The effect of immune microenvironment on the progression and prognosis of colorectal cancer

Cancer cells may escape from host immune responses through active suppression of the immune response, but the detailed mechanisms in colorectal cancer remain to be elucidated. In this study, 108 colorectal tumor samples and their peritumoral tissues were collected for immunohistochemistry of infiltrating lymphocytes. Th1 and Tregs cells were determined by the positive expression of T-bet and FOXP3 proteins, respectively. The Tr1 cells were identified by CD49b and LAG-3 protein expression. IL-17-positive cells were identified by IL-17 expression. Results showed that the percentage of T-bet-positive cells was significantly decreased, while the percentages of IL-17-, FOXP3-, CD49b-, and LAG-3-positive cells were significantly increased in tumor tissues compared to that in peritumoral tissues. The ratio of IL-17-, FOXP3-, CD49b-, and LAG3-positive cells to T-bet-positive cells was significantly higher in tumor tissues than in peritumoral tissues. The percentage of infiltrating IL-17-positive cells in tumor tissues was negatively associated with lymph metastasis, invasion, and TNM stage. The percentage of CD49b- and LAG-3-positive cells was positively associated with differentiation, lymph metastasis, invasion, TNM, and Duke stage of colorectal cancer. The percentage of positive Th17 and Tr1 cells is a marker for poor prognosis in patients with CRC. In conclusion, decreased composition of regulative Th1 cells and increased composition of FOXP+ Tregs-, CD49b+/LAG-3+ Tr1-, and IL-17-positive cells in tumor tissues may be associated with the progression of colorectal cancer. The high percentage of IL-17- and Tr1-positive cells in tumor tissues is a predictive marker for poor prognosis of colorectal cancer.