Gene delivery to the eye using adeno-associated viral vectors

Adeno-associated virus (AAV) vectors provide a useful way to deliver genes to the eye. They have a number of important properties which make them suitable for this purpose, not least their lack of significant pathogenicity and the potential for long-term transfection of retinal cells. The optimal methods for AAV-mediated gene delivery are determined by the location and characteristics of the target cell type. Efficient gene delivery to photoreceptors and pigment epithelial cells following subretinal injection of AAV has been achieved in various animal models. AAV-mediated gene therapy has been shown to slow photoreceptor loss in rodent models of primary photoreceptor diseases and in dogs with a naturally occurring disease similar to human Leber's congenital amaurosis (LCA). Efficient gene delivery to other cell types such as retinal ganglion cells (RGCs), however, has been more problematic. In this article, we review the potential uses of AAV-mediated gene delivery to the eye. We describe the selection of an appropriate AAV vector for ocular gene transfer studies and discuss the techniques used to deliver the virus to the eye and to assess ocular transfection. We emphasize our techniques for successful gene transfer to retinal ganglion cells, which have often proven challenging to transfect with high efficiency. Using a modified AAV incorporating a chicken beta-actin (CBA) promoter and the woodchuck hepatitis posttranscriptional regulatory element, we describe how our techniques allow approximately 85% of rat retinal ganglion cells to be transfected within 2 weeks of a single intravitreal virus injection. Our techniques facilitate the study of the pathogenesis of RGC diseases such as glaucoma and the development of novel new treatments based on gene therapy.