860. Tissue Distribution of Expression Using AAV8-Based Vectors after Intramuscular Injection and Other Routes of Delivery

Abstract

AAV8-based vectors are shown to be especially efficient in transducing liver and muscle and currently considered as one of the most promising vector system. In this study, we investigated tissue distribution of expression using AAV8-based vectors after intramuscular (IM) injection and other routes of delivery. For this purpose, AAV8-based vectors carrying luciferase gene (Luc) under CAG promoter was administered into tibialis anterior (TA) muscles of C57BL/6 mice. In vivo bioluminescence imaging analysis using IVIS system revealed robust transgene expression not only in lower limbs (around TA) but also in the upper abdominal region (suggesting liver). Analysis by ex vivo bioluminescence imaging after sacrifice confirmed expression in liver as well as TA muscles. To verify whether these findings are unique to AAV8, AAV1- and AAV2-based vectors were tested in the same manner. When AAV1- or AAV2-Luc was injected within TA muscles, Luc expression was confined to the injected sites. The level of transgene expression observed in liver after AAV8-Luc injection was comparable to that observed in lower limbs after AAV1-Luc injection. To substantiate ectopic expression after intramuscular injection, vector genomes within the tissues were quantitated at early time points. Vector genome copies were sharply decreased in muscle and increased in liver at 24 hours after injection in the case of AAV8-based vectors. When AAV8-Luc vector was administered intravenously (IV) or intraperitoneally (IP), luciferase expression was confined to liver. A sex-related difference in luciferase expression in liver was observed regardless of the route of administration. In addition to adults, we compared tissue distribution of expression in neonate by the routes of administration of AAV8-Luc vector. Surprisingly, liver specific Luc expression was observed only after IV injection; in IM and IP administration, transgene expression was confined to lower limbs and peritoneum, respectively. Moreover, sex-related difference in transgene expression was not observed in any tissues in neonatal injection. These data suggest remarkable affinity of AAV8-based vectors to liver, and will be useful in designing strategies for gene therapy using AAV8-based vectors in adult and neonate.