<PAGE>

                                                                    EXHIBIT 10.6

                             DENDREON CORPORATION

                           SERIES E PREFERRED STOCK

                              PURCHASE AGREEMENT

                               September 3, 1999
<PAGE>

                               TABLE OF CONTENTS

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                                                                            PAGE
<S>                                                                         <C>
1.   AGREEMENT TO SELL AND PURCHASE........................................    1

     1.1      Sale and Issuance of Shares..................................    1

     1.2      Closing......................................................    1

     1.3      Subsequent Sale of Shares....................................    2

     1.4      Delivery.....................................................    2

2.   REPRESENTATIONS AND WARRANTIES OF THE COMPANY.........................    2

     2.1      Organization; Good Standing; Qualifications..................    2

     2.2      Authorization................................................    3

     2.3      Valid Issuance of Preferred and Common Stock.................    3

     2.4      Governmental Consents........................................    3

     2.5      Capitalization and Voting Rights.............................    4

     2.6      Subsidiaries.................................................    5

     2.7      Financial Statements.........................................    5

     2.8      Tax Returns, Payments and Elections..........................    5

     2.9      Contracts and Other Commitments..............................    5

     2.10     Registration Rights..........................................    6

     2.11     Compliance With Other Instruments............................    6

     2.12     Litigation...................................................    6

     2.13     Disclosure...................................................    7

     2.14     Offering.....................................................    7

     2.15     Proprietary Information and Inventions Agreements............    7

     2.16     Section 83(b) Elections......................................    7

     2.17     Compliance with Applicable Securities Laws...................    7

     2.18     Compliance with Laws.........................................    7

     2.19     Patents, Trademarks, Etc.....................................    8

     2.20     Title to and Condition of Properties.........................    8

     2.21     Basic Financial Information And Reporting....................    8

3.   REPRESENTATIONS AND WARRANTIES OF INVESTORS...........................    9

     3.1      Authorization................................................    9

     3.2      Purchase Entirely for Own Account............................    9
</TABLE>

                                    i.

<PAGE>

                               TABLE OF CONTENTS
                                  (CONTINUED)

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     3.3      Reliance Upon Investors' Representations....................   10

     3.4      Receipt of Information......................................   10

     3.5      Investment Experience.......................................   10

     3.6      Accredited Investor or Qualified Regulation S Purchaser.....   10

     3.7      Restricted Securities.......................................   12

     3.8      Legends.....................................................   12

     3.9      Public Sale.................................................   13

     3.10     Investor Location...........................................   13

4.   CONDITIONS OF INVESTORS' OBLIGATIONS AT CLOSING......................   13

     4.1      Representations and Warranties..............................   14

     4.2      Performance.................................................   14

     4.3      Compliance Certificate......................................   14

     4.4      Qualifications..............................................   14

     4.5      Stockholders' Agreement.....................................   14

     4.6      Opinion of Company Counsel..................................   14

5.   CONDITIONS OF THE COMPANY'S OBLIGATIONS AT CLOSING...................   14

     5.1      Representations and Warranties..............................   14

     5.2      Qualifications..............................................   15

6.   MISCELLANEOUS........................................................   15

     6.1      Entire Agreement............................................   15

     6.2      Survival of Warranties......................................   15

     6.3      Successors and Assigns......................................   15

     6.4      Governing Law...............................................   15

     6.5      Counterparts................................................   15

     6.6      Titles and Subtitles........................................   16

     6.7      Notices.....................................................   16

     6.8      Payment of Fees and Expenses................................   16

     6.9      Amendments and Waivers......................................   16

     6.10     Severability................................................   16
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                                      ii.

<PAGE>

                               TABLE OF CONTENTS
                                  (CONTINUED)

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                                                                            PAGE
<S>                                                                         <C>
     6.11     California Corporate Securities Law.........................   16

     6.12     Effect of Amendment or Waiver...............................   17

     6.13     Rights of Investors.........................................   17

     6.14     Exculpation Among Investors.................................   17

     6.15     Qualified Small Business Stock..............................   17
</TABLE>

Schedule 1     -    First Closing Investors
Schedule 2     -    Schedule of Exceptions

                                     iii.
<PAGE>

                             DENDREON CORPORATION

                           SERIES E PREFERRED STOCK
                              PURCHASE AGREEMENT

     This Stock Purchase Agreement (the "Agreement") is made as of the 3rd day
of September 1999, by and between Dendreon Corporation, a Delaware corporation
(the "Company"), and each of those persons and entities, severally and not
jointly, whose names are set forth on Schedule 1 attached hereto (which persons
and entities are hereinafter collectively referred to as "Investors" and each
individually as an "Investor").

                                   Recitals

     Whereas, the Company has authorized the sale and issuance of an aggregate
of four million seven hundred five thousand eight hundred eighty-two (4,705,882)
shares of its Series E Preferred Stock (the "Shares");

     Whereas, the Investors desire to purchase the Shares on the terms and
conditions set forth herein; and

     Whereas, the Company desires to issue and sell the Shares to Investors on
the terms and conditions set forth herein.

     Now, Therefore, in consideration of the foregoing recitals and the mutual
promises hereinafter set forth, the parties hereto agree as follows:

     1.   Agreement to Sell and Purchase.

          1.1  Sale and Issuance of Shares.

               (a)  The Company shall adopt and file with the Secretary of State
of Delaware prior to the Closing (as defined below) an Amended and Restated
Certificate of Incorporation in the form attached hereto as Exhibit A (the
                                                            ---------
"Restated Certificate").


               (b)  Subject to the terms and conditions of this Agreement, each
Investor agrees, severally and not jointly, to purchase at the Closing and the
Company agrees to sell and issue to each Investor, severally and not jointly, at
the Closing that number of Shares set forth opposite each Investor's name on
Schedule 1 hereto at a price of $4.25 per share. The Shares will have the
rights, preferences and privileges set forth in the Restated Certificate.

          1.2  Closing.

               The first closing for the purchase and sale of the Shares shall
take place at the offices of Cooley Godward llp, Palo Alto, California, at 4:30
p.m., on September 3, 1999 (the "First Closing"), or at such other time and
place as the Company and Investors acquiring in the aggregate more than half the
Shares being sold pursuant hereto at such closing shall mutually agree, either
orally or in writing.

                                       1.
<PAGE>

          1.3  Subsequent Sale of Shares.

               Subject to the terms and conditions of this Agreement, in the
event that not all of the authorized Shares are sold at the First Closing the
Company may sell in one or more additional Closings, on or before December 31,
1999 (each, a "Subsequent Closing"), any authorized but unissued Shares at the
same price per share as the Shares purchased and sold at the First Closing. Any
such investor at a Subsequent Closing shall then become an "Investor" under this
Agreement. At or prior to a Subsequent Closing, any such Investor shall execute
a counterpart copy of this Agreement and any related agreements or other
documents required to be executed hereunder, and shall thereupon become a party
to this Agreement, the Stockholders' Agreement (as defined below) and any
Ancillary Agreements (as defined below), and shall have the rights and
obligations of an Investor hereunder and thereunder. The First Closing and any
Subsequent Closing shall be referred to collectively herein as the "Closings"
and singularly as a "Closing."

          1.4  Delivery.

               At the Closing, the Company shall deliver to each Investor a
certificate representing the Shares that such Investor is purchasing against
payment of the purchase price therefor by check, wire transfer, cancellation of
indebtedness, or such other form of payment as shall be mutually agreed upon by
such Investor and the Company.  In the event that payment by an Investor is
made, in whole or in part, by cancellation or conversion of indebtedness, then
such Investor shall surrender to the Company for cancellation at the Closing any
evidence of such indebtedness or shall execute an instrument of cancellation in
form and substance acceptable to the Company.  In addition, the Company at the
Closing shall deliver to any Investor choosing to pay any part of the purchase
price of the Shares by cancellation of indebtedness, a check in the amount of
any uncancelled interest accrued on such indebtedness through the Closing, or
the number of Shares such interest would purchase at the purchase price of $4.25
per share, plus a check in lieu of any fractional share in the amount of any
remaining interest in an amount less than $4.25.

     2.   Representations and Warranties of the Company.

          The Company hereby represents and warrants to each Investor that, on
the date of this Agreement, except as set forth in the Schedule of Exceptions
attached hereto as Schedule 2:

          2.1  Organization; Good Standing; Qualifications.

               The Company is a corporation duly organized, validly existing,
and in good standing under the laws of the State of Delaware, has all requisite
corporate power and authority to own and operate its properties and assets and
to carry on its business as now conducted and as proposed to be conducted, to
execute and deliver this Agreement, the Fourth Amended and Restated
Stockholders' Agreement attached hereto as Exhibit B (the "Stockholders'
                                           ---------
Agreement"), and any other agreement to which the Company is a party the
execution and delivery of which is contemplated hereby (the "Ancillary
Agreements"), to issue and sell the Shares and the Common Stock issuable upon
conversion thereof, and to carry out the provisions of this Agreement, the
Stockholders' Agreement, the Restated Certificate and any

                                       2.
<PAGE>

Ancillary Agreements. The Company is in possession of and operating in
compliance with all authorizations, licenses, permits, consents, certificates
and orders material to the conduct of its business, all of which are valid and
in full force and effect. The Company is duly qualified to transact business and
is in good standing in each jurisdiction in which the failure to qualify would
have a material adverse effect on its business, properties, prospects, or
financial condition.

          2.2  Authorization.

               All corporate action on the part of the Company, its officers,
directors and stockholders necessary for the authorization, execution and
delivery of this Agreement, the Stockholders' Agreement and any Ancillary
Agreements, the performance of all obligations of the Company hereunder and
thereunder at each Closing and the authorization, issuance (or reservation for
issuance), sale, and delivery of the Shares being sold hereunder and the Common
Stock issuable upon conversion thereof has been taken or will be taken prior to
each Closing, and this Agreement, the Stockholders' Agreement and any Ancillary
Agreements constitute valid and legally binding obligations of the Company,
enforceable in accordance with their respective terms, except (i) as limited by
applicable bankruptcy, insolvency, reorganization, moratorium, and other laws of
general application affecting enforcement of creditors' rights generally; (ii)
as limited by laws relating to the availability of specific performance,
injunctive relief, or other equitable remedies; and (iii) to the extent the
indemnification provisions contained in the Stockholders' Agreement may be
limited by applicable federal or state securities laws.

          2.3  Valid Issuance of Preferred and Common Stock.

               The Shares that are being purchased by the Investors hereunder,
when issued, sold, and delivered in accordance with the terms of this Agreement
for the consideration expressed herein, will be duly and validly issued, fully
paid, and nonassessable, and will be free of restrictions on transfer other than
restrictions on transfer under this Agreement and the Stockholders' Agreement
and under the Company's Bylaws (the "Bylaws") and applicable state and federal
securities laws. The Common Stock issuable upon conversion of the Shares
purchased under this Agreement has been duly and validly reserved for issuance
and, upon issuance in accordance with the terms of the Restated Certificate,
will be duly and validly issued, fully paid, and nonassessable and will be free
of restrictions on transfer other than restrictions on transfer under this
Agreement and the Stockholders' Agreement and under the Bylaws and applicable
state and federal securities laws.

          2.4  Governmental Consents.

               No consent, approval, qualification, order or authorization of,
or filing with, any local, state, or federal governmental authority is required
on the part of the Company in connection with the Company's valid execution,
delivery, or performance of this Agreement, the offer, sale or issuance of the
Shares by the Company or the issuance of Common Stock upon conversion of the
Shares, except (i) the filing of the Restated Certificate with the Secretary of
State of the State of Delaware, and (ii) such filings as have been made prior to
the Closing, and any notices of sale required to be filed with the Securities
and Exchange Commission under Regulation D of the Securities Act of 1933, as
amended (the "Securities Act"), or such post-

                                       3.
<PAGE>

closing filings as may be required under applicable state securities laws, which
will be timely filed within the applicable periods therefor.

          2.5  Capitalization and Voting Rights.

               The authorized capital stock of the Company consists, or will
consist prior to the Closing, of:

               (a)  Preferred Stock. 13,722,936 shares of Preferred Stock, $.001
par value (the "Preferred Stock"), of which 507,500 shares have been designated
Series A Preferred Stock, 499,999 of which are issued and outstanding; 4,264,375
shares have been designated Series B Preferred Stock, 4,264,346 of which are
issued and outstanding; 3,308,179 shares have been designated Series C Preferred
Stock, 3,308,179 of which are issued and outstanding; 937,000 shares have been
designated Series D Preferred Stock, 937,000 of which are issued and
outstanding; and 4,705,882 shares have been designated Series E Preferred Stock,
none of which will be issued and outstanding prior to the First Closing. The
rights, privileges and preferences of the Series A, Series B, Series C, Series D
and Series E Preferred Stock will be as stated in the Restated Certificate.

               (b)  Common Stock. 18,100,000 shares of common stock ("Common
Stock") $.001 par value, of which 961,911 shares are issued and outstanding.

               (c)  The outstanding shares of Common Stock have been issued in
accordance with the registration or qualification provisions of the Securities
Act and any relevant state securities laws or pursuant to valid exemptions
therefrom.

               (d)  There are no outstanding options, warrants, rights
(including conversion or preemptive rights and rights of first refusal), or
agreements for the purchase or acquisition from the Company of any shares of its
capital stock except for (a) the conversion privileges of the Series A, Series
B, Series C and Series D Preferred Stock outstanding or issuable pursuant to
outstanding warrants; (b) outstanding options to purchase 72,879 shares of the
Company's Common Stock pursuant to its 1993 Stock Option Plan (the "1993 Option
Plan"); (c) outstanding options to purchase 1,669,833 shares of the Company's
Common Stock pursuant to its 1996 Equity Incentive Plan (the "1996 Plan"); (d)
outstanding warrants to purchase 226,627 shares of the Company's Common Stock;
(e) outstanding warrants to purchase 7,500 shares of the Company's Series A
Preferred Stock; and (f) rights held by certain of the Company's stockholders
pursuant to the Third Amended and Restated Stockholders' Agreement, dated as of
July 10, 1998 (the " Prior Stockholders' Agreement"). The Company does not
anticipate issuing any additional options to purchase shares of its Common Stock
pursuant to the 1993 Option Plan. The Company has reserved 3,500,000 shares of
its Common Stock for issuance under the 1996 Plan, of which 1,024,978 shares
remain available for grant as of the date hereof. The Company is not a party or
subject to any agreement or understanding, and, to the best of the Company's
knowledge, there is no agreement or understanding between any persons that
affects or relates to the voting or giving of written consents with respect to
any security or the voting by a director of the Company, except for the
Stockholders' Agreement.

                                       4.
<PAGE>

          2.6  Subsidiaries.

               The Company has no subsidiaries and does not otherwise own or
control, directly or indirectly, any other corporation, association, or other
business entity.

          2.7  Financial Statements.

               The Company has delivered to each Investor its audited financial
statements (balance sheet, statement of profit and loss, statement of
stockholders equity and statement of cash flows) for the fiscal year ended
December 31, 1998, its unaudited financial statements (balance sheet, statement
of profit and loss, statement of stockholders equity and statement of cash
flows) for the three month period ended March 31, 1999 and its unaudited
financial statements (balance sheet, statement of profit and loss, statement of
stockholders equity and statement of cash flows) for the three month period
ended June 30, 1999 (collectively, the "Financial Statements").  The Financial
Statements have been prepared in accordance with generally accepted accounting
principles ("GAAP") (except that the unaudited financial statements do not
contain all footnotes required by GAAP) applied on a consistent basis throughout
the periods indicated.  The Financial Statements fairly present the financial
condition and operating results of the Company as of the dates, and for the
periods, indicated therein, subject, in the case of the unaudited financial
statements, to normal year-end audit adjustments, which adjustments the Company
believes will not be material.  Except for spending in accordance with its
current plan, since December 31, 1998, there has been no material adverse change
in the operations or financial condition of the Company.

          2.8  Tax Returns, Payments and Elections.

               All material tax returns required to be filed by the Company in
any jurisdiction (including foreign jurisdictions) have been timely filed, and
all material taxes, assessments, fees and other charges (including, without
limitation, withholding taxes, penalties and interest) due or claimed to be due
from the Company that are due and payable have been paid, other than those (i)
being contested in good faith and for which an adequate reserve or accrual has
been established or (ii) those currently payable without penalty or interest and
for which an adequate reserve or accrual has been established or extensions duly
filed. The Company knows of no actual or proposed additional tax assessments or
any reason for the imposition or proposal of any additional tax assessments for
any fiscal period against the Company that would, singly or in the aggregate,
reasonably be expected to have a material adverse effect on the Company. Neither
the Company's income nor franchise tax returns are under audit and no waivers of
the statute of limitations or extensions of time with respect to any tax returns
have been granted by the Company.

          2.9  Contracts and Other Commitments.

               The Company does not have any material contract, agreement, lease
or commitment, written or oral, absolute or contingent, other than (i) contracts
for the purchase of supplies and services that were entered into in the ordinary
course of business and that do not involve more than $200,000, and do not extend
for more than one (1) year beyond the date hereof; and (ii) contracts terminable
at will by the Company on no more than thirty (30) days'

                                       5.
<PAGE>

notice without cost or liability to the Company and that do not involve any
employment or consulting arrangement and are not material to the conduct of the
Company's business. For the purpose of this paragraph, material employment and
consulting contracts and contracts with labor unions, and license agreements and
any other agreements relating to the acquisition or disposition of the Company's
technology (other than standard end-user license agreements) shall not be
considered to be contracts entered into in the ordinary course of business.

          2.10  Registration Rights.

                Except as provided in the Stockholders' Agreement, the Company
is not obligated to register under the Securities Act any of its presently
outstanding securities or any of its securities that may subsequently be issued.

          2.11  Compliance With Other Instruments.

                The Company is not in violation or default in any respect of any
provision of its Restated Certificate or Bylaws or in any material respect of
any provision of any mortgage, indenture, agreement, instrument, or contract to
which it is a party or by which it is bound or, to the best of its knowledge, of
any federal or state judgment, order, writ, decree, statute, rule, or regulation
applicable to the Company. The execution, delivery, and performance by the
Company of this Agreement, the Stockholders' Agreement and any Ancillary
Agreements, and the consummation of the transactions contemplated hereby and
thereby will not result in any such violation or be in material conflict with or
constitute, with or without the passage of time or giving of notice, either a
material default under any such provision or an event that results in the
creation of any material lien, charge, or encumbrance upon any assets of the
Company or the suspension, revocation, impairment, forfeiture, or nonrenewal of
any material permit, license, authorization, or approval applicable to the
Company, its business or operations, or any of its assets or properties.

          2.12  Litigation.

                There is no action, suit, proceeding, or investigation pending
or currently threatened against the Company that (i) questions the validity of
this Agreement, the Stockholders' Agreement and any Ancillary Agreements or the
right of the Company to enter into such agreements, or to consummate the
transactions contemplated hereby or thereby, or (ii) that might result, either
individually or in the aggregate, in any material adverse change in the assets,
business, properties, prospects, or financial condition of the Company, or in
any material change in the current equity ownership of the Company. The
foregoing includes, without limitation, any action, suit, proceeding, or
investigation pending or currently threatened involving the prior employment of
any of the Company's employees, their use in connection with the Company's
business of any information or techniques allegedly proprietary to any of their
former employers, their obligations under any agreements with prior employers,
or negotiations by the Company with potential backers of, or investors in, the
Company or its proposed business. The Company is not a party to, or to the best
of its knowledge, named in any order, writ, injunction, judgment, or decree of
any court, government agency, or instrumentality. There is no action, suit, or
proceeding by the Company currently pending or that the Company currently
intends to initiate.

                                       6.
<PAGE>

          2.13  Disclosure.

                The Company has provided each Investor with all the information
reasonably available to it without undue expense that such Investor has
requested for deciding whether to purchase the Shares and all information that
the Company has and that it believes is reasonably necessary to enable such
Investor to make such decision.  Neither this Agreement nor any other written
statements or certificates made or delivered pursuant to this Agreement contain
any untrue statement of a material fact or omit to state a material fact
necessary to make the statements herein or therein not misleading.

          2.14  Offering.

                Subject in part to the truth and accuracy of each Investor's
representations set forth in this Agreement, the offer, sale and issuance of the
Shares as contemplated by this Agreement are exempt from the registration
requirements of the Securities Act, and neither the Company nor any authorized
agent acting on its behalf will take any action hereafter that would cause the
loss of such exemption.

          2.15  Proprietary Information and Inventions Agreements.

                Each employee and officer of the Company has executed a
Proprietary Information and Inventions Agreement substantially in the form
attached hereto as Exhibit D.
                   ---------

          2.16  Section 83(b) Elections.

                To the best of the Company's knowledge, all individuals who have
purchased shares of the Company's Common Stock that are subject to vesting
restrictions have timely filed elections under Section 83(b) of the Internal
Revenue Code and any analogous provisions of applicable state tax laws.

          2.17  Compliance with Applicable Securities Laws.

                The Company will comply with the requirements of Regulation S
promulgated under the Securities Act and/or Regulation D promulgated under the
Securities Act, as applicable, and with Section 25102(f) of the California
Corporate Securities Law, as amended, and any other applicable state securities
laws in connection with the offer and sale of Shares to any Investor.

          2.18  Compliance with Laws.

                The Company has obtained all licenses, permits, franchises or
other governmental authorizations necessary for the ownership or operation of
its properties or the conduct of its business as currently conducted, except as
would not have a material adverse effect on the Company. The Company is not in
violation of any law applicable to the ownership or operation of its properties
or the conduct of its business, except as would not have a material adverse
effect on the Company.

                                       7.
<PAGE>

          2.19  Patents, Trademarks, Etc.

                To the best of the Company's knowledge, the Company owns, or is
licensed under, and has the right to use, all patents, trademarks, trade names,
copyrights, technology, know how and processes (collectively, "Intellectual
Property") necessary for the conduct of its business as now conducted and as
proposed to be conducted.  The consummation of the transactions contemplated by
this Agreement will not alter or impair any such rights.  The Company has not
received any communications asserting the rights to use the Company's
Intellectual Property or challenging or questioning the validity or
effectiveness of any license or agreement related thereto, nor has the Company
received any communications asserting that the use of such Intellectual Property
by the Company infringes on the rights of any person.  No officer, director or
employee of the Company owns or holds, directly or indirectly, any interest in
the Company's Intellectual Property.  Neither the Company nor, to the best of
the Company's knowledge, any of its employees, is in violation of any agreement
or commitment to any prior employer or any other person in regard to the
ownership of inventions or developments or the maintenance of confidentiality of
trade secrets.

          2.20  Title to and Condition of Properties.

                Except (i) as reflected in the Financial Statements (as defined
in paragraph 2.7), (ii) for liens for current taxes not yet delinquent, (iii)
for liens imposed by law and incurred in the ordinary course of business for
obligations not past due to carriers, warehousemen, laborers, materialmen and
the like, (iv) for liens in respect of pledges or deposits under workers'
compensation laws or similar legislation, or (v) for minor defects in title,
none of which, individually or in the aggregate, materially interferes with the
use of such property, the Company (a) has good and marketable title to all the
real or personal properties and other assets (tangible, intangible or mixed) it
purports to own, free and clear of all material liens, and (b) enjoys peaceful
and undisturbed possession under all material leases to which the Company is a
party as lessee. All material leases and other material agreements to which the
Company is a party are valid and binding and in full force and effect. No
default has occurred or is continuing under such leases and other agreements,
and no consent need be obtained (other than consents that will be obtained prior
to the Closing) from any person in respect of any such lease or agreement in
connection with the transactions contemplated by this Agreement, except to the
extent that any such defaults, or the failure to obtain any such consents, could
not, singly or in the aggregate, reasonably be expected to have a material
adverse effect on the Company. The properties used in the conduct of the
business of the Company are in good repair and working order, except to such
extent as would not, singly or in the aggregate, reasonably be expected to have
a material adverse effect on the Company. The Company maintains such insurance
as may be required by law and such other insurance, to such extent and against
such hazards and liabilities, as the Company believes is reasonably necessary.

          2.21  Basic Financial Information And Reporting.

                (a)   As soon as practicable after the end of each fiscal year
of the Company, the Company will furnish each Investor a consolidated balance
sheet of the Company, as at the end of such fiscal year, and a consolidated
statement of income and a consolidated statement of cash flows of the Company,
for such year, all prepared in accordance with generally

                                       8.
<PAGE>

accepted accounting principles consistently applied and setting forth in each
case in comparative form the figures for the previous fiscal year, all in
reasonable detail. Such financial statements shall be accompanied by a report
and opinion thereon by independent public accountants of national standing
selected by the Company's Board of Directors.

                (b)   The Company will furnish each Investor, as soon as
practicable after the end of the first, second and third quarterly accounting
periods in each fiscal year of the Company, a consolidated balance sheet of the
Company as of the end of each such quarterly period, and a consolidated
statement of income and a consolidated statement of cash flows of the Company
for such period and for the current fiscal year to date, prepared in accordance
with generally accepted accounting principles, with the exception that no notes
need be attached to such statements and year-end audit adjustments may not have
been made.

     3.   Representations and Warranties of Investors.

          Each Investor hereby, severally and not jointly, represents and
          warrants that:

          3.1   Authorization.

                Such Investor has full power and authority to enter into this
Agreement and that this Agreement constitutes a valid and legally binding
obligation of such Investor.

          3.2   Purchase Entirely for Own Account.

                (a)  This Agreement is made with each Investor identified on
Schedule 1 as a Regulation D Investor (each a "Regulation D Investor") in
reliance upon such Investor's representation to the Company, which by such
Investor's execution of this Agreement such Investor hereby confirms, that the
Shares to be purchased by such Investor and the Common Stock issuable upon
conversion thereof (collectively, the "Regulation D Securities") will be
acquired for investment for such Investor's own account, not as a nominee or
agent, and not with a view to the resale or distribution of any part thereof,
and that such Investor has no present intention of selling, granting any
participation in, or otherwise distributing the same. By executing this
Agreement, each Investor further represents that such Investor does not have any
contract, undertaking, agreement or arrangement with any person to sell,
transfer or grant participations to such person or to any third person, with
respect to any of the Regulation D Securities.

                (b)  This Agreement is made with each Investor identified on
Schedule 1 as a Regulation S Investor (each a "Regulation S Investor") in
reliance upon such Investor's representation to the Company, which by such
Investor's execution of this Agreement such Investor hereby confirms, that the
Shares to be purchased by such Investor and the Common Stock issuable upon
conversion thereof (collectively, the "Regulation S Securities") (the Regulation
D Securities and the Regulation S Securities being sometimes collectively
referred to herein as the "Securities") will be acquired for investment for such
Investor's own account, not as a nominee or agent, and not with a view to the
resale or distribution of any part thereof in the United States or to a United
States resident, and that such Investor has no present intention of selling,
granting any participation in, or otherwise distributing the same. By executing
this Agreement, each Investor further represents that such Investor does not
have any

                                       9.
<PAGE>

contract, undertaking, agreement or arrangement with any person to sell,
transfer or grant participations to such person or to any third person in the
United States or to a United States Resident, with respect to any of the
Regulation S Securities.

          3.3   Reliance Upon Investors' Representations.

                Each Investor understands that the Securities are not, and any
Common Stock acquired on conversion thereof at the time of issuance may not be,
registered under the Securities Act on the ground that the sale provided for in
this Agreement and the issuance of securities hereunder is exempt from
registration under the Securities Act pursuant to Section 4(2) thereof (in the
case of Regulation D Securities) or Regulation S thereunder (in the case of
Regulation S Securities), and that the Company's reliance on such exemptions is
predicated on the Investors' representations set forth herein. Each Regulation D
Investor realizes that the basis for the exemption may not be present if,
notwithstanding such representations, the Investor has in mind merely acquiring
the Regulation D Securities for a fixed or determinable period in the future,
for sale if the market rises, or for sale if the market does not rise. No
Regulation D Investor has any such intention.

          3.4   Receipt of Information.

                Each Investor believes such Investor has received all the
information such Investor considers necessary or appropriate for deciding
whether to purchase the Shares. Each Investor further represents that such
Investor has had an opportunity to ask questions and receive answers from the
Company regarding the terms and conditions of the offering of the Shares and the
business, properties, prospects, and financial condition of the Company and to
obtain such additional information (to the extent the Company possessed such
information or could acquire it without unreasonable effort or expense)
necessary to verify the accuracy of any information furnished to such Investor
or to which such Investor had access. The foregoing, however, does not limit or
modify the representations and warranties of the Company in Section 2 of this
Agreement or the right of the Investors to rely thereon.

          3.5   Investment Experience.

                Each Investor represents that such Investor is experienced in
evaluating and investing in securities of companies in the early stages of
product research and development and acknowledges that such Investor is able to
fend for himself, herself or itself, can bear the economic risk of such
Investor's investment, and has such knowledge and experience in financial and
business matters that such Investor is capable of evaluating the merits and
risks of the investment in the Shares. If other than an individual, Investor
also represents that such Investor has not been organized for the purpose of
acquiring the Shares.

          3.6   Accredited Investor or Qualified Regulation S Purchaser.

                (a)  The term "Accredited Investor" as used herein refers to:

                     (i)      A person or entity who is a director or executive
officer of the Company;

                                      10.
<PAGE>

                     (ii)     Any bank as defined in Section 3(a)(2) of the
Securities Act, or any savings and loan association or other institution as
defined in Section 3(a)(5)(A) of the Securities Act whether acting in its
individual or fiduciary capacity; any broker or dealer registered pursuant to
Section 15 of the Securities Exchange Act of 1934; any insurance company as
defined in section 2(13) of the Act; any investment company registered under the
Investment Company Act of 1940 or a business development company as defined in
Section 2(a)(48) of that Act; any Small Business Investment Company licensed by
the U.S. Small Business Administration under Section 301(c) or (d) of the Small
Business Investment Act of 1958; any plan established and maintained by a state,
its political subdivisions, or any agency or instrumentality of a state or its
political subdivisions, for the benefit of its employees, if such plan has total
assets in excess of $5,000,000; any employee benefit plan within the meaning of
Title I of the Employee Retirement Income Security Act of 1974, if the
investment decision is made by a plan fiduciary, as defined in Section 3(21) of
such Act, which is either a bank, savings and loan association, insurance
Company, or registered investment adviser, or if the employee benefit plan has
total assets in excess of $5,000,000 or, if a self-directed plan, with
investment decisions made solely by persons that are accredited investors;

                     (iii)    Any private business development Company as
defined in Section 202(a)(22) of the Investment Advisers Act of 1940;

                     (iv)     Any organization described in Section 501(c)(3) of
the Internal Revenue Code, corporation, Massachusetts or similar business trust,
or partnership, not formed for the specific purpose of acquiring the securities
offered, with total assets in excess of $5,000,000;

                     (v)      Any natural person whose individual net worth, or
joint net worth with that person's spouse, at the time of such person's purchase
exceeds $1,000,000;

                     (vi)     Any natural person who had an individual income in
excess of $200,000 in each of the two most recent years or joint income with
that person's spouse in excess of $300,000 in each of those years and has a
reasonable expectation of reaching the same income level in the current year;

                     (vii)    Any trust, with total assets in excess of
$5,000,000, not formed for the specific purpose of acquiring the securities
offered, whose purchase is directed by a person who has such knowledge and
experience in financial and business matters that such person is capable of
evaluating the merits and risks of the prospective investment; or

                     (viii)   Any entity in which all of the equity owners are
accredited investors.

     As used in this Section 3.6(a), the term "net worth" means the excess of
total assets over total liabilities.  For the purpose of determining a person's
net worth, the principal residence owned by an individual should be valued at
fair market value, including the cost of improvements, net of current
encumbrances.  As used in this Section 3.6(a), "income" means actual economic
income, which may differ from adjusted gross income for income tax purposes.
Accordingly, each Investor should consider whether such Investor should add any
or all of the

                                      11.
<PAGE>

following items to such Investor's adjusted gross income for income tax purposes
in order to reflect more accurately such Investor's actual economic income: any
amounts attributable to tax-exempt income received, losses claimed as a limited
partner in any limited partnership, deductions claimed for depletion,
contributions to an IRA or Keogh retirement plan, and alimony payments.

                (b)  The term "Qualified Regulation S Purchaser" as used herein
refers to a person or entity who is not a United States person, as such term is
defined in Rule 902 promulgated under the Securities Act.

                (c)  Each Regulation D Investor, as to such Investor, severally
and not jointly, further represents to the Company that such Investor is an
Accredited Investor.

                (d)  Each Regulation S Investor, as to such Investor, severally
and not jointly, further represents to the Company that such Investor is a
Qualified Regulation S Purchaser.

          3.7   Restricted Securities.

                Each Investor understands that the Shares (and any Common Stock
issued on conversion thereof) may not be sold, transferred, or otherwise
disposed of without registration under the Securities Act or an exemption
therefrom, and that in the absence of an effective registration statement
covering the Shares (or the Common Stock issued on conversion thereof) or an
available exemption from registration under the Securities Act, the Shares (and
any Common Stock issued on conversion thereof) must be held indefinitely. In
particular, each Investor is aware that the Shares (and any Common Stock issued
on conversion thereof) may not be sold pursuant to Rule 144 promulgated under
the Securities Act unless all of the conditions of that Rule are met. Among the
conditions for use of Rule 144 may be the availability of current information to
the public about the Company. Such information is not now available and the
Company has no present plans to make such information available.

          3.8   Legends.

                To the extent applicable, each certificate or other document
evidencing any of the Shares or any Common Stock issued upon conversion thereof
shall be endorsed with the legends set forth below:

                (a)  The following legend under the Securities Act:

                     "THE SHARES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED
                     UNDER THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT
                     BE SOLD, TRANSFERRED, ASSIGNED, PLEDGED, OR HYPOTHECATED
                     UNLESS AND UNTIL REGISTERED UNDER SUCH ACT, OR UNLESS THE
                     COMPANY HAS RECEIVED AN OPINION OF COUNSEL OR OTHER
                     EVIDENCE SATISFACTORY TO THE COMPANY AND ITS COUNSEL, THAT
                     SUCH REGISTRATION IS NOT REQUIRED."

                                      12.
<PAGE>

               (b)  "THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO
                    CERTAIN RESTRICTIONS ON TRANSFER CONTAINED IN A STOCK
                    PURCHASE AGREEMENT BETWEEN THE HOLDER HEREOF OR SUCH
                    HOLDER'S PREDECESSOR AND DENDREON CORPORATION (THE
                    "COMPANY"). A COPY OF SUCH AGREEMENT IS AVAILABLE UPON
                    WRITTEN REQUEST FROM THE SECRETARY OF THE COMPANY.

               (c)  As to Regulation S Securities, the following legend under
                    the Securities Act:

                    "THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE BEEN
                    ACQUIRED PURSUANT TO REGULATION S OF THE SECURITIES ACT OF
                    1933 AND MAY NOT BE SOLD, MORTGAGED, PLEDGED, HYPOTHECATED
                    OR OTHERWISE TRANSFERRED EXCEPT IN ACCORDANCE THEREWITH."

               (d)  Any legend required by applicable state securities or "blue
                    sky" laws.


          3.9  Public Sale.

               Each Investor agrees not to make, without the prior written
consent of the Company, any public offering or sale of the Shares, or any Common
Stock issued upon the conversion thereof, although permitted to do so pursuant
to rule 144(k) promulgated under the Securities Act, until the earlier of (i)
the date on which the Company effects its initial registered public offering
pursuant to the Securities Act, (ii) the date on which the Company becomes a
registered company pursuant to Section 12(g) of the Securities Exchange Act of
1934, as amended, or (iii) five years after the Closing of the sale of the
Shares to such Investor by the Company.

          3.10 Investor Location.

               If the Investor is an individual, then such Investor resides in
the state or city specified in the address for such Investor set forth on the
signature page hereto, unless otherwise indicated on such page; if the Investor
is a partnership, corporation, limited liability company or other entity, then
the office or offices of such Investor in which its investment decision was made
is located at the address or addresses of the Investor set forth on the
signature page hereto, unless otherwise indicated on such page.

     4.   Conditions of Investors' Obligations At Closing.

          The obligations of each Investor under subparagraph 1.1(b) of this
Agreement are subject to the fulfillment on or before the Closing of each of the
following conditions, the waiver of which shall not be effective against any
Investor who does not consent in writing thereto:

                                      13.
<PAGE>

          4.1  Representations and Warranties.

               The representations and warranties of the Company contained in
Section 2 shall be true on and as of the Closing with the same effect as though
such representations and warranties had been made on and as of the date of the
Closing.

          4.2  Performance.

               The Company shall have performed and complied with all
agreements, obligations, and conditions contained in this Agreement that are
required to be performed or complied with by it on or before the Closing.

          4.3  Compliance Certificate.

               The Chief Executive Officer or Chief Financial Officer of the
Company shall deliver to each Investor at the Closing a certificate certifying
that the conditions specified in paragraphs 4.1, 4.2, 4.4 and 4.5 have been
fulfilled.

          4.4  Qualifications.

               All authorizations, approvals, or permits, if any, of any
governmental authority or regulatory body of the United States, of any state
therein, or of any foreign jurisdiction in which an Investor is located that are
required in connection with the lawful issuance and sale of the Shares pursuant
to this Agreement shall be duly obtained and effective as of the Closing.

          4.5  Stockholders' Agreement.

               The Fourth Amended and Restated Stockholders' Agreement
substantially in the form attached hereto as Exhibit B shall have been executed
                                             ---------
and delivered by the parties thereto.

          4.6  Opinion of Company Counsel.

               Each Investor shall have received from Company Counsel an opinion
in substantially the form attached hereto as Exhibit C.
                                             ---------

     5.   Conditions of The Company's Obligations at Closing.

          The obligations of the Company to each Investor under this Agreement
are subject to the fulfillment on or before each Closing of each of the
following conditions by such Investor:

          5.1  Representations and Warranties.

               The representations and warranties of each Investor contained in
Section 3 shall be true on and as of the Closing with the same effect as though
such representations and warranties had been made on and as of the date of the
Closing.

                                      14.
<PAGE>

          5.2  Qualifications.

               All authorizations, approvals, or permits, if any, of any
governmental authority or regulatory body of the United States, of any state
therein, or of any foreign jurisdiction in which an Investor is located that are
required in connection with the lawful issuance and sale of the Shares pursuant
to this Agreement shall be duly obtained and effective as of the Closing.

     6.   Miscellaneous.

          6.1  Entire Agreement.

               This Agreement and the documents referred to herein constitute
the entire agreement among the parties and no party shall be liable or bound to
any other party in any manner by any warranties, representations, or covenants,
except as specifically set forth herein or therein.

          6.2  Survival of Warranties.

               The warranties, representations, and covenants of the Company and
the Investors contained in or made pursuant to this Agreement shall survive the
execution and delivery of this Agreement and the Closing.

          6.3  Successors and Assigns.

               Except as otherwise provided herein, the terms and conditions of
this Agreement shall inure to the benefit of and be binding upon the respective
successors and assigns of the parties (including permitted transferees of any
Shares sold hereunder or any Common Stock issued upon conversion thereof).
Nothing in this Agreement, express or implied, is intended to confer upon any
party other than the parties hereto or their respective successors and assigns
any rights, remedies, obligations, or liabilities under or by reason of this
Agreement, except as expressly provided in this Agreement.

          6.4  Governing Law.

               This Agreement shall be governed by and construed under the laws
of the State of California as applied to agreements among California residents
entered into and to be performed entirely within California.

          6.5  Counterparts.

               This Agreement may be executed in two or more counterparts, each
of which shall be deemed an original, but all of which together shall constitute
one and the same instrument.

                                      15.
<PAGE>

          6.6  Titles and Subtitles.

               The titles and subtitles used in this Agreement are used for
convenience of reference only and are not to be considered in construing or
interpreting this Agreement.

          6.7  Notices.

               All notices and other communications required or permitted under
this Agreement shall be in writing and shall be mailed by first-class mail,
postage prepaid, sent by facsimile or delivered personally by hand or nationally
or internationally recognized courier (as the case may be) addressed to the
party to be notified at the address or facsimile number indicated for such
person on the signature page hereof, or at such other address or facsimile
number as such party may designate by ten (10) days' advance written notice to
the other parties hereto. All such notices and other written communications
shall be effective on the date of mailing, confirmed facsimile transfer or
delivery.

          6.8  Payment of Fees and Expenses.

               The Company and each Investor shall bear its, his or her own
expenses incurred on its behalf with respect to this Agreement and the
transactions contemplated hereby. If any action at law or in equity is necessary
to enforce or interpret the terms of this Agreement, the Stockholders'
Agreement, any Ancillary Agreements or the Restated Certificate, the prevailing
party shall be entitled to reasonable attorneys' fees, costs and necessary
disbursements in addition to any other relief to which such party may be
entitled.

          6.9  Amendments and Waivers.

               Any term of this Agreement may be amended and the observance of
any term of this Agreement may be waived (either generally or in a particular
instance and either retroactively or prospectively), only with the written
consent of the Company and the holders of more than 50% of the Common Stock not
previously sold to the public that is issued or issuable upon conversion of the
outstanding Shares. Any amendment or waiver effected in accordance with this
paragraph shall be binding upon each holder of any securities purchased under
this Agreement at the time outstanding (including securities into which such
securities have been converted), each future holder of all such securities, and
the Company.

          6.10 Severability.

               If one or more provisions of this Agreement are held to be
unenforceable under applicable law, such provision shall be excluded from this
Agreement and the balance of the Agreement shall be interpreted as if such
provision were so excluded and shall be enforceable in accordance with its
terms.

          6.11 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 SUCH

                                      16.
<PAGE>

SECURITIES OR THE PAYMENT OR RECEIPT OF ANY PART OF THE CONSIDERATION FOR SUCH
SECURITIES PRIOR TO SUCH QUALIFICATION IS UNLAWFUL, UNLESS THE SALE OF
SECURITIES IS EXEMPT FROM 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.

          6.12 Effect of Amendment or Waiver.

               Each Investor acknowledges that by the operation of paragraph 6.9
hereof the holders of more than fifty percent (50%) of the Common Stock not
previously sold to the public that is issued or issuable upon conversion of the
outstanding Shares will have the right and power to diminish or eliminate all
rights of such Investor under this Agreement.

          6.13 Rights of Investors.

               Each holder of Shares (and Common Stock issued upon conversion
thereof) shall have the absolute right to exercise or refrain from exercising
any right or rights that such holder may have by reason of this Agreement or any
Shares, including without limitation the right to consent to the waiver of any
obligation of the Company under this Agreement and to enter into an agreement
with the Company for the purpose of modifying this Agreement or any agreement
effecting any such modification, and such holder shall not incur any liability
to any other holder or holders of Shares (or Common Stock issued upon exercise
thereof) with respect to exercising or refraining from exercising any such right
or rights.

          6.14 Exculpation Among Investors.

               Each Investor acknowledges that such Investor is not relying upon
any person, firm, or corporation, other than the Company and its officers and
directors, in making this investment or decision to invest in the Company. Each
Investor agrees that no Investor nor the respective controlling persons,
officers, directors, partners, agents, or employees of any Investor shall be
liable for any action heretofore or hereafter taken or omitted to be taken by
any of them in connection with the Shares (and Common Stock issued upon
conversion thereof).

          6.15 Qualified Small Business Stock.

               The Company covenants that so long as any of the Shares that are
being purchased by the Investors hereunder, or the Common Stock into which such
shares are converted, are held by an Investor (or a transferee in whose hands
such Shares or Common Stock are eligible to qualify as Qualified Small Business
Stock as defined in Section 1202(c) of the Internal Revenue Code of 1986, as
amended (the "Code"), it will use reasonable efforts to comply with any
applicable filing or reporting requirements imposed by the Code on issuers of
Qualified Small Business Stock.

     In Witness Whereof, the parties have executed this Agreement as of the date
first above written.

                                      17.
<PAGE>

                                   Dendreon Corporation


                                   By: /s/ Martin A. Simonetti
                                      --------------------------------------
                                   Name: Martin A. Simonetti
                                        ------------------------------------
                                   Title: Chief Financial Officer
                                         -----------------------------------

                                   Address:  3005 First Avenue
                                             Seattle, WA 98121
                                             Facsimile No.: (206) 256-0571

                                      18.
<PAGE>

                                        * See Schedule 1


                                        ________________________________________
                                        Name of Investor


                                        ________________________________________
                                        Signature


                                        ________________________________________
                                        Name


                                        ________________________________________
                                        Title

                 [SERIES E PREFERRED STOCK PURCHASE AGREEMENT]
<PAGE>

                                   SCHEDULE 1
                                   ----------

Vulcan Ventures Inc.
GC&H Investments
Sears Living Trust Dtd 3/11/91
Martin A. & Mary Ann Simonetti

HealthCare Ventures V, L.P.
Sanderling Venture Partners IV Co-Investment Fund, L.P.

Kummell Investments Limited
New York Life Insurance Company

Shaw Venture Partners III, L.P.

Leavitt Investments, LP

China Development Industrial Bank
Johnson & Johnson Development Corporation
Pacific Wind LLC
Robert and Rebecca Forrester JT

                                      1.
<PAGE>

SCHEDULE 2
----------
                             SCHEDULE OF EXCEPTIONS

     This Schedule of Exceptions is made and given pursuant to Section 2 of the
Agreement.  The paragraph numbers in this Schedule of Exceptions correspond to
the paragraph numbers in the Agreement; however, any information disclosed
herein under any paragraph number shall be deemed to be disclosed and
incorporated into any other paragraph number under the Agreement where such
disclosure would be appropriate.  The inclusion of any matter herein as part of
this Schedule should not be interpreted as indicating that the Company has
determined that such matter is necessarily material to the Investors.  Any terms
defined in the Agreement shall have the same meaning when used in this Schedule
of Exceptions as when used in the Agreement unless the context otherwise
requires.

     Section 2.5
     -----------

     1.   The Company is currently negotiating with Fresenius AG the issuance of
          250,000 warrants to purchase the Company's Common Stock in connection
          with the termination of the License Agreement between the Company and
          Fresenius AG, dated February 27, 1998.

     Section 2.9
     -----------

     1.   Employment Agreement, by and between the Company and David L. Urdal,
          dated December 2, 1996.

     2.   Employment Agreement, by and between the Company and Christopher S.
          Henney, dated December 11, 1996.

     3.   Agreement for Consulting Services, by and between the Company and
          Lowell E. Sears, dated October 30, 1995.

     4.   License Agreement, by and between the Company and The Immune Response
          Corporation, dated April 30, 1997.

     5.   Restricted Stock Agreement, by and between the Company and Dr. Edgar
          G. Engleman, dated September 30, 1992.

     6.   Restricted Stock Agreement, by and between the Company and Dr. Sam
          Strober, dated September 30, 1992.

     7.   Restricted Stock Option Agreement, by and between the Company and Dr.
          Edgar G. Engleman, dated September 30, 1992.

     8.   Nonstatutory Stock Option Agreement, by and between the Company and
          Lowell E. Sears, dated October 30, 1995.

     9.   Vanni Business Park Industrial Lease, by and between the Company and
          Vanni Business Park General Partnership, dated October 27, 1992.

                                      2.
<PAGE>

     10.  Agreement (Strober Technology), by and between the Company and The
          Board of Trustees of the Leland Stanford Junior University, dated
          September 1, 1992.

     11.  Agreement (Engleman Technology), by and between the Company and The
          Board of Trustees of the Leland Stanford Junior University, dated
          September 1, 1992.

     12.  Agreement, by and between the Company and The Board of Trustees of the
          Leland Stanford Junior University, effective as of December 1, 1996.

     13.  Collaborative Agreement for Development and Production, by and between
          Dendreon Corporation and Protein Sciences Corporation, dated August
          12, 1999.

     14.  Cell Processing Center Collaboration Agreement, by and between the
          American National Red Cross and Dendreon Corporation, dated August 16,
          1999.

     15.  Research and License Agreement, by and between Dendreon Corporation
          and Kirin Brewery Co., Ltd., dated February 1, 1999.

     16.  Manufacturing and Supply Agreement, by and between Dendreon
          Corporation and Kirin Brewery Co., Ltd., dated July 27, 1999.

     17.  Collaborative License Agreement, by and between Dendreon Corporation
          and Kirin Brewery Co., Ltd., dated December 10, 1998.

     18.  Collaboration Agreement, by and between the Company and Trustees of
          Leland Stanford Junior University, dated September 24, 1996.

     19.  Research Purchase Agreement, by and between the Company and Pharmacia
          Biotech AB, effective as of August 27, 1996.

     20.  Resale Purchase Agreement, by and between the Company and Pharmacia
          Biotech AB, effective as of August 27, 1996, and addendum thereto,
          effective as of January 25, 1997.

     21.  Development and Supply Agreement, by and between the Company and
          BioTransplant, Inc., effective as of August 22, 1996.

     22.  Supply Agreement, by and between the Company and Osiris Therapeutics,
          Inc., effective as of February 28, 1997.

     23.  Clinical Trial Agreements, by and between the Company and MD Anderson
          Cancer Center, dated January 1, 1996; University of Chicago, dated May
          22, 1995; University of California San Francisco, dated March 13,
          1997; Sacramento Center for Blood Research, dated March 20, 1997 and
          May 1, 1998; Washington University, dated March 24, 1997; Stanford
          University, dated April 1, 1996 and April 1, 1998; Marin Oncology
          Associates, dated October 7, 1997; Mayo Foundation, dated November 19,
          1997; Scripps Clinic, dated January 6, 1998; and San Diego Hospital
          Association, dated April 15, 1998.

                                      3.
<PAGE>

     24.  Amended and Restated Stockholders' Agreement, dated August 15, 1997.

     25.  Series A Preferred Stock Purchase Agreement, dated October 27,
          1992.

     26.  Series B Preferred Stock Purchase Agreement, dated January 26,
          1996.

     27.  Series C Preferred Stock Purchase Agreement, dated June 20,
          1997.

     28.  Series D Preferred Stock Purchase Agreement, dated July 10,
          1998.

     29.  Collaboration Agreement, by and between the Company and the Mayo
          Foundation, dated July 10, 1997.

     30.  Letter Agreement, by and between the Company and New York Life
          Insurance Company, dated July 29, 1997.

     31.  Consent and Waiver, by and between the Company, The University of
          Brussels and The Immune Response Corporation, dated July 30, 1997.

     32.  Sales, Licensing and Technology Agreement between the Company and
          Micra Scientific, Inc., dated August 20, 1997.

     33.  Consulting Agreements with Samuel Strober and Edward Engleman, both
          dated October 27, 1997.

     34.  Loan and Security Agreement, dated July 30, 1999, between the Company
          and Transamerica Business Credit Corporation in the amount of
          $3,000,000.

     35.  License Agreement between the Company and Fresenius AG, dated February
          27, 1998.  The Company is negotiating a termination of this agreement
          whereby the Company contemplates issuing 250,000 warrants to purchase
          the Company's Common Stock.

     36.  License Agreement between the Company and Ludwig Institute for Cancer
          Research, dated April 28, 1998.

     37.  Master Lease Agreement dated July 31, 1998 between the Company and
          Alexander Real Estate for the lease of real property at 3005 First
          Avenue, Seattle, Washington.

     38.  Home Purchase Loan by and between the Company and Madhusadan Peshwa,
          dated March 26, 1999 in the amount of $25,000.

     39.  Home Purchase Loan by and between the Company and Reiner Laus, dated
          May 3, 1999 in the amount of $80,000.

     40.  Equipment Lease Agreement between the Company and Transamerica
          Business Credit Corporation, dated October 7, 1997 in the amount of
          $1,000,000, amended and restated on April 19, 1999 for an additional
          amount of $500,000.  A total of

                                      4.
<PAGE>

          six draw-downs have taken place as of August 25, 1999 for a total
          amount of $1,402,740.82.

     41.  Sub Lease Agreement dated March 19, 1999 between the Company and
          Halosource for the lease of real property at 3005 First Avenue,
          Seattle, Washington.

     42.  Sub Lease Agreement dated June 18, 1999 and amended July 27, 1999
          between the Company and Aviron for the lease of real property at 291
          North Bernardo Avenue, Mountain View, California.

     Section 2.19
     ------------

     From time to time, the Company will be required to license Intellectual
     Property in order to conduct its business. The Company is actively seeking
     rights to in-process technology to license antigens and other technology
     compatible with that of the Company.

     Section 2.20
     ------------

     In connection with the Master Lease Agreement between the Company and
     Transamerica Business Credit Corporation ("Transamerica"), dated December
     11, 1997 and amended and restated on April 28, 1999 and May 28, 1999,
     Transamerica has a security interest in certain of the Company's specific
     equipment.

                                      5.