T cell immunoglobulin- and mucin-domain-containing molecule-3 (TIM3) has been shown to be expressed on Th1 cells and negatively regulates these cell functions. TIM3 has been implicated in the Th1-driven pathogenesis of autoimmune disease and the viral infection. However, molecular mechanisms of TIM3 inhibiting Th1 cells and the efficacy of tumor vaccine expressing Tim3 blocker have not been well studied. In this study, I investigated the molecular mechanisms underlying down-regulation of cytokine production by human TIM3 expression in T cells and the effect of expression of Tim3-hIg, mouse Tim3 pathway blocker, on tumor growth in mice. First, reduced expression of IL-2 and IFN-γ was demonstrated in both primary CD4+ T cells with high level of TIM3 expression and Jurkat T cells-over expressing TIM3. TIM3-over expression reduced the activities of NFAT and AP-1, important transcription factors of IL-2 expression. The expression of c-Jun and dephosphorylation of NFAT were suppressed by TIM3 expression. The 7 a.a from E261 to I267 of TIM3 cytoplasmic tail was critical for down-regulation of cytokine production. The 54 a.a from E261 to P301 was involved in suppression of AP-1 activity and 34 a.a from E268 to P301 in suppression of NFAT activity.
On the other hands, I examined the effect of expression of mouse Tim3 pathway blocker, Tim3-hIg. The tumor growth in mice injected with Lewis lung carcinoma (3LL) cells was suppressed and the frequencies of CD4+CD25+Foxp3+ T cells were reduced. Furthermore, injection of Tim3 pathway inhibitor expressing cells significantly enhanced the efficacy of a prophylactic tumor vaccine and marginally enhanced the efficacy of a therapeutic tumor vaccine. However, when given in combination with 5-fluorouracil, a chemotherapeutic agent, therapeutic tumor vaccine capable of Tim3 pathway inhibition had no additional anti-tumor effect. These data demonstrate that TIM3 inhibits Th1-mediated cytokine production through the suppression of AP-1 and NFAT activity and Tim3 pathway inhibitor enhances the efficacy of tumor vaccination and derives anti-tumor immunity
