Mouse Studies Support Intravitreal Gene Therapy for Blue Cone Monochromacy

Abstract

Purpose : Subfoveal injection of recombinant adeno-associated virus (AAV)-based gene therapy to restore opsin expression in foveal cones poses a risk to the fragile central retinal structure in blue cone monochromacy (BCM), a rare X-linked retinal disease resulting from the congenital absence of L- and M- opsins. Although many (non-functional) cones are present in retina of patients with BCM, varying degrees of macular thinning present a challenge for subretinal delivery. We are developing ADVM-062 (AAV2.7m8-MNTC-hOPN1LW), an AAV vector for cone-specific expression of human L-opsin (hLopsin) and optimized for intravitreal (IVT) delivery. Pharmacological activity of this IVT injected vector was tested in wt C57BL/6 mice that naturally lack L-opsin.

Methods : Animals received a single IVT injection of ADVM-062 or vehicle; the contralateral eye served as a control. To isolate hLopsin-mediated function, ERG responses to 660 nm flashes of fixed intensity were measured in the presence of a ganzfeld background of 513 nm and varying intensities.
In addition, cone-isolating 25 Hz flicker ERG responses to 660 nm flashes were recorded. ERGs were recorded 3, 6 and 11 weeks post-dose. ERG amplitude measures from treated and control eyes were compared using 2 way ANOVA followed by post-hoc Sidak’s test. Anatomic localization of hLopsin expression was evaluated by immunofluorescence using an ADVM-062 surrogate engineered to express hLopsin with a myc-tag.

Results : Compared with naïve and vehicle controls, a single IVT dose of ADVM-062 resulted in significantly augmented ERG responses to long-wavelength stimuli presented on the desensitizing backgrounds (p<0.01). The augmented long-wavelength ERG response was evident as early as 3 weeks post-dose. Increased 25 Hz flicker ERG responses to 660 nm light confirm the cone-specific nature of this sensitization. Immunofluorescence demonstrated that hLopsin expression was localized exclusively to cone photoreceptor cells.

Conclusions : A single IVT dose of ADVM-062 expressing hLopsin effectively transduces murine cone photoreceptors and produces a de novo response to long wavelength stimuli. Expression occurred 3 weeks after injection and lasted for at least 11 weeks. Our previous studies in gerbils show that the IVT-augmented long wavelength ERG is sustained for at least 1 year. Findings support further evaluation of ADVM-062 as a potential IVT-delivered treatment for BCM patients.

This is a 2020 ARVO Annual Meeting abstract.