MYOBLAST GENE-THERAPY IN CANINE MUCOPOLYSACCHARIDOSIS-I - ABROGATION BY AN IMMUNE-RESPONSE TO ALPHA-L-IDURONIDASE

Three dogs with deficiency of the lysosomal enzyme alpha-L-iduronidase were treated by gene replacement therapy targeted at muscle, Direct i ntramuscular injections of plasmid encoding the alpha-L-iduronidase ge ne cDNA resulted in no detectable enzyme production, but may have resu lted in immunologic sensitization to iduronidase protein, which the do gs lack totally, Myoblasts were grown from skeletal muscle biopsies an d transduced with a retroviral vector containing the canine gene under control of the muscle creatine kinase enhancer, Several hundred-fold overexpression of enzyme production occurred in cultured cells; howeve r, following reintroduction of the cultured cells into dogs, enzyme pr oduction declined rapidly, Concurrent with the falling enzyme levels, there was production of specific immunoglobulin G (IgG) antibody again st iduronidase that was further associated with cellular infiltration of the myoblast injection sites, Most inflammatory cells were lymphocy tes and plasma cells, suggesting local humoral and cellular immune res ponses to the enzyme-producing muscle cells, PCR analysis of tissues c ollected 2-22 weeks after the final treatment showed the persistence o f Neo and canine alpha-L-iduronidase sequences in a progressively decr easing percentage of myoblasts, Results from this study in a canine mo del of mucopolysaccharidosis I underscore the fact that immunologic re actions to cells producing desirable, normal, but foreign, proteins ma y be as much an impediment to gene therapy as reactions to the viral v ectors used to introduce the foreign gene.