Endothelial colony-forming cells (ECFC) isolated from healthy smokers and COPD patients express higher levels of senescence markers, p21CIP1, p16INK4, SA-β-galactosidase and increased markers of DDR, gamma histone 2AX (γH2AX), and tumor protein P53 binding protein 1 (53BP1) compared to ECFC from healthy non-smokers.104. Here, CDKN1A is linked to chronic obstructive pulmonary disease.