Document:

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. 
 AMENDED AND
RESTATED 
 WARRANT AGREEMENT 

To Purchase Shares of Common Stock of 

X4 PHARMACEUTICALS, INC. 
 Dated
as of March 29, 2019 (the “Effective Date”) 
 WHEREAS, X4 Therapeutics, Inc., formerly known as X4 Pharmaceuticals, Inc., a Delaware
corporation (the “X4 Therapeutics”) previously entered into a Loan and Security Agreement, dated October 19, 2018 (as amended, 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, X4 Therapeutics is a wholly owned subsidiary of X4 Pharmaceuticals, Inc., a Delaware corporation, formerly known as Arsanis, Inc.; 

WHERAS, on October 19, 2018, X4 Therapeutics issued to Warrantholder a warrant to purchase shares of X4 Therapeutics valued at $396,000 (as modified, the
“Original Tranche 1 Warrant”); 
 WHEREAS, pursuant to a Warrant Modification Agreement dated as of December 11, 2018, the Original
Tranche 1 Warrant was modified to exercisable for shares of Arsanis Common Stock, as defined, therein. 
 WHEREAS, the parties desire to amend and restate
the Original Warrant; 
 NOW, THEREFORE, in consideration of the mutual covenants and agreements contained herein, the Company (as defined below) and the
Warrantholder hereby amend and restate the Original Tranche 1 Warrant and agree as follows: 
 SECTION 1. GRANT OF THE RIGHT TO
PURCHASE COMMON 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 Common 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., formerly known as Arsanis, 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). 
 “Exercise
Price” means $19.80 per share, subject to adjustment pursuant to Section 8; 
  

 “Merger Event” means (i) any sale, lease, exclusive license or other
transfer of all or substantially all assets of the Company; (ii)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 capital stock, other securities or property of another entity; or (iii) any sale by holders of the outstanding voting equity securities of the Company in a single transaction or series of related
transactions of shares constituting a majority of the outstanding combined voting power of the Company; 
 “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 Common Stock requested to be exercised under this Agreement pursuant to such exercise; 

“SEC” means the United States Securities and Exchange Commission; 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 Common 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) October 19, 2028 or (ii) termination pursuant to the terms hereunder. 

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 or its transfer
agent shall either (i) issue to the Warrantholder a certificate for the number of shares of Common Stock purchased or (ii) credit the same via book entry to the Warrantholder, and the Company 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 Common 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 Common Stock in accordance with the following formula: 

X = Y(A-B) 

            A 

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

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

 

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

  

	 	B =	 the then effective Exercise Price. 

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

 

	 	(i)	 Reserved. 

  

	 	(ii)	 

  
 2 

 (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 Common 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 Common Stock shall be deemed to be the per share value received by the holders of the Company’s Common 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 warrant 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 Common Stock subject
hereto, and if the then current fair market value of one share of the Common 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 Common 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 Common Stock, if any, the Warrantholder is to receive by reason of such automatic
exercise, and to issue or cause its transfer agent to issue a certificate or a book entry credit to the Warrantholder evidencing such shares. 

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 Common Stock to provide for the exercise of the rights to purchase Common Stock as provided for herein. If at any time during
the term hereof the number of authorized but unissued shares of Common Stock shall not be sufficient to permit exercise of this Warrant in full, the Company will use its commercially reasonable efforts to take such corporate action as may, in the
opinion of its counsel, be necessary to increase its authorized but unissued shares of Common Stock to such number of shares as shall be sufficient for such purposes. 

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 Common 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. 

  
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 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 in Section 12(g). 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 Common Stock purchasable hereunder are subject to adjustment, as follows: 
 (a) Merger
Event. If at any time there shall be a 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 Common 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 Common 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 Common 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, 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. 

(b) Reclassification of Shares. Except for Merger Events subject to Sections 8(a), 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. 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 Common Stock, (i) in the case
of a subdivision, the Exercise Price shall be proportionately decreased and the number of shares of Common 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 Common 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 Common Stock payable in Common 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 

  
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determination by a fraction (A) the numerator of which shall be the total number of shares of Common Stock outstanding immediately prior to such dividend or distribution, and (B) the
denominator of which shall be the total number of shares of Common Stock outstanding immediately after such dividend or distribution; or 

(ii) make any other dividend or distribution with respect to Common Stock, 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 Common Stock as of the record date fixed for the determination of the stockholders of the Company entitled to receive such dividend or distribution. 

(e) 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; or (iii) 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 Common Stock shall be entitled thereto) or for determining rights to vote in respect of such Merger Event, dissolution, liquidation or winding up; and (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 Common Stock shall be entitled to exchange their Common Stock for securities or other property
deliverable upon such Merger Event, dissolution, liquidation or winding up). 
 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). 

(f) 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(e), 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 Common Stock. The Common Stock issuable upon exercise of the Warrantholder’s rights has been 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 Common 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 Common 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 Common 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. 

  
 5 

 (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 Common Stock 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. 
 (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) Exempt Transaction. Subject to the accuracy of the Warrantholder’s representations in Section 10, the issuance of the
Common Stock upon exercise of this Agreement will 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. 
 (e) Compliance with Rule 144. The Company shall, at all times prior to the earlier to occur
of (i) the date of sale or other disposition by Warrantholder of this Warrant or all shares of Common Stock issued on exercise of this Warrant, or (ii) the expiration or earlier termination of this Warrant if the Warrant has not been
exercised in full or in part on such date, use all commercially reasonable efforts to timely file all reports required under the Exchange Act and otherwise timely take all actions necessary to permit the Warrantholder to sell or otherwise dispose of
this Warrant and the shares of Common Stock issued on exercise hereof pursuant to Rule 144 promulgated under the Act (“Rule 144”), provided that the foregoing shall not apply in the event of a Merger Event following which the successor or
surviving entity is not subject to the reporting requirements of the Exchange Act. If the Warrantholder proposes to sell Common Stock issuable upon the exercise of this Agreement 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. 
 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 Common 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 Common 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 Common 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. 

  
 6 

 (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) 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. 
 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. Notwithstanding anything herein to the contrary, the Company shall not require an opinion of counsel in connection with any sale, assignment or
other transfer by the Warrantholder of this Warrant (or any portion hereof or any interest herein) or of any shares of Common Stock issued upon any exercise hereof to an affiliate (as defined in Regulation D) of the Warrantholder, provided that such
affiliate is an “accredited investor” as defined in Regulation D. 
 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 shall 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. 

  
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 (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. 

(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:
legal@herculestech.com; bjadot@htgc.com 
 Telephone:
650-289-3060 
  

	(i)	 If to the Company: 

X4 Pharmaceuticals, Inc. 

Attention: Adam Mostafa and Brian Bowersox 

955 Massachusetts Avenue, 4th Floor 

Boston, MA 02139 
 Email:
adam.mostafa@x4pharma.com and brian.bowersox@x4pharma.com 
 Telephone:
617-542-6000 
 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 and the Original Tranche 1 Warrant). 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. 

  
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 (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. 

(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 Common 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. 

  
 9 

 (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. 
 [Remainder of Page Intentionally Left Blank] 

  
 10 

 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:	 	 /s/ Adam Mostafa

		  	Name:	 	Adam Mostafa
		  	Title:	 	Chief Financial Officer
		
	 WARRANTHOLDER:
	  	HERCULES CAPITAL, INC.
			
		  	By:	 	 /s/ Jennifer Choe

		  	Name:	 	Jennifer Choe
		  	Title:	 	Assistant General Counsel

  
 11 

 EXHIBIT I 

NOTICE OF EXERCISE 
  

	To:	 X4 PHARMACEUTICALS, INC. 

 

	(1)	 The undersigned Warrantholder hereby elects to purchase [_______] shares of the Common Stock of X4
Pharmaceuticals, Inc., pursuant to the terms of the Warrant Agreement, dated as of March 29, 2019 (the “Agreement”) between X4 Pharmaceuticals, Inc. 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 Common 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:	 	  

  
 12 

 EXHIBIT II 

ACKNOWLEDGMENT OF EXERCISE 
 The undersigned
[                    ], hereby acknowledges receipt of the “Notice of Exercise” from Hercules Capital, Inc., to purchase
[        ] shares of the Common Stock of X4 Pharmaceuticals, Inc., pursuant to the terms of the Warrant Agreement by and between X4 Pharmaceuticals, Inc. and Hercules Capital, Inc. dated as of March 29,
2019 (the “Agreement”), and further acknowledges that [        ] shares remain subject to purchase under the terms of the Agreement. 

 

					
	 COMPANY:
	  	X4 PHARMACEUTICALS, INC.
			
		  	By:	 	  

			
		  	Title:	 	  

			
		  	Date:	 	  

  
 13 

 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. 

  
 14EX-4.6

 Exhibit 4.6 

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 Common Stock of 

X4 PHARMACEUTICALS, INC. 
 Dated
as of March 18, 2019 (the “Effective Date”) 
 WHEREAS, X4 Therapeutics, Inc., formerly known as X4 Pharmaceuticals, Inc., a Delaware
corporation (the “X4 Therapeutics”) previously entered into a Loan and Security Agreement, dated October 19, 2018 (as amended, 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, X4 Therapeutics is a wholly owned subsidiary of X4 Pharmaceuticals, Inc., a Delaware corporation, formerly known as Arsanis, Inc.; 

WHEREAS, the parties desire to enter into this warrant agreement (this “Agreement”) to pursuant to the terms of the Loan Agreement; 

NOW, THEREFORE, in consideration of the mutual covenants and agreements contained herein, the Company (as defined below) and the Warrantholder agree as
follows: 
 SECTION 1. GRANT OF THE RIGHT TO PURCHASE COMMON 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 Common 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., formerly known as Arsanis, 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). 
 “Exercise
Price” means $19.80 per share, subject to adjustment pursuant to Section 8; 
 “Merger Event” means
(i) any sale, lease, exclusive license or other transfer of all or substantially all assets of the Company; (ii)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 capital stock, other securities or property of another entity; or (iii) any sale by holders of the outstanding voting equity securities of the
Company in a single transaction or series of related transactions of shares constituting a majority of the outstanding combined voting power of the Company; 

 “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 Common Stock requested to be exercised under this Agreement pursuant to such exercise; 

“SEC” means the United States Securities and Exchange Commission; and 

“Warrant Coverage” means $99,000. 

SECTION 2. TERM OF THE AGREEMENT. 
 Except
as otherwise provided for herein, the term of this Agreement and the right to purchase Common 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 after the Effective Date or (ii) termination pursuant to the terms hereunder. 
 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 or its transfer agent shall either (i) issue to the Warrantholder a certificate for the number of shares of Common Stock purchased or (ii) credit the same via book entry to the Warrantholder, and
the Company 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 Common 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 Common Stock in accordance with the following formula: 

X = Y(A-B) 

          A 

 

					
	Where:        	  	X =    	  	the number of shares of Common Stock to be issued to the Warrantholder.
			
		  	Y =	  	the number of shares of Common Stock requested to be exercised under this Agreement.
			
		  	A =	  	the fair market value of one (1) share of Common Stock at the time of exercise of such shares of Common Stock.
			
		  	B =	  	the then effective Exercise Price.

 For purposes of the above calculation, current fair market value of Common Stock shall mean with respect to each share of
Common Stock: 
 (i) Reserved. 

(ii) 

(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; 

  
 2 

 (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 Common 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 Common Stock shall be deemed to be the per share value received by the holders of the Company’s Common 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 warrant 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 Common Stock subject
hereto, and if the then current fair market value of one share of the Common 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 Common 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 Common Stock, if any, the Warrantholder is to receive by reason of such automatic
exercise, and to issue or cause its transfer agent to issue a certificate or a book entry credit to the Warrantholder evidencing such shares. 

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 Common Stock to provide for the exercise of the rights to purchase Common Stock as provided for herein. If at any time during
the term hereof the number of authorized but unissued shares of Common Stock shall not be sufficient to permit exercise of this Warrant in full, the Company will use its commercially reasonable efforts to take such corporate action as may, in the
opinion of its counsel, be necessary to increase its authorized but unissued shares of Common Stock to such number of shares as shall be sufficient for such purposes. 

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 Common 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 in Section 12(g). The Warrantholder may change such address by giving written notice of such changed address to the Company. 

  
 3 

 SECTION 8. ADJUSTMENT RIGHTS. 

The Exercise Price and the number of shares of Common Stock purchasable hereunder are subject to adjustment, as follows: 

(a) Merger Event. If at any time there shall be a 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 Common 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 Common 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 Common 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, 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. 
 (b) Reclassification of
Shares. Except for Merger Events subject to Sections 8(a), 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. 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 Common Stock, (i) in the case of a subdivision, the Exercise Price shall be proportionately decreased and the number of shares of Common 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 Common 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 Common Stock payable in Common 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 Common Stock outstanding immediately prior to such dividend or distribution, and (B) the denominator of which shall be the total number of shares of Common Stock outstanding immediately
after such dividend or distribution; or 

  
 4 

 (ii) make any other dividend or distribution with respect to Common Stock,
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 Common Stock as of the record date fixed for the determination of the stockholders of the Company entitled to receive such dividend or
distribution. 
 (e) 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; or (iii) 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 Common Stock shall be entitled thereto) or for determining rights to vote in respect of such Merger Event, dissolution, liquidation or winding up; and (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 Common Stock shall be entitled to exchange their Common Stock for
securities or other property deliverable upon such Merger Event, dissolution, liquidation or winding up). 
 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). 

(f) 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(e), 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 Common Stock. The Common Stock issuable upon exercise of the Warrantholder’s rights has been 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 Common 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 Common 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 Common 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 Common Stock 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 

  
 5 

 
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. 
 (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) Exempt Transaction. Subject to the accuracy of the Warrantholder’s representations in Section 10, the issuance of the
Common Stock upon exercise of this Agreement will 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. 
 (e) Compliance with Rule 144. The Company shall, at all times prior to the earlier to occur
of (i) the date of sale or other disposition by Warrantholder of this Warrant or all shares of Common Stock issued on exercise of this Warrant, or (ii) the expiration or earlier termination of this Warrant if the Warrant has not been
exercised in full or in part on such date, use all commercially reasonable efforts to timely file all reports required under the Exchange Act and otherwise timely take all actions necessary to permit the Warrantholder to sell or otherwise dispose of
this Warrant and the shares of Common Stock issued on exercise hereof pursuant to Rule 144 promulgated under the Act (“Rule 144”), provided that the foregoing shall not apply in the event of a Merger Event following which the successor or
surviving entity is not subject to the reporting requirements of the Exchange Act. If the Warrantholder proposes to sell Common Stock issuable upon the exercise of this Agreement 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. 
 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 Common 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 Common 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 Common 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) 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. 

  
 6 

 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. Notwithstanding anything herein to the contrary, the Company shall not require an opinion of counsel in connection with any sale, assignment or
other transfer by the Warrantholder of this Warrant (or any portion hereof or any interest herein) or of any shares of Common Stock issued upon any exercise hereof to an affiliate (as defined in Regulation D) of the Warrantholder, provided that such
affiliate is an “accredited investor” as defined in Regulation D. 
 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 shall 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. 

  
 7 

 (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:
legal@herculestech.com; bjadot@htgc.com 
 Telephone:
650-289-3060 
  

	(i)	 If to the Company: 

X4 Pharmaceuticals, Inc. 

Attention: Adam Mostafa and Brian Bowersox 

955 Massachusetts Avenue, 4th Floor 

Boston, MA 02139 
 Email:
adam.mostafa@x4pharma.com and brian.bowersox@x4pharma.com 
 Telephone:
617-542-6000 
 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. 

  
 8 

 (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. 
 (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 Common 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. 

  
 9 

 (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. 
 [Remainder of Page Intentionally Left Blank] 

  
 10 

 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:	 	 /s/ Adam Mostafa

		  	Name:	 	Adam Mostafa
		  	Title:	 	Chief Financial Officer
		
	 WARRANTHOLDER:
	  	HERCULES CAPITAL, INC.
			
		  	By:	 	 /s/ Jennifer Choe

		  	Name:	 	Jennifer Choe
		  	Title:	 	Assistant General Counsel

  
 11 

 EXHIBIT I 

NOTICE OF EXERCISE 
  

	To:	 X4 PHARMACEUTICALS, INC. 

 

	(1)	 The undersigned Warrantholder hereby elects to purchase [        ]
shares of the Common Stock of X4 Pharmaceuticals, Inc., pursuant to the terms of the Warrant Agreement, dated as of March 18, 2019 (the “Agreement”) between X4 Pharmaceuticals, Inc. 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 Common 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:	 	  

  
 12 

 EXHIBIT II 

ACKNOWLEDGMENT OF EXERCISE 
 The undersigned
[                    ], hereby acknowledges receipt of the “Notice of Exercise” from Hercules Capital, Inc., to purchase
[        ] shares of the Common Stock of X4 Pharmaceuticals, Inc., pursuant to the terms of the Warrant Agreement by and between X4 Pharmaceuticals, Inc. and Hercules Capital, Inc. dated as of March 18,
2019 (the “Agreement”), and further acknowledges that [    ] shares remain subject to purchase under the terms of the Agreement. 
  

					
	 COMPANY:
	  	X4 PHARMACEUTICALS, INC.
			
		  	By:	 	  

		  	Title:	 	  

		  	Date:	 	  

  
 13 

 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. 

  
 14

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