EXHIBIT 4.1


                         COMMON STOCK PURCHASE AGREEMENT

THIS COMMON STOCK PURCHASE AGREEMENT ("Agreement") is made and entered into as
of August 13, 2008 (the "Effective Date"), by and between GERON CORPORATION, a
Delaware corporation having its principal place of business at 230 Constitution
Drive, Menlo Park, California 94025 ("Geron"), and MPI Research, Inc., a
Michigan corporation having its principal place of business at 54943 North Main
Street, Mattawan, MI 49071 ("MPI").

      A.    Geron and MPI are the parties to that certain Master Agreement dated
            as of December 12, 2003 (the "Master Agreement"), and related
            Services Agreement Addenda under which Geron and MPI have agreed
            that MPI will perform certain services on behalf of Geron on the
            terms set forth therein.

      B.    Pursuant to the third amendment to the Master Agreement, dated
            August 13, 2008 ("Amendment No. 3"), Geron may pay for the price of
            such services by delivery of shares of Geron's Common Stock (the
            "Shares").

      C.    Geron has elected to make payment for such services through the
            delivery of Shares, pursuant to the terms and conditions of
            Amendment No. 3 and this Agreement.

THE PARTIES AGREE AS FOLLOWS:

1. ISSUANCE OF SHARES; ADJUSTMENTS.

      1.1   As payment of the price specified in Amendment No. 3, Geron will
            issue and deliver certificates for 226,062 Shares. Upon issuance and
            delivery of the certificate(s) for the Shares, all Shares shall be
            duly authorized and validly issued and represent fully paid shares
            of Geron's Common Stock.

2. CLOSING; DELIVERY.

      2.1   The consummation of the transaction contemplated by this Agreement
            (a "Closing") shall be held at such time and place as is mutually
            agreed upon between the parties, but in any event no later than five
            (5) business days after the Effective Date hereof (the "Closing
            Date"). At the Closing, Geron shall deliver to MPI one or more
            certificates representing all of the Shares, which Shares shall be
            issued in the name of MPI or its designee and in such denominations
            as MPI shall specify.

      2.2   Geron's obligations to issue and deliver the stock certificate(s)
            representing the Shares to MPI at the Closing shall be subject to
            the following conditions, which may be waived by Geron:

            2.2.1 the covenants and obligations that MPI is required to perform
                  or to comply with pursuant to this Agreement, at or prior to
                  the Closing, must have been duly performed and complied with
                  in all material respects; and

            2.2.2 the representations and warranties made by MPI herein shall be
                  true and correct in all material respects as of the Closing
                  Date.



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      2.3   MPI's obligation to accept delivery of the stock certificate(s)
            representing the Shares at the Closing shall be subject to the
            following conditions, any one or more of which may be waived by MPI:

            2.3.1 the covenants and obligations that Geron is required to
                  perform or to comply with pursuant to this Agreement, at or
                  prior to the Closing, must have been duly performed and
                  complied with in all material respects;

            2.3.2 Geron shall have available under its Certificate of
                  Incorporation sufficient authorized shares of Common Stock to
                  issue the Shares to MPI; and

            2.3.3 the representation and warranties made by Geron herein shall
                  be true and correct in all material respects as of any Closing
                  Date.

3. RESTRICTIONS ON RESALE OF SHARES.

      3.1   Legends. MPI understands and acknowledges that the Shares are not
            registered under the Securities Act of 1933 (the "Act"), and that
            under the Act and other applicable laws MPI may be required to hold
            such Shares for an indefinite period of time. Each stock certificate
            representing Shares shall bear the following legends:

            "THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER
            THE SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"). ANY TRANSFER OF
            SUCH SECURITIES SHALL BE INVALID UNLESS A REGISTRATION STATEMENT
            UNDER THE ACT IS IN EFFECT AS TO SUCH TRANSFER OR, IN THE OPINION OF
            COUNSEL REASONABLY ACCEPTABLE TO GERON, SUCH REGISTRATION IS
            UNNECESSARY FOR SUCH TRANSFER TO COMPLY WITH THE ACT. THE SECURITIES
            REPRESENTED HEREBY ARE SUBJECT TO THE TERMS OF THE COMMON STOCK
            PURCHASE AGREEMENT, DATED AS OF AUGUST 13, 2008. A COPY OF THE
            AGREEMENT CAN BE OBTAINED FROM THE SECRETARY OF GERON."

      3.2   Limits on Sales. MPI agrees that if it decides to resell some or all
            of the Shares, it will do so only through orderly sales executed
            through a top-tier brokerage house, and in an appropriate manner
            based upon whether the shares are registered or unregistered, i.e.,
            on the Nasdaq Global Market or in a Rule 144A compliant transaction.
            MPI further agrees that it will not engage in short selling with
            respect to the Stock.

4. REGISTRATION RIGHTS

      4.1   Geron agrees to make commercially reasonable efforts to file with
            the Securities and Exchange Commission (the "Commission") within ten
            (10) business days after the Closing Date, a registration statement
            under the Act (the "Registration Statement"), on Form S-3 or other
            appropriate form, so as to permit a non-underwritten public offering
            and resale of the Shares under the Act by MPI. Geron agrees to
            diligently pursue making the Registration Statement effective. Geron
            will notify MPI of the effectiveness of the Registration Statement
            within one (1) business day of receiving notice from the Commission.


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      4.2   Geron will maintain the Registration Statement and any
            post-effective amendment thereto filed under this Section 4
            effective under the Act until the earliest of (i) the date that none
            of the Shares covered by such Registration Statement are issued and
            outstanding, (ii) the date that all of the Shares have been sold
            pursuant to such Registration Statement, (iii) the date MPI receives
            an opinion of counsel from Geron, which counsel shall be reasonably
            acceptable to MPI, that the Shares may be sold under the provisions
            of Rule 144 without limitation as to volume, (iv) the date that all
            Shares have been otherwise transferred to persons who may trade such
            shares without restriction under the Act, and Geron has delivered a
            new certificate or other evidence of ownership for such securities
            not bearing a restrictive legend, or (v) the date all Shares may be
            sold at any time, without volume or manner of sale limitations
            pursuant to Rule 144 or any similar provision then in effect under
            the Act in the opinion of counsel to Geron, which counsel shall be
            reasonably acceptable to MPI.

      4.3   Geron, at its expense, shall furnish to MPI with respect to the
            Shares registered under the Registration Statement such reasonable
            number of copies of the Registration Statement, prospectuses and
            preliminary prospectuses in conformity with the requirements of the
            Act and such other documents as MPI may reasonably request, in order
            to facilitate the public sale or other disposition of all or any of
            the Shares by MPI, provided, however, that the obligation of Geron
            to deliver copies of prospectuses or preliminary prospectuses to MPI
            shall be subject to the receipt by Geron of reasonable assurances
            from MPI that MPI will comply with the applicable provisions of the
            Act and of such other securities or blue sky laws as may be
            applicable in connection with any use of such prospectuses or
            preliminary prospectuses.

      4.4   All fees, disbursements and out-of-pocket expenses and costs
            incurred by Geron in connection with the preparation and filing of
            the Registration Statement under Section 4.1 and in complying with
            applicable securities and Blue Sky laws (including, without
            limitation, all attorneys' fees of Geron) shall be borne by Geron.
            MPI shall bear the cost of fees and expenses of MPI's counsel.

      4.5   Geron will advise MPI promptly after it shall receive notice or
            obtain knowledge of the issuance of any stop order by the Commission
            delaying or suspending the effectiveness of the Registration
            Statement or of the initiation of any proceeding for that purpose,
            and Geron will use its commercially reasonable efforts to prevent
            the issuance of any stop order or to obtain its withdrawal at the
            earliest possible moment if such stop order should be issued.

      4.6   With a view to making available to MPI the benefits of Rule 144 (or
            its successor rule) and any other rule or regulation of the
            Commission that may at the time permit MPI to sell the Shares to the
            public without registration, Geron covenants and agrees to: (i) make
            and keep public information available, as those terms are understood
            and defined in Rule 144, until the earliest of (A) such date as all
            of the Shares may be resold pursuant to Rule 144 or any other rule
            of similar effect or (B) such date as all of the Shares shall have
            been resold; and (ii) file with the Commission in a timely manner
            all reports and other documents required of Geron under the Act and
            under the Exchange Act of 1934, as amended.


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      4.7   MPI will cooperate with Geron in all respects in connection with
            this Agreement, including timely supplying all information
            reasonably requested by Geron (which shall include all information
            regarding MPI and proposed manner of sale of the Shares required to
            be disclosed in any Registration Statement) and executing and
            returning all documents reasonably requested in connection with the
            registration and sale of the Shares and entering into and performing
            their obligations under any underwriting agreement, if the offering
            is an underwritten offering, in usual and customary form, with the
            managing underwriter or underwriters of such underwritten offering.
            Nothing in this Agreement shall obligate MPI to consent to be named
            as an underwriter in any Registration Statement.

5.    INDEMNIFICATION.

      5.1   Geron agrees to indemnify and hold harmless MPI (and each person, if
            any, who controls MPI within the meaning of Section 15 of the Act,
            and each officer and director of MPI) against any and all losses,
            claims, damages or liabilities (or actions or proceedings in respect
            thereof), joint or several, directly or indirectly based upon or
            arising out of (i) any untrue statement or alleged untrue statement
            of any material fact contained in the Registration Statement, any
            preliminary prospectus, final prospectus or summary prospectus
            contained therein or used in connection with the offering of the
            Shares, or any amendment or supplement thereto, or (ii) any omission
            or alleged omission to state a material fact required to be stated
            therein or necessary to make the statements therein not misleading;
            and Geron will reimburse each such indemnified party for any legal
            or any other expenses reasonably incurred by them in connection with
            investigating, preparing, pursuing or defending any such loss,
            claim, damage, liability, action or proceeding, except insofar as
            any such loss, claim, damage, liability, action, proceeding or
            expense (A) arises out of or is based upon an untrue statement or
            alleged untrue statement or omission or alleged omission made in the
            Registration Statement, any such preliminary prospectus, final
            prospectus, summary prospectus, amendment or supplement in reliance
            upon and in conformity with written information furnished to Geron
            by MPI or such other person expressly for use in the preparation
            thereof, (B) the failure of MPI to comply with its covenants and
            agreements contained in Sections 7.1 or 7.5.2 hereof or (C) any
            misstatement or omission in any prospectus that is corrected in any
            subsequent prospectus that was delivered to MPI prior to the
            pertinent sale or sales by MPI. Such indemnity shall remain in full
            force and effect, regardless of any investigation made by such
            indemnified party and shall survive the transfer of the Shares by
            MPI.

      5.2   MPI agrees to indemnify and hold harmless Geron (and each person, if
            any, who controls Geron within the meaning of Section 15 of the Act,
            each officer of Geron who signs the Registration Statement and each
            director of Geron) from and against losses, claims, damages or
            liabilities (or actions or proceedings in respect thereof), joint or
            several, directly or indirectly based upon or arising out of, (i)
            any failure of MPI to comply with the covenants and agreements
            contained in Sections 7.1 and 7.5.2 hereof or (ii) any untrue
            statement of a material fact contained in the Registration Statement
            or any omission of a material fact required to be stated in the
            Registration Statement or necessary in order to make the statements
            in the Registration Statement not misleading if such untrue
            statement or omission was made in reliance upon and in conformity
            with written information furnished to Geron by on behalf of MPI
            specifically for use in preparation of the Registration Statement;
            provided, however, that MPI shall not be liable in any such case for
            (A) any untrue statement or omission in the Registration Statement,
            prospectus, or other such document which statement is corrected by
            MPI and delivered to Geron prior to the sale from which such loss
            occurred, (B) any untrue statement or omission in any prospectus
            which is corrected by MPI in any subsequent prospectus, or
            supplement or amendment thereto, and delivered to Geron prior to the
            sale or sales from which a loss or liability arose, or (C) any
            failure by Geron to fulfill any of its obligations under Section 5.1
            hereof.


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      5.3   Promptly after receipt by any indemnified person of a notice of a
            claim or the beginning of any action in respect of which indemnity
            is to be sought against an indemnifying person pursuant to this
            Section 5, such indemnified person shall notify the indemnifying
            person in writing of such claim or of the commencement of such
            action, but the omission to so notify the indemnifying party will
            not relieve it from any liability which it may have to any
            indemnified party under this Section 5 (except to the extent that
            such omission materially and adversely affects the indemnifying
            party's ability to define such action) or from any liability
            otherwise than under this Section 5. Subject to the provisions
            hereinafter stated, in case any such action shall be brought against
            an indemnified person, the indemnifying person shall be entitled to
            participate therein, and, to the extent that it shall elect by
            written notice delivered to the indemnified party promptly after
            receiving the aforesaid notice from such indemnified party, shall be
            entitled to assume the defense thereof, with counsel reasonably
            satisfactory to such indemnified person. After notice from the
            indemnifying person to such indemnified person of its election to
            assume the defense thereof, such indemnifying person shall not be
            liable to such indemnified person for any legal expense subsequently
            incurred by such indemnified person in connection with the defense
            thereof, provided, however, that if there exists or shall exist a
            conflict of interest that would make inappropriate, in the
            reasonable opinion of counsel to the indemnified person, for the
            same counsel to represent both the indemnified person and such
            indemnifying person or any affiliate or associate thereof, the
            indemnified person shall be entitled to retain its own counsel at
            the expense of such indemnifying person; provided, however, that no
            indemnifying person shall be responsible for the fees and expenses
            of more than on separate counsel (together with appropriate local
            counsel) for all indemnified parties. In no event shall any
            indemnifying person be liable in respect to any amounts paid in
            settlement of any action unless the indemnifying person shall have
            approved the terms of such settlement. No indemnifying person shall,
            without the prior written consent of the indemnified person, effect
            any settlement of any pending or threatened proceeding in respect of
            which any indemnified person is or could have been a party and
            indemnification could have been sought hereunder by such indemnified
            person, unless such settlement includes an unconditional release of
            such indemnified person from all liability on claims that are the
            subject matter of such proceeding.

      5.4   The provisions of this Section 5 shall survive the termination of
            this Agreement.

   6. REPRESENTATIONS AND ACKNOWLEDGEMENT OF GERON.

      Geron hereby represents, warrants and covenants to MPI as follow:

      6.1   Organization, Good Standing and Qualification. Geron is a
            corporation duly organized, validly existing and in good standing
            under the laws of the State of Delaware and has all requisite
            corporate power and authority to carry on its business as now
            conducted and as presently proposed to be conducted. Geron is duly
            qualified to transact business and is in good standing as a foreign
            corporation in each jurisdiction in which the failure to so qualify
            would have a material adverse effect on its business or properties.


      6.2   Authorization. All corporate action on the party of Geron, its
            officers, directors and stockholders necessary for the
            authorization, execution and delivery of this Agreement, the
            performance of all obligations of Geron hereunder and the
            authorization, issuance and delivery of the Shares has been taken or
            will be taken prior to the Closing, and this Agreement, when
            executed and delivered will constitute valid and legally binding
            obligations of Geron, enforceable against Geron in accordance with
            their terms, except as limited by applicable bankruptcy, insolvency,
            reorganization, moratorium, fraudulent conveyance and other laws of
            general application affecting enforcement of creditors' rights
            generally, as limited by laws relating to the availability of
            specific performance, injunctive relief or other equitable remedies.


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      6.3   Valid Issuance of Common Stock. The Shares, when issued, sold and
            delivered in accordance with the terms hereof for the consideration
            expressed herein, will be duly and validly authorized and issued,
            fully paid and nonassessable and free of restrictions on transfer
            other than restrictions on transfer under this Agreement and
            applicable state and federal securities laws.

      6.4   Legal Proceedings and Orders. There is no action, suit, proceeding
            or investigation pending or threatened against Geron that questions
            the validity of this Agreement or the right of Geron to enter into
            this Agreement or to consummate this transactions contemplated
            hereby, nor is Geron aware of any basis for any of the forgoing.
            Geron is neither a party nor subject to the provisions of any order,
            writ, injunction, judgment or decree of any court or government
            agency or instrumentality that would affect the ability of Geron to
            enter into this Agreement or to consummate the transactions
            contemplated hereby.

   7. REPRESENTATIONS AND ACKNOWLEDGMENTS OF MPI.

      MPI hereby represents, warrants, acknowledges and agrees that:

      7.1   Investment. MPI is acquiring the Shares for MPI's own account, and
            not directly or indirectly for the account of any other person. MPI
            is acquiring the Shares for investment and not with a view to
            distribution or resale thereof, except in compliance with the Act
            and any applicable state law regulating securities.

      7.2   Access to Information. MPI has consulted with its own attorney,
            accountant, or investment advisor as MPI has deemed advisable with
            respect to the investment and has determined its suitability for
            MPI. MPI has had the opportunity to ask questions of, and to receive
            answers from, appropriate executive officers of Geron with respect
            to the terms and conditions of the transactions contemplated hereby
            and with respect to the business, affairs, financial condition and
            results of operations of Geron. MPI has had access to such financial
            and other information as is necessary in order for MPI to make a
            fully informed decision as to investment in Geron, and has had the
            opportunity to obtain any additional information necessary to verify
            any of such information to which MPI has had access. MPI
            acknowledges that neither Geron nor any of its officers, directors,
            employees, agents, representatives, or advisors have made any
            representation or warranty other than those specifically expressed
            herein.

      7.3   Business and Financial Expertise. MPI further represents and
            warrants that it has such business or financial expertise as to be
            able to evaluate its investment in Geron and purchase of the Shares.

      7.4   Speculative Investment. MPI acknowledges that the investment in
            Geron represented by the Shares is highly speculative in nature and
            is subject to a high degree of risk of loss in whole or in part; the
            amount of such investment is within MPI's risk capital means and is
            not so great in relation to MPI's total financial resources as would
            jeopardize the personal financial needs of MPI in the event such
            investment were lost in whole or in part.

      7.5   Unregistered Securities.  MPI acknowledges that:

            7.5.1 MPI must bear the economic risk of investment for an
                  indefinite period of time because the Shares have not been
                  registered under the Act and therefore cannot and will not be
                  sold unless they are subsequently registered under the Act or
                  an exemption from such registration is available. Geron has
                  made no agreements, covenants or undertakings whatsoever to
                  register any of the Shares under the Act, except as provided
                  in Section 4 above. Geron has made no representations,
                  warranties or covenants whatsoever as to whether any exemption
                  from the Act, including, without limitation, any exemption for
                  limited sales in routine brokers' transactions pursuant to
                  Rule 144 under the Act, will become available and any such
                  exemption pursuant to Rule 144, if available at all, will not
                  be available unless: (i) a public trading market then exists
                  in Geron's common stock, (ii) Geron has complied with the
                  information requirements of Rule 144, and (iii) all other
                  terms and conditions of Rule 144 have been satisfied.


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            7.5.2 Transfer of the Shares has not been registered or qualified
                  under any applicable state law regulating securities and,
                  therefore, the Shares cannot and will not be sold unless they
                  are subsequently registered or qualified under any such act or
                  an exemption therefrom is available. Geron has made no
                  agreements, covenants or undertakings whatsoever to register
                  or qualify any of the Shares under any such act. Geron has
                  made no representations, warranties or covenants whatsoever as
                  to whether any exemption from any such act will become
                  available.

            7.5.3 MPI hereby certifies that it is an "Accredited Investor" as
                  that term is defined in Rule 501 under the Act.

   8. TAX ADVICE. MPI acknowledges that MPI has not relied and will not rely
      upon Geron or Geron's counsel with respect to any tax consequences related
      to the ownership, purchase, or disposition of the Shares. MPI assumes full
      responsibility for all such consequences and for the preparation and
      filing of all tax returns and elections which may or must be filed in
      connection with the Shares.

   9. NOTICES. Any notice or other communication required or permitted hereunder
      shall be in writing and shall be deemed to have been duly given on the
      date of delivery if delivered personally or by facsimile, or one day, not
      including Saturdays, Sundays, or national holidays, after sending if sent
      by national overnight delivery service, or five days, not including
      Saturdays, Sundays, or national holidays, after mailing if mailed by first
      class United States mail, certified or registered with return receipt
      requested, postage prepaid, and addressed as follows:

            To Geron at:            Geron Corporation
                                    230 Constitution Drive
                                    Menlo Park, California  94025
                                    Attention: General Counsel
                                    Telephone:  (650) 473-7700
                                    Facsimile:  (650) 473-7750



            To MPI at:              MPI Research, Inc.
                                    54943 North Main Street
                                    Mattawan, MI 49071
                                    Telephone: 269.668.3336
                                    Facsimile: 269.668.4151

  10. BINDING EFFECT. This Agreement shall be binding upon the heirs,
      legal representatives and successors of Geron and of MPI; provided,
      however, that MPI may not assign any rights or obligations under this
      Agreement.

  11. GOVERNING LAW. This Agreement shall be governed by and construed in
      accordance with the laws of the State of California.

  12. INVALID PROVISIONS. In the event that any provision of this Agreement is
      found to be invalid or otherwise unenforceable by a court or other
      tribunal of competent jurisdiction, such invalidity or unenforceability
      shall not be construed as rendering any other provision contained herein
      invalid or unenforceable, and all such other provisions shall be given
      full force and effect to the same extent as though the invalid and
      unenforceable provision was not contained herein.


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  13. COUNTERPARTS. This Agreement may be executed in any number of identical
      counterparts, each of which shall be deemed an original, but all of which
      together shall constitute one and the same instrument.

  14. AMENDMENTS. This Agreement or any provision hereof may be changed, waived,
      or terminated only by a statement in writing signed by the party against
      whom such change, waiver or termination is sought to be enforced.

  15. FUTURE COOPERATION. Each of the parties hereto agrees to cooperate at all
      times from and after the date hereof with respect to all of the matters
      described herein, and to execute such further assignments, releases,
      assumptions, amendments of the Agreement, notifications and other
      documents as may be reasonably requested for the purpose of giving effect
      to, or evidencing or giving notice of, the transactions contemplated by
      this Agreement.

  16. ENTIRE AGREEMENT. This Agreement and the Master Agreement, including
      Amendment No. 3 thereto, constitute the entire agreement of the parties
      pertaining to the Shares and supersede all prior and contemporaneous
      agreements, representations, and understandings of the parties with
      respect thereto.

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

                                   Geron Corporation


                                           /s/ David L. Greenwood
                                   ---------------------------------------------
                                   By:     David L. Greenwood
                                   Title:  Executive Vice President and Chief
                                           Financial Officer


                                   MPI Research, Inc.


                                           /s/ William Harrison
                                   ---------------------------------------------
                                   By:     William Harrison
                                   Title:  President and Chief Operating Officer


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