Adicet Bio Inc美股招股说明书(2025-10-07版)

70,001,000 Shares of Common Stock Pre-Funded Warrants to Purchase 10,000,000 Shares of Common Stock We are offering 70,001,000 shares of our common stock, par value $0.0001 per share (the common stock), and, in lieu of common stock to certaininvestors that so choose, pre-funded warrants to purchase 10,000,000 shares of common stock (the pre-funded warrants), in a registered direct offering to alimited number of investors pursuant to this prospectus supplement and the accompanying prospectus. The purchase price of each pre-funded warrantequals the price per share at which shares of common stock are being sold in this offering, minus $0.0001, which is the exercise price of each pre-fundedwarrant. This prospectus supplement also relates to the offering of the shares of common stock issuable upon exercise of such pre-funded warrants. Our common stock is listed on the Nasdaq Global Market under the symbol “ACET.” On October 6, 2025, the last reported sale price of our commonstock was $1.00 per share. There is no established public trading market for the pre-funded warrants, and we do not expect a market to develop. Inaddition, we do not intend to apply for a listing of the pre-funded warrants on the Nasdaq Global Market, any other national securities exchange or anyother nationally recognized trading system. Investing in our securities involves a high degree of risk.You should carefully review the risks and uncertainties referenced under the heading“Risk Factors” beginning on page S-11of this prospectus supplement and in the documents incorporated by reference into this prospectussupplement. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities ordetermined if this prospectus supplement or accompanying prospectus is truthful or complete. Any representation to the contrary is a criminaloffense. (1)We have agreed to reimburse the underwriters for certain expenses. See the section titled “Underwriting” for additional disclosure regardingunderwriter compensation and estimated offering expenses. Delivery of the securities is expected to be made on or about October 8, 2025. Joint Book-Running Managers Jefferies Guggenheim Securities Joint BookrunnerTruist Securities Lead Managers H.C. Wainwright & Co. The date of this prospectus supplement is October 7, 2025 TABLE OF CONTENTS PROSPECTUS SUPPLEMENT PageAbout this Prospectus SupplementS-iCautionary Statement Regarding Forward-Looking StatementsS-1Prospectus Supplement SummaryS-3The OfferingS-9Risk FactorsS-11Use of ProceedsS-15Dividend PolicyS-16DilutionS-17Material U.S. Federal Income Tax Considerations For Investors in Common Stock and Pre-Funded WarrantsS-19Description of Pre-Funded WarrantsS-25UnderwritingS-27Legal MattersS-34ExpertsS-34Where You Can Find More InformationS-34Incorporation by ReferenceS-35 PROSPECTUS About this ProspectusRisk FactorsCautionary Statement Regarding Forward-Looking StatementsThe CompanyUse of ProceedsSecurities We May OfferDescription of Capital StockDescription of Debt SecuritiesDescription of WarrantsDescription of UnitsPlan of DistributionLegal MattersExpertsWhere You Can Find More InformationIncorporation by Reference ABOUT THIS PROSPECTUS SUPPLEMENT This document is part of the registration statement that we filed with the Securities and Exchange Commission (SEC), usinga “shelf” registration process and consists of two parts. The first part is this prospectus supplement, including the documentsincorporated by reference, which describes the specific terms of this offering. The second part, the accompanying prospectus datedMarch 6, 2025, included in our registration statement on Form S-3 (File No. 333-285609), as amended, including the documentsincorporated by reference, gives more general information, some of which may not apply to this offering. Generally, when we referto the “prospectus,” we are referring to both parts combined. This prospectus supplement and any related free writing prospectuswe authorize for use in connection with this offering may add to, update or change information in the accompanying prospectusand the documents incorporated by reference into this prospectus supplement or the accompanying prospectus. If information in this prospectus supplement is inconsistent with the accompanying prospectus or with any documentincorporated by reference that was filed with the SEC before the date of this prospectus supplement, you should rely on thisprospectus supplement. This prospectus supplement, the accompanying prospectus, the documents incorporated by reference intoeach and any free writing prospectus we authorize for use in connection with this offering include important information about us,the common stock, pre-funded warrants and other information you should consider before investing in the common stock or pre-funded warrants. See “Incorporation by Reference.” Before buying any of the shares of common stock or pre-fu