Background: Many studies have shown that
programmed cell death protein 1 (PD-1) and its
ligand, PD-L1, are expressed in advanced
gastric cancer. Furthermore, detection of these
proteins is associated with infiltrating CD8+ T-cells, indicating that an adaptive immune resistance mechanism occurs in advanced
gastric cancer. However, PD-L1 and PD-1 expression in gastric intraepithelial
neoplasia and early-stage
gastric cancer (EGC) has yet to be elucidated. Patients and methods: Fifty-four resections of low-grade intraepithelial
neoplasia (LGIN), high-grade intraepithelial
neoplasia (HGIN), and EGC were stained by immunohistochemistry for PD-1, PD-L1, and CD8. CD8+ T-cell densities both within
tumors and in the
tumor-stromal interface were analyzed. Flow cytometry (FACS) was used to analyze the PD-1 expression in
tumor tissues and peripheral blood mononuclear cells. Furthermore, the relationship between Helicobacter pylori (Hp)
infection and PD-1 and PD-L1 was also evaluated. Results: We demonstrated that PD-L1 expression was significantly increased in HGIN and EGC compared with LGIN, and both PD-1 and PD-L1 showed similar expression patterns, being mainly detected in infiltrating immune cells. FACS also showed that PD-1 was expressed on both CD4+ and CD8+ T-cells. However, no difference was found in CD8+ T-cell infiltration between LGIN and HGIN+EGC, and this was not not found to be associated with PD-L1 or PD-1 expression. However, Hp
infection was significantly associated with expression of PD-L1 and PD-1. Conclusions: The PD-1/PD-L1 checkpoint is involved in intraepithelial
neoplasia and EGC, but an adaptive immune resistance mechanism does not occur. Expression of PD-1/PD-L1 is also associated with Hp
infection, and so Hp
infection may be an important initiating factor. Clinical Trial Registration information: This study was approved by the Institutional Review Board of Ruijin Hospital and written informed consent was obtained from all patients.