Document:

EXHIBIT 4.1

                         COMMON STOCK PURCHASE AGREEMENT

     THIS COMMON STOCK PURCHASE AGREEMENT ("Agreement") is made and entered into
as of May 10, 2007 (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 EXPONENT, INC., a Delaware
corporation having its principal place of business at 149 Commonwealth Drive,
Menlo Park, CA 94025 ("Lessor").

          A.   Geron and Lessor are the parties to that certain Lease Agreement
               dated as of April 20, 2007 (the "Lease Agreement"), under which
               Geron has agreed to lease certain office space (the "Property")
               from Lessor in accordance with the terms of the Lease Agreement.

          B.   Pursuant to the Lease Agreement, Geron may pay the aggregate
               rental fee for the Property (the "Rental Fee") due under the
               Lease Agreement by delivery of shares of Geron's Common Stock
               (the "Shares").

THE PARTIES AGREE AS FOLLOWS:

     1.   ISSUANCE OF SHARES; ADJUSTMENTS.

          1.1  As payment of the Rental Fee, Geron will issue and deliver to
               Lessor certificates for 210,569 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
               Lessor one or more certificates representing all of the Shares,
               which Shares shall be issued in the name of Lessor or its
               designee and in such denominations as Lessor shall specify.

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

               2.2.1 the covenants and obligations that Lessor 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 Lessor herein
                    shall be true and correct in all material respects as of the
                    Closing Date.

          2.3  Lessor'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 Lessor:

               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;

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

               2.3.3 the representations and warranties made by Geron herein
                    shall be true and correct in all material respects as of the
                    closing date;

     3.   RESTRICTIONS ON RESALE OF SHARES.

          3.1  Legends. Lessor 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 Lessor 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 BY AND BETWEEN LESSOR AND
               LESSEE, DATED AS OF MAY 10, 2007. A COPY OF THE AGREEMENT CAN BE
               OBTAINED FROM THE SECRETARY OF GERON."

          3.2  Limits on Sales. Lessor 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 National Market or in a Rule
               144A or Rule 144 compliant transaction.

          3.3  Removal of Legends. Any legend endorsed on a certificate
               evidencing the Shares shall be removed, and Geron shall issue a
               certificate without such legend to the holder of such Shares, if
               such Shares are being sold pursuant to an effective registration
               statement under the Act or pursuant to Rule 144 promulgated
               thereunder, and the purchaser of Shares so sold may immediately
               resell such Shares without restriction and without registration;
               provided, however, that in the case of a sale pursuant to Rule
               144, such holder of Shares shall provide such information as is
               reasonably requested by Geron to ensure that such Shares may be
               sold in reliance on Rule 144.

     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 Lessor.
               Geron will exercise reasonable efforts to cause the form of the
               Registration Statement all applicable requirements of the Act and
               the regulations of the Commission thereunder. Geron agrees to
               diligently pursue making the Registration Statement effective.
               Geron will notify Lessor of the effectiveness of the Registration
               Statement within one (1) business day of receiving notice from
               the Commission.

          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

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               Lessor receives an opinion of counsel from Geron, which counsel
               shall be reasonably acceptable to Lessor, that all of the Shares
               may be sold in any three month period under the provisions of
               Rule 144, (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(k) or any similar provision then in effect
               under the Act in the opinion of counsel to Geron, which counsel
               shall be reasonably acceptable to Lessor.

          4.3  Geron, at its expense, shall furnish to Lessor 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 Lessor may
               reasonably request, in order to facilitate the public sale or
               other disposition of all or any of the Shares by Lessor,
               provided, however, that the obligation of Geron to deliver copies
               of prospectuses or preliminary prospectuses to Lessor shall be
               subject to the receipt by Geron of reasonable assurances from
               Lessor that Lessor 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. Lessor shall bear the cost of fees and expenses of
               Lessor's counsel.

          4.5  Geron will advise Lessor 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. If any event or circumstance occurs that causes
               the Registration Statement or any prospectus or supplement
               therein to not comply with the Act or the rules and regulations
               issued thereunder, Geron shall promptly notify Lessor and shall
               promptly amend or supplement the Registration Statement and/or
               prospectus so as to bring it into compliance with the Act and the
               rules and regulations thereunder. Upon such notification by Geron
               of the foregoing, Lessor will promptly suspend its offer and sale
               of Shares until Geron has notified Lessor that it has prepared
               and filed with the Commission a supplement or amendment to the
               Registration Statement and has been notified of the effectiveness
               of the Registration Statement, as supplemented or amended.

          4.6  With a view to making available to Lessor the benefits of Rule
               144 (or its successor rule) and any other rule or regulation of
               the Commission that may at the time permit Lessor 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(k) 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
               Securities Exchange Act of 1934 (the "Exchange Act"), as amended.

          4.7  Lessor 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 Lessor 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 Nothing in this
               Agreement shall obligate Lessor to consent to be named as an
               underwriter in any Registration Statement.

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          4.8  Geron shall prepare and file with the SEC such amendments and
               supplements to the Registration Statement as may be necessary to
               comply with the provisions of the Act with respect to the
               disposition of all Shares covered by the Registration Statement;
               provided, however, that before filing a registration statement or
               any amendments or supplements thereto, or comparable statements
               under securities or blue sky laws of any jurisdiction, Geron will
               furnish to one counsel to be designated by Lessor, copies of all
               such documents proposed to be filed.

     5.   INDEMNIFICATION.

          5.1  Geron agrees to indemnify and hold harmless Lessor (and each
               person, if any, who controls Lessor within the meaning of Section
               15 of the Act, and each officer and director of Lessor) 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 Lessor or such other person expressly for
               use in the preparation thereof, (B) the failure of Lessor 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 Lessor prior to the pertinent sale or sales by
               Lessor. 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 Lessor.

          5.2  Lessor 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 Lessor 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 or on behalf of Lessor specifically for use
               in preparation of the Registration Statement; provided, however,
               that Lessor 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 Lessor 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 Lessor 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 defend 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 one 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.

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

     6.   REPRESENTATIONS AND COVENANTS OF GERON.

          Geron hereby represents, warrants and covenants to Lessor as follows:

          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 part 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 the valid and legally
               binding obligations of Geron, enforceable against Geron in
               accordance with its 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

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               relating to the availability of specific performance, injunctive
               relief or other equitable remedies. The execution and performance
               by Geron of its obligations under this Agreement does not
               conflict with (a) the charter or bylaws of Geron or (b) any law,
               rule or regulation applicable to Geron which would have a
               material adverse effect on Geron's performance of its obligations
               hereunder, or to the best of Geron's knowledge as of the
               Effective Date, does not cause a material breach under or default
               of any material contract or agreement to which Geron is a party
               or by which any of its material properties or assets are bound.

          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 the
               transactions contemplated hereby, nor is Geron aware of any basis
               for any of the forgoing. Geron is neither a party to 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.

          6.5  Securities Compliance. To the best of its knowledge as of the
               Effective Date of this Agreement, Geron is in material compliance
               with all applicable requirements of the Act, and the rules of the
               Nasdaq National Market, and has made all filings required to be
               made by it with the Commission.

     7.   REPRESENTATIONS AND ACKNOWLEDGMENTS OF LESSOR.

          Lessor hereby represents, warrants, acknowledges and agrees that:

          7.1  Investment. Lessor is acquiring the Shares for Lessor's own
               account, and not directly or indirectly for the account of any
               other person. Lessor 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. Lessor has consulted with its own
               attorney, accountant, or investment advisor as Lessor has deemed
               advisable with respect to the investment and has determined its
               suitability for Lessor. Lessor 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. Lessor has had access to such financial and other
               information as is necessary in order for Lessor 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 Lessor has had access.
               Lessor acknowledges that neither Geron nor any of its officers,
               directors, employees, agents, representatives, or advisors has
               made any representation or warranty other than those specifically
               expressed herein.

          7.3  Business and Financial Expertise. Lessor 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.

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          7.4     Speculative Investment. Lessor 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 Lessor's risk capital means and is not so great in
                  relation to Lessor's total financial resources as would
                  jeopardize the personal financial needs of Lessor in the event
                  such investment were lost in whole or in part.

          7.5  Unregistered Securities. Lessor acknowledges that:

               7.5.1 Lessor 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.

               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
                    except as provided in Section 4 above. Geron has made no
                    representations, warranties or covenants whatsoever as to
                    whether any exemption from any such act will become
                    available.

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

     8.   TAX ADVICE. Lessor acknowledges that Lessor 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. Lessor 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, demand 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 Lessor at:      Exponent, Inc.
                                     149 Commonwealth Drive
                                     Menlo Park, CA 94025
                                     Attention: Richard L. Schlenker
                                     Telephone:
                                               --------------------------
                                     Facsimile:
                                               --------------------------

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

     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 Lease Agreement, 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

                                        Lessor

                                        /s/ Richard L. Schlenker
                                        ----------------------------------------
                                        By:     Richard L. Schlenker
                                        Title:  Chief Financial Officer and
                                                Corporate Secretary

                                       8EXHIBIT 4.2

                         COMMON STOCK PURCHASE AGREEMENT

     THIS COMMON STOCK PURCHASE AGREEMENT ("Agreement") is made and entered into
as of May 10, 2007 (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 Lonza Walkersville, Inc., a
Delaware corporation having its principal place of business at 8830 Biggs Ford
Road, Walkersville, Maryland 21793 ("Lonza"). Capitalized terms not otherwise
defined herein shall have the meaning set forth in the MSA and Project Order No.
1.

          A.   Geron and Cambrex Bio Science Walkersville, Inc. ("CBSW") entered
               that certain Master Services Agreement, dated as of September 1,
               2005 (the "MSA"), pursuant to which CBSW agreed to perform
               certain services on behalf of Geron related to the manufacture of
               a product containing human cells intended for therapeutic use in
               humans on the terms set forth therein.

          B.   Geron and CBSW entered into Project Order No. 1 to the MSA (the
               "Project Order No. 1") effective September 1, 2005, pursuant to
               which Geron is entitled, subject to certain conditions, to pay
               any compensation owed to CBSW for Services performed under
               Project Order No. 1 either in cash or in Geron's common stock
               (the "Common Stock").

          C.   Subject to the terms and conditions of the Second Amendment to
               Project Order No.1, dated as of March 1, 2006 ("Amendment No.
               2"), Geron and CBSW agreed that Geron shall, subject to certain
               conditions, be entitled to pay up to US$4,500,000 for Services
               under Project Order No. 1 by delivery of Shares.

          D.   Effective February 6, 2007, Lonza completed its acquisition of
               CBSW, and assumed all rights and obligations of CBSW under the
               MSA and Project Order No. 1, as amended.

THE PARTIES AGREE AS FOLLOWS:

     1.   ISSUANCE OF SHARES; ADJUSTMENTS.

          1.1  As payment of the fourth Installment Payment specified in Project
               Order No. 1, Geron will issue and deliver certificates for
               200,803 shares of Common Stock (the "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 of
               this Agreement (the "Closing Date"). At the Closing, Geron shall
               deliver to Lonza one or more certificates representing all of the
               Shares, which Shares shall be issued in the name of Lonza or its
               designee and in such denominations as Lonza shall specify.

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

               2.2.1 the covenants and obligations that Lonza 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

                                       1
<PAGE>

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

          2.3  Lonza'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
               Lonza:

               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 Lonza; and

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

     3.   RESTRICTIONS ON RESALE OF SHARES.

          3.1  Legends. Lonza 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 Lonza 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 BY AND BETWEEN GERON AND
               LONZA, DATED MAY 10, 2007. A COPY OF THE AGREEMENT CAN BE
               OBTAINED FROM THE SECRETARY OF GERON."

          3.2  Limits on Sales. Lonza agrees that if it decides to resell some
               or all of the Shares, it will do so only in an appropriate manner
               through orderly sales executed through a top-tier brokerage firm,
               and based upon whether the shares are registered or unregistered,
               i.e., on the Nasdaq National Market or in a Rule 144A compliant
               transaction.

          3.3  Further Limitations. Geron shall not be required (i) to transfer
               on its books any Shares that have been sold or otherwise
               transferred in violation of any of the provisions of this
               Agreement or applicable securities laws; or (ii) to treat as
               owner of such Shares or to accord the right to vote or pay
               dividends to any purchaser or other transferee to whom such
               Shares shall have been so transferred in violation of any of the
               provisions of this Agreement or applicable securities laws.

     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 Lonza.
               Geron agrees to diligently pursue making the Registration
               Statement effective. Geron will make commercially reasonable
               efforts to notify Lonza of the effectiveness of the Registration
               Statement within one (1) business day of receiving notice from
               the Commission declaring the Registration Statement effective,
               but no later than the close of business (Pacific Time) of the
               second business day after receipt of such notice from the
               Commission.

                                       2
<PAGE>

          4.2  Geron shall notify Lonza as promptly as possible of any review
               initiated by the Commission with respect to any such Registration
               Statement.

          4.3  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
               Lonza receives an opinion of counsel to Geron, which counsel
               shall be reasonably acceptable to Lonza, that the Shares may be
               sold under the provisions of Rule 144, (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 pursuant to Rule 144(k) or any
               similar provision then in effect under the Act in the opinion of
               counsel to Geron, which counsel shall be reasonably acceptable to
               Lonza.

          4.4  Geron, at its expense, shall furnish to Lonza 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 Lonza may
               reasonably request, in order to facilitate the public sale or
               other disposition of all or any of the Shares by Lonza, provided,
               however, that the obligation of Geron to deliver copies of
               prospectuses or preliminary prospectuses to Lonza shall be
               subject to the receipt by Geron of reasonable assurances from
               Lonza that Lonza 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.

          4.5  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. Lonza shall bear the cost of all fees and expenses of
               Lonza's counsel.

          4.6  Geron will advise Lonza 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 as promptly as possible if such stop order should
               be issued.

          4.7  With a view to making available to Lonza the benefits of Rule 144
               (or its successor rule) and any other rule or regulation of the
               Commission that may at the time permit Lonza 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(k) 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.

                                       3
<PAGE>

          4.8  Lonza 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 Lonza 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 Lonza to consent to be
               named as an underwriter in any Registration Statement.

     5.   INDEMNIFICATION.

          5.1  Geron agrees to indemnify and hold harmless Lonza (and each
               person, if any, who controls Lonza within the meaning of Section
               15 of the Act, and each officer and director of Lonza) 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 arises out of or is based upon (A) 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 Lonza or such other person expressly for
               use in the preparation thereof, (B) the failure of Lonza 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 Lonza prior to the pertinent sale or sales by
               Lonza. 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 Lonza.

          5.2  Lonza 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 officer and 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 Lonza
               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 or on behalf of Lonza specifically for use
               in preparation of the Registration Statement; provided, however,
               that Lonza 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 Lonza 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 Lonza 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.

                                       4
<PAGE>

          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 defend 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 one 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 a party, 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 Lonza 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. Geron has full right, power, authority and
               capacity to enter into this Agreement and to consummate the
               transactions contemplated hereby and thereby and has taken all
               necessary action to authorize the execution, delivery and
               performance of this Agreement. Upon execution and delivery, this
               Agreement will constitute a valid and binding obligation of Geron
               enforceable against Geron in accordance with its terms, except as
               such enforceability may be limited by applicable bankruptcy,
               insolvency, reorganization, moratorium, fraudulent transfer,
               liquidation or similar laws relating to, or affecting generally,
               the enforcement of creditor's rights and remedies or by other
               equitable principles of general application from time to time in
               effect.

                                       5
<PAGE>

          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 the
               transactions contemplated hereby, nor is Geron aware of any basis
               for any of the foregoing. 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 LONZA.

          Lonza hereby represents, warrants, acknowledges and agrees that:

          7.1  Investment. Lonza is acquiring the Shares for Lonza's own
               account, and not directly or indirectly for the account of any
               other person. Lonza 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. Lonza has consulted with its own attorney,
               accountant, or investment advisor as Lonza has deemed advisable
               with respect to the investment and has determined its suitability
               for Lonza. Lonza 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. Lonza has
               had access to such financial and other information as is
               necessary in order for Lonza 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 Lonza has had access. Lonza 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. Lonza 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. Lonza 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 Lonza's risk
               capital means and is not so great in relation to Lonza's total
               financial resources as would jeopardize the personal financial
               needs of Lonza in the event such investment were lost in whole or
               in part.

          7.5  Unregistered Securities. Lonza acknowledges that:

               7.5.1 Lonza 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

                                       6
<PAGE>

                    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.

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

          7.6  Authorization. Lonza has full right, power, authority and
               capacity to enter into this Agreement and to consummate the
               transactions contemplated hereby and thereby and has taken all
               necessary action to authorize the execution, delivery and
               performance of this Agreement. Upon execution and delivery, this
               Agreement will constitute a valid and binding obligation of Lonza
               enforceable against Lonza in accordance with its terms, except as
               such enforceability may be limited by applicable bankruptcy,
               insolvency, reorganization, moratorium, fraudulent transfer,
               liquidation or similar laws relating to, or affecting generally,
               the enforcement of creditor's rights and remedies or by other
               equitable principles of general application from time to time in
               effect.

     8.   TAX ADVICE. Lonza acknowledges that Lonza 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. Lonza 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: Chief Financial Officer
                                     Telephone:        (650) 473-7700
                                     Facsimile:        (650) 473-7750

                  With a copy to:    Geron Corporation
                                     230 Constitution Drive
                                     Menlo Park, California  94025
                                     Attention: Senior Director, Legal
                                     Telephone:        (650) 473-7775
                                     Facsimile:        (650) 566-7181

                                       7
<PAGE>

                  To Lonza at:       Lonza Walkersville, Inc.
                                     8830 Biggs Ford Road
                                     Walkersville, Maryland 21793
                                     Attention:  Tim Harrigan
                                     Telephone:        (301) 898-7025
                                     Facsimile:        (301) 845-6099

     10.  BINDING EFFECT. This Agreement shall be binding upon the heirs, legal
          representatives and successors of Geron and of Lonza.

     11.  GOVERNING LAW. This Agreement shall be governed by and construed in
          accordance with the laws of the State of Delaware, without giving
          effect to its conflicts of laws provisions.

     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.

     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 MSA, and Project Order No. 1
          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.

                      REST OF PAGE INTENTIONALLY LEFT BLANK

                                       8
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of
the Effective Date.

                                        Geron Corporation

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

                                        LonzaWalkersville, Inc.

                                        /s/ Shawn P. Cavanagh
                                        ----------------------------------------
                                        By:     Shawn P. Cavanagh
                                        Title:  President

                                        LonzaWalkersville, Inc.

                                        /s/ Vinny DeVito
                                        ----------------------------------------
                                        By:     Vinny DeVito
                                        Title:  Chief Financial Officer

                                       9

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