Tumor-infiltrating myeloid-derived suppressor cells are pleiotropic-inflamed monocytes/macrophages that bear M1- and M2-type characteristics

Role of Neutrophils and Myeloid-Derived Suppressor Cells in Glioma Progression and Treatment Resistance

Recent efforts in brain tumor research have been directed towards the modulation of the immune system for therapeutic interventions. Several human cancers, including gliomas, are infiltrated with immune cell types-including neutrophils and myeloid-derived suppressor cells-that contribute to tumor progression, invasiveness, and treatment resistance. The role of tumor-associated neutrophils and myeloid-derived suppressor cells in cancer biology remains elusive, as these cells can exert a multitude of pro-tumor and antitumor effects. In this review, we provide the current understanding and novel insights on the role of neutrophils and myeloid-derived suppressor cells in glioma progression and treatment resistance, as well as the mechanisms of pleiotropic behaviors in these cells during disease progression, with an emphasis on possible strategies to reprogram these cells towards their antitumor actions.

Tumor-Targeted Drug and CpG Delivery System for Phototherapy and Docetaxel-Enhanced Immunotherapy with Polarization toward M1-Type Macrophages on Triple Negative Breast Cancers

Cancer immunotherapy has achieved promising clinical responses in recent years owing to the potential of controlling metastatic disease. However, there is a limited research to prove the superior therapeutic efficacy of immunotherapy on breast cancer compared with melanoma and non-small-cell lung cancer because of its limited expression of PD-L1, low infiltration of cytotoxic T lymphocytes (CTLs), and high level of myeloid-derived suppressor cells (MDSCs). Herein, a multifunctional nanoplatform (FA-CuS/DTX@PEI-PpIX-CpG nanocomposites, denoted as FA-CD@PP-CpG) for synergistic phototherapy (photodynamic therapy (PDT), photothermal therapy (PTT) included) and docetaxel (DTX)-enhanced immunotherapy is successfully developed. The nanocomposites exhibit excellent PDT efficacy and photothermal conversion capability under 650 and 808 nm irradiation, respectively. More significantly, FA-CD@PP-CpG with no obvious side effects can remarkably inhibit the tumor growth in vivo based on a 4T1-tumor-bearing mice modal. A low dosage of loaded DTX in FA-CD@PP-CpG can promote infiltration of CTLs to improve efficacy of anti-PD-L1 antibody (aPD-L1), suppress MDSCs, and effectively polarize MDSCs toward M1 phenotype to reduce tumor burden, further to enhance the antitumor efficacy. Taken together, FA-CD@PP-CpG nanocomposites offer an efficient synergistic therapeutic modality in docetaxel-enhanced immunotherapy for clinical application of breast cancer.

The oncometabolite 2-hydroxyglutarate inhibits microglial activation via the AMPK/mTOR/NF-κB pathway

Microglia, the brain-resident macrophage, is known as the innate immune cell type in the central nervous system. Microglia is also the major cellular component of tumor mass of gliomas that plays a key role in glioma development. Mutations of isocitrate dehydrogenases 1 and 2 (IDH1/2) frequently occur in gliomas, which leads to accumulation of oncometabolic product 2-hydroxyglutarate (2HG). Moreover, IDH1/2 mutations were found to correlate with better prognosis in glioma patients. In the present study, we investigated the effects of the 2HG on microglial inflammatory activation. We showed that the conditioned media (CM) from GL261 glioma cells stimulated the activation of BV-2 microglia cells, evidenced by markedly increased expression of interleukin-6 (IL-6), IL-1β, tumor necrosis factor-α (TNF-α), CCL2 (C-C motif chemokine ligand 2) and CXCL10 (C-X-C motif chemokine 10). CM-induced expression of proinflammatory genes was significantly suppressed by pretreatment with a synthetic cell-permeable 2HG (1 mM) or a nuclear factor-κB (NF-κB) inhibitor BAY11-7082 (10 μM). In lipopolysaccharide (LPS)- or TNF-α-stimulated BV-2 microglia cells and primary microglia, pretreatment with 2HG (0.25-1 mM) dose-dependently suppressed the expression of proinflammatory genes. We further demonstrated that 2HG significantly suppressed LPS-induced phosphorylation of IκB kinase α/β (IKKα/β), IκBα and p65, IκB degradation, and nuclear translocation of p65 subunit of NF-κB, as well as NF-κB transcriptional activity. Similarly, ectopic expression of mutant isocitrate dehydrogenase 1 (IDH1) (R132H) significantly decreased TNF-α-induced activation of NF-κB signaling pathway. Finally, we revealed that activation of adenosine 5'-monophosphate-activated protein kinase (AMPK) and subsequent inhibition of mammalian target of rapamycin (mTOR) signaling contributed to the inhibitory effect of 2HG on NF-κB signaling pathway in BV-2 cells. Taken together, these results, for the first time, show that oncometabolite 2HG inhibits microglial activation through affecting AMPK/mTOR/NF-κB signaling pathway and provide evidence that oncometabolite 2HG may regulate glioma development via modulating microglial activation in tumor microenvironment.

Regulation of Immunity in Breast Cancer

Breast cancer affects millions of women worldwide, leading to many deaths and significant economic burden. Although there are numerous treatment options available, the huge potentials of immunotherapy in the management of localized and metastatic breast cancer is currently being explored. However, there are significant gaps in understanding the complex interactions between the immune system and breast cancer. The immune system can be pro-tumorigenic and anti-tumorigenic depending on the cells involved and the conditions of the tumor microenvironment. In this review, we discuss current knowledge of breast cancer, including treatment options. We also give a brief overview of the immune system and comprehensively highlight the roles of different cells of the immune system in breast tumorigenesis, including recent research discoveries. Lastly, we discuss some immunotherapeutic strategies for the management of breast cancer.

Myeloid-Derived Suppressor Cells: Ductile Targets in Disease

Myeloid-derived suppressor cells (MDSCs) represent a heterogeneous population of immature myeloid cells with major regulatory functions and rise during pathological conditions, including cancer, infections and autoimmune conditions. MDSC expansion is generally linked to inflammatory processes that emerge in response to stable immunological stress, which alter both magnitude and quality of the myelopoietic output. Inability to reinstate physiological myelopoiesis would fall in an “emergency state” that perpetually reprograms myeloid cells toward suppressive functions. While differentiation and reprogramming of myeloid cells toward an immunosuppressive phenotype can be considered the result of a multistep process that originates in the bone marrow and culminates in the tumor microenvironment, the identification of its driving events may offer potential therapeutic approaches in different pathologies. Indeed, whereas expansion of MDSCs, in both murine and human tumor bearers, results in reduced immune surveillance and antitumor cytotoxicity, placing an obstacle to the effectiveness of anticancer therapies, adoptive transfer of MDSCs has shown therapeutic benefits in autoimmune disorders. Here, we describe relevant mechanisms of myeloid cell reprogramming leading to generation of suppressive MDSCs and discuss their therapeutic ductility in disease.

CD30 ligand deficiency accelerates glioma progression by promoting the formation of tumor immune microenvironment

CD30 ligand (CD30L, CD153), belonging to the tumor necrosis factor superfamily, has been reported to act as an immune regulator mainly in several autoimmune diseases and Hodgkin's lymphoma. However, little is known about its regulation in the glioma microenvironment. In this study, using a GL261 mouse glioma model, we showed that CD30L deficiency in the host accelerated glioma growth and reduced mouse survival, which might be associated with the accumulation of tumor-infiltrating immune cells, especially tumor-associated macrophages, myeloid-derived suppressor cells and CD8⁺ PD-1⁺ T cells. Moreover, CD30L deficiency resulted in distinct subsets of tumor-associated macrophages compared with those of wild-type mice. Furthermore, compared with those of wild-type mice, tumor-associated macrophages and microglia in CD30L-deficient mice adopted a more pro-tumorigenic phenotype within tumors. CD8⁺ T cells in CD30L-deficient mice decreased the expression of ki-67. Therefore, these results suggest that CD30L deficiency promotes the exhaustion of CD8⁺ T cells and the infiltration of tumor-associated macrophages and microglia. Our findings provide evidence for a new potential immunotherapy for glioma targeting CD30/CD30L signaling.

Discovery and mechanisms of host defense to oncogenesis: targeting the β-defensin-1 peptide as a natural tumor inhibitor

Human beta-defensin-1 (hBD-1) is one of a number of small cationic host-defense peptides. Besides its well-known broad-spectrum antimicrobial function, hBD-1 has recently been identified as a chromosome 8p tumor-suppressor gene. The role of hBD-1 in modulating the host immune response to oncogenesis, associated with cell signaling and potential therapeutic applications, has become increasingly appreciated over time. In this study, multiple approaches were used to illustrate hBD-1 anti-tumor activities. Results demonstrate that hBD-1 peptide alters human epidermal growth factor receptor 2 (HER2) signal transduction and represses retroviral-mediated transgene expression in cancer cells. Loss of orthologous murine defense-1 (mBD1) in mice enhances nickel sulfate-induced leiomyosarcoma and causes mouse kidney cells to exhibit increased susceptibility to HPV-16 E6/7-induced neoplastic transformation. Furthermore, for the first time, a novel function of the urine-derived hBD-1 peptide was discovered to suppress bladder cancer growth and this may lead to future applications in the treatment of malignancy.

Harnessing Radiation Biology to Augment Immunotherapy for Glioblastoma

Glioblastoma is the most common adult primary brain tumor and carries a dismal prognosis. Radiation is a standard first-line therapy, typically deployed following maximal safe surgical debulking, when possible, in combination with cytotoxic chemotherapy. For other systemic cancers, standard of care is being transformed by immunotherapies, including checkpoint-blocking antibodies targeting CTLA-4 and PD-1/PD-L1, with potential for long-term remission. Ongoing studies are evaluating the role of immunotherapies for GBM. Despite dramatic responses in some cases, randomized trials to date have not met primary outcomes. Challenges have been attributed in part to the immunologically "cold" nature of glioblastoma relative to other malignancies successfully treated with immunotherapy. Radiation may serve as a mechanism to improve tumor immunogenicity. In this review, we critically evaluate current evidence regarding radiation as a synergistic facilitator of immunotherapies through modulation of both the innate and adaptive immune milieu. Although current preclinical data encourage efforts to harness synergistic biology between radiation and immunotherapy, several practical and scientific challenges remain. Moreover, insights from radiation biology may unveil additional novel opportunities to help mobilize immunity against GBM.

Iron as a Central Player and Promising Target in Cancer Progression

Iron is an essential element for virtually all organisms. On the one hand, it facilitates cell proliferation and growth. On the other hand, iron may be detrimental due to its redox abilities, thereby contributing to free radical formation, which in turn may provoke oxidative stress and DNA damage. Iron also plays a crucial role in tumor progression and metastasis due to its major function in tumor cell survival and reprogramming of the tumor microenvironment. Therefore, pathways of iron acquisition, export, and storage are often perturbed in cancers, suggesting that targeting iron metabolic pathways might represent opportunities towards innovative approaches in cancer treatment. Recent evidence points to a crucial role of tumor-associated macrophages (TAMs) as a source of iron within the tumor microenvironment, implying that specifically targeting the TAM iron pool might add to the efficacy of tumor therapy. Here, we provide a brief summary of tumor cell iron metabolism and updated molecular mechanisms that regulate cellular and systemic iron homeostasis with regard to the development of cancer. Since iron adds to shaping major hallmarks of cancer, we emphasize innovative therapeutic strategies to address the iron pool of tumor cells or cells of the tumor microenvironment for the treatment of cancer.

Splenectomy Promotes Macrophage Polarization in a Mouse Model of Concanavalin A- (ConA-) Induced Liver Fibrosis

Background

Splenectomy can improve liver function and survival in patients with autoimmune hepatitis (AIH) and liver cirrhosis. We investigated the underlying mechanism in a mouse model of concanavalin A- (ConA-) induced liver fibrosis.

Methods

We used ConA to induce immune liver fibrosis in BALB/c mice. Splenectomy was performed alone or with the administration of dexamethasone (DEX). Changes in blood and liver tissues were evaluated.

Results

Mice treated with ConA for 7 weeks developed advanced liver fibrosis, while splenectomy suppressed liver fibrosis. Although the populations of macrophages/monocytes and M1 macrophages decreased after splenectomy, the inflammatory factors associated with M2 macrophages increased after splenectomy. Furthermore, the population of circulating CD11b⁺Ly6C^high myeloid-derived suppressor cells (MDSCs) increased after splenectomy. After ConA treatment, elevated levels of activated and total NF-kBp65/p50 combined with DNA were observed in hepatic tissues. In contrast, the levels of NF-κB p65/p50 decreased after splenectomy.

Conclusions

Splenectomy may promote the polarization of CD11b⁺Ly6C^high MDSCs and the differentiation of M2 macrophages while restricting the level of NF-κB p65-p50 heterodimers. These factors may suppress the progression of liver fibrosis.

Targeting Multiple Receptors to Increase Checkpoint Blockade Efficacy

Immune checkpoint blockade therapy is a powerful treatment strategy for many cancer types. Many patients will have limited responses to monotherapy targeted to a single immune checkpoint. Both inhibitory and stimulatory immune checkpoints continue to be discovered. Additionally, many receptors previously identified to play a role in tumor formation and progression are being found to have immunomodulatory components. The success of immunotherapy depends on maximizing pro-anti-tumor immunity while minimizing immunosuppressive signaling. Combining immune checkpoint targeted approaches with each other or with other receptor targets is a promising schema for future therapeutic regimen designs.

Current Options and Future Directions in Immune Therapy for Glioblastoma

Glioblastoma is in need of innovative treatment approaches. Immune therapy for cancer refers to the use of the body's immune system to target malignant cells in the body. Such immune therapeutics have recently been very successful in treating a diverse group of cancerous lesions. As a result, many new immune therapies have gained Food and Drug Administration approval for the treatment of cancer, and there has been an explosion in the study of immune therapeutics for cancer treatment over the past few years. However, the immune suppression of glioblastoma and the unique immune microenvironment of the brain make immune therapeutics more challenging to apply to the brain than to other systemic cancers. Here, we discuss the existing barriers to successful immune therapy for glioblastoma and the ongoing development of immune therapeutics. We will discuss the discovery and classification of immune suppressive factors in the glioblastoma microenvironment; the development of vaccine-based therapies; the use of convection-enhanced delivery to introduce tumoricidal viruses into the tumor microenvironment, leading to secondary immune responses; the emerging use of adoptive cell therapy in the treatment of glioblastoma; and future frontiers, such as the use of cerebral microdialysis for immune monitoring and the use of sequencing to develop patient-specific therapeutics. Armed with a better understanding of the challenges inherent in immune therapy for glioblastoma, we may soon see more successes in immune-based clinical trials for this deadly disease.

The role of myeloid-derived suppressor cells (MDSC) in the inflammaging process

A chronic low-grade inflammation is one of the hallmarks of the aging process. This gradually augmenting inflammatory state has been termed inflammaging. Inflammaging is associated with increased myelopoiesis in the bone marrow. This myelopoiesis-biased process increases the generation not only of mature myeloid cells, e.g. monocytes, macrophages, and neutrophils, but also immature myeloid progenitors and myeloid-derived suppressor cells (MDSCs). It is known that the aging process is associated with a significant increase in the presence of MDSCs in the bone marrow, blood, spleen, and peripheral lymph nodes. Consequently, MDSCs will become recruited into inflamed tissues where they suppress acute inflammatory responses and trigger the resolution of inflammation. However, if the perpetrator cannot be eliminated, the long-term presence of MDSCs suppresses the host's immune defence and increases the susceptibility to infections and tumorigenesis. Chronic immunosuppression also impairs the clearance of waste products and dead cells, impairs energy metabolism, and disturbs tissue proteostasis. This immunosuppressive state is reminiscent of the immunosenescence observed in inflammaging. It seems that proinflammatory changes in tissues with aging stimulate the myelopoietic production of MDSCs which subsequently induces immunosenescence and maintains the chronic inflammaging process. We will briefly describe the functions of MDSCs and then examine in detail how inflammaging enhances the generation MDSCs and how MDSCs are involved in the control of immunosenescence occurring in inflammaging.

Iron in the Tumor Microenvironment-Connecting the Dots

Iron metabolism and tumor biology are intimately linked. Iron facilitates the production of oxygen radicals, which may either result in iron-induced cell death, ferroptosis, or contribute to mutagenicity and malignant transformation. Once transformed, malignant cells require high amounts of iron for proliferation. In addition, iron has multiple regulatory effects on the immune system, thus affecting tumor surveillance by immune cells. For these reasons, inconsiderate iron supplementation in cancer patients has the potential of worsening disease course and outcome. On the other hand, chronic immune activation in the setting of malignancy alters systemic iron homeostasis and directs iron fluxes into myeloid cells. While this response aims at withdrawing iron from tumor cells, it may impair the effector functions of tumor-associated macrophages and will result in iron-restricted erythropoiesis and the development of anemia, subsequently. This review summarizes our current knowledge of the interconnections of iron homeostasis with cancer biology, discusses current clinical controversies in the treatment of anemia of cancer and focuses on the potential roles of iron in the solid tumor microenvironment, also speculating on yet unknown molecular mechanisms.

Myeloid-derived suppressor cells induce multiple myeloma cell survival by activating the AMPK pathway

Multiple Myeloma (MM) is an incurable malignancy of terminally differentiated plasma cells, which are predominantly localized in the bone marrow. Myeloid-derived suppressor cells (MDSC) are described to promote MM progression by immunosuppression and induction of angiogenesis. However, their direct role in drug resistance and tumor survival is still unknown. In this study, we performed co-culture experiments of myeloma cells with 5TMM derived MDSC in vitro, leading to increased survival and proliferation of MM cells. Co-culture experiments resulted in MDSC-induced AMPK phosphorylation in MM cells, which was associated with an increase in the anti-apoptotic factors MCL-1 and BCL-2, and the autophagy-marker LC3II. In addition, 5TMM cells inoculated in mice showed a clear upregulation of AMPK phosphorylation in vivo. Targeting the AMPK pathway by Compound C resulted in apoptosis of human myeloma cell lines, primary MM cells and 5TMM cells. Importantly, we observed that the tumor-promoting effect of MDSC was partially mediated by AMPK activation. In conclusion, our data clearly demonstrate that MDSC directly increase the survival of MM cells, partially through AMPK activation, identifying this pathway as a new target in the treatment of MM patients.

Stereotactic Radiosurgery and Immune Checkpoint Inhibitors in the Management of Brain Metastases

Brain metastases traditionally carried a poor prognosis with an overall survival of weeks to months in the absence of treatment. Radiation therapy modalities include whole brain radiation therapy (WBRT) and stereotactic radiosurgery (SRS). WBRT delivers a relatively low dose of radiation, has neurocognitive sequelae, and has not been investigated for its immunostimulatory effects. Furthermore, WBRT exposes the entire intracranial tumor immune microenvironment to radiation. SRS delivers a high dose of conformal radiation with image guidance to minimize dose to surrounding normal brain tissue, and appears to promote anti-tumor immunity. In parallel with many of these discoveries, immune checkpoint inhibitors (ICIs) have demonstrated a survival advantage in multiple malignancies commonly associated with brain metastases (e.g., melanoma). Combination SRS and ICI are theorized to be synergistic in anti-tumor immunity directed to brain metastases. The purpose of this review is to explore the synergy of SRS and ICIs, including pre-clinical data, existing clinical data, and ongoing prospective trials.

Improved Cancer Immunochemotherapy via Optimal Co-delivery of Chemotherapeutic and Immunomodulatory Agents

It is highly demanded and still a big challenge to develop an effective formulation for immunochemotherapy against advanced tumors. We have previously reported a PEG-NLG-based immunostimulatory nanocarrier (PEG_2k-Fmoc-NLG919) for co-delivery of an IDO1 inhibitor (NLG919) and a chemotherapeutic agent (paclitaxel, PTX). Although antitumor immune responses were enhanced with a PTX-loaded nanocarrier, the accumulation of myeloid-derived suppressor cells (MDSCs) was also significantly increased, which may limit the overall efficacy of therapy. In the present work, we developed an improved dual-functional nanocarrier (PEG_5k-Fmoc-NLG₂) to co-load PTX and sunitinib (SUN, a multitarget receptor tyrosine kinase inhibitor) for improved cancer immunochemotherapy. We found that the recruited MDSCs negatively impacted the overall antitumor activity of the PTX-loaded PEG-NLG nanocarrier. Mechanistic study suggests that this is likely attributed to the PTX-mediated induction of a number of chemokines that are involved in the recruitment of MDSCs. We have further shown that the induction of these chemokines was drastically blocked by SUN. Co-delivery of PTX and SUN via the PEG_5k-Fmoc-NLG919₂ nanocarrier led to a further improvement in the therapeutic efficacy with a concomitant reduction in MDSCs.

Colon cancer-derived conditioned medium induces differentiation of THP-1 monocytes into a mixed population of M1/M2 cells

Macrophages play an important role in the immune response and in the maintenance of tissue homeostasis. It is well known that many tumors recruit monocytes from circulation and influence their differentiation, mainly into suppressive M2-like subsets. Since there are contradictory data concerning the importance of macrophages for colon cancer progression, we used in our experiments four colon cancer cell lines representing different stages of tumor development (HT29, LS180, SW948, SW620). An acute monocytic leukemia cell line THP-1 was used as a human model of monocytes. Our work revealed that conditioned medium from the tumor cell lines induced activation and differentiation of THP-1 cells. The changes involved increased expression of CD68, a macrophage differentiation marker. Moreover, we also observed increased expression of CD206 and CD163, which are widely considered as markers of tumor-associated macrophages. The tumor-derived conditioned medium decreased the proliferation of THP-1 cells and blocked their cell cycle at the G1 stage. The tumor-conditioned medium also upregulated the production of several cytokines and chemokines characteristic of both M1 and M2 subsets and induced the expression of important pro-angiogenic factors, vascular endothelial growth factor, and matrix metalloproteinase-9 in THP-1 cells. Moreover, the tumor-conditioned medium induced the expression of galectin-3, which is implicated in malignant transformation, and indoleamine 2,3-dioxygenase, that is, a key enzyme of the kynurenine pathway. Our data suggest that tumor cells can actively influence the phenotype of monocytes and switch their differentiation into a population of non-adherent mixed M1 and M2 cells. These preliminary studies suggest that colon cancer cells produce soluble factors that influence monocyte differentiation, most probably into suppressive subsets. These data provide a better understanding of the influence of colon cancer on polarization of monocytes.

CD169 macrophages regulate immune responses toward particulate materials in the circulating fluid

Tissue macrophages comprise heterogeneous subsets that differ in localization, phenotype and ontogeny. They acquire tissue-specific phenotype in order to maintain normal tissue physiology. This review summarizes the current knowledge about the functions of CD169-positive macrophage subset residing in the lymphoid organs and intestinal tract. Strategically positioned at the interface between tissue and circulating fluid, CD169+ macrophages in the lymphoid organs capture blood- and lymph-borne particulate materials. Antigen information relayed by CD169+ macrophages to neighbouring immune cells is important for enhancement of antimicrobial and antitumour immunity as well as induction of tolerance. In the intestinal tract, CD169+ macrophages localize distantly from epithelial border. Following mucosal injury, they exacerbate inflammation by producing CCL8 that recruits inflammatory monocytes. As such, a better understanding of CD169+ macrophage phenotypes may enable the design of tissue-specific therapies for both immunological and non-immunological diseases.

Glatiramer Acetate Enhances Myeloid-Derived Suppressor Cell Function via Recognition of Paired Ig-like Receptor B

Glatiramer acetate (GA; Copaxone) is a copolymer therapeutic that is approved by the Food and Drug Administration for the relapsing-remitting form of multiple sclerosis. Despite an unclear mechanism of action, studies have shown that GA promotes protective Th2 immunity and stimulates release of cytokines that suppress autoimmunity. In this study, we demonstrate that GA interacts with murine paired Ig-like receptor B (PIR-B) on myeloid-derived suppressor cells and suppresses the STAT1/NF-κB pathways while promoting IL-10/TGF-β cytokine release. In inflammatory bowel disease models, GA enhanced myeloid-derived suppressor cell-dependent CD4⁺ regulatory T cell generation while reducing proinflammatory cytokine secretion. Human monocyte-derived macrophages responded to GA by reducing TNF-α production and promoting CD163 expression typical of alternative maturation despite the presence of GM-CSF. Furthermore, GA competitively interacts with leukocyte Ig-like receptors B (LILRBs), the human orthologs of PIR-B. Because GA limited proinflammatory activation of myeloid cells, therapeutics that target LILRBs represent novel treatment modalities for autoimmune indications.

TGF-β1 programmed myeloid-derived suppressor cells (MDSC) acquire immune-stimulating and tumor killing activity capable of rejecting established tumors in combination with radiotherapy

Cancer-induced myeloid-derived suppressor cells (MDSC) play an important role in tumor immune evasion. MDSC programming or polarization has been proposed as a strategy for leveraging the developmental plasticity of myeloid cells to reverse MDSC immune suppressive functions, or cause them to acquire anti-tumor activity. While MDSC derived ex vivo from murine bone marrow precursor cells with tumor-conditioned medium efficiently suppressed T cell proliferation, MDSC derived from conditioned medium in presence of TGF-β1 (TGFβ-MDSC) acquired a novel immune-stimulatory phenotype, losing the ability to inhibit T cell proliferation and acquiring enhanced antigen-presenting capability. Altered immune function was associated with SMAD-2 dependent upregulation of maturation and costimulatory molecules, and downregulation of inducible nitric oxide synthase (iNOS), an effector mechanism of immunosuppression. TGFβ-MDSC also upregulated FAS-ligand expression, leading to FAS-dependent killing of murine human papillomavirus (HPV)-associated head and neck cancer cells and tumor spheroids in vitro and anti-tumor activity in vivo. Radiation upregulated FAS expression on tumor cells, and the combination of radiotherapy and intratumoral injection of TGFβ-MDSC strongly enhanced class I expression on tumor cells and induction of HPV E7 tetramer-positive CD8 + T cells, leading to clearance of established tumors and long-term survival. TGFβ-MDSC derived from human PBMC with tumor conditioned medium also lost immunosuppressive function and acquired tumor-killing activity. Thus, TGFβ1 mediated programming of nascent MDSC leads to a potent anti-tumor phenotype potentially suitable for adoptive immunotherapy.

Intraperitoneal neutrophils activated by KRAS-induced ovarian cancer exert antitumor effects by modulating adaptive immunity

Increased neutrophil counts are a hallmark of a poor prognosis for cancer. We previously reported that KRAS promoted tumorigenesis and increased neutrophil counts in a mouse peritoneal cancer model. In the current study, we evaluated the role of increased neutrophils in cancer progression, as well as their influence on the intraperitoneal microenvironment. A mouse peritoneal cancer model was established using the KRAS-transduced mouse ovarian cancer cell line, ID8-KRAS. Neutrophil function was assessed by neutrophil depletion in ID8-KRAS mice. Neutrophil depletion markedly accelerated tumor formation; this was accompanied by an increase in interleukin-6 concentrations in ascites. Neutrophil depletion significantly decreased the amount of local and systemic CD8⁺ T cells, while increasing the amount of local CD4⁺ T cells, accompanied by an increased amount of monocytic myeloid-derived suppressor cells (M-MDSCs) and regulatory T cells (Tregs) (P<0.05). The roles of peritoneal neutrophils (PENs) in CD8⁺ T cell activation were assessed in vitro. PENs of ID8-KRAS mice had a strong potential to enhance T cell proliferation with a higher expression of the T cell costimulatory molecules OX40 ligand (OX40L) and 4-1BB ligand (4-1BBL), as compared with peripheral blood neutrophils (PBNs). These findings suggest that neutrophils recruited into the KRAS-induced tumor microenvironment (TME) have antitumor properties with the potential to modulate the numbers of M-MDSCs and Tregs and activate CD8⁺ T cells through T cell costimulatory molecules.

HDACi Delivery Reprograms Tumor-Infiltrating Myeloid Cells to Eliminate Antigen-Loss Variants

Immune recognition of tumor-expressed antigens by cytotoxic CD8+ T cells is the foundation of adoptive T cell therapy (ACT) and has been shown to elicit significant tumor regression. However, therapy-induced selective pressure can sculpt the antigenicity of tumors, resulting in outgrowth of variants that lose the target antigen. We demonstrate that tumor relapse from ACT and subsequent oncolytic viral vaccination can be prevented using class I HDACi, MS-275. Drug delivery subverted the phenotype of tumor-infiltrating CD11b+ Ly6Chi Ly6G- myeloid cells, favoring NOS2/ROS secretion and pro-inflammatory genes characteristic of M1 polarization. Simultaneously, MS-275 abrogated the immunosuppressive function of tumor-infiltrating myeloid cells and reprogrammed them to eliminate antigen-negative tumor cells in a caspase-dependent manner. Elevated IFN-γ within the tumor microenvironment suggests that MS-275 modulates the local cytokine landscape to favor antitumor myeloid polarization through the IFN-γR/STAT1 signaling axis. Exploiting tumor-infiltrating myeloid cell plasticity thus complements T cell therapy in targeting tumor heterogeneity and immune escape.

Myeloid-derived suppressor cells (MDSC): an important partner in cellular/tissue senescence

The aging process is associated with a low-grade chronic inflammation and the accumulation of senescent cells into tissues. Diverse stresses can trigger cellular senescence, a cell fate characterized by cell-cycle arrest and flat morphology. Oncogenic signaling can also induce cellular senescence which has been termed oncogene-induced senescence (OIS). Senescent cells display a pro-inflammatory phenotype which has been called the senescence-associated secretory phenotype (SASP). The secretomes associated with SASP contain colony-stimulating factors and chemokines which stimulate the generation of myeloid-derived suppressor cells (MDSC) by enhancing myelopoiesis in bone marrow and spleen. Enhanced myelopoiesis and increased level of MDSCs have been observed in bone marrow, spleen, and blood in both tumor-bearing and aged mice. Immunosuppressive MDSCs are recruited via chemotaxis into inflamed tissues where they proliferate and consequently suppress acute inflammatory reactions by inhibiting the functions of distinct components of innate and adaptive immunity. For instance, MDSCs stimulate the activity of immunosuppressive regulatory T-cells (Tregs). They also increase the expression of amino acid catabolizing enzymes and the secretion of anti-inflammatory cytokines, e.g. IL-10 and TGF-β, and reactive oxygen species (ROS). On the other hand, the accumulation of MDSCs into tissues exerts harmful effects in chronic pathological disorders, e.g. tumors and many age-related diseases, since the immunosuppression induced by MDSCs impairs the clearance of senescent and cancer cells and also disturbs the maintenance of energy metabolism and tissue proteostasis. The co-operation between senescent cells and immunosuppressive MDSCs regulates not only tumorigenesis and chronic inflammatory disorders but it also might promote inflammaging during the aging process.

Myeloid-Derived Suppressor Cells Hinder the Anti-Cancer Activity of Immune Checkpoint Inhibitors

Immune checkpoint inhibitors (ICI) used for cancer immunotherapy were shown to boost the existing anti-tumor immune response by preventing the inhibition of T cells by tumor cells. Antibodies targeting two negative immune checkpoint pathways, namely cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1), and programmed cell death-ligand 1 (PD-L1), have been approved first for patients with melanoma, squamous non-small cell lung cancer (NSCLC), and renal cell carcinoma. Clinical trials are ongoing to verify the efficiency of these antibodies for other cancer types and to evaluate strategies to block other checkpoint molecules. However, a number of patients do not respond to this treatment possibly due to profound immunosuppression, which is mediated partly by myeloid-derived suppressor cells (MDSC). This heterogeneous population of immature myeloid cells can strongly inhibit anti-tumor activities of T and NK cells and stimulate regulatory T cells (Treg), leading to tumor progression. Moreover, MDSC can contribute to patient resistance to immune checkpoint inhibition. Accumulating evidence demonstrates that the frequency and immunosuppressive function of MDSC in cancer patients can be used as a predictive marker for therapy response. This review focuses on the role of MDSC in immune checkpoint inhibition and provides an analysis of combination strategies for MDSC targeting together with ICI to improve their therapeutic efficiency in cancer patients.

CSF1R-dependent myeloid cells are required for NK‑mediated control of metastasis

Myeloid leukocytes are essentially involved in both tumor progression and control. We show that neo-adjuvant treatment of mice with an inhibitor of CSF1 receptor (CSF1R), a drug that is used to deplete tumor-associated macrophages, unexpectedly promoted metastasis. CSF1R blockade indirectly diminished the number of NK cells due to a paucity of myeloid cells that provide the survival factor IL-15 to NK cells. Reduction of the number of NK cells resulted in increased seeding of metastatic tumor cells to the lungs but did not impact on progression of established metastases. Supplementation of mice treated with CSF1R-inhibitor with IL-15 restored numbers of NK cells and diminished metastasis. Our data suggest that CSF1R blockade should be combined with administration of IL-15 to reduce the risk of metastasis.

Redirecting tumor-associated macrophages to become tumoricidal effectors as a novel strategy for cancer therapy

Cancer research in recent decades has highlighted the potential influence of the tumor microenvironment on the progression and metastasis of most known cancer types. Within the established microenvironment, tumor-associated macrophages (TAMs) are one of the most abundant and crucial non-neoplastic cell types. The polarization of macrophages into tumor-suppressive M1 or tumor-promoting M2 types is a fundamental event in the establishment of the tumor microenvironment. Although ample evidence indicates that TAMs are primarily M2 polarized, the mechanisms responsible for the regulation and maintenance of M1 and M2 polarization imbalance remain unclear. The manipulation of this critical axis through three main approaches may provide new strategies for cancer therapy - (I) specific interference with M2-like TAM survival or inhibiting their signaling cascades, (II) repression of macrophage recruitment to tumors, and (III) repolarization of tumor-promoting M2-like TAMs to a tumoricidal M1-like phenotype. This review summarizes current strategies for cancer intervention via manipulation of macrophage polarization, with particular focus on composition of the tumor microenvironment and its influence on cancer progression and metastasis. It is clear that additional fundamental and preclinical research is required to confirm the efficacy and practicality of this novel and promising strategy for treating cancer.

Functional macrophages and gastrointestinal disorders

Macrophages (MΦ) differentiate from blood monocytes and participate in innate and adaptive immunity. Because of their abilities to recognize pathogens and activate bactericidal activities, MΦ are always discovered at the site of immune defense. MΦ in the intestine are unique, such that in the healthy intestine, they possess complex mechanisms to protect the gut from inflammation. In these complex mechanisms, they produce anti-inflammatory cytokines, such as interleukin-10 and transforming growth factor-β, and inhibit the inflammatory pathways mediated by Toll-like receptors. It has been demonstrated that resident MΦ play a crucial role in maintaining intestinal homeostasis, and they can be recognized by their unique markers. Nonetheless, in the inflamed intestine, the function of MΦ will change because of environmental variation, which may be one of the mechanisms of inflammatory bowel disease (IBD). We provide further explanation about these mechanisms in our review. In addition, we review recent discoveries that MΦ may be involved in the development of gastrointestinal tumors. We will highlight the possible therapeutic targets for the management of IBD and gastrointestinal tumors, and we also discuss why more details are needed to fully understand all other effects of intestinal MΦ.

Myeloid cells expressing high level of CD45 are associated with a distinct activated phenotype in glioma

Glioblastoma multiforme is characterized by high accumulation of microglia/macrophages. The function of these tumor-infiltrating myeloid cells is not sufficiently elucidated. Therefore, a better understanding of the precise immune cell composition and function in brain tumors is required. In rodent glioma models, two different myeloid cell populations exist, determined by the expression level of CD45, namely CD11b⁺CD45^low and CD11b⁺CD45^high. Previous analyses of cytokine and marker expression profiles were almost exclusively performed on the entire myeloid cell fraction. Consequently, described pro- and anti-tumoral characteristics were not assigned to the evident subpopulations. In the present study, we used a syngeneic glioblastoma mouse model and subsequent flow cytometric analyses to demonstrate the distinct properties of CD11b⁺CD45^high and the CD11b⁺CD45^low cells. First, the majority of CD11b⁺CD45^high cells expressed high level of GR1 and around 6% of IL10 representing in part features of myeloid-derived suppressor cells, while the CD11b⁺CD45^low fraction displayed no upregulation of these molecules. Second, we detected that specifically the CD11b⁺CD45^high population showed antigen-presenting, co-stimulatory, and inflammatory features. Here, we identified up to 80% of MHCII and approximately 50% of CD86 and TNFα-expressing cells. Investigation of MHCI and CD80 revealed a moderate upregulation. By contrast, in the CD11b⁺CD45^low cell fraction, merely MHCII and TNFα were marginally overexpressed. In summary, these data emphasize the specific phenotype of CD11b⁺CD45^high cells in glioma with suppressive as well as pro-inflammatory characteristics whereas the CD11b⁺CD45^low cells were almost unaffected. Hence, primarily, the subpopulation consisting of CD45^high-expressing cells is activated by the tumor and should be considered as therapeutic target.

On the origin of myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) have a strong immunosuppressive character that allows them to regulate immune responses and hinder overt inflammatory responses. In cancer, this leads to tumor immune evasion and disease progression. MDSCs come in at least two forms: monocytic (Mo-MDSCs) and granulocytic (G-MDSCs). The classical definition of MDSCs as immature myeloid cells blocked from differentiating has been challenged by recent studies suggesting that Mo-MDSCs and G-MDSCs may represent monocytes and granulocytes that have acquired immunosuppressive properties. The molecular mechanism behind their generation and their true origins are now widely debated. In this review we discuss the different proposed mechanisms of the generation of both types of MDSCs, with a special focus on human MDSCs in cancer.

Targeting Myeloid-Derived Suppressor Cells to Bypass Tumor-Induced Immunosuppression

The immune system has many sophisticated mechanisms to balance an extensive immune response. Distinct immunosuppressive cells could protect from excessive tissue damage and autoimmune disorders. Tumor cells take an advantage of those immunosuppressive mechanisms and establish a strongly immunosuppressive tumor microenvironment (TME), which inhibits antitumor immune responses, supporting the disease progression. Myeloid-derived suppressor cells (MDSC) play a crucial role in this immunosuppressive TME. Those cells represent a heterogeneous population of immature myeloid cells with a strong immunosuppressive potential. They inhibit an antitumor reactivity of T cells and NK cells. Furthermore, they promote angiogenesis, establish pre-metastatic niches, and recruit other immunosuppressive cells such as regulatory T cells. Accumulating evidences demonstrated that the enrichment and activation of MDSC correlated with tumor progression, recurrence, and negative clinical outcome. In the last few years, various preclinical studies and clinical trials targeting MDSC showed promising results. In this review, we discuss different therapeutic approaches on MDSC targeting to overcome immunosuppressive TME and enhance the efficiency of current tumor immunotherapies.

Increasing the efficacy of radiotherapy by modulating the CCR2/CCR5 chemokine axes

Although radiotherapy (RT) is widely used to control tumor growth across many cancer types, there is a relatively high incidence of RT failure exhibited by tumor recurrence, therefore a clear need exists to achieve improved effectiveness of RT. The RT-elicited immune response largely impacts the efficacy of RT and includes immune cells that kill tumor cells, but also immunosuppressive cells, which dampen anti-tumor immunity. Using murine models in which syngeneic tumor cell lines (Colon38, Glioma261, Line1) are grown intramuscularly and treated with 15 Gy local RT, we assessed the effects of RT on both the systemic and intratumoral immune response. Here we demonstrate that RT stimulates increased production of two chemokines, CCL2 and CCL5, at the tumor site. Further, that this leads to increased CCR2+ CCR5+ monocytes in circulation and subsequently alters the intratumoral immune infiltrate favoring the largely immunosuppressive CCR2+ CCR5+ monocytes. Importantly, a CCR2/CCR5 antagonist administered daily (15 mg/kg subcutaneously) starting two days prior to RT reduces both circulating and intratumoral monocytes resulting in increased efficacy of RT in radioresponsive tumors. Overall, these data have important implications for the mechanism of RT and present a means to improve RT efficacy across many cancer types.

Loss of SOCS3 in myeloid cells prolongs survival in a syngeneic model of glioma

In glioma, microglia and macrophages are the largest population of tumor-infiltrating cells, referred to as glioma associated macrophages (GAMs). Herein, we sought to determine the role of Suppressor of Cytokine Signaling 3 (SOCS3), a negative regulator of Signal Transducer and Activator of Transcription 3 (STAT3), in GAM functionality in glioma. We utilized a conditional model in which SOCS3 deletion is restricted to the myeloid cell population. We found that SOCS3-deficient bone marrow-derived macrophages display enhanced and prolonged expression of pro-inflammatory M1 cytokines when exposed to glioma tumor cell conditioned medium in vitro. Moreover, we found that deletion of SOCS3 in the myeloid cell population delays intracranial tumor growth and increases survival of mice bearing orthotopic glioma tumors in vivo. Although intracranial tumors from mice with SOCS3-deficient myeloid cells appear histologically similar to control mice, we observed that loss of SOCS3 in myeloid cells results in decreased M2 polarized macrophage infiltration in the tumors. Furthermore, loss of SOCS3 in myeloid cells results in increased CD8+ T-cell and decreased regulatory T-cell infiltration in the tumors. These findings demonstrate a beneficial effect of M1 polarized macrophages on suppressing glioma tumor growth, and highlight the importance of immune cells in the tumor microenvironment.

New extracellular factors in glioblastoma multiforme development: neurotensin, growth differentiation factor-15, sphingosine-1-phosphate and cytomegalovirus infection

Recent years have seen considerable progress in understanding the biochemistry of cancer. For example, more significance is now assigned to the tumor microenvironment, especially with regard to intercellular signaling in the tumor niche which depends on many factors secreted by tumor cells. In addition, great progress has been made in understanding the influence of factors such as neurotensin, growth differentiation factor-15 (GDF-15), sphingosine-1-phosphate (S1P), and infection with cytomegalovirus (CMV) on the 'hallmarks of cancer' in glioblastoma multiforme. Therefore, in the present work we describe the influence of these factors on the proliferation and apoptosis of neoplastic cells, cancer stem cells, angiogenesis, migration and invasion, and cancer immune evasion in a glioblastoma multiforme tumor. In particular, we discuss the effect of neurotensin, GDF-15, S1P (including the drug FTY720), and infection with CMV on tumor-associated macrophages (TAM), microglial cells, neutrophil and regulatory T cells (T_reg), on the tumor microenvironment. In order to better understand the role of the aforementioned factors in tumoral processes, we outline the latest models of intratumoral heterogeneity in glioblastoma multiforme. Based on the most recent reports, we discuss the problems of multi-drug therapy in treating glioblastoma multiforme.

Grapefruit-derived nanovectors deliver miR-18a for treatment of liver metastasis of colon cancer by induction of M1 macrophages

Liver metastasis accounts for many of the cancer deaths in patients. Effective treatment for metastatic liver tumors is not available. Here, we provide evidence for the role of miR-18a in the induction of liver M1 (F4/80⁺interferon gamma (IFNγ)⁺IL-12⁺) macrophages. We found that miR-18a encapsulated in grapefruit-derived nanovector (GNV) mediated inhibition of liver metastasis that is dependent upon the induction of M1 (F4/80⁺IFNγ⁺IL-12⁺) macrophages; depletion of macrophages eliminated its anti-metastasis effect. Furthermore, the miR-18a mediated induction of macrophage IFNγ by targeting IRF2 is required for subsequent induction of IL-12. IL-12 then activates natural killer (NK) and natural killer T (NKT) cells for inhibition of liver metastasis of colon cancer. This conclusion is supported by the fact that knockout of IFNγ eliminates miR-18a mediated induction of IL-12, miR-18a treatment has an anti-metastatic effects in T cell deficient mice but there is no anti-metastatic effect on NK and NKT deficient mice. Co-delivery of miR-18a and siRNA IL-12 to macrophages did not result in activation of co-cultured NK and NKT cells. Taken together our results indicate that miR-18a can act as an inhibitor for liver metastasis through induction of M1 macrophages.

Human glioblastoma-associated microglia/monocytes express a distinct RNA profile compared to human control and murine samples

Glioblastoma (GBM) is the most aggressive brain tumor in adults. It is strongly infiltrated by microglia and peripheral monocytes that support tumor growth. In the present study we used RNA sequencing to compare the expression profile of CD11b(+) human glioblastoma-associated microglia/monocytes (hGAMs) to CD11b(+) microglia isolated from non-tumor samples. Hierarchical clustering and principal component analysis showed a clear separation of the two sample groups and we identified 334 significantly regulated genes in hGAMs. In comparison to human control microglia hGAMs upregulated genes associated with mitotic cell cycle, cell migration, cell adhesion, and extracellular matrix organization. We validated the expression of several genes associated with extracellular matrix organization in samples of human control microglia, hGAMs, and the hGAMs-depleted fraction via qPCR. The comparison to murine GAMs (mGAMs) showed that both cell populations share a significant fraction of upregulated transcripts compared with their respective controls. These genes were mostly related to mitotic cell cycle. However, in contrast to murine cells, human GAMs did not upregulate genes associated to immune activation. Comparison of human and murine GAMs expression data to several data sets of in vitro-activated human macrophages and murine microglia showed that, in contrast to mGAMs, hGAMs share a smaller overlap to these data sets in general and in particular to cells activated by proinflammatory stimulation with LPS + INFγ or TNFα. Our findings provide new insights into the biology of human glioblastoma-associated microglia/monocytes and give detailed information about the validity of murine experimental models. GLIA 2016 GLIA 2016;64:1416-1436.

Germline polymorphisms in myeloid-associated genes are not associated with survival in glioma patients

Immune cells of myeloid origin, including microglia, macrophages, and myeloid-derived suppressor cells adopt immunosuppressive phenotypes that support gliomagenesis. Here, we tested an a priori hypothesis that single nucleotide polymorphisms (SNPs) in genes related to glioma-associated myeloid cell regulation and function are also associated with patient survival after glioma diagnosis. Subjects for this study were 992 glioma patients treated at The University of Texas MD Anderson Cancer Center in Houston, Texas between 1992 and 2008. Haplotype-tagging SNPs in 91 myeloid-associated genes were analyzed for association with survival by Cox regression. Individual SNP- and gene-based tests were performed separately in glioblastoma (WHO grade IV, n = 511) and lower-grade glioma (WHO grade II-III, n = 481) groups. After adjustment for multiple testing, no myeloid-associated gene variants were significantly associated with survival in glioblastoma. Two SNPs, rs147960238 in CD163 (p = 2.2 × 10-5) and rs17138945 in MET (p = 5.6 × 10-5) were significantly associated with survival of patients with lower-grade glioma. However, these associations were not confirmed in an independent analysis of 563 lower-grade glioma cases from the University of California at San Francisco Adult Glioma Study (p = 0.65 and p = 0.41, respectively). The results of this study do not support a role for inherited polymorphisms in myeloid-associated genes in affecting survival of patients diagnosed with glioblastoma or lower-grade glioma.

BAMBI promotes macrophage proliferation and differentiation in gliomas

The present study investigated the capacity of Bone morphogenic protein and activin membrane‑bound inhibitor homolog (BAMBI) to regulate the migration and differentiation of macrophages in gliomas. Using a migration assay, it was determined that BAMBI stimulated monocytes migration in a dose‑dependent effect. When induced by phorbol myristate acetate (PMA) the monocytes differentiated into macrophages, and BAMBI also increased the migration of PMA‑induced macrophages compared with control cells. The expression of CD68 and BAMBI protein and mRNA in glioma and normal specimens were detected using immunohistochemistry and reverse transcription‑quantitative polymerase chain reaction, respectively. The localization of BAMBI was primarily in macrophages, as demonstrated by staining for the macrophage marker CD68, and the mRNA expression of CD68 and BAMBI were higher in gliomas compared to normal tissues. In addition, the mRNA expression of CD68 and BAMBI were positively correlated (R2=0.64). After treatment with 50 nM PMA and 10 nM BAMBI for 48 h, RAW 264.7 macrophages were exhibited dendrite‑like morphology, indicating that the co‑treatment promoted the differentiation of monocytes to macrophages. The expression of specific markers of M1 [inducible nitric oxide synthase (iNOS) and interleukin (IL)-12] and M2 (IL-10 and arginase 1) type macrophages was determined following 10 nM BAMBI treatment. BAMBI promoted the expression of M1 markers, whereas the M2 markers were not affected, which indicated that BAMBI induced differentiation of M1 type macrophages. These results indicate that BAMBI may be involved in macrophage differentiation in gliomas.

The Peritoneal Macrophages in Inflammatory Diseases and Abdominal Cancers

Peritoneal macrophages (PMs) are the major cell type of peritoneal cells that participate in multiple aspects of innate and acquired immunity in the peritoneal cavity. PMs have an ability to release a large amount of proinflammatory and anti-inflammatory cytokines and therefore play a critical role in regulating the differentiation of innate immune cells and inflammatory T cells. Accumulating studies demonstrate that the immunological reactions and inflammatory responses of PMs are strongly related to the pathogenic processes of various inflammatory diseases and abdominal cancers. Consequently, the regulation of PM activation has gradually emerged as a promising target for immunotherapy, and better understanding of the distinctly biological function of PMs in individual diseases is crucial for designing specific and effective therapeutic agents. This review covers the characterization and immunological function of PMs in hosts with inflammatory diseases and abdominal cancers.

The increase in circulating myeloid-derived suppressor cells correlated with clinical stage of cervical carcinoma

The myeloid-derived suppressor cells (MDSCs) are important tumor-induced immune suppression cells which have gained great attention in recent years. In this study, the levels of MDSCs in peripheral blood of cervical carcinoma (CC) patients, cervical intraepithelial neoplastic (CIN) patients, and healthy donors were analyzed by flow cytometry. It was shown that the proportion of circulating MDSCs was elevated in CC and CIN patients compared to that in healthy donor (HD). Further analyses revealed that the percentage of MDSCs is increased along with the stage of CC, but has no difference among other clinicopathological factors, including age, tumor grade, lymph node invasion, and histopathology. Taken together, our results suggested that MDSC levels are indicative of suppressive functions within the tumor environment of CC. Therefore, large validation studies could help to develop new immunotherapeutic strategies for CC patients by inhibiting or eliminating MDSC functions.

Two is better than one: advances in pathogen-boosted immunotherapy and adoptive T-cell therapy

The recent tremendous successes in clinical trials take cancer immunotherapy into a new era and have attracted major attention from both academia and industry. Among the variety of immunotherapy strategies developed to boost patients' own immune systems to fight against malignant cells, the pathogen-based and adoptive cell transfer therapies have shown the most promise for treating multiple types of cancer. Pathogen-based therapies could either break the immune tolerance to enhance the effectiveness of cancer vaccines or directly infect and kill cancer cells. Adoptive cell transfer can induce a strong durable antitumor response, with recent advances including engineering dual specificity into T cells to recognize multiple antigens and improving the metabolic fitness of transferred cells. In this review, we focus on the recent prospects in these two areas and summarize some ongoing studies that represent potential advancements for anticancer immunotherapy, including testing combinations of these two strategies.

Myeloid-derived suppressor cell and macrophage exert distinct angiogenic and immunosuppressive effects in breast cancer

The immunosuppressive tumor microenvironment is a key obstacle to hinder a cancer immunotherapy. Myeloid-derived suppressor cells (MDSCs) have been considered as a major player in immunosuppression. In this study, we find that tumor-infiltrating MDSCs (tiMDSCs) are less immunosuppressive than tumor-associated macrophages (TAMs) in multiple murine orthotopic breast tumor models. Compared to TAMs, tiMDSCs produce higher levels of pro-inflammatory factors and lower levels of anti-inflammatory factors. Furthermore, tiMDSCs are preferentially located in hypoxic areas and are more pro-angiogenic than TAMs. Consistent with these functional disparities, a shift from tiMDSCs to TAMs is observed during the progression of breast cancer. Moreover, infiltration of tiMDSCs is also noted in distal colonization of breast cancer cells in the lung. Taken together, our findings indicate that tiMDSCs are more pro-angiogenic and promote tumor initiation, while TAMs are more immunosuppressive and facilitate tumor immune evasion. This study suggests that selectively targeting on TAMs could alleviate the immunosuppressive tumor microenvironment and potentiate cancer immunotherapy.

Prognostic significance of tumor-associated macrophages in ovarian cancer: A meta-analysis

OBJECTIVE

The role of tumor-associated macrophages (TAMs) in tumor microenvironment remains controversial due to the two different polarized subsets of TAMs. Here, we performed a meta-analysis to evaluate the correlation between subpopulations of TAMs and clinical outcomes in patients with ovarian cancer.

METHODS

A comprehensive search in PUBMED/Medline and EMBASE databases was performed. The association between TAMs and patient prognosis of ovarian cancer was estimated with hazard ratios (HRs) and their corresponding 95% confidence intervals (95% CIs) using a random-effect model. Additionally, sensitivity analysis and Begg's test were conducted.

RESULTS

Nine studies including 794 patients were enrolled in the meta-analysis. The results showed that higher M1/M2 ratio in tumor tissues was associated with a favorable overall survival (OS) (HR=0.449, 95% CI=0.283-0.712, P=0.001). Elevated intra-islet M1/M2 TAMs ratio showed a positive correlation for OS (HR=0.510, 95% CI=0.264-0.986, P=0.045). No significant relation was observed between OS and CD68+ TAMs (HR=0.99, 95% CI=0.88-1.11, P=0.859), CD163+ TAMs (HR=1.04, 95% CI=0.92-1.16, P=0.544) or CD163+/CD68+ TAMs ratio (HR=1.628, 95% CI=0.529-5.008, P=0.395). Worse progression-free survival (PFS) was associated with high density of CD163+ TAMs (HR=2.157, 95% CI=1.406-3.312, P=0.000) and higher ratio of CD163+/CD68+ TAMs (HR=3.223, 95% CI=1.805-5.755, P=0.000). Elevated M1/M2 TAMs ratio predicted better PFS of ovarian cancer (HR=0.490, 95% CI=0.270-0.890, P=0.019). Furthermore, high density of CD163+ and CD68+ TAMs was observed in ovarian cancer with advanced TNM stage.

CONCLUSION

In our study, it was revealed that CD163+ TAMs infiltration was associated with poor prognosis of ovarian cancer and high M1/M2 macrophages ratio in tumor tissues predicted better prognosis.

Tumor-Induced Myeloid-Derived Suppressor Cells

Myeloid-derived suppressor cells (MDSCs) represent a heterogeneous, immune-suppressive leukocyte population that develops systemically and infiltrates tumors. MDSCs can restrain the immune response through different mechanisms including essential metabolite consumption, reactive oxygen and nitrogen species production, as well as display of inhibitory surface molecules that alter T-cell trafficking and viability. Moreover, MDSCs play a role in tumor progression, acting directly on tumor cells and promoting cancer stemness, angiogenesis, stroma deposition, epithelial-to-mesenchymal transition, and metastasis formation. Many biological and pharmaceutical drugs affect MDSC expansion and functions in preclinical tumor models and patients, often reversing host immune dysfunctions and allowing a more effective tumor immunotherapy.

G Protein-Coupled Receptors in Macrophages

As the largest receptor gene family in the human genome, with >800 members, the signal-transducing G protein-coupled receptors (GPCRs) play critical roles in nearly all conceivable physiological processes, ranging from the sensing of photons and odorants to metabolic homeostasis and migration of leukocytes. Unfortunately, an exhaustive review of the several hundred GPCRs expressed by myeloid cells/macrophages (P.J. Groot-Kormelink, L .Fawcett, P.D. Wright, M. Gosling, and T.C. Kent, BMC Immunol 12:57, 2012, doi:10.1186/1471-2172-13-57) is beyond the scope of this chapter; however, we will endeavor to cover the GPCRs that contribute to the major facets of macrophage biology, i.e., those whose expression is restricted to macrophages and the GPCRs involved in macrophage differentiation/polarization, microbial elimination, inflammation and resolution, and macrophage-mediated pathology. The chemokine receptors, a major group of myeloid GPCRs, will not be extensively covered as they are comprehensively reviewed elsewhere.

Participation of Tumor-Associated Myeloid Cells in Progression of Amelanotic Melanoma (RMM Tumor Line) in F344 Rats, with Particular Reference to MHC Class II- and CD163-Expressing Cells

Tumor progression is often influenced by infiltration of myeloid cells; depending on the M1- or M2-like activation status, these cells may have either inhibitory or promoting effects on tumor growth. We investigated the properties of tumor-associated myeloid cells in a previously established homotransplantable amelanotic melanoma (RMM tumor line) in F344 rats. RMM tumor nodules were allowed to reach the sizes of 0.5, 1, 2 and 3 cm, respectively. Immunohistochemistry and flow cytometry was performed for macrophage markers CD68 and CD163, and for the antigen-presenting cell marker, MHC class II. Although no significant change was observed in the number of CD68⁺ and CD163⁺ macrophages during RMM progression, the number of MHC class II⁺ antigen-presenting cells was reduced in 3 cm nodules. Real-time RT-PCR of laser microdissection samples obtained from RMM regions rich in MHC class II⁺ cells demonstrated high expressions of M1-like factors: IFN-γ, GM-CSF and IL-12a. Furthermore, fluorescence-activated cell sorting, followed by real-time RT-PCR for CD11b⁺ MHC class II⁺ (myeloid antigen-presenting cells), CD11b⁺ CD163⁺ (M2 type myeloid cells), CD11b⁺ CD80⁺ (M1 type myeloid cells) and CD11b⁺ CD11c⁺ (dendritic cells) cells was performed. Based on the levels of inflammation- and tumor progression-related factors, MHC class II⁺ antigen-presenting cells showed polarization towards M1, while CD163⁺ macrophages, towards M2. CD80⁺ and CD11c⁺ myeloid cells did not show clear functional polarization. Our results provide novel information on tumor-associated myeloid cells in amelanotic melanoma, and may become useful in further research on melanoma immunity.

Engineering challenges for brain tumor immunotherapy

Malignant brain tumors represent one of the most devastating forms of cancer with abject survival rates that have not changed in the past 60years. This is partly because the brain is a critical organ, and poses unique anatomical, physiological, and immunological barriers. The unique interplay of these barriers also provides an opportunity for creative engineering solutions. Cancer immunotherapy, a means of harnessing the host immune system for anti-tumor efficacy, is becoming a standard approach for treating many cancers. However, its use in brain tumors is not widespread. This review discusses the current approaches, and hurdles to these approaches in treating brain tumors, with a focus on immunotherapies. We identify critical barriers to immunoengineering brain tumor therapies and discuss possible solutions to these challenges.