Long-term functional rescue following a AAV-based gene therapy in canine model of LRIT3-congenital stationary night blindness

Abstract

Purpose : Congenital stationary night blindness (CSNB) is a group of inherited retinal diseases in which either rod-to-ON-bipolar cell (ON-BC) signaling, or rod function is affected leading to impaired vision under low light conditions. The complete CSNB subtype has been associated with genes (NYX, GRM6, TRPM1, GPR179, and LRIT3) involved in the mGluR6 signaling cascade which takes place at the ON-BC dendritic tips. We have previously characterized a canine model of LRIT3-CSNB and demonstrated short-term safety and efficacy with ON-BC targeting by AAV-LRIT3 gene therapy. Herein, we report the long-term follow-up after subretinal injection of the therapeutic vector in the canine CSNB model.

Methods : A total of nine LRIT3-CSNB canines were enrolled in short (12-15 months) or long (25-32 months) term follow-up assessment after being injected with either AAV vectors (therapeutic or non-therapeutic control), or BSS via subretinal and/or intravitreal routes. The therapeutic vector had wildtype canine LRIT3 (cLRIT3) under the control of a modified mGluR6 (shGRM6) promoter and packaged into a mutant AAV^K9#4 capsid designed for effective ON-BC targeting via subretinal injection. ERGs were recorded at pre-injection and repeated for up to 32 months post-injection. RNA-in situ hybridization (ISH) and immunohistochemistry were performed using LRIT3-CSNB canine retinal cryosections.

Results : In the eyes subretinally injected with AAV^K9#4-shGRM6-cLRIT3-WPRE, scotopic b-wave recovery was sustained up to 32 months post-therapy compared to that in the controls. In the area subretinally treated with the therapeutic vector, expression of transgene LRIT3 was confirmed along with restoration of TRPM1 and nyctalopin localization in the outer plexiform layer. However, examination of LRIT3 transcript expression by RNA-ISH revealed that this AAV vector construct resulted in broad cell-type transgene expression, specifically the outer nuclear layer, lacking strict specificity to ON-BCs as would be expected from the selective capsid and the promoter used.

Conclusions : While the long-term therapeutic potential of AAV^K9#4-shGRM6-cLRIT3-WPRE is promising, further optimization such as testing of other cell targets could be beneficial ahead of moving toward clinical application.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.