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                                                                   EXHIBIT 10.16

                             XCYTE THERAPIES, INC.

                                 2000 STOCK PLAN


        1. PURPOSES OF THE PLAN. The purposes of this 2000 Stock Plan are to
attract and retain the best available personnel for positions of substantial
responsibility, to provide additional incentive to Employees and Consultants 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. Stock purchase rights may also be granted under the Plan.

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

           (a) "ADMINISTRATOR" means the Board or its Committee appointed
pursuant to Section 4 of the Plan.

           (b) "AFFILIATE" means an entity other than a Subsidiary (as defined
below) which, together with the Company, is under common control of a third
person or entity.

           (c) "APPLICABLE LAWS" means the legal requirements relating to the
administration of stock option and restricted stock purchase plans under
applicable U.S. state corporate laws, U.S. federal and applicable state
securities laws, the Code, any Stock Exchange rules or regulations and the
applicable laws of any other country or jurisdiction where Options or Stock
Purchase Rights are granted under the Plan, as such laws, rules, regulations and
requirements shall be in place from time to time.

           (d) "BOARD" means the Board of Directors of the Company.

           (e) "CHANGE OF CONTROL" means 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 surviving entity) more than 50% of the total voting power
represented by the voting securities of the Company, or such surviving entity,
outstanding immediately after such transaction.

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

           (g) "COMMITTEE" means one or more committees or subcommittees of the
Board appointed by the Board to administer the Plan in accordance with Section 4
below.

           (h) "COMMON STOCK" means the Common Stock of the Company.

           (i) "COMPANY" means Xcyte Therapies, Inc., a Delaware corporation.



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           (j) "CONSULTANT" means any person, including an advisor, who is
engaged by the Company or any Parent, Subsidiary or Affiliate to render services
and is compensated for such services, and any director of the Company whether
compensated for such services or not.

           (k) "CONTINUOUS SERVICE STATUS" means the absence of any interruption
or termination of service as an Employee or Consultant. Continuous Service
Status as an Employee or Consultant shall not be considered interrupted in the
case of: (i) sick leave; (ii) military leave; (iii) any other leave of absence
approved by the Administrator, provided that such leave is for a period of not
more than ninety (90) days, unless reemployment upon the expiration of such
leave is guaranteed by contract or statute, or unless provided otherwise
pursuant to Company policy adopted from time to time; or (iv) in the case of
transfers between locations of the Company or between the Company, its Parents,
Subsidiaries, Affiliates or their respective successors. A change in status from
an Employee to a Consultant or from a Consultant to an Employee will not
constitute an interruption of Continuous Service Status.

           (l) "CORPORATE TRANSACTION" means a sale of all or substantially all
of the Company's assets, or a merger, consolidation or other capital
reorganization of the Company with or into another corporation and includes a
Change of Control.

           (m) "DIRECTOR" means a member of the Board.

           (n) "EMPLOYEE" means any person employed by the Company or any
Parent, Subsidiary or Affiliate, with the status of employment determined based
upon such factors as are deemed appropriate by the Administrator in its
discretion, subject to any requirements of the Code or the Applicable Laws. The
payment by the Company of a director's fee to a Director shall not be sufficient
to constitute "employment" of such Director by the Company.

           (o) "EXCHANGE ACT" means the Securities Exchange Act of 1934, as
amended.

           (p) "FAIR MARKET VALUE" means, as of any date, the fair market value
of the Common Stock, as determined by the Administrator in good faith on such
basis as it deems appropriate and applied consistently with respect to
Participants. Whenever possible, the determination of Fair Market Value shall be
based upon the closing price for the Shares as reported in the Wall Street
Journal for the applicable date.

           (q) "INCENTIVE STOCK OPTION" means an Option intended to qualify as
an incentive stock option within the meaning of Section 422 of the Code, as
designated in the applicable Option Agreement.

           (r) "LISTED SECURITY" means any security of the Company that is
listed or approved for listing on a national securities exchange or designated
or approved for designation as a national market system security on an
interdealer quotation system by the National Association of Securities Dealers,
Inc.

           (s) "NAMED EXECUTIVE" means any individual who, on the last day of
the Company's fiscal year, is the chief executive officer of the Company (or is
acting in such



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capacity) or among the four most highly compensated officers of the Company
(other than the chief executive officer). Such officer status shall be
determined pursuant to the executive compensation disclosure rules under the
Exchange Act.

           (t) "NONSTATUTORY STOCK OPTION" means an Option not intended to
qualify as an Incentive Stock Option, as designated in the applicable Option
Agreement.

           (u) "OPTION" means a stock option granted pursuant to the Plan.

           (v) "OPTION AGREEMENT" means a written document, the form(s) of which
shall be approved from time to time by the Administrator, reflecting the terms
of an Option granted under the Plan and includes any documents attached to or
incorporated into such Option Agreement, including, but not limited to, a notice
of stock option grant and a form of exercise notice.

           (w) "OPTION EXCHANGE PROGRAM" means a program approved by the
Administrator whereby outstanding Options are exchanged for Options with a lower
exercise price or are amended to decrease the exercise price as a result of a
decline in the Fair Market Value of the Common Stock.

           (x) "OPTIONED STOCK" means the Common Stock subject to an Option.

           (y) "OPTIONEE" means an Employee or Consultant who receives an
Option.

           (z) "PARENT" means a "parent corporation," whether now or hereafter
existing, as defined in Section 424(e) of the Code, or any successor provision.

           (aa) "PARTICIPANT" means any holder of one or more Options or Stock
Purchase Rights, or the Shares issuable or issued upon exercise of such awards,
under the Plan.

           (bb) "PLAN" means this 2000 Stock Plan.

           (cc) "REPORTING PERSON" means an officer, Director, or greater than
ten percent stockholder of the Company within the meaning of Rule 16a-2 under
the Exchange Act, who is required to file reports pursuant to Rule 16a-3 under
the Exchange Act.

           (dd) "RESTRICTED STOCK" means Shares of Common Stock acquired
pursuant to a grant of a Stock Purchase Right under Section 11 below.

           (ee) "RESTRICTED STOCK PURCHASE AGREEMENT" means a written document,
the form(s) of which shall be approved from time to time by the Administrator,
reflecting the terms of a Stock Purchase Right granted under the Plan and
includes any documents attached to such agreement.

           (ff) "RULE 16B-3" means Rule 16b-3 promulgated under the Exchange
Act, as amended from time to time, or any successor provision.



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           (gg) "SHARE" means a share of the Common Stock, as adjusted in
accordance with Section 14 of the Plan.

           (hh) "STOCK EXCHANGE" means any stock exchange or consolidated stock
price reporting system on which prices for the Common Stock are quoted at any
given time.

           (ii) "STOCK PURCHASE RIGHT" means the right to purchase Common Stock
pursuant to Section 11 below.

           (jj) "SUBSIDIARY" means a "subsidiary corporation," whether now or
hereafter existing, as defined in Section 424(f) of the Code, or any successor
provision.

           (kk) "TEN PERCENT HOLDER" means a person who 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.

        3. STOCK SUBJECT TO THE PLAN. Subject to the provisions of Section 14 of
the Plan, the maximum aggregate number of Shares that may be sold under the Plan
is 2,100,000 Shares of Common Stock plus an annual increase on the first day of
each of the Company's fiscal years beginning in 2002 and ending in 2008 equal to
the lesser of (a) 500,000 Shares, (b) 3 % of the Shares outstanding on the last
day of the immediately preceding fiscal year, or (c) such lesser number of
Shares as the Board shall determine. The Shares may be authorized but unissued,
or reacquired Common Stock. If an award should expire or become unexercisable
for any reason without having been exercised in full, or is surrendered pursuant
to an Option Exchange Program, the unpurchased Shares that were subject thereto
shall, unless the Plan shall have been terminated, become available for future
grant under the Plan. In addition, any Shares of Common Stock which are retained
by the Company upon exercise of an award in order to satisfy the exercise or
purchase price for such award or any withholding taxes due with respect to such
exercise or purchase shall be treated as not issued and shall continue to be
available under the Plan. Shares issued under the Plan and later repurchased by
the Company pursuant to any repurchase right which the Company may have shall
not be available for future grant under the Plan.

        4. ADMINISTRATION OF THE PLAN.

           (a) GENERAL. The Plan shall be administered by the Board or a
Committee, or a combination thereof, as determined by the Board. The Plan may be
administered by different administrative bodies with respect to different
classes of Participants and, if permitted by the Applicable Laws, the Board may
authorize one or more officers to make awards under the Plan.

           (b) COMMITTEE COMPOSITION. If a Committee has been appointed pursuant
to this Section 4, 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 any Committee and appoint additional members thereof,
remove members (with or without cause) and appoint new members in substitution
therefor, fill vacancies (however caused) and remove all members of a Committee
and thereafter directly administer the Plan, all to the extent permitted by the



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Applicable Laws and, in the case of a Committee administering the Plan in
accordance with the requirements of Rule 16b-3 or Section 162(m) of the Code, to
the extent permitted or required by such provisions.

           (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, 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(p) of the Plan, provided that such determination shall
be applied consistently with respect to Participants under the Plan;

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

               (iii) to determine whether and to what extent Options and Stock
Purchase Rights are granted;

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

               (v) to approve the form(s) of agreement(s) used under the Plan;

               (vi) to determine the terms and conditions, not inconsistent with
the terms of the Plan, of any award granted hereunder, which terms and
conditions include but are not limited to the exercise or purchase price, the
time or times when awards may be exercised (which may be based on performance
criteria), any vesting acceleration or waiver of forfeiture restrictions, and
any restriction or limitation regarding any Option, Optioned Stock, Stock
Purchase Right or Restricted Stock, 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 10(c) instead of Common Stock;

               (viii) to implement an Option Exchange Program on such terms and
conditions as the Administrator in its discretion deems appropriate, provided
that no amendment or adjustment to an Option that would materially and adversely
affect the rights of any Optionee shall be made without the prior written
consent of the Optionee;

               (ix) to adjust the vesting of an Option held by an Employee or
Consultant as a result of a change in the terms or conditions under which such
person is providing services to the Company;

               (x) to construe and interpret the terms of the Plan and awards
granted under the Plan, which constructions, interpretations and decisions shall
be final and binding on all Participants; and



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               (xi) in order to fulfill the purposes of the Plan and without
amending the Plan, to modify grants of Options or Stock Purchase Rights to
Participants who are foreign nationals or employed outside of the United States
in order to recognize differences in local law, tax policies or customs.

        5. ELIGIBILITY.

           (a) RECIPIENTS OF GRANTS. Nonstatutory Stock Options and Stock
Purchase Rights may be granted to Employees and Consultants. Incentive Stock
Options may be granted only to Employees, provided that Employees of Affiliates
shall not be eligible to receive Incentive Stock Options.

           (b) TYPE OF OPTION. Each Option shall be designated in the Option
Agreement as either an Incentive Stock Option or a Nonstatutory Stock Option.

           (c) ISO $100,000 LIMITATION. Notwithstanding any designation under
Section 5(b), to the extent that the aggregate Fair Market Value of Shares with
respect to which Options designated as Incentive Stock Options are exercisable
for the first time by any Optionee during any calendar year (under all plans of
the Company or any Parent or Subsidiary) exceeds $100,000, such excess Options
shall be treated as Nonstatutory Stock Options. For purposes of this Section
5(c), Incentive Stock Options shall be taken into account in the order in which
they were granted, and the Fair Market Value of the Shares subject to an
Incentive Stock Option shall be determined as of the date of the grant of such
Option.

           (d) NO EMPLOYMENT RIGHTS. The Plan shall not confer upon any
Participant any right with respect to continuation of an employment or
consulting relationship with the Company, nor shall it interfere in any way with
such Participant's right or the Company's right to terminate his or her
employment or consulting relationship at any time, with or without Cause.

        6. TERM OF PLAN. The Plan shall become effective upon its adoption by
the Board of Directors. It shall continue in effect for a term of ten (10) years
unless sooner terminated under Section 16 of the Plan.

        7. TERM OF OPTION. The term of each Option shall be the term stated in
the Option Agreement; provided that the term shall be no more than ten years
from the date of grant thereof or such shorter term as may be provided in the
Option Agreement and provided further that, in the case of an Incentive Stock
Option granted to a person who at the time of such grant is a Ten Percent
Holder, the term of the Option shall be five years from the date of grant
thereof or such shorter term as may be provided in the Option Agreement.



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        8. LIMITATION ON GRANTS TO EMPLOYEES. Subject to adjustment as provided
in Section 14 below, the maximum number of Shares that may be subject to Options
and Stock Purchase Rights granted to any one Employee under this Plan for any
fiscal year of the Company shall be 1,000,000, provided that this Section 8
shall apply only after such time, if any, as the Common Stock becomes a Listed
Security.

        9. OPTION EXERCISE PRICE AND CONSIDERATION.

           (a) EXERCISE PRICE. 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 Administrator and set forth in the Option Agreement, 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 grant is a Ten
Percent Holder, the per Share exercise price shall be no less than 110% of the
Fair Market Value per Share on the date of grant; or

                   (B) granted to any other Employee, 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 such price as determined by the Administrator provided
that if such eligible person is, at the time of the grant of such Option, a
Named Executive of the Company, the per share Exercise Price shall be no less
than 100% of the Fair Market Value on the date of grant if such Option is
intended to qualify as performance-based compensation under Section 162(m) of
the Code.

               (iii) Notwithstanding the foregoing, Options may be granted with
a per Share exercise price other than as required above pursuant to a merger or
other corporate transaction.

           (b) PERMISSIBLE CONSIDERATION. 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) delivery of Optionee's promissory note with such
recourse, interest, security and redemption provisions as the Administrator
determines to be appropriate (subject to the provisions of Section 153 of the
Delaware General Corporation Law); (4) cancellation of indebtedness; (5) other
Shares that have a Fair Market Value on the date of surrender equal to the
aggregate exercise price of the Shares as to which the Option is exercised,
provided that in the case of Shares acquired, directly or indirectly, from the
Company, such Shares must have been owned by the Optionee for more than six
months on the date of surrender (or such other period as may be required to
avoid the Company's incurring an adverse accounting charge); (6) delivery of a
properly executed exercise notice together with such other documentation as the
Administrator and a securities broker approved by the Company shall require to
effect exercise of the Option and prompt delivery to



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the Company of the sale or loan proceeds required to pay the exercise price and
any applicable withholding taxes; or (7) 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 and the Administrator may, in
its sole discretion, refuse to accept a particular form of consideration at the
time of any Option exercise.

        10. EXERCISE OF OPTION.

           (a) GENERAL.

               (i) EXERCISABILITY. Any Option granted hereunder shall be
exercisable at such times and under such conditions as determined by the
Administrator, consistent with the term of the Plan and reflected in the Option
Agreement, including vesting requirements and/or performance criteria with
respect to the Company and/or the Optionee. The Administrator shall have the
discretion to determine whether and to what extent the vesting of Options shall
be tolled during any unpaid leave of absence; provided however that in the
absence of such determination, vesting of Options shall be tolled during any
such leave.

               (ii) MINIMUM EXERCISE REQUIREMENTS. An Option may not be
exercised for a fraction of a Share. The Administrator may require that an
Option be exercised as to a minimum number of Shares, provided that such
requirement shall not prevent an Optionee from exercising the full number of
Shares as to which the Option is then exercisable.

               (iii) PROCEDURES FOR AND RESULTS OF EXERCISE. An Option shall be
deemed 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 the Company has received full payment for the Shares
with respect to which the Option is exercised. Full payment may, as authorized
by the Administrator, consist of any consideration and method of payment
allowable under Section 9(b) of the Plan, provided that the Administrator may,
in its sole discretion, refuse to accept any form of consideration at the time
of any Option exercise.

        Exercise of an Option in any manner shall result in a decrease in the
number of Shares that 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.

               (iv) RIGHTS AS STOCKHOLDER. 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 stockholder shall exist with respect to the Optioned
Stock, notwithstanding the 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 14 of the Plan.

           (b) TERMINATION OF EMPLOYMENT OR CONSULTING RELATIONSHIP. Except as
otherwise set forth in this Section 10(b), the Administrator shall establish and
set forth in the applicable Option Agreement the terms and conditions upon which
an Option shall remain



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exercisable, if at all, following termination of an Optionee's Continuous
Service Status, which provisions may be waived or modified by the Administrator
at any time in the Administrator's sole discretion. To the extent that the
Optionee is not entitled to exercise an Option at the date of his or her
termination of Continuous Service Status, or if the Optionee (or other person
entitled to exercise the Option) does not exercise the Option to the extent so
entitled within the time specified in the Option Agreement or below (as
applicable), the Option shall terminate and the Optioned Stock underlying the
unexercised portion of the Option shall revert to the Plan. In no event may any
Option be exercised after the expiration of the Option term as set forth in the
Option Agreement (and subject to Section 7). In the event the period for
exercise of an Option following the termination of the Optionee's Continuous
Service Status, as provided in the Option Agreement or below, is longer than the
period permitted under Code Section 422 for an Incentive Stock Option, upon the
expiration of the period permitted under Code Section 422 such Option, if
designated as an Incentive Stock Option, shall be treated as a Nonstatutory
Stock Option.

        The following provisions shall apply to the extent an Option Agreement
does not specify the terms and conditions upon which an Option shall terminate
upon termination of an Optionee's Continuous Service Status:

               (i) TERMINATION OTHER THAN UPON DISABILITY OR DEATH. In the event
of termination of an Optionee's Continuous Service Status other than as a result
of disability or death, such Optionee may exercise an Option for three months
following such termination to the extent the Optionee was entitled to exercise
it at the date of such termination.

               (ii) DISABILITY OF OPTIONEE. In the event of termination of an
Optionee's Continuous Service Status as a result of his or her disability
(including a disability within the meaning of Section 22(e)(3) of the Code),
such Optionee may exercise an Option at any time within twelve months following
such termination to the extent the Optionee was entitled to exercise it at the
date of such termination.

               (iii) DEATH OF OPTIONEE. In the event of the death of an Optionee
during the period of Continuous Service Status, or within 30 days following
termination of Optionee's Continuous Service Status, the Option may be exercised
by Optionee's estate or by a person who acquired the right to exercise the
Option by bequest or inheritance at any time within twelve months following the
date of death, but only to the extent of the right to exercise that had accrued
at the date the Optionee's Continuous Service Status terminated.

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

        11. STOCK PURCHASE RIGHTS.

           (a) RIGHTS TO PURCHASE. When the Administrator determines that it
will offer Stock Purchase Rights under the Plan, it shall advise the offeree in
writing of the terms, conditions and restrictions related to the offer,
including the number of Shares that such person



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shall be entitled to purchase, the price to be paid, and the time within which
such person must accept such offer. The offer to purchase Shares subject to
Stock Purchase Rights shall be accepted by execution of a Restricted Stock
Purchase Agreement in the form determined by the Administrator.

           (b) REPURCHASE OPTION.

               (i) GENERAL. Unless the Administrator determines otherwise, the
Restricted Stock Purchase Agreement shall grant the Company a repurchase option
exercisable upon the voluntary or involuntary termination of the purchaser's
employment with the Company for any reason (including death or disability). The
purchase price for Shares repurchased pursuant to the Restricted Stock Purchase
Agreement shall be the original purchase price paid by the purchaser and may be
paid by cancellation of any indebtedness of the purchaser to the Company. The
repurchase option shall lapse at such rate as the Administrator may determine.

               (ii) TERMINATION FOR CAUSE. In the event of termination of a
Participant's Continuous Service for Cause, the Company shall have the right to
repurchase from the Participant vested Shares issued upon exercise of a Stock
Purchase Right at the Participant's original cost for the Shares. Such
repurchase shall be effected pursuant to such terms and conditions, and at such
time, as the Administrator shall determine. Nothing in this Section 11(b)(ii)
shall in any way limit the Company's right to purchase unvested Shares as set
forth in the applicable Restricted Stock Purchase Agreement.

           (c) OTHER PROVISIONS. The Restricted Stock Purchase Agreement shall
contain such other terms, provisions and conditions not inconsistent with the
Plan as may be determined by the Administrator in its sole discretion. In
addition, the provisions of Restricted Stock Purchase Agreements need not be the
same with respect to each purchaser.

           (d) RIGHTS AS A STOCKHOLDER. Once the Stock Purchase Right is
exercised, the purchaser shall have the rights equivalent to those of a
stockholder, and shall be a stockholder when his or her purchase is entered upon
the records of the duly authorized transfer agent of the Company. No adjustment
will be made for a dividend or other right for which the record date is prior to
the date the Stock Purchase Right is exercised, except as provided in Section 14
of the Plan.

        12. TAXES.

           (a) As a condition of the exercise of an Option or Stock Purchase
Right granted under the Plan, the Participant (or in the case of the
Participant's death, the person exercising the Option or Stock Purchase Right)
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 or
Stock Purchase Right 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 under this Section 12
(whether pursuant to Section 12(c), (d) or (e), or otherwise), the Administrator



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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.

           (b) In the case of an Employee and in the absence of any other
arrangement, the Employee shall be deemed to have directed the Company to
withhold or collect from his or her compensation an amount sufficient to satisfy
such tax obligations from the next payroll payment otherwise payable after the
date of an exercise of the Option or Stock Purchase Right.

           (c) This Section 12(c) shall apply only after the date, if any, upon
which the Common Stock becomes a Listed Security. In the case of Participant
other than an Employee (or in the case of an Employee where the next payroll
payment is not sufficient to satisfy such tax obligations, with respect to any
remaining tax obligations), in the absence of any other arrangement and to the
extent permitted under the Applicable Laws, the Participant shall be deemed to
have elected to have the Company withhold from the Shares to be issued upon
exercise of the Option or Stock Purchase Right that number of Shares having a
Fair Market Value determined as of the applicable Tax Date (as defined below)
equal to the amount required to be withheld. For purposes of this Section 12,
the Fair Market Value of the Shares to be withheld shall be determined on the
date that the amount of tax to be withheld is to be determined under the
Applicable Laws (the "Tax Date").

           (d) If permitted by the Administrator, in its discretion, a
Participant may satisfy his or her tax withholding obligations upon exercise of
an Option or Stock Purchase Right by surrendering to the Company Shares that
have a Fair Market Value determined as of the applicable Tax Date equal to the
amount required to be withheld. In the case of shares previously acquired from
the Company that are surrendered under this Section 12(d), such Shares must have
been owned by the Participant for more than six (6) months on the date of
surrender (or such other period of time as is required for the Company to avoid
adverse accounting charges).

           (e) Any election or deemed election by a Participant to have Shares
withheld to satisfy tax withholding obligations under Section 12(c) or (d) above
shall be irrevocable as to the particular Shares as to which the election is
made and shall be subject to the consent or disapproval of the Administrator.
Any election by a Participant under Section 12(d) above must be made on or prior
to the applicable Tax Date.

           (f) In the event an election to have Shares withheld is made by a
Participant and the Tax Date is deferred under Section 83 of the Code because no
election is filed under Section 83(b) of the Code, the Participant shall receive
the full number of Shares with respect to which the Option or Stock Purchase
Right is exercised but such Participant shall be unconditionally obligated to
tender back to the Company the proper number of Shares on the Tax Date.

        13. NON-TRANSFERABILITY OF OPTIONS AND STOCK PURCHASE RIGHTS.

           (a) GENERAL. Except as set forth in this Section 13, Options and
Stock Purchase Rights may not be sold, pledged, assigned, hypothecated,
transferred or disposed of in



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any manner other than by will or by the laws of descent or distribution. The
designation of a beneficiary by an Optionee will not constitute a transfer. An
Option or Stock Purchase Right may be exercised, during the lifetime of the
holder of an Option or Stock Purchase Right, only by such holder or a transferee
permitted by this Section 13.

           (b) LIMITED TRANSFERABILITY RIGHTS. Notwithstanding anything else in
this Section 13, prior to the date, if any, on which the Common Stock becomes a
Listed Security, the Administrator may in its discretion grant Nonstatutory
Stock Options that may be transferred by instrument to an inter vivos or
testamentary trust in which the Options are to be passed to beneficiaries upon
the death of the trustor (settlor) or by gift to "Immediate Family" (as defined
below), on such terms and conditions as the Administrator deems appropriate.
Following the date, if any, on which the Common Stock becomes a Listed Security,
the Administrator may in its discretion grant transferable Nonstatutory Stock
Options pursuant to Option Agreements specifying the manner in which such
Nonstatutory Stock Options are transferable. "Immediate Family" means any child,
stepchild, grandchild, parent, stepparent, grandparent, spouse, sibling,
mother-in-law, father-in-law, son-in-law, daughter-in-law, brother-in-law, or
sister-in-law, and shall include adoptive relationships.

        14. ADJUSTMENTS UPON CHANGES IN CAPITALIZATION, MERGER OR CERTAIN OTHER
TRANSACTIONS.

           (a) CHANGES IN CAPITALIZATION. Subject to any required action by the
stockholders of the Company, the number of Shares of Common Stock covered by
each outstanding Option or Stock Purchase Right, the numbers of Shares set forth
in Sections 3(a) and 8 above, and the number of Shares of Common Stock that have
been authorized for issuance under the Plan but as to which no Options or Stock
Purchase Rights have yet been granted or that have been returned to the Plan
upon cancellation or expiration of an Option or Stock Purchase Right, as well as
the price per Share of Common Stock covered by each such outstanding Option or
Stock Purchase Right, 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, recapitalization 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
Administrator, whose determination in that respect shall be final, binding and
conclusive. Except as expressly provided herein, no issuance 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
or Stock Purchase Right.

           (b) DISSOLUTION OR LIQUIDATION. In the event of the dissolution or
liquidation of the Company, each Option and Stock Purchase Right will terminate
immediately prior to the consummation of such action, unless otherwise
determined by the Administrator.

           (c) CORPORATE TRANSACTION.



                                      -12-
<PAGE>   13

               (i) In the event of a Corporate Transaction, each outstanding
Option and Stock Purchase Right shall be assumed or an equivalent option or
right shall be substituted by the successor corporation or a Parent or
Subsidiary of such successor corporation, unless such successor corporation does
not agree to assume the outstanding Options or Stock Purchase Rights or to
substitute equivalent options or rights, in which case such Options or Stock
Purchase Rights shall terminate upon the consummation of the transaction.

               (ii) In the event of a Change of Control, if the successor
corporation or a Parent or Subsidiary of such successor corporation agrees to
assume unexercised Options or Stock Purchase Rights or to substitute them with
equivalent options or stock purchase rights, the vesting and exercisability of
each outstanding Option and Stock Purchase Right shall accelerate such that the
Options and Stock Purchase Rights shall become vested and exercisable as to the
lesser of 25% of the Shares subject to the Option or Stock Purchase Right or the
remaining unvested Shares, and any repurchase right of the Company with respect
to Shares issued upon exercise of an Option or Stock Purchase Right shall lapse
as to the lesser of 25% of the Shares initially subject to the Company
repurchase right or the remaining Shares subject to the Company repurchase
right. The acceleration of vesting and lapse of repurchase rights provided for
in this Section 15(c)(ii) shall occur immediately prior to consummation of the
Change of Control and shall apply to Shares that would have vested last under
the vesting schedule applicable to the option or the shares subject to Company
repurchase right.

               (iii) In addition to the acceleration of vesting and lapse of
repurchase rights provided for in Section 15(c)(ii), in the event of the
Involuntary Termination within twelve (12) months of the Change of Control of a
Participant holding an Option or Stock Purchase Right that is assumed or
substituted by the Successor Corporation in the Change of Control, or holding
Restricted Stock issued upon exercise of an Option or Stock Purchase Right with
respect to which the Successor Corporation has succeeded to a repurchase right
as a result of the Change of Control, then any assumed or substituted Option or
Stock Purchase Right held by such Participant at the time of the Involuntary
Termination shall accelerate and become exercisable as to the lesser of 25% of
the Shares subject to the Option or Stock Purchase Right or the remaining
unvested Shares, and any repurchase right of the Company with respect to Shares
issued upon exercise of an Option or Stock Purchase Right shall lapse as to the
lesser of 25% of the Shares initially subject to the Company repurchase right or
the remaining Shares subject to the Company repurchase right. The acceleration
of vesting and lapse of repurchase rights provided for in this Section
15(c)(iii) shall occur as of the Participant's last day of Continuous Service
Status.

               (iv) In the event the Successor Corporation does not agree to
assume unexercised Options, or to substitute them with equivalent options or
stock purchase rights, the vesting and exercisability of each outstanding Option
and Stock Purchase Right shall accelerate such that the Options and Stock
Purchase Rights shall become vested and exercisable as to 100% of the remaining
unvested Shares, and any repurchase right of the Company with respect to Shares
issued upon exercise of an Option or Stock Purchase Right shall lapse as to 100%
of the remaining Shares subject to the Company repurchase right. The
acceleration of vesting and lapse



                                      -13-
<PAGE>   14

of repurchase rights provided for in this Section 15(c)(iv) shall occur
immediately prior to consummation of the Change of Control.

               (v) For purposes of this Section 15(c), an Option or a Stock
Purchase Right shall be considered assumed, without limitation, if, at the time
of issuance of the stock or other consideration upon a Corporate Transaction or
a Change of Control, as the case may be, each holder of an Option or Stock
Purchase Right would be entitled to receive upon exercise of the Option or Stock
Purchase Right the same number and kind of shares of stock or the same amount of
property, cash or securities as such holder would have been entitled to receive
upon the occurrence of the transaction if the holder had been, immediately prior
to such transaction, the holder of the number of Shares of Common Stock covered
by the Option or the Stock Purchase Right at such time (after giving effect to
any adjustments in the number of Shares covered by the Option or Stock Purchase
Right as provided for in this Section 15); provided however that if such
consideration received in the transaction is not solely common stock of the
successor corporation or its Parent, the Administrator may, with the consent of
the successor corporation, provide for the consideration to be received upon
exercise of the Option or Stock Purchase Right to be solely common stock of the
successor corporation or its Parent equal to the Fair Market Value of the per
Share consideration received by holders of Common Stock in the transaction.

               (vi) For purposes of this Section 15(c) "Involuntary Termination"
means termination of a Participant's Continuous Service under the following
circumstances: (A) termination without Cause by the Company or a Subsidiary,
Parent, Affiliate or successor thereto, as appropriate; or (B) voluntary
resignation by the Participant within 30 days following (I) a reduction in the
Participant's then-current base salary of more than 20%, other than in
connection with a similar reduction in the base salaries of similarly situated
employees or consultants as part of a general salary level reduction; or (II)
relocation by the Company or a Subsidiary, Parent, Affiliate or successor
thereto, as appropriate, of the Participant's work site to a facility or
location by more than 50 miles from the Participant's principal work site
immediately prior to such relocation.

               (vii) For purposes of this Section 15(c), "Cause" for termination
of a Participant's Continuous Service Status will exist if the Participant is
terminated for any of the following reasons: (A) Participant's material breach
of any of the terms of any written agreement between the Participant and the
Company; (B) Participant's conviction of a felony harmful to the reputation of
the Company or of a crime involving moral turpitude; (C) Participant's willful
misconduct in the performance of his or her duties and responsibilities to the
Company; (D) Participant's violation of his or her duty of loyalty or his or her
obligations with respect to proprietary information or trade secrets of the
Company or to any party to whom the Participant owes an obligation of
nondisclosure as a result of his or her relationship with the Company; (E)
Participant's violation of the Company's nondiscrimination policies or policies
prohibiting harassment; or (F) Participant's commission of any other intentional
wrongful act that could cause the Company to be liable to a third party. The
determination as to whether a Participant's Continuous Service is terminated for
Cause shall be made in good faith by the Company and shall be final and binding
on the Participant. The foregoing definition does not in any way limit



                                      -14-
<PAGE>   15

the Company's ability to terminate a Participant's employment or consulting
relationship at any time as provided in Section 5(d) above. The term "Company"
will be interpreted to include any Subsidiary, Parent, Affiliate or successor
thereto, as appropriate.

           (d) CERTAIN DISTRIBUTIONS. In the event of any distribution to the
Company's stockholders of securities of any other entity or other assets (other
than dividends payable in cash or stock of the Company) without receipt of
consideration by the Company, the Administrator may, in its discretion,
appropriately adjust the price per Share of Common Stock covered by each
outstanding Option or Stock Purchase Right to reflect the effect of such
distribution.

        15. TIME OF GRANTING OPTIONS AND STOCK PURCHASE RIGHTS. The date of
grant of an Option or Stock Purchase Right shall, for all purposes, be the date
on which the Administrator makes the determination granting such Option or Stock
Purchase Right, or such other date as is determined by the Administrator,
provided that in the case of any Incentive Stock Option, the grant date shall be
the later of the date on which the Administrator makes the determination
granting such Incentive Stock Option or the date of commencement of the
Optionee's employment relationship with the Company. Notice of the determination
shall be given to each Employee or Consultant to whom an Option or Stock
Purchase Right is so granted within a reasonable time after the date of such
grant.

        16. AMENDMENT AND TERMINATION OF THE PLAN.

           (a) AUTHORITY TO AMEND OR TERMINATE. The Board may at any time amend,
alter, suspend or discontinue the Plan, but no amendment, alteration, suspension
or discontinuation (other than an adjustment pursuant to Section 14 above) shall
be made that would materially and adversely affect the rights of any Optionee or
holder of Stock Purchase Rights under any outstanding grant, without his or her
consent. In addition, to the extent necessary and desirable to comply with the
Applicable Laws, the Company shall obtain stockholder approval of any Plan
amendment in such a manner and to such a degree as required.

           (b) EFFECT OF AMENDMENT OR TERMINATION. No amendment or termination
of the Plan shall materially and adversely affect Options or Stock Purchase
Rights already granted, unless mutually agreed otherwise between the Optionee or
holder of the Stock Purchase Rights and the Administrator, which agreement must
be in writing and signed by the Optionee or holder and the Company.

        17. CONDITIONS UPON ISSUANCE OF SHARES. Notwithstanding any other
provision of the Plan or any agreement entered into by the Company pursuant to
the Plan, the Company shall not be obligated, and shall have no liability for
failure, to issue or deliver any Shares under the Plan unless such issuance or
delivery would comply with the Applicable Laws, with such compliance determined
by the Company in consultation with its legal counsel. As a condition to the
exercise of an Option or Stock Purchase Right, the Company may require the
person exercising the award 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 law.



                                      -15-
<PAGE>   16

        18. RESERVATION OF SHARES. The Company, during the term of this Plan,
will at all times reserve and keep available such number of Shares as shall be
sufficient to satisfy the requirements of the Plan.

        19. AGREEMENTS. Options and Stock Purchase Rights shall be evidenced by
Option Agreements and Restricted Stock Purchase Agreements, respectively, in
such form(s) as the Administrator shall from time to time approve.

        20. STOCKHOLDER APPROVAL. If required by the Applicable Laws,
continuance of the Plan shall be subject to approval by the stockholders of the
Company within twelve (12) months before or after the date the Plan is adopted.
Such stockholder approval shall be obtained in the manner and to the degree
required under the Applicable Laws.

        21. INFORMATION AND DOCUMENTS TO OPTIONEES AND PURCHASERS. Prior to the
date, if any, upon which the Common Stock becomes a Listed Security and if
required by the Applicable Laws, the Company shall provide financial statements
at least annually to each Optionee and to each individual who acquired Shares
pursuant to the Plan, during the period such Optionee or purchaser has one or
more Options or Stock Purchase Rights outstanding, and in the case of an
individual who acquired Shares pursuant to the Plan, during the period such
individual owns such Shares. The Company shall not be required to provide such
information if the issuance of Options or Stock Purchase Rights under the Plan
is limited to key employees whose duties in connection with the Company assure
their access to equivalent information.

        22. AWARDS GRANTED TO CALIFORNIA RESIDENTS. Prior to the date, if any,
upon which the Common Stock becomes a Listed Security, Options or Stock Purchase
Rights granted under the Plan to persons resident in California shall be subject
to the provisions set forth in Attachment A hereto. To the extent the provisions
of the Plan conflict with the provisions set forth on Attachment A, the
provisions on Attachment A shall govern the terms of such Options.



                                      -16-
<PAGE>   17

                                  ATTACHMENT A
                    PROVISIONS APPLICABLE TO AWARD RECIPIENTS
                             RESIDENT IN CALIFORNIA

        Until such time as any security of the Company becomes a Listed Security
and if required by Applicable Laws, the following additional terms shall apply
to Options and Stock Purchase Rights, and Shares issued upon exercise of such
awards, granted under the 2000 Stock Plan (the "Plan") to persons resident in
California as of the grant date of any such award (each such person, a
"California Recipient"):

        1. In the case of an Option, whether an Incentive Stock Option or a
Nonqualified Stock Option, that is granted to a California Recipient who, at the
time of the grant of such Option, owns stock representing more than 10% of the
total combined 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 on the grant date.

        2. In the case of a Nonqualified Stock Option that is granted to any
other California Recipient, the per Share exercise price shall be no less than
85% of the Fair Market Value per Share on the grant date.

        3. In the case of a Stock Purchase Right granted to a California
Recipient, the purchase price applicable to stock purchased under such Stock
Award shall not be less than 85% of the Fair Market Value of the Shares as of
the Grant Date, or, in the case of a person owning stock representing more than
10% of the total combined voting power of all classes of stock of the Company or
any Parent or Subsidiary, the price shall not be less than 100% of the Fair
Market Value of the Shares as of the grant date.

        4. With respect to an Option or Stock Purchase Right issued to any
California Recipient who is not an Officer, Director or Consultant, such Option
or Stock Purchase Right shall become exercisable, or any repurchase option in
favor of the Company shall lapse, at the rate of at least 20% of the Shares per
year over five years from the grant date.

        5. The following rules shall apply to an Option issued to any California
Recipient or to stock issued to a California Recipient upon exercise of a Stock
Purchase Right, in the event of termination of the California Recipient's
employment or services with the Company:

           (a) If such termination was for reasons other than death or
disability, the California Recipient shall have at least 30 days after the date
of such termination (but in no event later than the expiration of the term of
such Option established by the Plan Administrator as of the grant date) to
exercise such Option.

           (b) If such termination was on account of the death or disability of
the California Recipient, the holder of the Option may, but only within six
months from the date of such termination (but in no event later than the
expiration date of the term of such Option established by the Plan Administrator
as of the grant date), exercise the Option to the extent the California
Recipient was otherwise entitled to exercise it at the date of such termination.
To the extent that the California Recipient was not entitled to exercise the
Option at the date of



<PAGE>   18

termination, or if the holder does not exercise such Option to the extent so
entitled within six months from the date of termination, the Option shall
terminate and the Common Stock underlying the unexercised portion of the Option
shall revert to the Plan.

        6. The Company shall provide financial statements at least annually to
each California Recipient during the period such person has one or more Options
or Stock Awards outstanding, and in the case of an individual who acquired
Shares pursuant to the Plan, during the period such individual owns such Shares.
The Company shall not be required to provide such information if the issuance of
awards under the Plan is limited to key employees whose duties in connection
with the Company assure their access to equivalent information.

        7. Unless defined below or otherwise in this Attachment, Capitalized
terms shall have the meanings set forth in the Plan. For purposes of this
Attachment, "Officer" means a person who is an officer of the Company within the
meaning of Section 16(a) of the Exchange Act and the rules and regulations
promulgated thereunder.



                                      -ii-