A fatality in the first patient dosed with a brain-penetrant viral vector developed by Capsida Biotherapeutics has unsettled researchers and companies working on gene therapies that cross the blood-brain barrier. The STAT report cited cerebral edema as the proximate cause and noted that extensive animal testing had not predicted the outcome. Companies developing similar neurotropic vectors are reviewing safety data and dosing strategies while regulators and investor teams reassess the risk profile for brain-targeted delivery platforms. "Brain-penetrant" vectors are engineered viral carriers designed to deliver genes into central nervous system tissue.