Lung stem cells: looking beyond the hype

The human lung is known to contain regional pools of progenitor cells that can give rise to specific lung structures, but a multipotent stem cell that can give rise to both endodermal and mesodermal lineages has not been described before and was thought to not exist. Jan Kajstura et al.(1) now provide evidence that might overturn this long-held belief. The investigators identified a set of potential stem cells in human lungs that were self renewing, clonogenic and multipotent in vitro and that could regenerate many different lung components-including bronchioles, alveoli, smooth muscle and pulmonary vessels-when injected into a mouse model of lung injury. We asked three experts to discuss the relevance of these findings to understanding of lung development and the implications for regenerative medicine to treat lung disease.