Directed evolution of liver-detargeted AAV vectors for systemic gene delivery to skeletal muscle and heart

Adeno-associated virus (AAV) gene therapies that require systemic administration of high vector doses are associated with hepatotoxicity risk, given the liver tropism of most AAV vectors. We combined screening of natural serotypes, targeted mutagenesis, and directed evolution to identify liver-detargeted muscle-tropic capsids. We found that AAVhu.32 is liver-detargeted compared to AAV9, and AAV5 exhibits high skeletal muscle biodistribution albeit with low transgene expression. Following two rounds of peptide insertion library-based directed evolution of AAV9.AAA (a previously described variant) and AAV5, we identified peptides NVG7 and NVG13, respectively, that confer increased muscle transduction compared to the base capsid with liver-detargeting compared to AAV9 in mouse. In non-human primate (NHP), the liver-detargeted profile of these capsids was confirmed in a pooled capsid study and via comparison to AAV9 NHP literature data. Incorporating AAA.NVG7 into AAVhu.32 led to further improved transduction in mouse heart and brain. The structure and phenotype of the loop insertion in AAV9.AAA.NVG7 is dependent on the sequence of an adjacent loop in a case of sign epistasis between the two sites. These capsids may provide an improved safety profile and increased activity in muscle compared to current AAV capsids.