13G Filing: James E. Flynn and Aclaris Therapeutics Inc (ACRS)

NAME OF REPORTING PERSONS

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

Deerfield Mgmt, 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

1,769,377 (1)

7.

SOLE DISPOSITIVE POWER

0

8.

SHARED DISPOSITIVE POWER

1,769,377 (1)

9.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

1,769,377 (1)

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

11.

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

5.90%

TYPE OF REPORTING PERSON*

PN

00461U105

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

1,769,377 (2)

7.

SOLE DISPOSITIVE POWER

0

8.

SHARED DISPOSITIVE POWER

1,769,377 (2)

9.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

1,769,377 (2)

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

11.

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

5.90%

TYPE OF REPORTING PERSON*

PN

00461U105

NAME OF REPORTING PERSONS

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

Deerfield Partners, 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

1,107,639

7.

SOLE DISPOSITIVE POWER

0

8.

SHARED DISPOSITIVE POWER

1,107,639

9.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

1,107,639

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

11.

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

3.69%

TYPE OF REPORTING PERSON*

PN

NAME OF REPORTING PERSONS

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

Deerfield Special Situations
Fund, 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

57,416

7.

SOLE DISPOSITIVE POWER

0

8.

SHARED DISPOSITIVE POWER

57,416

9.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

57,416

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

11.

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

0.19%

TYPE OF REPORTING PERSON*

PN

NAME OF REPORTING PERSONS

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

Deerfield International Master Fund, L.P.

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*

(a)
☐

(b) ☒

SEC USE ONLY

CITIZENSHIP OR PLACE OF ORGANIZATION

British Virgin Islands

 NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH

SOLE VOTING POWER

0

SHARED VOTING POWER

604,322

7.

SOLE DISPOSITIVE POWER

0

8.

SHARED DISPOSITIVE POWER

604,322

9.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

604,322

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

11.

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

2.01%

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

1,769,377 (3)

7.

SOLE DISPOSITIVE POWER

0

8.

SHARED DISPOSITIVE POWER

1,769,377 (3)

9.

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

1,769,377 (3)

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

11.

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

5.90%

TYPE OF REPORTING PERSON*

IN

Aclaris Therapeutics, Inc.

101 Lindenwood Drive, Suite 400

Malvern, PA 19355

James E. Flynn, Deerfield Mgmt, L.P., Deerfield
Management Company, L.P., Deerfield Partners, L.P., Deerfield International Master Fund, L.P., Deerfield Special Situations Fund,
L.P.

James E. Flynn, Deerfield Mgmt, L.P., Deerfield Management Company, L.P., Deerfield Partners, L.P., Deerfield
International Master Fund, L.P., Deerfield Special Situations Fund, L.P., 780 Third Avenue, 37th Floor, New York, NY 10017

Deerfield Mgmt, L.P., Deerfield Management Company,
L.P., Deerfield Partners, L.P., Deerfield Special Situations Fund, L.P. – Delaware limited partnerships;

Deerfield International Master
Fund, L.P. – British Virgin Islands limited partnership;

James E. Flynn – United States citizen

Common Stock

00461U105

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 Mgmt, L.P. – 1,769,377 shares

Deerfield Management Company,
L.P. – 1,769,377 shares

Deerfield Partners, L.P. –
1,107,639 shares

Deerfield International Master
Fund, L.P. – 604,322 shares

Deerfield
Special Situations Fund, L.P. – 57,416 shares

James E. Flynn – 1,769,377 shares

Deerfield Mgmt, L.P. – 5.90%

Deerfield Management Company,
L.P. – 5.90%

Deerfield Partners, L.P. –
3.69%

Deerfield International Master
Fund, L.P. – 2.01%

Deerfield
Special Situations Fund, L.P. – .19%

James E. Flynn – 5.90%

Deerfield Mgmt, L.P. – 1,769,377

Deerfield Management Company, L.P. – 1,769,377

Deerfield Partners, L.P. – 1,107,639

Deerfield International Master Fund, L.P. – 604,322

Deerfield Special Situations Fund, L.P. –
57,416

James E. Flynn – 1,769,377 

Sole power to dispose or to direct the disposition of:

Shared power to dispose or to direct the disposition
of:

Deerfield Mgmt, L.P. – 1,769,377

Deerfield Management Company, L.P. – 1,769,377

Deerfield Partners, L.P. – 1,107,639

Deerfield International Master Fund, L.P. – 604,322

Deerfield Special Situations Fund, L.P. –
57,416

James E. Flynn – 1,769,377

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.”