End Date"). The
          Guaranteed Severance Pay will be provided to you without regard to
          whether you obtain subsequent employment, including self-employment.

          If, within seven (7) calendar days of April 30, 2001 (the "Sixth
          Month"), you notify the Chief Executive Officer of the Company in
          writing that you have not secured subsequent employment, including
          self-employment, the Company will provide you with salary continuation
          in accordance with the Company's regular payroll practices at a rate
          of double your monthly base salary in effect as of October 16, 2001
          (the "Double Monthly Base"), less any and all applicable local, state
          and federal taxes and withholdings until (x) you secure subsequent
          employment, including self-employment, or (y) the expiration of three
          (3) months following the Sixth Month (the "Extended Severance
          Period"), whichever is earlier.

          In the event that you become self-employed (including as a consultant
          or an independent contractor) following the Sixth Month and prior to
          the Extended Severance Period and, within seven (7) calendar days
          after you secure such self-employment, you notify the Chief Executive
          Officer of the Company in writing of the identity of the entity or
          entities for whom you will be providing services, the nature of the
          self-employment and your


                                  Page 2 of 8

<PAGE>


          new monthly salary or service fee, the Company will pay you the
          difference, if any, between your new monthly salary or service fee and
          the Double Monthly Base, less any and all applicable local, state and
          federal taxes and withholdings (the "Differential"), but in no event
          will the Differential under this section 2(a) be paid for any work or
          services performed following the Extended Severance Period. The total
          amount of Differential will be paid to you in a lump sum on the tenth
          (10th) day after you provide the Chief Executive Officer of the
          Company with a copy of checks or other income statements reflecting
          all income you received from self-employment between the Sixth Month
          and the Extended Severance Period.

     (b)  BONUS. The Company agrees to pay you a lump sum cash payment of
          Seventy Thousand, Four Hundred Fifty-Five Dollars ($70,455)
          (representing 10/12 of the annual cash bonus for which you are
          eligible, less any and all applicable local, state and federal taxes
          and withholdings), at the same time that annual bonus payments are
          made to active executive employees of the Company; provided, however,
          that a bonus under this Section 2(b) shall only be paid if any active
          employee of the Company receives an annual bonus, whether in cash or
          in the form of stock, for the year 2001 under the Company's annual
          bonus program.

     (c)  RETENTION OF COMPANY PROPERTY. The Company agrees that you may retain
          as personal property the Company-provided Palm Pilot(TM) used by you
          during your employment; provided, however, you must first return any
          and all, and may not retain any, Company property stored in the Palm
          Pilot (TM), pursuant to the provisions of Section 4 below. The Palm
          Pilot(TM) will be retained by you strictly on an "as is" basis, and
          you shall assume responsibility for all costs related to it after the
          Termination Date. Further, the Company agrees to transfer the Nokia
          cellular phone that you used during your employment with the Company
          and the cellular phone account to you on an "as is" basis, and you
          shall assume responsibility for all costs related to maintaining the
          cellular phone and the cellular phone account following the
          Termination Date

     (d)  NON-DISPARAGEMENT. The Company agrees to direct its officers not to
          make any false, disparaging, derogatory or defamatory statements in
          public or in private regarding you or your employment with the
          Company. The Company also agrees to provide prospective employers that
          are referred to the Company's Human Resources Department with
          confirmation of your dates of employment (both with Eligix and the
          Company), your job responsibilities, your title, and confirmation that
          your separation from the Company was mutually agreed upon in order to
          assist you in pursuing other employment opportunities. The Company
          further agrees that Elliot Lebowitz will provide prospective employers
          seeking information regarding your employment with and separation from
          BioTransplant with the following statement: "Under Walter Ogier's
          leadership, Eligix grew from a start-up venture to a therapeutics
          company with commercial products. Most recently, he worked to realize
          the merger


                                  Page 3 of 8

<PAGE>


          of Eligix with BioTransplant, to secure Gambro BCT as a strategic
          alliance partner for BioTransplant, and to facilitate the operational
          integration of Eligix with BioTransplant. We thank him for his
          contributions and wish him the best of success in his future
          endeavors."

     (e)  COMPANY RELEASE. The Company, including any and all affiliates and
          subsidiaries, hereby fully, forever, irrevocably and unconditionally
          releases, remises and discharges you from any and all claims, charges,
          complaints, demands, actions, causes of action, suits, rights, debts,
          sums of money, costs, accounts, covenants, contracts, agreements,
          promises, doings, omissions, damages, executions, obligations,
          liabilities, and expenses (including attorneys' fees and costs), of
          every kind and nature arising out of your employment with and
          separation from BioTransplant; provided, however, that nothing in this
          section 2(e) shall release you from any obligation expressly set forth
          in this Agreement or any claims arising out of or related to your
          commission of acts involving fraud, criminal activity or deliberate
          misconduct committed during your employment with the Company. For
          purposes of this section 2(e), "deliberate misconduct" shall mean your
          direct act of forging or fabricating data, falsifying or inventing
          results, plagiarism, piracy, failing to comply with federal
          requirements affecting research, violating generally accepted research
          practices, misappropriating proprietary information of the Company or
          a third party, unauthorized use of the Company's confidential
          information, failing to disclose a conflict of interest, and
          intentionally or knowingly helping another to commit an act of
          deliberate misconduct.

3.   RELEASE OF CLAIMS - In consideration of the payment of the Enhanced
     Severance Benefits, which you acknowledge you would not otherwise be
     entitled to receive, you hereby fully, forever, irrevocably and
     unconditionally release, remise and discharge the Company and its current
     and former officers, directors, stockholders, corporate affiliates,
     subsidiaries, parent companies, predecessors, agents, employees and
     attorneys (the "Released Parties") from any and all claims, charges,
     complaints, demands, actions, causes of action, suits, rights, debts, sums
     of money, costs, accounts, covenants, contracts, agreements, promises,
     doings, omissions, damages, executions, obligations, liabilities, and
     expenses (including attorneys' fees and costs), of every kind and nature
     which you ever had or now have as of the date you execute this Agreement
     against the Released Parties including, but not limited to, all claims
     arising out of your employment with or separation from the Company, all
     employment discrimination claims under Title VII of the Civil Rights Act of
     1964, 42 U.S.C.sections 2000e ET SEQ., the Age Discrimination in Employment
     Act, 29 U.S.C. sections 621 ET SEQ., the Americans With Disabilities Act of
     1990, 42 U.S.C. sections 12101 ET SEQ., and the Massachusetts Fair
     Employment Practices Act, M.G.L. c.151B, sections 1 ET SEQ., all as
     amended; all claims arising out of the Fair Credit Reporting Act, 15 U.S.C.
     sections 1681 ET SEQ., the Employee Retirement Income Security Act of 1974
     ("ERISA"), 29 U.S.C. sections 1001 ET SEQ., the Massachusetts Civil Rights
     Act, M.G.L. c.12 sections 11H and 11I, the Massachusetts Equal Rights AcT,
     M.G.L. c.93 sections 102 and M.G.L. c.214, sections 1C, the Massachusetts
     Labor and Industries Act, M.G.L. c. 149, sections 1 ET SEQ., and the
     Massachusetts Privacy Act, M.G.L. c.214, sections 1B, all as amended; all


                                  Page 4 of 8

<PAGE>


     common law claims including, but not limited to, actions in tort,
     defamation and breach of contract; all claims to any ownership interest in
     the Company (contractual or otherwise) including, but not limited to,
     claims to stock or stock options; and any other claims or damages arising
     out of your employment with or separation from the Company (including a
     claim for retaliation) under any common law theory or any federal, state or
     local ordinance not expressly referenced above.

     Nothing contained in this Section 3 shall bar you from asserting a claim
     for any vested benefit (including, but not limited to under the Management
     Incentive Plan or the Eligix, Inc. 1997 Equity Incentive Plan, both as
     amended) or any obligation expressly set forth in this Agreement. Moreover,
     nothing contained in this Section 3 shall bar you from (i) asserting any
     claim against any Company officer stemming from an act or omission which
     would be considered a breach under section 2(d) of this Agreement if such
     Company officer were a party to this Agreement, or (ii) defending yourself
     against any claim brought against you by the Company or any other Released
     Party.

4.   RETURN OF COMPANY PROPERTY - You represent that you have returned to the
     Company all Company property in your possession, custody or control
     including, but not limited to, keys, Company files and records (and copies
     thereof), computer hardware and software, and cellular phones. You agree to
     leave intact all electronic Company documents, including those which you
     developed or helped develop during your employment. You further agree to
     cancel all accounts for your benefit, if any, in the Company's name
     including, but not limited to, credit cards, computer accounts, cellular
     phone accounts and telephone charge cards.

5.   CONFIDENTIALITY OBLIGATIONS UNDER INVENTION, NON-DISCLOSURE AND
     NON-COMPETITION AGREEMENT - You acknowledge your non-competition obligation
     to the Company and your obligation to keep confidential all non-public
     information concerning the Company which you acquired during the course of
     your employment with the Company, as stated more fully in the Invention,
     Non-Disclosure and Non-Competition Agreement you executed at the
     commencement of your employment as a condition of your employment with the
     Company, the terms of which remain in full force and effect.

6.   NON-DISPARAGEMENT - To the extent permitted by law, you understand and
     agree that, as a condition for the Enhanced Severance Benefits, you shall
     not make any false, disparaging, derogatory or defamatory statement in
     public or in private regarding the Company or any of the other Released
     Parties, or regarding the Company's business affairs, business prospects
     and financial condition.

7.   AMENDMENT - This Agreement shall be binding upon the parties and may not be
     modified in any manner, except by an instrument in writing of concurrent or
     subsequent date signed by duly authorized representatives of the parties.
     This Agreement is binding upon and shall inure to the benefit of the
     parties and their respective agents, assigns, heirs, executors, successors
     and administrators.

8.   WAIVER OF RIGHTS - No delay or omission by either party to this Agreement
     in exercising any right under this Agreement shall operate as a waiver of
     that or any


                                  Page 5 of 8

<PAGE>


     other right. A waiver or consent given by either party to the other on any
     one occasion shall be effective only in that instance and shall not be
     construed as a bar or waiver of any right on any other occasion.

9.   VALIDITY - Should any provision of this Agreement be declared or be
     determined by any court of competent jurisdiction to be illegal or invalid,
     the validity of the remaining parts, terms or provisions shall not be
     affected thereby, and said illegal or invalid part, term or provision shall
     be deemed not to be a part of this Agreement.

10.  CONFIDENTIALITY - To the extent permitted by law, you understand and agree
     that, as a condition for the Enhanced Severance Benefits, the terms and
     contents of this Agreement, and the contents of the negotiations and
     discussions resulting in this Agreement, shall be maintained as
     confidential by you and your agents and shall not be disclosed to any third
     party (with the exception of your counsel and your financial advisor)
     except to the extent required by federal or state law, or as otherwise
     agreed to in writing by the Company.

11.  COOPERATION - You agree to cooperate fully with the Company in the defense
     or prosecution of any claims or actions now in existence or which may be
     brought in the future against or on behalf of the Company. Your full
     cooperation in connection with such claims or actions shall include, but
     not be limited to, your being available to meet with Company counsel to
     prepare for trial or discovery or an administrative hearing and to act as a
     witness when requested by the Company at reasonable times designated by the
     Company. The Company agrees to reimburse you for all reasonable costs
     incurred by you as a result of such cooperation, provided, however, the
     Company will not reimburse you for any such costs if the Company is
     involved in the defense or prosecution of claims or actions arising out of
     or relating to any unlawful conduct participated in by you as an employee
     or director of the Company.

12.  NATURE OF AGREEMENT - You understand and agree that this Agreement is a
     severance agreement and does not constitute an admission of liability on
     the part of the Company.

13.  ACKNOWLEDGMENTS - You acknowledge that you have been given at least
     twenty-one (21) days to consider this Agreement, and that the Company
     advised you to consult with an attorney of your choosing prior to signing
     this Agreement. You understand that you may revoke this Agreement for a
     period of seven (7) days after you sign this Agreement, and the it shall
     not be effective or enforceable until the expiration of this seven (7) day
     Revocation Period. You understand and agree that, by entering into this
     Agreement, you are waiving any and all rights or claims you may have under
     the Age Discrimination In Employment Act, as amended by the Older Workers
     Benefit Protection Act, and that you have received consideration beyond
     that to which you were previously entitled.

14.  VOLUNTARY ASSENT - You affirm that no other promises or agreements of any
     kind have been made to or with you by any person or entity whatsoever to
     cause you to sign this Agreement, and that you fully understand the meaning
     and intent of this Agreement. You state and represent that you have had an
     opportunity to fully

                                  Page 6 of 8

<PAGE>

     discuss and review the terms of this Agreement with an attorney. You
     further state and represent that you have carefully read this Agreement,
     understand its contents, freely and voluntarily assent to all of its terms
     and conditions, and sign your name of your own free act.

15.  APPLICABLE LAW - This Agreement shall be interpreted and construed by the
     laws of the Commonwealth of Massachusetts, without regard to conflict of
     laws provisions. You hereby irrevocably submit to and acknowledge and
     recognize the jurisdiction of the courts of the Commonwealth of
     Massachusetts, or if appropriate, a federal court located in Massachusetts
     (which courts, for purposes of this Agreement, are the only courts of
     competent jurisdiction), over any suit, action or other proceeding arising
     out of, under or in connection with this Agreement or its subject matter.

16.  ENTIRE AGREEMENT - This Agreement contains and constitutes the entire
     understanding and agreement with respect to your severance benefits and the
     settlement of claims against the Company and cancels all previous oral and
     written negotiations, agreements, commitments, and writings, including the
     Offer Letter. However, nothing in this Section 16 or in this Agreement
     shall modify, cancel or supercede your obligations as set forth in the
     Invention Non-Disclosure and Non-Competition Agreement referenced in
     Section 5 of this Agreement, or shall alter in any way your participation
     in the Management Incentive Plan or the Eligix, Inc. 1997 Equity Incentive
     Plan, both as amended.

     If you choose to execute this Agreement, please return ALL PAGES of this
letter to me in the enclosed envelope NO LATER THAN NOVEMBER 7, 2001. You may
retain the enclosed copy of the letter for your records.

                                            Sincerely,

                                            BIOTRANSPLANT, INC.


                                            /S/ ELLIOT LEBOWITZ
                                            ----------------------------
                                            By: Elliot Lebowitz, Ph.D.
                                                Chief Executive Officer


I hereby agree to the terms and conditions set forth above. I have been given at
least twenty-one (21) days to consider this Agreement and I have chosen to
execute it on the date below. I intend that this Agreement become a binding
agreement between me and the Company.

/S/ WALTER OGIER
---------------------------------
Mr. Walter Ogier

Date: ________________, 2001



                                  Page 7 of 8


<PAGE>


                                    EXHIBIT 1


SHARES GRANTED PURSUANT TO THE MANAGEMENT EQUITY INCENTIVE PLAN

     You are entitled to receive up to an aggregate of 172,617 shares of Common
Stock of BioTransplant pursuant to the Management Incentive Plan. These shares
are subject to the terms of the Agreement and Plan of Merger dated December 8,
2000 (the "Agreement and Plan of Merger") and the Escrow Agreement you executed
pursuant to the Agreement and Plan of Merger.

SHARES GRANTED PURSUANT TO THE ASSUMED ELIGIX, INC. 1997 EQUITY INCENTIVE PLAN,
AS AMENDED

     You received two options to purchase shares of Eligix, Inc. Common Stock.
The following table provides details relating to these two option grants:

<TABLE>
<CAPTION>
------------------------- ---------------------- ------------------------------------------- --------------
                                                                                               Shares
                                                                                               Vested as of
                            Exercise Price on an    Shares Assumed by BioTransplant on an      October 1,
  Date of Option Grant      As Converted Basis               As Converted Basis                2001
------------------------- ---------------------- ------------------------------------------- --------------
<S>                         <C>                     <C>                                        <C>
10/17/97                    $1.60                   56,280                                     56,280
------------------------- ---------------------- ------------------------------------------- --------------
5/25/00                     $0.11                   56,280                                     56,280
------------------------- ---------------------- ------------------------------------------- --------------
</TABLE>

     Your right to exercise the shares granted under the option agreements
expires three months following the Termination Date. These shares are subject to
the terms of the Agreement and Plan of Merger and the Lock-Up Agreement.