Commitments and Contingencies	6 Months Ended
Jun. 30, 2022
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies License Agreements The Company has entered into license agreements with various parties under which it is obligated to make contingent and non-contingent payments (see Note 9). Operating Leases The Company has entered into an operating lease agreement with U.S. REIF Central Plaza Massachusetts, LLC with respect to its corporate headquarters located at 675 Massachusetts Avenue, Cambridge, Massachusetts. Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not aware of any claims under indemnification arrangements that will have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of June 30, 2022 or December 31, 2021. Legal Proceedings Two putative class action lawsuits have been filed against the Company and certain of its officers in the United States District Court for the Eastern District of New York, one captioned Richard S. Germond v. Spero Therapeutics, Inc., Ankit Mahadevia, and Satravrat Shukla, Case No. 1:22-cv-03125, filed on May 26, 2022, and the other captioned Kashif Memon v. Spero Therapeutics, Inc., Ankit Mahadevia, and Satyavrat Shukla Case No. 1:22-cv-04154, filed on July 15, 2022. Each complaint purports to be brought on behalf of stockholders who purchased the Company’s common stock, with the first complaint having a time period of October 28, 2021 through May 2, 2022 and the second having a time period of May 6, 2021 through May 2, 2022. Each complaint generally alleges that the Company and certain of its officers violated Sections 10(b) and/or 20(a) of the Securities Exchange Act of 1934 and Rule 10b-5 promulgated thereunder by making allegedly false and/or misleading statements concerning the New Drug Application for tebipenem HBr in an effort to lead investors to believe that the drug would receive approval from the FDA. Each complaint seeks unspecified damages, interest, attorneys’ fees, and other costs. On July 25, 2022, a motion was filed to consolidate the lawsuits into one action. On July 26, 2022, Plaintiff Memon filed a motion for appointment of lead plaintiff/lead counsel. Also on July 26, 2022, stockholder Nabil Saad filed a motion for appointment of lead plaintiff/lead counsel. The Company denies any allegations of wrongdoing and intends to vigorously defend against these lawsuits. However, there is no assurance that the Company will be successful in its defense or that insurance will be available or adequate to fund any settlement or judgment or the litigation costs of these actions. Moreover, the Company is unable to predict the outcomes or reasonably estimate a range of possible loss at this time. Additional lawsuits against the Company and certain of its officers or director may be filed in the future. If additional similar complaints are filed, absent new or different allegations that are material, the Company will not necessarily announce such additional filings.

Commitments and Contingencies

6 Months Ended

Jun. 30, 2022

Commitments and Contingencies Disclosure [Abstract]

7. Commitments and Contingencies

License Agreements

The Company has entered into license agreements with various parties under which it is obligated to make contingent and non-contingent payments (see Note 9).

Operating Leases

The Company has entered into an operating lease agreement with U.S. REIF Central Plaza Massachusetts, LLC with respect to its corporate headquarters located at 675 Massachusetts Avenue, Cambridge, Massachusetts.

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not aware

of any claims under indemnification arrangements that will have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its consolidated financial statements as of June 30, 2022 or December 31, 2021.

Legal Proceedings

Two putative class action lawsuits have been filed against the Company and certain of its officers in the United States District Court for the Eastern District of New York, one captioned Richard S. Germond v. Spero Therapeutics, Inc., Ankit Mahadevia, and Satravrat Shukla, Case No. 1:22-cv-03125, filed on May 26, 2022, and the other captioned Kashif Memon v. Spero Therapeutics, Inc., Ankit Mahadevia, and Satyavrat Shukla Case No. 1:22-cv-04154, filed on July 15, 2022. Each complaint purports to be brought on behalf of stockholders who purchased the Company’s common stock, with the first complaint having a time period of October 28, 2021 through May 2, 2022 and the second having a time period of May 6, 2021 through May 2, 2022. Each complaint generally alleges that the Company and certain of its officers violated Sections 10(b) and/or 20(a) of the Securities Exchange Act of 1934 and Rule 10b-5 promulgated thereunder by making allegedly false and/or misleading statements concerning the New Drug Application for tebipenem HBr in an effort to lead investors to believe that the drug would receive approval from the FDA. Each complaint seeks unspecified damages, interest, attorneys’ fees, and other costs. On July 25, 2022, a motion was filed to consolidate the lawsuits into one action. On July 26, 2022, Plaintiff Memon filed a motion for appointment of lead plaintiff/lead counsel. Also on July 26, 2022, stockholder Nabil Saad filed a motion for appointment of lead plaintiff/lead counsel. The Company denies any allegations of wrongdoing and intends to vigorously defend against these lawsuits. However, there is no assurance that the Company will be successful in its defense or that insurance will be available or adequate to fund any settlement or judgment or the litigation costs of these actions. Moreover, the Company is unable to predict the outcomes or reasonably estimate a range of possible loss at this time.

Additional lawsuits against the Company and certain of its officers or director may be filed in the future. If additional similar complaints are filed, absent new or different allegations that are material, the Company will not necessarily announce such additional filings.