Merger Agreement	6 Months Ended
Jun. 30, 2017
Business Combinations [Abstract]
Merger Agreement	Merger Agreement On May 15, 2017, Mirna, Meerkat Merger Sub, Inc., a Delaware corporation and a wholly-owned subsidiary of Mirna (“Merger Sub”), and Synlogic, entered into the Merger Agreement, pursuant to which, among other matters, and subject to the satisfaction or waiver of the conditions set forth in the Merger Agreement, at the effective time of the Merger, Merger Sub will merge with and into Synlogic, with Synlogic continuing as a wholly owned subsidiary of Mirna and the surviving corporation of the Merger. The Merger is intended to qualify for federal income tax purposes as a tax-free reorganization under the provisions of Section 368(a) of the Internal Revenue Code of 1986, as amended (the “Code”). Subject to the terms and conditions of the Merger Agreement, at the effective time of the Merger, (a) each outstanding share of Synlogic common stock and Synlogic preferred stock will be converted into the right to receive a number of shares of Mirna’s common stock equal to the exchange ratio (as described in the Merger Agreement); and (b) each outstanding Synlogic stock option that has not previously been exercised prior to the effective time of the Merger will be assumed by Mirna. Pursuant to the exchange ratio formula in the Merger Agreement, as of immediately after the Merger, the former Synlogic securityholders are expected to own approximately 83% of the outstanding shares of Mirna's common stock on a fully-diluted basis and securityholders of Mirna as of immediately prior to the Merger are expected to own approximately 17% of the outstanding shares of Mirna's common stock on a fully-diluted basis. The exchange ratio will be adjusted to the extent that Mirna’s net cash at closing is greater than or less than $40 million, as of immediately prior to the effective time of the Merger, as described further in the Merger Agreement. Consummation of the Merger is subject to certain closing conditions, including, among other things, approval by the stockholders of Mirna and Synlogic, and Mirna’s satisfaction of a minimum net cash threshold of $33.5 million immediately prior to the effective time of the Merger. In accordance with the terms of the Merger Agreement, (i) certain executive officers, directors and stockholders of Synlogic (solely in their respective capacities as Synlogic stockholders) holding approximately 77% of the shares of outstanding Synlogic capital stock (after giving effect to Synlogic’s Series C financing) have entered into support agreements with Mirna to vote all of their shares of Synlogic capital stock in favor of adoption of the Merger Agreement and approval of the transactions contemplated by the Merger Agreement (the “Synlogic Support Agreements”) and (ii) certain executive officers, directors and stockholders of Mirna (solely in their respective capacities as Mirna stockholders) holding approximately 33% of the outstanding shares of Mirna's common stock have entered into support agreements with Synlogic to vote all of their shares of Mirna common stock in favor of adoption of the Merger Agreement and approval of the transactions contemplated by the Merger Agreement (together with the Synlogic Support Agreements, the “Support Agreements”). The Support Agreements include covenants with respect to the voting of such shares in favor of approving the transactions contemplated by the Merger Agreement and against any competing acquisition proposals and place certain restrictions on the transfer of the shares of Mirna and Synlogic held by the respective signatories thereto. Concurrently with the execution of the Merger Agreement, certain officers, directors and stockholders of Mirna holding approximately 33% of the outstanding shares of Mirna common stock and certain officers, directors and stockholders of Synlogic holding approximately 81% of the outstanding shares of Synlogic capital stock (giving effect to Synlogic’s Series C financing) have entered into lock-up agreements pursuant to which, among other things, they have accepted certain restrictions on the transfer of shares of our common stock during the 180-day period following the closing of the Merger. The Merger Agreement contains certain termination rights for both Mirna and Synlogic, and further provides that, upon termination of the Merger Agreement under specified circumstances, either party may be required to pay the other party a termination fee of $2.0 million, or in some circumstances reimburse the other party’s expenses up to a maximum of $1.0 million. At the effective time of the Merger, the board of directors of Mirna is expected to consist of seven members, five of whom will be designated by Synlogic and two of whom will be designated by Mirna.

Merger Agreement

On May 15, 2017, Mirna, Meerkat Merger Sub, Inc., a Delaware corporation and a wholly-owned subsidiary of Mirna (“Merger Sub”), and Synlogic, entered into the Merger Agreement, pursuant to which, among other matters, and subject to the satisfaction or waiver of the conditions set forth in the Merger Agreement, at the effective time of the Merger, Merger Sub will merge with and into Synlogic, with Synlogic continuing as a wholly owned subsidiary of Mirna and the surviving corporation of the Merger. The Merger is intended to qualify for federal income tax purposes as a tax-free reorganization under the provisions of Section 368(a) of the Internal Revenue Code of 1986, as amended (the “Code”).

Subject to the terms and conditions of the Merger Agreement, at the effective time of the Merger, (a) each outstanding share of Synlogic common stock and Synlogic preferred stock will be converted into the right to receive a number of shares of Mirna’s common stock equal to the exchange ratio (as described in the Merger Agreement); and (b) each outstanding Synlogic stock option that has not previously been exercised prior to the effective time of the Merger will be assumed by Mirna.

Pursuant to the exchange ratio formula in the Merger Agreement, as of immediately after the Merger, the former Synlogic securityholders are expected to own approximately 83% of the outstanding shares of Mirna's common stock on a fully-diluted basis and securityholders of Mirna as of immediately prior to the Merger are expected to own approximately 17% of the outstanding shares of Mirna's common stock on a fully-diluted basis. The exchange ratio will be adjusted to the extent that Mirna’s net cash at closing is greater than or less than $40 million, as of immediately prior to the effective time of the Merger, as described further in the Merger Agreement.

Consummation of the Merger is subject to certain closing conditions, including, among other things, approval by the stockholders of Mirna and Synlogic, and Mirna’s satisfaction of a minimum net cash threshold of $33.5 million immediately prior to the effective time of the Merger. In accordance with the terms of the Merger Agreement, (i) certain executive officers, directors and stockholders of Synlogic (solely in their respective capacities as Synlogic stockholders) holding approximately 77% of the shares of outstanding Synlogic capital stock (after giving effect to Synlogic’s Series C financing) have entered into support agreements with Mirna to vote all of their shares of Synlogic capital stock in favor of adoption of the Merger Agreement and approval of the transactions contemplated by the Merger Agreement (the “Synlogic Support Agreements”) and (ii) certain executive officers, directors and stockholders of Mirna (solely in their respective capacities as Mirna stockholders) holding approximately 33% of the outstanding shares of Mirna's common stock have entered into support agreements with Synlogic to vote all of their shares of Mirna common stock in favor of adoption of the Merger Agreement and approval of the transactions contemplated by the Merger Agreement (together with the Synlogic Support Agreements, the “Support Agreements”). The Support Agreements include covenants with respect to the voting of such shares in favor of approving the transactions contemplated by the Merger Agreement and against any competing acquisition proposals and place certain restrictions on the transfer of the shares of Mirna and Synlogic held by the respective signatories thereto.

Concurrently with the execution of the Merger Agreement, certain officers, directors and stockholders of Mirna holding approximately 33% of the outstanding shares of Mirna common stock and certain officers, directors and stockholders of Synlogic holding approximately 81% of the outstanding shares of Synlogic capital stock (giving effect to Synlogic’s Series C financing) have entered into lock-up agreements pursuant to which, among other things, they have accepted certain restrictions on the transfer of shares of our common stock during the 180-day period following the closing of the Merger.

The Merger Agreement contains certain termination rights for both Mirna and Synlogic, and further provides that, upon termination of the Merger Agreement under specified circumstances, either party may be required to pay the other party a termination fee of $2.0 million, or in some circumstances reimburse the other party’s expenses up to a maximum of $1.0 million.

At the effective time of the Merger, the board of directors of Mirna is expected to consist of seven members, five of whom will be designated by Synlogic and two of whom will be designated by Mirna.