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Simone Iwabe, Sem Genini, Raghavi Sudharsan, Alfred S Lewin, Brian P Rossmiller, William W Hauswirth, Gustavo D Aguirre, William A Beltran; Assessment of AAV-mediated RHO Augmentation in the Canine T4R RHO Model of Autosomal Dominant Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3316.
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To determine if AAV2/5-mediated delivery of either mouse or human RHO cDNA to RHOT4R/+ dogs is safe and provides protection from light-induced retinal degeneration.
A total of 11 RHOT4R/+ dogs (ages: 12 - 34 wks) were used. Subretinal deliveries of 150 μl of an AAV2/5 construct (titer: 6.79 x 1011 vg/ml) carrying either full length mouse RHO (mRHO301) or human RHO (hRHO) cDNA under the control of a mouse rod opsin promoter (mOP) were performed respectively in 8 and 9 eyes under infrared light illumination. Four eyes were used as controls and were either sham-injected with BSS (1 eye), AAV2/5 carrying GFP (1 eye), or un-injected (2 eyes). Six to seven weeks after gene delivery retinas were exposed to a single, acute dose of white light delivered with a monocular Ganzfeld. Two doses (corneal irradiances: 0.5 mW/cm 2 or 1 mW/cm 2 for 1 min) which have been previously shown to cause acute light damage in the T4R RHO but not WT retina were used. ONL thickness within the treated retinal area was evaluated by non-invasive in vivo cSLO/sdOCT imaging before, and 6-7 weeks after transgene delivery, as well as 2 weeks post light exposure (LE).
Six to 7 weeks post injection, a 10% and 4% mean decrease in ONL thickness were found in the retinal areas treated, respectively, with mRHO301 (n=8) and hRHO (n=4). The single retina injected with BSS showed a 2% reduction. Retinas (n=4) treated with mRHO301 had an 87% decrease in ONL thickness 2 weeks after high dose light exposure; and an 83% reduction when exposed to the lower dose (n=1). The single retina injected with BSS had a 94% loss of ONL after high dose exposure. Retinas treated with hRHO and exposed to the high (n=1) and low (n=5) doses of light, had respectively a 92% and 93% loss of ONL thickness 2 weeks post LE. Results were comparable to that of the single un-injected retina after low dose LE (95%). Retinas that received the mRHO301 (n=3) or hRHO (n=3) transgenes but were unexposed to light had, respectively, only a 2% and 3% decrease in ONL thickness during that same 2 week period.
While AAV-mediated subretinal delivery of mRHO301 was associated with a mild ONL thinning (up to 10%), transduction of the hRHO transgene did not appear to be cytotoxic to RHO T4R/+ photoreceptors. Yet, RHO gene augmentation did not prevent light-induced retinal degeneration.
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