The drug substance is voretigene neparvovec, a replication-incompetent, recombinant AAV serotype 2 (AAV2) vector. It contains the complementary DNA (cDNA) of the human retinal pigment epithelial 65 kDa protein (RPE65) gene. Expression is driven by a chicken beta-actin (CBA) promoter and enhanced by a cytomegalovirus (CMV) enhancer. The drug substance is produced in human embryonic kidney (HEK293) cells via transient co-transfection with three plasmids. The drug substance is purified using a series of chromatography steps and formulated as a frozen bulk solution. A comprehensive set of release specifications, including identity, purity, potency, and safety, ensures the quality of each batch.