Enforcement and Defense. In the event that Northern or Spero becomes aware of a suspected infringement of any Northern Patent Right, or any such Northern Patent Right is challenged in any action or proceeding (other than any interferences, oppositions, reissue proceedings or reexaminations, which are addressed above), such Party shall notify the other Party promptly, and following such notification, the Parties shall confer. Except as otherwise provided below, Spero shall have the right, but shall not be obligated, to defend any such action or proceeding or bring an infringement action with respect to such infringement at its own expense, in its own name and entirely under its own direction and control, or settle any such action or proceeding by sublicense; provided that, if there exists an issued SC Patent to serve as the basis of the infringement action in connection with such Third Party activities, Spero will limit its enforcement action to such SC Patent if so doing does not materially decrease Spero’s likelihood of success. Prior to initiating an enforcement action that uses a Northern Patent Right other than an SC Patent as the basis for the claim of infringement, Spero shall meet with Northern to discuss ways to manage the potential risk to such Northern Patent Right in connection with such enforcement action, including limiting the number and scope of claims that are asserted in connection with such action. Spero shall use good faith efforts to employ any reasonable measures agreed to by the Parties to manage such potential risk. Northern shall reasonably assist Spero in any action or proceeding being defended or prosecuted if so requested, and shall join such action or proceeding if reasonably requested by Spero or required by applicable law at Spero’s expense. After Spero has recovered an amount equal to the cost it incurred in connection with any such action or proceeding, any remaining and received amounts of compensation and/or damages paid by a third party as awarded to Spero due to the above action or proceeding shall be shared ​ percent (​) to Spero and ​ percent (​) to Northern. With respect to infringements arising out of the activities of a Third Party with a compound that is an Other Compound, Northern shall have the right, but shall not be obligated, to defend any such action or proceeding or bring an infringement action with respect to such

infringement at its own expense, in its own name and entirely under its own direction and control, or settle any such action or proceeding by sublicense; provided that, if there exists an issued OC Patent to serve as the basis of the infringement action in connection with such Third Party activities, Northern will limit its enforcement action to such OC Patent if so doing does not materially decrease Northern’s likelihood of success and the roles of the Parties under this Section 5.3 shall be reversed, solely with respect to such action. Prior to initiating an enforcement action that uses a Northern Patent Right other than an OC Patent as the basis for the claim of infringement, Northern shall meet with Spero to discuss ways to manage the potential risk to such Northern Patent Right in connection with such enforcement action, including limiting the number and scope of claims that are asserted in connection with such action. Northern shall use good faith efforts to employ any reasonable measures agreed to by the Parties to manage such potential risk.

By Northern. Spero shall not knowingly permit any of the Northern Patent Rights to be abandoned in any country or their scope to be unreasonably limited (for example, to exclude Other Compounds) without Northern first being given an opportunity to assume full responsibility for the continued prosecution and maintenance of same. In the event that Spero decides not to continue the prosecution or maintenance of a patent application or patent within Northern Patent Rights in any country, Spero shall provide Northern with notice of this decision at least ​ prior to any pending lapse or abandonment thereof. Northern shall have the right to assume control of the continued prosecution or maintenance of any such patent application or patent (excluding any SC Patents) provided that Northern shall, if so requested by Spero, take such actions as may be reasonably requested by Spero to amend such patent applications or patents, to the extent feasible under applicable laws and regulations, to narrow the scope thereof so that such patent applications and patents no longer claim Licensed Compounds if such amendment is feasible without excluding Other Compounds from being so claimed. In the event that Northern elects to assume responsibility for such prosecution and maintenance within ​ of Spero’s notice, Section 5.2(a) shall thereafter apply to such patent application(s) and patent(s) except that the role of Spero and Northern shall be reversed thereunder, including that Northern shall be solely responsible for all costs arising from those activities and hence it shall be also deemed that the exclusive, even as to Spero, rights to said patent(s) and patent application(s) return to the full discretion of Northern and Northern shall redeem all its rights back to its ownership with the purchase price of one US dollar.

By Spero. Within ​ of the Effective Date, Northern shall mandate its patent attorneys (​, and ​) to provide Spero, at Spero’s cost, with copies of the complete prosecution files for all patents and patent applications listed on Exhibit C. Spero shall be solely responsible for the preparation, prosecution (including any interferences, oppositions, reissue proceedings and reexaminations) and maintenance of the Northern Patent Rights, and all filing, prosecution, and maintenance decisions with respect to the Northern Patent Rights shall be made by Spero, provided Northern shall retain the right to give comments to Spero on material aspects of those activities. Spero shall be responsible for all its costs incurred for such preparation, prosecution and maintenance. Each Party shall provide to the other Party copies of any papers relating to the filing, prosecution or maintenance of Northern Patent Rights promptly upon receipt. Northern shall not take any action with respect to the prosecution or maintenance of any Northern Patent Rights without the prior written consent of Spero, except as contemplated by Section 5.2(b). In addition to the foregoing, promptly following the Effective Date, Spero and Northern shall use reasonable best efforts to work together to prepare and file, where permitted under applicable laws and regulations, continuation applications, divisional applications or such other applications or filings related to the Northern Patent Rights that claim solely Other Compounds and their uses (such applications or filings and any patents issuing therefrom are the “OC Patents”). Spero shall pay the first ​ in out-of-pocket expenses incurred in connection with the preparation and filing of such patent applications and filings and thereafter the Parties shall ​ such costs and expenses. The OC Patents shall not be included in the Northern Patent Rights for any other purposes under this Agreement. For avoidance of doubt, as between the Parties, Northern and its designees shall have sole authority to pursue the further prosecution, maintenance and enforcement of the OC Patents. Furthermore, in an identical fashion, following the Effective Date, Spero and Northern shall use reasonable best efforts to work together, at Spero’s sole expense, to prepare and file, where permitted under applicable laws and regulations, continuation applications, divisional applications or such other applications or filings related to the Northern Patent Rights that do not claim any Other Compounds or their uses (such applications or filings and any patents issuing therefrom are the “SC Patents”. For avoidance of doubt, as between the Parties, Spero and its designees shall have sole authority to pursue the further prosecution, maintenance and enforcement of the SC Patents.