The transitional epithelial cells that emerge during pulmonary fibrosis described above express CDKN2A, CDKN1A, and other canonical genes associated with cellular senescence, but careful lineage tracing studies in mice and in human organoid systems suggest they are capable of differentiating into AT1 (10–13, 15, 18, 105). This evidence concerns the gene CDKN2A and pulmonary fibrosis.