Cytokine therapy is commonly used for tumor immunotherapy. Although early studies focused directly on the tumor, current investigations are more attentive of the tumor microenvironment. Various immune cells and related cytokines in the tumor microenvironment play/an important role in the occurrence and development of tumor. Interleukin (IL)-17 is the characteristic cytokine produced by Th17 cells. IL-17 has been associated with various immune 'responses. The results of previous studies showed that IL-17 can significantly reduce the size of transplanted tumors in tumor-bearing mice, albeit it has no effect on the survival time of mice. By investigating the effect of IL-17 in the number and distribution of lymphocyte infiltration in tumor tissues, the expression of cytokines and transcription factors associated with the subsets of CD4-ET cells in tumor tissues, the distribution of subsets of spleen lymphocyte in tumor-bearing mice, a preliminary investigation of the possible antitumor mechanism of IL-17 was performed. In conclusion, the antitumor effect of IL-17 gene transfection in the colon cancer of mice may be associated with the mechanisms whereby IL-17 gene transfection can change the distribution of different subsets of spleen lymphocytes in mice. IL-17 gene transfection can increase the number of lymphocyte infiltration in tumor tissues. IL-17 gene transfection can promote the high expression of interferon-gamma in tumor tissue, while reducing the expression of IL-10 and IL-13 factors, thus exerting an antitumor effect.