Granulocytic myeloid derived suppressor cells expand in human pregnancy and modulate T‐cell responses

Immune tolerance toward the semiallogeneic fetus plays a crucial role in the maintenance of pregnancy. Myeloid‐derived suppressor cells (MDSCs) are innate immune cells characterized by their ability to modulate T‐cell responses. Recently, we showed that MDSCs accumulate in cord blood of healthy newborns, yet their role in materno–fetal tolerance remained elusive. In the present study, we demonstrate that MDSCs with a granulocytic phenotype (GR‐MDSCs) are highly increased in the peripheral blood of healthy pregnant women during all stages of pregnancy compared with nonpregnant controls, whereas numbers of monocytic MDSCs were unchanged. GR‐MDSCs expressed the effector enzymes arginase‐I and iNOS, produced high amounts of ROS and efficiently suppressed T‐cell proliferation. After parturition, GR‐MDSCs decreased within a few days. In combination, our results show that GR‐MDSCs expand in normal human pregnancy and may indicate a role for MDSCs in materno–fetal tolerance.     

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 obstetrical and gynecological diseases

Myeloid‐derived suppressor cells (MDSCs) are a heterogeneous group of myeloid‐origin cells which have immunosuppressive activities in several conditions, such as cancer and inflammation. Recent research has also associated MDSCs with numerous obstetrical and gynecological diseases. During pregnancy, MDSCs accumulate to ensure maternal‐fetal immune tolerance, whereas they are decreased in patients who suffer from early miscarriage or pre‐eclampsia. While the etiology of endometriosis is still unknown, abnormal accumulation of MDSCs in the peripheral blood and peritoneal fluid, alongside an increased level of reactive oxygen species (ROS), has been observed in these patients, which is central to the cellular immune regulations by MDSCs. Additionally, the regulation of MDSCs observed in tumours is also applicable to gynecologic neoplasms, including ovarian cancer and cervical cancer. More recently, emerging evidence has shown that there are high levels of MDSCs in premature ovarian failure (POF) and in vitro fertilization (IVF), but the underlying mechanisms are unknown. In this review, the generation and mechanisms of MDSCs are summarized. In particular, the modulation of these cells in immune‐related obstetrical and gynecological diseases is discussed, including potential treatment options targeting MDSCs.     

Immune cells and molecules in pregnancy: friends or foes to the fetus?

Considering allograft rejection as a basic feature of the immune system, the mammalian pregnancy is an immunological paradox where the semi-allogeneic fetus is not rejected. How are the demands of pregnancy solved in the context of maternal immunity? Medawar’s original proposal of maternal immune inertness during pregnancy should be revised to active materno-placental tolerance. Multiple mechanisms are involved in peripheral and local tolerance induction that prevents fetal rejection while maintaining competent immune surveillance and protection. The goal of this review is to discuss the major cellular and molecular components of the immune system that control and promote fetal survival.     

Functional characterization of myeloid‐derived suppressor cell subpopulations during the development of experimental arthritis

Recent evidence indicates the existence of subpopulations of myeloid‐derived suppressor cells (MDSCs) with distinct phenotypes and functions. Here, we characterized the role of MDSC subpopulations in the pathogenesis of autoimmune arthritis in a collagen‐induced arthritis (CIA) mouse model. The splenic CD11b⁺Gr‐1⁺ MDSC population expanded in CIA mice, and these cells could be subdivided into polymorphonuclear (PMN) and mononuclear (MO) MDSC subpopulations based on Ly6C and Ly6G expression. During CIA, the proportion of splenic MO‐MDSCs was increased in association with the severity of joint inflammation, while PMN‐MDSCs were decreased. MO‐MDSCs expressed higher levels of surface CD40 and CD86 protein, but lower levels of Il10, Tgfb1, Ccr5, and Cxcr2 mRNA. PMN‐MDSCs exhibited a more potent capacity to suppress polyclonal T‐cell proliferation in vitro, compared with MO‐MDSCs. Moreover, the adoptive transfer of PMN‐MDSCs, but not MO‐MDSCs, decreased joint inflammation, accompanied by reduced levels of serum cytokine secretion and the frequencies of Th1 and Th17 cells in draining lymph nodes. These results suggest that there could be a shift from potently suppressive PMN‐MDSCs to poorly suppressive MO‐MDSCs during the development of experimental arthritis, which might reflect the failure of expanded MDSCs to suppress autoimmune arthritis.     

ORIGINAL ARTICLE: The Persistence of Paternal Antigens in the Maternal Body is Involved in Regulatory T‐Cell Expansion and Fetal‐Maternal Tolerance in Murine Pregnancy

Citation Zenclussen ML, Thuere C, Ahmad N, Wafula PO, Fest S, Teles A, Leber A, Casalis PA, Bechmann I, Priller J, Volk H‐D, Zenclussen AC. The persistence of paternal antigens in the maternal body is involved in regulatory T‐cell expansion and fetal‐maternal tolerance in murine pregnancy. Am J Reprod Immunol 2010; 63: 200–208 Problem Mammalian pregnancy is a state of immunological tolerance and CD4⁺ CD25⁺ regulatory T cells (Treg) contribute to its maintenance. Knowing that Treg act in an antigen‐specific way during pregnancy, we hypothesized that they are generated after maternal immune cells encounter paternal antigens. Method of study We mated wild type females with transgenic green fluorescent protein (GFP) males in an allogenic setting and killed them on different days of pregnancy. Results Presence of paternal and maternal MHC class II⁺ cells in vaginal lavage on day 0.5 of pregnancy was confirmed. Thus, antigen presentation may take place early during pregnancy in the periphery either by the direct or indirect pathways. Foxp3⁺ cells known to have regulatory activity could be detected on day 2 of pregnancy in lymph nodes and shortly after implantation at the fetal‐maternal interface. Conclusion Our data suggest that paternal antigens are processed early during pregnancy, which leads to the generation of Treg. The continuous release of placental antigens into the maternal circulation allows the maintenance of a Treg population which is specific for paternal antigens and mediates tolerance toward the semi‐allogeneic fetus until the time point of birth.     

Tumour‐activated liver stromal cells regulate myeloid‐derived suppressor cells accumulation in the liver

Regulating mechanisms underlying hepatic myeloid‐derived suppressor cell (MDSC) accumulation remain to be described. Here, we provide evidence for the involvement of tumour‐activated liver stromal cells in the process of hepatic MDSCs migration and accumulation. Our data showed an elevated frequency of MDSCs in the liver of tumour‐bearing mice. Moreover, tumour‐activated liver stromal cells promote MDSC migration into the liver site. Further investigation indicated higher levels of cytokine and chemokine expression in liver stromal cells after exposure to the tumour‐conditioned supernatant. Notably, the expression levels of proinflammatory factors, mainly including macrophage colony stimulating factor (M‐CSF), transforming growth factor‐β (TGF‐β), monocyte chemotactic protein‐1 (MCP‐1) and stromal‐derived factor‐1 (SDF‐1), increased after treatment with tumour‐conditioned supernatant, and blockade of MCP‐1 or SDF‐1 decreased the proportion of tumour infiltrated MDSCs in mice co‐transplanted with liver stromal cells and tumour cells, but not in mice with only tumour cells injection. These findings demonstrate that tumour‐activated liver stromal cells produce higher levels of chemokines and cytokines, which may contribute to MDSC accumulation into the liver site in patients with liver cancer.     

Neutrophilic myeloid‐derived suppressor cells in cord blood modulate innate and adaptive immune responses

Neonates show an impaired anti‐microbial host defence, but the underlying immune mechanisms are not understood fully. Myeloid‐derived suppressor cells (MDSCs) represent an innate immune cell subset characterized by their capacity to suppress T cell immunity. In this study we demonstrate that a distinct MDSC subset with a neutrophilic/granulocytic phenotype (Gr‐MDSCs) is highly increased in cord blood compared to peripheral blood of children and adults. Functionally, cord blood isolated Gr‐MDSCs suppressed T cell proliferation efficiently as well as T helper type 1 (Th1), Th2 and Th17 cytokine secretion. Beyond T cells, cord blood Gr‐MDSCs controlled natural killer (NK) cell cytotoxicity in a cell contact‐dependent manner. These studies establish neutrophilic Gr‐MDSCs as a novel immunosuppressive cell subset that controls innate (NK) and adaptive (T cell) immune responses in neonates. Increased MDSC activity in cord blood might serve as key fetomaternal immunosuppressive mechanism impairing neonatal host defence. Gr‐MDSCs in cord blood might therefore represent a therapeutic target in neonatal infections.     

HLA-G--母胎界面的一个免疫耐受分子

正常妊娠显示母体对同种异体胎儿的一种免疫耐受,HLA-G蛋白作为HLA移植抗原的代表限制性表达在母胎界面上,不仅不引起母体对胎儿的免疫排斥反应,相反被认为在母胎免疫耐受中起积极作用.     

Tumor‐induced myeloid‐derived suppressor cell subsets exert either inhibitory or stimulatory effects on distinct CD8+ T‐cell activation events

Tumor growth coincides with an accumulation of myeloid‐derived suppressor cells (MDSCs), which exert immune suppression and which consist of two main subpopulations, known as monocytic (MO) CD11b⁺CD115⁺Ly6G^?Ly6C^high MDSCs and granulocytic CD11b⁺CD115^?Ly6G⁺Ly6C^int polymorphonuclear (PMN)‐MDSCs. However, whether these distinct MDSC subsets hamper all aspects of early CD8⁺ T‐cell activation — including cytokine production, surface marker expression, survival, and cytotoxicity — is currently unclear. Here, employing an in vitro coculture system, we demonstrate that splenic MDSC subsets suppress antigen‐driven CD8⁺ T‐cell proliferation, but differ in their dependency on IFN‐γ, STAT‐1, IRF‐1, and NO to do so. Moreover, MO‐MDSC and PMN‐MDSCs diminish IL‐2 levels, but only MO‐MDSCs affect IL‐2Rα (CD25) expression and STAT‐5 signaling. Unexpectedly, however, both MDSC populations stimulate IFN‐γ production by CD8⁺ T cells on a per cell basis, illustrating that some T‐cell activation characteristics are actually stimulated by MDSCs. Conversely, MO‐MDSCs counteract the activation‐induced change in CD44, CD62L, CD162, and granzyme B expression, while promoting CD69 and Fas upregulation. Together, these effects result in an altered CD8⁺ T‐cell adhesiveness to the extracellular matrix and selectins, sensitivity to FasL‐mediated apoptosis, and cytotoxicity. Hence, MDSCs intricately influence different CD8⁺ T‐cell activation events in vitro, whereby some parameters are suppressed while others are stimulated.     

Non-classic sHLA class I in human oocyte culture medium

Soluble human leukocyte antigen (sHLA) class I molecules have been described in all human fluids. These molecules play a significant role in immune function. sHLA has been shown to produce tolerance and to induce apoptosis in cytotoxic alloreactive T cells. They are also present in the supernatant of many cultured cells. Similarly, non-classic HLA class I antigens in soluble form are present in human fluids. Among these, HLA-G is the most important because of its location in fetal tissue that suggests maternal immunological tolerance of the fetal semiallograft. In our present study we show that using two monoclonal antibodies, w6/32 and TP25.99, in the enzyme-linked immunosorbent assay allows the detection of non-classic sHLA class I molecules in the medium from human embryo cultures. The sample were collected from oocytes cultures. Oocyte donors were 11 women attending the in vitro fertilization program. The results showed a significant association (chi2 = 9.66, p = 0.002) between sHLA antigens and the oocyte cleavage rate measured 48 h after fertilization.     

Myeloid‐derived suppressor cells mediate tolerance induction in autoimmune disease

In multiple sclerosis (MS) T cells aberrantly recognize self‐peptides of the myelin sheath and attack the central nervous system (CNS). Antigen‐specific peptide immunotherapy, which aims to restore tolerance while avoiding the use of non‐specific immunosuppressive drugs, is a promising approach to combat autoimmune disease, but the cellular mechanisms behind successful therapy remain poorly understood. Myeloid‐derived suppressor cells (MDSCs) have been studied intensively in the field of cancer and to a lesser extent in autoimmunity. Because of their suppressive effect on the immune system in cancer, we hypothesized that the development of MDSCs and their interaction with CD4⁺ T cells could be beneficial for antigen‐specific immunotherapy. Hence, changes in the quantity, phenotype and function of MDSCs during tolerance induction in our model of MS were evaluated. We reveal, for the first time, an involvement of a subset of MDSCs, known as polymorphonuclear (PMN)‐MDSCs, in the process of tolerance induction. PMN‐MDSCs were shown to adopt a more suppressive phenotype during peptide immunotherapy and inhibit CD4⁺ T‐cell proliferation in a cell‐contact‐dependent manner, mediated by arginase‐1. Moreover, increased numbers of tolerogenic PMN‐MDSCs, such as observed over the course of peptide immunotherapy, were demonstrated to provide protection from disease in a model of experimental autoimmune encephalomyelitis.     

The immunosuppressive tumour network: myeloid‐derived suppressor cells,regulatory T cells and natural killer T cells

Myeloid‐derived suppressor cells (MDSC) and regulatory T (Treg) cells are major components of the immune suppressive tumour microenvironment (TME). Both cell types expand systematically in preclinical tumour models and promote T‐cell dysfunction that in turn favours tumour progression. Clinical reports show a positive correlation between elevated levels of both suppressors and tumour burden. Recent studies further revealed that MDSCs can modulate the de novo development and induction of Treg cells. The overlapping target cell population of Treg cells and MDSCs is indicative for the importance and flexibility of immune suppression under pathological conditions. It also suggests the existence of common pathways that can be used for clinical interventions aiming to manipulate the TME. Elimination or reprogramming of the immune suppressive TME is one of the major current challenges in immunotherapy of cancer. Interestingly, recent findings suggest that natural killer T (NKT) cells can acquire the ability to convert immunosuppressive MDSCs into immunity‐promoting antigen‐presenting cells. Here we will review the cross‐talk between MDSCs and other immune cells, focusing on Treg cells and NKT cells. We will consider its impact on basic and applied cancer research and discuss how targeting MDSCs may pave the way for future immunocombination therapies.     

Phenotypically resembling myeloid derived suppressor cells are increased in children with HIV and exposed/infected with Mycobacterium tuberculosis

Increased disease susceptibility during early life has been linked to immune immaturity, regulatory T‐cell/TH2 immune biasing and hyporesponsiveness. The contribution of myeloid derived suppressor cells (MDSCs) remains uninvestigated. Here, we assessed peripheral MDSC in HIV‐infected and ‐uninfected children with tuberculosis (TB) disease before, during and after TB treatment, along with matched household contacts (HHCs), HIV‐exposed, ‐infected and ‐uninfected children without recent TB exposure. Serum analytes and enzymes associated with MDSC accumulation/activation/function were measured by colorimetric‐ and fluorescence arrays. Peripheral frequencies of cells phenotypically resembling MDSCs were significantly increased in HIV‐exposed uninfected (HEU) and M.tb‐infected children, but peaked in children with TB disease and remained high following treatment. MDSC in HIV‐infected (HI) children were similar to unexposed uninfected controls; however, HAART‐mediated MDSC restoration to control levels could not be disregarded. Increased MDSC frequencies in HHC coincided with enhanced indoleamine‐pyrrole‐2,3‐dioxygenase (IDO), whereas increased MDSC in TB cases were linked to heightened IDO and arginase‐1. Increased MDSC were paralleled by reduced plasma IP‐10 and thrombospondin‐2 levels in HEU and significantly increased plasma IL‐6 in HI HHC. Current investigations into MDSC‐targeted treatment strategies, together with functional analyses of MDSCs, could endorse these cells as novel innate immune regulatory mechanism of infant HIV/TB susceptibility.     

REVIEW ARTICLE: Toll‐Like Receptors at the Maternal–Fetal Interface in Normal Pregnancy and Pregnancy Disorders

Citation Koga K, Mor G. Toll‐like receptors at the maternal–fetal interface in normal pregnancy and pregnancy disorders. Am J Reprod Immunol 2010 Toll‐like receptors (TLR) form the major family of pattern recognition receptors (PRR) that are involved in innate immunity. Innate immune responses against microorganisms at the maternal–fetal interface may have a significant impact on the success of pregnancy, as intrauterine infections have been shown to be strongly associated with certain disorders of pregnancy. At the maternal–fetal interface, TLRs are expressed not only in the immune cells but also in non‐immune cells such as trophoblasts and decidual cells; moreover, their expression patterns vary according to the stage of pregnancy. Here, we will describe potential functions of TLRs in these cells, their recognition and response to microorganisms, and their involvement in the innate immunity. The impact of TLR‐mediated innate immune response will be discussed via animal model studies, as well as clinical observations.     

Evaluation of membrane‐bound and soluble forms of human leucocyte antigen‐G in systemic sclerosis

Systemic sclerosis (SSc) is a complex disease characterized by immune dysregulation, extensive vascular damage and widespread fibrosis. Human leucocyte antigen‐G (HLA‐G) is a non‐classic class I major histocompatibility complex (MHC) molecule characterized by complex immunomodulating properties. HLA‐G is expressed on the membrane of different cell lineages in both physiological and pathological conditions. HLA‐G is also detectable in soluble form (sHLA‐G) deriving from the shedding of surface isoforms (sHLA‐G1) or the secretion of soluble isoforms (HLA‐G5). Several immunosuppressive functions have been attributed to both membrane‐bound and soluble HLA‐G molecules. The plasma levels of sHLA‐G were higher in SSc patients (444·27 ± 304·84 U/ml) compared to controls (16·74 ± 20·58 U/ml) (P < 0·0001). The plasma levels of transforming growth factor (TGF)‐β were higher in SSc patients (18 937 ± 15 217 pg/ml) compared to controls (11 099 ± 6081 pg/ml; P = 0·003), and a significant correlation was found between TGF‐β and the plasma levels of total sHLA‐G (r = 0·65; P < 0·01), sHLA‐G1 (r = 0·60; P = 0·003) and HLA‐G5 (r = 0·47; P = 0·02). The percentage of HLA‐G‐positive monocytes (0·98 ± 1·72), CD4⁺ (0·37 ± 0·68), CD8⁺ (2·05 ± 3·74) and CD4⁺CD8⁺ double‐positive cells (14·53 ± 16·88) was higher in SSc patients than in controls (0·11 ± 0·08, 0·01 ± 0·01, 0·01 ± 0·01 and 0·39 ± 0·40, respectively) (P < 0·0001). These data indicate that in SSc the secretion and/or shedding of soluble HLA‐G molecules and the membrane expression of HLA‐G by peripheral blood mononuclear cells (PBMC) is clearly elevated, suggesting an involvement of HLA‐G molecules in the immune dysregulation of SSc.     

Tumour YAP1 and PTEN expression correlates with tumour‐associated myeloid suppressor cell expansion and reduced survival in colorectal cancer

The expansion of myeloid‐derived suppressor cells (MDSCs) correlates with tumorigenesis in colorectal cancer (CRC). Here, we found a significant association between CD33⁺ MDSC number and Yes‐associated protein 1 (YAP1) and phosphatase and tensin homologue (PTEN) levels in CRC patients (P < 0·05). Moreover, the CD33⁺ MDSCs, YAP1 and PTEN were identified as predictors for the prognosis of CRC patients (P < 0·05). Notably, CD33⁺ MDSCs were an independent survival predictor for CRC patients through a Cox model analysis. In vitro data determined that the expression levels of YAP1 and PTEN in CRC‐derived cell lines were associated with CRC‐derived MDSC induction, and the blockade of YAP1 and PTEN decreased CRC‐derived MDSC induction. A mechanistic analysis revealed that YAP1 promoted CRC‐derived MDSC induction by suppressing PTEN expression to up‐regulate COX‐2, P‐AKT and P‐p65 in CRC‐derived cells, leading to secretion of the cytokine granulocyte–macrophage colony‐stimulating factor. Our findings establish a novel mechanism of pro‐tumorigenic MDSC induction mediated by ectopic YAP1 and PTEN expression in CRC.