252. Using Cre-Dependent In Vivo Selection to Identify AAV Variants That Enable Efficient and Widespread Gene Transfer to the Adult Central Nervous System

Recombinant adeno-associated viruses (rAAVs) are commonlyused vehicles for in vivo gene transfer. However, the tropismrepertoire of naturally occurring AAVs is limited, prompting thedevelopment of novel AAV capsids with more desirable transductioncharacteristics. We have developed a capsid selection method, calledCre-recombination-based AAV targeted evolution (CREATE), thatenables the identification of AAV capsids that more efficientlytransduce defined cell populations in vivo (Deverman et al. in press,Nature Biotechnology). We generated AAV capsid libraries andused CREATE to identify variants that cross the blood brain barrierand efficiently and widely transduce astrocytes in the mouse centralnervous system (CNS) after intravenous injection. One variant, AAVPHP.B, transfers genes throughout the adult CNS with an efficiencythat is 40- to 92-fold greater (depending on the CNS region) than thatof the current standard, AAV9. It transduces the majority of astrocytesand neurons across multiple CNS regions, and in vitro, it transduceshuman neurons and astrocytes more efficiently than does AAV9. Weare now evolving AAV-PHP.B for even greater transduction of specificCNS cell types as a means to both develop more effective vectorsand to gain insight into the mechanism of enhanced transduction.Our identification of AAV-PHP.B and several other enhanced vectorsafter only two rounds of selection establishes CREATE as a powerfulmethod to customize AAV vectors for biomedical applications.