Characterization of cytokine-induced myeloid-derived suppressor cells from normal human peripheral blood mononuclear cells

Myeloid-Derived Suppressor Cells in Infection: A General Overview

After initial infection, the immune response that serves to restrict the invading pathogen needs to be tightly calibrated in order to avoid collateral immunopathological damage. This calibration is performed by specialized suppressor mechanisms, which are capable of dampening overwhelming or unremitting inflammation in order to prevent tissue damage. Myeloid-derived suppressor cells (MDSC) are emerging as key players in counter-balancing inflammatory responses and pathogenesis during infection. However, some pathogens are able to exploit the suppressive activities of MDSC to favor pathogen persistence and chronic infections. In this article, we review the current knowledge about the importance of MDSC in the context of bacterial, virus, parasites, and fungal infections.

LncRNA MALAT1 negatively regulates MDSCs in patients with lung cancer

Myeloid-derived suppressor cells (MDSCs) have strong immunosuppressive functions and contribute to the formation of the tumor microenvironment. Long non-coding (Lnc) RNAs are highly important factors associated with tumors and may be used as markers for tumor diagnosis, which is valuable for targeted therapy. LncRNA MALAT1 is expressed in various tissues and plays a critical role in cell proliferation, including tumorigenesis and metastasis. However, the role of MALAT1 in MDSCs is unclear. In this study, we observed an increased proportion of MDSCs and elevated levels of the related molecule arginase-1 (ARG-1) in peripheral blood mononuclear cells (PBMCs) obtained from lung cancer patients. The proportion of CD8⁺ cytotoxic T lymphocyte (CTL) was significantly decreased in PBMCs from lung cancer patients. Moreover, the proportion of CTL cells was negatively correlated with the proportion of MDSCs. Furthermore, MALAT1 levels were decreased in PBMCs from lung cancer patients. The relative expression of MALAT1 was moderate negatively correlated with the proportion of MDSCs. In vitro results indicate that the knockdown of MALAT1 significantly increased the proportion of MDSCs. Our data provide the first evidence that lncRNA MALAT1 negatively regulates MDSCs and is decreased in PBMCs from lung cancer patients.

Cancer-related circulating and tumor-associated neutrophils - subtypes, sources and function

In recent years, the role of neutrophils in cancer biology has been a matter of increasing interest. Many patients with advanced cancer show high levels of neutrophilia, tumor neutrophils are connected to dismal prognosis, and the neutrophil-to-lymphocyte ratio has been introduced as a significant prognostic factor for survival in many types of cancer. Neutrophils constitute an important portion of the infiltrating immune cells in the tumor microenvironment, but controversy has long surrounded the function of these cells in the context of cancer. Multiple evidences have shown that neutrophils recruited to the tumor can acquire either protumor or antitumor function. These findings have led to the identification of multiple and heterogeneous neutrophil subsets in the tumor and circulation. In addition, tumor-associated neutrophils (TANs) were shown to demonstrate functional plasticity, driven by multiple factors present in the tumor microenvironment. In this review, we examine the current knowledge on cancer-related circulating neutrophils, their source and the function of the different subtypes, both mature and immature. We then discuss the pro vs antitumor nature of TANs in cancer, their functional plasticity and the mechanisms that regulate neutrophil recruitment and polarization. Although the vast majority of the knowledge on neutrophils in cancer comes from murine studies, recent work has been done on human cancer-related neutrophils. In the final paragraphs, we expand on the current knowledge regarding the role of neutrophils in human cancer and examine the question whether cancer-related neutrophils (circulating or intratumoral) could be a new possible target for cancer immunotherapy.

CD14+ CD15- HLA-DR- myeloid-derived suppressor cells impair antimicrobial responses in patients with acute-on-chronic liver failure

OBJECTIVE

Immune paresis in patients with acute-on-chronic liver failure (ACLF) accounts for infection susceptibility and increased mortality. Immunosuppressive mononuclear CD14⁺HLA-DR^- myeloid-derived suppressor cells (M-MDSCs) have recently been identified to quell antimicrobial responses in immune-mediated diseases. We sought to delineate the function and derivation of M-MDSC in patients with ACLF, and explore potential targets to augment antimicrobial responses.

DESIGN

Patients with ACLF (n=41) were compared with healthy subjects (n=25) and patients with cirrhosis (n=22) or acute liver failure (n=30). CD14⁺CD15^-CD11b⁺HLA-DR^- cells were identified as per definition of M-MDSC and detailed immunophenotypic analyses were performed. Suppression of T cell activation was assessed by mixed lymphocyte reaction. Assessment of innate immune function included cytokine expression in response to Toll-like receptor (TLR-2, TLR-4 and TLR-9) stimulation and phagocytosis assays using flow cytometry and live cell imaging-based techniques.

RESULTS

Circulating CD14⁺CD15^-CD11b⁺HLA-DR^- M-MDSCs were markedly expanded in patients with ACLF (55% of CD14+ cells). M-MDSC displayed immunosuppressive properties, significantly decreasing T cell proliferation (p=0.01), producing less tumour necrosis factor-alpha/interleukin-6 in response to TLR stimulation (all p<0.01), and reduced bacterial uptake of Escherichia coli (p<0.001). Persistently low expression of HLA-DR during disease evolution was linked to secondary infection and 28-day mortality. Recurrent TLR-2 and TLR-4 stimulation expanded M-MDSC in vitro. By contrast, TLR-3 agonism reconstituted HLA-DR expression and innate immune function ex vivo.

CONCLUSION

Immunosuppressive CD14⁺HLA-DR^- M-MDSCs are expanded in patients with ACLF. They were depicted by suppressing T cell function, attenuated antimicrobial innate immune responses, linked to secondary infection, disease severity and prognosis. TLR-3 agonism reversed M-MDSC expansion and innate immune function and merits further evaluation as potential immunotherapeutic agent.

Cancer-induced systemic myeloid dysfunction: Implications for treatment and a novel nanoparticle approach for its correction

Unlike other regulatory circuits, cancer-induced myeloid dysfunction involves more than an accumulation of impaired dendritic cells, protumoral macrophages, and myeloid derived suppressor cells in the tumor microenvironment. It is also characterized by "aberrant" myelopoiesis that results in the accumulation and expansion of immature myeloid precursors with a suppressive phenotype in the systemic circulation. The first part of this review briefly describes the evidence for and consequences of this systemic dysfunctional myelopoiesis and the possible reinforcement of this phenomenon by conventional treatments used in patients with cancer, in particular chemotherapy and granulocyte-colony stimulating factor. The second half of this review describes very small size particles, a novel immune-modulatory nanoparticle, and the evidence indicating a possible role of this agent in correcting or re-programming the dysfunctional myelopoiesis in different scenarios.

Granulocytic Myeloid-Derived Suppressor Cells (GR-MDSC) in Breast Milk (BM); GR-MDSC Accumulate in Human BM and Modulate T-Cell and Monocyte Function

Nosocomial bacterial infections (NBI) and necrotizing enterocolitis (NEC) are among the main reasons for death in preterm infants. Both are often caused by bacteria coming from the infected infant’s gut and feeding with breast milk (BM) seems beneficial in their pathogenesis. However, mechanisms causing the protective effect of BM are only incompletely understood. Myeloid-derived suppressor cells (MDSC) are myeloid cells with suppressive activity on other immune cells, recently described to play a role in mediating maternal–fetal tolerance during pregnancy and immune adaptation in newborns. Until now, nothing is known about occurrence and function of MDSC in BM. We analyzed MDSC in BM and peripheral blood of breastfeeding mothers and found that granulocytic MDSC, but not monocytic MDSC, accumulate in BM, exhibit an activated phenotype and increased suppressive activity and modulate TLR-expression on monocytes. Furthermore, we found that the lactotrophic hormones prolactin and oxytocin do not induce MDSC from peripheral blood. This is the first study to describe MDSC with immune-modulatory properties in human BM. Our results point toward a role for MDSC in local immune modulation in the gut possibly protecting infants from NBI and NEC.

Immune regulatory cell infusion for graft-versus-host disease prevention and therapy

Current approaches to prevent and treat graft-versus-host disease (GVHD) after stem cell transplantation rely principally on pharmacological immune suppression. Such approaches are limited by drug toxicity, nonspecific immune suppression, and a requirement for long-term therapy. Our increased understanding of the regulatory cells and molecular pathways involved in limiting pathogenic immune responses opens the opportunity for the use of these cell subsets to prevent and/or GVHD. The theoretical advantages of this approach is permanency of effect, potential for facilitating tissue repair, and induction of tolerance that obviates a need for ongoing drug therapy. To date, a number of potential cell subsets have been identified, including FoxP3⁺ regulatory T (Treg) and FoxP3^negIL-10⁺ (FoxP3-negative) regulatory T (Tr1), natural killer (NK) and natural killer T (NKT) cells, innate lymphoid cells, and various myeloid suppressor populations of hematopoietic (eg, myeloid derived suppressor cells) and stromal origin (eg, mesenchymal stem cells). Despite initial technical challenges relating to large-scale selection and expansion, these regulatory lineages are now undergoing early phase clinical testing. To date, Treg therapies have shown promising results in preventing clinical GVHD when infused early after transplant. Results from ongoing studies over the next 5 years will delineate the most appropriate cell lineage, source (donor, host, third party), timing, and potential exogenous cytokine support needed to achieve the goal of clinical transplant tolerance.

Accumulation of T-helper 22 cells, interleukin-22 and myeloid-derived suppressor cells promotes gastric cancer progression in elderly patients

Chronic inflammation and immunosuppression lead to aging and tumorigenesis. T-helper 22 (Th22) cells, interleukin 22 (IL-22) and myeloid-derived suppressor cells (MDSCs) serve an important role in inflammatory-immune diseases and cancer. However, the status of Th22 cells, IL-22 and MDSCs in aging and elderly gastric cancer progression is unknown. In the present study, 39 elderly patients with gastric cancer (EGC), 32 elderly healthy controls (HE) and 31 young healthy controls (HY) were enrolled, and the peripheral Th22, Th17 and Th1 cells, and MDSCs, were examined using flow cytometry. Plasma levels of IL-22, IL-6 and tumor necrosis factor-α (TNF-α) were examined using ELISA. IL-22 protein levels in tumor tissues were examined using immunohistochemistry. There were increased numbers of peripheral Th22 and Th17 cells, and MDSCs, as well as increased plasma levels of IL-22, IL-6 and TNF-α in EGC compared with HE and HY. However, HE exhibited significantly increased levels of peripheral Th22 and Th17 cells as well as IL-6 and TNF-α compared with HY. Immunohistochemical analysis demonstrated that IL-22 protein accumulated in tumor cells and lymphocytes in the tumor microenvironment. The results obtained demonstrated that peripheral Th22 and Th17 cells as well as IL-6 and TNF-α plasma levels increased with aging. Furthermore, Th22 and Th17 cells, MDSCs, and IL-22 may be used as prognostic markers for identifying gastric cancer in elderly patients.

Hepatoma-intrinsic CCRK inhibition diminishes myeloid-derived suppressor cell immunosuppression and enhances immune-checkpoint blockade efficacy

OBJECTIVE

Myeloid-derived suppressor cells (MDSCs) contribute to tumour immunosuppressive microenvironment and immune-checkpoint blockade resistance. Emerging evidence highlights the pivotal functions of cyclin-dependent kinases (CDKs) in tumour immunity. Here we elucidated the role of tumour-intrinsic CDK20, or cell cycle-related kinase (CCRK) on immunosuppression in hepatocellular carcinoma (HCC).

DESIGN

Immunosuppression of MDSCs derived from patients with HCC and relationship with CCRK were determined by flow cytometry, expression analyses and co-culture systems. Mechanistic studies were also conducted in liver-specific CCRK-inducible transgenic (TG) mice and Hepa1-6 orthotopic HCC models using CRISPR/Cas9-mediated Ccrk depletion and liver-targeted nanoparticles for interleukin (IL) 6 trapping. Tumorigenicity and immunophenotype were assessed on single or combined antiprogrammed death-1-ligand 1 (PD-L1) therapy.

RESULTS

Tumour-infiltrating CD11b⁺CD33⁺HLA-DR^- MDSCs from patients with HCC potently inhibited autologous CD8⁺T cell proliferation. Concordant overexpression of CCRK and MDSC markers (CD11b/CD33) positively correlated with poorer survival rates. Hepatocellular CCRK stimulated immunosuppressive CD11b⁺CD33⁺HLA-DR^- MDSC expansion from human peripheral blood mononuclear cells through upregulating IL-6. Mechanistically, CCRK activated nuclear factor-κB (NF-κB) via enhancer of zeste homolog 2 (EZH2) and facilitated NF-κB-EZH2 co-binding to IL-6 promoter. Hepatic CCRK induction in TG mice activated the EZH2/NF-κB/IL-6 cascade, leading to accumulation of polymorphonuclear (PMN) MDSCs with potent T cell suppressive activity. In contrast, inhibiting tumorous Ccrk or hepatic IL-6 increased interferon γ⁺tumour necrosis factor-α⁺CD8⁺ T cell infiltration and impaired tumorigenicity, which was rescued by restoring PMN-MDSCs. Notably, tumorous Ccrk depletion upregulated PD-L1 expression and increased intratumorous CD8⁺ T cells, thus enhancing PD-L1 blockade efficacy to eradicate HCC.

CONCLUSION

Our results delineate an immunosuppressive mechanism of the hepatoma-intrinsic CCRK signalling and highlight an overexpressed kinase target whose inhibition might empower HCC immunotherapy.

The Multifaceted Effects of Alpha1-Antitrypsin on Neutrophil Functions

Neutrophils are the predominant immune cells in human blood possessing heterogeneity, plasticity and functional diversity. The activation and recruitment of neutrophils into inflamed tissue in response to stimuli are tightly regulated processes. Alpha1-Antitrypsin (AAT), an acute phase protein, is one of the potent regulators of neutrophil activation via both -protease inhibitory and non-inhibitory functions. This review summarizes our current understanding of the effects of AAT on neutrophils, illustrating the interplay between AAT and the key effector functions of neutrophils.

Dysregulated IL-18 Is a Key Driver of Immunosuppression and a Possible Therapeutic Target in the Multiple Myeloma Microenvironment

Tumor-promoting inflammation and avoiding immune destruction are hallmarks of cancer. Here, we demonstrate that the pro-inflammatory cytokine interleukin (IL)-18 is critically involved in these hallmarks in multiple myeloma (MM). Mice deficient for IL-18 were remarkably protected from Vk^∗MYC MM progression in a CD8⁺ T cell-dependent manner. The MM-niche-derived IL-18 drove generation of myeloid-derived suppressor cells (MDSCs), leading to accelerated disease progression. A global transcriptome analysis of the immune microenvironment in 73 MM patients strongly supported the negative impact of IL-18-driven MDSCs on T cell responses. Strikingly, high levels of bone marrow plasma IL-18 were associated with poor overall survival in MM patients. Furthermore, our preclinical studies suggested that IL-18 could be a potential therapeutic target in MM.

Characterization of Multiple Cytokine Combinations and TGF-β on Differentiation and Functions of Myeloid-Derived Suppressor Cells

Myeloid-derived suppressor cells (MDSCs) regulate T cell immunity, and this population is a new therapeutic target for immune regulation. A previous study showed that transforming growth factor-β (TGF-β) is involved in controlling MDSC differentiation and immunoregulatory function in vivo. However, the direct effect of TGF-β on MDSCs with various cytokines has not previously been tested. Thus, we examined the effect of various cytokine combinations with TGF-β on MDSCs derived from bone marrow cells. The data show that different cytokine combinations affect the differentiation and immunosuppressive functions of MDSCs in different ways. In the presence of TGF-β, interleukin-6 (IL-6) was the most potent enhancer of MDSC function, whereas granulocyte colony-stimulating factors (G-CSF) was the most potent in the absence of TGF-β. In addition, IL-4 maintained MDSCs in an immature state with an increased expression of arginase 1 (Arg1). However, regardless of the cytokine combinations, TGF-β increased expansion of the monocytic MDSC (Mo-MDSC) population, expression of immunosuppressive molecules by MDSCs, and the ability of MDSCs to suppress CD4⁺ T cell proliferation. Thus, although different cytokine combinations affected the MDSCs in different ways, TGF-β directly affects monocytic-MDSCs (Mo-MDSCs) expansion and MDSCs functions.

Inhibiting HSP90 prevents the induction of myeloid-derived suppressor cells by melanoma cells

Metastatic melanoma is the most dangerous form of skin cancer, with an ever-increasing incidence worldwide. Despite encouraging results with immunotherapeutic approaches, long-term survival is still poor. This is likely partly due to tumour-induced immune suppression mediated by myeloid-derived suppressor cells (MDSCs), which were shown to be associated with response to therapy and survival. Thus, identifying pathways responsible for MDSC differentiation may provide new therapeutic targets and improve efficacy of existing immunotherapies. Therefore, we've analysed mechanisms by which tumour cells contribute to the induction of MDSCs. Established melanoma cell lines were pre-treated with inhibitors of different pathways and tested for their capacity to alleviate T cell suppression via MDSC differentiation in vitro. Targeting HSP70/90 in melanoma cells resulted in reduced induction of immune suppressive cells on a phenotypic and functional basis, for which a more potent effect was observed when HSP90 was inhibited under hypoxic conditions. This initial study suggests a novel mechanism in tumour cells responsible for the induction of MDSC in melanoma.

Neutrophil: A Cell with Many Roles in Inflammation or Several Cell Types?

Neutrophils are the most abundant leukocytes in the circulation, and have been regarded as first line of defense in the innate arm of the immune system. They capture and destroy invading microorganisms, through phagocytosis and intracellular degradation, release of granules, and formation of neutrophil extracellular traps after detecting pathogens. Neutrophils also participate as mediators of inflammation. The classical view for these leukocytes is that neutrophils constitute a homogenous population of terminally differentiated cells with a unique function. However, evidence accumulated in recent years, has revealed that neutrophils present a large phenotypic heterogeneity and functional versatility, which place neutrophils as important modulators of both inflammation and immune responses. Indeed, the roles played by neutrophils in homeostatic conditions as well as in pathological inflammation and immune processes are the focus of a renovated interest in neutrophil biology. In this review, I present the concept of neutrophil phenotypic and functional heterogeneity and describe several neutrophil subpopulations reported to date. I also discuss the role these subpopulations seem to play in homeostasis and disease.

Serum expression level of IL-6 at the diagnosis time contributes to the long-term prognosis of SCLC patients

Cytokines are vital mediators involved in tumor immunity. We aimed to explore whether the expression levels of IL-1β, TNF-α and IL-6 have impacts on prognosis of SCLC patients. In this study, we concluded 707 non-operable SCLC patients at stage III or IV into this study and analyzed the relationships between interleukins and OS/PFS by cox regression analysis and Kaplan-Meier analysis (log-rank test). As a result, under current standard chemotherapy, SCLC patients with higher IL-6 expression level had a shortened OS compared with those with normal level (HR: 0.381, 95%CI: 0.177-0.822, p=0.014). Furthermore, IL-6 expression level contributed mostly to patients without a smoking history. Non-smoking patients with a high IL-6 level showed a 6 months shortened OS than those with normal IL-6 level (10.50 vs 16.90 months, p=0.003 by Log-Rank test in Kaplan-Meier analysis). IL-6 had no obvious impacts on first-line PFS in these SCLC patients. To conclude, IL-6 acts as an independent factor of long-term prognosis of SCLC patients under current therapy.

CD33+ HLA-DR- Myeloid-Derived Suppressor Cells Are Increased in Frequency in the Peripheral Blood of Type1 Diabetes Patients with Predominance of CD14+ Subset

INTRODUCTION:

Type 1 Diabetes Mellitus (T1D) is an autoimmune disease that results from the destruction of insulin-producing beta cells of the pancreas by autoreactive T cells. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells that can potently suppress T cell responses.

AIM:

To detect the presence of MDSCs in T1D and compare their percentage in T1D versus healthy individuals.

METHOD:

Thirty T1D patients were included in the study. Diabetic patients with nephropathy (n = 18) and diabetic patients without nephropathy (n = 12). A control group of healthy individuals (n = 30) were also included. CD33⁺ and HLA-DR– markers were used to identify MDSCs by flow cytometry. CD14 positive and negative MDSCs subsets were also identified.

RESULTS:

MDSCs was significantly increased in T1D than the control group and diabetic patient with nephropathy compared to diabetic patients without nephropathy. M-MDSCs (CD14⁺ CD33⁺ HLA–DR⁻) were the most abundant MDSCs subpopulation in all groups, however their percentage decrease in T1D than the control group.

CONCLUSION:

MDSCs are increased in the peripheral blood of T1D with a predominance of the CD14⁺ MDSCs subset. Future studies are needed to test the immune suppression function of MDSCs in T1D.

Generation of Human Immunosuppressive Myeloid Cell Populations in Human Interleukin-6 Transgenic NOG Mice

The tumor microenvironment contains unique immune cells, termed myeloid-derived suppressor cells (MDSCs), and tumor-associated macrophages (TAMs) that suppress host anti-tumor immunity and promote tumor angiogenesis and metastasis. Although these cells are considered a key target of cancer immune therapy, in vivo animal models allowing differentiation of human immunosuppressive myeloid cells have yet to be established, hampering the development of novel cancer therapies. In this study, we established a novel humanized transgenic (Tg) mouse strain, human interleukin (hIL)-6-expressing NOG mice (NOG-hIL-6 transgenic mice). After transplantation of human hematopoietic stem cells (HSCs), the HSC-transplanted NOG-hIL-6 Tg mice (HSC-NOG-hIL-6 Tg mice) showed enhanced human monocyte/macrophage differentiation. A significant number of human monocytes were negative for HLA-DR expression and resembled immature myeloid cells in the spleen and peripheral blood from HSC-NOG-hIL-6 Tg mice, but not from HSC-NOG non-Tg mice. Engraftment of HSC4 cells, a human head and neck squamous cell carcinoma-derived cell line producing various factors including IL-6, IL-1β, macrophage colony-stimulating factor (M-CSF), and vascular endothelial growth factor (VEGF), into HSC-NOG-hIL-6 Tg mice induced a significant number of TAM-like cells, but few were induced in HSC-NOG non-Tg mice. The tumor-infiltrating macrophages in HSC-NOG-hIL-6 Tg mice expressed a high level of CD163, a marker of immunoregulatory myeloid cells, and produced immunosuppressive molecules such as arginase-1 (Arg-1), IL-10, and VEGF. Such cells from HSC-NOG-hIL-6 Tg mice, but not HSC-NOG non-Tg mice, suppressed human T cell proliferation in response to antigen stimulation in in vitro cultures. These results suggest that functional human TAMs can be developed in NOG-hIL-6 Tg mice. This mouse model will contribute to the development of novel cancer immune therapies targeting immunoregulatory/immunosuppressive myeloid cells.

Semaphorin 4D in human head and neck cancer tissue and peripheral blood: A dense fibrotic peri-tumoral stromal phenotype

The search for stromal biomarkers in carcinoma patients is a challenge in the field. Semaphorin 4D (Sema4D), known for its various developmental, physiological and pathological effects, plays a role in pro and anti-inflammatory responses. It is expressed in many epithelial tumors including head and neck squamous cell carcinoma (HNSCC). Recently, we found that HNSCC-associated Sema4D modulates an immune-suppressive, tumor-permissible environment by inducing the expansion of myeloid derived suppressor cells. The purpose of this study was to determine the value of Sema4D as a biomarker for the peri-tumoral stromal phenotype in human HNSCC. Our data showed Sema4D^+ve/high tumor cells in 34% of the studied cohort with positive correlation to Stage III (p=0.0001). Sema4D^+ve/high tumor cells correlated directly with dense fibrotic peri-tumoral stroma (p=0.0001) and inversely with infiltrate of Sema4D^+ve/high tumor-associated inflammatory cells (TAIs) (p=0.01). Most of the Sema4D^+ve/high TAIs were co-positive for the macrophage biomarker CD163. Knockdown of Sema4D in WSU-HN6 cells inhibited collagen production by fibroblasts, and decreased activated TGF-β1 levels in culture medium of HNSCC cell lines. In a stratification model of HNSCC using combined Sema4D and the programmed death ligand 1 (PDL-1), Sema4D^+ve/high tumor cells represented a phenotype distinct from the PDL-1 positive tumors. Finally,Sema4D was detected in plasma of HNC patients at significantly higher levels (115.44, ± 39.37) compared to healthy donors (38.60± 12.73) (p <0.0001). In conclusion, we present a novel HNSCC tumor stratification model, based on the expression of the biomarker Sema4D. This model opens new avenues to novel targeted therapeutic strategies.

Programmed Death-Ligand 1 on Antigen-presenting Cells Facilitates the Induction of Antigen-specific Cytotoxic T Lymphocytes: Application to Adoptive T-Cell Immunotherapy

Programmed death-ligand 1 (PD-L1) binds to programmed death-1 (PD-1) on activated T cells and contributes to T-cell exhaustion. PD-L1 expressed on antigen-presenting cells (APCs) could be thought to inhibit the induction of Ag-specific cytotoxic T lymphocytes (CTLs) by transducing negative signal into T cells; however, the roles of PD-L1 on APCs have not yet been well examined. Therefore, we evaluated the roles of PD-L1 on APCs in the induction of Ag-specific CTLs. CD3 T cells isolated from cytomegalovirus (CMV)-seropositive healthy donors were stimulated with mature dendritic cells pulsed with CMV pp65-derived HLA-restricted peptides in the presence of anti-PD-L1 blocking antibody. Unexpectedly, PD-L1 blockade resulted in a less efficient induction of CMV-specific CTLs, suggesting that PD-L1 play a positive role in the induction of Ag-specific CTLs. For further evaluations and application to adoptive immunotherapy, we generated K562-based artificial APCs, which were retrovirally transduced with HLA class I molecules and various combinations of CD80/86 and PD-L1. K562/HLA+CD80/86+PD-L1 cells produced significantly higher induction of CMV-specific CTLs than K562/HLA or K562/HLA+CD80/86 cells without causing excessive differentiation or functional exhaustion of the induced CTLs, whereas PD-L1 itself did not have a stimulatory effect. Furthermore, only K562/HLA+CD80/86+PD-L1 cells pulsed with HLA-A*24:02-restricted Wilms tumor 1 (WT1) peptide clearly expanded WT1-specific CTLs from healthy donors. Our findings presumed that PD-L1 expressed on APCs along with CD80/86 enhanced the induction of Ag-specific CTLs probably depending on fine-tuning excessive stimulation of CD80/86, and that K562/HLA+CD80/86+PD-L1 cells has therapeutic potential as a novel type of artificial APCs for adoptive immunotherapy.

Myeloid-Derived Suppressor Cells Ameliorate Cyclosporine A-Induced Hypertension in Mice

The calcineurin inhibitor cyclosporine A (CsA) suppresses the immune system but promotes hypertension, vascular dysfunction, and renal damage. CsA decreases regulatory T cells and this contributes to the development of hypertension. However, CsA's effects on another important regulatory immune cell subset, myeloid-derived suppressor cells (MDSCs), is unknown. We hypothesized that augmenting MDSCs would ameliorate the CsA-induced hypertension and vascular and renal injury and dysfunction and that CsA reduces MDSCs in mice. Daily interleukin-33 treatment, which increased MDSC levels, completely prevented CsA-induced hypertension and vascular and renal toxicity. Adoptive transfer of MDSCs from control mice into CsA-treated mice after hypertension was established dose-dependently reduced blood pressure and vascular and glomerular injury. CsA treatment of aortas and kidneys isolated from control mice for 24 hours decreased relaxation responses and increased inflammation, respectively, and these effects were prevented by the presence of MDSCs. MDSCs also prevented the CsA-induced increase in fibronectin in microvascular and glomerular endothelial cells. Last, CsA dose-dependently reduced the number of MDSCs by inhibiting calcineurin and preventing cell proliferation, as other direct calcineurin signaling pathway inhibitors had the same dose-dependent effect. These data suggest that augmenting MDSCs can reduce the cardiovascular and renal toxicity and hypertension caused by CsA.

A functional characteristic of cysteine-rich protein 61: Modulation of myeloid-derived suppressor cells in liver inflammation

There is increasing awareness of the immunologic roles of liver mononuclear populations, including myeloid-derived suppressor cells (MDSCs). We took advantage of a large well-defined cohort of 148 patients with liver inflammation and 45 healthy controls to focus on the qualitative and quantitative characteristics of MDSCs. We investigated the frequency, phenotype, and functional capacities of MDSCs by using peripheral blood MDSCs in a cohort of 55 patients with primary biliary cholangitis (PBC), 40 with autoimmune hepatitis, 39 with chronic hepatitis B, 14 with nonalcoholic fatty liver disease, and 45 healthy controls. This was followed by a liver-targeted determination in 27 patients with PBC, 27 with autoimmune hepatitis, 20 with chronic hepatitis B, 14 with nonalcoholic fatty liver disease, and 6 controls. We then focused on mechanisms of this expansion with PBC as an example, using both ursodeoxycholic acid-naive and treated patients. HLA-DR^-/low CD33⁺ CD11b⁺ CD14⁺ CD15^- monocytic MDSCs were elevated in diseases characterized by liver inflammation compared to healthy controls. Using PBC as a focus, there was a significant correlation between levels of circulating MDSCs and disease-related biochemical markers (alkaline phosphatase, total bilirubin). We found higher amounts of MDSCs in patients with PBC who were responsive to ursodeoxycholic acid. MDSCs from PBC were found to manifest a potent immunosuppressive function. There was a significant correlation in the accumulation of hepatic MDSCs in the inflamed lesions of PBC with histologic changes, such as fibrosis. We also found that cysteine-rich protein 61 (CCN1), a highly expressed protein in impaired cholangiocytes and hepatocytes, contributes to MDSC expansion and MDSC inducible nitric oxide synthase-associated immune suppression.

CONCLUSION

CCN1 modulates expansion and a suppressive function of MDSCs. Our data highlight the potential functions of CCN1 on MDSCs and suggest therapeutic implications in inflammatory liver diseases. (Hepatology HEPATOLOGY 2018;67:232-246).

Rhesus Macaque Myeloid-Derived Suppressor Cells Demonstrate T Cell Inhibitory Functions and Are Transiently Increased after Vaccination

Myeloid-derived suppressor cells (MDSCs) are major regulators of T cell responses in several pathological conditions. Whether MDSCs increase and influence T cell responses in temporary inflammation, such as after vaccine administration, is unknown. Using the rhesus macaque model, which is critical for late-stage vaccine testing, we demonstrate that monocytic (M)-MDSCs and polymorphonuclear (PMN)-MDSCs can be detected using several of the markers used in humans. However, whereas rhesus M-MDSCs lacked expression of CD33, PMN-MDSCs were identified as CD33⁺ low-density neutrophils. Importantly, both M-MDSCs and PMN-MDSCs showed suppression of T cell proliferation in vitro. The frequency of circulating MDSCs rapidly and transiently increased 24 h after vaccine administration. M-MDSCs infiltrated the vaccine injection site, but not vaccine-draining lymph nodes. This was accompanied by upregulation of genes relevant to MDSCs such as arginase-1, IDO1, PDL1, and IL-10 at the injection site. MDSCs may therefore play a role in locally maintaining immune balance during vaccine-induced inflammation.

mTOR inhibitor rapamycin induce polymorphonuclear myeloid-derived suppressor cells mobilization and function in protecting against acute graft-versus-host disease after bone marrow transplantation

The mammalian target of rapamycin (mTOR) inhibitor rapamycin (RAPA) has been shown to be an effective immunosuppressor in the management of acute graft-versus-host disease (aGVHD) after bone marrow transplantation. Myeloid-derived suppressor cells (MDSCs) also have a protective effect in aGVHD regulation. However, the relationship between RAPA and MDSCs in aGVHD models is unclear. Meanwhile, the effect of RAPA on different subgroups of MDSCs is also less well described. In this study, we demonstrate that in vivo administration of RAPA results in the expansion and functional enhancement of polymorphonuclear MDSCs (PMN-MDSCs) in a murine model of aGVHD. RAPA treatment can enhance the suppressive function of PMN-MDSCs via up-regulation of arginase1 (Arg1) and induced nitric oxide synthase (iNOS) at later time points. Moreover, RAPA can also induce a strong immunosuppressive function in PMN-MDSCs from murine bone marrow in vitro, but has a contrary effect on monocytic MDSCs (M-MDSCs). We found that RAPA-treated PMN-MDSCs can restrain the differentiation of Th1/Th2 cells and promote induction of regulatory T cells in in vitro studies.

Conditioned media from the renal cell carcinoma cell line 786.O drives human blood monocytes to a monocytic myeloid-derived suppressor cell phenotype

Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells critical in mediating immune suppression in cancer patients. To develop an in vitro assay system that functionally mimics the tumor microenvironment, we cultured human monocytes with conditioned media from several cancer cell lines. Conditioned media from five tumor cell lines induced survival and differentiation of monocytes into cells characteristically similar to macrophages and MDSCs. Notably, media from the 786.O renal cell carcinoma line induced monocytes to acquire a monocytic MDSC phenotype characterized by decreased HLA-DR expression, increased nitric oxide production, enhanced proliferation, and ability to suppress autologous CD3⁺ T cell proliferation. We further demonstrated that these in vitro MDSCs are phenotypically and functionally similar to patient-derived MDSCs. Inhibitors of STAT3, CK2, and GM-CSF resulted in partial reversal of the MDSC phenotype. MDSCs generated in vitro from 786.O tumor conditioned media represent a platform to identify potential therapeutics that inhibit MDSC activities.

Granulocytic myeloid-derived suppressor cells (GR-MDSC) accumulate in cord blood of preterm infants and remain elevated during the neonatal period

Preterm delivery is the leading cause of perinatal morbidity and mortality. Among the most important complications in preterm infants are peri- or postnatal infections. Myeloid-derived suppressor cells (MDSC) are myeloid cells with suppressive activity on other immune cells. Emerging evidence suggests that granulocytic MDSC (GR-MDSC) play a pivotal role in mediating maternal-fetal tolerance. The role of MDSC for postnatal immune-regulation in neonates is incompletely understood. Until the present time, nothing was known about expression of MDSC in preterm infants. In the present pilot study, we quantified GR-MDSC counts in cord blood and peripheral blood of preterm infants born between 23 + 0 and 36 + 6 weeks of gestation (WOG) during the first 3 months of life and analysed the effect of perinatal infections. We show that GR-MDSC are increased in cord blood independent of gestational age and remain elevated in peripheral blood of preterm infants during the neonatal period. After day 28 they drop to nearly adult levels. In case of perinatal or postnatal infection, GR-MDSC accumulate further and correlate with inflammatory markers C-reactive protein (CRP) and white blood cell counts (WBC). Our results point towards a role of GR-MDSC for immune-regulation in preterm infants and render them as a potential target for cell-based therapy of infections in these patients.

Myeloid-Derived Suppressor Cells in the Tumor Microenvironment: Current Knowledge and Future Perspectives

The current knowledge on tumor-infiltrating myeloid-derived suppressor cells (MDSCs) is based mainly on the extensive work performed in murine models. Data obtained for human counterparts are generated on the basis of tumor analysis from patient samples. Both sources of information led to determination of the main suppressive mechanisms used by these cell subsets in tumor-bearing hosts. As a result of the identification of protein targets responsible for MDSCs suppressive activity, different therapeutics agents have been used to eliminate/reduce their adverse effect. In the present work, we review the current knowledge on suppressive mechanisms of MDSCs and therapeutic treatments that interfere with their differentiation, expansion or activity. Based on the accumulation of new evidences supporting their importance for tumor progression and metastasis, the interest in these cell types is increasing. We revise the methods of MDSC generation/differentiation ex vivo that may help in overcoming problems associated with limited numbers of cells available from animals and patients for their study.

VEGF blockade enhances the antitumor effect of BRAFV600E inhibition

The development of resistance remains a major obstacle to long‐term disease control in cancer patients treated with targeted therapies. In BRAF‐mutant mouse models, we demonstrate that although targeted inhibition of either BRAF or VEGF initially suppresses the growth of BRAF‐mutant tumors, combined inhibition of both pathways results in apoptosis, long‐lasting tumor responses, reduction in lung colonization, and delayed onset of acquired resistance to the BRAF inhibitor PLX4720. As well as inducing tumor vascular normalization and ameliorating hypoxia, this approach induces remodeling of the extracellular matrix, infiltration of macrophages with an M1‐like phenotype, and reduction in cancer‐associated fibroblasts. At the molecular level, this therapeutic regimen results in a de novo transcriptional signature, which sustains and explains the observed efficacy with regard to cancer progression. Collectively, our findings offer new biological rationales for the management of clinical resistance to BRAF inhibitors based on the combination between BRAF^V600E inhibitors with anti‐angiogenic regimens.

Prime-boost immunization by both DNA vaccine and oncolytic adenovirus expressing GM-CSF and shRNA of TGF-β2 induces anti-tumor immune activation

A successful DNA vaccine for the treatment of tumors should break established immune tolerance to tumor antigen. However, due to the relatively low immunogenicity of DNA vaccines, compared to other kinds of vaccines using live virus or protein, a recombinant viral vector was used to enhance humoral and cellular immunity. In the current study, we sought to develop a novel anti-cancer agent as a complex of DNA and oncolytic adenovirus for the treatment of malignant melanoma in the C57BL/6 mouse model. MART1, a human melanoma-specific tumor antigen, was used to induce an increased immune reaction, since a MART1-protective response is required to overcome immune tolerance to the melanoma antigen MelanA. Because GM-CSF is a potent inducer of anti-tumor immunity and TGF-β2 is involved in tumor survival and host immune suppression, mouse GM-CSF (mGM-CSF) and shRNA of mouse TGF-β2 (shmTGF-β2) genes were delivered together with MART1 via oncolytic adenovirus. MART1 plasmid was also used for antigen-priming. To compare the anti-tumor effect of oncolytic adenovirus expressing both mGM-CSF and shmTGF-β2 (Ad^GshT) with that of oncolytic adenovirus expressing mGM-CSF only (Ad^G), each virus was intratumorally injected into melanoma-bearing C57BL/6 mice. As a result, mice that received Ad^GshT showed delayed tumor growth than those that received Ad^G. Heterologous prime-boost immunization was combined with oncolytic Ad^GshT and MART1 expression to result in further delayed tumor growth. This regression is likely due to the following 4 combinations: MART1-derived mouse melanoma antigen-specific immune reaction, immune stimulation by mGM-CSF/shmTGF-β2, tumor growth inhibition by shmTGF-β2, and tumor cell-specific lysis via an oncolytic adenovirus. Immune activation was mainly induced by mature tumor-infiltrating dendritic cell (TIDC) and lowered regulatory T cells in tumor-infiltrating lymphocytes (TIL). Taken together, these findings demonstrate that human MART1 induces a mouse melanoma antigen-specific immune reaction. In addition, the results also indicate that combination therapy of MART1 plasmid, together with an oncolytic adenovirus expressing MART1, mGM-CSF, and shmTGF-β2, is a promising candidate for the treatment of malignant melanoma.

CCR2+ monocytic myeloid-derived suppressor cells (M-MDSCs) inhibit collagen degradation and promote lung fibrosis by producing transforming growth factor-β1

Monocytes infiltrating scar tissue are predominantly viewed as progenitor cells. Here, we show that tissue CCR2⁺ monocytes have specific immunosuppressive and profibrotic functions. CCR2⁺ monocytic cells are acutely recruited to the lung before the onset of silica-induced fibrosis in mice. These tissue monocytes are defined as monocytic myeloid-derived suppressor cells (M-MDSCs) because they significantly suppress T-lymphocyte proliferation in vitro. M-MDSCs collected from silica-treated mice also express transforming growth factor (TGF)-β1, which stimulates lung fibroblasts to release tissue inhibitor of metalloproteinase (TIMP)-1, an inhibitor of metalloproteinase collagenolytic activity. By using LysMCreCCR2^loxP/loxP mice, we show that limiting CCR2⁺ M-MDSC accumulation reduces the pulmonary contents of TGF-β1, TIMP-1 and collagen after silica treatment. M-MDSCs do not differentiate into lung macrophages, granulocytes or fibrocytes during pulmonary fibrogenesis. Collectively, our data indicate that M-MDSCs contribute to lung fibrosis by specifically promoting a non-degrading collagen microenvironment. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Immunomodulatory Properties of Coriolus versicolor: The Role of Polysaccharopeptide

Traditional uses of herbal medicine have depended mostly on anecdotal evidence for much of history. The increasing application of scientific rigor to the study some of these traditional therapies in recent years has revealed potent bioactivity, notably demonstrated by the 2015 Nobel Prize for the discovery of an antimalarial compound from traditional Chinese herbs. Given the recent successes of immunotherapy and checkpoint blockade, there is a renewed interest in identifying new drugs with immunomodulatory effects. As an estimated 45-60% of cancer patients worldwide are reported to use complementary alternative medicine alongside traditional therapy, this review will highlight the literature on the immunomodulatory effects of one of these compounds. We report on the induction of a largely pro-inflammatory cytokine profile by the polysaccharopeptide (PSP) isolated from the Coriolus versicolor (Yun zhi) mushroom, as well as its effects on various immune subsets, and the clinical data that have led to its widespread adoption as an adjunct cancer therapeutic in many Eastern cultures. Particular focus is given to the potential mechanisms underlying the bioactivity of PSP and reports of its ability to promote antitumor immunity by helping overcome tolerogenic tumor microenvironments.

Ascites-derived IL-6 and IL-10 synergistically expand CD14+HLA-DR-/low myeloid-derived suppressor cells in ovarian cancer patients

Myeloid-derived suppressor cells (MDSC) play a key immunosuppressive role in various types of cancer, including ovarian cancer (OC). In this study, we characterized CD14⁺HLA-DR^–/lo MDSC with a typical monocytic phenotype (M-MDSC) in the peripheral blood (PB) and ascites from OC patients. Compared to healthy donors, OC patients had a significantly increased abundance of M-MDSC in both PB and ascites; importantly, their abundance in both compartments was inversely associated with the prognosis where OC patients with higher level of M-MDSC having a shorter relapse-free survival. Intriguingly, we demonstrated that M-MDSC could be readily induced by ascitic fluids (AF) from OC patients, which was predominantly dependent on IL-6, IL-10 and STAT3 activation as neutralization of IL-6 and/or IL-10 or inhibition of STAT3 abrogated MDSC's expansion while recombinant IL-6 and IL-10 recapitulated the expansive effect of AF; furthermore, predominantly elevated levels of IL-6 and IL-10 has been noted in the AF which was positively correlated with the abundance of M-MDSC as well as poor prognosis of OC patients. As expected, we observed that AF-driven STAT3 activation upregulated the expression of arginase (ARG1) and inducible nitric oxide synthase (iNOS) in induced M-MDSC through which these MDSC executed the immunosuppressive activity. Taken together, these results demonstrate that abundant M-MDSC are present in both periphery and ascites of OC patients whose accumulation and suppressive activity is critically attributable to ascites-derived IL-6 and IL-10 and their downstream STAT3 signal, thus providing a potentially novel therapeutic option by locally targeting MDSC to improve antitumor efficacy.

Stromal cyclin D1 promotes heterotypic immune signaling and breast cancer growth

The cyclin D1 gene encodes the regulatory subunit of a holoenzyme that drives cell autonomous cell cycle progression and proliferation. Herein we show cyclin D1 abundance is increased >30-fold in the stromal fibroblasts of patients with invasive breast cancer, associated with poor outcome. Cyclin D1 transformed hTERT human fibroblast to a cancer-associated fibroblast phenotype. Stromal fibroblast expression of cyclin D1 (cyclin D1^Stroma) in vivo, enhanced breast epithelial cancer tumor growth, restrained apoptosis, and increased autophagy. Cyclin D1^Stroma had profound effects on the breast tumor microenvironment increasing the recruitment of F4/80⁺ and CD11b⁺ macrophages and increasing angiogenesis. Cyclin D1^Stroma induced secretion of factors that promoted expansion of stem cells (breast stem-like cells, embryonic stem cells and bone marrow derived stem cells). Cyclin D1^Stroma resulted in increased secretion of proinflammatory cytokines (CCL2, CCL7, CCL11, CXCL1, CXCL5, CXCL9, CXCL12), CSF (CSF1, GM-CSF1) and osteopontin (OPN) (30-fold). OPN was induced by cyclin D1 in fibroblasts, breast epithelial cells and in the murine transgenic mammary gland and OPN was sufficient to induce stem cell expansion. These results demonstrate that cyclin D1^Stroma drives tumor microenvironment heterocellular signaling, promoting several key hallmarks of cancer.

Mass cytometry deep phenotyping of human mononuclear phagocytes and myeloid-derived suppressor cells from human blood and bone marrow

The monocyte phagocyte system (MPS) includes numerous monocyte, macrophage, and dendritic cell (DC) populations that are heterogeneous, both phenotypically and functionally. In this study, we sought to characterize those diverse MPS phenotypes with mass cytometry (CyTOF). To identify a deep phenotype of monocytes, macrophages, and DCs, a panel was designed to measure 38 identity, activation, and polarization markers, including CD14, CD16, HLA-DR, CD163, CD206, CD33, CD36, CD32, CD64, CD13, CD11b, CD11c, CD86, and CD274. MPS diversity was characterized for 1) circulating monocytes from healthy donors, 2) monocyte-derived macrophages further polarized in vitro (i.e., M-CSF, GM-CSF, IL-4, IL-10, IFN-γ, or LPS long-term stimulations), 3) monocyte-derived DCs, and 4) myeloid-derived suppressor cells (MDSCs), generated in vitro from bone marrow and/or peripheral blood. Known monocyte subsets were detected in peripheral blood to validate the panel and analysis pipeline. Then, using various culture conditions and stimuli before CyTOF analysis, we constructed a multidimensional framework for the MPS compartment, which was registered against historical M1 or M2 macrophages, monocyte subsets, and DCs. Notably, MDSCs generated in vitro from bone marrow expressed more S100A9 than when generated from peripheral blood. Finally, to test the approach in vivo, peripheral blood from patients with melanoma (n = 5) was characterized and observed to be enriched for MDSCs with a phenotype of CD14+HLA-DRlowS100A9high (3% of PBMCs in healthy donors, 15.5% in patients with melanoma, P < 0.02). In summary, mass cytometry comprehensively characterized phenotypes of human monocyte, MDSC, macrophage, and DC subpopulations in both in vitro models and patients.

C-C Chemokine Receptor Type 2-Dependent Migration of Myeloid-Derived Suppressor Cells in Protection of Islet Transplants

BACKGROUND

Islet transplantation is a promising therapeutic approach to restore the physical response to blood glucose in type 1 diabetes. Current chronic use of immunosuppressive reagents for preventing islet allograft rejection is associated with severe complications. In addition, many of the immunosuppressive drugs are diabetogenic. The induction of transplant tolerance to eliminate the dependency on immunosuppression is ideal, but remains challenging.

METHODS

Addition of hepatic stellate cells allowed generation of myeloid-derived suppressor cells (MDSC) from precursors in mouse bone marrow. Migration of MDSC was examined in an islet allograft transplant model by tracking the systemic administered MDSC from CD45.1 congenic mice.

RESULTS

The generated MDSC were expressed C-C chemokine receptor type 2 (CCR2), which was enhanced by exposure to interferon-γ. A single systemic administration of MDSC markedly prolonged survival of islet allografts without requirement of immunosuppression. Tracking the administered MDSC showed that they promptly migrated to the islet graft sites, at which point they exerted potent immune suppressive activity by inhibiting CD8 T cells, enhancing regulatory T cell activity. MDSC generated from CCR2 mice failed to be mobilized and lost tolerogenic activity in vivo, but sustained suppressive activity in vitro.

CONCLUSIONS

MDSC migration was dependent on expression of CCR2, whereas CCR2 does not directly participate in immune suppression. Expression of CCR2 needs to be closely monitored for quality control purpose when MDSC are generated in vitro for immune therapy.

LMP1-mediated glycolysis induces myeloid-derived suppressor cell expansion in nasopharyngeal carcinoma

Myeloid-derived suppressor cells (MDSCs) are expanded in tumor microenvironments, including that of Epstein–Barr virus (EBV)-associated nasopharyngeal carcinoma (NPC). The link between MDSC expansion and EBV infection in NPC is unclear. Here, we show that EBV latent membrane protein 1 (LMP1) promotes MDSC expansion in the tumor microenvironment by promoting extra-mitochondrial glycolysis in malignant cells, which is a scenario for immune escape initially suggested by the frequent, concomitant detection of abundant LMP1, glucose transporter 1 (GLUT1) and CD33⁺ MDSCs in tumor sections. The full process has been reconstituted in vitro. LMP1 promotes the expression of multiple glycolytic genes, including GLUT1. This metabolic reprogramming results in increased expression of the Nod-like receptor family protein 3 (NLRP3) inflammasome, COX-2 and P-p65 and, consequently, increased production of IL-1β, IL-6 and GM-CSF. Finally, these changes in the environment of malignant cells result in enhanced NPC-derived MDSC induction. One key step is the physical interaction of LMP1 with GLUT1 to stabilize the GLUT1 protein by blocking its K48-ubiquitination and p62-dependent autolysosomal degradation. This work indicates that LMP1-mediated glycolysis regulates IL-1β, IL-6 and GM-CSF production through the NLRP3 inflammasome, COX-2 and P-p65 signaling pathways to enhance tumor-associated MDSC expansion, which leads to tumor immunosuppression in NPC.

The expression of the Epstein-Barr virus (EBV) oncogenic protein denoted latent membrane protein 1 (LMP1) varies in patients with NPC and is linked to tumorigenesis and tumor immunosuppression, but the molecular mechanism through which LMP1 leads to tumor immune escape remains unknown. Work to date suggests that the expansion of tumor-associated myeloid-derived suppressor cells (MDSCs) is the main cause of tumor immunosuppression such as that found in NPC. Here, we found that tumor LMP1 expression is correlated with glucose transporter 1 (GLUT1) levels, CD33⁺ MDSC number and unfavorable survival in patients with NPC. Based on the results of our in vitro analysis, LMP1 promotes GLUT1-dependent glycolysis in NPC cells, resulting in activation of the Nod-like receptor family protein 3 (NLRP3) inflammasome, COX-2 and P-p65 signaling pathways and subsequently increased IL-1β, IL-6 and GM-CSF production. Importantly, LMP1 interacts with GLUT1 to stabilize the GLUT1 protein by disrupting its K48-linked ubiquitination and autolysosomal degradation in a p62-dependent manner and up-regulating the GLUT1 mRNA and protein levels by inducing p65 activation. Therefore, we determined that GLUT1-dependent glycolysis is required for tumor-induced MDSC differentiation and that this process is associated with LMP1 expression. Based on our findings, LMP1-mediated glycolysis is a key process involved in controlling tumor immunosuppression and directly contributes to oncogenesis.

Phenotype and Function of Myeloid-Derived Suppressor Cells Induced by Porphyromonas gingivalis Infection

Porphyromonas gingivalis, a major etiologic agent of periodontitis, has been reported to induce the expansion of myeloid-derived suppressor cells (MDSC); however, little is known regarding the subpopulations of MDSC expanded by P. gingivalis infection. Flow cytometry was used to evaluate bone marrow and spleen cells from mice infected with P. gingivalis and controls for surface expression of CD11b, Ly6G, and Ly6C. To characterize the phenotype of MDSC subpopulations induced by infection, cells were sorted based on the differential expression of Ly6G and Ly6C. Moreover, since MDSC are suppressors of T cell immune activity, we determined the effect of the induced subpopulations of MDSC on the proliferative response of OVA-specific CD4⁺ T cells. Lastly, the plasticity of MDSC to differentiate into osteoclasts was assessed by staining for tartrate-resistant acid phosphatase activity. P. gingivalis infection induced the expansion of three subpopulations of MDSC (Ly6G⁺⁺ Ly6C⁺, Ly6G⁺ Ly6C⁺⁺, and Ly6G⁺ Ly6C⁺); however, only CD11b⁺ Ly6G⁺ Ly6C⁺⁺-expressing cells exerted a significant suppressive effect on T cell proliferation. Inhibition of proliferative responses required T cell-MDSC contact and was mediated by inducible nitric oxide synthase and cationic amino acid transporter 2 via gamma interferon. Furthermore, only the CD11b⁺ Ly6G⁺ Ly6C⁺⁺ subpopulation of MDSC induced by P. gingivalis infection was able to differentiate into osteoclasts. Thus, the inflammatory response induced by P. gingivalis infection promotes the expansion of immune-suppressive cells and consequently the development of regulatory inhibitors that curtail the host response. Moreover, monocytic MDSC have the plasticity to differentiate into OC, thus perhaps contributing to the OC pool in states of periodontal disease.

MICA-Expressing Monocytes Enhance Natural Killer Cell Fc Receptor-Mediated Antitumor Functions

Natural killer (NK) cells are large granular lymphocytes that promote the antitumor response via communication with other cell types in the tumor microenvironment. Previously, we have shown that NK cells secrete a profile of immune stimulatory factors (e.g., IFNγ, MIP-1α, and TNFα) in response to dual stimulation with the combination of antibody (Ab)-coated tumor cells and cytokines, such as IL12. We now demonstrate that this response is enhanced in the presence of autologous monocytes. Monocyte enhancement of NK cell activity was dependent on cell-to-cell contact as determined by a Transwell assay. It was hypothesized that NK cell effector functions against Ab-coated tumor cells were enhanced via binding of MICA on monocytes to NK cell NKG2D receptors. Strategies to block MICA-NKG2D interactions resulted in reductions in IFNγ production. Depletion of monocytes in vivo resulted in decreased IFNγ production by murine NK cells upon exposure to Ab-coated tumor cells. In mice receiving trastuzumab and IL12 therapy, monocyte depletion resulted in significantly greater tumor growth in comparison to mock-depleted controls (P < 0.05). These data suggest that NK cell-monocyte interactions enhance NK cell antitumor activity in the setting of monoclonal Ab therapy for cancer. Cancer Immunol Res; 5(9); 778-89. ©2017 AACR.

Differential Phenotypes of Myeloid-Derived Suppressor and T Regulatory Cells and Cytokine Levels in Amnestic Mild Cognitive Impairment Subjects Compared to Mild Alzheimer Diseased Patients

Alzheimer disease (AD) is the most prevalent form of dementia although the underlying cause(s) remains unknown at this time. However, neuroinflammation is believed to play an important role and suspected contributing immune parameters can be revealed in studies comparing patients at the stage of amnestic mild cognitive impairment (aMCI) to healthy age-matched individuals. A network of immune regulatory cells including regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) maintains immune homeostasis but there are very few data on the role of these cells in AD. Here, we investigated the presence of these cells in the blood of subjects with aMCI and mild AD (mAD) in comparison with healthy age-matched controls. We also quantitated several pro- and anti-inflammatory cytokines in sera which can influence the development and activation of these cells. We found significantly higher levels of MDSCs and Tregs in aMCI but not in mAD patients, as well as higher serum IL-1β levels. Stratifying the subjects based on CMV serostatus that is known to influence multiple immune parameters showed an absence of differences between aMCI subjects compared to mAD patients and healthy controls. We suggest that the increase in MDSCs and Tregs number in aMCI subjects may have a beneficial role in modulating inflammatory processes. However, this protective mechanism may have failed in mAD patients, allowing progression of the disease. This working hypothesis obviously requires testing in future studies.

TLR9 expression and secretion of LIF by prostate cancer cells stimulates accumulation and activity of polymorphonuclear MDSCs

Proinflammatory signals promote prostate tumorigenesis and progression, but their origins and downstream effects remain unclear. We recently demonstrated that the expression of an innate immune receptor, TLR9, by prostate cancer cells is critical for their tumor-propagating potential. We investigated whether cancer cell-intrinsic TLR9 signaling alters composition of the prostate tumor microenvironment. We generated Ras/Myc (RM9) and Myc-driven (Myc-CaP) prostate cancer cells expressing the tetracycline-inducible gene Tlr9 (Tlr9^ON ) or the control LacZ (LacZ^ON ). When engrafted into mice and treated with tetracycline, Tlr9^ON , but not LacZ^ON , tumors showed accelerated growth kinetics compared with tumors in PBS-treated mice. Tlr9 upregulation in cancer cells triggered the selective accumulation of CD11b⁺Ly6G^HILy6C^LO myeloid cells, phenotypically similar to PMN-MDSCs. The PMN-MDSCs from tetracycline-treated RM9-Tlr9^ON tumors increased the immunosuppressive activity of the STAT3 transcription factor, thereby more potently inhibiting T cell proliferation. We identified LIF, an IL-6-type cytokine and STAT3 activator, as a potential mediator of crosstalk between TLR9-expressing prostate cancer cells and PMN-MDSCs. Antibody-mediated LIF neutralization reduced the percentage of tumor-infiltrating PMN-MDSCs and inhibited tumor growth in mice. The clinical relevance of LIF is confirmed by the correlation between TLR9 and LIF expression in prostate cancer specimens. Furthermore, blood samples from patients with prostate cancer showed elevated levels of LIF and high LIFR expression on circulating PMN-MDSCs. Our results suggest that TLR9⁺ prostate cancers promote immune evasion via LIF-mediated expansion and activation of PMN-MDSCs. Finally, targeting TLR9/LIF/STAT3 signaling using oligonucleotide-based inhibitors, such as CpG-STAT3dODN, can offer new opportunities for prostate cancer immunotherapy.

Glycolysis regulates the expansion of myeloid-derived suppressor cells in tumor-bearing hosts through prevention of ROS-mediated apoptosis

Immunotherapy aiming to rescue or boost antitumor immunity is an emerging strategy for treatment of cancers. The efficacy of immunotherapy is strongly controlled by the immunological milieu of cancer patients. Myeloid-derived suppressor cells (MDSCs) are heterogeneous immature myeloid cell populations with immunosuppressive functions accumulating in individuals during tumor progression. The signaling mechanisms of MDSC activation have been well studied. However, there is little known about the metabolic status of MDSCs and the physiological role of their metabolic reprogramming. In this study, we discovered that myeloid cells upregulated their glycolytic genes when encountered with tumor-derived factors. MDSCs exhibited higher glycolytic rate than their normal cell compartment did, which contributed to the accumulation of the MDSCs in tumor-bearing hosts. Upregulation of glycolysis prevented excess reactive oxygen species (ROS) production by MDSCs, which protected MDSCs from apoptosis. Most importantly, we identified the glycolytic metabolite, phosphoenolpyruvate (PEP), as a vital antioxidant agent able to prevent excess ROS production and therefore contributed to the survival of MDSCs. These findings suggest that glycolytic metabolites have important roles in the modulation of fitness of MDSCs and could be potential targets for anti-MDSC strategy. Targeting MDSCs with analogs of specific glycolytic metabolites, for example, 2-phosphoglycerate or PEP may diminish the accumulation of MDSCs and reverse the immunosuppressive milieu in tumor-bearing individuals.

The Sabotaging Role of Myeloid Cells in Anti-Angiogenic Therapy: Coordination of Angiogenesis and Immune Suppression by Hypoxia

Tumor angiogenesis has become a promising target for anti-tumor therapy. Unfortunately, the somewhat inevitable occurrence of resistance has limited the efficacy of anti-angiogenic therapy. In addition to their well-established role in immune suppression, bone marrow-derived myeloid cells actively contribute to tumor angiogenesis. More importantly, myeloid cells constitute one of the major mechanisms of resistance to angiogenesis inhibition. As the most pervasive feature in tumor microenvironment, hypoxia is able to initiate both pro-angiogenic and immunosuppressive capacities of myeloid cells. Tumor adapts to hypoxic stress primarily through signaling mediated by hypoxic inducible factors (HIFs) and consequently utilizes hypoxia to its own advantage. In this regard, hypoxia orchestrates both angiogenesis and immune evasion to support tumor growth. In this article, we will review available information on the sabotaging role of myeloid cells in anti-angiogenic therapy. We will also discuss how hypoxia coordinates the dual-role cellular and molecular participants in microenvironment to maximize the efficiency of angiogenesis and immunosuppression to promote tumor progression. J. Cell. Physiol. 232: 2312-2322, 2017. © 2016 Wiley Periodicals, Inc.

Glucocorticoid receptor promotes the function of myeloid-derived suppressor cells by suppressing HIF1α-dependent glycolysis

Immunomodulatory signaling imposes tight regulations on metabolic programs within immune cells and consequentially determines immune response outcomes. Although the glucocorticoid receptor (GR) has been recently implicated in regulating the function of myeloid-derived suppressor cells (MDSCs), whether the dysregulation of GR in MDSCs is involved in immune-mediated hepatic diseases and how GR regulates the function of MDSCs in such a context remains unknown. Here, we revealed the dysregulation of GR expression in MDSCs during innate immunological hepatic injury (IMH) and found that GR regulates the function of MDSCs through modulating HIF1α-dependent glycolysis. Pharmacological modulation of GR by its agonist (dexamethasone, Dex) protects IMH mice against inflammatory injury. Mechanistically, GR signaling suppresses HIF1α and HIF1α-dependent glycolysis in MDSCs and thus promotes the immune suppressive activity of MDSCs. Our studies reveal a role of GR-HIF1α in regulating the metabolism and function of MDSCs and further implicate MDSC GR signaling as a potential therapeutic target in hepatic diseases that are driven by innate immune cell-mediated systemic inflammation.

Neutrophils as active regulators of the immune system in the tumor microenvironment

In recent years, the role of immune cells in tumor progression has been a matter of increasing interest. Neutrophils constitute an important portion of the immune cells infiltrating the tumor microenvironment. Traditionally viewed as the first line of defense against infections, it is now well accepted that neutrophils also have an important role in multiple aspects of cancer biology. Multiple and heterogeneous neutrophil subsets have been identified in tumors and in circulation. Evidence from many studies now supports the notion that tumor-associated neutrophils (TANs) show functional plasticity driven by multiple factors present in the tumor microenvironment. In this review, we first concisely discuss the pro-tumor vs. anti-tumor nature of neutrophils in cancer, their functional plasticity, and the mechanisms that regulate neutrophil polarization. We then expand on the various crosstalks and mutual effects between TANs and other tumor-infiltrating immune cell types, emphasizing the active role of neutrophils as regulators of the immune system, promoting or inhibiting the establishment of a permissive tumor microenvironment. Finally, the possible modulation of cancer-related neutrophils by therapies directed toward immune checkpoints is discussed briefly.

Yes-associated protein mediates immune reprogramming in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a high degree of inflammation and profound immune suppression. Here we identify Yes-associated protein (Yap) as a critical regulator of the immunosuppressive microenvironment in both mouse and human PDAC. Within Kras:p53 mutant pancreatic ductal cells, Yap drives the expression and secretion of multiple cytokines/chemokines, which in turn promote the differentiation and accumulation of myeloid-derived suppressor cells (MDSCs) both in vitro and in vivo. Pancreas-specific knockout of Yap or antibody-mediated depletion of MDSCs promoted macrophage reprogramming, reactivation of T cells, apoptosis of Kras mutant neoplastic ductal cells and pancreatic regeneration after acute pancreatitis. In primary human PDAC, YAP expression levels strongly correlate with an MDSC gene signature, and high expression of YAP or MDSC-related genes predicts decreased survival in PDAC patients. These results reveal multifaceted roles of YAP in PDAC pathogenesis and underscore its promise as a therapeutic target for this deadly disease.

Characterization of human fibroblastic reticular cells as potential immunotherapeutic tools

Fibroblastic reticular cells (FRCs) are essential players during adaptive immune responses not only as a structural support for the encounter of antigen-presenting cells and naive T lymphocytes but also as a source of modulatory signals. However, little is known about this cell population in humans. To address the phenotypical and functional analysis of human FRCs here we established splenic (SP) and mesenteric lymph node (LN) CD45^-CD31^-CD90⁺podoplanin⁺ myofibroblastic cell cultures. They shared the phenotypical characteristics distinctive of FRCs, including the expression of immunomodulatory factors and peripheral tissue antigens. Nevertheless, human FRCs also showed particular features, some differing from mouse FRCs, like the lack of nitric oxide synthase (NOS2) expression after interferon (IFN)γstimulation. Interestingly, SP-FRCs expressed higher levels of interleukin (IL)-6, BMP4, CCL2, CXCL12 and Notch molecules, and strongly adapted their functional profile to lipopolysaccharide (LPS), polyinosinic:polycytidylic acid (Poly I:C) and IFNγ stimulation. In contrast, we found higher expression of transforming growth factor (TGF)β and Activin A in LN-FRCs that barely responded via Toll-Like Receptor (TLR)3 and constitutively expressed retinaldehyde dehydrogenase 1 enzyme, absent in SP-FRCs. This study reveals human FRCs can be valuable models to increase our knowledge about the physiology of human secondary lymphoid organs in health and disease and to explore the therapeutic options of FRCs.