When they were discovered, mesenchymal stem cells seemed ready to get in the swim of regenerative medicine. But they floundered. In hundreds of clinical trials, stem cells sank long before they could help patients.
Mesenchymal stem cells, which are found in bone marrow and can give rise to bone, fat, and muscle tissue, seem to do well enough in culture—a fact that led researchers from the Harvard Stem Cell Institute to wonder if the laboratory dish was serving as a kind of kiddy pool. Maybe all the attempts to put mesenchymal stem cells into the body amounted to having them dive into the deep end, sink-or-swim style.