REGENXBIO said the FDA has placed a clinical hold on RGX-121, its investigational gene therapy for mucopolysaccharidosis type II, after asymptomatic spine MRI findings were identified in five participants in the CAMPSIITE study.
The company said it does not expect to resubmit its Biologics License Application for RGX-121 in the near term. The therapy, also known as clemidsogene lanparvovec, is being developed as a one-time treatment for boys with MPS II, or Hunter syndrome.
The findings emerged through an expanded MRI monitoring plan that REGENXBIO introduced several months ago after a clinical hold related to RGX-111, its gene therapy candidate for MPS I. The enhanced monitoring included both brain and spine MRI examinations.
Five patients who received RGX-121 through intracisternal or intraventricular administration approximately three to six years earlier showed either a small spinal nodule or small cystic mass. Investigators deemed the findings nonserious, and radiologists believe they are likely benign, REGENXBIO said.
All five participants remain clinically well and have shown overall stability or improvement on neurocognitive and neurobehavioral assessments. The company said no brain nodules or masses were found in any brain MRI examinations, and there is no clinical or pathological evidence establishing the nature or cause of the spinal findings.
Spine MRI is not routinely conducted in MPS clinical practice or trials, meaning the background prevalence and clinical importance of comparable asymptomatic findings in the MPS II population are unknown, the company said. Investigators plan to continue observing the patients through periodic imaging.
REGENXBIO and its partner NS Pharma are reviewing additional patient imaging and longer-term follow-up data. The companies will incorporate FDA feedback, including the full clinical-hold letter once received, in determining the next steps for RGX-121.
MPS II is a rare X-linked disease caused by deficiency of the iduronate-2-sulfatase enzyme. The condition leads to accumulation of glycosaminoglycans in tissues and can cause cellular, organ and central nervous system dysfunction. About 2,000 people globally are diagnosed with MPS II, and more than 500 babies are born with the disease annually, REGENXBIO said.
The company said its Duchenne and retinal-disease programs remain on track, including a planned Duchenne BLA submission this quarter and topline pivotal data for wet age-related macular degeneration expected in the fourth quarter.
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