Regenxbio Hit by FDA Clinical Hold on RGX-121 After Spinal MRI Abnormalities Found

Regenxbio Inc. shares fell Monday following a regulatory update on its investigational gene therapy RGX-121, being developed for the treatment of mucopolysaccharidosis type II, also known as Hunter syndrome.

FDA Places Clinical Hold on RGX-121

The U.S. Food and Drug Administration placed a clinical hold on RGX-121 after asymptomatic spinal MRI abnormalities were detected in five participants in the CAMPSIITE study.

The company said it does not intend to resubmit the Biologics License Application for RGX-121 in the near term.

Five Participants Show Asymptomatic Spinal MRI Abnormalities

All five participants continue to do well clinically, demonstrating overall stability or improvement in neurocognitive and neurobehavioral assessments.

The abnormalities were identified through an expanded MRI surveillance program implemented by Regenxbio several months ago, which was initiated following a clinical hold related to RGX-111.

The enhanced surveillance, including brain and spinal MRIs, detected asymptomatic abnormalities in the spinal MRIs of five participants who received intracisternal or intraventricular injections of RGX-121 approximately three to six years ago, presenting as small nodules or small cystic masses.

Investigators believe these abnormalities are not serious, and radiologists consider them potentially benign.

There is no clinical or pathological evidence to confirm the nature or etiology of the spinal MRI abnormalities.

No brain nodules or masses were identified in any brain MRIs.

Regenxbio Continues to Monitor Patients

Since spinal MRIs are not typically performed in clinical practice or trials for MPS, the potential prevalence and clinical significance of such asymptomatic abnormalities in this patient population remain unknown.

Investigators plan to continue observing these patients with periodic imaging only.

The company and its partner NS Pharma are evaluating additional patient imaging and long-term follow-up data, and will incorporate FDA feedback into next steps for RGX-121 upon receipt of the full clinical hold letter.

RGX-121 Targets Rare Hunter Syndrome

MPS II is a rare X-linked recessive disorder caused by deficiency of the lysosomal enzyme I2S, leading to accumulation of glycosaminoglycans, including heparan sulfate, in tissues, ultimately resulting in cellular, tissue, and organ dysfunction, including dysfunction of the central nervous system.

Approximately 2,000 patients worldwide are diagnosed with MPS II, and about 500 infants are born with the condition globally each year.

RGX-121 is a one-time investigational gene therapy designed to deliver the iduronate-2-sulfatase gene to the central nervous system.

Delivery of the IDS gene to cells within the CNS can provide a durable source of secreted sulfatase protein beyond the blood-brain barrier, allowing long-term cross-correction of cells throughout the CNS.

The protein expressed by RGX-121 is structurally identical to normal I2S.

RGNX Share Performance: Based on Monday premarket trading data, Regenxbio shares fell 23.79% to $8.170.