86. Comparison of CNS Transduction by Different AAV Capsids in Mouse and Non-Human Primate

Abstract

Adeno-associated viral (AAV) vectors are a platform of great potential for therapeutic gene delivery. One of the major challenges regarding AAV gene therapy is to deliver the transgene of interest to target cells at levels that result in expression that is both safe and effective. The AAV vector capsid is a strong determinant of gross biodistribution, cellular tropism, transduction efficiency and transgene expression. Neurodegenerative disorders such as Friedreich's ataxia present a significant challenge in developing an effective gene therapy that provides clinically relevant distribution and expression in the central nervous system (CNS). Friedreich's ataxia is caused by an expanded GAA trinucleotide repeat in the first intron of the frataxin gene which leads to reduced levels of frataxin, a key mitochondrial protein. Pathological features include progressive degeneration of dorsal root ganglia and sensory axons, dorsal columns, Clarke's column, and dentate nuclei of the cerebellum. Elevation of frataxin in these anatomic regions is a therapeutic approach that is likely to be beneficial in addressing the neurological components of disease. However, AAV-mediated gene delivery for therapeutic expression of frataxin in the CNS and distribution to Clarke's column and cerebellar dentate nuclei, have not been investigated to a significant extent. Furthermore, a direct head-to-head comparison of multiple capsids (AAV2, 5, 6, 9, DJ, DJ8, rh10) with intrathecal dosing in non-human primates, a key translational step for therapy, has not been reported previously. Here, we used these 7 capsids to package a single-stranded (ss) vector genome (vg) containing the human frataxin gene driven by the chicken β-actin promoter, and compared frataxin expression in mouse and then non-human primate CNS. In the mouse, dramatic differences in frataxin expression were observed after intracerebroventricular injection of these capsids. Intrastriatal injection in the mouse resulted in frataxin expression patterns that differed qualitatively from those observed after intracerebroventricular injection. In vivo data from both mouse and non-human primate studies will be reported. These results will not only guide the selection and optimization of a capsid for AAV gene therapy of Friedreich's ataxia, but also provide useful information for engineering capsids for other CNS disorders.