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                                                                    Exhibit 10.1

*Certain confidential information contained in this document, marked by
brackets, has been omitted and filed with the Securities and Exchange Commission
pursuant to Rule 406 of the Securities Act of 1933, as amended.

                           SUPPLY TRANSFER AGREEMENT

THIS SUPPLY TRANSFER AGREEMENT ("Agreement") is made effective as of March 21,
2001, by and between IMMUNEX CORPORATION, a Washington corporation having its
principal place of business at 51 University Street, Seattle, Washington 98101
("Immunex"), and MEDIMMUNE, INC., a Delaware corporation, having its principal
place of business at 35 West Watkins Mill Road, Gaithersburg, Maryland 20878
("MedImmune").

WHEREAS, Immunex sells and distributes commercially the biopharmaceutical
product Enbrel(R) (etanercept) in the United States, pursuant to its approved
Biologics License Application ("BLA") for the product;

WHEREAS, MedImmune sells and distributes commercially the biopharmaceutical
product Synagis(R) (palivizumab) throughout the world, pursuant to its approved
product registrations therefor;

WHEREAS, Enbrel and Synagis are both currently manufactured by Boehringer
Ingelheim Pharma KG, a German corporation with a manufacturing operation located
in Biberach an der Riss, Federal Republic of Germany ("BIP"), pursuant to
separate supply agreements that BIP has entered into with Immunex and MedImmune,
respectively;

WHEREAS, Immunex is seeking to obtain additional manufacturing capacity for
Enbrel from BIP beyond the manufacturing capacity currently reserved for Enbrel
in the supply agreement between Immunex and BIP;

WHEREAS, MedImmune may, as a result of additional manufacturing capacity
obtained for Synagis elsewhere, be in a position to relinquish some of the
manufacturing capacity that it has reserved for Synagis at BIP [*]; and

WHEREAS, Immunex desires to obtain, and MedImmune desires to transfer to
Immunex, any such manufacturing capacity at BIP that MedImmune is able to
relinquish, all on the terms and conditions set forth in this Agreement.

NOW THEREFORE, in consideration of the mutual covenants contained herein, and
for other good and valuable consideration, the receipt and sufficiency of which
are hereby acknowledged, the Parties (as defined herein) hereto, intending to be
legally bound, do hereby agree as follows:

                            Article 1.  Definitions
                            -----------------------

1.1   "Affiliate" shall mean any corporation or business entity of which a Party
      owns directly or indirectly, fifty percent (50%) or more of the assets or
      outstanding stock, or any corporation which a Party directly or indirectly
      controls, or any parent corporation that owns, directly or indirectly,
      fifty percent (50%) or more of the assets or outstanding stock of a Party
      or directly or indirectly controls a Party. For purposes of this
      Agreement, American Home Products Corporation shall be deemed an Affiliate
      of Immunex.

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1.2   "BIP Facility" shall mean BIP's manufacturing campus located at
      Birkendorfer Strabe 65, 88397 Biberach an der Riss, Federal Republic of
      Germany, at which Enbrel (as defined herein) and Synagis (as defined
      herein) are manufactured.

1.3   "Enbrel" shall mean the pharmaceutical product etanercept, in any form.

1.4   "Enbrel Bulk Drug Substance" shall mean etanercept in bulk drug substance
      form.

1.5   "Enbrel Bulk Drug Substance Lot" shall mean a single [*] L fermentation
      scale lot of purified etanercept, processed to result in bulk drug
      substance.

1.6   "Enbrel Finished Product" shall mean Enbrel Bulk Drug Substance that has
      been formulated, compounded, filled into vials and lyophilized by BIP, and
      then labeled by a third party for commercial distribution, in accordance
      with the terms of the Enbrel Supply Agreement (as defined herein) and a
      third party supply agreement for the labeling and packaging operations for
      Enbrel.

1.7   "Enbrel Four-Pack" shall mean a unit that includes four (4) vials of
      Enbrel Finished Product and that has been labeled, packaged, and is
      commercially saleable as a unit.

1.8   "Enbrel Run" shall mean a single [*] fermentation scale run of the process
      for manufacturing Enbrel in bulk form.

1.9   "Enbrel Supply Agreement" shall mean the November 5, 1998 agreement among
      Immunex, BIP, and American Home Products Corporation for the manufacture
      of Enbrel at the BIP Facility, as amended by the parties thereto.

1.10  "Enhanced Yield Process" or "EYP" shall mean certain process steps and
      materials that MedImmune anticipates using at its Frederick, Maryland
      facility to manufacture Synagis, upon receiving approval from the U.S.
      Food and Drug Administration ("FDA") therefor.

1.11  "Party" or "Parties" shall mean Immunex and/or MedImmune, as the context
      requires.

1.12  "Successful Enbrel Run" shall mean an Enbrel Run that has resulted in any
      quantity of Enbrel Four-Packs that have been released for commercial sale
      according to the terms in the Enbrel Supply Agreement.

1.13  "Synagis" shall mean the pharmaceutical product palivizumab, in any form.

1.14  "Synagis Contract Runs" shall mean the production runs scheduled for the
      manufacture of Synagis at the BIP Facility under the Synagis Supply
      Agreement (as defined herein), [*].

1.15  "Synagis Supply Agreement" shall mean the agreement dated November 21,
      1997 between MedImmune and BIP for the manufacture of Synagis at the BIP
      Facility.

1.16  "Transferred Run(s)" means the Unused Synagis Run(s) as to which MedImmune
      provides written notice to Immunex under Section 2.1.

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1.17  "Unused Synagis Runs" shall mean, [*], that number of Synagis Contract
      Runs remaining in the particular calendar year that MedImmune releases to
      BIP.

                     Article 2.  Transfer of Synagis Runs
                     ------------------------------------

2.1   Production Runs
      ---------------

(a)   Immunex and MedImmune understand and agree that, within the sole
      discretion of MedImmune, MedImmune may release Synagis Contract Runs to
      BIP but that MedImmune is under no obligation to release any Synagis
      Contract Runs to BIP unless MedImmune has obtained approval from the FDA
      to implement the EYP at MedImmune's Frederick, Maryland manufacturing
      facility, and MedImmune, within its sole discretion, has determined that
      certain Synagis Contract Runs are not needed for MedImmune's commercial
      needs for Synagis. In such event, the obligation to release Synagis
      Contract Runs to Immunex shall only extend to those Synagis Contract Runs
      as to which MedImmune within its sole discretion has determined are not
      needed by MedImmune for MedImmune's commercial needs for Synagis.

(b)   MedImmune and Immunex agree that it is an important aspect of this
      Agreement that Immunex and BIP be made aware of potential Unused Synagis
      Runs as soon as possible. MedImmune agrees to notify Immunex of the
      scheduling of Synagis Contract Runs and to promptly notify Immunex when
      MedImmune decides to release or is obligated to release Synagis Contract
      Runs. Immunex and MedImmune each agree to use reasonable efforts to
      communicate with and work with each other and BIP in order to avoid any
      unnecessary delay in allowing Immunex to start an Enbrel Run as a result
      of the transfer of any Unused Synagis Run hereunder.

(c)   The parties understand and agree that MedImmune is under no obligation to
      ensure that BIP will allot Transferred Synagis Runs to Immunex and
      MedImmune has no liability to Immunex in the event that Transferred
      Synagis Runs are not alloted to Immunex.

2.2   Transfer.  Immunex shall become legally and financially responsible to BIP
      for any Transferred Run that is allotted to Immunex by BIP under the terms
      of the Enbrel Supply Agreement.

                           Article 3.  Compensation
                           ------------------------

3.1   Payment for Enbrel Run Starts.  Immunex shall pay MedImmune [*] for each
      Enbrel Run made available to Immunex by BIP as a result of a Transferred
      Run, which amount shall become due and payable within sixty (60) days
      after production [*] for each such Enbrel Run [*]. Immunex shall notify
      MedImmune when an Enbrel Run satisfies the criteria in this Section 3.1
      within [*] after such criteria are satisfied, and if so requested by
      MedImmune, Immunex shall instruct BIP to confirm same.

3.2   Payment for Successful Enbrel Runs.  In addition to the amount set forth
      in Section 3.1 above, Immunex shall pay MedImmune, for each Successful
      Enbrel Run, an amount based on the following formula:

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* Confidential Treatment Request

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(a)   A fraction shall be calculated as follows:

(i)   the numerator shall be the number of Enbrel Four-Packs obtained from the
      Successful Enbrel Run; and

(ii)  the denominator shall be the average number of Enbrel Four-Packs obtained
      from a Successful Enbrel Run during the year 2000.

(b)   The fraction calculated in Section 3.2(a) above shall be multiplied by [*]
      to determine the additional payment owed by Immunex for such Successful
      Enbrel Run.

Notwithstanding the foregoing, Immunex shall not be obligated to pay MedImmune
more than [*], pursuant to this Section 3.2, for each Successful Enbrel Run.

3.3   Additional MedImmune Costs and Expenses.  For [*]. Within [*] after
      incurring any such costs, MedImmune shall provide Immunex with a written
      statement of such costs, along with reasonable documentation therefor. [*]
      after receiving such properly prepared statement and documentation,
      Immunex shall pay to MedImmune any such amounts as provided in Section
      3.4.

3.4   Payment Method.  Within [*] after the last day of each calendar quarter
      during the term hereof during which Immunex incurs amounts that it owes
      MedImmune under Section 3.2, Immunex shall deliver to MedImmune a report
      setting forth the amounts owed hereunder incurred during such calendar
      quarter, along with payment of such amount. Such reports shall be
      considered Confidential Information of Immunex subject to the terms of
      Article 5 hereof.

3.5   Inspection of Books and Records.  Immunex shall maintain accurate books
      and records, which enable the calculation of amounts payable hereunder to
      be verified, and shall retain such books and records for each quarterly
      period for two (2) years after submission of the payment and corresponding
      report under Section 3.4 above. Upon at least thirty (30) days' prior
      written notice to Immunex, independent public accountants selected by
      MedImmune and reasonably acceptable to Immunex may have access to the
      books and records of Immunex during normal business hours to conduct a
      review or audit of such books and records, solely and to the extent
      necessary to confirm the accuracy of Immunex's calculation and payment of
      amounts due in accordance with the terms hereof. All information obtained
      during any such review or audit shall be Confidential Information of
      Immunex subject to the terms of Article 5 hereof, including information
      related to the number of Enbrel Four-Packs obtained during any Successful
      Enbrel Run and the average number of Enbrel Four Packs obtained from a
      Successful Enbrel Run during the year 2000. Any such review or audit shall
      be at the expense of MedImmune; provided, however, that if such
      accountants reasonably determine that such amounts have been, for any
      calendar quarter, understated by an amount equal to or greater than [*],
      Immunex shall, in addition, to remitting the additional amount determined
      to be due, pay all reasonable fees and expenses incurred by such
      accountants in making such determination.

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* Confidential Treatment Request

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                         Article 4.  Term; Termination
                         -----------------------------
4.1   Term.  This Agreement shall take effect as of the date set forth above
      and, unless earlier terminated as set forth in Section 4.2 below, shall
      expire on [*].

4.2   Termination for Breach.  Either Party may terminate this Agreement for
      material breach of the other terms hereof by the other Party, after
      providing at least [*] prior written notice to the other Party specifying
      the precise nature of the breach. In the event that the Party receiving
      such notice has not cured the breach within such [*] period (or within a
      longer reasonable period of time if the breaching Party delivers a written
      certification that such material breach is not reasonably capable of being
      cured within [*] and that such Party is working diligently to cure such
      breach), this Agreement shall be terminable immediately upon written
      notice by the non-breaching Party.

4.3   Amounts Due.  Expiration or termination of this Agreement for any reason
      shall not exempt either Party from paying to the other Party any amounts
      due to such Party and outstanding at the time of such expiration or
      termination.

                          Article 5.  Confidentiality
                         ----------------------------

5.1   Definition of Confidential Information.  For the purposes of this
      Agreement, "Confidential Information" shall mean any information disclosed
      by one Party ("Disclosing Party") to the other Party ("Receiving Party")
      and designated as "CONFIDENTIAL" in writing at the time of any written
      disclosure, or, in the event of oral disclosure or disclosure by
      demonstration, identified in writing as "CONFIDENTIAL" no later than
      thirty (30) days after such oral disclosure or disclosure by
      demonstration. Confidential Information shall also include such
      information or materials that would reasonably be identified or understood
      by the Receiving Party as the confidential or proprietary information of
      the Disclosing Party, even if they are not so identified as described in
      the previous sentence. Confidential Information shall not, however,
      include:

(a)   information which was already known by the Receiving Party at the time of
      its disclosure hereunder, as evidenced by the Receiving Party's written
      records;

(b)   information disclosed to the Receiving Party by a third party lawfully in
      possession of such information and not under an obligation of
      nondisclosure to the Disclosing Party in respect thereof;

(c)   information which at the time of disclosure is or subsequently becomes
      patented, published or otherwise part of the public domain, except by
      breach of this Agreement by the Receiving Party;

(d)   information developed by the Receiving Party independently of information
      obtained from the Disclosing Party; or

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(e)   information which is required to be disclosed by law, regulation or the
      order of a judicial or administrative authority; provided, however, that
      the Receiving Party (1) gives the Disclosing Party sufficient advance
      written notice to permit it to seek a protective order or other similar
      order with respect to such Confidential Information and (2) thereafter
      discloses only the minimum Confidential Information required to be
      disclosed in order to comply, whether or not a protective order or other
      similar order is obtained by such Disclosing Party.

5.2   Disclosure and Use of Confidential Information.
      ----------------------------------------------

(a)   Obligations.  The Receiving Party, its employees, and its agents shall not
      disclose Confidential Information of the Disclosing Party to any third
      party without the prior written consent of the Disclosing Party. In
      addition, the Receiving Party, its employees, and its agents shall not use
      Confidential Information of the Disclosing Party for any purpose other
      than for purposes consistent with this Agreement.

(b)   Exceptions.  Notwithstanding the foregoing, the Receiving Party may
      disclose Confidential Information (i) to its employees, Affiliates,
      consultants, agents or contractors who have a need to know such
      information for the Receiving Party to perform its obligations hereunder
      or for other purposes consistent with this Agreement, and (ii) to BIP for
      purposes consistent with this Agreement.

(c)   Maintenance of Confidentiality.  Each Party shall use reasonable and
      customary precautions to safeguard the other Party's Confidential
      Information, including ensuring that all employees, Affiliates,
      consultants, agents, or contractors who are provided access to such
      Confidential Information are informed of the confidential and proprietary
      nature of such Confidential Information and are under obligations of
      confidentiality with respect to such Confidential Information similar to
      those set forth herein.

5.3   Return of Confidential Information.  Upon expiration or termination of
      this Agreement, and upon written request by the Disclosing Party, the
      Receiving Party shall promptly return to the Disclosing Party all
      Confidential Information that the Receiving Party has received from the
      Disclosing Party hereunder. The Receiving Party may retain one copy of
      each item of Confidential Information disclosed to it hereunder, provided
      that such copy shall be retained and used solely for compliance purposes
      and shall be held in the Receiving Party's confidential files.

5.4   Remedies.  Either Party shall be entitled to seek injunctive relief to
      enforce the terms of this Article 5.

5.5   Survival.  The terms of this Article 5 shall survive expiration or
      termination of this Agreement and continue for a period of [*] thereafter.

5.6   Nonuse Obligations.  Except as expressly provided in this Agreement, no
      right or license, either express or implied, under any patent, trademark
      or proprietary right is granted hereunder by virtue of the execution of
      this Agreement or the disclosure by either Party of its Confidential
      Information to the other Party hereunder.

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* Confidential Treatment Request

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                       Article 6.  Consequential Damages
                       --------------------------------

6.1   Disclaimer of Consequential Damages.  In no event shall either Party be
      liable to the other Party hereunder for incidental or consequential
      damages.

      Article 7.  Press Releases; Use of Names, Disclosure of Agreement.
      ------------------------------------------------------------------

7.1   Press Releases.  No press release, publicity or other form of public
      written disclosure related to this Agreement shall be permitted by either
      Party to be published or otherwise disclosed unless the other Party has
      indicated its consent to the form of the release in writing.
      Notwithstanding the foregoing, if a Party is required by law, in the
      reasonable judgment of its counsel, to make a public disclosure regarding
      this Agreement to fulfill its applicable regulatory reporting or other
      legal disclosure obligations, such Party shall provide as much notice as
      reasonably possible to the other Party, shall permit the other Party an
      opportunity to review and comment on the disclosure to the extent
      reasonably practicable, and shall give due consideration to any such
      comments provided by the other Party.

7.2   Use of Names.  MedImmune shall not make use of the name of Immunex or any
      of its Affiliates in any advertising or promotional material, or
      otherwise, without the prior written consent of the entity named. Immunex
      shall not make use of the name of MedImmune or any of its Affiliates in
      any advertising or promotional material, or otherwise, without the prior
      written consent of the entity named.

7.3   Disclosure of Agreement.  Notwithstanding anything else herein to the
      contrary and except for public disclosures as provided in Section 7.1,
      both parties agree not to disclose any of the terms of this Agreement or
      the existence of this Agreement to any third person or entity except to
      the extent that a Party receives a written opinion of counsel that
      disclosure of this Agreement is required by applicable law, and in such
      case, such Party shall take all reasonable steps to ensure that such
      disclosure is subject to confidentiality obligations. Notwithstanding any
      other provision to the contrary in this Section 7.3, Immunex and MedImmune
      may disclose the existence but not the terms of this Agreement to BIP, and
      Immunex may disclose the terms of this Agreement to American Home Products
      Corporation and/or its Affiliates ("AHP"), provided AHP has agreed to be
      bound by obligations of non-disclosure at least as restrictive as those
      contained in this Agreement.

                            Article 8.  Assignment.
                            -----------------------

8.1   Assignment.  This Agreement shall be binding upon the successors and
      assigns of the Parties and the name of a Party appearing herein shall be
      deemed to include the names of its successors and assigns. Neither Party
      may assign its interest under this Agreement without the prior written
      consent of the other Party; provided, however, either Party may assign its
      interest under this Agreement, without the prior written consent of the
      other Party, (a) to an Affiliate, so long as the assigning Party
      unconditionally guarantees the obligations of such Affiliate or (b) to a
      successor of the assigning Party's business by reason of merger, sale of
      all or substantially all of its assets or other form of acquisition,
      provided that such successor agrees in writing to assume all of the
      obligations of the assigning Party under this Agreement. Such consent
      shall not be unreasonably withheld. Any purported assignment without a
      required consent shall be void. No assignment shall relieve either Party
      of responsibility for the performance of any obligation which accrued
      prior to the effective date of such assignment.

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                        Article 9.  Dispute Resolution.
                        -------------------------------
9.1   Exclusions.  Section 9.2 below shall not apply to any disputes arising
      under Article 5 (Confidentiality).

9.2   Dispute Resolution.  The Parties recognize that a bona fide dispute as to
      certain matters may from time to time arise during the term of this
      Agreement which relates to a Party's rights and/or obligations hereunder.
      In the event of the occurrence of such a dispute, either Party may, by
      notice to the other Party, have such dispute referred to their respective
      officers designated herein, or their successors or designees, for
      attempted resolution by good faith negotiations within thirty (30) days
      after such notice is received. Such designated officers are as follows:

          For Immunex - Mark Booth, Senior Vice President and General Manager,
Enbrel Franchise

          For MedImmune - Michael Richmann, Senior Vice President, Corporate
Development and Administration

In the event the designated officers are not able to resolve such dispute within
such thirty (30)-day period, or such other period of time as the Parties may
mutually agree in writing, each Party shall have the right to pursue any and all
remedies available at law or in equity.

                          Article 10.  Miscellaneous.
                          ---------------------------

10.1  Notices.  Any notice required or permitted to be given hereunder by either
      Party shall be in writing and shall be (a) delivered personally, (b) sent
      by registered mail, return receipt requested, postage prepaid, (c) sent by
      a nationally-recognized courier service guaranteeing next-day delivery,
      charges prepaid, or (d) delivered by facsimile (with the original promptly
      sent by any of the foregoing manners), to the addresses or facsimile
      numbers of the other Party set forth herein, or at such other addresses as
      may from time to time be furnished by similar notice by either Party. The
      effective date of any notice hereunder shall be the date of receipt by the
      receiving Party.

      If to MedImmune:  MedImmune, Inc.
                        35 West Watkins Mill Road
                        Gaithersburg, MD  20878
                        Attention:  Senior Vice President, Business Development
                        Fax:  301-527-4214
                        Phone:  301-527-4454

      If to Immunex:    Immunex Corporation
                        51 University Street
                        Seattle, Washington 98101
                        Attention:  Senior Vice President and General Manager
                                    Enbrel Franchise
                        Fax:  (206) 839-0806
                        Phone:  (206) 587-0430

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      with a copy to:   Immunex Corporation
                        51 University Street
                        Seattle, Washington 98101
                        Attention:  General Counsel
                        Fax:  (206) 292-9271
                        Phone:  (206) 587-0430

10.2  Applicable Law.  This Agreement shall be governed by and construed in
      accordance with the laws of the State of Maryland, exclusive of choice-of-
      law rules.

10.3  Headings.  All headings in this Agreement are for convenience of reference
      only and shall not affect the interpretation of this Agreement.

10.4  Severance.  If any provision of this Agreement is held to be invalid or
      unenforceable by a court of competent jurisdiction, all other provisions
      shall continue in full force and effect.

10.5  Independent Contractors.  Each of the Parties is an independent contractor
      and nothing herein contained shall be deemed to constitute the
      relationship of partners, joint venturers, nor of principal and agent
      between the Parties. Neither Party shall hold itself out to third parties
      as purporting to act on behalf of, or serving as the agent of, the other
      Party.

10.6  Waiver.  No waiver of any term, provision or condition of this Agreement,
      whether by conduct or otherwise in any one or more instances, shall be
      deemed to be or construed as a further or continuing waiver of any such
      term, provision or condition or of any other term, provision or condition
      of this Agreement.

10.7  Counterparts.  This Agreement and any amendment hereto may be executed in
      any number of counterparts, each of which shall for all purposes be deemed
      to be an original and all of which shall constitute the same instrument.

10.8  Survival.  The provisions of Articles 3, 5, 6, 7, 9 and 10 and Sections
      2.2, 4.3, 7.3 and 10.8 shall survive expiration or termination of this
      Agreement for the period of time stated therein, or if no period of time
      is stated therein, then indefinitely.

10.9  Entirety; Amendments.  This Agreement constitutes the full understanding
      of the Parties and a complete and exclusive statement of the terms of
      their agreement with respect to the subject matter hereof, and no terms,
      conditions, understandings or agreements purporting to modify or vary the
      terms thereof shall be binding unless it is hereafter made in writing and
      signed by both Parties. No modification to this Agreement shall be
      effected by the acknowledgment or acceptance of any purchase order or
      shipping instruction forms or similar documents containing terms or
      conditions at variance with or in addition to those set forth herein. In
      the event of a conflict between this Agreement and the exhibits hereto,
      the terms of this Agreement shall control. This Agreement may be amended
      and supplemented only by a written instrument signed by both Parties.

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IN WITNESS WHEREOF, the Parties have caused this Agreement to be executed as of
the Effective Date.

IMMUNEX CORPORATION                   MEDIMMUNE, INC.

By:    /s/ Mark D. Booth              By:    /s/ Melvin D. Booth
   ----------------------------------    ---------------------------------------
Name:  Mark D. Booth                  Name:  Melvin D. Booth
     --------------------------------      -------------------------------------
Title: General Manager, Enbrel        Title: President & Chief Operating Officer
      -------------------------------       ------------------------------------
Date:  March 26, 2001                 Date:  March 21, 2001
     --------------------------------      -------------------------------------

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