Evaluation Of AAV-mediated BEST1 Expression In The Canine Retina

Abstract

Purpose: : BEST1 gene mutations are responsible for Best vitelliform macular dystrophy (BVMD), an inherited RPE disorder leading to progressive vision loss in humans. Currently, there is no effective treatment for this disease. Canine multifocal retinopathy (cmr), caused by mutations in the dog ortholog, has been established as a model for BVMD. We have previously shown that AAV-mediated gene delivery under the human BEST1 (hBEST1) promoter specifically targets RPE cells in the canine retina. A single subretinal injection of AAV2-hGFP driven by hBEST1 promoter resulted in stable transgene expression up to the 6 months post injection without any adverse effects. Purpose of these studies was to test AAV-mediated BEST1 expression and assess the efficiency and safety of the treatment in cmr1 affected dogs.

Methods: : Nine month old cmr1 dogs exhibiting bilateral multifocal lesions were subretinally injected with AAV2 vector expressing either canine (2.61x10¹² vg/ml) or human (5.88x10¹² vg/ml) BEST1 under control of hBEST1 promoter. Each treated eye was monitored clinically and imaged serially in vivo using HRA/OCT. For morphological studies, treated and control tissue samples were collected 4 weeks after injection.

Results: : Specific bestrophin-1 signal was detected within the treated area, and comparable effectiveness was noted between human and canine AAV2 constructs. Based on the spectral-domain OCT analyses, lesions within the treated region disappeared within 3 months after AAV2-BEST1 injection, while untreated areas of the injected eye or contralateral control eye (non-injected or BSS injected) remained unchanged. Both, the in vivo imaging and immunohistochemical evaluation revealed no adverse effects secondary to the BEST1 gene replacement therapy with either construct.

Conclusions: : Our preliminary data suggest that BEST1 gene therapy is effective and safe in cmr1 mutant animals. Additional experiments determining long-term effects of AAV-mediated BEST1 expression are in progress.

Keywords: gene transfer/gene therapy • retinal pigment epithelium • gene/expression