Adeno-associated virus (AAV) vectors in cancer gene therapy

Abstract

Gene delivery vectors based on adeno-associated virus (AAV) have been utilized in a large number of gene therapy clinical trials, which have demonstrated their strong safety profile and increasingly their therapeutic efficacy for treating monogenic diseases. For cancer applications, AAV vectors have been harnessed for delivery of an extensive repertoire of transgenes to preclinical models and, more recently, clinical trials involving certain cancers. This review describes the applications of AAV vectors to cancer models and presents developments in vector engineering and payload design aimed at tailoring AAV vectors for transduction and treatment of cancer cells. We also discuss the current status of AAV clinical development in oncology and future directions for AAV in this field.

Keywords: AAV; Adeno-associated virus; Cancer; Gene delivery; Gene delivery vectors; Gene therapy.

Figure 1. Genomic structure of AAV and AAV vectors

(A) The 4.7kb AAV genome is composed of the rep and cap genes flanked by inverted terminal repeats (ITRs). The rep gene codes for non-structural proteins involved in viral replication, packaging, and genomic integration, while the cap gene encodes the structural proteins VP1, VP2, and VP3 that assemble to form the viral capsid in a ratio of 1:1:10, respectively, in a total of 60 protein subunits. The assembly-activating protein (AAP) is translated from an alternate open reading frame. Also depicted are capsid loop domains I through V (LI-LV), which contain variable regions that influence gene delivery properties. (B) Recombinant AAV vectors are generated by replacing the rep and cap genes with a gene expression cassette (e.g. promoter, transgene, poly(A) tail) flanked by the ITRs. Vectors are then packaged by supplying the rep and cap genes in trans as well as adenoviral helper genes required for AAV replication.

Figure 2. Representation of AAV2 capsid structure and individual monomeric protein

(A) Crystal structure of the AAV2 capsid [183], the most widely used and studied AAV serotype. Loop domains I through V are depicted following the same color scheme as in Figure 1A. (B) Residues that have been mutated to engineer vectors for transduction of cancer cells are mapped onto the AAV2 crystal structure and depicted in orange (tyrosine to phenylalanine mutations) or red (other mutations). (C) Mutated residues are similarly depicted in the individual VP3 monomer structure. Additionally, residues that have been removed to insert protein-binding peptides [58] are depicted in green. Images were produced with Pymol [184].