13G Filing: James E. Flynn and Mirna Therapeutics Inc. (MIRN)

87166L100

NAME OF REPORTING PERSONS

I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)

Deerfield Management
Company, L.P.

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

(a)
☐

(b) ☒

SEC USE ONLY

CITIZENSHIP OR PLACE OF ORGANIZATION

Delaware

 NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH

SOLE VOTING POWER

0

SHARED VOTING POWER

850,143 (1)

7.

SOLE DISPOSITIVE POWER

0

8.

SHARED DISPOSITIVE POWER

850,143 (1)

9.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

850,143 (1)

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN
SHARES*

11.

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

5.22%

TYPE OF REPORTING PERSON*

PN

87166L100

NAME OF REPORTING PERSONS

I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)

Deerfield Mgmt III, L.P.

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

(a)
☐

(b) ☒

SEC USE ONLY

CITIZENSHIP OR PLACE OF ORGANIZATION

Delaware

 NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH

SOLE VOTING POWER

0

SHARED VOTING POWER

850,143 (2)

7.

SOLE DISPOSITIVE POWER

0

8.

SHARED DISPOSITIVE POWER

850,143 (2)

9.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

850,143 (2)

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN
SHARES*

11.

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

5.22%

TYPE OF REPORTING PERSON*

PN

NAME OF REPORTING PERSONS

I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)

Deerfield Private Design Fund III, L.P.

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

(a)
☐

(b) ☒

SEC USE ONLY

CITIZENSHIP OR PLACE OF ORGANIZATION

Delaware

 NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH

SOLE VOTING POWER

0

SHARED VOTING POWER

850,143

7.

SOLE DISPOSITIVE POWER

0

8.

SHARED DISPOSITIVE POWER

850,143

9.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

850,143

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN
SHARES*

11.

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

5.22%

TYPE OF REPORTING PERSON*

PN

NAME OF REPORTING PERSONS

I.R.S. IDENTIFICATION NO. OF ABOVE PERSONS (ENTITIES ONLY)

James E. Flynn

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

(a)
☐

(b) ☒

SEC USE ONLY

CITIZENSHIP OR PLACE OF ORGANIZATION

United States

 NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH

SOLE VOTING POWER

0

SHARED VOTING POWER

850,143 (3)

7.

SOLE DISPOSITIVE POWER

0

8.

SHARED DISPOSITIVE POWER

850,143 (3)

9.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

850,143 (3)

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN
SHARES*

11.

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

5.22%

TYPE OF REPORTING PERSON*

IN

Synlogic, Inc.

200 Sidney St., Suite 320

Cambridge, MA 02139

James E. Flynn, Deerfield Management Company, L.P., Deerfield Mgmt III, L.P. and Deerfield Private Design Fund III, L.P.

James E. Flynn, Deerfield Mgmt III, L.P., Deerfield Management Company, L.P., Deerfield Private Design Fund III, L.P. 780
Third Avenue, 37th Floor, New York, NY 10017

Deerfield Mgmt III, L.P., Deerfield Private Design Fund III, L.P. and Deerfield Management Company, L.P. – Delaware limited
partnerships;

James E. Flynn – United States citizen

Common Stock

87166L100

If This Statement is Filed Pursuant to
Rule 13d-1(b), or 13d-2(b) or (c), Check Whether the Person Filing is a:

Broker or dealer registered under Section 15 of the
Exchange Act.

Insurance company as defined in Section 3(a)(19) of
the Exchange Act.

Investment company registered under Section 8 of the
Investment Company Act.

An employee benefit plan or endowment fund in accordance
with Rule 13d-1(b)(1)(ii)(F);

A parent holding company or control person in accordance
with Rule 13d-1(b)(1)(ii)(G);

(h)

A savings association as defined in Section 3(b) of
the Federal Deposit Insurance Act;

A church plan that is excluded from the definition
of an investment company under Section 3(c)(14) of the Investment Company Act;

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

Deerfield Management Company, L.P. – 850,143 shares

Deerfield Mgmt III, L.P. – 850,143 shares

Deerfield Private Design Fund
III, L.P. – 850,143 shares

James E. Flynn – 850,143 shares

Deerfield Management Company, L.P. – 5.22%

Deerfield Mgmt III, L.P. – 5.22%

Deerfield Private Design Fund III, L.P. – 5.22%

James E. Flynn – 5.22%

Deerfield
Management Company, L.P. – 850,143

Deerfield Mgmt III, L.P. – 850,143

Deerfield Private Design Fund III, L.P. – 850,143

James E. Flynn – 850,143

Sole power to dispose or to direct the disposition of:

Shared power to dispose or to direct the disposition
of:

Deerfield Management Company, L.P. – 850,143

Deerfield Mgmt III, L.P. – 850,143

Deerfield Private Design Fund III, L.P. –
850,143

James E. Flynn – 850,143

If this statement is being filed to report
the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the
class of securities check the following ☐.

If any other person
is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of,
such securities, a statement to that effect should be included in response to this item and, if such interest relates to more
than five percent of the class, such person should be identified. A listing of the shareholders of an investment company registered
under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not
required.

Identification and Classification of the Subsidiary
Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.

If a parent holding company or Control person has filed this
schedule, pursuant to Rule 13d-1(b)(1)(ii)(G), so indicate under Item 3(g) and attach an exhibit stating the identity and the
Item 3 classification of the relevant subsidiary. If a parent holding company or control person has filed this schedule pursuant
to Rule 13d-1(c) or Rule 13d-1(d), attach an exhibit stating the identification of the relevant subsidiary.

If a group has filed this schedule pursuant
to ss.240.13d-1(b)(1)(ii)(J), so indicate under Item 3(j) and attach an exhibit stating the identity and Item 3 classification
of each member of the group. If a group has filed this schedule pursuant to ss.240.13d-1(c) or ss.240.13d-1(d), attach an exhibit
stating the identity of each member of the group.

Notice of dissolution of a group may be furnished as an exhibit
stating the date of the dissolution and that all further filings with respect to transactions in the security reported on will
be filed, if required, by members of the group, in their individual capacity. See Item 5.

“By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired
and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities
and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect,
other than activities solely in connection with a nomination under §240.14a-11.”