Regenxbio reported a new clinical hold for its Hunter syndrome gene therapy, RGX-121 (clemidsogene lanparvovec), after regulators identified asymptomatic spine MRI findings in five treated patients in its Campsiite study. The company said it no longer expects to file for FDA approval in the near term. This is the second clinical hold Regenxbio has faced for the program this year, intensifying scrutiny on AAV-delivered therapies and their long-term safety signal monitoring. The company previously linked a similar spine/tumor-related event to an earlier patient in an MPS type I program. The development keeps the rare-disease gene-therapy field focused on risk mitigation and the regulatory bar for imaging and follow-up endpoints in pediatric cohorts.