Increased prevalence of interleukin-17-producing CD4(+) tumor infiltrating lymphocytes in human oral squamous cell carcinoma.

T helper 17 (Th17) and regulatory T cells share plasticity in the expression of interleukin (IL)-17 and forkhead box P3 (FOXP3), but their mutual presence in human diseases is unclear. IL-17 and FOXP3 were analyzed by immunohistostaining and flow cytometry. The cytokine milieu was analyzed by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Oral squamous cell carcinoma expresses high levels of IL-1β, IL-6, and transforming growth factor (TGF)-β. A unique subset of FOXP3(+) IL-17-producing CD4(+) T cells was consistently identified in tumor-infiltrating lymphocytes from advanced stages of cancer, but not in the circulation, at a frequency of 0.5% to 5.5 % of total CD4(+) T and positively correlated with the frequency of IL-17(+)FOXP3(-) T cells. The IL-17(+)FOXP3(+) T cells express CCR6 and suppress the proliferation of autologous CD4(+) CD25(-) responder T-cells in vitro. The prevalence of IL-17-producing FOXP3(+) CD4(+) tumor infiltrating lymphocytes is increased in oral squamous cell carcinoma.