Document:

<PAGE>

EXHIBIT 10.17

   THIRD AMENDMENT TO NORTHWEST BIOTHERAPEUTICS, INC. LOAN AGREEMENT, SECURITY
             AGREEMENT AND 10% CONVERTIBLE, SECURED PROMISSORY NOTE

      THIS THIRD AMENDMENT TO NORTHWEST BIOTHERAPEUTICS, INC. LOAN AGREEMENT,
SECURITY AGREEMENT AND 10% CONVERTIBLE, SECURED PROMISSORY NOTE (the "THIRD
AMENDMENT") is made and entered into as of November 14, 2005, by and among
NORTHWEST BIOTHERAPEUTICS, INC., a Delaware corporation (the "MAKER") and Toucan
Capital Fund II, L.P. (the "HOLDER"). This Second Amendment amends the Note (as
defined below).

                                    RECITALS

A. Section 17.6 of that certain Northwest Biotherapeutics, Inc. Loan Agreement,
Security Agreement and 10% Convertible, Secured Promissory Note, in the
principal amount of $50,000.00 amended and restated as of July 30, 2004 and
originally issued on February 2, 2004, by and between the Maker and the Holder
in the form attached to this Third Amendment as Exhibit A and as amended by that
First Amendment to Northwest Biotherapeutics, Inc. Loan Agreement, Security
Agreement and 10% Convertible, Secured Promissory Note in the form attached to
this Third Amendment as Exhibit B and as further amended by that Second
Amendment to Northwest Biotherapeutics, Inc. Loan Agreement, Security Agreement
and 10% Convertible, Secured Promissory Note in the form attached to this Third
Amendment as Exhibit C (as so amended, the "NOTE"), states that any provision of
such note may be amended or waived in writing by the Holder and the Maker; and

B. The Maker and the Holder wish to amend the Note as provided below.

                                    AGREEMENT

      NOW, THEREFORE, in consideration of these premises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

1. Section 1 of the Note is hereby amended to provide that the Maturity Date is
January 17, 2006.

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

3. This Third Amendment shall be governed by and construed under the laws of the
state of Delaware without giving effect to principles of conflicts of laws of
the State of Delaware or any other state.

                            [SIGNATURE PAGE FOLLOWS]

                                        1
<PAGE>

      IN WITNESS WHEREOF, the parties hereto have executed this THIRD AMENDMENT
TO NORTHWEST BIOTHERAPEUTICS, INC. LOAN AGREEMENT, SECURITY AGREEMENT AND 10%
CONVERTIBLE, SECURED PROMISSORY NOTE as of the date first above written.

MAKER:

NORTHWEST BIOTHERAPEUTICS, INC.,
a Delaware corporation

By: /s/ Alton L. Boynton
    --------------------
Name: Alton L. Boynton
Title: President

HOLDER:

Toucan Capital Fund II, L.P.

By: /s/ Linda Powers
    ---------------------------------
    Linda Powers, Managing Director

259035 v2/RE

                                       2<PAGE>

EXHIBIT 10.18

   THIRD AMENDMENT TO NORTHWEST BIOTHERAPEUTICS, INC. LOAN AGREEMENT, SECURITY
             AGREEMENT AND 10% CONVERTIBLE, SECURED PROMISSORY NOTE

      THIS THIRD AMENDMENT TO NORTHWEST BIOTHERAPEUTICS, INC. LOAN AGREEMENT,
SECURITY AGREEMENT AND 10% CONVERTIBLE, SECURED PROMISSORY NOTE (the "THIRD
AMENDMENT") is made and entered into as of November 14, 2005, by and among
NORTHWEST BIOTHERAPEUTICS, INC., a Delaware corporation (the "MAKER") and Toucan
Capital Fund II, L.P. (the "HOLDER"). This Second Amendment amends the Note (as
defined below).

                                    RECITALS

A. Section 17.6 of that certain Northwest Biotherapeutics, Inc. Loan Agreement,
Security Agreement and 10% Convertible, Secured Promissory Note, in the
principal amount of $50,000.00 amended and restated as of July 30, 2004 and
originally issued on March 1, 2004, by and between the Maker and the Holder in
the form attached to this Third Amendment as Exhibit A and as amended by that
First Amendment to Northwest Biotherapeutics, Inc. Loan Agreement, Security
Agreement and 10% Convertible, Secured Promissory Note in the form attached to
this Third Amendment as Exhibit B and as further amended by that Second
Amendment to Northwest Biotherapeutics, Inc. Loan Agreement, Security Agreement
and 10% Convertible, Secured Promissory Note in the form attached to this Third
Amendment as Exhibit C (as so amended, the "NOTE"), states that any provision of
such note may be amended or waived in writing by the Holder and the Maker; and

B. The Maker and the Holder wish to amend the Note as provided below.

                                    AGREEMENT

      NOW, THEREFORE, in consideration of these premises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

1. Section 1 of the Note is hereby amended to provide that the Maturity Date is
January 17, 2006.

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

3. This Third Amendment shall be governed by and construed under the laws of the
state of Delaware without giving effect to principles of conflicts of laws of
the State of Delaware or any other state.

                            [SIGNATURE PAGE FOLLOWS]

                                        1
<PAGE>

      IN WITNESS WHEREOF, the parties hereto have executed this THIRD AMENDMENT
TO NORTHWEST BIOTHERAPEUTICS, INC. LOAN AGREEMENT, SECURITY AGREEMENT AND 10%
CONVERTIBLE, SECURED PROMISSORY NOTE as of the date first above written.

MAKER:

NORTHWEST BIOTHERAPEUTICS, INC.,
a Delaware corporation

By: /s/ Alton L. Boynton
    --------------------
Name: Alton L. Boynton
Title: President

HOLDER:

Toucan Capital Fund II, L.P.

By: /s/ Linda Powers
    ---------------------------------
      Linda Powers, Managing Director

259036 v2/RE

                                        2<PAGE>

EXHIBIT 10.19

   THIRD AMENDMENT TO NORTHWEST BIOTHERAPEUTICS, INC. LOAN AGREEMENT, SECURITY
             AGREEMENT AND 10% CONVERTIBLE, SECURED PROMISSORY NOTE

      THIS THIRD AMENDMENT TO NORTHWEST BIOTHERAPEUTICS, INC. LOAN AGREEMENT,
SECURITY AGREEMENT AND 10% CONVERTIBLE, SECURED PROMISSORY NOTE (the "THIRD
AMENDMENT") is made and entered into as of November 14, 2005, by and among
NORTHWEST BIOTHERAPEUTICS, INC., a Delaware corporation (the "MAKER") and Toucan
Capital Fund II, L.P. (the "HOLDER"). This Second Amendment amends the Note (as
defined below).

                                    RECITALS

A. Section 17.6 of that certain Northwest Biotherapeutics, Inc. Loan Agreement,
Security Agreement and 10% Convertible, Secured Promissory Note, in the
principal amount of $500,000.00 amended and restated as of July 30, 2004 and
originally issued on April 26, 2004, by and between the Maker and the Holder in
the form attached to this Third Amendment as Exhibit A and as amended by that
First Amendment to Northwest Biotherapeutics, Inc. Loan Agreement, Security
Agreement and 10% Convertible, Secured Promissory Note in the form attached to
this Third Amendment as Exhibit B and as further amended by that Second
Amendment to Northwest Biotherapeutics, Inc. Loan Agreement, Security Agreement
and 10% Convertible, Secured Promissory Note in the form attached to this Third
Amendment as Exhibit C (as so amended, the "NOTE"), states that any provision of
such note may be amended or waived in writing by the Holder and the Maker; and

B. The Maker and the Holder wish to amend the Note as provided below.

                                    AGREEMENT

      NOW, THEREFORE, in consideration of these premises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

1. Section 1 of the Note is hereby amended to provide that the Maturity Date is
January 17, 2006.

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

3. This Third Amendment shall be governed by and construed under the laws of the
state of Delaware without giving effect to principles of conflicts of laws of
the State of Delaware or any other state.

                            [SIGNATURE PAGE FOLLOWS]

                                        1
<PAGE>

      IN WITNESS WHEREOF, the parties hereto have executed this THIRD AMENDMENT
TO NORTHWEST BIOTHERAPEUTICS, INC. LOAN AGREEMENT, SECURITY AGREEMENT AND 10%
CONVERTIBLE, SECURED PROMISSORY NOTE as of the date first above written.

MAKER:

NORTHWEST BIOTHERAPEUTICS, INC.,
a Delaware corporation

By: /s/ Alton L. Boynton
    ---------------------
Name: Alton L. Boynton
Title: President

HOLDER:

Toucan Capital Fund II, L.P.

By: /s/ Linda Powers
    ---------------------------------
      Linda Powers, Managing Director

259037 v2/RE

                                        2<PAGE>

EXHIBIT 10.20

  SECOND AMENDMENT TO NORTHWEST BIOTHERAPEUTICS, INC. LOAN AGREEMENT, SECURITY
             AGREEMENT AND 10% CONVERTIBLE, SECURED PROMISSORY NOTE

      THIS SECOND AMENDMENT TO NORTHWEST BIOTHERAPEUTICS, INC. LOAN AGREEMENT,
SECURITY AGREEMENT AND 10% CONVERTIBLE, SECURED PROMISSORY NOTE (the "SECOND
AMENDMENT") is made and entered into as of November 14, 2005, by and among
NORTHWEST BIOTHERAPEUTICS, INC., a Delaware corporation (the "MAKER") and Toucan
Capital Fund II, L.P. (the "HOLDER"). This Second Amendment amends the Note (as
defined below).

                                    RECITALS

A. Section 17.6 of that certain Northwest Biotherapeutics, Inc. Loan Agreement,
Security Agreement and 10% Convertible, Secured Promissory Note, in the
principal amount of $500,000.00 amended and restated as of July 30, 2004 and
originally issued on June 11, 2004, by and between the Maker and the Holder in
the form attached to this Second Amendment as Exhibit A and as amended by that
First Amendment to Northwest Biotherapeutics, Inc. Loan Agreement, Security
Agreement and 10% Convertible, Secured Promissory Note in the form attached to
this Second Amendment as Exhibit B (as so amended, the "NOTE"), states that any
provision of such note may be amended or waived in writing by the Holder and the
Maker; and

B. The Maker and the Holder wish to amend the Note as provided below.

                                    AGREEMENT

      NOW, THEREFORE, in consideration of these premises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

1. Section 1 of the Note is hereby amended to provide that the Maturity Date is
January 17, 2006.

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

3. This Second Amendment shall be governed by and construed under the laws of
the state of Delaware without giving effect to principles of conflicts of laws
of the State of Delaware or any other state.

                            [SIGNATURE PAGE FOLLOWS]

                                        1
<PAGE>

      IN WITNESS WHEREOF, the parties hereto have executed this SECOND AMENDMENT
TO NORTHWEST BIOTHERAPEUTICS, INC. LOAN AGREEMENT, SECURITY AGREEMENT AND 10%
CONVERTIBLE, SECURED PROMISSORY NOTE as of the date first above written.

MAKER:

NORTHWEST BIOTHERAPEUTICS, INC.,
a Delaware corporation

By: /s/ Alton L. Boynton
    --------------------
Name: Alton L. Boynton
Title: President

HOLDER:

Toucan Capital Fund II, L.P.

By: /s/ Linda Powers
    ---------------------------------
      Linda Powers, Managing Director

259031 v2/RE

                                        2

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