Safety and Efficacy of Retinal Optogenetic Therapy in Canine Models

Abstract

Purpose: Advanced retinal disease is a major cause of severe visual impairment. When conventional therapies have failed or are not available, limited vision could potentially be restored via an optogenetic approach - delivering microbially derived light-sensitive ion channels to remaining retinal neurons. The safety and efficacy of this strategy must be established in large animal models prior to clinical translation. Here, in canine models of retinal degeneration, we deliver a photosensitive hyperpolarizing chloride channel to degenerate photoreceptor cells lacking outer segments.

Methods: Adeno-associated virus serotype 9 (AAV 2/9) containing Natoromonas Halorhodopsin (NpHR) cDNA under control of the cone arrestin (CAR) promoter was injected into the eyes of dogs of the following strains: PDE6β^-/- (n=1), Crd3 (n=2), and wild type (n=2). Subretinal injections were carried out in all animals except for the oldest (Crd3), in which there was cataract and scarring of the retina. This animal was injected intravitreally. Dogs were followed post-operatively for surgical and immunological complications, and sera and peripheral blood mononuclear cells (PBMCs) were collected at baseline and serially post treatment. Efficacy was assessed by pre and post operative navigational behavior as well as quantitative pupillometry.

Results: Post-operative clinical exam and indirect ophthalmoscopy revealed no evidence of infection or inflammation. Qualitative evaluation of navigational videos show no diminution in navigational abilities of the wildtype dogs and suggestions of improvement in the PDE6β^-/- dog and the Crd3 dog which received sub-retinal injection, but not the Crd3 dog with intravitreal injection. NpHR is most sensitive at ~570 nm, and thus the pupillary light reflex was assessed at both blue and red wavelengths. There was no relative afferent pupillary defect (APD) in the Crd3 dog injected subretinally at either color. In the PDE6β^-/- dog, there was no APD with blue light, but with red light, the injected eye appears to be more light sensitive.

Conclusions: Retinal optogenetic therapy targeting degenerate photoreceptors in two different dog models appears safe in short term follow up. Efficacy studies suggest possible benefit in a PDE6β^-/- dog, and further outcome measures are ongoing.

Keywords: 538 gene transfer/gene therapy • 696 retinal degenerations: hereditary