Adeno-associated Virus Serotypes: Vector Toolkit for Human Gene Therapy

Abstract

Recombinant adeno-associated viral (AAV) vectors have rapidly advanced to the forefront of gene therapy in the past decade. The exponential progress of AAV-based vectors has been made possible by the isolation of several naturally occurring AAV serotypes and over 100 AAV variants from different animal species. These isolates are ideally suited to development into human gene therapy vectors due to their diverse tissue tropisms and potential to evade preexisting neutralizing antibodies against the common human AAV serotype 2. Despite their prolific application in several animal models of disease, the mechanisms underlying selective tropisms of AAV serotypes remain largely unknown. Efforts to understand cell surface receptor usage and intracellular trafficking pathways exploited by AAV continue to provide significant insight into the biology of AAV vectors. Such unique traits are thought to arise from differences in surface topology of the capsids of AAV serotypes and variants. In addition to the aforementioned naturally evolved AAV isolates, several strategies to engineer hybrid AAV serotype vectors have been formulated in recent years. The generation of mosaic or chimeric vectors through the transcapsidation or marker-rescue/domain-swapping approach, respectively, is notable in this regard. More recently, combinatorial strategies for engineering AAV vectors using error-prone PCR, DNA shuffling, and other molecular cloning techniques have been established. The latter library-based approaches can serve as powerful tools in the generation of low-immunogenic and cell/tissue type-specific AAV vectors for gene delivery. This review is focused on recent developments in the isolation of novel AAV serotypes and isolates, their production and purification, diverse tissue tropisms, mechanisms of cellular entry/trafficking, and capsid structure. Strategies for engineering hybrid AAV vectors derived from AAV serotypes and potential implications of the rapidly expanding AAV vector toolkit are discussed.

Cellular tropism and transduction properties of seven adeno-associated viral vector serotypes in adult retina after intravitreal injection

“…48 AAV6 can also bind to heparin sulphate proteoglycan receptors, 49,50 but unlike AAV2, AAV6 is not inhibited by soluble heparin. 51 Instead, AAV6 has been shown to be dependent on cell-bound sialic compounds presented on N-linked glycoproteins. 52 These different vector-cell interaction characteristics may cause the profile divergence seen between rAAV2/2 and rAAV2/6 in this study.…”

Neutralizing antibodies against adeno-associated virus examined prospectively in pediatric patients with hemophilia

“…4 Currently, 12 naturally occurring serotypes of AAV and several primate isolates have been isolated and studied as gene delivery vehicles. 5,6 Clinical trials with rAAV2 vectors have been performed in hemophilia B (factor IX deficiency) patients via intramuscular injection or by targeting the liver. 3,7 No specific side effects were observed from these trials.…”

Longevity of rAAV vector and plasmid DNA in blood after intramuscular injection in nonhuman primates: implications for gene doping

“…[5][6][7][8][9] Intramuscular (IM) injection is a convenient method owing to physical accessibility, mass of the tissue and access to the vasculature. [10][11][12] Moreover, recombinant adeno-associated viral (rAAV) vectors and naked plasmid are two different gene transfer systems used for IM delivery in animal models [13][14][15][16][17] and in humans. 18,19 Recently, regional vascular infusion of a vector to achieve skeletal muscle transduction has been reported for plasmid DNA (pDNA) 20,21 and for rAAV vectors.…”