EXHIBIT 10.4



                               JENNER TECHNOLOGIES
                             NOTE PURCHASE AGREEMENT

         This Agreement is made as of May 6, 1996 between Jenner Technologies, a
California corporation (the "Company") and Hayden Leason (the "Investor").

         1.       The Note.

                  1.1  The  Notes.  The  Investor  agrees,   on  the  terms  and
conditions  specified in this Agreement,  to lend to the Company  $3,000,0000 at
the Closing (as defined  below).  The  Investor's  loan shall be  evidenced by a
secured promissory note ("Note") dated as of the date of the Closing in the form
of Exhibit A. The Note shall not be convertible into any shares of the Company's
capital stock.

                  1.2 Place and Date of Closing. The closing of the purchase and
sale of the Note (the "Closing") will be held at the offices of Wilson, Sonsini,
Goodrich & Rosati,  650 Page Mill Road,  Palo Alto,  California at 10:00 a.m. on
May 6, 1996,  or at such other time and place as the  Company  and the  Investor
shall mutually agree (the "Closing Date").

                  1.3  Delivery.  At the Closing,  the Company shall deliver the
Note  to the  Investor,  and the  Investor  shall  deliver  to the  Company  the
principal amount thereof by check or wire transfer.

         2.       Representations and Warranties of the Company.

                  2.1  Organization  and Standing.  The Company is a corporation
duly  organized  and  validly  existing  under,  and by virtue  of,  the laws of
California  and is in  good  standing  under  such  laws.  The  Company  has all
requisite  corporate power and authority to own its properties and assets and to
carry on its  business as  presently  conducted.  The Company is qualified to do
business as a foreign  corporation in each  jurisdiction in which the failure to
be so  qualified  would  have  materially  adverse  impact  on the  business  or
financial condition of the Company taken as a whole.

                  2.2  Corporate  Power and  Authorization.  The Company has all
requisite  legal and corporate  power to execute and deliver this  Agreement and
the  Note,  and to sell and  issue  the Note to the  Investor  pursuant  to this
Agreement.  All corporate  action on the part of the Company,  its directors and
shareholders  necessary  for the sale and issuance of the Note has been taken or
will be taken prior to the Closing.  Each of the  Agreement  and the Note,  when
executed and  delivered by the Company,  shall  constitute a valid,  binding and
enforceable obligation of the Company,  except as the enforcement thereof may be
limited by applicable  bankruptcy,  insolvency,  reorganization  or similar laws
relating  to or  affecting  the  enforcement  of  creditor's  rights  and to the
availability of the remedy of specific  performance.  The execution and delivery
of this  Agreement  and the Note will not violate,  conflict with or result in a
material  breach of (i) the  Company's  Articles  of  Incorporation,  as amended
through the Closing Date; (ii) the Company's Bylaws;  (iii) any judgment,  order
or decree of any court or  arbitrator  to which the Company is a party;  or (iv)
any contract,  undertaking,  indenture or other agreement or instrument by which
the  Company  is now  bound or to which it is now a party.  The  Company  is not
subject to any judgment, order or decree of any court or arbitrator.  Except for
notices  required  or  permitted  to be filed  with  certain  state and  federal
securities commissions, which







notices the Company agrees to file on a timely basis, the execution and delivery
of the Note by the Company to the  Investor  will not  require any  governmental
consent or approval.

         3.       Representations, Warranties of the Investors and Restrictions
                  on Transfer Imposed by the Securities Act of 1933.

                  3.1  Representations  and  Warranties  of  the  Investor.  The
Investor represents and warrants to the Company as follows:

                       (a)  All  action  on the  part  of the  Investor  for the
authorization,  execution,  delivery  and  performance  by the  Investor of this
Agreement  has been taken,  and this  Agreement  constitutes a valid and binding
obligation of the Investor,  enforceable in accordance with its terms, except as
may be limited by applicable bankruptcy, insolvency, reorganization,  moratorium
or other similar laws  affecting the  enforcement  of creditor's  rights and the
availability of the remedy of specific performance.

                       (b)  The  Investor  is   experienced  in  evaluating  and
investing in new companies and companies with limited  operating  histories such
as the Company.

                       (c) The Investor is acquiring the Note for investment for
its own account and not with a view to, or for resale in  connection  with,  any
distribution.  The Investor  understands  that the Note has not been  registered
under the Securities Act of 1933, as amended (the "Act") by reason of a specific
exemption from the registration  provisions of the Act which depends upon, among
other things, the bona fide nature of the investment intent as expressed herein.

                       (d) The Investor  acknowledges that the Note must be held
indefinitely unless  subsequently  registered under the Act or an exemption from
such registration is available.  The Investor is aware of the provisions of Rule
144  promulgated  under  the Act which  permits  limited  resale  of  securities
purchased  in a  private  placement  subject  to  the  satisfaction  of  certain
conditions,  including,  in case the Investor has held the  securities  for less
than three years or is an  affiliate  of the Company,  among other  things:  the
availability of certain current public information about the Company, the resale
occurring  not less than two years after a party has  purchased and paid for the
securities  to be sold,  the sale being through a "broker's  transaction"  or in
transactions directly with a "market maker," and the number of shares being sold
during any three-month period not exceeding specified limitations.

                       (e) The Investor  understands  that no public  market now
exists for any of the  securities  issued by the Company and that it is unlikely
that a public market will ever exist for the Note.

                       (f) The Investor is a  sophisticated  investor  with such
knowledge and  experience in financial and business  matters so as to be capable
of evaluating  the merits and risks of a prospective  investment in the Note and
who is capable of bearing the economic risks of such


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investment.  The  Investor  is an  accredited  investor  within  the  meaning of
Regulation D promulgated by the Securities and Exchange  Commission  pursuant to
the Act.

                       (g) In taking any action or performing  any role relative
to  arranging  the  proposed  investment,  the  Investor has acted solely in the
Investor's own interest. Neither the Investor nor any of his agents or employees
has acted as an agent of the  Company,  or as an  issuer,  underwriter,  broker,
dealer or investment advisor relative to the Note.

                  3.2 Legends.  The  instrument  representing  the Note shall be
endorsed with the  following  legend (in addition to any legend  required  under
applicable state securities laws):

         THE SECURITIES  REPRESENTED  HEREBY HAVE NOT BEEN REGISTERED  UNDER THE
         SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"), OR UNDER THE SECURITIES
         LAWS OF CERTAIN STATES. THESE SECURITIES ARE SUBJECT TO RESTRICTIONS ON
         TRANSFERABILITY  AND RESALE AND MAY NOT BE TRANSFERRED OR RESOLD EXCEPT
         AS PERMITTED UNDER THE ACT AND THE APPLICABLE  STATE  SECURITIES  LAWS,
         PURSUANT TO REGISTRATION OR EXEMPTION THEREFROM.

                  The Company  need not record a transfer of the Note unless the
conditions  specified in the foregoing  legends are  satisfied.  The Company may
also  instruct its transfer  agent not to record the transfer of the Note unless
the conditions specified in the foregoing legends are satisfied.

                  3.3 Removal of Legends and Transfer  Restrictions.  The legend
relating to the Act endorsed on a certificate  pursuant to paragraph 3.2 of this
Agreement  and the stop  transfer  instructions  with respect  thereto  shall be
removed and the Company  shall issue a  certificate  without  such legend to the
holder thereof if the securities  represented by such certificate are registered
under the Act and a prospectus meeting the requirements of Section 10 of the Act
is available or if such holder provides to the Company an opinion of counsel for
such holder  reasonably  satisfactory to the Company,  or a no-action  letter or
interpretive opinion of the staff of the Securities and Exchange Commission (the
"Commission")  to the effect that a public sale,  transfer or  assignment of the
Note  may  be  made  without   registration  and  without  compliance  with  any
restriction such as Rule 144.

         4.       Miscellaneous.

                  4.1 General.  This Agreement shall be governed in all respects
by the laws of the State of  California  as such laws are applied to  agreements
between  California  residents entered into and to be performed  entirely within
California.  This  Agreement  and all  attached  exhibits  represent  the entire
agreement  between  the  Company and the  Investor  with  respect to the subject
matter  herein and  therein  and  supersedes  any and all prior oral and written
discussions  and  agreements.  This  Agreement  and the Note may only be waived,
modified or amended in writing signed by both the Company and the Investor.



                                       -3-





         4.2 Notices. Any notice,  demand or request required or permitted under
this  Agreement  or the Note shall be given in writing and shall be deemed given
upon (i) personal  delivery to the party to be  notified,  (ii)  transmittal  by
facsimile,  telecopy or  electronic  mail,  or (iii)  deposit  with an overnight
delivery  service  or with  the  United  States  Post  Office,  by  first-class,
registered or certified  mail,  postage prepaid and addressed to the party to be
notified at the address of such party set forth at the end of this Agreement, or
such other address as a party may request by notifying the other in writing.

         4.3 Tax Matters.  The Investor  understands  that the Investor (and not
the Company) shall be responsible for the Investor's own federal,  state,  local
or foreign tax liability and any of the Investor's other tax  consequences  that
may arise as a result of the  transactions  contemplated by this Agreement.  The
Investor  shall rely  solely on the  determinations  of the  Investor's  own tax
advisors or his own determinations, and not on any statements or representations
by the Company or any of its agents, with regard to all such tax matters.

                  4.4  California  Corporate  Securities  Law.  THE  SALE OF THE
SECURITIES  WHICH ARE THE SUBJECT OF THIS  AGREEMENT HAS NOT BEEN QUALIFIED WITH
THE  COMMISSIONER OF CORPORATIONS OF THE STATE OF CALIFORNIA AND THE ISSUANCE OF
THE  SECURITIES  OR THE  PAYMENT  OR  RECEIPT  OF ANY PART OF THE  CONSIDERATION
THEREFOR PRIOR TO SUCH  QUALIFICATION  IS UNLAWFUL UNLESS THE SALE OF SECURITIES
IS EXEMPT  FROM THE  QUALIFICATION  BY  SECTION  25100,  25102,  OR 25105 OF THE
CALIFORNIA  CORPORATIONS  CODE.  THE RIGHTS OF ALL PARTIES TO THIS AGREEMENT ARE
EXPRESSLY CONDITIONED UPON SUCH QUALIFICATION BEING OBTAINED, UNLESS THE SALE IS
SO EXEMPT.

                  4.5 Counterparts. This Agreement may be executed in any number
of counterparts,  each of which shall be an original,  but all of which together
shall constitute one instrument.

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

JENNER TECHNOLOGIES


By:/s/ ANTHONY E.  MAIDA                          /s/ HAYDEN LEASON
   -----------------------------                  ------------------------------
                                                  Hayden Leason
Title:CEO
      -----------------------------------

828 Eastbrook Avenue                              10 Monte Sol
Danville, CA  94506                               Palmas Del Mar
                                                  Humacao, Puerto Rico  00792




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                                    EXHIBIT A

THE SECURITIES  REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE SECURITIES
ACT OF 1933,  AS AMENDED (THE "ACT"),  OR UNDER THE  SECURITIES  LAWS OF CERTAIN
STATES.  THESE  SECURITIES ARE SUBJECT TO  RESTRICTIONS ON  TRANSFERABILITY  AND
RESALE AND MAY NOT BE  TRANSFERRED  OR RESOLD EXCEPT AS PERMITTED  UNDER THE ACT
AND THE APPLICABLE STATE SECURITIES LAWS,  PURSUANT TO REGISTRATION OR EXEMPTION
THEREFROM.


                               JENNER TECHNOLOGIES

                             SECURED PROMISSORY NOTE


$3,000,000.00                                              Danville, California
                                                                    May 6, 1996


         FOR VALUE RECEIVED, JENNER TECHNOLOGIES,  a California corporation (the
"Company")  hereby  absolutely  and  unconditionally  promises  to pay to Hayden
Leason (the  "Lender"),  or order,  the  principal  amount of Three  Million and
No/100 Dollars ($3,000,000.00),  together with simple interest on such principal
amount at the rate of 10% per annum.

         This Note is issued pursuant to the terms of a Note Purchase  Agreement
(the "Note  Purchase  Agreement")  dated the date hereof between the Company and
the Lender.

         1.       Repayments and Prepayments.

                  (a) All principal and accrued  interest  under this Note shall
be due and payable on May 6, 1999.

                  (b) The Company  may prepay  this Note at any time,  either in
whole or in part,  without  premium or penalty and without the prior  consent of
the Lender.

                  (c) All  payments  received  under  this Note shall be applied
first to accrued  interest  on the date of payment  and then to the  outstanding
principal balance of this Note.

         2.  Security.  The full and  timely  payment  of the  principal  of and
interest  on this Note is secured by the pledge by the  Company to the Lender of
all shares of capital  stock and rights to acquire  capital  stock of  TherAtid,
Incorporated,  a California corporation, now held or hereinafter acquired by the
Company,  pursuant to the terms of the Stock  Pledge  Agreement  dated as of the
date hereof (the "Stock Pledge Agreement") between the Company, as pledgor,  and
the Lender,  as pledgee.  Reference is made to the Stock Pledge  Agreement for a
more  detailed  description  of the  collateral  which secures this Note and the
rights of the Lender in respect of such collateral.










         3.       Events of Default; Acceleration.

                  (a) The principal amount of this Note is subject to prepayment
in whole or in part upon the occurrence and during the continuance of any of the
following  events (each,  an "Event of Default"):  (i) failure to pay any amount
owing by the Company  hereunder when due and payable,  or (ii) the initiation of
any bankruptcy,  insolvency,  moratorium,  receivership or  reorganization by or
against the Company,  or a general  assignment  of assets by the Company for the
benefit of creditors.  Upon the  occurrence of any Event of Default,  the entire
unpaid  principal  balance of this Note and all of the unpaid  interest  accrued
thereon shall be immediately due and payable.

                  (b) No remedy herein  conferred upon the Lender is intended to
be exclusive  of any other remedy and each and every remedy shall be  cumulative
and in addition to every other remedy hereunder now or hereafter existing at law
or in equity or otherwise.

         4.       Notices.

                  (a) All notices or other communications  required or permitted
to be given  hereunder  shall be  delivered  as  provided  in the Note  Purchase
Agreement.

         5.       Miscellaneous.

                  (a) This  Note may only be  waived,  modified  or  amended  in
writing signed by both the Company and the Investor.

                  (b) No failure or delay by the  Lender to  exercise  any right
hereunder  shall  operate as a waiver  thereof,  nor shall any single or partial
exercise of any right,  power or privilege  preclude  any other right,  power or
privilege.  The  provisions  of this Note are severable and if any one provision
hereof  shall  be held  invalid  or  unenforceable  in  whole  or in part in any
jurisdiction,  such  invalidity  or  unenforceability  shall  affect  only  such
provision in such jurisdiction.  This Note expresses the entire understanding of
the parties with respect to the transactions  contemplated  hereby.  The Company
and every endorser and guarantor of this Note  regardless of the time,  order or
place of signing hereby waives presentment,  demand, protest and notice of every
kind,  and assents to any extension or  postponement  of the time for payment or
any other indulgence,  to any  substitution,  exchange or release of collateral,
and to the  addition  or  release  of any  other  party or person  primarily  or
secondarily liable.

                  (c) If Lender retains an attorney for collection of this Note,
or if any suit or proceeding is brought for the recovery of all, or any part of,
or for protection of the indebtedness respected by this Note Agreement, then the
Company  agrees  to pay on  demand  all  costs  and  expenses  of  the  suit  or
proceeding,  or any appeal thereof,  incurred by the Lender,  including  without
limitation, reasonable attorneys' fees.



                                       -2-





                  (d) This Note  shall for all  purposes  be  governed  by,  and
construed  in  accordance  with the laws of the  State  of  California  (without
reference to conflict of laws).

                  (e) This Note shall be binding upon the  Company's  successors
and  assigns,  and shall inure to the  benefit of the  Lender's  successors  and
assigns.

         IN WITNESS WHEREOF,  the Company has caused this Note to be executed by
its duly  authorized  officer to take  effect as of the date  first  hereinabove
written.


                                        JENNER TECHNOLOGIES


                                        By:
                                           -----------------------------
                                        Title:
                                               -------------------------



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