Stable transduction of myogenic cells with lentiviral vectors expressing a minidystrophin

Gene therapy for Duchenne muscular dystrophy (DMD) will require sustained expression of therapeutic dystrophins in striated muscles. Lentiviral vectors have a relatively large transgene carrying capacity and can integrate into nondividing cells. We therefore explored the use of lentiviral vectors for transferring genes into mouse skeletal muscle cells. These vectors successfully transferred a minidystrophin expression cassette into mdx muscles, and minidystrophin expression persisted and prevented subsequent muscle fiber degeneration for at least 6 months. However, only low to moderate levels of skeletal muscle transduction could be obtained by intramuscular injection of the highest currently available lentiviral doses. Using cultured cells, the lentiviral vectors effectively transduced proliferating and terminally differentiated muscle cells, indicating that cell cycling is not essential for transduction of myogenic cells. We further showed that lentiviral vectors efficiently transduced both primary myoblasts and multipotent adult progenitor cells (MAPCs) in vitro, and the cells persistently expressed transgenes without any obvious toxicity. When mdx primary myoblasts were genetically modified with minidystrophin vectors and transplanted into mdx skeletal muscles, significant numbers of dystrophin-expressing myofibers formed. Finally, we showed that a short, highly active CK6 regulatory cassette directed muscle-specific activity in the context of the lentiviral vectors. The ability of lentiviral vectors to transduce myogenic progenitors using a minidystrophin cassette regulated by a muscle-specific promoter suggests that this system could be useful for ex vivo gene therapy of muscular dystrophy.