Regulatory T (T(reg)) cells mediate homeostatic peripheral tolerance by suppressing autoreactive T cells. Failure of host antitumor immunity may be caused by exaggerated suppression of tumor-associated antigen-reactive lymphocytes mediated by T(reg) cells; however, definitive evidence that T(reg) cells have an immunopathological role in human cancer is lacking. Here we show, in detailed studies of CD4(+)CD25(+)FOXP3(+) T(reg) cells in 104 individuals affected with ovarian carcinoma, that human tumor T(reg) cells suppress tumor-specific T cell immunity and contribute to growth of human tumors in vivo. We also show that tumor T(reg) cells are associated with a high death hazard and reduced survival. Human T(reg) cells preferentially move to and accumulate in tumors and ascites, but rarely enter draining lymph nodes in later cancer stages. Tumor cells and microenvironmental macrophages produce the chemokine CCL22, which mediates trafficking of T(reg) cells to the tumor. This specific recruitment of T(reg) cells represents a mechanism by which tumors may foster immune privilege. Thus, blocking T(reg) cell migration or function may help to defeat human cancer.

Tumor-associated macrophages are a prominent component of ovarian cancer stroma and contribute to tumor progression. B7-H4 is a recently identified B7 family molecule. We show that primary ovarian tumor cells express intracellular B7-H4, whereas a fraction of tumor macrophages expresses surface B7-H4. B7-H4+ tumor macrophages, but not primary ovarian tumor cells, suppress tumor-associated antigen-specific T cell immunity. Blocking B7-H4-, but not arginase-, inducible nitric oxide synthase or B7-H1 restored the T cell stimulating capacity of the macrophages and contributes to tumor regression in vivo. Interleukin (IL)-6 and IL-10 are found in high concentrations in the tumor microenvironment. These cytokines stimulate macrophage B7-H4 expression. In contrast, granulocyte/macrophage colony-stimulating factor and IL-4, which are limited in the tumor microenvironment, inhibit B7-H4 expression. Ectopic expression of B7-H4 makes normal macrophages suppressive. Thus, B7-H4+ tumor macrophages constitute a novel suppressor cell population in ovarian cancer. B7-H4 expression represents a critical checkpoint in determining host responses to dysfunctional cytokines in ovarian cancer. Blocking B7-H4 or depleting B7-H4+ tumor macrophages may represent novel strategies to enhance T cell tumor immunity in cancer.

Th17 cells play an active role in inflammation and autoimmune diseases. However, the nature and regulation of Th17 in the context of tumor immunity remain unknown. In this study, we show that parallel to regulatory T (Treg) cells, IL-17+ CD4+ and CD8+ T cells are kinetically induced in multiple tumor microenvironments in mice and humans. Treg cells play a crucial role in tumor immune pathogenesis and temper immune therapeutic efficacy. IL-2 is crucial for the production and function of Treg cells. We now show that IL-2 reduces IL-17+ T cell differentiation in the tumor microenvironment accompanied with an enhanced Treg cell compartment in vitro and in vivo. Altogether, our work demonstrates a dynamic differentiation of IL-17+ T cells in the tumor microenvironment, reveals a novel role for IL-2 in controlling the balance between IL-17+ and Treg cells, and provides new insight of IL-17+ T cells in tumor immune pathology and therapy.

CD4؉ CD25 ؉ regulatory T cells (Tregs) mediate peripheral T-cell homeostasis and contribute to self-tolerance. Their homeostatic and pathologic trafficking is poorly understood. Under homeostatic conditions, we show a relatively high prevalence of functional Tregs in human bone marrow. Bone marrow strongly expresses functional stromal-derived factor (CXCL12), the ligand for CXCR4. Human Tregs traffic to and are retained in bone marrow through CXCR4/CXCL12 signals as shown in chimeric nonobese diabetic/severe combined immunodeficient mice. Granulocyte colony-stimulating factor (G-CSF) reduces human bone marrow CXCL12 expression in vivo, associated with mobilization of marrow Tregs to peripheral blood in human volunteers. These findings show a mechanism for homeostatic Treg trafficking and indicate that bone marrow is a significant reservoir for Tregs. These data also suggest a novel mechanism explaining reduced acute graft-versus-host disease and improvement in autoimmune diseases following G-CSF treatment.

To directly dissect the role of each immune component in human tumor immunopathogenesis, we have studied the interaction between dendritic cells and T cells in the tumor environment of patients with ovarian carcinoma. We previously reported that functional plasmacytoid dendritic cells, but not functionally mature myeloid dendritic cells, accumulated in tumor microenvironments. We now show that tumor ascites macrophage-derived dendritic cells induced tumor-associated antigen-specific CD8+ T cells with effector functions. Strikingly, tumor ascites plasmacytoid dendritic cells induced interleukin-10+ CCR7+ CD45RO+ CD8+ regulatory T cells. Four characteristics have been identified in tumor plasmacytoid dendritic cell-induced CD8+ regulatory T cells: (a) induction of CD8+ regulatory T cells is independent of CD4+ CD25+ T cells; (b) CD8+ regulatory T cells significantly suppress myeloid dendritic cell-mediated tumor-associated antigen-specific T cell effector functions through interleukin-10; (c) repetitive myeloid dendritic cell stimulation can recover CD8+ regulatory T cell-mediated poor T cell proliferation, but not T cell effector function; (d) CD8+ regulatory T cells express functional CCR7, and efficiently migrate with lymphoid homing chemokine MIP-3beta. Primary suppressive CCR7+ CD45RO+ CD8+ T cells are found in the tumor environment of patients with ovarian cancers. Thus, tumor-associated plasmacytoid dendritic cells contribute to the tumor environmental immunosuppressive network. Collectively, tumors manipulate tumor microenvironmental dendritic cell subset distribution and function to subvert tumor immunity. The data are relevant to understanding tumor immunopathology as well as reevaluating tumor immunotherapeutic strategies.

Multiple modes of suppressive mechanisms including IL-10 are thought to be implicated in CD4+CD25+ regulatory T (Treg) cell-mediated suppression. However, the cellular source, role, and molecular mechanism of IL-10 in Treg cell biology remain controversial. We now studied the interaction between Treg cells and APCs. We demonstrate that Treg cells, but not conventional T cells, trigger high levels of IL-10 production by APCs, stimulate APC B7-H4 expression, and render APCs immunosuppressive. Initial blockade of B7-H4 reduces the suppressive activity mediated by Treg cell-conditioned APCs. Further, APC-derived, rather than Treg cell-derived, IL-10 is responsible for APC B7-H4 induction. Therefore, Treg cells convey suppressive activity to APCs by stimulating B7-H4 expression through IL-10. Altogether, our data provide a novel cellular and molecular mechanism for Treg cell-mediated immunosuppression at the level of APCs, and suggest a plausible mechanism for the suppressive effect of IL-10 in Treg cell-mediated suppression.

Angiogenesis is essential for both primary and metastatic tumor growth. Tumor blood vessel formation is complex and regulated by many factors. Ovarian carcinomas have a poor prognosis, often associated with multifocal intraperitoneal dissemination accompanied by intense neovascularization. To examine tumor angiogenesis in the tumor microenvironment, we studied malignant ascites of patients with untreated ovarian carcinoma. We observed high numbers of plasmacytoid dendritic cells (PDCs) and significant stromal-derived factor (CXCL-12/SDF)-1 in their malignant ascites, attracting PDCs into the tumor environment. We now show that tumor-associated PDCs induced angiogenesis in vivo through production of tumor necrosis factor ␣ and interleukin 8. By contrast, myeloid dendritic cells (MDCs) were absent from malignant ascites. MDCs derived in vitro suppressed angiogenesis in vivo through production of interleukin 12. Thus, the tumor may attract PDCs to augment angiogenesis while excluding MDCs to prevent angiogenesis inhibition, demonstrating a novel mechanism for modulating tumor neovascularization. Because dendritic cells (DCs) have long been known to affect tumor immunity, our data also implicate DCs in regulation of tumor neoangiogenesis, suggesting a novel role of DCs in tumor pathology.

Interleukin (IL)-2 is used in the immunotherapy of patients with certain cancer and HIV infection. IL-2 treatment reliably results in 16% to 20% objective clinical response rate in cancer patients, with significant durability of responses in selected patients. However, the mechanisms of therapeutic activity in responding versus nonresponding patients remain poorly understood. CD4 + CD25 + FOXP3 + regulatory T (Treg) cells contribute to immunosuppressive networks in human tumors. We treated 31 ovarian cancer patients with IL-2. We show that administration of IL-2 induces the proliferation of existent Treg cells in patients with ovarian cancer. The potency of Treg cell proliferation is negatively determined by the initial prevalence of Treg cells, suggesting that Treg cells are a factor for self-controlling Treg cell proliferation. After IL-2 cessation, the number of Treg cells more efficiently dropped in clinical responders than nonresponders. Furthermore, IL-2 treatment stimulates chemokine receptor CXCR4 expression on Treg cells, enables Treg cell migration toward chemokine CXCL12 in the tumor microenvironment, and may enforce Treg cell tumor accumulation. Our findings support the concept that administration of IL-2 numerically and functionally affects the Treg cell compartment. These data provide an important insight in evaluating the clinical benefit and therapeutic prediction of IL-2 treatment in patients with cancer. [Cancer Res 2007;67(15):7487-94]