Regenxbio’s Hunter syndrome gene therapy (RGX-121) ran into another FDA stop as the company reported a clinical hold after discovering asymptomatic spine MRI findings in five patients during the Campsiite study. With a near-term BLA resubmission effectively taken off the table, the next steps will depend on how the FDA frames safety evidence required for future review. In parallel, Regeneron terminated an early Phase I/IIa TITAN trial of its CD3-targeting monoclonal antibody REGN7041 for noninfectious uveitis after an unfavorable risk-versus-benefit safety review. Notably, the study had enrolled only a single patient before termination, with the underlying cause of the safety event still not identified publicly. Together, the updates show how rapidly safety signals—sometimes discovered before broader datasets exist—can redirect gene therapy and antibody development timelines.