“…This postnatal lung-growth model has been optimized in a variety of species, including rat, mouse and dog 84–87 , and was recently demonstrated to occur in a selected human case 88 . Most studies so far have suggested that lung growth after PNX involves rapid, coordinated proliferation of a broad diversity of lung lineages, including most epithelial and endothelial cells, and only a minority of reports suggest that specialized rare stem or progenitor cells, such as putative BASCs, have a specialized or initiating role in the process 85,89,90 . In marked contrast, when a highly selective injury model, such as naphthalene-induced ablation of mature club cells, is used, a rare subset of epithelial cells, variant club cells, that have survived the injury then reconstitute the airway in a process that shows features of classically defined facultative progenitors, including reactivation of proliferation.…”