Engraftment potential of dermal fibroblasts following in vivo myogenic conversion in immunocompetent dystrophic skeletal muscle.

Autologous dermal fibroblasts are promising candidates for enhancing muscle regeneration in Duchenne muscular dystrophy (DMD) due to their ease of isolation, immunological compatibility, and greater proliferative potential than DMD satellite cells. We previously showed that mouse fibroblasts, after MyoD-mediated myogenic reprogramming in vivo, engraft in skeletal muscle and supply dystrophin. Assessing the therapeutic utility of this system requires optimization of conversion and transplantation conditions and quantitation of engraftment so that these parameters can be correlated with possible functional improvements. Here we derived dermal fibroblasts from transgenic mice carrying mini-dystrophin, transduced them by lentivirus carrying tamoxifen-inducible MyoD, and characterized their myogenic and engraftment potential. After cell transplantation into muscles of immunocompetent dystrophic mdx4cv mice, tamoxifen treatment drove myogenic conversion and fusion into myofibers that expressed high levels of mini-dystrophin. Injecting 50,000 cells/microliter (1 × 106 total cells) resulted in a peak of ~600 mini-dystrophin positive myofibers in TA muscle single cross-sections. However, EDL muscles with up to 30% regional engraftment showed no functional improvements; similar limitations were obtained with whole muscle mononuclear cells. Despite the current lack of physiological improvement, this study suggests a viable initial strategy for using a patient-accessible dermal cell population to enhance skeletal muscle regeneration in DMD.