Persistent Gene Transfer to Skeletal Muscle Mediated by Stably Transfected Early Myogenic Progenitor Cells

Duchenne muscular dystrophy is a progressive muscle weakness characterized by a lack of dystrophin expression in the sarcolemma of muscle fibers. Both myoblast transplantation and gene therapy based on direct and ex vivo gene transfer techniques have been investigated as ways to deliver dystrophin in dystrophic muscle. Although the myoblast-mediated ex vivo gene transfer approach has been found capable of improving viral gene transfer to skeletal muscle, the poor survival rate of the injected cells as well as the immune response against the virally transduced cells has significantly hindered the success of this technique. For this paper, we investigated the use of non-viral vectors through the ex vivo approach based on early myogenic progenitor cells, which have been found highly capable of surviving post-implantation, to improve both the cell survival rate and the long-term persistence of gene transfer to skeletal muscle. We transfected a population of early myogenic progenitor cells derived from mdx mice with a plasmid encoding β-galactosidase, mini-dystrophin and the neomycin resistance gene. The selected muscle cells were capable of expressing β-galactosidase and differentiating into myotubes expressing dystrophin in vitro. More importantly, the transplantation of the transfected cells can be used to deliver β-galactosidase and dystrophin in skeletal muscle of adult mdx mice. The infiltration of CD4+ and CD8+ activated lymphocytes at the injected site suggests that the persistence of the transfected myofibers is limited by the immune response. On the other hand, the persistent transgene expression observed with the same approach in transgenic mdx mice that express β-galactosidase (mdx/β-gal) suggests that immune response is triggered by the βgalactosidase reporter gene.