Document:

Exhibit 10.1
    

    
      UNIT PURCHASE AGREEMENT
    

    
      THIS UNIT PURCHASE AGREEMENT (“Agreement”) is made
      effective as of the 14th day of April, 2009, by and among
      Opexa Therapeutics, Inc., a Texas corporation (the “Company”),
      and each of the persons executing a copy of this Agreement (each an “Investor”
      and, collectively, the “Investors”).
    

    
      Recitals
    

    
      A.  WHEREAS, the Investors wish to purchase from the
      Company, and the Company wishes to sell and issue to the Investors, upon
      the terms and conditions stated in this Agreement, up to Two Hundred
      (200) investment units (the “Units”) each composed
      of (i) a $10,000 secured promissory note in the form attached hereto as Exhibit
      A (individually, a “Note” and, collectively,
      the “Notes”)  and (ii) a warrant to purchase the
      number shares of the Company’s Common Stock, par value $0.50 per share
      (the “Common Stock”), equal to 5,000 divided by the
      greater of (i) $0.50 or (ii) the NASDAQ Official Closing Price of the
      Common Stock on April 14, 2009 plus $0.0625 in the form attached hereto
      as Exhibit B (individually, a “Series G Warrant”
      and, collectively, the “Series G Warrants”);
    

    
      WHEREAS, contemporaneous with the execution of this Agreement,
      the parties hereto will execute and deliver a Registration Rights
      Agreement, in the form attached hereto as Exhibit C (the “Registration
      Rights Agreement”), pursuant to which the Company will agree to
      provide certain registration rights under the Securities Act of 1933, as
      amended, and the rules and regulations promulgated thereunder, and
      applicable state securities laws; and
    

    
      WHEREAS, contemporaneous with the execution of this Agreement,
      the parties hereto will execute and deliver a Security Agreement, in the
      form attached hereto as Exhibit D (the “Security
      Agreement”), pursuant to which the Company will issue a security
      interest in substantially all of the Company’s assets in favor of the
      Investors.
    

    
      NOW, THEREFORE, in consideration of the mutual promises made
      herein and for other good and valuable consideration, the receipt and
      sufficiency of which are hereby acknowledged, the parties hereto agree
      as follows:
    

    
          1.  Definitions.  In addition
      to those terms defined above and elsewhere in this Agreement, for the
      purposes of this Agreement, the following terms shall have the meanings
      set forth below:
    

    
      “SEC Filings” has the meaning set forth in Section
      4.6.
    

    
      “1933 Act” means the Securities Act of 1933, as
      amended, or any successor statute, and the rules and regulations
      promulgated thereunder.
    

    
      “1934 Act” means the Securities Exchange Act of
      1934, as amended, or any successor statute, and the rules and
      regulations promulgated thereunder.
    

    
      
        

        

      

      
        

        

        
          

        

      

      
        

        

      

    

    
      “Affiliate” means, with respect to any Person, any
      other Person which directly or indirectly through one or more
      intermediaries Controls, is controlled by, or is under common control
      with, such Person.
    

    
      “Business Day” means a day, other than a Saturday or
      Sunday, on which banks in New York City are open for the general
      transaction of business.
    

    
      “Cambria” means Cambria Capital, LLC.
    

    
      “Cambria Notes” means those Notes which are issued
      as part of the Cambria Units.
    

    
      “Cambria Units” means those Units purchased by those
      Investors whom Cambria solicited for the purpose of entering into this
      Agreement.
    

    
      “Cambria Warrant Shares” means the Warrant Shares
      issuable upon the exercise of those Series G Warrants which are issued
      as part of the Cambria Units.
    

    
      “Closing” has the meaning set forth in Section 3.
    

    
      “Closing Date” means the date of the Closing.  In
      the event there is more than one Closing, the term “Closing
      Date” shall mean, with respect to each Investor, the date of the
      Closing set forth next to the signature of each Investor.
    

    
      “Common Stock” means the Company’s Common Stock.
    

    
      “Company’s Knowledge” means the actual
      knowledge of the executive officers (as defined in Rule 405 under the
      1933 Act) of the Company, after due inquiry.
    

    
      “Confidential Information” means trade secrets,
      confidential information and know-how (including but not limited to
      ideas, formulae, compositions, processes, procedures and techniques,
      research and development information, computer program code, performance
      specifications, support documentation, drawings, specifications,
      designs, business and marketing plans, and customer and supplier lists
      and related information).
    

    
      “Control” (including the terms “controlling”,
      “controlled by” or “under common control with”) means the possession,
      direct or indirect, of the power to direct or cause the direction of the
      management and policies of a Person, whether through the ownership of
      voting securities, by contract or otherwise.
    

    
      “Effective Date” means the date on which the initial
      Registration Statement is declared effective by the SEC.
    

    
      “Effectiveness Deadline” means the date on which the
      initial Registration Statement is required to be declared effective by
      the SEC under the terms of the Registration Rights Agreement.
    

    
      “Evaluation Date” has the meaning set forth in
      Section 4.14.
    

    
      
        

        

      

      
        
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      “GAAP” has the meaning set forth in Section 4.13.
    

    
      “Initial Closing Date” means the date of the first
      Closing.
    

    
      “Investor” has the meaning set forth in the Preamble.
    

    
      “Material Adverse Effect” means a material adverse
      effect on (i) the assets, liabilities, results of operations, condition
      (financial or otherwise), business, or prospects of the Company, taken
      as a whole, or (ii) the ability of the Company to perform its
      obligations under the Transaction Documents.
    

    
      “Notes” has the meaning set forth in the recitals.
    

    
      “Person” means an individual, corporation,
      partnership, limited liability company, trust, business trust,
      association, joint stock company, joint venture, sole proprietorship,
      unincorporated organization, governmental authority or any other form of
      entity not specifically listed herein.
    

    
      “Prohibited Transaction” has the meaning set forth
      in Section 5.11.
    

    
      “Purchase Price” means $10,000 for each Unit.
    

    
      “Registration Rights Agreement” has the meaning set
      forth in the recitals.
    

    
      “Registration Statement” has the meaning set forth
      in the Registration Rights Agreement.
    

    
      “SEC” means the Securities and Exchange Commission.
    

    
      “SEC Filings” has the meaning set forth in Section
      4.6.
    

    
      “Securities” means the Notes, the Series G Warrants
      and the Warrant Shares.
    

    
      “Security Agreement” has the meaning set forth in
      the Recitals.
    

    
      “Subsidiary” of any Person means another Person, an
      amount of the voting securities, other voting ownership or voting
      partnership interests of which is sufficient to elect at least a
      majority of its Board of Directors or other governing body (or, if there
      are no such voting interests, 50% or more of the equity interests of
      which) is owned directly or indirectly by such first Person.
    

    
      “Trading Affiliates” has the meaning set forth in
      Section 5.11.
    

    
      “Transaction Documents” means this Agreement, the
      Notes, the Series G Warrants, the Registration Rights Agreement and the
      Security Agreement.
    

    
      “Transfer Agent” has the meaning set forth in
      Section 7.7.
    

    
      “Unit” has the meaning set forth in the recitals.
    

    
      
        

        

      

      
        
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      “Warrants” has the meaning set forth in the recitals.
    

    
      “Warrant Exercise Price” means, with respect to each
      investor, 1.5 times the greater of (i) $0.50 or (ii) the closing bid
      price for a share of Common Stock as quoted on the NASDAQ Stock Market
      on the date of each Closing for such Investor plus $0.0625.
    

    
      “Warrant Shares” means the shares of Common Stock
      issuable upon the exercise of the Series G Warrants.
    

    
          2.  Purchase and Issuance of the
      Units.  Subject to the terms and conditions of this Agreement, each
      of the Investors shall severally, and not jointly, purchase, and the
      Company shall sell and issue to the Investors, the number of Units set
      forth opposite the Investors’ names on the signature pages attached
      hereto in exchange for the Purchase Price.
    

    
          3.  Closing.
    

    
            3.1.   Upon the satisfaction or waiver of the conditions herein,
      the initial purchase and sale of the Units shall take place remotely via
      the exchange of documents and signatures, on or before April 14, 2009,
      or at such other time and place as the Company and the Investors
      mutually agree upon, orally or in writing (which time and place are
      designated as the “Closing”).  In the event there is
      more than one closing, the term “Closing” shall mean
      the initial Closing and each such subsequent closing unless otherwise
      specified.
    

    
            3.2.  At each Closing, the Company shall deliver, or cause to be
      delivered, to each Investor (i) a secured promissory note, representing
      the Notes in the Units purchased by such Investor and (ii) a Series G
      Warrant representing the Series G Warrants in the Units purchased by
      such Investor, against delivery to the Company by the Investor of
      payment therefor in immediately available funds by wire transfer to an
      account designated by the Company. The Company shall also deliver such
      other documents as are called for herein.
    

    
            3.3.  After the initial Closing, the Company may sell, on the same
      terms and conditions as those contained in this Agreement but for the
      same price as in the initial Closing, additional Units so that as a
      result of all sales hereunder the Company receives gross proceeds of no
      more than Two Million Dollars ($2,000,000); provided that any such
      subsequent sale is consummated on or before thirty (30) days after
      Closing or, at the sole discretion of the Company, sixty (60) days after
      Closing and (ii) each additional Investor shall become a party to the
      Transaction Agreements by executing and delivering a counterpart
      signature page to each of the Transaction Agreements
    

    
          4.  Representations and Warranties
      of the Company.  The Company hereby represents and warrants to the
      Investors that as of the initial Closing Date, except as set forth in
      the schedules delivered herewith (collectively, the “Disclosure
      Schedules”):
    

    
            4.1.  Organization,
      Good Standing and Qualification.  The Company is a corporation duly
      organized, validly existing and in good standing under the laws of the
      jurisdiction of its incorporation and has all requisite corporate power
      and authority to carry on its business as now conducted and to own its
      properties.  The Company is duly qualified to do business as a foreign
      corporation and is in good standing in each jurisdiction in which the
      conduct of its business or its ownership or leasing of property makes
      such qualification or leasing necessary unless the failure to so qualify
      has not had and could not reasonably be expected to have a Material
      Adverse Effect.  The Company does not have any Subsidiaries.
    

    
      
        

        

      

      
        
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            4.2.  Authorization.  The
      Company has full power and authority and has taken all requisite action
      on the part of the Company, its officers, directors and stockholders
      necessary for (i) the authorization, execution and delivery of the
      Transaction Documents, (ii) the authorization of the performance of all
      obligations of the Company hereunder or thereunder, and (iii) the
      authorization, issuance (or reservation for issuance) and delivery of
      the Securities.  The Transaction Documents constitute the legal, valid
      and binding obligations of the Company, enforceable against the Company
      in accordance with their terms, subject to bankruptcy, insolvency,
      fraudulent transfer, reorganization, moratorium and similar laws of
      general applicability, relating to or affecting creditors’ rights
      generally.
    

    
            4.3.  Capitalization.  Schedule
      4.3 sets forth (a) the authorized capital stock of the Company on
      the date hereof; (b) the number of shares of capital stock issued and
      outstanding; (c) the number of shares of capital stock issuable pursuant
      to the Company’s stock plans; and (d) the number of shares of capital
      stock issuable and reserved for issuance pursuant to securities (other
      than the Series G Warrants) exercisable for, or convertible into or
      exchangeable for any shares of capital stock of the Company.  All of the
      issued and outstanding shares of the Company’s capital stock have been
      duly authorized and validly issued and are fully paid, nonassessable and
      free of pre-emptive rights and were issued in full compliance with
      applicable state and federal securities law and any rights of third
      parties.  Except as described on Schedule 4.3, no
      Person is entitled to pre-emptive or similar statutory or contractual
      rights with respect to any securities of the Company.  Except as
      described on Schedule 4.3, there are no outstanding warrants,
      options, convertible securities or other rights, agreements or
      arrangements of any character under which the Company is or may be
      obligated to issue any equity securities of any kind and except as
      contemplated by this Agreement, the Company is not currently in
      negotiations for the issuance of any equity securities of any
      kind.  Except as described on Schedule 4.3 and except
      for the Registration Rights Agreement, there are no voting agreements,
      buy-sell agreements, option or right of first purchase agreements or
      other agreements of any kind among the Company and any of the
      securityholders of the Company relating to the securities of the Company
      held by them.  Except as described on Schedule 4.3 and
      except as provided in the Registration Rights Agreement, no Person has
      the right to require the Company to register any securities of the
      Company under the 1933 Act, whether on a demand basis or in connection
      with the registration of securities of the Company for its own account
      or for the account of any other Person.
    

    
      Except as described on Schedule 4.3, the issuance and sale of the
      Securities hereunder will not obligate the Company to issue shares of
      Common Stock or other securities to any other Person (other than the
      Investors) and will not result in the adjustment of the exercise,
      conversion, exchange or reset price of any outstanding security.
    

    
      Except as described on Schedule 4.3, the Company does not have
      outstanding stockholder purchase rights or “poison pill” or any similar
      arrangement in effect giving any Person the right to purchase any equity
      interest in the Company upon the occurrence of certain events.
    

    
      
        

        

      

      
        
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            4.4.  Valid Issuance.  The
      Series G Warrants have been duly and validly authorized.  Upon the due
      exercise of the Series G Warrants, the Warrant Shares will be validly
      issued, fully paid and non-assessable free and clear of all encumbrances
      and restrictions, except for restrictions on transfer set forth in the
      Transaction Documents or imposed by applicable securities laws and
      except for those created by the Investors.  The Company has reserved a
      sufficient number of shares of Common Stock for issuance upon the
      exercise of the Series G Warrants, free and clear of all encumbrances
      and restrictions, except for restrictions on transfer set forth in the
      Transaction Documents or imposed by applicable securities laws and
      except for those created by the Investors.
    

    
            4.5.  Consents.  The
      execution, delivery and performance by the Company of the Transaction
      Documents and the offer, issuance and sale of the Securities require no
      consent of, action by or in respect of, or filing with, any Person,
      governmental body, agency, or official other than filings that have been
      made pursuant to applicable state securities laws and post-sale filings
      pursuant to applicable state and federal securities laws which the
      Company undertakes to file within the applicable time periods.  Subject
      to the accuracy of the representations and warranties of each Investor
      set forth in Section 5 hereof, the Company has taken all action
      necessary to exempt (i) the issuance and sale of the Securities, (ii)
      the issuance of the Warrant Shares upon due exercise of the Series G
      Warrants, and (iii) the other transactions contemplated by the
      Transaction Documents from any provision of the Company’s Articles of
      Incorporation or Bylaws that is or could reasonably be expected to
      become applicable to the Investors as a result of the transactions
      contemplated hereby.
    

    
            4.6.  Delivery of SEC
      Filings; Business.  The Company has made available to the Investors
      through the EDGAR system, true and complete copies of the Company’s most
      recent Annual Report on Form 10-K for the fiscal year ended December 31,
      2007 and the Company’s Quarterly Reports on Form 10-Q for the fiscal
      quarters ended March 31, 2008, June 30, 2008 and September 30, 2008, and
      all other reports filed by the Company pursuant to the 1934 Act since
      the filing of the Company’s most recent Quarterly Report on Form 10-Q
      for the fiscal quarter ended September 30, 2008 and prior to the date
      hereof (collectively, the “SEC Filings”).  The SEC
      Filings are the only filings required of the Company pursuant to the
      1934 Act for such period.  The Company is engaged in all material
      respects only in the business described in the SEC Filings and the SEC
      Filings contain a complete and accurate description in all material
      respects of the business of the Company, taken as a whole.
    

    
            4.7.  Use of Proceeds.  The
      net proceeds of the issuance and sale of the Notes and the Series G
      Warrants hereunder shall be used by the Company for working capital and
      general corporate purposes.
    

    
            4.8.  SEC Filings.  At
      the time of filing thereof, the SEC Filings complied as to form in all
      material respects with the requirements of the 1934 Act and did not
      contain any untrue statement of a material fact or omit to state any
      material fact necessary in order to make the statements made therein, in
      the light of the circumstances under which they were made, not
      misleading.
    

    
      
        

        

      

      
        
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            4.9.  No Conflict,
      Breach, Violation or Default.  The execution, delivery and
      performance of the Transaction Documents by the Company and the issuance
      and sale of the Securities will not conflict with or result in a breach
      or violation of any of the terms and provisions of, or constitute a
      default under (i) the Company’s Articles of Incorporation or the
      Company’s Bylaws, both as in effect on the date hereof (true and
      complete copies of which have been made available to the Investors
      through the EDGAR system), or (ii) any statute, rule, regulation or
      order of any governmental agency or body or any court, domestic or
      foreign, having jurisdiction over the Company or any of its assets or
      properties, except in the case of this clause (i) for such breaches,
      violations or defaults which would not, individually or in the
      aggregate, have a Material Adverse Effect or (iii) any agreement or
      instrument to which the Company is a party or by which the Company is
      bound, except in the case of this clause (iii) for such breaches,
      violations or defaults which would not, individually or in the
      aggregate, have a Material Adverse Effect.
    

    
           4.10.  Tax Matters.  The
      Company has timely prepared and filed all tax returns required to have
      been filed by the Company with all appropriate governmental agencies and
      timely paid all taxes shown thereon or otherwise owed by it.  The
      charges, accruals and reserves on the books of the Company in respect of
      taxes for all fiscal periods are adequate in all material respects, and
      there are no material unpaid assessments against the Company nor, to the
      Company’s Knowledge, any basis for the assessment of any additional
      taxes, penalties or interest for any fiscal period or audits by any
      federal, state or local taxing authority except for any assessment which
      is not material to the Company, taken as a whole.  All taxes and other
      assessments and levies that the Company is required to withhold or to
      collect for payment have been duly withheld and collected and paid to
      the proper governmental entity or third party when due.  There are no
      tax liens or claims pending or, to the Company’s Knowledge, threatened
      against the Company or any of its assets or property.  There are no
      outstanding tax sharing agreements or other such arrangements between
      the Company and any other corporation or entity.
    

    
           4.11.  Title to Properties.  Except
      as disclosed in the SEC Filings, the Company has good and marketable
      title to all real properties and all other properties and assets owned
      by it, in each case free from liens, encumbrances and defects that would
      materially affect the value thereof or materially interfere with the use
      made or currently planned to be made thereof by them or as disclosed in
      the SEC Filings; and except as disclosed in the SEC Filings, the Company
      holds any leased real or personal property under valid and enforceable
      leases with no exceptions that would materially interfere with the use
      made or currently planned to be made thereof by them.
    

    
           4.12.  Financial Statements.  The
      financial statements included in each SEC Filing present fairly, in all
      material respects, the consolidated financial position of the Company as
      of the dates shown and its consolidated results of operations and cash
      flows for the periods shown, and such financial statements have been
      prepared in conformity with United States generally accepted accounting
      principles applied on a consistent basis (“GAAP”)
      (except as may be disclosed therein or in the notes thereto).  Except as
      set forth in the financial statements of the Company included in the SEC
      Filings filed prior to the date hereof or as described on Schedule
      4.18, the Company has not incurred any liabilities, contingent or
      otherwise, except those incurred in the ordinary course of business,
      consistent (as to amount and nature) with past practices since the date
      of such financial statements, none of which, individually or in the
      aggregate, have had or could reasonably be expected to have a Material
      Adverse Effect.
    

    
      
        

        

      

      
        
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           4.13.  No Directed Selling
      Efforts or General Solicitation.  Neither the Company nor any Person
      acting on its behalf has conducted any general solicitation or general
      advertising (as those terms are used in Regulation D) in connection with
      the offer or sale of any of the Securities.
    

    
           4.14.  No Integrated Offering.  Neither
      the Company nor any of its Affiliates, nor any Person acting on its or
      their behalf has, directly or indirectly, made any offers or sales of
      any Company security or solicited any offers to buy any security, under
      circumstances that would adversely affect reliance by the Company on
      Section 4(2) for the exemption from registration for the transactions
      contemplated hereby or would require registration of the Securities
      under the 1933 Act.
    

    
           4.15.  Private Placement.  The
      offer and sale of the Securities to the Investors as contemplated hereby
      is exempt from the registration requirements of the 1933 Act.
    

    
           4.16.  Internal Controls.  The
      Company is in material compliance with the provisions of the
      Sarbanes-Oxley Act of 2002 currently applicable to the Company.  The
      Company maintains a system of internal accounting controls sufficient to
      provide reasonable assurance that (i) transactions are executed in
      accordance with management's general or specific authorizations, (ii)
      transactions are recorded as necessary to permit preparation of
      financial statements in conformity with GAAP and to maintain asset
      accountability, (iii) access to assets is permitted only in accordance
      with management's general or specific authorization, and (iv) the
      recorded accountability for assets is compared with the existing assets
      at reasonable intervals and appropriate action is taken with respect to
      any differences. The Company has established disclosure controls and
      procedures (as defined in 1934 Act Rules 13a-14 and 15d-14) for the
      Company and designed such disclosure controls and procedures to ensure
      that material information relating to the Company is made known to the
      certifying officers by others within those entities, particularly during
      the period in which the Company’s most recently filed period report
      under the 1934 Act, as the case may be, is being prepared.  The
      Company's certifying officers have evaluated the effectiveness of the
      Company's controls and procedures as of the end of the period covered by
      the most recently filed periodic report under the 1934 Act (such date,
      the "Evaluation Date").  The Company presented in its
      most recently filed periodic report under the 1934 Act the conclusions
      of the certifying officers about the effectiveness of the disclosure
      controls and procedures based on their evaluations as of the Evaluation
      Date.  Since the Evaluation Date, there have been no significant changes
      in the Company's internal controls (as such term is defined in Item 308
      of Regulation S-K) or, to the Company's Knowledge, in other factors that
      could significantly affect the Company's internal controls.  The Company
      maintains and will continue to maintain a standard system of accounting
      established and administered in accordance with GAAP and the applicable
      requirements of the 1934 Act.
    

    
          5.  Representations and Warranties
      of the Investors.  Each of the Investors hereby severally, and not
      jointly, represents and warrants to the Company that:
    

    
            5.1.  Organization and
      Existence.  Such Investor is either an individual or a validly
      existing corporation, limited partnership or limited liability company
      and has all requisite corporate, partnership or limited liability
      company power and authority to invest in the Securities pursuant to this
      Agreement.
    

    
      
        

        

      

      
        
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            5.2.  Authorization.  The
      execution, delivery and performance by such Investor of the Transaction
      Documents to which such Investor is a party have been duly authorized
      and will each constitute the valid and legally binding obligation of
      such Investor, enforceable against such Investor in accordance with
      their respective terms, subject to bankruptcy, insolvency, fraudulent
      transfer, reorganization, moratorium and similar laws of general
      applicability, relating to or affecting creditors’ rights generally.
    

    
            5.3.  Purchase Entirely
      for Own Account.  The Securities to be received by such Investor
      hereunder will be acquired for such Investor’s own account, not as
      nominee or agent, and not with a view to the resale or distribution of
      any part thereof in violation of the 1933 Act, and such Investor has no
      present intention of selling, granting any participation in, or
      otherwise distributing the same in violation of the 1933 Act without
      prejudice, however, to such Investor’s right at all times to sell or
      otherwise dispose of all or any part of such Securities in compliance
      with applicable federal and state securities laws.  Nothing contained
      herein shall be deemed a representation or warranty by such Investor to
      hold the Securities for any period of time.  Such Investor is not a
      broker-dealer registered with the SEC under the 1934 Act or an entity
      engaged in a business that would require it to be so registered.
    

    
            5.4.  Investment
      Experience.  Such Investor acknowledges that it can bear the
      economic risk and complete loss of its investment in the Securities and
      has such knowledge and experience in financial or business matters that
      it is capable of evaluating the merits and risks of the investment
      contemplated hereby.
    

    
            5.5.  Disclosure of
      Information.  Such Investor has had an opportunity to receive all
      information related to the Company requested by it and to ask questions
      of and receive answers from the Company regarding the Company, its
      business and the terms and conditions of the offering of the
      Securities.  Such Investor acknowledges receipt of copies of the SEC
      Filings.  Neither such inquiries nor any other due diligence
      investigation conducted by such Investor shall modify, amend or affect
      such Investor’s right to rely on the Company’s representations and
      warranties contained in this Agreement.
    

    
            5.6.  Restricted
      Securities.  Such Investor understands that the Securities are
      characterized as “restricted securities” under the U.S. federal
      securities laws inasmuch as they are being acquired from the Company in
      a transaction not involving a public offering and that under such laws
      and applicable regulations such securities may be resold without
      registration under the 1933 Act only in certain limited circumstances.
    

    
            5.7.  Legends.  It
      is understood that, except as provided below, certificates evidencing
      the Securities may bear the following or any similar legend:
    

    
                     (a)  “THE
      SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE
      SECURITIES ACT OF 1933 AS AMENDED (THE “ACT”), OR ANY STATE
      SECURITIES LAWS.  SUCH SECURITIES MAY NOT BE SOLD OR OTHERWISE
      TRANSFERRED EXCEPT AS PERMITTED UNDER THE ACT AND THE APPLICABLE STATE
      SECURITIES LAWS, PURSUANT TO REGISTRATION OR AN EXEMPTION
      THEREFROM.  THE ISSUER OF THESE SECURITIES MAY REQUIRE AN OPINION OF
      COUNSEL (WHICH MAY BE COUNSEL FOR THE COMPANY) IN FORM AND SUBSTANCE
      REASONABLY SATISFACTORY TO THE ISSUER TO THE EFFECT THAT ANY PROPOSED
      TRANSFER OR RESALE IS IN COMPLIANCE WITH THE ACT.”
    

    
      
        

        

      

      
        
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                     (b)  If required by the authorities of any state in
      connection with the issuance of sale of the Securities, the legend
      required by such state authority.
    

    
            5.8.  Accredited
      Investor.  Such Investor is an accredited investor as defined in
      Rule 501(a) of Regulation D, as amended, under the 1933 Act.
    

    
            5.9.  No General
      Advertisement.  Such Investor did not learn of the investment in the
      Securities as a result of any public advertisement, article, notice or
      other communication regarding the Securities published in any newspaper,
      magazine or similar media or broadcast over television, radio or
      internet or presented at any seminar or other general advertisement.
    

    
           5.10.  Brokers and Finders.  No
      Person will have, as a result of the transactions contemplated by the
      Transaction Documents, any valid right, interest or claim against or
      upon the Company or an Investor for any commission, fee or other
      compensation pursuant to any agreement, arrangement or understanding
      entered into by or on behalf of such Investor.
    

    
           5.11.  Prohibited Transactions.  During
      the last thirty (30) days prior to the date hereof, neither such
      Investor nor any Affiliate of such Investor which (x) had knowledge of
      the transactions contemplated hereby, (y) has or shares discretion
      relating to such Investor’s investments or trading or information
      concerning such Investor’s investments, including in respect of the
      Securities, or (z) is subject to such Investor’s review or input
      concerning such Affiliate’s investments or trading (collectively, “Trading
      Affiliates”) has, directly or indirectly, effected or agreed to
      effect any short sale, whether or not against the box, established any
      “put equivalent position” (as defined in Rule 16a-1(h) under the 1934
      Act) with respect to the Common Stock, granted any other right
      (including, without limitation, any put or call option) with respect to
      the Common Stock or with respect to any security that includes, relates
      to or derived any significant part of its value from the Common Stock or
      otherwise sought to hedge its position in the Securities (each, a “Prohibited
      Transaction”).  Prior to the earliest to occur of (i) the
      termination of this Agreement, (ii) the Effective Date or (iii) the
      Effectiveness Deadline, such Investor shall not, and shall cause its
      Trading Affiliates not to, engage, directly or indirectly, in a
      Prohibited Transaction.  Such Investor acknowledges that the
      representations, warranties and covenants contained in this Section 5.11
      are being made for the benefit of the Investors as well as the Company
      and that each of the other Investors shall have an independent right to
      assert any claims against such Investor arising out of any breach or
      violation of the provisions of this Section 5.11.
    

    
           5.12.  Financial Condition.  Investor
      acknowledges:
    

    
                     (a)  that the Company has current assets of less than
      $594,029 and that it is currently spending approximately $300,000 per
      month; and
    

    
                     (b)  that the sale of the Units will result in an
      adjustment of the Series F Warrants pursuant to Section 8(b) of the
      Series F Warrant, a copy of which is on file with the SEC; assuming the
      sale of $2,000,000 of Notes with a $0.50 conversion price, such
      adjustment will make each Series F Warrant exercisable for 1.16 shares
      of Common Stock.
    

    
      
        

        

      

      
        
          10
        

        
          

        

      

      
        

        

      

    

    
           5.13.  Transaction Fees.  The
      Investor acknowledges and understands that the Company (i) will pay
      commissions equal to 10% of the gross sales price of the Cambria Units
      sold pursuant to this Agreement, (ii) will also issue Series G Warrants
      to Cambria to acquire the number of shares of the Company’s Common Stock
      equal to 7% of the aggregate number of Cambria Warrant Shares and the
      shares of Common Stock issuable upon conversion of the Cambria Notes and
      (iii) will also pay the Cambria’s costs related to the placement of the
      Cambria Units, including fees of the Cambria’s attorneys, costs of
      complying with federal and state securities laws and regulations and all
      miscellaneous expenses.
    

    
          6.  Conditions to Closing.
    

    
            6.1.  Conditions to the
      Investors’ Obligations. The obligation of each Investor to
      purchase the Notes and the Series G Warrants at the Closing is subject
      to the fulfillment to such Investor’s satisfaction, on or prior to the
      Closing Date, of the following conditions, any of which may be waived by
      such Investor (as to itself only):
    

    
                     (a)  The representations and warranties made by the
      Company in Section 4 hereof qualified as to materiality shall be true
      and correct at all times prior to and on the Initial Closing Date,
      except to the extent any such representation or warranty expressly
      speaks as of an earlier date, in which case such representation or
      warranty shall be true and correct as of such earlier date, and, the
      representations and warranties made by the Company in Section 4 hereof
      not qualified as to materiality shall be true and correct in all
      material respects at all times prior to and on the Initial Closing Date,
      except to the extent any such representation or warranty expressly
      speaks as of an earlier date, in which case such representation or
      warranty shall be true and correct in all material respects as of such
      earlier date.  The Company shall have performed in all material respects
      all obligations and covenants herein required to be performed by it on
      or prior to the Initial Closing Date.
    

    
                     (b)  The Company shall have obtained any and all
      consents, permits, approvals, registrations and waivers necessary or
      appropriate for consummation of the purchase and sale of the Securities
      and the consummation of the other transactions contemplated by the
      Transaction Documents, all of which shall be in full force and effect.
    

    
                     (c)  The Company shall have executed and delivered the
      Registration Rights Agreement.
    

    
                     (d)  The Company shall have executed and delivered the
      Security Agreement.
    

    
                     (e)  No judgment, writ, order, injunction, award or
      decree of or by any court, or judge, justice or magistrate, including
      any bankruptcy court or judge, or any order of or by any governmental
      authority, shall have been issued, and no action or proceeding shall
      have been instituted by any governmental authority, enjoining or
      preventing the consummation of the transactions contemplated hereby or
      in the other Transaction Documents.
    

    
      
        

        

      

      
        
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                     (f)  The Company shall have delivered a Certificate,
      executed on behalf of the Company by its Chief Executive Officer, dated
      as of the Closing Date, certifying to the fulfillment of the conditions
      specified in subsections (a), (b), (e) and (h) of this Section 6.1.
    

    
                     (g)  The Company shall have delivered a Certificate,
      executed on behalf of the Company by its Secretary, dated as of the
      Closing Date, certifying the resolutions adopted by the Board of
      Directors of the Company approving the transactions contemplated by this
      Agreement and the other Transaction Documents and the issuance of the
      Securities, certifying the current versions of the Articles of
      Incorporation and Bylaws of the Company and certifying as to the
      signatures and authority of persons signing the Transaction Documents
      and related documents on behalf of the Company.
    

    
                     (h)  No stop order or suspension of trading shall have
      been imposed by the SEC or any other governmental or regulatory body
      with respect to public trading in the Common Stock.
    

    
            6.2.  Conditions to
      Obligations of the Company.  The Company's obligation to sell and
      issue the Shares and the Series G Warrants at the Closing is subject to
      the fulfillment to the satisfaction of the Company on or prior to the
      Closing Date of the following conditions, any of which may be waived by
      the Company:
    

    
                     (a)  The representations and warranties made by the
      Investors in Section 5 hereof (the “Investor Representations”),
      shall be true and correct in all material respects when made, and shall
      be true and correct in all material respects on the Closing Date with
      the same force and effect as if they had been made on and as of said
      date.  The Investment Representations shall be true and correct in all
      respects when made, and shall be true and correct in all respects on the
      Closing Date with the same force and effect as if they had been made on
      and as of said date.  The Investors shall have performed in all material
      respects all obligations and covenants herein required to be performed
      by them on or prior to the Closing Date.
    

    
                     (b)  The Investors shall have executed and delivered the
      Registration Rights Agreement.
    

    
                     (c)  The Investors shall have executed and delivered the
      Security Agreement.
    

    
                     (d)  The Investors shall have delivered the Purchase
      Price to the Company.
    

    
            6.3.  Termination of
      Obligations to Effect Closing; Effects.
    

    
                     (a)  The obligations of the Company, on the one hand, and
      the Investors, on the other hand, to effect the Closing shall terminate
      as follows:
    

    
      (i)       Upon the mutual written consent of the Company and the
      Investors;
    

    
      
        

        

      

      
        
          12
        

        
          

        

      

      
        

        

      

    

    
      (ii)      By the Company if any of the conditions set forth in Section
      6.2 shall have become incapable of fulfillment, and shall not have been
      waived by the Company;
    

    
      (iii)     By an Investor (with respect to itself only) if any of the
      conditions set forth in Section 6.1 shall have become incapable of
      fulfillment, and shall not have been waived by the Investor; or
    

    
      (iv)      By either the Company or any Investor (with respect to itself
      only) if the Closing has not occurred on or prior to 5:00 p.m., Houston
      time, on May 30, 2009;
    

    
      provided, however, that, except in the case of clause (i) above, the
      party seeking to terminate its obligation to effect the Closing shall
      not then be in breach of any of its representations, warranties,
      covenants or agreements contained in this Agreement or the other
      Transaction Documents if such breach has resulted in the circumstances
      giving rise to such party’s seeking to terminate its obligation to
      effect the Closing.
    

    
                     (b)  In the event of termination by the Company or any
      Investor of its obligations to effect the Closing pursuant to this
      Section 6.3, written notice thereof shall forthwith be given to the
      other Investors and the other Investors shall have the right to
      terminate their obligations to effect the Closing upon written notice to
      the Company and the other Investors.  Nothing in this Section 6.3 shall
      be deemed to release any party from any liability for any breach by such
      party of the terms and provisions of this Agreement or the other
      Transaction Documents or to impair the right of any party to compel
      specific performance by any other party of its obligations under this
      Agreement or the other Transaction Documents.
    

    
          7.  Covenants and Agreements of the
      Company.
    

    
            7.1.  Reservation of
      Common Stock.  The Company shall at all times reserve and keep
      available out of its authorized but unissued shares of Common Stock,
      solely for the purpose of providing for the exercise of the Series G
      Warrants, such number of shares of Common Stock as shall from time to
      time equal the number of shares sufficient to permit the exercise of the
      Series G Warrants issued pursuant to this Agreement in accordance with
      their respective terms.
    

    
            7.2.  Reports.  The
      Company will furnish to the Investors and/or their assignees such
      information relating to the Company and any Subsidiaries as from time to
      time may reasonably be requested by the Investors and/or their
      assignees; provided, however, that the Company shall not disclose
      material nonpublic information to the Investors, or to advisors to or
      representatives of the Investors, unless prior to disclosure of such
      information the Company identifies such information as being material
      nonpublic information and provides the Investors, such advisors and
      representatives with the opportunity to accept or refuse to accept such
      material nonpublic information for review and any Investor wishing to
      obtain such information enters into an appropriate confidentiality
      agreement with the Company with respect thereto.
    

    
      
        

        

      

      
        
          13
        

        
          

        

      

      
        

        

      

    

    
            7.3.  No Conflicting
      Agreements.  The Company will not take any action, enter into any
      agreement or make any commitment that would conflict or interfere in any
      material respect with the Company’s obligations to the Investors under
      the Transaction Documents.
    

    
            7.4.  Compliance with
      Laws.  The Company will comply in all material respects with all
      applicable laws, rules, regulations, orders and decrees of all
      governmental authorities.
    

    
            7.5.  Listing of
      Underlying Shares and Related Matters.  Promptly following the
      Closing, the Company shall take all necessary action to cause the
      Warrant Shares to be listed on the NASDAQ Stock Market as soon as
      practicable after the Closing Date.  Further, if the Company applies to
      have its Common Stock or other securities traded on any other principal
      stock exchange or market, it shall include in such application the
      Warrant Shares and will take such other action as is necessary to cause
      such Common Stock to be so listed.  Once approved for listing, the
      Company will use commercially reasonable efforts to continue the listing
      and trading of its Common Stock on the NASDAQ Stock Market and, in
      accordance, therewith, will use commercially reasonable efforts to
      comply in all respects with the Company’s reporting, filing and other
      obligations under the bylaws or rules of such market or exchange, as
      applicable.
    

    
            7.6.  Termination of
      Covenants.  The provisions of Sections 7.2 through 7.5 shall
      terminate and be of no further force and effect on the date on which the
      Company’s obligations under the Registration Rights Agreement to
      register or maintain the effectiveness of any registration covering the
      Registrable Securities (as such term is defined in the Registration
      Rights Agreement) shall terminate.
    

    
            7.7.  Removal of Legends.  Upon
      the earlier of (i) registration for resale pursuant to the Registration
      Rights Agreement or (ii) Rule 144 becoming available the to the
      applicable Investor with respect to the resale of the applicable
      Securities then held by such Investor, the Company shall (A) deliver to
      the transfer agent for the Common Stock (the “Transfer Agent”)
      irrevocable instructions that the Transfer Agent shall reissue a
      certificate representing shares of Common Stock without legends upon
      receipt by such Transfer Agent of the legended certificates for such
      shares, together with either (1) a customary representation by the
      Investor that Rule 144 applies to the shares of Common Stock represented
      thereby or (2) a statement by the Investor that such Investor has sold
      the shares of Common Stock represented thereby in accordance with the
      Plan of Distribution contained in the Registration Statement and, if
      applicable, in accordance with any prospectus delivery requirements, and
      (B) cause its counsel to deliver to the Transfer Agent one or more
      blanket opinions to the effect that the removal of such legends in such
      circumstances may be effected under the 1933 Act.  From and after the
      earlier of such dates, upon an Investor’s written request, the Company
      shall promptly cause certificates evidencing the Investor’s Securities
      to be replaced with certificates which do not bear such restrictive
      legends, and Warrant Shares subsequently issued upon due exercise of the
      Series G Warrants shall not bear such restrictive legends provided the
      provisions of either clause (i) or clause (ii) above, as applicable, are
      satisfied with respect to such Warrant Shares.  
    

    
      
        

        

      

      
        
          14
        

        
          

        

      

      
        

        

      

    

    
          8.  Survival and Indemnification.
    

    
            8.1.  Survival.  The
      representations, warranties, covenants and agreements contained in this
      Agreement shall survive the Closing of the transactions contemplated by
      this Agreement.
    

    
            8.2.  Indemnification.  The
      Company agrees to indemnify and hold harmless each Investor and its
      Affiliates and their respective directors, officers, employees and
      agents from and against any and all losses, claims, damages, liabilities
      and expenses (including without limitation reasonable attorney fees and
      disbursements and other expenses incurred in connection with
      investigating, preparing or defending any action, claim or proceeding,
      pending or threatened and the costs of enforcement thereof)
      (collectively, “Losses”) to which such Person may
      become subject as a result of any breach of representation, warranty,
      covenant or agreement made by or to be performed on the part of the
      Company under the Transaction Documents, and will reimburse any such
      Person for all such amounts as they are incurred by such Person.
    

    
            8.3.  Conduct of
      Indemnification Proceedings.  Promptly after receipt by any Person
      (the “Indemnified Person”) of notice of any demand,
      claim or circumstances which would or might give rise to a claim or the
      commencement of any action, proceeding or investigation in respect of
      which indemnity may be sought pursuant to Section 8.2, such Indemnified
      Person shall promptly notify the Company in writing and the Company
      shall assume the defense thereof, including the employment of counsel
      reasonably satisfactory to such Indemnified Person, and shall assume the
      payment of all fees and expenses; provided, however, that the failure of
      any Indemnified Person so to notify the Company shall not relieve the
      Company of its obligations hereunder except to the extent that the
      Company is materially prejudiced by such failure to notify.  In any such
      proceeding, any Indemnified Person shall have the right to retain its
      own counsel, but the fees and expenses of such counsel shall be at the
      expense of such Indemnified Person unless: (i) the Company and the
      Indemnified Person shall have mutually agreed to the retention of such
      counsel; or (ii) in the reasonable judgment of counsel to such
      Indemnified Person representation of both parties by the same counsel
      would be inappropriate due to actual or potential differing interests
      between them.  The Company shall not be liable for any settlement of any
      proceeding effected without its written consent, which consent shall not
      be unreasonably withheld, but if settled with such consent, or if there
      be a final judgment for the plaintiff, the Company shall indemnify and
      hold harmless such Indemnified Person from and against any loss or
      liability (to the extent stated above) by reason of such settlement or
      judgment.  Without the prior written consent of the Indemnified Person,
      which consent shall not be unreasonably withheld, the Company shall not
      effect any settlement of any pending or threatened proceeding in respect
      of which any Indemnified Person is or could have been a party and
      indemnity could have been sought hereunder by such Indemnified Party,
      unless such settlement includes an unconditional release of such
      Indemnified Person from all liability arising out of such proceeding.
    

    
          9.  Miscellaneous.
    

    
            9.1.  Successors and
      Assigns.  This Agreement may not be assigned by a party hereto
      without the prior written consent of the Company or the Investors, as
      applicable, provided, however, that an Investor may assign its rights
      and delegate its duties hereunder in whole or in part to an Affiliate or
      to a third party acquiring some or all of its Securities in a private
      transaction without the prior written consent of the Company or the
      other Investors, after notice duly given by such Investor to the Company
      provided, that no such assignment or obligation shall affect the
      obligations of such Investor hereunder.  The provisions of this
      Agreement shall inure to the benefit of and be binding upon the
      respective permitted successors and assigns of the parties.  Nothing in
      this Agreement, express or implied, is intended to confer upon any party
      other than the parties hereto or their respective successors and assigns
      any rights, remedies, obligations, or liabilities under or by reason of
      this Agreement, except as expressly provided in this Agreement.
    

    
      
        

        

      

      
        
          15
        

        
          

        

      

      
        

        

      

    

    
            9.2.  Counterparts;
      Faxes.  This Agreement may be executed in two or more counterparts,
      each of which shall be deemed an original, but all of which together
      shall constitute one and the same instrument.  This Agreement may also
      be executed via facsimile, which shall be deemed an original.
    

    
            9.3.  Titles and
      Subtitles.  The titles and subtitles used in this Agreement are used
      for convenience only and are not to be considered in construing or
      interpreting this Agreement.
    

    
            9.4.  Notices.  Unless
      otherwise provided, any notice required or permitted under this
      Agreement shall be given in writing and shall be deemed effectively
      given as hereinafter described (i) if given by personal delivery, then
      such notice shall be deemed given upon such delivery, (ii) if given by
      telex or telecopier, then such notice shall be deemed given upon receipt
      of confirmation of complete transmittal, (iii) if given by mail, then
      such notice shall be deemed given upon the earlier of (A) receipt of
      such notice by the recipient or (B) three days after such notice is
      deposited in first class mail, postage prepaid, and (iv) if given by an
      internationally recognized overnight air courier, then such notice shall
      be deemed given one Business Day after delivery to such carrier.  All
      notices shall be addressed to the party to be notified at the address as
      follows, or at such other address as such party may designate by ten
      days’ advance written notice to the other party:
    

    
      If to the Company:
    

    
      Opexa Therapeutics, Inc.
2635 Crescent Ridge Drive
The Woodlands,
      Texas 77381
Attention:  President
Facsimile:  (281)
      872-8585
    

    
      With a copy to:
    

    
      Vinson & Elkins, LLP
1001 Fannin, Suite 2500
Houston, Texas
      77002
Attention:  Michael C. Blaney
Facsimile:  (713)
      758-3487
    

    
      
        

        

      

      
        
          16
        

        
          

        

      

      
        

        

      

    

    
      If to the Investors:
    

    
      to the addresses set forth on the signature pages hereto.
    

    
            9.5.  Expenses.  The
      parties hereto shall pay their own costs and expenses in connection
      herewith.  In the event that legal proceedings are commenced by any
      party to this Agreement against another party to this Agreement in
      connection with this Agreement or the other Transaction Documents, the
      party or parties which do not prevail in such proceedings shall
      severally, but not jointly, pay their pro rata share of the reasonable
      attorneys’ fees (based upon the relative number of Units purchased
      hereunder by each Investor) and other reasonable out-of-pocket costs and
      expenses incurred by the prevailing party in such proceedings.
    

    
            9.6.  Amendments and
      Waivers.  Any term of this Agreement may be amended and the
      observance of any term of this Agreement may be waived (either generally
      or in a particular instance and either retroactively or prospectively),
      only with the written consent of the Company and the Investors.  Any
      amendment or waiver effected in accordance with this paragraph shall be
      binding upon each holder of any Securities purchased under this
      Agreement at the time outstanding, each future holder of all such
      Securities, and the Company.
    

    
            9.7.  Publicity.  Except
      as set forth below, no public release or announcement concerning the
      transactions contemplated hereby shall be issued by the Company or the
      Investors without the prior consent of the Company (in the case of a
      release or announcement by the Investors) or the Investors (in the case
      of a release or announcement by the Company) (which consents shall not
      be unreasonably withheld), except as such release or announcement may be
      required by law or the applicable rules or regulations of any securities
      exchange or securities market, in which case the Company or the
      Investors, as the case may be, shall allow the Investors or the Company,
      as applicable, to the extent reasonably practicable in the
      circumstances, reasonable time to comment on such release or
      announcement in advance of such issuance.  In addition, the Company will
      make such other filings and notices in the manner and time required by
      the SEC.  Notwithstanding the foregoing, the Company shall not publicly
      disclose the name of any Investor, or include the name of any Investor
      in any filing with the SEC (other than the Registration Statement and
      any exhibits to filings made in respect of this transaction in
      accordance with periodic filing requirements under the 1934 Act) or any
      regulatory agency, without the prior written consent of such Investor,
      except to the extent such disclosure is required by law or trading
      market regulations, in which case the Company shall provide the
      Investors with prior notice of such disclosure.
    

    
            9.8.  Severability.  Any
      provision of this Agreement that is prohibited or unenforceable in any
      jurisdiction shall, as to such jurisdiction, be ineffective to the
      extent of such prohibition or unenforceability without invalidating the
      remaining provisions hereof but shall be interpreted as if it were
      written so as to be enforceable to the maximum extent permitted by
      applicable law, and any such prohibition or unenforceability in any
      jurisdiction shall not invalidate or render unenforceable such provision
      in any other jurisdiction.  To the extent permitted by applicable law,
      the parties hereby waive any provision of law which renders any
      provision hereof prohibited or unenforceable in any respect.
    

    
            9.9.  Entire Agreement.  This
      Agreement, including the Exhibits and the Disclosure Schedules, and the
      other Transaction Documents constitute the entire agreement among the
      parties hereof with respect to the subject matter hereof and thereof and
      supersede all prior agreements and understandings, both oral and
      written, between the parties with respect to the subject matter hereof
      and thereof.
    

    
      
        

        

      

      
        
          17
        

        
          

        

      

      
        

        

      

    

    
           9.10.  Further Assurances.  The
      parties shall execute and deliver all such further instruments and
      documents and take all such other actions as may reasonably be required
      to carry out the transactions contemplated hereby and to evidence the
      fulfillment of the agreements herein contained.
    

    
           9.11.  Governing Law; Consent
      to Jurisdiction; Waiver of Jury Trial.  This Agreement shall be
      governed by, and construed in accordance with, the internal laws of the
      State of Texas without regard to the choice of law principles
      thereof.  Each of the parties hereto irrevocably submits to the
      exclusive jurisdiction of the courts of the State of Texas located in
      Harris County and the United States District Court for the Southern
      District of Texas for the purpose of any suit, action, proceeding or
      judgment relating to or arising out of this Agreement and the
      transactions contemplated hereby.  Service of process in connection with
      any such suit, action or proceeding may be served on each party hereto
      anywhere in the world by the same methods as are specified for the
      giving of notices under this Agreement.  Each of the parties hereto
      irrevocably consents to the jurisdiction of any such court in any such
      suit, action or proceeding and to the laying of venue in such
      court.  Each party hereto irrevocably waives any objection to the laying
      of venue of any such suit, action or proceeding brought in such courts
      and irrevocably waives any claim that any such suit, action or
      proceeding brought in any such court has been brought in an inconvenient
      forum.  EACH OF THE PARTIES HERETO WAIVES ANY RIGHT TO
      REQUEST A TRIAL BY JURY IN ANY LITIGATION WITH RESPECT TO THIS AGREEMENT
      AND REPRESENTS THAT COUNSEL HAS BEEN CONSULTED SPECIFICALLY AS TO THIS
      WAIVER.
    

    
           9.12.  Independent Nature of
      Investors' Obligations and Rights.  The obligations of each Investor
      under any Transaction Document are several and not joint with the
      obligations of any other Investor, and no Investor shall be responsible
      in any way for the performance of the obligations of any other Investor
      under any Transaction Document.  The decision of each Investor to
      purchase Securities pursuant to the Transaction Documents has been made
      by such Investor independently of any other Investor.  Nothing contained
      herein or in any Transaction Document, and no action taken by any
      Investor pursuant thereto, shall be deemed to constitute the Investors
      as a partnership, an association, a joint venture or any other kind of
      entity, or create a presumption that the Investors are in any way acting
      in concert or as a group with respect to such obligations or the
      transactions contemplated by the Transaction Documents.  Each Investor
      acknowledges that no other Investor has acted as agent for such Investor
      in connection with making its investment hereunder and that no Investor
      will be acting as agent of such Investor in connection with monitoring
      its investment in the Securities or enforcing its rights under the
      Transaction Documents.  Each Investor shall be entitled to independently
      protect and enforce its rights, including, without limitation, the
      rights arising out of this Agreement or out of the other Transaction
      Documents, and it shall not be necessary for any other Investor to be
      joined as an additional party in any proceeding for such purpose.  The
      Company acknowledges that each of the Investors has been provided with
      the same Transaction Documents for the purpose of closing a transaction
      with multiple Investors and not because it was required or requested to
      do so by any Investor.
    

    
      
        

        

      

      
        
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      [signature page follows]
    

    
      

      

      

      

      

    

    
      
        

        

      

      
        
          19
        

        
          

        

      

      
        

        

      

    

    
      IN WITNESS WHEREOF, the parties have executed this Agreement or caused
      their duly authorized officers to execute this Agreement as of the date
      first above written.
    

    
    	
          The Company:
        	
          OPEXA THERAPEUTICS, INC.
        
	

        	

        	
           
        
	

        	

        	
           
        
	

        	
          
            By:
          

        	
          
            /S/ NEIL K. WARMA
          

        
	

        	

        	
          Neil K. Warma
        
	

        	

        	
          President and Chief Executive Officer
        

    

    
      

      

      

    

    
      Company Signature Page
to Unit Purchase Agreement
    

    
      
        

        

      

      
        

        

        
          

        

      

      
        

        

      

    

    
    	
          The Investors:
        	

        	
           
        
	

        	

        	

        	
           
        
	

        	

        	

        	
           
        
	

        	

        	

        	
           
        
	

        	

        	
          
            By:
          

        	
          
             
          

        
	

        	

        	
          
            Name:
          

        	
          
             
          

        
	

        	

        	
          
            Title:
          

        	
          
             
          

        
	

        	

        	

        	
           
        
	

        	

        	

        	
           
        
	

        	

        	

        	
           
        
	
          
            Aggregate Purchase Price:
          

        	
          
            $
          

        	

        	

        
	
          Number of Units:
        	
           
        	

        	

        
	
          Date:
        	
           
        	

        	

        
	

        	

        	

        	
           
        
	

        	

        	

        	
           
        
	
          Address for Notices:
        	

        	
           
        
	

        	

        	
           
        
	

        	

        	
           
        
	

        	

        	
          
            Attention:
          

        	
          
             
          

        
	

        	

        	
          
            Facsimile:
          

        	
          
             
          

        
	

        	

        	
          
            Email:
          

        	
          
             
          

        

    

    
      

      

      

    

    

    

    

    

    

    

    
      Investor Signature Page
to Unit Purchase Agreement
    

    
      
        

        

      

      
        

        

        
          

        

      

      
        

        

      

    

    
      EXHIBIT A
    

    
      Form of Note
    

    
      (to be attached)
    

    
      

      

      

      

      EXHIBIT A
to Unit Purchase Agreement
    

    
      
        

        

      

      
        

        

        
          

        

      

      
        

        

      

    

    

    

    
      EXHIBIT B
    

    
      Form of Series G Warrant
    

    
      (to be attached)
    

    
      

      

      

      

      EXHIBIT B
to Unit Purchase Agreement
    

    
      
        

        

      

      
        

        

        
          

        

      

      
        

        

      

    

    
      EXHIBIT C
    

    
      Form of Registration Rights Agreement
    

    
      (to be attached)
    

    
      

      

      

      

      EXHIBIT C
to Unit Purchase Agreement
    

    
      
        

        

      

      
        

        

        
          

        

      

      
        

        

      

    

    
      EXHIBIT D
    

    
      Form of Security Agreement
    

    
      (to be attached)
    

    
      

      

      

      

      EXHIBIT D
to Unit Purchase AgreementExhibit 10-2
    

    
      OPEXA THERAPEUTICS, INC.
    

    
      10% CONVERTIBLE PROMISSORY NOTE
    

    
    	
          $____________
        	
          April 14, 2009
        

    

    
      THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE
      SECURITIES ACT OF 1933 AS AMENDED (THE “ACT”), OR ANY STATE
      SECURITIES LAWS.  SUCH SECURITIES MAY NOT BE SOLD OR OTHERWISE
      TRANSFERRED EXCEPT AS PERMITTED UNDER THE ACT AND THE APPLICABLE STATE
      SECURITIES LAWS, PURSUANT TO REGISTRATION OR AN EXEMPTION
      THEREFROM.  THE ISSUER OF THESE SECURITIES MAY REQUIRE AN OPINION OF
      COUNSEL (WHICH MAY BE COUNSEL FOR THE COMPANY) IN FORM AND SUBSTANCE
      REASONABLY SATISFACTORY TO THE ISSUER TO THE EFFECT THAT ANY PROPOSED
      TRANSFER OR RESALE IS IN COMPLIANCE WITH THE ACT.
    

    
      OPEXA THERAPEUTICS, INC., a Texas corporation (the “Company”),
      for value received, hereby promises to pay to the order of
      _______________ (“Investor”), whose address is
      _____________________________________________, at said address or such
      other addresses as may be designated in writing by Investor from time to
      time, or Investor's registered assigns, the principal amount of
      ___________________________________________ and No/100 Dollars
      ($_____________), together with interest thereon from the date of
      issuance of this 10% Convertible Promissory Note (the “Note”)
      on the unpaid principal balance at an annual rate of interest equal to
      ten percent (10%) per annum, compounded annually (on the basis of a
      360-day year), such principal and interest to be payable as provided
      below on April 14, 2011 (the “Maturity Date”).
    

    
      The following is a statement of rights of the holder of this Note and
      the conditions to which this Note is subject, to which the holder
      hereof, by the acceptance of this Note, assents:
    

    
      1.  Payment.
    

    
         (A)  Principal.  Subject to the
      provisions of Section 2 hereof relating to the conversion of this Note,
      the Company shall make payment of principal when due in coin or currency
      of the United States of America which at the time of payment is legal
      tender for the payment of public and private debts (“Legal
      Tender”).  
    

    
         (B)  Interest.  Subject to the
      provisions of Section 2 hereof relating to the conversion of this Note,
      the Company shall make payment of all accrued interest when due in
      either (i) Legal Tender or (ii) shares of the Company’s Common Stock,
      par value $0.50 per share (the “Common Stock”).  If
      paid by shares of Common Stock, the number of shares shall equal the
      interest due divided by the “Conversion Price.”  The
      Conversion Price equals $0.50.
    

    
         (C)  Pre-Payment.  Notwithstanding
      the foregoing, the Company may prepay all or any portion of the
      principal sum of and/or interest on this Note without penalty upon 15
      days prior written notice to the Investor, subject to the provisions of
      Section 2 hereof.
    

    
      
        

        

      

      
        

        

        
          

        

      

      
        

        

      

    

    
      2.  Conversion.
    

    
         (A)  Investor Conversion Rights.  At
      any time prior to the Maturity Date, the Investor may elect to convert
      all or part of the unpaid principal amount of this Note and any unpaid
      interest accrued thereon (the sum of such principal and accrued interest
      being hereinafter collectively referred to as the “Outstanding
      Balance”), into shares of Common Stock.  The number of shares of
      Common Stock into which this Note shall be convertible shall be
      determined by dividing (i) the Outstanding Balance by (ii) the
      Conversion Price.  Any failure by the Investor to provide such notice
      shall be deemed to be an election not to convert any portion of the
      Investor’s Outstanding Balance.  For the purposes of this Section 2(A),
      conversion shall be deemed to occur on the date that the Company
      receives written notice from the Investor of such conversion.
    

    
         (B)  Company Conversion Rights.  If
      (i) the NASDAQ Official Closing Price of the Company’s common stock
      equals or exceeds $1.00 per share (as adjusted for any stock splits,
      stock dividends or stock combinations) for twenty (20) consecutive
      trading days, (ii) the Company has an effective registration statement
      on file with the Securities and Exchange Commission that permits the
      immediate resale of the Common Stock into which this Note shall be
      convertible or all shares of such Common Stock are freely tradable by
      the holders thereof under applicable securities laws and the Company
      shall not have imposed any stop-order or other restriction in the sale
      thereof; and (iii) the Company enters into an agreement that will fund a
      Phase IIb or Phase III clinical trial for the further development of the
      Company’s product known as Tovaxin, the Company may elect at any time
      thereafter to convert all or part of the Outstanding Balance, into
      shares of Common Stock.  The number of shares of Common Stock into which
      this Note shall be convertible shall be determined by dividing (i) the
      Outstanding Balance by (ii) the Conversion Price.  The Company shall
      effect such conversion by sending written notice to the Investor at its
      address on the Company’s books.  Any failure by the Company to provide
      such notice shall be deemed to be an election not to convert any portion
      of the Outstanding Balance.  For the purposes of this Section 2(B),
      conversion shall be deemed to occur on the date that the Company sends
      such written notice to the Investor of such conversion.
    

    
         (C)  Surrender of Note.  Upon
      conversion of this Note into Common Stock as provided in this Section 2,
      the Investor shall surrender this Note at the offices of the Company at
      2635 North Crescent Ridge Drive, The Woodlands, Texas 77381 and the
      Company shall, at its expense, deliver to the Investor as soon as
      practicable a certificate representing the number of shares of Common
      Stock provided in Section 2(A) or Section 2(B), as applicable.  The
      Company will place on each certificate a legend substantially the same
      as that appearing on this Note, in addition to any legend required by
      any applicable state or federal law.  Irrespective of the date of
      issuance and delivery of any certificates with respect thereto, shares
      of Common Stock purchased by conversion under this Section 2 shall be,
      and be deemed to be, issued to the Investor as the record owner of such
      shares as of the close of business on the deemed date of conversion as
      provided in Section 2(A) and Section 2(B).
    

    
      
        

        

      

      
        
          2
        

        
          

        

      

      
        

        

      

    

    
         (D)  No Fractional Shares.  No
      fractional shares or scrip representing fractional shares shall be
      issued upon the conversion of this Note.  With respect to any fraction
      of a share called for upon the conversion exercise of this Note, an
      amount equal to such fraction multiplied by the then current price at
      which each share may be purchased hereunder shall be paid in cash to the
      Investor.
    

    
         (E)  General.  The foregoing
      conversion rights are subject in all respects to compliance by the
      Company with all applicable laws, rules and regulations.
    

    
      3.  Pari Passu.  This Note is one of several
      convertible promissory notes of the Company issued contemporaneously
      herewith (the “April 2009 Notes”) evidencing
      indebtedness incurred by the Company for interim financing provided to
      the Company.  This Note and the other April 2009 Notes shall rank pari
      passu as to the payment of principal and interest.  The Investor
      agrees that any payments or prepayments to Investor and to the holders
      of the other April 2009 Notes, whether principal, interest or otherwise,
      shall be made pro rata among  the Investor and the holders of the other
      April 2009 Notes based upon the aggregate unpaid principal amount of
      this Note and the other April 2009 Notes.  By accepting this Note, the
      Investor agrees that if the Investor or any other holder of a April 2009
      Note obtains any payments (whether voluntary, involuntary, by
      prepayment, set-off or otherwise) of the principal or interest on this
      Note or any other April 2009 Note in excess of such holder’s pro rata
      share of payments received by all holders of the April 2009 Notes, such
      holder shall purchase from the other holders of this Note and the other
      April 2009 Notes such participation in such promissory notes held by
      them as is necessary to cause all such holders to share the excess
      payment ratably among each of them as provided in this Section 3.
    

    
      4.  Adjustments.  Subject and pursuant to the
      provisions of this Section 4, the Conversion Price shall be subject to
      adjustment from time to time as set forth hereinafter.
    

    
         (A)      If the Company shall, at any time or from time to time while
      this Note is outstanding, pay a dividend or make a distribution on its
      Common Stock in shares of Common Stock, subdivide its outstanding shares
      of Common Stock into a greater number of shares or combine its
      outstanding shares of Common Stock into a smaller number of shares or
      issue by reclassification of its outstanding shares of Common Stock any
      shares of its capital stock (including any such reclassification in
      connection with a consolidation or merger in which the Company is the
      continuing corporation), then the Conversion Price in effect immediately
      prior to the date on which such change shall become effective shall be
      adjusted by multiplying such Conversion Price by a fraction, the
      numerator of which shall be the number of shares of Common Stock
      outstanding immediately prior to such change and the denominator of
      which shall be the number of shares of Common Stock outstanding
      immediately after giving effect to such change.  Such adjustments shall
      be made successively whenever any event listed above shall occur.
    

    
      
        

        

      

      
        
          3
        

        
          

        

      

      
        

        

      

    

    
         (B)  In case the Company shall fix a payment date for the making of a
      distribution to all holders of Common Stock (including any such
      distribution made in connection with a consolidation or merger in which
      the Company is the continuing corporation) of evidences of indebtedness
      or assets (other than cash dividends or cash distributions payable out
      of consolidated earnings or earned surplus or dividends or distributions
      referred to in Section 4(A)), or subscription rights or warrants, the
      Conversion Price to be in effect after such payment date shall be
      determined by multiplying the Conversion Price in effect immediately
      prior to such payment date by a fraction, the numerator of which shall
      be the total number of shares of Common Stock outstanding multiplied by
      the closing bid price of the Common Stock as listed on the NASDAQ Stock
      Market immediately prior to such payment date (the “Market
      Price”), less the fair market value (as determined by the
      Company’s Board of Directors in good faith) of said assets or evidences
      of indebtedness so distributed, or of such subscription rights or
      warrants, and the denominator of which shall be the total number of
      shares of Common Stock outstanding multiplied by such Market Price.  
    

    
         (C)  An adjustment to the Conversion Price shall become effective
      immediately after the payment date in the case of each dividend or
      distribution and immediately after the effective date of each other
      event which requires an adjustment.
    

    
         (D)  In the event that, as a result of an adjustment made pursuant to
      this Section 4, the Investor shall become entitled to receive any shares
      of capital stock of the Company other than shares of Common Stock, the
      number of such other shares so receivable upon conversion of this Note
      shall be subject thereafter to adjustment from time to time in a manner
      and on terms as nearly equivalent as practicable to the provisions with
      respect to the Conversion Shares.
    

    
      5.  Default Interest; Collection Fees; Waiver.  All
      past due principal and interest on this Note shall accrue interest at
      the highest lawful rate.  In the event of default hereunder and if this
      Note is placed in the hands of an attorney for collection (whether or
      not suit is filed), or if this Note is collected by suit or legal
      proceedings or through bankruptcy proceedings, the Company agrees to pay
      in addition to all sums then due hereunder, including outstanding
      principal and accrued unpaid interest, all reasonable attorneys’ fees.
    

    
      The Company hereby waives demand and presentment for payment, notice of
      nonpayment, protest, notice of protests, notice of dishonor, notice of
      intention to accelerate and notice of acceleration, bringing of suit and
      diligence in taking any action to collect amounts called for hereunder
      and in the handling of securities at any time existing in connection
      herewith. In addition, the Company is and shall be directly and
      primarily liable for the payment of all sums owing and to be owing
      hereon, regardless of and without any notice, diligence, act or omission
      as or with respect to the collection of any amount called for hereunder.
    

    
      
        

        

      

      
        
          4
        

        
          

        

      

      
        

        

      

    

    
      6.  Maximum Rate of Interest.  Notwithstanding
      any provisions to the contrary in this Note, or in any of the documents
      relating hereto, in no event shall this Note or such documents require
      the payment or permit the charging or collection of interest in excess
      of the maximum amount or highest lawful rate permitted by the applicable
      usury laws.  It is the intention of the Company and the Investor to
      comply in all respects with applicable usury laws, and in no event shall
      the Company pay, for the use, forebearance or detention of money,
      interest at a rate or in an amount in excess of the highest lawful rate
      permitted by applicable law.  If any such excess interest is contracted
      for, charged or received under this Note or under the terms of any of
      the documents relating hereto, or in the event the maturity of the
      indebtedness evidenced by this Note is accelerated in whole or in part,
      or in the event that all or part of the principal or accrued unpaid
      interest of this Note shall be prepaid, so that under any of such
      circumstances the amount of interest contracted for, charged or received
      under this Note or under any of the documents relating hereto, on the
      amount of principal actually outstanding from time to time under this
      Note, shall exceed the maximum amount of interest permitted by the
      applicable usury laws, then in any such event (a) the provisions of this
      Section 6 shall govern and control, (b) neither the Company nor any
      other person or entity now or hereafter liable for the payment hereof,
      shall be obligated to pay the amount of such interest to the extent that
      it is in excess of the maximum amount of interest permitted by the
      applicable usury laws, (c) any such excess which may have been collected
      shall be either applied as a credit against the then unpaid principal
      amount hereof or refunded to the Company, at the holder’s option, and
      (d) the effective rate of interest shall be automatically reduced to the
      maximum lawful rate of interest allowed under the applicable usury laws
      as now or hereafter construed by the courts having jurisdiction
      thereof.  It is further agreed that without limitation of the foregoing,
      all calculations of the rate of interest contracted for, charged or
      received under this Note or under such other documents which are made
      for the purpose of determining whether such rate exceeds the maximum
      lawful rate of interest, shall be made, to the extent permitted by the
      applicable usury laws, by amortizing, prorating, allocating and
      spreading during the period of the full stated term of the indebtedness
      evidenced hereby, all interest at any time contracted for, charged or
      received from the Company or otherwise by the holder or holders hereof
      in connection with such indebtedness.
    

    
      7.  Certain Events.  The Outstanding Balance of
      this Note shall become immediately due and payable upon any of the
      following events: (i) the admission in writing by the Company of its
      insolvency, (ii) the commission of any voluntary act of bankruptcy by
      the Company, (iii) the execution by the Company of a general assignment
      for the benefit of creditors, (iv) the filing by or against the Company
      of any petition in bankruptcy or any petition for relief under the
      provisions of the federal bankruptcy act or any other state or federal
      law for the relief of debtors and the continuation of such petition
      without dismissal for a period of sixty (60) days or more, (v) the
      failure of Company to perform any of its material obligations under this
      Note or any document, instrument or agreement executed in connection
      herewith, (vi) the appointment of a receiver or trustee to take
      possession of the property or assets of the Company, (vii) any
      dissolution of the Company, (viii) the adoption by the Company of any
      plan of liquidation, (ix) the sale by the Company in bulk of any of its
      assets pursuant to a plan of liquidation or for the purpose of
      liquidating its business, (x) the redemption or acquisition by the
      Company of any of its outstanding stock other than pursuant to a stock
      purchase agreement or stock repurchase agreements which may currently or
      hereafter exist between the Company and certain of its employees,
      consultants or directors, (xi) the commencement against the Company of
      any case, proceeding or other action seeking issuance of a warrant of
      attachment, execution, distraint or similar process against all or any
      substantial part of its assets which results in the entry of an order
      for any such relief which shall not have been vacated, discharged, or
      stayed or bonded pending appeal within sixty (60) days from the entry
      thereof, (xii) the cash or cash equivalents of the Company fall below
      $200,000, or (xiii) any challenge or contest by the Company or any
      affiliate of the Company in any action, suit or proceeding of the
      validity or enforceability of this Note or the warrants issued on even
      date herewith by the Company to Investor (each, individually, an “Event
      of Default”).
    

    
      
        

        

      

      
        
          5
        

        
          

        

      

      
        

        

      

    

    
      8.  Amendments and Waivers.  No
      provision of this Note may be waived or amended in any respect except by
      the written consent of the Company and the Investor; provided, however,
      that if holders of fifty-one percent (51%) or more in principal amount
      of the outstanding April 2009 Notes agree in writing to waive any
      provision of or otherwise amend such April 2009 Notes, then in such
      instance the provisions of this Note shall be so waived or amended;
      provided, further that no such waiver or amendment may reduce the
      principal amount of or interest on this Note or change the stated
      Maturity Date of this Note or reduce the percentage of holders of April
      2009 Notes necessary to waive or amend the provisions of this Note,
      without the written consent of Investor. Notwithstanding the foregoing,
      holders of sixty-six and two-thirds percent (66 2/3%) or more in
      principal amount of the outstanding April 2009 Notes shall be required
      to waive or amend the provisions of Section 2(B) hereof.
    

    
      9.  Miscellaneous.  The Company hereby waives to
      the full extent permitted by law all rights to plead any statute of
      limitations or laches as a defense to any action hereunder.  This Note
      cannot be changed orally, but only by an agreement in writing signed by
      holders of at least a majority of the outstanding principal balance of
      all then-outstanding April 2009 Notes.  This Note shall be governed by
      and construed in accordance with the laws of the State of Texas
      applicable to agreements made to be performed in Texas, without
      reference to any principles of choice of law or conflicts of law.
    

    
      

      

    

    
      IN WITNESS WHEREOF, the Company has caused this Note to be duly executed
      as of the date first written above.
    

    
    	
           
        	
          OPEXA THERAPEUTICS, INC.
        
	

        	

        	
           
        
	
          
             
          

        	
          
            By:
          

        	
          /S/ NEIL K. WARMA
        
	
          
             
          

        	
          
            Name:
          

        	
          Neil K. Warma
        
	
          
             
          

        	
          
            Title:
          

        	
          President and Chief Executive Officer
        

    

    

    

    
      ATTEST:
    

    
      /S/ NEIL K. WARMA
Neil K. Warma, Secretary
    

    
      

      

      

      6

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