On February 7 2026, the U.S. Food and Drug Administration issued a Complete Response Letter (CRL) for REGENXBIO’s RGX‑121 gene therapy, which the company announced on February 9 2026. The CRL cites concerns about study eligibility criteria, the comparability of natural‑history external controls, and the suitability of the cerebrospinal fluid HS D2S6 surrogate endpoint used to predict clinical benefit.
The CRL outlines several potential paths forward, including enrolling additional patients, extending follow‑up, and incorporating an untreated control arm. These options are difficult for an ultra‑rare disease population and would require significant additional investment and time.
The regulatory setback delays the company’s ability to bring RGX‑121 to market, postpones the expected revenue stream, and defers the sale of a priority‑review voucher that could provide up to $150 million in non‑dilutive cash.
The CRL underscores the high risk associated with REGENXBIO’s product pipeline and the uncertainty surrounding its transition from a licensing platform to a product‑centric business. The company has indicated it will request a Type A meeting with the FDA to discuss the letter and plan a resubmission.
Despite the setback, REGENXBIO remains confident in the long‑term potential of RGX‑121. CEO Curran Simpson emphasized the therapy’s promise for families affected by Hunter syndrome and the company’s commitment to addressing the FDA’s concerns.
The CRL follows the FDA’s acceptance of the RGX‑121 BLA under the accelerated approval pathway in May 2025, a milestone that had positioned the therapy as a potential first‑in‑class treatment for Hunter syndrome.
The content on EveryTicker is for informational purposes only and should not be construed as financial or investment advice. We are not financial advisors. Consult with a qualified professional before making any investment decisions. Any actions you take based on information from this site are solely at your own risk.