Document:

<PAGE>
                                                                   EXHIBIT 10.24

                                                          CONFIDENTIAL TREATMENT

                           MEMORANDUM OF UNDERSTANDING

                Revised P&GP / Alexion Pexelizumab Collaboration

This Memorandum represents a summary of the Parties' interests in renegotiating
their current Collaboration and it is binding as set forth in the final
paragraph hereof.

OVERVIEW AND MANAGEMENT OF THE COLLABORATION

     Scope: P&GP and Alexion propose to revise the Collaboration Agreement (the
     "Collaboration Agreement") dated January 25, 1999 in accordance with this
     Memorandum. P&GP and Alexion agree to negotiate in good faith to restate
     the Collaboration Agreement (the "Restatement") in accordance with this
     Memorandum.

     Collaboration Agreement. Except as specifically set forth herein, all terms
     of the Collaboration Agreement shall continue with full force and effect
     following the execution and delivery of this Memorandum.

     Definitions. Capitalized terms used but not defined herein have the
     meanings set forth in the Collaboration Agreement.

     Decisions - R&D, Health Registrations and Supply Issues: Alexion and P&GP
     will have equal decision-making authority for all R&D, Health Registration
     and Product Supply/Process Development issues. Such issues will be
     addressed and resolved through the R&D Steering Committee. Either party may
     refer an issue for further review and resolution to the President of
     Alexion and the President of Procter & Gamble Pharmaceuticals (the
     "Presidents"). Action will be delayed until such meeting or discussion
     between the Presidents. If the Presidents cannot resolve the issue within
     [*****] business days of such reference (or longer period mutually agreed
     by the Presidents), the matter will be submitted to a neutral arbitrator
     (the "Neutral") within [*****]

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                                                                   EXHIBIT 10.24

     business days thereafter. Both Parties agree to select a Neutral with
     experience in the U.S. pharmaceutical industry and to use their best
     efforts promptly to cooperate with any investigations and deliberations of
     the Neutral. The Parties will present to the Neutral their respective
     issues with proposed solutions for the Neutral to make a determination. The
     Neutral's determination will be limited to either Party's solution. The
     Neutral's determination will be final and binding on the Parties. The fees
     and costs of the Neutral will be shared equally between the Parties. The
     Parties agree to identify and engage a mutually acceptable Neutral promptly
     after execution of the Restatement, to avoid delay in the event the
     Neutral's determinations become necessary.

     Decisions - Commercialization Issues: The Parties shall form a
     Commercialization Steering Team (the "CST"), that will analyze, discuss and
     agree on all commercialization strategies, plans and budgets for
     commercialization of the product in the U.S. This team will have equal
     membership from both P&GP and Alexion. The CST will establish an annual
     commercialization plan, which shall be binding on the Parties. The CST will
     resolve all commercialization issues, including but not limited to
     Marketing, Promotion, Labeling, Phase IIIb/IV studies, Scientific Exchange
     and Education. Either party may refer a commercialization issue for further
     review and resolution to the Presidents. Action will be delayed until such
     meeting or discussion between the Presidents. If the Presidents cannot
     resolve the issue within [*****] business days of such meeting or
     discussion, the matter will be resolved by [*****].

     The development and execution of all commercialization strategies and plans
     in the ROW will remain the sole responsibility of P&GP.

     Executional Responsibilities:

     The executional responsibility of each Party for clinical programs is
     outlined on Schedule I which is attached and incorporated herein. While an
     individual Party has lead executional responsibility, the Parties agree
     there will be no unilateral decision-making by either Party on any aspect
     of the clinical program's execution. Both Parties will as soon as practical
     but in no event later than within [*****], share all significant
     information relating to the development of pexelizumab received from any
     Third Party related to the project, including but not limited to, FDA,
     CROs, clinical sites, or suppliers, about the programs. All other
     information relating to the development

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                                                                   EXHIBIT 10.24

     of pexelizumab will be shared at weekly updates. Prior to meeting with any
     such Third Party regarding the development of pexelizumab, each Party will
     give the other Party adequate advance notice and full ability to
     meaningfully participate. Unless otherwise agreed by the Parties, the
     executional teams, including the Clinical Strategy Team and Clinical
     Execution Team, will meet at a minimum of every week to discuss issues,
     including but not limited to, any executional changes to the protocol or
     plan, the status on any budgetary or spending changes, the status on
     recruitment rates, IRB approvals, etc. When a study is unblinded, each
     Party will participate equally in developing a consistent interpretation of
     the data. A senior management team consisting of Vice Presidents or
     Directors with senior authority for a function, will meet quarterly to
     review, resolve issues as necessary and comment on the status of the
     various clinical and product supply/ process development executional teams,
     including but not limited to, spending versus budget and progress against
     project milestones.

     [*****] will have full responsibility for management of the preparation of
     the global marketing applications with input from [*****]. [*****] will
     lead interactions with FDA regarding the BLA preparation (e.g., pre-BLA
     meetings). [*****] will be responsible for supplying global modular
     documents with input from [*****] to use in completing the CMC section of
     the global marketing applications. [*****] will have full responsibility
     for preparation, content and maintenance of the Product's labeling, subject
     to [*****] prior review and opportunity to comment.

     Clinical Databases: Clinical databases for CABG and AMI will continue to
     use P&GP systems and specifications and remain under P&GP control and
     ownership, in accordance with the Collaboration Agreement. P&GP will give
     Alexion current access to all such databases. Both Parties must agree prior
     to granting access to any portion of the database to a Third Party. In the
     event P&GP exercises the Opt Out option and the Collaboration Agreement is
     terminated, P&GP will without further consideration promptly transfer
     ownership of such databases to Alexion, and will provide Alexion other
     access reasonably needed by Alexion, including but not limited to,
     introducing Alexion to database vendors that P&GP license from and
     providing Alexion licenses to P&GP owned software exclusively for use in
     connection with the CABG and AMI clinical database, so Alexion is able to
     assume control of and to exploit the databases to the same extent as P&GP
     had been capable of internally.

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                                                                   EXHIBIT 10.24

RESEARCH AND DEVELOPMENT PLAN

     U.S. R&D Funding: P&GP will continue to control AMI Phase II and fund all
     out-of-pocket costs and in-house FTE costs for work performed pursuant to
     the R&D Plan for the AMI Phase II program. Alexion and P&GP will each pay
     50% of all pre-agreed out-of-pocket costs to Third Parties for work
     performed pursuant to the R&D Plan for the AMI Phase III U.S. program and
     the CABG Phase III U.S. program, plus mutually agreed Alexion and P&GP FTE
     costs in connection therewith. Prior to commencement of a program an
     overall budget ("Budget") must be pre-agreed in writing by the Parties.
     This Budget will be updated no less than every 6 months and all changes
     must be agreed to in writing. Out-of-pocket costs include any mutually
     agreed-to payments to Third Parties. Studies conducted outside the United
     States that are used to support either Phase III U.S. program shall be
     considered U.S. program costs. Any expenses incurred by either Party that
     were not pre-agreed to in writing as part of the Budget process will be the
     sole responsibility of the Party that incurred the expense.

          CABG. Alexion agrees to pay the first 50% of the total pre-agreed
          estimated costs in respect of the CABG Phase III U.S. program (i.e.,
          $[*****]). For clarity, P&GP's previous expenditure for CABG Phase
          III, the amount of which will be agreed as set forth below, will not
          be counted as part of Alexion's first 50% of costs. Unless agreed
          otherwise by the Parties in writing as part of the establishment of
          the Budgets, Alexion will pay the first $[*****] of such costs, P&GP
          will pay the second $[*****] of such costs, and the Parties will
          simultaneously, evenly pay any additional mutually-agreed costs. Upon
          completion or jointly agreed termination of the CABG Phase III U.S.
          program, if either Party has paid more than the other Party in
          connection therewith, the Party having paid less will promptly make a
          reconciliation payment to the other Party, such that each party has
          paid 50% of the total of such mutually-agreed costs. Each Party
          acknowledges that the other has incurred costs directly related to the
          CABG Phase III program prior to execution of this Memorandum.
          Accordingly, each Party will be credited with having already spent
          such amounts in evening the total costs to be absorbed by the Parties.
          A full accounting will be completed upon signing this Memorandum to
          itemize the specific CABG Phase III costs incurred by the Parties as
          of that date.

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                                                                   EXHIBIT 10.24

          AMI. Alexion and P&GP will determine a structure to result in their
          paying their respective 50% of AMI Phase III costs simultaneously.

          Clinical Supply Costs. All clinical supply costs incurred prior to
          initiation of the CABG Phase III program shall be expensed on
          initiation of the trial, and further such costs will be expensed when
          incurred.

     ROW R&D Funding: P&GP is free to re-use, outside the U.S., any data or
     information generated from any study performed for U.S. Health
     Registration, without incurring any additional expense. Alexion is free to
     use, within the U.S., any data or information generated by P&GP from any
     study performed solely for a ROW Health Registration, without incurring any
     additional expense. P&GP may elect to include ROW sites in U.S. led Phase
     IIIb and Phase IV studies. In the event ROW sites are included in such
     studies, P&GP will pay for the expenses specifically associated with
     patients enrolled solely for the ROW needs. If pre-agreed Phase IIIb and
     Phase IV studies are used in the U.S. and ROW for new marketing or labeling
     claims, P&GP will pay [*****] of the cost and Alexion will pay [*****]. All
     additional R&D expenses specifically and uniquely required for the Health
     Registration or commercialization of pexelizumab outside of the U.S. will
     be the responsibility of P&GP.

     P&GP OPT-OUT OPTION: P&GP may terminate ("Opt-Out") the Collaboration in
     its sole discretion by providing six months notice following [*****] and no
     later than the earlier of (i) 30 days after receipt of [*****] and (ii)
     [*****].

     In the event P&GP elects to exercise its Opt-Out option, P&GP has no
     responsibility for CABG Phase III expense other than (i) the mutually
     agreed expenses incurred prior to exercise of the Opt-Out that otherwise
     would be payable by P&GP pursuant to "CABG", above, and (ii) CABG Phase III
     amounts paid by P&GP prior to execution of this Memorandum. By way of
     example, if P&GP exercises the Opt-Out option and $[*****] has been
     expended on CABG Phase III, and it is determined that P&GP paid $[*****]
     prior to execution of this agreement in connection with CABG Phase III,
     Alexion would have paid $[*****] and P&GP [*****]. During the six month
     notice period, P&GP will continue to provide continuing executional support
     for AMI and CABG Phase

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                                                                   EXHIBIT 10.24

     III hereunder but will have no financial liability for any AMI or CABG
     Phase III expenses, other than in-house P&GP FTE costs, to be paid 100% by
     P&GP, provided such FTE costs and expenses are consistent with pre-agreed
     Budgets and provided the work will be transferred to Alexion as soon as
     practicable.

     In the event P&GP elects to exercise its Opt-Out option, Alexion agrees to
     purchase from P&GP all mutually pre-agreed pexelizumab related
     manufacturing assets at current book value and to reimburse P&GP for all
     [*****] including but not limited to, [*****]. Alexion will also agree to
     assume any mutually pre-agreed [*****] including, but not limited to,
     [*****]. All asset transfers, contract assignments, and payments must be
     complete prior to the end of the [*****] notice period. This paragraph
     shall apply only to [*****] of P&GP's assets, and commitments and fees, if
     within [*****] of P&GP's Opt-Out exercise Alexion certifies that it too
     [*****].

PRODUCT SUPPLY AND PROCESS DEVELOPMENT:

     PS/PDC. The Parties will form a Product Supply / Process Development
     Committee (PS/PDC) with equal representation from each Party. The PS/PDC
     will be sponsored by the R&D Steering Committee. The PS/PDC will analyze,
     discuss and agree on decisions related to process development, clinical and
     commercial product supply, including but not limited to, choice of
     supplier(s), capital expenditures and product development activities. The
     PS/PDC will be responsible for and have decision-making authority for
     process development and production of Product for the R&D Plan and for
     commercialization. If the PS/PDC cannot reach agreement on a product supply
     issue, either Party may refer the issue to the R&D Steering Committee. If
     the R&D Steering Committee does not reach agreement within five business
     days of the referral, the matter will be addressed through the R&D Steering
     Committee Dispute Resolution process established above. The PS/PDC will
     develop and agree in writing to a Process Development Plan ("PDP") and a
     Product Supply Sourcing Plan ("PSSP") for the U.S. P&GP and Alexion will
     jointly share project leadership for execution of the Product Supply
     Sourcing Plan, and P&GP will be the primary vendor contact to provide a
     single and focused point of contact to leverage existing relationships and
     corporate purchasing scale; Alexion will provide input on the vendor
     contacts on a co-equal basis. Alexion and P&GP will jointly share project
     leadership for process development. The process development execution will
     be conducted consistent with P&GP and Alexion

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                                                                   EXHIBIT 10.24

     requirements. Alexion will perform bulk drug development and
     characterization and P&GP will provide input on a co-equal basis. P&GP will
     take the lead on vialing and other supply chain activities and Alexion will
     provide input on a co-equal basis. All U.S. process development and product
     supply agreements will be mutually agreed. P&GP will be sole signatory on
     all process development and product supply agreements. Within [*****] of
     the PS/PDC agreeing upon a viable source of commercial supply for
     pexelizumab, the PS/PDC will agree to the Product Supply Sourcing Plan. The
     PSSP will include, among other items, detail on validation timing, launch
     readiness requirements and longer-term forecasted volumes.

     The Parties acknowledge that certain vendors may support supply for both
     the U.S. and ROW. In such cases, the PS/PDC will ensure that vendor costs
     for U.S. and ROW supply are equal on a unit basis.

     In the event that supplies are insufficient for worldwide demand forecasted
     as of launch, [*****] will be [*****]. P&GP will provide Alexion the ROW
     product sourcing plan for review and input. Following launch, if supply is
     insufficient to meet total demand, available supply will be allocated based
     on the past [*****] volume. In the event of a likely shortage of product in
     [*****], P&GP agrees not to [*****]. Unless otherwise agreed by the
     Parties, the PS/PDC will strive to meet these non-binding objectives of the
     PS/PDC that include but are not limited to: (i) the primary commercial
     source(s) of pexelizumab shall be validated in accordance with all relevant
     regulations [*****] before the currently anticipated first BLA filing date
     and (ii) [*****] of commercial supply shall be ready for sale before the
     currently anticipated United States launch date. Meeting these non-binding
     objectives will be balanced against technical and commercial feasibility
     and required investment.

     Capital. Capital expenditures will be [*****]. P&GP will purchase all
     capital as agreed to by the PS/PDC in the PSSP and all assets will be
     maintained on P&GP's ledgers. Until the first launch of pexelizumab,
     [*****] of the annual capital depreciation will be charged to Alexion.
     Following the first launch, depreciation will be charged to the [*****].
     Alexion will thereby be charged [*****]. Assets will be depreciated based
     on P&GP's corporate accounting policy, which includes a determination of
     useful life on an asset-by-asset basis. In the event that P&GP is required
     to write

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                                                                   EXHIBIT 10.24

     down pexelizumab assets due to project failure, etc. (not including assets
     related to [*****]), Alexion will reimburse P&GP for [*****] expense
     associated with the write down.

     Supplier Advances. Until the first launch of pexelizumab, all supplier
     advances that are required to be expensed due to cancellations (other than
     ROW cancellations), will be [*****] between the Parties. Following the
     first launch, all expensed supplier advances will be [*****].

     Expenses. All other outside expense pre-agreed in writing that is
     associated with process development and production, including but not
     limited to all validation and test run costs, will be [*****] insofar as
     the same are uniquely and specifically required to support production
     capacity for U.S. commercialization, including in-house FTE costs for
     process development and product supply work conducted under the R&D Plan. A
     process development and product supply Budget must be pre-agreed in writing
     by the Parties. This Budget must be established in conjunction with PS/PDC
     agreement to the Process Development Plan and Product Supply Sourcing Plan.
     This Budget will be updated no less than every 6 months and all changes
     must be agreed to in writing. Any expenses incurred by either Party that
     were not pre-agreed to in writing as part of the Budget process will be the
     sole responsibility of the Party that incurred the expense. Any expense
     that is uniquely and specifically required to support production capacity
     for ROW commercialization shall be borne by [*****] and not reimbursed by
     [*****], and if such expense supports both U.S. and ROW commercialization,
     P&GP will pay [*****] and Alexion will pay [*****] of the expense.

HEALTH REGISTRATIONS:

     Sponsorship. Within the U.S., Alexion will be the Sponsor of the IND for
     CABG and P&GP will be the Sponsor of the IND for AMI. Both Parties will
     jointly plan, prepare for, and participate in all FDA interactions. All
     meetings with FDA will be led by the Sponsor. The Parties agree to adhere
     to the protocol for involving each other as outlined in Schedule II, which
     is attached and hereby incorporated by reference. P&GP will sponsor the BLA
     and all subsequent sBLAs and be responsible for filing, prosecuting and all
     FDA interactions concerning the BLA or any subsequent sBLAs. In order for
     P&GP to prepare for filing the BLA, Alexion agrees to transfer the IND for
     CABG to P&GP no later than practically required before the expected filing
     of the BLA, but in no event later than the pre-BLA meeting. Outside of the
     U.S., P&GP will be the sponsor of all Health

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                                                                   EXHIBIT 10.24

     Registrations. In the event P&GP exercises the Opt Out option and the
     Collaboration is terminated, P&GP will without further consideration
     promptly transfer sponsorship of its INDs and BLAs throughout the world to
     Alexion or its nominated agent(s), and will provide Alexion access
     reasonably needed by Alexion to assume control of and to exploit such INDs
     and BLAs to the same extent as P&GP had been capable of internally.

     Funding. All mutually agreed out-of-pocket and in-house FTE costs
     associated with filing or maintaining the U.S. Health Registration will
     [*****]. All out of pocket and in-house FTE costs associated with filing or
     maintaining Health Registrations outside of the U.S. will be borne by P&GP.

MARKETING AND PROMOTION:

     Commercialization Costs. P&GP and Alexion agree to [*****] all mutually
     agreed out-of-pocket and FTE costs associated with the commercialization of
     the Product [*****]. [*****] shall be responsible for all such costs
     [*****]. The CST will establish an annual U.S. commercialization plan and
     Budget agreed to in writing on or before July 1 of each year. Any expenses
     incurred by either Party that were not pre-agreed to in writing as part of
     the Budget process will be the sole responsibility of the Party that
     incurred the expense. All mutually agreed out-of-pocket and internal
     Alexion and P&GP FTE U.S. costs shall include but are not limited to the
     following:

          1.   costs for marketing, market research, advertising, sampling, and
               promoting the Product, such as advertising agency fees,
               advertising development costs, sales materials, development
               costs, training materials and public communication costs, speaker
               programs and conferences and other scientific education and
               exchange program (SEEP) costs incurred prior to and following
               Product approval;
          2.   costs related to creating and distributing any communication
               notice mandated by a government authority (e.g. Dear Doctor
               letters);
          3.   costs associated with manufacturing, distributing and shipping
               the Product samples to Third Parties and the handling and
               disposing of return shipments;
          4.   costs associated with obtaining, maintaining or enforcing Product
               related trademarks and logos;

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                                                                   EXHIBIT 10.24

          5.   costs for Phase IIIb, Phase IV and grant studies mutually agreed
               by the parties;
          6.   epidemiological modeling and pharmacoeconomic study costs; and
          7.   costs associated with effecting any Product recall (i.e.,
               communication, shipping and reimbursement costs).

     [*****]

1.   P&GP will [*****]. P&GP will discuss all matters related to [*****] with
     Alexion and provide Alexion an opportunity to comment thereon; provided
     that the final decisions on all such matters shall be made by Procter &
     Gamble in its sole discretion. Alexion will be notified of and invited to
     all meetings [*****]. Each party will bear its own internal costs, and P&GP
     will bear all P&GP outside costs and expense [*****], in connection with
     [*****]. Alexion has the right [*****]. If [*****], P&GP and Alexion
     [*****]. [*****] agrees to grant [*****] a sublicense [*****] necessary to
     carry out the Agreement. [*****] shall reimburse [*****] all amounts
     [*****], except that (i) subject to Clause 2 below, [*****] shall be
     responsible for [*****] in respect of [*****] in the United States, [*****]
     and (ii) [*****] shall be responsible [*****] in respect of [*****] outside
     the United States. [*****] will not be entitled to amend or otherwise
     modify [*****] without the prior, written consent of [*****].

2.   Notwithstanding Clause 1 above, [*****] shall be responsible for [*****] of
     United States [*****] under the [*****] until the difference between the
     amount payable under this Clause 2 and the amount otherwise payable under
     Clause 1 above exceeds the lesser of (i) [*****] in respect of United
     States [*****] and (ii) [*****]. Thereafter, this Clause 2 shall no longer
     apply.

3.   The [*****] in the United States and outside the United States will be
     identical under [*****], and all [*****] shall be apportioned [*****]
     between [*****] in the United States and [*****] outside the United States,
     respectively.

4.   All other [*****] (other than as set forth in [*****] of the Collaboration
     Agreement) related to [*****] in the United States shall be handled
     pursuant to Section [*****] of the

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                                                                   EXHIBIT 10.24

     Collaboration Agreement (i.e., [*****] will [*****]). All other [*****]
     (other than as set forth in [*****]) related to [*****] Product outside the
     United States shall be handled pursuant to Section [*****] of the
     Collaboration Agreement (i.e., [*****] will [*****]).

5.   [*****]

6.   Example. Following is an example of the operation of this [*****]
     provision:

          Assuming:

               [*****]

               [*****]

               [*****]

               [*****]

               [*****]

          Then:

               [*****]

               [*****]

               [*****]

               [*****]

     Sales Efforts. It is expected that each Party [*****] selling efforts in
     the U.S., including but not limited to, the efforts of liaisons and
     hospital representatives as mutually agreed. The Parties will each pay
     their own sales force and liaison costs (salaries, benefits, autos, bonuses
     or other incentive program costs, etc.). In the event [*****] selling
     effort would not be possible, the Party assigned more than [*****] will be
     reimbursed for the extra costs borne by that Party.

     One year before launch of the Product, the Parties will enter into a
     Marketing Services Agreement (MSA). The MSA will describe but not be
     limited to, terms on budgeting, forecasting, co-promotion services
     (including requirements for accounting for requisite Details or other calls
     on target prescribers, coordination of sales effort, compliance with laws
     and applicable authorities,

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                                                                   EXHIBIT 10.24

     etc.), sales penalties, penalties for under performance, responsibilities
     and procedures for Product returns and recalls.

ROYALTIES AND MILESTONES:

     U.S. Contribution: Alexion shall receive [*****]% of U.S. Contribution
     (Contribution is defined as Net Sales minus COGS ) on sales of pexelizumab
     in the United States. Sections 8.2(a), 8.2(b) and 8.2(c) of the original
     Agreement are eliminated.

     ROW Return: Alexion will receive [*****]% of ROW Net Sales.

     Milestones: All milestones in the Collaboration Agreement are eliminated
     and replaced by the following non-refundable, non-creditable one-time
     milestone payments. Each of these milestones is contingent upon P&GP not
     having terminated the Collaboration prior to achievement of the milestone
     event.
<TABLE>
<CAPTION>
  MILESTONE                                                                                       AMOUNT
  ---------                                                                                       ------
                                                                                             (U.S. $ Million)
  <S>                                                                                        <C>
  PRE-HEALTH REGISTRATION EVENTS

  At initiation of dosing of CABG Phase III clinical trial program
  which the Research & Development Steering Committee agreed would
  constitute a pivotal trial for approval of a Product for a CABG
  Indication                                                                                      [*****]

  At initiation of dosing of AMI Phase III clinical trial program
  which the Research & Development Steering Committee agreed would
  constitute a pivotal trial for approval of a Product for an AMI
  Indication                                                                                      [*****]
</TABLE>

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                                                                   EXHIBIT 10.24
<TABLE>
  <S>                                                                                             <C>
  U.S. HEALTH REGISTRATION EVENTS

  On FDA acceptance for filing of the first U.S. Health Registration of a Product for an
  AMI Indication                                                                                  [*****]

  On first U.S. Health Registration approval of a Product for a CABG Indication                   [*****]

  On first U.S. Health Registration approval of a Product for an AMI Indication                   [*****]

  FOREIGN HEALTH REGISTRATION EVENTS (European Union
  filing/approval means in any country of the European Union.)

  On first filing for European Union Health Registration of
  a Product for a CABG Indication                                                                 [*****]

  On first filing for European Union Health Registration of
  a Product for an AMI Indication                                                                 [*****]

  On first European Union Health Registration approval of a Product
  for a CABG Indication                                                                           [*****]

  On first European Union Health Registration approval of a Product
  for an AMI Indication                                                                           [*****]
</TABLE>

MISCELLANEOUS

     FTE Funding. The cost of each internal FTE will be calculated at $[*****],
     multiplied by the percentage of such employee's time devoted to the
     Collaboration. The R&D Steering Committee will determine FTE effort of each
     Party in respect of R&D, Health Registration and Supply issues.

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                                                                   EXHIBIT 10.24

     The Parties will mutually agree on all other FTE efforts, and the
     categories of employee chargeable to the Collaboration.

     Term: The term of the Collaboration Agreement will continue in each country
     of the world until pexelizumab is no longer sold in such country.

     Termination by P&GP: In addition to both Parties rights to terminate under
     the original Agreement, as amended hereby, P&GP has the right to exercise
     the Opt-Out option.

     Publicity: The Parties will jointly prepare and agree upon the public
     announcement of execution of this Memorandum and the Restatement.
     Thereafter, each Party agrees to publish or otherwise disclose the
     material, non-public results of the R&D Plan or of development studies or
     of the commercialization plan (a "Disclosure") only upon prior written
     approval of the other Party, not to be unreasonably withheld or delayed. In
     the event either Party is aware of an upcoming Disclosure, the Party will
     strive to provide the other Party [*****] advance notice of the Disclosure
     and its content. If specific wording is not available at a minimum the
     Party proposing the Disclosure will provide the other Party information on
     the general content and key messages proposed. The Parties agree whenever
     possible to provide press releases containing any Disclosure [*****] prior
     to proposed release. Notwithstanding the foregoing, this restriction does
     not prohibit a party from making Disclosures required by, or highly
     advisable under, law or government regulation (as determined by opinion of
     counsel of the party proposing such Disclosure). If a Party decides, upon
     the advice of counsel that a Disclosure is required or highly advisable,
     the Party will, insofar as is reasonably practical, notify the other Party
     of the decision and provide the other Party an advance copy for review and
     comment.

     Indemnification: Section 12.1 (b), "Indemnification for Marketing", in the
     Collaboration Agreement remains in full force. Notwithstanding the above,
     P&GP will not indemnify and hold harmless Alexion from and against any
     losses to the extent due to Alexion's gross negligence or willful or
     intentional misconduct. In the event that the Collaboration is terminated,
     Alexion agrees to provide an indemnification to P&GP in respect of Product
     commercialized by Alexion after termination, consistent with
     "Indemnification for Marketing" Section 12.1(b) in the Collaboration
     Agreement.

                                       14

<PAGE>
                                                                   EXHIBIT 10.24
CHANGE IN CONTROL

     1.   Change in Control. Except as set forth in this provision ("Change in
          Control"), neither Party's consent is necessary to a Change in Control
          of the other Party, and the Collaboration Agreement shall be binding
          upon and inure to the benefit of either Party's successors in interest
          following any such Change in Control transaction. Section 13.7(a), (b)
          13.9 (c) of the Collaboration Agreement are deleted.

     2.   Notice. At any time during the Term, either P&GP or Alexion (the
          "Acquired Party") may notify (the "Notice") the other Party (the
          "Continuing Party") that it is contemplating a Change of Control
          transaction with a Third Party Company. All information provided in
          the Notice and otherwise provided in connection with the proposed
          Change of Control shall be maintained by the Continuing Party in the
          strictest confidence, including the fact that a Change of Control has
          been discussed and the name of the relevant Third Party Company, and
          the Continuing Party will restrict knowledge of such matters only to
          those of its employees who have a need to know the same.

     3.   Valuation Election. Within [*****] following receipt of the Notice,
          the Continuing Party may elect in writing (the "Election") delivered
          to the Acquired Party to cause a valuation to be made of the Acquired
          Company's entire interest in the Collaboration Agreement (the
          "Acquired Company's Agreement Interest") and the Continuing Company's
          entire interest in the Collaboration (the "Continuing Company's
          Agreement Interest", and together with the Acquired Company's
          Agreement Interest, the "Agreement Interest(s)"). Failure of the
          Continuing Party to provide such notice shall constitute waiver of its
          rights under this provision ("Change in Control"), and consent for the
          Change in Control to occur.

     4.   Valuation Process. Within [*****] of receipt of the Election, the
          Acquired Party and the Continuing Party shall each retain an
          internationally recognized investment banking firm to determine the
          value of the Agreement Interests (the "Prices"). If either Party fails
          to deliver notice to the other Party of its selection of an investment
          banking firm within such period, the Price determinations shall be
          rendered by the single investment banking firm so selected. If the

                                       15

<PAGE>
                                                                   EXHIBIT 10.24

          Continuing Party has elected to cause the valuation to be made, it
          shall pay all fees and expenses of the investment bank(s). The
          investment banking firms selected in accordance with the foregoing
          procedure shall each determine the values of the Agreement Interests
          and submit their determinations of such values to the Parties within
          seven days following their selection. The values of Alexion's
          Agreement Interest and P&GP's Agreement Interest will be determined as
          set forth in Clause 9 below. The Price of each Party's Agreement
          Interest shall be the sum of the relevant values determined by each
          firm therefor, divided by two; provided, however, that if there is
          more than a [*****] percent ([*****]%) difference between the two such
          values for either or both such Agreement Interests, then within
          [*****] of when they have determined such values, the first two firms
          shall select a third internationally recognized investment banking
          firm to determine the Price of the Agreement Interest(s) that diverged
          more than [*****] (which shall be determined by such firm [*****] of
          selection, and in no event be outside the range determined by the
          first two investment banking firms).

     5.   Put/Call Election. Within [*****] ([*****]) [*****] following
          determination of the Price, the Continuing Party will irrevocably
          elect to (i) allow the Change in Control to occur, (ii) require the
          Third Party Company to purchase the Continuing Party's Agreement
          Interest at the relevant price, (iii) purchase the Acquired Party's
          Agreement Interest at the relevant price.

     6.   Purchase Consummation. Any purchase and sale of an Agreement Interest
          effected pursuant to this provision ("Change in Control") shall be
          consummated at a closing at the offices of the Continuing Party on a
          business day within [*****] following the determination of the
          relevant Price upon at least [*****] notice by the Third Party Company
          to the other parties to the transaction; or the earliest time
          thereafter following receipt of necessary governmental or regulatory
          approvals with respect to such transaction and the Change in Control
          transaction contemplated by Clause 2 above. At such closing, the Third
          Party Company (or its designee) or the Continuing Party (or its
          designee), as the case may be, shall pay the relevant Price by
          certified check or wire transfer of funds. In no event will such
          purchase and sale of an Agreement Interest occur unless and until the
          Third Party Company identified under Clause 2 above consummates the
          Change in Control transaction with the Acquired Company contemplated
          by the Notice.

                                       16

<PAGE>
                                                                   EXHIBIT 10.24

     7.   Purchase Documentation. Upon the closing of the transactions
          contemplated by Clause 6 above, the Parties and the Third Party
          Company shall execute such customary instruments of transfer, licenses
          and other agreements as are necessary to transfer all of the relevant
          Agreement Interest to assure that the party acquiring such interest
          shall be able to enjoy the benefits thereof. The Party whose Agreement
          Interest is acquired shall license or sublicense all of its
          intellectual property necessary for the manufacture, use or sale of
          Products in the Field, and the party acquiring such Agreement Interest
          shall assume all obligations, including payment obligations, to any
          Third Party from whom the party whose Agreement Interest is acquired
          licenses such intellectual property. All other necessary agreements
          (e.g., supply) will also be transferred; or if not transferable, the
          benefits thereof will otherwise be provided.

     8.   Third Party Company. "Third Party Company" shall mean, in the case of
          P&GP, the five companies listed by it on Schedule III (together with
          their majority owned, direct or indirect subsidiaries), and in the
          case of Alexion, the five companies listed by it on Schedule III
          (together with their majority owned, direct or indirect subsidiaries).
          Each Party shall supply its initial list to the other following
          execution and delivery of this Memorandum. Either Party may revise its
          list by written notice to the other delivered within [*****] on or
          after [*****] and [*****] during the Term. Within [*****] on or after
          [*****] and [*****] during the Term, Alexion agrees to provide P&GP a
          written reminder of P&GP's rights under this Section. Neither Party
          shall have the right to amend its list of 5 companies after the
          Acquired Party publicly announces, or confidentially notifies the
          Continuing Party, that it proposes a Change of Control transaction
          with a company that is not on the list.

     9.   Agreement Interests. The retained investment banks shall be instructed
          to value P&GP's Agreement Interest at the amount that, on the basis of
          market and other conditions prevailing at such time could reasonably
          be expected to be paid by a third party in an arm's-length transaction
          for [*****]. The retained investment banks shall be instructed to
          value Alexion's Agreement Interest at the amount that, on the basis of
          market and other conditions prevailing at such time is the difference
          between what could reasonably be expected to be paid by a third party
          in (i) an arm's-length transaction for [*****].

                                       17

<PAGE>
                                                                   EXHIBIT 10.24

     10.  Closing Condition. Consummation of any Change In Control transaction
          will require that the Third Party Company agree to be bound by the
          terms of this provision ("Change in Control").

SUBSTANTIAL STOCK ACCUMULATION: Section 13.8 of the Collaboration Agreement
          applies only to accumulation in the equity of one Party hereto by a
          Third Party Company listed by the other Party hereto. Further, Section
          13.8 has no force or effect in regard to a Third Party following a
          Change of Control involving such Third Party.

EXECUTIONOF THIS MEMORANDUM OF UNDERSTANDING: Upon execution, the terms of this
          Memorandum will be in full force and effect. The Parties agree to
          diligently negotiate the terms of the Restatement. Prior to the
          Restatement being executed, in the event an issue is not addressed in
          this Memorandum but is in the Collaboration Agreement, the Parties
          will operate under the Collaboration Agreement on the issue. Prior to
          the Restatement being executed, the Parties agree Section 13.2 of the
          Collaboration Agreement, "Termination", remains in full force;
          provided, however, Section 13.2(a) of the Collaboration Agreement is
          deleted, and replaced by the following:"Procter & Gamble may terminate
          the Agreement upon six (6) months prior written notice to Alexion."

                                       18

<PAGE>
                                                                   EXHIBIT 10.24

IN WITNESS WHEREOF, the Parties have signed this Memorandum as of
December 11, 2001.

ALEXION PHARMACEUTICALS, INC.

By: /s/ David W. Keiser
    ------------------------------------
   Name:
   Title:

PROCTER & GAMBLE PHARMACEUTICALS, INC.

By: /s/ Mark A. Collar
    ------------------------------------
   Name:
   Title:

                                       19

<PAGE>
                                                                   EXHIBIT 10.24

                                   SCHEDULE 1

Executional Responsibilities:  Clinical Programs
<TABLE>
<CAPTION>
-------------------------------------------------------------------------------------------------------------
                                           CABG Phase III Program               AMI Phase III Program
                                           ----------------------               ---------------------
                                           ------------------------------------------------------------------
                Task                       R                    I                R                I
                                           -
-------------------------------------------------------------------------------------------------------------
<S>                                        <C>              <C>             <C>               <C>
           Project Leadership*               Shared           Shared           Shared           Shared
-------------------------------------------------------------------------------------------------------------
Program Physician-Global/NA                [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
           Program Physician-              [*****]          [*****]         [*****]           [*****]
               Europe/ROW
-------------------------------------------------------------------------------------------------------------
  CRO/Vendor Contracts, Bids and Scope     [*****]          [*****]         [*****]           [*****]
                 Changes
-------------------------------------------------------------------------------------------------------------
       Site Contracts and Budgets          [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
Statistics and Biometrics including DSMB   [*****]          [*****]         [*****]           [*****]
                data flow
-------------------------------------------------------------------------------------------------------------
               Clinops-NA                  [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
           CRO Interaction-NA              [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
  Vendor (e.g., Core Labs) Interaction     [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------------------
           Site Interaction-NA             [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
           Clinops-Europe/ROW              [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
   CRO/Vendor Interaction- Europe/ROW      [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
      Site Interaction- Europe/ROW         [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
            Clinical Supplies              [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
               Clinical QA                 [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------

-------------------------------------------------------------------------------------------------------------
        Pharmacovigilance NA ***           [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
</TABLE>

                                       20

<PAGE>
                                                                   EXHIBIT 10.24
<TABLE>
 <S>                                       <C>              <C>             <C>               <C>
------------------------------------------------------------------------------------------------------------
          Pharmacovigilance EU             [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
                PK and PD                  [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
            Pharmacoeconomics              [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
             Regulatory U.S.               [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
               Regulatory                  [*****]          [*****]         [*****]           [*****]
                   ROW
-------------------------------------------------------------------------------------------------------------
        Clinical Data Management           [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
             Medical Writing               [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
 Global Marketing Application Prep/Mgmt    [*****]          [*****]         [*****]           [*****]
-------------------------------------------------------------------------------------------------------------
</TABLE>

Abbreviations:  R = Responsibility; I = Input; P = P&GP: A = Alexion
*     Each company will appoint a project leader.
**    [*****] to have ability to set up initial site budget and contract in
      select cases
***   [*****] will have global responsibility for collecting and analyzing
      adverse events and will own the database. Sponsor will be responsible for
      filing the information with all regulatory authorities.

                                       21

<PAGE>
                                                                   EXHIBIT 10.24

                                   SCHEDULE II

                                     [*****]

This document provides some expectations for involvement of the partner company
in FDA interactions (Alexion for BB IND 8651 [AMI] and P&GP for BB IND 6592
[CPB]). These expectations apply to all aspects of the project, including CMC.

The primary expectation is that the partner should be involved in all FDA
interactions where strategic and executional issues are discussed, unless both
partners have agreed in advance that it is not necessary.

Both partners should be involved in all scheduled FDA interactions, unless there
is an agreement in advance. When possible, the Regulatory Affairs Managers in
both companies should discuss and anticipate FDA interactions and reach
agreements about the need for involvement in advance of the FDA interaction. In
the event of an unscheduled FDA interaction, both partners agree to use best
efforts to involve the other partner. Unscheduled FDA interactions with a
Sponsor company should be communicated immediately to the non-Sponsor company.
Strategic decisions should not be made with FDA unless both companies are
present in the conversation, or an agreement to make such decisions has been
made by both companies in advance.

Partner involvement is not expected for administrative FDA interactions which
include discussions about scheduling of interactions, response to FDA requests
for additional copies of IND submissions, response to FDA requests for updates
on status of DSMB review, etc.

Nearly all FDA interactions should be easily managed in one of these ways. It is
recognized that in rare instances an "informal" interaction may occur where
FDA's willingness to share perspective could be hampered by a delay or by the
presence of additional participants in the interaction. In those rare instances
it is expected that the partner company will be contacted immediately following
the interaction and fully informed in writing as to the content of the
discussion. Strategic decisions should not be made with FDA unless both
companies are present in the conversation or an agreement to make such decisions
has been made by both companies in advance. It is also expected that every
effort will be made to keep

                                       22

<PAGE>
                                                                   EXHIBIT 10.24

those advantageous informal discussions separate from the formal interactions
where partner presence is desired.

Each Party maintains the right to directly contact FDA, other regulatory
agencies, or other clinically responsible third parties (e.g., investigators,
IRBs, ) on any urgent safety or other medically significant concerns; provided,
however, that a non-Sponsor Party must first provide the Sponsor all information
regarding such concern and allow the Sponsor to be the Party that contacts the
FDA or such other agencies or third parties. If the Sponsor does not address the
non-Sponsor's concerns, and the non-Sponsor deems there is a regulatory or legal
requirement for reporting, the non-Sponsor reserves the right to directly
contact FDA, other regulatory agencies or other clinically responsible third
parties on the urgent safety or other medically significant concern. Prior to
making any third party contact the non-Sponsor will inform the Sponsor of its
decision.

                                       23

<PAGE>
                                                                   EXHIBIT 10.24

                                  SCHEDULE III

                    CHANGE IN CONTROL - THIRD PARTY COMPANIES

-------------------------------------------------------------------------------
Companies selected by Alexion:                Companies selected by P&GP:
-------------------------------------------------------------------------------
1.[*****]                                     1. [*****]
-------------------------------------------------------------------------------
2.[*****]                                     2. [*****]
-------------------------------------------------------------------------------
3.[*****]                                     3. [*****]
-------------------------------------------------------------------------------
4.[*****]                                     4. [*****]
-------------------------------------------------------------------------------
5.[*****]                                     5. [*****]
-------------------------------------------------------------------------------

[Each party to provide the other its list following execution and delivery of
this Memorandum]

                                       24<PAGE>
                                                                   Exhibit 10.44

                           PURCHASE AND SALE AGREEMENT

     THIS PURCHASE AND SALE AGREEMENT ("Agreement") is made as of________, 2002,
by and between 400 RIVER LIMITED PARTNERSHIP, a Massachusetts limited
partnership ("Seller"), and NAVISITE, INC., a Delaware corporation ("Buyer").

     In consideration of the mutual covenants and provisions herein contained
and other good and valuable consideration, the receipt and sufficiency of which
are hereby acknowledged, Seller and Buyer hereby agree as follows:

     1.   Agreement to Buy and to Sell.

          Subject to the terms and conditions in this Agreement, Seller agrees
to sell, assign, convey, and transfer to Buyer, and Buyer agrees to purchase,
all of Seller's right, title and interest in and to the land located in Andover,
Massachusetts, commonly known as 400 Minuteman Road, more particularly described
in Exhibit A hereto, all improvements on that land, and all fixtures affixed to
the land or the improvements, and all easements appurtenant to that land
(collectively, the "Premises"). The Premises are part of a larger development
commonly known as Minuteman Park.

     2.   Purchase Price. The purchase price (the "Purchase Price") to be paid
by Buyer to Seller for the Premises is Sixteen Million Three Hundred Fifty-six
Thousand Nine Hundred One Dollars ($16,356,901). The Premises is encumbered by
an existing Mortgage securing a loan (the "Loan") made by General American Life
Insurance Company ("Lender") to Seller. Buyer will purchase the Premises subject
to this Mortgage, and at the closing will receive a credit against the Purchase
Price equal to Ten Million Eight Hundred Fifty-six Thousand Nine Hundred One
Dollars ($10,856,901) on account of this Mortgage. The balance of the Purchase
Price, plus any other amounts that Buyer is required to pay pursuant to this
Agreement, will be paid by Buyer in sufficient time to permit the closing on the
closing date by federal wire transfer of immediately available U.S. funds to an
account of Chicago Title Insurance Company, Boston, Massachusetts (Sharon
Sbordan, Closing Officer), which will act as closing agent hereunder (the
"Closing Agent"), and hold those funds for payment to Seller on the closing.

     3.   Seller's Representations and Warranties. Seller represents and
warrants to Buyer that:

          (a)  Seller is: (i) in good standing and validly existing as a
Massachusetts Limited Partnership, qualified to do business in the Commonwealth
of Massachusetts, and (ii) has the power and authority to do all things required
of it by the terms of this Agreement.

          (b)  All internal approvals of Seller required for the execution of
this Agreement and the consummation of the transaction herein contemplated in
accordance with the terms of this Agreement have been obtained.

          (c)  This Agreement has been duly and validly executed and delivered
on behalf of Seller.

          (d)  This Agreement and each and every document and instrument to be
executed and delivered by Seller pursuant to this Agreement, when fully executed
and delivered, shall constitute the valid and binding obligations of Seller,
enforceable against Seller in accordance with their respective terms.

          (e)  It has not engaged any brokers, agents, finders or similar
parties in connection with this transaction who are due any commissions or
similar fees from Buyer.

          (f)  Seller is not a foreign person within the meaning of Section
1445(f)(3) of the Internal Revenue Code of 1986, as amended.

          (g)  To the best of Seller's knowledge (deemed to mean the actual
knowledge of Martin Spagat or John Kusmiersky, and not any imputed knowledge),
Seller has not received any written notice of any uncured violations of
applicable zoning or building codes or similar laws or environmental laws in
connection with the Premises (this representation and warranty does not extend
to any violations to the extent arising from the acts or omissions of Buyer or
its affiliates).

<PAGE>

     4.   Buyer's Representations and Warranties. Buyer represents and warrants
to Seller that:

          (a)  Buyer is: (i) in good standing and validly existing as a Delaware
corporation, qualified to do business in the Commonwealth of Massachusetts, and
(ii) has the power and authority to do all things required of it by the terms of
this Agreement.

          (b)  All internal approvals of Buyer required for the execution of
this Agreement and the consummation of the transaction herein contemplated in
accordance with the terms of this Agreement have been obtained.

          (c)  Buyer's federal tax identification number is___________. This
purchase and sale is undertaken at Buyer's request, is not a preference, and it
will not render Buyer insolvent or unable to pay its debts as they become due,
and the Purchase Price represents fair market value for the Premises.

          (d)  This Agreement has been duly and validly executed and delivered
on behalf of Buyer.

          (e)  This Agreement and each and every document and instrument to be
executed and delivered by Buyer pursuant to this Agreement, when fully executed
and delivered, shall constitute the valid and binding obligations of Buyer,
enforceable against Buyer in accordance with their respective terms.

          (f)  It has not engaged any brokers, agents, finders or similar
parties in connection with this transaction who are due any commissions or
similar fees from Seller.

     5.   Closing. Subject to the terms of this Agreement, the closing of this
transaction, including the delivery and recording of the Deed and the payment of
the Purchase Price by Buyer to Seller, will occur at the offices of the Closing
Agent in Boston, Massachusetts, on the date set forth for closing in that
certain Undertakings Agreement among Seller, ClearBlue Technologies, Inc. and
Farm Associates Limited Partnership (the "Undertakings Agreement"), or such
later date, if any, as they all may agree to in writing. Time is of the essence
of this Agreement.

     6.   Conditions to Closing.

          (a)  Seller's obligations to convey the Premises to Buyer and close
this transaction are subject to the satisfaction of the following conditions as
of the closing date in addition to any other conditions to Seller's obligations
specifically set forth in this Agreement or the Undertakings Agreement
(including, without limitation, the receipt of the "Lender Release or Agreement"
as defined in Section 4 thereof): Buyer's representations and warranties remain
true and correct in all material respects, and Buyer pays the Purchase Price in
full and materially performs all of its obligations under this Agreement to be
performed at or before the closing.

          (b)  Buyer's obligations to purchase the Premises from Seller, pay the
Purchase Price and close this transaction are subject to the satisfaction of the
following conditions as of the closing date in addition to any other conditions
to Buyer's obligations specifically set forth in this Agreement or the
Undertakings Agreement (including, without limitation, the receipt of the
"Lender Release or Agreement" as defined in Section 4 thereof): Seller's
representations and warranties remain true and correct in all material respects,
and Seller materially performs all of its obligations under this Agreement to be
performed at or before the closing.

     7.   Closing Obligations.

          (a)  On or before the closing, Seller will execute and deliver to
Buyer:

               (i)   A standard Massachusetts Quitclaim Deed conveying the
Premises to Buyer.

               (ii)  A certificate of non-foreign status.

               (iii) Such other documents as the Closing Agent may reasonably
require in order to close this transaction, provided that they are not
inconsistent with this Agreement.

          (b)  On or before the closing, Buyer will pay and deposit with the
Closing Agent the Purchase Price, less the credit described in Section 2, plus
any other amounts payable by Buyer hereunder, and execute and deliver such
documents as the Closing Agent may reasonably require in order to close this
transaction, provided that they are not inconsistent with this Agreement.

          (c)  Before the closing, the parties will jointly execute and deliver:

                                       2

<PAGE>

               (i)   Counterparts of a closing statement for this transaction,
and any escrow or closing instructions required by the Closing Agent.

               (ii)  Counterparts of the Lease Termination Agreement terminating
the existing Lease between Seller, as Landlord, and Buyer, as Tenant, under a
Lease, dated as of 5/14/1999 (as amended, the "Lease").

               (iii) Such other documents as the Closing Agent may reasonably
require in order to close this transaction, provided that they are not
inconsistent with this Agreement.

          (d)  Notwithstanding anything to the contrary, Seller will not be
required to execute or deliver any documents related to title insurance for the
Premises.

     8.   Apportionments; Closing Costs. There will be no prorations under this
Agreement. Buyer and Seller each will pay the fees of its respective counsel.
Buyer and Seller will equally share the costs for: deed stamps and other
transfer taxes or fees; recording charges; and fees of the Closing Agent. The
provisions of this Section 8 will survive the Closing.

     9.   "As Is;" Release.

          (a)  Except for the representations and warranties of Seller
specifically set forth in this Agreement, Buyer acknowledges that Seller is
selling, and Buyer will accept, the Premises in its "AS IS" condition, with "ALL
FAULTS" and subject to the Mortgage and all other matters of record and
exceptions to title, as of the date of closing, without any warranty or
representation by Seller, its employees, directors, officers, agents,
consultants, representatives, partners or affiliates, subsequent owners of the
Premises, anyone acting on their behalf, or their respective successors and
assigns (including Seller, collectively, "Seller's Affiliates"), whether
relating to the Premises or this transaction or otherwise. Buyer has been a
long-term tenant in and has had the opportunity to fully investigate the
Premises, and agrees that it is not relying on any information or documents
received from or made available by or on behalf of Seller's Affiliates.
Furthermore, Buyer agrees that except for the representations and warranties of
Seller specifically set forth in this Agreement, Seller's Affiliates have not
made and Buyer is not relying on any representation, warranty, inducement or
statement (including, without limitation, those regarding the accuracy or
completeness of any information or documents furnished, or the physical or
environmental condition of the Premises, or violations of laws, or other
matters).

          (b)  As of the closing, Buyer and its employees, shareholders,
directors, officers, agents, consultants, representatives, partners, affiliates,
successors and assigns (including Buyer, collectively, "Buyer's Affiliates"),
for good and valuable consideration, irrevocably agree to release, discharge,
and waive as against Seller's Affiliates all of the following (collectively, the
"Released Liabilities"): all claims, liabilities, obligations, costs, losses,
damages, penalties, judgements, actions, and causes of action of any type
(including, without limitation, attorneys' fees and costs), direct or indirect,
known or unknown, foreseen or unforeseen, including, without limitation, those
in connection with the Premises (including, without limitation, the physical and
environmental conditions thereof), the Lease, and this transaction. Buyer's
Affiliates will not commence, aid in any way, or prosecute against any of
Seller's Affiliates any claim involving or based on any of the Released
Liabilities. The provisions in this Article 9 extend to Released Liabilities
which the releasing parties may not know or suspect to exist in their favor at
the time these provisions are agreed to or at a later date, which if known to
them would materially affect their willingness to agree. The provisions of this
Article 9 will survive the closing or termination of this Agreement.

     10.  Default. A party will be in default hereunder if it materially
breaches its obligations hereunder and fails to cure within two (2) business
days after written notice from the other party, or if any of its representations
or warranties in this Agreement are materially untrue or incorrect when made or
as of the closing. Seller will indemnify, defend and hold harmless Buyer's
Affiliates from all claims, liabilities, obligations, costs, losses, damages,
penalties, judgements, actions, and causes of action of any type (including,
without limitation, attorneys' fees and costs) in connection with Seller's
breach of its representations, warranties and indemnities in this Agreement and
its obligations in this Agreement, if any, that survive the closing or the
termination of this Agreement. Buyer will indemnify, defend and hold harmless
Seller's Affiliates from all claims, liabilities, obligations, costs, losses,
damages, penalties, judgements, actions, and causes of action of any type
(including, without limitation, attorneys' fees and costs) in connection with
Buyer's breach of its representations, warranties and indemnities in this
Agreement, its obligations in the Lease that survive the expiration or
termination of the Lease, and its obligations in this Agreement, if any, that
survive the closing or the termination of this Agreement.

     11.  Notices. All notices under this Agreement will be in writing and will
be deemed to have been properly given if and when delivered in person, or on
delivery or attempted delivery (if delivery is refused) by a
nationally-recognized overnight courier, addressed to each party at the
addresses set forth below. Either party may change its addresses by written
notice as set forth above.

                                       3

<PAGE>

                                    If to Seller:

                                    400 River Limited Partnership
                                    c/o Brickstone Properties
                                    200 Brickstone Square
                                    Andover, Massachusetts 01810
                                    Attn: Martin Spagat

                                            -and-

                                    The Brickstone Companies
                                    The Plaza at Continental Park
                                    2101 Rosecrans Avenue
                                    Suite 5252
                                    El Segundo, CA 90245
                                    Attention: David A. Miller

                                    If to Buyer:

                                    NaviSite, Inc.
                                    400 Minuteman Road
                                    Andover, Massachusetts 01810

         12.      Miscellaneous Provisions.

                  (a) This Agreement is an integrated agreement and, except for
the agreements contemplated herein and the escrow instructions to accomplish
this agreement (including the Undertakings Agreement), it contains the entire
understanding between the parties with respect to the transaction contemplated
herein, and all prior agreements, understandings, representations and
statements, oral or written are merged into this Agreement. The delivery of the
deed by Seller will be deemed the full performance and discharge of every
obligation on the part of Seller to be performed hereunder, except for any
obligations of Seller which are expressly provided herein to survive the
closing. No provision of this Agreement may be waived except by an instrument
signed by the party against whom the enforcement of such waiver is sought. All
modifications (including any extensions) of this Agreement will be effective
only if signed by Seller and Buyer.

                  (b) This Agreement will be governed by, and construed in
accordance with, the local, internal laws of the Commonwealth of Massachusetts
applicable to agreements to be wholly performed therein, without regard to
conflicts of laws.

                  (c) This Agreement will be binding on and will inure to the
benefit of the parties hereto and their respective successors and assigns,
provided, however, that Buyer will not have the right or power to assign or
transfer this Agreement. This Agreement and its terms are for the sole benefit
of the parties hereto (including, without limitation, the released Seller's
Affiliates) and their permitted successors and assigns, if any, and no other
person or entity will have any right of action hereon or right to claim any
right or benefit from this Agreement or its terms or be deemed a third party
beneficiary hereunder. Except for the representations and warranties
specifically set forth in this Agreement, there are no representations and
warranties, express or implied, that are being made or relied on by the parties
hereto. All representations, warranties and indemnities hereunder will survive
the closing of this Agreement.

                  (d) Notwithstanding anything to the contrary in the Lease or
elsewhere, and without diminishing any amounts payable for the Purchase Price,
as of and after the closing Buyer, as Tenant under the Lease and in all other
capacities (and this Subsection 12(d) will be deemed to be an amendment of the
Lease if and to the extent necessary), and on its own behalf and on behalf of
Buyer's Affiliates, irrevocably will be deemed to have released and waived all
of its rights and any rights of Buyer's Affiliates in connection with the $2.5
Million "Additional Security" (as defined in the Lease), which may continue to
be used as collateral for the Loan and/or for Landlord's or the Lender's
conversion of all or part of the data center portion of the Building to office
space (because Buyer's use is so specialized) and/or for other Landlord or
Lender tenant improvements or otherwise. Buyer will promptly execute and deliver
(or cause to be executed and delivered) such other documents as Landlord or the
Lender reasonably require in order to evidence the terms of this Subsection
12(d). Buyer's release, waiver and covenants in this Section 12(d) will survive
the closing, and collectively are referred to as the "Additional Collateral
Obligations."

                  (e) The section titles or captions in this Agreement are for
convenience only and will not be deemed to be part of this Agreement for
purposes of interpreting, construing or enforcing any of the provisions of this
Agreement. All pronouns and any variations of pronouns will be deemed to refer
to the masculine, feminine, or neuter, singular or plural, as the identity of
the parties may require. Whenever the terms referred to herein are singular, the

                                        4

<PAGE>

same will be deemed to mean the plural, as the context indicates, and vice
versa. This Agreement will not be construed as if it had been prepared only by
Buyer or Seller but rather as if both Buyer and Seller had prepared and
negotiated it. This Agreement is severable, and if any term, covenant,
condition, or provision of this Agreement or the application thereof to any
person or circumstance will, at any time or to any extent, be invalid or
unenforceable, the remainder of this Agreement, or the application of such term
or provision to persons or circumstances other than those to which it is held
invalid or unenforceable, will not be affected thereby, and each term or
provision of this Agreement will be valid and will be enforced to the fullest
extent permitted by law.

                  (f) If the time period by which any right, option or election
provided under this Agreement must be exercised, or by which any act required
hereunder must be performed, or by which the closing must be held, expires on a
day which is a Saturday, Sunday, or official federal or Commonwealth of
Massachusetts holiday, then such time period will be automatically extended
through the close of business on the next business day.

                  (g) No Seller's Affiliate (other than Seller itself) will have
any personal liability hereunder, nor will any of them be named personally in
any suit, claim, action or proceeding concerning any matters hereunder nor will
any of their assets be attached, liened or levied or in any other way become
liable for any of the obligations of Seller hereunder, nor will either party
attempt to "pierce the corporate veil" of any of Seller's Affiliates or any of
Buyer's Affiliates.

                  (h) This agreement may be executed in two (2) or more
counterparts, each of which will be deemed to be an original, but all of which
taken together will constitute one and the same Agreement. All of the Exhibits
referenced in this Agreement will be deemed incorporated into this Agreement.

                  (i) If there is any dispute relating to this Agreement or a
breach hereunder, the prevailing party will be entitled to payment for all costs
and attorneys' fees (both trial and appellate) incurred in connection therewith.
All suits, actions, claims and proceedings will be filed, commenced and
prosecuted solely in the state or federal courts in Boston, Massachusetts, which
will have sole and exclusive jurisdiction and venue. The provisions in this
Subsection (i) will survive the closing or termination of this Agreement.

         In witness whereof, intending to be legally bound, the parties have
executed this Agreement under seal as of the date first set forth above.

SELLER:       400 RIVER LIMITED PARTNERSHIP, a Massachusetts limited partnership

              By:      Niuna-400 River, Inc., general partner

                       By:

                                Name:
                                Title:
                                Authorized Signature

BUYER:        NAVISITE, INC., a Delaware corporation

              By:

                       Name:
                       Title:
                       Authorized Signature

              By:

                       Name:
                       Title:
                       Authorized Signature

                                        5

<PAGE>

                                    EXHIBIT A

                               Description of Land

                                Ehibit A - Page 1

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