EFS-SpCas9 AAV (Serotype 9)

AAV is a non-enveloped Dependoparvovirus belonging to the Parvoviridae family, whose capsid contains 60 subunits of three different proteins (VP1, VP2, and VP3) that share a common C-terminus and are produced by alternative translation of the AAV cap gene. The AAV cap is the major determinant of native AAV cell/tissue tropism and is therefore a key modifiable genetic element for optimizing transduction efficiency. Each capsid subunit has nine variable regions, i.e., peptide loops protruding from the virion surface, that play a role in capsid assembly, genome packaging, cell receptor interactions, and antigenic determinants of anti-capsid cellular and humoral immune responses. Currently, more than 100 different AAV serotypes have been isolated from humans, non-human primates (NHPs), and other species, which display a wide range of tissue and cell tropisms, primarily determined by the primary attachment receptor and co-receptor specificity of each serotype. These different naturally occurring serotypes have been extensively screened for their ability to transduce a variety of target cell types and organs.

One promising application of AAV-based therapeutics is the delivery of gene-editing enzymes to correct defective genes. In preclinical studies, several research groups have reported the effective use of AAV-delivered CRISPR/Cas9 technology to edit genes in animal models to treat diseases such as Duchenne muscular dystrophy, hypercholesterolemia, and urea cycle disorders. Similarly, the use of gene-editing technologies to inactivate and eliminate viral reservoirs that cause persistent/chronic infections has also recently attracted much attention. In fact, recent reports of the elimination of viral genomes using meganucleases and CRISPR/Cas9 in animal models of chronic infection with HSV and HIV, respectively, support the use of AAV vectors to treat chronic viral infections. AAV-mediated delivery of antiviral therapies is not limited to gene-editing enzymes. For example, several research groups have used AAV vectors to deliver other antiviral therapies such as RNA interference molecules and virus-neutralizing antibodies.