脑再生科技美股招股说明书(2026-03-30版)

Filed Pursuant to Rule 424(b)(5)Registration No. 333-294722 PROSPECTUS SUPPLEMENT(To Prospectus dated March 30, 2026) REGENCELL BIOSCIENCE HOLDINGS LIMITED Up to $500,000,000 of Ordinary Shares We have entered into a sales agreement, or Sales Agreement, with Univest Securities, LLC, or Univest or the Sales Agent, datedMarch 30, 2026, relating to an at-the-market offering, or ATM Facility, and the sale of our ordinary shares, par value $0.00001 pershare, or Ordinary Shares, offered by this prospectus supplement. In accordance with the terms of the Sales Agreement, under this Our Ordinary Shares trade on the Nasdaq Capital Market under the trading symbol “RGC.” On March 27, 2026, the last reportedclosing price of our Ordinary Shares on the Nasdaq Capital Market was $25.67 per Ordinary Shares. Sales of our Ordinary Shares, if any, under this prospectus supplement and the accompanying prospectus may be made by anymethod that is deemed an “at-the-market offering” as defined in Rule 415 under the Securities Act of 1933, as amended, or theSecurities Act, including, without limitation, sales made directly on or through the Nasdaq Capital Market, to or through a marketmaker or otherwise, and/or other methods permitted by law, including in privately negotiated transactions, in each case at marketprices prevailing at the time of sale or at prices related to such prevailing market prices. If we and the Sales Agent agree on any Under the Sales Agreement, the Sales Agent is not required to sell any specific number or dollar amount of securities but will actas our sales agent to cause the sale of our Ordinary Shares requested to be sold by us using commercially reasonable efforts, consistentwith its normal trading and sales practices and applicable state and federal laws, rules and regulations and the rules of the NasdaqStock Market, or the Nasdaq, on mutually agreed terms between the Sales Agent and us. There is no arrangement for funds to be The Sales Agent will be entitled to compensation at a fixed commission rate equal to a percentage of the gross proceeds from suchsale, determined in accordance with a tiered schedule based on cumulative gross proceeds. The applicable commission rates are: 2.5%of gross proceeds for cumulative sales from $0 up to $100,000,000; 2.0% for cumulative sales in excess of $100,000,000 up to$300,000,000; and 1.75% for cumulative sales in excess of $300,000,000 up to $500,000,000. The applicable percentage will be In connection with the sale of our Ordinary Shares on our behalf, the Sales Agent may be deemed to be an “underwriter” withinthe meaning of the Securities Act, and the compensation of the Sales Agent may be deemed to be underwriting commissions or Investing in our Ordinary Shares involves a high degree of risk. See “Risk Factors” beginning on page S-12 of thisprospectussupplement and in the documents incorporated by reference into this prospectus supplement and the We are an emerging growth company as that term is used in the Jumpstart Our Business Startups Act of 2012, and, as such, aresubject to certain reduced public company reporting requirements. See “Prospectus Supplement Summary — Implications of Being an We are a foreign private issuer within the meaning of the rules under the Securities Exchange Act of 1934, or the Exchange Act,and as such we are exempt from certain provisions of the securities rules and regulations in the United States that are applicable toU.S. domestic issuers, such as the rules regulating solicitation of proxies and certain insider reporting and short-swing profit rules.Moreover, the information we are required to file with or furnish to the SEC will be less extensive and less timely compared to that Neither the SEC nor any state securities commission nor any other regulatory body has approved or disapproved of thesesecurities or passed upon the adequacy or accuracy of this prospectus supplement, and those included in the accompanying Univest Securities, LLC The date of this prospectus supplement is March 30, 2026 You should rely only on the information contained or incorporated by reference into this prospectus supplement, theaccompanying prospectus, any free writing prospectus or any other offering materials we filed by us with the SEC. We havenot, and the Sales Agent has not, authorized any other person to provide you with different information. If anyone providesyou with different or inconsistent information, you should not rely on it. The information contained in, or incorporated byreference into, this prospectus supplement and the accompanying prospectus or any free writing prospectus is current only asof their respective dates. Our business, financial condition, results of operations and prospects may have changed since those ABOUT THIS PROSPECTUS SUPPLEMENT This prospectus supplement and the accompanying prospectus are part of a registration statement that we filed with the SECusing a “shelf” registration process. Under the shel