Because IL-4 and CpG oligodeoxynucleotides (CpG-ODNs) are immune stimulants, we evaluated the antitumor effects of IL-4 gene therapy and CpG-ODN treatment in a poorly immunogenic murine cancer model. We used a murine colorectal cancer MC38 cell line overexpressing the IL-4 gene (MC38-IL4). Incubation with MC38-IL4 and CpG-ODN enhanced bone marrow-derived dendritic cell (DC) maturation in vitro. In addition, interferon (IFN)-γ production was significantly increased in naïve splenocytes after they were coincubated with MC38-IL4 and CpG-ODN. When mice bearing MC38 wild-type tumors were inoculated subcutaneously with MC38-IL4 cells and CpG-ODN, the outgrowth of established parental tumors was significantly suppressed compared to those in the MC38-IL4-treated group (IL-4 vs. IL-4 + CpG-ODN, p=0.015). A marked infiltration of CD8+ cells in the established parental tumors of mice treated with MC38-IL4 and CpG-ODN was confirmed by immunohistochemical analyses (MC38-IL4, 2.8±1.9 cells/field vs. MC38-IL4 + CpG-ODN, 20.7±15.3 cells/field, p=0.027). Significant tumor-specific cytolysis was detected when splenocytes of MC38-IL4 + CpG-ODN-treated mice were stimulated by γ-irradiated MC38-IL4 cells and CpG-ODN twice weekly in vitro and used as effector cells in a chromium-release assay (32.2±3.5% for MC38 cells vs. 3.2±1.1% for YAC-1 cells; at an effector to target ratio of 40). These results suggest that IL-4 and CpG-ODN treatment promotes potent Th1-type antitumor immune responses. Therefore, the combination of IL-4 gene therapy and CpG-ODN treatment for cancer should be evaluated in clinical trials.

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