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FDA halts Regenxbio's Hunter syndrome gene therapy a second time

Two gowned biomanufacturing staff in blue cleanroom scrubs, hairnets, safety glasses and gloves walk and talk in a glass-walled cleanroom corridor lined with bioprocessing equipment.

REGENXBIO Inc., via company manufacturing pagePress kit

The FDA placed a clinical hold on RGX-121, Regenxbio’s gene therapy for Hunter syndrome, on 24 August 2026. Investigators had found masses on the spines of five trial participants during MRI follow-up. Those participants were treated three to six years ago, show no symptoms and continue to do well clinically; Regenxbio says there is no clinical or pathological evidence confirming what the masses are or what caused them.

It is the second hold on the programme this year. In January the agency paused testing after a participant in a related MPS I programme developed a brain tumour, and in February it rejected the biologics licence application. The company now says it will not resubmit in the near term while it evaluates the data with its partner NS Pharma. Its shares fell more than 25 percent.

The finding matters beyond one company. An adeno-associated virus vector delivers a gene that persists, and the safety question it raises is not what happens in the first ninety days but what appears on a scan half a decade later. That question can only be answered by following patients long enough to see it, which is what happened here.

Sources

  1. [1]Safety concerns spur FDA to again halt testing of Regenxbio gene therapyBioPharma Dive··Article