Expression of Tie-2 by Human Monocytes and Their Responses to Angiopoietin-2

Influence of exercise training on proangiogenic TIE-2 monocytes and circulating angiogenic cells in patients with peripheral arterial disease

BACKGROUND

Inflammation is the driving force in atherosclerosis. One central strategy in the treatment of peripheral arterial disease (PAD) is the promotion of angiogenesis. Here, proangiogenic Tie-2 expressing monocytes (TEM) and circulating angiogenic cells (CAC) play a crucial role. Exercise training (ET) is recommended in PAD patients at Fontaine stage II to promote angiogenesis.

METHODS

40 patients with intermittend claudication (IC) [2 groups: supervised ET (SET) vs. non-supervised ET (nSET), each n = 20] and 20 healthy controls were included in the study. Analysis of TEM and CAC was performed from whole blood by flow-cytometry. TEM were identified via CD45, CD86, CD14, CD16 and analysed for the expression of Tie-2. CAC were identified via their expression of CD45 (CD45dim), CD34 and VEGF-R2 (CD309/KDR). Follow up was performed after mean of 7.65 ± 1.62 months.

RESULTS

In comparison to healthy controls, we found increased proportions of CAC (p < 0.0001) and similar TEM numbers in both ET groups. At follow-up (FU) TEM poroportions increased (p < 0.001) and CAC proportions decreased (p < 0.01), but both more significantly in SET (p < 0.001) than nSET (p = 0.01). Only in SET fibrinogen levels decreased and VEGF-A increased (both p < 0.05). Finally, we found in both ET groups a significant increase in absolute walking distance but with a higher individual increase in SET (p < 0.01). TEM and CAC proportions correlated inversely with the absolute walking distance (CAC: r = -0.296, p = 0.02; TEM: r = -0.270, p = 0.04) as well as with ABI (CAC: r = -0.394, p < 0.01; TEM: r = -0.382, p < 0.01).

CONCLUSIONS

ET influences the distribution of CAC and TEM proportions. nSET, although still effective in regard to an improved walking distance, is less effective in the influence of proangiogenic cells and inflammatory burden than SET. Our results indicate SET to be a more preferential exercise form, supporting the necessity to establish more SET programs.

Tie2-Expressing Monocytes Are Associated with Identification and Prognoses of Hepatitis B Virus Related Hepatocellular Carcinoma after Resection

BACKGROUND

Tie2-expressing monocytes (TEMs) are found in various tumors, involved in forming tumor blood vessels and expressing several important proangiogenic factors. The goals of this study were to evaluate the value of TEMs in diagnosing and predicting the prognosis of hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC).

METHODS

Flow cytometry was performed to identify and count TEMs in peripheral blood monocytes from HCC patients (n = 84) receiving hepatectomy, HBV cirrhotic patients (n = 21), benign tumors patients (n = 15) and healthy volunteers (n = 23). Angiopoietin-2 (Ang-2) levels in the plasma were determined by enzyme linked immunosorbent assay. The distribution of TEMs in tumor tissue was observed by immunofluorescence staining. Then we determined the vascular area as a percentage of tumor area (vascular area/tumor area) by immunohistochemical staining. Finally the prognostic significance of TEMs and other clinicopathologic factors was evaluated.

RESULTS

Percentage of TEMs in peripheral blood monocytes significantly increased in HCC patients compared with HBV cirrhotic patients and healthy donors (both P< 0.001). However there was no significance in benign liver tumor (P = 0.482). In addition, the percentage of circulating TEMs was positively correlated with plasma Ang-2 concentration (P<0.001, r2 = 0.294) and vascular area/tumor area (P<0.001, r2 = 0.126). Furthermore the percentage of intratumoral TEMs was significantly higher than that of paratumoral TEMs (P<0.001). Increased circulating TEMs was associated with poor overall survival (P = 0.043) and a shorter time to recurrence (P = 0.041). Multivariate Cox analysis also revealed that the percentage of TEMs in peripheral blood was an independent factor for HCC patients' prognosis.

CONCLUSIONS

TEMs may promote angiogenesis in HCC regarding the angiopoietin/Tie2 signal pathway. Percentage of TEMs in peripheral blood monocytes may be applied as a biomarker for identifying HBV-related HCC and predicting the prognosis of these patients after resection.

Analysis of circulating CD14+/CD16+ monocyte-derived macrophages (MDMs) in the peripheral blood of patients with oral squamous cell carcinoma

OBJECTIVES

Monocytes/macrophages are regarded as the first line of defense in tumors. Therefore, analyzing monocyte subtypes in oral squamous cell carcinoma (OSCC) may be of value in disease monitoring and to explore immunotherapeutic strategies for cancer patients.

STUDY DESIGN

Circulating peripheral blood CD14+/CD16+ monocyte-derived macrophages (MDMs) were evaluated in OSCC patients with oral squamous cell carcinoma (n = 44) compared with controls (n = 85). Moreover, epitope detection in monocytes (EDIM) technology was used to detect biomarkers Apo10 and transketolase-like-1 in CD14+/CD16+ MDMs.

RESULTS

Compared with controls, no significant (P = .3646) difference (control group 9.8%, OSCC group 8.8%) in CD14+/CD16+ MDM were noted in OSCC. However, EDIM-Apo10 and EDIM-TKTL1 scores detected in the CD14+/CD16+ MDMs were increased in OSCC compared with controls (P < .0001).

CONCLUSIONS

Analyzing CD14+/CD16+ MDMs represents a stable cell population for detecting biomarkers in cancer disease monitoring.

slanDCs selectively accumulate in carcinoma-draining lymph nodes and marginate metastatic cells

Dendritic cells (DCs) initiate adaptive immune responses to cancer cells by activating naive T lymphocytes. 6-sulfo LacNAc(+) DCs (slanDCs) represent a distinct population of circulating and tissue proinflammatory DCs, whose role in cancer immune surveillance is unknown. Herein, by screening a large set of clinical samples, we demonstrate accumulation of slanDCs in metastatic tumour-draining lymph nodes (M-TDLN) from carcinoma patients. Remarkably, slanDCs are absent at the primary carcinoma site, while their selective nodal recruitment follows the arrival of cancer cells to M-TDLN. slanDCs surround metastatic carcinoma deposits in close proximity to dead cells and efficiently phagocytose tumour cells. In colon carcinoma patients, the contingent of circulating slanDCs remains intact and competent in terms of IL-12p70 and tumour necrosis factor alpha production, induction of T-cell proliferation and migratory capacity to a set of chemokines produced in M-TDLN. We conclude that activated slanDCs represent previously unrecognized players of nodal immune responses to cancer cells.

The great escape; the hallmarks of resistance to antiangiogenic therapy

The concept of antiangiogenic therapy in cancer treatment has led to the approval of different agents, most of them targeting the well known vascular endothelial growth factor pathway. Despite promising results in preclinical studies, the efficacy of antiangiogenic therapy in the clinical setting remains limited. Recently, awareness has emerged on resistance to antiangiogenic therapies. It has become apparent that the intricate complex interplay between tumors and stromal cells, including endothelial cells and associated mural cells, allows for escape mechanisms to arise that counteract the effects of these targeted therapeutics. Here, we review and discuss known and novel mechanisms that contribute to resistance against antiangiogenic therapy and provide an outlook to possible improvements in therapeutic approaches.

TIE-2-expressing monocytes are lymphangiogenic and associate specifically with lymphatics of human breast cancer

In experimental mouse models of cancer, increasingly compelling evidence point toward a contribution of tumor associated macrophages (TAM) to tumor lymphangiogenesis. Corresponding experimental observations in human cancer remain scarce although lymphatic metastasis is widely recognized as a predominant route for tumor spread. We previously showed that, in malignant tumors of untreated breast cancer (BC) patients, TIE-2-expressing monocytes (TEM) are highly proangiogenic immunosuppressive cells and that TIE-2 and VEGFR signaling pathways drive TEM immunosuppressive function. We report here that, in human BC, TEM express the canonical lymphatic markers LYVE-1, Podoplanin, VEGFR-3 and PROX-1. Critically, both TEM acquisition of lymphatic markers and insertion into lymphatic vessels were observed in tumors but not in adjacent non-neoplastic tissues, suggesting that the tumor microenvironment shapes both TEM phenotype and spatial distribution. We assessed the lymphangiogenic activity of TEM isolated from dissociated primary breast tumors in vitro and in vivo using endothelial cells (EC) sprouting assay and corneal vascularization assay, respectively. We show that, in addition to their known hemangiogenic function, TEM isolated from breast tumor display a lymphangiogenic activity. Importantly, TIE-2 and VEGFR pathways display variable contributions to TEM angiogenic and lymphangiogenic activities across BC patients; however, combination of TIE-2 and VEGFR kinase inhibitors abrogated these activities and overcame inter-patient variability. These results highlight the direct contribution of tumor TEM to the breast tumor lymphatic network and suggest a combined use of TIE-2 and VEGFR kinase inhibitors as a therapeutic approach to block hem- and lymphangiogenesis in BC.

Angiopoietin-2 blocking antibodies reduce early atherosclerotic plaque development in mice

OBJECTIVE

Angiopoietin-2 (Ang-2) blocking agents are currently undergoing clinical trials for use in cancer treatment. Ang-2 has also been associated with rupture-prone atherosclerotic plaques in humans, suggesting a role for Ang-2 in plaque stability. Despite the availability of Ang-2 blocking agents, their clinical use is still lacking. Our aim was to establish if Ang-2 has a role in atheroma development and in the transition of subclinical to clinically relevant atherosclerosis. We investigated the effect of antibody-mediated Ang-2 blockage on atherogenesis after in a mouse model of atherosclerosis.

METHODS

Hypercholesterolemic (low-density lipoprotein receptor(-/-) apolipoprotein B(100/100)) mice were subjected to high-cholesterol diet for eight weeks, one group with and one group without Ang-2 blocking antibody treatment during weeks 4-8.To enhance plaque development, a peri-adventitial collar was placed around the carotid arteries at the start of antibody treatment. Aortic root, carotid arteries and brachiocephalic arteries were analyzed to evaluate the effect of Ang-2 blockage on atherosclerotic plaque size and stable plaque characteristics.

RESULTS

Anti-Ang-2 treatment reduced the size of fatty streaks in the brachiocephalic artery (-72%, p < 0.05). In addition, antibody-mediated Ang-2 blockage reduced plasma triglycerides (-27%, p < 0.05). In contrast, Ang-2 blockage did not have any effect on the size or composition (collagen content, macrophage percentage, adventitial microvessel density) of pre-existing plaques in the aortic root or collar-induced plaques in the carotid artery.

CONCLUSIONS

Ang-2 blockage was beneficial as it decreased fatty streak formation and plasma triglyceride levels, but had no adverse effect on pre-existing atherosclerosis in hypercholesterolemic mice.

The Role of Macrophage in the Pathogenesis of Brain Arteriovenous Malformation

Brain arteriovenous malformation (BAVM) is an important risk factor for intracranial hemorrhage, especially in children and young adults. Inflammation has been implicated in BAVM lesion progression. Among various inflammatory components, macrophage is one of the major inflammatory cells present in human ruptured and unruptured BAVM and in the BAVM lesions of animal models. The role of macrophage in BAVM pathogenesis is not fully understood. In this review, we summarize recent studies on macrophages and introduce a non-invasive imaging protocol as a potential tool for detecting macrophage in BAVM and predicting the risk of BAVM rupture.

Human and Mouse Mononuclear Phagocyte Networks: A Tale of Two Species?

Dendritic cells (DCs), monocytes, and macrophages are a heterogeneous population of mononuclear phagocytes that are involved in antigen processing and presentation to initiate and regulate immune responses to pathogens, vaccines, tumor, and tolerance to self. In addition to their afferent sentinel function, DCs and macrophages are also critical as effectors and coordinators of inflammation and homeostasis in peripheral tissues. Harnessing DCs and macrophages for therapeutic purposes has major implications for infectious disease, vaccination, transplantation, tolerance induction, inflammation, and cancer immunotherapy. There has been a paradigm shift in our understanding of the developmental origin and function of the cellular constituents of the mononuclear phagocyte system. Significant progress has been made in tandem in both human and mouse mononuclear phagocyte biology. This progress has been accelerated by comparative biology analysis between mouse and human, which has proved to be an exceptionally fruitful strategy to harmonize findings across species. Such analyses have provided unexpected insights and facilitated productive reciprocal and iterative processes to inform our understanding of human and mouse mononuclear phagocytes. In this review, we discuss the strategies, power, and utility of comparative biology approaches to integrate recent advances in human and mouse mononuclear phagocyte biology and its potential to drive forward clinical translation of this knowledge. We also present a functional framework on the parallel organization of human and mouse mononuclear phagocyte networks.

T-cell exhaustion in the tumor microenvironment

T-cell exhaustion was originally identified during chronic infection in mice, and was subsequently observed in humans with cancer. The exhausted T cells in the tumor microenvironment show overexpressed inhibitory receptors, decreased effector cytokine production and cytolytic activity, leading to the failure of cancer elimination. Restoring exhausted T cells represents an inspiring strategy for cancer treatment, which has yielded promising results and become a significant breakthrough in the cancer immunotherapy. In this review, we overview the updated understanding on the exhausted T cells in cancer and their potential regulatory mechanisms and discuss current therapeutic interventions targeting exhausted T cells in clinical trials.

The TIE Receptor Family

The endothelial TIE1 and TIE2 receptor tyrosine kinases form a distinct subfamily characterized by their unique extracellular domains. Together with the angiopoietin growth factors (ANGPT1, ANGPT2, ANGPT4, also abbreviated as ANG), the TIE receptors form an endothelial specific signaling pathway with important functions in the regulation of lymphatic and cardiovascular development and vascular homeostasis. Angiopoietins exist in multimeric forms that activate the TIE receptors via unique mechanism. In endothelial cell–cell contacts, angiopoietins induce the formation of homomeric in trans TIE receptor complexes extending across the cell junctions, whereas matrix-bound angiopoietin-1 (ANG1) activates the TIE receptors in a cis configuration. In comparison to the vascular endothelial growth factor receptors, the TIE receptors undergo little ubiquitin-mediated degradation after activation, whereas TIE2 signaling is negatively regulated by the vascular endothelial protein tyrosine phosphatase, VE-PTP. ANG1 activation of TIE2 supports vascular stabilization, whereas angiopoietin-2 (ANG2), a context-dependent weak TIE2 agonist/antagonist, promotes pathological tumor angiogenesis, vascular permeability, and inflammation. Recently, ANG2 has been found to mediate some of its vascular destabilizing and angiogenic functions via integrin signalling. The circulating levels of ANG2 are increased in cancer, and in several human diseases associated with inflammation and vascular leak, for example, in sepsis. Blocking of ANG2 has emerged as a potential novel therapeutic strategy for these diseases. In addition, preclinical results demonstrate that genetic TIE1 deletion in mice inhibits the vascularization and growth of tumor isografts and protects from atherosclerosis, with little effect on normal vascular homeostasis in adult mice. The ability of the ANG-TIE pathway to control vessel stability and angiogenesis makes it an interesting vascular target for the treatment of the various diseases.

Angiopoietin-2: a multifaceted cytokine that functions in both angiogenesis and inflammation

Angiogenesis and inflammation are two highly linked processes. In the last decade, several factors with dual function in both of these major pathways have been identified. This review focuses on angiopoietin-2 (Ang-2), an important proangiogenic factor that has more recently been implicated in mediating inflammatory processes as well. Ang-2 is upregulated in multiple inflammatory diseases and has been implicated in the direct control of inflammation-related signaling pathways. As a consequence of its multiple roles, designs for therapeutic targeting of Ang-2 should consider the dual function of this factor in regulating angiogenesis and inflammation.

Clinical significance of monocyte heterogeneity

Monocytes are primitive hematopoietic cells that primarily arise from the bone marrow, circulate in the peripheral blood and give rise to differentiated macrophages. Over the past two decades, considerable attention to monocyte diversity and macrophage polarization has provided contextual clues into the role of myelomonocytic derivatives in human disease. Until recently, human monocytes were subdivided based on expression of the surface marker CD16. "Classical" monocytes express surface markers denoted as CD14(++)CD16(-) and account for greater than 70% of total monocyte count, while "non-classical" monocytes express the CD16 antigen with low CD14 expression (CD14(+)CD16(++)). However, recognition of an intermediate population identified as CD14(++)CD16(+) supports the new paradigm that monocytes are a true heterogeneous population and careful identification of specific subpopulations is necessary for understanding monocyte function in human disease. Comparative studies of monocytes in mice have yielded more dichotomous results based on expression of the Ly6C antigen. In this review, we will discuss the use of monocyte subpopulations as biomarkers of human disease and summarize correlative studies in mice that may yield significant insight into the contribution of each subset to disease pathogenesis.

Multitargeting strategy using lenvatinib and golvatinib: maximizing anti-angiogenesis activity in a preclinical cancer model

Almost all cancers show intrinsic and/or evasive resistance to vascular endothelial growth factor (VEGF) inhibitors by multiple mechanisms. Serum angiopoietin-2 (Ang2) level has been proposed as a potential biomarker of VEGF inhibitor response in several cancers. From these clinical observations, the Ang2 and Tie2 (its receptor) axis has been focused on as a promising target. Here, we show a novel strategy to circumvent the resistance by combining multi-tyrosine kinase inhibitors lenvatinib (VEGF receptor, fibroblast growth factor receptor, and RET inhibitor) and golvatinib (E7050; c-Met, Tie2, and EphB4 inhibitor). Tie2 identifies a highly pro-angiogenic macrophage subset, Tie2-expressing macrophages (TEM). Angi-Tie2 and EphB4-EphrinB2 signaling plays critical roles in pericyte-mediated vessel stabilization. In vitro analyses suggested that golvatinib combined with lenvatinib inhibited pericyte-mediated vessel stabilization and TEM differentiation. In thyroid and endometrial cancer models, golvatinib and lenvatinib inhibited pericyte network development and TEM infiltration, resulting in severe perfusion disorder and massive apoptosis. Body weight loss was tolerable, and no macroscopic change was observed. These preclinical studies suggest that modulation of the tumor microenvironment by a strategic and well-tolerated combination of multi-targeting tyrosine kinase inhibitors may sensitize cancer to VEGF inhibitors.

Monocytes with angiogenic potential are selectively induced by liver resection and accumulate near the site of liver regeneration

Background

Monocytes reportedly contribute to liver regeneration. Three subsets have been identified to date: classical, intermediate, non-classical monocytes. The intermediate population and a subtype expressing TIE2 (TEMs) were suggested to promote angiogenesis. In a clinical setting, we investigated which monocyte subsets are regulated after liver resection and correlate with postoperative liver function.

Methods

In 38 patients monocyte subsets were evaluated in blood and subhepatic wound fluid by flow cytometry before and 1-3 days after resection of colorectal liver metastases. The monocyte-regulating cytokines macrophage colony stimulating factor (M-CSF), transforming growth factor beta 1 (TGFβ1), and angiopoietin 2 (ANG-2) were measured in patient plasma by ELISA. C-reactive protein (CRP) and liver function parameters were retrieved from routine hospital analyses.

Results

On post-operative day (POD) 1 blood monocytes shifted to significantly elevated levels of intermediate monocytes. In wound fluid, a delayed surge in intermediate monocytes was detected by POD 3. Furthermore, TEMs were highly enriched in wound fluid as compared to circulation. CRP and M-CSF levels were substantially increased in patient blood after surgery and correlated significantly with the frequency of intermediate monocytes. In addition, liver function parameters showed a significant association with intermediate monocyte levels on POD 3.

Conclusions

The reportedly pro-angiogenic subsets of monocytes are selectively increased upon liver resection and accumulate next to the site of liver regeneration. As previously proposed by in vitro experiments, the release of CRP and M-CSF may trigger the induction of intermediate monocytes. The correlation with liver parameters points to a functional involvement of these monocyte populations in liver regeneration which warrants further investigation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-014-0050-3) contains supplementary material, which is available to authorized users.

Tumor-associated macrophages as major players in the tumor microenvironment

During tumor progression, circulating monocytes and macrophages are actively recruited into tumors where they alter the tumor microenvironment to accelerate tumor progression. Macrophages shift their functional phenotypes in response to various microenvironmental signals generated from tumor and stromal cells. Based on their function, macrophages are divided broadly into two categories: classical M1 and alternative M2 macrophages. The M1 macrophage is involved in the inflammatory response, pathogen clearance, and antitumor immunity. In contrast, the M2 macrophage influences an anti-inflammatory response, wound healing, and pro-tumorigenic properties. Tumor-associated macrophages (TAMs) closely resemble the M2-polarized macrophages and are critical modulators of the tumor microenvironment. Clinicopathological studies have suggested that TAM accumulation in tumors correlates with a poor clinical outcome. Consistent with that evidence, experimental and animal studies have supported the notion that TAMs can provide a favorable microenvironment to promote tumor development and progression. In this review article, we present an overview of mechanisms responsible for TAM recruitment and highlight the roles of TAMs in the regulation of tumor angiogenesis, invasion, metastasis, immunosuppression, and chemotherapeutic resistance. Finally, we discuss TAM-targeting therapy as a promising novel strategy for an indirect cancer therapy.

Macrophage colony-stimulating factor augments Tie2-expressing monocyte differentiation, angiogenic function, and recruitment in a mouse model of breast cancer

Reports demonstrate the role of M-CSF (CSF1) in tumor progression in mouse models as well as the prognostic value of macrophage numbers in breast cancer patients. Recently, a subset of CD14+ monocytes expressing the Tie2 receptor, once thought to be predominantly expressed on endothelial cells, has been characterized. We hypothesized that increased levels of CSF1 in breast tumors can regulate differentiation of Tie2- monocytes to a Tie2+ phenotype. We treated CD14+ human monocytes with CSF1 and found a significant increase in CD14+/Tie2+ positivity. To understand if CSF1-induced Tie2 expression on these cells improved their migratory ability, we pre-treated CD14+ monocytes with CSF1 and used Boyden chemotaxis chambers to observe enhanced response to angiopoietin-2 (ANG2), the chemotactic ligand for the Tie2 receptor. We found that CSF1 pre-treatment significantly augmented chemotaxis and that Tie2 receptor upregulation was responsible as siRNA targeting Tie2 receptor abrogated this effect. To understand any augmented angiogenic effect produced by treating these cells with CSF1, we cultured human umbilical vein endothelial cells (HUVECs) with conditioned supernatants from CSF1-pre-treated CD14+ monocytes for a tube formation assay. While supernatants from CSF1-pre-treated TEMs increased HUVEC branching, a neutralizing antibody against the CSF1R abrogated this activity, as did siRNA against the Tie2 receptor. To test our hypothesis in vivo, we treated PyMT tumor-bearing mice with CSF1 and observed an expansion in the TEM population relative to total F4/80+ cells, which resulted in increased angiogenesis. Investigation into the mechanism of Tie2 receptor upregulation on CD14+ monocytes by CSF1 revealed a synergistic contribution from the PI3 kinase and HIF pathways as the PI3 kinase inhibitor LY294002, as well as HIF-1α-deficient macrophages differentiated from the bone marrow of HIF-1αfl/fl/LysMcre mice, diminished CSF1-stimulated Tie2 receptor expression.

Pancreatic ductal adenocarcinoma: a review of immunologic aspects

With the continued failures of both early diagnosis and treatment options for pancreatic cancer, it is now time to comprehensively evaluate the role of the immune system on the development and progression of pancreatic cancer. It is important to develop strategies that harness the molecules and cells of the immune system to treat this disease. This review will focus primarily on the role of immune cells in the development and progression of pancreatic ductal adenocarcinoma and to evaluate what is known about the interaction of immune cells with the tumor microenvironment and their role in tumor growth and metastasis. We will conclude with a brief discussion of therapy for pancreatic cancer and the potential role for immunotherapy. We hypothesize that the role of the immune system in tumor development and progression is tissue specific. Our hope is that better understanding of this process will lead to better treatments for this devastating disease.

Recruitment of bone marrow derived cells during anti-angiogenic therapy in GBM: the potential of combination strategies

Glioblastoma (GBM) is a highly vascular tumor characterized by rapid and invasive tumor growth, followed by oxygen depletion, hypoxia and neovascularization, which generate a network of disorganized, tortuous and permeable vessels. Recruitment of bone marrow derived cells (BMDC) is crucial for vasculogenesis. These cells may act as vascular progenitors by integrating into the newly formed blood vessels or as vascular modulators by releasing pro-angiogenic factors. In patients with recurrent GBM, anti-vascular endothelial growth factor (VEGF) therapy has been evaluated in combination with chemotherapy, yielding improvements in progression-free survival (PFS). However, benefits are temporary as vascular tumors acquire angiogenic pathways independently of VEGF. Specifically, acute hypoxia following prolonged VEGF depletion induces the recruitment of certain myeloid cell subpopulations, which highly contribute to treatment refractoriness. Here we review the molecular mechanisms of neovascularization in relation to bevacizumab therapy with special emphasis on the recruitment of BMDCs and possible combination therapies for GBM patients.

Angiopoietin-2 inhibition prevents transplant ischemia-reperfusion injury and chronic rejection in rat cardiac allografts

Transplant ischemia-reperfusion injury (Tx-IRI) and allograft dysfunction remain as two of the major clinical challenges after heart transplantation. We investigated the role of angiopoietin-2 (Ang2) in Tx-IRI and rejection using fully MHC-mismatched rat cardiac allografts. We report that plasma levels of Ang2 were significantly enhanced in the human and rat recipients of cardiac allografts, but not in the rat recipients of syngrafts, during IRI. Ex vivo intracoronary treatment of rat cardiac allografts with anti-Ang2 antibody before 4-h cold preservation prevented microvascular dysfunction, endothelial cell (EC) adhesion molecule expression and leukocyte infiltration, myocardial injury and the development of cardiac fibrosis and allograft vasculopathy. Recipient preoperative and postoperative treatment with anti-Ang2 antibody produced otherwise similar effects without effecting microvascular dysfunction, and in additional experiments prolonged allograft survival. Recipient preoperative treatment alone failed to produce these effects. Moreover, ex vivo intracoronary treatment of allografts with recombinant Ang2 enhanced Tx-IRI and, in an add-back experiment, abolished the beneficial effect of the antibody. We demonstrate that neutralization of Ang2 prevents EC activation, leukocyte infiltration, Tx-IRI and the development of chronic rejection in rat cardiac allografts. Our results suggest that blocking Ang2 pathway is a novel, clinically feasible, T cell-independent strategy to protect cardiac allografts.

The impact of the immune system on tumor: angiogenesis and vascular remodeling

Angiogenesis, the formation of new blood vessels, as well as inflammation with massive infiltration of leukocytes are hallmarks of various tumor entities. Various epidemiological, clinical, and experimental studies have not only demonstrated a link between chronic inflammation and cancer onset but also shown that immune cells from the bone marrow such as tumor-infiltrating macrophages significantly influence tumor progression. Tumor angiogenesis is critical for tumor development as tumors have to establish a blood supply in order to progress. Although tumor cells were first believed to fuel tumor angiogenesis, numerous studies have shown that the tumor microenvironment and infiltrating immune cell subsets are important for regulating the process of tumor angiogenesis. These infiltrates involve the adaptive immune system including several types of lymphocytes as well as cells of the innate immunity such as macrophages, neutrophils, eosinophils, mast cells, dendritic cells, and natural killer cells. Besides their known immune function, these cells are now recognized for their crucial role in regulating the formation and the remodeling of blood vessels in the tumor. In this review, we will discuss for each cell type the mechanisms that regulate the vascular phenotype and its impact on tumor growth and metastasis.

Dynamics of pulmonary endothelial barrier function in acute inflammation: mechanisms and therapeutic perspectives

The lungs provide a large inner surface to guarantee respiration. In lung alveoli, a delicate membrane formed by endo- and epithelial cells with their fused basal lamina ensures rapid and effective gas exchange between alveolar and vascular compartments while concurrently forming a robust barrier against inhaled particles and microbes. However, upon infectious or sterile inflammatory stimulation, tightly regulated endothelial barrier leakiness is required for leukocyte transmigration. Further, endothelial barrier disruption may result in uncontrolled extravasation of protein-rich fluids. This brief review summarizes some important mechanisms of pulmonary endothelial barrier regulation and disruption, focusing on the role of specific cell populations, coagulation and complement cascades and mediators including angiopoietins, specific sphingolipids, adrenomedullin and reactive oxygen and nitrogen species for the regulation of pulmonary endothelial barrier function. Further, current therapeutic perspectives against development of lung injury are discussed.

MicroRNA-542-3p inhibits tumour angiogenesis by targeting angiopoietin-2

Angiopoietin-2 (Angpt2) plays a critical role in angiogenesis and tumour progression. Therapeutic targeting of Angpt2 has been implicated as a promising strategy for cancer treatment. Whereas miRNAs are emerging as important modulators of angiogenesis, regulation of Angpt2 by miRNAs has not been established. Here we firstly report that Ang2 is targeted by a microRNA, miRNA-542-3p, which inhibits tumour progression by impairing Ang2's pro-angiogenic activity. In cultured endothelial cells, miR-542-3p inhibited translation of Angpt2 mRNA by binding to its 3' UTR, and addition of miR-542-3p to cultured endothelial cells attenuated angiogenesis. Administration of miR-542-3p to tumour-bearing mice reduced tumour growth, angiogenesis and metastasis. Furthermore, the level of miR-542-3p in primary breast carcinomas correlated inversely with clinical progression in primary tumour samples from stage III and IV patients. Together, these findings uncover a novel regulatory pathway whereby an anti-angiogenic miR-542-3p directly targets the key angiogenesis-promoting protein Angpt2, suggesting that miR-542-3p may represent a promising target for anti-angiogenic therapy and a potential marker for monitoring disease progression.

Local synovial engagement of angiogenic TIE-2 is associated with the development of persistent erosive rheumatoid arthritis in patients with early arthritis

OBJECTIVE

To examine the role of vascular endothelial growth factor (VEGF) and angiopoietin signaling in the diagnosis and disease outcome of patients with early arthritis.

METHODS

Fifty patients with early arthritis (disease duration <1 year) who had not been treated with disease-modifying antirheumatic drugs (DMARDs) were monitored prospectively and were classified at baseline and after 2 years as having undifferentiated arthritis (UA), rheumatoid arthritis (RA), or spondyloarthritis (SpA). All patients underwent arthroscopic synovial biopsy at baseline. Synovial expression of VEGF, VEGF receptor, angiopoietin 1 (Ang-1), Ang-2, TIE-2, and activated p-TIE-2 was evaluated by immunohistochemistry. Serum levels of VEGF, Ang-1, and Ang-2 were measured by enzyme-linked immunosorbent assay. Secreted products of macrophages stimulated with Ang-1 and Ang-2 were measured using a multiplex system.

RESULTS

Expression of Ang-1 was comparable between the patients with RA at baseline and patients with UA who fulfilled the criteria for RA over time (UA/RA), and it was significantly higher in patients with RA (P < 0.05) or UA/RA (P < 0.005) than in patients with SpA. TIE-2 and p-TIE-2 were more highly expressed in patients with RA (P < 0.005) or UA/RA (P < 0.05) than in patients with SpA. Ang-1 significantly enhanced the tumor necrosis factor-dependent macrophage production of cytokines and chemokines that are known to be elevated in the synovial fluid of patients with early RA. In RA, relative TIE-2 activation predicted the development of erosive disease (R(2) = 0.35, P < 0.05).

CONCLUSION

Local engagement of synovial TIE-2 is observed during the earliest phases of RA, suggesting that TIE-2 signaling may contribute to disease development and progression or may indicate an attempt to protect against these processes. Early therapeutic targeting of TIE-2 signaling may be useful in improving outcome in arthritis.

Tie2 signaling cooperates with TNF to promote the pro-inflammatory activation of human macrophages independently of macrophage functional phenotype

Angiopoietin (Ang) -1 and -2 and their receptor Tie2 play critical roles in regulating angiogenic processes during development, homeostasis, tumorigenesis, inflammation and tissue repair. Tie2 signaling is best characterized in endothelial cells, but a subset of human and murine circulating monocytes/macrophages essential to solid tumor formation express Tie2 and display immunosuppressive properties consistent with M2 macrophage polarization. However, we have recently shown that Tie2 is strongly activated in pro-inflammatory macrophages present in rheumatoid arthritis patient synovial tissue. Here we examined the relationship between Tie2 expression and function during human macrophage polarization. Tie2 expression was observed under all polarization conditions, but was highest in IFN-γ and IL-10 –differentiated macrophages. While TNF enhanced expression of a common restricted set of genes involved in angiogenesis and inflammation in GM-CSF, IFN-γ and IL-10 –differentiated macrophages, expression of multiple chemokines and cytokines, including CXCL3, CXCL5, CXCL8, IL6, and IL12B was further augmented in the presence of Ang-1 and Ang-2, via Tie2 activation of JAK/STAT signaling. Conditioned medium from macrophages stimulated with Ang-1 or Ang-2 in combination with TNF, sustained monocyte recruitment. Our findings suggest a general role for Tie2 in cooperatively promoting the inflammatory activation of macrophages, independently of polarization conditions.

The role of tumor-associated macrophages in tumor vascularization

Tumor vascularization is a highly complex process that involves the interaction between tumors and their surrounding stroma, as well as many distinct angiogenesis-regulating factors. Tumor associated macrophages (TAMs) represent one of the most abundant cell components in the tumor environment and key contributors to cancer-related inflammation. A large body of evidence supports the notion that TAMs play a critical role in promoting the formation of an abnormal tumor vascular network and subsequent tumor progression and invasion. Clinical and experimental evidence has shown that high levels of infiltrating TAMs are associated with poor patient prognosis and tumor resistance to therapies. In addition to stimulating angiogenesis during tumor growth, TAMs enhance tumor revascularization in response to cytotoxic therapy (e.g., radiotherapy), thereby causing cancer relapse. In this review, we highlight the emerging data related to the phenotype and polarization of TAMs in the tumor microenvironment, as well as the underlying mechanisms of macrophage function in the regulation of the angiogenic switch and tumor vascularization. Additionally, we discuss the potential of targeting pro-angiogenic TAMs, or reprograming TAMs toward a tumoricidal and angiostatic phenotype, to promote normalization of the tumor vasculature to enhance the outcome of cancer therapies.

Harnessing the antitumor potential of macrophages for cancer immunotherapy

Macrophages constitute a dominant fraction of the population of immune cells that infiltrate developing tumors. Recruited by tumor-derived signals, tumor-infiltrating macrophages are key orchestrators of a microenvironment that supports tumor progression. However, the phenotype of macrophages is pliable and, if instructed properly, macrophages can mediate robust antitumor functions through their ability to eliminate malignant cells, inhibit angiogenesis, and deplete fibrosis. While much effort has focused on strategies to block the tumor-supporting activity of macrophages, emerging approaches designed to instruct macrophages with antitumor properties are demonstrating promise and may offer a novel strategy for cancer immunotherapy.

Targeting endothelial CD146 attenuates neuroinflammation by limiting lymphocyte extravasation to the CNS

The ability to selectively block the entry of leukocytes into the central nervous system (CNS) without compromising the immune system is an attractive therapeutic approach for treating multiple sclerosis (MS). Using endothelial CD146-deficienct mice as a MS model, we found that endothelial CD146 plays an active role in the CNS-directed extravasation of encephalitogenic T cells, including CD146⁺ T_H1 and T_H17 lymphocytes. Moreover, treating both active and passive MS models with the anti-CD146 antibody AA98 significantly decreased the infiltrated lymphocytes in the CNS and decreased neuroinflammation. Interestingly, the ability of AA98 to inhibit the migration of CD146⁺ lymphocytes was dependent on targeting endothelial CD146, but not lymphocytic CD146. These results suggest a key molecular target located on the blood-brain barrier endothelium that mediates the extravasation of inflammatory cells into the CNS. In addition, our data suggest that the AA98 is a promising candidate for treating MS and other CNS autoimmune diseases.

The frequency of tumor-infiltrating Tie-2-expressing monocytes in renal cell carcinoma: its relationship to angiogenesis and progression

OBJECTIVE

To examine the frequency of tumor-infiltrating Tie-2-expressing monocytes (TEMs) in renal cell carcinoma (RCC) and its association with microvessel density (MVD) and other clinical-pathologic features.

MATERIALS AND METHODS

This study enrolled 65 consecutive patients with RCC treated with radical nephrectomy. The frequency of tumor-infiltrating TEMs, which was defined as CD14(+) Tie-2(+) cells, was assessed using flow cytometry. MVD was measured by immunohistochemistry using anti-CD34 antibody. The association between clinicopathologic parameters, MVD, and the frequency of tumor-infiltrating TEMs in RCC was assessed.

RESULTS

High frequency of tumor-infiltrating TEMs was significantly associated with advanced stage (P = .018), positive lymph nodes (P = .013), high grade (P = .019), and metastases (P = .006). Correlation analysis revealed that the frequency of TEMs was positively correlated with MVD.

CONCLUSION

Our findings revealed a significant association between prognostic tumor features, MVD, and the frequency of tumor-infiltrating TEMs in RCC and indicated that TEMs may play an important role in angiogenesis and progression of RCC.

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 role of immune-related myeloid cells in angiogenesis

Macrophage function is not restricted to the innate and adaptive immune responses, but also includes host defence, wound healing, angiogenesis and homeostatic processes. Within the spectrum of macrophage activation there are two extremes: M1 classically activated macrophages which have a pro-inflammatory phenotype, and M2 alternatively activated macrophages which are pro-angiogenic and anti-inflammatory. An important property of macrophages is their plasticity to switch from one phenotype to the other and they can be defined in their polarisation state at any point between the two extremes. In order to determine what stage of activation macrophages are in, it is essential to profile various phenotypic markers for their identification. This review describes the angiogenic role for myeloid cells: circulating monocytes, Tie-2 expressing monocytes (TEMs), myeloid-derived suppressor cells (MDSCs), tumour associated macrophages (TAMs), and neutrophils. Each cell type is discussed by phenotype, roles within angiogenesis and possible targets as a cell therapy. In addition, we also refer to our own research on myeloid angiogenic cells (MACs), outlining their ability to induce angiogenesis and their similarities to alternatively activated M2 macrophages. MACs significantly contribute to vascular repair through paracrine mechanisms as they lack the capacity to differentiate into endothelial cells. Since MACs also retain plasticity, phenotypic changes can occur according to disease states and the surrounding microenvironment. This pro-angiogenic potential of MACs could be harnessed as a novel cellular therapy for the treatment of ischaemic diseases, such as diabetic retinopathy, hind limb ischaemia and myocardial infarction; however, caution needs to be taken when MACs are delivered into an inflammatory milieu.

Preliminary evidence of sustained expression of angiopoietin-2 during monocyte differentiation in chronic hepatitis C

BACKGROUND

Monocytes are essential precursors of antigen-presenting cells, such as macrophages and dendritic cells, and contribute to the pathogenesis of chronic inflammatory diseases and cancer.

AIMS

As Tie2-expressing monocytes (TEMs) are increased in the peripheral blood of patients with chronic hepatitis C (CHC), we aimed to examine the expression of Tie2 and angiopoietins (Ang1 and Ang2) during monocyte differentiation and maturation in CHC.

METHODS

The expression of Tie2, CD11b, CD80, CD83, CD86 and MHC-II was measured by flow cytometry in peripheral blood monocytes and monocytes-derived cells (Mo-DCs) from nine healthy subjects and eight CHC patients whose HCV infection was unresolved after combination therapy. Ang1 and Ang2 levels were measured in cellular supernatants by ELISA.

RESULTS

Mo-DCs from CHC patients expressed differential patterns of maturation markers compared with controls--primarily with regard to CD80. Tie2 was downregulated during monocyte differentiation in controls and CHC patients, whereas Ang1 expression was constant. However, Ang2 levels fell significantly during the differentiation of control monocytes, in contrast with those from CHC patients in whom Ang2 expression remained stable throughout differentiation.

CONCLUSIONS

Altered expression of the Ang/Tie2 system in monocytes and Mo-DCs from CHC patients might account for the inflammatory and angiogenic disorders that are related to CHC. An increased understanding of Ang/Tie2 system regulation might be helpful in designing strategies to prevent CHC progression.

MMP1, MMP9, and COX2 expressions in promonocytes are induced by breast cancer cells and correlate with collagen degradation, transformation-like morphological changes in MCF-10A acini, and tumor aggressiveness

Tumor-associated immune cells often lack immune effector activities, and instead they present protumoral functions. To understand how tumors promote this immunological switch, invasive and noninvasive breast cancer cell (BRC) lines were cocultured with a promonocytic cell line in a Matrigel-based 3D system. We hypothesized that if communication exists between tumor and immune cells, coculturing would result in augmented expression of genes associated with tumor malignancy. Upregulation of proteases MMP1 and MMP9 and inflammatory COX2 genes was found likely in response to soluble factors. Interestingly, changes were more apparent in promonocytes and correlated with the aggressiveness of the BRC line. Increased gene expression was confirmed by collagen degradation assays and immunocytochemistry of prostaglandin 2, a product of COX2 activity. Untransformed MCF-10A cells were then used as a sensor of soluble factors with transformation-like capabilities, finding that acini formed in the presence of supernatants of the highly aggressive BRC/promonocyte cocultures often exhibited total loss of the normal architecture. These data support that tumor cells can modify immune cell gene expression and tumor aggressiveness may importantly reside in this capacity. Modeling interactions in the tumor stroma will allow the identification of genes useful as cancer prognostic markers and therapy targets.

Cyclooxygenase-2 inhibition blocks M2 macrophage differentiation and suppresses metastasis in murine breast cancer model

Tumor cells are often associated with abundant macrophages that resemble the alternatively activated M2 subset. Tumor-associated macrophages (TAMs) inhibit anti-tumor immune responses and promote metastasis. Cyclooxygenase-2 (COX-2) inhibition is known to prevent breast cancer metastasis. This study hypothesized that COX-2 inhibition affects TAM characteristics potentially relevant to tumor cell metastasis. We found that the specific COX-2 inhibitor, etodolac, inhibited human M2 macrophage differentiation, as determined by decreased CD14 and CD163 expressions and increased TNFα production. Several key metastasis-related mediators, such as vascular endothelial growth factor-A, vascular endothelial growth factor-C, and matrix metalloproteinase-9, were inhibited in the presence of etodolac as compared to untreated M2 macrophages. Murine bone marrow derived M2 macrophages also showed enhanced surface MHCII IA/IE and CD80, CD86 expressions together with enhanced TNFα expressions with etodolac treatment during differentiation. Using a BALB/c breast cancer model, we found that etodolac significantly reduced lung metastasis, possibly due to macrophages expressing increased IA/IE and TNFα, but decreased M2 macrophage-related genes expressions (Ym1, TGFβ). In conclusion, COX-2 inhibition caused loss of the M2 macrophage characteristics of TAMs and may assist prevention of breast cancer metastasis.

TIE2-expressing monocytes as a diagnostic marker for hepatocellular carcinoma correlates with angiogenesis

Angiogenesis is a critical step in the development and progression of hepatocellular carcinoma (HCC). Myeloid lineage cells, such as macrophages and monocytes, have been reported to regulate angiogenesis in mouse tumor models. TIE2, a receptor of angiopoietins, conveys pro-angiogenic signals and identifies a monocyte/macrophage subset with pro-angiogenic activity. Here, we analyzed the occurrence and kinetics of TIE2-expressing monocytes/macrophages (TEMs) in HCC patients. This study enrolled 168 HCV-infected patients including 89 with HCC. We examined the frequency of TEMs, as defined as CD14+CD16+TIE2+ cells, in the peripheral blood and liver. The localization of TEMs in the liver was determined by immunofluorescence staining. Micro-vessel density in the liver was measured by counting CD34+ vascular structures. We found that the frequency of circulating TEMs was significantly higher in HCC than non-HCC patients, while being higher in the liver than in the blood. In patients who underwent local radio-ablation or resection of HCC, the frequency of TEMs dynamically changed in the blood in parallel with HCC recurrence. Most TEMs were identified in the perivascular areas of tumor tissue. A significant positive correlation was observed between micro-vessel density in HCC and frequency of TEMs in the blood or tumors, suggesting that TEMs are involved in HCC angiogenesis. Receiver operating characteristic analyses revealed the superiority of TEM frequency to AFP, PIVKA-II and ANG-2 serum levels as diagnostic marker for HCC.

CONCLUSION

TEMs increase in patients with HCC and their frequency changes with the therapeutic response or recurrence. We thus suggest that TEM frequency can be used as a diagnostic marker for HCC, potentially reflecting angiogenesis in the liver.

Collaborating with the enemy: function of macrophages in the development of neoplastic disease

Due to the profile of released mediators (such as cytokines, chemokines, growth factors, etc.), neoplastic cells modulate the activity of immune system, directly affecting its components both locally and peripherally. This is reflected by the limited antineoplastic activity of the immune system (immunosuppressive effect), induction of tolerance to neoplastic antigens, and the promotion of processes associated with the proliferation of neoplastic tissue. Most of these responses are macrophages dependent, since these cells show proangiogenic properties, attenuate the adaptive response (anergization of naïve T lymphocytes, induction of Treg cell formation, polarization of immune response towards Th2, etc.), and support invasion and metastases formation. Tumor-associated macrophages (TAMs), a predominant component of leukocytic infiltrate, "cooperate" with the neoplastic tissue, leading to the intensified proliferation and the immune escape of the latter. This paper characterizes the function of macrophages in the development of neoplastic disease.

Circulating angiopoietin-2 is a marker for early cardiovascular disease in children on chronic dialysis

Cardiovascular disease (CVD) is increasingly recognised as a complication of childhood chronic kidney disease (CKD) even in the absence of diabetes and hypertension. We hypothesized that an alteration in angiopoietin-1 and -2, growth factors which regulate endothelial and vascular function could be involved. We report that the endothelial survival factor, angiopoietin-1 is low in children with pre-dialysis CKD whereas the pro-inflammatory angiopoietin-2 is elevated in children on dialysis. In dialysis patients, angiopoietin-2 positively correlated with time on dialysis, systolic blood pressure, and carotid artery intima media thickness. Elevated angiopoietin-2 levels in dialysis versus pre-dialysis CKD patients were also associated with an anti-angiogenic (high soluble VEGFR-1 and low VEGF-A) and pro-inflammatory (high urate, E-selectin, P-selectin and VCAM-1) milieu. Ang-2 was immunodetected in arterial biopsy samples whilst the expression of VEGF-A was significantly downregulated in dialysis patients. Serum urate correlated with angiopoietin-2 levels in dialysis patients and addition of uric acid was able to induce rapid release of angiopoietin-2 from cultured endothelial cells. Thus, angiopoietin-2 is a marker for cardiovascular disease in children on chronic dialysis and may act as an anti-angiogenic and pro-inflammatory effector in this context. The possibility that the release of angiopoietin-2 from endothelia is mediated by urate should be explored further.

Toward a refined definition of monocyte subsets

In a nomenclature proposal published in 2010 monocytes were subdivided into classical and non-classical cells and in addition an intermediate monocyte subset was proposed. Over the last couple of years many studies have analyzed these intermediate cells, their characteristics have been described, and their expansion has been documented in many clinical settings. While these cells appear to be in transition from classical to non-classical monocytes and hence may not form a distinct cell population in a strict sense, their separate analysis and enumeration is warranted in health and disease.

The diverse identity of angiogenic monocytes

BACKGROUND

The role of bone marrow-derived cells in stimulating angiogenesis, vascular repair or remodelling has been well established, but the nature of the circulating angiogenic cells is still controversial.

DESIGN

The existing literature on different cell types that contribute to angiogenesis in multiple pathologies, most notably ischaemic and tumour angiogenesis, is reviewed, with a focus on subtypes of angiogenic mononuclear cells and their local recruitment and activation.

RESULTS

A large number of different cells of myeloid origin support angiogenesis without incorporating permanently into the newly formed vessel, which distinguishes these circulating angiogenic cells (CAC) from endothelial progenitor cells (EPC). Although CAC frequently express individual endothelial markers, they all share multiple characteristics of monocytes and only express a limited set of discriminative surface markers in the circulation. When cultured ex vivo, or surrounding the angiogenic vessel in vivo, however, many of them acquire similar additional markers, making their discrimination in situ difficult.

CONCLUSION

Different subsets of monocytes show angiogenic properties, but the distinct microenvironment, in vitro or in vivo, is needed for the development of their pro-angiogenic function.

[Immunological analogies between ovarian cancer and pregnancy]

During pregnancy an environment allowing installation of tolerance toward the fetus is set up locally at the materno-fetal interface. Numerous effectors of immunity are involved in this tolerance (NK cell, T cell, Macrophages, dendritic cell). Specific mechanisms during pregnancy attract locally these immunological cells. In the decidua, they are educated toward tolerance. These mechanisms evolve during the pregnancy because at the end of the pregnancy, tolerance is broken to prepare and activate the labor. Ovarian tumors, after having surmounted the immunosurveillance, like trophoblast, chair the installation of a tolerance of their host facilitating the development of the disease. The blocking of these mechanisms of tolerance coupled with activation of mechanisms of defenses offer new perspectives in the treatment of the ovarian cancer. The authors suggest showing the analogies of the tolerance observed during ovarian cancer and pregnancy. The knowledge of the orchestration of the physiological mechanisms observed during pregnancy will offer new therapeutic targets.

Monocytes and macrophages in cancer: development and functions

Monocytes and tumor-associated macrophages are part of the myeloid family, a group of hematopoietic derived cells. Monocytes are direct precursors of hematopoietic stem cell-derived macrophages. After their recruitment into the tumor tissue, they can differentiate into tumor-associated macrophages, a very heterogeneous cell population in terms of phenotype and pro-tumor function, supporting tumor initiation, local progression and distant metastasis. Therefore, targeting monocytes and macrophages is a promising immunotherapeutic approach. This review will focus on the development of monocytes as macrophage precursors, the functions of tumor-associated macrophages and the possibility of interfering with tumor development and progression by targeting these myeloid cells.

Monocyte-derived cells of the brain and malignant gliomas: the double face of Janus

OBJECTIVE

Monocyte-derived cells of the brain (MDCB) are a diverse group of functional immune cells that are also highly abundant in gliomas. There is growing evidence that MDCB play essential roles in the pathogenesis of gliomas. The aim of this review was to collate and systematize contemporary knowledge about these cells as they relate to glioma progression and antiglioblastoma therapeutic modalities with a view toward improved effectiveness of therapy.

METHODS

We reviewed relevant studies to construct a summary of different MDCB subpopulations in steady state and in malignant gliomas and discuss their role in the development of malignant gliomas and potential future therapies.

RESULTS

Current studies suggest that MDCB subsets display different phenotypes and differentiation potentials depending on their milieu in the brain and exposure to tumoral influences. MDCB possess specific and unique functions, including those that are protumoral and those that are antitumoral.

CONCLUSIONS

Elucidating the role of mononuclear-derived cells associated with gliomas is crucial in designing novel immunotherapy strategies. Much progress is needed to characterize markers to identify cell subsets and their specific regulatory roles. Investigation of MDCB can be clinically relevant. Specific MDCB populations potentially can be used for glioma therapy as a target or as cell vehicles that might deliver cytotoxic substances or processes to the glioma microenvironment.

The three human monocyte subsets: implications for health and disease

Human blood monocytes are heterogeneous and conventionally subdivided into two subsets based on CD16 expression. Recently, the official nomenclature subdivides monocytes into three subsets, the additional subset arising from the segregation of the CD16+ monocytes into two based on relative expression of CD14. Recent whole genome analysis reveal that specialized functions and phenotypes can be attributed to these newly defined monocyte subsets. In this review, we discuss these recent results, and also the description and utility of this new segregation in several disease conditions. We also discuss alternative markers for segregating the monocyte subsets, for example using Tie-2 and slan, which do not necessarily follow the official method of segregating monocyte subsets based on relative CD14 and CD16 expressions.

Hypoxia-inducible factors as key regulators of tumor inflammation

Low levels of oxygen or hypoxia is often an obstacle in health, particularly in pathological disorders like cancer. The main family of transcription factors responsible for cell survival and adaptation under strenuous conditions of hypoxia are the "hypoxia-inducible factors" (HIFs). Together with prolyl hydroxylase domain enzymes (PHDs), HIFs regulates tumor angiogenesis, proliferation, invasion, metastasis, in addition to resistance to radiation and chemotherapy. Additionally, the entire HIF transcription cascade is involved in the "seventh" hallmark of cancer; inflammation. Studies have shown that hypoxia can influence tumor associated immune cells toward assisting in tumor proliferation, differentiation, vessel growth, distant metastasis and suppression of the immune response via cytokine expression alterations. These changes are not necessarily analogous to HIF's role in non-cancer immune responses, where hypoxia often encourages a strong inflammatory response.

Intermediate monocytes but not TIE2-expressing monocytes are a sensitive diagnostic indicator for colorectal cancer

We have conducted the first study to determine the diagnostic potential of the CD14++CD16+ intermediate monocytes as compared to the pro-angiogenic subset of CD14++CD16+TIE2+ TIE2-expressing monocytes (TEMs) in cancer. These monocyte populations were investigated by flow cytometry in healthy volunteers (N = 32) and in colorectal carcinoma patients with localized (N = 24) or metastatic (N = 37) disease. We further determined blood levels of cytokines associated with monocyte regulation. The results revealed the intermediate monocyte subset to be significantly elevated in colorectal cancer patients and to show the highest frequencies in localized disease. Multivariate regression analysis identified intermediate monocytes as a significant independent variable in cancer prediction. With a cut-off value at 0.37% (intermediate monocytes of total leukocytes) the diagnostic sensitivity and specificity ranged at 69% and 81%, respectively. In contrast, TEM levels were elevated in localized cancer but did not differ significantly between groups and none of the cytokines correlated with monocyte subpopulations. Of interest, in vitro analyses supported the observation that intermediate monocytes were more potently induced by primary as opposed to metastatic cancer cells which may relate to the immunosuppressive milieu established in the advanced stage of metastatic disease. In conclusion, intermediate monocytes as compared to TIE2-expressing monocytes are a more sensitive diagnostic indicator of colorectal cancer.