CMV-iGluSnFR AAV (Serotype 8)

Adeno-associated virus (AAV) gene delivery vectors are the most widely used vectors for in vivo gene therapy. AAV has attractive properties for clinical gene therapy and can be easily vectorized in a controlled manner. More than 100 different AAV variants (naturally occurring or synthetic) capsid sequences have been reported. However, the most studied are 11 AAV serotypes (AAV1 to AAV11) isolated from humans, simians, rhesus macaques, and cynomolgus monkeys. They are unable to replicate in the absence of a helper virus, and to date, no human pathogenicity has been found to be associated with wild-type AAV infection. Sustained long-term transgene expression levels can also be achieved when transducing both dividing and non-dividing cells.

AAV has been shown to enter the cytoplasm encapsidated in clathrin-coated endocytic vesicles. As a result, the capsid remains trapped in early endosomes and is transported through the endosomal-lysosomal network. The activity of the enzymatic PLA2 domain is required to disrupt the lysosomal membrane before the capsid is released into the cytoplasm. Exposure to acidification of endosomes is thought to be essential for AAV nuclear entry, followed by capsid uncoating and ultimately replication. In the case of AAV8, conformational changes in amino acids in the capsid structure have been shown to occur in response to decreasing pH. Decreases in ambient pH have been detected to trigger externalization of the N-terminal VP region, including the PLA2 domain and the nuclear localization signal (NLS) of VP1u. However, these dramatic conformational changes have never been directly observed structurally.