Ectopically Expressed Membrane-bound Form of IL-9 Exerts Immune-stimulatory Effect on CT26 Colon Carcinoma Cells

IL-9 is a known T cell growth factor with pleiotropic immunological functions, especially in parasite infection and colitis. However, its role in tumor growth is controversial. In this study, we generated tumor clones expressing the membrane-bound form of IL-9 (MB-IL-9) and investigated their influences on immune system. MB-IL-9 tumor clones showed reduced tumorigenicity but shortened survival accompanied with severe body weight loss in mice. MB-IL-9 expression on tumor cells had no effect on cell proliferation or major histocompatibility complex class I expression in vitro. MB-IL-9 tumor clones were effective in amplifying CD4⁺ and CD8⁺ T cells and increasing cytotoxic activity against CT26 cells in vivo. We also observed a prominent reduction in body weights and survival period of mice injected intraperitoneally with MB-IL-9 clones compared with control groups. Ratios of IL-17 to interferon (IFN)-γ in serum level and tumor mass were higher in mice implanted with MB-IL-9 tumor clones than those observed in mice implanted with control cells. These results indicate that the ectopic expression of the MB-IL-9 on tumor cells exerts an immune-stimulatory effect with toxicity. To exploit its benefits as a tumor vaccine, a strategy to control the toxicity of MB-IL-9 tumor clones should be developed.