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Kristin Lee Gardiner, William A Beltran, Gustavo D Aguirre; Association of long-term RPE65 expression and photoreceptor preservation in RPE65-gene therapy-treated canines. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5318.
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Retinal pigment epithelium-specific protein 65 kDa (RPE65) mutations result in deficiency of 11-cis-retinal, leading to multiple forms of retinal degeneration and early-onset blindness, including Leber congenital amaurosis (RPE65-LCA). Gene therapy trials in both canines and humans for RPE65-LCA have shown safety and efficacy, at least in the short term. We now have examined the association between photoreceptor (PR) structural preservation and RPE65 expression in treated areas in long-term studies of canine eyes.
The retinas of RPE65-/- dogs treated unilaterally by subretinal rAAV2-CBSB-hRPE65 were examined 4-5.5 years following treatment, and compared to untreated fellow eyes. All eyes were fixed in paraformaldehyde, posterior cups embedded in OCT media, and retinas serially sectioned. Histopathologic and immunohistochemical analysis of treated and untreated retinas was performed to characterize outer nuclear layer (ONL) thickness, outer segment (OS) and inner segment (IS) preservation, and RPE65 expression.
H&E staining of serial sections extending from optic nerve to ora serrata indicated increased ONL thickness and improved IS and OS preservation in treated areas with RPE65 expression compared with corresponding regions in the untreated contralateral eyes, albeit still decreased compared to age-matched normal control eyes. The ONL thickness was focally preserved in areas up to 4000 µm from the nearest area of RPE65 labeling, indicating potential 11-cis-retinal diffusion from treated to untreated areas of the retina. The ONL thickness in these regions was less than in areas with RPE65 expression, and there appeared to be a general gradient of ONL thinning and loss of IS/OS preservation with increasing distance from treated areas having RPE65 expression.
Results suggest that RPE65 expression induced by subretinal gene therapy is sustained and may exert its protective effects on photoreceptors beyond the treated area. It is possible that retinoid diffusion in the interphotoreceptor matrix (IPM) away from the treatment site mediates this effect.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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