Engineered AAV vectors for improved central nervous system gene delivery

Abstract

Adeno-associated viruses (AAV) are non-pathogenic members of the Parvoviridae family that are being harnessed as delivery vehicles for both basic research and increasingly successful clinical gene therapy. To address a number of delivery shortcomings with natural AAV variants, we have developed and implemented directed evolution—a high-throughput molecular engineering approach to generate novel biomolecules with enhanced function—to create novel AAV vectors that are designed to preferentially transduce specific cell types in the central nervous system (CNS), including astrocytes, neural stem cells, and cells within the retina. These novel AAV vectors—which have enhanced infectivity in vitro and enhanced infectivity and selectivity in vivo—can enable more efficient studies to further our understanding of neurogenesis, development, aging, and disease. Furthermore, such engineered vectors may aid gene or cell replacement therapies to treat neurodegenerative disease or injury.

Widespread transduction of astrocytes and neurons in the mouse central nervous system after systemic delivery of a self-complementary AAV-PHP.B vector

“…Complementary approaches to reducing off-target transduction aim at enhancing vector tropism for the desired organ or cell type, while (simultaneously) reducing tropism for off-target systems. De novo synthesis of novel AAV capsids, or modification of existing capsids (through directed evolution [15], mutagenesis of specific amino acids in the capsid [16], or incorporation of specific targeting peptides [17]) have all proved to improve CNS transduction, while decreasing transduction in peripheral organs. In 2016, Deverman et al [18] reported a significant advance in capsid design, when they published a selection method called Cre recombination-based AAV targeted evolution (CREATE)-which allows selection of AAV capsids that efficiently transduce defined Cre-expressing cell populations in vivo.…”

Gene therapy and genome surgery in the retina

“…One active area of research is the development of viral vectors with more precise cell-type-targeting capabilities via the directed evolution of AAV capsids. Several groups have generated libraries of AAV capsid proteins, applied them to animal models, and examined their transduction in a cell-type-specific manner (164,165). Deverman et al used such a method to develop an intravenously injected AAV vector capable of transducing the mouse brain 40-fold better than could be achieved with standard vectors (166).…”

Recombinant Viral Vectors as Neuroscience Tools

“…Variations on AAV serotypes occur either naturally or deliberately by introducing mutations in capsid proteins (Kotterman & Schaffer, ). Techniques such as Cre‐recombination‐based AAV targeted evolution (CREATE) help engineer capsids with desirable cell‐ or tissue‐targeting capabilities (Chan et al., ; Deverman et al., ; Kotterman & Schaffer, ; Kotterman, Vazin, & Schaffer, ).…”