EXHIBIT 10.1



                            FIRST AMENDMENT TO LEASE


          THIS AGREEMENT (hereinafter referred to as the "Amendment") made as of
the16 day of March  2001,  between  826  NEWTOWN  ASSOCIATES,  L.P.,  a Delaware
limited  partnership,  whose  address  is C/O First  Evergreen,  101  Eisenhower
Parkway, Roseland, New Jersey 07068 (hereinafter referred to as "Landlord"), and
AXCELL BIOSCIENCES CORPORATION,  a Delaware corporation (hereinafter referred to
as "Tenant"),  with offices at 826 Newtown-Yardley  Road, Newtown,  Pennsylvania
18940.


                              W I T N E S S E T H:


          WHEREAS, Tenant and Landlord's  predecessor-in-interest,  Yardley Road
Associates,  L.P.,  entered  into a Lease made as of July 23, 1999  (hereinafter
referred to as the  "Lease"),  whereby  Tenant is  presently  in  possession  of
premises  containing  approximately  9,146 gross  rentable  square feet of space
(hereinafter  referred to as the "Original Premises") in the building located at
826 Newtown Yardley Road, Newtown,  Pennsylvania (hereinafter referred to as the
"Building"); and

          WHEREAS, Tenant desires to lease additional space in the Building, and
Landlord  is willing to lease such  additional  space to Tenant on the terms and
provisions set forth in the Lease, except to the extent provided for herein; and

          WHEREAS,  the  parties  hereto  desire to amend the Lease  only in the
respects and on the conditions hereinafter stated.

          NOW, THEREFORE, Landlord and Tenant agree as follows:


          1. For purposes of this  Amendment,  capitalized  terms shall have the
meanings ascribed to them in the Lease unless otherwise defined herein.


          2. Landlord and Tenant hereby confirm that the expiration  date of the
Term with  respect to the  Original  Premises  is  currently  December  31, 2004
(hereinafter  referred to as the  "Original  Term1').  The term of the  Original
Premises shall not be extended by this Amendment.


          3.  From  and  after  the  Additional  Space   Commencement  Date  (as
hereinafter defined) and continuing through the Additional Space Expiration Date
(as hereinafter  defined),  Tenant hereby leases from Landlord  additional space
consisting  of  approximately  5,680 gross  rentable  square feet  ("hereinafter
referred  to as the  "Additional  Space")  which  Additional  Space  is shown on
Exhibit A attached hereto and made a part hereof.


<PAGE>


         4. The term for the Additional  Space  (hereinafter  referred to as the
"Additional  Space Term") shall commence on the date which is the first to occur
of (i) the date  "Landlord's  Work" (as  hereinafter  defined) in the Additional
Space is deemed  substantially  completed and possession of the Additional Space
is  delivered  to Tenant free from all  tenants,  occupants  and their  personal
property, or the date Landlord would have substantially  completed and delivered
possession of the Additional Space to Tenant but for any reason  attributable to
Tenant;  and (ii) the date upon which the Additional Space is occupied by Tenant
for the conduct of Tenant's business (hereinafter referred to as the "Additional
Space Commencement  Date"), and shall expire on 11:59 p.m. on the day preceeding
the fifth (5th)  anniversary of the Additional Space Rent  Commencement Date (as
hereinafter defined).


          5.  From  and  after  the  Additional  Space   Commencement  Date  and
continuing  through the expiration of the Original  Term,  the Demised  Premises
shall  be  deemed  to  include  the  Additional   Space  and  shall  consist  of
approximately  14,826 gross rentable  square feet of space and Sections 5 and 10
of the Preamble shall be deemed modified accordingly.


          6.  From  and  after  the  Additional  Space   Commencement  Date  and
continuing through the expiration of the Original Term,  Tenant's  Proportionate
Share shall be Twelve and 36/100 (12.36%) percent and Section 10 of the Preamble
shall be deemed modified accordingly.


          7. From and after the  expiration of the Original Term and  continuing
through the Additional  Space  Expiration  Date, and provided Tenant has elected
not to extend  the  Original  Term of this  Lease as set forth in Rider A to the
Lease,  the Demised  Premises shall mean the Additional Space only consisting of
approximately 5,680 gross rentable square feet of space and Sections 5 and 10 of
the preamble shall be deemed modified accordingly.


          8. From and after the  expiration of the Original Term and  continuing
through the Additional  Space  Expiration  Date, and provided Tenant has elected
not to extend  the  Original  Term of this  Lease as set forth in Rider A to the
Lease, Tenant's Proportionate Share shall be Four and 73/100 (4.73%) percent and
Section 10 of the Preamble shall be deemed modified accordingly.

          9.  From and  after  the  later to occur of (i) the  Additional  Space
Commencement  Date  and  (ii)  July  1,  2001  (hereinafter  referred  to as the
"Additional Space Rent  Commencement  Date"),  Tenant shall pay to Landlord,  in
addition  to the Fixed Basic Rent due and  payable  for the  Original  Premises,
Fixed Basic Rent for the Additional Space as follows:

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<PAGE>



--------------------------------------------------------------------------------
Period                Rate per              Annual Fixed             Monthly
                      Rentable              Basic Rent               Installment
                      Square foot           (based upon
                      (net of               twelve equal
                      operating costs       Monthly
                      and utilities)        Installments)
--------------------------------------------------------------------------------
Additional            $22.35                $126,948.00              $10,579.00
Space Rent
Commencement
Date-06/30/02
--------------------------------------------------------------------------------
07/01/02-             $22.85                $129,788.00              $10,815.67
06/30/03
--------------------------------------------------------------------------------
07/01/03-             $23.35                $132,628.00              $11,052.33
06/30/04
--------------------------------------------------------------------------------
07/01/04-             $23.85                $135,468.00              $11,289.00
06/30/05
--------------------------------------------------------------------------------
07/01/05-             $24.35                $138,308.00              $11,525.67
Additional
Space
Expiration Date
--------------------------------------------------------------------------------


                   The aforesaid  Monthly  Installments  of Fixed Basic Rent for
the  Additional  Space shall be payable in advance on or before the first day of
each calendar month commencing upon the Additional Space Rent  Commencement Date
and continuing  through the Additional Space  Expiration Date,  without set-off,
deduction, counterclaim or any previous demand therefor (except as otherwise set
forth in the Lease),  and Paragraph 7 of the Preamble and Section 6 of the Lease
shall be deemed modified  accordingly.  Landlord  acknowledges receipt, by check
subject to collection,  of the first Monthly Installment of Fixed Basic Rent due
and payable for the Additional Space.

          10. Tenant hereby  acknowledges  to Landlord that as of the Additional
Space  Commencement  Date, Tenant is leasing the Additional Space in its "AS IS"
condition as of the date hereof, except that Landlord hereby agrees to cause the
work set forth on Exhibit B annexed  hereto and made a part hereof  (hereinafter
referred to as  "Landlord's  Work") to be  performed  to the  Additional  Space.
Landlord hereby agrees to contribute  towards the cost of the preparation of the
plans and the  construction of the Landlord's Work an amount equal to the sum of
Twelve and 00/100  ($12.00)  Dollars per rentable square foot for the Additional
Space only for a total allowance not to exceed Sixty-eight  Thousand One Hundred
Sixty  and  00/100  ($68,160.00)  Dollars   (hereinafter   referred  to  as  the
"Construction Allowance").

                   Any costs in excess of the  Construction  Allowance  shall be
paid in full to  Landlord  by Tenant  immediately  upon  demand,  which shall be
deemed  Additional Rent due under the Lease and shall be subject to all remedies
for the collection of Rent pursuant to the Lease and by law. Occupancy by Tenant
or the  delivery of a  Certificate  of Occupancy  (temporary  or  permanent)  by
Landlord (if required  pursuant to local law) shall be prima facie evidence that
Landlord has  substantially  completed  all of Landlord's  Work,  subject to the
completion of such minor items as would typically be reflected in a "punchlist".


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<PAGE>

          11.  Tenant and Landlord  represent  and warrant one to the other that
Kelley &  Associates,  Inc.  (hereinafter  referred to as  "Broker") is the sole
broker which whom either party  negotiated in bringing  about this  transaction,
and Tenant and Landlord  agree to indemnify  and hold each other  harmless  (and
Tenant agrees to indemnify and hold Landlord's  mortgagee(s)  harmless) from any
and all claims of any brokers  arising out of or in connection  with any conduct
by such party inconsistent with the representations tendered by one to the other
herein.  In no event shall  Landlord's  mortgagee(s)  have any obligation to any
broker  alleged  or  determined  to  be  involved  in  this  transaction.  It is
specifically  understood and agreed that any  commission(s)  which may be due to
Broker  shall be paid by  Landlord  pursuant  to a  separate  agreement  between
Landlord and Broker.


          12. Upon  execution  of this  Amendment,  Tenant  shall  deposit  with
Landlord the sum of  Twenty-Three  Thousand  Fifty-one  and 33/100  ($23,051.33)
Dollars,  representing  security for the  Additional  Space,  and Three Thousand
Forty-eight and 67/100  ($3,048.67),  representing  additional  security for the
Original Premises,  so that Landlord shall have on hand for the remainder of the
Original Term, the total sum of Fifty-nine  Thousand Four Hundred Six and 68/100
($59,406.68)  Dollars as security  (representing two (2) Monthly Installments of
Fixed  Basic Rent for the  Original  Premises  and the  Additional  Space at the
rental  rates  payable  during  the  last  year of the  respective  terms),  and
Paragraph  11 of the  Preamble  and  Section  38 of the  Lease  shall be  deemed
modified accordingly.

                   From  and  after  the  expiration  of the  Original  Term and
continuing through the Additional Space Expiration Date, and provided Tenant has
elected not to extend the Original Term of this Lease as set forth in Rider A to
the  Lease,  Landlord  shall  have on  hand  the  sum of  Twenty-Three  Thousand
Fifty-one  and  33/100  ($23,051.33)  Dollars,  representing  security  for  the
Additional  Space and  Paragraph  11 of the Preamble and Section 38 of the Lease
shall be deemed modified accordingly.


          13. Cytogen  Corporation,  the Guarantor  under that certain  Guaranty
dated July 14, 1999,  executed in connection with the Lease, hereby ratifies and
affirms that the terms and conditions of said Guaranty  remain in full force and
effect and shall apply with respect to the terms and  provisions of the Lease as
amended by this Amendment.


          14.  Landlord  and Tenant  hereby agree that  Tenant's  right of early
termination  of the Lease as  provided  for in  Section 4 of the Lease  shall be
deemed null and void and Tenant shall have no further  right to  terminate  this
Lease pursuant to said Section 4.


          15. Nothing  contained  herein shall be deemed a waiver or exercise of
Tenant's renewal options as set forth in the Lease. The existing renewal options
for the Original Premises, if exercised,  shall include the Additional Space and
extend the Additional Space Term, and accordingly,  if exercised, the expiration
dates for the renewal terms of the Original  Premises and the  Additional  Space
shall be  coterminus  and occur on December 31, 2009 for the first  renewal term
and December 31, 2014 for the second renewal term.

                   The Rent for the Original Premises for the first renewal term
shall be  calculated  as set  forth in  Rider A to the  Lease.  The Rent for the
Additional  Space for the  period  from the  Additional  Space  Expiration  Date
through  December  31, 2009 shall be  calculated  as set forth in Rider A of the
Lease.  The Rent for the  Original  Premises  and the  Additional  Space for the
second  renewal term (e.g.  January 1, 2010 through  December 31, 2014) shall be
calculated as set forth in Rider A of the Lease.


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<PAGE>

          16. Tenant represents,  warrants and covenants that Landlord is not in
default  under  any of its  obligations  under the Lease and that to the best of
Tenant's knowledge, Tenant is not in default of any of its obligations under the
Lease and no event has occurred which, with the passage of time or the giving of
notice,  or both,  would  constitute  a  default  by either  Landlord  or Tenant
thereunder.


          17.  Landlord  represents,  warrants and covenants that to the best of
Landlord's  knowledge,  Tenant is not in  default  under any of its  obligations
under the Lease, and that to the best of Landlord's  knowledge,  Landlord is not
in default of any of its  obligations  under the Lease and no event has occurred
which,  with the  passage  of time or the  giving  of  notice,  or  both,  would
constitute a default by either Landlord or Tenant thereunder.

          18.  Except  as  modified  by this  Amendment,  the  Lease and all the
covenants,  agreements, terms, provisions and conditions thereof shall remain in
full force and  effect and are hereby  ratified  and  affirmed.  The  covenants,
agreements,  terms,  provisions and conditions contained in this Amendment shall
bind and  inure to the  benefit  of the  parties  hereto  and  their  respective
successors and assigns. In the event of any conflict between the terms contained
in this Amendment and the Lease,  the terms herein contained shall supersede and
control the obligations and liabilities of the parties.

          19.  The  submission  of  this  Amendment  for  examination  does  not
constitute a  reservation  of, or option for,  the  Additional  Space,  and this
Amendment becomes effective only upon execution and delivery thereof by Landlord
and Tenant. If required,  this Amendment is expressly  conditioned upon Landlord
receiving  the consent and  approval of  Landlord's  mortgagee  to its terms and
provisions.  If said  consent is required  but not  received,  Landlord  may, at
Landlord's  sole option,  cancel this Amendment and thereafter the parties shall
have no further obligations to each other with respect to this Amendment, except
that Tenant shall be entitled to the full refund of any and all monies delivered
to Landlord in connection with this Amendment.

                   IN WITNESS  WHEREOF,  Landlord  and Tenant have  hereunto set
their  hands  and  seals  as of the  date  and year  first  above  written,  and
acknowledge  the one to the other that they possess the  requisite  authority to
enter into this transaction and to sign this Amendment.


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<PAGE>


                                      LANDLORD:

                                    826 NEWTOWN ASSOCIATES, L.P.
                                    a Delaware limited partnership,


                                    By:   826 NEWTOWN REALTY CORP.,
                                          a Pennsylvania corporation,
                                          its sole general partner

                                          By :  /s/  Mark S. Green
                                                     Mark S. Green, President

                                      TENANT:
                                    AXCELL BIOSCIENCES CORPORATION, a
                                    DELAWARE corporation
                                    By:  /s/ Lawrence R. Hoffman
                                    Name:  Lawrence R. Hoffman
                                    Title:  Vice President & CFO

                                          GUARANTOR:

                                    CYTOGEN CORPORATION

                                    By:  /s/ Lawrence R. Hoffman
                                    Name:  Lawrence R. Hoffman
                                    Title:  Vice President & CFO


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<PAGE>


                                    EXHIBIT A

              Diagram of space at 826 Newtown Newtown-Yardley Road



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<PAGE>


                                    EXHIBIT B



(Exhibit B consists of plans prepared by JBH 3 & Associates  dated September 28,
2000, entitled "Axcell First Floor, Architectural Drawings.)











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