FDA Places Clinical Holds on Regenxbio’s RGX-111 and RGX-121 Gene Therapy Trials After Brain Tumor in Patient

The FDA has paused clinical trials for Regenxbio's RGX-111 (for MPS I/Hurler syndrome) and RGX-121 (for MPS II/Hunter syndrome) following the discovery of an intraventricular brain tumor in one asymptomatic five-year-old patient treated with RGX-111 four years prior.123

Preliminary analysis detected an AAV vector genome integration event linked to PLAG1 proto-oncogene overexpression in the tumor, but causality is undetermined and investigation continues.23

No neoplasms reported in nine other RGX-111 patients or 32 RGX-121 patients; the affected patient shows developmental gains.123

REGENXBIO expressed surprise at the RGX-121 hold, noting its separate profile and positive safety in over 30 patients, some dosed nearly seven years ago.23

The news, announced January 28, 2026, caused REGENXBIO stock (RGNX) to tumble 28%.13

Sources:

1. https://www.statnews.com/2026/01/28/fda-halts-regenxbio-gene-therapy-trials/

2. https://www.stocktitan.net/news/RGNX/regenxbio-announces-regulatory-update-on-ultra-rare-mps-7dcpe4htqein.html

3. https://au.investing.com/news/stock-market-news/regenxbio-stock-tumbles-after-fda-places-clinical-holds-on-gene-therapies-93CH-4226868