Form of Lock-Up Agreement, by each of the parties named in each agreement therein

Exhibit 2.3

FORM OF LOCK-UP AGREEMENT

AUGUST 5, 2019

This Lock-Up Agreement (this “Agreement”) is executed in connection with the Agreement and Plan of Merger (the “Merger Agreement”) by and among Aquinox Pharmaceuticals, Inc., a Delaware corporation (the “Parent”), Apollo Sub, Inc., a Delaware corporation and wholly owned subsidiary of Parent (“Merger Sub”), and Neoleukin Therapeutics, Inc., a Delaware corporation (the “Company”), dated as of August 5, 2019. Capitalized terms used herein but not defined shall have the meanings ascribed to such terms in the Merger Agreement.

In connection with, and as an inducement to, the parties entering into the Merger Agreement and for other good and valuable consideration the receipt and sufficiency of which is hereby acknowledged, the undersigned, by executing this Agreement, agrees that, without the prior written consent of the Parent and the Company, during the period commencing on the date hereof and continuing until the end of the Lock-Up Period (as hereinafter defined), the undersigned will not: (1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, make any short sale or otherwise transfer or dispose of or lend, directly or indirectly, any shares of Common Stock, $0.000001 par value per share, of Parent (the “Parent Common Stock”) or any securities convertible into, exercisable or exchangeable for or that represent the right to receive Parent Common Stock (including without limitation, Parent Common Stock which may be deemed to be beneficially owned by the undersigned in accordance with the rules and regulations of the Securities and Exchange Commission and securities which may be issued upon exercise of a stock option or warrant) whether now owned or hereafter acquired (the “Securities”); (2) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of the Securities, whether any such transaction described in clause (1) or (2) above is to be settled by delivery of Parent Common Stock or such other securities, in cash or otherwise; (3) make any demand for or exercise any right with respect to, the registration of any Parent Common Stock or any security convertible into or exercisable or exchangeable for Parent Common Stock; (4) except for the Parent Stockholder Support Agreement, grant any proxies or powers of attorney with respect to any Securities, deposit any Securities into a voting trust or enter into a voting agreement or similar arrangement or commitment with respect to any Securities; or (5) publicly disclose the intention to do any of the foregoing (each of the foregoing restrictions, the “Lock- Up Restrictions”).

Notwithstanding the terms of the foregoing paragraph, this Agreement and the Lock-Up Restrictions shall automatically terminate and cease to be effective on the date that is the earlier to occur of (i) the date of approval of the Parent Stockholder Matters by the stockholders of Parent, (ii) November 13, 2019 (such date, as the same may be extended, the “Lock-Up Outside Date”), provided, however, that such date may be extended one time by 30 calendar days if: (1) despite Parent’s good faith efforts to obtain the approval of Parent’s stockholders to the Parent Stockholder Matters, Parent has not obtained such approval of the Parent Stockholders’ Matters by the original Lock-Up Outside Date, and (2) Parent determines in good faith (and confirms in writing to the undersigned that it has so determined in a certificate executed on behalf of the Company by either the Chief Executive Officer or the Chief Financial

Officer thereof) that there is a reasonable prospect for obtaining such approval during such 30-day extension period; provided, further, that in no event shall the Lock-Up Outside Date, as extended, be later than December 13, 2019, after which this agreement shall automatically terminate and cease to be effective, (iii) the date of any amendment to the Merger Agreement (including any schedule or Exhibit thereto), or any action that would reasonably be expected to result in the amendment or modification, or a waiver of a provision therein in a manner that (A) alters or changes the amount or kind of consideration to be paid to the Company’s stockholders in connection with the Merger, (B) adversely affects the tax consequences of the Merger to Stockholder or (C) impedes or delays the consummation of the Merger, (iv) the date of any amendment to the terms of the Parent Convertible Preferred Stock, (v) the date of termination of the Parent Stockholder Support Agreement to which the undersigned is a party, (vi) the date of termination of the Merger Agreement or (vii) the mutual agreement of Parent and the undersigned to terminate this Agreement. The period during which the Lock-Up Restrictions apply to the Securities shall be deemed the “Lock-Up Period” with respect thereto.

The undersigned agrees that the Lock-Up Restrictions preclude the undersigned from engaging in any hedging or other transaction with respect to any then-subject Securities which is designed to or which reasonably could be expected to lead to or result in a sale or disposition of such Securities even if such Securities would be disposed of by someone other than the undersigned. Such prohibited hedging or other transactions would include without limitation any short sale or any purchase, sale or grant of any right (including without limitation any put or call option) with respect to such Securities or with respect to any security that includes, relates to, or derives any significant part of its value from such Securities.

Notwithstanding the foregoing, the undersigned may transfer any of the Securities (i) as a bona fide gift or charitable contribution, (ii) to any trust for the direct or indirect benefit of the undersigned or the immediate family of the undersigned, (iii) if the undersigned is a corporation, partnership, limited liability company, trust or other business entity (1) to another corporation, partnership, limited liability company, trust or other business entity that is a direct or indirect affiliate (as defined in Rule 405 promulgated under the Securities Act of 1933, as amended) of the undersigned or (2) as distributions or dividends of shares of Parent Common Stock or any security convertible into or exercisable for Parent Common Stock to limited partners, limited liability company members or stockholders of the undersigned or holders of similar equity interests in the undersigned, (iv) if the undersigned is a trust, to the beneficiary of such trust, (v) by testate succession or intestate succession, (vi) to any immediate family member, any investment fund, family partnership, family limited liability company or other entity controlled or managed by the undersigned, (vii) to a nominee or custodian of a person or entity to whom a disposition or transfer would be permissible under clauses (i) through (vi), (viii) to Parent in a transaction exempt from Section 16(b) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”) upon a vesting event of the Securities or upon the exercise of options to purchase Parent Common Stock on a “cashless” or “net exercise” basis or to cover tax withholding obligations of the undersigned in connection with such vesting or exercise (but for the avoidance of doubt, excluding all manners of exercise that would involve a sale in the open market of any securities relating to such options, whether to cover the applicable aggregate exercise price, withholding tax obligations or otherwise), (ix) to Parent in connection with the termination of employment or other termination of a service provider and pursuant to agreements in effect as of the Effective Time whereby Parent has the option to repurchase such shares or securities, (x) acquired by the undersigned in open market transactions after the Effective Time, (xi) pursuant to a bona fide third party tender offer, merger, consolidation, share purchase, business combination or other similar

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transaction made to all holders of the Parent’s capital stock involving a change of control of the Parent, provided that in the event that such tender offer, merger, consolidation, share purchase, business combination or other such transaction is not completed, the Securities shall remain subject to the restrictions contained in this Agreement, or (xii) pursuant to an order of a court or regulatory agency; provided, in the case of clauses (i)-(vii), that (A) such transfer shall not involve a disposition for value and (B) the transferee agrees in writing with Parent to be bound by the terms of this Agreement; and provided, further, in the case of clauses (i)-(x), no filing by any party under Section 16(a) of the Exchange Act shall be required or shall be made voluntarily in connection with such transfer. For purposes of this Agreement, “immediate family” shall mean any relationship by blood, marriage or adoption, not more remote than first cousin.

In addition, the foregoing restrictions shall not apply to (i) the exercise of stock options granted pursuant to equity incentive plans existing immediately following the Effective Time, including the “net” exercise of such options in accordance with their terms and the surrender of Parent Common Stock in lieu of payment in cash of the exercise price and any tax withholding obligations due as a result of such exercise (but for the avoidance of doubt, excluding all manners of exercise that would involve a sale in the open market of any securities relating to such options, whether to cover the applicable aggregate exercise price, withholding tax obligations or otherwise); provided that it shall apply to any of the Securities issued upon such exercise, or (ii) the establishment of any contract, instruction or plan (a “Plan”) that satisfies all of the requirements of Rule 10b5-1(c)(1)(i)(B) under the Exchange Act; provided that no sales of the Securities shall be made pursuant to such a Plan prior to the expiration of the Lock-Up Period, and such a Plan may only be established if no public announcement of the establishment or existence thereof and no filing with the Securities and Exchange Commission or other regulatory authority in respect thereof or transactions thereunder or contemplated thereby, by the undersigned, Parent or any other person, shall be required, and no such announcement or filing is made voluntarily, by the undersigned, Parent or any other person, prior to the expiration of the applicable Lock-Up Period.

Any attempted transfer in violation of this Agreement will be of no effect and null and void, regardless of whether the purported transferee has any actual or constructive knowledge of the transfer restrictions set forth in this Agreement, and will not be recorded on the share register of Parent. In furtherance of the foregoing, Parent and its transfer agent and registrar are hereby authorized to decline to make any transfer of shares of Parent Common Stock if such transfer would constitute a violation or breach of this Agreement.

The undersigned hereby represents and warrants that the undersigned has full power and authority to enter into this Agreement and that upon request, the undersigned will execute any additional documents reasonably necessary to ensure the validity or enforcement of this Agreement. All authority herein conferred or agreed to be conferred and any obligations of the undersigned shall be binding upon the successors, assigns, heirs or personal representatives of the undersigned.

The undersigned understands that Parent, the Merger Sub and the Company are entering into the Merger Agreement in reliance upon this Agreement. The undersigned further understands that this letter agreement is irrevocable and shall be binding upon the undersigned’s heirs, legal representatives, successors and assigns.

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This Agreement and any claim, controversy or dispute arising under or related to this Agreement shall be governed by, and construed in accordance with, the laws of the State of Delaware, without regard to the conflict of laws principles thereof.

(Signature Page Follows)

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This Agreement, and any certificates, documents, instruments and writings that are delivered pursuant hereto, constitutes the entire agreement and understanding of the Parent, the Company and the undersigned in respect of the subject matter hereof and supersedes all prior understandings, agreements or representations by or among the Parent, the Company and the undersigned, written or oral, to the extent they relate in any way to the subject matter hereof. The delivery of a fully executed Agreement (in counterparts or otherwise) by the undersigned by facsimile or electronic transmission in .pdf format shall be sufficient to bind the undersigned to the terms and conditions of this Agreement.