Pre-clinical efficacy testing of AAV-based gene therapy for KCNV2-deficiency.

Abstract

Purpose : Voltage-gated (Kv) potassium channels play an essential role in maintaining neuronal physiology and disrupting their normal function can have serious implications. This is clinically important as mutations in the silent modulatory Kv8.2 subunit are known to underlie a particular form of inherited irreversible blindness, cone dystrophy with supernormal rod response (CDSRR). This unique condition causes lifelong visual loss, characterized by reduced visual acuity, photoaversion, night blindness and abnormal colour vision, and presents phenotypically with a supernormal electrophysiological (ERG) retinal response to light. We have previously characterised a mouse model of CDSRR (Kv8.2 KO), which accurately mimics the human condition: a supernormal rod ERG response alongside reduced visual acuity. This study investigated the suitability of an AAV-based gene therapy approach as a potential treatment for CDSRR.

Methods : Kv8.2 KO mice were treated subretinally with one of two different AAV vectors optimised for specific photoreceptor targeting at three doses. The efficacy of the gene therapy to rescue vision was evaluated via ERG at 4, 8 and 12 weeks post-treatment, with optomotor testing and histological analysis at 12 weeks. Single-cell RNAseq and proteomics analysis was also performed on treated retinas and compared to age-matched wildtype and untreated Kv8.2 KO. Flow cytometry was used to evaluate the immune response to the treatment at 4 and 12 weeks.

Results : Our results show that treatment with either of our vectors was dose-dependent but had a significant impact on the ERG responses. We show a reduction in the supernormal b-wave, increased a-wave, recovery of the OP1 and c-wave timing and increased c-wave amplitude. Treated animals also showed recovery to wild-type levels of their scotopic contrast and acuity and photopic acuity via optomotor responses. KCNV2 gene and Kv8.2 protein expression were recovered in the treated areas of the retina, while no increased immune response was observed.

Conclusions : This study is the first to develop and validate in a Kv8.2 KO mouse model the efficacy and safety of a novel gene therapy treatment for CDSRR. Our proof-of-concept pre-clinical data supports the potential of this treatment and provide a strong basis for moving forwards towards a future clinical trial.

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