Restoration of Functional Full-Length Dystrophin After Intramuscular Transplantation of Foamy Virus-Transduced Myoblasts

Stem cell therapy is a promising strategy to treat muscle diseases such as Duchenne muscular dystrophy (DMD). To avoid immune rejection of donor cells or donor-derived muscle, autologous cells, which have been genetically modified to express dystrophin, are preferable to cells derived from healthy donors. Restoration of full-length dystrophin (FL-dys) using viral vectors is extremely challenging, due to the limited packaging capacity of the vectors, but we have recently shown that either a foamy viral or lentiviral vector is able to package FL-dys open-reading frame and transduce myoblasts derived from a DMD patient. Differentiated myotubes derived from these transduced cells produced FL-dys. Here, we transplanted the foamy viral dystrophin-corrected DMD myoblasts intramuscularly into mdx nude mice, and showed that the transduced cells contributed to muscle regeneration, expressing FL-dys in nearly all the muscle fibers of donor origin. Furthermore, we showed that the restored FL-dys recruited members of the dystrophin-associated protein complex and neuronal nitric oxide synthase within donor-derived muscle fibers, evidence that the restored dystrophin protein is functional. Dystrophin-expressing donor-derived muscle fibers expressed lower levels of utrophin than host muscle fibers, providing additional evidence of functional improvement of donor-derived myofibers. This is the first in vivo evidence that foamy virus vector-transduced DMD myoblasts can contribute to muscle regeneration and mediate functional dystrophin restoration following their intramuscular transplantation, representing a promising therapeutic strategy for individual small muscles in DMD.