Lentiviral-mediated gene therapy results in sustained expression of β-Glucuronidase for up to 12 Months in the Gus mps/mps and up to 18 Months in the Gus tm(L175F)Sly mouse models of mucopolysaccharidosis type VII

Abstract

A number of mucopolysaccharidosis type VII (MPS VII) mouse models with different levels of residual enzyme activity have been created replicating the range of clinical phenotypes observed in human MPS VII patients. In this study, a lentivirus encoding murine β-glucuronidase was administered intravenously at birth to both the severe (Gus(mps/mps) strain) and attenuated (Gus(tm(L175F)Sly) strain) mouse models of MPS VII. Circulating enzyme levels were normalized in the Gus(mps/mps) mice and were 3.5-fold higher than normal in the Gus(tm(L175F)Sly) mouse 12 and 18 months after administration. Tissue β-glucuronidase activity increased over untreated levels in all tissues evaluated in both strains at 12 months, and the elevated level was maintained in Gus(tm(L175F)Sly) tissues at 18 months. These elevated enzyme levels reduced glycosaminoglycan storage in the liver, spleen, kidney, and heart in both models. Bone mineral volume decreased toward normal in both models after 12 months of therapy and after 18 months in the Gus(tm(L175F)Sly) mouse. Open-field exploration was improved in 18-month-old treated Gus(tm(L175F)Sly) mice, while spatial learning improved in both 12- and 18-month-old treated Gus(tm(L175F)Sly) mice. Overall, neonatal administration of lentiviral gene therapy resulted in sustained enzyme expression for up to 18 months in murine models of MPS VII. Significant improvements in biochemistry and enzymology as well as functional improvement of bone and behavior deficits in the Gus(tm(L175F)Sly) model were observed. Therapy significantly increased the lifespan of Gus(mps/mps) mice, with 12 months being the longest reported lentiviral treatment for this strain. It is important to assess the long-term outcome on enzyme levels and effect on pathology for lentiviral gene therapy to be a potential therapy for MPS patients.