The aim of this study was to assess the significance of programmed cell death 1 ligand 1 (PD-L1) in esophageal squamous cell carcinoma (ESCC) and its association with IL-6 and radiation response. Weretrospectively enrolled 162 patients with ESCC, and examined the correlation between PD-L1 levels and clinical outcomes in esophageal cancer patients. Furthermore, the human esophageal SCC cell line CE81T and TE2 were selected for cellular experiments to investigate the role of PD-L1 in T cell functions and radiation response. Here we demonstrated that PD-L1 expression was significantly higher in esophageal cancer specimens than in non-malignant epithelium. In clinical outcome analysis, this staining of PD-L1 was positively linked to the clinical T4 stage (p=0.004), development of LN metastasis (p=0.012) and higher loco-regional failure rate (p=0.0001). In addition, the frequency of PD-L1 immunoreactivity was significantly higher in IL-6-positive esophageal cancer specimens. When IL-6 signaling was inhibited in vitro, the level of PD-L1 is significantly down-regulated. PD-L1 is a significant predictor for poor treatment response and shorter survival. As demonstrated through in vitro experiments, Irradiation increased PD-L1 expression in human esophageal cancer cells. The inhibition of T cell functions including proliferation and cytotoxicity against tumor cells might be the mechanisms responsible to the role of PD-L1 in radiation response. In conclusion, PD-L1 is important in determining the radiation response and could predict the prognosis of patients with esophageal SCC. Therefore, we suggest inhibition of PD-L1 as a potential strategy for the treatment of esophageal SCC.
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