Filing Details

The remainder of this cover page shall be filled out for a reporting persons initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

NAMES OF REPORTING PERSONS

Third Rock Ventures 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

9,741,636    

SOLE DISPOSITIVE POWER

0    

SHARED DISPOSITIVE POWER

9,741,636    

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

9,741,636    

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

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

34.4% (1)

TYPE OF REPORTING PERSON

PN

The percent of class was calculated based on 28,313,417shares of common stock issued and outstanding as of November 9, 2018, as disclosed in the Issuers Prospectus Supplement filed with the Securities and Exchange Commission on November 13, 2018.

NAMES OF REPORTING PERSONS

Third Rock Ventures GP 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

9,741,636    

SOLE DISPOSITIVE POWER

0    

SHARED DISPOSITIVE POWER

9,741,636    

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

9,741,636    

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

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

34.4% (1)

TYPE OF REPORTING PERSON

PN

NAMES OF REPORTING PERSONS

TRV GP III, LLC

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

9,741,636    

SOLE DISPOSITIVE POWER

0    

SHARED DISPOSITIVE POWER

9,741,636    

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

9,741,636    

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

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

34.4% (1)

TYPE OF REPORTING PERSON

OO

NAMES OF REPORTING PERSONS

Mark Levin

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

9,741,636    

SOLE DISPOSITIVE POWER

0    

SHARED DISPOSITIVE POWER

9,741,636    

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

9,741,636    

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

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

34.4% (1)

TYPE OF REPORTING PERSON

IN

NAMES OF REPORTING PERSONS

Kevin P. Starr

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

9,741,636    

SOLE DISPOSITIVE POWER

0    

SHARED DISPOSITIVE POWER

9,741,636    

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

9,741,636    

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

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

34.4% (1)

TYPE OF REPORTING PERSON

IN

NAMES OF REPORTING PERSONS

Robert I. Tepper

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

9,741,636    

SOLE DISPOSITIVE POWER

0    

SHARED DISPOSITIVE POWER

9,741,636    

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

9,741,636    

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

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

34.4% (1)

TYPE OF REPORTING PERSON

IN

40 Erie St., Suite 110

Cambridge, MA 02139

(i) Third Rock Ventures III, L.P. (TRV III);

(ii)  Third Rock Ventures GP III, L.P. (TRV GP III), which is the sole general partner of TRV III;

(iii)  TRV GP III, LLC (TRV GP III LLC), which is the sole general partner of TRV GP III;

(iv) Mark Levin (Levin), a managing member of TRV GP III LLC;

(v)   Kevin P. Starr (Starr), a managing member of TRV GP III LLC; and

(vi) Robert I. Tepper (Tepper, and collectively with TRV III, TRV GP III, TRV GP III LLC, Levin and Starr, the Reporting Persons), a managing member of TRV GP III LLC.

The address of the principal business office of each of the Reporting Persons is Third Rock Ventures, LLC, 29 Newbury Street, 3rd Floor, Boston, MA 02116.

Each of TRV III and TRV GP III is a Delaware limited partnership. TRV GP III LLC is a Delaware limited liability company. Levin, Tepper and Starr are United States citizens.

CUSIP Number:

64050Y100

Broker or dealer registered under Section 15 of the Act;

Bank as defined in Section 3(a)(6) of the Act;

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

Investment company registered under Section 8 of the Investment Company Act of 1940;

An investment adviser in accordance with Rule 13d-1(b)(1)(ii)(E);

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);

A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940;

A non-U.S. institution in accordance with Rule 240.13d-1(b)(1)(ii)(J);

Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K). If filing as a non-U.S. institution in accordance with Rule 240.13d-1(b)(1)(ii)(J), please specify the type of institution:

Reporting Person

TRV III

TRV GP III

TRV GP III LLC

Levin

Starr

Tepper

Sole power to vote or direct the vote

Shared power to vote or to direct the vote

Sole power to dispose or to direct the disposition of

Shared power to dispose or to direct the disposition of

Ownership of Five Percent or Less of a Class.

Ownership of More than Five Percent on Behalf of Another Person.

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

Identification and Classification of Members of the Group.

Notice of Dissolution of Group.

Certification.