Hemab Therapeutics Holdings, Inc. reporting persons led by RA Capital Management, L.P. report beneficial ownership of 7,729,773 shares of common stock, equal to 16.6% of the class. The filing states 46,705,410 shares outstanding as of May 4, 2026.
The filing discloses that the 7,729,773 figure reflects shared voting and shared dispositive power held by RA Capital and named individuals, and that 6,365,783 of those shares are held directly by RA Capital Healthcare Fund, L.P. The filing also explains delegation of voting and disposition authority to RA Capital and contains disclaimers of beneficial ownership by certain funds and the reporting persons.
Positive
None.
Negative
None.
Insights
Institutional holder reports material shared control and standard beneficial‑ownership disclaimers.
The filing shows RA Capital and related persons with shared voting and dispositive power over 7,729,773 shares, representing 16.6% of the outstanding common stock as of May 4, 2026. That level of reported shared power is large enough to warrant board and governance attention.
Dependencies include the delegation clause (powers delegated to RA Capital with a 61‑day notice restriction). Subsequent disclosures or transactions by RA Capital or the Fund could affect voting outcomes; timing of any such actions is not stated in the excerpt.
Large institutional position documented, with fund-level holdings and adviser control explained.
The filing itemizes that 6,365,783 shares are held directly by the RA Capital Healthcare Fund, L.P., plus 1,009,052 in Nexus Fund II and 354,938 in Nexus Fund IV, aggregated under RA Capital's advisory control.
Cash‑flow treatment and intended disposition plans are not stated; investor impact will depend on whether RA Capital exercises its delegated voting/disposition rights in future filings.
Key Figures
Aggregated shares reported:7,729,773 sharesPercentage of class:16.6%Fund direct holdings (Healthcare Fund):6,365,783 shares+3 more
6 metrics
Aggregated shares reported7,729,773 sharesShared voting/dispositive power reported in Schedule 13G
Percentage of class16.6%Based on 46,705,410 shares outstanding as of May 4, 2026
Fund direct holdings (Healthcare Fund)6,365,783 sharesHeld directly by RA Capital Healthcare Fund, L.P.
Nexus Fund II holdings1,009,052 sharesHeld directly by RA Capital Nexus II Fund, L.P.
Nexus Fund IV holdings354,938 sharesHeld directly by RA Capital Nexus IV Fund, L.P.
Shares outstanding used for basis46,705,410 sharesShares outstanding as of May 4, 2026 (filing basis for percentages)
"may be deemed a beneficial owner, for purposes of Section 13(d) of the Act"
Schedule 13Gregulatory
"The names of the persons filing this report (collectively, the "Reporting Persons")"
A Schedule 13G is a formal document that investors file with the government when they acquire a large ownership stake in a company, usually for investment purposes rather than control. It helps keep the public informed about who owns significant parts of a company's shares, which can influence how the company is managed and how investors make decisions. Filing this schedule is important for transparency and understanding the ownership landscape of publicly traded companies.
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 13G
UNDER THE SECURITIES EXCHANGE ACT OF 1934
Hemab Therapeutics Holdings, Inc.
(Name of Issuer)
Common Stock, par value $0.0001 per share
(Title of Class of Securities)
423494103
(CUSIP Number)
05/04/2026
(Date of Event Which Requires Filing of this Statement)
Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
Rule 13d-1(b)
Rule 13d-1(c)
Rule 13d-1(d)
schemaVersion:
SCHEDULE 13G
CUSIP Number(s):
423494103
1
Names of Reporting Persons
RA Capital Management, L.P.
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
7,729,773.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
7,729,773.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
7,729,773.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
16.6 %
12
Type of Reporting Person (See Instructions)
IA, PN
SCHEDULE 13G
CUSIP Number(s):
423494103
1
Names of Reporting Persons
Peter Kolchinsky
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
UNITED STATES
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
7,729,773.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
7,729,773.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
7,729,773.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
16.6 %
12
Type of Reporting Person (See Instructions)
HC, IN
SCHEDULE 13G
CUSIP Number(s):
423494103
1
Names of Reporting Persons
Rajeev Shah
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
UNITED STATES
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
7,729,773.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
7,729,773.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
7,729,773.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
16.6 %
12
Type of Reporting Person (See Instructions)
HC, IN
SCHEDULE 13G
CUSIP Number(s):
423494103
1
Names of Reporting Persons
RA Capital Healthcare Fund, L.P.
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
6,365,783.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
6,365,783.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
6,365,783.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
13.6 %
12
Type of Reporting Person (See Instructions)
PN
SCHEDULE 13G
Item 1.
(a)
Name of issuer:
Hemab Therapeutics Holdings, Inc.
(b)
Address of issuer's principal executive offices:
101 Main Street, Suite 1220, Cambridge, MA, 02142.
Item 2.
(a)
Name of person filing:
The names of the persons filing this report (collectively, the "Reporting Persons") are:
RA Capital Management, L.P. ("RA Capital")
Peter Kolchinsky ("Dr. Kolchinsky")
Rajeev Shah ("Mr. Shah")
RA Capital Healthcare Fund, L.P. (the "Fund")
The Reporting Persons expressly disclaim status as a "group" for purposes of this Schedule 13G.
(b)
Address or principal business office or, if none, residence:
The address of the principal business office of each of the Reporting Persons is:
c/o RA Capital Management, L.P., 200 Berkeley Street, 18th Floor, Boston MA 02116
(c)
Citizenship:
RA Capital and the Fund are Delaware limited partnerships.
Dr. Kolchinsky and Mr. Shah are United States citizens.
(d)
Title of class of securities:
Common Stock, par value $0.0001 per share
(e)
CUSIP Number(s):
423494103
Item 3.
If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)
Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)
Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)
Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)
Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)
An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)
An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)
A parent holding company or control person in accordance with § 240.13d-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)
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 (15 U.S.C. 80a-3);
(j)
A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution:
(k)
Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.
Ownership
(a)
Amount beneficially owned:
Row 9 of each Reporting Person's cover page to this Schedule 13G sets forth the aggregate number of shares of common stock of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
The Reporting Persons' ownership of the Issuer's securities includes (i) 6,365,783 shares of common stock held directly by the Fund; (ii)1,009,052 shares of common stock held directly by the RA Capital Nexus II Fund, L.P. (the "Nexus Fund II"); and (iii) 354,938 shares of common stock held directly by the RA Capital Nexus IV Fund, L.P. (the "Nexus Fund IV").
RA Capital Healthcare Fund GP, LLC is the general partner of the Fund, RA Capital Nexus Fund II GP, LLC is the general partner of the Nexus Fund II and RA Capital Nexus Fund IV GP, LLC is the general partner of the Nexus Fund IV. The general partner of RA Capital is RA Capital Management GP, LLC, of which Dr. Kolchinsky and Mr. Shah are the controlling persons. RA Capital serves as investment adviser for each of the Fund, The Nexus Fund II and the Nexus Fund IV and may be deemed a beneficial owner, for purposes of Section 13(d) of the Act, of any securities of the Issuer held by the Fund, the Nexus Fund II or the Nexus Fund IV. Each of the Fund, the Nexus Fund II and the Nexus Fund IV has delegated to RA Capital the sole power to vote and the sole power to dispose of all securities held in its portfolio, including the shares of the Issuer's common stock reported herein. Because each of the Fund, the Nexus Fund II and the Nexus Fund IV has divested itself of voting and investment power over the reported securities it holds and may not revoke that delegation on less than 61 days' notice, each of the Fund, the Nexus Fund II and the Nexus Fund IV disclaims beneficial ownership of the securities it holds for purposes of Section 13(d) of the Act and therefore disclaims any obligation to report ownership of the reported securities under Section 13(d) of the Act. As managers of RA Capital, Dr. Kolchinsky and Mr. Shah may be deemed beneficial owners, for purposes of Section 13(d) of the Act, of any securities of the Issuer beneficially owned by RA Capital. RA Capital, Dr. Kolchinsky, and Mr. Shah disclaim beneficial ownership of the securities reported in this Schedule 13G other than for the purpose of determining their obligations under Section 13(d) of the Act, and the filing of this Schedule 13G shall not be deemed an admission that either RA Capital, Dr. Kolchinsky, or Mr. Shah is the beneficial owner of such securities for any other purpose.
(b)
Percent of class:
Row 11 of each Reporting Person's cover page to this Schedule 13G sets forth the percentages of shares of common stock of the Issuer beneficially owned by such Reporting Person and is incorporated by reference. The percentage set forth in each row 11 is based upon 46,705,410 shares outstanding as of May 4, 2026, as reported in the Issuer's final prospectus dated April 30, 2026 filed with the Securities and Exchange Commission (the "SEC") on May 1, 2025.
(c)
Number of shares as to which the person has:
(i) Sole power to vote or to direct the vote:
Row 5 of each Reporting Person's cover page to this Schedule 13G sets forth the sole power to vote or to direct the vote of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
(ii) Shared power to vote or to direct the vote:
Row 6 of each Reporting Person's cover page to this Schedule 13G sets forth the shared power to vote or to direct the vote of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
(iii) Sole power to dispose or to direct the disposition of:
Row 7 of each Reporting Person's cover page to this Schedule 13G sets forth the sole power to dispose or to direct the disposition of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
(iv) Shared power to dispose or to direct the disposition of:
Row 8 of each Reporting Person's cover page to this Schedule 13G sets forth the shared power to dispose or to direct the disposition of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
Item 5.
Ownership of 5 Percent or Less of a Class.
Not Applicable
Item 6.
Ownership of more than 5 Percent on Behalf of Another Person.
Not Applicable
Item 7.
Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
Not Applicable
Item 8.
Identification and Classification of Members of the Group.
Not Applicable
Item 9.
Notice of Dissolution of Group.
Not Applicable
Item 10.
Certifications:
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.
SIGNATURE
After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.
RA Capital Management, L.P.
Signature:
/s/ Peter Kolchinsky
Name/Title:
By Peter Kolchinsky, Authorized Signatory
Date:
05/11/2026
Peter Kolchinsky
Signature:
/s/ Peter Kolchinsky
Name/Title:
Peter Kolchinsky
Date:
05/11/2026
Rajeev Shah
Signature:
/s/ Rajeev Shah
Name/Title:
Rajeev Shah
Date:
05/11/2026
RA Capital Healthcare Fund, L.P.
Signature:
/s/ Peter Kolchinsky
Name/Title:
By RA Capital Healthcare Fund GP, LLC, its General Partner, By Peter Kolchinsky, Manager
