Based on the evidence that IL-17 is a key cytokine involved in various inflammatory diseases, we explored the critical role of IL-17-producing cd T cells for tumor development in tumor-bearing mouse model. IL-17 À/À mice exhibited a significant reduction of tumor growth, concomitantly with the decrease of vascular density at lesion area, indicating a pro-tumor property of IL-17. Among tumor-infiltrating lymphocytes (TIL), cd T cells were the major cellular source of IL-17. Analysis of TCR repertoires in TIL-cd T cells showed that circulating cd T cells, but not skin resident Vc5 1 cd T cells, produced IL-17. Neutralizing antibodies against IL-23, IL-6, and TGF-b, which were produced within the tumor microenvironment, inhibited the induction of IL-17-producing cd T cells. IL-17 production by tumor-infiltrating cd T cells was blocked by anti-cdTCR or anti-NKG2D antibodies, indicating that these ligands, expressed within the tumor microenvironment, are involved in cd T-cell activation. The IL-17-producing TIL-cd T cells exhibited reduced levels of perforin mRNA expression, but increased levels of COX-2 mRNA expression. Together, our findings support the novel concept that IL-17-producing cd T cells, generated in response to tumor microenvironment, act as tumor-promoting cells by inducing angiogenesis. IntroductionIn order to understand how tumor cells can escape immune surveillance mechanisms and thus develop anti-tumor therapies, it is critically important to investigate the mechanisms by which the immune system interacts with the tumor microenvironment. The tumor microenvironment, which is mainly composed of tumor cells, stromal cells, and tumor-infiltrating immune cells, is entirely different from noncancerous tissues. This unique microenvironment potently inhibits immune responses against tumor cells via various soluble mediators and contact-dependent mechanisms [1,2]. Previously, it was suggested that T-cell Eur. J. Immunol. 2010. 40: 1927-1937 DOI 10.1002 Cellular immune response 1927 responses within the local tumor tissue are completely inhibited. However, this concept was abandoned following the discovery of the regulatory T-cell and Th17 cell subsets, which are activated rather than suppressed in the tumor microenvironment via TGF-b and/or IL-6. Thus, the tumor microenvironment is conducive to IL-17 production. In fact, it has been shown that IL-17 is produced in human and murine tumor tissues [3][4][5]. Tumor cells promote neo-vascularization into tumor tissues through hyperproduction of angiogenic factors, which also support their own abnormal proliferation and survival [6]. It has been reported that tumor cells over-expressing IL-17 significantly promote new vessel growth into the tumor tissues [5]; however, physiological effects of IL-17 on tumor progression remain to be defined. Th17 differentiation from naïve CD4 1 T cells is regulated by TGF-b and IL-6. Proliferation, maintenance and full maturation of these cells are controlled by . Recently, it has been shown that IL-17 is produced by diverse T...

CD11b+ Gr-1 + immature myeloid cells (

Immunosuppression in tumor microenvironments critically affects the success of cancer immunotherapy. Here, we focused on the role of interleukin (IL)-6/signal transducer and activator of transcription (STAT3) signaling cascade in immune regulation by human dendritic cells (DCs). IL-6-conditioned monocyte-derived DCs (MoDCs) impaired the presenting ability of cancer-related antigens. Interferon (IFN)-γ production attenuated by CD4+ T cells co-cultured with IL-6-conditioned MoDCs corresponded with decreased DC IL-12p70 production. Human leukocyte antigen (HLA)-DR and CD86 expression was significantly reduced in CD11b+CD11c+ cells obtained from peripheral blood mononuclear cells (PBMCs) of healthy donors by IL-6 treatment and was STAT3 dependent. Arginase-1 (ARG1), lysosomal protease, cathepsin L (CTSL), and cyclooxygenase-2 (COX2) were involved in the reduction of surface HLA-DR expression. Gene expressions of ARG1, CTSL, COX2, and IL6 were higher in tumor-infiltrating CD11b+CD11c+ cells compared with PBMCs isolated from colorectal cancer patients. Expression of surface HLA-DR and CD86 on CD11b+CD11c+ cells was down-regulated, and T cell-stimulating ability was attenuated compared with PBMCs, suggesting that an immunosuppressive phenotype might be induced by IL-6, ARG1, CTSL, and COX2 in tumor sites of colorectal cancer patients. There was a relationship between HLA-DR expression levels in tumor tissues and the size of CD4+ T and CD8+ T cell compartments. Our findings indicate that IL-6 causes a dysfunction in human DCs that activates cancer antigen-specific Th cells, suggesting that blocking the IL-6/STAT3 signaling pathway might be a promising strategy to improve cancer immunotherapy

Evaluation of immune dysfunction during the tumor-bearing state is a critical issue in combating cancer. In this study, we initially found that IL-6, one of the cachectic factors, suppressed CD4+ T cell–mediated immunity through downregulation of MHC class II by enhanced arginase activity of dendritic cells (DC) in tumor-bearing mice. We demonstrated that administration of Ab against IL-6R (anti–IL-6R mAb) greatly enhanced T cell responses and inhibited the growth of tumor in vivo. We also found that IL-6 upregulated the expression of arginase-1 and arginase activity of DC in vitro. Tumor-infiltrating CD11c+ DC exhibited upregulated mRNA expression of arginase-1 but reduced expression of MHC class II in parallel with the increase in serum IL-6 levels at the late stage in tumor-bearing hosts. However, the administration of anti–IL-6R mAb into tumor-bearing mice inhibited both the downmodulation of MHC class II and the upregulation of arginase-1 mRNA levels in DC. Furthermore, we noted that Nω-hydroxy-L-arginine or L-arginine, an arginase-1 inhibitor, blocked the reduction in MHC class II levels on CD11c+ DC during the tumor-bearing state. Finally, we demonstrated that the administration of Nω-hydroxy-L-arginine at the peritumor site significantly enhanced CD4+ T cell responses and inhibited tumor growth. Thus, IL-6–mediated arginase activation and the subsequent reduction in MHC class II expression on DC appeared to be critical mechanisms for inducing dysfunction of the immune system in the tumor-bearing state. Blockade of the IL-6–arginase cascade is a promising tool to overcome the dysfunction of antitumor immunity in tumor-bearing hosts.

Conquering immunosuppression in tumor microenvironments is crucial for effective cancer immunotherapy. It is well known that interleukin (IL)‐6, a pleiotropic cytokine, is produced in the tumor‐bearing state. In the present study, we investigated the precise effects of IL‐6 on antitumor immunity and the subsequent tumorigenesis in tumor‐bearing hosts. CT26 cells, a murine colon cancer cell line, were intradermally injected into wild‐type and IL‐6‐deficient mice. As a result, we found that tumor growth was decreased significantly in IL‐6‐deficient mice compared with wild‐type mice and the reduction was abrogated by depletion of CD8+ T cells. We further evaluated the immune status of tumor microenvironments and confirmed that mature dendritic cells, helper T cells and cytotoxic T cells were highly accumulated in tumor sites under the IL‐6‐deficient condition. In addition, higher numbers of interferon (IFN)‐γ‐producing T cells were present in the tumor tissues of IL‐6‐deficient mice compared with wild‐type mice. Surface expression levels of programmed death‐ligand 1 (PD‐L1) and MHC class I on CT26 cells were enhanced under the IL‐6‐deficient condition in vivo and by IFN‐γ stimulation in vitro. Finally, we confirmed that in vivo injection of an anti‐PD‐L1 antibody or a Toll‐like receptor 3 ligand, polyinosinic‐polycytidylic acid, effectively inhibited tumorigenesis under the IL‐6‐deficient condition. Based on these findings, we speculate that a lack of IL‐6 produced in tumor‐bearing host augments induction of antitumor effector T cells and inhibits tumorigenesis in vivo, suggesting that IL‐6 signaling may be a promising target for the development of effective cancer immunotherapies.