Regenxbio announces FDA places clinical hold on RGX-111

Regenxbio (RGNX) announced that the U.S. FDA placed a clinical hold on its investigational gene therapy, RGX-111, for the treatment of MPS I, also known as Hurler syndrome, following preliminary analysis of a single case of neoplasm in a participant treated in its Phase I/II study. The FDA also placed a clinical hold on RGX-121, for the treatment of MPS II, also known as Hunter Syndrome, citing the similarities in products, study populations, and shared risk between the clinical studies. The case was identified during a routine brain MRI of an asymptomatic five-year-old participant who received intracisternal RGX-111 four years prior. Preliminary genetic analysis of the resected tumor detected an AAV vector genome integration event associated with overexpression of a proto-oncogene, which is known to be susceptible to chromosomal rearrangements. The investigation to determine if this SAE is drug related is ongoing. The causality has not been established. The participant continues to be asymptomatic, with positive developmental advancements noted by the treating physician. No evidence of neoplasm has been reported in the nine other participants treated with RGX-111 nor in the 32 participants treated with RGX-121. Regenxbio has not yet received the full clinical hold letter and awaits additional details from the FDA.