The Yin and Yang of Myeloid Derived Suppressor Cells

The Role of Myeloid-Derived Suppressor Cells in Multiple Sclerosis and Its Animal Model

Myeloid-derived suppressor cells (MDSCs), a heterogeneous cell population that consists of mostly immature myeloid cells, are immunoregulatory cells mainly characterized by their suppressive functions. Emerging findings have revealed the involvement of MDSCs in multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). MS is an autoimmune and degenerative disease of the central nervous system characterized by demyelination, axon loss, and inflammation. Studies have reported accumulation of MDSCs in inflamed tissues and lymphoid organs of MS patients and EAE mice, and these cells display dual functions in EAE. However, the contribution of MDSCs to MS/EAE pathogenesis remains unclear. This review aims to summarize our current understanding of MDSC subsets and their possible roles in MS/EAE pathogenesis. We also discuss the potential utility and associated obstacles in employing MDSCs as biomarkers and cell-based therapies for MS.

Immunomodulatory actions of myeloid-derived suppressor cells in the context of innate immunity

Myeloid-derived suppressor cells (MDSCs) are notable innate immune cells, which are further divided into two subpopulations, i.e., monocytic and granulocytic. These cells are traditionally considered to mainly suppress the T-cell responses. However, more updated data indicate that their properties are rather immunomodulatory than solely immunosuppressive. Indeed, MDSCs display extensive crosstalk with other either innate or adaptive immune cells, and, according to the situation under which they are triggered, they may enhance or attenuate the immune response. However, their positive role in host's defense mechanisms under specific conditions is rarely discussed in the literature. In this mini-review, the authors briefly summarise the mechanisms of action of MDSCs under distinct conditions, such as infections and malignancies, with a particular emphasis on their role as components of the innate immunity system.

Functions of LncRNAs, exosomes derived MSCs and immune regulatory molecules in preeclampsia disease

Modulatory signaling pathway such as T cell immunoreceptor with Ig and ITIM domains (TIGIT), Cytotoxic T-Lymphocyte Associated Protein 4 (CTLA-4), P53 signaling and TIM (T-cell immunoglobin and mucin domain) are important in normal pregnancy and loss of their functions or dysregulation of related genes can lead to some disorders. Inflammation is a process by which your body's white blood cells and the things they make protect you from infection from outside invaders, such as bacteria and viruses. Some cellular and molecular signaling have been categorized to demonstrate the mechanism that protects tolerance to antigens. lncRNAs significantly impact physiological processes like immunity and metabolism, and are linked to tumors, cardiovascular diseases, nervous system disorders, and nephropathy.In this review article, we summarized recent studies about the role of TIGIT, CTLA-4, P53 and TIM regulatory molecules and reviewed dysregulation of these pathway in diseases.We will also talk about the role of lncRNAs and mesenchymal stem cells.

The recent progress of myeloid-derived suppressor cell and its targeted therapies in cancers

Myeloid-derived suppressor cells (MDSCs) are an immature group of myeloid-derived cells generated from myeloid cell precursors in the bone marrow. MDSCs appear almost exclusively in pathological conditions, such as tumor progression and various inflammatory diseases. The leading function of MDSCs is their immunosuppressive ability, which plays a crucial role in tumor progression and metastasis through their immunosuppressive effects. Since MDSCs have specific molecular features, and only a tiny amount exists in physiological conditions, MDSC-targeted therapy has become a promising research direction for tumor treatment with minimal side effects. In this review, we briefly introduce the classification, generation and maturation process, and features of MDSCs, and detail their functions under various circumstances. The present review specifically demonstrates the environmental specificity of MDSCs, highlighting the differences between MDSCs from cancer and healthy individuals, as well as tumor-infiltrating MDSCs and circulating MDSCs. Then, we further describe recent advances in MDSC-targeted therapies. The existing and potential targeted drugs are divided into three categories, monoclonal antibodies, small-molecular inhibitors, and peptides. Their targeting mechanisms and characteristics have been summarized respectively. We believe that a comprehensive in-depth understanding of MDSC-targeted therapy could provide more possibilities for the treatment of cancer.

T-cell dysfunction in natural killer/T-cell lymphoma

Natural killer/T-cell lymphoma (NKTCL) is an incurable aggressive T-cell lymphoma closely correlated with Epstein‒Barr virus (EBV) infection. Chronic and consistent viral infection induces T-cell exhaustion. Herein, we describe T-cell dysfunction in NKTCL patients for the first time. Peripheral blood mononuclear cells (PBMCs) from age-matched healthy donors (HDs) and NKTCL patients were collected, and lymphocyte distributions, multiple surface inhibitory receptors (IRs), effector cytokine production and cell proliferation were determined by flow cytometry. PBMCs from HDs were cocultured with NKTCL cell lines to verify the clinical findings. IR expression was further assessed in NKTCL tumor biopsies using multiplex immunohistochemistry (mIHC). NKTCL patients have higher frequencies than HDs of inhibitory T regulatory cells (Tregs) and myeloid-derived suppressor cells (MDSCs). T-cell distribution also varies between NKTCL patients and HDs. T cells from NKTCL patients demonstrated higher expression levels of multiple IRs than HDs. Meanwhile, T-cell proliferation and interferon-γ production was significantly reduced in NKTCL patients. More importantly, the number of EBV-specific cytotoxic cells was lower in NTKCL patients, and these cells demonstrated upregulation of multiple IRs and secreted fewer effector cytokines. Interestingly, NKTCL cells caused normal PBMCs to acquire T-cell exhaustion phenotypes and induced generation of Tregs and MDSCs. In line with ex vivo finding, mIHC results showed that CD8+ T cells from NKTCL tumor biopsies expressed much higher level of IRs compared with reactive lymphoid hyperplasia individuals. The immune microenvironment of NKTCL patients exhibited T-cell dysfunction and accumulation of inhibitory cell components, which may contribute to impaired antitumor immunity.

Myeloid-derived suppressor cells: Are they involved in gestational diabetes mellitus?

Gestational diabetes mellitus (GDM) is currently the most common metabolic complication during pregnancy, with an increasing prevalence worldwide. Maternal immune dysregulation might be partly responsible for the pathophysiology of GDM. Myeloid derived suppressor cells (MDSCs) are a heterogeneous population of cells, emerging as a new immune regulator with potent immunosuppressive capacity. Although the fate and function of these cells were primarily described in pathological conditions such as cancer and infection, accumulating evidences have spotlighted their beneficial roles in homeostasis and physiological conditions. Recently, several studies have explored the roles of MDSCs in the diabetic microenvironment. However, the fate and function of these cells in GDM are still unknown. The current review summarized the existing knowledges about MDSCs and their potential roles in diabetes during pregnancy in an attempt to highlight our current understanding of GDM-related immune dysregulation and identify areas where further study is required.

Peripheral expansion of myeloid-derived suppressor cells is related to disease activity and damage accrual in inflammatory myopathies

OBJECTIVE

To assess the proportion of myeloid-derived suppressor cells (MDSCs), their expression of arginase-1 and programmed cell death ligand 1 (PD-L1) and their relationship with the clinical phenotype of patients with idiopathic inflammatory myopathies (IIMs).

METHODS

We recruited 37 IIM adult patients and 10 healthy donors in Mexico City. We evaluated their clinical features, the proportion of MDSCs and their expression of PD-L1 and arginase-1 by flow cytometry. Polymorphonuclear (PMN)-MDSCs were defined as CD33dim, CD11b+ and CD66b+ while monocytic (M)-MDSCs were CD33+, CD11b+, HLA-DR- and CD14+. Serum cytokines were analysed with a multiplex assay. We compared the quantitative variables with the Kruskal-Wallis and Mann-Whitney U tests and assessed correlations with Spearman's ρ.

RESULTS

Most patients had dermatomyositis [n = 30 (81.0%)]. IIM patients had a peripheral expansion of PMN-MDSCs and M-MDSCs with an enhanced expression of arginase-1 and PD-L1. Patients with active disease had a decreased percentage {median 1.75% [interquartile range (IQR) 0.31-5.50 vs 10.71 [3.16-15.58], P = 0.011} of M-MDSCs and a higher absolute number of PD-L1+ M-MDSCs [median 23.21 cells/mm3 (IQR 11.16-148.9) vs 5.95 (4.66-102.7), P = 0.046] with increased expression of PD-L1 [median 3136 arbitrary units (IQR 2258-4992) vs 1961 (1885-2335), P = 0.038]. PD-L1 expression in PMN-MDSCs correlated with the visual analogue scale of pulmonary disease activity (r = 0.34, P = 0.040) and damage (r = 0.36, P = 0.031), serum IL-5 (r = 0.55, P = 0.003), IL-6 (r = 0.46, P = 0.003), IL-8 (r = 0.53, P = 0.018), IL-10 (r = 0.48, P = 0.005) and GM-CSF (r = 0.48, P = 0.012). M-MDSCs negatively correlated with the skeletal Myositis Intention to Treat Index (r = -0.34, P = 0.038) and positively with IL-6 (r = 0.40, P = 0.045).

CONCLUSION

MDSCs expressing arginase-1 and PD-L1 are expanded in IIM and correlate with disease activity, damage accrual and serum cytokines.

Myeloidderived suppressor cells: Escorts at the maternal-fetal interface

Myeloid-derived suppressor cells (MDSCs) are a novel heterogenous group of immunosuppressive cells derived from myeloid progenitors. Their role is well known in tumors and autoimmune diseases. In recent years, the role and function of MDSCs during reproduction have attracted increasing attention. Improving the understanding of their strong association with recurrent implantation failure, pathological pregnancy, and neonatal health has become a focus area in research. In this review, we focus on the interaction between MDSCs and other cell types (immune and non-immune cells) from embryo implantation to postpartum. Furthermore, we discuss the molecular mechanisms that could facilitate the therapeutic targeting of MDSCs. Therefore, this review intends to encourage further research in the field of maternal-fetal interface immunity in order to identify probable pathways driving the accumulation of MDSCs and to effectively target their ability to promote embryo implantation, reduce pathological pregnancy, and increase neonatal health.

The Function and Therapeutic Implications of TNF Signaling in MDSCs

Myeloid-derived suppressor cells (MDSCs) are a group of immature and heterogeneous myeloid cells with immunosuppressive functions. MDSCs play important roles in the pathogenesis of cancer, chronic inflammatory diseases, and many autoimmune disorders. The accumulation and activation of MDSCs can be regulated by tumor necrosis factor α (TNF-α). In this review, we summarize the roles played by TNF-α in the recruitment, immunosuppressive functions, and chemotaxis of MDSCs, and discuss the potential therapeutic effects of TNF-α upon these cells in tumor growth and some inflammatory disorders.

New Perspectives on Myeloid-Derived Suppressor Cells and Their Emerging Role in Haematology

Myeloid-derived suppressor cells (MDSCs) are immature cells of myeloid origin that have gained researchers’ attention, as they constitute promising biomarkers and targets for novel therapeutic strategies (i.e., blockage of development, differentiation, depletion, and deactivation) in several conditions, including neoplastic, autoimmune, infective, and inflammatory diseases, as well as pregnancy, obesity, and graft rejection. They are characterised in humans by the typical immunophenotype of CD11b⁺CD33⁺HLA-DR^–/low and immune-modulating properties leading to decreased T-cell proliferation, induction of T-regulatory cells (T-regs), hindering of natural killer (NK) cell functionality, and macrophage M2-polarisation. The research in the field is challenging, as there are still difficulties in defining cell-surface markers and gating strategies that uniquely identify the different populations of MDSCs, and the currently available functional assays are highly demanding. There is evidence that MDSCs display altered frequency and/or functionality and could be targeted in immune-mediated and malignant haematologic diseases, although there is a large variability of techniques and results between different laboratories. This review presents the current literature concerning MDSCs in a clinical point of view in an attempt to trigger future investigation by serving as a guide to the clinical haematologist in order to apply them in the context of precision medicine as well as the researcher in the field of experimental haematology.

Potential of chimeric antigen receptor (CAR)-redirected immune cells in breast cancer therapies: Recent advances

Despite substantial developments in conventional treatments such as surgery, chemotherapy, radiotherapy, endocrine therapy, and molecular-targeted therapy, breast cancer remains the leading cause of cancer mortality in women. Currently, chimeric antigen receptor (CAR)-redirected immune cell therapy has emerged as an innovative immunotherapeutic approach to ameliorate survival rates of breast cancer patients by eliciting cytotoxic activity against cognate tumour-associated antigens expressing tumour cells. As a crucial component of adaptive immunity, T cells and NK cells, as the central innate immune cells, are two types of pivotal candidates for CAR engineering in treating solid malignancies. However, the biological distinctions between NK cells- and T cells lead to differences in cancer immunotherapy outcomes. Likewise, optimal breast cancer removal via CAR-redirected immune cells requires detecting safe target antigens, improving CAR structure for ideal immune cell functions, promoting CAR-redirected immune cells filtration to the tumour microenvironment (TME), and increasing the ability of these engineered cells to persist and retain within the immunosuppressive TME. This review provides a concise overview of breast cancer pathogenesis and its hostile TME. We focus on the CAR-T and CAR-NK cells and discuss their significant differences. Finally, we deliver a summary based on recent advancements in the therapeutic capability of CAR-T and CAR-NK cells in treating breast cancer.

The role of pyroptosis in modulating the tumor immune microenvironment

The tumor immune microenvironment (TIME) plays a key role in immunosuppression in cancer, which results in tumorigenesis and tumor progression, and contributes to insensitivity to chemotherapy and immunotherapy. Understanding the mechanism of TIME formation is critical for overcoming cancer. Pyroptosis exerts a dual role in modulating the TIME. In this review, we summarize the regulatory mechanisms of pyroptosis in modulating the TIME and the potential application of targeted pyroptosis therapy in the clinic. Several treatments targeting pyroptosis have been developed; however, the majority of treatments are still in preclinical studies. Only a few agents have been used in clinic, but the outcomes are unsatisfactory. More studies are necessary to determine the role of pyroptosis in cancer, and more research is required to realize the application of treatments targeting pyroptosis in the clinic.

Myeloid Derived Suppressor Cells Migrate in Response to Flow and Lymphatic Endothelial Cell Interaction in the Breast Tumor Microenvironment

At the site of the tumor, myeloid derived suppressor cells (MDSCs) infiltrate and interact with elements of the tumor microenvironment in complex ways. Within the invading tumor, MDSCs are exposed to interstitial fluid flow (IFF) that exists within the chronic inflammatory tumor microenvironment at the tumor-lymphatic interface. As drivers of cell migration and invasion, the link between interstitial fluid flow, lymphatics, and MDSCs have not been clearly established. Here, we hypothesized that interstitial fluid flow and cells within the breast tumor microenvironment modulate migration of MDSCs. We developed a novel 3D model to mimic the breast tumor microenvironment and incorporated MDSCs harvested from 4T1-tumor bearing mice. Using live imaging, we found that sorted GR1+ splenocytes had reduced chemotactic index compared to the unsorted population, but their speed and displacement were similar. Using our adapted tissue culture insert assay, we show that interstitial fluid flow promotes MDSC invasion, regardless of absence or presence of tumor cells. Coordinating with lymphatic endothelial cells, interstitial fluid flow further enhanced invasion of MDSCs in the presence of 4T1 cells. We also show that VEGFR3 inhibition reduced both MDSC and 4T1 flow response. Together, these findings indicate a key role of interstitial fluid flow in MDSC migration as well as describe a tool to explore the immune microenvironment in breast cancer.

Myeloid-Derived Suppressor Cells (MDSC) in the Umbilical Cord Blood: Biological Significance and Possible Therapeutic Applications

Myeloid-derived suppressor cells (MDSCs) represent a heterogeneous population of myeloid cells that suppress immune responses in cancer, infection, and trauma. They mainly act by inhibiting T-cells, natural-killer cells, and dendritic cells, and also by inducing T-regulatory cells, and modulating macrophages. Although they are mostly associated with adverse prognosis of the underlying disease entity, they may display positive effects in specific situations, such as in allogeneic hematopoietic stem cell transplantation (HSCT), where they suppress graft-versus-host disease (GVHD). They also contribute to the feto-maternal tolerance, and in the fetus growth process, whereas several pregnancy complications have been associated with their defects. Human umbilical cord blood (UCB) is a source rich in MDSCs and their myeloid progenitor cells. Recently, a number of studies have investigated the generation, isolation, and expansion of UCB-MDSCs for potential clinical application associated with their immunosuppressive properties, such as GVHD, and autoimmune and inflammatory diseases. Given that a significant proportion of UCB units in cord blood banks are not suitable for clinical use in HSCT, they might be used as a significant source of MDSCs for research and clinical purposes. The current review summarizes the roles of MDSCs in the UCB, as well as their promising applications.

Chronic stress promotes breast carcinoma metastasis by accumulating myeloid-derived suppressor cells through activating β-adrenergic signaling

Numerous studies have found that chronic stress could promote tumor progression and this may be related to inhibtion of immune system. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells with immunosuppressive activity. MDSCs may represent a key link between chronic stress and tumor progression. However, the role of stress-induced MDSCs in breast cancer progression is unclear. The present study showed that pre-exposure of chronic stress could lead to MDSCs elevation and facilitated breast cancer metastasis in tumor-bearing mice. Adoptive transfer of MDSCs could significantly increase lung metastatic foci. In contrast, lung metastasis could be alleviated by depleting endogenous MDSCs with Gr-1 antibody. The concentration of norepinephrine in serum and the expression of tyrosine hydroxylase in bone marrow could be significantly elevated by chronic stress. Moreover, propranolol, an inhibitor of β-adrenergic signaling, could inhibit breast carcinoma metastasis and prevent the expansion of chronic stress-induced MDSCs. Further study revealed that the expressions of IL-6 and JAK/STAT3 signaling pathways were upregulated by chronic stress in mice, and this upregulation could be inhibited by propranolol. Blocking the IL-6 signal or inhibiting the activation of the JAK/STAT3 signaling pathway could reduce tumor growth and metastasis by attenuating the accumulation of MDSCs in vivo. Besides, propranolol inhibited the expression of IL-6 in supernatant of 4T1 cells induced by isoproterenol and reduced the proportion of inducible MDSCs in vitro. Taken together, these data indicated that chronic stress may accumulate MDSCs via activation of β-adrenergic signaling and IL-6/STAT3 pathway, thereby promoting breast carcinoma metastasis.

Postoperative Natural Killer Cell Dysfunction: The Prime Suspect in the Case of Metastasis Following Curative Cancer Surgery

Surgical resection is the foundation for the curative treatment of solid tumors. However, metastatic recurrence due to the difficulty in eradicating micrometastases remain a feared outcome. Paradoxically, despite the beneficial effects of surgical removal of the primary tumor, the physiological stress resulting from surgical trauma serves to promote cancer recurrence and metastasis. The postoperative environment suppresses critical anti-tumor immune effector cells, including Natural Killer (NK) cells. The literature suggests that NK cells are critical mediators in the formation of metastases immediately following surgery. The following review will highlight the mechanisms that promote the formation of micrometastases by directly or indirectly inducing NK cell suppression following surgery. These include tissue hypoxia, neuroendocrine activation, hypercoagulation, the pro-inflammatory phase, and the anti-inflammatory phase. Perioperative therapeutic strategies designed to prevent or reverse NK cell dysfunction will also be examined for their potential to improve cancer outcomes by preventing surgery-induced metastases.

The abnormal expression of Tim-3 is involved in the regulation of myeloid-derived suppressor cells and its correlation with preeclampsia

INTRODUCTION

Maternal immune system tolerance to the semi-allogeneic fetus is critical to a successful pregnancy. We previously reported that myeloid-derived suppressor cells (MDSC) was associated with maternal immune imbalance. T cell immunoglobulin and mucin-containing protein 3 (Tim-3)/Galectin-9 (Gal-9) pathway modulates function of various immune cells in maternal-fetal interface. However, the regulatory effects of Tim-3/Gal-9 signaling on MDSCs and its role in preeclampsia (PE) remain unclear.

METHODS

In the current study we investigated the expression of Tim-3 on MDSC in preeclampsia (PE) patients to further explore the pathogenesis of PE.

RESULTS

The proportion of Tim-3⁺ M-MDSC (monocytic MDSC) cells was higher in PE patients than in healthy control. Meanwhile, the protein expression of Gal-9, as the ligand of Tim-3, was increased in placenta of PE patients. M-MDSC also expressed a higher level of interferon-γ (IFN-γ) and a lower level of transforming growth factor-β (TGF-β) in PE. Furthermore, our study suggested that blocking Tim-3 could attenuate the inhibitory function of MDSC.

DISCUSSION

The abnormal expression of Tim-3 on MDSC might be involved in the pathogenesis of PE, and could be a marker to evaluate the immune function in PE.

Estradiol correlates with the accumulation of Monocytic Myeloid-Derived Suppressor Cells in Pre-term birth: A possible explanation of immune suppression in pre-term babies

Synergistic interplay of immune endocrine interaction is prerequisite for an effective maternal fetal tolerance. Pre-term birth (PTB) may be a consequence of altered immune-endocrine crosstalk during third trimester resulting in early breakdown of this tolerance. Myeloid derived suppressor cells (MDSCs), a heterogenous population of immature immune cells are increased in pregnant women and healthy newborns, but their role in PTB still remains obscure. We now report that granulocytic MDSCs (G-MDSCs) is decreased in women delivering prematurely, suggesting their potential role in maintaining maternal fetal tolerance. Interestingly, in contrast statistically significant increase in MDSCs and monocytic MDSCs (M-MDSCs) along with positive correlation with cord serum estradiol (E2), and overexpressed ER-α in placental tissue suggested E2 mediated accumulation of M-MDSCs in PTB babies. MDSCs mediated immune suppression is accompanied with subsequent decline in total T cells and its subtypes: Th and Tc in PTB babies, which signifies their potential contribution towards the impaired immune system of PTB babies.

Exploiting the obesity-associated immune microenvironment for cancer therapeutics

Obesity causes chronic low-grade inflammation and leads to changes in the immune landscape of multiple organ systems. Given the link between chronic inflammatory conditions and cancer, it is not surprising that obesity is associated with increased risk and worse outcomes in many malignancies. Paradoxically, recent epidemiological studies have shown that high BMI is associated with increased efficacy of immune checkpoint inhibitors (ICI), and a causal relationship has been demonstrated in the preclinical setting. It has been proposed that obesity-associated immune dysregulation underlies this observation by inadvertently creating a favourable microenvironment for increased ICI efficacy. The recent success of ICIs in obese cancer patients raises the possibility that additional immune-targeted therapies may hold therapeutic value in this context. Here we review how obesity affects the immunological composition of the tumor microenvironment in ways that can be exploited for cancer immunotherapies. We discuss existing literature supporting a beneficial role for obesity during ICI therapy in cancer patients, potential opportunities for targeting the innate immune system to mitigate chronic inflammatory processes, and how to pinpoint obese patients who are most likely to benefit from immune interventions without relying solely on body mass index. Given that the incidence of obesity is expanding on an international scale, we propose that understanding obesity-associated inflammation is necessary to reduce cancer mortalities and capitalize on novel therapeutic opportunities in the era of cancer immunotherapy.

Lysophosphatidic Acid: Promoter of Cancer Progression and of Tumor Microenvironment Development. A Promising Target for Anticancer Therapies?

Increased expression of the enzyme autotaxin (ATX) and the consequently increased levels of its product, lysophosphatidic acid (LPA), have been reported in several primary tumors. The role of LPA as a direct modulator of tumor cell functions—motility, invasion and migration capabilities as well as resistance to apoptotic death—has been recognized by numerous studies over the last two decades. Notably, evidence has recently been accumulating that shows that LPA also contributes to the development of the tumor microenvironment (TME). Indeed, LPA plays a crucial role in inducing angiogenesis and lymphangiogenesis, triggering cellular glycolytic shift and stimulating intratumoral fibrosis. In addition, LPA helps tumoral cells to escape immune surveillance. Treatments that counter the TME components, in order to deprive cancer cells of their crucial support, have been emerging among the promising new anticancer therapies. This review aims to summarize the latest knowledge on how LPA influences both tumor cell functions and the TME by regulating the activity of its different elements, highlighting why and how LPA is worth considering as a molecular target for new anticancer therapies.

Natural Killer Cell Interactions With Myeloid Derived Suppressor Cells in the Tumor Microenvironment and Implications for Cancer Immunotherapy

The tumor microenvironment (TME) is a complex and heterogeneous environment composed of cancer cells, tumor stroma, a mixture of tissue-resident and infiltrating immune cells, secreted factors, and extracellular matrix proteins. Natural killer (NK) cells play a vital role in fighting tumors, but chronic stimulation and immunosuppression in the TME lead to NK cell exhaustion and limited antitumor functions. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of myeloid cells with potent immunosuppressive activity that gradually accumulate in tumor tissues. MDSCs interact with innate and adaptive immune cells and play a crucial role in negatively regulating the immune response to tumors. This review discusses MDSC-mediated NK cell regulation within the TME, focusing on critical cellular and molecular interactions. We review current strategies that target MDSC-mediated immunosuppression to enhance NK cell cytotoxic antitumor activity. We also speculate on how NK cell-based antitumor immunotherapy could be improved.

Emerging roles for myeloid immune cells in bone metastasis

Metastasis, especially bone metastasis, is a major cause of cancer-related deaths, which is associated with long-term pain due to skeletal-related events and poor quality of life. Tumor cells alter the bone microenvironment through aberrant activation of osteoclasts and osteoblasts which induces bone osteolysis and release of growth factors leading to cancer growth. Though this phenomenon has been well characterized, bone-targeted therapies have shown little improvement in patient survival. Recent evidence indicates a growing appreciation for the complex bone environment, in addition to bone-remodeling stromal cells, which includes an abundance of myeloid immune cells that can either protect against or contribute to the progression of the disease within the bone cavity. Additionally, myeloid cells are recruited into primary tumor sites, where they promote development of the pre-metastatic niche and also can regulate tumor progression within the tumor-bone microenvironment through a milieu of complex mechanisms and involving heterogeneous myeloid populations. In this review, we have highlighted the complex roles of myeloid immunity in bone metastasis and hope to bring attention to the potential of novel immunotherapeutic interventions for the elimination of bone metastasis.

Gefitinib Results in Robust Host-Directed Immunity Against Salmonella Infection Through Proteo-Metabolomic Reprogramming

The global rise of antibiotic-resistant strains of Salmonella has necessitated the development of alternative therapeutic strategies. Recent studies have shown that targeting host factors may provide an alternative approach for the treatment of intracellular pathogens. Host-directed therapy (HDT) modulates host cellular factors that are essential to support the replication of the intracellular pathogens. In the current study, we identified Gefitinib as a potential host directed therapeutic drug against Salmonella. Further, using the proteome analysis of Salmonella-infected macrophages, we identified EGFR, a host factor, promoting intracellular survival of Salmonella via mTOR-HIF-1α axis. Blocking of EGFR, mTOR or HIF-1α inhibits the intracellular survival of Salmonella within the macrophages and in mice. Global proteo-metabolomics profiling indicated the upregulation of host factors predominantly associated with ATP turn over, glycolysis, urea cycle, which ultimately promote the activation of EGFR-HIF1α signaling upon infection. Importantly, inhibition of EGFR and HIF1α restored both proteomics and metabolomics changes caused by Salmonella infection. Taken together, this study identifies Gefitinib as a host directed drug that holds potential translational values against Salmonella infection and might be useful for the treatment of other intracellular infections.

Immune System Alterations in Multiple Myeloma: Molecular Mechanisms and Therapeutic Strategies to Reverse Immunosuppression

Simple Summary

A common characteristic of multiple myeloma (MM) is the dysfunction of patients’ immune system, a condition termed immunosuppression. This state is mainly due to alterations in the number and functionality of the principal immune populations. In this setting, immunotherapy has acquired high relevance in the last years and the investigation of agents that boost the immune system represent a field of interest. In the present review, we will summarize the main cellular and molecular alterations observed in MM patients’ immune system. Furthermore, we will describe the mechanisms of action of the four immunotherapeutic drugs approved so far for the treatment of MM, which are part of the group of monoclonal antibodies (mAbs). Finally, the immune-stimulating effects of several therapeutic agents are described due to their potential role in reversing immunosuppression and, therefore, in favoring the efficacy of immunotherapy drugs, such as mAbs, as part of future pharmacological combinations.

Abstract

Immunosuppression is a common feature of multiple myeloma (MM) patients and has been associated with disease evolution from its precursor stages. MM cells promote immunosuppressive effects due to both the secretion of soluble factors, which inhibit the function of immune effector cells, and the recruitment of immunosuppressive populations. Alterations in the expression of surface molecules are also responsible for immunosuppression. In this scenario, immunotherapy, as is the case of immunotherapeutic monoclonal antibodies (mAbs), aims to boost the immune system against tumor cells. In fact, mAbs exert part of their cytotoxic effects through different cellular and soluble immune components and, therefore, patients’ immunosuppressive status could reduce their efficacy. Here, we will expose the alterations observed in symptomatic MM, as compared to its precursor stages and healthy subjects, in the main immune populations, especially the inhibition of effector cells and the activation of immunosuppressive populations. Additionally, we will revise the mechanisms responsible for all these alterations, including the interplay between MM cells and immune cells and the interactions among immune cells themselves. We will also summarize the main mechanisms of action of the four mAbs approved so far for the treatment of MM. Finally, we will discuss the potential immune-stimulating effects of non-immunotherapeutic drugs, which could enhance the efficacy of immunotherapeutic treatments.

Acetylcholine ameliorates colitis by promoting IL-10 secretion of monocytic myeloid-derived suppressor cells through the nAChR/ERK pathway

The alteration of the enteric nervous system (ENS) and its role in neuroimmune modulation remain obscure in the pathogenesis of inflammatory bowel diseases (IBDs). Here, by using the xCell tool and the latest immunolabeling-enabled three-dimensional (3D) imaging of solvent-cleared organs technique, we found severe pathological damage of the entire ENS and decreased expression of choline acetyltransferase (ChAT) in IBD patients. As a result, acetylcholine (ACh), a major neurotransmitter of the nervous system synthesized by ChAT, was greatly reduced in colon tissues of both IBD patients and colitis mice. Importantly, administration of ACh via enema remarkably ameliorated colitis, which was proved to be directly dependent on monocytic myeloid-derived suppressor cells (M-MDSCs). Furthermore, ACh was demonstrated to promote interleukin-10 secretion of M-MDSCs and suppress the inflammation through activating the nAChR/ERK pathway. The present data reveal that the cholinergic signaling pathway in the ENS is impaired during colitis and uncover an ACh-MDSCs neuroimmune regulatory pathway, which may offer promising therapeutic strategies for IBDs.

Donor-Derived Myeloid Heme Oxygenase-1 Controls the Development of Graft-Versus-Host Disease

Graft-versus-host disease (GVHD) remains a major clinical drawback of allogeneic hematopoietic stem cell transplantation (HSCT). Here, we investigated how the stress responsive heme catabolizing enzyme heme oxygenase-1 (HO-1, encoded by HMOX1) regulates GVHD in response to allogeneic hematopoietic stem cell transplantation in mice and humans. We found that deletion of the Hmox1 allele, specifically in the myeloid compartment of mouse donor bone marrow, promotes the development of aggressive GVHD after allogeneic transplantation. The mechanism driving GVHD in mice transplanted with allogeneic bone marrow lacking HO-1 expression in the myeloid compartment involves enhanced T cell alloreactivity. The clinical relevance of these observations was validated in two independent cohorts of HSCT patients. Individuals transplanted with hematopoietic stem cells from donors carrying a long homozygous (GT)n repeat polymorphism (L/L) in the HMOX1 promoter, which is associated with lower HO-1 expression, were at higher risk of developing severe acute GVHD as compared to donors carrying a short (GT)n repeat (S/L or S/S) polymorphism associated with higher HO-1 expression. In this study, we showed the unique importance of donor-derived myeloid HO-1 in the prevention of lethal experimental GVHD and we corroborated this observation by demonstrating the association between human HMOX1 (GT)n microsatellite polymorphisms and the incidence of severe acute GVHD in two independent HSCT patient cohorts. Donor-derived myeloid HO-1 constitutes a potential therapeutic target for HSCT patients and large-scale prospective studies in HSCT patients are necessary to validate the HO-1 L/L genotype as an independent risk factor for developing severe acute GVHD.

The importance of advanced cytometry in defining new immune cell types and functions relevant for the immunopathogenesis of HIV infection

: In the last years, novel, exciting immunological findings of interest for HIV research and treatment were identified thanks to different cytometric approaches. The analysis of the phenotypes and functionality of cells belonging to the immune system could clarify their role in the immunopathogenesis of HIV infection, and to elaborate key concepts, relevant in the treatment of this disease. Important discoveries have been made concerning cells that are important for protective immunity like lymphocytes that display polyfunctionality, resident memory T cells, innate lymphoid cells, to mention a few. The complex phenotype of myeloid-derived suppressor cells has been investigated, and relevant changes have been reported during chronic and primary HIV infection, in correlation with changes in CD4 T-cell number, T-cell activation, and with advanced disease stage. The search for markers of HIV persistence present in latently infected cells, namely those molecules that are important for a functional or sterilizing cure, evidenced the role of follicular helper T cells, and opened a discussion on the meaning and use of different surface molecules not only in identifying such cells, but also in designing new strategies. Finally, advanced technologies based upon the simultaneous detection of HIV-RNA and proteins at the single cell level, as well as those based upon spectral cytometry or mass cytometry are now finding new actors and depicting a new scenario in the immunopathogenesis of the infection, that will allow to better design innovative therapies based upon novel drugs and vaccines.

The FGF/FGFR System in Breast Cancer: Oncogenic Features and Therapeutic Perspectives

One of the major challenges in the treatment of breast cancer is the heterogeneous nature of the disease. With multiple subtypes of breast cancer identified, there is an unmet clinical need for the development of therapies particularly for the less tractable subtypes. Several transduction mechanisms are involved in the progression of breast cancer, therefore making the assessment of the molecular landscape that characterizes each patient intricate. Over the last decade, numerous studies have focused on the development of tyrosine kinase inhibitors (TKIs) to target the main pathways dysregulated in breast cancer, however their effectiveness is often limited either by resistance to treatments or the appearance of adverse effects. In this context, the fibroblast growth factor/fibroblast growth factor receptor (FGF/FGFR) system represents an emerging transduction pathway and therapeutic target to be fully investigated among the diverse anti-cancer settings in breast cancer. Here, we have recapitulated previous studies dealing with FGFR molecular aberrations, such as the gene amplification, point mutations, and chromosomal translocations that occur in breast cancer. Furthermore, alterations in the FGF/FGFR signaling across the different subtypes of breast cancer have been described. Next, we discussed the functional interplay between the FGF/FGFR axis and important components of the breast tumor microenvironment. Lastly, we pointed out the therapeutic usefulness of FGF/FGFR inhibitors, as revealed by preclinical and clinical models of breast cancer.

Targeting Myeloid-Derived Suppressor Cells in Cancer Immunotherapy

Simple Summary

Myeloid-Derived Suppressor Cells (MDSCs) have been regarded as the main promoters of cancer development in recent years. They can protect tumor cells from being eliminated by neutralizing the anti-tumor response mediated by T cells, macrophages and dendritic cells (DCs). Therefore, different treatment methods targeting MDSCs, including chemotherapy, radiotherapy and immunotherapy, have been developed and proven to effectively inhibit tumor expansion. Herein, we summarize the immunosuppressive role of MDSCs in the tumor microenvironment and some effective treatments targeting MDSCs, and discuss the differences between different therapies.

Abstract

Myeloid-derived suppressor cells (MDSCs), which are activated under pathological conditions, are a group of heterogeneous immature myeloid cells. MDSCs have potent capacities to support tumor growth via inhibition of the antitumoral immune response and/or the induction of immunosuppressive cells. In addition, multiple studies have demonstrated that MDSCs provide potential therapeutic targets for the elimination of immunosuppressive functions and the inhibition of tumor growth. The combination of targeting MDSCs and other therapeutic approaches has also demonstrated powerful antitumor effects. In this review, we summarize the characteristics of MDSCs in the tumor microenvironment (TME) and current strategies of cancer treatment by targeting MDSCs.

Recent advances in myeloid-derived suppressor cell biology

In recent years, studying the role of myeloid-derived suppressor cells (MDSCs) in many pathological inflammatory conditions has become a very active research area. Although the role of MDSCs in cancer is relatively well established, their role in non-cancerous pathological conditions remains in its infancy resulting in much confusion. Our objectives in this review are to address some recent advances in MDSC research in order to minimize such confusion and to provide an insight into their function in the context of other diseases. The following topics will be specifically focused upon: (1) definition and characterization of MDSCs; (2) whether all MDSC populations consist of immature cells; (3) technical issues in MDSC isolation, estimation and characterization; (4) the origin of MDSCs and their anatomical distribution in health and disease; (5) mediators of MDSC expansion and accumulation; (6) factors that determine the expansion of one MDSC population over the other; (7) the Yin and Yang roles of MDSCs. Moreover, the functions of MDSCs will be addressed throughout the text.

Granulocytic Myeloid-Derived Suppressor Cells in Breast Milk (BM-MDSC) Correlate with Gestational Age and Postnatal Age and Are Influenced by Infant's Sex

BACKGROUND

Infections are the main cause of death in preterm infants. Causative agents often descend from the intestinal flora of the infected neonate, indicating insufficient protection by the mucosal barrier. Breast milk (BM) contains different subsets of immune cells. We recently showed that BM contains significant numbers of myeloid-derived suppressor cells (MDSC)-immune cells that actively suppress pro-inflammatory immune responses-and hypothesized that the transfer of BM-MDSC may modulate the mucosal immunity of the newborn.

METHODS

Percentages of MDSC in the BM from mothers of 86 preterm infants between 23 + 0 and 36 + 6 weeks of gestation during their first five postnatal weeks were analyzed by flow cytometry and correlated with maternal and infant characteristics.

RESULTS

Percentages of BM-MDSC positively correlated with gestational age and postnatal age. The expression of activation markers on BM-MDSC did not change with gestational age, but it decreased with postnatal age. Mothers who received antepartum tocolytics had lower percentages of BM-MDSC, and infant's sex strongly influenced percentages of BM-MDSC.

CONCLUSION

Our results point toward a role of BM-MDSC for immune regulation in the neonatal gut, making them a potential target of immune-based therapies shortly after birth.

Myeloid Cells in Circulation and Tumor Microenvironment of Colorectal Cancer Patients with Early and Advanced Disease Stages

Myeloid-derived suppressor cells (MDSCs) are a heterogenous population of cells that have been implicated in the development of an immunosuppressive environment, which promotes tumorigenesis and tumor progression. Numerous studies have reported expansion of MDSCs in circulation and the tumor microenvironment (TME) of cancer patients. However, due to the heterogenic nature of MDSCs and the different approaches for their identification, their detailed characterization and impact on disease progression in cancer patients are warranted. In this study, we investigated the levels of different myeloid cell subsets and antigen-presenting cells (APCs) using flow cytometry in unfractionated whole blood (WB), peripheral blood mononuclear cells (PBMCs), tumor tissue (TT), and adjacent normal tissue (NT) of colorectal cancer (CRC) patients. We found high levels of granulocytic myeloid cells (GMCs) in whole blood, but their levels were significantly lower in PBMCs. Importantly, we found significantly higher levels of GMCs in the TME compared to NT. In addition, monocytic myeloid cells (MMCs) showed significantly higher levels in PBMCs of CRC patients, compared to healthy donors (HDs). Notably, patients with advanced disease stages showed significantly higher levels of GMCs compared to early stages in whole blood, but PBMCs and tumor-infiltrating myeloid cells did not show any significant differences. Lastly, we found that levels of GMCs decreased, while IMCs increased in the TME with tumor budding. Our results highlight the importance of investigating the levels of different myeloid cell subsets in PBMCs versus whole blood of cancer patients and improve current knowledge on the potential prognostic significance of myeloid cells in CRC patients.

The pattern and prognostic relevance of immune activity scores and tumor-infiltrating immune cells in metastatic clear cell renal cell carcinoma: Evidence from multiple datasets

PURPOSE

To investigate the immune activity scores (IAS) and tumor-infiltrating immune cells (TIIC) in metastatic clear cell renal cell carcinoma (mccRCC) patients and to explore their patterns and potential prognostic values.

METHODS

The gene expression profiles and clinical information of ccRCC patients from multiple Gene Expression Omnibus (GEO) datasets and TCGA were used as study cohorts. Overall, 3 sets of 69 variables associated with tumor-immune interactions were collected from several tumor immunophenotype analysis websites. Least absolute shrinkage and selection operator (LASSO) and area under receiver operating characteristic (AUC) analyses were performed to establish and evaluate the predictive models.

RESULTS

Several TIIC and IAS variables are significantly different between patients and between different sites within the same patient. The AUC of the multivariable logistic models based on IAS and the two TIIC groups is 0.705 (95%CI 0.643-0.766), 0.719 (95%CI 0.650-0.788), and 0.685 (95%CI 0.623-0.747), respectively. The AUC of the LASSO model is 0.715 (95%CI 0.652-0.777). Certain subtypes identified by the consensus clustering method show a favorable OS (log-rank, p < 0.01) in both nonmetastatic and metastatic ccRCC patients.

CONCLUSION

IAS and TIIC could vary between patients and different sites within the same patient, and distinct patterns of these variables could correlate with clinical features. Heterogeneity might exist in the biological process of metastasis. LASSO logistic regression reveals that the infiltration of two TIICs would be a predictor of metastatic ccRCC. Last, certain subtypes may have a better prognosis in both ccRCC and mccRCC patients.

DNA methylation in the promoters of PD-L1, MMP9, ARG1, galectin-9, TIM-3, VISTA and TGF-β genes in HLA-DR- myeloid cells, compared with HLA-DR+ antigen-presenting cells

Myeloid cells, including antigen-presenting cells (APCs) and myeloid-derived suppressor cells (MDSCs) play opposing roles to orchestrate innate and adaptive immune responses during physiological and pathological conditions. We investigated the role of DNA methylation in regulating the transcription of inhibitory/suppressive molecules in myeloid suppressive cells (identified as CD33⁺HLA-DR^-) in comparison to APCs. We selected a number of immune checkpoints (ICs), IC ligands, and immunosuppressive molecules that have been implicated in MDSC function, including PD-L1, TIM-3, VISTA, galectin-9, TGF-β, ARG1 and MMP9. We examined their mRNA expression levels, and investigated whether DNA methylation regulates their transcription in sorted myeloid cell subpopulations. We found that mRNA levels of PD-L1, TIM-3, TGF-β, ARG1 and MMP9 in CD33⁺HLA-DR^- cells were higher than APCs. However, VISTA and galectin-9 mRNA levels were relatively similar in both myeloid subpopulations. CpG islands in the promoter regions of TGF-β1, TIM-3 and ARG1 were highly unmethylated in CD33⁺HLA-DR^-cells, compared with APCs, suggesting that DNA methylation is one of the key mechanisms, which regulate their expression. However, we did not find differences in the methylation status of PD-L1 and MMP9 between CD33⁺HLA-DR^- and APCs, suggesting that their transcription could be regulated via other genetic and epigenetic mechanisms. The promoter methylation status of VISTA was relatively similar in both myeloid subpopulations. This study provides novel insights into the epigenetic mechanisms, which control the expression of inhibitory/suppressive molecules in circulating CD33⁺HLA-DR^- cells in a steady-state condition, possibly to maintain immune tolerance and haemostasis.

Circulating CD14+HLA-DR-/low Myeloid-Derived Suppressor Cells as Potential Biomarkers for the Identification of Psoriasis TCM Blood-Heat Syndrome and Blood-Stasis Syndrome

Psoriasis is a chronic autoimmune disease. Identification of the biomarkers responsible for Traditional Chinese Medicine (TCM) syndromes of psoriasis can help researchers recognize the different aspects of psoriasis and find novel therapeutic targets for the treatment of psoriasis. The current study investigated the levels of circulating Mo-MDSCs and Mo-MDSC-associated immune factors in the peripheral blood of psoriasis patients with different TCM syndromes. We found that the frequency of Mo-MDSCs (CD14⁺HLA-DR^−/low cells) among CD14⁺ cells from plaque psoriasis patients with blood-stasis (BS) syndrome was significantly increased when compared with healthy controls (p < 0.001) and blood-heat (BH) syndrome group (p < 0.001), respectively. However, serum IL-2, IL-4, IL-6, IL-10, IL-17A, TNF-α, IFN-γ, iNOS, Arg-1, and NO concentration showed no statistically significant difference between healthy controls and psoriasis patients as well as no significant difference between the BH and BS syndrome groups. Compared with healthy controls, the mRNA expression of Arg-1, TNF-α, ROR-γ, and PD-L1 was increased, while the mRNA expression of PD-1 and IL-10 was decreased in PBMCs from psoriasis patients. Moreover, the mRNA expression of TNF-α and FOXP3 in PBMCs showed a pronounced statistical difference between the psoriatic BH syndrome group and the BS syndrome group. Therefore, we provide evidence that the percentage of CD14⁺HLA-DR^−/low MDSC/ CD14⁺ cells and TNF-α and Foxp3 mRNA expression levels in PBMCs are potential biomarkers for distinguishing TCM BH syndrome and BS syndrome.

Granulocyte Colony-Stimulating Factor Attenuates Renal Ischemia-Reperfusion Injury by Inducing Myeloid-Derived Suppressor Cells

BACKGROUND

Granulocyte colony-stimulating factor (G-CSF) can increase populations of myeloid-derived suppressor cells, innate immune suppressors that play an immunoregulatory role in antitumor immunity. However, the roles of myeloid-derived suppressor cells and G-CSF in renal ischemia-reperfusion injury remain unclear.

METHODS

We used mouse models of ischemia-reperfusion injury to investigate whether G-CSF can attenuate renal injury by increasing infiltration of myeloid-derived suppressor cells into kidney tissue.

RESULTS

G-CSF treatment before ischemia-reperfusion injury subsequently attenuated acute renal dysfunction, tissue injury, and tubular apoptosis. Additionally, G-CSF treatment suppressed renal infiltration of macrophages and T cells as well as renal levels of IL-6, MCP-1, IL-12, TNF-α, and IFN-γ, but it increased levels of IL-10, arginase-1, and reactive oxygen species. Moreover, administering G-CSF after ischemia-reperfusion injury improved the recovery of renal function and attenuated renal fibrosis on day 28. G-CSF treatment increased renal infiltration of myeloid-derived suppressor cells (F4/80^-CD11b⁺Gr-1^int), especially the granulocytic myeloid-derived suppressor cell population (CD11b⁺Ly6Gi^ntLy6C^low); splenic F4/80^-CD11b⁺Gr-1⁺ cells sorted from G-CSF-treated mice displayed higher levels of arginase-1, IL-10, and reactive oxygen species relative to those from control mice. Furthermore, these splenic cells effectively suppressed in vitro T cell activation mainly through arginase-1 and reactive oxygen species, and their adoptive transfer attenuated renal injury. Combined treatment with anti-Gr-1 and G-CSF showed better renoprotective effects than G-CSF alone, whereas preferential depletion of myeloid-derived suppressor cells by pep-G3 or gemcitabine abrogated the beneficial effects of G-CSF against renal injury.

CONCLUSIONS

G-CSF induced renal myeloid-derived suppressor cells, thereby attenuating acute renal injury and chronic renal fibrosis after ischemia-reperfusion injury. These results suggest therapeutic potential of myeloid-derived suppressor cells and G-CSF in renal ischemia-reperfusion injury.

Immune contexture of cholangiocarcinoma

PURPOSE OF REVIEW

Considering the failure of standard treatments (i.e. surgery, radiotherapy, chemotherapy) in treating cholangiocarcinoma (CCA), introduction of alternative interventions is urgently needed. During the past 2 decades, discoveries of the mechanisms of cancer immunosurveillance and tumor immune evasion have precipitated the emergence and clinical approval of immunotherapies in multiple malignant indications. Interest in their introduction for the care of CCA is recent and several immunotherapeutic approaches are undergoing a clinical evaluation. Undoubtedly, their efficient application, as monotherapy or in combination regimens, will rely on a deeper understanding of CCA immune contexture.

RECENT FINDINGS

CCA cells appeared very potent in recruiting protumorigenic cells and shaping an immunosuppressive microenvironment. Elevated densities of several immune cells with immunoinhibitory activities within the malignant bed have been associated with poor prognosis in patients. Particularly, macrophages and neutrophils (especially in their alternatively activated phenotype) were pointed out for their role in cancer progression. Dendritic cells were described as ineffective in priming CCA-specific T-cell responses.

SUMMARY

Quantitative and qualitative assessment of the innate and adaptive immune compartments of the CCA immune contexture, as well as their prognostic value, will benefit to the development of improved immunotherapeutic strategies.

Synergic effect of PD-1 blockade and endostar on the PI3K/AKT/mTOR-mediated autophagy and angiogenesis in Lewis lung carcinoma mouse model

BACKGROUND

Immunotherapy has been shown to be effective as a first-line treatment option for non-small cell lung cancer (NSCLC) patients. Unfortunately, it has failed to acquire an anticipant anti-tumour effect for relatively lower clinical benefit rates. It is therefore important to identify novel strategies for improving immunotherapy. Endostar is a novel recombinant human endostatin that exerts its anti-angiogenic effects via vascular endothelial growth factor (VEGF)-related signalling pathways. Anti-programmed death receptor 1 (PD-1) antibody is an immune checkpoint inhibitor that was developed to stimulate the immune system. In this study, the synergy of PD-1 blockade and endostar was assessed in a lung carcinoma mouse model.

METHODS

Lewis lung carcinoma (LLC)-bearing mice were randomly assigned into three groups: controls, anti-PD-1 and anti-PD-1+endostar. The levels of cytokines such as interleukin (IL)-17, transforming growth factor-β1 (TGF-β1) and interferon-γ (IFN-γ) were measured with enzyme-linked immune sorbent assay (ELISA). The expression of VEGF, CD34 and CD31 was assessed with immunohistochemistry (IHC). The proportion of mature dendritic cells (mDC) and myeloid-derived suppressor cells (MDSC) was analysed with flow cytometry. The major proteins in PI3K/AKT/mTOR and autophagy were quantified with Western blot.

RESULTS

Anti-PD-1 combined with endostar dramatically suppressed tumour growth in LLC mouse models. This synergistic effect resulted in decreased pro-inflammatory cytokine IL-17 and immunosuppressive factor TGF-β1 levels, increased IFN-γ secretion, reduced myeloid-derived suppressor cell (MDSC) accumulation, and reversed CD8 + T cell suppression. The expression of VEGF, CD34 and CD31 was significantly down-regulated, while tumour cell apoptosis and PI3K/AKT/mTOR-mediated autophagy was up-regulated.

CONCLUSION

The combination of anti-PD-1 and endostar has a remarkably synergic effect on LLC tumour growth by means of improving the tumour microenvironment and activating autophagy.

Multimodal Molecular Imaging of the Tumour Microenvironment

The tumour microenvironment (TME) surrounding tumour cells is a highly dynamic and heterogeneous composition of immune cells, fibroblasts, precursor cells, endothelial cells, signalling molecules and extracellular matrix (ECM) components. Due to the heterogeneity and the constant crosstalk between the TME and the tumour cells, the components of the TME are important prognostic parameters in cancer and determine the response to novel immunotherapies. To improve the characterization of the TME, novel non-invasive imaging paradigms targeting the complexity of the TME are urgently needed.The characterization of the TME by molecular imaging will (1) support early diagnosis and disease follow-up, (2) guide (stereotactic) biopsy sampling, (3) highlight the dynamic changes during disease pathogenesis in a non-invasive manner, (4) help monitor existing therapies, (5) support the development of novel TME-targeting therapies and (6) aid stratification of patients, according to the cellular composition of their tumours in correlation to their therapy response.This chapter will summarize the most recent developments and applications of molecular imaging paradigms beyond FDG for the characterization of the dynamic molecular and cellular changes in the TME.

Hypofractionated Irradiation Suppressed the Off-Target Mouse Hepatocarcinoma Growth by Inhibiting Myeloid-Derived Suppressor Cell-Mediated Immune Suppression

Background: Stereotactic radiotherapy treats hepatocellular carcinoma (HCC) at different stages effectively and safely. Besides its direct killing of cancer cells, radiotherapy stimulates host immunity against hepatoma. However, the role of myeloid-derived suppressor cells (MDSCs) in on-target and off-target anti-HCC effects induced by hypofractionated irradiation (IR) is unclear.

Methods and Materials: Hepa1-6 and H22 allogeneic transplanted tumors on hind limbs of C57BL/6 and Institute of Cancer Research (ICR) mice, respectively, were irradiated with 0, 2.5, 4, 6, or 8 Gy/fraction until the total dose reached 40 Gy. The off-target effect induced by the IR was investigated by subsequently inoculating the same HCC cells subcutaneously on the abdomen. MDSCs in peripheral blood and tumor tissues were measured by flow cytometry or immunofluorescence microscopy analysis. IL-6, regulated on activation normal T cell expressed and secreted (RANTES), and granulocyte colony-stimulating factor (G-CSF) in irradiated mouse plasma and hepatoma cell cultures were measured with ELISA kits. Conditioned media (CM) from irradiated HCC cell cultures on bone marrow cell differentiation and MDSC proliferation were examined by co-culture and flow cytometry.

Results: Our study showed that the IR of primarily inoculated HCC on hind limbs created an “in situ tumor vaccine” and triggered the antitumor immunity. The immunity was capable of suppressing the growth of the same type of HCC subcutaneously implanted on the abdomen, accompanied with reduced MDSCs in both blood and tumors. The decreased MDSCs were associated with low plasma levels of IL-6, RANTES, and G-CSF. The cytokines IL-6 and RANTES in the CM were lower in the high single IR dose group than in the control groups, but G-CSF was higher. The CM from high single-dose IR-Hepa1-6 cell culture reduced the differentiation of C57BL/6 mouse bone marrow cells into MDSCs, whereas CM from high single-dose IR-H22 cells reduced the proliferation of MDSCs, which might be due to the decreased p-STAT3 in bone marrow cells.

Conclusions: The hypofractionated IR on transplanted tumors at the primary location exerted a strong antitumor effect on the same tumor at a different location (off target). This abscopal effect is most likely through the reduction of MDSCs and decrease of IL-6, RANTES, and G-CSF.

Human monocytic myeloid-derived suppressor cells impair B-cell phenotype and function in vitro

Myeloid-derived suppressor cells (MDSCs) are key regulators of immunity that initially have been defined by their ability to potently suppress T-cell responses. Recent studies collectively demonstrate that the suppressive activity of MDSCs is not limited to T cells, but rather affects a broad range of immune cell subsets. However, relatively few studies have assessed the impact of MDSCs on B cells, particularly in the human context. Here, we report that human monocytic MDSCs (M-MDSCs) significantly interfere with human B-cell proliferation and function in vitro. We further show that the inhibition occurs independent of direct cell-contact and involves the expression of suppressive mediators such as indoleamine 2, 3-dioxygenase (IDO), arginase-1 (Arg1), and nitric oxide (NO). In addition, our studies demonstrate that the suppression of B cells by M-MDSCs is paralleled by a skewing in B-cell phenotype and gene expression signatures. M-MDSCs induced the downregulation of key surface markers on activated B cells, including IgM, HLA-DR, CD80, CD86, TACI, and CD95. Concurrently, M-MDSCs but not conventional monocytes elicited alterations in the transcription of genes involved in apoptosis induction, class-switch regulation, and B-cell differentiation and function. In summary, this study expands our understanding of the regulatory role of M-MDSCs for human B-cell responses.

Neutrophil Maturity in Cancer

Neutrophils are implicated in almost every stage of oncogenesis and paradoxically display anti- and pro-tumor properties. Accumulating evidence indicates that neutrophils display diversity in their phenotype resulting from functional plasticity and/or changes to granulopoiesis. In cancer, neutrophils at a range of maturation stages can be identified in the blood and tissues (i.e., outside of their developmental niche). The functional capacity of neutrophils at different states of maturation is poorly understood resulting from challenges in their isolation, identification, and investigation. Thus, the impact of neutrophil maturity on cancer progression and therapy remains enigmatic. In this review, we discuss the identification, prevalence, and function of immature and mature neutrophils in cancer and the potential impact of this on tumor progression and cancer therapy.

Long Non-coding RNAs: Regulators of the Activity of Myeloid-Derived Suppressor Cells

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous cell population with potent immunosuppressive functions. They play major roles in cancer and many of the pathologic conditions associated with inflammation. Long non-coding RNAs (lncRNAs) are untranslated functional RNA molecules. The lncRNAs are involved in the control of a wide variety of cellular processes and are dysregulated in different diseases. They can participate in the modulation of immune function and activity of inflammatory cells, including MDSCs. This mini review focuses on the emerging role of lncRNAs in MDSC activity. We summarize how lncRNAs modulate the generation, recruitment, and immunosuppressive functions of MDSCs and the underlying mechanisms.

T Cell Dysfunction in Cancer Immunity and Immunotherapy

In cancer, T cells become dysfunctional owing to persistent antigen exposure. Dysfunctional T cells are characterized by reduced proliferative capacity, decreased effector function, and overexpression of multiple inhibitory receptors. Due to the presence of various inhibitory signals in the complex tumor microenvironment, tumor-specific T cells have distinct dysfunction states. Therapeutic reactivation of tumor-specific T cells has yielded good results in cancer patients. Here, we review the hallmarks of T cell dysfunction in cancer. Also, we discuss the relationship between T cell dysfunction and cancer immunotherapy.

Multifaceted Role of the Placental Growth Factor (PlGF) in the Antitumor Immune Response and Cancer Progression

The sharing of molecules function that affects both tumor growth and neoangiogenesis with cells of the immune system creates a mutual interplay that impairs the host’s immune response against tumor progression. Increasing evidence shows that tumors are able to create an immunosuppressive microenvironment by recruiting specific immune cells. Moreover, molecules produced by tumor and inflammatory cells in the tumor microenvironment create an immunosuppressive milieu able to inhibit the development of an efficient immune response against cancer cells and thus fostering tumor growth and progression. In addition, the immunoediting could select cancer cells that are less immunogenic or more resistant to lysis. In this review, we summarize recent findings regarding the immunomodulatory effects and cancer progression of the angiogenic growth factor namely placental growth factor (PlGF) and address the biological complex effects of this cytokine. Different pathways of the innate and adaptive immune response in which, directly or indirectly, PlGF is involved in promoting tumor immune escape and metastasis will be described. PlGF is important for building up vascular structures and functions. Although PlGF effects on vascular and tumor growth have been widely summarized, its functions in modulating the immune intra-tumoral microenvironment have been less highlighted. In agreement with PlGF functions, different antitumor strategies can be envisioned.

The tumor microenvironment in renal cell cancer

PURPOSE OF REVIEW

In addition to the provision of nutrients and growth factors that facilitate tumor cell proliferation and metastasis, the tumor microenvironment (MEV) restricts immune surveillance of tumor-associated antigens and limits the efficacy of immune checkpoint inhibitors, tumor vaccines, and other immune therapies. This review will focus on the immunosuppressive mechanisms operative within the tumor MVE of renal cell carcinoma.

RECENT FINDINGS

Several of the immunosuppressive mechanisms within the tumor MEV have been identified and are potentially druggable. Clinical trials with agents that target several of these inhibitory pathways are currently underway.

SUMMARY

Although renal cell carcinoma is one of several tumor types responsive to immune checkpoint inhibitors, the effectiveness of these agents is likely to be limited by the various tumor-infiltrating bone marrow-derived myeloid cells that comprise the MEV. Several strategies to combat the recruitment of these cells into tumor tissue or to neutralize their immunosuppressive function have shown encouraging results in animal tumor models and clinical trials.