Continuous systemic secretion of a lysosomal enzyme by genetically modified mouse skin fibroblasts.

Lysosomal enzymes secreted or externally supplied into the extracellular medium can be internalized by cells and targeted to lysosomes after binding to specific membrane receptors. This process allows for the replacement of the missing enzyme activity in deficient cells. Using a retroviral vector, we have introduced the human beta-glucuronidase cDNA into primary mouse skin fibroblasts. The genetically modified cells were then engrafted into neo-organs that had been previously implanted into the peritoneal cavity of syngeneic recipient mice. The hypervascularized structures, made of collagen and basic fibroblast growth factor-coated synthetic fibers embedded into extracellular matrix gel, allowed in vivo survival of engrafted fibroblasts that expressed the human beta-glucuronidase cDNA for at least 3 months. The human enzyme was detected in the liver, lung, and spleen of experimental animals, but became undetectable after removal of the neo-organ. This observation indicated that the human enzyme was secreted into the serum and then captured by distant organs. The use of genetically modified fibroblasts implanted into neo-organs may, therefore, represent a convenient approach to enzyme replacement therapy in lysosomal storage diseases.