AAV–Mediated Gene Therapy Confers Partial Vision Rescue and Horizontal Cell Protection in a Mouse Model of Achromatopsia

Abstract

Purpose: : To assess the efficacy of AAV–mediated gene therapy in rescuing vision in the cpfl3 mouse model of achromatopsia (recessive cone α–transducin mutant). We previously reported complete rescue of cone electroretinogram (ERG) b–wave in cpfl3 mice using AAV vector technology. Here we assess cone–dependent visual function and horizontal cell morphology in treated mice.

Methods: : A normal mouse cone α–transducin cDNA was cloned into an AAV vector under control of the human red cone opsin promoter and packaged into serotype 5 capsids. Single eyes of cpfl3 mice were injected in the subretinal space on P25 with 0.6 microliters of virus (8x10¹³ vector genomes). Mice were then assayed for cone ERG rescue and visual function 1 and 3 months post–injection, respectively. We assessed visual function by measuring the contrast sensitivities of treated and untreated eyes with an optomotor response method (Optomotry©). We measured the contrast of a rotating vertical sinusoidal pattern necessary to evoke a threshold behavioral response of 70% correct detection of direction of pattern rotation. Responses of the mice to the rotating pattern were judged by an observer blinded to both the direction of rotation and to which eye was AAV treated. The mice were then sacrificed and their retinas were analyzed by DiI tracing and confocal microscopy to assess horizontal cell morphology, in which the investigators were also blinded.

Results: : Of seven treated eyes, six had varying levels of cone ERG rescue, and one had no rescue, when compared to WT. The six mice with partial cone rescue in their AAV–treated eyes also exhibited partial rescue of contrast sensitivity (∼10–fold increase) in the same eyes. Untreated cpfl3 mice showed no recovery of contrast sensitivity, and WT showed no loss. Confocal analysis of immunolabeled retinal sections depicted a normal distribution of cone pedicles and horizontal cell dendrites within the outer plexiform layer in both eyes, but DiI–labeling of horizontal cell dendritic fields in whole retinas showed a significantly larger dendritic area in the treated eye.

Conclusions: : Our data demonstrate partial restoration of vision and horizontal cell morphology after a single injection of our therapeutic AAV vector. To our knowledge these studies are the first to show cone–targeted improvement in retinal anatomy and vision.

Keywords: gene transfer/gene therapy • contrast sensitivity • retina: distal (photoreceptors, horizontal cells, bipolar cells)