We and previous studies found that there are P63+ and/or KRT5+ cells enriched in the damaged alveolar region of many lung disease patients (including those with COPD, pulmonary fibrosis and bronchiectasis) (Chilosi et al., 2002; Asano et al., 2011; Smirnova et al., 2016), which could be the progeny of endogenous SOX9+ BCs in the middle of differentiation process. This evidence concerns the gene KRT5 and chronic obstructive pulmonary disease.