Distribution characteristics and clinical significance of infiltrating T cells in the tumor microenvironment of pancreatic cancer

Tumor-infiltrating lymphocytes (TILs) are important components of the tumor microenvironment (TME). However, the distribution characteristics of TILs and their significance in pancreatic cancer (PC) remain largely unexplored. The levels of TILs, including the total number of T cells, cluster of differentiation (CD)4(+) T cells, CD8(+) cytotoxic T lymphocytes (CTLs), regulatory T-cells (Tregs), programmed cell death protein 1(+) T cells and programmed cell death ligand 1 (PD-L1)(+) T cells, in the TME of patients with PC were detected using multiple fluorescence immunohistochemistry. The associations between the number of TILs and the clinicopathological characteristics were investigated using χ(2) tests. In addition, Kaplan-Meier survival and Cox regression analyses were used to assess the prognostic value of these TIL types. Compared with paracancerous tissues, in PC tissues, the proportions of total T cells, CD4(+) T cells and CD8(+) CTLs were markedly decreased, while those of Tregs and PD-L1(+) T cells were significantly increased. The levels of CD4(+) T cell and CD8(+) CTL infiltrates were inversely associated with tumor differentiation. Higher infiltrates of Tregs and PD-L1(+) T cells were closely associated with advanced N and TNM stages. It is important to note that the infiltrates of total T cells, CD4(+) T cells, Tregs and PD-L1(+) T cells in the TME were independent risk factors for the prognosis of PC. PC was characterized by an immunosuppressive TME with a decrease in the number of CD4(+) T cells and CD8(+) CTLs, and an increase in the number of Tregs and PD-L1(+) T cells. Overall, the number of total T cells, CD4(+) T cells, Tregs and PD-L1(+) T cells in the TME was a potential predictive marker for the prognosis of PC.