In light of the majority of pancreatic cancer patients not responding to current immune checkpoint blockade, alternative immunotherapeutic targets need to be identified. In this study, we employed multiplex immunofluorescence to investigate the expression of co-stimulatory and inhibitory receptors by tumor-infiltrating T cells in human pancreatic cancer. A comprehensive analysis of the receptor pattern on tumor-infiltrating T cells is essential for the development of new therapeutic strategies, as well as personalized immunotherapy, to identify patients who are likely to benefit from targeting specific immune receptors.

T cells are the predominant immune cell population in the pancreatic tumor microenvironment. High CD8⁺ and Th1-polarized CD4⁺ T cell infiltration is associated with prolonged survival in human pancreatic ductal adenocarcinoma (PDAC). However, the expression pattern of co-stimulatory and inhibitory receptors by PDAC-infiltrating T cells and their prognostic significance are not well defined. In this study, we employed multiplex immunofluorescence to investigate the intratumoral expression of the co-stimulatory receptor inducible T-cell co-stimulator (ICOS), the inhibitory receptors lymphocyte-activation gene 3 (LAG-3), programmed death 1 (PD-1), and V-domain immunoglobulin suppressor of T cell activation (VISTA) by tumor-infiltrating T cells (CD3) in a cohort of 69 patients with resected PDAC. T cells were enriched particularly within the stromal area and were highly heterogeneous across tumors. Further, T cells were associated with prolonged disease-free survival (DFS). However, LAG-3 expression by PDAC-infiltrating T cells was correlated with reduced DFS. Our study highlights the biological importance of LAG-3 expression by tumor-infiltrating T cells. LAG-3⁺ T cells may represent a novel prognostic marker and a particularly attractive target for immunotherapeutic strategies in PDAC.