Systemic administration of novel engineered AAV capsids facilitates enhanced transgene expression in the macaque CNS

Adeno-associated virus (AAV) vectors are a promising vehicle for noninvasive gene delivery to the central nervous system via intravenous infusion. However, naturally occurring serotypes have a limited ability to transduce the brain, and translating engineered capsids from mice to nonhuman primates has proved challenging. In this study, we use an mRNA-based directed evolution strategy in multiple strains of mice as well as in a de novo selection in cynomolgus macaques to identify families of engineered vectors with increased potency in the brain and decreased tropism for the liver. We compare the transgene expression capabilities of several engineered vectors and show that while some of our novel macaque-derived variants significantly outperform AAV9 in transducing the macaque brain, mouse-derived variants-both those identified in this study and those reported by other groups-universally did not. Together, this work introduces a class of primate-derived engineered AAV capsids with increased therapeutic potential and underscores the critical need for using appropriate animal models to both identify and evaluate novel AAVs intended for delivery to the human central nervous system.