Liver toxicity has been reported following systemic administration of multiple AAV gene therapies in clinical trials. Liver safety is particularly important for muscle-directed gene therapy, where high doses are required when using naturally occurring AAV capsids.
We previously reported directed evolution of the MyoAAV class of capsids, which enables highly potent systemic gene delivery to skeletal muscles and heart across species. While the first generation of MyoAAV capsids were highly effective in transducing skeletal muscle and heart and thus lowering the efficacious dose, they resulted in similar number of vector genomes per diploid genome in the liver of non-human primates (NHPs) as equal doses of naturally occurring capsids (e.g., AAV8 and AAV9). To develop liver-detargeted capsid variants that also transduce muscles effectively, we used the DELIVER platform (Directed Evolution of AAV capsids Leveraging In Vivo Expression of transgene RNA) to simultaneously co-evolve liver-detargeting and muscle-targeting properties. Using this strategy, we successfully evolved capsid variants that functionally transduce skeletal muscles up to 9-fold and cardiac muscle up to 6-fold more effectively than AAV9, while also having 10-fold lower vector genomes when tested in a pooled experiment compared to AAV9 in the liver of NHPs. The top two liver-detargeted muscle-tropic capsid variants from the pooled benchmarking experiment in NHPs outperformed external engineered capsid variants used in various muscle gene therapy candidates, as well as the first generation MyoAAV capsids. Manufacturability analysis also showed that these new capsids can be produced with similar yields and can be purified by affinity chromatography with similar efficiency as AAV9. We will also present a head-to-head comparison of our top liver-detargeted muscle tropic capsid from this directed evolution campaign compared to AAV9 in NHPs.