Rockville, Md., Jan 28, 2026, 10:02 (EST)
- U.S. FDA orders clinical holds on Regenxbio’s RGX-111 and RGX-121 gene therapy trials for rare childhood disorders
- Company says a brain tumor was found in one RGX-111 trial participant; it is probing whether the event is treatment-related
- Stock was down about 20% in morning trading after a sharper premarket drop
The U.S. Food and Drug Administration has put Regenxbio’s experimental gene therapies RGX-111 and RGX-121 on clinical hold after a brain tumor was detected in a treated child, the company said on Wednesday. Regenxbio shares were down about 20% at $10.71 in morning trading, after sliding roughly 30% before the market open. The company said it has not yet received the FDA’s full clinical hold letter. (Reuters)
The hold hits Regenxbio’s two mucopolysaccharidosis (MPS) programs for Hurler and Hunter syndromes and comes with RGX-121 close to an FDA decision date expected on Feb. 8, Fierce Biotech reported. That timing raises the stakes because a delay would push out what investors had been treating as a near-term regulatory catalyst. (Fiercebiotech)
Leerink Partners analyst Mani Foroohar called the pause “a confusing and unexpected update” and said it fed broader worries about “FDA unpredictability” around gene therapy reviews. He wrote the sell-off looked like an overcorrection, pointing to Regenxbio’s Duchenne muscular dystrophy program as the bigger value driver and a potential rival to Sarepta Therapeutics’ approved Elevidys. (Investors)
Regenxbio said the tumor was found during a routine brain MRI in an asymptomatic five-year-old who received RGX-111 about four years earlier. Preliminary genetic testing of the removed tumor detected an adeno-associated virus (AAV) vector integration event linked to overexpression of PLAG1, a proto-oncogene — a gene that can help drive cancer when it is switched on — though the company said it has not established causality. Chief Executive Curran Simpson said, “We are surprised by FDA’s decision to place our RGX-121 program on hold,” adding that “patient safety is our top priority,” and the company reported no evidence of tumors in nine other RGX-111 participants or 32 patients treated with RGX-121. (PR Newswire)
A securities filing said the FDA placed the company’s investigational new drug applications for RGX-111 and RGX-121 on clinical hold, covering a Phase I/II trial for RGX-111 and a Phase I/II/III trial for RGX-121. (SEC)
Hurler and Hunter syndromes are rare genetic diseases that can cause cognitive and heart problems and are often fatal. Regenxbio’s treatments are designed to replace genes that do not work in patients with the conditions. (STAT)
Both programs use AAV as a delivery vehicle — a modified virus used to carry a therapeutic gene into cells. The integration signal flagged by the company suggests the vector’s DNA may have inserted into the patient’s genome, a type of finding regulators scrutinize because it can, in some cases, disrupt normal control of cell growth.
Regenxbio said its broader pipeline includes a Duchenne program and an eye-disease gene therapy effort with AbbVie, and that its MPS programs are partnered with Nippon Shinyaku. The company also said thousands of patients have been treated with its AAV platform, including those receiving Novartis’ Zolgensma. (SEC)
But the FDA has not said how long the holds could last, and an adverse finding on causality could force longer follow-up, additional testing, or changes to the studies. Even if the event remains inconclusive, a prolonged pause would still push back timelines in diseases where patients’ condition can worsen while treatment options remain limited.
