Side-by-side comparison of high transduction AAV8-Y733F-mediated gene therapy in two BCM mouse models

Abstract

Purpose : Blue cone monochromacy (BCM) is an X-linked congenital vision disorder caused by mutations in the OPN1LW/OPN1MW gene cluster that abolish or severely reduce L- and M-cone function. Our lab has demonstrated that AAV5-mediated gene therapy rescues cone function and structure in two BCM mouse lines which model either deletion mutations or a C203R missense mutation, the two most common causes of BCM. In the current study, we compare the efficacy and therapeutic window of AAV8-Y733F capsid-mediated gene expression between these two BCM mouse models.

Methods : AAV8-Y733F-mediated expression of hOPN1LW under a cone-specific PR2.1 promoter was delivered by subretinal injection at 3M, 5M, and 7M in Opn1mw^-/-Opn1sw^-/- (DKO) and Opn1mw^C198ROpn1sw^-/- (C198R) mice. Visual function was evaluated by electroretinography (ERG). Ultrastructure of DKO and C198R retinas was evaluated by transmission electron microscopy (TEM). Retinal cross-sections or flatmounts were used to examine expression and localization of OPN1LW, GNAT2, and PDE6H.

Results : Compared to our previous studies with AAV5, AAV8-Y733F-mediated gene therapy showed improved rescue efficacy and longevity. The number of rescued C198R vs. DKO eyes was 66.7% (n=15) vs 58.3% (n=24) at 3M+1M (injection at 3M+ERG 1M post-injection), 60% (n=15) vs. 52.4% (n=21) at 5M+1M, and 27.3% (n=11) vs. 23.1% (n=13) at 7M+1M when evaluated by L-cone ERG, suggesting that C198R cones rescue slightly better than DKO mice. Long-term rescue was more robust in C198R mice, as 3M+10M treated C198R eyes exhibited an average b-wave amplitude of 36.6µV±14.7µV (n=6) compared to 17.8µV±9.1µV in DKO (n=3) mice (p=0.086). AAV8-Y733-mediated gene therapy also resulted in restoration of cone outer segment (COS) proteins OPN1LW, GNAT2, and PDE6H. Strikingly, TEM revealed mitochondria with abnormal morphology and mislocalized centrioles within the inner segment in a portion of C198R and DKO 5M untreated cones.

Conclusions : AAV8-Y733F-mediated gene therapy demonstrates improved rescue efficacy and longevity in C198R and DKO cones compared to AAV5, with treated C198R cones demonstrating a slightly extended rescue period compared to DKO mice. Mislocalization of centrioles and aberrant mitochondria morphology in 5M untreated C198R and DKO cones may explain low rescue efficiency in aged mice.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.