PepGen Inc美股招股说明书(2025-09-25版)

31,250,000 Shares of Common Stock We are offering 31,250,000 shares of our common stock in this offering. Our common stock is listed on the Nasdaq Global Select Market under the symbol “PEPG.” On September24, 2025, the closing sale price of ourcommon stock on the Nasdaq Global Select Market was $2.66 per share. We are an emerging growth company as that term is used in the Jumpstart Our Business Startups Act of 2012, or the JOBS Act, and a smaller reportingcompany as defined under Rule 405 of the Securities Act of 1933, as amended, or the Securities Act, and, as such, are subject to certain reduced publiccompany reporting requirements. See “Prospectus Supplement Summary—Implications of Being an Emerging Growth Company and a SmallerReporting Company” on pageS-2of this prospectus supplement. Investing in our securities involves a high degree of risk. Please read “Risk Factors” beginning on pageS-4of thisprospectus supplement, page9 in the accompanying prospectus, and under similar headings in the documents that areincorporated by reference into this prospectus supplement concerning factors you should carefully consider beforeinvesting in our securities. PerShareTotalPublic offering price$3.200$100,000,000Underwriting discounts and commissions(1)$0.192$6,000,000Proceeds, before expenses, to us$3.008$94,000,000 (1)See the section titled “Underwriting” beginning on pageS-17for a description of the compensation payable to the underwriters. We have granted the underwriters an option for a period of 30 days from the date of this prospectus supplement to purchase up to an additional4,687,500 shares of our common stock at the public offering price, less the underwriting discounts and commissions. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities, orpassed upon the adequacy or accuracy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is acriminal offense. The underwriters expect to deliver the shares of common stock against payment therefor on or about September26, 2025. Joint Book-Running Managers Leerink Partners Stifel The date of this prospectus supplement is September 24, 2025 Table of Contents TABLE OF CONTENTS PROSPECTUS SUPPLEMENT ABOUT THIS PROSPECTUS SUPPLEMENTCAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTSPROSPECTUS SUPPLEMENT SUMMARYRISK FACTORSDIVIDEND POLICYUSE OF PROCEEDSDILUTIONMATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES FOR INVESTORS IN COMMON STOCKUNDERWRITINGLEGAL MATTERSEXPERTSWHERE YOU CAN FIND MORE INFORMATIONINCORPORATION OF CERTAIN INFORMATION BY REFERENCE PROSPECTUS ABOUT THIS PROSPECTUSWHERE YOU CAN FIND MORE INFORMATIONINCORPORATION OF CERTAIN INFORMATION BY REFERENCESPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTSABOUT THE COMPANYRISK FACTORSUSE OF PROCEEDSDIVIDEND POLICYGENERAL DESCRIPTION OF SECURITIESDESCRIPTION OF CAPITAL STOCKDESCRIPTION OF DEBT SECURITIESDESCRIPTION OF WARRANTSDESCRIPTION OF UNITSPLAN OF DISTRIBUTIONLEGAL MATTERSEXPERTS Table of Contents ABOUT THIS PROSPECTUS SUPPLEMENT This prospectus supplement is part of a registration statement on FormS-3(FileNo.333-280570)that we filed with the Securities and ExchangeCommission, or SEC, using a “shelf” registration process on June28, 2024, which was declared effective on July8, 2024. This document has two parts.The first part is this prospectus supplement, which describes the specific terms of this offering of common stock. The second part is the accompanyingprospectus, which provides more general information, some of which may not apply to this offering. The information included or incorporated byreference in this prospectus supplement also adds to, updates and changes information contained or incorporated by reference in the accompanyingprospectus. If information included or incorporated by reference in this prospectus supplement is inconsistent with the accompanying prospectus or theinformation incorporated by reference therein, then this prospectus supplement or the information incorporated by reference in this prospectussupplement will apply and will supersede the information in the accompanying prospectus and the documents incorporated by reference therein.However, if any statement in one of these documents is inconsistent with a statement in another document with a later date that is incorporated byreference herein, the statement in the document having the later date modifies and supersedes the earlier statement. Before buying any of the shares of common stock offered hereby, we urge you to read carefully this prospectus supplement and the accompanyingprospectus, together with the information incorporated herein by reference as described below under the heading “Incorporation of Certain Informationby Reference,” as well as the additional information described in this prospectus supplement under “Where You Can Find More Information.” We further note that the rep