REGENXBIO Announces Proposed Public Offering of Common Stock

REGENXBIO Inc. (Nasdaq: RGNX ) today announced that it intends to offer and sell, subject to market conditions, $100 million of its common stock in an underwritten public offering.

The offering is subject to market and other conditions, and there can be no assurance as to whether or when the offering may be completed, or the actual size or terms of the offering.

In addition, REGENXBIO intends to grant the underwriters a 30-day option to purchase additional common shares in an amount of up to 15% of the number of common shares sold in connection with the offering.

Morgan Stanley, J.P. Morgan, Leerink Partners and Mizuho are acting as joint book-running managers of the offering.

The securities described above are being offered by REGENXBIO pursuant to a shelf registration statement on Form S-3 that was filed with the Securities and Exchange Commission (the "SEC") on November 26, 2025 (File No. 333-291816) and declared effective on December 12, 2025.

A preliminary prospectus supplement relating to and describing the terms of the offering will be filed with the SEC and will be available on the SEC's website at www.sec.gov .

Copies of the preliminary prospectus supplement and the accompanying prospectus relating to this offering, when available, may be obtained from: Morgan Stanley & Co. LLC, Attention: Prospectus Department, 180 Varick Street, 2nd Floor, New York, NY 10014, or by email at [email protected] ; J.P. Morgan Securities LLC, c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, New York 11717 or by email at [email protected] and [email protected] ; Leerink Partners LLC, Attention: Syndicate Department, 53 State Street, 40th Floor, Boston, MA 02109, or by telephone at 1 (800) 808-7525, ext. 6105, or by email at [email protected] ; Mizuho Securities USA LLC, Attention: Equity Capital Markets, 1271 Avenue of the Americas, 3rd Floor, New York, NY 10022, by telephone (212) 205-7600, or by email: [email protected] .

The final terms of the offering will be disclosed in a final prospectus supplement to be filed with the SEC.

This press release shall not constitute an offer to sell or a solicitation of an offer to buy any of these securities, nor shall there be any sale of these securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the applicable securities laws of such state or jurisdiction.

ABOUT REGENXBIO Inc. REGENXBIO is a biotechnology company on a mission to improve lives through the curative potential of gene therapy. Since its founding in 2009, REGENXBIO has pioneered the field of AAV gene therapy. REGENXBIO is advancing a late-stage pipeline of one-time treatments for rare and retinal diseases, including RGX-202 for the treatment of Duchenne; surabgene lomparvovec (ABBV-RGX-314) for the treatment of wet AMD and diabetic retinopathy, in collaboration with AbbVie, and NAVSUNLI™ (clemidsogene lanparvovec-sngl, RGX-121) for the treatment of MPS II and RGX-111 for the treatment of MPS I, both in partnership with Nippon Shinyaku. Thousands of patients have been treated with REGENXBIO's AAV platform, including those receiving Novartis' ZOLGENSMA ® . REGENXBIO's investigational gene therapies have the potential to change the way healthcare is delivered for millions of people.

FORWARD-LOOKING STATEMENTS This press release includes "forward-looking statements," within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. These statements express a belief, expectation or intention and are generally accompanied by words that convey projected future events or outcomes such as "believe," "may," "will," "estimate," "continue," "anticipate," "assume," "design," "intend," "expect," "could," "plan," "potential," "predict," "seek," "should," "would" or by variations of such word...