Using expression of the c-kit antigen as an identifier, Brigham researchers Kajstura et al identified stem cells in adult human lungs (from unused donor lungs and a Brigham tissue bank), established a clonal cell line from the isolated stem cells, and infected those cells with a fluorescing lentivirus. With a cryoprobe, they destroyed some mice’s lung tissue, and injected the cultured stem cells into the cyclosporine-treated mice. Two weeks later, normal-appearing human bronchi, alveoli, and blood vessels had grown in the mice, and the new tissue contained the fluorescing protein and expressed human antigens. Researchers then harvested 20,000 human stem cells from each mouse, and reimplanted these into another group of lung-damaged mice. Again, human lung tissue grew that appeared normal from this apparently multipotent, clonal line of stem cells never before known to exist in adult lungs. ZOUNDS! NEJM 2011;364:1795-1806.