Changes in adeno-associated virus-mediated gene delivery in retinal degeneration

Gene therapies for retinal degeneration have relied on subretinal delivery of viral vectors carrying therapeutic DNA. The subretinal injection is clearly not ideal as it limits the viral transduction profile to a focal region at the injection site and negatively affects the neural retina by detaching it from the supportive retinal pigment epithelium (RPE). We assessed changes in adeno-associated virus (AAV) dispersion and transduction in the degenerating rat retina after intravitreal delivery. We observed a significant increase in AAV-mediated gene transfer in the diseased compared with normal retina, the extent of which depends on the AAV serotype injected. We also identified key structural changes that correspond to increased viral infectivity. Particle diffusion and transgene accumulation in normal and diseased retina were monitored via fluorescent labeling of viral capsids and quantitative PCR. Viral particles were observed to accumulate at the vitreoretinal junction in normal retina, whereas particles spread into the outer retina and RPE in degenerated tissue. Immunohistochemistry illustrates remarkable changes in the architecture of the inner limiting membrane, which are likely to underlie the increased viral transduction in diseased retina. These data highlight the importance of characterizing gene delivery vectors in diseased tissue as structural and biochemical changes can alter viral vector transduction patterns. Furthermore, these results indicate that gene delivery to the outer nuclear layer may be achieved by noninvasive intravitreal AAV administration in the diseased state.