Document:

<PAGE>
                                                                     EXHIBIT 4.2

                  AMENDMENT TO NORTHWEST BIOTHERAPEUTICS, INC.
                          STOCKHOLDER RIGHTS AGREEMENT

         This Amendment is made as of this 26th day of April, 2004, between
Northwest Biotherapeutics, Inc., a Delaware corporation (the "Company"), and
Mellon Investor Services LLC, a New Jersey limited liability company, as Rights
Agent ("Rights Agent"). This Amendment amends the Northwest Biotherapeutics,
Inc. Stockholder Agreement dated February 26, 2002 between the Company and the
Rights Agent (the "Rights Agreement").

         Whereas the Company intends to enter into a certain Recapitalization
Agreement (the "Recapitalization Agreement") with Toucan Capital Fund II, L.P.
("Investor") pursuant to which it is contemplated that the Company (i) will
issue to Investor one or more promissory notes that are convertible into capital
stock of the Company, will issue to Investor one or more warrants, and (ii) will
grant to Investor and Other Investors (as defined in the Recapitalization
Agreement) the right to acquire additional shares of the Company's capital stock
and other securities convertible into shares of the Company's capital stock.

         Whereas Investor, upon conversion of one ore more promissory notes
and/or exercise of warrants or its other rights under the Recapitalization
Agreement, will own more than 15% of the outstanding capital stock of the
Company.

         Whereas, if the recapitalization is fully implemented, Investor, Other
Investors and their respective Affiliates or Associates will own at least a
majority of the outstanding capital stock of the Company.

         Whereas pursuant to Section 27 of the Rights Agreement the Board of
Directors of the Company has determined that an amendment to the Rights
Agreement as set forth herein is necessary and desirable in order to reflect the
foregoing and the Company and the Rights Agent desire to evidence such an
amendment in writing.

         Now, therefore, intending to be legally bound the Company and the
Rights Agent hereby agree that the Rights Agreement is hereby amended as
follows:

         1. The first sentence of the definition "Acquiring Person" in Section 1
of the Rights Agreement is amended to read as follows:

         "Acquiring Person" shall mean any Person which, alone or together with
all Affiliates and Associates of such Person, shall become after the date
hereof, the Beneficial Owner of 15% or more of the Common Shares then
outstanding, but shall not include (a) NWBio, any subsidiary of NWBio, any
employee benefit plan of NWBio, or any of its subsidiaries, or any Person
holding Common Shares for or pursuant to the terms of any such employee benefit
plan, or any Common Shares or other securities of the Company that are
convertible into or

<PAGE>

exchangeable for Common Shares acquired by Investor, Other Investors (as defined
in the Recapitalization Agreement) or any of their respective Affiliates or
Associates pursuant to the terms of the Recapitalization Agreement or any
agreement or agreements executed in connection with the Recapitalization
Agreement, or (b) any such Person who has become such a beneficial owner solely
because (i) of a change in the aggregate number of Common Shares outstanding
since the last date on which such Person acquired Beneficial Ownership of any
Common Shares or (ii) it acquired beneficial ownership in a good faith belief
that such acquisition would not (y) cause such beneficial ownership to exceed
15% of the Common Shares then outstanding and such Person relied in good faith
in computing the percentage of its beneficial ownership on publicly filed
reports or documents of NWBio that are inaccurate or out of date or (z)
otherwise cause a distribution date or the adjustment provided for in Section
11(a) to occur.

         2. Section 1 of the Rights Agreement is amended to add the following
new definition:

         "`Recapitalization Agreement' shall mean the certain Recapitalization
Agreement dated as of April 26, 2004, between NWBio and Toucan Capital Fund II,
L.P."

         3. Section 3(b) of the Rights Agreement is amended to add the following
sentence at the end thereof:

         Notwithstanding anything in the Rights Agreement to the contrary, a
Distribution Date shall not be deemed to have occurred solely as a result of the
announcement, approval, execution or delivery of the Recapitalization Agreement,
any documents executed in connection with the Recapitalization Agreement, or the
consummation of the transactions contemplated by the Recapitalization Agreement.

         4. Section 27 of the Rights Agreement is amended to add the following
sentence at the end thereof:

         Notwithstanding any other provision of this Rights Agreement, no
further amendment or supplement shall be made to the definition of "Acquiring
Person" that would cause Investor or Other Investor to be deemed an "Acquiring
Person" for those Common Shares acquired in connection with the Recapitalization
Agreement.

         5. Effectiveness. This Amendment shall be effective as of April ___,
2004. Except as amended hereby, the Rights Agreement shall remain in full force
and effect and shall be otherwise unaffected hereby.

         6. Miscellaneous. This Amendment shall be deemed to be a contract made
under the laws of the state of Delaware and for all purposes shall be governed
by and construed in accordance with the laws of such state applicable to
contracts made and performed entirely within such state. This Amendment may be
executed in any number of counterparts, each of such counterparts shall for all
purposes be deemed to be an original and all such counterparts shall be deemed
to be an original and all such counterparts shall together constitute one and
the same instrument. If any provision, covenant or restriction of this Amendment
is held by a court

                                       2
<PAGE>

of competent jurisdiction or other authority to be invalid, illegal or
unenforceable, the remainder of the terms, provisions, covenants and
restrictions of this Amendment shall remain in full force and effect and shall
in no way be affected, impaired, or invalidated.

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed all as of the date and year first written above.

NORTHWEST BIOTHERAPEUTICS, INC.               MELLON INVESTOR SERVICES LLC,
                                              as Rights Agent

By /s/ Alton L. Boynton                       By /s/ Lisa Porter
   Its President                                 Its Client Service Manager

                                       3<PAGE>

                                                               EXECUTION VERSION

EXHIBIT 10.3

                               FIRST AMENDMENT TO
                       WARRANTS TO PURCHASE COMMON SHARES

      THIS FIRST AMENDMENT TO WARRANTS TO PURCHASE COMMON SHARES (the
"AMENDMENT") is made and entered into as of April 25, 2004, by and among
NORTHWEST BIOTHERAPEUTICS, INC., a Delaware corporation (the "COMPANY"), and the
undersigned holders of Warrants (as defined below) to acquire shares of the
Company's common stock (each a "WARRANTHOLDER" and, collectively, the
"WARRANTHOLDERS"). When signed by the holders of at least 50% of the common
stock subject to Warrants (as defined below) this Amendment will amend each of
the Warrants .

                                    RECITALS

      WHEREAS, the Company and the undersigned Warrantholder(s) desire to amend
all of the Company Warrants to Purchase Common Shares, of series Nos. BR-1
through BR-5, each dated as of November 13, 2003 (each, a "WARRANT" and,
collectively, the "WARRANTS"), as provided herein.

                                    AGREEMENT

      NOW, THEREFORE, in consideration of the mutual covenants and promises
contained herein, and for other good and valuable consideration, the receipt and
adequacy of which are hereby acknowledged, the parties agree as follows:

1.    Section 8(a) of each Warrant is hereby amended and restated in its
      entirety as follows:

            "(a) In the event of changes in the Common Stock by reason of stock
      dividends, splits, recapitalizations, reclassifications, combinations or
      exchanges of shares, separations, reorganizations, liquidations, or the
      like, the number and class of Warrant Shares available under this Warrant
      in the aggregate and the Warrant Price shall be correspondingly adjusted
      to give the Warrantholder, on exercise for the same Aggregate Warrant
      Price, the total number, class, and kind of shares as the Warrantholder
      would have owned had this Warrant been exercised prior to the event and
      had the Warrantolder continued to hold such shares until after the event
      requiring adjustment. Notwithstanding the foregoing, no adjustment to the
      number of Warrant Shares or the Warrant Price shall be made in the event
      of an issuance or deemed issuance of securities for consideration below
      the then current Warrant Price pursuant to this Section 8(a). For purposes
      of this Section 8(a), the "AGGREGATE WARRANT PRICE" shall mean the
      aggregate Warrant Price payable in connection with the exercise in full of
      this Warrant. The form of this Warrant need not be changed because of any
      adjustment in the number of Warrant Shares subject to this Warrant."

2.    The first paragraph of Section 8(d) of each Warrant is hereby amended and
      restated in its entirety to read as follows:

            "Except as provided in subsections (e) and (f) of this Section 8, if
      and whenever the Company shall issue or sell, or is, in accordance with
      any of subsections (d)(l) through (d)(6) hereof, deemed to have issued or
      sold, any shares of Common Stock for no consideration or for a
      consideration per share less than the Warrant Price in effect immediately
      prior to the time of such issue or sale, then and in each such case (a
      "Trigger Issuance") the then-existing Warrant Price, shall be reduced, as
      of the close of business on the effective date of the Trigger Issuance, to
      the lowest price per share at which any share of Common Stock was issued
      or sold or deemed to be issued or sold, but in no event shall the Warrant
      Price be reduced to less than the lesser of $0.10 per share (subject to
      adjustment as provided in Section 8(a)) or 35% discount to the average
      closing price during the twenty trading days prior to the first closing of
      the sale by the Company of Convertible Preferred Stock, par value $0.001
      per share as contemplated by that certain Recapitalization Agreement dated
      as of April 26, 2004 between the Company and Toucan Capital Fund II, L.P.;
      provided, however, that in no event will the Warrant Price be less than
      $.04 per share (subject to adjustment as provided in Section 8(a))"

3.    Section 8(f) of each Warrant is hereby amended and restated in its
      entirety to read as follows:

            "Anything to the contrary herein notwithstanding, in no event shall
      the then existing Warrant Price be reduced to less than the lesser of
      $0.10 per share (subject to adjustment as provided in Section 8(a)) or 35%
      discount to the average closing price during the twenty trading days prior
      to the first closing of the sale by the Company of Convertible Preferred
      Stock, par value $0.001 per share as contemplated by that certain
      Recapitalization Agreement dated as of April 26, 2004 between the Company
      and Toucan Capital Fund II, L.P.; provided, however, that in no event will
      the Warrant Price be less than $.04 per share (subject to adjustment as
      provided in Section 8(a)) pursuant to the adjustments provided for in
      Section 8(d)."
<PAGE>
                                                               EXECUTION VERSION

4.    Sections 8(b) and 8(c) of each Warrant are hereby deleted in their
      entirety.

5.    Section 18 of each Warrant is hereby deleted in its entirety.

6.    All other terms and conditions of the Warrants shall be unaffected hereby
      and remain in full force and effect.

7.    This Amendment shall be governed by and construed under the laws of the
      State of Washington as applied to agreements among Washington residents
      entered into and to be performed entirely within the State of Washington.

8.    This Amendment may be executed in one or more counterparts, each of which
      will be deemed an original but all of which together shall constitute one
      and the same agreement.

                            [SIGNATURE PAGE FOLLOWS]

                                       2.
<PAGE>
                                                               EXECUTION VERSION

      IN WITNESS WHEREOF, the parties hereto have executed this FIRST AMENDMENT
TO WARRANT TO PURCHASE COMMON SHARES as of the date first above written.

                                 COMPANY:

                                 NORTHWEST BIOTHERAPEUTICS, INC.,
                                 a Delaware corporation

                                 By:
                                    ----------------------------------------
                                 Name:
                                 Title:

                                 WARRANTHOLDERS:

                                 /s/ Alton L. Boynton
                                 --------------------------------------------
                                 Alton L. Boynton

                                 /s/ Marnix L. Bosch
                                 --------------------------------------------
                                 Marnix L. Bosch

                                 /s/ Eric H. Holmes
                                 --------------------------------------------
                                 Eric H. Holmes

                                 /S/ Larry L. Richards
                                 --------------------------------------------
                                 Larry Richards

              FIRST AMENDMENT TO WARRANT TO PURCHASE COMMON SHARES

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00066-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00066-of-00352.parquet"}]]