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A. M. Komaromy, J. J. Alexander, V. A. Chiodo, M. M. Garcia, J. C. Tanaka, C. M. Craft, G. M. Acland, W. W. Hauswirth, G. D. Aguirre; Long-Term Rescue of Cone Function in a Canine Model of Achromatopsia by rAAV-Mediated Gene Therapy. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1131.
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To evaluate long-term rescue of cone function following rAAV-mediated gene therapy in two canine models of achromatopsia as a function of age at treatment and gene promoter.
rAAV5 containing human CNGB3 cDNA was injected unilaterally into the subretinal space of dogs affected by either a null or missense mutation (D262N) of CNGB3. The dogs were 3 to 81 weeks old at the time of treatment. The transgene was under control of a truncated human red cone opsin promoter [three variations: PR0.5 (a short proximal promoter), 3LCR-PR0.5 (PR0.5 plus 3 copies of the 35bp LCR), and PR2.1 (PR0.5 plus about 1.5kbp surrounding the LCR)], or the human cone arrestin promoter (hCAR900). Depending on the size of the dog, the total volume injected varied between 50 and 180 µl containing between 3.73 and 16.5 x 1012 genome containing particles/ml. At least 4 weeks after treatment, cone function was evaluated behaviorally and by electroretinography (ERG) under photopic conditions.
Successful restoration of cone function was achieved in 10 dogs with either CNGB3 null or missense mutation. While positive results were seen with all 4 promoters, the longest version of the human red cone opsin promoter (PR2.1) led to the most robust restoration of cone function as assessed by ERG amplitudes and duration of rescue effect. Two dogs treated with PR2.1 were monitored for over 14 months, and no deterioration of the rescue effect was observed. Based on previous data with a GFP reporter gene, the human red cone opsin promoters drive expression only in the canine L/M-cones, while the human cone arrestin promoter drives expression in both L/M- and S-cones. The amplitude of the rescued cone function decreased with age at injection, with the best results achieved at 3 weeks and no detectable rescue when the injection occurred at 1 year of age.
Robust, long-term rescue of cone function could be achieved in 2 canine models of achromatopsia. The best outcome was observed when animals were treated at a young age. Our results are promising for future gene therapy in human patients with achromatopsia, or other diseases that affect cones.
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