B7 family molecules are favorably positioned at the human maternal-fetal interface

Progestogen-driven B7-H4 contributes to onco-fetal immune tolerance

Immune tolerance mechanisms are shared in cancer and pregnancy. Through cross-analyzing single-cell RNA-sequencing data from multiple human cancer types and the maternal-fetal interface, we found B7-H4 (VTCN1) is an onco-fetal immune tolerance checkpoint. We showed that genetic deficiency of B7-H4 resulted in immune activation and fetal resorption in allogeneic pregnancy models. Analogously, B7-H4 contributed to MPA/DMBA-induced breast cancer progression, accompanied by CD8+ T cell exhaustion. Female hormone screening revealed that progesterone stimulated B7-H4 expression in placental and breast cancer cells. Mechanistically, progesterone receptor (PR) bound to a newly identified -58 kb enhancer, thereby mediating B7-H4 transcription via the PR-P300-BRD4 axis. PR antagonist or BRD4 degrader potentiated immunotherapy in a murine B7-H4+ breast cancer model. Thus, our work unravels a mechanistic and biological connection of a female sex hormone (progesterone) to onco-fetal immune tolerance via B7-H4 and suggests that the PR-P300-BRD4 axis is targetable for treating B7-H4+ cancer.

Immune checkpoint molecules in solid organ transplantation: A promising way to prevent rejection

Immune checkpoint (IC) molecules modulate immune responses upon antigen presentation; the interaction between different IC molecules will result in the stimulation or, rather, the thwarting of such responses. Tumor cells express increased amounts of inhibitory IC molecules in an attempt to evade immune responses; therapeutic agents have been developed that bind inhibitory IC molecules, restoring tumor-directed immune responses and changing the prognosis of a number of cancers. Stimulation of inhibitory IC molecules could be beneficial in preventing rejection in the setting of solid organ transplantation (SOT), and in vivo as well as in vivo results obtained in animal models show this to indeed to be the case. With the exception of belatacept, a monoclonal antibody (mAb) in which an IgG Fc fragment is linked to the extracellular domain of CTLA-4, this has not yet translated into the generation of novel therapeutic approaches to prevent SOT rejection. We provide a review of state-of-the art knowledge on the role played by IC molecules in transplantation, confident that innovative research will lead to new avenues to manage rejection in solid organ transplant.

Extra villous trophoblast-derived PDL1 can ameliorate macrophage inflammation and promote immune adaptation associated with preeclampsia

INTRODUCTION

Severe preeclampsia (sPE) is a systemic syndrome that may originate from chronic inflammation. Maintaining maternal-fetal hemostasis by the co-inhibitory molecule programmed death ligand 1 (PDL1) can be favorable for ameliorating inflammation from immune cells. Apart from programmed death 1 (PD1) expression, decidual macrophages (dMs) produce inflammatory cytokines, in response to cells which express PDL1. However, strong evidence is lacking regarding whether the PDL1/PD1 interaction between trophoblasts and decidual macrophages affects inflammation during sPE development.

METHODS

To determine whether the trophoblast-macrophage crosstalk via the PDL1/PD1 axis modulates the inflammatory response in sPE-like conditions, at first, maternal-fetal tissues from sPE and normal patients were collected, and the PDL1/PD1 distribution was analyzed by Western blot, immunohistochemistry/ immunofluorescence and flow cytometry. Next, a coculture system was established and flow cytometry was used to identify how PDL1 was involved in macrophage-related inflammation under hypoxic stress. Transcriptional analysis was performed to clarify the inflammation-associated pathway induced by the PDL1/PD1 interaction. Finally, the Nω-nitro-L-arginine methyl ester hydrochloride (L-NAME) mouse model was used to examine the effect of PDL1 on macrophage-related inflammation by measuring PE-like symptoms.

RESULTS

In maternal-fetal tissue from sPE patients, placental extravillous trophoblasts (EVTs) and dMs had a surprisingly increase of PDL1 and PD1 expression, respectively, accompanied by a higher percentage of CD68 +CD86 + dMs. In vitro experiments showed that trophoblast-derived PDL1 under hypoxia interacted with PD1 on CD14 +CD80 +macrophages, leading to suppression of inflammation through the TNFα-p38/NFκB pathway. Accordingly, the PE-like mouse model showed a reversal of PE-like symptoms and a reduced F4/80 + CD86 + macrophage percentage in the uterus in response to recombinant PDL1 protein administration, indicating the protective effect of PDL1.

DISCUSSION

Our results initially explained an immunological adaptation of trophoblasts under placental hypoxia, although this protection was insufficient. Our findings suggest the possible capacity of modulating PDL1 expression as a potential therapeutic strategy to target the inflammatory response in sPE.

Single cell profiling at the maternal-fetal interface reveals a deficiency of PD-L1+ non-immune cells in human spontaneous preterm labor

The mechanisms that underlie the timing of labor in humans are largely unknown. In most pregnancies, labor is initiated at term (≥ 37 weeks gestation), but in a signifiicant number of women spontaneous labor occurs preterm and is associated with increased perinatal mortality and morbidity. The objective of this study was to characterize the cells at the maternal-fetal interface (MFI) in term and preterm pregnancies in both the laboring and non-laboring state in Black women, who have among the highest preterm birth rates in the U.S. Using mass cytometry to obtain high-dimensional single-cell resolution, we identified 31 cell populations at the MFI, including 25 immune cell types and six non-immune cell types. Among the immune cells, maternal PD1⁺ CD8 T cell subsets were less abundant in term laboring compared to term non-laboring women. Among the non-immune cells, PD-L1⁺ maternal (stromal) and fetal (extravillous trophoblast) cells were less abundant in preterm laboring compared to term laboring women. Consistent with these observations, the expression of CD274, the gene encoding PD-L1, was significantly depressed and less responsive to fetal signaling molecules in cultured mesenchymal stromal cells from the decidua of preterm compared to term women. Overall, these results suggest that the PD1/PD-L1 pathway at the MFI may perturb the delicate balance between immune tolerance and rejection and contribute to the onset of spontaneous preterm labor.

Immune Cell Functionality during Decidualization and Potential Clinical Application

Due to a vast influx in the secretory phase of the menstrual cycle, leukocytes represent 40-50% of the decidua at the time of implantation. Their importance for the implantation, maintenance of pregnancy, and parturition are known yet not fully understood. Thus, in idiopathic infertility, decidual immune-related factors are speculated to be the cause. In this review, the immune cell functions in the decidua were summarized, and clinical diagnostics, as well as interventions, were discussed. There is a rising number of commercially available diagnostic tools. However, the intervention options are still limited and/or poorly studied. In order for us to make big steps towards the proper use of reproductive immunology findings, we need to understand the mechanisms and especially support translational research.

PD-1/PD-L1 blockade inhibits epithelial-mesenchymal transition and improves chemotherapeutic response in breast cancer

Therapies targeting the PD-1/PD-L1 axis have recently been implemented for triple negative breast cancer (TNBC) management with limited efficacy, indicating that this axis may promote tumor growth by means other than immune suppression. Because PD-L1 overexpression causes resistance to the chemotherapeutic response in many cancers, here we explored the tumor promoting role of the PD-1/PD-L1 axis in breast cancer. We observed that the downregulation of PD-L1 by specific siRNA and pharmacological inhibitor significantly suppressed tumor cell proliferation, invasion and migration thereby enhancing T cell-mediated cell killing in vitro. We also showed that inhibiting PD-L1 improves cytotoxic sensitivity to chemotherapy in TNBC cells. Our in vivo results confirmed that combining a PD-L1 inhibitor with chemotherapy could significantly reduce tumor progression by inhibiting epithelial-mesenchymal transition. Overall, our results proved that PD-L1 contributes to the transformation and progression of breast cancer cells and that its intervention is a promising therapeutic strategy against breast cancer.

The human placenta shapes the phenotype of decidual macrophages

During human pregnancy, placenta-derived extravillous trophoblasts (EVTs) invade the decidua and communicate with maternal immune cells. The decidua distinguishes into basalis (decB) and parietalis (decP). The latter remains unaffected by EVT invasion. By defining a specific gating strategy, we report the accumulation of macrophages in decB. We describe a decidua basalis-associated macrophage (decBAM) population with a differential transcriptome and secretome compared with decidua parietalis-associated macrophages (decPAMs). decBAMs are CD11c^hi and efficient inducers of Tregs, proliferate in situ, and secrete high levels of CXCL1, CXCL5, M-CSF, and IL-10. In contrast, decPAMs exert a dendritic cell-like, motile phenotype characterized by induced expression of HLA class II molecules, enhanced phagocytosis, and the ability to activate T cells. Strikingly, EVT-conditioned media convert decPAMs into a decBAM phenotype. These findings assign distinct macrophage phenotypes to decidual areas depending on placentation and further highlight a critical role for EVTs in the induction of decB-associated macrophage polarization.

PD-1 expression in transbronchial biopsies of lung transplant recipients is a possible early predictor of rejection

Introduction

Chronic lung allograft dysfunction (CLAD) is the main cause of the reduced survival of lung transplanted (LTx) patients. The possible role of immune checkpoint molecules in establishing tolerance has been scarcely investigated in the setting of lung transplantation.

Methods

We conducted a retrospective, observational pilot study on a consecutive series of transbronchial cryobiopsies (TCB) obtained from 24 patients during LTx follow-up focusing on PD-1, one of the most investigated immune checkpoint molecules.

Results

Results showed that PD-1-expressing T lymphocytes were present in all TCB with a histological diagnosis of acute rejection (AR; 9/9), but not in most (11/15) of the TCB not resulting in a diagnosis of AR (p=0.0006). Notably, the presence of PD-1-expressing T lymphocytes in TCB resulted in a 10-times higher risk of developing chronic lung allograft dysfunction (CLAD), the main cause of the reduced survival of lung transplanted patients, thus being associated with a clearly worst clinical outcome.

Discussion

Results of this pilot study indicate a central role of PD-1 in the development of AR and its evolution towards CLAD and suggest that the evaluation of PD-1-expressing lymphocytes in TCB could offer a prognostic advantage in monitoring the onset of AR in patients who underwent lung transplantation.

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.

Gestationally dependent immune organization at the maternal-fetal interface

The immune system and placenta have a dynamic relationship across gestation to accommodate fetal growth and development. High-resolution characterization of this maternal-fetal interface is necessary to better understand the immunology of pregnancy and its complications. We developed a single-cell framework to simultaneously immuno-phenotype circulating, endovascular, and tissue-resident cells at the maternal-fetal interface throughout gestation, discriminating maternal and fetal contributions. Our data reveal distinct immune profiles across the endovascular and tissue compartments with tractable dynamics throughout gestation that respond to a systemic immune challenge in a gestationally dependent manner. We uncover a significant role for the innate immune system where phagocytes and neutrophils drive temporal organization of the placenta through remarkably diverse populations, including PD-L1⁺ subsets having compartmental and early gestational bias. Our approach and accompanying datasets provide a resource for additional investigations into gestational immunology and evoke a more significant role for the innate immune system in establishing the microenvironment of early pregnancy.

Local immune recognition of trophoblast in early human pregnancy: controversies and questions

The role of the maternal immune system in reproductive success in humans remains controversial. Here we focus on the events that occur in the maternal decidua during the first few weeks of human pregnancy, because this is the site at which maternal leukocytes initially interact with and can recognize fetal trophoblast cells, potentially involving allorecognition by both T cells and natural killer (NK) cells. NK cells are the dominant leukocyte population in first-trimester decidua, and genetic studies point to a role of allorecognition by uterine NK cells in establishing a boundary between the mother and the fetus. By contrast, definitive evidence that allorecognition by decidual T cells occurs during the first trimester is lacking. Thus, our view is that during the crucial period when the placenta is established, damaging T cell-mediated adaptive immune responses towards placental trophoblast are minimized, whereas NK cell allorecognition contributes to successful implantation and healthy pregnancy.

The mystery of the life tree: the placenta

The placenta is the interface between the fetal and maternal environments during mammalian gestation, critically safeguarding the health of the developing fetus and the mother. Placental trophoblasts origin from embryonic trophectoderm that differentiates into various trophoblastic subtypes through villous and extravillous pathways. The trophoblasts actively interact with multiple decidual cells and immune cells at the maternal-fetal interface and thus construct fundamental functional units, which are responsible for blood perfusion, maternal-fetal material exchange, placental endocrine, immune tolerance, and adequate defense barrier against pathogen infection. Various pregnant complications are tightly associated with the defects in placental development and function maintenance. In this review, we summarize the current views and our recent progress on the mechanisms underlying the formation of placental functional units, the interactions among trophoblasts and various uterine cells, as well as the placental barrier against pathogen infections during pregnancy. The involvement of placental dysregulation in adverse pregnancy outcomes is discussed.

Immunological Changes in Pregnancy and Prospects of Therapeutic Pla-Xosomes in Adverse Pregnancy Outcomes

Stringent balance of the immune system is a key regulatory factor in defining successful implantation, fetal development, and timely parturition. Interference in these primary regulatory mechanisms, either at adolescence or prenatal state led to adverse pregnancy outcomes. Fertility restoration with the help of injectable gonadotrophins/progesterone, ovulation-inducing drugs, immunomodulatory drugs (corticosteroids), and reproductive surgeries provides inadequate responses, which manifest its own side effects. The development of a potential diagnostic biomarker and an effectual treatment for adverse pregnancy outcomes is a prerequisite to maternal and child health. Parent cell originated bi-layered-intraluminal nano-vesicles (30-150 nm) also known as exosomes are detected in all types of bodily fluids like blood, saliva, breast milk, urine, etc. Exosomes being the most biological residual structures with the least cytotoxicity are loaded with cargo in the form of RNAs (miRNAs), proteins (cytokines), hormones (estrogen, progesterone, etc.), cDNAs, and metabolites making them chief molecules of cell-cell communication. Their keen involvement in the regulation of biological processes has portrayed them as the power shots of cues to understand the disease's pathophysiology and progression. Recent studies have demonstrated the role of immunexosomes (immunomodulating exosomes) in maintaining unwavering immune homeostasis between the mother and developing fetus for a healthy pregnancy. Moreover, the concentration and size of the exosomes are extensively studied in adverse pregnancies like preeclampsia, gestational diabetes mellitus (GDM), and preterm premature rupture of membrane (pPROMs) as an early diagnostic marker, thus giving in-depth information about their pathophysiology. Exosomes have also been engineered physically as well as genetically to enhance their encapsulation efficiency and specificity in therapy for cancer and adverse pregnancies. Successful bench to bedside discoveries and interventions in cancer has motivated developmental biologists to investigate the role of immunexosomes and their active components. Our review summarizes the pre-clinical studies for the use of these power-shots as therapeutic agents. We envisage that these studies will pave the path for the use of immunexosomes in clinical settings for reproductive problems that arise due to immune perturbance in homeostasis either at adolescence or prenatal state.

Chronic Inflammatory Placental Disorders Associated With Recurrent Adverse Pregnancy Outcome

Chronic inflammatory placental disorders are a group of rare but devastating gestational syndromes associated with adverse pregnancy outcome. This review focuses on three related conditions: villitis of unknown etiology (VUE), chronic histiocytic intervillositis (CHI) and massive perivillous fibrin deposition (MPFD). The hallmark of these disorders is infiltration of the placental architecture by maternal immune cells and disruption of the intervillous space, where gas exchange between the mother and fetus occurs. Currently, they can only be detected through histopathological examination of the placenta after a pregnancy has ended. All three are associated with a significant risk of recurrence in subsequent pregnancies. Villitis of unknown etiology is characterised by a destructive infiltrate of maternal CD8+ T lymphocytes invading into the chorionic villi, combined with activation of fetal villous macrophages. The diagnosis can only be made when an infectious aetiology has been excluded. VUE becomes more common as pregnancy progresses and is frequently seen with normal pregnancy outcome. However, severe early-onset villitis is usually associated with fetal growth restriction and recurrent pregnancy loss. Chronic histiocytic intervillositis is characterised by excessive accumulation of maternal CD68+ histiocytes in the intervillous space. It is associated with a wide spectrum of adverse pregnancy outcomes including high rates of first-trimester miscarriage, severe fetal growth restriction and late intrauterine fetal death. Intervillous histiocytes can also accumulate due to infection, including SARS-CoV-2, although this infection-induced intervillositis does not appear to recur. As with VUE, the diagnosis of CHI requires exclusion of an infectious cause. Women with recurrent CHI and their families are predisposed to autoimmune diseases, suggesting CHI may have an alloimmune pathology. This observation has driven attempts to prevent CHI with a wide range of maternal immunosuppression. Massive perivillous fibrin deposition is diagnosed when >25% of the intervillous space is occupied by fibrin, and is associated with fetal growth restriction and late intrauterine fetal death. Although not an inflammatory disorder per se, MPFD is frequently seen in association with both VUE and CHI. This review summarises current understanding of the prevalence, diagnostic features, clinical consequences, immune pathology and potential prophylaxis against recurrence in these three chronic inflammatory placental syndromes.

Expression of the Costimulatory Molecule B7-H4 in the Decidua and Placental Tissues in Patients with Placental Abruption

B7 homolog 4 protein (B7-H4), a member of the B7 family, is a immunomodulatory membrane protein. The aim of the study was to evaluate the expression of this protein in the decidua and placental tissues in case of placental abruption (PA) compared to cases of retained placental tissue (RPT) and controls. Tissue samples were obtained from 47 patients with PA, 60 patients with RPT, and 41 healthy controls. The samples were stained for B7-H4 expression, analyzed by an expert pathologist, and a semi-quantitative scale was applied. A statistical analysis revealed that the expression of B7-H4 was significantly higher in the decidua in PA samples compared to samples from patients with RPT (p-value < 0.001) and healthy controls (p-value < 0.001). The expression of B7-H4 in the placental chorionic villus was significantly higher in PA samples in relation to samples from healthy controls (p-value < 0.001) but not in relation to RPT samples (p-value = 0.0853). This finding suggests that B7-H4 might play an important role in mechanisms restoring reproductive tract homeostasis. Further research is necessary in regard to the role of B7-H4 in PA.

The Role of the Immune Checkpoint Molecules PD-1/PD-L1 and TIM-3/Gal-9 in the Pathogenesis of Preeclampsia—A Narrative Review

Preeclampsia is a pregnancy-specific disease which is characterized by abnormal placentation, endothelial dysfunction, and systemic inflammation. Several studies have shown that the maternal immune system, which is crucial for maintaining the pregnancy by ensuring maternal-fetal-tolerance, is disrupted in preeclamptic patients. Besides different immune cells, immune checkpoint molecules such as the programmed cell death protein 1/programmed death-ligand 1 (PD-1/PD-L1 system) and the T-cell immunoglobulin and mucin domain-containing protein 3/Galectin-9 (TIM-3/Gal-9 system) are key players in upholding the balance between pro-inflammatory and anti-inflammatory signals. Therefore, a clear understanding about the role of these immune checkpoint molecules in preeclampsia is essential. This review discusses the role of these two immune checkpoint systems in pregnancy and their alterations in preeclampsia.

Immune Checkpoints Expression in Chronic Lung Allograft Rejection

Chronic lung allograft dysfunction (CLAD) is the main cause of poor survival and low quality of life of lung transplanted patients. Several studies have addressed the role of dendritic cells, macrophages, T cells, donor specific as well as anti-HLA antibodies, and interleukins in CLAD, but the expression and function of immune checkpoint molecules has not yet been analyzed, especially in the two CLAD subtypes: BOS (bronchiolitis obliterans syndrome) and RAS (restrictive allograft syndrome). To shed light on this topic, we conducted an observational study on eight consecutive grafts explanted from patients who received lung re-transplantation for CLAD. The expression of a panel of immune molecules (PD1/CD279, PDL1/CD274, CTLA4/CD152, CD4, CD8, hFoxp3, TIGIT, TOX, B-Cell-Specific Activator Protein) was analyzed by immunohistochemistry in these grafts and in six control lungs. Results showed that RAS compared to BOS grafts were characterized by 1) the inversion of the CD4/CD8 ratio; 2) a higher percentage of T lymphocytes expressing the PD-1, PD-L1, and CTLA4 checkpoint molecules; and 3) a significant reduction of exhausted PD-1-expressing T lymphocytes (PD-1^pos/TOX^pos) and of exhausted Treg (PD-1^pos/FOXP3^pos) T lymphocytes. Results herein, although being based on a limited number of cases, suggest a role for checkpoint molecules in the development of graft rejection and offer a possible immunological explanation for the worst prognosis of RAS. Our data, which will need to be validated in ampler cohorts of patients, raise the possibility that the evaluation of immune checkpoints during follow-up offers a prognostic advantage in monitoring the onset of rejection, and suggest that the use of compounds that modulate the function of checkpoint molecules could be evaluated in the management of chronic rejection in LTx patients.

Expression of Immune Checkpoint Receptors in Placentae With Infectious and Non-Infectious Chronic Villitis

Pregnancy is an immunological paradox whereby maternal immunity accepts a genetically unique fetus (or fetuses), while maintaining protective innate and adaptive responses to infectious pathogens. This close contact between the genetically diverse mother and fetus requires numerous mechanisms of immune tolerance initiated by trophoblast cell signals. However, in a placental condition known as villitis of unknown etiology (VUE), there appears to be a breakdown in this tolerance allowing maternal cytotoxic T-cells to traffic into the placenta to destroy fetal villi. VUE is associated with several gestational complications and an increased risk of recurrence in a subsequent pregnancy, making it a significant obstetrical diagnosis. The cause of VUE remains unclear, but dysfunctional signaling through immune checkpoint pathways, which have a critical role in blunting immune responses, may play an important role. Therefore, using placental tissue from normal pregnancy (n=8), VUE (n=8) and cytomegalovirus (CMV) infected placentae (n=4), we aimed to identify differences in programmed cell death 1 (PD-1), programmed death ligand-1 (PD-L1), LAG3 and CTLA4 expression between these etiologies by immunohistochemistry (IHC). Results demonstrated significantly lower expression of PD-L1 on trophoblast cells from VUE placentae compared to control and CMV infection. Additionally, we observed significantly higher counts of PD-1+ (>100 cells/image) and LAG3+ (0-120 cells/image) cells infiltrating into the villi during VUE compared to infection and control. Minimal CTLA4 staining was observed in all placentae, with only a few Hofbauer cells staining positive. Together, this suggests that a loss of tolerance through immune checkpoint signaling may be an important mechanism leading to the activation and trafficking of maternal cells into fetal villi during VUE. Further mechanistic studies are warranted to understand possible allograft rejection more clearly and in developing effective strategies to prevent this condition from occurring in utero.

Immunosuppressive Protein Signatures Carried by Syncytiotrophoblast-Derived Exosomes and Their Role in Human Pregnancy

The syncytiotrophoblast (STB) of human placenta constitutively and throughout pregnancy produces and secretes exosomes - nanometer-sized membrane-bound extracellular vesicles from the endosomal compartment that convey cell-cell contact 'by proxy' transporting information between donor and recipient cells locally and at a distance. Released in the maternal blood, STB-derived exosomes build an exosomal gradient around the feto-placental unit acting as a shield that protects the fetus from maternal immune attack. They carry signal molecules and ligands that comprise distinct immunosuppressive protein signatures which interfere with maternal immune mechanisms, potentially dangerous for the ongoing pregnancy. We discuss three immunosuppressive signatures carried by STB exosomes and their role in three important immune mechanisms 1) NKG2D receptor-mediated cytotoxicity, 2) apoptosis of activated immune cells and 3) PD-1-mediated immunosuppression and priming of T regulatory cells. A schematic presentation is given on how these immunosuppressive protein signatures, delivered by STB exosomes, modulate the maternal immune system and contribute to the development of maternal-fetal tolerance.

Relevance of microRNAs to the regulation of the brain-placental axis in mice

INTRODUCTION

The development of fetal brain is intricately dependent upon placental functions. Recently, we showed that the placenta and fetal brain express genes in a coordinated manner in mice. But, how the brain-placental axis is regulated at the molecular level remains poorly understood. The microRNAs (miRNAs) play diverse roles in pregnancy including regulation of placenta function as well as brain development. Thus, we hypothesized that specific miRNAs are expressed in the placenta and fetal brain to coordinate gene regulation in the brain-placental axis.

METHODS

To test this hypothesis, we performed deep sequencing of small RNAs in mouse placenta and fetal brain of both sexes.

RESULTS

The findings study show that miRNAs are potent regulators of gene expression in the placenta and fetal brain. Our data provides evidence that fetal sex influences the regulation of miRNAs between the placenta and fetal brain. Functional annotation of known target genes of the differentially expressed miRNAs show that they are significantly enriched with specific signaling and transporter pathways.

DISCUSSION

Together, the results of this study suggest that placental miRNAs are potent regulators of fetal brain development in mice.

Placenta-Derived Exosomes as a Modulator in Maternal Immune Tolerance During Pregnancy

Exosomes are a subset of extracellular vesicles with an average diameter of ~100nm. Exosomes are released by all cells through an endosome-dependent pathway and carry nucleic acids, proteins, lipids, cytokines and metabolites, mirroring the state of the originating cells. The function of exosomes has been implicated in various reproduction processes, such as embryo development, implantation, decidualization and placentation. Placenta-derived exosomes (pEXO) can be detected in the maternal blood as early as 6 weeks after conception and their levels increase with gestational age. Importantly, alternations in the molecular signatures of pEXO are observed in pregnancy-related complications. Thus, these differentially expressed molecules could be the potential biomarkers for diagnosis of the pregnancy-associated diseases. Recent studies have demonstrated that pEXO play a key role in the establishment of maternal immune tolerance, which is critical for a successful pregnancy. To gain a better understanding of the underlying mechanism, we highlighted the advanced studies of pEXO on immune cells in pregnancy.

Fetomaternal Immune Tolerance: Crucial Mechanisms of Tolerance for Successful Pregnancy in Humans

For many years, the question of how the maternal immune system tolerates the foreign fetus has remained unanswered, and numerous studies have considerably attempted to elucidate underlying mechanisms for fetomaternal tolerance. This review aimed at discussing various significant mechanisms in fetomaternal compatibility. At the fetomaternal interface, in addition to having efficient control against infections, innate and adaptive maternal immune systems selectively prevent fetal rejection. In general, understanding the complex mechanisms of fetomaternal tolerance is critical for immunologic tolerance induction and spontaneous abortion prevention in high-risk populations. Different cells and molecules, such as regulatory T-cells, dendritic cells, decidua cells, IDO, Class I HLA molecules, TGF-β, and IL-10, induce maternal immune tolerance in the fetus in numerous ways. The findings on fetomaternal immune tolerance have remained controversial and require further research.

Gamma/Delta T Cells in the Course of Healthy Human Pregnancy: Cytotoxic Potential and the Tendency of CD8 Expression Make CD56+ γδT Cells a Unique Lymphocyte Subset

To date, pregnancy is an immunological paradox. The semi-allogenic fetus must be accepted by the maternal immune system, while defense against pathogens and immune surveillance cannot be compromised. Gamma/delta T cells are believed to play an important role in this immunological puzzle. In this study, we analyzed peripheral blood CD56+ γδT cells from pregnant women (1^st, 2^nd, and 3^rd trimester) and non-pregnant women by multicolor flow cytometry. Interestingly, γδT cells represent almost half of CD3+/CD56+ cells. Among γδT cells, the CD56+ population expands in the 2^nd and 3^rd trimester. CD56+ γδT cells maintained a predominantly CD4–/CD8– or CD8+ phenotype, while CD56– γδT cells were in similar rates CD4–/CD8– or CD4+ during pregnancy. Investigation of the lysosomal degranulation marker CD107a revealed a preserved elevated rate of potentially cytotoxic CD56+ γδT cells in pregnancy, while their cytotoxic strength was reduced. Furthermore, CD56+ γδT cells continuously showed a higher prevalence of PD-1 expression. CD56+ γδT cells’ rate of PD-1 increased in the 1^st trimester and decreased hereafter back to normal level. We correlated the cytotoxic potential and the expression of the inhibitory immune checkpoint PD-1 and were able to demonstrate that highly cytotoxic cells within this CD56+ γδT population tend to express PD-1, which might allow the inhibition of these cells after binding its ligand in the placenta. These findings should support the understanding of the complex processes, which ensure the maintenance of pregnancy.

Immunohistochemical Analysis of Programmed Death-Ligand 1 Expression in Equine Sarcoids

The aim of the study was to assess the expression of the immune checkpoint inhibitor programmed death-ligand 1 (PD-L1) in equine sarcoids (ES). Programmed death-ligand 1 is expressed by various cancer cells to block T cell-mediated elimination of tumor cells. Antibodies targeting human PD-L1 were tested by immunohistochemistry for their cross-reactivity with equine PD-L1 using formalin-fixed, paraffin-embedded tissues. Our results do not support an important role of PD-L1-mediated immune evasion in ES disease and hence do not offer a rationale for anti-PD-1/PD-L1-based immunotherapy against ES.

The new role for an old guy: MYC as an immunoplayer

As an oncogene, myelocytomatosis oncogene (MYC) is implicated in the concept of "oncogene addiction," where switching off the oncogene leads to the cell cycle arrest and cell differentiation. However, recent data suggest that MYC also controls the establishment of the tumour microenvironment and that "oncogene addiction" actually has a strong immune background. Evaluation of the MYC role in the immunoediting process led to the speculation that cancer just uses and distorts the physiological mechanism by which MYC normally prevents rapidly proliferating cells from the elicitation of an autoimmune response. Concordantly, elevated levels of MYC and induction of immunosuppressive molecules are observed during the processes of growth and development, tissue repair, placenta development, and so forth, implying that MYC may be involved in saving regular physiologically proliferating cells from the immune system attack. Even more, a growing body of evidence suggests MYC involvement in the shaping of the adaptive immune response, immunological memory development, and establishment of immunotolerance. This paper offers an overview of MYC actions in the context of modulation of the immune response in pathological and physiological conditions. The determination of such a new role for a well-known oncogene opens new perspectives in biomedicine, and consequently, in the treatment of various pathological conditions.

Cytotrophoblasts suppress macrophage-mediated inflammation through a contact-dependent mechanism

PROBLEM

Gestational membrane (GM) infection provokes inflammation and can result in preterm prelabor rupture of membranes (PPROM). The choriodecidual layer of the GM includes decidual stromal cells (DSC), cytotrophoblasts (CTB), and macrophages (Mφ). Our laboratory has previously shown that DSCs suppress Mφ TNF-α production through secreted prostaglandin E₂ . We hypothesized that CTBs would also inhibit Mφ cytokine expression through secreted mediators.

METHOD OF STUDY

THP.1 Mφ-like cells with an NF-κB reporter construct or human blood monocyte-derived Mφ were co-cultured with the Jeg3 CTB cell line or primary human CTBs and challenged with group B streptococcus (GBS) or Toll-like receptor (TLR) agonists. Conditioned medium generated from CTB cultures was applied to Mφ cultures before infection or treatment. Alternatively, CTBs were co-incubated with, but physically separated from, Mφ and GBS or TLR-stimulated. NF-κB was assessed via alkaline phosphatase assay, and proinflammatory mediators were assessed by qRT-PCR and ELISA.

RESULTS

CTBs suppressed GBS- or TLR-stimulated Mφ NF-κB activity, and TNF-α and MMP9 production. Direct physical contact between CTBs and Mφ was required for full immunosuppression. Immunosuppression could be overcome by increasing the ratio of Mφ to CTB.

CONCLUSIONS

CTBs limit Mφ NF-κB activation and production of TNF-α and MMP9 through an as-yet unknown, cell-to-cell contact-mediated mechanism. This suppression is distinct from the PGE₂ -mediated Mφ TNF-α suppression by DSC, suggesting that DSCs and CTBs regulate Mφ inflammation through distinct mechanisms. How Mφ integrates these signals in an intact GM will be paramount to determining causes and prevention of PPROM.

T Helper (Th) Cell Profiles in Pregnancy and Recurrent Pregnancy Losses: Th1/Th2/Th9/Th17/Th22/Tfh Cells

During pregnancy, various immune effectors and molecules participating in the immune-microenvironment establish specific maternal tolerance toward the semi-allogeneic fetus. Activated maternal immune effectors by the trophoblast antigens, such as T helper (Th), T cytotoxic (Tc), T regulatory (Treg), and B cells, are involved in the regulation of adaptive immunity. Recognition of active signal through the T cell receptors stimulate the differentiation of naive CD3⁺CD4⁺ T cells into specific T cell subsets, such as Th1, Th2, Th9, Th17, Th22, and follicular Th cells (Tfh). Each of these subsets has a significant and distinct role in human pregnancy. Th1 immunity, characterized by immune-inflammatory responses, becomes dominant during the peri-implantation period, and the “controlled” Th1 immunity benefits the invading trophoblasts rather than harm. Quickly after the placental implantation, the early inflammatory Th1 immunity is shifted to the Th2 anti-inflammatory immune responses. The predominant Th2 immunity, which overrules the Th1 immunity at the placental implantation site, protects a fetus by balancing Th1 immunity and accommodate fetal and placental development. Moreover, Treg and Th9 cells regulate local inflammatory immune responses, potentially detrimental to the fetus. Th17 cells induce protective immunity against extracellular microbes during pregnancy. However, excessive Th17 immunity may induce uncontrolled neutrophil infiltration at the maternal-fetal interface. Other Th cell subsets such as Tfh cells, also contribute to pregnancy by setting up favorable humoral immunity during pregnancy. However, dysregulation of Th cell immunity during pregnancy may result in obstetrical complications, such as recurrent pregnancy losses (RPL) and preeclampsia (PE). With this review, we intend to deliver a comprehensive overview of CD4⁺ Th cell subsets, including Th1, Th2, Th9, Th17, Th22, and Tfh cells, in human pregnancy by reviewing their roles in normal and pathological pregnancies.

Analysis of TCR Repertoire and PD-1 Expression in Decidual and Peripheral CD8+ T Cells Reveals Distinct Immune Mechanisms in Miscarriage and Preeclampsia

CD8⁺ T cells, the most abundant T cell subset in the decidua, play a critical role in the maintenance of pregnancy. The majority of decidual CD8⁺ T cells have an effector memory phenotype, while those in the peripheral blood display a naive phenotype. An increased amount of highly differentiated CD8⁺ T cells in the decidua indicates local antigen stimulation and expansion, albeit these CD8⁺ T cells are suppressed. In decidual CD8⁺ T cells, co-inhibitory molecules such as PD-1, TIM-3, LAG-3, and CTLA-4 are upregulated, reflecting the suppression of cytotoxicity. Previous studies established the importance of the PD-1/PD-L1 interaction for feto-maternal tolerance. CD8⁺ T cells could directly recognize fetal-specific antigens, such as HLA-C, expressed by trophoblasts. However, although fetal-specific CD8⁺ T cells have been reported, their TCR repertoires have not been identified. In this study, we analyzed the TCR repertoires of effector memory CD8⁺ T cells (CD8⁺ EM cells) and naive CD8⁺ T cells (CD8⁺ N cells) in the decidua and peripheral blood of women with normal or complicated pregnancy and examined PD-1 expression at a single-cell level to verify whether antigen-specific CD8⁺ T cells accumulate in the decidua and to identify immunological differences related to the suppression of antigen-specific CD8⁺ T cells between normal pregnancy, miscarriage, and preeclampsia. We observed that some TCRβ repertoires, which might recognize fetal or placental antigens, were clonally expanded. The population size of clonally expanded CD8⁺ EM cells was higher in the decidua than in the peripheral blood. CD8⁺ EM cells began to express PD-1 during the course of normal pregnancy. We found that the total proportion of decidual CD8⁺ EM cells not expressing PD-1 was increased both in miscarriage and in preeclampsia cases, although a different mechanism was responsible for this increase. The amount of cytotoxic CD8⁺ EM cells increased in cases of miscarriage, whereas the expression of PD-1 in clonally expanded CD8⁺ EM cells was downregulated in preeclampsia cases. These results demonstrated that decidual CD8⁺ EM cells were able to recognize fetal-specific antigens at the feto-maternal interface and could easily induce fetal rejection.

Trophoblast-secreted soluble-PD-L1 modulates macrophage polarization and function

Decidual macrophages are in close contact with trophoblast cells during placenta development, and an appropriate crosstalk between these cellular compartments is crucial for the establishment and maintenance of a healthy pregnancy. During different phases of gestation, macrophages undergo dynamic changes to adjust to the different stages of fetal development. Trophoblast-secreted factors are considered the main modulators responsible for macrophage differentiation and function. However, the phenotype of these macrophages induced by trophoblast-secreted factors and the factors responsible for their polarization has not been elucidated. In this study, we characterized the phenotype and function of human trophoblast-induced macrophages. Using in vitro models, we found that human trophoblast-educated macrophages were CD14⁺ CD206⁺ CD86^- and presented an unusual transcriptional profile in response to TLR4/LPS activation characterized by the expression of type I IFN-β expression. IFN-β further enhances the constitutive production of soluble programmed cell death ligand 1 (PD-L1) from trophoblast cells. PD-1 blockage inhibited trophoblast-induced macrophage differentiation. Soluble PD-L1 (sPD-L1) was detected in the blood of pregnant women and increased throughout the gestation. Collectively, our data suggest the existence of a regulatory circuit at the maternal fetal interface wherein IFN-β promotes sPD-L1 expression/secretion by trophoblast cells, which can then initiate a PD-L1/PD-1-mediated macrophage polarization toward an M2 phenotype, consequently decreasing inflammation. Macrophages then maintain the expression of sPD-L1 by the trophoblasts through IFN-β production induced through TLR4 ligation.

The Role of B7 Family Molecules in Maternal-Fetal Immunity

Pregnancy is a complex but well-arranged process, and a healthy fetus requires immune privilege and surveillance in the presence of paternally derived antigens. Maternal and fetal cells interact at the maternal–fetal interface. The upregulation and downregulation of maternal immunity executed by the leukocyte population predominantly depend on the activity of decidual natural killer cells and trophoblasts and are further modulated by a series of duplex signals. The B7 family, which consists of B7-1, B7-2, B7-H1, B7-DC, B7-H2, B7-H3, B7-H4, B7-H5, BTNL2, B7-H6, and B7-H7, is one of the most characterized and widely distributed signaling molecule superfamilies and conducts both stimulatory and inhibitory signals through separate interactions. In particular, the roles of B7-1, B7-2, B7-H1, and their corresponding receptors in the progression of normal pregnancy and some pregnancy complications have been extensively studied. Together with the TCR–MHC complex, B7 and its receptors play a critical role in cell proliferation and cytokine secretion. Depending on this ligand–receptor crosstalk, the balance between the tolerance and rejection of the fetus is perfectly maintained. This review aims to provide an overview of the current knowledge of the B7 family and its functions in regulating maternal–fetal immunity through individual interactions.

PD-1 and PD-L1 expression on T-cell subsets in women with unexplained recurrent pregnancy losses

PROBLEM

Does programmed death-1 (PD-1)/programmed death ligand-1 (PD-L1) expression on the T-cell subsets such as T helper (Th) 1, Th17, and Treg cells differentiate women with recurrent pregnancy losses (RPL) from normal fertile women?

METHOD OF STUDY

The study was designed as a prospective cohort study. Forty-five women with two or more RPL of unknown etiology and twenty fertile women who had at least one or more live-born infants were enrolled prospectively from Jan 2017 to Jul 2019. PD-1 and PD-L1 expression on T-cell subsets were measured by flow cytometric analysis.

RESULTS

The proportions of PD-1⁺ Th1 (CD4⁺ /IFN-γ⁺ /CD279⁺ and CD4⁺ /TNF-α⁺ /CD279⁺ ) and PD-1⁺ Th17 cells (CD4⁺ /IL17⁺ /CD279⁺ ) were significantly lower in RPL group than those of controls (P < .05, respectively). The proportion of PD-1⁺ Tregs (CD4⁺ /CD25⁺ /CD127^dim/- /CD279⁺ ) in RPL group was not different from that of controls. The proportion of PD-L1⁺ Th17 cells (CD4⁺ IL17⁺ CD274⁺ ) was significantly lower as compared with that of /controls (P < .05). However, the proportions of PD-L1⁺ Th1 (CD4⁺ /IFN-γ⁺ /CD274⁺ and CD4⁺ /TNF-α⁺ /CD274⁺ ) and PD-L1⁺ Treg (CD4⁺ /CD25⁺ /CD127^dim/- /CD274⁺ ) cells were not different between the RPL group and controls (P > .05, respectively). In Th1, Th17 and Treg cells, the proportions of PD-L1⁺ (CD274⁺ ) cells were significantly higher than those of PD-1⁺ (CD279⁺ ) cells in both RPL group and controls (P < .05, respectively).

CONCLUSION

PD-1 and PD-L1 expressions on Th17 cells as well as PD-1 expression on Th1 cells were significantly downregulated in women with RPL, which may lead to increased Th1 and Th17 immunity, and imbalance between Th17, Th1, and Treg cells in women with RPL.

The structural features that distinguish PD-L2 from PD-L1 emerged in placental mammals

Programmed cell death protein 1 (PD-1) is an inhibitory receptor on T lymphocytes that is critical for modulating adaptive immunity. As such, it has been successfully exploited for cancer immunotherapy. Programmed death ligand 1 (PD-L1) and PD-L2 are ligands for PD-1; the former is ubiquitously expressed in inflamed tissues, whereas the latter is restricted to antigen-presenting cells. PD-L2 binds to PD-1 with 3-fold stronger affinity compared with PD-L1. To date, this affinity discrepancy has been attributed to a tryptophan (W110_PD-L2) that is unique to PD-L2 and has been assumed to fit snuggly into a pocket on the PD-1 surface. Contrary to this model, using surface plasmon resonance to monitor real-time binding of recombinantly-expressed and -purified proteins, we found that W110_PD-L2 acts as an "elbow" that helps shorten PD-L2 engagement with PD-1 and therefore lower affinity. Furthermore, we identified a "latch" between the C and D β-strands of the binding face as the source of the PD-L2 affinity advantage. We show that the 3-fold affinity advantage of PD-L2 is the consequence of these two opposing features, the W110_PD-L2 "elbow" and a C-D region "latch." Interestingly, using phylogenetic analysis, we found that these features evolved simultaneously upon the emergence of placental mammals, suggesting that PD-L2-affinity tuning was part of the alterations to the adaptive immune system required for placental gestation.

Dynamic Function and Composition Changes of Immune Cells During Normal and Pathological Pregnancy at the Maternal-Fetal Interface

A successful pregnancy requires a fine-tuned and highly regulated balance between immune activation and embryonic antigen tolerance. Since the fetus is semi-allogeneic, the maternal immune system should exert tolerant to the fetus while maintaining the defense against infection. The maternal-fetal interface consists of different immune cells, such as decidual natural killer (dNK) cells, macrophages, T cells, dendritic cells, B cells, and NKT cells. The interaction between immune cells, decidual stromal cells, and trophoblasts constitute a vast network of cellular connections. A cellular immunological imbalance may lead to adverse pregnancy outcomes, such as recurrent spontaneous abortion, pre-eclampsia, pre-term birth, intrauterine growth restriction, and infection. Dynamic changes in immune cells at the maternal-fetal interface have not been clearly stated. While many studies have described changes in the proportions of immune cells in the normal maternal-fetus interface during early pregnancy, few studies have assessed the immune cell changes in mid and late pregnancy. Research on pathological pregnancy has provided clues about these dynamic changes, but a deeper understanding of these changes is necessary. This review summarizes information from previous studies, which may lay the foundation for the diagnosis of pathological pregnancy and put forward new ideas for future studies.

Human Miscarriage Is Associated With Dysregulations in Peripheral Blood-Derived Myeloid Dendritic Cell Subsets

Dendritic cells (DC) are critically involved in decisions related to the acceptance or rejection of the foreign fetal antigens by the maternal immune system. However, particularly for human peripheral blood DCs (PBDC), available literature is rather inconsistent and the factors regulating these cells are ill-defined. Here, we investigated the phenotype and functionality of different human PBDC subsets during normal and pathologic pregnancies and studied an involvement of human chorionic gonadotropin (hCG) in PBDC regulation. Peripheral blood samples were obtained from normal pregnant women in all three trimesters, from first trimester miscarriage patients and from healthy non-pregnant women. Samples were analyzed for plasma hCG levels, for regulatory T (Treg) cell numbers, for frequencies of total and mature plasmacytoid (PDC) and myeloid (MDC1 and MDC2) PBDC subsets and for their cytokine secretion. In vitro assays, culturing PDC, MDC1 or MDC2 in the presence of two trophoblast cell lines, placenta explant supernatants or two hCG preparations were performed. The Treg-inducing capability of hCG- or non-hCG-treated stimulated MDC1 was assessed. Total and mature MDC1 and MDC2 frequencies increased during the first and second trimester of normal pregnancy, respectively. Miscarriage was associated with a reduced MDC1 and an increased MDC2 activation profile. PDC were not altered neither during normal pregnancy progression nor during miscarriage. In vitro, the culture of isolated PBDC subsets in the presence of placenta-derived factors impaired the maturation of MDC1 and differentially affected PDC maturation. An inhibitory effect on MDC1 and PDC maturation was also proven for the urine-derived hCG preparation. Finally, we observed a Treg cell elevation during early normal pregnancy that was not present in miscarriages. Stimulated MDC1 induced Treg cells in vitro, however, hCG was not involved in this process. Our findings suggest that during normal pregnancy PBDC subsets are differentially regulated dependent on gestational age. Miscarriage seems to be associated with dysregulations in the myeloid PBDC subsets and with disturbances in Treg cell frequencies. Moreover, our results propose an interdependency between MDC1 and Treg cells during early pregnancy. hCG, although shown to impair MDC1 maturation, does not seem to be a key regulator of PBDC alterations during pregnancy.

Pregnancy with successful foetal and maternal outcome in a melanoma patient treated with nivolumab in the first trimester: case report and review of the literature

Although T-cell checkpoint blockade has revolutionized melanoma therapy, metastatic melanoma in pregnancy remains a challenging area of unmet need. Treatment with anti-PD1 therapy decreases foetal-maternal tolerance and increases the risk of pregnancy loss in animal studies and is considered category D by the Food and Drug Administration. We describe a unique case of conception and pregnancy, with successful maternal and foetal outcomes, in a patient with metastatic melanoma who had received combination anti-CTLA-4 and anti-PD1 therapy. A 32-year-old G0P0 lady, with a 10-year history of infertility of unclear cause, was found to be 7 weeks pregnant after 14 months of nivolumab maintenance therapy, having previously received combination ipilimumab and nivolumab. Nivolumab was ceased upon discovery of pregnancy in the first trimester. The patient had an uneventful pregnancy, followed by spontaneously premature labour, and delivered by caesarean section at 33 weeks' gestation. The foetus had moderate intrauterine growth restriction, as well as congenital hypothyroidism, which possibly constitutes the first documented case of foetal immune-related adverse event from maternal anti-PD1 exposure. No adverse events were noted in the mother. At 6 months of follow-up postpartum, the mother had a sustained complete response to treatment, and the baby had appropriate weight gain with normal developmental milestones. We summarize and discuss the available literature of immune checkpoint inhibitor exposure in pregnancy, which consists of a total of three case reports.

DNA damage response and repair in ovarian cancer: Potential targets for therapeutic strategies

Ovarian cancer is among the most lethal gynecologic malignancies with a poor survival prognosis. The current therapeutic strategies involve surgery and chemotherapy. Research is now focused on novel agents especially those targeting DNA damage response (DDR) pathways. Understanding the DDR process in ovarian cancer necessitates having a detailed knowledge on a series of signaling mediators at the cellular and molecular levels. The complexity of the DDR process in ovarian cancer and how this process works in metastatic conditions is comprehensively reviewed. For evaluating the efficacy of therapeutic agents targeting DNA damage in ovarian cancer, we will discuss the components of this system including DDR sensors, DDR transducers, DDR mediators, and DDR effectors. The constituent pathways include DNA repair machinery, cell cycle checkpoints, and apoptotic pathways. We also will assess the potential of active mediators involved in the DDR process such as therapeutic and prognostic candidates that may facilitate future studies.

Immune Checkpoint Molecules in Reproductive Immunology

Immune checkpoint molecules, like CTLA-4, TIM-3, PD-1, are negative regulators of immune responses to avoid immune injury. Checkpoint regulators are thought to actively participate in the immune defense of infections, prevention of autoimmunity, transplantation, and tumor immune evasion. Maternal-fetal immunotolerance represents a real immunological challenge for the immune system of the mother: beside acceptance of the semiallogeneic fetus, the maternal immune system has to be prepared for immune defense mostly against infections. In this particular situation, the role of immune checkpoint molecules could be of special interest. In this review, we describe current knowledge on the role of immune checkpoint molecules in reproductive immunology.

Elevated Soluble PD-L1 in Pregnant Women's Serum Suppresses the Immune Reaction

Background: Programmed death-ligand 1 (PD-L1) is expressed not only on some cancer cells, but also on the outer surface of placental syncytiotrophoblasts, which is assumed to induce maternal immune tolerance to fetal tissue via programmed death-1 (PD-1) receptors on T cells. Recently, levels of soluble forms of PD-L1 (sPD-L1) were reported to be higher in the serum of pregnant women (PW) than in non-pregnant women (non-PW). However, there have been no reports of the functional significance of PW's serum containing high sPD-L1 levels. Therefore, the aim of the present study was to clarify the role of sPD-L1 in the sera of PW as an immunosuppressive molecule by in vitro assays. Methods: As a post-hoc analysis of our previous cohort study, 330 pairs of serum from PW during the third trimester and cord blood (CB) from paired offspring without major complications were examined. Serum levels of sPD-L1 and sPD-1 were measured by ELISA. On mixed lymphocyte culture (MLC), 3H-thymidine uptakes in the presence of PW's, offspring's, or non-PW's serum were compared. Peripheral blood mononuclear cells (PBMCs) were cultured in the presence of PW's serum stimulated with PHA, and then cytokine levels were measured in supernatants by multiple cytokine analysis with or without anti-PD-L1blocking antibody. Results: The median sPD-L1 level was 8.3- and 6.9-fold higher in PW than in offspring and non-PW, respectively, whereas sPD-1 levels were lower in PW and offspring than in non-PW. On MLC, 3H-thymidine uptake in the presence of autoantigen was strongly reduced by co-culture with serum of both PW and offspring, compared with serum of non-PW. In contrast, uptake in the presence of alloantigen was moderately inhibited by PW's serum, whereas it was less suppressed by offspring's serum, compared with non-PW's serum. In the culture of PBMCs, tumor necrosis factor-α, interferon gamma, interleukin (IL)-2, and IL-4 levels were significantly higher in the presence of anti-PD-L1 blocking antibody than in culture not treated with antibody (all P < 0.05) or culture treated with isotype control antibody (all P < 0.05). Conclusion: The levels of sPD-L1 are elevated in PW's serum, which may, at least in part, suppress maternal immunity.

Involvement of the PD-1/PD-L1 Co-Inhibitory Pathway in the Pathogenesis of the Inflammatory Stage of Early-Onset Preeclampsia

The programmed cell death protein 1 (PD-1) receptor has been reported to downregulate T cell activation effectively via binding to its ligands PD-L1 or PD-L2 in a negative co-stimulatory manner. Little is known about the involvement of PD-1 mediated immunoregulation in pregnancy and in pregnancy-related disorders. In this work, we investigated the possible role of the PD-1 co-stimulatory pathway in the pathogenesis of the clinical phase of early-onset preeclampsia characterized by a systemic maternal inflammatory response. We performed a cross-sectional study for comparative analysis of phenotypic and functional characteristics of peripheral blood mononuclear cells in women with early-onset preeclampsia and third-trimester healthy pregnant controls. According to our findings, enhanced expression of either PD-1 or its ligand PD-L1, or both, on the cell surface of effector cells (T cells, natural killer (NK) cells, natural killer T (NKT)-like cells) and Tregs could be observed, but PD-1 expression did not correlate with effector cells exhaustion. These results suggest the failure of the axis to downregulate Th1 responses, contributing thereby to the exaggerated immunoactivation observed in early-onset preeclampsia.

Investigation of the Role That NADH Peroxidase Plays in Oxidative Stress Survival in Group B Streptococcus

Macrophages play an important role in defending the host against infections by engulfing pathogens and containing them inside the phagosome, which consists of a harsh microbicidal environment. However, many pathogens have developed mechanisms to survive inside macrophages despite this challenge. Group B Streptococcus (GBS), a leading cause of sepsis and meningitis in neonates, is one such pathogen that survives inside macrophages by withstanding phagosomal stress. Although a few key intracellular survival factors have been identified, the mechanisms by which GBS detoxifies the phagosome are poorly defined. Transcriptional analysis during survival inside macrophages revealed strong upregulation of a putative NADH peroxidase (npx) at 1 and 24 h post-infection. A deletion mutant of npx (Δnpx) was more susceptible to killing by a complex in vitro model of multiple phagosomal biochemical/oxidant stressors or by hydrogen peroxide alone. Moreover, compared to an isogenic wild type GBS strain, the Δnpx strain demonstrated impaired survival inside human macrophages and a reduced capacity to blunt macrophage reactive oxygen species (ROS) production. It is therefore likely that Npx plays a role in survival against ROS production in the macrophage. A more thorough understanding of how GBS evades the immune system through survival inside macrophages will aid in development of new therapeutic measures.

Analysis of PD-L1 expression in trophoblastic tissues and tumors

The immune checkpoint proteins, programmed death receptor 1 (PD-1) and programmed death ligand 1 (PD-L1), are crucial for maintaining fetomaternal immune tolerance and immune escape in cancers. In this study, we performed a comprehensive immunohistochemical study of PD-L1 expression in a large cohort of trophoblastic tissues and tumors. We found that normal villi and hydatidiform moles showed a heterogeneous PD-L1 staining among trophoblast (strong in syncytiotrophoblast, moderate in intermediate trophoblast, and weak/negative in cytotrophoblast). Eleven exaggerated placental sites (100%) showed variable PD-L1 staining, whereas 7 (36.8%) of 19 placental site nodules/plaques were weakly positive for PD-L1 (P < .001). All gestational choriocarcinomas (CCs; n = 63), epithelioid trophoblastic tumors (n = 12), and placental site trophoblastic tumors (n = 41) were PD-L1 positive, with most showing strong staining. However, PD-L1 expression was lower in epithelioid trophoblastic tumors compared with placental site trophoblastic tumors and CCs (P = .004). Three presumably germ cell-derived pure CCs, the CC elements in 13 mixed germ cell tumors, and 4 gastric/rectal CCs were also positive for PD-L1, with widespread staining. The background nontrophoblastic tissues, such as endometrial glands, squamous cells, and adenocarcinomas, were PD-L1 negative. Western blot analysis showed that PD-L1 was expressed in all 3 trophoblastic cell lines. We conclude that PD-L1 is a sensitive but nonspecific marker for trophoblast and related tumors. The frequent strong PD-L1 expression suggests that immune checkpoint blockade could be a promising approach in treating trophoblastic tumors that merits further investigation.

Evaluating Macrophages in Immunotoxicity Testing

Macrophages are a heterogeneous group of cells that have a multitude of functions depending on their differentiation state. While classically known for their phagocytic and antigen presentation abilities, it is now evident that these cells fulfill homeostatic functions beyond the elimination of invading pathogens. In addition, macrophages have also been implicated in the downregulation of inflammatory responses following pathogen removal, tissue remodeling, repair, and angiogenesis. Alterations in macrophage differentiation and/or activity due to xenobiotic exposure can have grave consequences on organismal homeostasis, potentially contributing to disease due to immunosuppression or chronic inflammatory responses, depending upon the pathways affected. In this chapter, we provide an overview of the macrophages subtypes, their origin and a general discussion of several different assays used to assess their functional status.

Placental immune editing switch (PIES): learning about immunomodulatory pathways from a unique case report

The hypothesis of this work is that, in order to escape the natural immune surveillance mechanisms, cancer cells and the surrounding microenvironment might express ectopically genes that are physiologically present in the placenta to mediate fetal immune-tolerance. These natural “placental immune-editing switch” mechanisms (PIES) may represent the result of millions of years of mammalian evolution developed to allow materno-fetal tolerance. Here, we introduce genes of the immune regulatory pathways that are either similarly over- or under-expressed in tumor vs normal tissue. Our analysis was carried out in primary breast cancer with metastatic homolateral axillary lymph nodes as well as placenta tissue (both uterine decidual tissue and term placenta tissue) from a pregnant woman. Gene expression profiling of paired non-self and self tissues (i.e. placenta/uterus; breast cancer/normal breast tissue; metastatic lymphnode/normal lymphnode tissue) was performed using the PanCancer Immune gene panel, a 770 Nanostring gene expression panel. Our findings reveal overlapping in specific immune gene expression in placenta and cancer tissue, suggesting that these genes might play an important role in maintaining immune tolerance both physiologically (in the placenta) and pathologically (in the cancer setting).

Immune checkpoint molecules soluble program death ligand 1 and galectin-9 are increased in pregnancy

PROBLEM

Pregnancy requires balance between tolerance to the haploidentical fetus and the mother's ability to mount immune responses. There are parallels to this phenomenon that occur in metastatic cancer. We assessed soluble program death ligand-1 soluble PD-L1 (sPD-L1) and galectin-9 in the blood of pregnant women during gestation as these molecules are highly involved in immune suppression during cancer.

METHOD OF STUDY

Maternal blood was collected from 30 primigravida women at monthly intervals during pregnancy, delivery and 6-week post-partum. Blood was analyzed for sPD-L1 and galectin-9 concentrations by ELISA. Term placentas were collected in formalin and IHC was completed for PD-L1 and galectin-9 expression.

RESULTS

Maternal blood levels of sPD-L1 (0.438 ng/mL) and galectin-9 (1976 pg/mL) were elevated early in normal pregnancies compared to non-pregnant controls (0.242 ng/mL and 773 pg/mL, respectively). sPD-L1 increased throughout gestation, whereas galectin-9 remained elevated until parturition; both proteins returned to control levels post-partum. Women carrying male fetuses had significantly higher galectin-9 levels, but not sPD-L1, than those carrying females (2263 pg/mL vs 1874 pg/mL; P = .0005). Trophoblast cells of the term placenta coexpress galectin-9 and PD-L1.

CONCLUSION

Immune-regulatory molecules galectin-9 and sPD-L1 increased during pregnancy and may play a role in immune tolerance that is critical for the fetus.

Programmed Death-Ligand 1 Expression in a Large Cohort of Pediatric Patients With Solid Tumor and Association With Clinicopathologic Features in Neuroblastoma

Purpose

Programmed death-ligand 1 (PD-L1) expression represents a potential predictive biomarker of immune checkpoint blockade response. However, literature about the prevalence of PD-L1 expression in the pediatric cancer setting is discordant.

Methods

PD-L1 expression was analyzed using immunohistochemistry in 500 pediatric tumors (including neuroblastoma, sarcomas, and brain cancers). Tumors with ≥ 1% cells showing PD-L1 membrane staining of any intensity were scored as positive. Positive cases were further characterized, with cases with weak intensity PD-L1 staining reported as having low PD-L1 expression and cases with a moderate or strong intensity of staining considered to have high PD-L1 expression.

Results

PD-L1–positive staining was identified in 13% of cases, whereas high PD-L1 expression was found in 3% of cases. Neuroblastoma (n = 254) showed PD-L1 expression of any intensity in 18.9% of cases and was associated with longer overall survival ( P = .045). However, high PD-L1 expression in neuroblastoma (3.1%) was significantly associated with an increased risk of relapse ( P = .002). Positive PD-L1 staining was observed more frequently in low- and intermediate-risk patients ( P = .037) and in cases lacking MYCN amplification ( P = .002).

Conclusion

In summary, high PD-L1 expression in patients with neuroblastoma may represent an unfavorable prognostic factor associated with a higher risk of cancer relapse. This work proposes PD-L1 immunohistochemical assessment as a novel parameter for identifying patients with an increased likelihood of cancer recurrence.

Changes in expression of the CD200 tolerance-signaling molecule and its receptor (CD200R) by villus trophoblasts during first trimester missed abortion and in chronic histiocytic intervillositis

PROBLEM

Expression of CD200 at the feto-maternal interface is associated with successful murine and human pregnancy. CD200 binding to CD200 receptors on lymphomyeloid cells suppresses inflammation and induces Tregs. CD200 receptors are also expressed on mouse and human placental trophoblast cells. What is the expression of CD200 and CD200R in human missed abortions which have preserved Treg levels and in chronic histiocytic intervillositis (CHI) where maternal inflammatory cells cause IUGR?

METHODS

Immunohistiochemistry for CD200, CD200R, and Ki67 using human placental sections from missed abortions, term placenta, and CHI. PCR testing was done for trisomy in missed abortion.

RESULTS

CD200 and CD200R were expressed by human villus trophoblasts from 2 weeks post-implantation to term. Cytotrophoblast proliferation (Ki-67⁺ count) decreased at term. In first trimester missed abortion cases, CD200>CD200R villus trophoblasts accompanied missed abortion of non-trisomic male fetuses. CD200 and Ki67⁺ trophoblast proliferation was preserved in CHI with maternal inflammatory cell infiltration but CD200R was greatly decreased.

CONCLUSION

Residual CD200 activity may prevent completion of abortions via induction of Treg cells. In CHI, infiltrating maternal effector T cells may block Treg induction. An autocrine role for CD200-CD200R interaction versus inhibition of soluble CD200 by soluble CD200R is discussed.

MYC: Master Regulator of Immune Privilege

Cancers are often initiated by genetic events that activate proto-oncogenes or inactivate tumor-suppressor genes. These events are also crucial for sustained tumor cell proliferation and survival, a phenomenon described as oncogene addiction. In addition to this cell-intrinsic role, recent evidence indicates that oncogenes also directly regulate immune responses, leading to immunosuppression. Expression of many oncogenes or loss of tumor suppressors induces the expression of immune checkpoints that regulate the immune response, such as PD-L1. We discuss here how oncogenes, and in particular MYC, suppress immune surveillance, and how oncogene-targeted therapies may restore the immune response against tumors.