Document:

EX-4.1

 Exhibit 4.1 
  

 
  
 THIS CERTIFIES THAT is the owner of CUSIP DATED COUNTERSIGNED AND
REGISTERED: COMPUTERSHARE TRUST COMPANY, N.A. TRANSFER AGENT AND REGISTRAR, FULLY-PAID AND NON-ASSESSABLE SHARES OF COMMON STOCK OF X4 Pharmaceuticals, Inc. (hereinafter called the "Company"), transferable on the books of the Company in person or by
duly authorized attorney, upon surrender of this Certificate properly endorsed. This Certificate and the shares represented hereby, are issued and shall be held subject to all of the provisions of the Certificate of Incorporation, as amended, and
the By-Laws, as amended, of the Company (copies of which are on file with the Company and with the Transfer Agent), to all of which each holder, by acceptance hereof, assents. This Certificate is not valid unless countersigned and registered by the
Transfer Agent and Registrar. Witness the facsimile seal of the Company and the facsimile signatures of its duly authorized officers. COMMON STOCK PAR VALUE $0.001 COMMON STOCK SEE REVERSE FOR CERTAIN DEFINITIONS Certificate Number Shares . X4
PHARMACEUTICALS, INC. INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE President Treasurer By AUTHORIZED SIGNATURE August 2, 2010 DELAWARE CO R PO RATE X4 PHARMACEUTICALS, INC. ZQ|CERT#|COY|CLS|RGSTRY|ACCT#|TRANSTYPE|RUN#|TRANS# 98420X 10 3
DD-MMM-YYYY * * 000000* * * * * * * * * * * * * * * * * * * * * 000000* * * * * * * * * * * * * * * * * * * * * 000000* * * * * * * * * * * * * * * * * * * * * 000000* * * * * * * * * * * * * * * * * * * * * 000000* * * * * * * * * * * * * * ** Mr.
Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample
**** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David
Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander
David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr.
Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample
**** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David
Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Sample **** Mr. Sample
**000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares***
*000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****
000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****0
00000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****00
0000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000
000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****0000
00**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****00000
0**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000
**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000*
*Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**
Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**S ***ZERO HUNDRED THOUSAND ZERO HUNDRED AND ZERO*** MR. SAMPLE & MRS. SAMPLE & MR. SAMPLE &
MRS. SAMPLE ZQ00000000 Certificate Numbers 1234567890/1234567890 1234567890/1234567890 1234567890/1234567890 1234567890/1234567890 1234567890/1234567890 1234567890/1234567890 Total Transaction Num/No. 123456 Denom. 123456 Total 1234567 MR A SAMPLE
DESIGNATION (IF ANY) ADD 1 ADD 2 ADD 3 ADD 4 955 Massachusetts Avenue, 4th Floor, Cambridge, MA 02139 CUSIP/IDENTIFIER 98420X 10 3 Holder ID XXXXXXXXXX Insurance Value 1,000,000.00 Number of Shares 123456 DTC 12345678 123456789012345 THIS
CERTIFICATE IS TRANSFERABLE IN CITIES DESIGNATED BY THE TRANSFER AGENT, AVAILABLE ONLINE AT www.computershare.com 

 

 
 The IRS requires that the named transfer agent (“we”) report the cost basis of certain shares or units acquired after
January 1, 2011. If your shares or units are covered by the legislation, and you requested to sell or transfer the shares or units using a specific cost basis calculation method, then we have processed as you requested. If you did not specify a
cost basis calculation method, then we have defaulted to the first in, first out (FIFO) method. Please consult your tax advisor if you need additional information about cost basis. If you do not keep in contact with the issuer or do not have any
activity in your account for the time period specified by state law, your property may become subject to state unclaimed property laws and transferred to the appropriate state. For value received, hereby sell, assign and transfer unto Shares
Attorney Dated: 20Signature:Signature: Notice: The signature to this assignment must correspond with the name as written upon the face of the certificate, in every particular, without alteration or enlargement, or any change whatever. PLEASE INSERT
SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER OF ASSIGNEE (PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING POSTAL ZIP CODE, OF ASSIGNEE) of the common stock represented by the within Certificate, and do hereby irrevocably constitute and appoint
to transfer the said stock on the books of the within-named Incorporation with full power of substitution in the premises. . X4 PHARMACEUTICALS, INC. THE COMPANY WILL FURNISH WITHOUT CHARGE TO EACH SHAREHOLDER WHO SO REQUESTS, A SUMMARY OF THE
POWERS, DESIGNATIONS, PREFERENCES AND RELATIVE, PARTICIPATING, OPTIONAL OR OTHER SPECIAL RIGHTS OF EACH CLASS OF STOCK OF THE COMPANY AND THE QUALIFICATIONS, LIMITATIONS OR RESTRICTIONS OF SUCH PREFERENCES AND RIGHTS, AND THE VARIATIONS IN RIGHTS,
PREFERENCES AND LIMITATIONS DETERMINED FOR EACH SERIES, WHICH ARE FIXED BY THE CERTIFICATE OF INCORPORATION OF THE COMPANY, AS AMENDED, AND THE RESOLUTIONS OF THE BOARD OF DIRECTORS OF THE COMPANY, AND THE AUTHORITY OF THE BOARD OF DIRECTORS TO
DETERMINE VARIATIONS FOR FUTURE SERIES. SUCH REQUEST MAY BE MADE TO THE OFFICE OF THE SECRETARY OF THE COMPANY OR TO THE TRANSFER AGENT. THE BOARD OF DIRECTORS MAY REQUIRE THE OWNER OF A LOST OR DESTROYED STOCK CERTIFICATE, OR HIS LEGAL
REPRESENTATIVES, TO GIVE THE COMPANY A BOND TO INDEMNIFY IT AND ITS TRANSFER AGENTS AND REGISTRARS AGAINST ANY CLAIM THAT MAY BE MADE AGAINST THEM ON ACCOUNT OF THE ALLEGED LOSS OR DESTRUCTION OF ANY SUCH CERTIFICATE. Signature(s) Guaranteed:
Medallion Guarantee Stamp THE SIGNATURE(S) SHOULD BE GUARANTEED BY AN ELIGIBLE GUARANTOR INSTITUTION (Banks, Stockbrokers, Savings and Loan Associations and Credit Unions) WITH MEMBERSHIP IN AN APPROVED SIGNATURE GUARANTEE MEDALLION PROGRAM,
PURSUANT TO S.E.C. RULE 17Ad-15. The following abbreviations, when used in the inscription on the face of this certificate, shall be construed as though they were written out in full according to applicable
laws or regulations: TEN COM—as tenants in common UNIF GIFT MIN ACT ............................................ Custodian................................................ (Cust) (Minor) TEN ENT—as tenants by the entireties under Uniform
Gifts to Minors Act........................................................ (State) JT TEN—as joint tenants with right of survivorship UNIF TRF MIN ACT -............................................ Custodian (until
age................................ ) and not as tenants in common (Cust) ............................. under Uniform Transfers to Minors Act................... (Minor) (State) Additional abbreviations may also be used though not in the above list.EX-4.2

 Exhibit 4.2 

THIS WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”), OR
THE SECURITIES LAWS OF ANY STATE AND, EXCEPT AS SET FORTH IN SECTIONS 5.3 AND 5.4 BELOW, MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED UNLESS AND UNTIL REGISTERED UNDER SAID ACT AND LAWS OR, IN THE OPINION OF LEGAL COUNSEL IN FORM AND
SUBSTANCE SATISFACTORY TO THE ISSUER, SUCH OFFER, SALE, PLEDGE OR OTHER TRANSFER IS EXEMPT FROM SUCH REGISTRATION. 
 WARRANT TO PURCHASE
STOCK 
 Company: X4 Pharmaceuticals, Inc., a Delaware corporation 

Number of Shares: As set forth in Paragraph A below 

Type/Series of Stock: Series A Preferred Stock, $0.001 par value per share 

Warrant Price: $1.88 per Share, subject to adjustment as set forth herein 

Issue Date: October 25, 2016 
 Expiration Date:
October 24, 2026 See also Section 5.1(b). 

	Credit Facility:	 This Warrant to Purchase Stock (“Warrant”) is issued in connection with that certain
Mezzanine Loan and Security Agreement of even date herewith between Silicon Valley Bank and the Company (as amended and/or modified and in effect from time to time, the “Loan Agreement”) [and the participation therein of Life
Science Loans, LLC pursuant to an agreement between Silicon Valley Bank and Life Science Loans, LLC]. 

 THIS WARRANT
CERTIFIES THAT, for good and valuable consideration, [SILICON VALLEY BANK / LIFE SCIENCE LOANS, LLC] (together with any successor or permitted assignee or transferee of this Warrant or of any shares issued upon exercise hereof,
“Holder”) is entitled to purchase up to such number of fully paid and non-assessable shares of the above-stated Type/Series of Stock (the “Class”) of the
above-named company (the “Company”) as determined pursuant to Paragraph A below, at the above-stated Warrant Price, all as set forth above and as adjusted pursuant to Section 2 of this Warrant, subject to the provisions
and upon the terms and conditions set forth in this Warrant. [Reference is made to Section 5.4 of this Warrant whereby Silicon Valley Bank shall transfer this Warrant to its parent company, SVB Financial Group.] 

A.    Number of Shares. This Warrant shall be exercisable for the Initial Shares, plus the Additional Shares, if
any (collectively, and as may be adjusted from time to time in accordance with the provisions of this Warrant, the “Shares”). 

(1)    Initial Shares. As used herein “Initial Shares” means 27,128 shares of the Class,
subject to adjustment from time to time in accordance with the provisions of this Warrant. 
 (2)    Additional
Shares. Upon the making, if any, of the Term B Loan Advance (as defined in the Loan Agreement) to the Company in any amount, this Warrant automatically shall become exercisable for an additional 18,085 shares of the Class, as such number may be
adjusted from time to time in accordance with the provisions of this Warrant (the “Additional Shares”), including, without limitation, adjustments in respect of events occurring prior to the

 
date, if any, on which this Warrant becomes exercisable for the Additional Shares as if they constituted “Shares” hereunder at all times from and after the Issue Date. 

SECTION 1. EXERCISE.  

1.1    Method of Exercise. Holder may at any time and from time to time exercise this Warrant, in whole or in part,
by delivering to the Company the original of this Warrant together with a duly executed Notice of Exercise in substantially the form attached hereto as Appendix 1 and, unless Holder is exercising this Warrant pursuant to a cashless exercise set
forth in Section 1.2, a check, wire transfer of same-day funds (to an account designated by the Company), or other form of payment acceptable to the Company for the aggregate Warrant Price for the Shares
being purchased. 
 1.2    Cashless Exercise. On any exercise of this Warrant, in lieu of payment of the
aggregate Warrant Price in the manner as specified in Section 1.1 above, but otherwise in accordance with the requirements of Section 1.1, Holder may elect to receive Shares equal to the value of this Warrant, or portion hereof as to which
this Warrant is being exercised. Thereupon, the Company shall issue to the Holder such number of fully paid and non-assessable Shares as are computed using the following formula: 

 

	 	X =	 Y(A-B)/A 

where: 
  

	 	X =	 the number of Shares to be issued to the Holder; 

 

	 	Y =	 the number of Shares with respect to which this Warrant is being exercised (inclusive of the Shares surrendered
to the Company in payment of the aggregate Warrant Price); 

  

	 	A =	 the Fair Market Value (as determined pursuant to Section 1.3 below) of one Share; and

  

	 	B =	 the Warrant Price. 

1.3    Fair Market Value. If the Company’s common stock is then traded or quoted on a nationally recognized
securities exchange, inter-dealer quotation system or over-the-counter market (a “Trading Market”) and the Class is common stock, the fair
market value of a Share shall be the closing price or last sale price of a share of common stock reported for the Business Day immediately before the date on which Holder delivers this Warrant together with its Notice of Exercise to the Company. If
the Company’s common stock is then traded in a Trading Market and the Class is a series of the Company’s convertible preferred stock, the fair market value of a Share shall be the closing price or last sale price of a share of the
Company’s common stock reported for the Business Day immediately before the date on which Holder delivers this Warrant together with its Notice of Exercise to the Company multiplied by the number of shares of the Company’s common stock
into which a Share is then convertible. If the Company’s common stock is not traded in a Trading Market, the Board of Directors of the Company shall determine the fair market value of a Share in its reasonable good faith judgment. 

  
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 1.4    Delivery of Certificate and New Warrant. Within a
reasonable time after Holder exercises this Warrant in the manner set forth in Section 1.1 or 1.2 above, the Company shall deliver to Holder a certificate representing the Shares issued to Holder upon such exercise and, if this Warrant has not
been fully exercised and has not expired, a new warrant of like tenor representing the Shares not so acquired. 

1.5    Replacement of Warrant. On receipt of evidence reasonably satisfactory to the Company of the loss, theft,
destruction or mutilation of this Warrant and, in the case of loss, theft or destruction, on delivery of an indemnity agreement reasonably satisfactory in form, substance and amount to the Company or, in the case of mutilation, on surrender of this
Warrant to the Company for cancellation, the Company shall, within a reasonable time, execute and deliver to Holder, in lieu of this Warrant, a new warrant of like tenor and amount. 

1.6    Treatment of Warrant Upon Acquisition of Company. 

(a)    Acquisition. For the purpose of this Warrant, “Acquisition” means any transaction or
series of related transactions involving: (i) the sale, lease, exclusive license, or other disposition of all or substantially all of the assets of the Company; (ii) any merger or consolidation of the Company into or with another person or
entity (other than a merger or consolidation effected exclusively to change the Company’s domicile), or any other corporate reorganization, in which the stockholders of the Company in their capacity as such immediately prior to such merger,
consolidation or reorganization, own less than a majority of the Company’s (or the surviving or successor entity’s) outstanding voting power immediately after such merger, consolidation or reorganization (or, if such Company stockholders
beneficially own a majority of the outstanding voting power of the surviving or successor entity as of immediately after such merger, consolidation or reorganization, such surviving or successor entity is not the Company); or (iii) any sale or
other transfer by the stockholders of the Company of shares representing at least a majority of the Company’s then-total outstanding combined voting power. 

(b)    Treatment of Warrant at Acquisition. In the event of an Acquisition in which the consideration to be
received by the Company’s stockholders consists solely of cash, solely of Marketable Securities or a combination of cash and Marketable Securities (a “Cash/Public Acquisition”), and the fair market value of one Share as
determined in accordance with Section 1.3 above would be greater than the Warrant Price in effect on such date immediately prior to such Cash/Public Acquisition, and Holder has not exercised this Warrant pursuant to Section 1.1 above as to
all Shares, then this Warrant shall automatically be deemed to be Cashless Exercised pursuant to Section 1.2 above as to all Shares effective immediately prior to and contingent upon the consummation of a Cash/Public Acquisition. In connection
with such Cashless Exercise, Holder shall be deemed to have restated each of the representations and warranties in Section 4 of the Warrant as of the date thereof and the Company shall promptly notify the Holder of the number of Shares (or such
other securities) issued upon exercise. In the event of a Cash/Public Acquisition where the fair market value of one Share as determined in accordance with Section 1.3 above would be less than the Warrant Price in effect immediately prior to
such Cash/Public Acquisition, then this Warrant will expire immediately prior to the consummation of such Cash/Public Acquisition. 

  
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 (c)    Upon the closing of any Acquisition other than a Cash/Public
Acquisition, the acquiring, surviving or successor entity shall assume the obligations of this Warrant, and this Warrant shall thereafter be exercisable for the same securities and/or other property as would have been paid for the Shares issuable
upon exercise of the unexercised portion of this Warrant as if such Shares were outstanding on and as of the closing of such Acquisition, subject to further adjustment from time to time in accordance with the provisions of this Warrant. 

(d)    As used in this Warrant “Marketable Securities” means securities meeting all of the
following requirements: (i) the issuer thereof is then subject to the reporting requirements of Section 13 or Section 15(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and is then
current in its filing of all required reports and other information under the Act and the Exchange Act; (ii) the class and series of shares or other security of the issuer that would be received by Holder in connection with the Acquisition were
Holder to exercise this Warrant on or prior to the closing thereof is then traded in a Trading Market, and (iii) following the closing of such Acquisition, Holder would not be restricted from publicly
re-selling all of the issuer’s shares and/or other securities that would be received by Holder in such Acquisition were Holder to exercise this Warrant in full on or prior to the closing of such
Acquisition, except to the extent that any such restriction (x) arises solely under federal or state securities laws, rules or regulations, and (y) does not extend beyond six (6) months from the closing of such Acquisition. 

1.7    Voting Agreement. Upon any exercise of this Warrant, Holder shall, if the Company so requests in writing,
become a party to, by execution and delivery to the Company of a counterpart signature page, joinder agreement, instrument of accession or similar instrument, that certain Amended and Restated Voting Agreement, dated August 15, 2015 by and
among the Company and the other parties thereto and the other parties thereto, as amended and/or restated and in effect from time to time (the “Voting Agreement”), solely with respect to the Shares issued upon such exercise
(and the shares of common stock, if any, issued upon conversion of such Shares), solely to the extent that all holders of outstanding shares of the Class are then parties thereto, and solely to the extent that such agreement is then by its
terms in force and effect. 
 SECTION 2. ADJUSTMENTS TO THE SHARES AND WARRANT PRICE. 

2.1    Stock Dividends, Splits, Etc. If the Company declares or pays a dividend or distribution on the outstanding
shares of the Class payable in common stock or other securities or property (other than cash), then upon exercise of this Warrant, for each Share acquired, Holder shall receive, without additional cost to Holder, the total number and kind of
securities and property which Holder would have received had Holder owned the Shares of record as of the date the dividend or distribution occurred. If the Company subdivides the outstanding shares of the Class by reclassification or otherwise
into a greater number of shares, the number of Shares purchasable hereunder shall be proportionately increased and the Warrant Price shall be proportionately decreased. If the outstanding shares of the Class are combined or consolidated, by
reclassification or otherwise, into a lesser number of shares, the Warrant Price shall be proportionately increased and the number of Shares shall be proportionately decreased. 

2.2    Reclassification, Exchange Combinations or Substitution. Upon any event whereby all of the outstanding
shares of the Class are reclassified, exchanged, combined, substituted, or replaced for, into, with or by Company securities of a different class and/or series, 

  
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then from and after the consummation of such event, this Warrant will be exercisable for the number, class and series of Company securities that Holder would have received had the Shares been
outstanding on and as of the consummation of such event, and subject to further adjustment thereafter from time to time in accordance with the provisions of this Warrant. The provisions of this Section 2.2 shall similarly apply to successive
reclassifications, exchanges, combinations, substitutions, replacements or other similar events. 
 2.3    Conversion
of Preferred Stock. If the Class is a class and series of the Company’s convertible preferred stock, in the event that all outstanding shares of the Class are converted, automatically or by action of the holders thereof, into
common stock pursuant to the provisions of the Company’s Certificate of Incorporation, including, without limitation, in connection with the Company’s initial, underwritten public offering and sale of its common stock pursuant to an
effective registration statement under the Act (the “IPO”) then from and after the date on which all outstanding shares of the Class have been so converted, this Warrant shall be exercisable for such number of shares of
common stock into which the Shares would have been converted had the Shares been outstanding on the date of such conversion, and the Warrant Price shall equal the Warrant Price in effect as of immediately prior to such conversion divided by the
number of shares of common stock into which one Share would have been converted, all subject to further adjustment thereafter from time to time in accordance with the provisions of this Warrant. 

2.4    Adjustments for Diluting Issuances. Without duplication of any adjustment otherwise provided for in this
Section 2, the number of shares of common stock issuable upon conversion of the Shares shall be subject to anti-dilution adjustment from time to time in the manner set forth in the Company’s Certificate of Incorporation as if the Shares
were issued and outstanding on and as of the date of any such required adjustment. 
 2.5    No Fractional Share.
No fractional Share shall be issuable upon exercise of this Warrant and the number of Shares to be issued shall be rounded down to the nearest whole Share. If a fractional Share interest arises upon any exercise of the Warrant, the Company shall
eliminate such fractional Share interest by paying Holder in cash the amount computed by multiplying the fractional interest by (i) the fair market value (as determined in accordance with Section 1.3 above) of a full Share, less
(ii) the then-effective Warrant Price. 
 2.6    Notice/Certificate as to Adjustments. Upon each adjustment
of the Warrant Price, Class and/or number of Shares, the Company, at the Company’s expense, shall notify Holder in writing within a reasonable time setting forth the adjustments to the Warrant Price, Class and/or number of Shares and
facts upon which such adjustment is based. The Company shall, upon written request from Holder, furnish Holder with a certificate of its Chief Financial Officer, including computations of such adjustment and the Warrant Price, Class and number
of Shares in effect upon the date of such adjustment. 
 SECTION 3. REPRESENTATIONS AND COVENANTS OF THE COMPANY. 

3.1    Representations and Warranties. The Company represents and warrants to, and agrees with, the Holder as
follows: 

  
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 (a)    The initial Warrant Price referenced on the first page of this
Warrant is not greater than the price per share at which shares of the Class were last sold and issued prior to the Issue Date hereof in an arms-length transaction in which at least $500,000 of such shares were sold. 

(b)    All Shares which may be issued upon the exercise of this Warrant, and all securities, if any, issuable upon
conversion of the Shares, shall, upon issuance in accordance with the terms of this Warrant (and, in the case of any such conversion securities, the terms of the Company’s Certificate of Incorporation), be duly authorized, validly issued, fully
paid and non-assessable, and free of any liens and encumbrances except for restrictions on transfer provided for herein, under applicable federal and state securities laws or under the Voting Agreement (to the
extent Holder is then a party thereto or is required by the terms of Section 1.7 above to become a party). The Company covenants that it shall at all times cause to be reserved and kept available out of its authorized and unissued capital stock
such number of shares of the Class, common stock and other securities as will be sufficient to permit the exercise in full of this Warrant and the conversion of the Shares into common stock or such other securities. 

(c)    The Company’s capitalization table attached hereto as Schedule 1 is true and complete, in all material
respects, as of the Issue Date. 
 3.2    Notice of Certain Events. If the Company proposes at any time to: 

(a)    declare any dividend or distribution upon the outstanding shares of the Class or common stock, whether in
cash, property, stock, or other securities and whether or not a regular cash dividend; 
 (b)    offer for subscription
or sale pro rata to the holders of the outstanding shares of the Class any additional shares of any class or series of the Company’s stock (other than pursuant to contractual pre-emptive rights);

 (c)    effect any reclassification, exchange, combination, substitution, reorganization or recapitalization of the
outstanding shares of the Class; 
 (d)    effect an Acquisition or to liquidate, dissolve or wind up; or 

(e)    effect an IPO; 

then, in connection with each such event, the Company shall give Holder: 

(1)    in the case of the matters referred to in (a) and (b) above, at least seven (7) Business
Days prior written notice of the earlier to occur of the effective date thereof or the date on which a record will be taken for such dividend, distribution, or subscription rights (and specifying the date on which the holders of outstanding shares
of the Class will be entitled thereto) or for determining rights to vote, if any; 
 (2)    in the
case of the matters referred to in (c) and (d) above at least seven (7) Business Days prior written notice of the date when the same will take 

  
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place (and specifying the date on which the holders of outstanding shares of the Class will be entitled to exchange their shares for the securities or other property deliverable upon the
occurrence of such event and such reasonable information as Holder may reasonably require regarding the treatment of this Warrant in connection with such event giving rise to the notice); and 

(3)    with respect to the IPO, at least seven (7) Business Days prior written notice of the date on
which the Company proposes to file its registration statement in connection therewith. 
 The Company will also provide information requested by Holder that
is reasonably necessary to enable Holder to comply with Holder’s accounting or reporting requirements. 
 SECTION 4. REPRESENTATIONS
AND WARRANTIES OF THE HOLDER.  
 The Holder represents and warrants to the Company as follows: 

4.1    Purchase for Own Account. This Warrant and the securities to be acquired upon exercise of this Warrant by
Holder are being acquired for investment for Holder’s account, not as a nominee or agent, and not with a view to the public resale or distribution within the meaning of the Act. Holder also represents that it has not been formed for the
specific purpose of acquiring this Warrant or the Shares. 
 4.2    Disclosure of Information. Holder is aware of
the Company’s business affairs and financial condition and has received or has had full access to all the information it considers necessary or appropriate to make an informed investment decision with respect to the acquisition of this Warrant
and its underlying securities. Holder further has had an opportunity to ask questions and receive answers from the Company regarding the terms and conditions of the offering of this Warrant and its underlying securities and to obtain additional
information (to the extent the Company possessed such information or could acquire it without unreasonable effort or expense) necessary to verify any information furnished to Holder or to which Holder has access. 

4.3    Investment Experience. Holder understands that the purchase of this Warrant and its underlying securities
involves substantial risk. Holder has experience as an investor in securities of companies in the development stage and acknowledges that Holder can bear the economic risk of such Holder’s investment in this Warrant and its underlying
securities and has such knowledge and experience in financial or business matters that Holder is capable of evaluating the merits and risks of its investment in this Warrant and its underlying securities and/or has a preexisting personal or business
relationship with the Company and certain of its officers, directors or controlling persons of a nature and duration that enables Holder to be aware of the character, business acumen and financial circumstances of such persons. 

4.4    Accredited Investor Status. Holder is an “accredited investor” within the meaning of Regulation D
promulgated under the Act. 
 4.5    The Act. Holder understands that this Warrant and the Shares issuable upon
exercise hereof have not been registered under the Act in reliance upon a specific exemption therefrom, which exemption depends upon, among other things, the bona fide nature of the 

  
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Holder’s investment intent as expressed herein. Holder understands that this Warrant and the Shares issued upon any exercise hereof must be held indefinitely unless subsequently registered
under the Act and qualified under applicable state securities laws, or unless exemption from such registration and qualification are otherwise available. Holder is aware of the provisions of Rule 144 promulgated under the Act. 

4.6    Market Stand-off Agreement. The Holder agrees that the Shares shall
be subject to the Market Standoff provisions in Section 2.11 of the Company’s Investor Rights Agreement, as amended and in effect from time to time. 

4.7    No Voting Rights. Holder, as a Holder of this Warrant, will not have any voting rights until the exercise of
this Warrant. 
 SECTION 5. MISCELLANEOUS. 

5.1    Term; Automatic Cashless Exercise Upon Expiration. 

(a)    Term. Subject to the provisions of Section 1.6 above, this Warrant is exercisable in whole or in part
at any time and from time to time on or before 6:00 PM, Pacific time, on the Expiration Date and shall be void thereafter. 

(b)    Automatic Cashless Exercise upon Expiration. In the event that, upon the Expiration Date, the fair market
value of one Share (or other security issuable upon the exercise hereof) as determined in accordance with Section 1.3 above is greater than the Warrant Price in effect on such date, then this Warrant shall automatically be deemed on and as of
such date to be exercised pursuant to Section 1.2 above as to all Shares (or such other securities) for which it shall not previously have been exercised, and the Company shall, within a reasonable time, deliver a certificate representing the
Shares (or such other securities) issued upon such exercise to Holder. 
 5.2    Legends. Each certificate
evidencing Shares (and each certificate evidencing securities issued upon conversion of any Shares, if any) shall be imprinted with a legend in substantially the following form: 

THE SHARES EVIDENCED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE
“ACT”) OR THE SECURITIES LAWS OF ANY STATE AND, EXCEPT AS SET FORTH IN THAT CERTAIN WARRANT TO PURCHASE STOCK ISSUED BY THE ISSUER TO [SILICON VALLEY BANK / LIFE SCIENCE LOANS, LLC] DATED OCTOBER 25, 2016, MAY NOT BE
OFFERED, SOLD, PLEDGED OR OTHERWISE TRANSFERRED UNLESS AND UNTIL REGISTERED UNDER SAID ACT AND LAWS OR, IN THE OPINION OF LEGAL COUNSEL IN FORM AND SUBSTANCE SATISFACTORY TO THE ISSUER, SUCH OFFER, SALE, PLEDGE OR OTHER TRANSFER IS EXEMPT FROM SUCH
REGISTRATION. 
 5.3    Compliance with Securities Laws on Transfer. This Warrant and the Shares issued upon
exercise of this Warrant (and the securities issuable, directly or indirectly, upon conversion of the Shares, if any) may not be transferred or assigned in whole or in part except in compliance 

  
 8 

 
with applicable federal and state securities laws by the transferor and the transferee (including, without limitation, the delivery of investment representation letters and legal opinions
reasonably satisfactory to the Company, as reasonably requested by the Company). The Company shall not require Holder to provide an opinion of counsel if the transfer is to [SVB Financial Group (Silicon Valley Bank’s parent company) or any
other] [an] affiliate of Holder, provided that [any] such [transferee / affiliate] is an “accredited investor” as defined in Regulation D promulgated under the Act. Additionally, the Company shall also not require an opinion of counsel if
there is no material question as to the availability of Rule 144 promulgated under the Act. 
 5.4    Transfer
Procedure. [After receipt by Silicon Valley Bank of the executed Warrant, Silicon Valley Bank will transfer all of this Warrant to its parent company, SVB Financial Group. By its acceptance of this Warrant, SVB Financial Group hereby makes to
the Company each of the representations and warranties set forth in Section 4 hereof and agrees to be bound by all of the terms and conditions of this Warrant as if the original Holder hereof.] Subject to the provisions of Section 5.3 and
upon providing the Company with written notice, [SVB Financial Group and any subsequent] Holder may transfer all or part of this Warrant or the Shares issued upon exercise of this Warrant (or the securities issued upon conversion of the Shares, if
any) to any transferee, provided, however, in connection with any such transfer, [SVB Financial Group or any subsequent] Holder will give the Company notice of the portion of the Warrant and/or Shares (and/or securities issued upon conversion of the
Shares, if any) being transferred with the name, address and taxpayer identification number of the transferee and Holder will surrender this Warrant to the Company for reissuance to the transferee(s) (and Holder if applicable); and provided further,
that any subsequent transferee [other than SVB Financial Group] shall agree in writing with the Company to be bound by all of the terms and conditions of this Warrant. Notwithstanding any contrary provision herein, at all times prior to the IPO,
Holder may not, without the Company’s prior written consent, transfer this Warrant or any portion hereof, or any Shares issued upon any exercise hereof, or any shares or other securities issued upon any conversion of any Shares issued upon any
exercise hereof, to any person or entity who directly competes with the Company, except in connection with an Acquisition of the Company by such a direct competitor. 

5.5    Notices. All notices and other communications hereunder from the Company to the Holder, or vice versa, shall
be deemed delivered and effective (i) when given personally, (ii) on the third (3rd) Business Day after being mailed by first-class registered or certified mail, postage prepaid,
(iii) upon actual receipt if given by facsimile or electronic mail and such receipt is confirmed in writing by the recipient, or (iv) on the first Business Day following delivery to a reliable overnight courier service, courier fee
prepaid, in any case at such address as may have been furnished to the Company or Holder, as the case may be, in writing by the Company or such Holder from time to time in accordance with the provisions of this Section 5.5. All notices to
Holder shall be addressed as follows until the Company receives notice of a change of address in connection with a transfer or otherwise: 

[___] 
 Attn: [___] 

[___] 
 [___] 

Telephone: [___] 
 Facsimile:
[___] 

  
 9 

 Email address: [___] 

Notice to the Company shall be addressed as follows until Holder receives notice of a change in address: 

X4 Pharmaceuticals, Inc. 
 Attn:
Chief Financial Officer 
 784 Memorial Drive, Suite 140 

Cambridge, MA 02139 
 Telephone:

 Facsimile: 
 Email: 

With a copy (which shall not constitute notice) to: 

Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C. 

Attn: Meryl J. Epstein, Esq. 
 One
Financial Center, Boston, MA 02111 
 Telephone: (617) 348-1635 

Facsimile: (617) 542-2241 

Email: mjepstein@mintz.com 

5.6    Waiver. This Warrant and any term hereof may be changed, waived, discharged or terminated (either generally
or in a particular instance and either retroactively or prospectively) only by an instrument in writing signed by the party against which enforcement of such change, waiver, discharge or termination is sought. 

5.7    Attorneys’ Fees. In the event of any dispute between the parties concerning the terms and provisions of
this Warrant, the party prevailing in such dispute shall be entitled to collect from the other party all costs incurred in such dispute, including reasonable attorneys’ fees. 

5.8    Counterparts; Facsimile/Electronic Signatures. This Warrant may be executed in counterparts, all of which
together shall constitute one and the same agreement. Any signature page delivered electronically or by facsimile shall be binding to the same extent as an original signature page with regards to any agreement subject to the terms hereof or any
amendment thereto. 
 5.9    Governing Law. This Warrant shall be governed by and construed in accordance with
the laws of the State of California, without giving effect to its principles regarding conflicts of law. 

5.10    Headings. The headings in this Warrant are for purposes of reference only and shall not limit or otherwise
affect the meaning of any provision of this Warrant. 
 5.11    Business Days. “Business
Day” is any day that is not a Saturday, Sunday or a day on which [Silicon Valley Bank is] [banks in Washington are] closed. 

[Remainder of page left blank intentionally] 

  
 10 

 [Signature page follows] 

  
 11 

 IN WITNESS WHEREOF, the parties have caused this Warrant to Purchase Stock to be executed by
their duly authorized representatives effective as of the Issue Date written above. 
  

			
	 “COMPANY”
  

X4 PHARMACEUTICALS, INC.

		
	By:	 	 
	Name:	 	  

		 	 (Print)

	Title:	 	  

  
  

			
	 “HOLDER”
  

[SILICON VALLEY BANK / LIFE SCIENCE LOANS, LLC]

		
	By:	 	 
	Name:	 	  

		 	 (Print)

	Title:	 	  

  

 APPENDIX 1 

NOTICE OF EXERCISE 

1.    The undersigned Holder hereby exercises its right to purchase _____________ shares of the Common/Series _______
Preferred [circle one] Stock of ____________________ (the “Company”) in accordance with the attached Warrant To Purchase Stock, and tenders payment of the aggregate Warrant Price for such shares as follows: 

 

	 	[    ]	 check in the amount of $____________ payable to order of the Company enclosed herewith 

 

	 	[    ]	 Wire transfer of immediately available funds to the Company’s account 

 

	 	[    ]	 Cashless Exercise pursuant to Section 1.2 of the Warrant 

 

	 	[    ]	 Other [Describe] _______________________________ 

2.    Please issue a certificate or certificates representing the Shares in the name specified below: 

 
  

Holder’s Name 
  

 
  

 
 (Address) 

3.    By its execution below and for the benefit of the Company, Holder hereby restates each of the representations and
warranties in Section 4 of the Warrant to Purchase Stock as of the date hereof. 
  

			
	 HOLDER:
  

 

		
	By:	 	 
		
	Name:	 	 
		
	Title:	 	 
		
	(Date):	 	 
		 	

  
 Appendix 1

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