FDA Places Clinical Hold on REGENXBIO’s RGX-111 and RGX-121 Gene Therapy Trials

The FDA has placed a clinical hold on REGENXBIO’s investigational gene therapies RGX-111 and RGX-121 following the diagnosis of a brain tumour in a patient treated with RGX-111 for mucopolysaccharidosis (MPS) type I (Hurler syndrome).

In the Phase I/II RGX-111 study (NCT03580083), a five-year-old patient, asymptomatic at the time, was found to have an intraventricular CNS tumour during a routine MRI, four years after intracisternal dosing. Preliminary analysis revealed AAV vector genome integration linked to overexpression of the PLAG1 proto-oncogene. No other cases of neoplasm have been reported among nine other RGX-111 patients or 32 RGX-121 patients with MPS II (Hunter syndrome).

Following the announcement, REGENXBIO stock dropped 28.4%, from $13.41 to $9.60, with the company’s market cap at $566M. The FDA letter is pending further details.

31-01-2026