In this study, we present an evaluation of the DC subset and CD4/CD8 + T cells in peripheral blood and cancer tissue samples as well as Foxp3 + Tregs and IDO expression in gastric cancer tissue, with the objective of determining whether peripheral and tumor‐infiltrating CD4/CD8 + T cells, DC subsets, and Tregs were correlated with each other and IDO expression as well as correlated with the clinicopathological features of gastric cancer and its prognosis. The gene discussed is IDO1; the disease is cancer.