<PAGE>

                                                                    EXHIBIT 10.1

As Filed with the Securities and Exchange Commission on October 24, 2001.
*INFORMATION HAS BEEN OMITTED PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT
AND HAS BEEN FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION.


                            PSMA SUBLICENSE AGREEMENT

                                 BY AND BETWEEN

                               CYTOGEN CORPORATION

                                       AND

                         NORTHWEST BIOTHERAPEUTICS INC.

                                      DATED

                                      AS OF

                                 AUGUST 28, 2000



<PAGE>
As Filed with the Securities and Exchange Commission on October 24, 2001.
*INFORMATION HAS BEEN OMITTED PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT
AND HAS BEEN FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE COMMISSION.


                            PSMA SUBLICENSE AGREEMENT

                           Dated as of August 28, 2000


        CYTOGEN CORPORATION ("Cytogen"), a Delaware corporation, having its
place of business at 600 College Road East, Princeton, New Jersey 08540 and
NORTHWEST BIOTHERAPEUTICS INC. ("NWBio"), a Delaware corporation, having its
principal place of business at 2203 Airport Way South, Suite 200, Seattle,
Washington 98134, hereby agree as follows:

        1. BASIS FOR AGREEMENT. The following chronology and purposes form the
basis for the agreements hereunder:

                1.1 MISROCK'S SPONSORSHIP OF RESEARCH ON MOAB 7E11. At the
request of Dr. Gerald P. Murphy, then Director of Roswell Park Memorial
Institute, Buffalo, New York, S. Leslie Misrock ("Misrock"), who subsequently
founded Prostagen Inc. ("Prostagen"), financially sponsored the research of Dr.
Julius S. Horoszewicz which led to the discovery of MoAb 7E11, one subclone of
which is MoAb 7E11-C5 and another subclone is 7E11-C5.3 which is denominated by
Cytogen as CYT-3511. The specific antibody utilized by Drs. Horoszewicz and
Murphy is described in Anticancer Research, 7:927-936 (1987), entitled
"Monoclonal Antibodies to a New Antigenic Marker in Epithelial Prostatic Cells
and Serum of Prostatic Cancer Patients." Additionally, Misrock was responsible
for Cytogen's acquisition of Horoszewicz patent rights covering MoAb 7E11 and
its subclones.

                1.2 SKICR'S USE OF MOAB 7E11-C5 TO ISOLATE PSMA GENE AND
PROTEIN. Cytogen furnished MoAb 7E11-C5 to Drs. Ron S. Israeli, Warren D. Heston
and William R. Fair at the Sloan-Kettering Institute For Cancer Research
("SKICR"), New York, New York, where these investigators isolated and
characterized the gene for prostate specific membrane antigen and subsequently
expressed and characterized the protein PSMA (as defined in Section 2) encoded
by such gene. The research by Drs. Israeli, Heston and Fair on the isolation and
characterization of the PSMA gene and protein is described in Cancer Research,
53:227-230 (1993), entitled "Cloning of a Complementary DNA Encoding a
Prostate-Specific Membrane Antigen."

                1.3 SKICR FILES FOR PATENT RIGHTS COVERING ITS PSMA
DEVELOPMENTS. With funding from Cytogen, SKICR filed a series of United States
and foreign counterpart patent applications on its PSMA developments in the
names of Drs. Israeli, Heston and Fair, on one of which applications United
States Patent No. 5,538,866 was granted on July 23, 1996. The `866 patent,
together with all United States patent applications and foreign counterparts
filed by or on behalf of SKICR covering its PSMA developments.

                1.4 CYTOGEN OBTAINS AND EXERCISES OPTION TO LICENSE SKICR PATENT
RIGHTS. Pursuant to the Option and License Agreement ("SKICR Agreement")
effective July 1, 1993, by and between Cytogen and SKICR, Cytogen was granted
the exclusive option to obtain an exclusive worldwide license to technology and
patent rights relating to SKICR's



<PAGE>

developments relating to PSMA for a term commencing July 1, 1993 and extending
until six (6) months after the issuance of the first United States patent on
this technology. Since the `866 patent was granted July 23, 1996, Cytogen's
option extended until January 23, 1997. Cytogen has advised and represented to
NWBio that it had exercised its option under the SKICR Agreement prior to
December 9, 1996.

                1.5 CYTOGEN SUBLICENSES PROSTAGEN. Pursuant to the PSMA
Therapeutics Sublicense Agreement (as defined in Section 2) Cytogen granted to
Prostagen the exclusive right and sublicense throughout the world, with the
right to grant sublicenses to others, under the SKICR Patent Rights, inter alia,

                        (a) to develop therapeutic products utilizing PSMA,
        prostate specific membrane peptides ("PSMP") containing any peptide
        sequence appearing within the PSMA protein, mimetopes of such peptides,
        DNA and/or RNA of PSMA and/or PSMP and/or mimetopes thereof, for the
        immunotherapeutic treatment of prostate cancer; and

                        (b) to produce, process or otherwise manufacture or have
        produced, processed or otherwise manufactured, to use or have used, to
        sell or have sold, any products for immunotherapy of prostate cancer (1)
        that contain PSMA, PSMP, mimetopes thereof, the DNA and/or RNA
        corresponding to such protein or peptides; (2) that are either (i)
        covered in whole or in part by a Valid Claim in the country in which
        such product is made, used or sold; or (ii) manufactured by using a
        process that is covered in whole or in part by a Valid Claim in the
        country in which such process is used; or (iii) used according to a
        method which is covered in whole or in part by a Valid Claim in the
        country in which such method is used; and (3) that embody or are made in
        accordance with any of the SKICR Patent Rights.

                1.6 TERMINATION OF PRIOR AGREEMENTS. Prostagen and NWBio entered
into a PSMA Therapeutic Product Sublicense Agreement, dated July 16, 1997 and
Prostagen and Northwest Clinical LLC entered into a PSMA Production Sublicense
Agreement, dated July 16, 1997, both of those agreements and the PSMA
Therapeutic Sublicense Agreement (as defined in Section 2) have been terminated
simultaneously with the execution of this Agreement.

        2. DEFINITIONS. For the purposes of this Agreement, the following terms,
whether used in the singular or plural, shall have the following meanings.

                2.1 AFFILIATE. The term "Affiliate" shall mean any person,
corporation, company, partnership, joint venture and/or firm which controls, is
controlled by, or is under common control with, a party. For purposes of this
definition, "control" shall mean (a) in the case of corporate entities, direct
or indirect ownership of at least fifty percent (50%) or, if less than fifty
percent (50%), the maximum percentage, as allowed by applicable law, of the
stock or participating shares entitled to vote for the election of directors;
and (b) in the case of noncorporate entities, direct or indirect ownership of at
least fifty (50%) or, if less than fifty percent (50%), the maximum percentage,
as allowed by applicable law, of the equity interest with the power to direct
the management and policies of such noncorporate entity.



                                       2
<PAGE>

                2.2 COMMERCIAL SALE. The term "Commercial Sale" shall mean the
commercial sale of Licensed Products by NWBio.

                2.3 CONTRACT PERIOD. The term "Contract Period" shall mean the
period beginning with the Effective Date of the Agreement and ending upon the
date on which this Agreement shall expire or terminate in accordance with the
provisions of Section 8 hereof.

                2.4 EFFECTIVE DATE. The term "Effective Date of this Agreement"
shall mean July 18, 2000.

                2.5 FDA. The term "FDA" shall mean the United States Food and
Drug Administration.

                2.6 IMMUNOTHERAPY. The term "immunotherapy" shall mean and
collectively include those ex vivo therapeutic interventions which result in the
activation and/or expression of effector cell function by B lymphocytes, T
lymphocytes, NK cells, macrophages, expression of mucosal immunity, and/or
passive immunity by which immune agents are generated ex vivo and transferred to
a patient.

                2.7 IND. The term "IND" shall mean an application for
investigation of a new drug that has been submitted to the FDA pursuant to the
Federal Food Drug and Cosmetic Act, as amended [Title 21, United States Code]
and the regulations promulgated thereunder, or an equivalent application to
another Regulatory Authority.

                2.8 LICENSED PROCESSES. The term "Licensed Processes" shall mean
any process for the immunotherapy of prostate cancer in patients by [  ***  ]
including, but not limited to [  ***  ], ex vivo, with a composition including
PSMA and/or PSMP, and/or the mimetopes of PSMA or PSMP, and [  ***  ] the use or
practice of which would, but for the licenses granted herein, infringe one or
more Valid Claims of an issued patent or pending patent application included in
SKICR Patent Rights.

                2.9 PSMA. The term "PSMA" shall mean prostate specific membrane
antigen and shall include the PSMA protein described in Cancer Research,
53:227-230 (1993).

                2.10 PSMP. The term "PSMP" shall mean prostate specific membrane
peptides which shall include any peptide sequence appearing within the PSMA
protein.

                2.11 LICENSED PRODUCTS. The term "Licensed Products" shall mean
products for the immunotherapy of prostate cancer which are produced by
[  ***  ], with a composition including PSMA and/or PSMP, and/or the mimetopes
of PSMA or PSMP, and [  ***  ], the manufacture, use and/or sale of


[  ***  ]INFORMATION HAS BEEN OMITTED PURSUANT TO A REQUEST FOR CONFIDENTIAL
TREATMENT AND HAS BEEN FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION.



                                       3
<PAGE>

which would, but for the licenses granted herein, infringe one or more Valid
Claims of an issued patent or pending patent application included in SKICR
Patent Rights.

                2.12 MAJOR MARKET. The term "Major Market" shall mean any of the
United States, United Kingdom, France, Germany, Italy, Spain, Japan or Canada.


                2.13 MOAB 7E11. The term "MoAb 7E11 shall mean and collectively
include that certain antibody to PSMA known as MoAb 7E11-C5, which such antibody
is claimed in United States Patent No 5,162,504, granted November 10, 1992, and
entitled "Monoclonal Antibodies to a New Antigenic Marker in Epithelial
Prostatic Cells and Serum of Prostate Cancer Patients." One subclone of MoAb
7E11 is MoAb 7E11-C5.3.

                2.14 NDA. The term "NDA" shall mean either a New Drug
Application and/or a Pre-Market Approval for a Licensed Product that has been
submitted to the FDA pursuant to the Federal Food, Drug and Cosmetic Act, as
amended [Title 21, United States Code] and the regulations promulgated
thereunder or an equivalent application to another Regulatory Authority.

                2.15 PHASE III CLINICAL TRIAL. The term "Phase III Clinical
Trial" shall mean a pivotal random clinical trial having a sufficient number of
patients to provide statistically significant results regarding safety and
efficacy of a particular Licensed Product in the treatment of prostate cancer.
The Phase III Clinical Trial shall be conducted pursuant to the requirements of
the Federal Drug, Food and Cosmetic Act, as amended [Title 21, United States
Code] and regulations promulgated thereunder, and shall commence on the first
day the first patient is treated under the protocol of such Phase III Clinical
Trial.

                2.16 PSMA THERAPEUTICS SUBLICENSE AGREEMENT. The term "PSMA
Therapeutics Sublicense Agreement" shall mean the PSMA Therapeutics Sublicense
Agreement, dated December 9, 1996, by and between Cytogen and Prostagen, and all
amendments thereto.

                2.17 REGULATORY APPROVAL. The term "Regulatory Approval" shall
mean the approval of an NDA by a Regulatory Authority granting the rights to
manufacture, market and import a therapeutic agent for use by human patients.

                2.18 REGULATORY AUTHORITY. The term "Regulatory Authority" shall
mean the applicable Government authority (which, in the United States, is the
FDA) which is responsible for approval for manufacturing, marketing or importing
a therapeutic agent in a particular country for human use.

                2.19 SKICR. The term "SKICR" shall mean the Sloan-Kettering
Institute for Cancer Research, a not-for-profit New York corporation, having its
principal place of business at 1275 York Avenue, New York, New York 10021-6007.

                2.20 SKICR AGREEMENT. The "SKICR Agreement" shall mean the
Option and License Agreement effective July 1, 1993, by and between SKICR and
Cytogen, and



                                       4
<PAGE>

all amendments thereto. The SKICR Agreement is annexed to be PSMA Therapeutics
Sublicense Agreement as Exhibit A.

                2.21 SKICR PATENT RIGHTS. The "SKICR Patent Rights" shall mean
and collectively include

                        (a) all patentable inventions specifically pertaining to
        the Technological Field (1) which are subject to protection under the
        provisions of the Patent Act [Title 35, United States Code] and/or any
        foreign patent laws; (2) which were in existence on the effective date
        of the PSMA Therapeutics Sublicense Agreement and/or which may be made
        at any time during the term of that agreement at SKICR; and (3) which
        were legally and/or beneficially owned or otherwise controlled or
        licensable by Cytogen as at its election under the SKICR Agreement.

                        (b) any and all patents and patent applications set
        forth in Schedule A of the PSMA Therapeutics Sublicense Agreement and
        any and all existing or future divisions, continuations,
        continuations-in-part and renewals thereof, any and all patents which
        may be granted thereon, and any and all reissues and extensions thereof.
        Cytogen shall promptly notify NWBio of any change in the status of any
        patent application or patent included in Schedule A of the PSMA
        Therapeutics Sublicense Agreement. Any Improvements relating to the
        Licensed Product and/or Licensed Processes shall be included in the
        SKICR Patent Rights to the extent that such Improvements have been
        licensed to Cytogen by SKICR.

                2.22 VALID CLAIM. The term "Valid Claim" with respect to any
jurisdiction shall mean any claim of any duly issued patent within the SKICR
Patent Rights in such jurisdiction that has not expired, lapsed or been declared
invalid by a decision of a court of competent jurisdiction from which an appeal
cannot be taken or in respect of which the applicable period of appeal has
expired, and any claim in any then pending application for patent within the
SKICR Patent Rights in such jurisdiction that has not been the subject of a
rejection notice from which an appeal cannot be taken or in respect of which the
applicable period of appeal has expired.

                2.23 IMPROVEMENTS. The term "Improvements" shall mean any
enhancement made by NWBio or its sublicensees to the SKICR Patent Rights.

                2.24 NET SALES. The term "Net Sales" shall mean the [  ***  ]
from a third party attributable to NWBio or its sublicensee's use, sale or
transfer of any Licensed Product [  ***  ] directly attributable to such use,
sale or transfer and actually allowed and borne by NWBio or its sublicensee.
Such [  ***  ]


[  ***  ]INFORMATION HAS BEEN OMITTED PURSUANT TO A REQUEST FOR CONFIDENTIAL
TREATMENT AND HAS BEEN FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION.



                                       5
<PAGE>
[  ***  ] Whenever a product is sold in the form of a combination product
containing a Licensed Product and one or more active ingredients, agents or
compounds that are proprietary, either by ownership or license, to NWBio, its
Affiliates or a third party (other than the Licensed Product), the Net Sales for
such combination product shall be calculated by [  ***  ]. If, on a country by
country basis, the Licensed Product and such other active ingredients, agents or
compounds in the combination product are not sole separately in such country by
NWBio or its sublicensees, Net Sales for purposes of determining royalties on
the combination product shall be calculated by [  ***  ].

                2.25 TECHNOLOGICAL FIELD. The term "Technological Field" shall
mean and collectively include the NWBio Operating Field and the Excluded Field,
each of which terms is defined below:

                        2.25.1 NWBIO OPERATING FIELD. The term "NWBio Operating
        Field" shall mean (a) the manufacture, production, purification or use
        of PSMA, PSMP and/or any mimetopes of PSMA or PSMP; (b) the use of the
        gene(s) encoding PSMA or PSMP solely for the manufacture or production
        of such protein or peptides; (c) the sale of PSMA, PSMP and/or mimetopes
        of PSMA or PSMP to NWBio's sublicensees; (d) the sale of PSMA, PSMP
        and/or mimetopes of PSMA or PSMP to sublicensees for ex vivo clinical
        use, and/or to others for non-clinical research purposes; and (e) the
        manufacture, production or use of Licensed Processes and/or Licensed
        Products; in each case for the immunotherapy of prostate cancer. The
        term "NWBio Operating Field" shall not include any gene therapy with
        PSMA and/or any PSMP or the use of the DNA or RNA encoding such proteins
        and/or peptides to pulse any antigen-presenting cells ex vivo.

                        2.25.2 EXCLUDED FIELD. The term "Excluded Field" shall
        mean the use of any technology and related SKICR Patent Rights for any
        purpose other than the NWBio Operating Field.

        3. REPRESENTATIONS AND WARRANTIES. The following provisions relate to
representations and warranties by the parties:

                3.1 BY CYTOGEN. Prostagen represents and warrants to NWBio that
all of the facts set forth in Article I of this Agreement are true and accurate,
and further represents and warrants, as follows:


[  ***  ]INFORMATION HAS BEEN OMITTED PURSUANT TO A REQUEST FOR CONFIDENTIAL
TREATMENT AND HAS BEEN FILED SEPARATELY WITH THE SECURITIES AND EXCHANGE
COMMISSION.



                                       6
<PAGE>

                        3.1.1 POWER TO ACT. Cytogen has all necessary corporate
        power to enter into and perform its obligations under this Agreement and
        has taken all necessary corporate action under the laws of the State of
        Delaware and its charter and bylaws to authorize the execution and
        consummation of this Agreement.

                        3.1.2 SKICR PATENT RIGHTS. With respect to the SKICR
        Patent Rights,

                                (a) Cytogen is the exclusive licensee under and
        has the right to grant sublicense rights under the SKICR Patent Rights
        in the Technological Field, including the right to preclude unauthorized
        use of such SKICR Patent Rights;

                                (b) that the list of patents and patent
        applications set forth in Schedule A of the PSMA Therapeutics Sublicense
        Agreement represents a full and complete list of all patents and patent
        applications (1) which are included in the SKICR Patent Rights within
        the Technological Field; and (2) which were in existence as of the
        effective date of the PSMA Therapeutics Sublicense Agreement; and

                                (c) that Cytogen had no knowledge of (1) any
        impediment to the enforceability of any patent within the SKICR Patent
        Rights; or (2) any materially relevant prior art reference(s) which has
        not been cited in the United States Patent and Trademark Office with
        respect to the prosecution of any of the United States patents or patent
        applications within such SKICR Patent Rights.

Cytogen has not made any warranty or representation to NWBio as to the
enforceability or validity of any patent within the SKICR Patent Rights.

                        3.1.3 [INTENTIONALLY BLANK]

                        3.1.4 NO LITIGATION. On the Effective Date, there is no
        action, suit, claim, proceeding or governmental investigation pending or
        threatened against Cytogen or Prostagen with respect to any of the SKICR
        Patent Rights, either at law or in equity, before any court or
        administrative agency or before any governmental department, commission,
        board, bureau, agency or instrumentality, whether United States or
        foreign, and Cytogen has no belief that there are basis or grounds for
        any such actions, suits or claims.

                        3.1.5 NO DEFAULT. On the Effective Date, Cytogen is not
        in default with respect to any term or provision of any agreement,
        charter, bylaw, mortgage, indenture, statute, rule or regulation
        applicable to either of them or with respect to any order, writ,
        injunction, decree, rule or regulation of any court or administrative
        agency, which will preclude the performance of its obligations under
        this Agreement.

                        3.1.6 NO MATERIAL CONTRACTS. Cytogen is not subject to
        any contract or agreement materially affecting any of the SKICR Patent
        Rights which will preclude the performance of Cytogen's obligations
        under this Agreement.



                                       7
<PAGE>

                        3.1.7 NO CONFLICTS. Neither the execution nor delivery
        of this Agreement, nor the consummation of the transactions herein
        contemplated, nor the fulfillment of or compliance with the terms and
        provisions hereof will (a) violate any provisions of law, administrative
        regulation or court decree applicable to Cytogen; or (b) conflict with
        or result in a breach of any of the terms, conditions or provisions of
        or constitute a default under the certificate of incorporation or bylaws
        of Cytogen, or of any agreement or instrument to which Cytogen is a
        party or by which Cytogen is bound.

                        3.1.8 NO ADVERSE ACTIVITY. During the term of this
        Agreement, Cytogen shall engage in no activity or omission that would
        adversely affect the rights of NWBio under this Agreement.

                3.2 BY NWBIO. NWBio represents and warrants to Cytogen, as
follows:

                        3.2.1 POWER TO ACT. NWBio has all necessary power to
        enter into and perform its obligations under this Agreement and has
        taken all necessary action under the laws of the State of Washington and
        its articles of incorporation and bylaws to authorize the execution and
        consummation of this Agreement.

                        3.2.2 NO DEFAULT. NWBio is not in default with respect
        to any term or provision of any agreement, charter, bylaw, mortgage,
        indenture, statute, rule or regulation applicable to it, or with respect
        to any order writ, injunction, decree, rule or regulation of any court
        or administrative agency, which will preclude the performance of its
        obligations under this Agreement.

                        3.2.3 NO MATERIAL CONTRACTS. NWBio is not subject to any
        contract or agreement which will preclude the performance of NWBio
        obligations under this Agreement.

                        3.2.4 NO CONFLICTS. Neither the execution nor delivery
        of this Agreement, nor the consummation of the transactions herein
        contemplated nor the fulfillment of or compliance with the terms and
        provisions hereof will (a) violate any provisions of law, administrative
        regulation or court decree applicable to NWBio; or (b) conflict with or
        result in a breach of any of the terms, conditions or provisions of or
        constitute a default under the articles of incorporation or bylaws of
        NWBio, or of any agreement or instrument to which NWBio is a party or by
        which it is bound.

                4. LICENSES. The following provisions relate to the rights and
licenses granted hereunder:

                4.1 GRANT BY CYTOGEN. Subject to the terms and conditions herein
contained, Cytogen hereby grants to NWBio the exclusive right and sublicense
throughout the world only in the NWBio Operating Field, with the right to grant
sublicenses to others,

                        (a) to make, have made, distribute, import, export, use
        and sell, and sell Licensed Products, and



                                       8
<PAGE>

                        (b) to practice and use Licensed Processes

        embodying or made in accordance with the appropriate SKICR Patent
Rights.

Nothing contained herein shall be construed as granting NWBio any right or
license to practice the SKICR Patent Rights within the Excluded Field or for any
purpose other than within the NWBio Operating Field.

                4.2 LIMITED RIGHT TO MOAB 7E11-C5.3. To enable NWBio to utilize
MoAb 7E11-C 5.3 in connection with the development, manufacturing, testing, or
conducting quality control tests on Licensed Products and to practice Licensed
Processes all in accordance with Section 4.1, Cytogen hereby grants NWBio the
right to use MoAb 7E11-C.5.3 solely for such purposes.

                        4.2.1 ANTIBODY REQUIREMENTS. NWBio agrees to purchase
        its requirements of MoAb 7E11-C5.3 from Cytogen, and Cytogen agrees to
        supply NWBio requirements of MoAb 7E11-C5.3, on terms and conditions
        satisfactory to both Cytogen and NWBio.

                        4.2.2 CONTINGENT LICENSE. In the event that Cytogen is
        unable or unwilling to supply NWBio requirements of MoAb 7E11-C5.3,
        Cytogen shall, upon written request of NWBio, provide to NWBio, at no
        cost to NWBio, a viable sample of a hybridoma capable of producing MoAb
        7E11-C5.3, and thereafter NWBio shall have the right to use the
        hybridoma and to produce and use MoAb 7E11-C5.3 for the purposes set
        forth in this Paragraph 4.2.

        5. DILIGENCE. NWBio shall use reasonable commercial efforts to promptly
develop, obtain Regulatory Approval for, manufacturing, marketing and selling
Licensed Products. In the event that Cytogen, from time to time during the term
of this Agreement, determines, in the exercise of its reasonable business
discretion after interaction and discussion with NWBio, that NWBio is not using
reasonable commercial efforts to develop, obtain Regulatory Approval for,
manufacturing, marketing and selling Licensed Products within the United States
and at least one other Major Market, then the resolution of such matter will be
finally settled by binding arbitration in Seattle, Washington in accordance with
the then current rules and procedures of the American Arbitration Association,
by one (1) arbitrator appointed in accordance with such rules. The arbitrators
shall apply the laws of the State of Washington, without reference to rules of
conflict of law or statutory rules of arbitration, to the merits of any dispute
or claim and shall have the right to grant injunctive relief. Judgment on the
award rendered by the arbitrators may be entered in any Court having
jurisdiction thereof.

        6. MILESTONE PAYMENTS AND ROYALTIES. The following provisions relate to
milestone and royalty payments to be made by NWBio hereunder:

                6.1 MILESTONE PAYMENTS. The following provisions relate to the
milestone payments to be made by NWBio hereunder:



                                       9
<PAGE>

                        6.1.1 FIRST MILESTONE PAYMENT. Within thirty (30) days
        of the issuance of the first Regulatory Approval for the use of a
        Licensed Product in a Major Market, other than for PSMA and/or PSMP,
        NWBio shall pay Cytogen the sum of Two Hundred Fifty Thousand Dollars
        ($250,000.00).

                        6.1.2 FINAL MILESTONE PAYMENT. NWBio shall pay Cytogen
        the sum of Seven Hundred Fifty Thousand Dollars ($750,000); which amount
        shall be payable in installments in accordance with Subsections 6.5.2
        and 6.5.3, each of which shall be equal to two percent (2%) of the Net
        Sales for the immediately preceding calendar quarter. Such installments
        shall commence on the last day of the month during which the first
        Commercial Sale transpires and continue until the earlier of (i) two (2)
        years or (ii) the aggregate amount of such payments equals $750,000. In
        the event that that aggregate amount of the such payments is less than
        $750,000 then the amount of the final payment shall be increased so that
        the aggregate amount of all payments made pursuant to this Subsection
        6.1.2 is equal to $750,000. Notwithstanding anything to the contrary in
        this Agreement, in no event shall the $750,000 sum be fully paid by
        NWBio to Cytogen later than two (2) years from the first payment
        specified above in this Subsection 6.1.2.

                6.2 MINIMUM ANNUAL PAYMENTS. During each twelve (12) month
period of the Agreement commencing on the Effective Date, until the commencement
of the Phase III Clinical Trial (including pro-rata the last 12 month period),
NWBio agrees to pay Cytogen minimum annual payments of Ten Thousand Dollars
($10,000) per year.

                6.3 ROYALTY PAYMENTS. NWBio shall, during the Contract Period,
pay Cytogen a royalty of five percent (5%) on all Net Sales. Such payments will
be paid in accordance with Subsections 6.5.2 and 6.5.3 below.

                6.4 BOOKS AND RECORDS. NWBio agrees to keep adequate and
complete records showing all Net Sales, with respect to which earned royalties
are due Cytogen hereunder. Such records shall include all information necessary
to verify the total amount and computation of earned royalties hereunder, and
shall be open to inspection by Cytogen during reasonable business hours to the
extent necessary to verify the amount thereof. Such inspection shall be made no
more often than once each calendar year at the expense of Cytogen by an auditor
appointed by Cytogen and to whom NWBio has no reasonable objection, provided
that such auditor shall be under a confidentiality obligation to NWBio to reveal
only that information, and only to Cytogen, necessary to verify the royalties
due hereunder. In addition, such inspection shall be limited to a period not to
extend beyond two (2) years after the date of the receipt by Cytogen of a report
from NWBio relating to such records pursuant to Section 6.5.1. After such two
(2) year period, any such report and the records upon which such report was
based shall be deemed presumptively correct.

                6.5 REPORTS AND ROYALTY PAYMENTS. The following provisions
relate to reports and royalty payments by NWBio:



                                       10
<PAGE>

                        6.5.1 REPORTS. On or before the last day of each
        February, May, August, and November throughout the Contract Period,
        NWBio shall furnish Cytogen with a written report, signed by an
        authorized officer or agent of NWBio showing all Net Sales with respect
        to which earned royalties are due Cytogen hereunder.

                        6.5.2 ROYALTY PAYMENTS. With each such quarterly report,
        NWBio shall remit to Cytogen the total amount of earned royalties shown
        thereby to be due. All payments shall be made in lawful funds of the
        United States of America.

                        6.5.3 CURRENCY CONTROL RESTRICTIONS. In the event that
        NWBio is precluded from transferring royalties due Cytogen hereunder at
        any time during the Contract Period because NWBio has failed after due
        diligence to obtain the approval of such transfer from the appropriate
        governmental agency responsible for control of currency exchanges of a
        particular country in which NWBio has sold Licensed Products, then NWBio
        agrees (a) to deposit or to cause the deposit of such royalties to the
        account of Cytogen in a bank in such country designated by Cytogen; (b)
        to provide or to cause the providing of Cytogen with documentary
        evidence of such deposits; and (c) to remit or to cause remittance of
        such deposits to Cytogen immediately upon the subsequent approval of
        such transfers by such governmental agency. NWBio further agrees that
        the form of such depository account shall permit Cytogen to withdraw the
        deposited amounts at will, but shall permit NWBio to withdraw the
        deposited amounts solely for the purpose of remitting such amounts to
        Cytogen pursuant to the provisions of this Section 6.5.3.

        7. PRODUCT LIABILITY DISCLAIMERS. The following provisions relate to
product liability disclaimers:

                7.1 PRODUCT LIABILITY DISCLAIMER BY CYTOGEN. Cytogen assumes no
responsibility for the manufacturer, product specifications, end-use or
provision of any Licensed Products which are manufactured or provided by or for,
or sold by NWBio. All warranties in connection with such Licensed Products made
or provided by NWBio shall not directly or impliedly obligate Cytogen in any
manner whatsoever under such warranties or otherwise.

                7.2 PRODUCT LIABILITY DISCLAIMER BY NWBIO. NWBio assumes no
responsibility for the manufacture or product specifications or end-use of any
products which are manufactured by or for Cytogen except for the manufacture or
product specifications of materials made by or for NWBio and sold to Cytogen.
Any warranties in connection with such products made by Cytogen as user of such
products shall nor directly or impliedly obligate NWBio.

        8. TERM AND TERMINATION. The following provisions relate to the term and
termination of this Agreement:

                8.1 TERM. Unless sooner terminated in a manner herein provided,
this Agreement shall continue in force until the expiration of the last to
expire patent included in SKICR Patent Rights.



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<PAGE>

                8.2 TERMINATION. This Agreement may be terminated, in whole or
in part, at any time prior to the term set forth in Paragraph 8.1 hereof, as
follows:

                        8.2.1 BY NWBIO. At any time after December 31, 2000,
        NWBio may terminate this Agreement by giving Cytogen at least sixty (60)
        days notice in writing.

                        8.2.2 BY BREACH. In the event either party shall
        materially breach any of the terms, conditions or agreements contained
        herein to be kept, observed and performed by it, then the other party
        may give written notice thereof to the breaching party. If the breaching
        party has not cured the breach within sixty (60) days after receipt of
        such notice, then the non-breaching party may commence arbitration of
        such matter pursuant to the arbitration provisions set forth in Section
        5 above.

                        8.2.3 BY BANKRUPTCY, INSOLVENCY OR SUSPENSION OF
        BUSINESS. In the event (a) NWBio on the one hand or Cytogen on the other
        hand shall become insolvent or shall suspend business, or shall file a
        voluntary petition or any answer admitting the jurisdiction of the Court
        and the material allegations of, or shall consent to an involuntary
        petition pursuant to or purporting to be pursuant to any reorganization
        or insolvency law of any jurisdiction, or shall make an assignment for
        the benefit of creditors, or shall apply for or consent to the
        appointment of a receiver or trustee of a substantial part of its
        property, and (b) no Affiliate of such party shall undertake to assume
        its obligations under the provisions of this Agreement within ninety
        (90) days from the date on which such party becomes so disabled, then to
        the extent permitted by law the other party may thereafter immediately
        terminate this Agreement by giving written notice of termination to the
        disabled party.

                8.3 ACCRUED RIGHTS AND OBLIGATIONS. Termination of this
Agreement shall not relieve any party of any rights and obligations then accrued
hereunder or which extend beyond the date of such termination. In the event that
this Agreement is terminated pursuant to Sections 8.2.2 or 8.2.3 due to the
breach, bankruptcy, insolvency or business suspension of Cytogen, NWBio shall
have the right to use the licenses granted under this Agreement until the last
to expire patent included in SKICR Patent Rights; provided, however, NWBio shall
adhere to all terms and conditions, including making any payments specified
herein. If the Agreement is terminated by Cytogen pursuant to the terms of this
Agreement, all licenses granted to NWBio shall immediately cease and NWBio will
return any and all Cytogen materials. NWBio shall have the right to sell-off any
inventory of Licensed Products manufactured prior to the termination date, under
the terms and conditions specified in this Agreement.

        9. ASSIGNABILITY. Neither this Agreement nor any interest hereunder
shall be assignable by either party without the written consent of the other,
and any attempted assignment without such consent shall be null and void. For
the purposes of this Section 9, a change of corporate domicile by either party
hereof shall not result in an assignment of this Agreement or any interest
hereunder. This Agreement shall be binding upon the successors and permitted
assignees of the parties. Any such successor or permitted assignee shall be
subject to the same rights and obligations as the original party hereunder.



                                       12
<PAGE>

        10. EXPORT LICENSES. This Agreement is subject to any restrictions
concerning the export of products or technical information from the United
States which may be imposed by the United States. Accordingly, each party agrees
that it will not export directly or indirectly, any technical information
acquired under this Agreement or any products utilizing any such technical
information to any country for which the United States Government or any agency
thereof at the time of export requires an export license or other governmental
approval, without first obtaining the written consent to do so from the
Department of Commerce or other agency of the United States Government when
required by an applicable statute or regulation.

        11. MISCELLANEOUS PROVISIONS. The following miscellaneous provisions
shall apply to this Agreement:

                11.1 NOTICES. All notices and communications provided for
hereunder shall be in writing and shall be mailed or delivered to the business
address of the respective parties aforementioned, or to such other address as
either party shall designate in writing to the others.

                11.2 INDEPENDENT CONTRACTORS. No agency, partnership or joint
venture is hereby established. Neither Cytogen nor NWBio shall enter into, or
incur, or hold itself out to third parties as having authority to enter into or
incur on behalf of the other party any contractual obligations, expenses or
liabilities whatsoever, except as expressly provided herein.

                11.3 COUNTERPARTS. This Agreement may be executed simultaneously
in multiple counterparts, each of which shall be deemed to be an original but
all of which together shall constitute one and the same agreement.

                11.4 ENTIRE UNDERSTANDING. This Agreement constitutes the entire
understanding between the parties hereto with respect to the subject matter
hereof. No modifications, extensions, or waiver of any provisions hereof or any
release of any right hereunder shall be valid, unless the same is in writing,
contains reference to this Agreement and sets forth the plan or intention to
modify same, and is consented to by all parties hereto.

                11.5 HEADINGS. The headings of this Agreement are intended
solely for convenience of reference and shall be given no effect in the
construction or interpretation of this Agreement.

                11.6 NO IMPLIED RIGHTS. Except as expressly provided for in this
Agreement, nothing contained herein shall be construed as conferring any license
or other rights, by implication or estoppel, under any patent (including design
patent and utility model patent) or patent application, or any copyrights,
trademarks, trade names or trade dress.

                11.7 NO WAIVER. The failure of either party hereto at any time
or times to require performance of any provision hereof shall in no manner
affect the right of such party at a later time to enforce the same. No waiver by
any party hereto of any condition, or of the breach of any provision, term,
covenant, representation, or warranty contained in this Agreement, whether by
conduct or otherwise, in any one or more instances, shall be deemed to be or



                                       13
<PAGE>

construed as a further or continuing waiver of any such condition or of the
breach of any other provision, term, covenant, representation, or warranty of
this Agreement.

                11.8 PROMOTION AND ADVERTISING. Nothing contained in this
Agreement shall be construed as conferring any right to use in advertising,
publicity or other promotional activities any name, trade name, trademark, or
other designation (including any contraction, abbreviation, or simulation of any
of the foregoing); and, each party hereto agrees not to use any designation of
the other party in any promotional activity associated with this Agreement, or
with product licensed thereunder, without the express written approval of the
other party.

                11.9 GOVERNING LAW. This Agreement shall be interpreted,
construed, and governed in accordance with the laws of the State of Washington,
without reference to conflict of laws principles.

        IN WITNESS WHEREOF, the parties have each caused their respective
corporate seals to be hereto affixed and duly witnessed and these present to be
signed by their respective corporate officers thereunto duly authorized.

CYTOGEN CORPORATION                         NORTHWEST BIOTHERAPEUTICS INC.



By                                          By
  ----------------------------------          ----------------------------------

Title                                       Title
     -------------------------------             -------------------------------

Date:  August 28, 2000                      Date:  August 28, 2000



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