The Study of Mucosal-Associated Invariant T Cells in Colon Cancer and Roles in Immune Activities

INTRODUCTION: Mucosal-associated invariant T (MAIT) cells are a group of unconventional T cells, which strongly express CD161 and are involved in defending against infectious pathogens and inflammatory diseases. They are activated by inflammatory cytokines, secrete various cytokines and cytotoxic molecules, and express chemokine receptors and integrins. However, the underlying mechanisms of MAIT cells in colon cancer are still not fully understood. METHODS: The phenotype and frequency of circulating MAIT cells were investigated by flow cytometry in colon cancer patients and healthy donors. CD161 was examined in cancerous and paracancerous nontumor tissues of colon cancer patients by immunohistochemistry. The serum levels of IFN-γ and IL-17A were analyzed by ELISA. Finally, MAIT cells were also detected in peripheral blood and tumor tissues in a CT26 tumor-bearing mice model. RESULTS: The percentages of CD4(+)CD8(−) MAIT cells, CD4(−)CD8(+) MAIT cells, and CD4(−)CD8(−) MAIT cells increased in the peripheral blood of colon cancer patients compared with healthy donors. The expression of CD161 protein in colon cancer cancerous tissues was higher than that in the paracancerous nontumor tissues. The killer cell lectin-like receptor B1 (KLRB1), a coding gene for CD161, was positively associated with the gene expressions of immune inhibitory receptors, such as CTLA4, HAVCR2, PDCD1, and CD274 in colon cancer. Furthermore, the serum levels of IFN-γ and CEA were positively correlated with CD8(+) MAIT cells in the peripheral blood of colon cancer patients. CONCLUSION: Taken together, our data suggest that the circulating MAIT cells and the expression of CD161 protein in the tumor tissues increased in colon cancer patients, and MAIT cells may participate immune activities in colon cancer.