The Lessons of rAAV Mediated RPE65 Gene Delivery from Mouse and Dog Models of LCA

Abstract

Abstract: : Purpose: To compare the response to recombinant adenoassociated virus (rAAV) mediated RPE65 gene expression in the Rpe65-/- mouse and Briard dog models of Leber’s Congenital Amarousis (LCA). Methods: Animals were subretinally injected with rAAV.RPE65 and at different time points subjected to behavioral studies,and electroretinography (ERG) recordings. Following euthanasia the enucleated eyes were analyzed by histology, immunohistochemistry and electronmicroscopy. Results: Following subretinal injection, rAAV.GFP and rAAV.RPE65 transgene expression was readily detectable by fluorescent microscopy and immunohistochemistry, respectively in both models and was maintained up to 18 months as shown in the mouse. ERGs showed that dark-adapted b-wave amplitudes recovered to an average of 25% of normal, and light adapted b-wave amplitudes to 20% of normal amplitudes in the mouse model and slightly more in the dog model and were not reduced in dogs during a 9-12 months follow-up period. No systemic side effects were observed in either model but 75% of rAAV.RPE65-injected dogs developed uveitis. Ultrastructurally a reversal of RPE lipid droplet accumulation at the rAAV.RPE65 injection site was observed in both animals models. In the mouse model there was a recovery of up to 50% of short wavelength cone opsin-positive cells. However, this functional recovery was not accompanied by a reduction of the degenerative process of photoreceptors in affected mice. Conclusions: These observations have significant clinical implications as they suggest that gene therapy might provide a treatment that can prevent blindness or delay the onset of blindness in LCA sufferers, potentially for decades.

Keywords: animal model • gene transfer/gene therapy • retinal degenerations: hereditary