Gene therapy mediates cone rescue and rejuvenation in the R91W mutant form of Rpe65‐deficiency mice

Abstract

Abstract Purpose Given the advances of gene therapy studies to cure RPE65‐derived Leber Congenital Amaurosis (LCA) (clinical trials phase I), it is of prime importance to examine how cones can be rescued in different mutant contexts. Consequently, we evaluated the effect on retinal activity and cone survival of lentivirus‐mediated gene therapy in the R91W knock‐in mouse model expressing the mutant Rpe65R91W gene. Methods An HIV‐1‐derived lentiviral vector (LV) expressing either the GFP or the mouse Rpe65 cDNA under the control of a 0.8 kb fragment of the human Rpe65 promoter (R0.8) was produced. LV‐R0.8‐RPE65 or GFP was injected into 5‐days‐old (P5) or 1 month‐old R91W mice. Functional and morphological retinal rescues were investigated at 4 months of age. Results Increased light sensitivity was detected by ERG and pupillary light responses in animals injected with LV‐R0.8‐RPE65 at both P5 and 1 month compared to controls. Histological analysis showed improved expression of cone markers and cone outersegment morphology. Furthermore, the density of cones in the region of RPE65 delivery after treatment at P5 reached the wild type level. However, before injection at 1 month of age, only a fraction of the cones (40% of the number found in WT animals) in the Rpe65R91W/R91W mice expressed cone transducin, this fraction increased to 64% after treatment. Moreover, these cones appeared normal. Conclusion We show that lentivirus‐mediated Rpe65 gene transfer is very efficacious in early treatments and still efficient during the course of cone degeneration. Moreover, the treatment at 1 month shows a rejuvenation process of the diseased cones. Thus patient suffering from R91W mutation might benefit from a prolonged therapeutic window.