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                                                                   EXHIBIT 10.15

                             XCYTE THERAPIES, INC.

                   (FORMERLY KNOWN AS CDR THERAPEUTICS, INC.)

                   AMENDED AND RESTATED 1996 STOCK OPTION PLAN

        1. Purposes of the Plan. The purposes of this Stock Option Plan are to
attract and retain the best available personnel for positions of substantial
responsibility, to provide additional incentive to Employees and Consultants of
the Company and any Parent or Subsidiary and to promote the success of the
Company's business. Options granted under the Plan may be Incentive Stock
Options or Nonstatutory Stock Options, as determined by the Administrator at the
time of grant of an option and subject to the applicable provisions of Section
422 of the Code and the regulations promulgated thereunder.

        2. Definitions. As used herein, the following definitions shall apply:

               (a) "Administrator" means the Board or any of its Committees
appointed pursuant to Section 4 of the Plan.

               (b) "Board" means the Board of Directors of the Company.

               (c) "Code" means the Internal Revenue Code of 1986, as amended.

               (d) "Committee" means a Committee appointed by the Board of
Directors in accordance with Section 4 of the Plan.

               (e) "Common Stock" means the Common Stock of the Company.

               (f) "Company" means Xcyte Therapies, Inc., formerly known as CDR
Therapeutics, Inc.

               (g) "Consultant" means any person who is engaged by the Company
or any Parent or Subsidiary to render consulting or advisory services and is
compensated for such services, and any director of the Company whether
compensated for such services or not. If and in the event the Company registers
any class of any equity security pursuant to the Exchange Act, the term
Consultant shall thereafter not include directors who are not compensated for
their services or are paid only a director's fee by the Company.

               (h) "Continuous Status as an Employee or Consultant" means that
the employment or consulting relationship with the Company, any Parent or
Subsidiary is not interrupted or terminated. Continuous Status as an Employee or
Consultant shall not be considered interrupted in the case of (i) any leave of
absence approved by the Company or (ii) transfers between locations of the
Company or between the Company, its Parent, any Subsidiary, or any successor. A
leave of absence approved by the Company shall include sick leave, military
leave, or any other personal leave. For purposes of Incentive Stock Options, no
such leave may exceed 90 days, unless reemployment upon expiration of such leave
is guaranteed by statute or contract, including Company policies. If
reemployment upon expiration of a leave of absence


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approved by the Company is not so guaranteed, on the 181st day of such leave any
Incentive Stock Option held by the Optionee shall cease to be treated as an
Incentive Stock Option and shall be treated for tax purposes as a Nonstatutory
Stock Option.

               (i) "Disability" means total and permanent disability as defined
in Section 22(e)(3) of the Code.

               (j) "Employee" means any person, including officers and
directors, employed by the Company or any Parent or Subsidiary of the Company.
The payment of a director's fee by the Company shall not be sufficient to
constitute "employment" by the Company.

               (k) "Exchange Act" means the Securities Exchange Act of 1934, as
amended.

               (1) "Fair Market Value" means, as of any date, the value of
Common Stock determined as follows:

                      (i) If the Common Stock is listed on any established stock
exchange or a national market system, including without limitation the Nasdaq
National Market or The Nasdaq SmallCap Market of The Nasdaq Stock Market, its
Fair Market Value shall be the closing sales price for such stock (or the
closing bid, if no sales were reported) as quoted on such exchange or system for
the last market trading day prior to the time of determination, as reported in
The Wall Street Journal or such other source as the Administrator deems
reliable;

                      (ii) If the Common Stock is regularly quoted by a
recognized securities dealer but selling prices are not reported, its Fair
Market Value shall be the mean between the high bid and low asked prices for the
Common Stock on the last market trading day prior to the day of determination;
or

                      (iii) In the absence of an established market for the
Common Stock, the Fair Market Value shall be determined in good faith by the
Administrator.

               (m) "Incentive Stock Option" means an Option intended to qualify
as an incentive stock option within the meaning of Section 422 of the Code.

               (n) "Nonstatutory Stock Option" means an Option not intended to
qualify as an Incentive Stock Option.

               (o) "Option" means a stock option granted pursuant to the Plan.

               (p) "Optioned Stock" means the Common Stock subject to an Option.

               (q) "Optionee" means an Employee or Consultant who receives an
Option.

               (r) "Parent" means a "parent corporation," whether now or
hereafter existing, as defined in Section 424(e) of the Code.

               (s) "Plan" means this 1996 Stock Option Plan.


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               (t) "Section 16(b)" means Section 16(b) of the Securities
Exchange Act of 1934, as amended.

               (u) "Share" means a share of the Common Stock, as adjusted in
accordance with Section 11 below.

               (v) "Subsidiary" means a "subsidiary corporation," whether now or
hereafter existing, as defined in Section 424(f) of the Code.

        3. Stock Subject to the Plan. Subject to the provisions of Section 11 of
the Plan, the maximum aggregate number of Shares which may be optioned and sold
under the Plan is 700,000 Shares. The Shares may be authorized, but unissued, or
reacquired Common Stock.

               If an Option expires or becomes unexercisable without having been
exercised in full, or is surrendered pursuant to an option exchange program
authorized by the Administrator, the unpurchased Shares which were subject
thereto shall become available for future grant or sale under the Plan (unless
the Plan has terminated); provided, however, that Shares that have actually been
issued under the Plan shall not be returned to the Plan and shall not become
available for future distribution under the Plan, except that if unvested Shares
are repurchased by the Company at their original purchase price, such Shares
shall become available for future grant under the Plan.

        4. Administration of the Plan.

               (a) Initial Plan Procedure. Prior to the date, if any, upon which
the Company becomes subject to the Exchange Act, the Plan shall be administered
by the Board or a committee appointed by the Board.

               (b) Plan Procedure After the Date, If Any, Upon Which the Company
Becomes Subject to the Exchange Act.

                      (i) Administration With Respect to Directors and Officers
Subject to Section 16(b). With respect to Option grants made to Employees who
are also Officers or Directors subject to Section 16(b) of the Exchange Act, the
Plan shall be administered by (A) the Board, if the Board may administer the
Plan in a manner complying with the rules under Rule 16b-3 relating to the
disinterested administration of employee benefit plans under which Section 16(b)
exempt discretionary grants and awards of equity securities are to be made, or
(B) a committee designated by the Board to administer the Plan, which committee
shall be constituted to comply with the rules under Rule 16b-3 relating to the
disinterested administration of employee benefit plans under which Section 16(b)
exempt discretionary grants and awards of equity securities are to be made. Once
appointed, such Committee shall continue to serve in its designated capacity
until otherwise directed by the Board. From time to time the Board may increase
the size of the Committee and appoint additional members, remove members (with
or without cause) and substitute new members, fill vacancies (however caused),
and remove all members of the Committee and thereafter directly administer the
Plan, all to the extent permitted by the rules under Rule 16b-3 relating to the
disinterested administration of employee benefit


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plans under which Section 16(b) exempt discretionary grants and awards of equity
securities are to be made.

                      (ii) Administration With Respect to Other Persons. With
respect to Option grants made to Employees or Consultants who are neither
Directors nor Officers of the Company, the Plan shall be administered by (A) the
Board or (B) a committee designated by the Board, which committee shall be
constituted to satisfy the legal requirements, if any, relating to the
administration of incentive stock option plans of state corporate and securities
laws, of the Code, and of any stock exchange or national market system upon
which the Common Stock is then listed or traded (the "Applicable Laws"). Once
appointed, such Committee shall serve in its designated capacity until otherwise
directed by the Board. The Board may increase the size of the Committee and
appoint additional members, remove members (with or without cause) and
substitute new members, fill vacancies (however caused), and remove all members
of the Committee and thereafter directly administer the Plan, all to the extent
permitted by Applicable Laws.

               (c) Powers of the Administrator. Subject to the provisions of the
Plan and, in the case of a Committee, the specific duties delegated by the Board
to such Committee, and subject to the approval of any relevant authorities,
including the approval, if required, of any stock exchange or national market
system upon which the Common Stock is then listed, the Administrator shall have
the authority, in its discretion:

                      (i) to determine the Fair Market Value of the Common
Stock, in accordance with Section 2(1) of the Plan;

                      (ii) to select the Consultants and Employees to whom
Options may from time to time be granted hereunder;

                      (iii) to determine whether and to what extent Options are
granted hereunder;

                      (iv) to determine the number of shares of Common Stock to
be covered by each such award granted hereunder;

                      (v) to approve forms of agreement for use under the Plan;

                      (vi) to determine the terms and conditions, not
inconsistent with the terms of the Plan, of any award granted hereunder. Such
terms and conditions may include, but are not limited to, the exercise price,
the time or times when Options may be exercised, any vesting acceleration or
waiver of forfeiture restrictions, and any restriction or limitation regarding
any Option or the Shares relating thereto, based in each case on such factors as
the Administrator, in its sole discretion, shall determine;

                      (vii) to determine whether and under what circumstances an
Option may be settled in cash under Section 9(e) instead of Common Stock;


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                      (viii) to reduce the exercise price of any Option to the
then current Fair Market Value if the Fair Market Value of the Common Stock
covered by such Option has declined since the date the Option was granted;

                      (ix) to provide for the early exercise of Options for the
purchase of unvested Shares, subject to such terms and conditions as the
Administrator may determine; and

                      (x) to construe and interpret the terms of the Plan and
awards granted pursuant to the Plan.

               (d) Effect of Administrator's Decision. All decisions,
determinations and interpretations of the Administrator shall be final and
binding on all Optionees and any other holders of any Options.

        5. Eligibility.

               (a) Nonstatutory Stock Options may be granted to Employees and
Consultants. Incentive Stock Options may be granted only to Employees. An
Employee or Consultant who has been granted an Option may, if otherwise
eligible, be granted additional Options.

               (b) Each Option shall be designated in the written option
agreement as either an Incentive Stock Option or a Nonstatutory Stock Option.
However, notwithstanding such designation, to the extent that the aggregate Fair
Market Value of the Shares with respect to which Incentive Stock Options are
exercisable for the first time by the Optionee during any calendar year (under
all plans of the Company and any Parent or Subsidiary) exceeds $100,000, such
Options shall be treated as Nonstatutory Stock Options.

               For purposes of this Section 5(b), Incentive Stock Options shall
be taken into account in the order in which they were granted, and the Fair
Market Value of the Shares shall be determined as of the time the Option with
respect to such Shares is granted.

               (c) The Plan shall not confer upon any Optionee any right with
respect to the continuation of the Optionee's employment or consulting
relationship with the Company, nor shall it interfere in any way with the
Optionee's right or the Company's right to terminate the Optionee's employment
or consulting relationship at any time, with or without cause.

        6. Term of Plan. The Plan shall become effective upon the earlier to
occur of its adoption by the Board of Directors or its approval by the
shareholders of the Company, as described in Section 17 of the Plan. It shall
continue in effect for a term of ten (10) years unless sooner terminated under
Section 13 of the Plan.

        7. Term of Option. The term of each Option shall be the term stated in
the Option Agreement; provided, however, that the term shall be no more than ten
(10) years from the date of grant thereof. However, in the case of an Incentive
Stock Option granted to an Optionee who, at the time the Option is granted, owns
stock representing more than ten percent (10%) of the


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voting power of all classes of stock of the Company or any Parent or Subsidiary,
the term of the Option shall be five (5) years from the date of grant thereof or
such shorter term as may be provided in the Option Agreement.

        8. Option Exercise Price and Consideration.

               (a) The per share exercise price for the Shares to be issued
pursuant to exercise of an Option shall be such price as is determined by the
Board, but shall be subject to the following:

                      (i) In the case of an Incentive Stock Option

                             (A) granted to an Employee who, at the time of the
grant of such Incentive Stock Option, owns stock representing more than ten
percent (10%) of the voting power of all classes of stock of the Company or any
Parent or Subsidiary, the per Share exercise price shall be no less than 110% of
the Fair Market Value per Share on the date of grant.

                             (B) granted to any Employee other than an Employee
described in the preceding paragraph, the per Share exercise price shall be no
less than 100% of the Fair Market Value per Share on the date of grant.

                      (ii) In the case of a Nonstatutory Stock Option, the per
share exercise price shall be determined by the Administrator.

               (b) The consideration to be paid for the Shares to be issued upon
exercise of an Option, including the method of payment, shall be determined by
the Administrator (and, in the case of an Incentive Stock Option, shall be
determined at the time of grant) and may consist entirely of (1) cash, (2)
check, (3) promissory note, (4) other Shares which (x) in the case of Shares
acquired upon exercise of an Option have been owned by the Optionee for more
than six months on the date of surrender and (y) have a Fair Market Value on the
date of surrender equal to the aggregate exercise price of the Shares as to
which such Option shall be exercised, (5) delivery of a properly executed
exercise notice together with such other documentation as the Administrator and
the broker, if applicable, shall require to effect an exercise of the Option and
delivery to the Company of the sale or loan proceeds required to pay the
exercise price, or (6) any combination of the foregoing methods of payment. In
making its determination as to the type of consideration to accept, the
Administrator shall consider if acceptance of such consideration may be
reasonably expected to benefit the Company.

        9. Exercise of Option.

               (a) Procedure for Exercise: Rights as a Shareholder. Any Option
granted hereunder shall be exercisable at such times and under such conditions
as determined by the Administrator, including performance criteria with respect
to the Company and/or the Optionee, and as shall be permissible under the terms
of the Plan.


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                      An Option may not be exercised for a fraction of a Share.

                      An Option shall be deemed to be exercised when written
notice of such exercise has been given to the Company in accordance with the
terms of the Option by the person entitled to exercise the Option and full
payment for the Shares with respect to which the Option is exercised has been
received by the Company. Full payment may, as authorized by the Administrator,
consist of any consideration and method of payment allowable under Section 8(b)
of the Plan. Until the issuance (as evidenced by the appropriate entry on the
books of the Company or of a duly authorized transfer agent of the Company) of
the stock certificate evidencing such Shares, no right to vote or receive
dividends or any other rights as a shareholder shall exist with respect to the
Optioned Stock, notwithstanding the exercise of the Option. The Company shall
issue (or cause to be issued) such stock certificate promptly upon exercise of
the Option. No adjustment will be made for a dividend or other right for which
the record date is prior to the date the stock certificate is issued, except as
provided in Section 11 of the Plan.

                      Exercise of an Option in any manner shall result in a
decrease in the number of Shares which thereafter may be available, both for
purposes of the Plan and for sale under the Option, by the number of Shares as
to which the Option is exercised.

               (b) Termination of Employment or Consulting Relationship. Upon
termination of an Optionee's Continuous Status as an Employee or Consultant,
other than upon the Optionee's death or Disability, the Optionee may exercise
his or her Option, but only within such period of time as is specified in the
Notice of Grant, and only to the extent that the Optionee was entitled to
exercise it at the date of termination (but in no event later than the
expiration of the term of such Option as set forth in the Notice of Grant). In
the absence of a specified time in the Notice of Grant, the Option shall remain
exercisable for three (3) months following the Optionee's termination. In the
case of an Incentive Stock Option, such period of time for exercise shall not
exceed three (3) months from the date of termination. If, on the date of
termination, the Optionee is not entitled to exercise the Optionee's entire
Option, the Shares covered by the unexercisable portion of the Option shall
revert to the Plan. If, after termination, the Optionee does not exercise his or
her Option within the time specified by the Administrator, the Option shall
terminate, and the Shares covered by such Option shall revert to the Plan.

               Notwithstanding the above, in the event of an Optionee's change
in status from Consultant to Employee or Employee to Consultant, an Optionee's
Continuous Status as an Employee or Consultant shall not automatically terminate
solely as a result of such change in status. However, in such event, an
Incentive Stock Option held by the Optionee shall cease to be treated as an
Incentive Stock Option and shall be treated for tax purposes as a Nonstatutory
Stock Option three months and one day following such change of status.

               (c) Disability of Optionee. In the event of termination of an
Optionee's Continuous Status as an Employee or Consultant as a result of his or
her Disability, the Optionee may, but only within twelve (12) months from the
date of such termination (and in no event later than the expiration date of the
term of his or her Option as set forth in the Option Agreement), exercise the
Option to the extent the Optionee was otherwise entitled to exercise it on the
date of


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such termination. To the extent that the Optionee is not entitled to exercise
the Option on the date of termination, or if the Optionee does not exercise the
Option to the extent so entitled within the time specified herein, the Option
shall terminate, and the Shares covered by the Option shall revert to the Plan.

               (d) Death of Optionee. In the event of the death of an Optionee,
the Option may be exercised at any time within twelve (12) months following the
date of death (but in no event later than the expiration of the term of such
Option as set forth in the Notice of Grant), by the Optionee's estate or by a
person who has acquired the right to exercise the Option by bequest or
inheritance, but only to the extent that the Optionee was entitled to exercise
the Option at the date of death. If, at the time of death, the Optionee was not
entitled to exercise his or her entire Option, the Shares covered by the
unexercisable portion of the Option shall immediately revert to the Plan. If,
after death, the Optionee's estate or a person who acquires the right to
exercise the Option by bequest or inheritance does not exercise the Option
within the time specified herein, the Option shall terminate, and the Shares
covered by such Option shall revert to the Plan.

               (e) Buyout Provisions. The Administrator may at any time offer to
buy out for a payment in cash or Shares, an Option previously granted, based on
such terms and conditions as the Administrator shall establish and communicate
to the Optionee at the time that such offer is made.

               (f) Rule l6b-3. Options granted to persons subject to Section
16(b) of the Exchange Act must comply with Rule 16b-3 and shall contain such
additional conditions or restrictions as may be required thereunder to qualify
for the maximum exemption from Section 16 of the Exchange Act with respect to
Plan transactions.

        10. Non-Transferability of Options. Options may not be sold, pledged,
assigned, hypothecated, transferred, or disposed of in any manner other than by
will or by the laws of descent or distribution and may be exercised, during the
lifetime of the Optionee, only by the Optionee.

        11. Adjustments Upon Changes in Capitalization or Merger.

               (a) Changes in Capitalization. Subject to any required action by
the shareholders of the Company, the number of shares of Common Stock covered by
each outstanding Option, and the number of shares of Common Stock which have
been authorized for issuance under the Plan but as to which no Options have yet
been granted or which have been returned to the Plan upon cancellation or
expiration of an Option, as well as the price per share of Common Stock covered
by each such outstanding Option, shall be proportionately adjusted for any
increase or decrease in the number of issued shares of Common Stock resulting
from a stock split, reverse stock split, stock dividend, combination or
reclassification of the Common Stock, or any other increase or decrease in the
number of issued shares of Common Stock effected without receipt of
consideration by the Company; provided, however, that conversion of any
convertible securities of the Company shall not be deemed to have been "effected
without receipt of consideration." Such adjustment shall be made by the Board,
whose determination in that respect shall be final, binding and conclusive.
Except as expressly provided herein, no issuance


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by the Company of shares of stock of any class, or securities convertible into
shares of stock of any class, shall affect, and no adjustment by reason thereof
shall be made with respect to, the number or price of shares of Common Stock
subject to an Option.

               (b) Dissolution or Liquidation. In the event of the proposed
dissolution or liquidation of the Company, the Administrator shall notify each
Optionee as soon as practicable prior to the effective date of such proposed
transaction. The Administrator in its discretion may provide for an Optionee to
have the right to exercise his or her Option until ten (10) days prior to such
transaction as to all of the Optioned Stock covered thereby, including Shares as
to which the Option would not otherwise be exercisable. In addition, the
Administrator may provide that any Company repurchase option applicable to any
Shares purchased upon exercise of an Option shall lapse as to all such Shares,
provided the proposed dissolution or liquidation takes place at the time and in
the manner contemplated. To the extent it has not been previously exercised, an
Option will terminate immediately prior to the consummation of such proposed
action.

               (c) Acquisition, Merger or Change in Control.

                      (i) In the event of a sale of all or substantially all of
the Company's assets, or any merger or consolidation of the Company with or into
another corporation other than a merger or consolidation in which the holders of
more than 50% of the shares of capital stock of the Company outstanding
immediately prior to such transaction continue to hold (either by the voting
securities remaining outstanding or by their being converted into voting
securities of the Successor Corporation) more than 50% of the total voting power
represented by the voting securities of the Company, or such Successor
Corporation, outstanding immediately after such transaction (a "Change in
Control"), the exercisability of each outstanding Option shall automatically be
accelerated completely so that one hundred percent (100%) of the number of
shares of Common Stock covered by such Option shall be fully vested immediately
prior to the consummation of the Change in Control; provided, however, that each
outstanding Option shall automatically be accelerated by only twenty-five
percent (25%) of the number of shares of Common Stock covered by such Option
that are unvested immediately prior to the consummation of the Change in Control
if and to the extent: (A) such Option is either to be assumed by the Successor
Corporation at the consummation of the Change in Control or be replaced with a
comparable option to purchase shares of the capital stock of the Successor
Corporation at the consummation of the Change in Control, or (B) such Option is
to be replaced by a comparable cash incentive program of the Successor
Corporation based on the value of the Option at the time of the consummation of
the Change in Control, or (C) the acceleration of such Option is subject to
other limitations imposed by the Administrator at the time of grant.

                      (ii) The Administrator shall have the authority, in the
Administrator's sole discretion, to provide for the automatic acceleration of
any outstanding Option upon the occurrence of a Change in Control, but only to
the extent that such acceleration does not interfere with any "pooling of
interests" accounting treatment used in connection with the Change in Control.


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                      (iii) Notwithstanding the foregoing, no Incentive Stock
Option shall become exercisable pursuant to this Section 11(c) without the
Optionee's consent if the result would be to cause such Option not to be treated
as an Incentive Stock Option.

        12. Time of Granting Options. The date of grant of an Option shall, for
all purposes, be the date on which the Administrator makes the determination
granting such Option, or such other date as is determined by the Administrator.
Notice of the determination shall be given to each Employee or Consultant to
whom an Option is so granted within a reasonable time after the date of such
grant.

        13. Amendment and Termination of the Plan.

               (a) Amendment and Termination. The Board may at any time amend,
alter, suspend or discontinue the Plan, but no amendment, alteration, suspension
or discontinuation shall be made which would impair the rights of any Optionee
under any grant theretofore made, without his or her consent. In addition, to
the extent necessary and desirable to comply with Rule 16b-3 under the Exchange
Act or with Section 422 of the Code (or any other applicable law or regulation,
including the requirements of any stock exchange or national market system upon
which the Common Stock is then listed), the Company shall obtain shareholder
approval of any Plan amendment in such a manner and to such a degree as
required.

               (b) Effect of Amendment or Termination. Any such amendment or
termination of the Plan shall not affect Options already granted, and such
Options shall remain in full force and effect as if this Plan had not been
amended or terminated, unless mutually agreed otherwise between the Optionee and
the Board, which agreement must be in writing and signed by the Optionee and the
Company.

        14. Conditions Upon Issuance of Shares. Shares shall not be issued
pursuant to the exercise of an Option unless the exercise of such Option and the
issuance and delivery of such Shares pursuant thereto shall comply with all
relevant provisions of law, including, without limitation, the Securities Act of
1933, as amended, the Exchange Act, the rules and regulations promulgated
thereunder, and the requirements of any stock exchange or national market system
upon which the Common Stock is then listed or traded, and shall be further
subject to the approval of counsel for the Company with respect to such
compliance.

               As a condition to the exercise of an Option, the Company may
require the person exercising such Option to represent and warrant at the time
of any such exercise that the Shares are being purchased only for investment and
without any present intention to sell or distribute such Shares if, in the
opinion of counsel for the Company, such a representation is required by any of
the aforementioned relevant provisions of law.

        15. Reservation of Shares. The Company, during the term of this Plan,
shall at all times reserve and keep available such number of Shares as shall be
sufficient to satisfy the requirements of the Plan.


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               The inability of the Company to obtain authority from any
regulatory body having jurisdiction, which authority is deemed by the Company's
counsel to be necessary to the lawful issuance and sale of any Shares hereunder,
shall relieve the Company of any liability in respect of the failure to issue or
sell such Shares as to which such requisite authority shall not have been
obtained.

        16. Agreements. Options shall be evidenced by written agreements in such
form as the Administrator shall approve from time to time.

        17. Shareholder Approval. Continuance of the Plan shall be subject to
approval by the shareholders of the Company within twelve (12) months before or
after the date the Plan is adopted. Such shareholder approval shall be obtained
in the degree and manner required under applicable state and federal law and the
rules of any stock exchange or national market system upon which the Common
Stock is then listed or traded.

        18. Tax Withholding. As a condition of the exercise of an Option granted
under the Plan and, if applicable, in connection with the vesting of an award,
the Optionee (or in the case of the Optionee's death, the person exercising the
Option) shall make such arrangements as the Administrator may require for the
satisfaction of any applicable federal, state, local or foreign withholding tax
obligations that may arise in connection with the exercise of the Option and the
issuance of Shares. The Company shall not be required to issue any Shares under
the Plan until such obligations are satisfied. If the Administrator allows the
withholding or surrender of Shares to satisfy a Participant's tax withholding
obligations, the Administrator shall not allow Shares to be withheld in an
amount that exceeds the minimum statutory withholding rates for federal and
state tax purposes, including payroll taxes.




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                                    EXHIBIT A


                      AMENDED AND RESTATED 1996 STOCK PLAN
                                 EXERCISE NOTICE


Xcyte Therapies, Inc.
1124 Columbia Street
Suite 130
Seattle, WA  98104

Attention:  Chief Financial Officer

        1. Exercise of Option. Effective as of today, ___________, 20__, the
undersigned ("Optionee") hereby elects to exercise Optionee's option to purchase
_________ shares of the Common Stock (the "Shares") of Xcyte Therapies, Inc.
(the "Company") under and pursuant to the 1996 Stock Plan (the "Plan") and the
Stock Option Agreement dated ________, 20__ (the "Option Agreement").

        2. Delivery of Payment. Purchaser herewith delivers to the Company the
full purchase price of the Shares, as set forth in the Option Agreement.

        3. Representations of Optionee. Optionee acknowledges that Optionee has
received, read and understood the Plan and the Option Agreement and agrees to
abide by and be bound by their terms and conditions.

        4. Rights as Shareholder. Until the issuance of the Shares (as evidenced
by the appropriate entry on the books of the Company or of a duly authorized
transfer agent of the Company), no right to vote or receive dividends or any
other rights as a shareholder shall exist with respect to the Optioned Stock,
notwithstanding the exercise of the Option. The Shares shall be issued to the
Optionee as soon as practicable after the Option is exercised. No adjustment
shall be made for a dividend or other right for which the record date is prior
to the date of issuance except as provided in Section 11 of the Plan.

        5. Company's Right of First Refusal. Before any Shares held by Optionee
or any transferee (either being sometimes referred to herein as the "Holder")
may be sold or otherwise transferred (including transfer by gift or operation of
law), the Company or its assignee(s) shall have a right of first refusal to
purchase the Shares on the terms and conditions set forth in this Section (the
"Right of First Refusal").

               (a) Notice of Proposed Transfer. The Holder of the Shares shall
deliver to the Company a written notice (the "Notice") stating: (i) the Holder's
bona fide intention to sell or otherwise transfer such Shares; (ii) the name of
each proposed purchaser or other transferee


<PAGE>   13

("Proposed Transferee"); (iii) the number of Shares to be transferred to each
Proposed Transferee; and (iv) the bona fide cash price or other consideration
for which the Holder proposes to transfer the Shares (the "Offered Price"), and
the Holder shall offer the Shares at the Offered Price to the Company or its
assignee(s).

               (b) Exercise of Right of First Refusal. At any time within thirty
(30) days after receipt of the Notice, the Company and/or its assignee(s) may,
by giving written notice to the Holder, elect to purchase all, but not less than
all, of the Shares proposed to be transferred to any one or more of the Proposed
Transferees, at the purchase price determined in accordance with subsection (c)
below.

               (c) Purchase Price. The purchase price ("Purchase Price") for the
Shares purchased by the Company or its assignee(s) under this Section shall be
the Offered Price. If the Offered Price includes consideration other than cash,
the cash equivalent value of the non-cash consideration shall be determined by
the Board of Directors of the Company in good faith.

               (d) Payment. Payment of the Purchase Price shall be made, at the
option of the Company or its assignee(s), in cash (by check), by cancellation of
all or a portion of any outstanding indebtedness of the Holder to the Company
(or, in the case of repurchase by an assignee, to the assignee), or by any
combination thereof within 30 days after receipt of the Notice or in the manner
and at the times set forth in the Notice.

               (e) Holder's Right to Transfer. If all of the Shares proposed in
the Notice to be transferred to a given Proposed Transferee are not purchased by
the Company and/or its assignee(s) as provided in this Section, then the Holder
may sell or otherwise transfer such Shares to that Proposed Transferee at the
Offered Price or at a higher price, provided that such sale or other transfer is
consummated within 120 days after the date of the Notice, that any such sale or
other transfer is effected in accordance with any applicable securities laws and
that the Proposed Transferee agrees in writing that the provisions of this
Section shall continue to apply to the Shares in the hands of such Proposed
Transferee. If the Shares described in the Notice are not transferred to the
Proposed Transferee within such period, a new Notice shall be given to the
Company, and the Company and/or its assignees shall again be offered the Right
of First Refusal before any Shares held by the Holder may be sold or otherwise
transferred.

               (f) Exception for Certain Family Transfers. Anything to the
contrary contained in this Section notwithstanding, the transfer of any or all
of the Shares during the Optionee's lifetime or on the Optionee's death by will
or intestacy to the Optionee's immediate family or a trust for the benefit of
the Optionee's immediate family shall be exempt from the provisions of this
Section. "Immediate Family" as used herein shall mean spouse, lineal descendant
or antecedent, father, mother, brother or sister. In such case, the transferee
or other recipient shall receive and hold the Shares so transferred subject to
the provisions of this Section, and there shall be no further transfer of such
Shares except in accordance with the terms of this Section.


                                      -2-
<PAGE>   14

               (g) Termination of Right of First Refusal. The Right of First
Refusal shall terminate as to any Shares upon the first sale of Common Stock of
the Company to the general public pursuant to a registration statement filed
with and declared effective by the Securities and Exchange Commission under the
Securities Act of 1933, as amended.

        6. Tax Consultation. Optionee understands that Optionee may suffer
adverse tax consequences as a result of Optionee's purchase or disposition of
the Shares. Optionee represents that Optionee has consulted with any tax
consultants Optionee deems advisable in connection with the purchase or
disposition of the Shares and that Optionee is not relying on the Company for
any tax advice.

        7. Restrictive Legends and Stop-Transfer Orders.

               (a) Legends. Optionee understands and agrees that the Company
shall cause the legends set forth below or legends substantially equivalent
thereto, to be placed upon any certificate(s) evidencing ownership of the Shares
together with any other legends that may be required by the Company or by state
or federal securities laws:

                      THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED
                      UNDER THE SECURITIES ACT OF 1933 (THE "ACT") AND MAY NOT
                      BE OFFERED, SOLD OR OTHERWISE TRANSFERRED, PLEDGED OR
                      HYPOTHECATED UNLESS AND UNTIL REGISTERED UNDER THE ACT OR,
                      IN THE OPINION OF COMPANY COUNSEL SATISFACTORY TO THE
                      ISSUER OF THESE SECURITIES, SUCH OFFER, SALE OR TRANSFER,
                      PLEDGE OR HYPOTHECATION IS IN COMPLIANCE THEREWITH. THE
                      SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO
                      CERTAIN RESTRICTIONS ON TRANSFER AND A RIGHT OF FIRST
                      REFUSAL HELD BY THE ISSUER OR ITS ASSIGNEE(S) AS SET FORTH
                      IN THE EXERCISE NOTICE BETWEEN THE ISSUER AND THE ORIGINAL
                      HOLDER OF THESE SHARES, A COPY OF WHICH MAY BE OBTAINED AT
                      THE PRINCIPAL OFFICE OF THE ISSUER. SUCH TRANSFER
                      RESTRICTIONS AND RIGHT OF FIRST REFUSAL ARE BINDING ON
                      TRANSFEREES OF THESE SHARES.

               (a)Stop-Transfer Notices. Optionee agrees that, in order to
ensure compliance with the restrictions referred to herein, the Company may
issue appropriate "stop transfer" instructions to its transfer agent, if any,
and that, if the Company transfers its own securities, it may make appropriate
notations to the same effect in its own records.



                                      -3-
<PAGE>   15

               (b) Refusal to Transfer. The Company shall not be required (i) to
transfer on its books any Shares that have been sold or otherwise transferred in
violation of any of the provisions of this Agreement or (ii) to treat as owner
of such Shares or to accord the right to vote or pay dividends to any purchaser
or other transferee to whom such Shares shall have been so transferred.

        2. Successors and Assigns. The Company may assign any of its rights
under this Agreement to single or multiple assignees, and this Agreement shall
inure to the benefit of the successors and assigns of the Company. Subject to
the restrictions on transfer herein set forth, this Agreement shall be binding
upon Optionee and his or her heirs, executors, administrators, successors and
assigns.

        3. Interpretation. Any dispute regarding the interpretation of this
Agreement shall be submitted by Optionee or by the Company forthwith to the
Administrator which shall review such dispute at its next regular meeting. The
resolution of such a dispute by the Administrator shall be final and binding on
all parties.

        4. Governing Law; Severability. This Agreement is governed by the
internal substantive laws but not the choice of law rules, of Washington.

        5. Entire Agreement. The Plan and Option Agreement are incorporated
herein by reference. This Agreement, the Plan, the Option Agreement and the
Investment Representation Statement constitute the entire agreement of the
parties with respect to the subject matter hereof and supersede in their
entirety all prior undertakings and agreements of the Company and Optionee with
respect to the subject matter hereof, and may not be modified adversely to the
Optionee's interest except by means of a writing signed by the Company and
Optionee.


Submitted by:                           Accepted by:

OPTIONEE:                               XCYTE THERAPIES, INC.

-----------------------------------     By:
Signature                                  ------------------------------------

-----------------------------------     Its:
Print Name                                  -----------------------------------

Address:                                Address:

-----------------------------------     2203 Airport Way South
                                        Suite 300
-----------------------------------     Seattle, WA 98134



                                      -4-
<PAGE>   16

                                    EXHIBIT B

                       INVESTMENT REPRESENTATION STATEMENT


OPTIONEE:

COMPANY:                     XCYTE THERAPIES, INC.

SECURITY:                    COMMON STOCK
AMOUNT:
DATE:


        In connection with the purchase of the above-listed Securities, the
undersigned Optionee represents to the Company the following:

               1. Optionee is aware of the Company's business affairs and
financial condition and has acquired sufficient information about the Company to
reach an informed and knowledgeable decision to acquire the Securities. Optionee
is acquiring these Securities for investment for Optionee's own account only and
not with a view to, or for resale in connection with, any "distribution" thereof
within the meaning of the Securities Act of 1933, as amended (the "Securities
Act").

               2. Optionee acknowledges and understands that the Securities
constitute "restricted securities" under the Securities Act and have not been
registered under the Securities Act in reliance upon a specific exemption
therefrom, which exemption depends upon, among other things, the bona fide
nature of Optionee's investment intent as expressed herein. In this connection,
Optionee understands that, in the view of the Securities and Exchange
Commission, the statutory basis for such exemption may be unavailable if
Optionee's representation was predicated solely upon a present intention to hold
these Securities for the minimum capital gains period specified under tax
statutes, for a deferred sale, for or until an increase or decrease in the
market price of the Securities, or for a period of one year or any other fixed
period in the future. Optionee further understands that the Securities must be
held indefinitely unless they are subsequently registered under the Securities
Act or an exemption from such registration is available. Optionee further
acknowledges and understands that the Company is under no obligation to register
the Securities. Optionee understands that the certificate evidencing the
Securities will be imprinted with a legend which prohibits the transfer of the
Securities unless they are registered or such registration is not required in
the opinion of counsel satisfactory to the Company, a legend prohibiting their
transfer without the consent of the Commissioner of Corporations of the State of
Washington and any other legend required under applicable state securities laws.

               3. Optionee is familiar with the provisions of Rule 701 and Rule
144, each promulgated under the Securities Act, which, in substance, permit
limited public resale of "restricted


<PAGE>   17

securities" acquired, directly or indirectly from the issuer thereof, in a
non-public offering subject to the satisfaction of certain conditions. Rule 701
provides that if the issuer qualifies under Rule 701 at the time of the grant of
the Option to the Optionee, the exercise will be exempt from registration under
the Securities Act. In the event the Company becomes subject to the reporting
requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934,
ninety (90) days thereafter (or such longer period as any market stand-off
agreement may require) the Securities exempt under Rule 701 may be resold,
subject to the satisfaction of certain of the conditions specified by Rule 144,
including: (1) the resale being made through a broker in an unsolicited
"broker's transaction" or in transactions directly with a market maker (as said
term is defined under the Securities Exchange Act of 1934); and, in the case of
an affiliate, (2) the availability of certain public information about the
Company, (3) the amount of Securities being sold during any three month period
not exceeding the limitations specified in Rule 144(e), and (4) the timely
filing of a Form 144, if applicable.

        In the event that the Company does not qualify under Rule 701 at the
time of grant of the Option, then the Securities may be resold in certain
limited circumstances subject to the provisions of Rule 144, which requires the
resale to occur not less than one year after the later of the date the
Securities were sold by the Company or the date the Securities were sold by an
affiliate of the Company, within the meaning of Rule 144; and, in the case of
acquisition of the Securities by an affiliate, or by a non-affiliate who
subsequently holds the Securities less than two years, the satisfaction of the
conditions set forth in sections (1), (2), (3) and (4) of the paragraph
immediately above.

               4. Optionee further understands that in the event all of the
applicable requirements of Rule 701 or 144 are not satisfied, registration under
the Securities Act, compliance with Regulation A, or some other registration
exemption will be required; and that, notwithstanding the fact that Rules 144
and 701 are not exclusive, the Staff of the Securities and Exchange Commission
has expressed its opinion that persons proposing to sell private placement
securities other than in a registered offering and otherwise than pursuant to
Rules 144 or 701 will have a substantial burden of proof in establishing that an
exemption from registration is available for such offers or sales, and that such
persons and their respective brokers who participate in such transactions do so
at their own risk. Optionee understands that no assurances can be given that any
such other registration exemption will be available in such event.

                         (SIGNATURES ON FOLLOWING PAGE)



                                      -2-
<PAGE>   18


                                        Signature of Optionee:




                                        ---------------------------------------
                                        Date:                      , 20
                                             ----------------------    --------





                                      -3-