PM2.5, cigarette smoke and B[a]P has been shown to induce PD-1 ligand (PD-L1) in lung epithelial cells and macrophages, and the therapeutic effects of anti-PD-L1 antibody treatment (pembrolizumab) appear to be limited to lung cancers with high AhR expression levels, in both patients and mouse models [38,301]. Here, CD274 is linked to lung cancer.