Endogenous IL-33 exerts CD8+ T cell antitumor responses overcoming pro-tumor effects by regulatory T cells in a colon carcinoma model.

Interleukin-33 (IL-33) is a nuclear-associated cytokine of the IL-1 family. IL-33 and its receptor ST2 axis exert conflicting anti-tumor and pro-tumor effects in various tumors. In this study, we examined the role of endogenously produced IL-33 in the colon-26 tumor model, in which involvement of the IL-33:ST2 pathway was negligible on the tumor side. We found that the generation of regulatory T cells (Tregs) and CD8+ T cells, and IFN-γ expression by both CD4+ and CD8+ T cells (T cell activation) were impaired in IL-33-deficient mice. Overall antitumor responses, assessed by tumor growth and IFN-γ expression by tumor-infiltrating CD8+ T cells, were also impaired, even after Treg adjustment prior to tumor inoculation. These results indicate that endogenous IL-33 augmented CD8+ T cell-mediated antitumor responses in this colon carcinoma model, with higher CD8+ T cell-infiltration and overcoming pro-tumor effects by increased Tregs. Exogenous application of IL-33 into the tumors did not enhance CD8+ T cell-mediated antitumor responses despite marked elevation of innate responses showing upregulation of proinflammatory cytokine/chemokine expression, neutrophil recruitment, and dendritic cell activation. Our results suggest a dual role for endogenous IL-33 in antitumor responses and suggest that the balance of CD8+ T cells:Tregs in the tumor microenvironment is one of key factors for estimating the contribution of IL-33-mediated antitumor responses. Therefore, the development of IL-33-based cancer immunotherapy may require a target cell-specific approach.

HPV16 E2 protein promotes innate immunity by modulating immunosuppressive status.

The balance between active immune responses against human papillomavirus (HPV) and HPV-induced immune escape regulates viral clearance and carcinogenesis. To understand the role of the early viral protein HPV16 E2 in host innate immune responses, the HPV16 E2-transfected murine squamous cell carcinoma cell line SCCVII (SCC/E2) was generated and anti-tumor responses in T-cell-depleted mice were evaluated. Tumor growth of SCC/E2 was markedly reduced. Cytotoxicity against the NK-sensitive targets YAC-1 and SCCVII was clearly enhanced in SCC/E2-inoculated mice. Despite the comparable ratio of NK cells, the proportion of CD11b(+)Gr-1(+) myeloid-derived suppressor cells (MDSCs) was significantly decreased in SCC/E2-inoculated mice. The transcription of MDSC-related mediators such as inducible nitric oxide synthase, indoleamine 2,3-dioxygenase, and heme oxygenase-1 was significantly impaired in the SCC/E2-inoculated tumor tissues on day 3. Our results suggest that HPV16 E2 promotes anti-tumor innate effector function by modulating immunoregulatory events mediated by MDSCs and their mediators. This report describes a new role for HPV16 E2 as a local immunomodulator at infected sites.