EX-10.3





 Exhibit 10.3 

Lock-Up Agreement 

February [    ], 2020 

Ladies and Gentlemen: 

The undersigned (the “Stockholder”) understands that: (i) TOCAGEN
INC., a Delaware corporation (“Parent”), has entered into an Agreement and Plan of Merger and Reorganization, dated as of February 19, 2020 (the “Merger Agreement”), with
FORTE BIOSCIENCES, INC., a Delaware corporation (the “Company”) and TELLURIDE MERGER SUB, INC., a Delaware
corporation and wholly-owned subsidiary of Parent (“Merger Sub”), pursuant to which Merger Sub will be merged with and into the Company (the “Merger”) and the separate corporate existence of Merger Sub
will cease and the Company will continue as the surviving corporation; and (ii) in connection with the Merger, stockholders of the Company will receive shares of Parent Common Stock. Capitalized terms used but not otherwise defined herein shall
have the respective meanings ascribed to such terms in the Merger Agreement. 
 As a material inducement to the willingness
of each of the Parties to enter into the Merger Agreement, and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the Stockholder hereby agrees that the Stockholder will not, subject to the
exceptions set forth in this letter agreement, during the period commencing upon the Effective Time and ending on the date that is 180 days after the Closing Date (the “Restricted Period”), (a) offer, pledge, sell, contract
to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, or otherwise transfer or dispose of, directly or indirectly, any shares of Parent Common Stock or any
securities convertible into or exercisable or exchangeable for Parent Common Stock, including without limitation, Parent Common Stock or such other securities which may be deemed to be beneficially owned by the Stockholder in accordance with the
rules and regulations of the SEC and securities of Parent which may be issued upon exercise of a stock option or warrant (collectively, the “Stockholder’s Shares”), (b) enter into any swap or other agreement that
transfers, in whole or in part, any of the economic consequences of ownership of the Stockholder’s Shares, regardless of whether any such transaction described in clause (a) or (b) above is to be settled by delivery of Parent Common Stock
or such other securities, in cash or otherwise or (c) make any demand for or exercise any right with respect to the registration of any shares of Parent Common Stock or any security convertible into or exercisable or exchangeable for Parent
Common Stock, in each case other than (i) transfers of the Stockholder’s Shares as charitable gifts or donations, (ii) transfers or dispositions of the Stockholder’s Shares to any trust for the direct or indirect benefit of the
Stockholder or the immediate family of the Stockholder, (iii) transfers or dispositions of the Stockholder’s Shares by will, other testamentary document or intestate succession to the legal representative, heir, beneficiary or a member of
the immediate family of the Stockholder, (iv) transfers of the Stockholder’s Shares to stockholders, direct or indirect affiliates (within the meaning set forth in Rule 405 under the Securities Act), current or former partners (general or
limited), members or managers of the Stockholder, as applicable, or to the estates of any such stockholders, affiliates, partners, members or managers, or to another corporation, partnership, limited liability company or other business entity that
controls, is controlled by or is under common control with the Stockholder, (v) transfers that occur by operation of law pursuant to a qualified domestic relations order or in connection with a divorce settlement, (vi) transfers or
dispositions not involving a change in beneficial ownership, and (vii) if the Stockholder is a trust, transfers or dispositions to any beneficiary of the Stockholder or the estate of any such beneficiary; provided that, in each
case, the transferee agrees in writing to be bound by the terms and conditions of this letter agreement and either the Stockholder or the transferee provides Parent with a copy of such agreement promptly upon consummation of any such transfer; and
provided, further, that in each case, no filing by any party (donor, donee, transferor or transferee) under the Exchange Act or other public announcement shall be required or


  
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shall be made voluntarily in connection with such transfer or distribution (other than filings made in respect of involuntary transfers or dispositions or a filing on a Form 5 made after the
expiration of the Restricted Period) and any such transfer or distribution shall not involve a disposition for value. For purposes of this letter agreement, “immediate family” shall mean any relationship by blood, marriage or adoption, not
more remote than first cousin. 
 Notwithstanding the restrictions imposed by this letter agreement, the Stockholder may
(a) exercise an option or warrant (including a net or cashless exercise of such option or warrant) to purchase shares of Parent Common Stock, (b) transfer shares of Parent Common Stock to cover tax withholding obligations of the
Stockholder in connection with any option exercise or the vesting of any restricted stock or restricted stock unit award, (c) establish a trading plan pursuant to Rule 10b5-1 under the Exchange Act for
the transfer of Parent Common Stock, provided that such plan does not provide for any transfers of Parent Common Stock during the Restricted Period, or (d) transfer or dispose of shares of Parent Common Stock acquired on the open
market following the Closing Date, provided that, no filing under the Exchange Act or other public announcement shall be required or shall be made voluntarily in connection with the establishment of such a plan, provided
that reasonable notice shall be provided to Parent prior to any such filing, and provided further that, for the avoidance of doubt, the underlying shares of Parent Common Stock shall continue to be subject to the
restrictions on transfer set forth in this letter agreement. 
 Any attempted transfer in violation of this letter agreement
will be of no effect and null and void, regardless of whether the purported transferee has any actual or constructive knowledge of the transfer restrictions set forth in this letter agreement, and will not be recorded on the stock transfer books of
Parent. In order to ensure compliance with the restrictions referred to herein, the Stockholder agrees that Parent may issue appropriate “stop transfer” certificates or instructions. Parent may cause the legend set forth below, or a legend
substantially equivalent thereto, to be placed upon any certificate(s) or other documents or instruments evidencing ownership of the Stockholder’s Shares: 

THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO AND MAY ONLY BE TRANSFERRED IN COMPLIANCE WITH A LOCK-UP AGREEMENT, A COPY OF WHICH IS ON FILE AT THE PRINCIPAL OFFICE OF THE COMPANY. 

The Stockholder hereby represents and warrants that the Stockholder has full power and authority to enter into this letter
agreement. All authority conferred or agreed to be conferred and any obligations of the Stockholder under this letter agreement will be binding upon the successors, assigns, heirs or personal representatives of the Stockholder. 

In the event that any holder of Parent’s securities that is subject to a substantially similar agreement entered into by
such holder, other than the Stockholder, is permitted by Parent to sell or otherwise transfer or dispose of shares of Parent Common Stock for value other than as permitted by this or a substantially similar agreement entered into by such holder, the
same percentage of shares of Parent Common Stock held by the Stockholder shall be immediately and fully released on the same terms from any remaining restrictions set forth herein (the “Pro-Rata
Release”); provided, however, that such Pro-Rata Release shall not be applied unless and until permission has been granted by Parent to an equity holder or equity
holders to sell or otherwise transfer or dispose of all or a portion of such equity holders’ shares of Parent Common Stock in an aggregate amount in excess of 1% of the number of shares of Parent Common Stock originally subject to a
substantially similar agreement. 
 Upon the release of any of the Stockholder’s Shares from this letter agreement,
Parent will cooperate with the Stockholder to facilitate the timely preparation and delivery of certificates representing the Stockholder’s Shares without the restrictive legend above or the withdrawal of any stop transfer instructions. 

  
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 The Stockholder understands that each of Parent and the Company is relying
upon this letter agreement in proceeding toward consummation of the Merger. The Stockholder further understands that this letter agreement is irrevocable and is binding upon the Stockholder’s heirs, legal representatives, successors and
assigns. 
 This letter agreement and any claim, controversy or dispute arising under or related to this letter agreement
shall be governed by and construed in accordance with the laws of the State of Washington, without regard to the conflict of laws principles thereof. 

The Stockholder understands that if the Merger Agreement is terminated in accordance with its terms, the Stockholder will be
released from all obligations under this letter agreement. 
 This letter agreement may be executed by electronic (i.e.,
PDF) transmission, which is deemed an original. 
 [Signature Page Follows] 

  
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		 	 Very truly yours,

		
	 Print Name of
Stockholder:        
	 	  

		
		 	 Signature (for individuals):

 

		
		 	 Signature (for entities):

 

			
		 	 By:
	 	  

			
		 		 	
Name:                      
                                         
       

			
		 		 	
Title:                      
                                         
         



 [SIGNATURE PAGE TO LOCK-UP
AGREEMENT]