Efficient transduction and optogenetic stimulation of retinal bipolar cells by a synthetic adeno‐associated virus capsid and promoter

Abstract

In this report, we describe the development of a modified adeno-associated virus (AAV) capsid and promoter for transduction of retinal ON-bipolar cells. The bipolar cells, which are post-synaptic to the photoreceptors, are important retinal targets for both basic and preclinical research. In particular, a therapeutic strategy under investigation for advanced forms of blindness involves using optogenetic molecules to render ON-bipolar cells light-sensitive. Currently, delivery of adequate levels of gene expression is a limiting step for this approach. The synthetic AAV capsid and promoter described here achieves high level of optogenetic transgene expression in ON-bipolar cells. This evokes high-frequency (∼100 Hz) spiking responses in ganglion cells of previously blind, rd1, mice. Our vector is a promising vehicle for further development toward potential clinical use.

Optogenetic Approaches to Restoring Vision

“…Doroudchi et al (2011) were the first to achieve its expression in ON bipolar cells under the control of the mGluR6 promoter via a subretinal injection of an AAV2/8 vector combination that harbored a capsid mutation and a self-complementary AAV cassette; this improved viral transduction efficiency in ON bipolar cells and restored visually guided behavior in multiple blinded mouse lines. Two recent studies further improved transduction efficiency in ON bipolar cells by using a new AAV2/2-based capsid variant (Mace et al 2015) and the combination of a capsid variant of AAV2/8 and an enhanced mGluR6 promoter (Cronin et al 2014). …”

Let There Be Light: Gene and Cell Therapy for Blindness

“…As such, it has been extensively explored for its ability to target various groups of cells in the retina. [23][24][25][26][27][28] As an example, it has been engineered to provide gene delivery into deeper layers of the retina after intravitreal administration, removing the need for subretinal detachment. [23][24][25]29 One such AAV variant, called 7m8, was able to ensure efficient pan-retinal delivery of the therapeutic gene from the vitreous, with long-term histological and functional rescue of Xlinked retinoschisis and Leber congenital amaurosis (LCA) phenotypes in mice and provided superior retinal gene delivery in nonhuman primates.…”

Vectors and Gene Delivery to the Retina

“…AAV5, 8, and 9 have the advantage of giving rise to faster onset gene expression compared to AAV2 as well as gene expression in cone photoreceptors (Alexander et al 2007, Komáromy et al 2010, Mancuso et al 2009). Photoreceptors can also be targeted via intravitreal injections of engineered AAV capsids (Cronin et al 2014;Dalkara et al 2013;Kay et al 2013;Petrs-Silva et al 2009, 2011. Directed evolution and rational design yielded AAV capsids capable of efficient outer retinal gene delivery from the vitreous.…”