Study On The Expression And Function Of Mucosal Associated Invariant T(MAIT) Cells In Colorectal Cancer Patients

Mucosal associated invariant T(MAIT) cells are important for immune defense against infectious pathogens and regulate the pathogenesis of various inflammatory diseases. However, their roles in the development of colorectal cancer(CRC) are still unclear. AimWith immunology, cytology, molecular biology and other experimental techniques, in vivo and in vitro experiments, this study focus on the following aspects: 1. The expression and distribution of MAIT cells in CRC patients. 2. The correlation between MAIT cells and clinical parameters in CRC patients. 3. The secretory function of MAIT cells and its potential impact on the growth of CRC cell line. Method1. Detection of the expression of MAIT cells in peripheral blood mononuclear cells(PBMC), tumor-infiltrating lymphocytes(TIL) from the center of the tumor tissue and non-tumor infiltrating lymphocytes(NIL) from the surrounding of the tumor tissue of CRC patients. Besides, analysis of the corresponding phenotype of MAIT cells. The PBMC from healthy controls(HC) and lamina propria mononuclear cells(LPMC) from non-tumor controls(NT) were used as controls. Immunofluorescence assay was used to detect the distribution of MAIT cells in the center or the surrounding of the tumor tissue from CRC patients.2. Stratified analysis according to CRC tumor TNM staging system and the levels of serum carcinoembryonic antigen(CEA) was used to explore the relationship between the frequencies of MAIT cells and the progression of CRC. CRC patients underwent postoperative chemotherapy were follow-up to observe the effect of adjuvant chemotherapy on the frequency of MAIT cells.3. In vitro, cytokines secreted by MAIT cells was detected by cytometric bead array(CBA) kit. Quantitative real-time PCR was used to detect the relative transcript levels of TCRVα7.2-Jα33, TNF-α, IFN-γ and IL-17 A m RNA within the center or the surrounding of the tumor tissue. Simulating the tumor microenvironment, a Transwell co-culture system was built to detect the secretory function of MAIT cells during HCT116 cell existence. Propidium iodide(PI) staining was used to evaluate the cell cycling of HCT116 cells and Ed U assay was used to detect the proliferation of HCT116 cells. Result1. The frequencies of circulating MAIT cells from CRC patients was less than that in HC, especially for the reduced memory CD8 + MAIT cell subsets. The frequency of MAIT cells from TIL was higher than that in LPMC and NIL, especially for the increased CD8 + MAIT cell subsets. Immunofluorescence assay found that MAIT cells preferentially gathered in the center of the tumor tissue, rather than the surrounding tissue.2. Stratified analysis showed that the reduced frequencies of circulating MAIT cells from advanced CRC patients were significantly less than that from early CRC patients. No matter in early or advanced CRC patients, the frequencies of MAIT cells in TIL were higher than that in autologous NIL and PBMC. Furthermore, the frequencies of MAIT cells in TIL showed significantly negative correlation with that in autologous PBMC. In addition, the levels of serum CEA were significantly positive correlation with the frequencies of MAIT cells in autologous TIL. Interestingly, the levels of serum CEA from advanced CRC patients showed a moderate negative correlation with the frequencies of autologous circulating MAIT cells. Noticely, following the cycles of chemotherapy, the frequencies of circulating MAIT cells were recovery..3. The secreting characteristic of MAIT cells was similar as both Th1 and Th17 cells, but it does tend to Th17 cells in CRC patients. In the Transwell co-culture system, activated of MAIT cells induced cell cycle arrest in G2 phase of HCT116 cells in a contact- and dose-dependent manner, which was abrogated by treatment with anti-MR1. ConclusionThe results of this study show that MAIT cells have the characteristics that infiltrating into the colorectal tumor tissue from the peripheral blood. MAIT cells could be used as potential biomarkers to assess CRC staging and prognosis; MAIT cells are involved in tumor immune surveillance of CRC.