Intra-Articular AAV9 α-l-Iduronidase Gene Replacement in the Canine Model of Mucopolysaccharidosis Type I

Mucopolysaccharidosis type I (MPS I), an inherited lysosomal storage disorder characterized by deficiency of α-l-iduronidase (IDUA) activity, causes multisystemic pathology due to sequelae of accumulated heparan and dermatan sulfates (HS and DS), the substrates of IDUA. Current treatments, though life-prolonging, inadequately address skeletal dysplasia and do not forestall progressive and painful degenerative joint disease. Previous studies demonstrated that intra-articular enzyme replacement cleared cellular lysosomal storage and reduced joint inflammation. Three nontolerized MPS I canines were studied to assess safety, efficacy, and durability of IDUA gene replacement therapy delivered via intra-articular injection. After baseline joint tissue biopsies, the right shoulder and stifle of each animal were injected in the intra-articular space with AAV9-IDUA and contralateral joints with AAV9-eGFP. Animals received either 5E11 or 5E12 vector genomes/joint. Necropsy was performed at 2- or 52-week postinjection. All animals tolerated injections without adverse effects. At two weeks, supraphysiologic IDUA enzyme activity was measured in AAV9-IDUA-treated but not AAV9-eGFP-treated synovium, with corresponding normalization of HS content and synoviocyte morphology. The AAV9-IDUA-treated cartilage had normal physiologic levels of IDUA enzyme, reduced but not normalized HS and DS levels compared to untreated MPS I cartilage, and healthy chondrocyte morphology. Liver IDUA transgene and IDUA enzyme activity were identified, as was serum IDUA activity which was 40% of wild-type serum enzyme activity. At 52-week postinjection, AAV9-IDUA-treated synovium and cartilage IDUA enzyme activity declined in both animals, corresponding to high tissue HS and DS levels and severe lysosomal storage. Liver and serum IDUA activity levels were undetectable. A dose-dependent serum anti-IDUA antibody response was observed which, together with loss of transgene with age, likely contributed to decline in tissue enzyme activity and treatment efficacy. Our study demonstrates successful proof-of-concept for intra-articular gene replacement therapy as a treatment for MPS-related joint dysplasia. Our observations suggest the possibility of multimodal gene replacement therapy to address multiple refractory manifestations of MPS I. Subsequent studies, in conjunction with immune tolerization and functional assessments of joint pathology, will investigate this possibility.