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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION
Washington,

WASHINGTON, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of
the

Securities Exchange Act of 1934 (Amendment

(Amendment No.    )

SYNLOGIC, INC.

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MIRNA THERAPEUTICS, INC.
2150 Woodward Street, Suite 100
Austin, Texas 78744

NOTICE OF ANNUAL MEETING OF STOCKHOLDERS
TO BE HELD ON JUNE 29, 2016

To Our Stockholders:

You are cordially invited to attend the Stockholders2019 annual meeting of Mirna Therapeutics,stockholders of Synlogic, Inc.:

        The Annual Meeting of Stockholders, or the Annual Meeting, of Mirna Therapeutics, Inc., a Delaware corporation, or the Company, will to be held at 9:00 a.m. Eastern Time on Wednesday, June 29, 20165, 2019 at 8:00 a.m. local time301 Binney Street, Suite 402, Cambridge, MA 02142.

Details regarding the meeting, the business to be conducted at the officesmeeting, and information about Synlogic that you should consider when you vote your shares are described in this proxy statement.

At the annual meeting, three people will be elected to our Board of Latham & Watkins LLP, 885 Third Avenue, New York, New York for the following purposes:

1.

To elect three Class I directorsDirectors. In addition, we will ask stockholders to hold office until the 2019 Annual Meeting of Stockholders or until their successors are elected;



2.

To ratify the selection by the audit committee of our board of directors, of Ernst & YoungKPMG LLP as theour independent registered public accounting firm of the Company for itsour fiscal year ending December 31, 2016; and



3.

To transact such2019. The Board of Directors recommends the approval of each of the two proposals. Such other business will be transacted as may properly come before the Annual Meeting or any adjournment or postponement thereof.

        The foregoing items of business are more fully described inUnder Securities and Exchange Commission rules that allow companies to furnish proxy materials to stockholders over the proxy statement accompanying this Notice. Only stockholders who owned the Company's common stock at the close of business on May 2, 2016 may vote at the Annual Meeting or any adjournments that take place.

        WeInternet, we have elected to providedeliver our proxy materials to the majority of our stockholders over the internet as permitted byInternet. This delivery process allows us to provide stockholders with the rulesinformation they need, while at the same time conserving natural resources and lowering the cost of the U.S. Securities and Exchange Commission. As a result,delivery. On April 18, 2019, we are mailing most ofintend to begin sending to our stockholders a paper copy of the Notice of Internet Availability of Proxy Materials or the Notice, but not a paper copy of our proxy statement. This process allows us to provide our proxy materials to our stockholders in a timelier and more readily accessible manner, while reducing the environmental impact and lowering the costs of printing and distributing our proxy materials. The Notice contains(the “Notice”) containing instructions on how to access those documents over the internet.our proxy statement for our 2019 annual meeting of stockholders and our 2019 annual report to stockholders. The Notice also containsprovides instructions on how to request a paper copy of our proxy materials, including this proxy statementvote online or by telephone and a form of proxy card or voting instruction card. All stockholders who have previously requested a paper copy of our proxy materials will continuehow to receive a paper copy of the proxy materials by mail.

We hope you will be able to attend the annual meeting. Whether you plan to attend the annual meeting or not, it is important that you cast your vote either in person or by proxy. You may vote over the Internet as well as by telephone or by mail. When you have finished reading the proxy statement, you are urged to vote in accordance with the instructions set forth in this proxy statement. We encourage you to vote by proxy so that your shares will be represented and voted at the meeting, whether or not you can attend.

Thank you for your continued support of Synlogic. We look forward to seeing you at the annual meeting.

Sincerely,

Aoife Brennan

President and CEO, CMO

April 18, 2019

NOTICE OF 2019 ANNUAL MEETING OF STOCKHOLDERS

TIME: 9:00 a.m. Eastern Time

DATE: Wednesday, June 5, 2019

PLACE: Synlogic, Inc., 301 Binney Street, Suite 402, Cambridge, MA 02142

PURPOSES:

1. To elect three Class I directors to serve three-year terms expiring in 2022;

2. To ratify the appointment of KPMG LLP as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2019; and

3. To transact such other business that is properly presented at the annual meeting and any adjournments or postponements thereof.

WHO MAY VOTE:

You may vote if you were the record owner of Synlogic, Inc. common stock at the close of business on April 10, 2019. A list of stockholders of record will be available at the annual meeting and, during the 10 days prior to the annual meeting, at our principal executive offices located at 301 Binney Street, Suite 402, Cambridge, MA 02142.

All stockholders are cordially invited to attend the Annual Meeting in person. annual meeting.Whether or not you plan to attend the Annual Meeting, pleaseannual meeting or not, we urge you to vote as soon as possible. by following the instructions in the Notice of Internet Availability of Proxy Materials that you previously received and submit your proxy by the Internet, telephone or mail in order to ensure the presence of a quorum.You may vote overchange or revoke your proxy at any time before it is voted at the internet or by a toll-free telephone number. If, however, you requested to receive paper proxy materials, then you may vote by mailing a complete, signed and dated proxy card or voting instruction card in the envelope provided. Please note that any stockholder attending the Annual Meeting may vote in person, even if the stockholder has already returned a proxy card or voting instruction card.meeting.

        Our board of directors recommends that you vote "FOR" the election of the director nominees named in Proposal No. 1 of the proxy statement and "FOR" the ratification of the appointment of Ernst & Young LLP as our independent registered public accounting firm as described in Proposal No. 2 of the proxy statement.

BY ORDER OF THE BOARD OF DIRECTORS

Maiken Keson-Brookes

Secretary

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SYNLOGIC, INC.

MIRNA THERAPEUTICS, INC.
2150 Woodward301 Binney Street, Suite 100
Austin, Texas 78744402

PROXY STATEMENT
FOR THE 2019 ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD ON JUNE 29, 20165, 2019

This proxy statement, along with the accompanying notice of 2019 annual meeting of stockholders, contains information about the 2019 annual meeting of stockholders of Synlogic, Inc., including any adjournments or postponements of the annual meeting. We are holding the annual meeting at 9:00 a.m., Eastern Time, on Wednesday, June 5, 2019, at our corporate offices located at 301 Binney Street, Suite 402, Cambridge, MA 02142.

In this proxy statement, we refer to Synlogic, Inc. as “Synlogic,” “the Company,” “we”, and “us.”

This proxy statement relates to the solicitation of proxies by our Board of Directors, or Board, for use at the annual meeting.

On or about April 18, 2019, we intend to begin sending to our stockholders the Important Notice Regarding the Availability of Proxy Materials containing instructions on how to access our proxy statement for our 2019 annual meeting of stockholders and our 2018 annual report to stockholders.

EXPLANATORY NOTE

On August 28, 2017, Synlogic, Inc., formerly known as Mirna Therapeutics, Inc. (NASDAQ: MIRN) (“Mirna”), completed its business combination with Synlogic, Inc. (“Private Synlogic”) in accordance with the terms of the Agreement and Plan of Merger and Reorganization, dated as of May 15, 2017, by and among Mirna, Meerkat Merger Sub, Inc. (“Merger Sub”), and Private Synlogic (the “Merger Agreement”), pursuant to which includesMerger Sub merged with and into Private Synlogic, with Private Synlogic surviving as a wholly owned subsidiary of Mirna (the “Merger”). On August 28, 2017, immediately after completion of the Merger, Mirna changed its name to “Synlogic, Inc.” (“Public Synlogic”) (NASDAQ: SYBX).

In this proxy statement, unless the context specifically indicates otherwise, “the Company”, “we”, “us”, “our”, and “Synlogic” refer to Public Synlogic and its subsidiaries following the Merger, effective on August 28, 2017, and to Private Synlogic and its subsidiaries prior to the Merger. References to“Pre-Merger Mirna” means Mirna prior to the Merger effective on August 28, 2017.

IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS FOR THE

SHAREHOLDER MEETING TO BE HELD ON JUNE 5, 2019

This proxy statement, the Notice of Annual Meeting of Stockholders, our form of proxy card and our 2018 annual report to stockholders are available for viewing, printing and downloading at www.proxyvote.com. To view these materials please have your12-digit control number(s) available that appears on your Notice or proxy card. On this website, you can also elect to receive future distributions of our proxy statements and annual reports to stockholders by electronic delivery.

Additionally, you can find a copy of our Annual Report on Form10-K, which includes our financial statements, for the fiscal year ended December 31, 2015, are available2018 on the website of the Securities and Exchange Commission, or the SEC, atwww.sec.gov, or in the “Financials” section of the “Investors & Media” section of our website at www.mirnarx.comwww.synlogictx.com. You may also obtain a printed copy of our Annual Report on Form10-K, including our financial statements, free of charge, from us by sending a written request to: Investor Relations, Synlogic, Inc., 301 Binney Street, Suite 402, Cambridge, MA 02142. Exhibits will be provided upon written request and at www.proxyvote.com.payment of an appropriate processing fee.

QUESTIONSIMPORTANT INFORMATION ABOUT THE ANNUAL MEETING AND ANSWERS REGARDING THE PROXY MATERIALS
AND THE VOTING PROCESS

Why am I receiving these proxy materials?

        We have made these proxy materials available to you on the internet or, upon your request, have delivered paper proxy materials to you, because the board of directors of Mirna Therapeutics, Inc., oris the Company Soliciting My Proxy?

The Board of Synlogic is soliciting your proxy to vote at the 2019 annual meeting of stockholders to be held at 301 Binney Street, Suite 402, Cambridge MA 02142, on Wednesday, June 5, 2019, at 9:00 a.m. Eastern Time and any adjournments of the meeting, which we refer to as the annual meeting. The proxy statement along with the accompanying Notice of Annual Meeting of Stockholders summarizes the purposes of the meeting and the information you need to know to vote at the annual meeting.

We have made available to you on the Internet or have sent you this proxy statement, the Notice of Annual Meeting or any adjournments that take place. The Annual Meeting will be held on Wednesday, June 29, 2016 at 8:00 a.m. local time at the offices of Latham & Watkins LLP, 885 Third Avenue, New York, New York. As a stockholder, you are invited to attend the Annual Meeting and are requested to vote on the proposals described in this proxy statement. However, you do not need to attend the Annual Meeting to vote.

What is included inStockholders, the proxy materials?

        The proxy materials include:

•

This proxy statement, which includes information regarding the proposals to be voted on at the Annual Meeting, the voting process, corporate governance, the compensationcard and a copy of our directors and certain executive officers, and other required information;



•

Our Annual Report on Form10-K for the fiscal year ended December 31, 2015;2018because you owned shares of Synlogic, Inc. common stock on the record date. The Company intends to commence distribution of the Important Notice Regarding the Availability of Proxy Materials, which we refer to throughout this proxy statement as the Notice, and,



•

The proxy card or a voting instruction card for if applicable, the Annual Meeting.

        The proxy materials are being mailed or made available to stockholders on or about April 27, 2016.18, 2019.

Why didDid I receiveReceive a Notice ofin the Mail Regarding the Internet Availability of Proxy Materials or the Notice, in the mail insteadInstead of a complete setFull Set of paper proxy materials?Proxy Materials?

        We have elected to provideAs permitted by the rules of the SEC, we may furnish our proxy materials to our stockholders overby providing access to such documents on the internet as permitted by the rulesInternet, rather than mailing printed copies of these materials to each stockholder. Most stockholders will not receive printed copies of the U.S. Securities and Exchange Commission (the "SEC"). As a result, we are mailing mostproxy materials unless they request them. We believe that this process should expedite stockholders’ receipt of our stockholders a paper copyproxy materials, lower the costs of the annual meeting and help to conserve natural resources. If you received the Notice butby mail or electronically, you will not receive a paperprinted or email copy of the proxy materials. This process allows usmaterials, unless you request one by following the instructions included in the Notice. Instead, the Notice instructs you as to provide our proxy materials to our stockholders in a timelierhow you may access and more readily accessible manner, while reducing the environmental impact and lowering the costsreview all of printing and distributing our proxy materials. The Notice contains instructions on how to access the proxy materials overand submit your proxy on the Internet, and how to request a paper copy of the proxy materials. All stockholders who have

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previously elected to receive a paper copy of our proxy materials will continue to receiveInternet. If you requested a paper copy of the proxy materials, you may authorize the voting of your shares by mail untilfollowing the stockholder terminates such election.instructions on the proxy card, in addition to the other methods of voting described in this proxy statement.

Why did I receive a complete set of paper proxy materials in the mail instead of a Notice of Internet Availability of Proxy Materials?Who Can Vote?

        We are providingOnly stockholders who have previously requested to receive paper copies of the proxy materials with paper copies of the proxy materials instead of the Notice. If you would like to reduce the environmental impact and the costs incurred by us in printing and distributing the proxy materials, you may elect to receive all future proxy materials electronically via email or the internet. To sign up for electronic delivery, please follow the instructions provided with your proxy materials and on your proxy card or voting instruction card.

Who can vote at the 2015 Annual Meeting?

        Only stockholders of recordowned our common stock at the close of business on May 2, 2016 (the "Record Date") will beApril 10, 2019 are entitled to vote at the Annual Meeting. As of April 20, 2016,annual meeting. On this record date, there were 20,830,55525,388,643 shares of our common stock outstanding and entitled to vote. Our common stock is our only class of voting stock.

Stockholder of Record:You do not need to attend the annual meeting to vote your shares. Shares Registeredrepresented by valid proxies, received in Your Name

        If,time for the annual meeting and not revoked prior to the annual meeting, will be voted at the closeannual meeting. For instructions on how to change or revoke your proxy, see “May I Change or Revoke My Proxy?” below.

How Many Votes Do I Have?

Each share of businessourcommon stock that you own entitles you to one vote.

How Do I Vote?

Whether you plan to attend the annual meeting or not, we urge you to vote by proxy. All shares represented by valid proxies that we receive through this solicitation, and that are not revoked, will be voted in accordance with your instructions on the Record Date,proxy card or as instructed via Internet or telephone. You may specify whether your

shares should be voted for or withheld for each nominee for director, and whether your shares wereshould be voted for, against or abstain with respect to the other proposal. If you properly submit a proxy without giving specific voting instructions, your shares will be voted in accordance with the Board’s recommendations as noted below. Voting by proxy will not affect your right to attend the annual meeting. If your shares are registered directly in your name withthrough our stock transfer agent, American Stock Transfer & Trust Company, LLC, thenor you arehave stock certificates registered in your name, you may vote:

Telephone and returning the enclosed proxy card or vote by proxy over the telephone orInternet voting facilities for stockholders of record will be available 24 hours a day and will close at 11:59 p.m. Eastern Time on the internet as instructed below to ensureJune 4, 2019.

If your vote is counted.

Beneficial Owner: Shares Registeredshares are held in “street name” (held in the Namename of a Broker or Bank

        If, at the close of business on the Record Date, your shares were not held in your name, but rather in an account at a brokerage firm, bank, dealer or other similar organization, then you are the beneficial owner of shares held in "street name" and these proxy materials are being forwarded to you by that organization. The organization holding your account is considered to be the stockholder of record for purposes of voting at the Annual Meeting. As a beneficial owner, you have the right to direct your broker or other agent howholder of record), you will receive instructions from the holder of record. You must follow the instructions of the holder of record in order for your shares to vote thebe voted. Telephone and Internet voting also will be offered to stockholders owning shares through certain banks and brokers. If your shares are not registered in your account. You are also invitedown name and you plan to attend the Annual Meeting. However, because you are not the stockholder of record, you may not vote your shares in person at the Annual Meeting unlessannual meeting, you request and obtain a valid proxy from your broker or other agent.

What proposals are scheduled for a vote?

        There are two proposals scheduled for a vote at the Annual Meeting:

•

Proposal No. 1—To elect three Class I directors to hold office until the 2019 Annual Meeting of Stockholders or until their successors are elected; and



•

Proposal No. 2—To ratify the selection, by the audit committee of our board of directors, of Ernst & Young LLP as the independent registered public accounting firm of the Company for the fiscal year ending December 31, 2016.

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How do I vote?

        For Proposal No. 1, you may either vote "FOR" all nominees to the board of directors or you may "WITHHOLD" your vote for any nominee you specify. For Proposal No. 2, you may either vote "FOR" or "AGAINST" or you may abstain from voting.

        The procedures for voting are as follows:

Stockholder of Record: Shares Registered in Your Name

        If you are a stockholder of record, you may vote in person at the Annual Meeting or vote by proxy by telephone or internet or by mail. Whether or not you plan to attend the Annual Meeting, please vote as soon as possible to ensure your vote is counted. You may still attend the Annual Meeting and vote in person even if you have already voted by proxy.

•

To vote in person.  You may attend the Annual Meeting and we will give you a ballot when you arrive. If you need directions to the meeting, please visit http://investor.mirnarx.com/events.cfm.



•

To vote by proxy by telephone or internet.  If you have telephone or internet access, you may submit your proxy by following the instructions provided in the Notice, or if you received paper proxy materials by mail, by following the instructions provided with your proxy materials and on your proxy card or voting instruction card.



•

To vote by proxy by mail.  If you received paper proxy materials, you may submit your proxy by mail by completing and signing your proxy card and mailing it in the enclosed envelope. Your shares will be voted as you have instructed.

Beneficial Owner: Shares Registered in the Name of Broker or Bank

        If you are a beneficial owner of shares registered in the name of your broker, bank, dealer or other similar organization, you should have received a proxy card and voting instructions with these proxy materials from that organization rather than from us. Simply complete and mail the proxy card to ensure that your vote is counted. Alternatively, you may vote by telephone or over the internet as instructed by your broker or other agent. To vote in person at the Annual Meeting, you must obtain a valid proxy from your broker or other agent. Follow the instructions from your broker or other agent included with these proxy materials, or contact your broker or bankagent to requestobtain a legal proxy form.

Can I vote my shares by completing and returning the Notice?

        No. The Notice will, however, provide instructions on how to vote by telephone, by internet, by requesting and returning a paperor broker’s proxy card or voting instruction card, or by submitting a ballotand bring it to the annual meeting in person atorder to vote.

How Does the Annual Meeting.Board Recommend That I Vote on the Proposals?

How many votes do I have?The Board recommends that you vote as follows:

 On each matter to be voted upon, you have one vote for each share of the Company's common stock you own as of the Record Date.

If any other matter is properly presented at the Annual Meeting, your proxyholder (one of the individuals named onannual meeting, your proxy card) will voteprovides that your shares will be voted by the proxy holder listed in the proxy in accordance with his or her discretion.

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Who is paying forbest judgment. At the time this proxy solicitation?statement was first made available, we knew of no matters that needed to be acted on at the annual meeting, other than those discussed in this proxy statement.

May I Change or Revoke My Proxy?

If you give us your proxy, you may change or revoke it at any time before the annual meeting. You may change or revoke your proxy in any one of the following ways:

 We will pay for

Your most current vote, whether by telephone, Internet or by other means of communication. Directors, officers and employeesproxy card is the one that will not be paid any additional compensation for soliciting proxies.counted.

What does it mean if I Receive More Than One Notice or Proxy Card?

You may receive more than one proxy card?

        If you receive more than oneNotice or proxy card yourif you hold shares are registeredof our common stock in more than one nameaccount, which may be in registered form or are registeredheld in different accounts.street name. Please complete, sign and returnvote in the manner described above under “How Do I Vote?” for each proxy cardaccount to ensure that all of your shares are voted.

CanWill My Shares be Voted if I change my vote after submitting my proxy?Do Not Vote?

        Yes. You can revoke your proxy at any time before the final vote at the Annual Meeting. If you are the stockholder of record of your shares are registered in your name or if you may revoke your proxy in any one of three ways:

•

You may submit another properly completed proxy with a later date.



•

You may send a timely written notice that you are revoking your proxy to the Company's Corporate Secretary at Mirna Therapeutics, Inc., 2150 Woodward Street, Austin, Texas 78744.



•

You may attend the Annual Meeting and vote in person. Simply attending the Annual Meetinghave stock certificates, they will not by itself, revoke your proxy.

be counted if you do not vote as described above under “How Do I Vote?” If your shares are held by yourin street name and you do not provide voting instructions to the bank, broker or other agent, you should follow the instructions provided by your broker or agent.

What is the quorum requirement?

        A quorum of stockholders is necessary to hold a valid meeting. A quorum will be present if stockholders holding at least a majority of the outstanding shares entitled to vote are present at the Annual Meeting. On April 20, 2016, there were 20,830,555 shares outstanding and entitled to vote. Accordingly, we expect that the holders of at least 10,415,278 shares must be present at the Annual Meeting to have a quorum. Your shares will be counted toward the quorum at the Annual Meeting only if you vote in person at the meeting, or you submit a valid proxy vote.

        Abstentions and broker non-votes (as described below) will be counted towards the quorum requirement. If there is no quorum, the holders of a majority of shares present and entitled to vote at the meeting in person or represented by proxy may adjourn the Annual Meeting to another date.

How are votes counted?

        Votes will be counted by the Inspector of Elections appointed for the Annual Meeting. The Inspector of Elections will separately count "FOR," "WITHHOLD" and broker non-votes for Proposal No. 1 (the election of directors) and "FOR" and "AGAINST" votes, abstentions and, if any, broker non-votes for Proposal No. 2 (the ratification of the selection of Ernst & Young LLP as the independent registered accounting firm of the Company for the fiscal year ending December 31, 2016).

        If your shares are held by your broker or other agent as your nominee (that is, held beneficially in "street name"), you will need to obtain a proxy form from the institution that holds your shares and followas described above, the instructions included on that form regarding how to instruct yourbank, broker or other agentnominee that holds your shares has the authority to vote your shares. Ifunvoted shares only with respect to Proposal 2. Therefore, we encourage you do not giveto provide voting instructions to your bank, broker or other agent,nominee. This ensures your shares will be voted at the annual meeting and in the manner you desire. A “brokernon-vote” will occur if your broker or other agent can onlycannot vote your shares with respect to "routine" matters (as described below).

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What are "broker non-votes"?

        Ifon a particular matter because it has not received instructions from you hold shares beneficially in street name and dodoes not providehave discretionary voting authority on that matter or because your broker with voting instructions, your shares may constitute "broker non-votes." Broker non-votes occurchooses not to vote on a matter when a brokerfor which it does have discretionary voting authority.

What Vote is not permittedRequired to Approve Each Proposal and How are Votes Counted?

Is Voting Confidential?

We will keep all the beneficial ownerproxies, ballots and instructions are not given. These matters are referred to as "non-routine" matters. Proposal No. 1, to elect directors, is a non-routine matter, but Proposal No. 2, to ratify the selectionvoting tabulations private. We only let our Inspector of Election, our independent registered public accounting firm, is a "routine" matter. Broker non-votesSecretary,examine these documents. Management will not know how you voted on a specific proposal unless it is necessary to meet legal requirements. We will, however, forward to management any written comments you make on the proxy card or otherwise provide.

Where Can I Find the Voting Results of the Annual Meeting?

The preliminary voting results will be counted toward the vote total for any proposalannounced at the Annual Meeting.annual meeting, and we will publish preliminary results, or final results if available, in a Current Report on Form8-K within four business days of the annual meeting. If final results are unavailable at the time we file the Form8-K, then we will file an amended report on Form8-K to disclose the final voting results within four business days after the final voting results are known.

How many votes are needed to approve each proposal?What Are the Costs of Soliciting these Proxies?

•

Proposal No. 1—To elect three Class I

We will pay all of the costs of soliciting these proxies. Our directors to hold office until the 2019 Annual Meeting of Stockholders or until their successors are elected. The two nominees receiving the most "FOR" votes (from the votes of shares presentand employees may solicit proxies in person or representedby telephone, fax or email. We will pay these employees and directors no additional compensation for these services. We will ask banks, brokers and other institutions, nominees and fiduciaries to forward these proxy materials to their principals and to obtain authority to execute proxies. We will then reimburse them for their expenses.

What Constitutes a Quorum for the Annual Meeting?

The presence, in person or by proxy, and entitled to vote on the election of directors) will be elected. Broker non-votes will not be counted towards the vote total for this proposal.



•

Proposal No. 2—To ratify the selection, by the audit committee of our board of directors, of Ernst & Young LLP as the independent registered public accounting firm of the Company for the fiscal year ending December 31, 2016. "FOR" votes from the holders of a majority of the voting power of all outstanding shares cast (excludingof our common stockentitled to vote at the annual meeting is necessary to constitute a quorum at the annual meeting. Votes of stockholders of record who are present at the annual meeting in person or by proxy, abstentions, and broker non-votes)non-votes are required to approve this proposal. Because Proposal No. 2 is consideredcounted for purposes of determining whether a "routine" matter, broker non-votes are not expected in connection with this proposal.

How can I find out the results of the voting atAttending the Annual Meeting?Meeting

        WeThe annual meeting will disclose final voting results in a Current Report on Form 8-K filed with the SEC within four business days after the Annual Meeting. If final voting results are unavailablebe held at that time, then we intend to file a Current Report on Form 8-K to disclose preliminary voting results and file an amended Current Report on Form 8-K within four business days after the date the final voting results are available.

9:00 a.m. Eastern timeon Wednesday, June 5, 2019at 301 Binney Street, Suite 402, Cambridge, MA 02142. When are stockholder proposals due for next year's annual meeting?

        To be considered for inclusion in the proxy materials for the 2017 Annual Meeting of Stockholders, your proposal must be submitted in writing by December 27, 2016you arrive, signs will direct you to the Company's Corporate Secretary at Mirna Therapeutics, Inc., 2150 Woodward Street, Suite 100, Austin, Texas 78744. However,appropriate meeting rooms. You do not need to attend the annual meeting in order to vote.

Householding of Annual Disclosure Documents

SEC rules concerning the delivery of annual disclosure documents allow us or your broker to send a single Notice or, if the meeting is more than 30 days from June 29, 2017, then the deadline will beapplicable, a reasonable time before we begin to print and mailsingle set of our proxy materials forto any household at which two or more of our stockholders reside, if we or your broker believe that meeting.the stockholders are members of the same family. This practice, referred to as “householding,” benefits both you and us. It reduces the volume of duplicate information received at your household and helps to reduce our expenses. The rule applies to our Notices, annual reports, proxy statements and information statements. Once you receive notice from your broker or from us that communications to your address will be “householded,” the practice will continue until you are otherwise notified or until you revoke your consent to the practice. Stockholders who participate in householding will continue to have access to and utilize separate proxy voting instructions.

If your household received a single Notice or, if applicable, a single set of proxy materials this year, but you would prefer to receive your own copy, please contact our corporate secretary at Synlogic, Inc., 301 Binney Street, Suite 402, Cambridge MA 02142.

If you do not wish to submitparticipate in “householding” and would like to receive your own Notice or, if applicable, set of Synlogic’s proxy materials in future years, follow the instructions described below. Conversely,

if you share an address with another Synlogic stockholder and together both of you would like to receive only a proposal beforesingle Notice or, if applicable, set of proxy materials, follow these instructions:

Electronic Delivery of Company Stockholder Communications

Most stockholders can elect to view or receive copies of future proxy materials over the Internet instead of receiving paper copies in the mail.

You can choose this option and save the Company the cost of producing and mailing these documents by:

SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

The following table sets forth certain information with respect to the beneficial ownership of our common stock as of April 1, 2019 for (a) the executive officers named in the Summary Compensation Table on page 19 of this proxy statement, (b) each of our directors and director nominees, (c) all of our current directors and executive officers as a group and (d) each stockholder known by us to own beneficially more than 5% of our common stock. Beneficial ownership is determined in accordance with the rules of the SEC and includes voting or investment power with respect to the securities. We deem shares of common stock that may be acquired by an individual or group within 60 days of April 1, 2019 pursuant to the exercise of options to be outstanding for the purpose of computing the percentage ownership of such individual or group, but are not deemed to be outstanding for the purpose of computing the percentage ownership of any other person shown in the table. Except as indicated in footnotes to this table, we believe that the stockholders or nominate a director at the 2017 Annual Meetingnamed in this table have sole voting and investment power with respect to all shares of Stockholders, but you are not requesting that your proposal or nominationcommon stock shown to be included in the proxy materials for that meeting, then you must follow the procedures set forth in our bylaws and, among other things, notify the Company's Corporate Secretary in writing between Marchbeneficially owned by them based on information provided to us by these stockholders. Percentage of ownership is based on 25,388,643 shares of common stock outstanding on April 1, 2017 and March 31, 2017. However, if the date of the 2017 Annual Meeting of Stockholders is more than 30 days before or more than 60 days after June 29, 2017, then you must give notice not later than the 90^th day prior to that meeting or, if later, the 10^th day following the day on which public disclosure of that annual meeting date is first made. You are also advised to review our bylaws, which contain additional requirements regarding advance notice of stockholder proposals and director nominations.

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PROPOSAL NO. 1
ELECTION OF DIRECTORS
2019.

MANAGEMENT AND CORPORATE GOVERNANCE

The Board of Directors

Our boardbylaws provide that our business is to be managed by or under the direction of directorsour Board. Our Board is divided into three classes. Eachclasses for purposes of election. One class consists, as nearly as possible,is elected at each annual meeting of one-third of the total number of directors, and each class hasstockholders to serve for a three-year term. ExceptOur Board currently consists of eight members, classified into three classes as otherwise provided by law, vacancies onfollows: (1) Aoife Brennan, Patricia Hurter and Richard P. Shea constitute a class with a term ending at the board of directors may be filled only by individuals elected by2019 annual meeting; (2) Peter Barrett, Edward Mathers and Michael Powell constitute a majorityclass with a term ending at the 2020 annual meeting; and (3) Chau Khuong and Nick Leschlyconstitute a class with a term ending at the 2021 annual meeting.

On March 5, 2019, our Board accepted the recommendation of the remaining directors. A director elected byNominating and Governance Committee and voted to nominate Aoife Brennan, Patricia Hurter and Richard P. Shea for election at the board of directors to fillannual meeting for a vacancy in a particular class, including a vacancy created by an increase in the number of directors, shall serve for the remainder of the full term of that classthree years to serve until the 2022 annual meeting of stockholders, and until such director's successor istheir respective successors have been elected and qualified or until such director'sdirector’s earlier death, resignation or removal.

        Our boardSet forth below are the names of directors currently consists of eightthe persons nominated as directors and no vacancies, divided intodirectors whose terms do not expire this year, their ages, their offices in the three following classes:

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The Class ICompany, if any, their principal occupations or employment for at least the past five years, the length of their tenure as directors are Elaine V. Jones, Ph.D., Matthew Winkler, Ph.D. and Peter S. Greenleaf, whose current terms will expirethe names of other public companies in which such persons hold or have held directorships during the past five years. Additionally, information about the specific experience, qualifications, attributes or skills that led to our Board’s conclusion at the Annual Meeting;



•

The Class II directors are Lawrence M. Alleva and Michael Powell, Ph.D., whose current terms will expire at the 2017 Annual Meetingtime of Stockholders; and



•

The Class III directors are Paul Lammers, M.D., M.Sc., Edward Mathers and Clay B. Siegall, Ph.D., whose current terms will expire at the 2018 Annual Meetingfiling of Stockholders.

        Dr. Winkler, Mr. Greenleaf and Dr. Perry Nisen, M.D., Ph.D. have been nominated tothis proxy statement that each person listed below should serve as Class I directors and have agreed to stand for election. If the nominees for Class I are elected at the Annual Meeting, then each nominee will serve for a three-year term expiring at the 2019 Annual Meeting of Stockholders, or until his or her successordirector is elected and qualified, or until his or her earlier death, resignation or removal.

        Our directors are elected by a plurality of the votes cast. If a choice is specified on the proxy card by a stockholder, the shares will be voted as specified. If a choice is not specified on the proxy card, and authority to do so is not withheld, the shares will be voted "FOR" the election of the three nominees for Class I above. If any of the nominees becomes unavailable for election as a result of an unexpected occurrence, shares that would have been voted for the nominee will instead be voted for the election of a substitute nominee proposed by the Company's management or the board of directors. Each person nominated for election has agreed to serve if elected. Our management has no reason to believe that any nominee will be unable to serve.set forth below:

 The following is a brief biography and discussion of the specific attributes, qualifications, experience and skills of each nominee for director and each director whose term will continue after the Annual Meeting. Our board of directors and management encourage each nominee for director and each continuing director to attend the Annual Meeting.

THE BOARD OF DIRECTORS RECOMMENDS A VOTE
"FOR" EACH OF THE THREE CLASS I NOMINEES FOR DIRECTOR.

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        The following table sets forth, for the Class I nominees and for our other current directors who will continue in office after the Annual Meeting, information with respect to their ages and position held within the Company. Dr. Winkler is standing for re-election and Dr. Nisen and Mr. Greenleaf are standing for their initial election by our stockholders.

Nominees for Election to a Three-Year Term Expiring at the 2019 Annual Meeting of StockholdersNick Leschly.

        Perry Nisen, M.D.Aoife Brennan, MB, BCh, BAO, MMSc., Ph.D.    Dr. Nisen is standing for election at our Annual Meeting. Heage 43, has beenserved as President and Chief Executive Officer and a member of Sanford Burnham Prebys Medical Discovery Institute, a non-profit medical research institute,our Board since August 2014 and holds the Donald Bren Chief Executive Chair. From June 2004 toOctober 2018. In September 2014,2016, Dr. NisenBrennan served in various roles at GlaxoSmithKline, including most recently Senior Vice President of Science and Innovation, as well as Chief Medical Officer Seniorof Private Synlogic and was responsible for the oversight and direction of its clinical development strategy and operations. From May 2011 to August 2016, Dr. Brennan was Vice President and Oncology Therapy Area Head Senior Vice President of Cancer Research, Senior Vice Presidentthe Rare Disease Innovation Unit at Biogen, a biotechnology company, where she was responsible for research and development of the Biogen rare disease portfolio, which involved programs ranging frompre-clinical to commercial, including the approval of ALPROLIX^®, ELOCTATE^® and SPINRAZA^®. From 2008 to 2011, Dr. Brennan was director of clinical development at Tolerx, Inc., astart-up biotechnology company focusing on immunotherapy for Type 1 diabetes. Dr. Brennan serves on the board of directors of Ra Pharmaceuticals, Inc., a clinical stage publicly-traded biopharmaceutical company focused on the development of next-generation therapeutics for complement-mediated diseases. Dr. Brennan holds a medical degree from Trinity College Dublin, Ireland and completed her post-graduate training in internal medicine, endocrinology and metabolism at the Royal College of Physicians in Ireland. Additionally, she completed her post-doctoral training in clinical research and metabolism at the Beth

Israel Deaconess Medical Center in Boston and is a graduate of the Harvard Medical School Scholars in Clinical Pharmacology and Discovery Medicine. BeforeScience Program. The Board has concluded that Dr. Nisen was Divisional Vice PresidentBrennan possesses specific attributes that qualify her to serve as a member of Cancer Research and Oncology Development at Abbott Laboratories. Dr. Nisen holds a B.S. from Stanford University and M.D. and Ph.D. degrees from the Albert Einstein College of Medicine. Dr. Nisen has been chosen to join our Board, because of his medicalincluding the perspective and scientificexperience she brings as our Chief Executive Officer and Chief Medical Officer, which brings operational expertise experience in the healthcare industry and broad management experience.to our Board.

        Matthew Winkler, Ph.D.Richard P. Shea    Dr. Matthew Winkler was our founder and, age 67, has served as a member of our Board since the Merger closed on August 28, 2017. Mr. Shea has served as the Chief Financial Officer of Syndax Pharmaceuticals, Inc. since February 2017. Mr. Shea previously served as a member of the Syndax Pharmaceuticals board of directors from January 2014 to February 2017. From July 2007 through December 2016, Mr. Shea served as Senior Vice President and Chief Financial Officer of Momenta Pharmaceuticals Inc., a publicly-traded biotechnology company, and was its Vice President and Chief Financial Officer since October 2003. Prior to joining Momenta, Mr. Shea served as Chief Operating Officer and Chief Financial Officer of Variagenics Inc., a publicly-traded pharmacogenomics company, that was merged with Hyseq Pharmaceuticals Inc., and as Vice President, Finance of Genetics Institute, Inc., a publicly-traded biotechnology company, which was acquired by Wyeth Pharmaceuticals, Inc., which was then acquired by Pfizer, Inc. Mr. Shea received an A.B. from Princeton University and an M.B.A. from the Public Management Program at Boston University. The Board has concluded Mr. Shea possesses specific attributes that qualify him to serve as a member of our Board, including his experience with the healthcare and pharmaceutical industries and his broad life sciences industry knowledge.

Patricia Hurter, Ph.D., age 55, has served as a member of Synlogic’s Board since February 2019. Dr. Hurter has been Senior Vice President at Vertex since 2011, during which time her responsibilities grew to include all CMC and preclinical development activities of Vertex’s R&D portfolio, as well as the internal GMP manufacturing facility that provides drug substance and product for clinical development and commercial supply. From 2013 to 2014, she served as Interim Head of Global Regulatory Affairs at Vertex and oversaw the submission of the new drug application for Orkambi^®, as well as several label expansions for Kalydeco^®. She has played a leadership role in the development and commercialization of four transformative therapies for Vertex: Incivek^®, Kalydeco^®, Orkambi^® and Symdeko^®. Prior to joining Vertex, Dr. Hurter was Director, Formulation Design and Characterization for Merck where she was a key member of the early development team for Januvia^®, a treatment for Type II diabetes. Dr. Hurter serves as a member of the Board of Trustees of Harvard Conservation Trust. She holds a Ph.D. in chemical engineering from the Massachusetts Institute of Technology, an M.S. in mechanical engineering from West Virginia University and earned a B.Sc. in chemical engineering,cum laude, from the University of KwaZulu-Natal in Durban, South Africa. The Board has concluded that Dr. Hurter possesses specific attributes that qualify her to serve as a member of our Board, including her experience in drug research and development, global regulatory affairs and GMP manufacturing.

Peter Barrett, Ph.D., age 66, has served as Chairman of our Board since the Merger closed on August 28, 2017, and prior to that time served as the Chairman of the Private Synlogic board of directors since December 2007, includingMarch 2014. Dr. Barrett joined Atlas Venture L.P., an early-stage venture capital fund, in 2002, and currently serves as Chairman until October 2012. During 2008a Partner. From 1998 to 2009,2002, Dr. Winkler servedBarrett was Executive Vice President and Chief Business Officer of Celera Genomics Group (now Celera Corporation, a subsidiary of Quest Diagnostics), a biotechnology company, whichhe co-founded. From 1979 to 1998, Dr. Barrett held senior management positions at Perkin-Elmer Corporation, most recently serving as our Executive Chairman. Since January 2013,Vice President, Corporate Planning and Business Development. Dr. Winkler has beenBarrett currently serves on the Chairman of the boardboards of directors of Asuragen, Inc. ("Asuragen"), a molecular diagnostic and pharmacogenomics service company, where he also served as the Chief Executive Officer from 2006 to December 2012. Prior to Asuragen, Dr. Winkler was the founder and Chief Executive Officer of Ambion,PerkinElmer, Inc., aZafgen, Inc. and several privately held company that developedcompanies. Dr. Barrett is a Senior Fellow at Harvard Business School and sold research reagents for RNA analysis. Until March 2016, Dr. Winkler served onis the faculty chair of the key advisory board of Second Genome,the Blavatnik Fellowship Program. Dr. Barrett is a biotherapeutics company.member of the research council at Boston Children’s Hospital. Dr. Winkler receivedBarrett holds a B.S. in GeneticsChemistry from Lowell Technological Institute (now the University of Massachusetts, Lowell) and a Ph.D. in ZoologyAnalytical Chemistry from the University of California at Berkeley.Northeastern University. He also completed Harvard Business School’s Management Development Program. The Board has concluded that Dr. Winkler was an Assistant and Associate Professor of Zoology at the University of Texas from 1983 to 1991. Dr. Winkler has been chosenBarrett possesses specific attributes that qualify him to serve on our boardas a member and chairman of directors due tothe Board, including his managementextensive leadership, executive, managerial and business experience with life sciences companies, including experience in the formation, development and business strategy of multiplestart-up companies in the life sciences and pharmaceutical industries.sector.

        Peter S. Greenleaf.Edward Mathers, age 59, has served as a member of our Board since October 2012. Mr. GreenleafMathers previously served on the Private Synlogic board of directors since July 2014. Since 2008, Mr. Mathers has been the Chief Executive Officer and a Director of Sucampo Pharmaceuticals, Inc. since March 2014 and was appointed chairman of the board in January

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2016. In addition, Mr. Greenleaf is currentlyPartner at NEA, a Director of Mast Therapeutics, Inc. and has served since November 2015. Prior to his leadership of Sucampo, Mr. Greenleaf was CEO and a board member of Histogenics Corporation, a regenerative medicine company, from June 2013 through February 2014. From April 2006 to June 2013, Mr. Greenleaf was employed by MedImmune LLC, the global biologics arm of AstraZeneca, where he most recently served as President. While at MedImmune, Mr. Greenleaf was instrumental in driving the expansion of MedImmune's pipeline into over 120 clinical and pre-clinical programs and the commercialization of its marketed products. Mr. Greenleaf also served as President of MedImmune Ventures from January 2010 to June 2013, a wholly ownedprivate venture capital fund within the AstraZeneca Group, where he led investment in emerging biopharmaceutical, medical device,firm focusing on technology and diagnostic companies. Prior to serving as President of MedImmune,healthcare investments. Mr. Greenleaf was the Chief Commercial Officer of the company, responsible for its commercial, corporate development and strategy functions. Mr. Greenleaf has also held senior commercial roles at Centocor Biotech, Inc. (now Jansen Biotechnology, Johnson & Johnson) from 1998 to 2006 and prior to that Boehringer Mannheim G.m.b.H. (now Roche Holdings) from 1996 to 1998. Mr. Greenleaf currently chairs the Maryland Venture Fund Authority, whose vision is to oversee implementation of InvestMaryland, a public-private partnership to spur venture capital investment in the state. Mr. Greenleaf is also a member ofMathers serves on the board of directors of the Biotechnology Industry Organization (BIO), where hefollowing publicly-traded pharmaceutical companies: ObsEva SA, Ra Pharmaceuticals, Inc. and Rhythm Pharmaceuticals, Inc. Mr. Mathers also serves on the Governing Board of the Emerging Companies Section. He is also a member of the board of directors of the Pharmaceutical Researchseveral privately held companies. From 2002 to 2008, Mr. Mathers served as Executive Vice President, Corporate Development and Manufacturers of America (PhRMA).Venture at MedImmune, Inc., a biopharmaceutical company, and led its venture capital subsidiary, MedImmune Ventures, Inc. Before joining MedImmune in 2002, Mr. Greenleaf's previous Board appointments include the University of Maryland Baltimore Foundation,Mathers was Vice President, Marketing and Corporate Licensing and Acquisitions at Inhale Therapeutic Systems, a biotechnology company. Previously, Mr. Mathers spent 15 years at Glaxo Wellcome, Inc.; Rib-X Pharmaceuticals; LigoCyte Pharmaceuticals; (GlaxoSmithKline), a pharmaceutical company, where he held various sales and Corridor Pharmaceuticals. Hemarketing positions. Mr. Mathers received a Master of Business Administration degreeB.S. in Chemistry from St. Joseph's University and a Bachelor of Science degree from Western ConnecticutNorth Carolina State University. The Board has concluded that Mr. Greenleaf has been chosenMathers possesses specific attributes that qualify him to serve on our board of directors due to his leadership experience and extensive commercialization, strategic planning, and drug development experience in the biopharmaceutical industry.

THE BOARD OF DIRECTORS RECOMMENDS A VOTE
FOR THE ELECTION OF EACH OF THE ABOVE NAMED NOMINEES

Directors Continuing in Office Until the 2017 Annual Meeting of Stockholders

        Lawrence M. Alleva.    Mr. Lawrence M. Alleva joined our board in July 2014. Prior to his retirement in June 2010, Mr. Alleva worked with PricewaterhouseCoopers LLP, or PwC, for 39 years, 28 of which as a partnermember our Board, including his experience with the firm. Mr. Alleva served clients primarily in the technology sector, including numeroushealthcare and pharmaceutical industries and biotechnology companies. Additionally, he served PwC in a variety of office, regional and national practice leadership roles, most recently as the U.S. Ethics and Compliance Leader (Assurance) for PwC from 2006 until his retirement. Mr. Alleva is a Certified Public Accountant (inactive). Mr. Alleva received a Bachelor of Science degree from Ithaca College (magna cum laude) and attended Columbia University's Executive MBA program. Mr. Alleva also serves as a director for public companies Tesaro Inc. and Bright Horizons Family Solutions, and previously served on the board of GlobalLogic Inc. Mr. Alleva has been chosen to serve on our board of directors due to his financial and accounting experience as a director and a public accounting partner serving multiple healthcare, pharmaceutical and biopharmaceutical companies.broad management experience.

Michael Powell, Ph.D., age 64, has served as a member of our Board since October 2012. Dr. Michael Powell haspreviously served as Chairman of our board of directors sinceBoard from October 2012.2012 until the Merger closed on August 28, 2017. Since 1997, Dr. Powell has been a General Partner of Sofinnova Ventures, a venture capital firm. Previously, Dr. Powell has held positions at Genentech, Inc., a biotechnology company, Cytel Inc., a research and development company, and Syntex Research Group, a pharmaceutical company. Dr. Powell is currently a directorserves on the board of Dauntless Pharmaceuticals, a biopharmaceutical company, Alvine Pharmaceuticals, a biopharmaceutical company, Ascenta Therapeutics, a biopharmaceutical company, Checkmate Pharmaceuticals, a biopharmaceutical company, Dauntless 1, a biopharmaceutical company, and Ocera Therapeutics, a publicly traded biopharmaceutical company.directors of numerous privately-held companies. Dr. Powell is an Adjunct

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Professor at the University of Kansas. Dr. Powell is the Board President of the AIDS Vaccine Advocacy Coalition and serves on the advisory board of the Institute for the Advancement of Medical Innovation at the University of Kansas. Dr. Powell received a B.S. in Chemistry from Scarborough College, a Ph.D. in Physical Chemistry from the University of Toronto and completed his post-doctoratepost-doctoral work in Bioorganic Chemistry at the University of California. The Board has concluded that Dr. Powell has been chosenpossesses specific attributes that qualify him to serve onas a member of our board of directors due toBoard, including his experience with the life sciences and pharmaceutical industries and the venture capital industry.

Directors Continuing in Office Until the 2018 Annual Meeting of Stockholders

        Paul Lammers, M.D.Chau Khuong, M.Sc.    Dr. Paul Lammersage 43, has served as a member of our board of directorsBoard since the Merger closed on August 28, 2017, and as our President and Chief Executive Officer since November 2009. Previously, Dr. Lammers wasprior to that time served on the President of Repros Therapeutics Inc., or Repros Therapeutics, a biopharmaceutical company, from February 2009 until October 2009. From August 2002 until September 2008, Dr. Lammers served as the Chief Medical Officer for EMD Serono, Inc., a biopharmaceutical division of Merck KGaA, a global pharmaceutical and chemical group. Previously, Dr. Lammers served as the Senior Vice President of clinical and regulatory affairs at Zonagen, Inc., which later became Repros Therapeutics. Dr. Lammers began his career with Organon International, a pharmaceutical company, spending eight years in the commercial and clinical operations in Europe and the United States. Dr. Lammers received a M.Sc. and M.D. from the Catholic University (Radboud University) in Nijmegen, The Netherlands. Dr. Lammers has been chosen to serve on our board of directors due to his management experience in multiple pharmaceutical and biopharmaceutical companies and drug development.

        Edward Mathers.    Mr. Edward Mathers has served as a member of ourPrivate Synlogic board of directors since October 2012. Since August 2008,February 2016. Mr. MathersKhuong has beenworked at OrbiMed Advisors LLC, a Partner at New Enterprise Associates, Inc., or NEA, a private equity and venture capital firm, focusing on technologysince 2003 and is Private Equity Partner. Mr. Khuong gained experiencein start-up operations and business development at Veritas Medicine, Inc., a healthcare investments.company, and in basic science research at the Yale School of Medicine and Massachusetts General Hospital. Mr. MathersKhuong currently serves on the board of directorsas a director of the following pharmaceuticalpublicly-traded companies: AmplyxAerpio Pharmaceuticals, Inc., ObsEva SA, SunLogic, LLC, Ziarco Group Limited, Envisia Therapeutics, Inc., Ra and Pieris Pharmaceuticals, Inc., Rhythm Pharmaceuticals, and Lumos Pharma. Mr. MathersKhuong also serves on the board of directors of Liquidia Technologies, a biotechnology company. From 2002 to 2008,several privately held companies. Mr. Mathers served as Executive Vice President, Corporate Development and Venture at MedImmune, Inc. ("MedImmune"), and led its venture capital subsidiary, MedImmune Ventures, Inc. Before joining MedImmune in 2002, he was Vice President, Marketing and Corporate Licensing and Acquisitions at Inhale Therapeutic Systems. Previously, Mr. Mathers spent 15 years at Glaxo Wellcome, Inc. where he held various sales and marketing positions. Mr. Mathers receivedKhuong holds a B.S. in ChemistryMolecular, Cellular and Developmental Biology with concentration in Biotechnology and an M.P.H. with concentration in Infectious Diseases, both from North Carolina StateYale University. The Board has concluded that Mr. Mathers has been chosenKhuong possesses specific attributes that qualify him to serve on our board of directors due to his experience with the healthcare and pharmaceutical industries and his broad management experience.

        Clay B. Siegall, Ph.D.    Dr. Clay B. Siegall has servedas a member of our boardBoard, including his experience as an investor, particularly with respect to healthcare companies, and his broad life sciences industry knowledge. Mr. Khuong also has extensive experience overseeing the operations and research and development of directors since January 2013. Dr. Siegall founded Seattle Genetics, Inc. ("Seattle Genetics")biotechnology companies.

Nick Leschly, a biotechnology company, in 1997, where heage 46, has served as a member of our Board since the Chief Executive Officer since November 2002, asMerger closed on August 28, 2017, and prior to that time served on the President since June 2000 and as the Chairman of thePrivate Synlogic board of directors since March 2004. Dr. Siegall also2016. Mr. Leschly has served as the President and Chief ScientificExecutive Officer of Seattle Geneticsbluebird bio, Inc. (“bluebird bio”), a publicly-traded clinical-stage biotechnology company, since September 2010. Previously, he served as the Interim Chief Executive Officer of bluebird bio from December 1997 until November 2002. Dr. Siegall currentlyMarch 2010 to September 2010. Formerly a partner of Third Rock Ventures, L.P. (“Third Rock”) since its founding in 2007, Mr. Leschly played an integral role in the overall formation, development and business strategy of several of Third Rock’s portfolio companies, including Agios Pharmaceuticals, Inc. and Edimer Pharmaceuticals, Inc. Prior to joining Third Rock, he worked at Millennium Pharmaceuticals, Inc. (now a subsidiary of Takeda), leading several early-stage drug development programs and served as the product and

alliance leader for VELCADE^®. Mr. Leschly also founded and served as Chief Executive Officer of MedXtend Corporation. He received his B.S. in Molecular Biology from Princeton University and his M.B.A. from Wharton Business School. He serves on the board of directors of Alder BioPharmaceuticals, Inc., a biopharmaceutical company,Biotechnology Innovation Organization (BIO) and Ultragenyx Pharmaceutical, a pharmaceutical company. Prior to co-founding Seattle Genetics, Dr. Siegall was withProclara Biosciences. He also serves on the Bristol-Myers Squibb Pharmaceutical Research Institute from 1991 to 1997, most recently as a Principal Scientist. From 1988 to 1991, Dr. Siegall was a Staff Fellow/Biotechnology Fellow at the National Cancer Institute, National Institutes of Health. Dr. Siegall received a B.S. in Zoology from theadvisory boards for Princeton University of Maryland and a Ph.D. in Genetics from George Washington University. Dr. Siegall has been chosen to serve on our board of directors due to his experience as a director and executive of multiple healthcare and biopharmaceutical companies.

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PROPOSAL NO. 2
RATIFICATION OF SELECTION OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

        The audit committee of our board of directors has selected Ernst & Young LLP, or EY, as our independent registered public accounting firm for the year ending December 31, 2016, and is seeking ratification of such selection by our stockholders at the Annual Meeting. EY has audited our financial statements for the fiscal years ended December 31, 2015 and 2014. Representatives of EY are expected to be present at the Annual Meeting. They will have an opportunity to make a statement if they so desire and will be available to respond to appropriate questions

        Neither our bylaws nor other governing documents or law require stockholder ratification of the selection of EY as our independent registered public accounting firm. However, the audit committee is submitting the selection of EY to our stockholders for ratification as a matter of good corporate practice. If our stockholders fail to ratify the selection, the audit committee will reconsider whether or not to retain EY. Even if the selection is ratified, the audit committee in its discretion may select a different independent registered public accounting firm at any time during the year if they determine that such a change would be in the best interests of the Company and our stockholders.

Principal Accountant Fees and Services

        For the fiscal years ended December 31, 2015 and 2014, EY billed the approximate fees set forth below. All fees included below were approved by the audit committee.

Pre-Approval Policies and Procedures

        The audit committee has adopted a policy for the pre-approval of all audit and non-audit services to be performed for the Company by the independent registered public accounting firm. This policy is set forth in the charter of the audit committee and available at http://investor.mirnarx.com/corporate-governance.cfm. The audit committee approved all of the audit, audit-related, tax and other services provided by EY since our initial public offering in September 2015Molecular Biology Department and the estimated costsSpecial Olympics of those services. Actual amounts billed, to the extent in excess of the estimated amounts, are periodically reviewed and approved by the audit committee.Massachusetts. The audit committee has considered the role of EY in providing audit and audit-related services to the Company andBoard has concluded that such services are compatible with EY's roleMr. Leschly possesses specific attributes that qualify him to serve as a member of our Board, including his experience in the Company's independent registered public accounting firm.venture capital industry and drug research and development.

THE BOARD OF DIRECTORS RECOMMENDS A VOTEFOR RATIFICATION OF OUR INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM.

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REPORT OF THE AUDIT COMMITTEE OF THE BOARD OF DIRECTORS

The material in this report is not "soliciting material," is not deemed "filed" with the SEC, and is not to be incorporated by reference into any filingCommittees of the Company under the Securities ActBoard of 1933, as amended, or the Securities Exchange Act of 1934, as amended.Directors and Meetings

        The primary purpose of the audit committee is to oversee our financial reporting processes on behalf of our board of directors. The audit committee's functions are more fully described in its charter, which is available on our website at http://investor.mirnarx.com/corporate-governance.cfm.

        In fulfilling its oversight responsibilities, the audit committee reviewed and discussed with management the Company's audited financial statements forMeeting Attendance. During the fiscal year ended December 31, 2015. The audit committee has discussed with EY, the Company's independent registered public accounting firm, the matters required to be discussed by Auditing Standard No. 16, "Communications with Audit Committees," issued by the Public Company Accounting Oversight2018, Synlogic’s Board or PCAOB. In addition, the audit committee has discussed with EY their independence, and received from EY the written disclosuresheld four meetings, and the letter required by Ethics and Independence Rule 3526 of the PCAOB. Finally, the audit committee discussed with EY, with and without management present, the scope and results of EY's audit of the financial statements for the fiscal year ended December 31, 2015.

        Based on these reviews and discussions, the audit committee has recommended to our board of directors that such audited financial statements be included in our Annual Report on Form 10-K for the year ended December 31, 2015 for filing with the SEC.

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CORPORATE GOVERNANCE

Board Composition

Director Independence

        Our board of directors currently consists of eight members. Our board of directors has determined that all of our directors, other than Dr. Paul Lammers, qualify as "independent" directors in accordance with the NASDAQ listing requirements. Dr. Lammers is not considered independent because he is an employee of Mirna. The NASDAQ independence definition includes a series of objective tests, such as that the director is not, and has not been for at least three years, one of our employees and that neither the director nor any of his family members has engaged in various types of business dealings with us. In addition, as required by NASDAQ rules, our board of directors has made a subjective determination as to each independent director that no relationships exist, which, in the opinion of our board of directors, would interfere with the exercise of independent judgment in carrying out the responsibilities of a director. In making these determinations, our board of directors reviewed and discussed information provided by the directors and us with regard to each director's business and personal activities and relationships as they may relate to us and our management. There are no family relationships among any of our directors or executive officers.

Classified Board of Directors

        In accordance with our amended and restated certificate of incorporation, our board of directors is divided into three classes with staggered, three-year terms as set forth below. At each annual meeting of stockholders, the successors to directors whose terms then expire will be elected to serve from the time of election and qualification until the third annual meeting following election.

•

The Class I directors are Dr. Jones, Dr. Winkler and Mr. Greenleaf, and their terms will expire at the Annual Meeting;



•

The Class II directors are Mr. Alleva and Dr. Powell, and their terms will expire at the 2017 Annual Meeting of Stockholders; and



•

The Class III directors are Dr. Lammers, Mr. Mathers and Dr. Siegall, and their terms will expire at 2018 Annual Meeting of Stockholders.

        The authorized number of directors may be changed only by resolution of the board of directors. Any additional directorships resulting from an increase in the number of directors will be distributed among the three classes so that, as nearly as possible, each class will consist of one-third of the directors. The division of our board of directors into three classes with staggered three-year terms may delay or prevent a change of our management or a change in control of our company.

Leadership Structure of the Board

        Our board of directors has separated the positions of Chairman of the board and Chief Executive Officer. Separating these positions allows our Chief Executive Officer to focus on our day-to-day business, while allowing the Chairman of the board to lead the board in its fundamental role of providing advice to and independent oversight of management. The board recognizes the time, effort and energy that the Chief Executive Officer is required to devote to his position in the current business environment, as well as the commitment required to serve as Chairman of the board, particularly as the board's oversight responsibilities continue to grow. While our bylaws and corporate governance guidelines do not require that our Chairman and Chief Executive Officer positions be separate, the board believes that having separate positions and having an independent outside director serve as Chairman is the appropriate leadership structure for us and demonstrates our commitment to good

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corporate governance. However, our board of directors will continue to periodically review our leadership structure and may make such changes in the future as it deems appropriate.

Role of Board in Risk Oversight Process

        Risk assessment and oversight are an integral part of our governance and management processes. Our board of directors encourages management to promote a culture that incorporates risk management into our corporate strategy and day-to-day business operations. Management discusses strategic and operational risks at regular management meetings, and conducts specific strategic planning and review sessions during the year that include a focused discussion and analysis of the risks facing us. Throughout the year, senior management reviews these risks with the board of directors at regular board meetings as part of management presentations that focus on particular business functions, operations or strategies, and presents the steps taken by management to mitigate or eliminate such risks.

        Our board of directors does not have a standing risk management committee, but rather administers this oversight function directly through our board of directors as a whole, as well as through various standing committees of our board of directors that address risks inherent in their respective areas of oversight. In particular, our board of directors is responsible for monitoring and assessing strategic risk exposure, our audit committee is responsible for overseeing our major financial risk exposures and the steps our management has taken to monitor and control these exposures. The audit committee also monitors compliance with legal and regulatory requirements. Our nominating and governance committee monitors the effectiveness of our corporate governance guidelines and considers and approves or disapproves any related-persons transactions. Our compensation committee assesses and monitors whether any of our compensation policies and programs has the potential to encourage excessive risk-taking.

Meetings of the Board met a total of Directors and Committees

        During 2015, the board oftwelve times. All directors met thirteen times, the audit committee met six times, and the compensation committee met one time. The nominating and corporate governance committee did not meet during 2015. In that year, each incumbent director attended at least 75% of the total number of meetings of the boardBoard and of directors andcommittees of the committeesBoard on which he served.or she served during fiscal 2018. Synlogic’s annual meeting was held on June 13, 2018 and five of Synlogic’s six directors attended the meeting. We encourage our directors to attend the annual meeting.

Board Committees

Audit Committee

. Synlogic’s Audit Committee met seven times during fiscal 2018. This committee currently has three members, Richard P. Shea (Chairman), Peter Barrett and Michael Powell. Our audit committee oversees our corporate accountingAudit Committee’s role and financial reporting process. Among other matters,responsibilities are set forth in the audit committee:

•

appointsAudit Committee’s written charter and include the authority to retain and terminate the services of our independent registered public accounting firm;



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evaluatesfirm. In addition, the independent registered publicAudit Committee reviews annual financial statements, considers matters relating to accounting firm's qualifications, independencepolicy and performance;



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determines the engagement of the independent registered public accounting firm;



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reviewsinternal controls and approvesreviews the scope of the annual audit and the audit fee;



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discusses with management and the independent registered public accounting firm the resultsaudits. All members of the annual auditAudit Committee satisfy the current independence standards promulgated by the Securities and Exchange Commission and by the review of our quarterly financial statements;



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approves the retention of the independent registered public accounting firmNasdaq Stock Market, as such standards apply specifically to perform any proposed permissible non-audit services;

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monitors the rotation of partners of the independent registered public accounting firm on our engagement team as required by law;



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is responsible for reviewing our financial statements and our management's discussion and analysis of financial condition and results of operations to be included in our annual and quarterly reports to be filed with the SEC;



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reviews our critical accounting policies and estimates; and



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annually reviews the audit committee charter and the committee's performance.

        The current members of our audit committee are Mr. Alleva, who serves as the chairman of the committee, Dr. Jones and Dr. Siegall. After the Annual Meeting, assuming the election of the three Class I nominees set forth herein, our audit committee will be composed of Mr. Alleva, as chairman, Mr. Greenleaf and Dr. Nisen.

        Assuming the election of the three Class I nominees set forth herein, each of the expected members of our audit committee will meet the requirements for financial literacy under the applicable rules and regulations of the SEC and NASDAQ. Our board of directorscommittees. The Board has determined that Mr. AllevaBarrett is an audit committee financial expert as definedindependent even though he falls outside the “safe harbor” definition set forth in Rule10A-3(e)(1)(ii) under the applicable rulesSecurities Exchange Act of 1934, as amended (the “Exchange Act”) because Atlas Venture L.P. and its affiliates own in excess of 10% of our common stock. Among other things, the SECBoard considered Mr. Barrett’s history of service and has the requisite financial sophistication as defined underpercentage of common stock held by others, and it determined that he is not an “affiliated person” of our company who would be ineligible to serve on the applicable rules and regulations of NASDAQ. Under the rules of the SEC, members of the audit committee must also meet heightened independence standards. Our board of directorsAudit Committee. The Board has determined that assumingMr. Shea is an “audit committee financial expert,” as the electionSecurities and Exchange Commission has defined that term in Item 407 of RegulationS-K. Please also see the report of the three Class I nomineesAudit Committee set forth herein, each the expected members of our audit committee will be independent under the heightened independence standards under the applicable rules of NASDAQ. The audit committee operates under a written charter that satisfies the applicable standards of the SEC and NASDAQ. elsewhere in this proxy statement.

A copy of the audit committeeAudit Committee’s written charter is publicly available to security holders on the Company'sour website at http://investor.mirnarx.com/corporate-governance.cfm.www.synlogictx.com.

Compensation Committee

. Synlogic’s Compensation Committee met three times during fiscal 2018. This committee currently has three members, Edward Mathers (Chairman), Chau Khuong and Nick Leschly. Our Compensation Committee’s role and responsibilities are set forth in the Compensation Committee’s written charter and includes reviewing, approving and making recommendations regarding our compensation committeepolicies, practices and procedures to ensure that legal and fiduciary responsibilities of the Board are carried out and that such policies, practices and procedures contribute to our success. Our Compensation Committee also administers our 2015 Equity Incentive Award Plan and 2017 Stock Incentive Plan. The Compensation Committee reviews and recommends policies relating to compensation and benefits of our officers and employees. The compensation committeeCompensation Committee reviews and recommends corporate goals and objectives relevant to compensation of our Chief Executive Officer and other executive officers, evaluates the performance of these officers in light of those goals and objectives and recommends to our board of directorsmay approve the compensation of thesethe executive officers, other than the Chief Executive Officer, whose compensation the Compensation Committee recommends to the Board, based on such evaluations. The compensation committeeCompensation Committee also recommends to our board of directorsthe Board the issuance of stock options and other awards under our stock plans. The compensation committee will review and evaluate, at least annually, the performanceBoard has delegated authority to our Chief Executive Officer to grant options to new hire employees as well as certain other employees in connection with their promotion who (i) are not then subject or who are reasonably expected to become subject to Section 16 of the compensation committee and its members, including compliance by the compensation committee with its charter. The current members of our compensation committee are Dr. Powell, who serves as the chairperson of the committee, Dr. Siegall and Mr. Mathers. Each of the members of our compensation committee is independent under the applicable rules and regulations of NASDAQ, is a "non-employee director" as defined in Rule 16b-3 promulgated under the Exchange Act, and is an "outside director" as that term is defined inor (iii) persons

then or who are reasonably expected to be “covered employees” for purposes of Section 162(m) of the U.S. Internal Revenue Code of 1986, as amended, or Section 162(m).amended. The compensation committee operates under a written charter that satisfiespurpose of this delegation of authority is to enhance the applicable standardsflexibility of option administration within the Company and to facilitate the timely grant of options within specified limits approved by the Board. All members of the SECCompensation Committee qualify as independent under the definition promulgated by the Nasdaq Stock Market.

The Compensation Committee has the authority to directly retain the services of independent consultants and NASDAQ. A copyother experts to assist in fulfilling its responsibilities. The Compensation Committee has engaged the services of the compensation committee charter is available to security holders on the Company's website at http://investor.mirnarx.com/corporate-governance.cfm.

        Our compensation committee has retained Radford, Inc. ("Radford") a nationally recognizedbusiness unit of Aon plc (“Radford”), a national executive compensation consulting firm, to serve as its independent compensation consultantreview and to conduct market research and analysis on our various executive positions, to assistprovide recommendations concerning all of the committee in developing appropriate incentive plans for our executives on an annual basis, to providecomponents of the committee with advice and ongoing recommendations regarding materialCompany’s executive compensation decisions,program. Radford performs services solely on behalf of the Compensation Committee and has no relationship with the Company or management except as it may relate to review

Tableperforming such services. Radford assists the Committee in defining the appropriate market of Contents

the Company’s peer companies for executive compensation proposalsand practices and in benchmarking our executive compensation program against the peer group each year. Radford also assists the Committee in benchmarking our director compensation program and practices against those of management. Radford reports directly to the compensation committee and does not provide any non-compensation related services to us.our peers. In compliance with the disclosure requirementsSEC and the corporate governance rules of the SEC regardingNasdaq Stock Market, Radford provided the independence of compensation consultants, Radford addressedCompensation Committee with a letter addressing each of the six independence factors established by the SEC with our compensation committee. Itsfactors. Their responses affirmedaffirm the independence of Radford and the partners, consultants, and employees who service the Compensation Committee on executive compensation matters. Based on this assessment, our compensation committee determined that the engagement of Radford does not raise any conflicts of interest or similar concerns. In addition, our compensation committee evaluated the independence of its other outside advisors to the compensation committee, including outside legal counsel, considering the same independence factorsmatters and concluded their work for our compensation committee does not raise any conflicts of interest. Our compensation committee operates under a written charter that satisfies the applicable standards of the SEC and NASDAQ.governance issues.

Nominating and Corporate Governance Committee

        The nominating and corporate governance committee is responsible for making recommendations to our board of directors regarding candidates for directorships and the size and composition of our board of directors. In addition, the nominating and corporate governance committee is responsible for overseeing our corporate governance policies and reporting and making recommendations to our board of directors concerning governance matters. The current members of our nominating and corporate governance committee are Mr. Mathers, who serves as the chairman of the committee, Dr. Siegall and Mr. Alleva. Mr. Mathers serves as the chairman of the committee. Each of the members of our nominating and corporate governance committee is an independent director under the applicable rules and regulations of NASDAQ relating to nominating and corporate governance committee independence. The nominating and corporate governance committee operates under a written charter. A copy of the nominating and corporate governance committeeCompensation Committee’s written charter is publicly available on our website atwww.synlogictx.com.

Nominating and Governance Committee. Synlogic’s Nominating and Governance Committee met two times during fiscal 2018. This committee currently has three members, Michael Powell (Chairman), Peter Barrett and Patricia Hurter. Our Board has determined that all members of the Nominating and Governance Committee qualify as independent under the definition promulgated by the Nasdaq Stock Market. The Nominating and Governance Committee’s responsibilities are set forth in the Nominating and Governance Committee’s written charter and include:

 Our nominating

Generally, our Nominating and Governance Committee considers candidates recommended by stockholders as well as from other sources such as other directors or officers, third party search firms or other appropriate sources. Once identified, the case of vacancies, appointing),Nominating and the board of directors,Governance Committee will evaluate a candidate’s qualifications in approving such candidates, will take into account many factors, including the following:

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accordance with our Corporate Governance Guidelines. Threshold criteria include: personal and professional integrity;



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integrity, ethics and values;



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experience in corporate management, such as serving as an officer or former officer

of a publicly held company;

Tablejudgment, including the ability to make independent analytical inquiries; and any other relevant qualifications, attributes or skills. Our Nominating and Governance Committee has not adopted a formal diversity policy in connection with the consideration of Contentsdirector nominations or the selection of nominees. However, the Nominating and Governance Committee will consider issues of diversity among its members in identifying and considering nominees for director and strive where appropriate to achieve a diverse balance of backgrounds, perspectives, business and career experience on the Board and its committees.

If a stockholder wishes to propose a candidate for consideration as a nominee for election to the Board, it must follow the procedures described in our bylaws and in “Stockholder Proposals and Nominations for Director” at the end of this proxy statement. In general, persons recommended by stockholders will be considered in accordance with our Corporate Governance Guidelines. Any such recommendation should be made in writing to the Nominating and Governance Committee, care of our Secretary at our principal office and should be accompanied by the following information concerning each recommending stockholder and the beneficial owner, if any, on whose behalf the nomination is made:

 Currently, our board

The recommendation must also be accompanied by the following information concerning the proposed nominee:

A copy of the Nominating and Governance Committee’s written charter, including its appendices, is publicly available on the Company’s website atwww.synlogictx.com.

Board Leadership Structure and Role in Risk Oversight

Leadership Structure of the Board

Our Board has separated the positions of Chairman of the Board and Chief Executive Officer. Separating these positions allows our Chief Executive Officer to focus onour day-to-day business, while allowing the Chairman of our Board to lead the Board in its fundamental role of providing advice to and independent oversight of management. Our Board recognizes the time, effort and energy that the Chief Executive Officer is required to devote to such position in the current business environment, as well as the commitment required to serve as Chairman of our Board, particularly as the Board’s oversight responsibilities continue to grow. While our bylaws and corporate governance guidelines do not require that the Chairman and Chief Executive Officer positions be separate, our Board believes that having separate positions and having an independent outside director serve as Chairman is the appropriate leadership structure for us and demonstrates our commitment to good corporate governance. However, our Board will continue to periodically review our leadership structure and may make such changes in the future as it deems appropriate.

Role of Board in Risk Oversight Process

Risk assessment and oversight are an integral part of our governance and management processes. Our Board encourages management to promote a culture that incorporates risk management into our corporate strategyand day-to-day business operations. Management discusses strategic and operational risks at regular management meetings and conducts specific strategic planning and review sessions during the year that include a focused discussion and analysis of the risks facing us. Throughout the year, senior management reviews these risks with our Board at regular Board meetings as part of management presentations that focus on particular business functions, operations or strategies, and presents the steps taken by management to mitigate or eliminate such risks.

Our Board does not have a standing risk management committee, but rather administers this oversight function directly through the Board as a whole, as well as through various standing committees of the Board that address risks inherent in their respective areas of oversight. In particular, our Board is responsible for monitoring and assessing strategic risk exposure and the Audit Committee is responsible for overseeing our major financial risk exposures and the steps management has taken to monitor and control these exposures. The Audit Committee also monitors compliance with legal and regulatory requirements and considers and approves or disapproves any related-persons transactions. Our Nominating and Governance Committee monitors the effectiveness of our corporate governance. The Compensation Committee assesses and monitors whether any of our compensation policies and programs has the potential to encourage excessive risk-taking.

Stockholder Communications to the Board

Generally, stockholders who have questions or concerns should contact our Investor Relations department at (617) 639 9122. However, any stockholders who wish to address questions regarding our business directly with the objective of assembling a group that can best maximize the success of the business and represent stockholder interests through the exercise of sound judgment using its diversity of experience in these various areas.

Code of Business Conduct and Ethics

        We have adopted a code of business conduct and ethics that applies to all of our employees, officers and directors, including those officers responsible for financial reporting. The code of business conduct and ethics is available on our website at http://investor.mirnarx.com/corporate-governance.cfm. We will disclose any substantive amendments to the code of business conduct and ethics,Board, or any waiver of its provisions, on our website. The reference to our website does not constitute incorporation by reference of the information contained at or available through our website.

Limitation on Liability and Indemnification Matters

        Our amended and restated certificate of incorporation contains provisions that limit the liability of our directors for monetary damages to the fullest extent permitted by Delaware law. Consequently, our directors will not be personally liable to us or our stockholders for monetary damages for any breach of fiduciary duties as directors, except liability for:

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any breach of the director's duty of loyalty to us or our stockholders;



•

any act or omission not in good faith or that involves intentional misconduct or a knowing violation of law;



•

unlawful payments of dividends or unlawful stock repurchases or redemptions as provided in Section 174 of the Delaware General Corporation Law; or



•

any transaction from which theindividual director, derived an improper personal benefit.

        Our amended and restated certificate of incorporation and amended and restated bylaws provide that we are required to indemnify our directors and officers, in each case to the fullest extent permitted by Delaware law. Our amended and restated bylaws also provide that we are obligated to advance expenses incurred by a director or officer in advance of the final disposition of any action or proceeding, and permit us to secure insurance on behalf of any officer, director, employee or other agent for any liability arising out ofshould direct his or her actionsquestions in writing to the Chairman of the Board at Synlogic, Inc., 301 Binney Street, Suite 402, Cambridge MA 02142. Communications will be distributed to the Board, or to any individual director or directors as appropriate, depending on the facts and circumstances outlined in the communications. Items that capacity regardlessare unrelated to the duties and responsibilities of whether we would otherwisethe Board may be permitted to indemnify him or her under Delaware law.excluded, such as:

 We have entered

In addition, any of these individualsmaterial that is unduly hostile, threatening, or illegal in any action or proceeding brought against them by reason of the fact that they are or were our agents. We believe that these provisions in our amended and restated certificate of incorporation and amended and restated bylaws and indemnification agreements are necessary to attract and retain qualified directors and officers. We also maintain directors' and officers' liability insurance. This description of the limitation of liability and indemnification provisions of our amended and restated certificate of incorporation, of our amended and restated bylaws and of our indemnification agreements is qualified in its entirety by reference to these documents.

        The limitation of liability and indemnification provisions in our amended and restated certificate of incorporation and amended and restated bylaws may discourage stockholders from bringing a lawsuit against our directors and officers for breach of their fiduciary duty. They may also reduce the likelihood of derivative litigation against our directors and officers, even though an action, if successful,

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might benefit us and our stockholders. Further, a stockholder's investmentnature may be adversely affectedexcluded, provided that any communication that is filtered out will be made available to the extent that we pay the costs of settlement and damage. To the extent the indemnification for liabilities arising under the Securities Act may be permitted to our directors, officers and controlling persons pursuant to the foregoing provisions, or otherwise, we have been advised that, in the opinion of the SEC, such indemnification is against public policy as expressed in the Securities Act and is, therefore, unenforceable. At present, there is no pending litigation or proceeding involving any of our directors, officers or employees for which indemnification is sought, and we are not aware of any threatened litigation that may result in claims for indemnification.outside director upon request.

Director Attendance at Annual MeetingsExecutive Officers

        Our board of directors has a policy of encouraging director attendance at our annual meetings of stockholders, but attendance is not mandatory. Our board of directors and management team encourage all of our directors to attend the Annual Meeting.

Stockholder Communications with the Board of Directors

        A stockholder may communicate with the board of directors, or an individual director, by sending written correspondence to the Company's Corporate Secretary at Mirna Therapeutics, Inc., 2150 Woodward Street, Suite 100, Austin, Texas 78744. The Corporate Secretary will review such correspondence and forward it to the board of directors, or an individual director, as appropriate.

Compensation Committee Interlocks and Insider Participation

        During 2015, Dr. Powell, Mr. Mathers, and Dr. Siegall served as members of our compensation committee. During 2015, none of the members of our compensation committee has at any time been one of our officers or employees. None offollowing table sets forth certain information regarding our executive officers currently serves, or in the past year has served, as a member of the board of directors or compensation committee of any entity that has one or more executive officers on our board of directors or compensation committee.

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CERTAIN RELATIONSHIPS AND RELATED PARTY TRANSACTIONS

        The following is a description of transactions since January 1, 2015 to which we have been a party, in which the amount involved exceeds $120,000, and in which any of our directors, executive officers or holders of more than 5% of our capital stock, or an affiliate or immediate family member thereof, had or will have a direct or indirect material interest.

Indemnification Agreements and Directors' and Officers' Liability Insurance

who are not also directors. We have entered into indemnificationemployment agreements with each of our directorsexecutive officers.

Todd Shegog, age 54, joined Synlogic in September 2016 as Chief Financial Officer and is responsible for the oversight and direction of our financial strategy and management as well as facilities and information systems. From April 2014 to August 2016, Mr. Shegog served as senior vice president and chief financial officer at Forum Pharmaceuticals Inc., a pharmaceutical company, where he was responsible for finance, operations and information systems in support of the pursuit of innovative therapies for schizophrenia and Alzheimer’s disease. From 1998 to March 2014, Mr. Shegog worked in a variety of roles at Millennium Pharmaceuticals, including as Senior Vice President and Chief Financial Officer from 2008 to 2014, where he was responsible for management of Millennium’s financial resources, corporate planning, financial reporting and compliance. During his tenure at Millennium Pharmaceuticals, Mr. Shegog held key leadership roles supporting the early evolution of Millennium and its transformation from a genomics company to a fully-integrated drug developer, the approval and launch of its flagship oncology product, VELCADE^®, and the $8.8 billion acquisition of Millennium Pharmaceuticals by Takeda Pharmaceutical Co Ltd. Mr. Shegog began his career in healthcare at Genetics Institute, Inc. (now Pfizer), a biotechnology research and development company, in a variety of financial positions supporting its research and development organizations and was a member of the commercial operations team that supported the launch of BeneFIX^®. Mr. Shegog holds an M.B.A. from the Tepper School of Management at Carnegie Mellon University and a bachelor’s degree in electrical engineering from Lafayette College.

EXECUTIVE OFFICER AND DIRECTOR COMPENSATION

Summary Compensation Table

The following table presents information regarding the total compensation paid or accrued during the last two fiscal years for (1) our Chief Executive Officer, (2) our twonext most highly compensated executive officers. Theseofficers who earned more than $100,000 during the fiscal year ended December 31, 2018 and were serving as executive officers as of such date and (3) the Company’s former Chief Executive Officer (collectively the “Named Executive Officers”).

Narrative Disclosure to Summary Compensation Table

Historically, the Company’s executive compensation program has reflected our innovative and growth- oriented corporate culture and is designed to attract, retain and incentivize and align executives with both short- and long-term company objectives. To date, the compensation of the Company’s Chief Executive Officer and our other executive officers has consisted of a combination of base salary, cash bonuses and long-term incentive compensation paid in the form of equity. The named executive officers, like all full-time employees, are eligible to participate in the Company’s health and welfare benefit plans. The Company will continue to evaluate its compensation values and philosophy and compensation plans and arrangements as circumstances require. The Company will review executive compensation from time to time at the discretion of the Compensation Committee. As part of this review process, the Board and Compensation Committee will apply the values and philosophy, while considering the compensation levels needed to ensure the organization’s executive compensation program remains competitive and aligns incentives with the goals of the organization.

Base Salary

In March 2018, the Compensation Committee and the Board approved an annual increase in base salaries for certain employees resulting in an annual base salary of $397,901 for Dr. Brennan, $366,488 for Mr. Shegog, and $401,980 for Mr. Gengos. In May 2018, the Board approved an annual increase in base salary for Dr. Brennan to $474,701 in connection with her appointment as Interim President and Chief Executive Officer and in October 2018 an increase to $490,000 in connection with her transition to President and Chief Executive Officer. In March 2019, the Compensation Committee and the Board approved base salary increases for certain members of the Company’s management team effective January 1, 2019, resulting in an annual base salary of $505,000 for Dr. Brennan and $377,500 for Mr. Shegog.

Annual Bonuses

The Company’s employment agreements among other things, require uswith its executive officers provide for the opportunity to indemnifyearn a cash bonus based upon achievement of both corporate and individual goals determined by the Board based on a target percentage of annual base salary. In March 2019, the Board awarded Dr. Brennan a cash bonus of $186,200, which represented 38.0% of her annual base salary, in recognition of her services provided in the year ended December 31, 2018 and in accordance with the terms of her amended employment agreement and bonus assessment. In March 2019, the Compensation Committee awarded Mr. Shegog a cash bonus of $103,300, which represented 28.2% of his annual base salary in recognition of his services provided in the year ended December 31, 2018 and in accordance with the terms of his employment agreement and bonus assessment.

2019 Stock Awards

In 2019, in connection with the Compensation Committee and the Board’s assessment of 2018 performance, the Company granted the following options to its current named executive officers: Dr. Brennan was granted an option to purchase 185,000 shares of common stock and Mr. Shegog was granted an option to purchase 58,500 shares of common stock with each directoroption having an exercise price of $8.59 per share and subject to vesting at a rate of 1/48th of the total number of shares subject thereto per month over four years.

Outstanding Equity Awards at Fiscal Year End

The following table presents the outstanding equity awards held by each of the named executive officerofficers as of December 31, 2018. All equity awards set forth in the table below were granted under the 2015 Stock Incentive Plan except for the awards with a grant date of May 15, 2017 which were granted under the 2017 Equity Incentive Award Plan.

Synlogic Reorganization and Merger

Synlogic, LLC completed a corporate reorganization from an LLC to a corporation on May 15, 2017. As part of the reorganization, equity incentive awards granted by Synlogic, LLC were converted into equity incentive awards for shares of Private Synlogic common stock. Common units of Synlogic, LLC were converted one for one into shares of Private Synlogic common stock and incentive units of Synlogic, LLC were converted into a number of shares of Private Synlogic common stock equal to (x) the value of the appreciation of such incentive units between the date of grant and immediately prior to the fullestreorganization divided by (y) the value of a share of Private Synlogic common stock on the date of such reorganization. To the extent permitted by Delaware law, including indemnificationthat such shares of expenses such as attorneys' fees, judgments, penalties fines and settlement amounts incurredPrivate Synlogic common stock were unvested, they remained Private Synlogic restricted stock. All shares of

Private Synlogic restricted stock were issued under the Private Synlogic 2017 Stock Incentive Plan which was assumed by the director or executive officerCompany in any action or proceeding, including any action or proceeding by or in right of us, arising outthe Merger and continue to vest on the same schedule as the original restricted stock awards.

All equity awards set forth above are set forth on a post-Merger basis. Pursuant to the terms of the person's servicesMerger Agreement and after giving effect to the 1:7 reverse stock split, at the effective time of the Merger (the “Effective Time”), each outstanding share of capital stock of Private Synlogic was converted into the right to receive approximately 0.5532 shares of Company common stock on a post-Merger basis (the “Exchange Ratio”). In addition, at the Effective Time, the Company assumed all outstanding options to purchase shares of common stock of Private Synlogic, which were exchanged for options to purchase shares of the Company’s common stock, in each case appropriately adjusted based on the Exchange Ratio and all shares of Private Synlogic restricted stock were exchanged for shares of Company common stock in accordance with the Exchange Ratio and continue to vest on the same schedule as the original restricted stock awards.

Employment Agreements and Potential Payments Upon Termination of Employment or Change in Control

The Company has entered into employment agreements with each of our named executive officers as described below, as well as standard confidential information and/or inventions assignment agreements under which each of the named executive officers has agreed not to disclose confidential information. These employment agreements provide for “at will” employment.

Aoife M. Brennan, MB, BCh, BAO, MMSc

We originally entered into an employment agreement with Dr. Brennan in June 2016 that initially provided for a director base salary of $345,000, subject to review and adjustment. Dr. Brennan’s base salary was subsequently increased to $349,036 for 2017 and $397,901 for 2018. Pursuant to the June 2017 amendment to the original employment agreement, Dr. Brennan was eligible to earn an annual cash incentive bonus of up to 30% of her base salary based on the achievement of corporate and/or executive officer.individual performance goals, as determined by the Board. Dr. Brennan is also eligible to participate in the employee benefit plans available to employees, subject to the terms of those plans. In addition, Dr. Brennan’s original employment agreement, as amended, also provided her with a signing bonus of $85,000, plus a gross up for taxes to be paid on such compensation in connection with her commencement of employment.

Investor Rights AgreementsIn connection with her appointment as Interim President and Chief Executive Officer, we entered into an amendment to Dr. Brennan’s employment arrangement in June 2018, pursuant to which Dr. Brennan received (i) an additional cash payment of $6,400 per calendar month for the period which Dr. Brennan served as Interim President and Chief Executive Officer, (ii) a target bonus of 40% for the period which Dr. Brennan served as Interim President and Chief Executive Officer and (iii) a grant of an option to purchase an aggregate of 54,000 shares of the Company’s common stock at an exercise price of $9.55 (the fair market value on the date of the grant) which option vests in equal monthly installments for 48 months.

        We haveIn connection with her appointment as President and Chief Executive Officer in October 2018, we entered into an amended and restated investor rightsemployment arrangement with Dr. Brennan (the “Amended and Restated Employment Agreement”), pursuant to which Dr. Brennan was entitled to receive (i) an annual base salary of $490,000 commencing as of October 2, 2018 (the “CEO Salary”), (ii) a target bonus of 40% of the CEO Salary and (iii) aone-time grant of an option to purchase an aggregate of 150,000 shares of common stock at an exercise price of $7.91 (the fair market value on the date of the grant), which option will vest as toone-fourth of the shares on the first anniversary of Dr. Brennan’s start date as President and Chief Executive Officer and as to the remainder in equal monthly installments for the following 36 months, continuing for so long as Dr. Brennan continues to serve as the Company’s President and Chief Executive Officer. In March 2019, the Board, upon recommendation of the Compensation Committee, approved an increase in Dr. Brennan’s base salary to $505,000, effective as of January 1, 2019, and an increase in the target annual cash bonus amount for 2019 for Dr. Brennan from 40% of base salary to 50% of base salary.

The Amended and Restated Employment Agreement provides that, in the event that Dr. Brennan’s employment is terminated for any reason other than for “cause,” death or “disability,” or by Dr. Brennan for “good reason” (each as defined in the Amended and Restated Employment Agreement), she will be entitled to receive (i) continuing severance pay at a rate equal to 100% of her base salary, as then in effect, for a period of 12 months from the date of such termination, to be paid periodically in accordance with normal Company payroll practices; (ii) the right to continue health care benefits under COBRA, paid by the Company until the earlier of (a) 12 months from termination, or (b) the date on which Dr. Brennan becomes eligible for healthcare insurance with a subsequent employer, and (iii) alump-sum payment equal to the prorated portion of the target bonus for the fiscal year in which Dr. Brennan is terminated.

The Amended and Restated Employment Agreement provides that, in the event Dr. Brennan’s employment is terminated on account of death, “disability,” resignation for “good reason” or without “cause,” in any case, within the12-month period immediately following or the30-day period immediately prior to a “change in control,” then Dr. Brennan’s outstanding unvested restricted stock and/or options shall become fully vested.

In addition, Dr. Brennan has entered into anon-solicitation andnon-competition agreement that applies for 12 months following her employment.

Todd Shegog

We entered into an employment agreement with certain holdersMr. Shegog in June 2016 that initially provided for a base salary of our common stock. As$345,000, subject to review and adjustment. Mr. Shegog’s base salary was increased to $349,036 for 2017 and $366,488 for 2018. In February 2019, Mr. Shegog’s base salary was increased to $377,500, effective as of December 31, 2015,January 1, 2019. Pursuant to the holdersMay 8, 2017 amendment to his employment agreement, Mr. Shegog was eligible to earn an annual cash incentive bonus of approximately 13.9 million sharesup to 30% of our common stock arehis base salary based on the achievement of corporate and/or individual performance goals, as determined by the Board. Mr. Shegog is also eligible to participate in the employee benefit plans available to employees, subject to the terms of those plans. In March 2019, the Compensation Committee approved an increase in the target annual cash bonus amount for 2019 for Mr. Shegog from 30% of base salary to 40% of base salary.

Mr. Shegog’s employment agreement provides that, in the event that Mr. Shegog’s employment is terminated for any reason other than for “cause,” death or “disability,” or by Mr. Shegog for “good reason” (each as defined in his employment agreement), he will be entitled to rightsreceive (i) continuing severance pay at a rate equal to 100% of his base salary, as then in effect, for a period of six months from the date of such termination, to be paid periodically in accordance with respectnormal Company payroll practices; (ii) the right to continue health care benefits under COBRA, paid by the Company until the earlier of (a) six months from termination, or (b) the date on which Mr. Shegog becomes eligible for healthcare insurance with a subsequent employer, and (iii) alump-sum payment equal to the registrationprorated portion of their shares under the Securities Act.

Policies and Procedures for Related Party Transactions

        Our board of directors has adopted a written related person transaction policy setting forth the policies and procedurestarget bonus for the review and approval or ratification of related person transactions. This policy covers, with certain exceptions set forth in Item 404 of Regulation S-K under the Securities Act, any transaction, arrangement or relationship, or any series of similar transactions, arrangements or relationshipsfiscal year in which we wereMr. Shegog is terminated.

Mr. Shegog’s employment agreement provides that, in the event Mr. Shegog’s employment is terminated on account of death, “disability,” resignation for “good reason” or arewithout “cause,” in any case, within the12-month period immediately following or the30-day period immediately prior to be a participant, where“change in control,” then Mr. Shegog’s outstanding unvested restricted stock and/or options shall become fully vested.

In addition, Mr. Shegog has entered into anon-solicitation andnon-competition agreement that applies for 12 months following his employment.

The following definitions apply to Dr. Brennan’s and Mr. Shegog’s employment agreements:

“Cause” is defined as the amount involved exceeds $120,000 and a related person had or will have a direct or indirect material interest, including, without limitation, purchases of goods or services by or from the related person or entities in which the related person has a material interest, indebtedness, guarantees of indebtedness and employment by usexecutive’s (i) conviction of a related person. In reviewing and approving any such transactions, our audit committee is taskedfelony, plea of guilty or “no contest” to consider all relevant facts and circumstances,a felony, or confession of guilt to a felony, in each case whether or not in connection with the performance of the executive’s

duties to the Company,; (ii) act or omission which constitutes willful misconduct or negligence that results in loss, damage or injury to the Company or its prospects, including, but not limited to whether(A) disloyalty, dishonesty or a breach of fiduciary duty to the transaction is on terms comparable to those that could be obtained in an arm's length transaction with an unrelated third party and the extentCompany or Stockholders, (B) theft, fraud, embezzlement or other illegal conduct, or (C) deliberate disregard of a rule or policy of the Company; (iii) failure, refusal or unwillingness to perform, to the reasonable satisfaction of the Board determined in good faith, any duty or responsibility assigned to the executive, which failure of performance continues for a period of more than two weeks after written notice thereof has been provided by the Board, setting forth in reasonable detail the nature of such failure of performance; or (iv) the material breach by the executive of any of the provisions of the employment agreement or its related person's interestagreements.

“Good reason” is defined as a resignation that occurs within 30 days following: (i) a change in the transaction.

principal location at which the executive provides services to the Company beyond 50 miles from Cambridge, Massachusetts; (ii) a reduction in the executive’s compensation or a material reduction in the executive’s benefits, except such a reduction in connection with a general reduction in compensation or other benefits of all senior executives of the Company; (iii) a material breach of the executive’s employment agreement by the Company that has not been cured within 10 days after written notice thereof by the executive; or (iv) a failure by the Company to obtain the assumption of the employment agreement by any successor of the Company.

Table“Disability” is defined as the executive’s inability, due to physical or mental illness or disease, to perform the functions then performed by the executive for 180 consecutive days, accompanied by the likelihood, in the opinion of Contentsa physician chosen by the Company and reasonably acceptable to the executive, that the executive will be unable to perform such functions within the reasonably foreseeable future, provided that the foregoing definition shall not include a disability for which the Company is required to provide reasonable accommodation pursuant to the Americans with Disabilities Act or other similar statute or regulation.

“Change in control” is defined as (i) the sale of the Company by merger in which the stockholders in their capacity as such no longer own a majority of the outstanding equity securities of the Company (or its successor); (ii) any sale of all or substantially all of the assets or capital stock of the Company (other than in a
spin-offNON-EMPLOYEE DIRECTOR COMPENSATION
or similar transaction) or (iii) any other acquisition of the business of the Company, as determined by the board of directors in its sole discretion. For the avoidance of doubt, in no event shall a bona fide equity or debt financing, including a financing in which greater than 50% of the Company’s outstanding equity securities are acquired by a third-party, be deemed a “change in control.”

        WhileOther Benefits

Executive officers are eligible to participate in all of the Company’s employee benefit plans, including life insurance, medical, dental and vision, a 401(k)-retirement plan and a flex spending account plan. We also providepaid-time-off benefits to all similarly-situated employees.

Terms and Conditions of Dr. Gutierrez-Ramos’s Separation Agreement

On May 10, 2018, we did not maintainentered into an agreement (the “Gutiérrez-Ramos Separation Agreement”) with Dr. Gutiérrez-Ramos related to his resignation as our President and Chief Executive Officer that provides Dr. Gutiérrez-Ramos the following severance and benefits: (i) continued payments of his base salary for 13 months following his cessation of employment; (ii) continued vesting of all of his outstanding equity awards in accordance with their terms through June 9, 2018; (iii) payment or reimbursement of COBRA premiums for Dr. Gutiérrez-Ramos for up to 13 months following his cessation of employment or until the date on which Dr. Gutiérrez-Ramos becomes eligible for healthcare insurance with a formal director compensation policy from January 1,subsequent employer; and (iv) alump-sum payment of $83,592 equal to the prorated portion of Dr. Gutiérrez-Ramos’ target bonus for 2018. In addition, pursuant to the terms of the Gutiérrez-Ramos Separation Agreement, Dr. Gutiérrez-Ramos continued to vest in his previously granted restricted stock award grant dated May 14, 2015 until our initial public offering in October 2015, during this period, our independent directors, who we considered to be those non-employee directors not associated withNovember 15, 2018.

The Gutiérrez-Ramos Separation Agreement includes a principal investor in our company, including Drs. Goodman and Siegall and Mr. Alleva, received an annual cash retainerrelease of $25,000 for service as a director, pro-rated for partial years of service, and an additional cash retainer of $3,000 per meeting of the board or a committee of the board attended in person and $2,000 per meeting of the board or committee of the board attended telephonically.

claims by Dr. Gutiérrez-Ramos against us. In connection with the entry into the Gutiérrez-Ramos Separation Agreement, Dr. Gutiérrez-Ramos agreed that he would continue to be subject to the Invention andNon-Disclosure Agreement and theNon-Compete andNon-Solicitation Agreement between us and Dr. Gutiérrez-Ramos that contains a covenant protecting our initial public offering in October 2015, we approvedconfidential information.

Terms and Conditions of Mr. Gengos’ Separation Agreement

On December 17, 2018, the Company entered into a compensation policy for our non-employee directors, orseparation agreement (the “Gengos Separation Agreement”) with Mr. Gengos, pursuant to which Mr. Gengos’ employment with the Director Compensation Program.Company was terminated without cause as a result of his role at the Company being materially diminished. Pursuant to the terms of the Gengos Separation Agreement, Mr. Gengos was employed by the Company as its Chief Operating Officer and Head of Corporate Development through January 15, 2019.

Under the Gengos Separation Agreement, in exchange for a full general release of claims and continued compliance with the Invention and Nondisclosure Agreement and theNon-Competition andNon-Solicitation Agreement entered into between Mr. Gengos and the Company, which covers a period of 12 months following his employment, Mr. Gengos will receive: (i) continued payments of his base salary for six months following his cessation of employment; (ii) continued vesting of all of his outstanding equity awards in accordance with their terms through his cessation of employment; (iii) payment or reimbursement of COBRA premiums for Mr. Gengos for up to six months following his cessation of employment or until the date on which Mr. Gengos becomes eligible for healthcare insurance with a subsequent employer; and (iv)(a) alump-sum payment amount of $121,558.78 equal to Mr. Gengos’ target bonus for 2018 and (b) alump-sum payment amount of $5,781.91 equal to Mr. Gengos’ target bonus for 2019,pro-rated for 15 days.

SYNLOGIC DIRECTOR COMPENSATION

The following table shows the total compensation paid or accrued during the fiscal year ended December 31, 2018 to each of ournon-employee directors. Directors who are employed by us are not compensated for their service on our Board.

Pursuant to the Amended and RestatedNon-EmployeeDirector Compensation Program, ournon-employee directors are entitled to receive cash compensation, paid quarterly in arrears, as follows:

•

EachEach non-employee director receives an annual cash retainer in the amount of $35,000 per year.

Anynon-employee



•

Any non-employee Chairman receives an additional annual cash retainer in the amount of $25,000$30,000 per year.



•

20,000 shares of our common stock (subject to adjustment as provided in the applicable equity plan). In addition, eachnon-employee director who has been serving as a director for at least three months prior to any annual stockholder meeting following the date of this offering and will continue to serve as a director immediately following such annual stockholder meeting will be automatically granted, on the date of such annual stockholder meeting, an option (the Annual Grant) to purchase 6,00010,000 shares of our common stock (subject to adjustment as provided in the applicable equity plan). The Initial Grant will vest in substantially equal installments on each of the first three anniversaries of the applicable grant date, subject to continued service through each applicable vesting date, and the Annual Grant will vest in full on the earlier of the first anniversary of the applicable grant date or immediately prior to the next annual stockholder meeting after the applicable grant date, subject to continued service through such vesting date. In addition, pursuant to the terms of the Amended and Restated Director Compensation Program, all equity awards outstanding and held by anon-employee director will vest in full immediately prior to the occurrence of a change in control. No Initial Grants or Annual Grants were made to our directors during fiscal year 2015, although we did grant options to our directors in connection with our initial public offering as described in more detail below. In March

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2016, the Director Compensation Program was amended to increase the Initial Grant to be an option to purchase 20,000 shares and the Annual Grant to be an option to purchase 10,000 shares.

        In fiscal 2015, prior to our initial public offering, our board of directors granted options to purchase shares of our common stock to each independent director pursuant to our 2008 Long term Incentive Plan, as amended. In March 2015, we granted to each of Drs. Siegall and Goodman an option to purchase 4,000 shares of our common stock and Mr. Alleva an option to purchase 2,666 shares of our common stock, in consideration for their service as independent directors on our board and each having an exercise price equal to $6.15. In June 2015, we granted to (i) each of Drs. Powell and Siegall an option to purchase 6,666 shares of our common stock, (ii) each of Drs. Jones and Winkler and Mr. Mathers an option to purchase 4,000 shares of our common stock, (iii) Dr. Goodman an option to purchase 13,333 shares of our common stock and (iv) Mr. Alleva an option to purchase 8,000 shares of our common stock, all having an exercise price equal to $6.45. Each option grant made to our independent directors was immediately vested and exercisable with respect to 20% of the shares underlying the option and the remaining shares vest and become exercisable in substantially equal installments every six months over four years, subject to continued service. In the event of a change of control while an independent director is still providing services to us, the options held by the independent director will become fully vested and exercisable immediately prior to such change in control.

        Upon the pricing of our initial public offering in October 2015, each of Drs. Powell, Jones and Winkler and Mr. Mathers was granted an option to purchase 7,200 shares of our common stock, Mr. Alleva was granted an option to purchase 10,533 shares of our common stock and Dr. Siegall was granted an option to purchase 12,000 shares of our common stock, each having an exercise price per share equal to $7.00 per share. The options vest and become exercisable in substantially equal installments on each of the first three anniversaries of the applicable grant date, subject to continued service through each applicable vesting date.

We reimburse all of ournon-employee directors for all reasonable and customary business expenses incurred providing services to us in accordance with Company policy.

2015 Director Compensation Table

EQUITY COMPENSATION PLAN INFORMATION

The following table setsprovides certain aggregate information with respect to all of the Company’s equity compensation plans in effect as of December 31, 2018.

Summary Description of the Company’s 2015 Equity Incentive Award Plan

In August 2015, the Company adopted the Mirna 2015 Equity Incentive Award Plan (the “2015 Plan”). The terms of the 2015 Plan provide for the grant of stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, deferred stock awards, dividend equivalent awards, stock payment awards, performance awards and other stock-based awards. Stock options may be granted under the 2015 Plan with an exercise price not less than 100% of the fair market value of the common stock on the date of grant. Stock options under the 2015 Plan may be granted with terms of up to ten years The total number of shares of the Company’s common stock initially reserved for issuance under the 2015 Plan was equal to the sum of (i) 238,828 shares, plus (ii) any shares subject to awards under the Mirna Therapeutics, Inc. 2008 Long Term Incentive Plan that, on or after September 30, 2015, terminate, expire or lapse for any reason, up to a maximum of 116,951 shares. Additionally, the number of shares of common stock that may be issued under the 2015 Plan automatically increase on each January 1, beginning with January 1, 2016, and continuing until January 1, 2025 by an amount equal to the lesser of (i) 5% of the number of outstanding shares of common stock on that date and (ii) an amount determined by the Board; provided, however, that no more than 2,000,000 shares will be issued under the 2015 Plan as incentive stock options. As of December 31, 2018, 477,414 shares of common stock were available for future grants under the 2015 Plan.

Summary Description of the Company’sNon-Stockholder Approved Equity Compensation Plan

Private Synlogic adopted the Synlogic, Inc. 2017 Stock Incentive Plan (the “2017 Plan”) on May 11, 2017. The 2017 Plan will expire in 2027. Pursuant to the 2017 Reorganization, Private Synlogic issued restricted common stock awards under the 2017 Plan to replace the canceled incentive units pursuant to the termination of the 2015 LLC Plan. In addition, Private Synlogic also issued stock options to certain employees prior to the Merger. Pursuant to the Merger Agreement, each restricted common stock award of Private Synlogic under the 2017 Plan that was outstanding immediately prior to the Merger and each option to purchase common stock of Private Synlogic under the 2017 Plan that was outstanding and unexercised immediately prior to the Merger was converted into and became restricted common stock and options to purchase shares of the Company’s common stock, respectively, based on the merger exchange ratio of 0.5532. In connection with the Merger, the Company assumed the 2017 Plan. The Board is authorized to administer the 2017 Plan. In addition, the Board or any

committee to which the Board delegates authority may, with the consent of the affected plan participants,re-price or otherwise amend outstanding awards consistent with the terms of the 2017 Plan.

Upon a merger, consolidation or sale of all or substantially all of our assets, the Board or any committee to which the Board delegates authority, or the Board of any corporation assuming our obligations, may, in its sole discretion, take any one or more of the following actions pursuant to the 2017 Plan, as to some or all outstanding awards, to the extent not otherwise agreed under any individual agreement provide that outstanding options will be assumed or substituted for options of the successor corporation; provide that the outstanding options must be exercised within a certain number of days, either to the extent the options are then exercisable, or at the Board’s discretion, any such options being made partially or fully exercisable; terminate outstanding options in exchange for a cash payment of an amount equal to the difference between (a) the consideration payable upon consummation of the corporate transaction to a holder of the number of shares into which such option would have been exercisable to the extent then exercisable, or in the Board’s discretion, any such options being made partially or fully exercisable, and (b) the aggregate exercise price of those options; provide that outstanding stock grants will be substituted for shares of the successor corporation or consideration payable with respect to our outstanding stock in connection with the corporate transaction; and terminate outstanding stock grants in exchange for payment of an amount equal to the consideration payable upon consummation of the corporate transaction to a holder of the same number of shares comprising the stock grant, to the extent the stock grant is no longer subject to any forfeiture or repurchase rights, or at the Board’s discretion, all forfeiture and repurchase rights being waived upon the corporate transaction. For purposes of determining such payments, in the case of a corporate transaction the consideration for which, in whole or in part, is other than cash, the consideration other than cash shall be valued at the fair market value thereof as determined in good faith by the Board.

REPORT OF AUDIT COMMITTEE

The Audit Committee of the Board, which consists entirely of directors who meet the independence and experience requirements of Nasdaq, has furnished the following report:

The Audit Committee assists the Board in overseeing and monitoring the integrity of our financial reporting process, compliance with legal and regulatory requirements and the quality of internal and external audit processes. This committee’s role and responsibilities are set forth informationin our charter adopted by the Board, which is available on our website atwww.synlogictx.com. This committee reviews and reassesses our charter annually and recommends any changes to the Board for approval. The Audit Committee is responsible for overseeing our overall financial reporting process, and for the appointment, compensation, retention, and oversight of the work of KPMG LLP. In fulfilling its responsibilities for the financial statements for fiscal year 2018, the Audit Committee took the following actions:

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EXECUTIVE OFFICERS

        The following table sets forth information regarding our executive officers as of March 31, 2016.

        Dr. Lammers' biographical information is set forth in "Proposal No. 1—Election of Directors" in this proxy statement.

        Miguel Barbosa, Ph.D.    Dr. Barbosa has served as our Chief Scientific Officer since September 2015. From April 2015 to September 2015, Dr. Barbosa served as an Executive in Residence, Therapeutic Innovation, at Johnson & Johnson Innovation, a pharmaceutical company and part of The Johnson & Johnson Family of Companies ("J&J") where he led the identification and development of new research and development and business models. Previously, Dr. Barbosa served as Vice President, Immunology Research & External Innovation, from June 2010 to March 2015 and as Vice President, Immunology Research, from June 2009 to June 2010 at Janssen Research & Development L.L.C., a J&J company. From 2005 to 2009, Dr. Barbosa served in various roles, including Vice President, Discovery Research, at Centocor Research & Development, Inc., a J&J company. Dr. Barbosa received a B.S. in Genetics from the University of California, Davis, and a Ph.D. in Microbiology & Immunology from the University of California, Los Angeles.

        Vincent O'Neill, M.D.    Dr. O'Neill has served as Chief Medical Officer since April 2016. He previously served as the Chief Medical Officer of Exosome Diagnostics, a healthcare company, from June 2014 to March 2016. From June 2012 to May 2014, Dr. O'Neill served as the Global Head of Personalized Medicine and Companion Diagnostics at Sanofi S.A., a multinational pharmaceutical company. Before that, Dr. O'Neill was employed as a Group Director at Genentech, Inc. from February 2009 to June 2012. Dr. O'Neill has also served at GlaxoSmithKline, Beatson Oncology Centre, F. Hoffmann La-Roche and the University of Glasgow. Dr. O'Neill holds a BSc (Hons), MBChB and an M.D. from the University of Glasgow.

        Alan Fuhrman.    Alan Fuhrman has served as our Chief Financial Officer since September 2015. Mr. Fuhrman previously served as the Chief Financial Officer of Ambit Biosciences Corporation, a biopharmaceutical company, from October 2010 through the company's initial public offering in 2013 and until its sale to Daiichi Sankyo for up to $410 million. Prior to this role, Mr. Fuhrman served as Chief Financial Officer of Naviscan, Inc., a privately-held medical imaging company, from November 2008 until September 2010, and as Chief Financial Officer of Sonus Pharmaceuticals, Inc., a pharmaceutical company, from September 2004 until August 2008. Mr. Fuhrman is a member of the board of directors of Loxo Oncology, Inc. Earlier in Mr. Fuhrman's career he practiced as a CPA with Coopers and Lybrand. Mr. Fuhrman received a B.S. in both Business Administration and Agricultural Economics from Montana State University.

        Casi DeYoung.    Ms. Casi DeYoung has served as our Chief Business Officer since March 2014. From May 2008 to December 2013, Ms. DeYoung served as the Vice President of Business Development for Reata Pharmaceuticals, Inc., a biopharmaceutical company. Previously, Ms. DeYoung served as the Vice President of Business Development for ODC Therapy, Inc., an immunotherapy company. From 2000 to 2005, Ms. DeYoung served in various roles, including the Director of Global Oncology Operations, for EMD Pharmaceuticals, Inc., the U.S. affiliate of Merk KGaA, a global

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healthcare company. Ms. DeYoung received a B.S. in Chemistry from Southwestern University and an M.B.A. from the University of Texas at Austin.

        Jon Irvin.    Mr. Jon Irvin has served at our company since November 2012, first as a Chief Financial Officer Consultant with Bridgepoint Consulting, LLC, or Bridgepoint, a consulting firm providing financial consulting assistance to various organizations, and then as our employee beginning in April 2013. Mr. Irvin currently serves as our Vice President of Finance. From December 2010 to March 2012, Mr. Irvin was an independent consultant in Austin, Texas. From September 2005 to December 2010, Mr. Irvin served as the Chief Executive Officer and Vice President of Finance for Voxpath Networks, Inc., a telecommunications and intellectual property company. Previously, Mr. Irvin held various finance positions at Reddwerks Corporation, a software company, Esoterix, Inc., a medical labs company, Topaz Technologies, a pharmaceutical software company, and BioNumerik Pharmaceuticals, Inc., a pharmaceutical company. Mr. Irvin was previously an accountant with Price Waterhouse and Ernst & Young. Mr. Irvin received a B.S. in Accounting from the University of Illinois.

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EXECUTIVE COMPENSATION

        The following is a discussion and analysis of compensation arrangements of our named executive officers ("NEOs"). As an "emerging growth company" as defined in the JOBS Act, we are not required to include a Compensation Discussion and Analysis section and have elected to comply with the scaled disclosure requirements applicable to emerging growth companies.

        We seek to ensure that the total compensation paid to our executive officers is reasonable and competitive. Compensation of our executives is structured around the achievement of individual performance and near-term corporate targets as well as long-term business objectives.

        Our NEOs for fiscal year 2015 were as follows:

•

Paul Lammers, M.D., M.Sc., President and Chief Executive Officer;



•

Miguel Barbosa, Ph.D., Chief Scientific Officer; and



•

Alan Fuhrman, Chief Financial Officer.

        Dr. Barbosa and Mr. Fuhrman each commenced employment with us in September 2015.

2015 Summary Compensation Table

        The following table shows information regarding the compensation of our named executive officers for services performed in the year ended December 31, 2015.

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Outstanding Equity Awards at 2015 Fiscal Year EndSynlogicAudit Committee

        The following table sets forth all outstanding equity awards held by each of the named executive officers as of December 31, 2015.

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Narrative to 2015 Summary Compensation Table and Outstanding Equity Awards at 2015 Fiscal Year End

Terms and Conditions of Employee Arrangements with our NEOs

        We have entered into agreements with each of the NEOs in connection with his or her employment with us. These agreements set forth the terms and conditions of employment of each named executive officer, including base salary, initial stock option grants, and standard employee benefit plan participation. Our board of directors or the compensation committee reviews each NEO's base salary from time to time to ensure compensation adequately reflects the NEO's qualifications, experience, role and responsibilities. Each of the NEOs are also subject to certain confidentiality, non-competition, non-solicitation and arbitration restrictive covenants. For fiscal year 2015, Dr. Lammers' annual base salary was $387,625 Miguel Barbosa's base salary was $350,000 and Alan Fuhrman's annual base salary was $325,000.

        Pursuant to Mr. Fuhrman's employment agreement, we reimbursed Mr. Fuhrman for his reasonable and necessary documented moving expenses, including the incidental expenses to the sale of his primary residence in Escondido, California and the purchase of his primary residence in the Austin, Texas area (which amounted to a total of $25,407 in fiscal 2015). These relocation expenses will not be earned until September 8, 2016, and if Mr. Fuhrman resigns his employment with us on or prior to September 8, 2016, he will be required to repay us in full for all of the relocation expenses we reimbursed.

        Pursuant to Dr. Barbosa's employment agreement, we reimbursed Dr. Barbosa for his reasonable and necessary documented moving expenses, including the incidental expenses to the sale of his primary residence in San Diego, California and the purchase of his primary residence in the Austin, Texas area (which amounted to a total of $16,583 in fiscal 2015). The relocation expenses will not be earned until September 28, 2016, and if Dr. Barbosa resigns his employment with us on or prior to such date, he will be required to repay us in full for all of the relocation expenses we reimbursed. In addition, pursuant to his employment agreement, Dr. Barbosa was awarded a sign-on bonus of $330,575 in connection with his commencement of employment with us, which was paid to him in January 2016. The signing bonus is subject to claw back if Dr. Barbosa's employment with us is terminated for cause or partial claw back if he voluntarily terminates employment, in each case, prior to September 28, 2016. As a result, Dr. Barbosa earned $84,902 of the sign-on bonus based on his service in 2015 from September 28 through December 31.

        In connection with our initial public offering in October 2015, we entered into change in control severance agreements with each of our NEOs that provide for severance payments and benefits upon certain qualifying terminations of employment. Pursuant to the terms of the change in control severance agreements, in the event an NEO's employment is terminated by us other than for "cause" or the executive experiences a "constructive termination" (each as defined below), then the NEO will receive as severance nine months (or 12 months in the case of Dr. Lammers) of base salary in a single cash lump sum payment and up to nine months (or 12 months in the case of Dr. Lammers) of healthcare continuation coverage premium reimbursement; provided, that if the termination or resignation occurs within the period commencing on a "change in control" (as defined below) and ending 12 months after a change in control, the severance will consist of 12 months (or 18 months in the case of Dr. Lammers) of base salary paid in a single cash lump sum, 100% (or 150% in the case of Dr. Lammers) of the executive's target bonus paid in a single cash lump sum, up to 12 months (or

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18 months in the case of Dr. Lammers) of healthcare continuation coverage premium reimbursement and full vesting acceleration for each stock option and other equity award held by the NEO. The NEO must timely deliver an effective release of claims to us in order to be eligible for the foregoing severance benefits.

        For purposes of the change in control severance agreements, "cause" means (i) the conviction of the NEO by a court of competent jurisdiction of a crime involving moral turpitude; (ii) the commission, or attempted commission, by the NEO of an act of fraud on us; (iii) the misappropriation, or attempted misappropriation, by the NEO of any of our funds or property; (iv) the failure by the NEO to perform in any material respect his or her obligations under the terms of his or her agreement, which such failure has gone unremedied within 10 days after we provide the NEO with written notice of such failure; (v) the knowing engagement by the NEO, without the written approval of our board of directors, in any direct, material conflict of interest with us without compliance with our conflict of interest policy; (vi) the knowing engagement by the NEO, without written approval of our board of directors, in any activity which competes with our business or which would result in a material injury to us or which otherwise violates any provision of his or her agreement, employment agreement or any confidentiality agreement; or (vii) the knowing engagement by the NEO in any activity that would constitute a material violation of the provisions of our business ethics policy, employee handbook or similar policies, if any, then in effect.

        For purposes of the change in control severance agreements, "constructive termination" means the NEO's resignation from all positions he or she then holds with us if: (i) without the NEO's prior written consent, (a) there is a material diminution in his or her duties and responsibilities with us;provided,however, that a change in title or reporting relationship will not be a constructive termination; (b) there is a material reduction of the NEO's then-existing base salary;provided,however, that a material reduction in his or her base salary pursuant to a salary reduction program affecting all or substantially all of our employees and that does not adversely affect the NEO to a greater extent than other similarly situated employees will not be a constructive termination; or (c) the NEO is required to relocate his or her primary work location to a facility or location that would increase his or her one-way commute distance by more than 50 miles from his or her primary work location as of immediately prior to such change, (ii) the NEO provides written notice outlining such conditions, acts or omissions to us within 30 days immediately following such material change or reduction, (iii) such material change or reduction is not remedied by us within 30 days following our receipt of such written notice and (iv) the NEO's resignation is effective not later than 30 days after the expiration of such 30 day cure period.

        For purposes of the change in control severance agreements, "change in control" generally means (i) the transfer or exchange in a single transaction or series of related transactions by our stockholders of more than 50% of our voting stock to a person or group; (ii) a change in the composition of our board of directors over a two-year period such that 50% or more of the members of the board of directors were elected through one or more contested elections; (iii) a merger, consolidation, reorganization or business combination in which we are involved, directly or indirectly, other than a merger, consolidation, reorganization or business combination which results in our outstanding voting securities immediately before the transaction continuing to represent a majority of the voting power of the acquiring company's outstanding voting securities and after which no person or group beneficially owns 50% or more of the outstanding voting securities of the surviving entity immediately after the transaction; or (iv) the sale, exchange, or transfer of all or substantially all of our assets.

Terms and Conditions of Annual Bonuses

        For 2015, all of the NEOs were eligible for cash performance-based bonuses pursuant to the achievement of certain performance objectives. The performance targets are approved annually by our board of directors. When determining the 2015 performance bonus program for the NEOs, the board

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of directors set certain performance goals, using a mixture of performance objectives after receiving recommendations from the compensation committee and input from our Chief Executive Officer. These performance objectives included certain financial, organizational, clinical, intellectual property and development measures. After determining performance targets, each performance target is given a different weight when determining the overall bonus amount based on the importance to the success of the Company for each performance target. For fiscal year 2015, the financial performance targets were weighted at 45%, the organizational and clinical targets were each weighted at 20% and the intellectual property and development targets were each weighted at 7.5%. For each of these performance targets under the annual bonus program, the board of directors set general performance goals, but there was no minimum or maximum achievement for each performance target; instead, the board of directors weighed the achievement, partial achievement or non-achievement for each performance target when deciding the overall achievement level. These performance goals were not expected to be attained based on average or below-average performance. The board of directors intended for the performance targets to require significant effort on the part of the NEOs and, therefore, set these targets at levels they believed would be difficult to achieve, such that average or below-average performance would not satisfy these targets.

        Each NEO's target bonus opportunity is expressed as a percentage of base salary which can be achieved by meeting the corporate performance goals. For each of the NEOs, the compensation committee (or, for Dr. Lammers, the board of directors) originally set these target percentages and review them annually to ensure they are adequate, and, while reviewing these target percentages the compensation committee (or, for Dr. Lammers, the board of directors) does not follow a formula but rather uses the factors as general background information prior to determining the target bonus opportunity rates for the participating NEOs. The compensation committee (or, for Dr. Lammers, the board of directors) sets these rates based on each participating executive's experience in his role with the company and the level of responsibility held by each executive, which the board of directors believes directly correlates to his ability to influence corporate results. For 2015, the board of directors used a guideline target bonus opportunity of 35% for Dr. Lammers and 25% for Dr. Barbosa and Mr. Fuhrman (pro-rated for their partial service in 2015).

        Corporate goals and performance targets are reviewed and approved by the compensation committee (or, for Dr. Lammers, the board of directors) prior to any allocation of the annual bonuses. In early 2016, the compensation committee (or, for Dr. Lammers, the board of directors) reviewed our 2015 company-wide performance with respect to determining bonuses for executive officers and determined achievement of the performance goals at 113%. Following its review and determinations, the compensation committee (or, for Dr. Lammers, our board of directors) awarded 2015 cash bonuses to the NEOs of $128,885 for Dr. Lammers, $21,689 for Dr. Barbosa and $24,425 for Mr. Fuhrman, which was equal to 113% of their target bonus amount. Dr. Barbosa's and Mr. Fuhrman's bonuses were each pro-rated for their partial service in 2015. The NEOs' 2015 bonuses are set forth in the "2015 Summary Compensation Table" above.

        In addition, in July 2015, at the recommendation of our compensation committee, our board of directors approved a one-time discretionary performance bonus to Dr. Lammers equal to $135,700. Dr. Lammers' one-time discretionary bonus is set forth in the "2015 Summary Compensation Table" above.

Terms and Conditions of Equity Award Grants

        Each of our NEOs received an option to purchase our common stock in fiscal year 2015. The table above entitled "Outstanding Equity Awards at 2015 Fiscal Year End" describes the material terms of other option awards made in past fiscal years to our NEOs.

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        In March 2015, we granted Dr. Lammers an option to purchase 20,000 shares of our common stock having an exercise price per share equal to $6.15. The option vests and becomes exercisable as to 25% of the shares subject to the option on January 1, 2016, and as to 1/48th of the shares subject to the option on each monthly anniversary thereafter, subject to Dr. Lammers continuing to provide services to us through such vesting date. In June 2015, we awarded Dr. Lammers another option to purchase 112,885 shares of our common stock having an exercise price per share equal to $6.45. The option vests and becomes exercisable as to 1/48th of the shares subject to the option on each monthly anniversary of May 1, 2015, subject to Dr. Lammers continuing to provide services to us through such vesting date.

        In connection with our initial public offering in October 2015 and pursuant to Dr. Barbosa's and Mr. Fuhrman's employment agreements, each of Drs. Lammers and Barbosa and Mr. Fuhrman were granted an option to purchase 76,666, 284,206 and 167,180 shares of our common stock, respectively, having an exercise price per share equal to $7.00. The options vest and become exercisable as to 25% of the shares subject to the option on the first anniversary of the pricing of the offering for Dr. Lammers and the commencement of employment for Dr. Barbosa and Mr. Fuhrman, and as to 1/48th of the shares subject to the option on each monthly anniversary thereafter, subject to the NEOs continuing to provide services to us through such vesting date.

Terms and Conditions of 401(k) Plan

        Our U.S. eligible employees, including our NEOs, participate in our 401(k) plan. Enrollment in the 401(k) plan is automatic for employees who meet eligibility requirements unless they decline participation. The 401(k) plan is intended to qualify under Section 401(k) of the Internal Revenue Service Code of 1986, as amended, so that contributions to the 401(k) plan by employees or by us, and the investment earnings thereon, are not taxable to the employees until withdrawn from the 401(k) plan, and so that contributions by us, if any, will be deductible by us when made. Under the 401(k) plan, employees may elect to reduce their current compensation by up to the statutorily prescribed annual limit and to have the amount of such reduction contributed to the 401(k) plan. Under the 401(k), for fiscal year 2015, we provide matching contributions of $0.50 per dollar up to 8% of an employee's compensation.

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SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

        The following table sets forth information relating to the beneficial ownership of our common stock as of March 31, 2016 by:

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each person, or group of affiliated persons, known by us to beneficially own more than 5% of our outstanding shares of common stock;



•

each of our directors and nominees for director;



•

each of our NEOs; and



•

all directors, nominees and executive officers as a group.

        The number of shares beneficially owned by each entity, person, director, nominee or executive officer is determined in accordance with the rules of the SEC, and the information is not necessarily indicative of beneficial ownership for any other purpose. Under such rules, beneficial ownership includes any shares over which the individual has sole or shared voting power or investment power as well as any shares that the individual has the right to acquire within 60 days of March 31, 2016 through the exercise of stock options or other rights. Except as otherwise indicated, and subject to applicable community property laws, the persons named in the table have sole voting and investment power with respect to all shares of common stock held by that person.

        The percentage of shares beneficially owned is computed on the basis of 20,830,555 shares of our common stock outstanding as of March 31, 2016. Shares of our common stock that a person has the right to acquire within 60 days of March 31, 2016 are deemed outstanding for purposes of computing the percentage ownership of the person holding such rights, but are not deemed outstanding for purposes of computing the percentage ownership of any other person, except with respect to the percentage ownership of all directors and executive officers as a group. Unless otherwise indicated below, the address for each beneficial owner listed is c/o Mirna Therapeutics, Inc., at 2150 Woodward Street, Suite 100, Austin, Texas 78744.

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