PD-1 expression on circulating CD8 ⁺ T-cells as a prognostic marker for patients with gastric cancer

Background: Programmed death-1 (PD1) is an immunoinhibitory receptor, and PD1 overexpression on T-cells is involved in immune evasion in cancer. This study investigated the prognostic significance of PD1 expression on T-cells in gastric cancer. Materials and Methods: PD1 expression on CD4 ⁺ and CD8 ⁺ T-cells obtained from peripheral blood mononuclear cells was evaluated by multicolor flow cytometry. Results: Based on cutoff values from receiver operating characteristic analysis, patients were sub-grouped according to PD1 positivity as having high or low PD1 ⁺ CD4 ⁺ T-cell (cutoff ≥34.2%) and PD1 ⁺ CD8 ⁺ T-cell (cutoff ≥28.7%) frequencies. Five-year overall survival rates differed significantly between the groups with low and high frequency of PD1 ⁺ CD4 ⁺ T-cells (75.1% vs. 27.2%, respectively; p=0.0008). The 5-year overall survival rates were 78.3% and 37.2%, respectively, for the corresponding PD1 ⁺ CD8 ⁺ T-cell subgroups (p=0.0004). Multivariate analysis revealed that the frequency of PD1 ⁺ CD8 ⁺ T-cells was an independent prognostic indicator. Conclusion: The frequency of PD1 ⁺ CD8 ⁺ T-cells may predict the prognosis of patients with gastric cancer.