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                                                                   EXHIBIT 10.31

                         STANDARD FORM COMMERCIAL LEASE
                         ------------------------------

1. PARTIES                    Silver Lake Realty Trust, P.O. Box 269, Newton, MA
   (fill in)                  02160,                                            
                              
                              LESSOR, which expression shall include its heirs,
                              successors, and assigns where the context so
                              admits, does hereby lease to Kalisto Biologicals,
2. PREMISES                   Inc., a Delaware corporation, 46 Jodie Road,
   (fill in and include,      Framingham, MA 01702,
   if applicable, suite       LESSEE, which expression shall include its        
   number, floor              successors, executors, administrators, and assigns
   number, and                where the context so admits, and the LESSEE hereby
   square feet)               leases the following described premises:          
                              
                                         Approx. 12,000 gross sq.ft. of space, 
                              including Lessee's proportionate share of building
                              common area, on the second floor of the building
                              located at 1480 Soldier's Field Road, Brighton,
                              Mass., as shown on the attached PLAN,

                              together with the right to use in common, with
                              others entitled thereto, the hallways, stairways,
                              xxx xxxxxx necessary for access to said leased
                              premises, xxxxxxxx Except as otherwise provided
                              herein, premises to be delivered "as-is".

3. TERM                       The term of this lease shall be for five (5) years
   (fill in)                  commencing on November 1, 1997 and ending on 
                              October 31, 2002. See 22.A. for Extension
                              Privilege.                    
                           

4. RENT                       The LESSEE shall pay to the LESSOR rent at the   
  (fill in)                   rate xx as specified in 22.A., 22.B. and          
                              xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
                              22.C. herein.                                     
                                                            

5. SECURITY                   Upon the execution of this lease, the LESSEE shall
   DEPOSIT                    pay to the LESSOR the amount of $10,500.00        
  (fill in)                   dollars, which shall be held as a security for 
                              the LESSEE's performance as herein provided and
                              refunded to the LESSEE at the end of this lease   
                              subject to the LESSEE's satisfactory compliance   
                              with the conditions hereof.                       
                              

6. RENT                       xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx      xxxxxxxxxxxxx
   ADJUSTMENT                 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx 
   (fill in)            
                              See 22.C. for Additional Rent.
                              
                              


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7. UTILITIES                  xxxxxxxxxxxxxxxx LESSEE shall pay for all LESSEE's
   (fill in or delete)        utilities, water and sewer use charges, xxxxxx    
   and services               including heating fuel xxxxx and electricity for  
                              lights, power and air conditioning, and any other 
                              utility it may consume.                           
                              
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8. USE OF LEASED              The LESSEE shall use the leased premises only for 
   PREMISES                   the purpose of office and laboratory and light 
   (fill in)                  manufacturing space, and related uses.


9. COMPLIANCE                 The LESSEE acknowledges that no trade or  
   WITH LAWS                  occupation shall be conducted in the leased 
                              premises or use made thereof which will be 
                              unlawful, improper, noisy or offensive, or  
                              contrary to any municipal by-law or ordinance in
                              force in the city or town in which the premises
                              are situated. 
    



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10. FIRE            The LESSEE shall not permit any use of the leased premises
    INSURANCE       which will make voidable any insurance on the property of
                    which the leased premises are a part, or on the contents of
                    said property or which shall be contrary to any law or
                    regulation from time to time established by the New England
                    Fire Insurance Rating Association, or any similar body
                    succeeding to its powers. The LESSEE shall on demand
                    reimburse the LESSOR, and all other tenants, all extra
                    insurance premiums caused by the LESSEE's use of the
                    premises.

11. MAINTENANCE     The LESSEE agrees to maintain the leased premises in the
    OF PREMISES     same condition as they are at the commencement of the term
                    or as they may be put in during the term of this lease,
                    reasonable wear and tear, damage by fire and other casualty
                    only excepted, and whenever necessary, to replace plate
                    glass and other glass therein, acknowledging that the leased
                    premises are now in good order and the glass whole. The
                    LESSEE shall not permit the leased premises to be
                    overloaded, damaged, stripped, or defaced, nor suffer any
                    waste. LESSEE shall obtain written consent of LESSOR before
                    erecting any sign on the premises. such consent of Lessor
                    not to be unreasonably withheld. Continued in 22.D.

12. ALTERATIONS-    The LESSEE shall not make structural alterations or
    ADDITIONS       additions to the leased premises, but may make
                    non-structural alterations provided the LESSOR consents
                    thereto in writing, which consent shall not be unreasonably
                    withheld or delayed. All such allowed alterations shall be
                    at LESSEE's expense and shall be in quality at least equal
                    to the present construction. LESSEE shall not permit any
                    mechanics' liens, or similar liens, to remain upon the
                    leased premises for labor and material furnished to LESSEE
                    or claimed to have been furnished to LESSEE in connection
                    with work of any character performed or claimed to have been
                    performed at the direction of LESSEE and shall cause any
                    such lien to be released of record forthwith without cost to
                    LESSOR. Any alterations or improvements made by the LESSEE
                    shall become the property of the LESSOR at the termination
                    of occupancy as provided herein. No cutting or patching
                    walls, roof, or floors without Lessor's prior approval.

13. ASSIGNMENT-     The LESSEE shall not assign or sublet the whole or any part
    SUBLEASING      of the leased premises without LESSOR's prior written
                    consent, which consent shall not be unreasonably withheld or
                    delayed. Notwithstanding such consent, LESSEE shall remain
                    liable to LESSOR for the payment of all rent and for the
                    full performance of the covenants and conditions of this
                    lease.

14. SUBORDINATION   This lease shall be subject and subordinate to any and all
                    mortgages, deeds of trust and other instruments in the
                    nature of a mortgage, now or at any time hereafter, a lien
                    or liens on the property of which the leased premises are a
                    part and the LESSEE shall, when requested, promptly execute
                    and deliver such written instruments as shall be necessary
                    to show the subordination of this lease to said mortgages,
                    deeds of trust or other such instruments in the nature of a
                    mortgage.

15. LESSOR'S        The LESSOR or agents of the LESSOR may, at reasonable times,
    ACCESS          enter to view the leased premises and may remove placards
                    and signs not approved and affixed as herein provided, and
                    make repairs and alterations as LESSOR should elect to do
                    and may show the leased premises to others, and at any time
                    within three (3) months before the expiration of the term,
                    may affix to any suitable part of the leased premises a
                    notice for letting or selling the leased premises or
                    property of which the leased premises are a part and keep
                    the same so affixed without hindrance or molestation.

16. INDEMNIFI-      The LESSEE shall save the LESSOR harmless from all loss and
    CATION AND      damage to Lessee's property occasioned by the use or escape
    LIABILITY       of water or by the bursting of pipes, as well as from any
    (fill in)       claim or damage resulting from neglect in not removing snow
                    and ice from the roof of the building or from the sidewalks
                    bordering upon the premises so leased, or by any nuisance
                    made or suffered on the leased premises, unless such loss is
                    caused by the neglect of the LESSOR. The removal of snow
                    and ice from the sidewalks bordering upon the leased
                    premises shall be Lessee's responsibility. The Lessor shall
                    machine snow-plow the paved parking area.

17. LESSEE'S        The LESSEE shall maintain with respect to the leased
    LIABILITY       premises and the property, of which the leased premises are
    INSURANCE       a part, comprehensive public liability insurance in the
    (fill in)       amount of $1,000,000. 
                           with property damage insurance in limits of $300,000.
                                           in responsible companies qualified to
                    do business in Massachusetts and in good standing therein
                    insuring the LESSOR as well as LESSEE against injury to
                    persons or damage to property as provided. The LESSEE shall
                    deposit with the LESSOR certificates for such insurance at
                    or prior to the commencement of the term, and thereafter
                    within thirty (30) days prior to the expiration of any such
                    policies. All such insurance certificates shall provide that
                    such policies shall not be cancelled without at least ten
                    (10) days prior written notice to each assured named
                    therein.

18. FIRE,           Should a substantial portion of the leased premises, or of
    CASUALTY-       the property of which they are a part, be substantially
    EMINENT         damaged by fire or other casualty, or be taken by eminent
    DOMAIN          domain, the LESSOR may elect to terminate this lease. When
                    such fire, casualty, or taking renders the leased premises
                    substantially unsuitable for their intended use, a just and
                    proportionate abatement of rent shall be made, and the
                    LESSEE may elect to terminate this lease if:

                         (a)  The LESSOR fails to give written notice within
                              thirty (30) days of intention to restore leased
                              premises, or

                         (b)  The LESSOR fails to restore the leased premises to
                              a condition substantially suitable for their
                              intended use within ninety (90) days of said fire,
                              casualty, or taking.

                    The LESSOR reserves, and the LESSEE grants to the LESSOR,
                    all rights which the LESSEE may have for damages or injury
                    to the leased premises for any taking by eminent domain,
                    except for damage to the LESSEE's fixtures, property, or
                    equipment.







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19. DEFAULT         In the event that:
    AND                  (a)  The LESSEE shall default in the payment of any
    BANKRUPTCY                installment of rent or other sum herein specified
                              and such default shall continue for ten (10) days
                              after written notice thereof; or 
                         (b)  The LESSEE shall default in the observance or
                              performance of any other of the LESSEE's
                              covenants, agreements, or obligations hereunder
                              and such default shall not be corrected within
                              thirty (30) days after written notice thereof; or
                         (c)  The LESSEE shall be declared bankruptcy or
                              insolvent according to law, or, if any assignment
                              shall be made of LESSEE's property for the benefit
                              of creditors,

                    then the LESSOR shall have the right thereafter, while such
                    default continues, to re-enter and take complete possession
                    of the leased premises, to declare the term of this lease
                    ended, and remove the LESSEE's effects, without prejudice to
                    any remedies which might be otherwise used for arrears of
                    rent or other default. The LESSEE shall indemnify the LESSOR
                    against all loss of rent and other payments which the LESSOR
                    may incur by reason of such termination during the residue
                    of the term. If the LESSEE shall default, after reasonable
                    notice thereof, in the observance or performance of any
                    conditions or covenants on LESSEE's part to be observed or
                    performed under or by virtue of any of the provisions in any
                    article of this lease, the LESSOR, without being under any
                    obligation to do so and without thereby waiting such
                    default, may remedy such default for the account and at the
                    expense of the LESSEE. If the LESSOR makes any expenditures
                    or incurs any obligations for the payment of money in
                    connection therewith, including but not limited to,
                    reasonable attorney's fees in instituting, prosecuting or
                    defending any action or proceeding, such sums paid or
                    obligations insured, with interest at the rate of six (6)
                    per cent per annum and costs, shall be paid to the LESSOR by
                    the LESSEE as additional rent.
 
   
20. NOTICE          Any notice from the LESSOR to the LESSEE relating to the
    (fill in)       leased premises or to the occupancy thereof, shall be deemed
                    duly served, if mailed to the leased premises, registered or
                    certified mail, return receipt requested, postage
                    prepaid, addressed to the LESSEE. Any notice from the LESSEE
                    to the LESSOR relating to the leased premises or to the
                    occupancy thereof, shall be deemed duly served, if mailed to
                    the LESSOR by registered or certified mail, return receipt
                    requested, postage prepaid, addressed to the LESSOR at such
                    address as the LESSOR may from time to time advise in
                    writing. All rent and notices shall be paid and sent to the
                    LESSOR at P.O. Box 269, Newton, MA 02160.


21. SURRENDER       The LESSEE shall at the expiration or other termination of
                    this lease remove all LESSEE's goods and effects from the
                    leased premises, (including, without hereby limiting the
                    generality of the foregoing, all signs and lettering affixed
                    or painted by the LESSEE, either inside or outside the
                    leased premises). LESSEE shall deliver to the LESSOR the
                    leased premises and all keys, locks thereto, and other
                    fixtures connected therewith and all alterations and
                    additions made to or upon the leased premises, in the same
                    condition as they were at the commencement of the term, or
                    as they were put in during the term hereof, reasonable wear
                    and tear and damage by fire or other casualty only excepted.
                    In the event of the LESSEE's failure to remove any of
                    LESSEE's property from the premises, LESSOR is hereby
                    authorized, without liability to LESSEE for loss or damage
                    thereto, and at the sole risk of LESSEE, to remove and store
                    any of the property at LESSEE's expense, or to retain same
                    under LESSOR's control or to sell at public or private sale,
                    without notice any or all of the property not so removed and
                    to apply the net proceeds of such sale to the payment of any
                    sum hereunder, or to destroy such property.


22.  OTHER          It is also understood and agreed that the attached RIDER,
     PROVISION      PLAN, and GUARANTY are parts of this lease.

     
                   
                    
                    IN WITNESS WHEREOF, the LESSOR and LESSEE have hereunto set
                    their hands and common seals this 24th day of October 1997


                                          /s/ John Sain     
                                          -----------------------------------
                                          LESSOR Silver Lake Realty Trust


                                          /s/ Francis E. Capitanio, President
                                          -----------------------------------
                                          LESSEE  Kalisto Biologicals, Inc.
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RIDER TO LEASE, DATED OCTOBER 24, 1997, BETWEEN SILVER LAKE REALTY TRUST AND
KALISTO BIOLOGICALS, INC., FOR PREMISES AT 1480 SOLDIERS FIELD ROAD, BRIGHTON,
MASS.:

22.A. EXTENSION PRIVILEGE
       AND RENT:       The Lessee shall have the right to extend the lease for
                       one additional term of five years commencing November 1,
                       2002, exercisable by notice to the Lessor, as provided in
                       Section 20. herein, on or before May 1, 2002.

                       During the extension term, if exercised, the base rent
                       shall be $153,600. per year, adjusted annually to reflect
                       the change in the cost of living according to the change
                       in the Consumer Price Index (CPI-U*) over that for 2001,
                       according to the following formula:

                        Rent for year commencing = $153,600.00 x CPI-U July 200x
                           November 1,200x                       ---------------
                                                                 CPI-U July 2001

                                * where the CPI-U is the Consumer Price Index,
                                All Urban Consumers, All Items, (1982-84 = 100),
                                Boston, Mass. Should this index be unavailable
                                or inapplicable, comparable data shall be used.

                       Notwithstanding the above, the base rent for the
                       extension term shall not be less than $153,600. per year,
                       nor be reduced from one year to the next.

22.B. BASE RENT:       The Lessee shall pay to the Lessor Base Rent as per the 
                       following schedule:


                                                      
                       Nov. 1, 1997- April 30, 1998:      $10,500. per month;
                       May 1, 1998 - Oct. 31, 1998:       $11,000. per month;
                       Nov. 1, 1998 - Oct. 31, 1999:     $138,000. per year,   $11,500. per mo.;
                       Nov. 1, 1999 - Oct. 31, 2000:     $144,000. per year,   $12,000. per mo.;
                       Nov. 1, 2000 - Oct. 31, 2001:     $148,800. per year,   $12,400. per mo.;
                       Nov. 1, 2001 - Oct. 31, 2002:     $153,600. per year,   $12,800. per mo.


                       Base rent shall be payable in advance on the first day of
                       each month. Base Rent for November 1997 shall be paid
                       upon execution of the lease.

                       Rents or other sums due hereunder not received by the
                       10th day of the month shall be subject to interest at the
                       rate of 18% per annum from the first day of the month.

22.C. ADDITIONAL RENT: Lessee shall pay to the Lessor as Additional Rent:

                     - Reimbursement for 50% of real estate taxes levied against
                       the land and building of which the premises are a part.

                     - Reimbursement for 50% of premiums for "all-risk"
                       insurance, including loss of rent, on the building and
                       improvements thereto.

                     - Reimbursement for 100% of common area costs including but
                       not limited to landscaping, snowplowing, and exterior
                       lighting. (If and when other tenant(s) occupy the
                       building, an equitable adjustment will be made.) The
                       Lessor represents that such common area costs shall be
                       typical of similar buildings in the area.

                       Lessee shall pay this Additional Rent as estimated by
                       Lessor, in 1/12th installments payable in advance on the
                       first day of each month. At reasonable intervals, Lessor
                       shall provide Lessee with updated estimates of these
                       expenses, and over- or under-payments shall be credited
                       or debited to the Lessee. Lessor's initial estimate of
                       the Additional Rent is $3,000.00 per month.

                       Lessee shall pay the Additional Rent for November 1997
                       upon execution of this lease.









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22.D. MAINTENANCE
       (Continued):      Any sign to be erected by Lessee shall be installed in
                         accordance with applicable building codes, and in
                         accordance with section 11. herein.

                         The Lessor shall be responsible for the structural
                         integrity of the building, the roof, and repairs and
                         maintenance of the building common areas and exterior.

                         The Lessee shall be responsible for interior cleaning,
                         disposal of debris, maintenance, and repairs, including
                         maintenance and repairs to the freight elevator, HVAC,
                         electrical and plumbing systems servicing its premises.

22.E. LEASEHOLD
      IMPROVEMENTS:      Upon execution of the lease, the Lessor shall put all
                         building systems, including the freight elevator, in
                         good working order; and segregate the utilities to
                         provide separate metering. Lessor shall also be
                         responsible for putting the associated parking lot and
                         landscaping in good condition. Lessor shall complete
                         such work in a timely manner.

                         The Lessee shall be responsible for the installation of
                         vinyl tile throughout the lab areas (including removal
                         of existing carpet) as well as any other changes or
                         improvements associated with Lessee's intended use. The
                         Lessee shall also be responsible for the removal of any
                         resulting debris. Lessee will obtain Lessor's
                         permission pursuant to section 12. herein prior to
                         making any alterations to the leased premises. All work
                         to be done according to applicable building codes and
                         in a good and workmanlike manner.

                         Upon full execution of this lease, including payment of
                         security deposit and first month's rent, Lessee may
                         have early occupancy of the premises to commence its
                         improvements.

22.F. PARKING:           The Lessee shall have the use of 35 parking spaces in
                         the associated common parking lot. Lessor reserves the
                         right to establish reasonable rules and regulations
                         governing parking for the property.

22.G. LABORATORY USE:    The Lessee shall comply with all applicable
                         governmental codes and regulations in its use of the
                         laboratory within the premises, and shall effect, at
                         its sole expense, any modifications to the premises
                         required for such compliance.

22.H. ENVIRONMENT:       The Lessee shall not permit any hazardous materials or
                         substances to be used, stored, or disposed of
                         improperly or in conflict with any law, ordinance or
                         code, and Lessee shall be solely responsible for any
                         and all contamination or other damage associated with
                         use, control or disposal of same by Lessee.

22.I. ELEVATOR:          Lessor shall modify the area on the first floor of the
                         building as shown on the attached PLAN in order to
                         provide Lessee access to the freight elevator.









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                                      PLAN
                                      ----




                 PREMISES LEASE TO KALISTO  BIOLOGICALS, INC.
                                  (2nd Floor)




                              [SECOND FLOOR PLAN]




                               [FIRST FLOOR PLAN]
                                 (not included)




               1480 SOLDIERS FIELD ROAD, BRIGHTON, MASSACHUSETTS
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                                    GUARANTY

         FOR VALUE RECEIVED, and in consideration for and as an inducement to
the Lessor to make the forgoing lease with Kalisto Biologicals, Inc., as Lessee,
the undersigned Advanced Magnetics, Inc. 725 Concord Ave., Cambridge, MA 02138,
unconditionally guarantees the full performance and observance of the provisions
of the lease to be performed and observed by Lessee, Lessee's successors' and
assigns, and expressly agrees that the validity of this agreement and the
obligations of the guarantor hereunder shall in no ways be terminated, affected
or impaired by reason of the granting by the Lessor of any indulgences to Lessee
or by reason of the assertion by Lessor against Lessee of any of the rights or
remedies reserved to Lessor pursuant to the lease.

         The undersigned guarantor has duly executed this instrument this 24th
day of October, 1997.





                             ---------------------------------------------------
                             Advanced Magnetics, Inc.

                             By Jerome Goldstein its CEO & CHAIRMAN OF THE BOARD
                                ----------------     ---------------------------





                          COMMONWEALTH OF MASSACHUSETTS

               ss. Middlesex                          Date 10/24/97

         Then personally appeared the above named JEROME GOLDSTEIN, and
acknowledged the foregoing to be his free act and deed, before me,


                                        /s/ Marlene Kaplan Goldstein    
                                        ----------------------------------------
                                        Notary Public
                                        My Commission Expires: 4/7/00