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K. Narfstrom, R. Bragadottir, T.M. Redmond, E.P. Rakoczy, M.L. Katz; Long-term Ultrastructural Studies in RPE65-/- Dogs with and without Unilateral rAAV.RPE65 Gene Transfer Treatment . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3589.
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Purpose: Previous studies have shown electroretinographic (ERG) recovery up to 32% of normal photopic b-wave amplitudes in the treated eyes of RPE65-/- dogs following subretinal gene transfer using rAAV.RPE65. Long-term follow-up ERG studies also showed slight recovery in photopic responses in the contralateral, untreated eye. Ultrastructural studies were undertaken to determine whether there are morphological changes that correlate with the functional recovery of the rAAV.RPE65 treated eye but also of the untreated, fellow eye. Methods: A large group of RPE65 null mutation dogs underwent gene transfer via subretinal injections of rAAV.RPE65 into one eye. One dog, treated at age 4 mo., was euthanized 10 mo. following unilateral gene transfer. An untreated affected littermate was euthanized at the same time as a control. After enucleation, eyecups were immersion fixed for electron microscopy and dissected to obtain regions both within and outside the area of treatment. Similar areas were examined in eyecups of the control dog. Results: In the rAAV.RPE65 treated area almost no RPE lipoid inclusions, characteristic of the RPE65 null mutation, were observed. In the opposite untreated eye the numbers and sizes of lipid droplets were diminished, relative to those present in an eye of the untreated dog. Rod and cone outer segment morphology appeared orderly and elongated in the treated eye compared to that of the untreated littermate. In the contralateral, untreated eye of the gene transfer dog, there appeared to be saving only of cone morphology. Conclusions: These results establish a basis for the functional recovery of scotopic and photopic ERG responses in the eye treated by gene transfer and also in the contralateral, untreated eye. Molecular and further structural studies are needed to elucidate the exact mechanisms for these surprising functional and structural effects. It is possible that transfer of the gene therapy effect from one eye to the other was the result of RPE65 protein transfer from the treated to the untreated eye. CR: None Support: Foundation Fighting Blindness, Research to Prevent Blindness
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