Evaluation of AAV2tYF-GRK1-RPGR vectors in a canine model of RPGR-XLRP

Abstract

Purpose : In previous studies, an AAV2tYF capsid and GRK1 promoter were more efficient than an AAV5 and IRBP promoter for transducing primate photoreceptors, and two stable human RPGR cDNAs (the full length codon-optimized RPGRco or stablized RPGRstb ) were both effective at early-stage disease in the XLPRA2 dog model of XLRP due to a mutation in the RPGR gene. We now compared the efficacy of 3 dose levels of RPGRco and RPGRstb vectors with a AAV2tYF capsid and GRK1 promoter in XLPRA2 dogs at mid-stage disease (~12 wks of age).

Methods : Two dogs per group received a 0.15 mL subretinal injection of AAV2tYF-RPGRco in one eye and AAV2tYF-RPGRstb in the other eye at each of 3 doses (1.2 x 10¹¹, 6 x 10¹¹ or 3 x 10¹² vg/ml). One dog received the mid-dose of AAV5-RPGRco and 1 dog received vehicle, in both eyes. Rescue of photoreceptor structure was assessed by clinical examination, and histology/IHC on retinal cryosections at termination 8 wks post-injection.

Results : No abnormal ophthalmic findings were noted in any eyes at the mid- or low-dose levels, but there was retinal inflammation and retinal detachment in the 4 eyes treated with the high-dose of either vector. Retinal perivascular infiltration consisting primarily in T cytotoxic (CD8) and B (CD20) lymphocytes, with some T helper (CD4) cells were found in the bleb area of all eyes treated with the high doses and one eye with AAV2tYF-RPGRco at mid-dose.
Both RPGRco and RPGRstb vectors achieved dose-dependent RPGR transgene expression in photoreceptors, with greater RPGR expression in eyes injected with RPGRco vector than in contralateral eyes injected with RPGRstb vector at the same dose levels. Correction of rod opsin and middle/long wavelength (M/L) cone opsin mislocalization was demonstrated in all AAV-RPGR treated eyes. Müller cell activation was decreased in eyes injected with the low and mid-doses but not in eyes injected with the high dose, likely due to the associated inflammation and retinal detachment.

Conclusions : With the AAV2tYF capsid and GRK1 promoter, greater RPGR expression was achieved with the vector expressing the RPGRco cDNA than with the vector expressing the RPGRstb cDNA. Optimal correction at mid-stage disease with limited inflammation, including improved structure of cones, correction of rod and M/L cone opsin mislocalization and reduced reactivity of Müller cells, was achieved in this model with the mid-doses of both vectors (0.15 mL at 6 x 10¹¹ vg/ml).

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.