Breast cancer-derived transforming growth factor-ß and tumor necrosis factor-α compromise interferon-α production by tumor-associated plasmacytoid dendritic cells.

We previously reported that plasmacytoid dendritic cells (pDCs) infiltrating breast tumors are impaired for their interferon-α (IFN-α) production, resulting in local regulatory T cells amplification. We designed our study to decipher molecular mechanisms of such functional defect of tumor-associated pDC (TApDC) in breast cancer. We demonstrate that besides IFN-α, the production by Toll-like receptor (TLR)-activated healthy pDC of IFN-ß and TNF-α but not IP-10/CXCL10 nor MIP1-α/CCL3 is impaired by the breast tumor environment. Importantly, we identified TGF-ß and TNF-α as major soluble factors involved in TApDC functional alteration. Indeed, recombinant TGF-ß1 and TNF-α synergistically blocked IFN-α production of TLR-activated pDC, and neutralization of TGF-ß and TNF-α in tumor-derived supernatants restored pDCs' IFN-α production. The involvment of tumor-derived TGF-ß was further confirmed in situ by the detection of phosphorylated Smad2 in the nuclei of TApDC in breast tumor tissues. Mechanisms of type I IFN inhibition did not involve TLR downregulation but the inhibition of IRF-7 expression and nuclear translocation in pDC after their exposure to tumor-derived supernatants or recombinant TGF-ß1 and TNF-α. Our findings indicate that targeting TApDC to restore their IFN-α production might be an achievable strategy to induce antitumor immunity in breast cancer by combining TLR7/9-based immunotherapy with TGF-ß and TNF-α antagonists.

Inducible costimulator (ICOS) is a marker for highly suppressive antigen-specific T cells sharing features of TH17/TH1 and regulatory T cells.

BACKGROUND: CD4(+)CD25(+) regulatory T (Treg) cells are involved in the downmodulation of numerous immune responses to pathogens, tumors, or allergens. OBJECTIVE: In this study, we further characterized the nature of Treg cells that control skin inflammatory reactions to haptens. METHODS: In a model of contact hypersensitivity to 2,4-dinitro-fluorobenzene, we have investigated the phenotype, the specificity, and the origin of Treg cells that modulate the priming of effector CD8(+) T cells responsible for the development of the pathology. RESULTS: 2,4-Dinitrofluorobenzene immunization induced a population of CD4(+)CD25(+) Treg cells that controlled CD8(+) T-cell effector responses in a hapten-specific manner in vivo. High levels of inducible costimulator (ICOS) expression defined a population of CD4(+)CD25(+)FoxP3(+) (forkhead box protein 3) Treg cells that presented superior suppressive activity. Importantly, ICOS(+) Treg cells were distinguishable from all other FoxP3(+) Treg cells by the expression of IL-10, IL-17, and IFN-gamma. Hapten-specific Treg cells proliferating in response to their cognate antigen in vivo predominantly displayed a CD25(+)FoxP3(+)ICOS(+) phenotype. By using reporter mice, we showed that ICOS(+) Treg cells derived from the expansion of natural CD4(+)FoxP3(+) Treg cells rather than generation of adaptive Treg cells. Furthermore, the generation of ICOS(+) Treg cells depended on innate cells rather than the effector CD8(+) T-cell population. CONCLUSION: Taken together, our data show that a population of CD4(+)CD25(+)FoxP3(+) T cells upregulates ICOS on in vivo sensitization and specifically suppresses hapten-reactive CD8(+) T cells both in vivo and in vitro.

Expression of TAM-R in Human Immune Cells and Unique Regulatory Function of MerTK in IL-10 Production by Tolerogenic DC.

Tumor-infiltrating myeloid cells are a key component of the immune infiltrate often correlated with a poor prognosis due to their capacities to sustain an immunosuppressive environment. Among membrane receptors implicated in myeloid cell functions, Tyro3, Axl, and MerTK, which are a family of tyrosine kinase receptors (TAM-R), have been described in the regulation of innate cell functions. Here, we have identified MerTK among TAM-R as the major marker of both human M2 macrophages and tolerogenic dendritic cells (DC). In situ, MerTK expression was found within the immune infiltrate in multiple solid tumors, highlighting its potential role in cancer immunity. TAM-R ligands Gas6 and PROS1 were found to be constitutively produced by myeloid cells in vitro. Importantly, we describe a novel function of MerTK/PROS1 axis in the regulation of IL-10 production by tolerogenic DC. Finally, the analysis of TAM-R expression within the lymphoid compartment following activation revealed that MerTK, but not Axl or Tyro3, is expressed on activated B lymphocytes and regulatory T cells, as well as CD4+ and CD8+ T cells. Thus, our findings deepen the implication of MerTK in the regulation of myeloid cell-mediated immunosuppression and identified new cellular targets expressing MerTK that could participate in the antitumor immune response.

Impaired IFN-α production by plasmacytoid dendritic cells favors regulatory T-cell expansion that may contribute to breast cancer progression.

Infiltration and dysfunction of immune cells have been documented in many types of cancers. We previously reported that plasmacytoid dendritic cells (pDC) within primary breast tumors correlate with an unfavorable prognosis for patients. The role of pDC in cancer remains unclear but they have been shown to mediate immune tolerance in other pathophysiologic contexts. We postulated that pDC may interfere with antitumor immune response and favor tolerance in breast cancer. The present study was designed to decipher the mechanistic basis for the deleterious impact of pDC on the clinical outcome. Using fresh human breast tumor biopsies (N = 60 patients), we observed through multiparametric flow cytometry increased tumor-associated (TA) pDC (TApDC) rates in aggressive breast tumors, i.e., those with high mitotic index and the so-called triple-negative breast tumors (TNBT). Furthermore, TApDC expressed a partially activated phenotype and produced very low amounts of IFN-α following toll-like receptor activation in vitro compared with patients' blood pDC. Within breast tumors, TApDC colocalized and strongly correlated with TA regulatory T cells (TATreg), especially in TNBT. Of most importance, the selective suppression of IFN-α production endowed TApDC with the unique capacity to sustain FoxP3(+) Treg expansion, a capacity that was reverted by the addition of exogenous IFN-α. These findings indicate that IFN-α-deficient TApDC accumulating in aggressive tumors are involved in the expansion of TATreg in vivo, contributing to tumor immune tolerance and poor clinical outcome. Thus, targeting pDC to restore their IFN-α production may represent an attractive therapeutic strategy to overcome immune tolerance in breast cancer.