Cross-correction of beta-glucuronidase deficiency by retroviral vector-mediated gene transfer

An in vitro model for cross-correction of lysosomal storage disorders from genetically modified cells was developed to approximate the physiological conditions needed for gene therapy in vivo. beta-Glucuronidase (GUSB)-deficient mucopolysaccharidosis (MPS) type VII (Sly disease) cells were studied to determine the amount and stability of enzyme transfer. Gene transfer by retroviral vectors encoding rat or human GUSB corrected the enzymatic deficiency in cultured MPS VII fibroblasts from humans, dogs, and mice. The vector-transduced cells released GUSB into the culture supernatant in amounts proportional to the amounts of cellular GUSB activity. The activity of the exported GUSB was stable in tissue culture medium for at least two weeks. Uninfected MPS VII target cells incorporated GUSB from the medium when the vector-infected donor cells were separated from the deficient target cells by a fluid-permeable membrane. The high level of GUSB in the cross-corrected target cells decreased rapidly after the enzyme donor cells were removed.