XFOWW X4 Pharmaceuticals Inc (PK)

(1) Includes 518,501 Shares issuable upon the exercise of certain Pre-Funded Warrants (defined in Item 4). Excludes 11,924 Shares underlying certain Pre-Funded Warrants that may not be exercised due to the Pre-Funded Blocker (defined in Item 4).

Excludes 450,314 Shares underlying certain Class A Warrants (defined in Item 4) that may not be exercised due to the Class A Blocker (defined in Item 4).

Excludes 518,856 Shares underlying certain Class B Warrants (defined in Item 4) that may not be exercised due to the Class B Blocker (defined in Item 4).

Excludes 259,739 Shares underlying certain Pre-Funded B Warrants (defined in Item 4) that may not be exercised due to the Pre-Funded B Blocker (defined in Item 4).

(1) Includes 518,501 Shares issuable upon the exercise of certain Pre-Funded Warrants. Excludes 11,924 Shares underlying certain Pre-Funded Warrants that may not be exercised due to the Pre-Funded Blocker.

Excludes 450,314 Shares underlying certain Class A Warrants that may not be exercised due to the Class A Blocker.

Excludes 518,856 Shares underlying certain Class B Warrants that may not be exercised due to the Class B Blocker.

Excludes 259,739 Shares underlying certain Pre-Funded B Warrants that may not be exercised due to the Pre-Funded B Blocker.

(1) Excludes 428,704 Shares underlying certain Pre-Funded Warrants that may not be exercised due to the Pre-Funded Blocker.

Excludes 363,810 Shares underlying certain Class A Warrants that may not be exercised due to the Class A Blocker.

Excludes 385,449 Shares underlying certain Class B Warrants that may not be exercised due to the Class B Blocker.

Excludes 204,465 Shares underlying certain Pre-Funded B Warrants that may not be exercised due to the Pre-Funded B Blocker.

(1) Excludes 428,704 Shares underlying certain Pre-Funded Warrants that may not be exercised due to the Pre-Funded Blocker.

Excludes 363,810 Shares underlying certain Class A Warrants that may not be exercised due to the Class A Blocker.

Excludes 385,449 Shares underlying certain Class B Warrants that may not be exercised due to the Class B Blocker.

Excludes 204,465 Shares underlying certain Pre-Funded B Warrants that may not be exercised due to the Pre-Funded B Blocker.

(1) Excludes 76,534 Shares underlying certain Pre-Funded Warrants that may not be exercised due to the Pre-Funded Blocker.

Excludes 64,996 Shares underlying certain Class A Warrants that may not be exercised due to the Class A Blocker.

Excludes 66,236 Shares underlying certain Class B Warrants that may not be exercised due to the Class B Blocker.

Excludes 35,796 Shares underlying certain Pre-Funded B Warrants that may not be exercised due to the Pre-Funded B Blocker.

(1) Excludes 76,534 Shares underlying certain Pre-Funded Warrants that may not be exercised due to the Pre-Funded Blocker.

Excludes 64,996 Shares underlying certain Class A Warrants that may not be exercised due to the Class A Blocker.

Excludes 66,236 Shares underlying certain Class B Warrants that may not be exercised due to the Class B Blocker.

Excludes 35,796 Shares underlying certain Pre-Funded B Warrants that may not be exercised due to the Pre-Funded B Blocker.

(1) Includes 518,501 Shares issuable upon the exercise of certain Pre-Funded Warrants. Excludes 440,628 Shares underlying certain Pre-Funded Warrants that may not be exercised due to the Pre-Funded Blocker.

Excludes 814,124 Shares underlying certain Class A Warrants that may not be exercised due to the Class A Blocker.

Excludes 904,305 Shares underlying certain Class B Warrants that may not be exercised due to the Class B Blocker.

Excludes 464,204 Shares underlying certain Pre-Funded B Warrants that may not be exercised due to the Pre-Funded B Blocker.

(1) Includes 518,501 Shares issuable upon the exercise of certain Pre-Funded Warrants. Excludes 554,499 Shares underlying certain Pre-Funded Warrants that may not be exercised due to the Pre-Funded Blocker.

Excludes 910,750 Shares underlying certain Class A Warrants that may not be exercised due to the Class A Blocker.

Excludes 1,000,000 Shares underlying certain Class B Warrants that may not be exercised due to the Class B Blocker.

Excludes 500,000 Shares underlying certain Pre-Funded B Warrants that may not be exercised due to the Pre-Funded B Blocker.

(1) Includes 518,501 Shares issuable upon the exercise of certain Pre-Funded Warrants. Excludes 554,499 Shares underlying certain Pre-Funded Warrants that may not be exercised due to the Pre-Funded Blocker.

Excludes 910,750 Shares underlying certain Class A Warrants that may not be exercised due to the Class A Blocker.

Excludes 1,000,000 Shares underlying certain Class B Warrants that may not be exercised due to the Class B Blocker.

Excludes 500,000 Shares underlying certain Pre-Funded B Warrants that may not be exercised due to the Pre-Funded B Blocker.

(1) Includes 518,501 Shares issuable upon the exercise of certain Pre-Funded Warrants. Excludes 554,499 Shares underlying certain Pre-Funded Warrants that may not be exercised due to the Pre-Funded Blocker.

Excludes 910,750 Shares underlying certain Class A Warrants that may not be exercised due to the Class A Blocker.

Excludes 1,000,000 Shares underlying certain Class B Warrants that may not be exercised due to the Class B Blocker.

Excludes 500,000 Shares underlying certain Pre-Funded B Warrants that may not be exercised due to the Pre-Funded B Blocker.

(1) Includes 518,501 Shares issuable upon the exercise of certain Pre-Funded Warrants. Excludes 554,499 Shares underlying certain Pre-Funded Warrants that may not be exercised due to the Pre-Funded Blocker.

Excludes 910,750 Shares underlying certain Class A Warrants that may not be exercised due to the Class A Blocker.

Excludes 1,000,000 Shares underlying certain Class B Warrants that may not be exercised due to the Class B Blocker.

Excludes 500,000 Shares underlying certain Pre-Funded B Warrants that may not be exercised due to the Pre-Funded B Blocker.

X4 Pharmaceuticals, Inc., a Delaware corporation (the “Issuer”).

955 Massachusetts Avenue, 4th Floor

Cambridge, Massachusetts 02139

Biotechnology Value Fund, L.P. (“BVF”)

44 Montgomery St., 40th Floor

San Francisco, California 94104

Citizenship: Delaware

BVF I GP LLC (“BVF GP”)

44 Montgomery St., 40th Floor

San Francisco, California 94104

Citizenship: Delaware

Biotechnology Value Fund II, L.P. (“BVF2”)

44 Montgomery St., 40th Floor

San Francisco, California 94104

Citizenship: Delaware

BVF II GP LLC (“BVF2 GP”)

44 Montgomery St., 40th Floor

San Francisco, California 94104

Citizenship: Delaware

Biotechnology Value Trading Fund OS LP (“Trading Fund OS”)

PO Box 309 Ugland House

Grand Cayman, KY1-1104

Cayman Islands

Citizenship: Cayman Islands

BVF Partners OS Ltd. (“Partners OS”)

PO Box 309 Ugland House

Grand Cayman, KY1-1104

Cayman Islands

Citizenship: Cayman Islands

BVF GP Holdings LLC (“BVF GPH”)

44 Montgomery St., 40th Floor

San Francisco, California 94104

Citizenship: Delaware

BVF Partners L.P. (“Partners”)

44 Montgomery St., 40th Floor

San Francisco, California 94104

Citizenship: Delaware

BVF Inc.

44 Montgomery St., 40th Floor

San Francisco, California 94104

Citizenship: Delaware

Mark N. Lampert (“Mr. Lampert”)

44 Montgomery St., 40th Floor

San Francisco, California 94104

Citizenship: United States

Each of the foregoing is referred to as a “Reporting Person” and collectively as the “Reporting Persons.”

Common Stock, $0.001 par value (the “Shares”)

98420X103

As of the close of business on December 31, 2019, the Reporting Persons held 910,750 Class A Warrants (the “Class A Warrants”) exercisable into an aggregate of 910,750 Shares. Each Class A Warrant has an exercise price per Share equal to $13.20 and expires 60 months from the date of issuance. The Class A Warrants are exercisable, at the option of each holder, provided that the holder will be prohibited, subject to certain exceptions, from exercising the Class A Warrants for Shares to the extent that immediately prior to or after giving effect to such exercise, the holder, together with its affiliates and other attribution parties, would own more than 9.99% of the total number of Shares then issued and outstanding (the “Class A Blocker”). As of the close of business on December 31, 2019, the Class A Blocker limits the aggregate exercise of Class A Warrants by the Reporting Persons to zero out of 910,750 Shares underlying the Class A Warrants owned by the Reporting Persons in the aggregate. BVF holds Class A Warrants to purchase 450,314 additional Shares which are excluded herein as a result of the Class A Blocker. BVF2 holds Class A Warrants to purchase 363,810 additional Shares which are excluded herein as a result of the Class A Blocker. BVTOS holds Class A Warrants to purchase 64,996 additional Shares which are excluded herein as a result of the Class A Blocker. The Reporting Persons through a certain Partners managed account (the “Partners Managed Account”) holds Class A Warrants to purchase 31,630 additional Shares which are excluded herein as a result of the Class A Blocker.

As of the close of business on December 31, 2019, the Reporting Persons held 1,000,000 Class B Warrants (the “Class B Warrants”) exercisable into an aggregate of 1,000,000 Shares. Each Class B Warrant has an exercise price per Share equal to $15.00 and will expire on the date that is the earlier of (a) the date that is thirty (30) calendar days following the date on which the Issuer issues a press release regarding topline data from its Phase III clinical trial of mavorixafor for the treatment of WHIM syndrome (or, if such date is not a business day, the following business day) and (b) 60 months from the date of issuance. The Class B Warrants are exercisable, at the option of each holder, provided that the holder will be prohibited, subject to certain exceptions, from exercising the Class B Warrants for Shares to the extent that immediately prior to or after giving effect to such exercise, the holder, together with its affiliates and other attribution parties, would own more than 9.99% of the total number of Shares then issued and outstanding (the “Class B Blocker”). As of the close of business on December 31, 2019, the Class B Blocker limits the aggregate exercise of Class B Warrants by the Reporting Persons to zero out of 1,000,000 Shares underlying the Class B Warrants owned by the Reporting Persons in the aggregate. BVF holds Class B Warrants to purchase 518,856 additional Shares which are excluded herein as a result of the Class B Blocker. BVF2 holds Class B Warrants to purchase 385,449 additional Shares which are excluded herein as a result of the Class B Blocker. BVTOS holds Class B Warrants to purchase 66,236 additional Shares which are excluded herein as a result of the Class B Blocker. The Reporting Persons through the Partners Managed Account holds Class B Warrants to purchase 29,459 additional Shares which are excluded herein as a result of the Class B Blocker.

As of the close of business on December 31, 2019, the Reporting Persons held 1,073,000 Pre-Funded Warrants (the “Pre-Funded Warrants”) exercisable into an aggregate of 1,073,000 Shares. Each Pre-Funded Warrant has an exercise price per Share equal to $0.001 per Share. The Pre-Funded Warrants are exercisable at any time after their original issuance and do not expire. However, under the Pre-Funded Warrants, the Issuer may not effect the exercise of any Pre-Funded Warrant, and a holder will not be entitled to exercise any portion of any Pre-Funded Warrant, which, upon giving effect to such exercise, would cause (i) the aggregate number of Shares beneficially owned by the holder (together with its affiliates) to exceed 9.99% of the number of Shares outstanding immediately after giving effect to the exercise, or (ii) the combined voting power of the Issuer’s securities beneficially owned by the holder (together with its affiliates) to exceed 9.99% of the combined voting power of all of the Issuer’s securities then outstanding immediately after giving effect to the exercise, as such percentage ownership is determined in accordance with the terms of the Pre-Funded Warrants (the “Pre-Funded Blocker”). In providing beneficial ownership described herein, the Reporting Persons have assumed that Pre-Funded Warrants held by BVF to acquire 518,501 Shares would be exercised, which would bring the Reporting Persons to the aggregate 9.99% limitation, and the remaining Pre-Funded Warrants exercisable into 11,924 Shares owned by BVF, Pre-Funded Warrants exercisable into 428,704 Shares owned by BVF2, Pre-Funded Warrants exercisable into 76,534 Shares owned by Trading Fund OS, and the Pre-Funded Warrants exercisable into 37,337 Shares held in the Partners Managed Account, would not be exercised due to the Pre-Funded Blocker.

As of the close of business on December 31, 2019, the Reporting Persons held 500,000 Pre-Funded B Warrants (the “Pre-Funded B Warrants”) exercisable into an aggregate of 500,000 Shares. Each Pre-Funded Warrant has an exercise price per Share equal to $0.001 per Share. The Pre-Funded B Warrants are exercisable at any time after their original issuance and do not expire. However, under the Pre-Funded B Warrants, the Issuer may not effect the exercise of any Pre-Funded B Warrant, and a holder will not be entitled to exercise any portion of any Pre-Funded B Warrant, which, upon giving effect to such exercise, would cause (i) the aggregate number of Shares beneficially owned by the holder (together with its affiliates) to exceed 9.99% of the number of Shares outstanding immediately after giving effect to the exercise, or (ii) the combined voting power of the Issuer’s securities beneficially owned by the holder (together with its affiliates) to exceed 9.99% of the combined voting power of all of the Issuer’s securities then outstanding immediately after giving effect to the exercise, as such percentage ownership is determined in accordance with the terms of the Pre-Funded B Warrants (the “Pre-Funded B Blocker” and together with the Class A Blocker, the Class B Blocker and the Pre-Funded Blocker, the “Beneficial Ownership Limitation”). As of the close of business on December 31, 2019, the Pre-Funded B Blocker limits the exercise of Pre-Funded B Warrants by the Reporting Persons to zero out of the 500,000 Shares underlying the Pre-Funded B Warrants owned by the Reporting Persons in the aggregate. BVF holds Pre-Funded B Warrants to purchase 259,739 additional Shares which are excluded herein as a result of the Pre-Funded B Blocker. BVF2 holds Pre-Funded B Warrants to purchase 204,465 additional Shares which are excluded herein as a result of the Pre-Funded B Blocker. BVTOS holds Pre-Funded B Warrants to purchase 35,796 additional Shares which are excluded herein as a result of the Pre-Funded B Blocker.

The Reporting Persons may choose to exercise the Class A Warrants, the Class B Warrants, the Pre-Funded Warrants or the Pre-Funded B Warrants in other amounts among the Reporting Persons, while continuing to comply with the Beneficial Ownership Limitation.

As of the close of business on December 31, 2019, (i) BVF beneficially owned 1,093,434 Shares, including 518,501 Shares issuable upon the exercise of the Pre-Funded Warrants, (ii) BVF2 beneficially owned 441,427 Shares, and (iii) Trading Fund OS beneficially owned 75,803 Shares.

BVF GP, as the general partner of BVF, may be deemed to beneficially own the 1,093,434 Shares beneficially owned by BVF.

BVF2 GP, as the general partner of BVF2, may be deemed to beneficially own the 441,427 Shares beneficially owned by BVF2.

Partners OS, as the general partner of Trading Fund OS, may be deemed to beneficially own the 75,803 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 1,534,861 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 1,660,475 Shares beneficially owned in the aggregate by BVF, BVF2, Trading Fund OS, and the Partners Managed Account, including 49,811 Shares held in the Partners Managed Account.

BVF Inc., as the general partner of Partners, may be deemed to beneficially own the 1,660,475 Shares beneficially owned by Partners.

Mr. Lampert, as a director and officer of BVF Inc., may be deemed to beneficially own the 1,660,475 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, 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.

The following percentages are based on a denominator that is the sum of (i) 16,102,872 Shares outstanding as disclosed in the Issuer’s Prospectus Supplement filed with the Securities and Exchange Commission on November 27, 2019 and (ii) the 518,501 Shares issuable upon the exercise of the Pre-Funded Warrants, as applicable.

As of the close of business on December 31, 2019, (i) BVF beneficially owned approximately 6.6% of the outstanding Shares, (ii) BVF2 beneficially owned approximately 2.7% 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 6.6% of the outstanding Shares, (v) BVF2 GP may be deemed to beneficially own approximately 2.7% 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 is held in the Partners Managed Account).

See Cover Pages Items 5-9.

See Cover Pages Items 5-9.

See Cover Pages Items 5-9.

See Cover Pages Items 5-9.

Not Applicable.

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 the Partners Managed Account.

Not Applicable.

See Exhibit 99.1.

Not Applicable.

By signing below each of the undersigned certifies that, to the best of its 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.

SIGNATURE

After reasonable inquiry and to the best of his knowledge and belief, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

Dated: February 14, 2020