Syn-NES-jRGECO1a AAV (Serotype 8)

Adeno-associated virus (AAV) provides an ideal foundation for clinical gene transfer based on recombinant AAV (rAAV) vectors due to its lack of significant clinical pathogenicity. rAAV can package and deliver transgenes to a variety of dividing and non-dividing cells and maintain stable, potentially long-term transgene expression (particularly in cells that divide slowly or do not divide, including the liver, retina, and central nervous system). In addition, AAV has relatively low immunogenicity, and optimized production protocols allow high titer and high purity manufacturing for clinical use. Importantly, because the rAAV genome is primarily maintained in a free form in cells, complications associated with insertional mutagenesis inherent to some other viral vectors used in clinical gene therapy are minimized.

AAV consists of a single-stranded DNA (ssDNA) genome of approximately 4.7 Kb, encapsidated by a capsid of approximately 26 nm in diameter. The AAV genome is flanked by two T-shaped hairpin structures - inverted terminal repeats (ITRs). Overlapping genes with alternative splicing and multiple translation start sites allow efficient utilization of the AAV genome and produce three capsid proteins (Cap), four replication proteins (Rep), and an assembly activator protein that promotes virion assembly in certain serotypes. Together, these three genes mediate genome replication and packaging, capsid production, and integration. There are multiple AAV serotypes that share the same overall genome structure and greater than 80% homology in nucleotide sequence. The differences between serotypes are primarily in the amino acid sequence of their capsid proteins. Differences in capsid sequence and the presence of receptors or coreceptors on host cells determine the cell/tissue tropism of a particular AAV serotype.