Document:

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                                                                 EXHIBIT 10.28

                            FIRST AMENDMENT TO LEASE

         THE FIRST AMENDMENT TO LEASE (this "FIRST AMENDMENT") is made as of the
17th day of November, 1998, by and between BIOLEASE, INC., a Massachusetts
corporation ("Landlord") and BIOTRANSPLANT INCORPORATED, a Delaware corporation
"TENANT").

         WHEREAS, Landlord and Tenant have entered into that certain Lease dated
March 17, 1994 (the "LEASE"), with respect to that building in the so-called
Charlestown Navy Yard section of the City of Boston known as Building 75 (the
"BUILDING") located at Third Avenue; and

         WHEREAS, Landlord and Tenant now desire to amend the Lease as
hereinafter provided;

         NOW, THEREFORE, in consideration of the foregoing and the mutual
covenants contained herein and other good and valuable consideration, the
receipt and sufficiency of which is hereby acknowledged, Landlord and Tenant
hereby agree as follows:

         1.  SECTION 1.1 of the Lease is hereby amended as follows:

         (a) The definition of "Original Term" is hereby deleted in its entirety
and the following inserted in its place:

             Original
             Term: Commencing on October 5, 1994 (the "COMMENCEMENT DATE") and
                   expiring as of October 31, 2009.

         (b) The definition of "Annual Fixed Rent" is hereby deleted in its
entirety and the following inserted in its place:

                  Annual
                  Fixed
                  Rent:    (i) For the period commencing on the Commencement
                           Date and ending on the day preceding the date hereof,
                           One Million Thirteen Thousand Four Hundred
                           Sixty-Three and 96/100 Dollars ($1,013,463.96) per
                           annum, Eighty Four Thousand Four Hundred Fifty-Five
                           and 33/100 Dollars ($84,455.33) per month;

                           (ii) For the period commencing on the date hereof and
                           ending on the date preceding the fifth anniversary of
                           the Commencement Date, One Million Twenty Thousand
                           and 00/100 Dollars ($1,020,000.00) per annum, Eighty
                           Five Thousand and 00/100 Dollars ($85,000.00) per
                           month.

                           (iii) For the period commencing on the fifth
                           anniversary of the Commencement Date and ending on
                           October 31, 2009, One Million Twenty-Five Thousand
                           and 00/100 Dollars ($1,025,000.00) per annum,

                                      -1-

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                           Eighty Five Thousand Four Hundred Sixteen and 67/100
                           Dollars ($85,416.67) per month.

         2. SECTION 2.1 of the Lease is hereby amended by adding the following
sentence at the end of the first paragraph thereof:

                           Landlord and Tenant agree that the Building shall be
                           deemed to contain 29,000 square feet of rentable area
                           from and after [_______ __, 1998 [the date hereof]].

         3. SECTION 2.3 of the Lease is hereby amended by deleting the first
paragraph therein and replacing it with the following paragraph:

                           2.3 EXTENSION OPTION. So long as there exists no
                           Default of Tenant, this Lease is still in full force
                           and effect, and Tenant shall not have sublet,
                           assigned or otherwise transferred all or any portion
                           of its interest under this Lease (other than to
                           Affiliates), Tenant shall have the right to extend
                           the term of this Lease for one (1) additional period
                           (the "EXTENDED TERM") of five (5) years. The Extended
                           Term shall commence on the day succeeding the
                           expiration of the Original Term and shall end on the
                           day immediately preceding the fifth anniversary of
                           the commencement of the Extended Term. All of our
                           terms, covenants and provisions of this Lease shall
                           apply to each such Extended Term except that (i) the
                           Annual Fixed Rent for the Extended Term shall be the
                           Market Rate (as hereinafter defined) for the Property
                           determined as of the commencement of the Extended
                           Term, as designated by Landlord by notice to Tenant
                           ("LANDLORD'S NOTICE"), but subject to Tenant's right
                           to dispute as hereinafter provided; and (ii) Tenant
                           shall have no further right to extend the term of
                           this Lease beyond the Extended Term hereinabove
                           provided. If Tenant fails to give any such notice to
                           Landlord, this Lease shall automatically terminate at
                           the end of the Original Term then in effect, and
                           Tenant shall have no further option to extend the
                           term of this Lease, it being agreed that time is of
                           the essence with respect to the giving of any such
                           notice. If Tenant gives such notice, the extension of
                           this Lease shall be automatically effected without
                           the execution of any additional documents, subject to
                           Tenant's right to cancel such election as hereinafter
                           provided.

  SECTION 2.3 of the Lease is further amended by (i) deleting "applicable" from
  the second line of the second paragraph therein, (ii) deleting "applicable"
  from the third and fourth lines of the sixth paragraph therein, (iii) deleting
  "or the Extended Term (as applicable)" from the eighth and ninth lines of the
  sixth paragraph therein, (iv) deleting "either of its options" from the second
  line of the seventh paragraph therein and replacing it with "the option", (v)
  deleting "or the preceding Extended Term (as applicable") from the fourth and
  fifth lines of the first sub-paragraph on page 8 of the Lease, (vi) deleting
  "applicable" from the sixth line of the first sub-paragraph on page 8 of the
  Lease, (vii) deleting "or the Extended Term" from the fourth line of

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  the second sub-paragraph on Page 8 of the Lease, and (viii) deleting
  "applicable" from the eight line of the eighth paragraph therein.

         4. ARTICLE 4 is hereby amended by adding the following Section 4.2.7
thereto:

                           4.2.7 GROUND LESSOR PAYMENTS. Landlord and Tenant
                           agree that Tenant shall pay, as Additional Rent, any
                           and all additional rent due and payable by Tenant to
                           Ground Lessor pursuant to Sections 3.1 [(C)(1)] and
                           (3) of the Ground Lease.

         5. Landlord, by the execution hereof, consents to Tenant's performance
  of the alterations to the Mezzanine (as defined in the Lease) described in
  EXHIBIT __ subject, in all events however, to Tenant's compliance with the
  requirements of SECTION 6.2.4 of the Lease and Article 7 of the Ground Lease.

         6. Tenant hereby acknowledges that Landlord has satisfactorily
performed all of Landlord's Work (as defined in SECTION 3.2 of the Lease).

         7. Tenant warrants and represents that it has dealt with no broker in
  connection with the consummation of this First Amendment, and in the event of
  any brokerage claims from a broker dealing or claiming to have dealt with
  Tenant, against Landlord, Tenant agrees to defend same and indemnify and hold
  Landlord harmless against any such claim. Landlord warrants and represents
  that it has dealt with no broker in connection with the consummation of this
  First Amendment, and in the event of any brokerage claims from a broker
  dealing or claiming to have dealt with Landlord, including, but not limited
  to, Lynch, Murphy, Walsh and Partners against Tenant, Landlord agrees to
  defend same and indemnify and hold Tenant harmless against any such claim.

         8. As amended hereby, the Lease is hereby ratified and confirmed.

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         IN WITHNESS WHEREOF, Landlord and Tenant have executed this First
Amendment as a sealed instrument as of the date first above written.

                                       LANDLORD:

                                       BIOLEASE, INC.

                                       By: /s/ Neil St. John Raymond
                                           -----------------------------
                                          Name: Neil St. John Raymond
                                                ------------------------
                                          Title:
                                                ------------------------

                                       TENANT:

                                       BIOTRANSPLANT INCORPORATED

                                       By: /s/ Richard Capasso
                                           -----------------------------
                                          Name: Richard Capasso
                                                ------------------------
                                          Title: VP Finance and Treasurer
                                                ------------------------<PAGE>

                                                                    Exhibit 10.2

                                 LEASE AGREEMENT

     This Lease Agreement (the "Agreement") entered into at Knoxville,
Tennessee, effective as of July 1, 1999 by and between P. C. Powell, Jr. and
Wilma Powell, husband and wife (hereinafter "Landlord"), and Photogen, Inc. a
Tennessee Corporation (hereinafter "Tenant").

     WHEREAS, Landlord and Genase, L.L.C., a Tennessee corporation, are
parties to that certain Lease Agreement effective as of July 1, 1996 and
terminating June 30, 1999 for the lease of land, building and improvements
consisting of 3000 sq. ft. located at 7327 Oak Ridge Highway, Unit A, Knoxville,
Knox County, Tennessee ("Unit A Lease").

     WHEREAS, Landlord and Tenant are parties to that certain Lease
Agreement effective as of June 1, 1997 and terminating May 31, 2000 for the
lease of land, building and improvements consisting of 1000 sq. ft. located at
7327 Oak Ridge Highway, Unit B, Knoxville, Knox County, Tennessee ("Unit B
Lease").

     WHEREAS, Landlord and Tenant desire to terminate the Unit B Lease on
the effective date hereof and lease both Unit A (3000 sq. ft.) and Unit B (1000
sq. ft.) all on the terms and conditions set forth herein.

     IN CONSIDERATION of the mutual covenants and agreements set forth above
and hereinafter contained, the parties hereto agree as follows:

1.   PREMISES. In consideration of the rent, covenants and conditions that
     Tenant herein agrees to pay, keep and perform, Landlord hereby leases to
     Tenant land, building and improvements located at 7327 Oak Ridge Highway,
     Units A and B, Knoxville, Knox County, Tennessee, hereinafter referred to
     collectively as the "Premises".

2.   TERM. The Lease Agreement shall commence as of the date first entered above
     and terminate May 31, 2000.

3.   RENT. Tenant agrees to pay Landlord the sum of $2,700.00 per month for
     rental of the Premises and for the option to purchase, as provided herein,
     said payments beginning as of the date entered above.

4.   OPTION TO RENEW. Tenant shall have two (2) options to extend the term of
     the lease agreement for additional terms of one year each at a rental to be
     negotiated, and upon the same terms and conditions as set forth herein.
     Notice shall be given Landlord, within 30 days of expiration of Lease term,
     of Tenant's intent to exercise this option.

5.   AUTOCLAVE. Tenant desires to lease the "Autoclave" and related equipment
     during the term of the lease and any extensions thereof according to the
     terms described below:

          A.   The additional equipment to be leased includes the
               autoclave, steam generator, and any required auxiliary
               equipment (such as the gas water preheater) located on
               the Premises.

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          B.   Landlord agrees to have the units inspected and obtain
               all necessary operating permits.

          C.   Operational status will be demonstrated by having
               signed inspection and operating permit from the
               appropriate State Authorities.

          D.   Tenant agrees to provide, at Tenant cost, all necessary
               on-going maintenance during the term of the lease and
               any extensions thereof, including periodic inspections
               as required by state authorities.

          E.   Tenant will indemnify Landlord against any claim as a
               result of injury to any Tenant personnel as a result of
               operating the autoclave. Landlord will provide
               insurance sufficient to cover the building against
               damage caused as a result of operation of the
               autoclave. Tenant will indemnify Landlord against all
               loss of or damage to Tenants equipment as a result of
               operating the autoclave.

          F.   Tenant shall have the option at its discretion to
               purchase its own autoclave and install it on the
               Premises at Tenants expense.

          G.   Tenant agrees to pay Landlord $100.00 per month during
               the term of the Lease and any extensions thereof for
               use of the autoclave and related equipment. Should
               Tenant provide its own autoclave the lease payment
               shall be reduced by $100.00 per month.

8.   OPTION TO PURCHASE. Landlord hereby grants to Tenant the first right of
     refusal and option to purchase the Premises at any time during the term
     hereof or during any renewal period. In the event of a binding third party
     offer, Landlord shall give Tenant written notice of such offer including
     all terms and conditions and Tenant shall have a first right of refusal for
     forty-five (45) days to purchase the premises under the same terms as
     proposed to by the third party and as set forth in the offer.

9.   TAXES. Landlord shall be responsible for payment of all taxes, assessments
     or other governmental charges applicable to the Premises.

10.  UTILITIES. Tenant shall pay for use of all gas, electricity, sewer, water
     and other utilities consumed or wasted upon the Premises. Tenant shall
     provide its own janitor and cleaning service. Tenant will pay all ongoing
     usage fees.

11.  MAINTENANCE AND REPAIRS. Landlord, at its expense, shall be responsible for
     all maintenance and repairs to the building, including, but not limited to
     the roof, floor, foundation, walls, general heating and air conditioning
     systems, septic tank and lateral lines, and electrical and plumbing
     systems. Tenant shall be responsible, at its own expense, for routine minor
     maintenance and upkeep such as, repairing faucet leaks, and replacing light
     bulbs. Tenant agrees to be responsible for the routine maintenance of the
     back-up generator, which shall include the battery, oil changes and
     periodic starting. In the event the Landlord shall fail to proceed with and
     complete any repairs and

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     restorations which it may be required to make hereunder within a reasonable
     time, Tenant, upon notice to Landlord, may contact designated repair
     service personnel charging their services directly to the Landlord. Any
     repairs made by the Tenant shall be such as are reasonably necessary to
     protect the Premises and improvements for the account of and at the expense
     of the Landlord.

12.  IMPROVEMENTS AND ALTERATIONS. Tenant may, at its own expense, obtain,
     maintain, and install in the Premises such trade fixtures as the Tenant
     needs in order to operate its business, and may place such temporary
     partitions, lighting fixtures, personal property, machines, motors and the
     like in the premises, and may make such improvement and alterations to the
     Premises, as it may desire, provided only, that such improvements and
     alterations do not materially reduce the value of the Premises. All
     improvements, alterations heretofore or hereafter made or installed or paid
     for by Tenant, shall remain property of the Tenant.

     In case of damage or destruction thereto by fire or other causes, Tenant
     shall have the right to recover such items from any insurance with which it
     has insured the same, notwithstanding that any such items might be
     considered a part of real property. Tenant may remove all or any of such
     items at any time during the term of this Agreement or any extension
     thereof. Tenant may abandon the same, in whole or in part, to Landlord at
     the end of the term or any extension thereof, or such other expiration of
     the term, by vacating the Premises without removing the same. In the event
     of removal of such items, Tenant shall repair any damage caused by such
     removal.

     Tenant shall be responsible for replacement and/or repairs to Premises for
     any damage to Premises caused by abuse, neglect, or accident not recovered
     by insurance that result directly from Tenant use of the Premises except as
     provided for in Paragraph 5. It is understood by the Parties hereto that
     the Landlord may enter the Premised during normal business hours to inspect
     the building and to make routine repairs.

13.  INSURANCE.

     A.   Landlord at its own expense and throughout the term of this Lease
          Agreement and any extensions thereof, shall maintain insurance with
          respect to the Premises of the following types and in the following
          amounts:

                    1.   Fire insurance with full standard form extended
                         coverage, in an amount not less than eighty percent
                         (80%) of the full replacement value of the building.

                    2.   Public liability insurance protecting against claims
                         for personal injury, death and property damage
                         occurring upon, in or about the Premises with limits of
                         liability of not less than One Million Dollars
                         ($1,000,000) per occurrence. Tenant will likewise
                         maintain public liability insurance protecting against
                         claims for personal injury, death and property damage
                         occurring upon, in or

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                         about the Premises with limits of liability of not
                         less than One Million Dollars ($1,000,000) per
                         occurrence.

     B.   Tenant, at its own expense and throughout the term of this Lease
          Agreement and any extension thereof, shall maintain insurance of
          contents of building.

     C.   All insurance required under the provisions of the Paragraph shall be
          carried in favor of the Landlord or Tenant as their respective
          interests may appear. All policies shall provide that same cannot be
          canceled without giving at least ten (10) days prior written notice to
          the other party.

14.  DAMAGE TO PREMISES. If the Premises are destroyed or damaged to such an
     extent as to be rendered substantially unfit for occupancy, when considered
     as a whole, and the destruction or damage is not reasonably repairable
     within ninety (90) days after it occurs, the lease shall terminate as of
     the date the destruction or damage occurred and rent shall be abated
     accordingly. If the Premises are destroyed or damaged as aforesaid, but the
     destruction or damage is reasonably repairable within ninety (90) days
     after it occurs, or if the Premises are damaged but not to such an extent
     as to be rendered substantially unfit for occupancy when considered as a
     whole, Landlord shall proceed diligently to repair the Premises and the
     rent shall be abated or reduced, as may be equitable, while repairs are
     being made.

15.  CONDEMNATION. If any part of the Premises is taken, appropriated or
     condemned for public use, the lease shall terminate as to the part taken on
     the date of the taking or sale. In such event, Tenant may elect to
     terminate the lease as to the remainder of the Premises, by mailing to the
     Landlord written notice of Tenant's receipt of written notice of the taking
     and Tenants statement of its desire to terminate, if the part taken or sold
     renders the remainder unsuitable and insufficient to serve the business
     needs of the Tenant.

16.  MECHANICS LIENS. No mechanic's lien for labor or materials shall attach to
     or affect Tenant's interest in the Premises. Landlord shall pay or
     discharge by bond or deposit any and all mechanic's liens or other liens,
     which are filed on any interest in the Premises for labor or materials,
     furnished to Landlord.

17.  DEFAULT BY TENANT. If Tenant defaults in performance of any of the
     provisions, covenants or conditions of the lease and such default continues
     for thirty (30) days after the Tenant is notified in writing by Landlord to
     cure it or, if such default is of such a nature that it cannot be cured
     within such thirty (30) day period and continues for longer than the period
     reasonably required to cure it, or if Tenant abandons or vacates the
     Premises at any time during the term of the Lease, or if Tenant makes an
     assignment for the benefit of creditors, or if the interest of the Tenant
     in the Premises is attached, levied upon or seized by a legal process, or
     if Tenant is found to be bankrupt or insolvent by a court of competent
     jurisdiction, or if a receiver is appointed for Tenant by any such court,
     or if the Lease is assigned or terminated by the operation of law, then
     immediately or any time thereafter, with reasonable notice given to Tenant,
     Landlord may re-enter and take possession of the Premises by an action in
     forcible entry and detainer or otherwise.

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     Landlord may thereupon elect, either (a) to declare the Lease terminated,
     in which event Landlord may thereafter possess and enjoy the Premises as
     though the Lease had never been made without prejudice to any and all
     rights of action which the Landlord may have against Tenant at the time of
     such termination for rent, damages or breach of covenant previously
     accruing or occurring, or (b) to re-let the Premises on behalf of the
     Tenant.

18.  ASSIGNMENTS AND SUBLEASES. Tenant shall not assign this lease or sublet any
     part of the Premises without the written consent of the Landlord, which
     shall not be unreasonably withheld.

19.  QUIET ENJOYMENT. Landlord warrants that Landlord has the right to Lease the
     Premises to Tenant. So long as Tenant pays the rent herein provided and
     observes and performs the covenants and conditions of the Lease, Tenant
     shall be entitled to peaceably and quietly possess, occupy and enjoy the
     Premises during the term of the Lease without disturbance or eviction by
     the Landlord or by any other person lawfully claiming under the Landlord.

20.  SUCCESSORS AND INTEREST. The Lease Agreement shall be binding upon, inure
     to the benefit of, and be enforceable by and against the heirs, executors,
     administrators, successors and assigns of the Landlord and Tenant. No
     assignment of the Lease or Sublease hereunder, whether by act of Tenant or
     by operation of law, in violation of any provisions of this lease shall
     vest in any assignee or sublessee any right, title or interest whatsoever.

21.  NOTICES. Any notice, statement or payment required or permitted by the
     provisions of this Lease, is to be considered given, furnished or made when
     mailed to the parties at the following addresses:
<TABLE>
                           <S>                       <C>
                           LANDLORD:                 Mr. P. C. Powell
                                                     8303 Beaver Ridge Road
                                                     Knoxville, TN 37931

                           TENANT:                   Photogen, Inc.
                                                     Mr. John Smolik
                                                     7327 Oak Ridge Hwy.
                                                     Knoxville, TN 37931
</TABLE>

22.  EXPENSES. Any expense incurred as a result of performance of this Lease
     except for those expenses set forth in Paragraphs 9 and 10 above will be
     the responsibility of the person or entity, either Landlord or Tenant,
     incurring the obligation.

23.  HAZARDOUS SUBSTANCES. As used herein, "Hazardous Substances" means any
     substance that is considered toxic and is the subject of any Local, State
     or Federal regulation, and other substances that are considered flammable.

     Tenant intends to use the Premises as a biological research and development
     facility. Tenant may, from time to time, use small amounts of materials
     that may be considered

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     "Hazardous". "Small" amounts mean volumes of less than a few liters per
     month as a worst case.

     Tenant will take all reasonable precautions for the storage and use of any
     "Hazardous" materials as prescribed by law and good laboratory practice.
     Tenant will indemnify Landlord against personal injury to any Tenant
     employee and damage to the Premises caused as a result of the use of
     "Hazardous" materials.

24.  EFFECT OF THIS LEASE. This lease combines, amends and restates the Unit A
     Lease and the Unit B Lease, both of which prior lease agreements shall have
     no further force or effect.

IN WITNESS WHEREOF, Landlord and Tenant have executed this Lease Agreement the
day ad year first above written.

<TABLE>
<CAPTION>
LANDLORD:                                             TENANT:
<S>                                                   <C>

            /s/ P.C. Powell                           Photogen, Inc.
-------------------------------
P. C. Powell

                                                             /s/ John Smolik
                                                      -------------------------
                                                      John Smolik, President

            /s/ Wilma Powell
-------------------------------
Wilma Powell
</TABLE>

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