Poster Session II: Intravitreal gene therapy in primate reaches extrafoveal cones.

Intravitreal delivery of gene therapy vectors to the retina carries lower risk of adverse events versus subretinal injections, but efficiently targeting cones is a challenge. We used a new adeno-associated vector (AAV) to deliver genes to primate cone photoreceptors. The vector carries a cassette directing expression of an engineered 493 nm opsin to long- and middle-wavelength (L/M) cones, and was injected into the vitreous of the left eye of an adult macaque. An identical AAV carrying a fusion of the engineered opsin to green fluorescent protein (GFP) was injected into the right eye. Electroretinograms were performed on the left eye before and after injection to measure isolated 493 nm light responses; 5 weeks post-injection, response increased modestly. A central strip of the right eye was prepared for histology with cryosections; we found ~30% of cones in the fovea had been transduced, with a preference toward L/M cones (see https://iovs.arvojournals.org/article.aspx?articleid=2782955). Upon close examination of GFP in the peripheral retina, we were surprised to find extensive expression in cones across the retina. Here, we report patches of expression from the perifovea to the retinal margin which reaches ~10% of cones. Expression patches appeared stochastically, or in regions containing blood vessels or disrupted Muller cells. This demonstrates that extrafoveal expression is attainable using intravitreal injection of gene therapy vectors in an adult primate.