Document:

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                                                                   Exhibit 10.28
                                                                   -------------

                       AMENDMENT TO EMPLOYMENT AGREEMENT

     THIS AMENDMENT (the "Amendment"), effective as of February 29, 2000, by and
between IndyMac Mortgage Holdings, Inc., a Delaware corporation ("Employer"),
and David S. Loeb ("Officer"), amends that certain Employment Agreement, dated
as of December 30, 1998, by and between Employer and Officer (the "Employment
Agreement").

     In consideration of the mutual promises and covenants herein contained, the
parties hereto agree as follows:

     1.  Termination of Affiliation with Countrywide.  The last paragraph of
         -------------------------------------------
Section 3 of the Employment Agreement is hereby deleted in its entirety and
replaced by the following:

     "Employer and Officer acknowledge that the Employment Agreement formerly
     recognized and permitted Officer's service as an officer and director of
     Countrywide Credit Industries, Inc. ("Countrywide") and certain of its
     subsidiaries.  However, due to the potential conflict of interest presented
     by Officer's continued affiliation with Countrywide or its subsidiaries or
     affiliates, Officer shall immediately resign from the Board of Directors of
     Countrywide and from any position(s) he currently holds with any subsidiary
     or affiliate of Countrywide and shall not hereafter, during the term of
     this Agreement as the same may be extended from time to time, accept any
     position as an employee, director, consultant or otherwise with Countrywide
     or any subsidiary or affiliate of Countrywide; provided, however, that
     nothing herein shall prohibit Officer from (i) participating in any health
     or welfare benefit plan of Countrywide, (ii) accepting an honorary title at
     Countrywide as long as such title does not require or entitle Officer to
     vote or engage in consultation or similar activities, or (iii) part-time
     employment with Countrywide or its subsidiaries or affiliates pursuant to
     that certain Part-Time Employment Agreement between Officer and
     Countrywide, dated as of February 28, 2000, receipt of a copy of which
     Employer hereby acknowledges."

     2.  Annual Stock Option Grants.  The parenthetical phrase in the second
         --------------------------
sentence of Section 4(c) of the Employment Agreement is hereby deleted in its
entirety.  The following sentence is added as the third sentence in Section 4(c)
of the Employment Agreement:

     "Notwithstanding the foregoing sentence, beginning with Fiscal Year 2000
     and in each Fiscal Year thereafter during the term of this Agreement,
     Officer shall be granted stock options to purchase 125,000 shares of common
     stock of the Company."

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     3.  Exercise of Stock Options.  The following sentence is hereby added at
         -------------------------
the end of Section 4(c) of the Employment Agreement:

     "Notwithstanding the terms of the 1998 Plan (or other applicable stock
     incentive plan) to the contrary, Officer shall have the right, upon
     termination of his employment hereunder, other then for Cause, to exercise
     stock options governed by this Section 4(c) for a period twelve (12) months
     after such termination (but in no event later then their applicable
     expiration dates)."

     4.  Ratification of Employment Agreement.  As amended hereby, the
         ------------------------------------
Employment Agreement shall be and remain in full force and effect.

     IN WITNESS WHEREOF, the parties have executed this Amendment as of the date
first above written.

                                INDYMAC MORTGAGE HOLDINGS, INC.

ATTEST

                             By:
------------------------        ---------------------------
Secretary

                             Title:
                                   ------------------------

                             OFFICER

                             ------------------------------
                             David S. Loeb, in his individual capacity

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                                                                    EXHIBIT 10.3

                              AMENDED AND RESTATED

                        1990 INCENTIVE AND NON-INCENTIVE

                               STOCK OPTION PLAN

                                       OF
                            NEXELL THERAPEUTICS INC.
                  (FORMERLY NAMED VIMRx PHARMACEUTICALS INC.)

                      (AS AMENDED THROUGH MARCH 16, 2000)

1.  Purpose of Plan.

The purpose of this Incentive and Non-Incentive Stock Option Plan ("Plan") is to
further the growth and development of VIMRx Pharmaceuticals Inc. ("Company") and
any subsidiaries thereof by encouraging selected employees, directors and other
persons who contribute and are expected to contribute materially to the
Company's success to obtain a proprietary interest in the Company through the
ownership of stock, thereby providing such persons with an added incentive to
promote the best interests of the Company and affording the Company a means of
attracting to its service persons of outstanding ability.

2.  Stock Subject to the Plan.

An aggregate of 2,400,000 shares of the Company's Common Stock, $.001 par value
("Common Stock") subject, however, to adjustment or change pursuant to paragraph
12 hereof, shall be reserved for issuance upon the exercise of options which may
be granted from time to time in accordance with the Plan ("Options"). Such
shares may be, in whole or in part, authorized but unissued shares or issued
shares which have been reacquired by the Company. If, for any reason, an Option
shall lapse, expire or terminate without having been exercised in full, the
unpurchased shares covered thereby shall again be available for purposes of the
Plan.

3.  Administration.

       (a) Except as provided in paragraph (c) below,  the Plan shall be
       administered by the Committee. The Board of Directors shall appoint the
       Committee from among its members. Such Committee shall be composed of two
       or more Directors who, to the extent practicable, shall be "outside
       directors" as defined in regulations under Section 162(m) of the Internal
       Revenue Code of 1986, as amended (the "Code"), and "non-employee
       directors" as defined by Regulation 240.16b-3 under the Securities
       Exchange Act of 1934, as amended. Such Committee shall have and may
       exercise any and all of the powers relating to the administration of the
       Plan and the grant of Options thereunder as are set forth in subparagraph
       3(b) hereof as the Board of Directors shall confer and delegate. The
       Board of Directors shall have power at any time to fill vacancies in, to
       change the membership of, or to discharge such Committee. The Committee
       shall select one of its members as its chairman and shall hold its
       meetings at such time and at such places as it shall deem advisable. A
       majority of such Committee shall constitute a quorum and such majority
       shall determine its action. Any action may be taken without a meeting by
       written consent of all the members of the Committee. The Committee shall
       keep minutes of its proceedings and shall report the same to the Board of
       Directors at the meeting next succeeding.

       (b) The Committee shall administer the Plan and, subject to the
       provisions of the Plan, shall have sole authority in its discretion to
       determine the persons to whom, and the time or times at which, Options
       shall be granted; the number of shares to be subject to each such Option;
       the provisions regarding exercisability of each Option; the expiration
       date of each Option; whether the Option shall contain a "cashless
       exercise" provision; whether all or any portion of the Options shall be
       incentive stock options ("Incentive Options") qualifying under Section
       422A of the Code or stock options which do not so qualify ("Non-Incentive
       Options"); whether a Non-Incentive Option shall have limited
       transferability as permitted under the Plan; and whether a Non-Incentive
       Option granted to a non-employee shall terminate following the non-
       employee's termination of engagement in performing services for the
       Company or its subsidiaries pursuant to Section 9 of the Plan. Both
       Incentive Options and Non-Incentive Options may be granted to the same
       person at the same time provided each type of Option is clearly
       designated. In making such determinations, the Committee may take into
       account the nature of the services rendered by such persons, their
       present and potential contribution to the Company's success and such
       other factors as the Committee in its sole discretion may deem relevant.
       Subject to the express provisions of the Plan, the Committee shall also
       have authority to interpret the Plan; to prescribe, amend and rescind
       rules and regulations relating thereto; to determine the terms and
       provisions of the respective Option Agreements, which shall be
       substantially in the forms attached hereto as Exhibit A and Exhibit B; to
       amend the provisions of outstanding Options to provide for accelerated
       exercisability or the extension of the expiration date of such Options;
       and to make all other determinations necessary or advisable for the
       administration of the Plan, all of which determinations shall be
       conclusive and not subject to review.

       (c) The Board of Directors may administer the Plan, in lieu of and with
       the same powers as the Committee, with respect to any Options granted or
       to be granted under the Plan, provided that such administration is
       consistent with the provisions of Section 162(m) of the Code.
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4.  Eligibility for Receipt of Options.

       (a) Incentive Options. Incentive Options may be granted only to employees
       (including officers) of the Company and/or any of its subsidiaries. A
       director of the Company or any subsidiary who is not an employee of the
       Company or of one of its subsidiaries is not eligible to receive
       Incentive Options under the Plan. Further, Incentive Options may not be
       granted to any person who, at the time the Incentive Option is granted,
       owns (or is considered as owning within the meaning of Section 425(d) of
       the Code) stock possessing more than 10% of the total combined voting
       power of all classes of stock of the Company or any subsidiary (10%
       Owner), unless at the time the Incentive Option is granted to the 10%
       Owner, the option price is at least 110% of the fair market value of the
       Common Stock subject thereto and such Incentive Option by its terms is
       not exercisable subsequent to five years from the date of grant. The
       aggregate fair market value (determined as of the time an Incentive
       Option is granted) of the shares of the Company's Common Stock initially
       purchasable upon exercise of an Incentive Option during any calendar year
       may not exceed $100,000.

       (b) Non-Incentive Options. Non-Incentive Options may be granted to any
       employees (including employees who have been granted Incentive Options),
       directors, consultants, agents, independent contractors and other persons
       whom the Board of Directors (or Committee) determines will contribute to
       the Company's success.

       (c) The maximum number of shares that may be subject to options under
       this Plan granted during any calendar year to any executive officer of
       the Company is 800,000 shares.

       (d) In the event on outstanding Incentive Option or a portion thereof no
       longer qualifies as an incentive stock option under Section 422A of the
       Code, such Option or portion thereof, as applicable, thereafter shall be
       deemed a Non-Incentive Option under the Plan.

5.  Option Price.

The purchase price of the shares of Common Stock under each Option shall be
determined by the Committee, which determination shall be conclusive and not
subject to review, but in no event shall the purchase price be less than 100% of
the fair market value of the Common Stock on the date of grant in the case of
Incentive Options (110% of fair market value in the case of Incentive Options
granted to a 10% Owner) and 50% of the fair market value of the Common Stock on
the date of the grant in the case of Non-Incentive Options.

For purposes of the Plan, unless the Committee determines otherwise, the "fair
market value" of a share of Common Stock as of a certain date shall be the
closing sale price of the Common Stock on The Nasdaq Stock Market or, if the
Common Stock is not then traded on The Nasdaq Stock Market, such national
securities exchange on which the Common Stock is then traded, on the trading
date immediately preceding the date fair market value is being determined. The
Committee may make such other determination of fair market value, based on other
factors, as it shall deem appropriate.

For purposes of the Plan, the date of grant of an Option shall be the date on
which the Committee shall by resolution duly authorize such Option.

6.  Term of Options.

The term of each Option shall be such number of years as the Committee shall
determine, subject to earlier termination as herein provided, but in no event
more than ten years from the date such Option is granted.

7.  Exercise of Options.

       (a) Each Option shall be exercisable to the extent determined by the
       Committee, but in no event shall an Option be exercisable until at least
       six months from the date of grant, except as otherwise provided in
       paragraph 13 herein.

       (b) An Option may not be exercised for fractional shares of the Company's
       Common Stock.

       (c) Except as provided in paragraphs 9, 10 and 11 hereof, and unless
       determined otherwise by the Committee with respect to Non-Incentive
       Options granted to non-employees, no Option shall be exercisable unless
       the holder thereof shall have been an employee, director, consultant,
       agent, independent contractor or other person employed by or engaged in
       performing services for the Company and/or a subsidiary continuously from
       the date of grant to the date of exercise.

       (d) The exercise of an Option shall be contingent upon receipt from the
       holder thereof of a written representation that at the time of such
       exercise it is the optionee's then present intention to acquire the
       Option shares for investment and not with a view to the distribution or
       resale thereof (unless a Registration Statement covering the shares
       purchasable upon exercise of the Options shall have been declared
       effective by the Securities and Exchange Commission) and upon receipt by
       the Company of cash, or a check to its order, for the full purchase price
       of such shares. The Committee may, in its discretion, include a "cashless
       exercise" provision in the applicable Option Agreement, in which event
       the optionee will be permitted (i) to deliver previously owned shares of
       Common Stock with a fair market value equal to the exercise price in
       payment of the full purchase price of such shares, or (ii) to request
       that the Company withhold shares of Common Stock issuable upon
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       exercise of such Option with a fair market value equal to the exercise
       price of the shares being purchased under the Option (thereby reducing
       the number of shares issuable upon exercise of the Option).

       (e) The holder of an Option shall have none of the rights of a
       stockholder with respect to the shares purchasable upon exercise of the
       Option until a certificate for such shares shall have been issued to the
       holder upon due exercise of the Option.

       (f) The proceeds received by the Company upon exercise of an Option shall
       be added to the Company's working capital and be available for general
       corporate purposes.

8.  Transferability of Options.

No Option granted pursuant to the Plan shall be transferable otherwise than by
will or the laws of descent or distribution and an Option may be exercised
during the lifetime of the holder only by such holder, provided, however, that
the Committee may provide for transferability of a Non-Incentive Option to an
optionee's family members or family trusts.

9.  Termination of Employment or Engagement.

       (a) Except as provided in paragraph (b) below, In the event the
       employment of the holder of an Option shall be terminated by the Company
       or a subsidiary for any reason other than by reason of death or
       disability, or the engagement of a non-employee holder of a Non-Incentive
       Option shall be terminated by the Company or a subsidiary for any reason,
       such holder may, within three months from the date of such termination,
       exercise such Option to the extent such Option was exercisable by such
       holder at the date of such termination. Notwithstanding the foregoing, no
       Option may be exercised subsequent to the date of its expiration. Absence
       on leave approved by the employer corporation shall not be considered an
       interruption of employment for any purpose under the Plan. In addition,
       at the discretion of the Committee, the exercisability of an outstanding
       Non-Incentive Option may be extended to a date determined by the
       Committee but not beyond ten years from the date of grant.

       (b) The Committee may, in its discretion, at the time of grant or by
       amending the applicable outstanding Non-Incentive Option, delete the
       foregoing termination provision with respect to a Non-Incentive Option
       granted to a non-employee of the Company or its subsidiaries.

       (c) Nothing in the Plan or in any Option Agreement granted hereunder
       shall confer upon any Optionholder any right to continue in the employ of
       the Company or any subsidiary or obligate the Company or any subsidiary
       to continue the engagement of any Optionholder or interfere in any way
       with the right of the Company or any such subsidiary to terminate such
       Optionholder's employment or engagement at any time.

10. Disability of Holder of Option.

If the employment of the holder of an Option shall be terminated by reason of
such holder's disability, such holder may, within twelve months from the date of
such termination, exercise such option to the extent such Option was exercisable
by such holder at the date of such termination. Notwithstanding the foregoing,
no Option may be exercised subsequent to the date of its expiration.

11. Death of Holder of Option.

If the holder of any Option shall die while in the employ of, or while
performing services for, the Company or one or more of its subsidiaries (or
within six months following termination of employment due to disability), the
Option theretofore granted to such person may be exercised, but only to the
extent such Option was exercisable by the holder at the date of death (or, with
respect to employees, the date of termination of employment due to disability)
by the legatee or legatees of such person under such person's Last Will, or by
such person's personal representative or distributees, within twelve months from
the date of death but in no event subsequent to the expiration date of the
Option.

12. Adjustments Upon Changes in Capitalization.

If at any time after the date of grant of an Option, the Company shall by stock
dividend, split-up, combination, reclassification or exchange, or through merger
or consolidation or otherwise, change its shares of Common Stock into a
different number or kind or class of shares or other securities or property,
then the number of shares covered by such Option and the price per share thereof
shall be proportionately adjusted for any such change by the Committee whose
determination thereon shall be conclusive.

13. Acceleration of Exercisability Upon Change in Control.

Upon the occurrence of a "change in control" of the Company (as defined below),
all outstanding Options shall become immediately fully exercisable. For purposes
of the Plan, a "change in control" of the Company shall mean (i) the acquisition
at any time by a "person" or "group" (as such terms are used Sections 13(d) and
14(d)(2) of the Exchange Act of beneficial ownership (as defined in Rule 13d-3
under the Exchange Act), directly or indirectly, of securities representing 50%
or more of the combined voting power in the election of directors of the then
outstanding securities of the Company or any successor or the Company; (ii) the
termination of service of directors, for any reason other than death, disability
or
<PAGE>

retirement from the Board of Directors, during any period of two consecutive
years or less, of individuals who at the beginning of such period constituted a
majority of the Board of Directors, unless the election of or nomination for
election of each new director during such period was approved by a vote of at
least two-thirds of the directors still in office who were directors at the
beginning of the period; (iii) approval by the stockholders of the Company of
any merger, consolidation, or statutory share exchange as a result of which the
Common Stock shall be changed, converted or exchanged (other than a merger,
consolidation or share exchange with a wholly-owned Subsidiary) or liquidation
of the Company or any sale or disposition of 80% or more of the assets or
earning power or the Company; or (iv) approval by the stockholders of the
Company of any merger, consolidation, or statutory share exchange to which the
Company is a party as a result of which the persons who were stockholders
immediately prior to the effective date of the merger, consolidation or share
exchange shall have beneficial ownership of less than 50% of the combined voting
power in the election of directors of the surviving corporation; provided,
however, that no change in control shall be deemed to have occurred if, prior to
such time as a change in control would otherwise be deemed to have occurred, the
Company's Board of Directors deems otherwise.

14. Vesting of Rights Under Options.

Neither anything contained in the Plan nor in any resolution adopted or to be
adopted by the Committee, the Board of Directors or the stockholders of the
Company shall constitute the vesting of any rights under any Option. The vesting
of such rights shall take place only when a written Option Agreement,
substantially in the form of the Incentive Stock Option Agreement attached
hereto as Exhibit A or the Non-Incentive Stock Option Agreement attached hereto
as Exhibit B, shall be duly executed and delivered by and on behalf of the
Company and the person to whom the Option shall be granted.

15. Withholding Taxes.

Whenever under the Plan shares are to be issued in satisfaction of the exercise
of Options granted thereunder, the Company shall have the right to require the
recipient to remit to the Company an amount sufficient to satisfy federal, state
and local withholding tax requirements prior to the delivery of any certificate
or certificates for such shares.

16. Termination and Amendment.

The Plan, which was adopted by the Board of Directors on July 10, 1990 and
approved by the shareholders of the Company, shall terminate on July 9, 2000 and
no Option shall be granted under the Plan after such date. The Board of
Directors may at any time prior to such date terminate the Plan or make such
modifications or amendments thereto as it shall deem advisable, provided,
however, that shareholder approval shall be required:

       (i) to increase the number of shares reserved for issuance under the
       Plan;

       (ii) to materially increase the benefits accruing to participants under
       the Plan;

       (iii) to materially modify the requirements of eligibility for
       participation in the Plan; or

       (iv) if otherwise required to comply with the incentive stock option
       provisions of Section 162(m) of the Code or the listed company
       requirements of The Nasdaq Stock Market or of a national securities
       exchange on which the Common Stock is then traded,

and, provided, further, that no modification or amendment shall adversely affect
the rights of a holder of an Option previously granted under the Plan without
such holder's written consent.

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