AAV2/5 Mediated Gene Augmentation Rescues Photoreceptors in Canine Models of RPGR-XLRP

Abstract

Purpose: : Mutations in the RPGR gene are the most common cause of X-linked RP in man. Two naturally-occurring canine models (XLPRA1 and XLPRA2) with distinct deletions in RPGRORF15 recapitulate the spectrum of disease phenotypes found in humans. Both models were used to test if AAV-mediated gene transfer of human RPGRORF15 cDNA can rescue photoreceptors when delivered prior to (XLPRA1) or after (XLPRA2) the onset of degeneration.

Methods: : Two AAV2/5 vector constructs (titer: 1.51 x E11 vg/ml) carrying full-length human RPGRORF15 cDNA under the control of either a hGRK1 or hIRBP promoter were injected subretinally in XLPRA1 (150 ul at 28 weeks), and XLPRA2 (70 ul at 5 weeks) dogs. Contra-lateral eyes were sham-injected with BSS and served as controls. Photoreceptor structure and function was assessed by means of non-invasive retinal imaging (cSLO/ SD-OCT) and ERG, and by morphology/IHC at termination.

Results: : In vivo retinal imaging showed preserved ONL thickness and IS/OS structure in the treated retinal areas. Rod and cone function was greater in treated than in control retinas. Morphology studies confirmed the rescue of photoreceptor structure within the treated areas, as well as the reversal of rod and M/L cone opsin mislocalization and the prevention of rod neurite sprouting. Potent expression of the hRPGR transgene was found exclusively in photoreceptors located within the treated areas.

Conclusions: : These results show for the first time that gene transfer of the full length human RPGRORF15 cDNA provides both structural and functional rescue in an animal model of RPGR-XLRP.

Keywords: gene transfer/gene therapy • retina • photoreceptors