Transduction of satellite cells after prenatal intramuscular administration of lentiviral vectors

Background. We have previously reported long-term expression of lacZ in myocytes after in utero intramuscular injection of Mokola and Ebola pseudotyped lentiviral vectors. In further experiments, we have noted that these vectors also transduce small cells at the periphery of the muscle fibers that have the morphology of satellite cells, or muscle stem cells. In this study we performed experiments to further define the morphology and function of these cells. Methods. Balb/c mice at 14-15 days gestation were injected intramuscularly with Ebola or Mokola pseudotyped lentiviral vectors carrying CMV-lacZ. Animals were harvested at various time points, muscles were stained with X-gal, and processed for electron microscopy (EM) and immunofluorescence. To determine whether transduced satellite cells were functionally capable of regenerating injured muscles, animals were injected with notexin in the same area 8 weeks after the in utero injection of viral vector. Results. Transmission EM of transduced cells confirmed the ultrastructural appearance of satellite cells. Double immunofluorescence for β-galactosidase and satellite cell markers demonstrated co-localization of these markers in transduced cells. In the notexin-injured animals, small blue cells were seen at the areas of regeneration that co-localized β-galactosidase with markers of regenerating satellite cells. Central nucleated blue fibers were seen at late time points, indicating regenerated muscle fibers arising from a transduced satellite cell. Conclusions. This study demonstrates transduction of muscle satellite cells following prenatal viral vector mediated gene transfer. These findings may have important implications for gene therapy strategies directed toward muscular dystrophy.