EX-4.5





 Exhibit 4.5 

THIS WARRANT, AND THE SECURITIES ISSUABLE UPON THE EXERCISE OF THIS WARRANT, HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE
“ACT”), OR ANY STATE SECURITIES LAWS. THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED, OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT RELATED THERETO OR AN OPINION OF COUNSEL (WHICH MAY BE COMPANY COUNSEL) REASONABLY
SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED UNDER THE ACT, OR ANY APPLICABLE STATE SECURITIES LAWS. 
 WARRANT
AGREEMENT 
 To Purchase Shares of Preferred Stock of 

X4 PHARMACEUTICALS, INC. 
 Dated as
of October 19, 2018 (the “Effective Date”) 
 WHEREAS, X4 Pharmaceuticals, Inc., a Delaware corporation, has entered into a Loan and
Security Agreement of even date herewith (the “Loan Agreement”) with Hercules Capital, Inc., a Maryland corporation, in its capacity as administrative and collateral agent, and Hercules Capital, Inc. (the
“Warrantholder”) and the other lender parties thereto; 
 WHEREAS, the Company (as defined below) desires to grant to the Warrantholder, in
consideration for, among other things, the financial accommodations provided for in the Loan Agreement, the right to purchase shares of Preferred Stock (as defined below) pursuant to this Warrant Agreement (the “Agreement”); 

NOW, THEREFORE, in consideration of the Warrantholder executing and delivering the Loan Agreement and providing the financial accommodations contemplated
therein, and in consideration of the mutual covenants and agreements contained herein, the Company and the Warrantholder agree as follows: 

SECTION 1. GRANT OF THE RIGHT TO PURCHASE PREFERRED STOCK. 

For value received, the Company hereby grants to the Warrantholder, and the Warrantholder is entitled, upon the terms and subject to the conditions
hereinafter set forth, to subscribe for and purchase, from the Company, an aggregate number of fully paid and non-assessable shares of the Preferred Stock equal to the quotient derived by dividing (a) the
Warrant Coverage (as defined below) by (b) the Exercise Price (defined below). The Exercise Price of such shares is subject to adjustment as provided in Section 8. As used herein, the following terms shall have the following meanings: 

“Act” means the Securities Act of 1933, as amended. 

“Charter” means the Company’s Articles of Incorporation, Certificate of Incorporation or other constitutional document,
as may be amended from time to time. 
 “Common Stock” means the Company’s common stock, $0.001 par value per share;

 “Company” means X4 Pharmaceuticals, Inc., a Delaware corporation, and any successor or surviving entity that assumes the
obligations of the Company under this Agreement pursuant to Section 8(a). 
 “Equity Round” means any non-public offering of equity securities by the Company, after the Effective Date but prior to the consummation of an Initial Public Offering that results in the conversion of all preferred stock of the Company into
Common Stock, in a transaction or series of related transactions principally for equity financing purposes in which the cash is received by the Company and/or debt of the Company is cancelled or converted in exchange for equity securities of the
Company; provided that Equity Round shall not include additional closings of the Company’s Series B Preferred Stock round of financing. 

  
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 “Exercise Price” means (a) if Preferred Stock means Series B Preferred
Stock, $1.88 per share, or (b) if Preferred Stock means Next Round Stock, the lowest price per share of Next Round Stock paid by investors in the Next Round, in either case subject to adjustment pursuant to Section 8; 

“Initial Public Offering” means the initial underwritten public offering of the Company’s Common Stock pursuant to a
registration statement under the Act, which public offering has been declared effective by the Securities and Exchange Commission (“SEC”); 

“Merger Event” means (i) any sale, lease, exclusive license or other transfer of all or substantially all assets of the
Company or any merger or consolidation involving the Company in which the Company is not the surviving entity, or in which the outstanding shares of the Company’s capital stock are otherwise converted into or exchanged for shares of preferred
stock, other securities or property of another entity; or (ii) any Deemed Liquidation Event as such term is defined in the Charter; 

“Next Round” means the next Equity Round in which the Company issues and sells shares of its preferred stock and any options,
warrants, rights or other securities that are exercisable, convertible or exchangeable into, or otherwise provide the right to purchase or acquire shares of such preferred stock for aggregate gross cash proceeds of at least $25,000,000; 

“Preferred Stock” means, at the election of the Warrantholder, (A) the Series B Preferred Stock of the Company or
(B) upon the closing of the Next Round, the class and series of the preferred stock of the Company and any options, warrants, rights or other securities that are exercisable, convertible or exchangeable into, or otherwise provide the right to
purchase or acquire shares of preferred stock (such preferred stock, the “Next Round Stock”), and, to the extent provided in Sections 8(a) and (b), any other stock into or for which such Preferred Stock may be converted or
exchanged, provided, that notwithstanding anything to the contrary contained in this Warrant, if all of the preferred stock of the Company is converted into Common Stock (automatically upon an Initial Public Offering or otherwise), “Preferred
Stock”: shall thereafter refer to Common Stock, with the appropriate adjustment to the number of such shares of Common Stock issuable upon exercise of this Warrant; 

“Purchase Price” means, with respect to any exercise of this Agreement, an amount equal to the Exercise Price as of the
relevant time multiplied by the number of shares of Preferred Stock requested to be exercised under this Agreement pursuant to such exercise; and 

“Warrant Coverage” means $396,000. 

SECTION 2. TERM OF THE AGREEMENT. 

Except as otherwise provided for herein, the term of this Agreement and the right to purchase Preferred Stock as granted herein (the “Warrant) shall
commence on the Effective Date and shall be exercisable for a period ending upon the earlier to occur of (i) ten (10) years from the Effective Date. 

SECTION 3. EXERCISE OF THE PURCHASE RIGHTS. 

(a) Exercise. The purchase rights set forth in this Agreement are exercisable by the Warrantholder, in whole or in part, at any time,
or from time to time, prior to the expiration of the term set forth in Section 2, by tendering to the Company at its principal office a notice of exercise in the form attached hereto as Exhibit I (the “Notice of
Exercise”), duly completed and executed. Promptly upon receipt of the Notice of Exercise and the payment of the Purchase Price in accordance with the terms set forth below, and in no event later than three (3) days thereafter, the
Company shall issue to the Warrantholder a certificate for the number of shares of Preferred Stock purchased and shall execute the acknowledgment of exercise in the form attached hereto as Exhibit II (the “Acknowledgment of
Exercise”) indicating the number of shares which remain subject to future purchases, if any. 
 The Purchase Price may be paid at the
Warrantholder’s election either (i) by cash or check, or (ii) by surrender of all or a portion of the Warrant for shares of Preferred Stock to be exercised under this Agreement and, if applicable, an amended Agreement representing the
remaining number of shares purchasable hereunder, as determined below (“Net Issuance”). If the Warrantholder elects the Net Issuance method, the Company will issue Preferred Stock in accordance with the following formula: 

  
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 X = Y(A-B) 

            A 

Where:   X =       the number of shares of Preferred Stock to be issued to the Warrantholder. 

 

	 	Y =	 the number of shares of Preferred Stock requested to be exercised under this Agreement. 



 

	 	A =	 the fair market value of one (1) share of Preferred Stock at the time of issuance of such shares of
Preferred Stock. 


  

	 	B =	 the Exercise Price. 



For purposes of the above calculation, current fair market value of Preferred Stock shall mean with respect to each share of Preferred Stock: 

(i) if the exercise is in connection with an Initial Public Offering, and if the Company’s Registration Statement relating
to such Initial Public Offering has been declared effective by the SEC, then the fair market value per share shall be the initial “Price to Public” of the Common Stock specified in the final prospectus with respect to the offering; 

(ii) if the exercise is after, and not in connection with an Initial Public Offering, and: 

(A) if the Common Stock is traded on a securities exchange, the fair market value shall be deemed to be the prior day closing
price before the day the current fair market value of the securities is being determined; or 
 (B) if the Common Stock is
traded over-the-counter, the fair market value shall be deemed to be the prior day closing bid and asked price quoted on the NASDAQ system (or similar system) before the
day the current fair market value of the securities is being determined; 
 (iii) if at any time the Common Stock is not
listed on any securities exchange or quoted in the NASDAQ National Market or the over-the-counter market, the current fair market value of Preferred Stock shall be the
highest price per share which the Company could obtain from a willing buyer (not a current employee or director) for shares of Common Stock sold by the Company, from authorized but unissued shares, as determined in good faith by its Board of
Directors, unless the Company shall become subject to a Merger Event, in which case the fair market value of Preferred Stock shall be deemed to be the per share value received by the holders of the Company’s Preferred Stock on a common
equivalent basis pursuant to such Merger Event. 
 Upon partial exercise by either cash or Net Issuance, the Company shall promptly issue an amended
Agreement representing the remaining number of shares purchasable hereunder. All other terms and conditions of such amended Agreement shall be identical to those contained herein, including, but not limited to the Effective Date hereof. 

(b) Exercise Prior to Expiration. To the extent this Agreement is not previously exercised as to all shares of Preferred Stock subject
hereto, and if the fair market value of one share of the Preferred Stock is greater than the Exercise Price then in effect, this Agreement shall be deemed automatically exercised pursuant to Section 3(a) (even if not surrendered) immediately
before its expiration. For purposes of such automatic exercise, the fair market value of one share of the Preferred Stock upon such expiration shall be determined pursuant to Section 3(a). To the extent this Agreement or any portion thereof is
deemed automatically exercised pursuant to this Section 3(b), the Company agrees to promptly notify the Warrantholder of the number of shares of Preferred Stock, if any, the Warrantholder is to receive by reason of such automatic exercise. 


  
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 SECTION 4. RESERVATION OF SHARES. 

During the term of this Agreement, the Company will at all times have authorized and reserved a sufficient number of shares of its Preferred Stock to provide
for the exercise of the rights to purchase Preferred Stock as provided for herein, and shall have authorized and reserved a sufficient number of shares of its Common Stock to provide for the conversion of the shares of Preferred Stock issuable
hereunder. 
 SECTION 5. NO FRACTIONAL SHARES OR SCRIP. 

No fractional shares or scrip representing fractional shares shall be issued upon the exercise of this Agreement, but in lieu of such fractional shares the
Company shall make a cash payment therefor upon the basis of the then fair market value of one share of Preferred Stock. 
 SECTION
6. NO RIGHTS AS SHAREHOLDER/STOCKHOLDER. 
 This Agreement does not entitle the Warrantholder to any voting rights or other rights as a
shareholder/stockholder of the Company prior to the exercise of this Agreement. 
 SECTION 7. WARRANTHOLDER REGISTRY. 

The Company shall maintain a registry showing the name and address of the registered holder of this Agreement. The Warrantholder’s initial address, for
purposes of such registry, is set forth below the Warrantholder’s signature on this Agreement. The Warrantholder may change such address by giving written notice of such changed address to the Company. 

SECTION 8. ADJUSTMENT RIGHTS. 
 The
Exercise Price and the number of shares of Preferred Stock purchasable hereunder are subject to adjustment, as follows: 
 (a) Merger
Event. If at any time there shall be Merger Event, this Warrant shall, on and after the closing thereof, automatically and without further action on the part of any party or other person, represent the right to receive the consideration
(including, without limitation, cash, securities or other property (collectively, “Reference Property”)) payable on or in respect of all shares of Preferred Stock that are issuable hereunder as of immediately prior to the closing of
such Merger Event less the Purchase Price for all such shares of Preferred Stock, and such Merger Event consideration shall be paid to Warrantholder as and when it is paid to the holders of the outstanding shares of Preferred Stock and this Warrant
shall thereupon automatically terminate. Appropriate adjustment (as determined in good faith by the Company’s Board of Directors and reasonably acceptable to the Warrantholder) shall be made in the application of the provisions of this
Agreement with respect to the rights and interests of the Warrantholder after the Merger Event to the end that the provisions of this Agreement (including adjustments of the Exercise Price, the ability of the Warrantholder to elect the class and
series of Preferred Stock as set forth in the definition thereof, and adjustments to ensure that the provisions of this Section 8 shall thereafter be applicable, as nearly as possible, to the purchase rights under this Agreement in relation to
any Reference Property thereafter acquirable upon exercise of such purchase rights) shall continue to be applicable in their entirety, and to the greatest extent possible. To the extent this Warrant or any portion thereof is deemed automatically
exercised pursuant to this Section 8(a), the Company agrees to promptly notify the Warrantholder of the Reference Property, if any, the Warrantholder is to receive by reason of such automatic exercise. Notwithstanding anything to the contrary
in this Warrant, if the aggregate fair market value of the Reference Property payable under this Section 8(a) is less than the aggregate Exercise Price of this Warrant, then this Warrant shall automatically terminate immediately prior to the
closing of such Merger Event without and Reference Property or other consideration being paid to the Warrantholder. 

  
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 (b) Reclassification of Shares. Except for Merger Events subject to Sections 8(a) and
8(e), if the Company at any time shall, by combination, reclassification, exchange or subdivision of securities or otherwise, change any of the securities as to which purchase rights under this Agreement exist into the same or a different number of
securities of any other class or classes, this Agreement shall thereafter represent the right to acquire such number and kind of securities as would have been issuable as the result of such change with respect to the securities which were subject to
the purchase rights under this Agreement immediately prior to such combination, reclassification, exchange, subdivision or other change; provided to the extent the Warrantholder has the right to elect to receive upon exercise either Series B
Preferred Stock or Next Round Stock, the adjustment under this clause (b) shall apply solely to the class and series of preferred stock that has been so combined, reclassified, exchanged or subdivided and shall not impair the
Warrantholder’s right to elect to exercise the purchase rights for any other class or series of preferred stock. The provisions of this Section 8(b) shall similarly apply to any successive combination, reclassification, exchange,
subdivision or other change. 
 (c) Subdivision or Combination of Shares. If the Company at any time shall combine or subdivide its
Preferred Stock, (i) in the case of a subdivision, the Exercise Price shall be proportionately decreased and the number of shares of Preferred Stock issuable hereunder shall be proportionately increased, or (ii) in the case of a
combination, the Exercise Price shall be proportionately increased and the number of shares of Preferred Stock issuable hereunder shall be proportionately decreased. 

(d) Dividends. If the Company at any time while this Agreement is outstanding and unexpired shall: 

(i) pay a dividend with respect to the Preferred Stock payable in Preferred Stock, then the Exercise Price shall be adjusted,
from and after the date of determination of stockholders entitled to receive such dividend or distribution, to that price determined by multiplying the Exercise Price in effect immediately prior to such date of determination by a fraction
(A) the numerator of which shall be the total number of shares of Preferred Stock outstanding immediately prior to such dividend or distribution, and (B) the denominator of which shall be the total number of shares of Preferred Stock
outstanding immediately after such dividend or distribution; or 
 (ii) make any other dividend or distribution with respect
to Preferred Stock (or stock into which the Preferred Stock is convertible), except any dividend or distribution specifically provided for in any other clause of this Section 8, then, in each such case, provision shall be made by the Company
such that the Warrantholder shall receive upon exercise or conversion of this Warrant a proportionate share of any such dividend or distribution as though it were the holder of the Preferred Stock (or other stock for which the Preferred Stock is
convertible) as of the record date fixed for the determination of the stockholders of the Company entitled to receive such dividend or distribution. 

(e) Antidilution Rights. Additional antidilution rights applicable to the Preferred Stock purchasable hereunder are as set forth in the
Charter and shall be applicable with respect to the Preferred Stock issuable hereunder. The Company shall promptly provide the Warrantholder with any restatement, amendment, modification or waiver of the Charter; provided, that no such
amendment, modification or waiver shall impair or reduce the antidilution rights applicable to the Preferred Stock as of the date hereof unless such amendment, modification or waiver affects the rights of the Warrantholder with respect to the
Preferred Stock in the same manner as it affects all other holders of Preferred Stock. The Company shall provide the Warrantholder with prior written notice of any issuance of its stock or other equity security to occur after the Effective Date of
this Agreement, which notice shall include (a) the price at which such stock or security is to be sold, (b) the number of shares to be issued, and (c) such other information as necessary for the Warrantholder to determine if a
dilutive event has occurred. For the avoidance of doubt, there shall be no duplicate anti-dilution adjustment pursuant to this subsection (e), the forgoing subsection (d) and the Charter. 

  
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 (f) Notice of Adjustments. If: (i) the Company shall declare any dividend or
distribution upon its stock, whether in stock, cash, property or other securities; (ii) there shall be any Merger Event; (iii) there shall be an Initial Public Offering; or (iv) there shall be any voluntary dissolution, liquidation or
winding up of the Company; then, in connection with each such event, the Company shall send to the Warrantholder: (A) at least thirty (30) days’ prior written notice of the date on which the books of the Company shall close or a
record shall be taken for such dividend, distribution, subscription rights (specifying the date on which the holders of Preferred Stock shall be entitled thereto) or for determining rights to vote in respect of such Merger Event, dissolution,
liquidation or winding up; (B) in the case of any such Merger Event, dissolution, liquidation or winding up, at least thirty (30) days’ prior written notice of the date when the same shall take place (and specifying the date on which
the holders of Preferred Stock shall be entitled to exchange their Preferred Stock for securities or other property deliverable upon such Merger Event, dissolution, liquidation or winding up); and (C) in the case of an Initial Public Offering,
the Company shall give the Warrantholder at least thirty (30) days’ written notice prior to the effective date thereof. 
 Each such written
notice shall set forth, in reasonable detail, (i) the event requiring the notice, and (ii) if any adjustment is required to be made, (A) the amount of such adjustment, (B) the method by which such adjustment was calculated,
(C) the adjusted Exercise Price (if the Exercise Price has been adjusted), and (D) the number of shares subject to purchase hereunder after giving effect to such adjustment, and shall be given in accordance with Section 12(g) below.

 (g) Timely Notice. Failure to timely provide such notice required by Section 8(f) above shall entitle the Warrantholder to
retain the benefit of the applicable notice period notwithstanding anything to the contrary contained in any insufficient notice received by the Warrantholder. For purposes of this Section 8(g), and notwithstanding anything to the contrary in
Section 12(g), the notice period shall begin on the date the Warrantholder actually receives a written notice containing all the information required to be provided in such Section 12(g). 

SECTION 9. REPRESENTATIONS, WARRANTIES AND COVENANTS OF THE COMPANY. 

(a) Reservation of Preferred Stock. The Preferred Stock issuable upon exercise of the Warrantholder’s rights has been or, in the
case of Preferred Stock issuable in the Next Round, will be duly and validly reserved and, when issued in accordance with the provisions of this Agreement, will be validly issued, fully paid and
non-assessable, and will be free of any taxes, liens, charges or encumbrances of any nature whatsoever; provided, that the Preferred Stock issuable pursuant to this Agreement may be subject to
restrictions on transfer under state and/or federal securities laws. The Company has made available to the Warrantholder true, correct and complete copies of its Charter and current bylaws. The issuance of certificates for shares of Preferred Stock
upon exercise of this Agreement shall be made without charge to the Warrantholder for any issuance tax in respect thereof, or other cost incurred by the Company in connection with such exercise and the related issuance of shares of Preferred Stock;
provided, that the Company shall not be required to pay any tax which may be payable in respect of any transfer and the issuance and delivery of any certificate in a name other than that of the Warrantholder. 

(b) Due Authority. The execution and delivery by the Company of this Agreement and the performance of all obligations of the Company
hereunder, including the issuance to the Warrantholder of the right to acquire the shares of Preferred Stock and the Common Stock into which it may be converted, have been duly authorized by all necessary corporate action on the part of the Company.
This Agreement: (i) does not violate the Charter or the Company’s current bylaws; (ii) does not contravene any law or governmental rule, regulation or order applicable to the Company; and (iii) does not and will not contravene
any provision of, or constitute a default under, any indenture, mortgage, contract or other instrument to which the Company is a party or by which it is bound. This Agreement constitutes a legal, valid and binding agreement of the Company,
enforceable in accordance with its terms. 

  
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 (c) Consents and Approvals. No consent or approval of, giving of notice to,
registration with, or taking of any other action in respect of any state, federal or other governmental authority or agency is required with respect to the execution, delivery and performance by the Company of its obligations under this Agreement,
except for the filing of notices pursuant to Regulation D under the Act and any filing required by applicable state securities law, which filings will be effective by the time required thereby. 

(d) Issued Securities. All issued and outstanding shares of Common Stock, Preferred Stock or any other securities of the Company have
been duly authorized and validly issued and are fully paid and nonassessable. All outstanding shares of Common Stock, Preferred Stock and any other securities were issued in full compliance with all federal and state securities laws. In addition, as
of the date immediately preceding the date of this Agreement: 
 (i) The authorized capital of the Company consists of (A)
116,500,000 shares of Common Stock, of which 4,830,406 shares are issued and outstanding, (B) 2,313,523 shares of Series Seed Preferred Stock, of which 1,516,136 shares are issued and outstanding and are convertible into an aggregate of 1,516,136
shares of Common Stock, (C) 22,000,000 shares of Series A Preferred Stock, of which 19,946,842 shares are issued and outstanding and are convertible into an aggregate of 19,946,842 shares of Common Stock, and (B) 25,100,000 shares of Series B
Preferred Stock, of which 18,616,569 shares are issued and outstanding and are convertible into an aggregate of 18,616,569 shares of Common Stock. 

(ii) The Company has reserved 10,200,000 shares of Common Stock for issuance under its Stock Option Plan(s), under which
7,572,819 options are outstanding. The Company has warrants presently outstanding to purchase 1,646,494 shares of Series A Preferred Stock and warrants presently outstanding to purchase 3,294,268 shares of Series B Preferred Stock. There are no
other options, warrants, conversion privileges or other rights presently outstanding to purchase or otherwise acquire any authorized but unissued shares of the Company’s capital stock or other securities of the Company. 

(iii) In accordance with the Company’s Charter, no stockholder of the Company has preemptive rights to purchase new
issuances of the Company’s capital stock. 
 (e) Registration Rights. The Company agrees that the shares of Common Stock issued
and issuable upon conversion of the shares of Preferred Stock issued and issuable upon exercise of this Warrant, and, at all times (if any) when the Preferred Stock shall be Common Stock, the shares of Preferred Stock issued and issuable upon
exercise of this Warrant, shall have the “Piggyback,” and S-3 registration rights pursuant to and as set forth in the Company’s investor rights agreement or similar agreement (the
“Investor Rights Agreement”) on a pari passu basis with the holders of outstanding shares of Preferred Stock who are parties thereto. The provisions set forth in the Company’s Investor Rights Agreement or similar agreement
relating to such registration rights in effect as of the Effective Date may not be amended, modified or waived without the prior written consent of the Warrantholder unless such amendment, modification or waiver affects the rights associated with
the shares of Preferred Stock issued and issuable upon exercise hereof in the same manner as such amendment, modification, or waiver affects the rights associated with all outstanding shares of Preferred Stock whose holders are parties thereto. 

(f) Other Commitments to Register Securities. Except as set forth in this Agreement, the Company is not, pursuant to the terms of any
other agreement currently in existence, under any obligation to register under the Act any of its presently outstanding securities or any of its securities which may hereafter be issued. 

  
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 (g) Exempt Transaction. Subject to the accuracy of the Warrantholder’s
representations in Section 10, the issuance of the Preferred Stock upon exercise of this Agreement, and the issuance of the Common Stock upon conversion of the Preferred Stock, will each constitute a transaction exempt from (i) the
registration requirements of Section 5 of the Act, in reliance upon Section 4(2) thereof, and (ii) the qualification requirements of the applicable state securities laws. 

(h) Compliance with Rule 144. If the Warrantholder proposes to sell Preferred Stock issuable upon the exercise of this Agreement, or
the Common Stock into which it is convertible, in compliance with Rule 144 promulgated by the SEC, then, upon the Warrantholder’s written request to the Company, the Company shall furnish to the Warrantholder, within ten days after receipt of
such request, a written statement confirming the Company’s compliance with the filing requirements of the SEC as set forth in such Rule, as such Rule may be amended from time to time. 

(i) Information Rights. During the term of this Warrant, in order to establish the valuation of the Warrant, the Warrantholder shall be
entitled to the information rights contained in Sections 7.1(b) and 7.1(c) of the Loan Agreement, and Sections 7.1(b) and 7.1(c) of the Loan Agreement are hereby incorporated into this Agreement by this reference as though fully set forth herein,
provided, however, that the Company shall not be required to deliver a Compliance Certificate once all Indebtedness (as defined in the Loan Agreement) owed by the Company to the Warrantholder has been repaid. The information rights set forth in this
Section 9(i) are subject to the Warrantholder having confidentiality obligations with respect thereto reasonably acceptable to the Company. 

SECTION 10. REPRESENTATIONS AND COVENANTS OF THE WARRANTHOLDER. 

This Agreement has been entered into by the Company in reliance upon the following representations and covenants of the Warrantholder: 

(a) Investment Purpose. The right to acquire Preferred Stock is being acquired for investment and not with a view to the sale or
distribution of any part thereof, and the Warrantholder has no present intention of selling or engaging in any public distribution of such rights or the Preferred Stock except pursuant to an effective registration statement or an exemption from the
registration requirements of the Act. 
 (b) Private Issue. The Warrantholder understands (i) that the Preferred Stock issuable
upon exercise of this Agreement is not registered under the Act or qualified under applicable state securities laws on the ground that the issuance contemplated by this Agreement will be exempt from the registration and qualifications requirements
thereof, and (ii) that the Company’s reliance on such exemption is predicated on the representations set forth in this Section 10. 

(c) Financial Risk. The Warrantholder has such knowledge and experience in financial and business matters as to be capable of
evaluating the merits and risks of its investment, and has the ability to bear the economic risks of its investment. 
 (d) Risk of No
Registration. The Warrantholder understands that if the Company does not register with the SEC pursuant to Section 12 of the Securities Exchange Act of 1934 (the “1934 Act”), or file reports pursuant to Section 15(d)
of the 1934 Act, or if a registration statement covering the securities under the Act is not in effect when it desires to sell (i) the rights to purchase Preferred Stock pursuant to this Agreement or (ii) the Preferred Stock issuable upon
exercise of the right to purchase, it may be required to hold such securities for an indefinite period. The Warrantholder also understands that any sale of (A) its rights hereunder to purchase Preferred Stock or (B) Preferred Stock issued
or issuable hereunder which might be made by it in reliance upon Rule 144 under the Act may be made only in accordance with the terms and conditions of that Rule. 

(e) Accredited Investor. The Warrantholder is an “accredited investor” within the meaning of the Securities and Exchange Rule
501 of Regulation D, as presently in effect. 

  
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 SECTION 11. TRANSFERS. 

Subject to compliance with applicable federal and state securities laws, this Agreement and all rights hereunder are transferable, in whole or in part, without
charge to the holder hereof (except for transfer taxes) upon surrender of this Agreement properly endorsed. Each taker and holder of this Agreement, by taking or holding the same, consents and agrees that this Agreement, when endorsed in blank,
shall be deemed negotiable, and that the holder hereof, when this Agreement shall have been so endorsed and its transfer recorded on the Company’s books, shall be treated by the Company and all other persons dealing with this Agreement as the
absolute owner hereof for any purpose and as the person entitled to exercise the rights represented by this Agreement. The transfer of this Agreement shall be recorded on the books of the Company upon receipt by the Company of a notice of transfer
in the form attached hereto as Exhibit III (the “Transfer Notice”), at its principal offices and the payment to the Company of all transfer taxes and other governmental charges imposed on such transfer. Until the Company receives
such Transfer Notice, the Company may treat the registered owner hereof as the owner for all purposes. 
 SECTION 12. MISCELLANEOUS.

 (a) Effective Date. The provisions of this Agreement shall be construed and shall be given effect in all respects as if it had
been executed and delivered by the Company on the date hereof. This Agreement shall be binding upon any successors or assigns of the Company. 

(b) Remedies. In the event of any default hereunder, the non-defaulting party may proceed to
protect and enforce its rights either by suit in equity and/or by action at law, including but not limited to an action for damages as a result of any such default, and/or an action for specific performance for any default where the Warrantholder
will not have an adequate remedy at law and where damages will not be readily ascertainable. The Company expressly agrees that it shall not oppose an application by the Warrantholder or any other person entitled to the benefit of this Agreement
requiring specific performance of any or all provisions hereof or enjoining the Company from continuing to commit any such breach of this Agreement. 

(c) No Impairment of Rights. The Company will not, by amendment of its Charter or through any other means, avoid or seek to avoid the
observance or performance of any of the terms of this Agreement, but will at all times in good faith assist in the carrying out of all such terms and in the taking of all such actions as may be necessary or appropriate in order to protect the rights
of the Warrantholder against impairment. 
 (d) Additional Documents. The Company, upon execution of this Agreement, shall provide
the Warrantholder with certified resolutions with respect to the representations, warranties and covenants set forth in Sections 9(a) through 9(d), 9(f) and 9(g). The Company shall also supply documentation reasonably necessary to evaluate whether
to exercise this Warrant, including without limitation, (i) any merger/purchase/asset sale agreement and related documents and estimated payout allocations to each of the respective shareholders, warrant and option holders in connection with a
Merger Event, (ii) the most recent capitalization tables, and (iii) the most recent Charter, in the case of information provided pursuant to clauses (i) and (ii) above, subject to the Warrantholder having confidentiality obligations
with respect thereto reasonably acceptable to the Company. 
 (e) Attorney’s Fees. In any litigation, arbitration or court
proceeding between the Company and the Warrantholder relating hereto, the prevailing party shall be entitled to attorneys’ fees and expenses and all costs of proceedings incurred in enforcing this Agreement. For the purposes of this
Section 12(e), attorneys’ fees shall include without limitation fees incurred in connection with the following: (i) contempt proceedings; (ii) discovery; (iii) any motion, proceeding or other activity of any kind in connection
with an insolvency proceeding; (iv) garnishment, levy, and debtor and third party examinations; and (v) post-judgment motions and proceedings of any kind, including without limitation any activity taken to collect or enforce any judgment.


  
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 (f) Severability. In the event any one or more of the provisions of this Agreement
shall for any reason be held invalid, illegal or unenforceable, the remaining provisions of this Agreement shall be unimpaired, and the invalid, illegal or unenforceable provision shall be replaced by a mutually acceptable valid, legal and
enforceable provision, which comes closest to the intention of the parties underlying the invalid, illegal or unenforceable provision. 

(g) Notices. Except as otherwise provided herein, any notice, demand, request, consent, approval, declaration, service of process or
other communication that is required, contemplated, or permitted under this Agreement or with respect to the subject matter hereof shall be in writing, and shall be deemed to have been validly served, given, delivered, and received upon the earlier
of: (i) the day of transmission by facsimile or hand delivery if transmission or delivery occurs on a business day at or before 5:00 pm in the time zone of the recipient, or, if transmission or delivery occurs on a non-business day or after such time, the first business day thereafter, or the first business day after deposit with an overnight express service or overnight mail delivery service; or (ii) the third (3rd) calendar day after deposit in the United States mails, with proper first class postage prepaid, and shall be addressed to the party to be notified as follows: 

If to the Warrantholder: 
 HERCULES CAPITAL, INC.

 Legal Department 
 Attention:
Chief Legal Officer and Bryan Jadot 
 400 Hamilton Avenue, Suite 310 

Palo Alto, CA 94301 
 Email: 

Telephone: 
 (i) If to the Company: 

X4 Pharmaceuticals, Inc. 

Attention: Adam Mostafa and Brian Bowersox 

955 Massachusetts Avenue, 4th Floor 

Boston, MA 02139 
 Email: 

Telephone: 
 or to such other address as each
party may designate for itself by like notice. 
 (h) Entire Agreement; Amendments. This Agreement constitutes the entire agreement
and understanding of the parties hereto in respect of the subject matter hereof, and supersedes and replaces in their entirety any prior proposals, term sheets, letters, negotiations or other documents or agreements, whether written or oral, with
respect to the subject matter hereof (including the Warrantholder’s proposal letter dated September 13, 2018). None of the terms of this Agreement may be amended except by an instrument executed by each of the parties hereto. 

(i) Headings. The various headings in this Agreement are inserted for convenience only and shall not affect the meaning or
interpretation of this Agreement or any provisions hereof. 
 (j) No Strict Construction. The parties hereto have participated
jointly in the negotiation and drafting of this Agreement. In the event an ambiguity or question of intent or interpretation arises, this Agreement shall be construed as if drafted jointly by the parties hereto and no presumption or burden of proof
shall arise favoring or disfavoring any party by virtue of the authorship of any provisions of this Agreement. 
 (k) No Waiver. No
omission or delay by the Warrantholder at any time to enforce any right or remedy reserved to it, or to require performance of any of the terms, covenants or provisions hereof by the Company at any time designated, shall be a waiver of any such
right or remedy to which the Warrantholder is entitled, nor shall it in any way affect the right of the Warrantholder to enforce such provisions thereafter. 

  
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 (l) Survival. All agreements, representations and warranties contained in this
Agreement or in any document delivered pursuant hereto shall be for the benefit of the Warrantholder and shall survive the execution and delivery of this Agreement and the expiration or other termination of this Agreement. 

(m) Governing Law. This Agreement has been negotiated and delivered to Warrantholder in the State of California, and shall have been
accepted by the Warrantholder in the State of California. Delivery of Preferred Stock to the Warrantholder by the Company under this Agreement is due in the State of California. This Agreement shall be governed by, and construed and enforced in
accordance with, the laws of the State of Delaware, excluding conflict of laws principles that would cause the application of laws of any other jurisdiction. 

(n) Consent to Jurisdiction and Venue. All judicial proceedings arising in or under or related to this Agreement may be brought in any
state or federal court of competent jurisdiction located in the State of California. By execution and delivery of this Agreement, each party hereto generally and unconditionally: (i) consents to personal jurisdiction in Santa Clara County,
State of California; (ii) waives any objection as to jurisdiction or venue in Santa Clara County, State of California; (c) agrees not to assert any defense based on lack of jurisdiction or venue in the aforesaid courts; and
(iii) irrevocably agrees to be bound by any judgment rendered thereby in connection with this Agreement. Service of process on any party hereto in any action arising out of or relating to this Agreement shall be effective if given in accordance
with the requirements for notice set forth in Section 12(g), and shall be deemed effective and received as set forth in Section 12(g). Nothing herein shall affect the right to serve process in any other manner permitted by law or shall
limit the right of either party to bring proceedings in the courts of any other jurisdiction. 
 (o) Mutual Waiver of Jury Trial.
Because disputes arising in connection with complex financial transactions are most quickly and economically resolved by an experienced and expert person and the parties wish applicable state and federal laws to apply (rather than arbitration
rules), the parties desire that their disputes be resolved by a judge applying such applicable laws. EACH OF THE COMPANY AND THE WARRANTHOLDER SPECIFICALLY WAIVES ANY RIGHT IT MAY HAVE TO TRIAL BY JURY OF ANY CAUSE OF ACTION, CLAIM, CROSS-CLAIM,
COUNTERCLAIM, THIRD PARTY CLAIM OR ANY OTHER CLAIM (COLLECTIVELY, “CLAIMS”) ASSERTED BY THE COMPANY AGAINST THE WARRANTHOLDER OR ITS ASSIGNEE OR BY THE WARRANTHOLDER OR ITS ASSIGNEE AGAINST THE COMPANY. This waiver extends to all such
Claims, including Claims that involve Persons other than the Company and the Warrantholder; Claims that arise out of or are in any way connected to the relationship between the Company and the Warrantholder; and any Claims for damages, breach of
contract, specific performance, or any equitable or legal relief of any kind, arising out of this Agreement. 
 (p) Judicial
Reference. If the waiver of jury trial set forth above is ineffective or unenforceable, the parties agree that all Claims shall be resolved by reference to a private judge sitting without a jury, pursuant to Code of Civil Procedure
Section 638, before a mutually acceptable referee or, if the parties cannot agree, a referee selected by the Presiding Judge of Santa Clara County, California. Such proceeding shall be conducted in Santa Clara County, California, with Delaware
rules of evidence and discovery applicable to such proceeding. 
 (q) Prejudgment Relief. In the event Claims are to be resolved by
arbitration, either party may seek from a court of competent jurisdiction identified in Section 12(n), any prejudgment order, writ or other relief and have such prejudgment order, writ or other relief enforced to the fullest extent permitted by
law notwithstanding that all Claims are otherwise subject to resolution by judicial reference. 
 (r) Counterparts. This Agreement
and any amendments, waivers, consents or supplements hereto may be executed in any number of counterparts, and by different parties hereto in separate counterparts, each of which when so delivered shall be deemed an original, but all of which
counterparts shall constitute but one and the same instrument. 

  
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 [Remainder of Page Intentionally Left Blank] 

  
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 IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be executed by its officers thereunto
duly authorized as of the Effective Date. 
  

			
	COMPANY:	 	X4 PHARMACEUTICALS, INC.

 
			
		
	By: 	 	 


 
			
	Name: Adam Mostafa
	Title: Chief Financial Officer


  

			
	WARRANTHOLDER:	 	HERCULES CAPITAL, INC.

 
			
		
	By: 	 	 


 
			
	Name: Jennifer Choe
	Title: Assistant General Counsel



  
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 EXHIBIT I 

NOTICE OF EXERCISE 
  

	To:	 X4 PHARMACEUTICALS, INC. 



 

	(1)	 The undersigned Warrantholder hereby elects to purchase [_______] shares of the Series [__] Preferred Stock of
[_________________], pursuant to the terms of the Warrant Agreement dated the 19th day of October, 2018 (the “Agreement”) between [_________________] and the Warrantholder, and [CASH
PAYMENT: tenders herewith payment of the Purchase Price in full, together with all applicable transfer taxes, if any.] [NET ISSUANCE: elects pursuant to Section 3(a) of the Agreement to effect a Net Issuance.] 



 

	(2)	 Please issue a certificate or certificates representing said shares of Series [__] Preferred Stock in the name
of the undersigned or in such other name as is specified below. 


  

			
	 
	(Name)
	 
	(Address)
	



			
		
	WARRANTHOLDER:	  	HERCULES CAPITAL, INC.

 
			
		
	By:	 	 


 
			
	Name:	 	 


 
			
	Title:	 	 


 
			
	Date:	 	 



  
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 EXHIBIT II 

ACKNOWLEDGMENT OF EXERCISE 
 The undersigned
[____________________________________], hereby acknowledges receipt of the “Notice of Exercise” from Hercules Capital, Inc., to purchase [____] shares of the Series [__] Preferred Stock of [_________________], pursuant to the terms of the
Warrant Agreement by and between X4 Pharmaceuticals, Inc. and Hercules Capital, Inc. dated September [__], 2018 (the “Agreement”), and further acknowledges that [______] shares remain subject to purchase under the terms of the Agreement.

  

			
	 COMPANY:
	  	X4 PHARMACEUTICALS, INC.

  

			
	By:	 	 


 
			
	Title:	 	 


 
			
	Date:	 	 



  
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 EXHIBIT III 

TRANSFER NOTICE 
 (To transfer or assign the
foregoing Agreement execute this form and supply required information. Do not use this form to purchase shares.) 
 FOR VALUE RECEIVED, the foregoing
Agreement and all rights evidenced thereby are hereby transferred and assigned to 
  

			
	                                      
                                         
                                         
                                    	  	
	(Please Print)	  	
		
	whose address
is                                        
                                         
                                         
        	  	
		
	                                      
                                         
                                         
                                    	  	

  

			
		  	Dated:                                    
                                         
                                         
  
		
		  	Holder’s
Signature:                                       
                                         
                    
		
		  	Holder’s
Address:                                       
                                         
                      
		
		  	                                     
                                         
                                         
             

 Signature
Guaranteed:                                       
                                         
                                         

 NOTE: The signature to this Transfer Notice must correspond with the name as it appears on the face of the Agreement, without alteration or
enlargement or any change whatever. Officers of corporations and those acting in a fiduciary or other representative capacity should file proper evidence of authority to assign the foregoing Agreement. 

  
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