Document:

<PAGE>   1
                                                                     EXHIBIT 4.2

                         COMMON STOCK PURCHASE AGREEMENT

        This Common Stock Purchase Agreement (the "Agreement") is made as of
August 27, 2001, by and between Geron Corporation, a Delaware corporation ("the
Company"), and University Technology Corporation, a Colorado not-for-profit
corporation ("UTC").

        WHEREAS, UTC and the Company have entered into a First Amendment to
Intellectual Property License Agreement (the "Agreement") having an effective
date of July 23, 2001.

        WHEREAS, pursuant to Section 17 of the Agreement, the Company has agreed
to issue to UTC one hundred thousand (100,000) shares of the Company's Common
Stock (the "Shares") in consideration of the execution of the Agreement and the
mutual promises and covenants thereunder.

        NOW, THEREFORE, for good and valuable consideration, the receipt and
adequacy of which is hereby acknowledged, the Company and UTC hereby agree as
follows:

        1.      The Company agrees to issue to UTC the Shares. The issuance of
the Shares shall take place at such time and place upon which the Company and
UTC mutually agree, either orally or in writing, but, in no event later than
seven (7) days after the effective date of the Form S-3 registration of the
Shares by the Company (the "Closing"). The Company agrees to file such an S-3
registration statement within ten (10) business days after the date of execution
of the Agreement, and to diligently pursue making that registration statement
effective. At the Closing, or within ten (10) business days thereafter, the
Company will deliver to UTC a certificate representing the Shares, which shall
be freely tradeable.

        2.      In connection with the issuance of the Shares, UTC represents to
the Company the following:

               (a) UTC is aware of the Company's business affairs and financial
condition and has acquired sufficient information about the Company to reach an
informed and knowledgeable decision to acquire the Shares.

               (b) UTC represents that UTC has consulted with any tax
consultants UTC deems advisable in connection the acquisition or disposition of
the Shares and that UTC is not relying on the Company for any tax advice.

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

        4.      This Agreement shall be governed by and construed in accordance
with the laws of the State of Colorado applicable to contracts entered into and
to be performed entirely within the State of Colorado by residents of the State
of Colorado. This Agreement constitutes the entire agreement of the parties
pertaining to the Shares and supersedes all prior and contemporaneous
agreements, representations, and understandings of the parties.

                                   Page 1 of 2

<PAGE>   2
        IN WITNESS WHEREOF, the undersigned, by each of their respective duly
authorized officers and representatives, have set forth their hands hereto to be
effective as of the date first set forth above.

GERON CORPORATION                         UNIVERSITY TECHNOLOGY CORPORATION

--------------------------------------    -------------------------------------
Name:  David L. Greenwood                 Name:
Title:  Sr. Vice President, Corporate          --------------------------------
Development and CFO                       Title:

Date:  August 27, 2001                          -------------------------------
                                          Date:
                                                -------------------------------

                                  Page 2 of 2<PAGE>   1
                                                                     EXHIBIT 4.3

THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED (THE "SECURITIES ACT"), OR ANY STATE SECURITIES LAWS, AND HAS BEEN
ACQUIRED FOR INVESTMENT AND NOT WITH A VIEW TO, OR IN CONNECTION WITH, THE SALE
OR DISTRIBUTION THEREOF. NO SUCH SALE OR DISPOSITION MAY BE EFFECTED WITHOUT AN
EFFECTIVE REGISTRATION STATEMENT RELATED THERETO OR AN OPINION OF COUNSEL,
REASONABLY SATISFACTORY TO THE COMPANY, THAT SUCH REGISTRATION IS NOT REQUIRED
UNDER THE SECURITIES ACT.

Warrant No. UTC-200                                   Number of Shares:  100,000
Date of Issuance:  August 27, 2001                       (subject to adjustment)

                                GERON CORPORATION

                         COMMON STOCK WARRANT AGREEMENT

        Geron Corporation (the "Company"), for value received, hereby certifies
that University Technology Corporation ("UTC"), or its registered assigns (in
accordance with Section 3 below) (the "Registered Holder"), is entitled, subject
to the terms set forth below, to purchase from the Company, at any time after
the date hereof and on or before the Expiration Date (as defined in Section 6
below), up to One Hundred Thousand (100,000) shares of Common Stock of the
Company (as adjusted from time to time pursuant to the terms of this Warrant) at
a purchase price of $14.60 per share. The shares purchasable upon exercise of
this Warrant are hereinafter referred to as the "Warrant Stock." The exercise
price per share of Warrant Stock is hereinafter referred to as the "Purchase
Price."

        1.      EXERCISE.

               (a) MANNER OF EXERCISE. This Warrant may be exercised by the
Registered Holder, in whole or in part, by surrendering this Warrant, with the
purchase form appended hereto as Exhibit A duly executed by such Registered
Holder or by such Registered Holder's duly authorized attorney-in-fact, at the
principal office of the Company, or at such other office or agency as the
Company may designate, accompanied by payment in full by cash, check or wire
transfer of the Purchase Price payable in respect of the number of shares of
Warrant Stock purchased upon such exercise.

               (b) EFFECTIVE TIME OF EXERCISE. Each exercise of this Warrant
shall be deemed to have been effected immediately prior to the close of business
on the day on which this Warrant shall have been surrendered to the Company,
with payment of the applicable Purchase Price, as provided in Section 1(a)
above. At such time, the person or persons in whose name or names any
certificates for Warrant Stock shall be issuable upon such exercise as provided
in Section 1(c) below shall be deemed to have become the holder or holders of
record of the Warrant Stock represented by such certificates.

               (c) DELIVERY TO REGISTERED HOLDER. As soon as practicable after
the exercise of this Warrant, and in any event within ten (10) days thereafter,
the Company at its expense will cause to be issued in the name of, and delivered
to, the Registered Holder, or as such Registered Holder (upon payment by such
Registered Holder of any applicable transfer taxes) may direct, a certificate or
certificates for the number of shares of Warrant Stock to which such Registered
Holder shall be entitled.

                                  Page 1 of 7

<PAGE>   2
        2.      CERTAIN ADJUSTMENTS.

               (a) MERGERS OR CONSOLIDATIONS. If at any time there shall be a
capital reorganization (other than a combination or subdivision of Warrant Stock
otherwise provided for herein), or a merger or consolidation of the Company with
another corporation, then, as a part of such reorganization, merger or
consolidation, lawful provision shall be made so that the Registered Holder
shall thereafter be entitled to receive upon exercise of this Warrant, during
the period specified in this Warrant and upon payment of the Purchase Price, the
number of shares of stock or other securities or property of the Company or the
successor corporation resulting from such reorganization, merger or
consolidation, to which a holder of the Common Stock deliverable upon exercise
of this Warrant would have been entitled under the provisions of the agreement
in such reorganization, merger or consolidation if this Warrant had been
exercised immediately before that reorganization, merger or consolidation. In
any such case, appropriate adjustment (as determined in good faith by the
Company's Board of Directors) shall be made in the application of the provisions
of this Warrant with respect to the rights and interests of the Registered
Holder after the reorganization, merger or consolidation to the end that the
provisions of this Warrant (including adjustment of the Purchase Price then in
effect and the number of shares of Warrant Stock) shall be applicable after that
event, as near as reasonably may be, in relation to any shares or other property
deliverable after that event upon exercise of this Warrant.

               (b) SPLITS AND SUBDIVISIONS; DIVIDENDS. In the event the Company
should at any time or from time to time fix a record date for the effectuation
of a split or subdivision of the outstanding shares of Common Stock or the
determination of the holders of Common Stock entitled to receive a dividend or
other distribution payable in additional shares of Common Stock or other
securities or rights convertible into, or entitling the holder thereof to
receive directly or indirectly, additional shares of Common Stock (hereinafter
referred to as the "Common Stock Equivalents") without payment of any
consideration by such holder for the additional shares of Common Stock or Common
Stock Equivalents (including the additional shares of Common Stock issuable upon
conversion or exercise thereof), then, as of such record date (or the date of
such distribution, split or subdivision if no record date is fixed), the per
share Purchase Price shall be appropriately decreased and the number of shares
of Warrant Stock shall be appropriately increased in proportion to such increase
(or potential increase) of outstanding shares.

               (c) COMBINATION OF SHARES. If the number of shares of Common
Stock outstanding at any time after the date hereof is decreased by a
combination of the outstanding shares of Common Stock, the per share purchase
price shall be appropriately increased and the number of shares of Warrant Stock
shall be appropriately decreased in proportion to such decrease in outstanding
shares.

               (d) ADJUSTMENT CERTIFICATE. When any adjustment is required to be
made in the securities issuable upon exercise of this Warrant, the Company shall
mail to the Registered Holder a certificate setting forth a statement of the
facts requiring such adjustment. Such certificate shall also set forth the kind
and amount of stock or other securities or property into which this Warrant
shall be exercisable following the occurrence of any of the events specified in
this Section 2.

                                  Page 2 of 7

<PAGE>   3
        3.      TRANSFER RESTRICTIONS; REPRESENTATIONS.

               (a) The Registered Holder of this Warrant acknowledges that this
Warrant and the Warrant Stock have not been registered under the Securities Act,
and agrees not to sell, pledge, distribute, offer for sale, transfer or
otherwise dispose of this Warrant or any Warrant Stock issued upon its exercise
in the absence of (i) an effective registration statement under the Securities
Act as to this Warrant or such Warrant Stock and registration or qualification
of this Warrant or such Warrant Stock or (ii) an opinion of counsel, reasonably
satisfactory to the Company, that such registration and qualification are not
required. Within ten (10) days after the written request of the Registered
Holder and the Registered Holder's exercise of the Warrant upon the effective
date of the registration statement, the Company shall file a registration
statement for the Warrant Stock on Form S-3, and will diligently pursue making
that registration statement effective. This Warrant is not transferable without
the prior written consent of the Company. It is understood and agreed that the
preceding sentence does not apply to, or limit the sale, pledge, distribution,
offers for sale, transfer or other disposition of, Warrant Stock.

               (b) The Registered Holder hereby further represents and warrants
to the Company with respect to the issuance of the Warrant as follows:

                      (i) PURCHASE ENTIRELY FOR OWN ACCOUNT. This Warrant is
issued to the Registered Holder in reliance upon such Registered Holder's
representation to the Company, which by such Registered Holder's execution of
this Warrant such Registered Holder hereby confirms, that the Warrant is being
acquired for investment for such Registered Holder'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 Registered Holder has no present intention of selling,
granting any participation in, or otherwise distributing the same.

                      (ii) KNOWLEDGE AND EXPERIENCE; ABILITY TO BEAR ECONOMIC
RISKS. The Registered Holder has such knowledge and experience in financial and
business matters that it is capable of evaluating the merits and risks of the
investment contemplated by this Warrant and such party is able to bear the
economic risk of its investment in the Company (including a complete loss of its
investment).

                      (iii) RESALE. The Registered Holder understands that the
Warrant being issued hereunder is characterized as "restricted securities" under
the federal securities laws inasmuch as they are being acquired from the Company
in a transaction not involving a public offering and that under such laws and
applicable regulations, such securities may be resold without registration under
the Securities Act only in certain circumstances. In this regard, the Registered
Holder represents that it is familiar with SEC Rule 144, as presently in effect,
and understands the resale limitations imposed thereby and by the Securities
Act.

                      (iv) LEGENDS. The Registered Holder acknowledges that all
stock certificates representing shares of stock issued to the Registered Holder
upon exercise of this Warrant may, if such Warrant Stock is not registered under
the Securities Act, have affixed thereto a legend substantially in the following
form:

                      (x) "THE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE
SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE SOLD, TRANSFERRED,

                                  Page 3 of 7

<PAGE>   4
ASSIGNED OR HYPOTHECATED UNLESS THERE IS AN EFFECTIVE REGISTRATION STATEMENT
UNDER SUCH ACT COVERING SUCH SECURITIES, OR THE COMPANY RECEIVES AN OPINION OF
COUNSEL IN A FORM SATISFACTORY TO THE COMPANY, STATING THAT SUCH SALE, TRANSFER,
ASSIGNMENT OR HYPOTHECATION IS EXEMPT FROM THE REGISTRATION AND PROSPECTUS
DELIVERY REQUIREMENTS OF SUCH ACT."

                      (y) Any legend required by the laws of any state in which
the securities will be issued.

               (c) Except as stated in the next sentence of this Section 3(c),
and subject to the provisions of Section 3(a) hereof, this Warrant and all
rights hereunder are transferable in whole but not in part upon surrender of the
Warrant with a properly executed assignment (in the form of Exhibit B hereto) at
the principal office of the Company. Subject to the provisions of Section 3(a)
hereof, the rights in the Warrant may be transferred in part to holders of
beneficial interests in the Warrant under the University of Colorado's
intellectual property policy.

               (d) The Company may treat the Registered Holder of this Warrant
as the absolute owner hereof for all purposes; provided, however, that if and
when this Warrant is properly assigned in blank, the Company may (but shall not
be required to) treat the bearer hereof as the absolute owner hereof for all
purposes, notwithstanding any notice to the contrary.

               (e) The Company will maintain a register containing the name and
address of the Registered Holder(s) of this Warrant. Any Registered Holder may
change such Registered Holder's address as shown on the warrant register by
written notice to the Company requesting such change.

               (f) The Company hereby represents and warrants to the Registered
Holder as follows:

                      (i) The Company is a corporation validly existing and in
good standing under the laws of the State of Delaware.

                      (ii) The Company has full corporate right, power and
authority (including the due authorization by all necessary corporate action) to
enter into this Warrant and to perform its obligations hereunder without the
need for the consent of any other person; and this Warrant has been duly
authorized, executed and delivered and constitutes legal, valid and binding
obligations of the Company enforceable against it in accordance with the terms
hereof and thereof. The execution, delivery and performance of this Warrant by
the Company does not contravene or violate any laws, rules or regulations
applicable to it.

                      (iii) The Company has taken such corporate action as is
necessary or appropriate to enable it to perform its obligations hereunder,
including, but not limited to, the issuance, sale and delivery of the Warrant.

                      (iv) The Warrant Stock, when issued and paid for in
compliance with the provisions of this Warrant, will be validly issued, fully
paid and non-assessable.

                                  Page 4 of 7

<PAGE>   5
        4.      NO IMPAIRMENT. The Company will not, by amendment of its charter
or through reorganization, consolidation, merger, dissolution, sale of assets or
any other voluntary action, avoid or seek to avoid the observance or performance
of any of the terms of this Warrant, but will at all times in good faith assist
in the carrying out of all such terms and in the taking of all such action as
may be necessary or appropriate in order to protect the rights of the holder of
this Warrant against impairment.

        5.      TERMINATION. This Warrant (and the right to purchase securities
upon exercise hereof) shall terminate upon the tenth anniversary of the Date of
Issuance (the "Expiration Date").

        6.      NOTICES OF CERTAIN TRANSACTIONS. In case:

               (a) the Company shall take a record of the holders of its Common
Stock (or other stock or securities at the time deliverable upon the exercise of
this Warrant) for the purpose of entitling or enabling them to receive any
dividend or other distribution, or any right to subscribe for, purchase or
otherwise acquire any shares of stock of any class or any other securities or
property, or to receive any other right; or

               (b) of any capital reorganization of the Company, any
reclassification of the capital stock of the Company, any consolidation or
merger of the Company, any consolidation or merger of the Company with or into
another corporation (other than a consolidation or merger in which the Company
is the surviving entity), or any transfer of all or substantially all of the
assets of the Company, or

               (c) of the voluntary or involuntary dissolution, liquidation or
winding-up of the Company,

then, and in each such case, the Company will mail or cause to be mailed to the
Registered Holder of this Warrant a notice specifying, as the case may be, (i)
the date on which a record is to be taken for the purpose of such dividend,
distribution or right, and stating the amount and character of such dividend,
distribution or right, and (ii) the effective date on which such reorganization,
reclassification, consolidation, merger, transfer, dissolution, liquidation or
winding-up is expected to take place, and the record date for determining
shareholders entitled to vote thereon. Such notice shall be mailed at least ten
(10) calendar days prior to the record date or effective date for the event
specified in such notice.

        7.      RESERVATION OF STOCK. The Company will at all times reserve and
keep available, solely for the issuance and delivery upon the exercise of this
Warrant, such shares of Warrant Stock or other stock or securities, as from time
to time shall be issuable upon the exercise of this Warrant.

        8.      EXCHANGE OF WARRANTS. Upon the surrender by the Registered
Holder of any Warrant, properly endorsed, to the Company at the principal office
of the Company, the Company will, subject to the provisions of Section 3(a)
hereof, issue and deliver to or upon the order of such Registered Holder, at the
Company's expense, a new Warrant of like tenor, in the name of such Registered
Holder or as such Registered Holder (upon payment by such Registered Holder of
any applicable transfer taxes) may direct, calling in the aggregate on the face
or faces

                                  Page 5 of 7

<PAGE>   6
thereof for the number of shares of Common Stock called for on the face or faces
of the Warrant so surrendered.

        9.      REPLACEMENT OF WARRANTS. Upon receipt of evidence reasonably
satisfactory to the Company of the loss, theft, destruction or mutilation of
this Warrant and (in the case of loss, theft or destruction) upon delivery of an
indemnity agreement (with surety if reasonably required) in an amount reasonably
satisfactory to the Company, or (in the case of mutilation) upon surrender and
cancellation of this Warrant, the Company will issue, in lieu thereof, a new
Warrant of like tenor.

        10.     MAILING OF NOTICES. Any notice required or permitted by this
Warrant shall be in writing and shall be deemed sufficient upon receipt, when
delivered personally or by a nationally-recognized delivery service (such as
Federal Express or UPS) or confirmed facsimile, or forty-eight (48) hours after
being deposited in the U.S. mail as certified or registered mail with postage
prepaid, if such notice is addressed to the party to be notified at such party's
address or facsimile number as set forth below or as subsequently modified by
written notice.

        11.     NO RIGHTS AS STOCKHOLDER. Until the exercise of this Warrant,
the Registered Holder of this Warrant shall not have or exercise any rights by
virtue hereof as a stockholder of the Company (including without limitation the
right to notification of stockholder meetings or the right to receive any notice
or other communication concerning the business or affairs of the Company).

        12.     NO FRACTIONAL SHARES. No fractional shares of Common Stock will
be issued in connection with any exercise hereunder. In lieu of any fractional
shares which would otherwise be issuable, the Company shall pay cash equal to
the product of such fraction multiplied by the fair market value of one share of
Common Stock on the date of exercise, as determined in good faith by the
Company's Board of Directors.

        13.     AMENDMENT OR WAIVER. Any term of this Warrant may be amended or
waived only by an instrument in writing signed by the party against which
enforcement of the amendment or waiver is sought.

        14.     HEADINGS. The headings in this Warrant are for purposes of
reference only and shall not limit or otherwise affect the meaning of any
provision of this Warrant.

        15.     SUCCESSORS AND ASSIGNS. The terms and provisions of this Warrant
shall inure to the benefit of, and be binding upon, the Company and the
Registered Holder and their respective permitted successors and assigns (in the
case of the Registered Holder, in accordance with Section 3).

        16.     GOVERNING LAW. This Warrant shall be governed, construed and
interpreted in accordance with the laws of the State of California, without
giving effect to principles of conflicts of law.

                                  Page 6 of 7

<PAGE>   7
GERON CORPORATION                          REGISTERED HOLDER

----------------------------------------   ------------------------------------
Signature                                  Signature

Name:      David L. Greenwood              Name:
           -----------------------------              -------------------------

Title:     Sr. Vice President, Corporate   Title:
           Development and CFO
           -----------------------------              -------------------------

Address:   230 Constitution Drive          Address:
           Menlo Park, CA 94025
           -----------------------------              -------------------------

Facsimile: 650-473-7701                    Facsimile:
           -----------------------------              -------------------------

Dated:     August 27, 2001                 Dated:
           -----------------------------              -------------------------

                                  Page 7 of 7

<PAGE>   8
                                    EXHIBIT A

                                  PURCHASE FORM

To:     GERON CORPORATION                          Dated:
                                                         ----------------------

        The undersigned, pursuant to the provisions set forth in the attached
Warrant, hereby irrevocably elects to purchase ___________ shares of the Common
Stock covered by such Warrant and herewith makes payment of $___________,
representing the full purchase price for such shares at the price per share
provided for in such Warrant.

        The undersigned hereby confirms and acknowledges the investment
representations and warranties made in Section 3 of the Warrant and accepts such
shares subject to the restrictions of the Warrant, copies of which are available
from the Secretary of the Company.

--------------------------------------
Signature

Name:
         -------------------------------

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

Address:
         -------------------------------

<PAGE>   9
                                    EXHIBIT B

                                 ASSIGNMENT FORM

FOR VALUE RECEIVED, _________________________________________ hereby sells,
assigns and transfers all of the rights of the undersigned under the attached
Warrant with respect to the number of shares of Common Stock covered thereby set
forth below, unto:

<TABLE>
<CAPTION>
     NAME OF ASSIGNEE                ADDRESS                NO. OF SHARES
     ----------------                -------                -------------
<S>                                  <C>                    <C>

</TABLE>

--------------------------------------            -----------------------
Signature                                         Dated:

Witness:
             --------------------------

             --------------------------

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