Retrovirus vector-mediated correction and cross-correction of lysosomal alpha-mannosidase deficiency in human and feline fibroblasts

Lysosomal alpha-mannosidase (EC 3.2.1.24) is an exoglycosidase in the glyco protein degradation pathway. A deficiency of this enzyme causes the lysosom al storage disease alpha-mannosidosis. Retrovirus vector transfer of a new human alpha-mannosidase cDNA resulted in high-level expression of alpha-man nosidase enzymatic activity in deficient human and feline fibroblasts. The expressed alpha-mannosidase had the same biochemical properties (thermal st ability, pH profile, inhibitor/activator sensitivity) as the native enzyme expressed in normal cells. The transferred enzyme colocalized with a contro l lysosomal hydrolase in cell fractionation experiments. The vector-encoded enzyme also was released at high levels from the corrected cells, and was taken up by untreated mutant cells via the mannose 6-phosphate receptor-med iated endocytic pathway (cross-correction). It is envisioned that genetic c orrection of a subset of cells (e.g., hematopoietic stem cells) in patients will provide a source of corrective enzyme for other affected tissues in t his multisystem disease. Development of a vector expressing high levels of alpha-mannosidase that cross-corrects mutant cells will enable somatic gene transfer experiments in the cat model of human alpha-mannosidosis.