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A. M. Komaromy, J. S. Rowlan, J. J. Alexander, V. A. Chiodo, W. W. Hauswirth, G. M. Acland, G. D. Aguirre; Photoreceptor Deconstruction by CNTF Enhances rAAV-Mediated Gene Replacement Therapy Outcome in Adult Dogs With CNGB3 Achromatopsia. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4299.
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© ARVO (1962-2015); The Authors (2016-present)
To study the effect of intravitreal CNTF administration on retinal function, and enhancement of therapeutic efficiency with rAAV-mediated gene replacement therapy in adult dogs with CNGB3 achromatopsia.
Baseline full-field ERGs were recorded on 5 achromatopsia affected dogs. One eye of each dog was injected intravitreally with 12µg (30µL) CNTF (kindly provided by Dr. Rong Wen, Bascom Palmer Eye Institute), while the fellow eyes were injected with 30µL of PBS. After 7 days, ERG recordings were repeated, and 4 dogs (age range: 14 - 26 months) were treated bilaterally with subretinal injections of rAAV5-PR2.1-hCNGB3. The injected volumes varied between 140 - 180 µL containing 1.02 - 4.02 x 1013 particles per mL. Full-field ERGs were recorded again 5 weeks post CNTF (4 weeks after subretinal injection). Retinas were collected from 2 dogs for measurement of transgene expression and cone-specific gene expression levels by qRT-PCR.
Baseline ERGs confirmed normal rod-mediated function, but lack of cone-mediated responses. One week following intravitreal CNTF application, conventional full-field ERG responses were almost completely extinguished, but remained normal in the PBS injected eyes. Rod ERG responses recovered at 5 weeks post CNTF injection. Cone function was restored with the CNTF/ rAAV5-PR2.1-hCNGB3 combination, but not with the rAAV-mediated gene therapy alone or in combination with intravitreal PBS injections. High levels of hCNGB3 transgene expression were found in all rAAV injected eyes, regardless of success (intravitreal CNTF) / failure (intravitreal PBS) in restoring cone function. Clinically, no long-term adverse effects were observed after intravitreal CNTF injection.
Intravitreal administration of CNTF leads to a fully reversible depression of outer retinal function (present study), and dedifferentiation of photoreceptors (Beltran et al., 2007) in dogs, a process we now term photoreceptor deconstruction. We posit that the improved success rate of cone directed gene therapy in older mutant animals may result from treatment of cones that have dedifferentiated, and are able to reform the molecular components of the outer segment following redifferentiation.
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