Differential macrophage programming in the tumor microenvironment

License for destruction: tumor-specific cytokine targeting

Stroma is an integral part of solid tumors and plays a key role in growth promotion and immune suppression. Most current therapies focus on destroying tumors and/or abnormal vasculature. However, evidence is emerging that anticancer efficacy improves with vessel normalization rather than destruction. Specific targeting of cytokines into tumors provides proof-of-concept that tumor stroma is dynamic and can be remodeled to increase drug access and alleviate immune suppression. Changing the inflammatory milieu 'opens' tumors for therapy and thus provides a license for destruction. This involves reprogramming of paracrine signaling networks between multiple stromal components to break the vicious cycle of angiogenesis and immune suppression. With active immunotherapy rapidly moving into the clinic, local cytokine delivery emerges as an attractive adjuvant.

miR-125a-5p regulates differential activation of macrophages and inflammation

Macrophage activation is a central event in immune responses. Macrophages undergoing classical activation (M1 macrophages) are proinflammatory, whereas alternatively activated macrophages (M2 macrophages) are generally anti-inflammatory. miRNAs play important regulatory roles in inflammatory response. However, the manner in which miRNAs regulate macrophage activation in response to different environmental cues has not been well defined. In this study, we found that M-BMM macrophages (M2) express greater levels of miR-125a-5p than do GM-BMM macrophages (M1). Stimulation of macrophages through TLR2 and TLR4 but not through TLR3 enhanced miR-125a-5p expression. Up-regulation of miR-125a-5p after TLR2/4 activation requires the adaptor MYD88 but not TRIF. Overexpression of miR-125a-5p diminished M1 phenotype expression induced by LPS but promoted M2 marker expression induced by IL-4. In contrast, knockdown of miR-125a-5p promoted M1 polarization and diminished IL-4-induced M2 marker expression. We found that miR-125a-5p targets KLF13, a transcriptional factor that has an important role in T lymphocyte activation and inflammation. KLF13 knockdown had similar effects on M1 activation as did miR-125a-5p overexpression. In addition, miR-125a-5p regulates phagocytic and bactericidal activities of macrophages. Our data suggest that miR-125a-5p has an important role in suppressing classical activation of macrophages while promoting alternative activation.

The role of lipid-activated nuclear receptors in shaping macrophage and dendritic cell function: From physiology to pathology

Nuclear receptors are ligand-activated transcription factors linking lipid signaling to the expression of the genome. There is increasing appreciation of the involvement of this receptor network in the metabolic programming of macrophages and dendritic cells (DCs), essential members of the innate immune system. In this review we focus on the role of retinoid X receptor, retinoic acid receptor, peroxisome proliferator-associated receptor γ, liver X receptor, and vitamin D receptor in shaping the immune and metabolic functions of macrophages and DCs. We also provide an overview of the contribution of macrophage- and DC-expressed nuclear receptors to various immunopathologic conditions, such as rheumatoid arthritis, inflammatory bowel disease, systemic lupus erythematosus, asthma, and some others. We suggest that systematic analyses of the roles of these receptors and their activating lipid ligands in immunopathologies combined with complementary and focused translational and clinical research will be crucial for the development of new therapies using the many molecules available to target nuclear receptors.

Cell type-dependent pathogenic functions of overexpressed human cathepsin B in murine breast cancer progression

The cysteine protease cathepsin B (CTSB) is frequently overexpressed in human breast cancer and correlated with a poor prognosis. Genetic deficiency or pharmacological inhibition of CTSB attenuates tumor growth, invasion and metastasis in mouse models of human cancers. CTSB is expressed in both cancer cells and cells of the tumor stroma, in particular in tumor-associated macrophages (TAM). In order to evaluate the impact of tumor- or stromal cell-derived CTSB on Polyoma Middle T (PyMT)-induced breast cancer progression, we used in vivo and in vitro approaches to induce human CTSB overexpression in PyMT cancer cells or stromal cells alone or in combination. Orthotopic transplantation experiments revealed that CTSB overexpression in cancer cells rather than in the stroma affects PyMT tumor progression. In 3D cultures, primary PyMT tumor cells showed higher extracellular matrix proteolysis and enhanced collective cell invasion when CTSB was overexpressed and proteolytically active. Coculture of PyMT cells with bone marrow-derived macrophages induced a TAM-like macrophage phenotype in vitro, and the presence of such M2-polarized macrophages in 3D cultures enhanced sprouting of tumor spheroids. We employed a doxycycline (DOX)-inducible CTSB expression system to selectively overexpress human CTSB either in cancer cells or in macrophages in 3D cocultures. Tumor spheroid invasiveness was only enhanced when CTSB was overexpressed in cancer cells, whereas CTSB expression in macrophages alone did not further promote invasiveness of tumor spheroids. We conclude that CTSB overexpression in the PyMT mouse model promotes tumor progression not by a stromal effect, but by a direct, cancer cell-inherent mode of action: CTSB overexpression renders the PyMT cancers more invasive by increasing proteolytic extracellular matrix protein degradation fostering collective cell invasion into adjacent tissue.

Mesenchymal stroma: primary determinant and therapeutic target for epithelial cancer

Multifocal and recurrent epithelial tumors, originating from either dormant or de novo cancer cells, are major causes of morbidity and mortality. The age-dependent increase of cancer incidence has long been assumed to result from the sequential accumulation of cancer-driving or -facilitating mutations with induction of cellular senescence as a protective mechanism. However, recent evidence suggests that the initiation and development of epithelial cancer results from a close interplay with its altered tissue microenvironment, with chronic inflammation, stromal senescence, autophagy, and the activation of cancer-associated fibroblasts (CAFs) playing possible primary roles. We will discuss recent progress in these areas, and highlight how this understanding may be used for devising novel preventive and therapeutic approaches to the epithelial cancer problem.

CSF-1R inhibition alters macrophage polarization and blocks glioma progression

Glioblastoma multiforme (GBM) comprises several molecular subtypes including proneural GBM. Most therapeutic approaches targeting glioma cells have failed. An alternative strategy is to target cells in the glioma microenvironment, such as tumor-associated macrophages and microglia (TAMs). Macrophages depend upon colony stimulating factor (CSF)-1 for differentiation and survival. A CSF-1R inhibitor was used to target TAMs in a mouse proneural GBM model, which dramatically increased survival, and regressed established tumors. CSF-1R blockade additionally slowed intracranial growth of patient-derived glioma xenografts. Surprisingly, TAMs were not depleted in treated mice. Instead, glioma-secreted factors including GM-CSF and IFN-γ facilitated TAM survival in the context of CSF-1R inhibition. Alternatively activated/ M2 macrophage markers decreased in surviving TAMs, consistent with impaired tumor-promoting functions. These gene signatures were associated with enhanced survival in proneural GBM patients. Our results identify TAMs as a promising therapeutic target for proneural gliomas, and establish the translational potential of CSF-1R inhibition for GBM.

Tissues in different anatomical sites can sculpt and vary the tumor microenvironment to affect responses to therapy

The tumor microenvironment can promote tumor growth and reduce treatment efficacy. Tumors can occur in many sites in the body, but how surrounding normal tissues at different anatomical sites affect tumor microenvironments and their subsequent response to therapy is not known.We demonstrated that tumors from renal, colon, or prostate cell lines in orthotopic locations responded to immunotherapy consisting of three agonist antibodies, termed Tri-mAb, to a much lesser extent than the same tumor type located subcutaneously. A tissue-specific response to Tri-mAb was confirmed by ex vivo separation of subcutaneous (SC) or orthotopic tumor cells from stromal cells, followed by reinjection of tumor cells into the opposite site. Compared with SC tumors, orthotopic tumors had a microenvironment associated with a type 2 immune response, related to immunosuppression, and an involvement of alternatively activated macrophages in the kidney model. Orthotopic kidney tumors were more highly vascularized than SC tumors. Neutralizing the macrophage- and Th2-associated molecules chemokine (C-C motif) ligand 2 or interleukin-13 led to a significantly improved therapeutic effect. This study highlights the importance of the tissue of implantation in sculpting the tumor microenvironment. These are important fundamental issues in tumor biology and crucial factors to consider in the design of experimental models and treatment strategies.

Phenotypic skewing of macrophages in vitro by secreted factors from colorectal cancer cells

Macrophages are cells with many important functions in both innate and adaptive immune responses and have been shown to play a complex role in tumor progression since they harbour both tumor preventing (M1 macrophages) and tumor promoting (M2 macrophages) activities. In many human cancers, infiltrating macrophages have been associated with a poor patient prognosis, and therefore suggested to be mainly of an M2 phenotype. However, we and others have previously shown that increased macrophage density in colorectal cancer (CRC) instead is correlated with an improved prognosis. It is an intriguing question if the different roles played by macrophages in various cancers could be explained by variations in the balance between M1 and M2 macrophage attributes, driven by tumor- or organ-specific factors in the tumor microenvironment of individual cancers. Here, we utilized an in vitro cell culture system of macrophage differentiation to compare differences and similarities in the phenotype (morphology, antigen-presentation, migration, endocytosis, and expression of cytokine and chemokine genes) between M1/M2 and tumor activated macrophages (TAMs), that could explain the positive role of macrophages in CRC. We found that secreted factors from CRC cells induced TAMs of a “mixed” M1/M2 phenotype, which in turn could contribute to a “good inflammatory response”. This suggests that re-education of macrophages might allow for important therapeutic advances in the treatment of human cancer.

Impact of tumour associated macrophages in pancreatic cancer

During cancer progression, bone marrow derived myeloid cells, including immature myeloid cells and macrophages, progressively accumulate at the primary tumour site where they contribute to the establishment of a tumour promoting microenvironment. A marked infiltration of macrophages into the stromal compartment and the generation of a desmoplastic stromal reaction is a particular characteristic of pancreatic ductal adenocarcinoma (PDA) and is thought to play a key role in disease progression and its response to therapy. Tumour associated macrophages (TAMs) foster PDA tumour progression by promoting angiogenesis, metastasis, and by suppressing an anti-tumourigenic immune response. Recent work also suggests that TAMs contribute to resistance to chemotherapy and to the emergence of cancer stem-like cells. Here we will review the current understanding of the biology and the pro-tumourigenic functions of TAMs in cancer and specifically in PDA, and highlight potential therapeutic strategies to target TAMs and to improve current therapies for pancreatic cancer.

Fusobacterium nucleatum potentiates intestinal tumorigenesis and modulates the tumor-immune microenvironment

Increasing evidence links the gut microbiota with colorectal cancer. Metagenomic analyses indicate that symbiotic Fusobacterium spp. are associated with human colorectal carcinoma, but whether this is an indirect or causal link remains unclear. We find that Fusobacterium spp. are enriched in human colonic adenomas relative to surrounding tissues and in stool samples from colorectal adenoma and carcinoma patients compared to healthy subjects. Additionally, in the Apc(Min/+) mouse model of intestinal tumorigenesis, Fusobacterium nucleatum increases tumor multiplicity and selectively recruits tumor-infiltrating myeloid cells, which can promote tumor progression. Tumors from Apc(Min/+) mice exposed to F. nucleatum exhibit a proinflammatory expression signature that is shared with human fusobacteria-positive colorectal carcinomas. However, unlike other bacteria linked to colorectal carcinoma, F. nucleatum does not exacerbate colitis, enteritis, or inflammation-associated intestinal carcinogenesis. Collectively, these data suggest that, through recruitment of tumor-infiltrating immune cells, fusobacteria generate a proinflammatory microenvironment that is conducive for colorectal neoplasia progression.

Immune infiltrates as predictive markers of survival in pancreatic cancer patients

Pancreatic cancer is a devastating disease with dismal prognosis. The tumor microenvironment is composed by multiple cell types, molecular factors, and extracellular matrix forming a strong desmoplastic reaction, which is a hallmark of the disease. A complex cross-talk between tumor cells and the stroma exists with reciprocal influence that dictates tumor progression and ultimately the clinical outcome. In this context, tumor infiltrating immune cells through secretion of chemokine and cytokines exert an important regulatory role. Here we review the correlation between the immune infiltrates, evaluated on tumor samples of pancreatic cancer patients underwent surgical resection, and disease free and/or overall survival after surgery. Specifically, we focus on tumor infiltrating lymphocytes (TILs), mast cells (MCs) and macrophages that all contribute to a Th2-type inflammatory and immunosuppressive microenvironment. In these patients tumor immune infiltrates not only do not contribute to disease eradication but rather the features of Th2-type inflammation and immunosuppression is significantly associated with more rapid disease progression and reduced survival.

Recent molecular discoveries in angiogenesis and antiangiogenic therapies in cancer

Four decades ago, angiogenesis was recognized as a therapeutic target for blocking cancer growth. Because of its importance, VEGF has been at the center stage of antiangiogenic therapy. Now, several years after FDA approval of an anti-VEGF antibody as the first antiangiogenic agent, many patients with cancer and ocular neovascularization have benefited from VEGF-targeted therapy; however, this anticancer strategy is challenged by insufficient efficacy, intrinsic refractoriness, and resistance. Here, we examine recent discoveries of new mechanisms underlying angiogenesis, discuss successes and challenges of current antiangiogenic therapy, and highlight emerging antiangiogenic paradigms.

The irradiated tumor microenvironment: role of tumor-associated macrophages in vascular recovery

Radiotherapy is an important modality used in the treatment of more than 50% of cancer patients in the US. However, despite sophisticated techniques for radiation delivery as well as the combination of radiation with chemotherapy, tumors can recur. Thus, any method of improving the local control of the primary tumor by radiotherapy would produce a major improvement in the curability of cancer patients. One of the challenges in the field is to understand how the tumor vasculature can regrow after radiation in order to support tumor recurrence, as it is unlikely that any of the endothelial cells within the tumor could survive the doses given in a typical radiotherapy regimen. There is now considerable evidence from both preclinical and clinical studies that the tumor vasculature can be restored following radiotherapy from an influx of circulating cells consisting primarily of bone marrow derived monocytes and macrophages. The radiation-induced influx of bone marrow derived cells (BMDCs) into tumors can be prevented through the blockade of various cytokine pathways and such strategies can inhibit tumor recurrence. However, the post-radiation interactions between surviving tumor cells, recruited immune cells, and the remaining stroma remain poorly defined. While prior studies have described the monocyte/macrophage inflammatory response within normal tissues and in the tumor microenvironment, less is known about this response with respect to a tumor after radiation therapy. The goal of this review is to summarize existing research studies to provide an understanding of how the myelomonocytic lineage may influence vascular recovery within the irradiated tumor microenvironment.

The immune network in pancreatic cancer development and progression

The presence of stromal desmoplasia is a hallmark of spontaneous pancreatic ductal adenocarcinoma, forming a unique microenvironment that comprises many cell types. Only recently, the immune system has entered the pathophysiology of pancreatic ductal adenocarcinoma development. Tumor cells in the pancreas seem to dysbalance the immune system, thus facilitating spontaneous cancer development. This review will try to assemble all relevant data to demonstrate the implications of the immune network on spontaneous cancer development.

MicroRNA-19a-3p inhibits breast cancer progression and metastasis by inducing macrophage polarization through downregulated expression of Fra-1 proto-oncogene

One of the hallmarks of malignancy is the polarization of tumor-associated macrophages (TAMs) from a pro-immune (M1-like) phenotype to an immune-suppressive (M2-like) phenotype. However, the molecular basis of the process is still unclear. MicroRNA (miRNA) comprises a group of small, non-coding RNAs that are broadly expressed by a variety of organisms and are involved in cell behaviors such as suppression or promotion of tumorigenesis. Here, we demonstrate that miR-19a-3p, broadly conserved among vertebrates, was downregulated in RAW264.7 macrophage cells of the M2 phenotype in conditoned medium of 4T1 mouse breast tumor cells. This downregulation correlated with an increased expression of the Fra-1 gene, which was reported to act as a pro-oncogene by supporting the invasion and progression of breast tumors. We found significant upregulation of miR-19a-3p in RAW264.7 macrophages after transfection with a miR-19a-3p mimic that resulted in a significant suppression of the expression of this gene. In addition, we could measure the activity of binding between miR-19a-3p and Fra-1 with a psiCHECK luciferase reporter system. Further, transfection of RAW264.7 macrophage cells with the miR-19a-3p mimic decreased the expression of the Fra-1 downstream genes VEGF, STAT3 and pSTAT3. Most importantly, the capacity of 4T1 breast tumor cells to migrate and invade was impaired in vivo by the intratumoral injection of miR-19a-3p. Taken together, these findings indicate that miR-19a-3p is capable of downregulating the M2 phenotype in M2 macrophages and that the low expression of this miRNA has an important role in the upregulation of Fra-1 expression and induction of M2 macrophage polarization.

MerTK inhibition in tumor leukocytes decreases tumor growth and metastasis

MerTK, a receptor tyrosine kinase (RTK) of the TYRO3/AXL/MerTK family, is expressed in myeloid lineage cells in which it acts to suppress proinflammatory cytokines following ingestion of apoptotic material. Using syngeneic mouse models of breast cancer, melanoma, and colon cancer, we found that tumors grew slowly and were poorly metastatic in MerTK-/- mice. Transplantation of MerTK-/- bone marrow, but not wild-type bone marrow, into lethally irradiated MMTV-PyVmT mice (a model of metastatic breast cancer) decreased tumor growth and altered cytokine production by tumor CD11b+ cells. Although MerTK expression was not required for tumor infiltration by leukocytes, MerTK-/- leukocytes exhibited lower tumor cell-induced expression of wound healing cytokines, e.g., IL-10 and growth arrest-specific 6 (GAS6), and enhanced expression of acute inflammatory cytokines, e.g., IL-12 and IL-6. Intratumoral CD8+ T lymphocyte numbers were higher and lymphocyte proliferation was increased in tumor-bearing MerTK-/- mice compared with tumor-bearing wild-type mice. Antibody-mediated CD8+ T lymphocyte depletion restored tumor growth in MerTK-/- mice. These data demonstrate that MerTK signaling in tumor-associated CD11b+ leukocytes promotes tumor growth by dampening acute inflammatory cytokines while inducing wound healing cytokines. These results suggest that inhibition of MerTK in the tumor microenvironment may have clinical benefit, stimulating antitumor immune responses or enhancing immunotherapeutic strategies.

Induction of M2-macrophages by tumour cells and tumour growth promotion by M2-macrophages: a quid pro quo in pancreatic cancer

INTRODUCTION

More effective therapies are required to improve survival of pancreatic cancer. Possible immunologic targets include tumour associated macrophages (TAMs), generally consisting of M1- and M2-macrophages. We have analysed the impact of TAMS on pancreatic cancer in a syngeneic orthotopic murine model.

METHODS

6606PDA murine pancreatic cancer cells were orthotopically injected into C57BL6 mice. Tumour growth was monitored using MRI. Macrophages were depleted by clodronate liposomes. Tumours including microvessel density were evaluated using immunohistochemistry, immunofluorescence and/or cytometric beads assays. Naïve macrophages were generated employing peritoneal macrophages. In vitro experiments included culturing of macrophages in tumour supernatants as well as tumour cells cultured in macrophage supernatants using arginase as well as Griess assays.

RESULTS

Clodronate treatment depleted macrophages by 80% in livers (p = 0.0051) and by 60% in pancreatic tumours (p = 0.0169). MRI revealed tumour growth inhibition from 221.8 mm(3) to 92.3 mm(3) (p = 0.0216). Micro vessel densities were decreased by 44% (p = 0.0315). Yet, MCP-1-, IL-4- and IL-10-levels within pancreatic tumours were unchanged. 6606PDA culture supernatants led to a shift from naïve macrophages towards an M2-phenotype after a 36 h treatment (p < 0.0001), reducing M1-macrophages at the same time (p < 0.037). In vivo, M2-macrophages represented 85% of all TAMs (p < 0.0001). Finally, culture supernatants of M2-macrophages induced tumour growth in vitro by 63.2% (p = 0.0034).

CONCLUSIONS

This quid pro quo of tumour cells and M2-macrophages could serve as a new target for future immunotherapies that interrupt tumour promoting activities of TAMs and change the iNOS-arginase balance towards their tumoricidal capacities.

MR - eyes for cancer: looking within an impenetrable disease

Probe development is a critical component in cancer imaging, and novel probes are making major inroads in several aspects of cancer detection and image-guided treatments. Intrinsic MR probes such as signals from metabolites and their chemical shifts have been used for more than a decade to understand cancer physiology and metabolism. Through the integration of technology, molecular biology, and chemistry, the last few years have witnessed an explosion of extrinsic probes for molecular and functional imaging of cancer that, together with techniques such as CEST and hyperpolarization, have significantly expanded the repertoire of MR techniques in basic and translational investigations of many different aspects of cancer. Furthermore, incorporation of MR probes into multifunctional nanoparticles and multimodality imaging platforms have opened new opportunities for MR in image-guided diagnosis and therapy of cancer. Here we have provided an overview of recent innovations that have occurred in the development of MRI probes for molecular and functional imaging of cancer. Although most of these novel probes are not clinically available, they offer significant promise for future translational applications. In this review, we have highlighted the areas of future development that are likely to have a profound impact on cancer detection and treatment.

A poor prognosis subtype of HNSCC is consistently observed across methylome, transcriptome, and miRNome analysis

PURPOSE

Distant metastasis after treatment is observed in about 20% of squamous cell carcinoma of the head and neck (HNSCC). In the absence of any validated robust biomarker, patients at higher risk for metastasis cannot be provided with tailored therapy. To identify prognostic HNSCC molecular subgroups and potential biomarkers, we have conducted genome-wide integrated analysis of four omic sets of data.

EXPERIMENTAL DESIGN

Using state-of-the-art technologies, a core set of 45 metastasizing and 55 nonmetastasizing human papillomavirus (HPV)-unrelated HNSCC patient samples were analyzed at four different levels: gene expression (transcriptome), DNA methylation (methylome), DNA copy number (genome), and microRNA (miRNA) expression (miRNome). Molecular subgroups were identified by a model-based clustering analysis. Their clinical relevance was evaluated by survival analysis, and functional significance by pathway enrichment analysis.

RESULTS

Patient subgroups selected by transcriptome, methylome, or miRNome integrated analysis are associated with shorter metastasis-free survival (MFS). A common subgroup, R1, selected by all three omic approaches, is statistically more significantly associated with MFS than any of the single omic-selected subgroups. R1 and non-R1 samples display similar DNA copy number landscapes, but more frequent chromosomal aberrations are observed in the R1 cluster (especially loss at 13q14.2-3). R1 tumors are characterized by alterations of pathways involved in cell-cell adhesion, extracellular matrix (ECM), epithelial-to-mesenchymal transition (EMT), immune response, and apoptosis.

CONCLUSIONS

Integration of data across several omic profiles leads to better selection of patients at higher risk, identification of relevant molecular pathways of metastasis, and potential to discover biomarkers and drug targets.

ROS play a critical role in the differentiation of alternatively activated macrophages and the occurrence of tumor-associated macrophages

Differentiation to different types of macrophages determines their distinct functions. Tumor-associated macrophages (TAMs) promote tumorigenesis owing to their proangiogenic and immune-suppressive functions similar to those of alternatively activated (M2) macrophages. We report that reactive oxygen species (ROS) production is critical for macrophage differentiation and that inhibition of superoxide (O²⁻) production specifically blocks the differentiation of M2 macrophages. We found that when monocytes are triggered to differentiate, O²⁻ is generated and is needed for the biphasic ERK activation, which is critical for macrophage differentiation. We demonstrated that ROS elimination by butylated hydroxyanisole (BHA) and other ROS inhibitors blocks macrophage differentiation. However, the inhibitory effect of ROS elimination on macrophage differentiation is overcome when cells are polarized to classically activated (M1), but not M2, macrophages. More importantly, the continuous administration of the ROS inhibitor BHA efficiently blocked the occurrence of TAMs and markedly suppressed tumorigenesis in mouse cancer models. Targeting TAMs by blocking ROS can be a potentially effective method for cancer treatment.

Angiopoietin-1 elicits pro-inflammatory responses in monocytes and differentiating macrophages

The angiopoietin/Tie2 system is an important regulator of angiogenesis and inflammation. In addition to its functions in endothelial cells, Tie2 expression on non-endothelial cells allows for angiopoietin ligands to stimulate the cells. Although Ang1 is a strong Tie2 receptor agonist, little is known regarding the effect of Ang1 on non-endothelial cells, such as monocytes and macrophages. In this study, we found that Ang1 functionally binds to and stimulates monocytes via p38 and Erk1/2 phosphorylation. Ang1-mediated monocyte stimulation is associated with proinflammatory cytokine TNF-α expression. We also determined that Ang1 switched macrophage differentiation toward a pro-inflammatory phenotype, even in the presence of an anti-inflammatory mediator. These findings suggest that Ang1 plays a role in stimulating pro-inflammatory responses and could provide a new strategy by which to manage inflammatory responses.

Expression of M2-Polarized Macrophages is Associated with Poor Prognosis for Advanced Epithelial Ovarian Cancer

Macrophages are polarized into two functionally distinct forms, M1 and M2, in response to different microenvironment. Tumor-associated macrophages (TAMs) generally have M2 phenotype and promote tumor progression. Few studies to date have described the infiltration of M2-polarized macrophages in ovarian cancer. We used two macrophages markers, CD68 and CD163, to analyze the expression of TAMs and to clarify the relationship between the M2 form and survival in advanced ovarian cancer. Clinical data of 110 patients with stages III-IV epithelial ovarian cancer at Sun Yat-sen University Cancer Center between 1999 and 2007 were retrospectively reviewed. Immunohistochemical staining of CD68 and CD163 was performed. Correlations between macrophage density and patient survival were analyzed. Our data showed that no significant difference was observed in survival between patients in the high- and the low-CD68 expression groups. In contrast, the progression-free survival (PFS) rates ( p = 0.003) and overall survival (OS) rates ( p = 0.004) were significantly higher in the low-CD163 expression group than in the high-CD163 expression group, respectively. Similarly, we also observed significantly improved 3-year PFS (49.8% vs. 11.0%, p < 0.001) and OS (77.4% vs. 45.0%, p < 0.001) rates in patients in the low-CD163/CD68 ratio group when compared with the high-CD163/CD68 ratio group. Multivariate analysis identified the density of CD163-positive cells as well as the ratio of CD163/CD68 as negative predictors for PFS and OS, respectively. Our results show that the infiltration of CD163-positive M2 macrophages as well as activation of macrophages towards the M2 phenotype may contribute to poor survival in advanced ovarian cancer.

A New Herbal Formula, KSG-002, Suppresses Breast Cancer Growth and Metastasis by Targeting NF- κ B-Dependent TNF α Production in Macrophages

Tumor-associated macrophages (TAMs) in tumor microenvironment regulate cancer progression and metastases. In breast cancer, macrophage infiltration is correlated with a poor prognosis. While metastatic breast cancer is poor prognostic with a severe mortality, therapeutic options are still limited. In this study, we demonstrate that KSG-002, a new herbal composition of radices Astragalus membranaceus and Angelica gigas, suppresses breast cancer via inhibiting TAM recruitment. KSG-002, an extract of radices Astragalus membranaceus and Angelica gigas at 3 : 1 ratio, respectively, inhibited MDA-MB-231 xenograft tumor growth and pulmonary metastasis in nude mice, while KSG-001, another composition (1 : 1 ratio, w/w), enhanced tumor growth, angiogenesis, and pulmonary metastasis, in vivo. KSG-002 further decreased the infiltrated macrophage numbers in xenograft tumor cohorts. In Raw264.7 cells, KSG-002 but not KSG-001 inhibited cell proliferation and migration and reduced TNF-alpha (TNF α ) production by inhibiting NF- κ B pathway. Furthermore, a combinatorial treatment of KSG-002 with TNF α inhibited a proliferation and migration of both MDA-MB-231 and Raw264.7 cells. Taken together, we conclude that KSG-002 suppresses breast cancer growth and metastasis through targeting NF- κ B-mediated TNF α production in macrophages.

Acute inflammation induced by the biopsy of mouse mammary tumors promotes the development of metastasis

Development of metastasis in peripheral tissues is a major problem in the fight to cure breast cancer. Although it is becoming evident that chronic inflammation can contribute to tumor progression and metastasis, the effect of acute inflammation in primary tumor is less known. Using mouse models for breast cancer here we show that biopsy of mammary tumors increases the frequency of lung metastases. This effect is associated with the recruitment of inflammatory cells to the lung and elevated levels of certain cytokines such as IL-6 in the lung airways. Antiinflammatory treatment prior to and after the biopsy reduces the development of metastases triggered by the biopsy. In addition, while lack of IL-6 does not affect primary tumor development, it protects from increasing number of metastases upon biopsy. Thus, our studies show that in addition to chronic inflammation, acute immune response caused by invasive procedures in the primary tumor may cause an increased risk on peripheral metastases, but the risk could be decreased by anti-inflammatory treatments.

MicroRNA let-7c regulates macrophage polarization

Macrophages demonstrate a high level of plasticity, with the ability to undergo dynamic transition between M1 and M2 polarized phenotypes. The role of microRNAs (miRNAs) in regulating macrophage polarization has been largely undefined. In this study, we found that miRNA let-7c is expressed at a higher level in M-BMM (M2 macrophages) than in GM-BMM (M1 macrophages). let-7c levels are also greater in alveolar macrophages from fibrotic lungs as compared with those from normal lungs. let-7c expression was decreased when M-BMM converted to GM-BMM, whereas it increased when GM-BMM converted to M-BMM. LPS stimulation reduced let-7c expression in M-BMM. We found that overexpression of let-7c in GM-BMM diminished M1 phenotype expression while promoting polarization to the M2 phenotype. In contrast, knockdown of let-7c in M-BMM promoted M1 polarization and diminished M2 phenotype expression. We found that let-7c targets C/EBP-δ, a transcriptional factor that plays an important role in inflammatory response. Furthermore, we found that let-7c regulates bactericidal and phagocytic activities of macrophages, two functional phenotypes implicated in macrophage polarization. Our data suggest that the miRNA let-7c plays an important role in regulating macrophage polarization.

Tumor-associated macrophages: functional diversity, clinical significance, and open questions

Inflammation is now a well-recognized hallmark of cancer progression. Tumor-associated macrophages (TAMs) are one of the major inflammatory cells that infiltrate murine and human tumors. While epidemiological studies indicate a clear correlation between TAM density and poor prognosis in a number of human cancers, transgenic studies and transcriptome profiling of TAMs in mice have established their crucial role in cancer progression. In fact, TAMs affect diverse aspects of cancer progression including tumor cell growth and survival, invasion, metastasis, angiogenesis, inflammation, and immunoregulation. New evidences have extended the repertoire of these cells to other tumor promoting activities like interactions with cancer stem cells, response to chemotherapy, and tumor relapse. These findings have triggered efforts to target TAMs and their associated molecules to modulate tumor progression. In particular, "re-education" to activate their anti-tumor potential or elimination of tumor promoting TAMs are strategies undergoing preclinical and clinical evaluation. Proof-of-principle studies indicate that TAM-centered therapeutic strategies may contribute to cancer therapy.

SSAO inhibitors suppress hepatocellular tumor growth in mice

Vascular adhesion protein-1 (VAP-1) is both an endothelial adhesion molecule involved in leukocytes emigration, and an oxidase belonging to the family of semicarbazide-sensitive amine oxidases (SSAOs). The enzyme activity of VAP-1 plays an important role in the migration of myeloid-derived suppressor cells (MDSCs) into tumor site, and SSAO inhibitors can block the function of VAP-1. The effects of SSAO inhibitors on leukocyte infiltration and tumor progression were evaluated in H22 hepatocellular carcinoma-bearing C57BL/6 mice. Tumor weight and volume were measured after SSAO inhibitor treatment. Then, MDSCs recruitment and neo-angiogenesis were determined using immunostaining. SSAO inhibitors significantly blocked the catalytic activity of VAP-1 in tumor, attenuated tumor progression, and reduced neo-angiogenesis. CD11b(+) and Gr-1(+) MDSCs, which normally infiltrate into tumors, were significantly diminished in tumor-bearing mice treated with SSAO inhibitors. The present study demonstrated that SSAO inhibitors might have an anti-tumor effect on hepatocellular carcinoma by inhibiting recruitment of CD11b(+) and Gr-1(+) cells and hindering angiogenesis, which could be attributed to impairing the catalytic activity of VAP-1.

BMP-6 in renal cell carcinoma promotes tumor proliferation through IL-10-dependent M2 polarization of tumor-associated macrophages

Dysregulated bone morphogenetic proteins (BMP) may contribute to the development and progression of renal cell carcinoma (RCC). Herein, we report that BMP-6 promotes the growth of RCC by interleukin (IL)-10-mediated M2 polarization of tumor-associated macrophages (TAM). BMP-6-mediated IL-10 expression in macrophages required Smad5 and STAT3. In human RCC specimens, the three-marker signature BMP-6/IL-10/CD68 was associated with a poor prognosis. Furthermore, patients with elevated IL-10 serum levels had worse outcome after surgery. Together, our results suggest that BMP-6/macrophage/IL-10 regulates M2 polarization of TAMs in RCC.

Collagen VI in cancer and its biological mechanisms

Collagen VI is a widely distributed extracellular matrix protein highly expressed in a variety of cancers that favors tumor growth and progression. A growing number of studies indicate that collagen VI directly affects malignant cells by acting on the Akt-GSK-3β-β-catenin-TCF/LEF axis, enhancing the production of protumorigenic factors and inducing epithelial-mesenchymal transition. Moreover, it affects the tumor microenvironment by increasing the recruitment of macrophages and endothelial cells, thus promoting tumor inflammation and angiogenesis. Furthermore, collagen VI promotes chemotherapy resistance and can be regarded as a potential biomarker for cancer diagnosis. Collectively, these findings strongly support a role for collagen VI as an important regulator in tumors and provide new targets for cancer therapies.

IL-17-mediated M1/M2 macrophage alteration contributes to pathogenesis of bisphosphonate-related osteonecrosis of the jaws

PURPOSE

Osteonecrosis of the jaw (ONJ) is emerging as one of the important complications in cancer patients treated with antiresorptive agents. This study explored the potential role of interleukin (IL)-17-mediated M1/M2 macrophage alterations in the pathogenesis of bisphosphonate-related osteonecrosis of the jaw (BRONJ).

EXPERIMENTAL DESIGN

The expression of IL-17 and M1 and M2 macrophage markers at the local mucosal site of human BRONJ lesions was examined by immunofluorescence studies. BRONJ-like disease was induced in C57BL/6 mice and multiple myeloma-burdened mice by intravenous injection of zoledronate to evaluate the correlation of elevated IL-17 levels with changes in M1 and M2 macrophage phenotypes and the therapeutic effects of blocking IL-17 on pathogenesis of BRONJ-like disease.

RESULTS

Increased T-helper (TH)17 cells and IL-17 cytokine correlate with an increase in M1/M2 macrophages ratio at the local mucosal site of both murine and human BRONJ lesion. Convincingly, in mice burdened with multiple myeloma, a combination of elevated suprabasal level and drug-induced IL-17 activity augmented the incidence of BRONJ; both systemic increase of IL-17 and disease severity could be reversed by adoptive transfer of ex vivo expanded M2 macrophages. Targeting IL-17 via specific neutralizing antibodies or a small inhibitory molecule, laquinimod, significantly decreased M1/M2 ratio and concomitantly suppressed BRONJ-like condition in mice. Mechanistically, IL-17 enhanced IFN-γ-induced M1 polarization through augmenting STAT-1 phosphorylation while suppressing IL-4-mediated M2 conversion via inhibiting STAT-6 activation.

CONCLUSIONS

These findings have established a compelling linkage between activated IL-17-mediated polarization of M1 macrophages and the development of BRONJ-like conditions in both human disease and murine models.

Significance of podoplanin expression in cancer-associated fibroblasts: a comprehensive review

Cancer-associated fibroblasts (CAFs) are well-known to be part of the tumor microenvironment. This heterogeneous population of cells of the tumor microenvironment via secretion of various growth factors and cytokines was shown to contribute to increased cancer cell proliferation rate, migration, invasiveness and other key processes such as angiogenesis and lymphangiogenesis. Recent studies identified podoplanin as a marker of CAFs in various malignancies and its expression in these cells was shown to influence cancer progression. In some studies it yielded a prognostic impact on patient survival which was strongly dependent on the entity of the tumor. This review summarizes recent findings concerning the biology of podoplanin in cancer progression with particular emphasis on its expression in CAFs.

Two-photon luminescence properties of gold nanorods

Gold nanorods can be internalized by macrophages (an important early cellular marker in atherosclerosis and cancer) and used as an imaging contrast agent for macrophage targeting. Objective of this study is to compare two-photon luminescence (TPL) properties of four aspect ratios of gold nanorods with surface plasmon resonance at 700, 756, 844 and 1060 nm respectively. TPL from single nanorods and Rhodamine 6G particles was measured using a laser-scanning TPL microscope. Nanorod TPL emission spectrum was recorded by a spectrometer. Quadratic dependence of luminescence intensity on excitation power (confirming a TPL process) was observed below a threshold (e.g., <1.6 mW), followed by photobleaching at higher power levels. Dependence of nanorod TPL intensity on excitation wavelength indicated that the two-photon action cross section (TPACS) is plasmon-enhanced. Largest TPACS of a single nanorod (12271 GM) was substantially larger than a single Rhodamine 6G particle (25 GM) at 760 nm excitation. Characteristics of nanorod TPL emission spectrum can be explained by plasmon-enhanced interband transition of gold. Comparison results of TPL brightness, TPACS and emission spectrum of nanorods can guide selection of optimal contrast agent for selected imaging applications.

Macrophage regulation of tumor responses to anticancer therapies

Tumor-associated macrophages (TAMs) promote key processes in tumor progression, like angiogenesis, immunosuppression, invasion, and metastasis. Increasing studies have also shown that TAMs can either enhance or antagonize the antitumor efficacy of cytotoxic chemotherapy, cancer-cell targeting antibodies, and immunotherapeutic agents--depending on the type of treatment and tumor model. TAMs also drive reparative mechanisms in tumors after radiotherapy or treatment with vascular-targeting agents. Here, we discuss the biological significance and clinical implications of these findings, with an emphasis on novel approaches that effectively target TAMs to increase the efficacy of such therapies.

MicroRNAs in immune response and macrophage polarization

Inflammation is essential to combat invading microbial pathogens. In this process, the involvement of multiple immune cell populations is crucial in mounting an optimum immune response. In the past decade, a new class of noncoding small RNAs, called microRNAs (miRNAs), has emerged as important regulators in biological processes. The important role of miRNAs in inflammation and immune response is highlighted by studies in which deregulation of miRNAs was demonstrated to accompany diseases associated with excessive or uncontrolled inflammation. In this brief review, we summarize the roles of miRNAs that have been characterized in innate and adaptive immune responses. We discuss the role of miRNAs in macrophage polarization, a molecular event that has clear effect on inflammation.

Design and pharmacology of a highly specific dual FMS and KIT kinase inhibitor

Inflammation and cancer, two therapeutic areas historically addressed by separate drug discovery efforts, are now coupled in treatment approaches by a growing understanding of the dynamic molecular dialogues between immune and cancer cells. Agents that target specific compartments of the immune system, therefore, not only bring new disease modifying modalities to inflammatory diseases, but also offer a new avenue to cancer therapy by disrupting immune components of the microenvironment that foster tumor growth, progression, immune evasion, and treatment resistance. McDonough feline sarcoma viral (v-fms) oncogene homolog (FMS) and v-kit Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog (KIT) are two hematopoietic cell surface receptors that regulate the development and function of macrophages and mast cells, respectively. We disclose a highly specific dual FMS and KIT kinase inhibitor developed from a multifaceted chemical scaffold. As expected, this inhibitor blocks the activation of macrophages, osteoclasts, and mast cells controlled by these two receptors. More importantly, the dual FMS and KIT inhibition profile has translated into a combination of benefits in preclinical disease models of inflammation and cancer.

MicroRNA-mediated control of macrophages and its implications for cancer

Deregulation of microRNAs (miRNAs) can drive oncogenesis, tumor progression, and metastasis by acting cell-autonomously in cancer cells. However, solid tumors are also infiltrated by large amounts of non-neoplastic stromal cells, including macrophages, which express several active miRNAs. Tumor-associated macrophages (TAMs) enhance angiogenic, immunosuppressive, invasive, and metastatic programming of neoplastic tissue and reduce host survival. Here, we review the role of miRNAs (including miR-155, miR-146, and miR-511) in the control of macrophage production and activation, and examine whether reprogramming miRNA activity in TAMs and/or their precursors might be effective for controlling tumor progression.

The role of IL-1β in the early tumor cell-induced angiogenic response

In this study, we assessed the involvement of IL-1β in early angiogenic responses induced by malignant cells using Matrigel plugs supplemented with B16 melanoma cells. We found that during the angiogenic response, IL-1β and vascular endothelial growth factor (VEGF) interact in a newly described autoinduction circuit, in which each of these cytokines induces the other. The IL-1β and VEGF circuit acts through interactions between bone marrow-derived VEGF receptor 1(+)/IL-1R1(+) immature myeloid cells and tissue endothelial cells. Myeloid cells produce IL-1β and additional proinflammatory cytokines, which subsequently activate endothelial cells to produce VEGF and other proangiogenic factors and provide the inflammatory microenvironment for angiogenesis and tumor progression. These mechanisms were also observed in a nontumor early angiogenic response elicited in Matrigel plugs by either rIL-1β or recombinant VEGF. We have shown that IL-1β inhibition stably reduces tumor growth by limiting inflammation and inducing the maturation of immature myeloid cells into M1 macrophages. In sharp contrast, only transient inhibition of tumor growth was observed after VEGF neutralization, followed by tumor recurrence mediated by rebound angiogenesis. This occurs via the reprogramming of VEGF receptor 1(+)/IL-1R1(+) cells to express hypoxia inducible factor-1α, VEGF, and other angiogenic factors, thereby directly supporting proliferation of endothelial cells and blood vessel formation in a paracrine manner. We suggest using IL-1β inhibition as an effective antitumor therapy and are currently optimizing the conditions for its application in the clinic.

New insights into understanding the mechanisms, pathogenesis, and management of malignant mesotheliomas

Malignant mesothelioma (MM) is a relatively rare but devastating tumor that is increasing worldwide. Yet, because of difficulties in early diagnosis and resistance to conventional therapies, MM remains a challenge for pathologists and clinicians to treat. In recent years, much has been revealed regarding the mechanisms of interactions of pathogenic fibers with mesothelial cells, crucial signaling pathways, and genetic and epigenetic events that may occur during the pathogenesis of these unusual, pleiomorphic tumors. These observations support a scenario whereby mesothelial cells undergo a series of chronic injury, inflammation, and proliferation in the long latency period of MM development that may be perpetuated by durable fibers, the tumor microenvironment, and inflammatory stimuli. One culprit in sustained inflammation is the activated inflammasome, a component of macrophages or mesothelial cells that leads to production of chemotactic, growth-promoting, and angiogenic cytokines. This information has been vital to designing novel therapeutic approaches for patients with MM that focus on immunotherapy, targeting growth factor receptors and pathways, overcoming resistance to apoptosis, and modifying epigenetic changes.

Tumor-associated macrophages as a prognostic parameter in multiple myeloma

The interaction between multiple myeloma (MM) cells and the bone marrow stroma constitutes the basis of myeloma pathogenesis and has led the way for the corresponding therapeutic strategies. The aim of this study is to evaluate tumor-associated macrophages (TAMs) which is an important element of bone marrow stroma and its prognostic relevance in newly diagnosed MM patients. We also wanted to determine the association between TAMs and microvessel density (MVD). Sixty-eight patients, who were diagnosed with MM at the Department of Hematology, Gazi University Hospital, between January 2000 and January 2011, were reviewed retrospectively. Tumor-associated macrophages were evaluated by staining with anti-CD68 and anti-CD163 monoclonal antibodies, and MVD was evaluated by factor VIII staining. Median age was 60 (range, 40-84) years with 36 males and 32 females. The number of both CD 68+ and CD 163+ cells had a negative impact on OS at 6 years (p = 0.013 vs. 0.036; p = 0.015 vs. 0.039) in univariate and multivariate analysis in which age, sex, ISS, the induction treatment, and response to induction treatment are included as variables. High-grade MVD was found to be associated with increased CD163+ cell count. In conclusion, TAMs seems to be a promising prognostic histopathological marker in newly diagnosed MM patients.

Neutralizing tumor-promoting chronic inflammation: a magic bullet?

There have been substantial advances in cancer diagnostics and therapies in the past decade. Besides chemotherapeutic agents and radiation therapy, approaches now include targeting cancer cell-intrinsic mediators linked to genetic aberrations in cancer cells, in addition to cancer cell-extrinsic pathways, especially those regulating vascular programming of solid tumors. More recently, immunotherapeutics have entered the clinic largely on the basis of the recognition that several immune cell subsets, when chronically activated, foster tumor development. Here, we discuss clinical and experimental studies delineating protumorigenic roles for immune cell subsets that are players in cancer-associated inflammation. Some of these cells can be targeted to reprogram their function, leading to resolution, or at least neutralization, of cancer-promoting chronic inflammation, thereby facilitating cancer rejection.

Obesity-driven inflammation and cancer risk: role of myeloid derived suppressor cells and alternately activated macrophages

During carcinogenesis, tumors induce dysfunctional development of hematopoietic cells. Myeloid lineage cells, in the form of myeloid derived suppressor cells (MDSCs) and alternatively polarized M2 macrophages, influence almost all types of cancers by regulating diverse facets of immunosuppression, angiogenesis, cell proliferation, growth and metastasis. One-third of Americans are obese, and accumulating evidence suggests that obesity is a risk factor for various cancers. However, the relationship between these immune players and obesity are not well-described. In this review, we evaluate potential mechanisms through which different aspects of obesity, namely insulin resistance, increased estrogen, adiposity and low grade chronic inflammation from adipose tissue macrophages, may coalesce to promote MDSC induction and M2 macrophage polarization, thereby facilitating cancer development. Detailed understanding of the interplay between obesity and myeloid mediated immunosuppression may provide novel avenues for therapeutic targeting, with the goal to reduce the challenge obesity presents towards gains made in cancer outcomes.

Immunotherapy of human papilloma virus induced disease

Immunotherapy is the generic name for treatment modalities aiming to reinforce the immune system against diseases in which the immune system plays a role. The design of an optimal immunotherapeutic treatment against chronic viruses and associated diseases requires a detailed understanding of the interactions between the target virus and its host, in order to define the specific strategies that may have the best chance to deliver success at each stage of disease. Recently, a first series of successes was reported for the immunotherapy of Human Papilloma Virus (HPV)-induced premalignant diseases but there is definitely room for improvement. Here I discuss a number of topics that in my opinion require more study as the answers to these questions allows us to better understand the underlying mechanisms of disease and as such to tailor treatment.

PGE(2) induces macrophage IL-10 production and a regulatory-like phenotype via a protein kinase A-SIK-CRTC3 pathway

The polarization of macrophages into a regulatory-like phenotype and the production of IL-10 plays an important role in the resolution of inflammation. We show in this study that PGE(2), in combination with LPS, is able to promote an anti-inflammatory phenotype in macrophages characterized by high expression of IL-10 and the regulatory markers SPHK1 and LIGHT via a protein kinase A-dependent pathway. Both TLR agonists and PGE(2) promote the phosphorylation of the transcription factor CREB on Ser(133). However, although CREB regulates IL-10 transcription, the mutation of Ser(133) to Ala in the endogenous CREB gene did not prevent the ability of PGE(2) to promote IL-10 transcription. Instead, we demonstrate that protein kinase A regulates the phosphorylation of salt-inducible kinase 2 on Ser(343), inhibiting its ability to phosphorylate CREB-regulated transcription coactivator 3 in cells. This in turn allows CREB-regulated transcription coactivator 3 to translocate to the nucleus where it serves as a coactivator with the transcription factor CREB to induce IL-10 transcription. In line with this, we find that either genetic or pharmacological inhibition of salt-inducible kinases mimics the effect of PGE(2) on IL-10 production.

Imaging interactions between macrophages and tumour cells that are involved in metastasis in vivo and in vitro

Tumour-associated macrophages participate in several protumour functions including tumour growth and angiogenesis, and facilitate almost every step of the metastatic cascade. Interfering with macrophage functions may therefore provide an important strategy in the clinical management of cancer and metastatic disease. Our understanding of macrophage functions has been greatly expanded by direct observations of macrophage-carcinoma cell interactions using light microscopy. Imaging approaches include intravital microscopy of tumours in mouse models of cancer and visualization of macrophage-carcinoma cell interactions in in vitro assays; whether atop 2D substrates, embedded in 3D matrices or in more complex assemblies of multiple cell types that mimic specific topologies of the tumour microenvironment. Such imaging and reconstitution approaches have provided us with a wealth of information on the motile behaviour and physical associations between macrophages and carcinoma cells and the role of the tumour microenvironment in influencing the movement of these cells. Finally, high-resolution imaging techniques have permitted researchers to correlate motility patterns with specific gene signatures and biochemical pathways in cells, pointing to potential targets for intervention. Here, we review experimental approaches employed in the study of macrophage interactions with carcinoma cells with an emphasis on imaging invasive and metastatic cell motility in breast carcinomas.

Macrophage plasticity and polarization in tissue repair and remodelling

Mononuclear phagocyte plasticity includes the expression of functions related to the resolution of inflammation, tissue repair and remodelling, particularly when these cells are set in an M2 or an M2-like activation mode. Macrophages are credited with an essential role in remodelling during ontogenesis. In extraembryonic life, under homeostatic conditions, the macrophage trophic and remodelling functions are recapitulated in tissues such as bone, mammary gland, decidua and placenta. In pathology, macrophages are key components of tissue repair and remodelling that occur during wound healing, allergy, parasite infection and cancer. Interaction with cells bearing stem or progenitor cell properties is likely an important component of the role of macrophages in repair and remodelling. These properties of cells of the monocyte-macrophage lineage may represent a tool and a target for therapeutic exploitation.