Adenoassociated virus (AAV) has emerged as the leading vector for gene therapy delivery. Compared with options such as lentivirus and adenovirus, AAV exhibits a strong safety profile because it has low pathogenicity and requires a helper virus to replicate. AAV is also capable of long-term gene expression, and it can infect both dividing and nondividing cells (1–5). Developers of advanced therapies have found such advantages to be quite attractive. As of January 2021, two gene therapy products have gained US…