EXHIBIT 10.21 

AMENDMENT
TO EMPLOYMENT
AGREEMENT

     This
Amendment to Employment Agreement (the “Amendment”) is entered into as of
December 19, 2008 (the “Effective Date”), between Thomas Okarma (“Employee”) and
Geron Corporation (the “Company”).

RECITALS 

     WHEREAS,
on January 21, 2003, Employee and the Company entered into an Employment
Agreement (the “Agreement”) which sets forth the terms of Employee’s employment
with the Company and provides for benefits upon the occurrence of certain
terminations of employment; and 

     WHEREAS,
the parties wish to amend certain provisions of the Agreement to reflect recent
changes affecting the taxation of deferred compensation arrangements under
Section 409A of the Internal Revenue Code of 1986, as amended (the “Code”),
pursuant to the terms and conditions set forth below. 

AGREEMENT 

     NOW
THEREFORE, in consideration of the foregoing and the mutual agreements contained
herein, the parties hereby agree as follows effective as of the Effective Date.
Except as otherwise defined herein, capitalized terms shall have the meanings
assigned to them in the Agreement. 

     1. Section 1.5 of the Agreement shall be
amended in its entirety to read as follows: 

     ““COVERED TERMINATION” means an
Involuntary Termination Without Cause that occurs at any time, provided that
such termination constitutes a “separation from service” within the meaning of
Section 409A of the Code and the regulations promulgated thereunder, including
Treasury Regulation Section 1.409A-1(h) (a “Separation from Service”).”


     2. Section 4.1 of the Agreement shall be
amended in its entirety to read as follows: 

     “SEVERANCE BENEFITS. If Employee’s
employment terminates due to a Covered Termination after the date of execution
of this Agreement, Employee shall receive: 

	     	
      (i) any annual base salary and
      bonus compensation that has accrued but is unpaid as of the date of such
      Covered Termination;

      (ii) on the date sixty (60) days
      following the date on which the Covered Termination occurred, a lump sum
      payment equal to One Hundred Fifty percent (150%) of Employee's annual
      base salary as in effect during the last regularly scheduled payroll
      period immediately preceding the Covered Termination.
  



Notwithstanding the foregoing, the
amounts payable under this Article IV shall be reduced by the amount of
severance or other cash compensation, if any, payable under the Company’s Change
of Control Severance Plan. All of the amounts payable under this Agreement shall
be subject to applicable tax withholding.




In addition, Employee and Employee’s
covered dependents will be eligible to continue their health care benefit
coverage as permitted by COBRA (Internal Revenue Code Section 4980B) at the same
cost to Employee as in effect immediately prior to the Covered Termination for
the one (l)-year period following the Covered Termination, and be entitled to
maintain coverage for Employee and Employee's eligible dependents at Employee's
own expense for the balance of the period that Employee is entitled to coverage
under COBRA.”

    
3. The first sentence of Section 4.3 of the Agreement shall be amended in
its entirety to read as follows: 

    
“Within fifty (50) days following the occurrence of a Covered
Termination, and prior to the receipt of any benefits under Section 4.1 (except
pursuant to clause (i) thereof) and Section 4.2 on account of the occurrence of
such Covered Termination, Employee shall execute a Release (the “Release”) in
substantially the form of Exhibit A (as such form may be modified to take into
account changes in the law).”

    
4. The following shall be added as Section 4.4 of the Agreement:


    
“Notwithstanding any provision to the contrary in this Agreement, if
Employee is deemed by the Company at the time of the Separation from Service to
be a “specified employee” for purposes of Section 409A(a)(2)(B)(i) of the Code,
to the extent delayed commencement of any portion of the benefits to which
Employee is entitled under this Agreement is required in order to avoid a
prohibited distribution under Section 409A(a)(2)(B)(i) of the Code, such portion
of Employee’s benefits shall not be provided to Employee prior to the earlier of
(a) the expiration of the six-month period measured from the date of Employee’s
Separation from Service or (b) the date of Employee’s death. Upon the first
business day following the expiration of the applicable Code Section
409A(a)(2)(B)(i) period, all payments deferred pursuant to this Section 4.4
shall be paid in a lump sum to Employee (or Employee’s estate or beneficiaries),
and any remaining payments due under the Agreement shall be paid as otherwise
provided herein. For purposes of Section 409A of the Code, Employee’s right to
receive the payments of compensation pursuant to the Agreement shall be treated
as a right to receive a series of separate payments and accordingly, each
payment shall at all times be considered a separate and distinct payment.”


    
5. Except as set forth herein, all other terms and conditions of the
Agreement shall remain in full force and effect.

    
6. This Amendment shall be governed by the law of the State of California
as such laws are applied to agreements between California residents entered into
and to be performed entirely within the State of California. 

2 




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

		EMPLOYEE  	
			 	
		/s/ Thomas Okarma  	
		Thomas Okarma  	
			 	
			 	
		GERON
      CORPORATION  	
			 	
		By:  	/s/ David L. Greenwood  	 
			 	
		Its:  	EVP  	



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