Animals used in this study.

Mucopolysaccharidosis VI (MPS VI) is a rare, autosomal recessive lysosomal storage disease caused by mutations in the arylsulfatase B gene (ARSB). Ocular manifestations of MPS VI include progressive corneal clouding, leading to vision loss. Herein, an adeno-associated virus (AAV) ARSB corneal gene addition strategy was evaluated in a naturally occurring MPS VI feline model. The AAV serotype 8 capsid was packaged with a single-strand optimized human ARSB expression cassette (optARSB) and administered to MPS VI feline corneas at a dose of 1e9 vector genomes via intrastromal injection. All AAV8-optARSB injections were well tolerated, resulting in a complete reversal of pre-existing corneal clouding within 2–3 weeks, which was maintained throughout the study. Sequential dosing of the contralateral cornea 7 weeks after the first dose also cleared the storage disease with similar kinetics despite more advanced disease. Confocal microscopy, histological analyses, and electron microscopy revealed disorganization in the posterior corneal stroma in untreated animals with AAV8-optARSB-treated corneas demonstrating improved morphology and tissue organization. Human arylsulfatase B was observed throughout the corneal stroma with decreased smooth muscle actin staining following AAV8-optARSB treatment. The collective results demonstrate that reversing feline MPS VI corneal clouding using intrastromal low-dose AAV8-optARSB is safe and effective. Furthermore, as this strategy relied on the same AAV capsid, vector dose, genetic cassette context, injection type, and volume deemed safe and effective for the treatment of MPS I, the data derived herein support a standardized pipeline for AAV corneal gene therapy.