Entry into a Material Definitive Agreement. On August 28, 2026, Spero Therapeutics, Inc., a Delaware corporation (the “Company”), entered into an Open Market Sale Agreement℠ (the “Sale Agreement”) with Jefferies LLC, as agent (“Jefferies”), pursuant to which the Company may offer and sell shares (the “Shares”) of its common stock, $0.001 par value per share (the “Common Stock”), from time to time through Jefferies (the “Offering”). The Company has filed a universal shelf Registration Statemen…

and in the press release furnished as Exhibit 99.1 hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended, or incorporated by reference in any filing with the U.S. Securities and Exchange Commission made by the Company, whether made before or after the date hereof, regardless of any general incorporation langua…

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. The information set forth under “Royalty Financing Agreements” in

Other Events. Cash Runway Based upon the Company’s current plans and forecasted expenses, the Company estimates that the net proceeds from the royalty financing transaction, together with the Company’s existing cash and cash equivalents, will enable the Company to fund its operating expenses and capital expenditure requirements into the second half of 2029. The Company has based this estimate on assumptions that may prove to be wrong, and the Company could use its available capital resources…

Entry into a Material Definitive Agreement. Innovent License Agreement On July 8, 2026, Spero Therapeutics, Inc. (the “Company”) entered into a license agreement (the “Innovent Agreement”) with Innovent Biologics (Suzhou) Co., Ltd. and Fortvita Biologics (USA), Inc. (collectively, “Innovent”), pursuant to which Innovent granted the Company an exclusive (even as to Innovent and its affiliates, subject to Innovent’s right to directly or indirectly conduct certain research, non-clinical developm…

Approval of the 2026 Stock Incentive Plan

Other Events. On June 17, 2026, the Company issued a press release announcing that the FDA has granted approval for Utebzi (tebipenem pivoxil), an oral antibiotic for the treatment of cUTIs, including pyelonephritis, caused by certain susceptible pathogens in adult patients who have limited or no alternative oral treatment option. This is the first and only oral carbapenem antibiotic approved for these patients. This approval is a result of GSK’s development and exclusive global licensing agr…

and in the press release furnished as Exhibit 99.1 hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended, or incorporated by reference in any filing with the U.S. Securities and Exchange Commission made by the Company, whether made before or after the date hereof, regardless of any general incorporation langua…

and in the press release furnished as Exhibit 99.1 hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended, or incorporated by reference in any filing with the U.S. Securities and Exchange Commission made by the Company, whether made before or after the date hereof, regardless of any general incorporation langua…

Director — Ankit Mahadevia, MD: Dr. Mahadevia resigned due to other professional commitments.

Other Events. On December 19, 2025, Spero Therapeutics, Inc. (the “Company”) announced that its tebipenem HBr development partner, GlaxoSmithKline Intellectual Property (No. 3) Limited (“GSK”), filed a New Drug Application (“NDA”) resubmission to the U.S. Food and Drug Administration for tebipenem HBr, an investigational oral carbapenem antibiotic being developed for the treatment of complicated urinary tract infections (cUTI), including pyelonephritis. The NDA submission triggers a $25 milli…

and in the press release furnished as Exhibit 99.1 hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended (the “Securities Act”), or incorporated by reference in any filing with the U.S. Securities and Exchange Commission made by the Company, whether made before or after the date hereof, re…

and in the press release furnished as Exhibit 99.1 hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended (the “Securities Act”), nor shall it be deemed incorporated by reference in any filing under the Securities Act or the Exchange Act, except as expressly set forth by specific reference…

The filing is about an amendment to the Company’s stock incentive plan, not a management change.

Other Events. On May 28, 2025, the Company along with its development partner GSK plc (“GSK”) announced that the pivotal Phase 3 PIVOT-PO trial evaluating tebipenem HBr, an investigational oral treatment for cUTIs, including pyelonephritis, met its primary endpoint and will stop early for efficacy. The decision follows a recommendation from an Independent Data Monitoring Committee (“IDMC”) that completed a pre-specified interim analysis of data from 1,690 patients enrolled in the trial. The P…

and in the press release furnished as Exhibit 99.1 hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended, or incorporated by reference in any filing with the U.S. Securities and Exchange Commission made by the Company, whether made before or after the date hereof, regardless of any general incorporation langua…

President and Chief Executive Officer — Esther Rajavelu: Ms. Rajavelu was promoted from Interim President and CEO to permanent roles of President, CEO, while continuing as CFO and Treasurer.

and in the press release furnished as Exhibit 99.1 hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended, or incorporated by reference in any filing with the U.S. Securities and Exchange Commission made by the Company, whether made before or after the date hereof, regardless of any general incorporation langua…

Notice of Delisting or Failure to Satisfy a Continued Listing Rule or Standard; Transfer of Listing. On February 25, 2025, Spero Therapeutics, Inc., a Delaware corporation (the “Company”) received a deficiency letter (the “Deficiency Letter”) from the Listing Qualifications Department of the Nasdaq Stock Market, LLC (“Nasdaq”) notifying the Company that, for the preceding 30 consecutive trading days, the closing bid price of its common stock was below the $1.00 per share minimum bid price req…

Results of Operations and Financial Condition. On January 10, 2025, Spero Therapeutics, Inc. (the “Company”) issued a press release providing a corporate update, along with an updated investor presentation (each described below). In its press release, the Company disclosed that it had estimated cash and cash equivalents of approximately $52.9 million (unaudited) as of December 31, 2024. The Company estimates that its existing cash and cash equivalents, together with earned and non-contingent…

The filing appears to be introductory and does not specify any particular movement or event.

Other Events. SEC Investigation On January 9, 2025, the Company responded to a “Wells Notice” from the staff of the Boston Regional Office (“Staff”) of the U.S. Securities and Exchange Commission (the “SEC”) regarding its preliminary determination to recommend a civil enforcement action or administrative proceeding against the Company, its former Chief Executive Officer and current Chairman of the Board of Directors, Ankit Mahadevia, M.D. (“Dr. Mahadevia”), and its former Chief Financial Offi…

and in the press release furnished as Exhibit 99.1 hereto shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that Section or Sections 11 and 12(a)(2) of the Securities Act of 1933, as amended, or incorporated by reference in any filing with the U.S. Securities and Exchange Commission made by the Company, whether made before or after the date hereof, regardless of any general incorporation langua…

Costs Associated with Exit or Disposal Activities On October 29, 2024, the Company announced an update to its strategic priorities and corresponding reduction in workforce by approximately 39%. The reduction in force reflects the Company’s determination to refocus its strategic priorities around tebipenem HBr and other research and development efforts. The workforce reduction is expected to be substantially completed by the fourth quarter of 2024. The Company estimates that it will incur aggr…

Results of Operations and Financial Condition. On October 29, 2024, Spero Therapeutics, Inc. (the “Company”) issued a press release related to the restructuring of its operations, as described below in Item 2.05, in which it disclosed that it had estimated cash and cash equivalents of approximately $76.3 million as of September 30, 2024. A copy of the press release is filed as Exhibit 99.1 hereto. The estimated cash and cash equivalents as of September 30, 204 are preliminary and may change,…