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

Unexplained Recurrent Pregnancy Loss: Clinical Application of Immunophenotyping

PROBLEM

Recurrent pregnancy loss (RPL) is defined as the failure of two or more pregnancies and affects approximately 5% of couples, often without a clear cause. The etiologies of RPL include factors such as maternal age, endocrine dysfunction, uterine abnormalities, chromosomal abnormalities, thrombophilias, infections, and autoimmune disorders. However, these conditions account for only 50%-60% of RPL cases. Research has explored whether an altered immune system, compared to the physiological state, may be linked to RPL. This review aims to determine whether specific immunophenotypes are associated with unexplained Recurrent Pregnancy Loss (uRPL) and whether targeted therapies addressing specific immunophenotypic alterations can improve pregnancy outcomes.

METHODS

A literature review was conducted using Pubmed/Medline, Scopus, and Embase databases, analyzing data from 95 articles published between 2001 and 2023. The roles of various cells of the immune system (B lymphocytes, T lymphocytes, natural killer cells, macrophages) in different tissues (peripheral blood, menstrual blood) were specifically investigated in women with uRPL.

DISCUSSION AND CONCLUSION

Specific immunophenotypes have been demonstrated to be associated with this condition. However, there is a need to standardize immunophenotyping assays and conduct more trials to stratify RPL risk and improve potential therapeutic strategies.

CD4+ T cell heterogeneity in gestational age and preeclampsia using single-cell RNA sequencing

A balance between pro-inflammatory decidual CD4+ T cells and FOXP3+ regulatory T cells (FOXP3+ Tregs) is important for maintaining fetomaternal tolerance. Using single-cell RNA-sequencing and T cell receptor repertoire analysis, we determined that diversity and clonality of decidual CD4+ T cell subsets depend on gestational age. Th1/Th2 intermediate and Th1 subsets of CD4+ T cells were clonally expanded in both early and late gestation, whereas FOXP3+ Tregs were clonally expanded in late gestation. Th1/Th2 intermediate and FOXP3+ Treg subsets showed altered gene expression in preeclampsia (PE) compared to healthy late gestation. The Th1/Th2 intermediate subset exhibited elevated levels of cytotoxicity-related gene expression in PE. Moreover, increased Treg exhaustion was observed in the PE group, and FOXP3+ Treg subcluster analysis revealed that the effector Treg like subset drove the Treg exhaustion signatures in PE. The Th1/Th2 intermediate and effector Treg like subsets are possible inflammation-driving subsets in PE.

Chronic malaria exposure is associated with inhibitory markers on T cells that correlate with atypical memory and marginal zone-like B cells

Chronic immune activation from persistent malaria infections can induce immunophenotypic changes associated with T-cell exhaustion. However, associations between T and B cells during chronic exposure remain undefined. We analyzed peripheral blood mononuclear cells from malaria-exposed pregnant women from Papua New Guinea and Spanish malaria-naïve individuals using flow cytometry to profile T-cell exhaustion markers phenotypically. T-cell lineage (CD3, CD4, and CD8), inhibitory (PD1, TIM3, LAG3, CTLA4, and 2B4), and senescence (CD28-) markers were assessed. Dimensionality reduction methods revealed increased PD1, TIM3, and LAG3 expression in malaria-exposed individuals. Manual gating confirmed significantly higher frequencies of PD1+CD4+ and CD4+, CD8+, and double-negative (DN) T cells expressing TIM3 in malaria-exposed individuals. Increased frequencies of T cells co-expressing multiple markers were also found in malaria-exposed individuals. T-cell data were analyzed with B-cell populations from a previous study where we reported an alteration of B-cell subsets, including increased frequencies of atypical memory B cells (aMBC) and reduction in marginal zone (MZ-like) B cells during malaria exposure. Frequencies of aMBC subsets and MZ-like B cells expressing CD95+ had significant positive correlations with CD28+PD1+TIM3+CD4+ and DN T cells and CD28+TIM3+2B4+CD8+ T cells. Frequencies of aMBC, known to associate with malaria anemia, were inversely correlated with hemoglobin levels in malaria-exposed women. Similarly, inverse correlations with hemoglobin levels were found for TIM3+CD8+ and CD28+PD1+TIM3+CD4+ T cells. Our findings provide further insights into the effects of chronic malaria exposure on circulating B- and T-cell populations, which could impact immunity and responses to vaccination.

Higher Circulating Lymphocytes and the Incidence of Pre-eclampsia and Eclampsia

Excessive immune activation contributes to the onset of early dysfunction of the maternal-fetal interface, and it is closely linked to the development of pre-eclampsia. However, the effect of specific immune cells on the risk of pre-eclampsia and eclampsia remains controversial. We investigated the causal relationship between immune cells and pre-eclampsia and eclampsia. For exposure, we extracted genetic variants associated with immune cell-related traits, and for outcomes, we used summary genetic data of pre-eclampsia/eclampsia. A two-sample Mendelian randomization (MR) analysis was then performed to assess the causal relationship. Robustness of the MR results was then evaluated through colocalization analysis. We found that genetically proxied circulating lymphocyte absolute count was causally associated with total eclampsia (odds ratio (OR) = 1.53, 95% confidence interval (CI) (1.31-1.79), p = 1.15E - 07) and pre-eclampsia (OR = 1.50, 95% CI (1.28-1.77), p = 9.18E - 07); T cell absolute count was causally associated with total eclampsia (OR = 1.49, 95% CI (1.28-1.73), p = 2.73E - 07) and pre-eclampsia (OR = 1.47, 95% CI (1.25-1.72), p = 1.76E - 06). And CD28- CD25+ CD8+ T cell absolute count was causally associated with total eclampsia (OR = 1.83, 95% CI (1.44-2.32), p = 7.11E - 07) and pre-eclampsia (OR = 1.77, 95% CI (1.38-2.26), p = 6.55E - 06). Colocalization analysis revealed that immune cell-related traits shared the same variant with pre-eclampsia/eclampsia. Our study suggested causal effects of genetic predisposition to high lymphocyte absolute count levels, T cell absolute count, and CD28- CD25+ CD8+ T cell absolute count on eclampsia, particularly pre-eclampsia risk, providing crucial new insights into the potential prevention target for eclampsia and pre-eclampsia.

Immunological regulation and the role of autophagy in preeclampsia

Autophagy is a bulk degradation system that maintains cellular homeostasis by producing energy and/or recycling excess proteins. During early placentation, extravillous trophoblasts invade the decidua and uterine myometrium, facing maternal immune cells, which participate in the immune suppression of paternal and fetal antigens. Regulatory T cells will likely increase in response to a specific antigen before and during early pregnancy. Insufficient expansion of antigen-specific Treg cells, which possess the same T cell receptor, is associated with the pathophysiology of preeclampsia, suggesting sterile systemic inflammation. Autophagy is involved in reducing inflammation through the degradation of inflammasomes and in the differentiation and function of regulatory T cells. Autophagy dysregulation induces protein aggregation in trophoblasts, resulting in placental dysfunction. In this review, we discuss the role of regulatory T cells in normal pregnancies. In addition, we discuss the association between autophagy and regulatory T cells in the development of preeclampsia based on reports on the role of autophagy in autoimmune diseases.

Immunologic aspects of preeclampsia

Preeclampsia is a syndrome with multiple etiologies. The diagnosis can be made without proteinuria in the presence of dysfunction of at least 1 organ associated with hypertension. The common pathophysiological pathway includes endothelial cell activation, intravascular inflammation, and syncytiotrophoblast stress. There is evidence to support, among others, immunologic causes of preeclampsia. Unlike defense immunology, reproductive immunology is not based on immunologic recognition systems of self/non-self and missing-self but on immunotolerance and maternal-fetal cellular interactions. The main mechanisms of immune escape from fetal to maternal immunity at the maternal-fetal interface are a reduction in the expression of major histocompatibility complex molecules by trophoblast cells, the presence of complement regulators, increased production of indoleamine 2,3-dioxygenase, activation of regulatory T cells, and an increase in immune checkpoints. These immune protections are more similar to the immune responses observed in tumor biology than in allograft biology. The role of immune and nonimmune decidual cells is critical for the regulation of trophoblast invasion and vascular remodeling of the uterine spiral arteries. Regulatory T cells have been found to play an important role in suppressing the effectiveness of other T cells and contributing to local immunotolerance. Decidual natural killer cells have a cytokine profile that is favored by the presence of HLA-G and HLA-E and contributes to vascular remodeling. Studies on the evolution of mammals show that HLA-E, HLA-G, and HLA-C1/C2, which are expressed by trophoblasts and their cognate receptors on decidual natural killer cells, are necessary for the development of a hemochorial placenta with vascular remodeling. The activation or inhibition of decidual natural killer cells depends on the different possible combinations between killer cell immunoglobulin-like receptors, expressed by uterine natural killer cells, and the HLA-C1/C2 antigens, expressed by trophoblasts. Polarization of decidual macrophages in phenotype 2 and decidualization of stromal cells are also essential for high-quality vascular remodeling. Knowledge of the various immunologic mechanisms required for adequate vascular remodeling and their dysfunction in case of preeclampsia opens new avenues of research to identify novel biological markers or therapeutic targets to predict or prevent the onset of preeclampsia.

The Protective Effect of Abortion on Preeclampsia: An Analysis of Current Research

A review of the current literature on preeclampsia (PE) confirms that this pregnancy complication remains a common cause of maternal mortality. Within the last several decades, obstetric and gynecological researchers worldwide have indicated an association between prior abortions and the development of PE. Different studies have debated whether abortion is a protective or risk factor for PE. However, the most current literature demonstrates a stronger likelihood that a positive history of abortions will offer a protective effect against PE. This association has been supported by advancements in the reproductive immunology literature, which states complex fetal and paternal pathological mechanisms help to build maternal immunological tolerance, thus protecting expectant mothers from pregnancy complications. This literature review will compare studies supporting prior abortions offering a protective effect against PE with those stating prior abortions are a risk factor for the development of PE. Additionally, this critical review will discuss the advancements and current understanding of reproductive immunology and how it pertains to this association between positive abortion history and PE.

Role of immune cells in the establishment of implantation and maintenance of pregnancy and immunomodulatory therapies for patients with repeated implantation failure and recurrent pregnancy loss

Background

Immune cells play an important role in the establishment of pregnancy, and abnormalities in the immune system can cause implantation failure and miscarriage.

Methods

Previous papers have been summarized and the role of immune cells in reproduction is reviewed.

Results

The immune environment in the uterus changes drastically from before implantation to after pregnancy to maintain pregnancy. In allogeneic pregnancies, immature dendritic cells (DCs) that induce immune tolerance from outside the uterus flow into the uterus, and mature DCs that remain in the uterus express programmed cell death ligand 2, which suppresses the immune response. Macrophages are classified into M1-macrophages, which induce inflammation, and M2-macrophages, which suppress inflammation; M1-macrophages are required for luteinization, and M2-macrophages induce the differentiation of endometrial epithelial cells to enable implantation. Regulatory T cells, which suppress rejection, are essential for the implantation and maintenance of allogeneic pregnancies. Implantation failure and fetal loss are associated with decreased numbers or qualitative abnormalities of DCs, macrophages, and regulatory T cells. The clinical usefulness of immunomodulatory therapies in patients with repeated implantation failure and recurrent pregnancy loss has been reported.

Conclusion

The provision of individualized medical care in cases of implantation failure or miscarriage may improve clinical outcomes.

Decreased serum soluble programmed cell death ligand-1 level as a potential biomarker for missed miscarriage

STUDY QUESTION

Can maternal serum levels of soluble programmed cell death-1 (sPD-1) and its ligand (sPD-L1) serve as biomarkers for missed miscarriage (MM)?

SUMMARY ANSWER

Serum sPD-L1 levels are significantly decreased in MM patients and may serve as a potential predictive biomarker for miscarriage.

WHAT IS KNOWN ALREADY

Programmed cell death-1 (PD-1) and its ligand (PD-L1) comprise important immune inhibitory checkpoint signaling to maintain pregnancy. Their soluble forms are detectable in human circulation and are associated with immunosuppression.

STUDY DESIGN, SIZE, DURATION

Three independent cohorts attending tertiary referral hospitals were studied. The first (discovery) cohort was cross-sectional and included MM patients and healthy pregnant (HP) women matched on BMI. The second validation cohort contained MM patients and women with legally induced abortion (IA). The third prospective observational study recruited subjects requiring IVF treatment.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In the discovery cohort, we enrolled 108 MM patients and 115 HP women who had a full-term pregnancy at 6-14 weeks of gestation. In the validation cohort, we recruited 25 MM patients and 25 women with IA. Blood samples were collected at the first prenatal visit for HP women or on the day of dilatation and curettage surgery (D&C) for MM and IA subjects to determine serum sPD-1 and sPD-L1 levels. Placenta samples were harvested during the D&C within the validation cohort to measure gene and protein expression. The prospective cohort collected serial blood samples weekly from 75 volunteers with embryo transfer (ET) after IVF.

MAIN RESULTS AND THE ROLE OF CHANCE

Circulating sPD-L1 levels were reduced by 50% in patients with MM (55.7 ± 16.04 pg/ml) compared to HP controls (106.7 ± 58.46 pg/ml, P < 0.001) and the difference remained significant after adjusting for maternal age and gestational age, whereas no significant differences in sPD-1 level were observed. Likewise, serum sPD-L1 was lower in MM patients than in IA subjects and accompanied by downregulated PD-L1-related gene expression levels in the placenta. In the IVF cohort, applying the changing rate of sPD-L1 level after ET achieved a predictive performance for miscarriage with receiver operating characteristics = 0.73 (95% CI: 0.57-0.88, P < 0.01).

LIMITATIONS, REASONS FOR CAUTION

The study was mainly confined to East Asian pregnant women. Further large prospective pregnancy cohorts are required to validate the predictive performance of sPD-L1 on miscarriage.

WIDER IMPLICATIONS OF THE FINDINGS

Reduced circulating sPD-L1 level and downregulated placental PD-L1 expression in miscarriage indicate that dysfunction in PD-L1 signals is a potential underlying mechanism for pregnancy loss. Our findings further extend the importance of the PD-L1 axis in pregnancy maintenance in early pregnancy.

STUDY FUNDING/COMPETING INTEREST(S)

This study was financially supported by grants from the Subject Innovation Team of Shaanxi University of Chinese Medicine (2019-Y502), General Research Fund (14122021), and Key Laboratory of Model Animal Phenotyping and Basic Research in Metabolic Diseases (2018KSYS003). The authors declare that they have no competing interests to be disclosed.

TRIAL REGISTRATION NUMBER

N/A.

Immunosequencing and Profiling of T Cells at the Maternal-Fetal Interface of Women with Preterm Labor and Chronic Chorioamnionitis

T cells are implicated in the pathophysiology of preterm labor and birth, the leading cause of neonatal morbidity and mortality worldwide. Specifically, maternal decidual T cells infiltrate the chorioamniotic membranes in chronic chorioamnionitis (CCA), a placental lesion considered to reflect maternal anti-fetal rejection, leading to preterm labor and birth. However, the phenotype and TCR repertoire of decidual T cells in women with preterm labor and CCA have not been investigated. In this study, we used phenotyping, TCR sequencing, and functional assays to elucidate the molecular characteristics and Ag specificity of T cells infiltrating the chorioamniotic membranes in women with CCA who underwent term or preterm labor. Phenotyping indicated distinct enrichment of human decidual effector memory T cell subsets in cases of preterm labor with CCA without altered regulatory T cell proportions. TCR sequencing revealed that the T cell repertoire of CCA is characterized by increased TCR richness and decreased clonal expansion in women with preterm labor. We identified 15 clones associated with CCA and compared these against established TCR databases, reporting that infiltrating T cells may possess specificity for maternal and fetal Ags, but not common viral Ags. Functional assays demonstrated that choriodecidual T cells can respond to maternal and fetal Ags. Collectively, our findings provide, to our knowledge, novel insight into the complex processes underlying chronic placental inflammation and further support a role for effector T cells in the mechanisms of disease for preterm labor and birth. Moreover, this work further strengthens the contribution of adaptive immunity to the syndromic nature of preterm labor and birth.

Antigen-specific decidual CD8+ T cells include distinct effector memory and tissue-resident memory cells

Maternal decidual CD8+ T cells must integrate the antithetical demands of providing immunity to infection while maintaining immune tolerance for fetal and placental antigens. Human decidual CD8+ T cells were shown to be highly differentiated memory T cells with mixed signatures of dysfunction, activation, and effector function. However, no information is present on how specificity for microbial or fetal antigens relates to their function or dysfunction. In addition, a key question, whether decidual CD8+ T cells include unique tissue-resident memory T cells (Trm) or also effector memory T cell (Tem) types shared with peripheral blood populations, is unknown. Here, high-dimensional flow cytometry of decidual and blood CD8+ T cells identified 2 Tem populations shared in blood and decidua and 9 functionally distinct Trm clusters uniquely found in decidua. Interestingly, fetus- and virus-specific decidual CD8+ Trm cells had similar features of inhibition and cytotoxicity, with no significant differences in their expression of activation, inhibitory, and cytotoxic molecules, suggesting that not all fetus-specific CD8+ T cell responses are suppressed at the maternal-fetal interface. Understanding how decidual CD8+ T cell specificity relates to their function and tissue residency is crucial in advancing understanding of their contribution to placental inflammation and control of congenital infections.

The immune checkpoint protein PD-1: Its emerging regulatory role in memory T cells

Immunological memory helps the body rapidly develop immune defense when it re-encounters a bacterial or viral strain or encounters a similar mutation in healthy cells. The immune checkpoint molecule programmed cell death 1 (PD-1) influences memory T cell differentiation. However, the mechanism by which PD-1 regulates the development and maintenance of memory T cells and its impact on memory T cells function remain unclear. In this review, we first discuss the structure and function of PD-1 and then summarize the roles of PD-1 as a marker of tumor memory T cells and in tumor immunotherapy. We also discuss the potential mechanisms through which PD-1 regulates memory T cells development and maintenance during immune diseases such as viral infection-mediated diseases, psoriasis, and rheumatoid arthritis, and list the effects of PD-1 on memory T cells in pregnancy and their function in maternal-fetal immune balance. A complete understanding of how PD-1 influences the development, maintenance, and function of memory T cells will provide new insights into the prevention and treatment of immune-related diseases.

T cell immunity and the etiology and pathogenesis of preeclampsia

Preeclampsia is more common in nulliparous women, their first pregnancies with a new partner in multiparous women, pregnant women with short duration of cohabitation, and in pregnancies with donor eggs, where the fetus is completely foreign to the mother. The epidemiological study findings strongly suggest that inadequate induction of tolerance to paternal/fetal antigens is involved in the pathogenesis of preeclampsia. This review proposes that preeclampsia may be caused by a reduction in paternal/fetal antigen-specific regulatory T (Treg) cells and decreased PD-1 expression on clonally expanded CD8+ effector memory T (TEM) cells, resulting in a breakdown of mother-to-fetus tolerance. The immune environment of preeclampsia is clearly different from that of recurrent pregnancy loss (RPL). In preeclampsia, cloned Treg cells decreases, and PD-1 expression on cloned CD8+TEM decreased. In RPL, the total number of Treg cells decreased, and the total number of clonally expanded CD8+TEM cells increases. In addition to these changes, increased differentiation of Th17 cells has also been observed in preeclampsia. This change is caused by soluble endoglin, that is increased in preeclampsia, neutralizing TGFβ. These immunological changes make the fetus more susceptible to attacks from maternal T cells.

The unique expression pattern of human leukocyte antigen in trophoblasts potentially explains the key mechanism of maternal-fetal tolerance and successful pregnancy

The success of pregnancy mainly depends on immune tolerance of the mother for the semi-allogeneic fetus. The placenta carrying paternal antigens develops in the maternal uterus without suffering immune attack, making the underlying mechanism of maternal tolerance an enduring mystery. As we all know, human leukocyte antigen (HLA) plays an important role in antigen processing and presentation, thus inducing specific immune responses. Therefore, it is reasonable to speculate that the absence of classical HLA class-I（HLA-I) and HLA class-II (HLA-II) molecules in trophoblasts may account for the maternal-fetal tolerance. Here, we review the HLA-involved interactions between trophoblast cells and decidual immune cells, which contribute to the immunotolerance in the development of normal pregnancy. We also compare the similarity between the maternal-fetal interface and tumor-immune microenvironment because the important role of HLA molecules in tumor immune invasion can provide some references to studies of maternal-fetal immune tolerance. Besides, the abnormal HLA expression is likely to be associated with unexplained miscarriage, making HLA molecules potential therapeutic targets. The advances reported by these studies may exert profound influences on other research areas, including tumor immunity, organ transplantation and autoimmune disease in the future.

Proteogenomic and V(D)J Analysis of Human Decidual T Cells Highlights Unique Transcriptional Programming and Clonal Distribution

Immunological tolerance toward the semiallogeneic fetus is one of many maternal adaptations required for a successful pregnancy. T cells are major players of the adaptive immune system and balance tolerance and protection at the maternal-fetal interface; however, their repertoire and subset programming are still poorly understood. Using emerging single-cell RNA sequencing technologies, we simultaneously obtained transcript, limited protein, and receptor repertoire at the single-cell level, from decidual and matched maternal peripheral human T cells. The decidua maintains a tissue-specific distribution of T cell subsets compared with the periphery. We find that decidual T cells maintain a unique transcriptome programming, characterized by restraint of inflammatory pathways by overexpression of negative regulators (DUSP, TNFAIP3, ZFP36) and expression of PD-1, CTLA-4, TIGIT, and LAG3 in some CD8 clusters. Finally, analyzing TCR clonotypes demonstrated decreased diversity in specific decidual T cell populations. Overall, our data demonstrate the power of multiomics analysis in revealing regulation of fetal-maternal immune coexistence.

Role of regulation of PD-1 and PD-L1 expression in sepsis

Long term immunosuppression is problematic during sepsis. The PD-1 and PD-L1 immune checkpoint proteins have potent immunosuppressive functions. Recent studies have revealed several features of PD-1 and PD-L1 and their roles in sepsis. Here, we summarize the overall findings of PD-1 and PD-L1 by first reviewing the biological features of PD-1 and PD-L1 and then discussing the mechanisms that control the expression of PD-1 and PD-L1. We then review the functions of PD-1 and PD-L1 in physiological settings and further discuss PD-1 and PD-L1 in sepsis, including their involvement in several sepsis-related processes and their potential therapeutic relevance in sepsis. In general, PD-1 and PD-L1 have critical roles in sepsis, indicating that their regulation may be a potential therapeutic target for sepsis.

Immune checkpoint inhibitors and reproductive failures

The human conceptus is a semi-allograft, which is antigenically foreign to the mother. Hence, the implantation process needs mechanisms to prevent allograft rejection during successful pregnancy. Immune checkpoints are a group of inhibitory pathways expressed on the surface of various immune cells in the form of ligand receptors. Immune cells possess these pathways to regulate the magnitude of immune responses and induce maternal-fetal tolerance. Briefly, 1) CTLA-4 can weaken T cell receptor (TCR) signals and inhibit T cell response; 2) The PD-1/PD-L1 pathway can reduce T cell proliferation, enhance T cell anergy and fatigue, reduce cytokine production, and increase T regulatory cell activity to complete the immunosuppression; 3) TIM3 interacts with T cells by binding Gal-9, weakening Th1 cell-mediated immunity and T cell apoptosis; 4) The LAG-3 binding to MHC II can inhibit T cell activation by interfering with the binding of CD4 to MHC II, and; 5) TIGIT can release inhibitory signals to NK and T cells through the ITIM structure of its cytoplasmic tail. Therefore, dysregulated immune checkpoints or the application of immune checkpoint inhibitors may impair human reproduction. This review intends to deliver a comprehensive overview of immune checkpoints in pregnancy, including CTLA-4, PD-1/PD-L1, TIM-3, LAG-3, TIGIT, and their inhibitors, reviewing their roles in normal and pathological human pregnancies.

Expression of inhibitory receptors PD-1, CTLA-4, and Tim-3 by peripheral T cells during pregnancy

Background. Inhibitory receptors and their ligands (also called checkpoint molecules) are important feedback regulators of the immune response. However, their role in immunological adaptation during pregnancy remains poorly understood.

The aim of the study was to evaluate the level of checkpoint molecule (PD-1, CTLA-4, Tim-3) expression in peripheral T cells in pregnant women compared with fertile non-pregnant women.

Materials and methods. The study included 36 women in the second half of pregnancy without pregnancy complications, 12 of whom had extragenital pathology. The control group consisted of 28 age-matched fertile non-pregnant women. The proportion of CD8+PD-1+, CD8+TIM-3+, CD8+PD-1+TIM-3+, CD4+PD-1+, CD4+TIM-3+, and CD4+PD-1+TIM-3+ was evaluated by flow cytometry using the corresponding monoclonal antibodies (BD Biosciences, USA).

Results. The proportion of CD4+Tim-3+ and CD8+PD-1+ Т cells and CD4+ and CD8+ Т lymphocytes co-expressing PD-1 and Tim-3 in the peripheral blood of pregnant women was statistically significantly higher than in non-pregnant women. An increase in CD4+Tim-3+ and CD8+PD-1+ T cells was observed both in pregnant women with and without extragenital pathology. However, pregnant women with extragenital pathology were characterized by a higher CD8+PD-1+ count and a smaller number of CD8+Tim-3+ cells, as well as by a lack of an increase in PD-1+Tim-3+ T cells typical of pregnant women. The number of comorbidities was directly correlated with the proportion of CD8+PD-1+ lymphocytes and inversely correlated with the proportion of CD8+Tim-3+ and CD4+ PD-1+Tim-3+ cells. In addition, the expression of checkpoint molecules was associated with gestational age (a direct correlation was found with the proportion of CD8+Tim-3+, CD4+PD-1+Tim-3+, and CD8+PD-1+Tim-3+ cells) and to a lesser extent – with the age of pregnant women (an inverse relationship was found with the proportion of CD8+Tim-3+ cells).

Conclusion. Pregnant women in the second half of pregnancy are characterized by increased expression of PD-1 and Tim-3 molecules in peripheral T cells. At the same time, concomitant extragenital pathology affects the expression of these molecules.

Update on Immune Mechanisms in Hypertension

The contribution of immune cells in the initiation and maintenance of hypertension is undeniable. Several studies have established the association between hypertension, inflammation, and immune cells from the innate and adaptive immune systems. Here, we provide an update to our 2017 American Journal of Hypertension review on the overview of the cellular immune responses involved in hypertension. Further, we discuss the activation of immune cells and their contribution to the pathogenesis of hypertension in different in vivo models. We also highlight existing gaps in the field of hypertension that need attention. The main goal of this review is to provide a knowledge base for translational research to develop therapeutic strategies that can improve cardiovascular health in humans.

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.

A bias away from Th2 in amniotic fluid is involved in preeclampsia

Inflammatory cytokines contribute to the pathophysiology of preeclampsia. However, whether the imbalance of Th1/Th2 cytokines in amniotic fluid is associated with preeclampsia is not well defined. In the present study, we collected peripheral blood and amniotic fluid from normal pregnancy (n = 25) and preeclampsia (n = 22) at last trimester during cesarean section. The Th1/Th2 cytokine levels in amniotic fluid supernatant were detected by a bead-based immunoassay. The percentage of IFN-γ⁺CD4⁺ T cells, TNF-α⁺CD4⁺ T cells, IL-4⁺CD4⁺ T cells and IL-10⁺CD4⁺ T cells in peripheral blood was detected by flow cytometry. We found that in normal pregnancy, the IFN-γ/IL-4 and IFN-γ/IL-5 ratios were decreased in amniotic fluid supernatant compared to that in plasma, indicating a Th2 bias. However, IFN-γ/IL-4 (P = 0.014), IFN-γ/IL-5 (P = 0.005) and IFN-γ/IL-13 (P = 0.047) ratios in amniotic fluid supernatant was significantly increased in preeclampsia patients. The percentage of IFN-γ⁺CD4⁺ T cells (20.70 ± 7.61% vs 16.55 ± 4.96%, P = 0.041) and TNF-α⁺CD4⁺ T cells (31.78 ± 10.66% vs 19.47 ± 13.54%, P = 0.048) was significantly elevated in preeclampsia compared to normal pregnancy. Our finding demonstrates that a shift away from Th2 bias in amniotic fluid and circulating CD4⁺ T cells is involved in the pathogenesis of preeclampsia. This study suggests restoring the Th2 bias in amniotic fluid might be a therapeutic target of preeclampsia.

TCR Coexpression Signature Predicts Immunotherapy Resistance in NSCLC

Background: Lung cancer has the highest morbidity and mortality rate among types of malignant tumors, and as such, research into prolonging the survival time of patients is vital. The emergence of immune checkpoint inhibitors (ICIs) has greatly improved the survival of patients with non-small cell lung cancer (NSCLC), however, the lack of effective biomarkers to predict the prognosis of immunotherapy has made it difficult to maximize the benefits. T cell receptor (TCR) is one of the most important components for recognizing tumor cells, and with this study we aim to clarify the relationship between TCR coexpression and the prognosis of NSCLC patients receiving immunotherapy.

Methods: Univariate COX regression, logistics regression, and KM survival analysis were used to evaluate the relationship between TCR coexpression and the prognosis of immunotherapy. Additionally, CIBERSORT, Gene Set Enrichment Analysis (GSEA), and single-sample GSEA (ssGSEA) algorithms were used to evaluate the tumor immune microenvironment (TIME) of NSCLC patients.

Results: Univariate Cox regression analysis showed that the TCR coexpression signature can be used as a clinical prognostic indicator for NSCLC patients receiving immunotherapy (p = 0.0205). In addition, those in the NSCLC group with a high TCR coexpression signature had significantly improved progression-free survival (PFS) (p = 0.014). In the ICI treatment cohort (GSE35640). In addition, there was a high infiltration of CD8+T cells, activated memory CD4+T cells, and M1 macrophages in the TIME of those with a high TCR coexpression signature. The results of pathway enrichment analysis showed that patients with a high TCR coexpression signature had significantly activated signal pathways such as lymphocyte proliferation and activation, chemokine binding, and inflammatory cytokine production. Also, we found that patients with a high TCR coexpression signature had an elevated T cell inflammation gene expression profile (GEP).

Conclusion: We show that the TCR coexpression signature may be useful as a new biomarker for the prognosis of NSCLC patients undergoing immunotherapy, with high signatures indicating better treatment response. Additionally, we found that patients with a high TCR coexpression signature had tumor immune microenvironments with beneficial anti-tumor characteristics.

Serial changes in two immune checkpoint receptors and ligands, Tim-3/Gal-9 and PD-1/PD-L1 in peripheral blood prior to miscarriage: Comparison with pregnancies resulting in a live birth

PROBLEM

Immune checkpoints Tim-3/Gal-9 and PD-1/PL-1 are involved in the maintenance of maternal-fetal immune tolerance systematically and locally. This study aimed to compare the serial changes of Tim-3/Gal-9, and PD-1/PL-1 in peripheral blood over a 4-week period after blastocyst transfer, between women who had a live birth and those who miscarried.

METHODS OF STUDY

Serial blood samples were obtained on the day of ET, and 9, 16, 23, and 30 days after ET for the measurement of Tim-3 and PD-1 expressions on various lymphocytes by flow cytometry. Concentrations of serum Gal-9 and PD-L1 were measured by ELISA.

RESULTS

In pregnancies that resulted in a live birth, a significant and sustained increase in the proportion of Tim-3⁺ pNK cells was observed from the 9^th to 30^th days after ET, whilst the concentration of serum PD-L1 was significantly increased on the 23^rd and 30^th days after ET when compared to the day of ET. In pregnancies that later miscarried, none of the parameters were significantly changed across all the time points examined. When comparing the results between the two groups, the proportion of Tim-3⁺ CD56^dim NK cells in the women who had a live birth was significantly higher than that in women who miscarried from the 9^th to 30^th day after ET.

CONCLUSION

A significant and sustained increase in the proportion of Tim-3⁺ pNK cells was observed in pregnancies resulting in a live birth but not in pregnancies resulting in a miscarriage, suggesting the changes may be associated with successful pregnancy outcomes.

Histone methyltransferase Nsd2 ensures maternal–fetal immune tolerance by promoting regulatory T-cell recruitment

Regulatory T cells (Tregs) are fundamentally important for maintaining systemic immune homeostasis and are also required for immune tolerance at the maternal-fetal interface during pregnancy. Recent studies have suggested that epigenetic regulation is critically involved in Treg development and function. However, the role of H3K36me has not yet been investigated. Here, we found that the H3K36me2 methyltransferase Nsd2 was highly expressed in Tregs. Although loss of Nsd2 did not impair systemic Treg development or function, the level of Tregs at the maternal-fetal interface was significantly decreased in pregnant Nsd2 conditional knockout mice. Consequently, maternal-fetal immune tolerance was disrupted in the absence of Nsd2 in Tregs, and the pregnant mice showed severe fetal loss. Mechanistically, Nsd2 was found to upregulate CXCR4 expression via H3K36me2 modification to promote Treg cell recruitment into the decidua and suppress the anti-fetal immune response. Overall, our data identified Nsd2 as a critical epigenetic regulator of Treg recruitment for maternal-fetal tolerance.

Upregulated serum granulysin levels in women with antiphospholipid antibody‐associated recurrent miscarriage are downregulated by heparin treatment

Purpose

Granulysin is a cytotoxic protein that simultaneously activates innate and cellular immunity. The authors aimed to evaluate whether granulysin is associated with the antiphospholipid antibody syndrome and whether heparin changes the granulysin levels.

Methods

A cohort study was performed with women with antiphospholipid antibody‐positive recurrent pregnancy loss (RPL). The authors examined granulysin levels under RPL and evaluated the changes in serum granulysin levels before and 1 week after the commencement of heparin treatment.

Results

Serum granulysin levels before heparin treatment were significantly higher in women who tested positive for one or more types of antiphospholipid antibodies (2.75 ± 1.03 vs. 2.44 ± 0.69, p = 0.0341 by Welch's t test), particularly anti‐phosphatidylethanolamine antibodies (IgG: 2.98 ± 1.09 vs. 2.51 ± 0.86, p = 0.0013; IgM: 2.85 ± 1.09 vs. 2.47 ± 0.77, p = 0.0024 by Welch's t test). After heparin treatment for 1 week, serum granulysin levels were significantly reduced (p = 0.0017 by the paired t test). The miscarriage rate was significantly higher in women whose serum granulysin levels were not reduced by heparin treatment (p = 0.0086 by Fisher's exact probability test).

Conclusion

The results suggest that heparin may reduce the incidence of miscarriage by suppressing serum granulysin levels.

We examined granulysin levels under recurrent pregnancy loss and evaluated the changes in serum granulysin with heparin treatment. The miscarriage rate was significantly higher in women whose serum granulysin levels were not reduced by heparin treatment. The results suggest that heparin may reduce the incidence of miscarriage by suppressing serum granulysin levels.

Next generation of immune checkpoint molecules in maternal-fetal immunity

Successful pregnancy is a unique situation requires the maternal immune system to recognize and tolerate a semi-identical fetus and allow normal invasion of trophoblast cells. Although efforts have been made, the deep mechanisms of the maternal-fetal crosstalk have not yet been fully deciphered. Immune checkpoint molecules (ICMs) are a group of negative modulators of the immune response that avoid immune damage. They have been extensively studied in the fields of oncology and transplantation, while the latest evidence suggests that they are closely associated with pregnancy outcomes via multiple inhibitory mechanisms. Although studies have mostly demonstrated the regulatory role of the well-known PD-1, CTLA-4 at the maternal-fetal interface, what is unique about the newly discovered multiple ICMs remains a mystery. Here, we review the latest knowledge on ICMs, focusing on the first generation of checkpoints (PD-1, CTLA-4) and the next generation (Tim-3, Tigit, Lag-3, VISTA) highlighting their immunoregulatory roles in maternal-fetal tolerance and decidual vascular remodeling, and their involvement in pathological pregnancies. The content covers three aspects: the characteristics they possess, the dynamic expression profile of their expression at the maternal-fetal interface, and their involvement in pathological pregnancy. In immunotherapy strategies for pregnancy complications, upregulation of immune checkpoints may play a role. Meanwhile, the impact on pregnancy outcomes when using ICMs in clinical cancer treatment during pregnancy is a topic worth exploring. These may serve as a guide for future basic research and clinical applications of maternal-fetal immunity.

Progress in the understanding of the pathophysiology of immunologic maladaptation related to early-onset preeclampsia and metabolic syndrome related to late-onset preeclampsia

Among mammalian species, human reproduction has 2 outstanding features. The human hemochorial placentation is characterized by a very deep endovascular trophoblast invasion in the spiral arteries, reaching deep into the myometrium. This requires an agonistic direct cell-cell interaction between the maternal immune system and semiallogeneic trophoblast. The second feature is preeclampsia, a heterogeneous syndrome, a uniquely human condition. The human female is one of the few mammals exposed to her partner's semen on multiple occasions before conception. Regulatory T cells, especially paternal antigen-specific regulatory T cells, play an important role in the maintenance of pregnancy. Sexual intercourse increases the number of dendritic cells in the uterus that play an important role in the induction of paternal antigen-specific regulatory T cells. Paternal antigen-specific regulatory T cells maintain pregnancy by inducing tolerance. In the decidua basalis of preeclamptic cases, clonal regulatory T cells are reduced; these would normally monoclonally expand to recognize fetal or paternal antigens. Programmed cell death-1 expressed on T cells regulate cytotoxic T-cell activity and protect the fetus against maternal rejection. Programmed cell death-1 expression on clonal cytotoxic T cells is reduced in preeclampsia especially in early-onset preeclampsia, making the fetus and placenta vulnerable to attack by cytotoxic T cells. These phenomena can explain the epidemiologic phenomenon that preeclampsia is more common in couples using condom contraception, with shorter cohabitation periods, first pregnancies, first pregnancies in multiparous women when they change partner, and pregnancies after assisted reproduction using donated gametes. In contrast to its importance in early-onset preeclampsia, shallow trophoblast invasion does not play a role in the development of preeclampsia, that is, immune maladaptation does not seem to be involved. Late-onset preeclampsia (>34 weeks' gestation), representing 80% to 90% of preeclampsia in most developed countries with a "Western lifestyle," is strongly associated with maternal cardiometabolic variables (metabolic syndrome). Although the underlying pathophysiology might be quite different, syncytiotrophoblast stress is the final common pathway leading to the maternal syndrome among the subtypes of preeclampsia by causing an imbalance between proangiogenic factors (placental growth factor and vascular endothelial growth factor) and antiangiogenic factors (soluble fms-like tyrosine kinase-1 and soluble endoglin). Low-dose aspirin, started before 16 week's gestation, will prevent up to 60% of early-onset preeclampsia but will not prevent late-onset preeclampsia. Optimizing prepregnancy weight and controlling gestational weight gain may be the most effective ways to prevent preeclampsia.

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.

The association between chronic deciduitis and preeclampsia

Chronic deciduitis (CD) is slight inflammation of the decidua found during pregnancy. The cause of preeclampsia is thought to be placental hypoplasia, and various theories have been proposed to explain the detailed mechanism; however, its association with decidual inflammation is unclear. A retrospective case control study was conducted in a single university. Subjects were cases who delivered by cesarean section between January 1, 2013 and June 30, 2020 and whose placentas were pathological assessed. CD was diagnosed by CD138 immunostaining of placental decidua tissue, and the perinatal prognosis and incidences of hypertensive disorder of pregnancy and preeclmpsia were examined according to the presence or absence of CD. A logistic regression analysis was performed to evaluate the association between preeclampsia and 11 explanatory variables (10 patient or perinatal background factors and CD). The study population included 76 patients (non-CD, n = 54; CD, n = 22). The rate of preeclampsia was significantly higher in the CD group (P = 0.0006). Patients with CD gave birth at a significantly earlier gestational age (P=0.040) with a lower birth weight (P = 0.001), and a higher rate of LFD (P = 0.005). The Apgar scores at 1 and 5 min and umbilical artery pH were lower (P = 0.0003, 0.021 and 0.002, respectively) in the CD group. The logistic regression analysis revealed that CD was positively associated with preeclampsia. A retrospective examination of the placenta found that patients with CD had a significantly higher incidence of preeclampsia and CD is considered to be a factor that is associated with poor perinatal outcomes.

Reconsideration of the Role of Regulatory T Cells during Pregnancy: Differential Characteristics of Regulatory T Cells between the Maternal-Fetal Interface and Peripheral Sites and between Early and Late Pregnancy

Regulatory T (Treg) cells play an important role in implantation of the embryo and maintenance of pregnancy after allogeneic mating. Implantation failure, miscarriage, and preeclampsia are associated with decreased numbers of Treg cells or with dysfunctional Treg cells. Treg cells are classified into naturally occurring Treg (nTreg) cells or thymus-derived Treg (tTreg) cells that differentiate in the thymus and induce tolerance to self-antigens, while induced Treg (iTreg) or peripheral Treg (pTreg) cells differentiate in the periphery and induce transient tolerance to foreign antigens. Memory nTreg or iTreg cells were recently reported to accumulate in the uterus during early pregnancy and contribute to the establishment of pregnancy. Miscarriage is characterized by the downregulation of the total numbers of Treg cells rather than a downregulation of the numbers of paternal/fetal antigen-specific Treg cells. In addition to the volume of paternal/fetal antigen-specific CD8+ T cells, the number of paternal/fetal antigen-specific Treg cells, which protect the fetus/placenta against maternal immune cell attack, increases after the second trimester of pregnancy. Clonal Treg cells which are surrogate markers of paternal/fetal antigen-specific Treg cells in humans may be involved in the development of preeclampsia during the mid- to late pregnancy stage, as evidenced by their downregulation in the decidua of preeclamptic cases. This review summarizes recent findings on Treg cells and discusses the roles, in the maintenance of pregnancy, of different types of Treg cells such as paternal/fetal antigen-specific Treg, pregnancy-associated memory Treg, nTreg (or tTreg), and iTreg (or pTreg cells).

Cellular immune responses in the pathophysiology of preeclampsia

Preeclampsia, defined as new-onset hypertension accompanied by proteinuria occurring at 20 weeks of gestation or later, is a leading cause of perinatal morbidity and mortality worldwide. The pathophysiology of this major multi-systemic syndrome includes defective deep placentation, oxidative stress, endothelial dysfunction, the presence of an anti-angiogenic state, and intravascular inflammation, among others. In this review, we provide a comprehensive overview of the cellular immune responses involved in the pathogenesis of preeclampsia. Specifically, we summarize the role of innate and adaptive immune cells in the maternal circulation, reproductive tissues, and at the maternal-fetal interface of women affected by this pregnancy complication. The major cellular subsets involved in the pathogenesis of preeclampsia are regulatory T cells, effector T cells, NK cells, monocytes, macrophages, and neutrophils. We also summarize the literature on those immune cells that have been less characterized in this clinical condition, such as γδ T cells, invariant natural killer T cells, dendritic cells, mast cells, and B cells. Moreover, we discuss in vivo studies utilizing a variety of animal models of preeclampsia to further support the role of immune cells in this disease. Finally, we highlight the existing gaps in knowledge of the immunobiology of preeclampsia that require further investigation. The goal of this review is to promote translational research leading to clinically relevant strategies that can improve adverse perinatal outcomes resulting from the obstetrical syndrome of preeclampsia.

Investigation and Validation of Molecular Characteristics of Endometrium in Recurrent Miscarriage and Unexplained Infertility from a Transcriptomic Perspective

Recurrent miscarriage (RM) and unexplained infertility (UI) are gordian knots in reproductive medicine, which are troubling many patients, doctors, and researchers. Although these two diseases of early pregnancy have a significant impact on human reproductive health, little is known about the specific mechanisms, which caused treatment difficulties. This study focused on the molecular signatures underlying the pathological phenotypes of two diseases, with the hope of using statistical methods to identify the significant core genes. An unbiased Weighted Correlation Network Analysis (WGCNA) algorithm was used for endometrial transcriptome data analysis and the disease-related gene modules were screened out. Through enrichment analysis of the candidate genes, we found similarities between both diseases and shared enrichment of immune-related pathways. Therefore, we used immune algorithms to assess the infiltration of immune cells and found abnormal increases of CD8+T cells and neutrophils. In order to explore the molecular profile behind the immunophenotypic changes, we used the SVM algorithm and LASSO regression to identify the core genes with diagnostic capacity in both diseases and discussed their significance of immune disorders in the endometrium. In the end, the satisfactory diagnostic ability of these core genes was verified in the broader group. Our results demonstrated the presence of immune disorders in non-pregnancy tissues of RM and UI, and identified the core molecules of this phenotype, and discuss mechanisms. This provides exploratory evidence for the in-depth understanding of the mechanism of RM and UI and may provide potential targets for their future treatment.

HLA-G: An Important Mediator of Maternal-Fetal Immune-Tolerance

Maternal-fetal immune-tolerance occurs throughout the whole gestational trimester, thus a mother can accept a genetically distinct fetus without immunological aggressive behavior. HLA-G, one of the non-classical HLA class I molecules, is restricted-expression at extravillous trophoblast. It can concordantly interact with various kinds of receptors mounted on maternally immune cells residing in the uterus (e.g. CD4+ T cells, CD8+ T cells, natural killer cells, macrophages, and dendritic cells) for maintaining immune homeostasis of the maternal-fetus interface. HLA-G is widely regarded as the pivotal protective factor for successful pregnancies. In the past 20 years, researches associated with HLA-G have been continually published. Indeed, HLA-G plays a mysterious role in the mechanism of maternal-fetal immune-tolerance. It can also be ectopically expressed on tumor cells, infected sites and other pathologic microenvironments to confer a significant local tolerance. Understanding the characteristics of HLA-G in immunologic tolerance is not only beneficial for pathological pregnancy, but also helpful to the therapy of other immune-related diseases, such as organ transplant rejection, tumor migration, and autoimmune disease. In this review, we describe the biological properties of HLA-G, then summarize our understanding of the mechanisms of fetomaternal immunologic tolerance and the difference from transplant tolerance. Furthermore, we will discuss how HLA-G contributes to the tolerogenic microenvironment during pregnancy. Finally, we hope to find some new aspects of HLA-G in fundamental research or clinical application for the future.

The New Old CD8+ T Cells in the Immune Paradox of Pregnancy

CD8+ T cells are the most frequent T cell population in the immune cell compartment at the feto-maternal interface. Due to their cytotoxic potential, the presence of CD8+ T cells in the immune privileged pregnant uterus has raised considerable interest. Here, we review our current understanding of CD8+ T cell biology in the uterus of pregnant women and discuss this knowledge in relation to a recently published immune cell Atlas of human decidua. We describe how the expansion of CD8+ T cells with an effector memory phenotype often presenting markers of exhaustion is critical for a successful pregnancy, and host defense towards pathogens. Moreover, we review new evidence on the presence of long-lasting immunological memory to former pregnancies and discuss its impact on prospective pregnancy outcomes. The formation of fetal-specific memory CD8+ T cell subests in the uterus, in particular of tissue resident, and stem cell memory cells requires further investigation, but promises interesting results to come. Advancing the knowledge of CD8+ T cell biology in the pregnant uterus will be pivotal for understanding not only tissue-specific immune tolerance but also the etiology of complications during pregnancy, thus enabling preventive or therapeutic interventions in the future.

Regulation of the innate immune cells during pregnancy: An immune checkpoint perspective

The foetus can be regarded as a half‐allograft implanted into the maternal body. In a successful pregnancy, the mother does not reject the foetus because of the immune tolerance mechanism at the maternal‐foetal interface. The innate immune cells are a large part of the decidual leukocytes contributing significantly to a successful pregnancy. Although the contributions have been recognized, their role in human pregnancy has not been completely elucidated. Additionally, the accumulated evidence demonstrates that the immune checkpoint molecules expressed on the immune cells are co‐inhibitory receptors regulating their activation and biological function. Therefore, it is critical to understand the immune microenvironment and explore the function of the innate immune cells during pregnancy. This review summarizes the classic immune checkpoints such as PD‐1, CTLA‐4 and some novel molecules recently identified, including TIM‐3, CD200, TIGIT and the Siglecs family on the decidual and peripheral innate immune cells during pregnancy. Furthermore, it emphasizes the role of the immune checkpoint molecules in pregnancy‐associated complications and reproductive immunotherapy.

Decreased Expression of Cytotoxic Proteins in Decidual CD8+ T Cells in Preeclampsia

Simple Summary

CD8⁺ T cells are prominent decidual cells in the third trimester of healthy human pregnancy. They have a cytotoxic capacity which may control invasion of extravillous trophoblast and therefore affect placentation and play the role in development of preeclampsia. In this study, we examined the expression of CD8⁺ T cells in decidual tissue and peripheral blood of women with severe and mild preeclampsia in comparison to gestational age-matched healthy pregnancies. Additionally, the expression of cytotoxic proteins in CD8⁺ T cells was examined in order to specify their subpopulations.

Abstract

In our study, we aimed to establish expression of cytotoxic CD8⁺ T cells in the decidua basalis and the maternal peripheral blood (mPBL) of severe and mild preeclampsia (PE) and compare to healthy pregnancies. Decidual tissue and mPBL of 10 women with mild PE, 10 women with severe PE, and 20 age-matched healthy pregnancy controls were analyzed by double immunofluorescence and qPCR, respectively. By double immunofluorescence staining, we found a decreased total number of cells/mm² in decidua basalis of granulysin (GNLY)⁺ (p ˂ 0.0001), granzyme B (GzB)⁺(p ˂ 0.0001), GzB⁺CD8⁺(p ˂ 0.0001), perforin (PRF1)⁺ (p ˂ 0.0001), and PRF1⁺CD8⁺ (p ˂ 0.01) in the severe PE compared to control group. Additionally, we noticed the trend of lower mRNA expression for GNLY, granzyme A (GZMA), GzB, and PRF1 in CD8⁺ T cells of mPBL in mild and severe PE, with the latter marker statistically decreased in severe PE (p ˂ 0.001). Forkhead box P3 (FOXP3) mRNA in CD8⁺ T cells mPBL was increased in mild PE (p ˂ 0.001) compared to controls. In conclusion, severe PE is characterized by altered expression of cytotoxic CD8⁺ T cells in decidua and mPBL, suggesting their role in pathophysiology of PE and fetal-maternal immune tolerance.

Activated γδ T Cells With Higher CD107a Expression and Inflammatory Potential During Early Pregnancy in Patients With Recurrent Spontaneous Abortion

Previous studies have reported the involvement of γδ T cells in recurrent spontaneous abortion (RSA); however, both pathogenic and protective effects were suggested. To interrogate the role of γδ T cells in RSA, peripheral blood from RSA patients and healthy women with or without pregnancy were analyzed for γδ T cells by flow cytometry (n = 9–11 for each group). Moreover, the decidua from pregnant RSA patients and healthy controls (RSA-P and HC-P group, respectively) was simultaneously stained for γδ T cells by immunohistochemistry (IHC) and bulk sequenced for gene expression. Our results demonstrated that the frequencies of peripheral γδ T cells and their subpopulations in RSA patients were comparable to that in healthy subjects, but the PD1 expression on Vδ2⁺ cells was increased in pregnant patients. Furthermore, peripheral Vδ2⁺ cells in RSA-P patients demonstrated significantly increased expression of CD107a, as compared to that in pregnant healthy controls. In addition, RSA-P patients had higher proportion of IL-17A-secreting but not IL-4-secreting Vδ2⁺ cells compared to the control groups. In decidua, an inflammatory microenvironment was also evident in RSA-P patients, in which CCL8 expression and the infiltration of certain immune cells were higher than that in the HC-P group, as revealed by transcriptional analysis. Finally, although the presence of γδ T cells in decidua could be detected during pregnancy in both RSA patients and healthy subjects by multicolor IHC analysis, the expression of CD107a on γδ T cells was markedly higher in the RSA-P group. Collectively, our results indicated that the increased activation, cytotoxicity, and inflammatory potential of peripheral and/or local γδ T cells might be responsible for the pathogenesis of RSA. These findings could provide a better understanding of the role of γδ T cells in RSA and shed light on novel treatment strategies by targeting γδ T cells for RSA patients.

Effect of Intralipid infusion on peripheral blood T cells and plasma cytokines in women undergoing assisted reproduction treatment

Objectives

Intravenous infusion of Intralipid is an adjunct therapy in assisted reproduction treatment (ART) when immune‐associated infertility is suspected. Here, we evaluated the effect of Intralipid infusion on regulatory T cells (Treg cells), effector T cells and plasma cytokines in peripheral blood of women undertaking IVF.

Methods

This prospective, observational pilot study assessed Intralipid infusion in 14 women exhibiting recurrent implantation failure, a clinical sign of immune‐associated infertility. Peripheral blood was collected immediately prior to and 7 days after intravenous administration of Intralipid. Plasma cytokines were measured by Luminex, and T‐cell subsets were analysed by flow cytometry.

Results

A small increase in conventional CD8⁺ T cells occurred after Intralipid infusion, but no change was seen in CD4⁺ Treg cells, or naïve, memory or effector memory T cells. Proliferation marker Ki67, transcription factors Tbet and RORγt, and markers of suppressive capacity CTLA4 and HLA‐DR were unchanged. Dimensionality‐reduction analysis using the tSNE algorithm confirmed no phenotype shift within Treg cells or other T cells. Intralipid infusion increased plasma CCL2, CCL3, CXCL8, GM‐CSF, G‐CSF, IL‐6, IL‐21, TNF and VEGF.

Conclusion

Intralipid infusion elicited elevated pro‐inflammatory cytokines, and a minor increase in CD8⁺ T cells, but no change in pro‐tolerogenic Treg cells. Notwithstanding the limitation of no placebo control, the results do not support Intralipid as a candidate intervention to attenuate the Treg cell response in women undergoing ART. Future placebo‐controlled studies are needed to confirm the potential efficacy and clinical significance of Intralipid in attenuating cytokine induction and circulating CD8⁺ T cells.

Cytokines, Hormones and Cellular Regulatory Mechanisms Favoring Successful Reproduction

Its semi-allogeneic nature renders the conceptus vulnerable to attack by the maternal immune system. Several protective mechanisms operate during gestation to correct the harmful effects of anti-fetal immunity and to support a healthy pregnancy outcome. Pregnancy is characterized by gross alterations in endocrine functions. Progesterone is indispensable for pregnancy and humans, and it affects immune functions both directly and via mediators. The progesterone-induced mediator - PIBF - acts in favor of Th2-type immunity, by increasing Th2 type cytokines production. Except for implantation and parturition, pregnancy is characterized by a Th2-dominant cytokine pattern. Progesterone and the orally-administered progestogen dydrogesterone upregulate the production of Th2-type cytokines and suppress the production of Th1 and Th17 cytokine production in vitro. This is particularly relevant to the fact that the Th1-type cytokines TNF-α and IFN-γ and the Th17 cytokine IL-17 have embryotoxic and anti-trophoblast activities. These cytokine-modulating effects and the PIBF-inducing capabilities of dydrogesterone may contribute to the demonstrated beneficial effects of dydrogesterone in recurrent spontaneous miscarriage and threatened miscarriage. IL-17 and IL-22 produced by T helper cells are involved in allograft rejection, and therefore could account for the rejection of paternal HLA-C-expressing trophoblast. Th17 cells (producing IL-17 and IL-22) and Th22 cells (producing IL-22) exhibit plasticity and could produce IL-22 and IL-17 in association with Th2-type cytokines or with Th1-type cytokines. IL-17 and IL-22 producing Th cells are not harmful for the conceptus, if they also produce IL-4. Another important protective mechanism is connected with the expansion and action of regulatory T cells, which play a major role in the induction of tolerance both in pregnant women and in tumour-bearing patients. Clonally-expanded Treg cells increase at the feto-maternal interface and in tumour-infiltrating regions. While in cancer patients, clonally-expanded Treg cells are present in peripheral blood, they are scarce in pregnancy blood, suggesting that fetal antigen-specific tolerance is restricted to the foeto-maternal interface. The significance of Treg cells in maintaining a normal materno-foetal interaction is underlined by the fact that miscarriage is characterized by a decreased number of total effector Treg cells, and the number of clonally-expanded effector Treg cells is markedly reduced in preeclampsia. In this review we present an overview of the above mechanisms, attempt to show how they are connected, how they operate during normal gestation and how their failure might lead to pregnancy pathologies.

Abnormal expression of the costimulatory molecule B7-H4 in placental chorionic villous and decidual basalis tissues of patients with preeclampsia and HELLP syndrome

BACKGROUND

B7-H4, a checkpoint molecule of the B7 family, regulates a broad spectrum such as T-cell activation, cytokine secretion, tumour progression, and invasion capacities. Our previous data revealed that soluble B7-H4 (sB7-H4) blood serum levels are elevated in women at high risk for the hypertensive pregnancy disorder preeclampsia (PE) in the first trimester, as well as in patients with confirmed early/late-onset PE.

AIM

We here aim to investigate the expression pattern of B7-H4 in placental tissues of PE and HELLP Syndrome versus control group.

METHODS

B7-H4 protein expression and localization were investigated by immunoblotting and co-immunohistochemistry in placental chorionic villous and decidual basalis tissues.

RESULTS

B7-H4 protein was prominently expressed at the cell membrane, in the cytoplasm of the syncytiotrophoblast (STB) and interstitial extravillous trophoblast (EVT). B7-H4 protein levels in placental chorionic villous tissue were significantly higher in women with early-onset/late-onset PE and HELLP, while it was decreased in decidual basalis tissues of early-onset PE and HELLP compared with controls.

CONCLUSION

B7-H4 was inversely expressed in placental chorionic villous and decidual basalis tissues of PE and HELLP patients. The increase in B7-H4 in the STB in PE and HELLP may lead to excessive apical expression and release of soluble B7-H4 in the maternal circulation. In contrast, the decrease in B7-H4 in decidual basalis tissues could be related to the decrease in invasion ability of the EVT in PE. Thus, the current results strongly suggest that B7-H4 is involved in the pathogenesis of PE and HELLP.

One-Sided Chronic Intervillositis of Unknown Etiology in Dizygotic Twins: A Description of 3 Cases

Chronic intervillositis of unknown etiology (CIUE) is a rare, poorly understood, histopathological diagnosis of the placenta that is frequently accompanied by adverse pregnancy outcomes including miscarriage, fetal growth restriction, and intrauterine fetal death. CIUE is thought to have an immunologically driven pathophysiology and may be related to human leukocyte antigen mismatches between the mother and the fetus. Dizygotic twins with one-sided CIUE provide an interesting context to study the influence of immunogenetic differences in such cases. The main immune-cell subsets were investigated using immunohistochemistry. We identified three dizygotic twin pregnancies in which CIUE was present in only one of the two placentas. Two of the pregnancies ended in term delivery and one ended in preterm delivery. Presence of CIUE was correlated with lower placental weight and lower birthweight. Relative number of CD68, CD56, CD20, and CD3 positive cells were comparable between co-twins. The presence of one-sided CIUE in dizygotic twin pregnancy was associated with selective growth restriction in the affected twin. This suggests a unique fetal immunogenetic contribution to the pathogenesis of CIUE. Further study of dizygotic and monozygotic placentas affected by CIUE could identify new insights into its pathophysiology and into the field of reproductive immunology.

Aggrephagy Deficiency in the Placenta: A New Pathogenesis of Preeclampsia

Aggrephagy is defined as the selective degradation of aggregated proteins by autophagosomes. Protein aggregation in organs and cells has been highlighted as a cause of multiple diseases, including neurodegenerative diseases, cardiac failure, and renal failure. Aggregates could pose a hazard for cell survival. Cells exhibit three main mechanisms against the accumulation of aggregates: protein refolding by upregulation of chaperones, reduction of protein overload by translational inhibition, and protein degradation by the ubiquitin-proteasome and autophagy-lysosome systems. Deletion of autophagy-related genes reportedly contributes to intracellular protein aggregation in vivo. Some proteins recognized in aggregates in preeclamptic placentas include those involved in neurodegenerative diseases. As aggregates are derived both intracellularly and extracellularly, special endocytosis for extracellular aggregates also employs the autophagy machinery. In this review, we discuss how the deficiency of aggrephagy and/or macroautophagy leads to poor placentation, resulting in preeclampsia or fetal growth restriction.

The role of decidual regulatory T cells in the induction and maintenance of fetal antigen-specific tolerance: Imbalance between regulatory and cytotoxic T cells in pregnancy complications

Fetal antigen-specific tolerance is important for maintaining allogeneic pregnancies. Maternal conventional T cells recognize fetal antigens; however, regulatory T (Treg) cells suppress immune reactions against the fetus. Fetal antigen-specific Treg cells are induced in the decidua upon contact with antigen-presenting cells and extravillous trophoblasts (EVTs). Functional alteration of cytotoxic T cells (CTLs) in the decidua also contributes to maintaining the pregnancy. Reduced, dysfunctional, and imbalanced Treg cell distribution likely contributes to the pathogenesis of pregnancy complications, such as miscarriage and preeclampsia. Recent studies have revealed differences in Treg cell characteristics during preeclampsia and miscarriage. Treg cell reduction in the decidua is likely associated with miscarriage. Insufficient expansion of fetal antigen-specific Treg cells in the decidua probably plays a role in preeclampsia pathogenesis. In addition, the balance between Treg cell-mediated tolerance and functional alteration of CTLs is important. Further investigations of functional molecules in Treg cells will contribute to the development of immunotherapy for pregnancy complications.

Crosstalk Between Trophoblasts and Decidual Immune Cells: The Cornerstone of Maternal-Fetal Immunotolerance

The success of pregnancy relies on the fine adjustment of the maternal immune system to tolerate the allogeneic fetus. Trophoblasts carrying paternal antigens are the only fetal-derived cells that come into direct contact with the maternal immune cells at the maternal–fetal interface. The crosstalk between trophoblasts and decidual immune cells (DICs) via cell–cell direct interaction and soluble factors such as chemokines and cytokines is a core event contributing to the unique immunotolerant microenvironment. Abnormal trophoblasts–DICs crosstalk can lead to dysregulated immune situations, which is well known to be a potential cause of a series of pregnancy complications including recurrent spontaneous abortion (RSA), which is the most common one. Immunotherapy has been applied to RSA. However, its development has been far less rapid or mature than that of cancer immunotherapy. Elucidating the mechanism of maternal–fetal immune tolerance, the theoretical basis for RSA immunotherapy, not only helps to understand the establishment and maintenance of normal pregnancy but also provides new therapeutic strategies and promotes the progress of immunotherapy against pregnancy-related diseases caused by disrupted immunotolerance. In this review, we focus on recent progress in the maternal–fetal immune tolerance mediated by trophoblasts–DICs crosstalk and clinical application of immunotherapy in RSA. Advancement in this area will further accelerate the basic research and clinical transformation of reproductive immunity and tumor immunity.

Navigating the murky waters of maternal fetal tolerance: Put big data at the helm

The last 20 years have seen significant progress in our understanding of the maternal T cell response to the fetus. However, major questions still remain. In this review, we discuss the contribution of Big Data approaches to our evolving understanding of maternal fetal tolerance. This includes investigations which have employed systems immunology, high dimensional mass spectrometry, whole genome transcriptomics, as well as single-cell RNA-sequencing. These studies reveal "new" mechanisms of T cell dysfunction that are conserved across immune responses and highlight the breadth and magnitude of the systemic maternal response to the fetus during pregnancy.

Molecular and immunological developments in placentas

Cytotrophoblasts differentiate in two directions during early placentation: syncytiotrophoblasts (STBs) and extravillous trophoblasts (EVTs). STBs face maternal immune cells in placentas, and EVTs, which invade the decidua and uterine myometrium, face the cells in the uterus. This situation, in which trophoblasts come into contact with maternal immune cells, is known as the maternal-fetal interface. Despite fetuses and fetus-derived trophoblast cells being of the semi-allogeneic conceptus, fetuses and placentas are not rejected by the maternal immune system because of maternal-fetal tolerance. The acquired tolerance develops during normal placentation, resulting in normal fetal development in humans. In this review, we introduce placental development from the viewpoint of molecular biology. In addition, we discuss how the disruption of placental development could lead to complications in pregnancy, such as hypertensive disorder of pregnancy, fetal growth restriction, or miscarriage.

Recurrent pregnancy loss

Recurrent pregnancy loss is a distressing pregnancy disorder experienced by ~2.5% of women trying to conceive. Recurrent pregnancy loss is defined as the failure of two or more clinically recognized pregnancies before 20-24 weeks of gestation and includes embryonic and fetal losses. The diagnosis of an early pregnancy loss is relatively straightforward, although progress in predicting and preventing recurrent pregnancy loss has been hampered by a lack of standardized definitions, the uncertainties surrounding the pathogenesis and the highly variable clinical presentation. The prognosis for couples with recurrent pregnancy loss is generally good, although the likelihood of a successful pregnancy depends on maternal age and the number of previous losses. Recurrent pregnancy loss can be caused by chromosomal errors, anatomical uterine defects, autoimmune disorders and endometrial dysfunction. Available treatments target the putative risk factors of pregnancy loss, although the effectiveness of many medical interventions is controversial. Regardless of the underlying aetiology, couples require accurate information on their chances of having a baby and appropriate support should be offered to reduce the psychological burden associated with multiple miscarriages. Future research must investigate the pathogenesis of recurrent pregnancy loss and evaluate novel diagnostic tests and treatments in adequately powered clinical trials.

Placental autophagy failure: A risk factor for preeclampsia

Hypertensive disorders of pregnancy, including preeclampsia, directly affect maternal and perinatal morbidity and mortality. As the pathophysiology of preeclampsia is multi-factorial and has been studied using different approaches, we have demonstrated that impaired autophagy is an intertwined risk factor for preeclampsia. This concept has been verified in both in vitro and in vivo experiments. Autophagy is primarily involved in maintaining cellular homeostasis, and in immune regulation, longevity, cytokines secretion and a variety of other biological functions. Here, we review the role of autophagy in normal embryogenesis and placentation. Once placental autophagy is impaired by metabolic stress such as hypoxia, endoplasmic reticulum stress or starvation, placental development could be disrupted, resulting in functional maladaptations at the maternal-fetal interface. These malfunctions may result in fetal growth restriction or preeclampsia.