Stem cells from human fat differentiate into muscle cells and produce dystrophin (green) when injected into mice.

DMD is caused by a lack of the cytoskeletal protein dystrophin, which provides muscle cells with structural stability. Several treatment strategies for DMD are under investigation, including gene therapy to replace the defective dystrophin gene, and stem cell transplantation to generate new dystrophin-producing muscle cells.

Previous work by this group and others revealed the presence of stem cells in human fat tissue, but their longevity in vitro and capacity to differentiate in vivo had not been explored. Rodriguez et al. now show that fat tissue from young donors yielded self-renewing stem cells that could differentiate into muscle, bone, or fat cells in culture, even after 100 or more cell divisions. Similar stem cells have been found previously in bone marrow, but fat, the authors point out, provides a more plentiful and easily accessible source of these cells.

Injection of the stem cells into the muscles of dystrophin-deficient mice restored dystrophin production and decreased muscle cell necrosis, without eliciting an immune response against the human dystrophin protein—a protein that is normally highly immunogenic in mice. Why the immune system does not respond to this foreign protein is not known.Another unknown is how these stem cells become dystrophin-producing muscle cells. One possibility—illustrated in recent reports of stem cell therapy in mice—is that the stem cells fuse with local tissue cells rather than differentiating de novo into new cells.