Nature of the Business and Basis of Presentation	9 Months Ended
Sep. 30, 2022
Accounting Policies [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Spero Therapeutics, Inc., together with its consolidated subsidiaries (the “Company” or “Spero”), is a multi-asset, clinical-stage biopharmaceutical company focused on identifying, developing, and commercializing novel treatments for bacterial infections, including multi-drug resistant (“MDR”) bacterial infections, and rare diseases. The Company's lead product candidate, SPR720, is an oral antimicrobial agent in development for the treatment of nontuberculous mycobacterial (“NTM”) pulmonary disease, a rare orphan disease. The Company's partnership directed programs consist of SPR206 and tebipenem HBr, which through the Company's business development efforts, have partnership relationships supporting their ongoing development. SPR206 is an IV-administered agent being developed as an innovative option to treat MDR Gram-negative bacterial infections in the hospital setting. Tebipenem HBr is designed to be the first broad-spectrum oral carbapenem-class antibiotic for use to treat certain bacterial infections that cause complicated urinary tract infections (“cUTIs”) including pyelonephritis, caused by certain microorganisms, in adult patients who have limited oral treatment options. The Company is subject to risks and uncertainties common to companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, risks of failure or unsatisfactory results of nonclinical studies and clinical trials, the need to obtain marketing approval for its product candidates, the need to successfully commercialize and gain market acceptance of its product candidates and the ability to secure additional capital to fund operations. The Company’s product candidates will require additional preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. The pandemic caused by COVID-19 has resulted, and is likely to continue to result, in significant national and global economic disruption and may adversely affect our business. The Company has experienced impacts to its clinical and development timelines due to the worldwide spread of COVID-19 and its variants. However, to date, the Company has not experienced material impacts to liquidity, nor has it incurred impairment of any assets as a result of COVID-19 or its variants. The Company continues to monitor this situation and the possible effects on its business, results of operations and financial condition, including manufacturing, clinical trials, research and development costs and employee-related amounts. The accompanying consolidated financial statements of the Company have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its consolidated subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. Since inception, the Company has funded its operations with proceeds from sales of preferred units (including bridge units, which converted into preferred units), payments received in connection with its collaboration agreements, funding from government contracts, licensing agreements and through the sale of the Company’s common and preferred stock. The Company has incurred recurring losses since inception, including net losses of $11.7 million and $22.5 million for the three months ended September 30, 2022 and 2021, respectively, and $73.2 million and $60.5 million for the nine months ended September 30, 2022 and 2021, respectively. In addition, as of September 30, 2022, the Company had an accumulated deficit of $440.6 million. The Company expects to continue to generate operating losses for the foreseeable future. In accordance with Accounting Standards Update (“ASU”) 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40), the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the consolidated financial statements are issued. As of the issuance date of these quarterly consolidated financial statements, the Company expects its current operating plan, existing cash, cash equivalents and marketable securities and the initial upfront payments of $66.0 million the Company is entitled to receive under the GSK License Agreement and $9.0 million the Company received under the GSK SPA (as defined below) will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months from the issuance date of these quarterly consolidated financial statements. Beyond that point, the Company will require additional funding to fund the development of its product candidates through regulatory approval and commercialization, and to support its continued operations. The Company will seek additional funding through public or private financings, debt financing, collaboration agreements, government grants or other venues. The COVID-19 pandemic has resulted in ongoing volatility in financial markets. If our access to capital is restricted or associated borrowing costs increase as a result of developments in financial markets, including relating to the COVID-19 pandemic or its variants, our operations and financial condition could be adversely impacted. There is no assurance that the Company will be successful in obtaining sufficient funding on acceptable terms, if at all, and it could be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could materially adversely affect its business prospects or its ability to continue operations. The accompanying consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty. Accordingly, the consolidated financial statements have been prepared on a basis that assumes the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business. Interim Financial Information The consolidated balance sheet at December 31, 2021 was derived from audited financial statements, but does not include all disclosures required by GAAP. The accompanying unaudited condensed consolidated financial statements as of September 30, 2022, and for the three and nine months ended September 30, 2022, have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2021, included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2021, on file with the SEC. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of the Company’s financial position as of September 30, 2022, and results of operations for the three and nine months ended September 30, 2022, and cash flows for the nine months ended September 30, 2022 and 2021 have been made. The results of operations for the three and nine months ended September 30, 2022 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2022.

Nature of the Business and Basis of Presentation

9 Months Ended

Sep. 30, 2022

Nature of the Business and Basis of Presentation

1. Nature of the Business and Basis of Presentation

Spero Therapeutics, Inc., together with its consolidated subsidiaries (the “Company” or “Spero”), is a multi-asset, clinical-stage biopharmaceutical company focused on identifying, developing, and commercializing novel treatments for bacterial infections, including multi-drug resistant (“MDR”) bacterial infections, and rare diseases. The Company's lead product candidate, SPR720, is an oral antimicrobial agent in development for the treatment of nontuberculous mycobacterial (“NTM”) pulmonary disease, a rare orphan disease. The Company's partnership directed programs consist of SPR206 and tebipenem HBr, which through the Company's business development efforts, have partnership relationships supporting their ongoing development. SPR206 is an IV-administered agent being developed as an innovative option to treat MDR Gram-negative bacterial infections in the hospital setting. Tebipenem HBr is designed to be the first broad-spectrum oral carbapenem-class antibiotic for use to treat certain bacterial infections that cause complicated urinary tract infections (“cUTIs”) including pyelonephritis, caused by certain microorganisms, in adult patients who have limited oral treatment options.

The Company is subject to risks and uncertainties common to companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, risks of failure or unsatisfactory results of nonclinical studies and clinical trials, the need to obtain marketing approval for its product candidates, the need to successfully commercialize and gain market acceptance of its product candidates and the ability to secure additional capital to fund operations. The Company’s product candidates will require additional preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. The pandemic caused by COVID-19 has resulted, and is likely to continue to result, in significant national and global economic disruption and may adversely affect our business. The Company has experienced impacts to its clinical and development timelines due to the worldwide spread of COVID-19 and its variants. However, to date, the Company has not experienced material impacts to liquidity, nor has it incurred impairment of any assets as a result of COVID-19 or its variants. The Company continues to monitor this situation and the possible effects on its business, results of operations and financial condition, including manufacturing, clinical trials, research and development costs and employee-related amounts.

The accompanying consolidated financial statements of the Company have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of the Company and its consolidated subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.

Since inception, the Company has funded its operations with proceeds from sales of preferred units (including bridge units, which converted into preferred units), payments received in connection with its collaboration agreements, funding from government contracts, licensing agreements and through the sale of the Company’s common and preferred stock. The Company has incurred recurring losses since inception, including net losses of $11.7 million and $22.5 million for the three months ended September 30, 2022 and 2021, respectively, and $73.2 million and $60.5 million for the nine months ended September 30, 2022 and 2021, respectively. In addition, as of September 30, 2022, the Company had an accumulated deficit of $440.6 million. The Company expects to continue to generate operating losses for the foreseeable future.

In accordance with Accounting Standards Update (“ASU”) 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40), the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the consolidated financial statements are issued. As of the issuance date of these quarterly consolidated financial statements, the Company expects its current operating plan, existing cash, cash equivalents and marketable securities and the initial upfront payments of $66.0 million the Company is entitled to receive under the GSK License Agreement and $9.0 million the Company received under the GSK SPA (as defined below) will be sufficient to fund its operating expenses and capital expenditure requirements for at least 12 months from the issuance date of these quarterly consolidated financial statements. Beyond that point, the Company will require additional funding to fund the development of its product candidates through regulatory approval and commercialization, and to support its continued operations. The Company will seek additional funding through public or private financings, debt financing, collaboration agreements, government grants or other venues. The COVID-19 pandemic has resulted in ongoing volatility in financial markets. If our access to capital is restricted or associated borrowing costs increase as a result of developments in financial markets, including relating to the COVID-19 pandemic or its variants, our operations and financial condition could be adversely impacted. There is no assurance that the Company will be successful in obtaining sufficient funding on acceptable terms, if at all, and it could be

forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could materially adversely affect its business prospects or its ability to continue operations.

The accompanying consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty. Accordingly, the consolidated financial statements have been prepared on a basis that assumes the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business.

Interim Financial Information

The consolidated balance sheet at December 31, 2021 was derived from audited financial statements, but does not include all disclosures required by GAAP. The accompanying unaudited condensed consolidated financial statements as of September 30, 2022, and for the three and nine months ended September 30, 2022, have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2021, included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2021, on file with the SEC. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of the Company’s financial position as of September 30, 2022, and results of operations for the three and nine months ended September 30, 2022, and cash flows for the nine months ended September 30, 2022 and 2021 have been made. The results of operations for the three and nine months ended September 30, 2022 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2022.