Targeting Channelrhodopsin-2 to ON-bipolar Cells With Vitreally Administered AAV Restores ON and OFF Visual Responses in Blind Mice

Abstract

Most inherited retinal dystrophies display progressive photoreceptor cell degeneration leading to severe visual impairment. Optogenetic reactivation of retinal neurons mediated by adeno-associated virus (AAV) gene therapy has the potential to restore vision regardless of patient-specific mutations. The challenge for clinical translatability is to restore a vision as close to natural vision as possible, while using a surgically safe delivery route for the fragile degenerated retina. To preserve the visual processing of the inner retina, we targeted ON bipolar cells, which are still present at late stages of disease. For safe gene delivery, we used a recently engineered AAV variant that can transduce the bipolar cells after injection into the eye's easily accessible vitreous humor. We show that AAV encoding channelrhodopsin under the ON bipolar cell-specific promoter mediates long-term gene delivery restricted to ON-bipolar cells after intravitreal administration. Channelrhodopsin expression in ON bipolar cells leads to restoration of ON and OFF responses at the retinal and cortical levels. Moreover, light-induced locomotory behavior is restored in treated blind mice. Our results support the clinical relevance of a minimally invasive AAV-mediated optogenetic therapy for visual restoration.

Insight into the mechanisms of enhanced retinal transduction by the engineered AAV2 capsid variant ‐7m8

“…The insertion is composed of a variable heptamer (LGETTRP) region and 3 amino acids used as linkers for creating the library from which the variant was chosen. This new vector, AAV2-7m8, was recently used for therapeutic inner and outer retinal gene delivery in various animal models of retinal disease leading to successful proof-on-concept gene therapies (Byrne et al, 2014;Byrne et al, 2015;Dalkara et al, 2013;Macé et al, 2014).…”

A New Promoter Allows Optogenetic Vision Restoration with Enhanced Sensitivity in Macaque Retina

“…[7][8][9][10][11][12][13][14][15] Expression of channelrhodopsin in RGCs might allow greater spatial resolution and acuity than that achieved with current prosthetic devices. This has motivated a large body of proof-of-concept studies in rodents and other small animals, which have shown the feasibility of the approach, [7][8][9][10][16][17][18] and a first-in-human phase 1 clinical trial was initiated recently (ClinicalTrials.gov NCT02556736). However, the use of genetically encoded opsins for vision restoration has several setbacks in terms of clinical development.…”

Highly Efficient Delivery of Adeno-Associated Viral Vectors to the Primate Retina

“…Significant improvements in transduction of rodents were achieved with two variants in particular, AAV2-7m8 and AAV2(quadY-F+T-V), capable of transducing all layers of the rodent retina including photoreceptors. 20,31,49,51 Although improved in terms of magnitude of expression in primates, these variants still produced the restrictive pattern of expression limited to the foveal area and large blood vessels (see Ref. 20, and S.E.…”