Combined toll-like receptor 3/7/9 deficiency on host cells results in T-cell-dependent control of tumour growth.

Toll-like receptors (TLRs) are located either on the cell surface or intracellularly in endosomes and their activation normally contributes to the induction of protective immune responses. However, in cancer their activation by endogenous ligands can modulate tumour progression. It is currently unknown how endosomal TLRs regulate endogenous anti-tumour immunity. Here we show that TLR3, 7 and 9 deficiencies on host cells, after initial tumour growth, result in complete tumour regression and induction of anti-tumour immunity. Tumour regression requires the combined absence of all three receptors, is dependent on both CD4 and CD8 T cells and protects the mice from subsequent tumour challenge. While tumours in control mice are infiltrated by higher numbers of regulatory T cells, tumour regression in TLR-deficient mice is paralleled by altered vascular structure and strongly induced influx of cytotoxic and cytokine-producing effector T cells. Thus, endosomal TLRs may represent a molecular link between the inflamed tumour cell phenotype, anti-tumour immunity and the regulation of T-cell activation.

Human neutrophils: Their role in cancer and relation to myeloid-derived suppressor cells.

Increased frequencies of peripheral blood neutrophils as well as tumor-infiltrating (associated) neutrophils (TAN) have been observed in many tumor entities. Although the most frequent cell type in the peripheral blood, neutrophils are outnumbered by other leukocyte subsets in the tumor microenvironment. Nevertheless, a number of recent meta-analyses identified TAN as well as high neutrophil-lymphocyte ratio in the blood as one of the most powerful immunologic prognostic parameters in human oncology. This clinical impact is based on an intense bidirectional crosstalk of neutrophils and tumor cells resulting in changes in neutrophil as well as tumor cell biology. These changes eventually lead to TAN equipped with various tumor promoting features, which enhance angiogenesis, cancer cell invasion and metastasis. Many of the pro-tumor features of TAN are shared with PMN-MDSC (myeloid-derived suppressor cells). Consequently, the distinction of these two cell populations is a matter of intensive debate and also specifically discussed in this article. The importance of neutrophils in cancer progression has triggered numerous efforts to therapeutically target these cells. Current strategies in this area focus on the inhibition of either TAN recruitment or pro-tumorigenic function.

Survival of residual neutrophils and accelerated myelopoiesis limit the efficacy of antibody-mediated depletion of Ly-6G+ cells in tumor-bearing mice.

Expansion of Ly-6G(+) myeloid cells has been reported in most murine cancer models. However, divergent findings exist regarding the role and effect of these cells on host immunity and tumor progression. Antibody-mediated depletion of Ly-6G(+) cells is a common technique to assess the in vivo relevance of these cells. Interpretation of results crucially depends on the efficacy and course of depletion. We established murine head and neck cancer models and analyzed the efficacy of antibody-mediated depletion by flow cytometry, conventional histology, and intravital imaging with a novel Ly-6G-transgenic mouse model. The first phase of depletion was characterized by effective elimination of Ly-6G(+) cells from the peripheral blood. Nevertheless, viable, resistant cells were found to reside in the tumor tissue and spleen. This peripheral depletion phase was associated with high systemic levels of granulocyte colony-stimulating factor and KC and enhanced splenic production of Ly-6G(+) cells. Even under sustained treatment with either αGr-1 or αLy-6G antibodies, peripheral blood depletion ended after approximately 1 wk and was followed by reappearance of immature Ly-6G(+) cells with an immunoregulatory phenotype. Reappearance of these depletion-resistant immature cells was enhanced in tumor-bearing, compared with naïve, control mice. Collectively, our data suggest that depletion of Ly-6G(+) myeloid cells in tumor-bearing mice is counteracted by the persistence of intratumoral cells, enhanced extramedullary granulopoiesis, and accelerated reappearance of immature cells. Hence, extensive monitoring of in vivo kinetics and tissue distribution of Ly-6G(+) cells is required in depletion studies.

The kinship of neutrophils and granulocytic myeloid-derived suppressor cells in cancer: cousins, siblings or twins?

Neutrophils in the tumor host may promote tumor progression by enhancing angiogenesis, invasion and metastasis. Granulocytic myeloid-derived suppressor cells (MDSC) share many features with neutrophils. Classically, MDSC are viewed as and defined as immunosuppressive cells. In this article we summarize and critically review evidence for a role of MDSC in promoting angiogenesis, invasion and metastasis of solid tumors. We also attempt to provide a critical evaluation of the relationship between neutrophils and G-MDSC in the tumor host with a particular focus on human cancer.

Neutrophils and granulocytic myeloid-derived suppressor cells: immunophenotyping, cell biology and clinical relevance in human oncology.

Accumulating evidence indicates that myeloid cells are critically involved in the pathophysiology of human cancers. In contrast to the well-characterized tumor-associated macrophages, the significance of granulocytes in cancer has only recently begun to emerge. A number of studies found increased numbers of neutrophil granulocytes and granulocytic myeloid-derived suppressor cells (GrMDSCs) both in the peripheral blood and in the tumor tissues of patients with different types of cancer. Most importantly, granulocytes have been linked to poor clinical outcome in cancer patients which suggests that these cells might have important tumor-promoting effects. In this review, we will address in detail the following major topics: (1) neutrophils and GrMDSCs in the peripheral blood of cancer patients-phenotype and functional changes; (2) neutrophils and GrMDSCs in the tumor tissue-potential mechanisms of tumor progression and (3) relevance of neutrophils and GrMDSCs for the clinical outcome of cancer patients. Furthermore, we will discuss the advantages and disadvantages of the current strategies used for identification and monitoring of human MDSCs. We propose a six-color immunophenotyping protocol that discriminates between monocytic MDSCs (MoMDSCs), two subsets of GrMDSCs and two subsets of immature myeloid cells in human cancer patients, thus, allowing for an improved characterization and understanding of these multifaceted cells.