Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

The remainder of this cover page shall be filled out for a reporting person’s 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

  5,524,031

  SOLE DISPOSITIVE POWER

  0

  SHARED DISPOSITIVE POWER

  5,524,031

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  5,524,031

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

  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

  7.5% (1)

  TYPE OF REPORTING PERSON

  PN

The percent of class was calculated based on 73,687,114 shares of common stock issued and outstanding as of November 4, 2021, as disclosed in the Issuer’s 10-Q filed with the Securities and Exchange Commission on November 10, 2021.

  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

  5,524,031

  SOLE DISPOSITIVE POWER

  0

  SHARED DISPOSITIVE POWER

  5,524,031

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  5,524,031

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

  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

  7.5% (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

  5,524,031

  SOLE DISPOSITIVE POWER

  0

  SHARED DISPOSITIVE POWER

  5,524,031

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  5,524,031

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

  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

  7.5% (1)

  TYPE OF REPORTING PERSON

  OO

  NAMES OF REPORTING PERSONS

  Third Rock Ventures IV, 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

  1,419,900

  SOLE DISPOSITIVE POWER

  0

  SHARED DISPOSITIVE POWER

  1,419,900

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  1,419,900

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

  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

  1.9% (1)

  TYPE OF REPORTING PERSON

  PN

  NAMES OF REPORTING PERSONS

  Third Rock Ventures GP IV, 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

  1,419,900

  SOLE DISPOSITIVE POWER

  0

  SHARED DISPOSITIVE POWER

  1,419,900

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  1,419,900

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

  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

  1.9% (1)

  TYPE OF REPORTING PERSON

  PN

  NAMES OF REPORTING PERSONS

  TRV GP IV, 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

  1,419,900

  SOLE DISPOSITIVE POWER

  0

  SHARED DISPOSITIVE POWER

  1,419,900

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  1,419,900

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

  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

  1.9% (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

  129,259 (2)

  SHARED VOTING POWER

  5,524,031

  SOLE DISPOSITIVE POWER

  129,259 (2)

  SHARED DISPOSITIVE POWER

  5,524,031

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  5,653,290 (2)

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

  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

  7.7% (1)

  TYPE OF REPORTING PERSON

  IN

Includes 12,925 shares of Common Stock held directly by the Levin Family 2014 Irrevocable Trust.

  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

  129,256

  SHARED VOTING POWER

  5,524,031

  SOLE DISPOSITIVE POWER

  129,256

  SHARED DISPOSITIVE POWER

  5,524,031

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  5,653,287

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

  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

  7.7% (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

  129,258

  SHARED VOTING POWER

  5,524,031

  SOLE DISPOSITIVE POWER

  129,258

  SHARED DISPOSITIVE POWER

  5,524,031

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  5,653,289

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

  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

  7.7% (1)

  TYPE OF REPORTING PERSON

  IN

700 Saginaw Drive

Redwood City, California 94063

(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) Third Rock Ventures IV, L.P. (“TRV IV”);

(v)   Third Rock Ventures GP IV, L.P. (“TRV GP IV”), which is the sole general partner of TRV IV;

(vi) TRV GP IV, LLC (“TRV GP IV LLC”), which is the sole general partner of TRV GP IV;

(vii) Mark Levin (“Levin”), a managing member of TRV GP III LLC;

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

(ix) Robert I. Tepper (“Tepper,” and collectively with TRV III, TRV GP III, TRV GP III LLC, TRV IV, TRV GP IV, TRV GP IV 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, TRV GP III, TRV IV and TRV GP IV is a Delaware limited partnership. Each of TRV GP III LLC and TRV GP IV LLC is a Delaware limited liability company. Levin, Tepper and Starr are United States citizens.

CUSIP Number:

76155X100

Item 3.

If this statement is filed pursuant to Rules 13d-1(b), or 13d-2(b) or (c), check whether the person filing is a:

(a)

Broker or dealer registered under Section 15 of the Act;

(b)

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

(c)

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

(d)

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

(e)

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

(f)

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

(g)

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

(h)

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

(i)

(j)

(k)

(i) TRV III directly owns 5,524,031 shares of Common Stock (the “III Shares”), which represents approximately 7.5% of the outstanding shares of Common Stock.

(ii)  TRV GP III is the general partner of TRV III and may be deemed to beneficially own the III Shares.

(iii)  TRV GP III LLC is the general partner of TRV GP III and may be deemed to beneficially own the III Shares.

(iv) TRV IV directly owns 1,419,900 shares of Common Stock (the “IV Shares”), which represents approximately 2.1% of the outstanding shares of Common Stock.

(v)   TRV GP IV is the general partner of TRV IV and may be deemed to beneficially own the IV Shares.

(vi) TRV GP IV LLC is the general partner of TRV GP IV and may be deemed to beneficially own the IV Shares.

(vii) As a managing member of TRV GP III LLC, Levin may be deemed to beneficially own the III Shares. Additionally, Levin directly owns 116,334 shares of Common Stock and the Levin Family 2014 Irrevocable Trust directly owns 12,925 shares of Common Stock (the “Trust Shares”). As Levin’s spouse is a trustee of the Levin Family 2014 Irrevocable Trust, Levin may be deemed to beneficially own the Trust Shares.

(viii)As a managing member of TRV GP III LLC Tepper may be deemed to beneficially own the III Shares. Additionally, Tepper directly owns 129,258 shares of Common Stock.

(ix) As a managing member of TRV GP III LLC, Starr may be deemed to beneficially own the III Shares. Additionally, Starr directly owns 129,256 shares of Common Stock.

Reporting Person

TRV III

TRV GP III

TRV GP III LLC

TRV IV

TRV GP IV

TRV GP IV LLC

Levin

Starr

Tepper

(i) Sole power to vote or direct the vote

(ii)  Shared power to vote or to direct the vote

(iii)  Sole power to dispose or to direct the disposition of

(iv) Shared power to dispose or to direct the disposition of

Ownership of Five Percent or Less of a Class.

Not applicable.

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

Not applicable.

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

Not applicable.

Identification and Classification of Members of the Group.

Not applicable.

Notice of Dissolution of Group.

Not applicable.

Certification.

Not applicable.