Biotechnology Value Fund and affiliated entities disclosed beneficial ownership stakes in X4 Pharmaceuticals (XFOR). Collectively certain Reporting Persons hold 2,243,659 shares, representing approximately 9.9% of the outstanding common stock on the filing date. Individually, BVF holds 1,168,649 shares (~5.2%), BVF2 holds 906,855 shares (~4.0%), and Biotechnology Value Trading Fund OS holds 123,369 shares (less than 1%). The reporting group also holds pre-funded warrants exercisable for an aggregate of 1,288,288 shares at $0.001 per share, subject to a blocker that limits current exercisable warrants to 9,917 shares for the Reporting Persons as of August 20, 2025. The filing clarifies shared voting and dispositive powers among fund entities, GP entities, Partners, BVF Inc. and Mark N. Lampert and includes a joint filing agreement as Exhibit 99.1.
Positive
None.
Negative
None.
Insights
TL;DR: The filing reveals significant passive stakes and immediate exercisable warrants, but exercise is limited by a 9.99% blocker.
The disclosure shows BVF-affiliated entities hold meaningful ownership in XFOR: combined beneficial ownership of 2,243,659 shares (approx. 9.9%). Pre-funded warrants for 1,288,288 shares exist with an exercise price of $0.001, however a pre-funded warrants blocker restricts exercise so the Reporting Persons can currently exercise only 9,917 of those warrants. Percentages are calculated using an adjusted share base that includes recent issuances. For valuation or market impact analysis, note the structure (shared voting/dispositive rights) and the materiality threshold approaching 10% which could influence liquidity and investor perception.
TL;DR: Ownership is disclosed across multiple related entities with clear disclaimers and shared control; governance impact is possible but not asserted.
The filing carefully allocates beneficial ownership and disclaims beneficial ownership among related entities while noting shared voting and dispositive power among GPs, Partners, BVF Inc. and an individual director/officer. The joint filing agreement (Exhibit 99.1) formalizes coordinated reporting. The 9.99% cap on exercise of pre-funded warrants is an important governance/ownership control feature that limits immediate dilution and control shifts. No admission of intent to influence control is made in the certification.
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 13G
UNDER THE SECURITIES EXCHANGE ACT OF 1934
X4 Pharmaceuticals, Inc
(Name of Issuer)
Common Stock, par value $0.001 per share
(Title of Class of Securities)
98420X202
(CUSIP Number)
08/13/2025
(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)
SCHEDULE 13G
CUSIP No.
98420X202
1
Names of Reporting Persons
BIOTECHNOLOGY VALUE 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
1,168,649.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
1,168,649.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
1,168,649.00
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)
5.2 %
12
Type of Reporting Person (See Instructions)
PN
SCHEDULE 13G
CUSIP No.
98420X202
1
Names of Reporting Persons
BVF I GP LLC
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
1,168,649.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
1,168,649.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
1,168,649.00
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)
5.2 %
12
Type of Reporting Person (See Instructions)
OO
SCHEDULE 13G
CUSIP No.
98420X202
1
Names of Reporting Persons
BIOTECHNOLOGY VALUE FUND II LP
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
906,855.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
906,855.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
906,855.00
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)
4.0 %
12
Type of Reporting Person (See Instructions)
PN
SCHEDULE 13G
CUSIP No.
98420X202
1
Names of Reporting Persons
BVF II GP LLC
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
906,855.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
906,855.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
906,855.00
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)
4.0 %
12
Type of Reporting Person (See Instructions)
OO
SCHEDULE 13G
CUSIP No.
98420X202
1
Names of Reporting Persons
Biotechnology Value Trading Fund OS LP
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
CAYMAN ISLANDS
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
123,369.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
123,369.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
123,369.00
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)
0.6 %
12
Type of Reporting Person (See Instructions)
PN
SCHEDULE 13G
CUSIP No.
98420X202
1
Names of Reporting Persons
BVF Partners OS Ltd.
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
CAYMAN ISLANDS
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
123,369.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
123,369.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
123,369.00
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)
0.6 %
12
Type of Reporting Person (See Instructions)
CO
SCHEDULE 13G
CUSIP No.
98420X202
1
Names of Reporting Persons
BVF GP HOLDINGS LLC
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
2,075,504.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
2,075,504.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
2,075,504.00
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)
9.2 %
12
Type of Reporting Person (See Instructions)
OO
SCHEDULE 13G
CUSIP No.
98420X202
1
Names of Reporting Persons
BVF PARTNERS L P/IL
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
2,243,659.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
2,243,659.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
2,243,659.00
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)
9.9 %
12
Type of Reporting Person (See Instructions)
IA, PN
SCHEDULE 13G
CUSIP No.
98420X202
1
Names of Reporting Persons
BVF INC/IL
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
2,243,659.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
2,243,659.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
2,243,659.00
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)
9.9 %
12
Type of Reporting Person (See Instructions)
CO
SCHEDULE 13G
CUSIP No.
98420X202
1
Names of Reporting Persons
LAMPERT MARK N
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
2,243,659.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
2,243,659.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
2,243,659.00
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)
9.9 %
12
Type of Reporting Person (See Instructions)
IN
SCHEDULE 13G
Item 1.
(a)
Name of issuer:
X4 Pharmaceuticals, Inc
(b)
Address of issuer's principal executive offices:
61 North Beacon Street, 4th Floor, Boston, Massachusetts 02134
Item 2.
(a)
Name of person filing:
Biotechnology Value Fund, L.P. ("BVF")
BVF I GP LLC ("BVF GP")
Biotechnology Value Fund II, L.P. ("BVF2")
BVF II GP LLC ("BVF2 GP")
Biotechnology Value Trading Fund OS LP ("Trading Fund OS")
BVF Partners OS Ltd. ("Partners OS")
BVF GP Holdings LLC ("BVF GPH")
BVF Partners L.P. ("Partners")
BVF Inc.
Mark N. Lampert ("Mr. Lampert")
Each of the foregoing is referred to as a "Reporting Person" and collectively as the "Reporting Persons."
(b)
Address or principal business office or, if none, residence:
Biotechnology Value Fund, L.P.
44 Montgomery St., 40th Floor
San Francisco, California 94104
BVF I GP LLC
44 Montgomery St., 40th Floor
San Francisco, California 94104
Biotechnology Value Fund II, L.P.
44 Montgomery St., 40th Floor
San Francisco, California 94104
BVF II GP LLC
44 Montgomery St., 40th Floor
San Francisco, California 94104
Biotechnology Value Trading Fund OS LP
PO Box 309 Ugland House
Grand Cayman, KY1-1104
Cayman Islands
BVF Partners OS Ltd.
PO Box 309 Ugland House
Grand Cayman, KY1-1104
Cayman Islands
BVF GP Holdings LLC
44 Montgomery St., 40th Floor
San Francisco, California 94104
BVF Partners L.P.
44 Montgomery St., 40th Floor
San Francisco, California 94104
BVF Inc.
44 Montgomery St., 40th Floor
San Francisco, California 94104
Mark N. Lampert
44 Montgomery St., 40th Floor
San Francisco, California 94104
(c)
Citizenship:
Biotechnology Value Fund, L.P.
Delaware
BVF I GP LLC
Delaware
Biotechnology Value Fund II, L.P.
Delaware
BVF II GP LLC
Delaware
Biotechnology Value Trading Fund OS LP
Cayman Islands
BVF Partners OS Ltd.
Cayman Islands
BVF GP Holdings LLC
Delaware
BVF Partners L.P.
Delaware
BVF Inc.
Delaware
Mark N. Lampert
United States
(d)
Title of class of securities:
Common Stock, par value $0.001 per share
(e)
CUSIP No.:
98420X202
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:
As of the close of business on August 20, 2025, the Reporting Persons and a certain Partners managed account (the "Partners Managed Account") held Pre-Funded Common Stock Purchase Warrants (the "Pre-Funded Warrants") exercisable for an aggregate of 1,288,288 shares of the Issuer's common stock, par value $0.001 per share (the "Shares"). The Pre-Funded Warrants are exercisable immediately, do not expire, and have an exercise price of $0.001 per Share. The Reporting Persons and the Partners Managed Account (together with their affiliates and other attribution parties) may not exercise any portion of the Pre-Funded Warrants they hold to the extent that, immediately after giving effect to such issuance after exercise, they would beneficially own more than 9.99% of the outstanding Shares (the "Pre-Funded Warrants Blocker"). As of the close of business on August 20, 2025, the Pre-Funded Warrants Blocker limits the exercise of the Pre-Funded Warrants held by the Reporting Persons and the Partners Managed Account to 9,917 out of 1,288,288 Shares underlying the Pre-Funded Warrants held by them.
As of the close of business on August 20, 2025, (i) BVF beneficially owned 1,168,649 Shares, including 9,917 Shares underlying the Pre-Funded Warrants held by it and excluding 658,370 Shares underlying certain Pre-Funded Warrants held by it, (ii) BVF2 beneficially owned 906,855 Shares, excluding 523,019 Shares underlying Pre-Funded Warrants held by it, and (iii) Trading Fund OS beneficially owned 123,369 Shares, excluding 71,152 Shares underlying certain Pre-Funded Warrants held by it.
BVF GP, as the general partner of BVF, may be deemed to beneficially own the 1,168,649 Shares beneficially owned by BVF.
BVF2 GP, as the general partner of BVF2, may be deemed to beneficially own the 906,855 Shares beneficially owned by BVF2.
Partners OS, as the general partner of Trading Fund OS, may be deemed to beneficially own the 123,369 Shares beneficially owned by Trading Fund OS.
BVF GPH, as the sole member of each of BVF GP and BVF2 GP, may be deemed to beneficially own the 2,075,504 Shares beneficially owned in the aggregate by BVF and BVF2.
Partners, as the investment manager of BVF, BVF2 and Trading Fund OS, and the sole member of Partners OS, may be deemed to beneficially own the 2,243,659 Shares beneficially owned in the aggregate by BVF, BVF2 and Trading Fund OS and held in the Partners Managed Account, including 44,786 Shares held in the Partners Managed Account, which excludes 25,830 Shares underlying the Pre-Funded Warrants held by it.
BVF Inc., as the general partner of Partners, may be deemed to beneficially own the 2,243,659 Shares beneficially owned by Partners.
Mr. Lampert, as a director and officer of BVF Inc., may be deemed to beneficially own the 2,243,659 Shares beneficially owned by BVF Inc.
The foregoing should not be construed in and of itself as an admission by any Reporting Person as to beneficial ownership of any Shares owned by another Reporting Person. BVF GP disclaims beneficial ownership of the Shares beneficially owned by BVF. BVF2 GP disclaims beneficial ownership of the Shares beneficially owned by BVF2. Partners OS disclaims beneficial ownership of the Shares beneficially owned by Trading Fund OS. BVF GPH disclaims beneficial ownership of the Shares beneficially owned by BVF and BVF2. Each of Partners, BVF Inc. and Mr. Lampert disclaims beneficial ownership of the Shares beneficially owned by BVF, BVF2 and Trading Fund OS and held in the Partners Managed Account, and the filing of this statement shall not be construed as an admission that any such person or entity is the beneficial owner of any such securities.
(b)
Percent of class:
The following percentages are based upon a denominator that was calculated as follows: (i) 11,408,357 Shares outstanding as of August 4, 2025, as reported in the Issuer's Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission on August 8, 2025, plus (ii) 11,040,776 Shares issued and sold by the Issuer pursuant to a Securities Purchase Agreement, dated August 12, 2025, as set forth in the Issuer's Current Report on Form 8-K filed with the Securities and Exchange Commission on August 13, 2025, plus (iii) 9,917 Shares issuable upon the exercise of certain Pre-Funded Warrants held by the Reporting Persons, as applicable.
As of the close of business on August 20, 2025, (i) BVF beneficially owned approximately 5.2% of the outstanding Shares, (ii) BVF2 beneficially owned approximately 4.0% of the outstanding Shares, (iii) Trading Fund OS beneficially owned less than 1% of the outstanding Shares, (iv) BVF GP may be deemed to beneficially own approximately 5.2% of the outstanding Shares, (v) BVF2 GP may be deemed to beneficially own approximately 4.0% of the outstanding Shares, (vi) Partners OS may be deemed to beneficially own less than 1% of the outstanding Shares, (vii) BVF GPH may be deemed to beneficially own approximately 9.2% of the outstanding Shares, and (viii) each of Partners, BVF Inc. and Mr. Lampert may be deemed to beneficially own approximately 9.99% of the outstanding Shares (less than 1% of the outstanding Shares are held in the Partners Managed Account).
(c)
Number of shares as to which the person has:
(i) Sole power to vote or to direct the vote:
See Cover Pages Items 5-9.
(ii) Shared power to vote or to direct the vote:
See Cover Pages Items 5-9.
(iii) Sole power to dispose or to direct the disposition of:
See Cover Pages Items 5-9.
(iv) Shared power to dispose or to direct the disposition of:
See Cover Pages Items 5-9.
Item 5.
Ownership of 5 Percent or Less of a Class.
Item 6.
Ownership of more than 5 Percent on Behalf of Another Person.
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 5 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.
BVF GP, BVF GPH, Partners, BVF Inc. and Mr. Lampert share voting and dispositive power over the Shares beneficially owned by BVF. BVF GPH, Partners, BVF Inc. and Mr. Lampert share voting and dispositive power over the Shares beneficially owned by BVF2. Partners, BVF Inc. and Mr. Lampert share voting and dispositive power over the Shares beneficially owned by Trading Fund OS and held in the Partners Managed Account.
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.
If a group has filed this schedule pursuant to §240.13d-1(b)(1)(ii)(K), so indicate under Item 3(k) 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 §240.13d-1(c) or §240.13d-1(d), attach an exhibit stating the identity of each member of the group.
See Exhibit 99.1.
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.
How many XFOR shares do Biotechnology Value Fund entities beneficially own?
The Reporting Persons beneficially own a combined 2,243,659 shares, representing approximately 9.9% of XFOR outstanding shares as disclosed.
What pre-funded warrants are held by the Reporting Persons in XFOR?
The Reporting Persons and a Partners Managed Account hold pre-funded warrants exercisable for an aggregate of 1,288,288 shares at an exercise price of $0.001 per share.
Are the pre-funded warrants fully exercisable?
No. A Pre-Funded Warrants Blocker prevents exercises that would result in beneficial ownership above 9.99%; as of August 20, 2025, exercisable warrants were limited to 9,917 shares for the Reporting Persons.
Who may be deemed to exercise voting or dispositive power over the disclosed shares?
The filing states that GPs, BVF GPH, Partners, BVF Inc. and Mark N. Lampert may be deemed to share voting and dispositive power over the disclosed shares, with various disclaimers of beneficial ownership.
What is the share count used to calculate the ownership percentages?
Percentages are based on an adjusted denominator: 11,408,357 shares reported outstanding on August 4, 2025, plus 11,040,776 shares issued under an August 12, 2025 purchase agreement, plus applicable exercisable warrants.
