AAV-mediated gene augmentation restores retinal function and vision in the canine model of NPHP5 Leber congenital amaurosis

Abstract

Purpose : A C-terminal truncation of NPHP5 (IQCB1) causes a photoreceptor (PR) ciliopathy with an early onset, rapidly progressive retinal degeneration in dogs. By 6 wks of age, rod responses are markedly reduced in amplitude or absent, and cone responses are not recordable. The absence of cone function correlates with the lack of cone outer segments even though there is preservation of cone inner segments. To examine therapeutic approaches for this severe disease, we used AAV-canineNPHP5 vectors for gene augmentation.

Methods : We injected subretinally 70 µl of either AAV2/5-hIRBP-cNPHP5 or scAAV2/8 (Y733F)-hGRK1-cNPHP5 in one eye of affected dogs at 6 or 7.5 wks of age, with fellow eyes serving as untreated controls. PR structure and function were quantified by sdOCT and full-field ERGs. Visual behavior was assessed ~ 1 year after treatment using an obstacle avoidance course to test separately the treated and contralateral control eyes.

Results : Treatment at 7.5 wks of age with 1.5x10¹¹ vg/ml titer of AAV2/5-hIRBP-cNPHP5 did not rescue function at any time point up to 33 wks. A 10-fold increase in titer at a treatment age of 6 wks had a positive but modest effect in restoring cone/rod function, and preserved ERG and vision for 1.3 yrs, the latest point examined. Treatment at 6 wk with the scAAV2/8 (Y733F)-hGRK1-cNPHP5 vector (1.5x10¹¹ vg/ml titer) resulted in functional recovery that was comparable to the higher dose AAV2/5-hIRBP-cNPHP5 vector. In contrast, a 1.5x10¹² titer resulted in remarkable recovery of cone function, and preservation of cone/rod ERG and vision for the 1.3 yr observation time period. Treatment blebs were associated with significantly retained photoreceptor ONL short term, but there was ONL thinning long term. Thus either an insufficient number of PRs were transduced, or the level or duration of transgene expression needed to preserve normal structure was insufficient for fully stable correction.

Conclusions : In spite of the very severe and rapidly progressive photoreceptor degeneration in NPHP5-LCA affected dogs, AAV-mediated gene augmentation restores rod and cone function, and preserves vision for at least 1.3 yrs. Because progressive degeneration continues, albeit at a slower rate, these findings indicate that vector and promoter optimization will be required for more stable and permanent correction of the PR disease.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.