Monica Rimoldi

Macrophage polarization in tumour progression

Macrophages are a fundamental part of the innate defense mechanisms, which can promote specific immunity by inducing T cell recruitment and activation. Despite this, their presence within the tumour microenvironment has been associated with enhanced tumour progression and shown to promote cancer cell growth and spread, angiogenesis and immunosuppression. This paradoxical role of macrophages in cancer finds an explanation in their functional plasticity, that may result in the polarized expression of either pro- or anti-tumoural functions. Key players in the setting of their phenotype are the microenvironmental signals to which macrophages are exposed, which selectively tune their functions within a functional spectrum encompassing the M1 and M2 extremes. Here, we discuss recent findings suggesting that targeting tumour-associated macrophages (TAMs) polarization may represent a novel therapeutic strategy against cancer.

Tolerance and M2 (alternative) macrophage polarization are related processes orchestrated by p50 nuclear factor κB

Cells of the monocyte–macrophage lineage play a central role in the orchestration and resolution of inflammation. Plasticity is a hallmark of mononuclear phagocytes, and in response to environmental signals these cells undergo different forms of polarized activation, the extremes of which are called classic or M1 and alternative or M2. NF-κB is a key regulator of inflammation and resolution, and its activation is subject to multiple levels of regulation, including inhibitory, which finely tune macrophage functions. Here we identify the p50 subunit of NF-κB as a key regulator of M2-driven inflammatory reactions in vitro and in vivo. p50 NF-κB inhibits NF-κB–driven, M1-polarizing, IFN-β production. Accordingly, p50-deficient mice show exacerbated M1-driven inflammation and defective capacity to mount allergy and helminth-driven M2-polarized inflammatory reactions. Thus, NF-κB p50 is a key component in the orchestration of M2-driven inflammatory reactions.

M2 Macrophages Phagocytose Rituximab-Opsonized Leukemic Targets More Efficiently than M1 Cells In Vitro

Because macrophages have been implicated as major players in the mechanism of action of rituximab, we have investigated the factors that modulate their tumor cell killing potential. Human macrophages, differentiated in vitro from peripheral blood monocytes, were used in binding and phagocytosis assays using B-chronic lymphocytic leukemia or lymphoma target cells opsonized with rituximab. Phagocytosis was maximal at 0.1 μg/ml rituximab and was not significantly affected by CD20 expression levels or by CD16A polymorphism at position 158 (Val/Phe). The role of FcγRs was demonstrated by complete inhibition of phagocytosis by excess human Igs. Because macrophages can be differentiated to M1- or M2-type cells with either GM-CSF or M-CSF, respectively, and can be classically activated by proinflammatory stimuli (IFN-γ/LPS) or undergo alternative activation with cytokines such as IL-4 or IL-10, we have analyzed the effect of these different polarization programs on the phagocytosis mediated by rituximab. Macrophages differentiated in presence of M-CSF showed a 2- to 3-fold greater phagocytic capacity compared with GM-CSF-induced cells. Furthermore, addition of IL-10 significantly increased, whereas IL-4 decreased phagocytosis by both M-CSF- and GM-CSF-differentiated macrophages. LPS/IFN-γ had little effect. Expression of CD16, CD32, and CD64 in different macrophage populations correlated with phagocytic activity. Interestingly, several B lymphoma cell lines were observed to secrete 400-1300 pg/ml IL-10 in vitro, and coculture of human macrophages with lymphoma conditioned medium increased significantly their phagocytic capacity. Our data suggest that cytokines secreted by lymphoma cells can favor alternate activation of macrophages with a high phagocytic capacity toward rituximab-opsonized targets.

Intestinal epithelial cells control dendritic cell function.

Abstract: Dendritic cells (DCs) comprise a family of cells specializing in antigen capture and presentation to T cells. We have recently shown that DC play an active role in bacterial uptake across mucosal surfaces. Indeed, DC are able to open tight junctions and to sample antigens directly across epithelia, both in vitro and in vivo. Because DC express tight junction proteins, the integrity of the epithelial barrier is preserved. In this study we have analyzed the possible involvement of epithelial cells in controlling DC function. We developed an in vitro model in our laboratory consisting of a three‐player system of dendritic cells, epithelial cell monolayers, and bacteria. The crosstalk between epithelial cells and dendritic cells was analyzed, and epithelial cells were tested for their capacity to release cytokines and chemokines that induce the migration and activation of DC. We show that the capacity of epithelial cells to produce cytokines and activate DC is dependent on the invasiveness of the bacteria tested. In particular, invasive bacteria stimulate epithelial cells to release proinflammatory cytokines and to induce the maturation state of DC. By contrast, noninvasive bacteria are unable to stimulate epithelial cells, but can activate DC directly when DC translocate to the apical side. In conclusion, epithelial cells are not simply a barrier to bacteria entering via the oral route, but actively influence the activating properties of bystander DC.

Targeting tumour-associated macrophages.

Clinical and experimental evidence have highlighted that a major leukocyte population present in tumours, the so-called tumour-associated macrophages (TAM), is the principal component of the leukocyte infiltrate supporting tumour growth. Over the years the mechanisms supporting the protumoural functions of TAM have become increasingly clear and in several experimental tumour models, the activation of an inflammatory response (most frequently mediated by macrophages) has been shown to play an essential role for full neoplastic transformation and progression. This evidence strongly supports the idea that TAM are central orchestrators of the inflammatory networks expressed in the tumour microenvironment, and suggest these cells as possible targets of anticancer therapies.

Toll-like receptor 4 is not required for the full maturation of dendritic cells or for the degradation of Gram-negative bacteria

Toll‐like receptor 4 (TLR4) has been recently associated with cellular responses to lipopolysaccharide (LPS), and mice mutated in tlr4, such as C57BL/10ScCr or C3H/HeJ mice, become hyporesponsive to LPS. In this study, we have analyzed the capacity of bone marrow‐derived dendritic cells (BMDC) from C57BL/10ScCr (ScCr‐BMDC) or C3H/HeJ (HeJ‐BMDC) mice to respond to LPS or to Gram‐negative bacteria. We show that ScCr‐ or HeJ‐BMDC are insensitive to LPS, but can mature in response to live and killed Gram‐negative bacteria. Interestingly, only ScCr‐BMDC but not HeJ‐BMDC, stimulated with bacteria, have reduced capacity to produce pro‐ and anti‐inflammatory cytokines as compared to BMDC from control mice, probably due to genetic defects unrelated to the tlr4 mutation. Nevertheless, ScCr‐BMDC and ScCr BM‐macrophages (BM‐Mϕ) phagocytose Salmonella typhimurium similarly to control cells, indicating that TLR4 is not compulsory for bacterial uptake. Moreover, BM‐Mϕ, but not BM‐DC from B10ScCr or C3H/HeJ mice, are impaired in their capacity to kill intracellular bacteria and to produce NO as compared to wild type controls. However, the bacteria killing property of BM‐Mϕ is completely restored by pretreating the cells with IFN‐γ. Hence, TLR4 plays different roles in DC versus Mϕ.

Origin and Functions of Tumor-Associated Myeloid Cells (TAMCs)

The construction of an inflammatory microenvironment provides the fuel for cancer development and progression. Hence, solid tumors promote the expansion and the recruitment of leukocyte populations, among which tumor-associated myeloid cells (TAMCs) represent a paradigm for cancer-promoting inflammation. TAMCs group heterogeneous phagocytic populations stemming from a common myeloid progenitor (CMP), that orchestrate various aspects of cancer, including: diversion and skewing of adaptive responses; immunosuppression; cell growth; angiogenesis; matrix deposition and remodelling; construction of a metastatic niche and actual metastasis. Several evidence indicate that TAMCs show plasticity and/or functional heterogeneity, suggesting that tumour-derived factors promote their functional “reprogramming” towards protumoral activities. While recent studies have attempted to address the role of microenvironment signals, the interplay between cancer cells, innate and adaptive immunity is now emerging as a crucial step of the TAMCs reprogramming. Here we discuss the evidence for the differentiation of TAMCs during the course of tumor progression and the molecular mechanisms that regulate such event.

Monocyte-derived Dendritic Cells from Crohn Patients Show Differential NOD2/CARD15-dependent Immune Responses to Bacteria

Background: Three common mutations in the NOD2/CARD15 gene are strongly associated with Crohns disease (CD). NOD2 is an intracellular receptor of muramyl dipeptide (MDP), a component of peptidoglycan present in the cell wall of Gram‐positive (G+) and Gram‐negative (G−) bacteria. Methods: We generated monocyte‐derived dendritic cells (MoDCs) from CD patients mutated or not for CARD15 (n = 53) or from healthy donors (n = 12) and analyzed their activation in response to live Salmonella typhimurium as a model of pathogenic G− bacteria. Results: MoDCs carrying the L1007fs mutation, although phenotypically activated by bacteria, produced a significantly reduced amount of tested cytokines. MoDCs carrying R702W or compound G908R/R702W NOD2 mutations displayed an increased basal level of IL‐8 release. After a bacterial encounter, these cells were phenotypically activated and produced levels of cytokines similar to healthy controls. Interestingly, although L1007fs/WT mutations conferred reduced production of cytokines, including IL‐12, these cells were perfectly capable of inducing T‐cell polarization toward the Th1 phenotype. Conclusions: NOD2 mutations affect the basal characteristics of MoDCs and their response to G− bacteria differently. MoDCs could be involved in CD onset because they have defects in releasing inflammatory cytokines and in polarizing T‐cell responses.

Erratum: Corrigendum: Intestinal immune homeostasis is regulated by the crosstalk between epithelial cells and dendritic cells

Corrigendum: Intestinal immune homeostasis is regulated by the crosstalk between epithelial cells and dendritic cells

Erratum : Intestinal immune homeostasis is regulated by the crosstalk between epithelial cells and dendritic cells (Nature Immunology (2005) 6 (507-514))

Corrigendum: Intestinal immune homeostasis is regulated by the crosstalk between epithelial cells and dendritic cells