Delivery of therapeutic transgenes to retinal photoreceptors using adeno-associated virus (AAV) vectors has traditionally required subretinal injection. Recently, retinal transduction efficiency following intravitreal injection (IVT) has been improved in rodent models through use of capsid-mutant AAV vectors; but remains limited in large animal models. Reasons for this inter-species variation remains undefined. The studies described herein compare the performance of newly developed AAV vectors containing capsid amino acid substitutions following IVT in dogs. The ability of these novel vectors to transduce inner and outer retinal cell populations was determined and compared to prior reports in dogs as well as other large animal models. Multiple previously described barriers to IVT retinal gene therapy were evaluated and manipulated to assess their specific role in attenuating the performance of the vectors. The ability of two promoter constructs to restrict reporter transgene expression to photoreceptors was also evaluated. When progressive intraocular inflammation developed during one investigation, the study plan was modified to allow detailed characterization of the etiology as a secondary goal. The collective results provide crucial insight into factors impacting AAV retinal transduction efficiency, and guidance in avoiding adverse effects following IVT administration of vectors in dogs. Ultimate translation of these findings into the human gene therapy field will provide groundwork for maximizing safety and efficacy of IVT retinal AAV gene therapy for patients affected by both heritable and acquired blinding retinal diseases.
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