{"url_path":"/sec/spro/proxy/2026-04-27/000119312526182256","section_key":"body","section_title":"DEFA14A body","topic":"sec","document":{"doc_type":"DEFA14A","doc_date":"2026-04-27","source_url":"https://www.sec.gov/Archives/edgar/data/1701108/0001193125-26-182256-index.html","accession_number":"0001193125-26-182256","cik":"0001701108","ticker":"SPRO","issuer_name":"Spero Therapeutics, Inc.","edgar_url":"https://www.sec.gov/Archives/edgar/data/1701108/0001193125-26-182256-index.html","primary_entity_key":"0001701108","primary_entity_name":"Spero Therapeutics, Inc."},"word_count":504,"has_tables":true,"body_markdown":"DEFA14A\n1\nd120525ddefa14a.htm\nDEFA14A\n\nDEFA14A\n\n**UNITED STATES**\n\n**SECURITIES AND EXCHANGE COMMISSION**\n\n**WASHINGTON, D.C. 20549**\n\n**SCHEDULE 14A**\n\n**Proxy\nStatement Pursuant to Section 14(a) of the**\n\n**Securities Exchange Act of 1934**\n\n**(Amendment No. )**\n\nFiled by the\nRegistrant ☒        Filed by a Party other than the Registrant ☐\n\nCheck the appropriate\nbox:\n\n☐\n\nPreliminary Proxy Statement\n\n☐\n\n**Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))**\n\n☐\n\nDefinitive Proxy Statement\n\n☒\n\nDefinitive Additional Materials\n\n☐\n\nSoliciting Material Under §240.14a-12\n\n**Spero\nTherapeutics, Inc.**\n\n**(Name of Registrant as Specified in its Charter)**\n\n**(Name of Person(s) Filing Proxy Statement, if other than the Registrant)**\n\nPayment of Filing Fee (Check the appropriate box all boxes that apply):\n\n☒\n\nNo fee required.\n\n☐\n\nFee paid previously with preliminary materials.\n\n☐\n\nFee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-1.\n\nYou invested in SPERO\nTHERAPEUTICS, INC. and it’s time to vote!\n\nYou have the right to vote on proposals being presented at the Annual\nMeeting. **This is an important notice regarding the availability of proxy materials for the stockholder meeting to be held on June 23, 2026.**\n\nGet informed before you vote\n\nView the Notice and Proxy Statement and Form 10-K online OR you can receive a free paper or email copy of the material(s) by\nrequesting prior to June 9, 2026. If you would like to request a copy of the material(s) for this and/or future stockholder meetings, you may (1) visit www.ProxyVote.com, (2) call 1-800-579-1639 or (3) send an email to sendmaterial@proxyvote.com. If\nsending an email, please include your control number (indicated below) in the subject line. Unless requested, you will not otherwise receive a paper or email copy.\n\n*Please check the meeting materials for any special requirements for meeting attendance.\n\n**Vote at www.ProxyVote.com**\n\n**THIS IS NOT A VOTABLE BALLOT**\n\nThis is an overview of the proposals being presented at the\n\nupcoming stockholder meeting. Please follow the\ninstructions on\n\nthe reverse side to vote these important matters.\n\n** Voting Items**\n\n**Board**\n\n**Recommends**\n\n 1.\n\nTo elect two Class III directors to serve until the Company’s 2029 Annual Meeting of Stockholders or until their respective successors are elected and qualified.\n\n**Nominees:**\n\n 1a.\n\nMilind Deshpande, Ph.D.\n\n**For**\n\n 1b.\n\nKathleen Tregoning\n\n**For**\n\n 2.\n\nTo ratify the appointment of PricewaterhouseCoopers LLP as the Company’s independent registered public accounting firm for the\nfiscal year ending December 31, 2026.\n\n**For**\n\n 3.\n\nTo approve by an advisory vote the compensation of the Company’s named executive officers, as disclosed in the proxy\nstatement.\n\n**For**\n\n 4.\n\nTo approve an amendment to the Company’s Amended and Restated Certificate of Incorporation to increase the total number of shares\nof common stock authorized for issuance thereunder from 120,000,000 shares to 240,000,000 shares.\n\n**For**\n\n 5.\n\nTo approve adoption of the 2026 Spero Therapeutics, Inc. Stock Incentive Plan.\n\n**For**\n\n**NOTE:**To transact such\nother business that is properly presented at the annual meeting and any adjournments or postponements thereof.\n\nPrefer to receive an email instead? While voting on www.ProxyVote.com, be sure to click “Delivery Settings”.\n\nV94175-P48493"}