A number of recent studies have shown positive correlations between smoking and PD-L1 expression: Wang et al. (2019) have shown that tobacco smoke induces PD-L1 expression in lung epithelial cells; and Nguyen et al. (2019) have found that nicotine induces α9 nAChR activity promoting melanoma cell proliferation in a dose- and time-dependent manner by stimulating the α9-mediated Akt, ERK, and STAT3 signaling pathways. The gene discussed is CD274; the disease is melanoma.