Targeting ON-bipolar cells by AAV gene therapy stably reverses LRIT3-congenital stationary night blindness

Abstract

AAV gene therapies aimed at curing inherited retinal diseases to date have typically focused on photoreceptors and retinal pigmented epithelia within the relatively accessible outer retina. However, therapeutic targeting in diseases such as congenital stationary night blindness (CSNB) that involve defects in ON-bipolar cells (ON-BCs) within the mid-retina has been challenged by the relative inaccessibility of the target cell in intact retinas, the limited transduction efficiency of these cells by existing AAV serotypes, poor availability of established ON-BC-specific promoters, and absence of appropriate patient-relevant large animal models. Here, we demonstrate safe and effective ON-BC targeting by AAV gene therapy in a recently characterized naturally-occurring canine model of CSNB, LRIT3-CSNB. To effectively target ON-BCs, new AAV capsid variants with ON-BC tropism and ON-BC specific modified GRM6 promoters were adopted to ensure cell-specific transgene expression. Notably, subretinal injection of one vector, AAVK9#4-shGRM6-cLRIT3-WPRE, significantly recovered rod-derived b-wave in all treated eyes (6/6) of adult dogs injected at 1-3 years of age. The robust therapeutic effect was evident 7 weeks post-injection and was sustained for at least 1 year in all treated eyes. Scotopic vision was significantly improved in treated eyes based on visually-guided obstacle course navigation. Restoration of LRIT3 signals was confirmed by immunohistochemistry. Thus, we report on the first ON-BC functional rescue in a large animal model using a novel AAV capsid variant and modified promoter construct optimized for ON-BC specificity, thereby establishing both proof-of-concept and a novel translational platform for treatment of CSNB in patients with defects in photoreceptor-to-bipolar signaling.

Improving adeno-associated viral (AAV) vector-mediated transgene expression in retinal ganglion cells: comparison of five promoters

“…The promoter regulates the level of transgene expression and determines cellspecificity, as the activation state of the promoter is dependent on the transcription factor machinery present in the transduced cells. There has been great interest in identifying promoters for optimal transduction of different cell types within the retina [14,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] and an ideal promoter would preferably be small, to make the incorporation of large and complex cargos possible.…”

Hotspots and trends in ophthalmology in recent 5 years: Bibliometric analysis in 2017–2021

“…Cataracts and posterior capsular opacification were previously thought to be treated only with surgery, but in the recent years, there had been new developments in research into drugs that inhibit cataract formation (5,6). With the advances in the field of ophthalmology, new hope has emerged in areas previously considered untreatable or treatable only through non-pharmaceutical interventions (7)(8)(9)(10). However, it is not feasible to analyze the overall overview of the field of ophthalmology and to explore its research hotspots and trends with a traditional systematic review, which is not conducive to the development of the field.…”

LRIT3 expression in cone photoreceptors restores post-synaptic bipolar cell signalplex assembly and function in Lrit3-/- mice

“…Some ERG rescue was present in animals when LRIT3 expression was targeted to DBCs, although the extent of scotopic ERG rescue was greater when photoreceptors were targeted (Varin et al, 2021). In another study LRIT3 was targeted to DBCs in a Lrit3 -/canine model of cCSNB (Miyadera et al, 2022. This partially restored the scotopic ERG b-wave, and resulted in recovery of visual function under scotopic conditions as assessed by behavioral tests (Das et al, 2019;Miyadera et al, 2022). In neither of these studies was there any rescue of cone DBC function as assessed by photopic ERGs.…”

“…This unexpected result suggests that LRIT3 can act as a trans-synaptic organizer of the post-synaptic signalplex. Two other studies, one in mouse and one in dog LRIT3 deficient models, restored rod BC signalplex function using postsynaptic targeting of LRIT3 (Miyadera et al, 2022;Varin et al, 2021).…”