Embryonic stem cell-based reduction of central nervous system sulfatide storage in an animal model of metachromatic leukodystrophy.

Pluripotency, virtually unlimited self-renewal and amenability to genetic modification make embryonic stem (ES) cells an attractive donor source for cell-mediated gene therapy. In this proof of concept study, we explore whether glial precursors derived from murine ES cells (ESGPs) and engineered to overexpress human arylsulfatase A (hASA) can cross-correct the metabolic defect in an animal model of metachromatic leukodystrophy (MLD). Transfected ES cells showed an up to 30-fold increase in ASA activity. Following in vitro differentiation, high expression of ASA was found in all stages of neural and glial differentiation. hASA-overexpressing ESGPs maintained their ability to differentiate into astrocytes and oligodendrocytes in vitro and in vivo. After transplantation into the brain of neonatal ASA-deficient mice, hASA-overexpressing ESGPs were found to incorporate into a variety of host brain regions. Four weeks after engraftment, immunofluorescence analyses with an antibody to sulfatide revealed a 46.7+/-4.0% reduction of immunoreactive sulfatide deposits in the vicinity of the hASA-positive engrafted cells, thereby significantly extending the rate of sulfatide reduction achieved by the endogenous ASA activity of non-hASA-transfected control cells (21.1+/-5.8%). These findings provide first in vivo evidence that ES cells may serve as a potential donor source for cell-mediated enzyme delivery in storage disorders such as MLD.