Document:

Exhibit 10.2

 

EXECUTION COPY

 

STOCK ISSUANCE AGREEMENT

 

This
Agreement (“Agreement”) is made and entered into as of August 10, 2015 (the “Effective Date”),
by and among Synthetic Biologics, Inc., a Nevada corporation (the “Company”), and Intrexon Corporation, a Virginia
corporation (“Intrexon”).

 

A.           Concurrently
with the execution of this Agreement, the Company is entering into on the Effective Date an Exclusive Channel Collaboration Agreement
with Intrexon (the “PKU Channel Agreement”), pursuant to which Intrexon is licensing the rights to certain technology
to the Company; and

 

B.           In
partial consideration of Intrexon’s license to the Company under the PKU Channel Agreement, the Company has agreed to issue
to Intrexon certain shares of the Company’s common stock, par value $0.001 per share, (the “Common Stock”)
in accordance with the terms and conditions of this Agreement.

 

AGREEMENT

 

In consideration of the
mutual covenants contained in this Agreement and for other good and valuable consideration, the receipt of which is hereby acknowledged,
the Company and Intrexon hereby agree as follows:

 

sECTION
1.      Authorization
of Issuance of Shares.

 

1.1         PKU
Technology Access Fee. Subject to the terms and conditions of this Agreement, the Company has authorized the issuance
to Intrexon of a certain number of shares of the Company’s Common Stock at the PKU Technology Access Fee Closing (as hereinafter
defined) as a PKU Technology Access Fee (the “PKU Technology Access Fee Shares”), which number of PKU Technology
Access Fee Shares has a collective Fair Market Value equal to three million United States Dollars ($3,000,000). For the purposes
of this Agreement, “Fair Market Value” shall have the meaning as set forth in the PKU Channel Agreement.

 

1.2         Milestones.
Subject to the terms and conditions of this Agreement and the PKU Channel Agreement, upon the attainment of the Clinical Milestone
Event for each Collaboration Product developed under the PKU Channel Agreement, the Company has agreed to make a milestone payment
(each, whether in cash or equity, a “Clinical Milestone Payment” and together “Clinical Milestone Payments”)
set forth below in Section 1.2(a) to Intrexon, payable either in cash or in shares of Company Common Stock at the option of the
Company (subject to the conditions set forth in the PKU Channel Agreement), on certain dates following achievement of each Clinical
Milestone Event. For the purposes of this Agreement, the terms “Clinical Milestone Event” and “Collaboration
Product” shall each respectively have the meanings as set forth in the PKU Channel Agreement.

 

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(a)          Upon
each occurrence of the Clinical Milestone Event, Company will pay to Intrexon in accord with the terms and conditions of the PKU
Channel Agreement one of (i) two million United States dollars ($2,000,000) in cash, or (ii) that number of shares of Company’s
Common Stock (the “Clinical Milestone Shares”) having a collective Fair Market Value equaling two million United
States dollars ($2,000,000). Following each achievement of the Clinical Milestone The number of shares of Common Stock to be issued
to Intrexon hereunder shall be rounded down to the nearest whole share, with any balance being due in cash. A Clinical Milestone
Payment shall be due within thirty days following the date of the occurrence of a Clinical Milestone Event.

 

1.3         [RESERVED]

 

1.4         Capital
Adjustments. If after the date hereof (i) the outstanding shares of the Company’s Common Stock shall be subdivided or
split into a greater number of shares or a dividend in Common Stock shall be paid in respect of such Common Stock or (ii) the outstanding
shares of Common Stock are combined, then all share quantities in this Agreement not yet issued shall be appropriately adjusted
to reflect such stock split, stock dividend or conjunction. If after the date hereof (i) the Company shall pay a dividend in securities
of the Company (other than in Common Stock) or of other property (including cash) on the Common Stock, or (ii) there shall occur
any merger, consolidation, capital reorganization or reclassification in which the Common Stock is converted or exchanged for securities,
cash or other property, the class or series of stock constituting the Common Stock for purposes of this Agreement, shall be appropriately
adjusted to reflect such other dividend, merger, consolidation, capital reorganization or reclassification. After any event referenced
in clauses (i) through (ii) of the immediately preceding sentence is consummated, if applicable, all references herein to the Company’s
Common Stock shall be deemed to refer to the capital stock or property (including cash) into or for which the Common Stock was
converted or exchanged, with the necessary changes in detail. Nothing contained in this Section 1.2 or elsewhere in this Agreement
will prevent or prohibit the dilution of Intrexon’s ownership interest in the Company or grant to Intrexon any preemptive
rights.

 

1.5         Company
Sale. In the event that the Company consummates a Company Sale (as defined below) prior to any one of the Subsequent Closings
(as defined below), and the PKU Channel Agreement is transferred or assigned to the buyer or assigned to the buyer in connection
with such Company Sale, the Company and Intrexon agree that payments under Sections 1.2 and 1.3 of this Agreement shall be payable
only in cash following the Company Sale.

 

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sECTION
2.      Closing and
Delivery

 

2.1         Sale
and Purchase Price of Shares. Subject to the terms and conditions of this Agreement and in reliance upon the representations,
warranties and agreements contained herein, the Company will issue and sell to Intrexon, and Intrexon will purchase from the Company,
at each of the PKU Technology Access Fee Closing as set forth in Section 2.2(a), and the Milestone Closings (as hereinafter defined)
if the Company has not elected to make the Clinical Milestone Payment in cash, the applicable number of shares as set forth above
in Sections 1.1 and 1.2. The Parties agree that the consideration received by the Company hereunder shall be the execution and
delivery by Intrexon of the PKU Channel Agreement which consideration is at least equal to the par value of the shares issued or
issuable under this Agreement.

 

2.2         Closings.
The closings of the purchase and sale of the shares to be issued pursuant to this Agreement shall be held at the offices of Gracin
& Marlow, LLP, Chrysler Building, 405 Lexington Avenue, 26th Floor, New York, New York 10174 or at such other place as the
Company and Intrexon may agree, as follows:

 

(a)          the
closing of the purchase and sale of the PKU Technology Access Fee Shares will occur, subject to the conditions set forth in Section
7.1 hereof and applicable to the PKU Technology Access Fee Closing, subject to the timeframes set forth in Section 5.1 of the PKU
Channel Agreement, (i) on the tenth business day following approval of the PKU Channel Agreement by NYSE MKT (the “NYSE
MKT Approval”), or (ii) on such other date as Intrexon and the Company may agree upon (in either case, the “PKU
Technology Access Fee Closing”); and

 

(b)          the
closing of the purchase and sale of each occurrence of Clinical Milestone Shares or the payment of each cash Milestone Payment
will occur, subject to the conditions set forth in Section 7.2 hereof and applicable to the Milestone Closing, (A) if NYSE MKT
approval (or approval of any other exchange upon which the Common Stock may be listed) is required, on the tenth (10th)
business day after such approval is received, but in no event later than one hundred twenty (120) days after the respective Milestone
Event, or (B) if NYSE MKT approval (or approval of any other exchange upon which the Common Stock may be listed) is not required,
on the earlier of (i) the thirtieth (30th) day following the occurrence of the respective Milestone Event, and (ii)
such other date as Intrexon and the Company may agree (the “Milestone Closing”).

 

The PKU Technology Access Fee Closing and each
of the Milestone Closings may be collectively herein referred to as the “Closings” and individually as a “Closing”.
Further, each of the Milestones Closing may alternatively be collectively herein referred to as the “Subsequent Closings”
and individually as a “Subsequent Closing”.

 

2.3         Delivery
of the Shares. Promptly following a Closing at which shares are issued to Intrexon, the Company shall deliver to Intrexon a
certificate representing the number of shares purchased at such Closing, registered in the name of Intrexon.

 

sECTION
3.      Representations
and Warranties of the Company.

 

Subject to and except as
set forth in the SEC Documents or on the Schedule of Exceptions which is arranged in sections corresponding to the sub-section
numbered provisions contained below in this Section, the Company hereby represents and warrants to, and covenants with, Intrexon
as of the date hereof as follows:

 

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3.1         Organization,
Good Standing and Power.

 

(a)          The
Company is a corporation duly incorporated, validly existing and in good standing under the laws of the State of Nevada and has
the requisite corporate power to own, lease and operate its properties and assets and to conduct its business as it is now being
conducted and as described in the reports filed by the Company with the Securities and Exchange Commission (the “Commission”)
pursuant to the reporting requirements of the Securities Exchange Act of 1934, as amended (the “Exchange Act”),
since the end of its most recently completed fiscal year through the date hereof, including, without limitation, its most recent
report on Form 10-Q. The Company does not have any subsidiaries other than those identified in its most recent report on Form 10-K.
The Company is qualified to do business as a foreign corporation and is in good standing in every jurisdiction in which the nature
of the business conducted or property owned by it makes such qualification necessary, except for any jurisdiction(s) (alone or
in the aggregate) in which the failure to be so qualified will not have a Material Adverse Effect. For the purposes of this Agreement,
“Material Adverse Effect” means any effect on the business, operations, properties or financial condition of
the Company that is material and adverse to the Company, taken as a whole, and any condition, circumstance or situation that would
prohibit the Company from entering into and performing any of its obligations hereunder.

 

3.2         Authorization;
Enforcement. The Company has the requisite corporate power and authority to enter into and perform this Agreement and to issue
and sell the shares in accordance with the terms hereof. The execution, delivery and performance of this Agreement by the Company
and the consummation by it of the transactions contemplated hereby have been duly and validly authorized by all necessary corporate
action, and no further consent or authorization of the Company, its board of directors or stockholders is required, except pursuant
to Section 7. When executed and delivered by the Company, this Agreement shall constitute a valid and binding obligation of the
Company enforceable against the Company in accordance with its terms, except as such enforceability may be limited by applicable
bankruptcy, reorganization, moratorium, liquidation, conservatorship, receivership or similar laws relating to, or affecting generally
the enforcement of, creditor’s rights and remedies or by other equitable principles of general application. The Company’s
board of directors, at a meeting duly called and held, adopted resolutions approving the transactions contemplated hereby, including
the issuance of the PKU Technology Access Fee Shares, and the Clinical Milestone Shares issuable upon occurrence of the various
Milestone Events in a manner consistent with and that meets the requirements of Nevada Corporate Code contained in Chapter 78 of
the Nevada Revised Statutes.

 

3.3         Issuance
of Shares. The shares to be issued and sold hereunder have been duly authorized by all necessary corporate action and, when
paid for and issued in accordance with the terms hereof, will be validly issued, fully paid and nonassessable. In addition, such
shares will be free and clear of all liens, claims, charges, security interests or agreements, pledges, assignments, covenants,
restrictions or other encumbrances created by, or imposed by, the Company (collectively, “Encumbrances”) and
rights of refusal of any kind imposed by the Company (other than restrictions on transfer under applicable securities laws) and
the holder of such shares shall be entitled to all rights accorded to a holder of Common Stock. As of the date hereof, 88,515,086
shares of the Company’s Common Stock are outstanding.

 

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3.4         No
Conflicts; Governmental Approvals. The execution, delivery and performance of the Agreement by the Company and the consummation
by the Company of the transactions contemplated hereby do not and will not (i) violate any provision of the Company’s Articles
of Incorporation or Bylaws, each as amended to date, (ii) conflict with, or constitute a default (or an event which with notice
or lapse of time or both would become a default) under, or give to others any rights of termination, amendment, acceleration or
cancellation of, any agreement, mortgage, deed of trust, indenture, note, bond, license, lease agreement, instrument or obligation
to which the Company is a party or by which the Company’s properties or assets are bound, or (iii) result in a violation
of any federal, state, local or foreign statute, rule, regulation, order, judgment or decree (including federal and state securities
laws and regulations) applicable to the Company or by which any property or asset of the Company is bound or affected, except for
such conflicts, defaults, terminations, amendments, acceleration, cancellations and violations as would not, individually or in
the aggregate, have a Material Adverse Effect. The Company is not required under federal, state, foreign or local law, rule or
regulation to obtain any consent, authorization or order of, or make any filing or registration with, any court or governmental
agency in order for it to execute, deliver or perform any of its obligations under this Agreement or issue and sell the shares
in accordance with the terms hereof (other than any filings, consents and approvals which may be required to be made by the Company
under applicable state and federal securities laws, rules or regulations prior to or subsequent to the Closing). The sale and issuance
of the shares hereunder will be required to be approved in advance by NYSE MKT.

 

3.5         SEC
Documents, Financial Statements. The Common Stock of the Company is registered pursuant to Section 12(b) of the Exchange Act.
During the two year period preceding the execution of this Agreement, the Company has timely filed all reports, schedules, forms,
statements and other documents required to be filed by it with the Commission pursuant to the reporting requirements of the Exchange
Act (the “SEC Documents”). At the times of their respective filing, all such reports, schedules, forms, statements
and other documents complied in all material respects with the requirements of the Exchange Act and the rules and regulations of
the Commission promulgated thereunder. At the times of their respective filings, such reports, schedules, forms, statements and
other documents did not contain any untrue statement of a material fact or omit to state a material fact required to be stated
therein or necessary in order to make the statements therein, in light of the circumstances under which they were made, not misleading.
As of their respective dates, the financial statements of the Company included in the SEC Documents complied in all material respects
with applicable accounting requirements and the published rules and regulations of the Commission or other applicable rules and
regulations with respect thereto. Such financial statements have been prepared in accordance with generally accepted accounting
principles applied on a consistent basis during the periods involved (except (i) as may be otherwise indicated in such financial
statements or the notes thereto or (ii) in the case of unaudited interim statements, to the extent they may not include footnotes
or may be condensed or summary statements), and fairly present in all material respects the consolidated financial position of
the Company as of the dates thereof and the results of operations and cash flows for the periods then ended (subject, in the case
of unaudited statements, to normal year-end audit adjustments).

 

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3.6         Accountants.
BDO USA, LLP, whose report on the financial statements of the Company is filed with the SEC in the Company’s Annual Report
on Form 10-K for the year ended December 31, 2014 filed with the SEC on March 16, 2015, were, at the time such report was issued,
independent registered public accountants as required by the Securities Act of 1933 and the rules and regulations promulgated thereunder
(together, the “Securities Act”). Except as described in the SEC Documents and as preapproved in accordance
with the requirements set forth in Section 10A of the Exchange Act, to the Company’s knowledge, BDO USA, LLP has not engaged
in any non-audit services prohibited by subsection (g) of Section 10A of the Exchange Act on behalf of the Company.

 

3.7         Internal
Controls. The Company has established and maintains a system of internal accounting controls sufficient to provide reasonable
assurances that: (i) transactions are executed in accordance with management’s general or specific authorization; (ii) transactions
are recorded as necessary to permit preparation of financial statements in conformity with generally accepted accounting principles
in the United States and to maintain accountability for assets; (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 existing assets at reasonable
intervals and appropriate action is taken with respect to any differences.

 

3.8         Corporate
Governance. The Company’s board of directors meets the independence requirements of, and has established an audit committee
that meets the independence requirements of, the rules and regulations of the Commission and the NYSE MKT (formerly the American
Stock Exchange). The Audit Committee has reviewed the adequacy of its charter within the past 12 months.

 

3.9         Disclosure
Controls. The Company has established and maintains disclosure controls and procedures (as such term is defined in Rules 13a-15
and 15d-15 under the Exchange Act). Since the date of the most recent evaluation of such disclosure controls and procedures, there
have been no significant changes in internal controls or in other factors that could significantly affect internal controls, including
any corrective actions with regard to significant deficiencies and material weaknesses. The Company is in compliance in all material
respects with all provisions currently in effect and applicable to the Company of the Sarbanes-Oxley Act of 2002, and all rules
and regulations promulgated thereunder or implementing the provisions thereof.

 

3.10      No
Material Adverse Change. Except as disclosed in the SEC Documents, since March 31, 2015, the Company has not (i) experienced
or suffered any Material Adverse Effect, (ii) incurred any material liabilities, obligations, claims or losses (whether liquidated
or unliquidated, secured or unsecured, absolute, accrued, contingent or otherwise) other than those incurred in the ordinary course
of the Company’s business or (iii) declared, made or paid any dividend or distribution of any kind on its capital stock.

 

3.11     
No Undisclosed Events or Circumstances. Except as disclosed in the SEC Documents, since March 31, 2015,
except for the consummation of the transactions contemplated herein, to the Company’s knowledge, no event or
circumstance has occurred or exists with respect to the Company or its businesses, properties, prospects, operations or
financial condition, which, under applicable law, rule or regulation, requires public disclosure or announcement by the
Company but which has not been so publicly announced or disclosed.

 

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3.12      Litigation.
No action, suit, proceeding or investigation is currently pending or, to the knowledge of the Company, has been threatened in
writing against the Company that: (i) concerns or questions the validity of this Agreement; (ii) concerns or questions the right
of the Company to enter into this Agreement; or (iii) is reasonably likely to have a Material Adverse Effect. The Company is neither
a party to nor subject to the provisions of any material order, writ, injunction, judgment or decree of any court or government
agency or instrumentality. There is no action, suit, proceeding or investigation by the Company currently pending or that the
Company intends to initiate that would have a Material Adverse Effect.

 

3.13      Compliance.
Except for defaults or violations which are not reasonably likely to have a Material Adverse Effect, the Company is not (i) in
default under or in violation of (and no event has occurred that has not been waived that, with notice or lapse of time or both,
would result in a default by the Company under), nor has the Company received notice of a claim that it is in default under or
that it is in violation of, any indenture, loan or credit agreement or any other agreement or instrument to which it is a party
or by which it or any of its properties is bound (whether or not such default or violation has been waived), (ii) is in violation
of any order of any court, arbitrator or governmental body, or (iii) is or has been in violation of any statute, rule or regulation
of any governmental authority, including without limitation all foreign, federal, state and local laws, applicable to its business,
except in each case for such defaults or violations as would not have a Material Adverse Effect.

 

3.14      Intellectual
Property

 

(a)          To
the best of its knowledge, the Company has entered into agreements with each of its current and former officers, employees and
consultants involved in research and development work, including development of the Company’s products and technology providing
the Company, to the extent permitted by law, with title and ownership to patents, patent applications, trade secrets and inventions
conceived, developed, reduced to practice by such person, solely or jointly with other of such persons, during the period of employment
by the Company except where the failure to have entered into such an agreement would not have a Material Adverse Effect. The Company
is not aware that any of its employees or consultants is in material violation thereof.

 

(b)          To
the Company’s knowledge, the Company owns or possesses adequate rights to use all, if any, trademarks, service marks, trade
names, domain names, copyrights, patents, patent applications, inventions, know how (including trade secrets and other unpatented
and/or unpatentable proprietary or confidential information, systems or procedures), and other intellectual property rights (“Intellectual
Property”) as are necessary for the conduct of its business as described in the SEC Documents. Except as described in
the SEC Documents, (i) to the knowledge of the Company, there is no infringement, misappropriation or violation by third parties
of any such Intellectual Property; (ii) there is no pending or, to the knowledge of the Company, threatened action, suit,
proceeding or claim by others against the Company challenging the Company’s rights in or to any such Intellectual Property;
(iii) the Intellectual Property owned by the Company and, to the knowledge of the Company, the Intellectual Property licensed
to the Company has not been adjudged invalid or unenforceable by a court of competent jurisdiction or applicable government agency,
in whole or in part, and there is no pending or, to the knowledge of the Company, threatened action, suit, proceeding or claim
by others challenging the validity or scope of any such Intellectual Property; (iv) there is no pending or, to the knowledge of
the Company, threatened action, suit, proceeding or claim by others against the Company that the Company infringes, misappropriates
or otherwise violates any Intellectual Property or other proprietary rights of others, and the Company has not received any written
notice of such claim; and (v) to the Company’s knowledge, no employee of the Company is the subject of any claim or
proceeding involving a violation of any term of any employment contract, patent disclosure agreement, invention assignment agreement,
non-competition agreement, non-solicitation agreement, nondisclosure agreement or any restrictive covenant to or with a former
employer where the basis of such violation relates to such employee’s employment with the Company or actions undertaken by
the employee while employed with the Company, in each of (i) through (v), for any instances which would not, individually or in
the aggregate, result in a Material Adverse Effect.

 

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3.15      FDA
Compliance.

 

(a)          Except
as described in the SEC Documents, the Company: (i) is in material compliance with all statutes, rules or regulations applicable
to the ownership, testing, development, manufacture, packaging, processing, use, distribution, marketing, labeling, promotion,
sale, offer for sale, storage, import, export or disposal of any product that is under development, manufactured or distributed
by the Company (“Applicable Laws”); (ii) has not received any FDA Form 483, notice of adverse finding, warning
letter, untitled letter or other correspondence or notice from the U.S. Food and Drug Administration (the “FDA”)
or any other federal, state, local or foreign governmental or regulatory authority alleging or asserting material noncompliance
with any Applicable Laws or any licenses, certificates, approvals, clearances, authorizations, permits and supplements or amendments
thereto required by any such Applicable Laws (“Authorizations”), which would not, individually or in the aggregate,
result in a Material Adverse Effect; (iii) possesses all material Authorizations necessary for the operation of its business as
described in the SEC Documents and such Authorizations are valid and in full force and effect and the Company is not in material
violation of any term of any such Authorizations; and (iv) since December 31, 2014: (A) has not received notice of any claim, action,
suit, proceeding, hearing, enforcement, investigation, arbitration or other action from the FDA or any other federal, state, local
or foreign governmental or regulatory authority or third party alleging that any product operation or activity is in material violation
of any Applicable Laws or Authorizations and the Company has no knowledge that the FDA or any other federal, state, local or foreign
governmental or regulatory authority or third party is considering any such claim, litigation, arbitration, action, suit, investigation
or proceeding; (B) has not received notice that the FDA or any other federal, state, local or foreign governmental or regulatory
authority has taken, is taking or intends to take action to limit, suspend, modify or revoke any material Authorizations and has
no knowledge that the FDA or any other federal, state, local or foreign governmental or regulatory authority is considering such
action; (C) has filed, obtained, maintained or submitted all material reports, documents, forms, notices, applications, records,
claims, submissions and supplements or amendments as required by any Applicable Laws or Authorizations and that all such reports,
documents, forms, notices, applications, records, claims, submissions and supplements or amendments were materially complete and
correct on the date filed (or were corrected or supplemented by a subsequent submission); and (D) has not, either voluntarily or
involuntarily, initiated, conducted, or issued or caused to be initiated, conducted or issued, any recall, market withdrawal or
replacement, safety alert, post sale warning, “dear doctor” letter, or other notice or action relating to the alleged
lack of safety or efficacy of any product or any alleged product defect or violation and, to the Company’s knowledge, no
third party has initiated, conducted or intends to initiate any such notice or action.

 

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(b)          Since
January 1, 2015, and except to the extent disclosed in the SEC Documents, the Company has not received any notices or correspondence
from the FDA or any other federal, state, local or foreign governmental or regulatory authority requiring the termination, suspension
or material modification of any studies, tests or preclinical or clinical trials conducted by or on behalf of the Company.

 

3.16       General
Healthcare Regulatory Compliance.

 

(a)          As
used in this subsection:

 

(i)          “Governmental
Entity” means any national, federal, state, county, municipal, local or foreign government, or any political subdivision,
court, body, agency or regulatory authority thereof, and any Person exercising executive, legislative, judicial, regulatory, taxing
or administrative functions of or pertaining to any of the foregoing.

 

(ii)         “Law”
means any federal, state, local, national or foreign law, statute, code, ordinance, rule, regulation, order, judgment, writ, stipulation,
award, injunction, decree or arbitration award or finding.

 

(b)          The
Company has not committed any act, made any statement or failed to make any statement that would reasonably be expected to provide
a basis for the FDA or any other Governmental Entity to invoke its policy with respect to “Fraud, Untrue Statements of Material
Facts, Bribery, and Illegal Gratuities”, or similar policies, set forth in any applicable Laws. Neither the Company, nor,
to the knowledge of the Company, any of its officers, key employees or agents has been convicted of any crime or engaged in any
conduct that has resulted, or would reasonably be expected to result, in debarment under applicable Law, including, without limitation,
21 U.S.C. Section 335a. No claims, actions, proceedings or investigations that would reasonably be expected to result in such a
material debarment or exclusion are pending, or to the knowledge of the Company, threatened, against the Company or any of its
respective officers, employees or agents.

 

(c)          Each
of the Company and, to its knowledge, its directors, officers, employees, and agents (while acting in such capacity) is, and at
all times has been, in material compliance with all health care Laws applicable to the Company or by which any of its properties,
businesses, products or other assets is bound or affected, including, without limitation, the federal Anti-kickback Statute (42
U.S.C. § 1320a-7b(b)), the Anti-Inducement Law (42 U.S.C. § 1320a-7a(a)(5)), the civil False Claims Act (31 U.S.C.
§§ 3729 et seq.), the administrative False Claims Law (42 U.S.C. § 1320a-7b(a)), the Health Insurance Portability
and Accountability Act of 1996 (42 U.S.C. § 1320d et seq.), the exclusion laws (42 U.S.C. § 1320a-7), the Food Drug and
Cosmetic Act (21 U.S.C. §§ 301 et seq.) (collectively, “Health Care Laws”). The Company has not received
any notification, correspondence or any other written or oral communication from any Governmental Entity, including, without limitation,
the FDA, the Centers for Medicare and Medicaid Services, and the Department of Health and Human Services Office of Inspector General,
of potential or actual material non-compliance by, or liability of, the Company under any Health Care Laws.

 

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(d)          The
Company is not a party to any corporate integrity agreements, monitoring agreements, consent decrees, settlement orders, or similar
agreements with or imposed by any Governmental Entity.

 

3.17       Application
of Takeover Protections. The issuance of the shares hereunder and Intrexon’s ownership thereof is not prohibited by the
business combination statutes of the state of Nevada. The Company has not adopted any stockholder rights plan, “poison pill”
or similar arrangement that would trigger any right, obligation or event as a result of the issuance of such shares and Intrexon’s
ownership of such shares and there are no similar anti-takeover provisions under the Company's charter documents.

 

3.18       Listing
and Maintenance Requirements. The Company is in compliance with the requirements of the NYSE MKT for continued listing of the
Company common stock thereon and has not received any notification that, and has no knowledge that NYSE MKT is contemplating terminating
such listing. The issuance and sale of the shares hereunder does not contravene the rules and regulations of the NYSE MKT in any
material respect, provided such sale and issuance is approved in advance by NYSE MKT.

 

3.19       Private
Placement. Neither the Company nor its Affiliates, nor any Person acting on its or their behalf, (i) has engaged in any form
of general solicitation or general advertising (within the meaning of Regulation D under the Securities Act) in connection with
the offer or sale of the shares hereunder, (ii) has, directly or indirectly, made any offers or sales of any security or solicited
any offers to buy any security, under any circumstances that would require registration of the sale and issuance by the Company
of the PKU Technology Access Fee Shares, the Clinical Milestone Shares under the Securities Act or (iii) has issued any shares
of Common Stock or shares of any series of preferred stock or other securities or instruments convertible into, exchangeable for
or otherwise entitling the holder thereof to acquire shares of Common Stock which would be integrated with the sale of the Common
Stock to Intrexon for purposes of the Securities Act or of any applicable stockholder approval provisions, including, without limitation,
under the rules and regulations of any exchange or automated quotation system on which any of the securities of the Company are
listed or designated, nor will the Company or any of its subsidiaries or affiliates take any action or steps that would require
registration of any of the Common Stock under the Securities Act or cause the offering of the Common Stock to be integrated with
other offerings. Assuming the accuracy of the representations and warranties of Intrexon, the offer and sale of the Common Stock
by the Company to Intrexon pursuant to this Agreement will be exempt from the registration requirements of the Securities Act.

 

3.20       No
Manipulation of Stock. The Company has not taken and will not, in violation of applicable law, take, any action outside
the ordinary course of business designed to or that might reasonably be expected to cause or result in unlawful manipulation of
the price of the Common Stock.

 

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3.21       Brokers.
Neither the Company nor any of the officers, directors or employees of the Company has employed any broker or finder in connection
with the transaction contemplated by this Agreement. The Company shall indemnify Intrexon from and against any broker’s,
finder’s or agent’s fees for which the Company is responsible.

 

sECTION
4.      Representations,
Warranties and Covenants of Intrexon.

 

Intrexon hereby represents
and warrants to, and covenants with, the Company as of the date hereof as follows:

 

4.1         Purchaser
Sophistication. Intrexon (a) is knowledgeable, sophisticated and experienced in making, and is qualified to make decisions
with respect to, investments in shares presenting an investment decision like that involved in the purchase of the shares, including
investments in securities issued by the Company and investments in comparable companies, and has requested, received, reviewed
and considered all information it deemed relevant in making an informed decision to purchase the shares; (b) Intrexon, in connection
with its decision to purchase the shares, relied only upon the SEC Documents, other publicly available information, and the representations
and warranties of the Company contained herein; (c) Intrexon is an "accredited investor" pursuant to Rule 501 of Regulation
D under the Securities Act; (d) Intrexon is acquiring the shares for its own account for investment only and with no present intention
of distributing any of such shares or any arrangement or understanding with any other persons regarding the distribution of such
shares; (e) Intrexon has not been organized, reorganized or recapitalized specifically for the purpose of investing in the shares;
(f) Intrexon will not, directly or indirectly, offer, sell, pledge, transfer or otherwise dispose of (or solicit any offers
to buy, purchase or otherwise acquire to take a pledge of) any of the shares except in compliance with the Securities Act and applicable
state securities laws; (g) Intrexon understands that the shares are being offered and sold to it in reliance upon specific exemptions
from the registration requirements of the Securities Act and state securities laws, and that the Company is relying upon the truth
and accuracy of, and Intrexon’s compliance with, the representations, warranties, agreements, acknowledgments and understandings
of Intrexon set forth herein in order to determine the availability of such exemptions and the eligibility of Intrexon to acquire
the shares; (h) Intrexon understands that its investment in the shares involves a significant degree of risk, including a risk
of total loss of Intrexon’s investment (provided that such acknowledgment in no way diminishes the representations, warranties
and covenants made by the Company hereunder); and (i) Intrexon understands that no United States federal or state agency or any
other government or governmental agency has passed upon or made any recommendation or endorsement of the shares.

 

4.2         Authorization
and Power. Intrexon has the requisite power and authority to enter into and perform this Agreement and to purchase the shares
being sold to it hereunder. The execution, delivery and performance of this Agreement by Intrexon and the consummation by it of
the transactions contemplated hereby have been duly authorized by all necessary corporate action, and no further consent or authorization
of Intrexon or its board of directors or stockholders is required. When executed and delivered by Intrexon, this Agreement shall
constitute a valid and binding obligation of Intrexon enforceable against Intrexon in accordance with its terms, except as such
enforceability may be limited by applicable bankruptcy, insolvency, reorganization, moratorium, liquidation, conservatorship, receivership
or similar laws relating to, or affecting generally the enforcement of, creditor’s rights and remedies or by other equitable
principles of general application.

 

    	 	11.	 

     

    

 

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4.3         No
Conflict. The execution, delivery and performance of this Agreement by Intrexon and the consummation by Intrexon of the transactions
contemplated hereby do not and will not (i) violate any provision of Intrexon’s charter or organizational documents, (ii)
conflict with, or constitute a default (or an event which with notice or lapse of time or both would become a default) under, or
give to others any rights of termination, amendment, acceleration or cancellation of, any agreement, mortgage, deed of trust, indenture,
note, bond, license, lease agreement, instrument or obligation to which Intrexon is a party or by which Intrexon’s properties
or assets are bound, or (iii) result in a violation of any federal, state, local or foreign statute, rule, regulation, order, judgment
or decree (including federal and state securities laws and regulations) applicable to Intrexon or by which any property or asset
of Intrexon are bound or affected, except, in all cases, other than violations (with respect to federal and state securities laws)
above, for such conflicts, defaults, terminations, amendments, acceleration, cancellations and violations as would not, individually
or in the aggregate, materially and adversely affect Intrexon’s ability to perform its obligations under the Agreement.

 

4.4         Restricted
Shares. Intrexon acknowledges that the PKU Technology Access Fee Shares and the Milestone Shares are restricted securities
and must be held indefinitely unless subsequently registered under the Securities Act or the Company receives an opinion of counsel
reasonably satisfactory to the Company that such registration is not required. Intrexon is aware of the provisions of Rule 144
promulgated under the Securities Act which permit limited resale of stock purchased in a private placement subject to the satisfaction
of certain conditions, including, among other things, the existence of a public market for the stock, the availability of certain
current public information about the Company, the resale occurring not less than one year after a party has purchased and paid
for the stock to be sold, the sale being through a “broker’s transaction” or a transaction directly with a “market
maker” and the number of shares of the stock being sold during any three-month period not exceeding specified limitations.
Intrexon further acknowledges and understands that the Company may not be satisfying the current public information requirement
of Rule 144 at the time Intrexon wishes to sell the shares and, if so, Intrexon would be precluded from selling the shares under
Rule 144 even if the one year minimum holding period has been satisfied.

 

4.5         Ownership
of Common Stock. As of the date hereof, Intrexon (8,675,768) and its Affiliates (NRM VII Holdings, LLC - 3,625,000) beneficially
own 12,300,768 shares of Common Stock of the Company.

 

4.6         Stock
Legends. Intrexon acknowledges that certificates evidencing the shares shall bear a restrictive legend in substantially the
following form (and including related stock transfer instructions and record notations):

 

    	 	12.	 

     

    

 

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THESE SECURITIES
HAVE NOT BEEN REGISTERED WITH THE SECURITIES AND EXCHANGE COMMISSION OR THE SECURITIES COMMISSION OF ANY STATE IN RELIANCE UPON
AN EXEMPTION FROM REGISTRATION UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), AND, ACCORDINGLY,
MAY NOT BE OFFERED OR SOLD EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT OR PURSUANT TO AN AVAILABLE
EXEMPTION FROM, OR IN A TRANSACTION NOT SUBJECT TO, THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT AND IN ACCORDANCE WITH
APPLICABLE STATE SECURITIES LAWS OR BLUE SKY LAWS AS EVIDENCED BY A LEGAL OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE COMPANY.

 

sECTION
5.      Survival of
Representations, Warranties and Agreements.

 

Notwithstanding any investigation
made by any party to this Agreement, all representations and warranties made by the Company and Intrexon herein shall survive the
execution of this Agreement and the issuance and sale to Intrexon of the shares and shall terminate two years after the PKU Technology
Access Fee Closing, provided, however, the representations and warranties in Sections 3.1, 3.2, 3.3, 4.1, 4.3, 4.4, 4.5 and 4.6
shall survive for so long as Intrexon continues to hold any of the shares issued hereunder.

 

sECTION
6.      Covenants.

 

6.1         Notifications.

 

(a)          During
the period prior to the PKU Technology Access Fee Closing, the Company will promptly advise Intrexon in writing of (i) any Material
Adverse Effect, or (ii) any notice or other communication from any third person or entity alleging that the consent of the third
person is required in connection with the transactions contemplated by this Agreement.

 

(b)          During
the period prior to each of the Milestone Closings, each party shall promptly notify the other of any action, suit or proceeding
that is instituted or specifically threatened in writing against such party to restrain, prohibit or otherwise challenge the legality
of any transaction contemplated by this Agreement.

 

(c)          Information
received by Intrexon pursuant to this Section 6.1 shall be considered “Confidential Information” as such term is defined
in the PKU Channel Agreement and Intrexon agrees to treat such information in accordance with the provisions of Article 7 of the
PKU Channel Agreement.

 

6.2         Compliance.
The Company shall use commercially reasonable best efforts to (i) cause the Common Stock to continue to be registered under the
Exchange Act, file all periodic reports thereunder and continue the listing or trading of the Common Stock on the NYSE MKT or any
successor market (or other exchange upon which the Common Stock may be listed) in good standing and to comply in all material respects
with all applicable rules and regulations of the Commission and all reporting requirements under the rules and regulations of the
Exchange Act and (ii) to satisfy the current public information requirement of Rule 144, in each case for so long as and at all
times during which Intrexon holds any shares.

 

6.3         [RESERVED]

 

    	 	13.	 

     

    

 

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6.4         Best
Efforts. Each party will use its reasonable best efforts to satisfy in a timely fashion each of the conditions to be satisfied
by it under Section 8 of this Agreement.

 

6.5         Press
Release. The Company shall issue any press releases announcing the transaction contemplated by this Agreement in compliance
with the terms and conditions of the PKU Channel Agreement.

 

6.6         Approval.
In each case where the Company determines that the approval of Company investors or any exchange or other listing upon which the
Common Stock may be listed is required for the issuance of Common Stock to Intrexon, the Company shall use commercially reasonable
efforts to secure such approval as promptly as possible. In the event, notwithstanding the foregoing obligation, the Company is
unable to secure the approval with respect to the issuance of any shares to be issued hereunder, the Company shall negotiate the
terms of an alternate form of consideration of equivalent value to such unissued shares.

 

6.7         [RESERVED].

 

6.8         No
Poison Pill. The Company will not adopt any stockholder rights plan, “poison pill” or similar arrangement, or adopt
any anti-takeover provisions under its Charter documents, that would trigger any right, obligation or event as a result of the
issuance of the shares hereunder to Intrexon.

 

6.9         No
Standstill. The parties agree that Intrexon's acquisition of Common Stock pursuant to this Agreement shall not trigger any
standstill provisions set forth in any prior agreements between the parties including in the Stock Purchase Agreement executed
November 18, 2011 by and between Intrexon and Adeona Pharmaceuticals, Inc., and that any such standstill provisions from prior
agreements shall remain otherwise unaffected by this Agreement or the PKU Channel Agreement.

 

6.10     
 Intrexon Proposals. Notwithstanding any of the foregoing provisions of Section 6.9, the Company further
agrees that nothing herein shall limit the ability of Intrexon to confidentially propose to the executive management of the
Company and its board of directors, and/or advocate for, any transaction between the Company and any third party unaffiliated
with Intrexon or its Affiliates.

 

6.11       NYSE
MKT Approval. In each case where the Company determines that the approval of the NYSE MKT (or any other exchange upon which
the Common Stock may be listed) is required for the issuance of Common Stock to Intrexon, the Company shall use commercially reasonable
efforts to secure such approval as promptly as possible. In the event, notwithstanding the foregoing obligation, the Company is
unable to secure the NYSE MKT (or any other exchange upon which the Common Stock may be listed) approval with respect to the issuance
of any shares to be issued hereunder, the Company shall negotiate the terms of an alternate form of consideration of equivalent
value to such unissued shares.

 

    	 	14.	 

     

    

 

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sECTION
7.      Conditions to
Closing.

 

7.1         The
obligation hereunder of the Company to issue and sell shares to Intrexon at each Closing is subject to the satisfaction or waiver,
at or before the Closing of the conditions set forth below. These conditions are for the Company’s sole benefit and may be
waived by the Company at any time in its sole discretion.

 

(a)          Accuracy
of Intrexon’s Representations and Warranties. The representations and warranties of Intrexon shall be true and correct
as of the date when made and as of the Closing Date as though made at that time, except for representations and warranties that
are expressly made as of a particular date, which shall be true and correct as of such date.

 

(b)          No
Injunction. No statute, rule, regulation, executive order, decree, ruling or injunction shall have been enacted, entered, promulgated
or endorsed by any court or governmental authority of competent jurisdiction which prohibits the consummation of any of the transactions
contemplated by this Agreement.

 

(c)          Performance
by Intrexon. Intrexon shall have performed, satisfied and complied in all material respects with all covenants, agreements
and conditions required by this Agreement to be performed, satisfied or complied by Intrexon at or prior to the Closing Date.

 

(d)          Channel
Partnership Agreement. The PKU Channel Agreement shall have been entered into by the Company and Intrexon and shall be in full
force and effect.

 

(e)          No
Proceedings or Litigation. No action, suit or proceeding before any arbitrator or any governmental authority shall have been
commenced, and no investigation by any governmental authority shall have been threatened in writing against Intrexon or any of
the officers, directors or Affiliates of Intrexon seeking to restrain, prevent or change the transactions contemplated by this
Agreement, or seeking damages in connection with such transactions.

 

(f)       
   Officer’s Certificate. On each Closing, Intrexon shall have delivered to the Company a
certificate signed by its Chief Financial Officer or Secretary on behalf of Intrexon, dated as of such Closing, confirming on
behalf of Intrexon the conditions precedent set forth in paragraphs (a), (b), (c) and (e) of this Section 7.1 as of such
Closing; provided, however, if the Company has elected to make the Milestone Cash Payment, the officer’s certificate to
be delivered at the Milestone Closing by Intrexon will address only the conditions precedent set forth in paragraphs (b) and
(e) of this Section 7.1.

 

7.2         The
obligation hereunder of Intrexon to receive shares and consummate the transactions contemplated by this Agreement, other than the
payment by the Company of cash in lieu of issuance of any of the Clinical Milestone Shares, is subject to the satisfaction or waiver,
at or before each Closing, of each of the conditions set forth below. These conditions are for Intrexon’s sole benefit and
may be waived by Intrexon at any time in its sole discretion. For clarity, neither the satisfaction nor the waiver of any of the
events, circumstances, deliveries or conditions set forth below is a condition precedent to the obligation of Intrexon to accept
the any cash payments in lieu of the Company’s issuing the Clinical Milestone Shares to Intrexon.

 

    	 	15.	 

     

    

 

EXECUTION COPY

 

(a)          Accuracy
of the Company’s Representations and Warranties. Each of the representations and warranties of the Company in this Agreement
shall be true and correct as of the Closing Date, except for representations and warranties that speak as of a particular date,
which shall be true and correct as of such date.

 

(b)          Performance
by the Company. The Company shall have performed, satisfied and complied in all material respects with all covenants, agreements
and conditions required by this Agreement to be performed, satisfied or complied with by the Company at or prior to the Closing
Date.

 

(c)          Channel
Partnership Agreement. The PKU Channel Agreement shall have been entered into by the Company and Intrexon and shall be in full
force and effect.

 

(d)          No
Suspension, Etc. Trading in the common stock shall not have been suspended by the Commission or the NYSE MKT.

 

(e)          No
Injunction. No statute, rule, regulation, executive order, decree, ruling or injunction shall have been enacted, entered, promulgated
or endorsed by any court or governmental authority of competent jurisdiction which prohibits the consummation of any of the transactions
contemplated by this Agreement.

 

(f)          No
Proceedings or Litigation. No action, suit or proceeding before any arbitrator or any governmental authority shall have been
commenced, and no investigation by any governmental authority shall have been threatened in writing against the Company or any
of the officers, directors or Affiliates of the Company seeking to restrain, prevent or change the transactions contemplated by
this Agreement, or seeking damages in connection with such transactions.

 

(g)          Execution
of Rights Agreement. On the date of the PKU Technology Access Fee Closing, each party shall have delivered its signature to
the Second Amendment to Registration Rights Agreement substantially in the form attached as Exhibit A to this Agreement
to the other party, and such agreement shall be in full force and effect as of that Closing Date.

 

(h)          Opinion.
Counsel for the Company shall have delivered to Intrexon opinion letters containing legal opinions substantially in the form attached
hereto as Exhibit B.

 

(i)    
      Officer’s Certificate. On each Closing, the Company shall have delivered
to Intrexon a certificate signed by its Chief Financial Officer or Secretary on behalf of the Company (the
“Officer’s Certificate”), dated as of such Closing, confirming on behalf of the Company the
conditions precedent set forth in paragraphs (a), (b), (d), (e), (i) and (j) of this Section 7.2 as of such Closing, and
attaching and certifying a copy of the resolutions of the Company’s board of directors referred to in the last sentence
of Section 3.2.

 

(j)    
      No Material Adverse Effect. Since the date of this Agreement, there shall not
have occurred any Material Adverse Effect.

 

    	 	16.	 

     

    

 

EXECUTION COPY

 

(k)          Approvals.
Any requisite shareholder, board, or exchange approvals relating to the issuance of the PKU Technology Access Fees or the Clinical
Milestone Shares (as the case may be) have been obtained in advance by Company.

 

sECTION
8.      Notices.

 

All notices or other communications which are
required or permitted hereunder shall be in writing and addressed as follows:

 

	If to the Company:	Synthetic Biologics, Inc.
	 	617 Detroit Street, Suite 100
	 	Ann Arbor, MI  48104
	 	Attention:  Chief Executive Officer
	 	Fax No.:  (734) 332-7878
	 	 
	If to Intrexon:	Intrexon Corporation
	 	20374 Seneca Meadows Parkway
	 	Germantown, MD 20876
	 	Attention: Legal Department
	 	Fax No.:  (301) 556-9902

 

or to such other address as the party to whom
notice is to be given may have furnished to the other party in writing in accordance herewith. Any such communication shall be
deemed to have been given when delivered if personally delivered or sent by facsimile (provided that the party providing such notice
promptly confirms receipt of such transmission with the other party by telephone), on the business day after dispatch if sent by
a nationally-recognized overnight courier and on the third business day following the date of mailing if sent by certified mail,
postage prepaid, return receipt requested.

 

sECTION
9.      Miscellaneous.

 

9.1         Fees
and Expenses. Each party shall pay the fees and expenses of its advisors, counsel, accountants and other experts, if any, and
all other expenses, incurred by such party incident to the negotiation, preparation, execution, delivery and performance of this
Agreement.

 

9.2         Waivers
and Amendments. Neither this Agreement nor any provision hereof may be changed, waived, discharged, terminated, modified or
amended except upon the written consent of the parties hereto.

 

9.3         Headings.
The headings of the various sections of this Agreement have been inserted for convenience of reference only and shall not be deemed
to be part of this Agreement.

 

    	 	17.	 

     

    

 

EXECUTION COPY

 

9.4         Severability.
If any provision hereof should be held invalid, illegal or unenforceable in any respect, then, to the fullest extent permitted
by law, (a) all other provisions hereof shall remain in full force and effect and shall be liberally construed in order to carry
out the intentions of the Parties as nearly as may be possible and (b) the parties shall use their best efforts to replace the
invalid, illegal or unenforceable provision(s) with valid, legal and enforceable provision(s) which, insofar as practical, implement
the purposes of such provision(s) in this Agreement.

 

9.5         Governing
Law. This Agreement shall be governed by and construed in accordance with the laws of the State of New York as applied to contracts
entered into and performed entirely in the State of New York by New York residents, without regard to conflicts of law principles.

 

9.6         Counterparts.
This Agreement may be executed in two or more counterparts, each of which shall constitute an original, but all of which, when
taken together, shall constitute but one instrument, and shall become effective when one or more counterparts have been signed
by each party hereto and delivered to the other parties.

 

9.7         Successors
and Assigns. Except as otherwise expressly provided herein, the provisions hereof shall inure to the benefit of, and be binding
upon, the successors, assigns, heirs, executors and administrators of the parties hereto, provided that Intrexon shall not assign
its rights or obligations hereunder unless Intrexon assigns such rights in whole and not in part to an assignee of such rights
and obligations which shall agree in writing with the Company to be bound by this Agreement and that Intrexon’s rights under
Sections 6.3, 6.4, 6.5 and 7 shall not be assignable.

 

9.8         No
Third Party Beneficiaries. This Agreement is intended for the benefit of the parties hereto and their respective permitted
successors and assigns and is not for the benefit of, nor may any provision hereof be enforced by, any other person.

 

9.9         Expenses.
Each party shall pay all costs and expenses that it incurs with respect to the negotiation, execution, delivery and performance
of this Agreement.

 

9.10     
Entire Agreement. This Agreement, the PKU Channel Agreement, the Rights Agreement and other documents
delivered pursuant hereto and thereto, including the exhibits, constitute the full and entire understanding and agreement
between the parties with regard to the subjects hereof and thereof. Except as explicitly set forth herein, nothing in this
Agreement is intended to alter the rights or obligations of the parties pursuant to the Stock Purchase Agreement executed
November 18, 2011 by and between Intrexon and Adeona Pharmaceuticals, Inc.

 

9.11      Publicity.
Except as otherwise provided herein or in the PKU Channel Agreement, no party shall issue any press releases or otherwise make
any public statement with respect to the transactions contemplated by this Agreement without the prior written consent of the other
party, except as may be required by applicable law or regulations, in which case such party shall provide the other parties with
reasonable notice of such publicity and/or opportunity to review such disclosure.

 

    	 	18.	 

     

    

 

EXECUTION COPY

 

9.12       Waiver
of Rule of Construction. Each Party has had the opportunity to consult with counsel in connection with the review, drafting
and negotiation of this Agreement. Accordingly, the rule of construction that any ambiguity in this Agreement shall be construed
against the drafting Party shall not apply.

 

9.13       Further
Assurances. From and after the date of this Agreement, upon the reasonable request of Intrexon or the Company, the Company
and Intrexon shall execute and deliver such instruments, documents and other writings as may be reasonably necessary or desirable
to confirm and carry out and to effectuate fully the intent and purposes of this Agreement.

 

9.14       Company
Sale. For purposes of this Agreement, a “Company Sale” shall mean the sale of the Company, whether
in a single transaction or in a series of related transactions that are consummated contemporaneously (or consummated pursuant
to contemporaneous agreements), to one or more unaffiliated third parties on an arm’s-length basis, pursuant to
which such unaffiliated third party or parties acquires (i) (whether by merger, consolidation, sale or transfer
of capital stock, recapitalization, or otherwise) more than fifty percent (50%) of the Company's common stock or (ii)
all or substantially all of the assets of the Company determined on a consolidated basis.

 

[Remainder of page intentionally left blank.]

 

    	 	19.	 

     

    

 

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In
Witness Whereof, the parties hereto have caused this Stock Issuance Agreement to be executed by their duly authorized
representatives as of the day and year first above written.

 

	 	SYNTHETIC BIOLOGICS, INC.	 
	 	 	 
	 	By:	/s/ Jeffrey Riley	 
	 	Name:	Jeffrey Riley	 
	 	Title:	Chief Executive Officer, President, and Director	 
	 	 	 	 	 
	 	INTREXON CORPORATION	 
	 	 	 	 	 
	 	By:	/s/ Donald P. Lehr	 
	 	Name:	Donald P. Lehr	 
	 	Title:	Chief Legal Officer	 

 

SIGNATURE PAGE FOR STOCK ISSUANCE AGREEMENT

 

    	 	20.	 

     

    

 

Exhibit A

 

FORM OF LEGAL OPINION

 

		1.	The Company has been duly incorporated and is a validly
existing corporation in good standing under the laws of the State of Nevada.

 

		2.	The Company has the requisite corporate power to own,
lease and operate its property and assets, and to conduct its business as described in the SEC Documents.

 

		3.	The Company is duly qualified to do business as a foreign
corporation and is in good standing in the State of Michigan.

 

		4.	The Company has the requisite corporate power to execute,
deliver and perform its obligations under the Agreement, the PKU Channel Agreement and the Rights Agreement (collectively, the
“Transaction Documents”), including, without limitation, to issue, sell and deliver the shares as contemplated
by the Agreement.

 

		5.	All corporate action on the part of the Company necessary
for the authorization, execution and delivery of the Transaction Documents by the Company, the authorization, sale, issuance and
delivery of the shares and the performance by the Company of its obligations to be performed at the Closing under the Transaction
Documents has been taken. Each of the Transaction Documents has been duly and validly authorized, executed and delivered by the
Company. The Agreement and the Rights Agreement (together, the “Equity Documents”) each constitutes a valid
and binding agreement of the Company enforceable against the Company in accordance with its respective terms.

 

		6.	The Company has the authorized capital stock as set forth
in the SEC Documents. The shares have been duly authorized and, when issued, sold and delivered against payment therefor in accordance
with the terms of the Agreement, will be validly issued, fully paid and nonassessable.

 

		7.	There are no pre-emptive rights or similar rights contained
in the Company’s Articles of Incorporation, as amended, or Bylaws, as amended, or any Material Agreement.

 

		8.	The execution and delivery of the Equity Documents and
the issuance of the shares pursuant thereto do not violate any provision of the Company’s Articles of Incorporation or Bylaws,
do not constitute a default under or a material breach of any Material Agreement and do not (a) violate any U. S. Federal or state
statute, rule or regulation which in the experience of such counsel is typically applicable to transactions of the nature contemplated
by the Equity Documents or (b) violate any order, writ, judgment, injunction, decree, determination or award which has been entered
against the Company and of which such counsel is aware, except, with respect to clauses (a) and (b), where such violation would
not materially and adversely affect the Company.

 

    		- i -	 

     

    

 

		9.	To the knowledge of such counsel, there is no action,
proceeding or investigation pending or overtly threatened against the Company before any court or administrative agency that questions
the validity of the Transaction Documents or that could reasonably be expected to result, either individually or in the aggregate,
in a material adverse effect on the Company.

 

		10.	All consents, approvals, authorizations, or orders of,
and filings, registrations and qualifications with any U.S. Federal or state regulatory authority or governmental body required
for the issuance of the shares have been made or obtained, except (a) for the filing of a Form D pursuant to Securities and Exchange
Commission Regulation D and (b) and any requisite blue sky filing(s).

 

		11.	Subject to the accuracy of Intrexon’s representations
in Section 4 of the Agreement and assuming (a) that neither the Company nor any person acting on behalf of the Company has offered
or sold the shares by any form of general solicitation or general advertising within the meaning of Rule 502(c) of Regulation
D promulgated (the “Regulation D”) under the Securities Act; (b) that no offerings or sales of securities of the Company
after the date hereof in a transaction can be “integrated” with any sales of the shares, the offer and sale of the
shares in conformity with the terms of the Agreement constitute transactions that are exempt from the registration requirements
of the Securities Act of 1933, as amended, subject to the timely filing of a Form D pursuant to Regulation D.

 

		12.	The Company is not, and, after giving effect to the offering
and sale of the shares and the application of the proceeds thereof in accordance with the business plans of the Company to which
such counsel is aware, will not be an “investment company” as defined in the Investment Company Act of 1940, as amended.

 

		13.	To the knowledge of such counsel, there are no written
contracts, agreements or understandings between the Company and any person granting such person the right (other than rights which
have been waived in writing or otherwise satisfied) to require the Company to include any securities of the Company in any registration
statement contemplated by Section 2(a) of the Rights Agreement.

 

    		- ii -Exhibit 10.3

 

EXECUTION COPY

 

SECOND AMENDMENT TO REGISTRATION RIGHTS
AGREEMENT

 

This Second Amendment
to Registration Rights Agreement (the “Second Amendment”) is made and entered into as of August 10, 2015, by
and among Synthetic Biologics, Inc., a Nevada corporation, previously known as Adeona Pharmaceuticals, Inc. (the “Company”),
and Intrexon Corporation, a Virginia corporation (“Intrexon”) to amend the Registration Rights Agreement dated
December 5, 2011, by and among the Company and Intrexon (the “Registration Rights Agreement”).

 

WHEREAS, the Company
and Intrexon entered into the Registration Rights Agreement and that certain Stock Purchase Agreement between the Company and Intrexon
dated as of November 18, 2011 (the “Purchase Agreement”) in connection with their execution and delivery of
that certain Exclusive Channel Collaboration Agreement dated November 18, 2011,  for the development and commercialization
of products for the treatment of pulmonary arterial hypertension (the “PAH ECC”);

 

WHEREAS, on August 6,
2012 concurrently Company and Intrexon executed a Stock Issuance Agreement (the “Issuance Agreement”), an exclusive
channel collaboration agreement with respect to the development and commercialization of products based on exogenous recombinant
human antibodies for the treatment of certain toxins and infectious diseases (the “mAb ECC”), and a First
Amendment to the Registration Rights Agreement (the “First Amendment”) which First Amendment amended the terms
of the Registration Rights Agreement;

 

WHEREAS, concurrently
on August 10, 2015 Company and Intrexon executed a Stock Issuance Agreement (the “Second Issuance Agreement”)
and an exclusive channel collaboration agreement with respect to the development and commercialization of certain products for
the treatment of phenylketonuria (the “PKU ECC”), and pursuant to the Second Issuance Agreement Company
and Intrexon agreed to executed a further amendment to the Registration Rights Agreement (as previously amended by the First Amendment);

 

WHEREAS, now pursuant
to the terms of the Second Issuance Agreement and the PKU ECC, the Company will issue and sell to Intrexon, upon Intrexon’s
request to the Company, certain shares of the Company’s common stock in exchange for rights to certain technology of Intrexon;

 

THEREFORE, the Company
and Intrexon hereby agree to further amend the Registration Rights Agreement (after giving full effect to the First Amendment)
as follows:

 

1.           The
following defined terms shall be added to Section 1:

 

(a)        “Clinical
Milestone Shares” shall have the meaning set forth in the Second Issuance Agreement.

 

(b)        “PKU
Technology Access Fee Shares” shall have the meaning set forth in the Second Issuance Agreement.

 

     

     

    

 

EXECUTION COPY

 

(c)        “Second
Issuance Agreement” shall mean that certain Stock Issuance Agreement, dated August 10, 2015, by and between the Company
and Intrexon.

 

2.           The
definition of “Filing Date” shall be amended and replaced in its entirety with the following:

 

(a)        “Filing
Date” means, (i) with respect to the First Tranche Shares, April 4, 2012; (ii) with respect to the Second Tranche Shares,
the Technology Access Fee Shares, the IND Milestone Shares, the Approval Milestone Shares, and the Field Expansion Shares, April
30, 2013; (iii) with respect to the PKU Technology Access Fee Shares, 120 days from the date of issuance of the PKU Technology
Access Fee Shares; and (iv) with respect to the Clinical Milestone Shares, 120 days from each respective issuance of Clinical Milestone
Shares per the terms of the Second Issuance Agreement.

 

3.           The
definition of “Registrable Securities” shall be amended and replaced in its entirety with the following:

 

(a)        “Registrable
Securities” means the First Tranche Shares and Second Tranche Shares (as such terms are defined in the Purchase Agreement),
the Technology Access Fee Shares, the IND Milestone Shares, the Approval Milestone Shares, and the Field Expansion Shares (as such
terms are defined in the Issuance Agreement), and the PKU Technology Access Fee Shares and the Clinical Milestone Shares (as such
terms are defined in the Second Issuance Agreement) issued or issuable to Intrexon and any securities issued with respect to, or
in exchange for or in replacement of such shares of Common Stock upon any stock split, stock dividend, recapitalization, subdivision,
merger or similar event; provided, however, that the applicable Holder has completed and delivered to the Company a Selling Stockholder
Questionnaire; and provided further that such securities shall no longer be deemed Registrable Securities if such securities have
been sold pursuant to a Registration Statement, or (ii) such shares have been sold in compliance with Rule 144 or all such shares
may be sold without limitation pursuant to Rule 144.

 

4.           Subsection
(b) of Section 7 shall be amended and replaced in its entirety with the following:

 

(a)        Entire
Agreement; Amendment. This Agreement, the Purchase Agreement, the Issuance Agreement, and the Second Issuance Agreement contain
the entire understanding and agreement of the parties with respect to the matters covered hereby and, except as specifically set
forth herein, in the Purchase Agreement, in the Issuance Agreement, or in the Second Issuance Agreement, neither the Company nor
any Holder make any representation, warranty, covenant or undertaking with respect to such matters, and they supersede all prior
understandings and agreements with respect to said subject matter, all of which are merged herein. No provision of this Agreement
may be waived or amended other than by a written instrument signed by the Company and the Holders of at least a majority of all
Registrable Securities then outstanding. Any amendment or waiver effected in accordance with this Section 7(b) shall be binding
upon each Holder (and their permitted assigns) and the Company.

 

    2

     

    

 

EXECUTION COPY

 

5.           All
other provisions of the Registration Rights Agreement, as previously amended by the First Amendment, shall remain in effect.

 

[Remainder of page intentionally
left blank.]

 

    3

     

    

 

EXECUTION COPY

 

IN WITNESS WHEREOF,
the parties hereto have caused this Second Amendment to Registration Rights Agreement to be duly executed by their respective authorized
officers as of the date first above written.

 

	SYNTHETIC BIOLOGICS, INC.
	 
	By:	/s/ Jeffrey Riley
	 	Name: Jeffrey Riley
	 	Title: Chief Executive Officer, President, and Director
	 	 
	INTREXON CORPORATION
	 
	By:	/s/Donald P. Lehr
	 	Name: Donald P. Lehr
	 	Title: Chief Legal Officer
	
        
	 

SIGNATURE PAGE TO SECOND AMENDMENT TO REGISTRATION

RIGHTS AGREEMENT

 

    4

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