KRT5 and endothelial dysfunction: Alternative sources of regenerative cells in these studies include rare lineage-negative epithelial stem/progenitor cells, distal airway stem cells expressing p63 and keratin 5 (DASCp63/Krt5), and a Wnt-responsive subpopulation of AT2 cells.58–60 Building on these results, it may be possible to determine whether failure of regenerative programs, distinct from ongoing viral replication, microvascular thrombosis and endothelial dysfunction, and deleterious inflammation, is a cause of persistent lung dysfunction in COVID-19.