Evaluation of adeno-associated virus-mediated gene transfer into the rat retina by clinical fluorescence photography

The purpose of this study was to evaluate recombinant adeno-associated viru s (AAV) as an in vivo gene transfer vector for the retina and to explore th e possibility of monitoring the expression of green fluorescent protein (GF P) using a noninvasive method. Rats were injected subretinally with rAAV-gf p or rAAV-lacZ, Strong expression of the reporter gene in a circular area s urrounding the injection site was observed in retinal whole mounts and tiss ue sections, Higher magnification revealed that cells demonstrating high le vels of green fluorescence were hexagonal in shape, indicating they were re tinal pigment epithelium (RPE) cells. Histological observation of retinal s ections demonstrated that recombinant AAV specifically transduced RPE cells . Ten animals were injected with rAAV-gfp for longitudinal studies and the fluorescence was monitored by retinal fluorescence photography. The GFP sig nal was detected in 100% of the animals as early as 2 weeks postinjection a nd remained present throughout the experimental period of 4 months. After 2 weeks, a gradual increase in the number of transduced cells occurred befor e reaching maximal levels of GFP expression at 8 weeks. This was followed b y a small decrease over 4 weeks before reaching stable expression at 16 wee ks. Our results demonstrated that rAAV efficiently transduces rat RPE cells and that retinal fluorescence photography is suitable for monitoring GFP e xpression. By using this noninvasive technique, we demonstrated that repeti tive measurements of GFP expression in vivo in the rAAV-gfp-transduced reti na are possible. This study demonstrated that retinal fluorescence photogra phy is a potent tool for studying AAV-mediated gene delivery in the retina.