Plasmacytoid Dendritic Cells and ICOS⁺ Regulatory T Cells Predict Poor Prognosis in Gastric Cancer: A Pilot Study

Background: Regulatory T cells (Tregs) and plasmacytoid dendritic cells (pDCs) are the main immunosuppressive cells in tumor microenvironment of gastric cancer (GC). In this prospective study, the association of prognosis with Tregs subsets and pDCs were further analyzed. Methods: pDCs, Tregs population and its expression of inducible costimulator (ICOS) were analyzed in peripheral blood from 41 GC patients by multicolor flow cytometry. These cell populations in carcinoma tissue, peritumor tissue and normal gastric mucosa from 87 GC patients were also detected by immunohistochemistry and double immunofluorescence. Results: Both ICOS⁺Foxp3⁺Treg cells (P=0.0341 and P=0.0298, respectively) and pDC (P=0.0237 and P=0.0083, respectively) in peripheral blood and tumor tissue could predict poor clinical outcome in GC patients. However, the total Foxp3⁺Tregs in the GC tissue didn't correlated with the outcome (P=0.4299). No correlation of CD4⁺ T cell or CD8⁺ T cell frequency could be found with clinical outcome neither in peripheral blood nor in tumor tissue. Conclusions: ICOS⁺Tregs and pDCs could predict poor prognosis of GC, targeting ICOS-L/ICOS costimulation axis may be a potential treatment for GC.