Myeloid-derived suppressor cells are essential for maintaining feto-maternal immunotolerance via STAT3 signaling in mice

Immunological Indicators of Recurrent Pregnancy Loss: A Mendelian Randomization Study

Recurrent pregnancy loss (RPL) is thought to be related to maternal-fetal immune tolerance disorders. Immune monitoring of RPL patients mainly involves two aspects: inflammatory factors and immune cells. However, most observational studies have reported controversial findings. This study aimed to confirm whether abnormal inflammatory factors and immune cells in peripheral blood may lead to RPL, and guide clinical immune monitoring. We demonstrated causality using two-sample Mendelian randomization. Sensitivity analysis, reverse Mendelian randomization and meta-analysis were used to enhance the effectiveness of the results. There was a causal relationship between the level of IL-12 (OR = 1.78, 95% CI = 1.25-2.55; P = 0.00149) and RPL for 41 inflammatory factors. We screened 5 groups of immune cell subtypes that were causally associated with RPL: switched memory B-cell absolute count (OR = 0.66, 95% CI = 0.49-0.87, P = 0.00406), IgD + CD24 + B-cell absolute count (OR = 0.69, 95% CI = 0.53-0.88, P = 0.00319), CD39 + resting CD4 regulatory T-cell %CD4 regulatory T-cell (OR = 0.86, 95% CI = 0.78-0.95, P = 0.00252), activated & resting CD4 regulatory T-cell %CD4 regulatory T-cell (OR = 0.89, 95% CI = 0.82-0.97, P = 0.00938) and CD45 RA + CD28-CD8 + T-cell %CD8 + T-cell (OR = 0.99, 95% CI = 0.98-1.00, P = 0.01231). In terms of inflammatory factors, a causal relationship between IL-12 and RPL in peripheral blood was confirmed. We also identified five immune cell phenotypes that play a protective role. This suggests that there may be protective B cells and CD8 + T-cell subsets in peripheral blood, and the protective effect of Tregs was proved again. Immune monitoring of peripheral blood in patients with RPL seems to be necessary and the foundation for precision medicine.

Plasmodium yoelii Infection Enhances the Expansion of Myeloid-Derived Suppressor Cells via JAK/STAT3 Pathway

Myeloid-derived suppressor cells (MDSCs), the negative immune regulators, have been demonstrated to be involved in immune responses to a variety of pathological conditions, such as tumors, chronic inflammation, and infectious diseases. However, the roles and mechanisms underlying the expansion of MDSCs in malaria remain unclear. In this study, the phenotypic and functional characteristics of splenic MDSCs during Plasmodium yoelii NSM infection are described. Furthermore, we provide compelling evidence that the sera from P. yoelii-infected C57BL/6 mice containing excess IL-6 and granulocyte-macrophage colony-stimulating factor promote the accumulation of MDSCs by inducing Bcl2 expression. Serum-induced MDSCs exert more potent suppressive effects on T cell responses than control MDSCs within both in vivo P. yoelii infection and in vitro serum-treated bone marrow cells experiments. Serum treatment increases the MDSC inhibitory effect, which is dependent on Arg1 expression. Moreover, mechanistic studies reveal that the serum effects are mediated by JAK/STAT3 signaling. By inhibiting STAT3 phosphorylation with the JAK inhibitor JSI-124, effects of serum on MDSCs are almost eliminated. In vivo depletion of MDSCs with anti-Gr-1 or 5-fluorouracil significantly reduces the parasitemia and promotes Th1 immune response in P. yoelii-infected C57BL/6 mice by upregulating IFN-γ expression. In summary, this study indicates that P. yoelii infection facilitates the accumulation and function of MDSCs by upregulating the expression of Bcl2 and Arg1 via JAK/STAT3 signaling pathway in vivo and in vitro. Manipulating the JAK/STAT3 signaling pathway or depleting MDSCs could be promising therapeutic interventions to treat malaria.

Blocking OLFM4/galectin-3 axis in placental polymorphonuclear myeloid-derived suppressor cells triggers intestinal inflammation in newborns

Fetal growth restriction (FGR) is a major cause of premature and low-weight births, which increases the risk of necrotizing enterocolitis (NEC); however, the association remains unclear. We report a close correlation between placental polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) and NEC. Newborns with previous FGR exhibited intestinal inflammation and more severe NEC symptoms than healthy newborns. Placental PMN-MDSCs are vital regulators of fetal development and neonatal gut inflammation. Placental single-cell transcriptomics revealed that PMN-MDSCs populations and olfactomedin-4 gene (Olfm4) expression levels were significantly increased in PMN-MDSCs in later pregnancy compared to those in early pregnancy and non-pregnant females. Female mice lacking Olfm4 in myeloid cells mated with wild-type males showed FGR during pregnancy, with a decreased placental PMN-MDSCs population and expression of growth-promoting factors (GPFs) from placental PMN-MDSCs. Galectin-3 (Gal-3) stimulated the OLFM4-mediated secretion of GPFs by placental PMN-MDSCs. Moreover, GPF regulation via OLFM4 in placental PMN-MDSCs was mediated via hypoxia inducible factor-1α (HIF-1α). Notably, the offspring of mothers lacking Olfm4 exhibited intestinal inflammation and were susceptible to NEC. Additionally, OLFM4 expression decreased in placental PMN-MDSCs from pregnancies with FGR and was negatively correlated with neonatal morbidity. These results revealed that placental PMN-MDSCs contributed to fetal development and ameliorate newborn intestinal inflammation.

Bushen Antai recipe ameliorates immune microenvironment and maternal-fetal vascularization in STAT3-deficient abortion-prone mice

ETHNOPHARMACOLOGICAL RELEVANCE

Spontaneous abortion (SA) is an intricate disorder affecting women of reproductive age. Previous studies have confirmed the indispensable role of signal transducer and activator of transcription (STAT) 3 in normal pregnancy. Bushen Antai recipe (BAR) is a satisfactory formula commonly used in practice, based on the rationale of traditional Chinese medicine (TCM) for SA.

AIM OF THE STUDY

The current study explores the potential therapeutic effects and mechanistic insights of BAR in STAT3-deficient abortion-prone mice.

MATERIALS AND METHODS

A STAT3-deficient abortion-prone mouse model was developed using intraperitoneal injection of stattic from embryo day (ED) 5.5 to ED9.5 among pregnant females (C57BL/6). We separately administered BAR1 (5.7 g/kg), BAR2 (11.4 g/kg), progesterone (P4), or distilled water at 10 ml/kg/day from ED0.5 until ED10.5. The embryo resorption rate and placenta-uterus structure were observed on ED10.5. The systemic immune status was examined by analyzing the frequency of immunosuppressive myeloid-derived suppressor cells (MDSCs), the ratio of two macrophage (M) subtypes, and the protein expression of associated molecules. Morphological observation, immunohistochemistry, and western blotting were used to evaluate the vascularization conditions at the maternal-fetal interface.

RESULTS

BAR1, BAR2, or P4 treatment exerted remarkable effects in alleviating embryo resorption rate and disordered placental-uterus structure in STAT3-deficient abortion-prone mice. Western blotting indicated the deficiency of phosphorylated STAT3 and two prime target molecules, PR and HIF-1α, at the maternal-fetal interface under STAT3 inhibition. Simultaneously, BAR2 treatment significantly upregulated their expression levels. The systemic immune environment was disrupted, indicated by the reduced serum cytokine concentrations, MDSCs frequency, M2/M1 ratio, and the expression of immunomodulatory factors. Nonetheless, BAR2 or P4 treatment revived the immune tolerance for semi-allogenic embryos by enhancing the immune cells and factors. Besides, the western blot and immunohistochemistry results revealed that BAR2 or P4 treatment upregulated VEGFA/FGF2 and activated ERK/AKT phosphorylation. Therefore, BAR2 or P4 facilitated vascularization at the maternal-fetal interface in STAT3-deficient abortion-prone mice.

CONCLUSIONS

BAR sustained pregnancy by reviving the systemic immune environment and promoting angiogenesis at the maternal-fetal interface in STAT3-deficient abortion-prone mice.

Research progress on the STAT signaling pathway in pregnancy and pregnancy-associated disorders

Signal transducer and activator of transcription (STAT) proteins, pivotal regulators of signaling cascades, undergo activation in response to the stimulation of cytokines and growth factors, and participate in biological processes, including inflammation, immune responses, cell proliferation, and differentiation. During the process of pregnancy, STAT signaling is involved in regulating embryonic implantation, endometrial decidualization, and establishing and maintaining maternal-fetal immune tolerance. Increasing evidence suggests that aberrant STAT signaling contributes to the occurrence and development of pregnancy disorders, including repeated implantation failure (RIF), preeclampsia (PE), recurrent spontaneous abortion (RSA), preterm birth (PTB) and gestational diabetes mellitus (GDM). Elucidating the molecular mechanisms of the STAT signaling pathway holds promise for further understanding the establishment and maintenance of normal pregnancy, and thereby providing potent targets and strategic avenues for the prevention and management of ailments associated with pregnancy. In this review, we summarized the roles of the STAT signaling pathway and its related regulatory function in embryonic implantation, endometrial decidualization, and maternal-fetal immune tolerance. In conclusion, in-depth research on the mechanism of the STAT signaling pathway not only enhances our understanding of normal pregnancy processes but also offers STAT-based therapeutic approaches to protect women from the burden of pregnancy-related disorders.

Bushen Antai recipe alleviates embryo absorption by enhancing immune tolerance and angiogenesis at the maternal-fetal interface via mobilizing MDSCs in abortion-prone mice

BACKGROUND

Recurrent pregnancy loss (RPL) is a tricky puzzle that disturbs female reproduction worldwide. According to previous research, Bushen Antai recipe (BAR), a classic Chinese herbal formula widely used in clinic for miscarriage, exhibited multifaceted benefits in improving embryo implantation and attenuating early pregnancy loss. Myeloid-derived suppressor cells (MDSCs), a set of immunoregulatory cells critical in inflammation balance, get growing attention for their indispensable role in successful pregnancy.

PURPOSE

To investigate the therapeutic efficacy of BAR in abortion-prone mice and explore the potential mechanisms of BAR regarding MDSCs.

METHODS

RPL mice (CBA/J females paired with DBA/2 males, BALB/c males were used as the control) were administered with BAR1 (5.7 g/kg), BAR2 (11.4 g/kg), progesterone (P4), or distilled water from embryo day (D) 0.5 until D10.5. The rate of embryo absorption on D10.5 and the health status of progeny were measured. The systemic inflammatory states and the placenta-uterus milieu were assessed by serum cytokine levels, placenta-uterus architecture, and related protein expression at the maternal-fetal interface. Flow cytometry analysis was carried out to measure the frequency of MDSCs. Furthermore, we established the MDSCs-depletion mouse model by using C57BL/6 females mated with BALB/c males via intraperitoneal injection of anti-Gr-1 antibody on D6.5, while irrelative LTF antibody was used as the control. Similarly, BAR1, BAR2, P4, or distilled water was separately applied. Embryo absorption rate, systemic inflammatory states, placenta-uterus milieu, and MDSCs frequency were evaluated as mentioned above.

RESULTS

Significantly, embryo absorption rate was increased with disrupted placenta-uterus milieu and exorbitant proinflammatory cytokines in RPL mice, meanwhile, MDSCs number in the placenta-uterus unit were apparently reduced (⁎⁎⁎p < 0.001). BAR treatment markedly alleviated the poor conditions above and increased MDSCs number (####p < 0.0001). Flow cytometry analysis validated the efficacy of anti-Gr-1 antibody and the raised embryo absorption rate confirmed the essentiality of MDSCs in normal pregnancy (⁎⁎p < 0.01). Besides, the placenta-uterus milieu was destroyed, accompanied by the impaired expression of immune tolerance and angiogenesis related factors in the MDSCs-depletion mice. Even though, BAR treatment reversed the embryo resorption phenotype and optimized the serum cytokine milieu, mobilizing MDSCs and rejuvenating active intercellular communication. Thereby, BAR facilitated the expression of MDSCs-related functional molecules, promoting immune tolerance and vascular remodeling at the placenta-uterus unit.

CONCLUSION

We unfurled the remarkable therapeutic ability of BAR in abortion-prone mice, and this was achieved by mobilizing MDSCs, thus favoring immune tolerance and angiogenesis at the maternal-fetal interface.

Supramolecular Biomaterials for Cancer Immunotherapy

Cancer immunotherapy has achieved tremendous successful clinical results and obtained historic victories in tumor treatments. However, great limitations associated with feeble immune responses and serious adverse effects still cannot be neglected due to the complicated multifactorial etiology and pathologic microenvironment in tumors. The rapid development of nanomedical science and material science has facilitated the advanced progress of engineering biomaterials to tackle critical issues. The supramolecular biomaterials with flexible and modular structures have exhibited unparalleled advantages of high cargo-loading efficiency, excellent biocompatibility, and diversiform immunomodulatory activity, thereby providing a powerful weapon for cancer immunotherapy. In past decades, supramolecular biomaterials were extensively explored as versatile delivery platforms for immunotherapeutic agents or designed to interact with the key moleculars in immune system in a precise and controllable manner. In this review, we focused on the crucial role of supramolecular biomaterials in the modulation of pivotal steps during tumor immunotherapy, including antigen delivery and presentation, T lymphocyte activation, tumor-associated macrophage elimination and repolarization, and myeloid-derived suppressor cell depletion. Based on extensive research, we explored the current limitations and development prospects of supramolecular biomaterials in cancer immunotherapy.

LILRB4 regulates the function of decidual MDSCs via the SHP-2/STAT6 pathway during Toxoplasma gondii infection

BACKGROUND

Toxoplasma gondii infection can cause adverse pregnancy outcomes, such as recurrent abortion, fetal growth restriction and infants with malformations, among others. Decidual myeloid-derived suppressor cells (dMDSCs) are a novel immunosuppressive cell type at the fetal-maternal interface which play an important role in sustaining normal pregnancy that is related to their high expression of the inhibitory molecule leukocyte immunoglobulin-like receptor B4 (LILRB4). It has been reported that the expression of LILRB4 is downregulated on decidual macrophages after T. gondii infection, but it remains unknown whether T. gondii infection can induce dMDSC dysfunction resulting from the change in LILRB4 expression.

METHODS

LILRB4-deficient (LILRB4^-/-) pregnant mice infected with T. gondii with associated adverse pregnancy outcomes, and anti-LILRB4 neutralized antibodies-treated infected human dMDSCs were used in vivo and in vitro experiments, respectively. The aim was to investigate the effect of LILRB4 expression on dMDSC dysfunction induced by T. gondii infection.

RESULTS

Toxoplasma gondii infection was observed to reduce STAT3 phosphorylation, resulting in decreased LILRB4 expression on dMDSCs. The levels of the main functional molecules (arginase-1 [Arg-1], interleukin-10 [IL-10]) and main signaling molecules (phosphorylated Src-homology 2 domain-containing protein tyrosine phosphatase [p-SHP2], phosphorylated signal transducer and activator of transcription 6 [p-STAT6]) in dMDSCs were all significantly reduced in human and mouse dMDSCs due to the decrease of LILRB4 expression induced by T. gondii infection. SHP-2 was found to directly bind to STAT6 and STAT6 to bind to the promoter of the Arg-1 and IL-10 genes during T. gondii infection.

CONCLUSIONS

The downregulation of LILRB4 expression on dMDSCs induced by T. gondii infection could regulate the expression of Arg-1 and IL-10 via the SHP-2/STAT6 pathway, resulting in the dysfunction of dMDSCs, which might contribute to adverse outcomes during pregnancy by T. gondii infection.

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

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

Here, There, and Everywhere: Myeloid-Derived Suppressor Cells in Immunology

Myeloid-derived suppressor cells (MDSCs) were initially identified in humans and mice with cancer where they profoundly suppress T cell- and NK cell-mediated antitumor immunity. Inflammation is a central feature of many pathologies and normal physiological conditions and is the dominant driving force for the accumulation and function of MDSCs. Therefore, MDSCs are present in conditions where inflammation is present. Although MDSCs are detrimental in cancer and conditions where cellular immunity is desirable, they are beneficial in settings where cellular immunity is hyperactive. Because MDSCs can be generated ex vivo, they are being exploited as therapeutic agents to reduce damaging cellular immunity. In this review, we discuss the detrimental and beneficial roles of MDSCs in disease settings such as bacterial, viral, and parasitic infections, sepsis, obesity, trauma, stress, autoimmunity, transplantation and graft-versus-host disease, and normal physiological settings, including pregnancy and neonates as well as aging. The impact of MDSCs on vaccination is also discussed.

In vitro-Generated MDSCs Reduce the Pregnancy Complications in an Abortion-Prone Murine Model

Recurrent spontaneous abortion (RSA) is one of the major pregnancy-related complications. The roles of different immune cells have been studied in pregnancy complications. The current study aimed to investigate myeloid-derived suppressor cells (MDSCs) in a murine abortion model and introduce a therapeutic approach by using in vitro-generated MDSCs in this model. CBA/J × DBA/2 (abortion prone) and CBA/J × Balb/C (normal pregnancy) mice were used. The frequency of granulocytic MDSCs, monocytic MDSCs, and Tregs was checked in the bone marrow and uteroplacental tissue of mice on three gestational days (gd9.5, gd13.5, and gd17.5) using the flow cytometry approach. MDSCs were generated in vitro from bone marrow-isolated cells using GM-CSF and IL-6 cytokines. Abortion-prone mice were injected intravenously with in vitro-generated MDSCs at gd0.5, and pregnancy outcomes were recorded in treated mice. The frequency of G-MDSCs and M-MDSCs in the bone marrow of abortion-prone mice was decreased at gd9.5 (p = 0.026 and p = 0.05, respectively). In uteroplacental tissue, the frequency of G-MDSCs was significantly lower at gd9.5 and gd13.5 (p = 0.001, p = 0.029, respectively), while M-MDSCs only showed decreased number at gd9.5 (p = 0.05) in abortion-prone mice. Injection of in vitro-generated MDSCs resulted in the increased fetus and placenta weights (p = 0.049 and p = 0.012, respectively) but showed no effect on the number of live fetuses and abortion rate. The reduced frequency of both G-MDSCs and M-MDSCs in the bone marrow and at the feto-maternal interface is associated with pregnancy complications. In vitro-generated MDSCs could be considered as a potential approach to reduce these complications.

MDSCs in pregnancy and pregnancy-related complications: an update†

Maternal-fetal immune tolerance is a process that involves complex interactions of the immune system, and myeloid-derived suppressor cells have emerged as one of the novel immunomodulator in the maintenance of maternal-fetal immune tolerance. Myeloid-derived suppressor cells are myeloid progenitor cells with immunosuppressive activities on both innate and adaptive cells through various mechanisms. Emerging evidence demonstrates the accumulation of myeloid-derived suppressor cells during healthy pregnancy to establish maternal-fetal immune tolerance, placentation, and fetal-growth process. By contrast, the absence or decreased myeloid-derived suppressor cells in pregnancy complications like preeclampsia, preterm birth, stillbirth, and recurrent spontaneous abortion have been reported. Here, we have summarized the origin, mechanisms, and functions of myeloid-derived suppressor cells during pregnancy along with the recent advancements in this dynamic field. We also shed light on the immunomodulatory activity of myeloid-derived suppressor cells, which can be a foundation for potential therapeutic manipulation in immunological pregnancy complications.

TRAINED IMMUNITY: A POTENTIAL APPROACH FOR IMPROVING HOST IMMUNITY IN NEONATAL SEPSIS

ABSTRACT

Sepsis, a dysregulated host immune response to infection, is one of the leading causes of neonatal mortality worldwide. Improved understanding of the perinatal immune system is critical to improve therapies to both term and preterm neonates at increased risk of sepsis. Our narrative outlines the known and unknown aspects of the human immune system through both the immune tolerant in utero period and the rapidly changing antigen-rich period after birth. We will highlight the key differences in innate and adaptive immunity noted through these developmental stages and how the unique immune phenotype in early life contributes to the elevated risk of overwhelming infection and dysregulated immune responses to infection upon exposure to external antigens shortly after birth. Given an initial dependence on neonatal innate immune host responses, we will discuss the concept of innate immune memory, or "trained immunity," and describe several potential immune modulators, which show promise in altering the dysregulated immune response in newborns and improving resilience to sepsis.

Relaxin contributes to the elevation of monocytic myeloid-derived suppressor cells in peripheral blood of pregnant canines

Tolerance towards fetal alloantigens in the maternal immune system is essential for maintaining pregnancy. Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells characterized by their ability to suppress immune activity and maintain maternal-fetal immune tolerance. However, the mechanisms underlying MDSC induction have not been elucidated. Herein, we investigated the myeloid-derived suppressor cells (MDSCs) in the peripheral blood of pregnant canines and its induction mechanism. By analyzing the concentration of MDSCs in the peripheral blood of pregnant canines, elevation of MDSCs has been observed during pregnancy. In addition, MDSCs from pregnant canines inhibit T cell activation. These results suggest that the elevated MDSCs in canine pregnancy may contribute to reduces maternal immune activity. To clarify the cause of MDSCs elevation in canine pregnancy, we analyzed the relationship between pregnancy-related hormones (estradiol, progesterone, and relaxin) and MDSCs. Serum relaxin levels, but not estradiol and progesterone, were correlated with the ratio of monocyte MDSCs. Additionally, relaxin induced monocytic MDSCs as well as inhibited T cell activation in vitro. Therefore, relaxin contributes to the elevation of monocytic MDSCs in the peripheral blood of pregnant canines. Our findings highlight the novel role of relaxin in pregnancy and contribute to a better understanding of maternal-fetal immune tolerance.

Myeloidderived suppressor cells: Escorts at the maternal-fetal interface

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

Minding the Bathwater: Fertility and Reproductive Toxicity in the Age of Immuno-Oncology

Immune checkpoint inhibition has resulted in significant efficacy across many cancer types, including melanoma. Melanoma is the second most common cancer among those of reproductive age, yet the reproductive toxicities of adjuvant and first-line immunotherapy are largely unknown.The normal innate and adaptive immune systems play a vital role in reproductive organ homeostasis of men and women and are essential for implantation, fertility, and a successful pregnancy. The programmed cell death-1 receptor/programmed cell death receptor ligand-1 (PD-1/PD-L1) pathway is essential in several aspects of fertility and pregnancy. Recent studies have largely focused on the role of the PD-1/PD-L1 pathway in fetomaternal tolerance, highlighting the importance of intact immune regulation in promoting a successful pregnancy.In this review, we describe a case of a reproductive-aged female with stage IIIC melanoma who sought guidance on family planning after pembrolizumab therapy. We discuss the known fertility-related toxicities of immune checkpoint inhibitors, the potential targets for reproductive toxicity in males and nonpregnant females, and the implications of anti-PD-1 therapy in relation to fetomaternal tolerance. Informed decision making will benefit from data and consensus.

Myeloid-derived suppressor cells: Cancer, autoimmune diseases, and more

Although cancer immunotherapy using immune checkpoint inhibitors (ICIs) has been recognized as one of the major treatment modalities for malignant diseases, the clinical outcome is not uniform in all cancer patients. Myeloid-derived suppressor cells (MDSCs) represent a heterogeneous population of immature myeloid cells that possess various strong immunosuppressive activities involving multiple immunocompetent cells that are significantly accumulated in patients who did not respond well to cancer immunotherapies. We reviewed the perspective of MDSCs with emerging evidence in this review. Many studies on MDSCs were performed in malignant diseases. Substantial studies on the participation of MDSCs on non-malignant diseases such as chronic infection and autoimmune diseases, and physiological roles in obesity, aging, pregnancy and neonates have yet to be reported. With the growing understanding of the roles of MDSCs, variable therapeutic strategies and agents targeting MDSCs are being investigated, some of which have been used in clinical trials. More studies are required in order to develop more effective strategies against MDSCs.

Decreased Polymorphonuclear Myeloid-Derived Suppressor Cells and ROS Production Correlated Closely with Bronchopulmonary Dysplasia in Preterm Infants

Background. Bronchopulmonary dysplasia (BPD) is one of the most serious complications in premature infants. Myeloid-derived suppressor cells (MDSCs) have been indicated to promote immune tolerance and induce anti-inflammatory responses during the neonatal stage. However, the role of MDSCs in BPD has not been completely expounded. Methods. 130 cases of newborns were collected from six tertiary hospitals in Guangzhou from August 2019 to June 2022. They were divided into BPD group, non-BPD preterm infants group, and term infants group according to gestational age and presence of BPD. The peripheral blood was collected and used to analyze the proportion, phenotypic, and function of MDSCs at 3 to 7 days and 8 to 14 days after birth, respectively. Results. We indicated that the number of both MDSCs in premature infants is reduced, and the number of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) in peripheral blood of BPD infants was significantly lower than that of non-BPD infants under 34 weeks of gestational age ( $P<0.05$ ). Furthermore, PMN-MDSCs from peripheral blood of patients presented inhibitory effect on proliferation of CD4+T and CD8+T cells in each group. However, PMN-MDSCs from BPD group had obviously weaker inhibitory effect on proliferation of CD4+T and CD8+T cells than that from non-BPD preterm infants group. In addition, we demonstrated that the expression of NADPH oxidase (Nox2) and reactive oxygen species (ROS) in PMN-MDSCs of BPD children was significantly lower than that in non-BPD preterm infants, suggesting that ROS pathway was affected in BPD in premature infants. Conclusion. This study preliminarily revealed the role of PMN-MDSCs in the pathogenesis of BPD in premature infants. The specific immune regulation mechanism of PMN-MDSCs in BPD will provide new ideas and strategies for clinical prevention and treatment of BPD in premature infants.

Adenosine Alleviates Necrotizing Enterocolitis by Enhancing the Immunosuppressive Function of Myeloid-Derived Suppressor Cells in Newborns

Necrotizing enterocolitis (NEC) is a common disorder in premature infants that is characterized by hyperinflammation and severe necrosis in the intestine. The pathogenesis of NEC remains to be elucidated. In this study, we demonstrate that adenosine, a metabolite more abundant in infants than in adults, plays an important role in the prevention of NEC. Administration of adenosine or its analog, adenosine-5'-N-ethyluronamide (NECA), dramatically relieved the severity of NEC in neonatal mice. Meanwhile, adenosine treatment significantly enhanced the immunosuppressive function, antibacterial activity, and migration of myeloid-derived suppressor cells (MDSCs). However, depletion of MDSCs or inhibition of their migration using the CXCR2 inhibitor SB225002 almost completely abrogated the protective effect of adenosine on NEC. Mechanistic studies showed that MDSCs in newborns expressed abundant adenosine receptor A2B (A2BR) that elicits intracellular cAMP signaling and its downstream target NF-κB. Importantly, intestinal tissues from patients with NEC showed significantly lower infiltration of A2BR-positive MDSCs than those from healthy donors. These observations revealed that adenosine-induced MDSCs represent an essential immune axis for intestinal homeostasis in newborns.

Intracellular Lipid Accumulation Drives the Differentiation of Decidual Polymorphonuclear Myeloid-Derived Suppressor Cells via Arachidonic Acid Metabolism

Decidual polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) are essential to immune tolerance during pregnancy. A reduction in the number of these cells is associated with unexplained recurrent pregnancy loss (URPL). In our previous study, we reported that PMN-MDSCs are a group of mature neutrophils that are activated by the decidua microenvironment. In the present study, we show that the decidua microenvironment induces substantial lipid accumulation in neutrophils during their differentiation to PMN-MDSCs. Lower levels of lipid accumulation are detected in PMN-MDSCs from URPL patients, and the amount of lipid in the PMN-MDSCs is positively correlated with the proportion of PMN-MDSCs. Next, we demonstrate that decidua-derived IL6 with the presence of arachidonic acid upregulates fatty acid-binding protein 5 (FABP5) via the phosphorylation of signal transducer and activator of transcription 3 (STAT3). Fy -60ABP5 then continuously stimulates intracellular lipid accumulation. Increased intracellular lipid accumulation mediates arachidonic acid metabolism, a pathway that is significantly activated by the induction of the decidua microenvironment, to stimulate the synthesis of prostaglandin E2 (PGE2) and finally induce the differentiation of PMN-MDSCs. To summarize, decidua-derived IL6 facilitates the differentiation of PMN-MDSCs from neutrophils via the pSTAT3/FABP5/PGE2 pathway. Defects in the process may result in impaired differentiation and dysfunction of PMN-MDSCs in URPL. These findings enhance our understanding of the physiological mechanisms of immune tolerance in pregnancy and provide therapeutic options for URPL.

G-CSF induces CD15+ CD14+ cells from granulocytes early in the physiological environment of pregnancy and the cancer immunosuppressive microenvironment

Objectives

Recombinant granulocyte colony-stimulating factor (G-CSF) is frequently administered to patients with cancer to enhance granulocyte recovery post-chemotherapy. Clinical trials have also used G-CSF to modulate myeloid cell function in pregnancy and inflammatory diseases. Although the contribution of G-CSF to expanding normal granulocytes is well known, the effect of this cytokine on the phenotype and function of immunosuppressive granulocytic cells remains unclear. Here, we investigate the impact of physiological and iatrogenic G-CSF on an as yet undescribed granulocyte phenotype and ensuing outcome on T cells in the settings of cancer and pregnancy.

Methods

Granulocytes from patients treated with recombinant G-CSF, patients with late-stage cancer and women enrolled on a trial of recombinant G-CSF were phenotyped by flow cytometry. The ability and mechanism of polarised granulocytes to suppress T-cell proliferation were assessed by cell proliferation assays, flow cytometry and ELISA.

Results

We observed that G-CSF leads to a significant upregulation of CD14 expression on CD15⁺ granulocytes. These CD15⁺CD14⁺ cells are identified in the blood of patients with patients undergoing neutrophil mobilisation with recombinant G-CSF, and physiologically in women early in pregnancy or in those treated as a part of a clinical trial. Immunohistochemistry of tumor tissue or placental tissue identified the expression of G-CSF. The G-CSF upregulates the release of reactive oxygen species (ROS) in CD15⁺CD14⁺ cells leading to the suppression of T-cell proliferation.

Conclusions

G-CSF induces a population of ROS⁺ immunosuppressive CD15⁺CD14⁺ granulocytes. Strategies for how recombinant G-CSF can be scheduled to reduce effects on T-cell therapies should be developed in future clinical studies.

Specific innate immune cells uptake fetal antigen and display homeostatic phenotypes in the maternal circulation

Pregnancy represents a period when the mother undergoes significant immunological changes to promote tolerance of the fetal semi-allograft. Such tolerance results from the exposure of the maternal immune system to fetal antigens (Ags), a process that has been widely investigated at the maternal-fetal interface and in the adjacent draining lymph nodes. However, the peripheral mechanisms of maternal-fetal crosstalk are poorly understood. Herein, we hypothesized that specific innate immune cells interact with fetal Ags in the maternal circulation. To test this hypothesis, a mouse model was utilized in which transgenic male mice expressing the chicken ovalbumin (OVA) Ag under the beta-actin promoter were allogeneically mated with wild-type females to allow for tracking of the fetal Ag. Fetal Ag-carrying Ly6G+ and F4/80+ cells were identified in the maternal circulation, where they were more abundant in the second half of pregnancy. Such innate immune cells displayed unique phenotypes: while Ly6G+ cells expressed high levels of MHC-II and CD80 together with low levels of pro-inflammatory cytokines, F4/80+ cells up-regulated the expression of CD86 as well as the anti-inflammatory cytokines IL-10 and TGF-β. In vitro studies using allogeneic GFP+ placental particles revealed that maternal peripheral Ly6G+ and F4/80+ cells phagocytose fetal Ags in mid and late murine pregnancy. Importantly, cytotrophoblast-derived particles were also engulfed in vitro by CD15+ and CD14+ cells from women in the second and third trimester, providing translational evidence that this process also occurs in humans. Collectively, this study demonstrates novel interactions between specific maternal circulating innate immune cells and fetal Ags, thereby shedding light on the systemic mechanisms of maternal-fetal crosstalk.

Human Leucocyte Antigen G and Murine Qa-2 Are Critical for Myeloid Derived Suppressor Cell Expansion and Activation and for Successful Pregnancy Outcome

During pregnancy, maternal immune system has to balance tightly between protection against pathogens and tolerance towards a semi-allogeneic organism. Dysfunction of this immune adaptation can lead to severe complications such as pregnancy loss, preeclampsia or fetal growth restriction. In the present study we analyzed the impact of the murine MHC class Ib molecule Qa-2 on pregnancy outcome in vivo. We demonstrate that lack of Qa-2 led to intrauterine growth restriction and increased abortion rates especially in late pregnancy accompanied by a disturbed trophoblast invasion and altered spiral artery remodeling as well as protein aggregation in trophoblast cells indicating a preeclampsia-like phenotype. Furthermore, lack of Qa-2 caused imbalanced immunological adaptation to pregnancy with altered immune cell and especially T-cell homeostasis, reduced T_reg numbers and decreased accumulation and functional activation of myeloid-derived suppressor cells. Lastly, we show that application of sHLA-G reduced abortion rates in Qa-2 deficient mice by inducing MDSC. Our results highlight the importance of an interaction between HLA-G and MDSC for pregnancy success and the therapeutic potential of HLA-G for treatment of immunological pregnancy complications.

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

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

Myeloid-derived suppressor cells in the era of increasing myeloid cell diversity

Myeloid-derived suppressor cells (MDSCs) are pathologically activated neutrophils and monocytes with potent immunosuppressive activity. They are implicated in the regulation of immune responses in many pathological conditions and are closely associated with poor clinical outcomes in cancer. Recent studies have indicated key distinctions between MDSCs and classical neutrophils and monocytes, and, in this Review, we discuss new data on the major genomic and metabolic characteristics of MDSCs. We explain how these characteristics shape MDSC function and could facilitate therapeutic targeting of these cells, particularly in cancer and in autoimmune diseases. Additionally, we briefly discuss emerging data on MDSC involvement in pregnancy, neonatal biology and COVID-19.

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

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

MDSCs interactions with other immune cells and their role in maternal-fetal tolerance

MDSCs (myeloid-derived suppressor cells) are a population of immature and heterogeneous bone marrow cells with immunosuppressive functions, and they are mainly divided into two subgroups: granulocytic MDSCs (G-MDSCs) and monocytic MDSCs (M-MDSCs). Immunosuppression is the main and most important function of MDSCs, and they mainly exert an inhibitory effect through endoplasmic reticulum stress and some enzymes related to inhibitors, as well as some cytokines and other factors. In addition, MDSCs also interact with other immune cells, especially NK cells, DCs and Tregs, to participate in immune regulation. A large number of MDSCs are found during normal pregnancy. Combined with their immunosuppressive effects, these results suggest that MDSCs are likely to be closely related to maternal-fetal immune tolerance. This review mainly shows the interaction of MDSCs with other immune cells and the important role of MDSCs in maternal-fetal tolerance. The current research shows that MDSCs are mainly mediated by STAT3, HLA-G, CXCR2, Arg-1 and HIF1-α in immune regulation during pregnancy. Interpreting maternal-fetal tolerance from the perspective of MDSCs provides a special perspective for research on immune regulation and maternal-fetal tolerance of MDSCs to obtain a more comprehensive understanding of immune regulation and immune tolerance.

The Role of Immune Cells in Recurrent Spontaneous Abortion

Recurrent spontaneous abortion affects approximately 1–2% of women of childbearing, and describes a condition in which women suffer from three or more continuous spontaneous miscarriages. However, the origin of recurrent spontaneous abortion (RSA) remains unknown, preventing effective treatment and placing stress upon patients. It has been acknowledged that successful pregnancy necessitates balanced immune responses. Therefore, immunological aberrancy may be considered a root cause of poor pregnancy outcomes. Considerable published studies have investigated the relationship between various immune cells and RSA. Here, we review current knowledge on this area, and discuss the five main categories of immune cells involved in RSA; these include innate lymphocytes (ILC), macrophages, decidual dendritic cells (DCs), and T cells. Furthermore, we sought to summarize the impact of the multiple interactions of various immune cells on the emergence of RSA. A good understanding of pregnancy-induced immunological alterations could reveal new therapeutic strategies for favorable pregnancy outcomes.

Continuous activation of polymorphonuclear myeloid-derived suppressor cells during pregnancy is critical for fetal development

The maternal immune system is vital in maintaining immunotolerance to the semiallogeneic fetus for a successful pregnancy. Although studies have shown that myeloid-derived suppressor cells (MDSCs) play an important role in maintaining feto-maternal tolerance, little is known about the role of MDSCs in pregnancies with intrauterine growth retardation (IUGR). Here, we reported that the activation of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) during pregnancy was closely associated with fetal growth. In humans, class E scavenger receptor 1 (SR-E1), a distinct marker for human PMN-MDSCs, was used to investigate PMN-MDSC function during pregnancy. Continuous activation of SR-E1⁺ PMN-MDSCs was observed in all stages of pregnancy, accompanied by high cellular levels of ROS and arginase-1 activity, mediated through STAT6 signaling. However, SR-E1⁺ PMN-MDSCs in pregnancies with IUGR showed significantly lower suppressive activity, lower arginase-1 activity and ROS levels, and decreased STAT6 phosphorylation level, which were accompanied by an increase in inflammatory factors, compared with those in normal pregnancies. Moreover, the population of SR-E1⁺ PMN-MDSCs was negatively correlated with the adverse outcomes of newborns from pregnancies with IUGR. In mice, decreases in cell population, suppressive activity, target expression levels, and STAT6 phosphorylation levels were also observed in the pregnancies with IUGR compared with the normal pregnancies, which were rescued by the adoptive transfer of PMN-MDSCs from pregnant mice. Interestingly, the growth-promoting factors (GPFs) secreted by placental PMN-MDSCs in both humans and mice play a vital role in fetal development. These findings collectively support that PMN-MDSCs have another new role in pregnancy, which can improve adverse neonatal outcomes.

Decidua-derived granulocyte macrophage colony-stimulating factor induces polymorphonuclear myeloid-derived suppressor cells from circulating CD15+ neutrophils

STUDY QUESTION

Do decidua-derived factors stimulate the conversion of circulating neutrophils to polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) in early human pregnancy?

SUMMARY ANSWER

Circulating neutrophils can acquire PMN-MDSC-like phenotypes and function via phosphorylated signal transducer and activator of transcription 5/programmed death ligand 2 (pSTAT5/PD-L2) signalling after stimulation with decidua-derived granulocyte macrophage colony-stimulating factor (GM-CSF).

WHAT IS KNOWN ALREADY

PMN-MDSCs are an important immunoregulatory cell type in early pregnancy. Neutrophils are of high heterogeneity and plasticity and can polarize to immunosuppressive PMN-MDSCs upon stimulation.

STUDY DESIGN, SIZE, DURATION

For analysis of myeloid-derived suppressor cell (MDSC) subset proportions, 12 endometrium tissues and 12 peripheral blood samples were collected from non-pregnant women, and 40 decidua tissues and 16 peripheral blood samples were obtained from women with normal early pregnancy undergoing elective surgical pregnancy termination for nonmedical reasons with gestation age of 6-10 weeks. Twenty-nine decidua tissues were collected for isolation of CD15+ PMN-MDSCs. Twenty endometrium tissues and 30 decidua tissues were collected for cytokine analysis, immunohistochemistry or neutrophil stimulation. Peripheral blood samples were obtained from 36 healthy donors for isolation of CD3+ T cells and CD15+ neutrophils.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The proportion of MDSC subsets in the decidua and peripheral blood of normal early pregnancy, endometrium and peripheral blood of non-pregnant women was analysed by flow cytometry. The phenotypes and function of decidual PMN-MDSCs and circulating neutrophils were compared by flow cytometry. Circulating neutrophils were stimulated with decidual explant supernatant (DES) and the phenotypes were measured by flow cytometry and immunofluorescence. The suppressive capacity of decidual PMN-MDSCs and DES-conditioned neutrophils was analysed by flow cytometry with or without anti-programmed cell death-1 (PD-1) antibody. Cytokines from DES and endometrial explant supernatant (EES) were detected by a Luminex assay. GM-CSF expression was determined by ELISA and immunohistochemistry. Neutrophils were stimulated with DES, EES, DES with anti-GM-CSF antibody or EES with GM-CSF. CD11b, lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), PD-L2 and pSTAT5 expression were measured by flow cytometry.

MAIN RESULTS AND THE ROLE OF CHANCE

The frequency of PMN-MDSCs was significantly increased in the decidua of early pregnancy compared with peripheral blood of non-pregnant women, the endometrium of non-pregnant women or peripheral blood during early pregnancy. Decidual PMN-MDSCs suppressed T-cell proliferation and cytokine production. Phenotypes of decidual PMN-MDSCs were similar to mature activated neutrophils. DES-induced CD11b, LOX-1, PD-L2 expression and STAT5 phosphorylation in neutrophils. The PD-L2 expression in neutrophils was dependent on STAT5 phosphorylation. Both decidual PMN-MDSCs and DES-conditioned neutrophils suppressed T-cell proliferation via PD-1 signalling. GM-CSF was up-regulated in the decidua and induced CD11b, LOX-1 and PD-L2 expression on neutrophils. DES significantly induced CD11b, LOX-1, PD-L2 expression and STAT5 phosphorylation. Anti-GM-CSF antibody remarkably blocked such stimulation in neutrophils. EES did not induce CD11b, LOX-1, PD-L2 expression or STAT5 phosphorylation, while GM-CSF treatment sufficiently stimulated CD11b, LOX-1, PD-L2 expression and STAT5 phosphorylation in neutrophils.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

The study was based on in vitro experiments and we were not able to evaluate neutrophils differentiation to PMN-MDSCs in other sites before entering the maternal-foetal interface due to the limited availability of human samples. This needs to be explored using murine models.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study demonstrating that decidual PMN-MDSCs are a group of immunoregulatory cells with mature status, and that neutrophils can be induced to a PMN-MDSC-like phenotype with decidua-derived GM-CSF via pSTAT5/PD-L2 signalling. This study indicates that GM-CSF can facilitate immune tolerance of early pregnancy through regulating PMN-MDSCs and further provides a potential role of GM-CSF in prevention and treatment for pregnancy complications.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the National Natural Science Foundation of China (81671481) and National Natural Science Foundation of China (81871179). All authors have no competing interests to declare.

Impaired myeloid-derived suppressor cells are associated with recurrent implantation failure: A case-control study

BACKGROUND

Studies have reported that myeloid-derived suppressor cells (MDSCs) contribute to maintain pregnancy. The aim of this case-control study was to test whether there is a dysregulation of peripheral MDSCs in recurrent implantation failure (RIF).

METHODS

26 RIF patients and 30 controls were recruited. Flow cytometry was applied to characterize polymorphonuclear (PMN)-MDSCs, monocytic-MDSCs (M-MDSCs), effector T cells (Teffs) and regulatory T cells (Tregs) in blood. ELISA was used to define MDSCs correlative cytokines and chemokines in serum from all patients.

RESULTS

Compared with controls, RIF patients showed significant reductions of blood PMN-MDSCs, M-MDSCs, Tregs and NO production by PMN-MDSCs, whereas the expression of ζ chain on CD4⁺T cell receptor (TCR) and CD8⁺TCR displayed a remarkable upregulation in RIF patients. Moreover, RIF patients presented a lower concentration of serum chemokine (C-C motif) ligand (CCL) 5 and transforming growth factor (TGF)-β than those from controls. Furthermore, the level of TCR ζ chain on CD4⁺ and CD8⁺ Teffs was negatively correlated not only with the percentage of PMN-MDSCs, but also with the amount of NO produced by PMN-MDSCs. The frequency of PMN-MDSCs had positive correlations with the concentration of CCL5 and TGF-β.

CONCLUSIONS

This study indicated that the dysregulation of MDSCs might impair maternal-fetal immune balance thus resulting in RIF.

Treatment With Endothelin-A Receptor Antagonist BQ123 Attenuates Acute Inflammation in Mice Through T-Cell-Dependent Polymorphonuclear Myeloid-Derived Suppressor Cell Activation

The endothelin-A receptor antagonist BQ123 is an effective treatment agent for hypertension and obese cardiomyopathy. However, the role of BQ123 in controlling acute inflammatory diseases and its underlying mechanisms are not well understood. Here, we showed that BQ123 activated polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) in mice and that the IL13/STAT6/Arg1 signaling pathway is involved in this process. Importantly, both treatment with BQ123 and the transfer of BQ123-induced PMN-MDSCs (BQ123-MDSCs) were effective in relieving inflammation, including dextran sulfate sodium (DSS)-induced colitis, papain-induced pneumonia, and concanavalin A (ConA)-induced hepatitis, in mice. The treatment effects were mediated by the attenuation of the inflammation associated with the accumulation of PMN-MDSCs in the colon, lung, and liver. However, concurrent injection of Gr1 agonistic antibody with BQ123 induced PMN-MDSC aggravated the observed acute inflammation. Interestingly, no remission of inflammation was observed in Rag2 knockout mice administered BQ123-MDSCs, but co-injection with CD3⁺ T cells significantly relieved acute inflammation. In summary, BQ123-induced PMN-MDSCs attenuated acute inflammation in a T cell-dependent manner, providing a novel potential strategy to prevent the occurrence of acute inflammation.

Myeloid-Derived Suppressor Cells: Facilitators of Cancer and Obesity-Induced Cancer

Immature myeloid cells at varied stages of differentiation, known as myeloid-derived suppressor cells (MDSC), are present in virtually all cancer patients. MDSC are profoundly immune-suppressive cells that impair adaptive and innate antitumor immunity and promote tumor progression through nonimmune mechanisms. Their widespread presence combined with their multitude of protumor activities makes MDSC a major obstacle to cancer immunotherapies. MDSC are derived from progenitor cells in the bone marrow and traffic through the blood to infiltrate solid tumors. Their accumulation and suppressive potency are driven by multiple tumor- and host-secreted proinflammatory factors and adrenergic signals that act via diverse but sometimes overlapping transcriptional pathways. MDSC also accumulate in response to the chronic inflammation and lipid deposition characteristic of obesity and contribute to the more rapid progression of cancers in obese individuals. This article summarizes the key aspects of tumor-induced MDSC with a focus on recent progress in the MDSC field.

Dexamethasone and lactoferrin induced PMN-MDSCs relieved inflammatory adverse events of anti-cancer therapy without tumor promotion

In this era of immune checkpoint inhibitors, inflammatory adverse events of anti-cancer therapies continue to pose a major challenge. Glucocorticoids, as the mainstay, were limited by serious side effects. Glucocorticoids induce myeloid-derived suppressor cells (MDSCs), and lactoferrin-induced polymorphonuclear MDSCs (PMN-MDSCs) were shown to relieve inflammatory conditions. Combined treatment with dexamethasone (DXM) and lactoferrin increased the generation of PMN-MDSCs in vitro (DXM/lactoferrin PMN-MDSCs) compared to DXM or lactoferrin treatment alone. DXM/lactoferrin PMN-MDSCs were distinct from tumor PMN-MDSCs in vivo with regard to gene expression profiles. DXM upregulated the myeloid cell response to lactoferrin by inducing the lactoferrin receptor Lrp1. DXM/lactoferrin PMN-MDSCs presented anti-bacterial capability, increased PGE2 production, increased survival capability, and decreased tumor tissue homing. Transfer of DXM/lactoferrin PMN-MDSCs relieved cisplatin-induced acute kidney failure, bleomycin-induced interstitial pneumonia, and allergic pneumonitis effectively without promoting tumor development. Our study shows that DXM/lactoferrin PMN-MDSCs are a promising cell therapy for inflammatory adverse events of anti-cancer therapies.

TFF3 mediates the NF-κB/COX2 pathway to regulate PMN-MDSCs activation and protect against necrotizing enterocolitis

Intestinal trefoil factor 3 (TFF3) plays an important role in repairing the intestinal mucosa. However, the detailed mechanism regarding immune regulation by TFF3 is not well defined. Here, we reported that treatment of mouse BM cells and human peripheral blood mononuclear cells from healthy volunteers with TFF3 activated polymorphnuclear myeloid-derived suppressor cells (PMN-MDSCs) in vitro. We also found that prostaglandin E2 is a major TFF3-mediated MDSC target, and that NF-κB/COX2 signaling was involved in this process. Moreover, TFF3 treatment or transfer of TFF3-derived PMN-MDSCs (TFF3-MDSCs) to experimental necrotizing enterocolitis (NEC) mice caused PMN-MDSC accumulation in the lamina propria (LP), which was associated with decreased intestinal inflammation, permeability, bacterial loading, and prolonged survival. Interestingly, no NEC severity remission was observed in Rag1 KO mice that were given TFF3-MDSCs, but coinjection with CD4⁺ T cells significantly relieved NEC inflammation. Overall, TFF3 mediates the NF-κB/COX2 pathway to regulate PMN-MDSC activation and attenuates NEC in a T-cell-dependent manner, which suggests a novel mechanism in preventing NEC occurrence.

Extracellular vesicles released by myeloid-derived suppressor cells from pregnant women modulate adaptive immune responses

Immunological pregnancy complications are a main challenge in reproductive medicine. Mechanisms regulating the adaptation of the maternal immune system to pregnancy are incompletely understood and therapeutic options limited. Myeloid derived suppressor cells (MDSC) are immune-modulatory cells expanding during healthy pregnancy and seem to play a crucial role for maternal-fetal tolerance. Recent studies showed that exosomes produced by MDSC have immune-modulatory effects corresponding to their parental cells under different pathological conditions. Here, we investigated immunological effects of exosomes of GR-MDSC during pregnancy. Isolated GR-MDSC exosomes from peripheral blood of pregnant women were tested for functionality in different in vitro assays. We show that GR-MDSC exosomes exhibited profound immune-modulatory effects such as suppression of T-cell proliferation, T helper 2 (Th2)-cell polarization, induction of regulatory T-cells and inhibition of lymphocyte cytotoxicity. Our results confirm that MDSC-derived exosomes functionally correspond to their parental cells and identify them as an interesting therapeutic target for immunological pregnancy complications.

On use of animal models

Human pregnancy, critical for our species survival, is inefficient and prone to complications such as infertility, spontaneous miscarriages and preeclampsia (PE). Immunological factors may be important as the embryo is 50% paternal and foreign to the mother. Mouse pregnancy models, and in particular the murine CBA/J x DBA/2 mating combination, has been widely used to investigate mechanisms causing and preventing partner-specific recurrent miscarriages (RM) and PE. Occult losses can represent T cell-mediated rejection, and antigen-specific regulatory T cells (Tregs) with classical αβ T cell receptors (TcR) activated by semen antigens at the time of mating are protective. If there is no occult loss, an inadequate Treg response can also predispose to RM. In RM, proinflammatory cytokines from natural killer (NK)-type cells and macrophages of the innate immune system are responsible and cells with γδ TcR protect via release of TGF-β-type molecules. Immunization of abortion-prone female CBA/J mice or administration of cell-associated or soluble CD200, an immune check point inhibitor, can prevent abortions by augmenting uterine decidual suppressor cell activity. Human studies suggest that is also true in couples with RM. Environmental activators of the innate immune system, such as bacterial LPS and stress, can cause abortions as well as occult losses. The endogenous level of Tregs and activation of Tregs specific for the male H-Y antigen may determine success rates and alter the male:female birth ratio. Intralipid alters LPS clearance, prevents abortions in the CBAxDBA/2 model, and is effective in increasing live birth rates in couples undergoing IVF treatment.

Myeloid-Derived Suppressor Cells in Pregnancy and the Neonatal Period

During pregnancy, the immune systems of mother and offspring are challenged by their close adjacency to balance tolerance and rejection. After birth the neonate has to continue this balance towards its new environment by tolerating commensals while rejecting pathogens and towards its developing tissues to avoid inflammatory damage while overcoming immunosuppression. Our group was the first to link immunosuppressive features of myeloid derived suppressor cells (MDSC) to materno-fetal tolerance, neonatal susceptibility to infection and inflammation control. Here we summarize recent advances in this dynamic field.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Sildenafil might impair maternal-fetal immunotolerance by suppressing myeloid-derived suppressor cells in mice

Myeloid-derived suppressor cells (MDSCs) as an important population of immune cells were found to restrain T cell function, polarize T-helper cells (Th) 1/Th2 toward Th2 response and induce regulatory T cells (Tregs), therefore enhancing the immunotolerance during pregnancy. Sildenafil has been applied for poor endometrial quality in implantation failure patients. Nevertheless, investigations have shown that sildenafil could reduce MDSCs-dependent immunosuppression. Whether sildenafil affects embryo implantation by suppressing MDSCs? To address this question, using the mice model, we investigated the amounts of immune cells in peripheral blood and endometrial cells from control group (CG), sildenafil low-dose group (LDG) and high-dose group (HDG). We found that both treatment groups displayed a marked deficiency in polymorphonuclear (PMN)-MDSCs and Th2 from mice blood and endometrium as compared to these from CG. The frequency of Tregs in endometrium from HDG was lower than those from CG. Th1/Th2 ratio in both periphery and uterus from study groups showed a significant increase as compared to those from CG. By relevance analysis, we found that the level of Tregs positively correlated with the level of PMN-MDSCs, whereas the Th1/Th2 ratio negatively correlated with the frequency of PMN-MDSCs in uterus. Moreover, there was a positive relationship between the amount of blood PMN-MDSCs and endometrial PMN-MDSCs. These results suggest that we should carefully weigh the pros and cons of using sildenafil when applied to patients with poor endometrial receptivity.

Upregulated TRAIL and Reduced DcR2 Mediate Apoptosis of Decidual PMN-MDSC in Unexplained Recurrent Pregnancy Loss

Myeloid-derived suppressor cells (MDSC), especially polymorphonuclear MDSC (PMN-MDSC), accumulate in maternal-fetal interface during pregnancy and are involved in the maintenance of immune tolerance. Decreased PMN-MDSC is associated with pregnancy complications such as unexplained recurrent pregnancy loss (URPL). In the present study we showed decreased PMN-MDSC in the URPL group compared with the normal pregnancy (NP) group, and PMN-MDSC was the major subset of MDSC in human decidua with potent immune suppression activity. We then performed gene expression profile and found that human decidual PMN-MDSC in the NP and URPL groups showed different gene and pathway signature, including apoptosis. Apoptosis of decidual PMN-MDSC was mediated by TNF-related apoptosis–induced ligand (TRAIL) in a Caspase 3 dependent manner. TRAIL was expressed in decidua and upregulated in decidua of the URPL group. Notably, of all the membrane TRAIL receptors, only DcR2 was down-regulated in PMN-MDSC in the URPL group. In vitro experiment demonstrated that DcR2 blockade sensitized PMN-MDSC to TRAIL-mediated apoptosis. Together, these data indicate that increased TRAIL and reduced DcR2 on PMN-MDSC sensitize PMN-MDSC response to TRAIL-induced apoptosis in the URPL group, which is responsible for decreased accumulation of PMN-MDSC in URPL.

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.

Cord blood granulocytic myeloid-derived suppressor cells impair monocyte T cell stimulatory capacity and response to bacterial stimulation

BACKGROUND

Neonatal sepsis is a leading cause of perinatal morbidity and mortality. In comparison to adults, neonates exhibit a higher susceptibility to infections. Myeloid-derived suppressor cells (MDSCs) are myeloid cells with suppressive activity on other immune cells accumulating during foetal life and controlling inflammation in neonates. Most studies investigating the mechanisms for MDSC-mediated immune suppression have been focused on T-cells. Thus far, little is known about the role of MDSC for monocyte function.

METHODS

The impact of human cord blood MDSCs (CB-MDSCs) on monocytes was investigated in an in vitro model. CB-MDSCs were co-cultured with peripheral blood mononuclear cells and monocytes were analysed for expression of surface markers, T cell stimulatory and phagocytic capacity, as well as the production of intracellular cytokines by flow cytometry.

RESULTS

CB-MDSCs increased the expression of co-inhibitory molecules and decreased the expression of major histocompatibility complex class II molecules on monocytes, leading to an impaired T-cell stimulatory capacity. Upon bacterial stimulation, expression of phagocytosis receptors, phagocytosis rates and production of tumor necrosis factor-α by monocytes was diminished by CB-MDSCs.

CONCLUSION

We show that CB-MDSCs profoundly modulate monocyte functions, thereby indirectly impairing T-cell activation. Further research is needed to figure out if MDSCs could be a therapeutic target for inflammatory diseases in neonates like neonatal sepsis.

Antiestrogens in combination with immune checkpoint inhibitors in breast cancer immunotherapy

Breast cancers (BCs) with expression of estrogen receptor-alpha (ERα) occur in more than 70% of newly-diagnosed patients in the U.S. Endocrine therapy with antiestrogens or aromatase inhibitors is an important intervention for BCs that express ERα, and it remains one of the most effective targeted treatment strategies. However, a substantial proportion of patients with localized disease, and essentially all patients with metastatic BC, become resistant to current endocrine therapies. ERα is present in most resistant BCs, and in many of these its activity continues to regulate BC growth. Fulvestrant represents one class of ERα antagonists termed selective ER downregulators (SERDs). Treatment with fulvestrant causes ERα down-regulation, an event that helps overcome several resistance mechanisms. Unfortunately, full antitumor efficacy of fulvestrant is limited by its poor bioavailability in clinic. We have designed and tested a new generation of steroid-like SERDs. Using ERα-positive BC cells in vitro, we find that these compounds suppress ERα protein levels with efficacy similar to fulvestrant. Moreover, these new SERDs markedly inhibit ERα-positive BC cell transcription and proliferation in vitro even in the presence of estradiol-17β. In vivo, the SERD termed JD128 significantly inhibited tumor growth in MCF-7 xenograft models in a dose-dependent manner (P < 0.001). Further, our findings indicate that these SERDs also interact with ER-positive immune cells in the tumor microenvironment such as myeloid-derived suppressor cells (MDSC), tumor infiltrating lymphocytes and other selected immune cell subpopulations. SERD-induced inhibition of MDSCs and concurrent actions on CD8+ and CD4 + T-cells promotes interaction of immune checkpoint inhibitors with BC cells in preclinical models, thereby leading to enhanced tumor killing even among highly aggressive BCs such as triple-negative BC that lack ERα expression. Since monotherapy with immune checkpoint inhibitors has not been effective for most BCs, combination therapies with SERDs that enhance immune recognition may increase immunotherapy responses in BC and improve patient survival. Hence, ERα antagonists that also promote ER downregulation may potentially benefit patients who are unresponsive to current endocrine therapies.

MDSCs in pregnancy: Critical players for a balanced immune system at the feto-maternal interface

Myeloid-derived suppressor cells (MDSCs) have emerged as a new immune regulator at the feto-maternal interface. Although the phenotypes and functions of these cells were primarily studied in pathological conditions such as cancers and infections, new evidence has underscored their beneficial roles in homeostasis and physiological circumstances such as normal pregnancy. In this regard, studies have shown an increased number of MDSCs, particularly granulocytic MDSCs, at the feto-maternal interface. These cells participate in maintaining immunological tolerance between mother and semi-allograft fetus through various mechanisms. They further seem to play critical roles in placentation and fetus growth process. The absence or dysregulation of MDSCs during pregnancy have been reported in several pregnancy complications. These cells are also abundant in the cord blood of neonates so as to balance the immune responses and prevent aggressive inflammatory responses. The current review summarizes and organizes detailed data on MDSCs and their roles during pregnancy.

Neutrophil Diversity in Health and Disease

New evidence has challenged the outdated dogma that neutrophils are a homogeneous population of short-lived cells. Although neutrophil subpopulations with distinct functions have been reported under homeostatic and pathological conditions, a full understanding of neutrophil heterogeneity and plasticity is currently lacking. We review here current knowledge of neutrophil heterogeneity and diversity, highlighting the need for deep genomic, phenotypic, and functional profiling of the identified neutrophil subpopulations to determine whether these cells truly represent bona fide novel neutrophil subsets. We suggest that progress in understanding neutrophil heterogeneity will allow the identification of clinically relevant neutrophil subpopulations that may be used in the diagnosis of specific diseases and lead to the development of new therapeutic approaches.

Myeloid-Derived Suppressor Cells: Not Only in Tumor Immunity

Since the realization that immature myeloid cells are powerful modulators of the immune response, many studies on “myeloid-derived suppressor cells” (MDSCs) have documented their ability to promote tumor progression in melanoma and other cancers. Whether MDSCs are induced solely pathologically in tumorigenesis, or whether they also represent physiological immune control mechanisms, is not well-understood, but is particularly important in the light of ongoing attempts to block their activities in order to enhance anti-tumor immunity. Here, we briefly review studies which explore (1) how best to identify MDSCs in the context of cancer and how this compares to other conditions in humans; (2) what the suppressive mechanisms of MDSCs are and how to target them pharmacologically; (3) whether levels of MDSCs with various phenotypes are informative for clinical outcome not only in cancer but also other diseases, and (4) whether MDSCs are only found under pathological conditions or whether they also represent a physiological regulatory mechanism for the feedback control of immunity. Studies unequivocally document that MDSCs strongly influence cancer outcomes, but are less informative regarding their relevance to infection, autoimmunity, transplantation and aging, especially in humans. So far, the results of clinical interventions to reverse their negative effects in cancer have been disappointing; thus, developing differential approaches to modulate MSDCs in cancer and other diseases without unduly comprising any normal physiological function requires further exploration.

Estrogen stimulates female cancer progression by inducing myeloid-derived suppressive cells: investigations on pregnant and non-pregnant experimental models

Objective

To investigate the clinical implications of 17β-estradiol (E2) in estrogen receptor α (ERα)-negative female cancer progression as well as the underlying biological mechanisms.

Methods

Clinical data from 306 locally-advanced cervical cancer (stage IIB-IVA) patients were analyzed in order to investigate the relationships between age, serum E2 levels, and treatment outcomes. Clinical samples, ERα-negative cervical and breast cancer cell lines, and mouse xenograft models of cervical and breast cancers were employed in order to elucidate the mechanisms responsible for the E2- and pregnancy-mediated progression of cervical and breast cancers, with a focus on the role of myeloid-derived suppressor cells (MDSC).

Results

Younger patients with elevated E2 levels showed significantly shorter progression-free survival (P = 0.040) and overall survival (P = 0.039). The exogenous E2 treatment stimulated the mobilization of MDSC from bone marrow and directly augmented their suppressive activities, leading to the progression of ERα-negative cervical and breast cancers. The co-administration of an anti-Gr-1 neutralizing antibody with E2 prevented the E2-mediated induction of MDSC, and attenuated E2-mediated tumor growth in cervical and breast cancer xenografts. Significantly increased MDSC numbers and enhanced tumor growth were observed during pregnancy in mice with cervical or breast cancer. Significantly increased MDSC numbers were also observed during pregnancy in cervical cancer patients.

Conclusions

E2 facilitates the progression of ERα-negative cervical or breast cancer under non-pregnant and pregnant conditions by inducing MDSC. MDSC inhibition therapy may have therapeutic efficacy in premenopausal or pregnant female cancer patients.