BEST1 gene augmentation therapy corrects light-modulated retinal micro-detachments

Abstract

Purpose : BEST1 gene mutations are associated with one of the most common forms of monogenic macular degeneration worldwide characterized by retina-wide electrophysiological defect and formation of subretinal lesions. The pathophysiology of interaction between retinal pigment epithelium (RPE) and photoreceptors (PRs) preceding development of clinically obvious lesions remains not well understood. Using three canine BEST1 models (cBest), we explored the earliest disease expression, and evaluated outcomes following AAV2-BEST1 gene augmentation therapy.

Methods : cBest (n=12) and control (n=10) dogs underwent sequential cSLO/SD-OCT imaging after dark-adaptation overnight followed by incremental exposure to light. Outer retinal structure was measured. Subretinal injections were performed with AAV2-VMD2-hBEST1 (0.1-5E+11 vg/mL) or BSS control. Retinal structure was examined before disease onset or 52-103 weeks post injection by immunohistochemistry (IHC) and confocal microscopy. Human patients with autosomal recessive bestrophinopathy (ARB) were studied with structural and functional measures to gain insight into the distribution of retina-wide disease beyond the clinically detectable lesions.

Results : Ex vivo assessments of young cBest retinas before clinical disease onset revealed major structural alterations at the RPE-PR interface associated with retina-wide underdevelopment of RPE apical microvilli. In vivo imaging demonstrated a diffuse retina-wide RPE-PR micro-detachment, which contracted with dark-adaptation and expanded upon exposure to moderate lights. Subretinal AAV2-BEST1 gene augmentation reversed not only clinically detectable lesions, but also the light-modulated micro-detachments. IHC analyses confirmed correction of the structural alterations at the RPE-PR interface in areas with BEST1 transgene expression. ARB patients showed retinotopic distribution of structural and functional defects beyond that expected from photoreceptor degeneration.

Conclusions : Loss of RPE apical microvilli and resulting retina-wide micro-detachment represent the earliest cBest disease features modulated by light exposure. This primary subclinical defect as well as the gross localized lesions is reversible with AAV2-mediated BEST1 gene augmentation therapy. Human translation of canine BEST1 gene therapy has promise to alter positively the otherwise negative disease course in patients affected with bestrophinopathies.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.