Document:

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                                                                   Exhibit 10.16

                                  PLAN SUMMARY
                                  ------------
                               IMMUNEX CORPORATION
                   STOCK OPTION PLAN FOR NONEMPLOYEE DIRECTORS
                    As Amended and Restated on April 18, 2000

           __________________________________________________________

     This Plan Summary is part of a Prospectus that relates to 1,200,000/4/
shares of Common Stock of Immunex Corporation that have been reserved for
issuance upon the exercise of stock options under Immunex's Stock Option Plan
for Nonemployee Directors, as amended and restated on April 18, 2000. The Plan
and the agreements between you and Immunex govern the terms and conditions of
the offer and sale of Immunex's Common Stock, including the prices of the
shares. The Immunex Stock is traded on the Nasdaq National Market under the
symbol "IMNX."

     The Plan Summary is not an offer by Immunex to sell or a solicitation of an
offer to buy any securities in any jurisdiction to any person to whom it is
unlawful for Immunex to make such offer or solicitation.

     This Plan Summary supersedes the Plan Summary for the Immunex Stock Option
Plan for Nonemployee Directors dated September 1, 1999.

           __________________________________________________________

     THIS PLAN SUMMARY IS PART OF A PROSPECTUS COVERING SECURITIES THAT HAVE
BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933.

__________________

     /4/ When the Stock Option Plan For Nonemployee Directors was setup, it
originally covered 100,000 shares. The number of shares grew to 1,200,000 as a
result of a 2-for-1 stock split on March 25, 1999, a 2-for-1 stock split on
August 26, 1999 and a 3-for-1 stock split on March 20, 2000.

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                                    CONTENTS

<TABLE>
<S>                                                                              <C>
BACKGROUND ....................................................................   1
DESCRIPTION OF THE PLAN .......................................................   1
   What Is the Purpose of the Plan? ...........................................   1
   Who Administers the Plan? ..................................................   1
   Who Is Eligible to Participate in the Plan? ................................   1
   What Options Are Granted Under the Plan? ...................................   1
   How Is the Option Exercise Price Determined? ...............................   1
   When Do My Options Vest? ...................................................   1
   How Do I Exercise My Vested Options? .......................................   2
   How Do I Pay the Option Exercise Price? ....................................   2
   How Long Do I Have to Exercise My Options? .................................   2
   Can I Transfer My Options? .................................................   2
   What Happens if There Is a Stock Split or Other Change in Capitalization?...   2
   What Happens if There Is a Change of Control? ..............................   3
   Can the Plan Be Amended or Terminated? .....................................   3
FEDERAL INCOME TAX CONSEQUENCES ...............................................   3
OTHER MATTERS .................................................................   4
   Shares Authorized for Issuance .............................................   4
   Limitation of Rights .......................................................   4
   Inapplicability of Certain Statutes; Unfunded Plan .........................   4
   Securities Registration ....................................................   4
   Restrictions on Resale of Shares ...........................................   4
   Where You Can Find More Information ........................................   5
</TABLE>

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BACKGROUND

     This Plan Summary is only a summary of the Plan and is subject to and
qualified by reference to the Plan. A separate option letter agreement between
you and Immunex governs each stock option granted under the Plan. You should
carefully read your option letter agreement to fully understand the key terms of
your grant. You should not rely solely on this Plan Summary. You can inspect or
request a copy of the Plan during normal business hours at the office of the
Corporate Secretary of Immunex Corporation, at 51 University Street, Seattle,
Washington, 98101. Telephone requests may be directed to (206) 587-0430.

DESCRIPTION OF THE PLAN

     What Is the Purpose of the Plan?

     The Plan authorizes the automatic grant of stock options to nonemployee
directors of Immunex. The purposes of the Plan are to attract and retain the
services of experienced and knowledgeable nonemployee directors and to provide
an incentive for such directors by providing an opportunity for stock ownership
in Immunex.

     Who Administers the Plan?

     The Plan is administered by the Immunex Board of Directors (the "Board").
Subject to the terms of the Plan, the Board has the power to construe the
provisions of the Plan, determine all questions arising under the Plan, and
adopt and amend such rules and regulations for administering the Plan as the
Board deems desirable.

     Who Is Eligible to Participate in the Plan?

     Each director of Immunex who is not otherwise an employee of Immunex, any
parent or subsidiary of Immunex, or a director appointed by American Cyanamid
Company or American Home Products Corporation pursuant to the Amended and
Restated Governance Agreement dated as of December 15, 1992 (an "eligible
director"), is eligible to participate in the Plan.

     What Options Are Granted Under the Plan?

     The Plan provides that (a) each eligible director who is elected or
appointed for the first time after the date of adoption of the Plan shall
automatically receive the grant of an option to purchase 10,000 shares of
Immunex Stock on the day such eligible director is initially elected or
appointed, and (b) each eligible director continuing service as an eligible
director immediately following an Annual Meeting of Shareholders will
automatically receive an option to purchase 5,000 shares of Immunex Stock
immediately following such meeting as an annual grant, except that an eligible
director who has received an initial grant of an option to purchase 10,000
shares of Immunex Stock on such date will not receive an annual grant until the
next Annual Meeting.

     How Is the Option Exercise Price Determined?

     The exercise price per share for each option is the closing price, or if
there is no closing price, the mean between the high and low sale prices of the
shares covered by the option as reported on the Nasdaq National Market on the
day the option is granted or, if no Immunex Stock was traded on such date, on
the immediately preceding date on which Immunex Stock was so traded (the "fair
market value").

     When Do My Options Vest?

     Your options will vest and become exercisable 20% after each year from the
date of grant so that your options are fully vested five years after the date of
grant. Notwithstanding the foregoing, your options become

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100% vested and exercisable if your service as a member of the Board ends on
account of your death, provided that when you die you have served as a member of
the Board for at least two years.

     How Do I Exercise My Vested Options?

     You may exercise part or all of your vested options at any time during the
option period by giving written notice, signed by you, to Immunex stating the
number of shares of Immunex Stock with respect to which the option is being
exercised, accompanied by payment in full of the option exercise price for the
number of shares to be purchased. You may not purchase fewer than 100 shares (or
the remaining shares then purchasable under the option, if less than 100 shares)
upon any exercise. No option may at any time be exercised with respect to a
fractional share.

     How Do I Pay the Option Exercise Price?

     You may pay the option exercise price (a) in cash or by check, (b) in
shares of Immunex Stock you already own (generally you must have owned the stock
for at least six months) and having an aggregate fair market value on the date
of exercise equal to the option exercise price, or (c) by delivery of a properly
executed exercise notice together with irrevocable instructions to a broker to
promptly deliver to Immunex the amount of sale or loan proceeds to pay the
exercise price, all in accordance with the regulations of the Federal Reserve
Board.

     How Long Do I Have to Exercise My Options?

     If your service as a director of Immunex terminates before the end of the
option term for any reason, the unvested portion of your option will terminate
automatically without any further notice to you. Only your unvested options
terminate, thus, if your service as a director of Immunex ends as a result of
your death and your unvested options immediately vest, those vested options do
not terminate upon your death. You must exercise the vested portion of your
option no later than the earliest of the following dates after termination of
                         --------
your service as a director:

       (a)    Ten years from the date of grant;

       (b)    Three months after termination, if termination was for any reason
              other than death; and

       (c)    Twelve months after termination, if termination was due to death.

     Can I Transfer My Options?

     During your lifetime, an option may be exercised only by you. Your right to
exercise an option is not assignable or transferable other than by will or by
the applicable laws of descent and distribution, except that you may designate
in writing during your lifetime a beneficiary to receive and exercise the
options in the event of your death.

     What Happens if There Is a Stock Split or Other Change in Capitalization?

     The aggregate number and class of shares with respect to which options may
be granted under the Plan, the number and class of shares subject to each
outstanding option and the price per share specified in such options (but not
the total price) will all be proportionately adjusted for any stock dividends,
stock splits, recapitalizations, combinations or exchanges of shares, split-ups,
split-offs, spin-offs or other similar changes in capitalization. However, if an
initial or annual grant occurs within 90 days following any such change in
capitalization, the number and class of shares subject to the grant will be
proportionately adjusted to be the same

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number and class of shares that would be subject to the grant had it been
outstanding immediately prior to the date of the change in capitalization.

     In the event of any adjustment in the number of shares of Immunex Stock
covered by any option, any fractional shares resulting from such adjustment will
be disregarded and each such option will cover only the number of full shares
resulting from such adjustment.

     What Happens if There Is a Change of Control?

     Upon the effective date of a dissolution or liquidation of Immunex, or of a
reorganization, merger or consolidation of Immunex with one or more corporations
that results in more than 70% of the outstanding voting shares of Immunex being
owned by one or more affiliated corporations or other affiliated entities, or of
a transfer of all or substantially all the assets or more than 70% of the then
outstanding shares of Immunex to another corporation or other entity, the Plan
and all options granted under it will terminate. In the event of such
dissolution, liquidation, reorganization, merger, consolidation, transfer of
assets or transfer of stock, each optionee will be entitled, for a period of 20
days prior to the effective date of the transaction, to purchase the full number
of shares under his or her option which he or she otherwise would have been
entitled to purchase during the remaining term of the option.

     Can the Plan Be Amended or Terminated?

     The Board may amend, terminate or suspend the Plan at any time, in its sole
and absolute discretion, except that if required to qualify the Plan as a
formula plan for purposes of Rule 16b-3 promulgated under Section 16(b) of the
Securities Exchange Act of 1934, no amendment may be made more than once every
six months that would change the amount, price, timing or vesting of the
options, other than to comply with changes in the Internal Revenue Code of 1986,
as amended (the "Code"), or the rules and regulations promulgated thereunder.
Also, no amendment that would increase the number of shares that may be issued
under the Plan or otherwise require shareholder approval under any applicable
law or regulation may be made without the approval of Immunex's shareholders.
The Plan will continue in effect until December 13, 2003, unless it is sooner
terminated by action of the Board or Immunex's shareholders.

FEDERAL INCOME TAX CONSEQUENCES

     The federal income tax consequences to Immunex and you of the grant and
exercise of options under existing applicable provisions of the Code and the
regulations thereunder are substantially as follows:

     All options granted under the Plan will be nonstatutory options not
intended to qualify as "incentive stock options" under Section 422 of the Code.
You will not be deemed to receive any income at the time an option is granted
nor will Immunex be entitled to a deduction at that time. When any part of an
option is exercised, you will recognize ordinary income at the time of exercise
in an amount equal to the difference between the option exercise price and the
then fair market value of the shares acquired. Generally, upon a subsequent
disposition of the shares, your basis for determining taxable gain or loss will
be the amount paid for such shares plus the amount that was includible in your
income at the time of exercise. Any gain recognized on such disposition would
generally be taxed as long-term or short-term capital gain, depending on the
length of time you are deemed to have held the shares.

     Subject to the applicable provisions of the Code, Immunex will be entitled
to a deduction for federal income tax purposes in the year in which and in an
amount for which you recognize ordinary income taxable as compensation in
respect of an option.

     The foregoing is only a brief summary of the applicable federal income tax
laws and regulations. It does not address the federal estate and gift tax
consequences or the state, local or foreign tax consequences of the options, nor
does it discuss the federal income tax consequences to an optionee who is a
foreign resident.

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Furthermore, it does not address all possible tax aspects of transactions that
may arise under the Plan, such as restrictions that Immunex may place on Immunex
Stock or the use of previously acquired Immunex Stock to exercise options. The
tax laws and regulations are complex and are subject to change.

FOR THE FOREGOING REASONS, IT IS IMPORTANT THAT YOU, BEFORE EXERCISING AN OPTION
AND BEFORE DISPOSING OF THE SHARES ACQUIRED PURSUANT TO SUCH EXERCISE, CONSULT A
TAX ADVISOR AS TO THE INCOME TAX CONSEQUENCES OF SUCH AN EXERCISE OR
DISPOSITION.

OTHER MATTERS

     Shares Authorized for Issuance

     Immunex has authorized a total of up to 1,200,000/5/ shares of Immunex
Stock for issuance under the Plan, subject to adjustment from time to time as
provided in the Plan. The shares will be presently authorized but unissued
shares. If any option granted under the Plan expires or terminates for any
reason without having been exercised in full, the unpurchased or forfeited
shares will again be available for purposes of the Plan.

     Limitation of Rights

     Nothing in the Plan or in any options granted under the Plan constitutes
evidence of your right to a continued service relationship with Immunex. Neither
you nor your successors in interest will have any rights as a shareholder of
Immunex until we have issued shares of Immunex Stock to you.

     Inapplicability of Certain Statutes; Unfunded Plan

     We believe that the Plan is not subject to (a) the participation, vesting
or minimum funding provisions of the Employee Retirement Income Security Act of
1974 (ERISA) or (b) the provisions governing a pension, profit-sharing or stock
bonus plan qualified under Section 401(a) of the Code. The Plan will be unfunded
and will not create a trust or a separate fund or funds. The Plan does not
create any fiduciary relationship between you and Immunex. Your rights under any
options will not exceed the rights of general unsecured creditors of Immunex.
The cash proceeds received by Immunex from the issuance of shares under the Plan
are general funds of Immunex.

     Securities Registration

     We have filed an effective registration statement with the Securities and
Exchange Commission (the "SEC") with respect to the shares that will be issued
under the Plan. We intend to maintain this registration but have no obligation
to do so. If the registration ceases to be effective, you will not be able to
exercise the options without an exemption from registration under federal and
state securities laws. Exemptions from registration are very limited and might
be unavailable.

     Restrictions on Resale of Shares

     You and your spouse, certain other relatives and any trust, estate,
corporation or other organization controlled by any of the foregoing persons may
be deemed to be an affiliate of Immunex. An "affiliate" is

__________________
    /5/ This number has been adjusted for the 2-for-1 stock split on March 25,
1999, the 2-for-1 stock split on August 26, 1999 and the 3-for-1 stock split on
March 20, 2000.

<PAGE>

defined as a person who directly or indirectly controls, is controlled by or is
under common control with Immunex. Affiliates of Immunex will be obligated as a
precondition to any prospective sale of shares acquired upon the exercise of
options granted under the Plan to comply with Rule 144 of the Securities Act of
1933 and the rules and regulations promulgated thereunder. Rule 144 limits not
only the manner of sale but also the amount of Immunex Stock that may be sold in
specified time periods. You should consult legal counsel as to whether you, your
family members or your donees would be subject to any of the foregoing
restrictions on resale.

     Under certain circumstances, you may, pursuant to Section 16(b) of the
Securities Exchange Act of 1934, be subject to liability for certain short-swing
profits from the sale of shares you acquire upon exercise of options.

     Where You Can Find More Information

     We file annual, quarterly and special reports, and other information with
the SEC. You may view Immunex's SEC filings on the SEC's web site at
http://www.sec.gov. You may also read and copy any document Immunex files at the
SEC's public reference rooms in Washington, D.C., New York, New York, and
Chicago, Illinois. Please call the SEC at 1-800-SEC-0330 for further information
on the public reference rooms.

     The SEC allows Immunex to "incorporate by reference" into this Plan Summary
the information we file with it, which means that Immunex can disclose important
information to you by referring you to those documents. The information
incorporated by reference is considered to be part of this Plan Summary, and
later information filed with the SEC will update and supersede this information.
Immunex incorporates by reference the documents listed below and any future
filings made with the SEC under Sections 13(a), 13(c), 14 and 15(d) of the
Securities Exchange Act of 1934 until this offering is completed:

        (a) Immunex's Annual Report on Form 10-K for the fiscal year ended
December 31, 1999, filed on March 7, 2000. This document contains the most
recent certified annual financial statements that we have filed;

        (b) All other reports filed by Immunex under Section 13(a) or 15(d) of
the Exchange Act since the end of the fiscal year covered by the Annual Report
on Form 10-K referred to in (a) above; and

        (c) The description of the Immunex Stock contained in Immunex's
Registration Statement on Form 8-A filed on May 12, 1983, under Section 12(g) of
the Exchange Act, including any amendments or reports filed for the purpose of
updating such description.

     Upon written or oral request, Immunex will provide you, without charge,
additional information about the Plan and a copy of any or all documents
referred to above other than exhibits to such documents. Please direct your
requests to the Corporate Secretary of Immunex at its headquarters, at 51
University Street, Seattle, Washington 98101. You may direct telephone requests
to (206) 587-0430. If you previously received a copy of any of the documents
described above, you may obtain an additional copy, without charge, upon written
request directed to the Corporate Secretary.

     You should rely only on the information incorporated by reference or
provided in this Plan Summary or any supplements. We have not authorized anyone
to give you different information. You should not assume that the information
incorporated by reference or provided in this Plan Summary or any supplements is
accurate as of any date other than the date on the front of the document.<PAGE>

                                                                   Exhibit 10.17

                                    ADDENDUM
                                     TO THE
                               IMMUNEX CORPORATION
                   STOCK OPTION PLAN FOR NONEMPLOYEE DIRECTORS

        WHEREAS, Immunex Corporation (the "Company") maintains the Stock Option
Plan for Nonemployee Directors (the "Plan"); and

        WHEREAS, the Company desires to adjoin an addendum (this "Addendum") to
the Plan to address the effects of the transactions contemplated by the
Agreement and Plan of Merger by and between Amgen Inc., AMS Acquisition Inc. and
the Company dated as of December 16, 2001 (the "Merger Agreement");

         NOW, THEREFORE, notwithstanding anything in the Plan to the contrary,
this Addendum is hereby adopted, effective as of the Effective Time (as defined
in the Merger Agreement):

    Section 1. At the Effective Time, each option granted pursuant the Plan
shall be treated in accordance with the applicable terms of the Merger
Agreement.

    Section 2. In the event that an optionee ceases to be a director of the
Company or Amgen Inc. for any reason immediately prior to, at, or during the
fifteen (15) months following the Effective Time, each option held by such
optionee for common stock of Amgen Inc. shall immediately vest in full and shall
remain exercisable until the earlier of (x) the first anniversary of the date
such optionee ceases to be a director of the Company or Amgen Inc. or (y) the
end of the term of such option.

    Section 3. This Addendum shall be effective only upon the Effective Time. In
the event that the Merger Agreement terminates according to its terms, this
Addendum shall be of no force or effect.

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