Demand for gene therapies based on adenoassociated virus (AAV) vectors continues to exceed manufacturing capacity. Part of the imbalance stems from the growing number of AAV-based candidates that are advancing through clinical studies. Zhao et al. report that, in September 2021, researchers were enrolling participants for and/or conducting 137 trials for such products (1). As of August 2022, three AAV-based therapies have received commercial authorization in the United States and/or European Union, and other products have received conditional approval (2–5).…