Document:

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                                                                  Exhibit 10.83

March 8, 2001

Alessandro Sette, Ph.D.
5551 Linda Rosa Avenue
La Jolla, California 92037

Re: Amendment to Severance Benefits Agreement

Dear Alex:

This amendment (the "Amendment") to the Severance Benefits Agreement (the
"Agreement") dated February 5, 1998 by and between EPIMMUNE INC. (the
"Company"), and ALESSANDRO SETTE, PH.D. (the "Employee") is entered into as of
March 8, 2001 (the "Amendment Date").

1.      The Company agrees that the paragraph on page 3 of the Agreement which
        formerly read:

        If, within 365 days following the occurrence of a Change in Control,
        your employment is involuntarily terminated without Cause or you
        voluntarily terminate your employment for Good Reason, then (1) within
        30 days of such termination you will receive a lump-sum payment equal to
        six months of base salary subject to any applicable withholding of
        federal, state or local taxes and (2) the vesting of any stock option
        for Company stock and the time during which such option may be exercised
        immediately will be accelerated as to 50% of the then unvested shares.

is hereby amended and restated as follows:

        If, within 365 days following the occurrence of a Change in Control,
        your employment is involuntarily terminated without Cause or you
        voluntarily terminate your employment for Good Reason, then (1) within
        30 days of such termination you will receive a lump-sum payment equal to
        twelve (12) months of your then current base salary subject to any
        applicable withholding of federal, state or local taxes and (2) the
        vesting of any stock option for Company stock and the time during which
        such option may be exercised immediately will be accelerated as to 100%
        of the then unvested shares, so that all such unvested shares will be
        immediately vested and exercisable as of the date of termination.

2.      Except as specifically amended by this Amendment, the terms and
conditions of the Agreement shall remain in full force and effect.

3.      This Amendment shall be governed by and construed in accordance with the
laws of the State of California.

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

Very truly yours,

EPIMMUNE INC.

Robert De Vaere
Chief Financial Officer

Agreed and Accepted:

/s/ Alessandro Sette
---------------------------------
ALESSANDRO SETTE, PH.D.

                                        2<PAGE>   1

                                  Exhibit 10.84

March 8, 2001

Robert W. Chesnut, Ph.D.
1473 Kings Cross Drive
Cardiff, California 92007

Re: Amendment to Severance Benefits Agreement

Dear Bob:

This amendment (the "Amendment") to the Severance Benefits Agreement (the
"Agreement") dated February 5, 1998 by and between EPIMMUNE INC. (the
"Company"), and ROBERT W. CHESNUT, PH.D. (the "Employee") is entered into as of
March 8, 2001 (the "Amendment Date").

1.      The Company agrees that the paragraph on page 3 of the Agreement which
formerly read:

        If, within 365 days following the occurrence of a Change in Control,
        your employment is involuntarily terminated without Cause or you
        voluntarily terminate your employment for Good Reason, then (1) within
        30 days of such termination you will receive a lump-sum payment equal to
        six months of base salary subject to any applicable withholding of
        federal, state or local taxes and (2) the vesting of any stock option
        for Company stock and the time during which such option may be exercised
        immediately will be accelerated as to 50% of the then unvested shares.

is hereby amended and restated as follows:

        If, within 365 days following the occurrence of a Change in Control,
        your employment is involuntarily terminated without Cause or you
        voluntarily terminate your employment for Good Reason, then (1) within
        30 days of such termination you will receive a lump-sum payment equal to
        twelve (12) months of your then current base salary subject to any
        applicable withholding of federal, state or local taxes and (2) the
        vesting of any stock option for Company stock and the time during which
        such option may be exercised immediately will be accelerated as to 100%
        of the then unvested shares, so that all such unvested shares will be
        immediately vested and exercisable as of the date of termination.

2.      Except as specifically amended by this Amendment, the terms and
conditions of the Agreement shall remain in full force and effect.

                                        1

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3.      This Amendment shall be governed by and construed in accordance with the
laws of the State of California.

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

Very truly yours,

EPIMMUNE INC.

Robert De Vaere
Chief Financial Officer

Agreed and Accepted:

/s/ Robert W. Chesnut
----------------------------------
ROBERT W. CHESNUT, PH.D.

                                        2<PAGE>   1

                                                                  Exhibit 10.85

March 8, 2001

Mark Newman
6603A Santa Isabel St.
Carlsbad, CA 92009

Re: Amendment to Severance Benefits Agreement

Dear Mark:

This amendment (the "Amendment") to the Severance Benefits Agreement (the
"Agreement") dated May 4, 2000 by and between EPIMMUNE INC. (the "Company"), and
MARK NEWMAN (the "Employee") is entered into as of March 8, 2001 (the "Amendment
Date").

1.      The Company agrees that the paragraph on page 3 of the Agreement which
formerly read:

        If, within 365 days following the occurrence of a Change in Control,
        your employment is involuntarily terminated without Cause or you
        voluntarily terminate your employment for Good Reason, then (1) within
        30 days of such termination you will receive a lump-sum payment equal to
        six months of base salary subject to any applicable withholding of
        federal, state or local taxes and (2) the vesting of any stock option
        for Company stock and the time during which such option may be exercised
        immediately will be accelerated as to 50% of the then unvested shares.

is hereby amended and restated as follows:

        If, within 365 days following the occurrence of a Change in Control,
        your employment is involuntarily terminated without Cause or you
        voluntarily terminate your employment for Good Reason, then (1) within
        30 days of such termination you will receive a lump-sum payment equal to
        twelve (12) months of your then current base salary subject to any
        applicable withholding of federal, state or local taxes and (2) the
        vesting of any stock option for Company stock and the time during which
        such option may be exercised immediately will be accelerated as to 100%
        of the then unvested shares, so that all such unvested shares will be
        immediately vested and exercisable as of the date of termination.

2.      Except as specifically amended by this Amendment, the terms and
conditions of the Agreement shall remain in full force and effect.

3.      This Amendment shall be governed by and construed in accordance with the
laws of the State of California.

                                        1

<PAGE>   2

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

Very truly yours,

EPIMMUNE INC.

Robert De Vaere
Chief Financial Officer

Agreed and Accepted:

/s/ Mark Newman
----------------------------------
MARK NEWMAN

                                        2<PAGE>   1

                                                                  Exhibit 10.86

March 8, 2001

Robert De Vaere
2815 Crystal Ridge Road
Encinitas, California 92024

Re: Amendment to Severance Benefits Agreement

Dear Bob:

This amendment (the "Amendment") to the Severance Benefits Agreement (the
"Agreement") dated May 4, 2000 by and between EPIMMUNE INC. (the "Company"), and
ROBERT DE VAERE (the "Employee") is entered into as of March 8, 2001 (the
"Amendment Date").

1.      The Company agrees that the paragraph on page 3 of the Agreement which
formerly read:

        If, within 365 days following the occurrence of a Change in Control,
        your employment is involuntarily terminated without Cause or you
        voluntarily terminate your employment for Good Reason, then (1) within
        30 days of such termination you will receive a lump-sum payment equal to
        six months of base salary subject to any applicable withholding of
        federal, state or local taxes and (2) the vesting of any stock option
        for Company stock and the time during which such option may be exercised
        immediately will be accelerated as to 50% of the then unvested shares.

is hereby amended and restated as follows:

        If, within 365 days following the occurrence of a Change in Control,
        your employment is involuntarily terminated without Cause or you
        voluntarily terminate your employment for Good Reason, then (1) within
        30 days of such termination you will receive a lump-sum payment equal to
        twelve (12) months of your then current base salary subject to any
        applicable withholding of federal, state or local taxes and (2) the
        vesting of any stock option for Company stock and the time during which
        such option may be exercised immediately will be accelerated as to 100%
        of the then unvested shares, so that all such unvested shares will be
        immediately vested and exercisable as of the date of termination.

2.      Except as specifically amended by this Amendment, the terms and
conditions of the Agreement shall remain in full force and effect.

3.      This Amendment shall be governed by and construed in accordance with the
laws of the State of California.

                                        1

<PAGE>   2

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

Very truly yours,

EPIMMUNE INC.

Robert W. Chesnut, Ph.D.
Acting President

Agreed and Accepted:

/s/ Robert De Vaere
---------------------------
ROBERT DE VAERE

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