Examination of cell marker genes showed that COPD airway epithelium expressed higher levels of the basal cell marker keratin 5 (KRT5) (Figure 4B), consistent with previous findings demonstrating exhaustion of airway basal progenitor cells [20] and increased numbers of basal cells epigenetically committed to forming distinct metaplastic lesions in the lungs of COPD patients [21]. The gene discussed is KRT5; the disease is chronic obstructive pulmonary disease.