Low circulating CD4(+) CD25(+) Foxp3(+) T regulatory cell levels predict miscarriage risk in newly pregnant women with a history of failure

IL-2/JES6-1 Antibody Complex Expands the Maternal T-Regulatory Cell Pool and Alleviates Fetal Loss in Abortion-Prone Mice

Regulatory T (Treg) cells are essential for immune tolerance of embryo implantation, and insufficient Treg cells are implicated in early pregnancy loss. An abortion-prone mouse model was used to evaluate the utility of IL-2 complexed with JES6-1 anti-IL-2 antibody (IL-2/JES6-1) to boost uterine Treg cells and improve reproductive success. IL-2/JES6-1, but not IL-2/IgG control, administered in the periconception phase to CBA/J females mated with DBA/2 males elicited a greater than twofold increase in the proportion of CD4+ T cells expressing forkhead box P3 (FOXP3), and an increase in the ratio of FOXP3+ Treg cells/FOXP3- T conventional cells, in the uterus and its draining lymph nodes at embryo implantation that was sustained into midgestation. An attenuated phenotype was evident in both thymic-derived and peripheral Treg cells with elevated cytotoxic T-lymphocyte antigen-4, CD25, and FOXP3, indicating improved suppressive function, as well as increased proliferative marker Ki-67. IL-2/JES6-1 treatment reduced fetal loss from 31% to 10%, but this was accompanied by a 6% reduction in late gestation fetal weight, despite comparable placental size and architecture. Similar effects of IL-2/JES6-1 on Treg cells and fetal growth were seen in CBA/J females with healthy pregnancies sired by BALB/c males. These findings show that expanding the uterine Treg cell pool through targeting IL-2 signaling is a strategy worthy of further investigation for mitigating immune-mediated fetal loss.

Immunologic insights in recurrent spontaneous abortion: Molecular mechanisms and therapeutic interventions

Recurrent spontaneous abortion refers to the occurrence of two or more spontaneous abortions before or during the early stages of pregnancy. The immune system plays a crucial role in the maintenance of pregnancy and embryo implantation. Various immune cells, cytokines, and immune regulatory pathways are involved in the complex immune balance required for a stable pregnancy. Studies suggest that immune abnormalities may be associated with some recurrent spontaneous abortion cases, particularly those involving the dysregulation of immune cell function, autoimmune responses, and placental immunity. In terms of treatment, interventions targeting immune mechanisms are crucial. Various therapeutic approaches, including immunomodulatory drugs, immunoadsorption therapies, and immunocellular therapies, are continually being researched and developed. These approaches aim to restore the immune balance, enhance the success rate of pregnancies, and provide more effective treatment options for patients with recurrent spontaneous abortion.

Impact of SARS-CoV-2 infection during pregnancy on the placenta and fetus

Pregnant people and their fetuses are vulnerable to adverse health outcomes from coronavirus 2019 disease (COVID-19) due to infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). COVID-19 has been associated with higher rates of maternal mortality, preterm birth, and stillbirth. While SARS-CoV-2 infection of the placenta and vertical transmission is rare, this may be due to the typically longer time interval between maternal infection and testing of the placenta and neonate. Placental injury is evident in cases of SARS-CoV-2-associated stillbirth with massive perivillous fibrin deposition, chronic histiocytic intervillositis, and trophoblast necrosis. Maternal COVID-19 can also polarize fetal immunity, which may have long-term effects on neurodevelopment. Although the COVID-19 pandemic continues to evolve, the impact of emerging SARS-CoV-2 variants on placental and perinatal injury/mortality remains concerning for maternal and perinatal health. Here, we highlight the impact of COVID-19 on the placenta and fetus and remaining knowledge gaps.

Beyond Immune Balance: The Pivotal Role of Decidual Regulatory T Cells in Unexplained Recurrent Spontaneous Abortion

Recurrent spontaneous abortion (RSA) is defined as two or more consecutive pregnancy failures, which brings tremendous stress to women of childbearing age and seriously affects family well-being. However, the reason in about 50% of cases remains unknown and is defined as unexplained recurrent spontaneous abortion (URSA). The immunological perspective in URSA has attracted widespread attention in recent years. The embryo is regarded as a semi-allogeneic graft to the mother. A successful pregnancy requires transition to an immune environment conducive to embryo survival at the maternal-fetal interface. As an important member of regulatory immunity, regulatory T (Treg) cells play a key role in regulating immune tolerance at the maternal-fetal interface. This review will focus on the phenotypic plasticity and lineage stability of Treg cells to illustrate its relationship with URSA.

A disrupted FOXP3 transcriptional signature underpins systemic regulatory T cell insufficiency in early pregnancy failure

Regulatory T (Treg) cell defects are implicated in disorders of embryo implantation and placental development, but the origins of Treg cell dysfunction are unknown. Here, we comprehensively analyzed the phenotypes and transcriptional profile of peripheral blood Treg cells in individuals with early pregnancy failure (EPF). Compared to fertile subjects, EPF subjects had 32% fewer total Treg cells and 54% fewer CD45RA+CCR7+ naive Treg cells among CD4+ T cells, an altered Treg cell phenotype with reduced transcription factor FOXP3 and suppressive marker CTLA4 expression, and lower Treg:Th1 and Treg:Th17 ratios. RNA sequencing demonstrated an aberrant gene expression profile, with upregulation of pro-inflammatory genes including CSF2, IL4, IL17A, IL21, and IFNG in EPF Treg cells. In silico analysis revealed 25% of the Treg cell dysregulated genes are targets of FOXP3. We conclude that EPF is associated with systemic Treg cell defects arising due to disrupted FOXP3 transcriptional control and loss of lineage fidelity.

The effectiveness and safety of intrauterine infusion of autologous regulatory T cells (Tregs) in patients with recurrent pregnancy loss and low levels of endometrial FoxP3+ cells: A retrospective cohort study

PROBLEM

Regulatory T cells (Tregs) are a specialized type of T cells that help maintain immune tolerance and homeostasis. The potential of Tregs cell-based therapies in treating diseases has been demonstrated in several clinical trials, which have shown promising outcomes and high safety in autoimmune diseases, transplant rejection, and graft-versus-host disease. However, their effectiveness and safety in improving endometrial receptivity and reducing pregnancy loss in human reproduction are unknown.

METHOD OF STUDY

The study used a retrospective design and included patients with recurrent pregnancy loss (RPL) and lower levels of endometrial FoxP3⁺ Tregs. Patients in the Tregs group (n = 33) received intrauterine Tregs infusion three times during the follicular phase, while the control group (n = 28) did not receive any intrauterine infusion.

RESULTS

The intrauterine infusion of autologous Tregs increased the levels of FoxP3⁺ Tregs and CD56⁺ NK cells. Patients in the Treg group had higher live birth rates and lower miscarriage rates, especially early miscarriage rates. However, the two groups had no differences in the implantation rate, clinical pregnancy rate, and percentage of preterm delivery.

CONCLUSIONS

The findings suggest that intrauterine Tregs infusion may be a potential therapeutic approach for RPL. Further research in larger clinical trials is needed to confirm these findings.

T Cell Subsets and the Expression of Related MicroRNAs in Patients with Recurrent Early Pregnancy Loss

This study explored the role of T cell subsets and the expression of related microRNAs in patients with recurrent early pregnancy loss (EPL). Fifty patients with EPL loss between May 2018 and May 2021 were randomly selected as the EPL group, and 50 pregnant women with normal pregnancies or normal delivery outcomes were randomly selected as the control group. The expression levels of T cell subset-related markers and T cell subset-related miRNAs, in addition to the frequencies of T cell subsets, in peripheral blood of the two groups were analyzed. In terms of T cell-related markers, the results showed that the expression levels of the transcriptional regulator TBX-21 (T-bet) and interferon regulatory factor 4 (IRF4) were significantly upregulated in peripheral blood of the patients in the EPL group ( $P<0.05$ ), whereas the expression levels of GATA binding protein 3 (GATA3) and glucocorticoid-induced tumor necrosis factor receptor (GITR) were significantly downregulated ( $P<0.05$ ). In the EPL group, the expression of mir-106b, mir-93, and mir-25 was upregulated ( $1.51\pm 0.129$ , $1.43\pm 0.132$ , and $1.73\pm 0.156$ , respectively) in regulatory T (Treg) cell-related T cell subsets, whereas the expression of miR-146a and miR-155 was downregulated ( $P<0.05$ ). The frequencies of Treg and exhausted T cells in the EPL group were significantly lower than those in the control group ( $P<0.05$ ). The cell frequencies of T helper 17 (Th17) cells and exhausted Treg cells in the EPL group were significantly higher than those in the control group ( $P<0.05$ ). In conclusion, immune cells and associated miRNA profiles can be used as prognostic biomarkers for the treatment of human reproductive disorders, such as EPL.

Recurrent Abortion and the Involvement of Killer-Cell Immunoglobulin-like Receptor (KIR) Genes, Activated T Cells, NK Abnormalities, and Cytokine Profiles

Immune tolerance at the feto-maternal interface is crucial for the growth of the semi-allograft fetus in the womb. The outcome of pregnancy is dependent on a fine balance between various immunological forces. For a long time, the potential role of the immune system in pregnancy disorders has remained enigmatic. Current evidence has revealed that natural killer (NK) cells are the predominant immune cell population in the uterine decidua. NK cells cooperate with T-cells to provide an optimal microenvironment for the growth of the developing fetus by producing cytokines, chemokines, and angiogenic factors. These factors support trophoblast migration and angiogenesis which regulates the process of placentation. NK cells differentiate between "self" and "non-self" through their surface receptors known as killer-cell immunoglobulin-like receptors (KIRs). They induce immune tolerance through communication via their KIR and fetal human leucocyte antigens (HLA). KIRs are surface receptors of NKs that comprise both activating and inhibiting receptors. Due to the wide diversity manifested by its genes, the KIR repertoire is different in each individual. Significant evidence has implicated KIRs in recurrent spontaneous abortion (RSA); however, maternal KIR gene diversity in RSA is still unclear. Research has shown that immunological aberrancies including activating KIRs, NK abnormalities, and T cell downregulation are risk factors for RSA. In this review, we discuss relevant data from experimental studies on NK cell abnormalities, KIR, and T-cells in the incidence of recurrent spontaneous abortion.

Migration and homeostasis of regulatory T cells in rheumatoid arthritis

Regulatory T (T_reg) cells are garnering increased attention in research related to autoimmune diseases, including rheumatoid arthritis (RA). They play an essential role in the maintenance of immune homeostasis by restricting effector T cell activity. Reduced functions and frequencies of T_reg cells contribute to the pathogenesis of RA, a common autoimmune disease which leads to systemic inflammation and erosive joint destruction. T_reg cells from patients with RA are characterized by impaired functions and by an altered phenotype. They show increased plasticity towards Th17 cells and a reduced suppressive capacity. Besides the suppressive function of T_reg cells, their effectiveness is determined by their ability to migrate into inflamed tissues. In the past years, new mechanisms involved in T_reg cell migration have been identified. One example of such a mechanism is the phosphorylation of vasodilator-stimulated phosphoprotein (VASP). Efficient migration of T_reg cells requires the presence of VASP. IL-6, a cytokine which is abundantly present in the peripheral blood and in the synovial tissue of RA patients, induces posttranslational modifications of VASP. Recently, it has been shown in mice with collagen-induced arthritis (CIA) that this IL-6 mediated posttranslational modification leads to reduced T_reg cell trafficking. Another protein which facilitates T_reg cell migration is G-protein-signaling modulator 2 (GPSM2). It modulates G-protein coupled receptor functioning, thereby altering the cellular activity initiated by cell surface receptors in response to extracellular signals. The almost complete lack of GPSM2 in T_reg cells from RA patients contributes to their reduced ability to migrate towards inflammatory sites. In this review article, we highlight the newly identified mechanisms of T_reg cell migration and review the current knowledge about impaired T_reg cell homeostasis in RA.

Immune determinants of endometrial receptivity: a biological perspective

Immune cells are essential for endometrial receptivity to embryo implantation and early placental development. They exert tissue-remodeling and immune regulatory roles-acting to promote epithelial attachment competence, regulate the differentiation of decidual cells, remodel the uterine vasculature, control and resolve inflammatory activation, and suppress destructive immunity to paternally inherited alloantigens. From a biological perspective, the endometrial immune response exerts a form of "quality control"-it promotes implantation success when conditions are favorable but constrains receptivity when physiological circumstances are not ideal. Women with recurrent implantation failure and recurrent miscarriage may exhibit altered numbers or disturbed function of certain uterine immune cell populations-most notably uterine natural killer cells and regulatory T cells. Preclinical and animal studies indicate that deficiencies or aberrant activation states in these cells can be causal in the pathophysiological mechanisms of infertility. Immune cells are, therefore, targets for diagnostic evaluation and therapeutic intervention. However, current diagnostic tests are overly simplistic and have limited clinical utility. To be more informative, they need to account for the full complexity and reflect the range of perturbations that can occur in uterine immune cell phenotypes and networks. Moreover, safe and effective interventions to modulate these cells are in their infancy, and personalized approaches matched to specific diagnostic criteria will be needed. Here we summarize current biological understanding and identify knowledge gaps to be resolved before the promise of therapies to target the uterine immune response can be fully realized.

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.

Allogeneic lymphocytes immunotherapy in female infertility: Lessons learned and the road ahead

The endometrium is an essential tissue in the normal immunologic dialogue between the mother and the conceptus, which is necessary for the proper establishment and maintenance of a successful pregnancy. It's become evident that the maternal immune system plays a key role in the normal pregnancy's initiation, maintenance, and termination. In this perspective, the immune system contributes to regulating all stages of pregnancy, thus immunological dysregulation is thought to be one of the major etiologies of implantation failures. Many researchers believe that immune therapies are useful tactics for improving the live births rate in certain situations. Lymphocyte immunotherapy (LIT) is an active form of immunotherapy that, when used on the relevant subgroups of patients, has been shown in multiple trials to dramatically enhance maternal immunological balance and pregnancy outcome. The primary goal of LIT is to regulate the immune system in order to create a favorable tolerogenic immune milieu and tolerance for embryo implantation. However, there are a plethora of influential factors influencing its therapeutic benefits that merit to be addressed. The objective of our study is to discuss the mechanisms and challenges of allogeneic LIT.

Understanding human immunity in idiopathic recurrent pregnancy loss

Miscarriage, defined as the loss of a pregnancy before a viable gestation, affects 1 in 6 couples. Recurrent pregnancy loss (RPL), defined as two or more miscarriages, affects up to 1.9% of couples. The physical, psychological, and financial impact of miscarriage can be substantial. However, despite its multifactorial etiology, for up to 50% of couples a reason behind this condition cannot be identified, termed 'idiopathic RPL'. Much recent research has strived to understand this, with immune dysregulation being a source of particular interest. In this short review we summarize the current evidence on the complex role of the immune system both pre- and early post-conception in RPL. A key question is whether systemic peripheral blood markers, in particular natural killer cell and T cells, may be utilized to accurately predict and/ or diagnose those pregnancies at high risk of loss. Given the invasive nature of endometrial testing, identification of reliable peripheral immune biomarkers is particularly appealing. Clinical trials using potent immunomodulatory agents, including intravenous immunoglobulin, donor leukocyte immunization, and tumor necrosis factor (TNF)-α inhibitors, have been undertaken with the primary objective of preventing miscarriage in women with RPL. Standardisation of both diagnostic and prognostic immune cell testing assays is required to permit accurate identification of those women who may benefit from immunomodulation. Prompt clarification is required to meet the increasing expectation from couples and clinicians, as without these advancements women are at risk of exposure to potent immune-therapies and subsequent studies are at risk of failure, generating further controversy regarding the role of immune dysregulation in women with RPL. Through this review we highlight clear gaps in our current knowledge on immune activity in RPL.

The Role of Type I and Type II NKT Cells in Materno-Fetal Immunity

NKT cells represent a small but significant immune cell population as being a part of and bridging innate and adaptive immunity. Their ability to exert strong immune responses via cytotoxicity and cytokine secretion makes them significant immune effectors. Since pregnancy requires unconventional maternal immunity with a tolerogenic phenotype, investigation of the possible role of NKT cells in materno-fetal immune tolerance mechanisms is of particular importance. This review aims to summarize and organize the findings of previous studies in this field. Data and information about NKT cells from mice and humans will be presented, focusing on NKT cells characteristics during normal pregnancy in the periphery and at the materno-fetal interface and their possible involvement in female reproductive failure and pregnancy complications with an immunological background.

Glucocorticoid therapy in assisted reproduction

As glucocorticoids are well-known as important regulators of stress and the immune system, their function and clinical use have elicited substantial interest in the field of reproduction. In particular, the effect of glucocorticoid therapy on endometrial receptivity during assisted reproduction, including in vitro fertilization (IVF) cycles, has led to a great deal of interest and controversy. However, previous studies have not been able to provide consistent and reliable evidence due to their small, non-controlled designs and use of different criteria. Considering the potential risk of exposure to glucocorticoids for mothers and fetuses in early pregnancy, the use of glucocorticoids in IVF cycles should be carefully evaluated, including the balance between risk and benefit. To date, there is no conclusive evidence that the use of glucocorticoids improves the pregnancy rate in IVF cycles with unselected subjects, and a further investigation should be considered with a proper study design.

Natural killer cells: functional differences in recurrent spontaneous abortion†

Recurrent spontaneous abortion (RSA) is one of the major pregnancy disorders and poses a serious risk to both the mother and the fetus. Although a number of research efforts have been conducted, therapeutic advances for treating RSA have not lived up to their expectations. Hence, other treatments should be explored. The important role of natural killer (NK) cells in immunotherapy is attracting increasing attention, both as a pharmaceutical target and for cell therapies. NK cells are abundant in the endometrium and play a role in implantation and placentation in normal pregnancy. As research progresses, NK cells are increasingly regarded as playing essential roles in the emergence and development of RSA. In this article, I review recent findings on the role of uterine NK cells in the pathophysiology of RSA. These cells may become therapeutic NK cell-related targets. In conclusion, although several issues regarding NK cells in RSA remain unresolved and require further investigation, extensive evidence is available for the treatment of RSA.

Prednisolone in early pregnancy inhibits regulatory T cell generation and alters fetal and placental development in mice

Corticosteroids have been utilised in the assisted reproduction setting with the expectation of suppressing aberrant immune activation and improving fertility in women. However, the effects of corticosteroids on fertility, and on pregnancy and offspring outcomes, are unclear. In this study, mice were administered prednisolone (1 mg/kg) or PBS daily in the pre-implantation phase, and effects on the adaptive immune response, the implantation rate, fetal development and postnatal outcomes were investigated. Prednisolone disrupted the expected expansion of CD4+ T cells in early pregnancy, inhibiting generation of both regulatory T cells (Treg cells) and effector T cells and suppressing IFNG required for T cell functional competence. Prednisolone caused an 8-20% increase in the embryo implantation rate and increased the number of viable pups per litter. In late gestation, fetal and placental weights were reduced in a litter size-dependent manner, and the canonical inverse relationship between litter size and fetal weight was lost. The duration of pregnancy was extended by ~ 0.5 day and birth weight was reduced by ~ 5% after prednisolone treatment. Viability of prednisolone-exposed offspring was comparable to controls, but body weight was altered in adulthood, particularly in male offspring. Thus, while prednisolone given in the pre-implantation phase in mice increases maternal receptivity to implantation and resource investment in fetal growth, there is a trade-off in long-term consequences for fetal development, birth weight and offspring health. These effects are associated with, and likely caused by, prednisolone suppression of the adaptive immune response at the outset of pregnancy.

T helper cell immunity in pregnancy and influence on autoimmune disease progression

Pregnancy presents the maternal immune system with a unique immunological challenge since it has to defend against pathogens while tolerating paternal allo-antigens expressed by fetal tissues. T helper (Th) cells play a central role in modulating immune responses and recent advances have defined distinct contributions of various Th cell subsets throughout each phase of human pregnancy, while dysregulation in Th responses show association with multiple obstetrical complications. In addition to localized decidual mechanisms, modulation of Th cell immunity during gestation is mediated largely by oscillations in sex hormone concentrations. Aberrant Th cell responses also underlie several autoimmune disorders while pregnancy-induced changes in the balance of Th cell immunity has been shown to exert favorable outcomes in the progression Th1 and Th17 driven autoimmune conditions only to be followed by post-partal exacerbations in disease.

Chronic histiocytic intervillositis: A breakdown in immune tolerance comparable to allograft rejection?

Chronic histiocytic intervillositis (CHI) is a pregnancy disorder characterized by infiltration of maternal macrophages into the intervillous space of the human placenta, often with accompanying perivillous fibrin deposition. CHI is associated strongly with foetal growth restriction and increased risk of miscarriage and stillbirth. Although rare, affecting 6 in every 10 000 pregnancies beyond 12 weeks' gestation, the rate of recurrence is high at 25%-100%. To date, diagnosis of CHI can only be made post-delivery upon examination of the placenta due to a lack of diagnostic biomarkers, and criteria vary across publications. No treatment options have shown proven efficacy, and CHI remains a serious obstetric conundrum. Although its underlying aetiology is unclear, due to the presence of maternal macrophages and the reported increased incidence in women with autoimmune disease, CHI is hypothesized to be an inappropriate immune response to the semi-allogeneic foetus. Given this lack of understanding, treatment approaches remain experimental with limited rationale. However, there is recent evidence that immunosuppression and antithrombotic therapies may be effective in preventing recurrence of associated adverse pregnancy outcomes. With similarities noted between the pathological features of CHI and acute rejection of solid organ transplants, further investigation of this hypothesis may provide a basis for tackling CHI and other immune-related placental conditions. This review will explore parallels between CHI and allograft rejection and identify areas requiring further confirmation and exploitation of this comparison.

Autoimmune Hepatitis: Tolerogenic Immunological State During Pregnancy and Immune Escape in Post-partum

The maternal immune system engages in a fine balancing act during pregnancy by simultaneously maintaining immune tolerance to the fetus and immune responses to protect against invading organisms. Pregnancy is an intricately orchestrated process where effector immune cells with fetal specificity are selectively silenced. This requires a sustained immune suppressive state not only by expansion of maternal Foxp3+ regulatory T cells (Tregs) but also by leaning the immune clock toward a Th2 dominant arm. The fetus, known as a semi-allograft or temporary-self, leads to remission of autoimmune hepatitis during pregnancy. However, this tolerogenic immune state reverts back to a Th1 dominant arm, resulting in post-partum flare of AIH. Various hormones play a significant role in endocrine-immune axis during pregnancy. The placenta functions as a barrier between the maternal immune system and the fetus also plays a pivotal role in creating a tolerogenic environment during pregnancy. We review the evidence of immune tolerance during pregnancy and immune escape at post-partum period, focusing on patients with autoimmune hepatitis.

MicroRNA miR-155 is required for expansion of regulatory T cells to mediate robust pregnancy tolerance in mice

The immune-regulatory microRNA miR-155 is reduced in recurrent miscarriage, suggesting that miR-155 contributes to immune tolerance in pregnancy. Here we show miR-155 is induced in the uterine mucosa and draining lymph nodes (dLN) during the female immune response to male seminal fluid alloantigens. Mice with null mutation in miR-155 (miR-155^-/-) exhibited a reduced CD4⁺ T cell response after mating, with a disproportionate loss of CD25+FOXP3+ Treg cells. miR-155 deficiency impaired expansion of both peripheral and thymic Treg cells, distinguished by neuropilin-1 (NRP1), and fewer Treg cells expressed Ki67 proliferation marker and suppressive function marker CTLA4. Altered Treg phenotype distribution in miR-155^-/- mice was confirmed by t-distributed neighbor embedding (tSNE) analysis. Fewer dendritic cells (DCs) and macrophages trafficked to the dLN of miR-155^-/- mice, associated with lower CCR7 on DCs, and reduced uterine Ccl19 expression, implicating compromised antigen presentation in the stunted Treg cell response. miR-155^-/- mice exhibited elevated susceptibility to inflammation-induced fetal loss and fetal growth restriction compared with miR-155^+/+ controls, but outcomes were restored by transfer of wild-type Tregs. Thus miR-155 is a key regulator of immune adaptation to pregnancy and is necessary for sufficient Tregs to achieve robust pregnancy tolerance and protect against fetal loss.

Role of Regulatory T Cells in Regulating Fetal-Maternal Immune Tolerance in Healthy Pregnancies and Reproductive Diseases

Regulatory T cells (Tregs) are a specialized subset of T lymphocytes that function as suppressive immune cells and inhibit various elements of immune response in vitro and in vivo. While there are constraints on the number or function of Tregs which can be exploited to evoke an effective anti-tumor response, sufficient expansion of Tregs is essential for successful organ transplantation and for promoting tolerance of self and foreign antigens. The immune-suppressive property of Tregs equips this T lymphocyte subpopulation with a pivotal role in the establishment and maintenance of maternal tolerance to fetal alloantigens, which is necessary for successful pregnancy. Elevation in the level of pregnancy-related hormones including estrogen, progesterone and human chorionic gonadotropin promotes the recruitment and expansion of Tregs, directly implicating these cells in the regulation of fetal-maternal immune tolerance. Current studies have provided evidence that a defect in the number or function of Tregs contributes to the etiology of several reproductive diseases, such as recurrent spontaneous abortion, endometriosis, and pre-eclampsia. In this review, we provide insight into the underlying mechanism through which Tregs contribute to pregnancy-related immune tolerance and demonstrate the association between deficiencies in Tregs and the development of reproductive diseases.

Reduced frequency and functional defects of CD4+CD25highCD127low/- regulatory T cells in patients with unexplained recurrent spontaneous abortion

BACKGROUND

Unexplained recurrent spontaneous abortion (URSA) is defined as two or more consecutive pregnancy losses, generally of unknown cause; it is related to a failure of fetal-maternal immunological tolerance. Regulatory T cells (Tregs) exert immunosuppressive effects, which are essential to maintain fetal-maternal immunological tolerance and regulate immune balance. In this study, we used the specific cell-surface phenotype of CD4⁺CD25^highCD127^low/- Tregs to investigate the number and suppressive function of Tregs isolated from the peripheral blood of patients with URSA with the aim of expanding our understanding of their role in URSA.

METHODS

We isolated a relatively pure population of peripheral CD4⁺CD25^highCD127^low/- Tregs and CD4⁺CD25^- responder T cells (Tresps) from the patients with URSA and normal fertile nonpregnant control women via fluorescence-activated cell sorting. We compared the frequency, suppressive capacity, and forkhead box transcription factor P3 (FOXP3) expression of Tregs in the peripheral blood between patients with URSA and normal controls.

RESULTS

The frequency of CD4⁺CD25^highCD127^low/- Tregs in the peripheral blood was lower in URSA patients than in the controls (P < 0.05). The mean fluorescence intensity of FOXP3 and FOXP3 mRNA expression in Tregs was also significantly lower in the URSA patients (P < 0.01). Tregs suppressed the activity of autologous Tresps stimulated with anti-CD3/CD28 beads in a concentration-dependent manner, with the strongest suppression occurring in cocultures with a 1:1 Treg:Tresp ratio in both groups; however, patient-derived Tregs exhibited a poorer capacity to suppress the proliferation of autologous Tresps than the Tregs from normal controls (P < 0.01). Moreover, Tregs isolated from URSA patients inhibited the proliferation of Tresps from normal controls less potently than the Tregs from normal controls (P < 0.01), and Tresps from URSA patients were less effectively suppressed by autologous Tregs than by those from normal controls (P < 0.01). Tresp activity were intact in both groups.

CONCLUSIONS

We observed a lower frequency of peripheral CD4⁺CD25^highCD127^low/- Tregs with lower FOXP3 expression in the peripheral blood of URSA patients. In addition, highly purified Tregs from patients with URSA exhibited impaired suppressive effects. The defect in immune regulation in URSA patients appears to be primarily related to impaired Tregs, and not to increased resistance of Tresps to suppression. Our findings reveal a potential novel therapeutic target for URSA.

Innate and Adaptive Immune Responses in HELLP Syndrome

Innate and adaptive immune involvement in hemolysis, elevated liver enzymes and low platelet (HELLP) syndrome is an understudied field, although it is of high clinical importance. This syndrome implies a risk of serious morbidity and mortality to both the mother and the fetus during pregnancy. It was proposed that HELLP syndrome occurs in a circulatory inflammatory milieu, that might in turn participate in a complex interplay between the secreted inflammatory immunomodulators and immune cell surface receptors. Meanwhile, reported immune cell attenuation during HELLP may consequently lead to a prolonged immunoactivation and tissue damage. In this regard, learning more about the immune components of this syndrome should widen the understanding of the HELLP pathophysiology and eventually enable development of novel immune-based therapeutics. This review aims to summarize and discuss the recent and previous findings of the innate and adaptive immune responses during HELLP in order to update the current knowledge of the immune involvement in HELLP pathogenesis.

Altered decidual and placental catabolism of vitamin D may contribute to the aetiology of spontaneous miscarriage

INTRODUCTION

Vitamin D catabolizing enzymes, along with vitamin D receptor (VDR) and vitamin D binding protein (DBP) are expressed in the decidua and placenta during pregnancy and capable of synthesizing active vitamin D. Vitamin D plays roles in immunoregulation and trophoblast invasion, key features of a successful pregnancy. Epidemiological data suggests that vitamin D deficiency is associated with both spontaneous and recurrent miscarriage but few studies have investigated the expression of the key vitamin D catabolizing enzymes in miscarriage.

METHODS

Placenta and decidua were collected after termination of apparently normal pregnancies (controls, n = 22) or spontaneous miscarriage (n = 20). Immunohistochemical staining, Western Blot and qRT-PCR were performed for CYP27B1, CYP24A1, CYP2R1, VDR and DBP (not qRT-PCR). HTR-8/SVneo cells were cultured in CoCL₂ (hypoxic mimetic) or LPS (bacterial infection mimetic) for 24 h, RNA extracted and qRT-PCR performed for CYP27B1, CYP24A1, CYP2R1 and VDR.

RESULTS

In spontaneous miscarriage, placental and decidual expression of CYP27B1 was reduced, while expression of CYP24A1, VDR and DBP was increased. When a trophoblast cell line was treated with CoCL₂ expression of CYP27B1 was increased and CYP24A1 was reduced, while LPS induced expression of VDR.

DISCUSSION

This is the first report of altered utero-placental vitamin D catabolism in spontaneous miscarriage. It is becoming accepted that women who are undergoing assisted reproductive technologies should ensure they have sufficient vitamin D levels prior to pregnancy, these data support that all women should ensure they are vitamin D replete before planning to get pregnant.

The Tolerogenic Function of Regulatory T Cells in Pregnancy and Cancer

Regulatory T cells, a subpopulation of suppressive T cells, are potent mediators of self-tolerance and essential for the suppression of triggered immune responses. The immune modulating capacity of these cells play a major role in both transplantation, autoimmune disease, allergy, cancer and pregnancy. During pregnancy, low numbers of regulatory T cells are associated with pregnancy failure and pregnancy complications such as pre-eclampsia. On the other hand, in cancer, low numbers of immunosuppressive T cells are correlated with better prognosis. Hence, maternal immune tolerance toward the fetus during pregnancy and the escape from host immunosurveillance by cancer seem to be based on similar immunological mechanisms being highly dependent on the balance between immune activation and suppression. As regulatory T cells hold a crucial role in several biological processes, they may also be promising subjects for therapeutic use. Especially in the field of cancer, cell therapy and checkpoint inhibitors have demonstrated that immune-based therapies have a very promising potential in treatment of human malignancies. However, these therapies are often accompanied by adverse autoimmune side effects. Therefore, expanding the knowledge to recognize the complexities of immune regulation pathways shared across different immunological scenarios is extremely important in order to improve and develop new strategies for immune-based therapy. The intent of this review is to highlight the functional characteristics of regulatory T cells in the context of mechanisms of immune regulation in pregnancy and cancer, and how manipulation of these mechanisms potentially may improve therapeutic options.

Memory T Cells in Pregnancy

Adaptations of the maternal immune response are necessary for pregnancy success. Insufficient immune adaption is associated with pregnancy pathologies such as infertility, recurrent miscarriage, fetal growth restriction, spontaneous preterm birth, and preeclampsia. The maternal immune system is continuously exposed to paternal-fetal antigens; through semen exposure from before pregnancy, through fetal cell exposure in pregnancy, and through microchimerism after pregnancy. This results in the generation of paternal-fetal antigen specific memory T cells. Memory T cells have the ability to remember previously encountered antigens to elicit a quicker, more substantial and focused immune response upon antigen reencounter. Such fetal antigen specific memory T cells could be unfavorable in pregnancy as they could potentially drive fetal rejection. However, knowledge on memory T cells in pregnancy has shown that these cells might play a favorable role in fetal-maternal tolerance rather than rejection of the fetus. In recent years, various aspects of immunologic memory in pregnancy have been elucidated and the relevance and working mechanisms of paternal-fetal antigen specific memory T cells in pregnancy have been evaluated. The data indicate that a delicate balance of memory T cells seems necessary for reproductive success and that immunologic memory in reproduction might not be harmful for pregnancy. This review provides an overview of the different memory T cell subtypes and their function in the physiology and in complications of pregnancy. Current findings in the field and possible therapeutic targets are discussed. The findings of our review raise new research questions for further studies regarding the role of memory T cells in immune-associated pregnancy complications. These studies are needed for the identification of possible targets related to memory mechanisms for studies on preventive therapies.

Therapeutic Potential of Regulatory T Cells in Preeclampsia-Opportunities and Challenges

Inflammation is a central feature and is implicated as a causal factor in preeclampsia and other hypertensive disorders of pregnancy. Inflammatory mediators and leukocytes, which are elevated in peripheral blood and gestational tissues, contribute to the uterine vascular anomalies and compromised placental function that characterize particularly the severe, early onset form of disease. Regulatory T (Treg) cells are central mediators of pregnancy tolerance and direct other immune cells to counteract inflammation and promote robust placentation. Treg cells are commonly perturbed in preeclampsia, and there is evidence Treg cell insufficiency predates onset of symptoms. A causal role is implied by mouse studies showing sufficient numbers of functionally competent Treg cells must be present in the uterus from conception, to support maternal vascular adaptation and prevent later placental inflammatory pathology. Treg cells may therefore provide a tractable target for both preventative strategies and treatment interventions in preeclampsia. Steps to boost Treg cell activity require investigation and could be incorporated into pregnancy planning and preconception care. Pharmacological interventions developed to target Treg cells in autoimmune conditions warrant consideration for evaluation, utilizing rigorous clinical trial methodology, and ensuring safety is paramount. Emerging cell therapy tools involving in vitro Treg cell generation and/or expansion may in time become relevant. The success of preventative and therapeutic approaches will depend on resolving several challenges including developing informative diagnostic tests for Treg cell activity applicable before conception or during early pregnancy, selection of relevant patient subgroups, and identification of appropriate windows of gestation for intervention.

Immune responses at the maternal-fetal interface

Pregnancy poses an immunological challenge because a genetically distinct (nonself) fetus must be supported within the pregnant female for the required gestational period. Placentation, or the establishment of the fetally derived placenta, is a common strategy used by eutherian mammals to protect the fetus and promote its growth. However, the substantial morphological differences of the placental architecture among species suggest that the process of placentation results from convergent evolution. Although there are considerable similarities in placental function across placental mammals, there are important differences that arise owing to species-specific immunological (and other biological) constraints. This Review focuses on the immunological similarities and differences that occur at the maternal-fetal interface in the context of human and mouse pregnancies. We discuss how the decidua and placenta of these different species form key immunological barriers that sustain maternal tolerance yet generate innate immune responses that prevent microbial infections.

Inhibitory Receptors and Pathways of Lymphocytes: The Role of PD-1 in Treg Development and Their Involvement in Autoimmunity Onset and Cancer Progression

Regulatory T (Treg) cells represent a subpopulation of suppressor CD4⁺ T cells critically involved in the establishment of peripheral tolerance through the inhibition of effector T (Teff) cells and the suppression of the immune-mediated tissue destruction toward self-antigens. Treg generation, their suppressive properties and also Treg-Teff cell interactions could be modulated at least in part by programmed cell death-1 (PD-1) expression on their surface and through binding between PD-1 and programmed cell death ligand-1 (PD-L1). Defects involving PD-1 and Tregs can lead to the development of pathological conditions, including autoimmune disorders or promote cancer progression by favoring tumor evasion from the host immune response. At the same time, PD-1 and Tregs could represent attractive targets for treatment, as demonstrated by the therapeutic blockade of PD-L1 applied for the management of different cancer conditions in humans. In the present Review, we focus specifically the role of PD-1/PD-L1 on Treg development and activity.

Regulatory T cells in embryo implantation and the immune response to pregnancy

At implantation, the embryo expresses paternally derived alloantigens and evokes inflammation that can threaten reproductive success. To ensure a robust placenta and sustainable pregnancy, an active state of maternal immune tolerance mediated by CD4+ regulatory T cells (Tregs) is essential. Tregs operate to inhibit effector immunity, contain inflammation, and support maternal vascular adaptations, thereby facilitating trophoblast invasion and placental access to the maternal blood supply. Insufficient Treg numbers or inadequate functional competence are implicated in idiopathic infertility and recurrent miscarriage as well as later-onset pregnancy complications stemming from placental insufficiency, including preeclampsia and fetal growth restriction. In this Review, we summarize the mechanisms acting in the conception environment to drive the Treg response and discuss prospects for targeting the T cell compartment to alleviate immune-based reproductive disorders.

Immunological Basis for Recurrent Fetal Loss and Pregnancy Complications

Pregnancy stimulates an elaborate assortment of dynamic changes, allowing intimate approximation of genetically discordant maternal and fetal tissues. Although the cellular and molecular details about how this works remain largely undefined, important clues arise from evaluating how a prior pregnancy influences the outcome of a future pregnancy. The risk of complications is consistently increased when complications occurred in a prior pregnancy. Reciprocally, a prior successful pregnancy protects against complications in a future pregnancy. Here, we summarize immunological perturbations associated with fetal loss, with particular focus on how both harmful and protective adaptations may persist in mothers. Immunological aberrancy as a root cause of pregnancy complications is also considered, given their shared overlapping risk factors and the sustained requirement for averting maternal-fetal conflict throughout pregnancy. Understanding pregnancy-induced immunological changes may expose not only new therapeutic strategies for improving pregnancy outcomes but also new facets of how immune tolerance works that may be applicable to other physiological and pathological contexts.

Elevated percentage of CD3+T cells and pregnancy outcome in women with recurrent pregnancy loss

BACKGROUND

Even though the immune factor is not yet established as a cause of recurrent pregnancy loss (RPL), tons of other studies have shown that a significant proportion of immune abnormalities exist in RPL.

METHODS

We conducted a retrospective cohort study with 850 women who were diagnosed with RPL. The percentages of CD3⁺, CD3⁺CD4⁺ and CD3⁺CD8⁺T cells of each participant, detected by flow cytometry, were obtained before pregnancy and at 6 weeks of gestation as part of their routine medical examination.

RESULTS

Peripheral blood CD3⁺ T cells prior to pregnancy (at baseline), increased significantly in women who had a miscarriage compared with the subsequent live birth group. Moreover, the percentage of CD3⁺ and CD3⁺CD4⁺T cells during pregnancy increased significantly as compared with the baseline level. After adjusting for potential confounders, the multiple regression equation showed that the CD3⁺ T cells <67.84% was associated with the risk of miscarriage (OR 1.05, 95% CI, 1.01 to 1.11, p = .04). Additionally, a nonlinear relationship was observed between the percentage of CD3⁺T cells and the risk of miscarriage.

CONCLUSIONS

The risk of miscarriage increased as the percentage of population with CD3+ value below 67.84% has increased, nevertheless, the miscarriage risk did not increase further when the level of CD3⁺T cells was >67.84%.

Modulatory effect of intravenous immunoglobulin on Th17/Treg cell balance in women with unexplained recurrent spontaneous abortion

Recurrent spontaneous abortion (RSA) is a growing problem worldwide. In a majority of cases, the cause remains unknown but there is increasing evidence that immunologic factors play an important role. Intravenous immunoglobulin (IVIg) therapy has been proposed to have immune modulatory effects and therefore been applicable for the treatment of patients with RSA. Although its efficacy is still controversial, several recent studies suggest that IVIg treatment may improve pregnancy outcomes. CD4⁺ T cells and their related cytokines play an important role in maternal-fetal immune regulation, and an imbalance of Th17/Treg cell ratio has been proposed as a cause for RSA. We review the scientific evidence supporting a modulatory effect of IVIg on Th17/Treg cell balance and discuss the potential mechanisms how IVIg might enhance Treg cells function. We propose that correction of Th17/Treg cell dysregulation could be one of the mechanisms that can explain the positive therapeutic effects of IVIg therapy. Consequently, selecting patients with abnormal Th17/Treg cell ratios could increase the success of IVIg therapy.

Estradiol Attenuates the Severity of Primary Toxoplasma gondii Infection-Induced Adverse Pregnancy Outcomes Through the Regulation of Tregs in a Dose-Dependent Manner

Estradiol (E2) plays a crucial and intricate role during pregnancy to mediate several aspects of the pregnancy process. A perplexing phenomenon in congenital toxoplasmosis is that the severity of Toxoplasma gondii (T. gondii)-mediated adverse pregnancy outcome is closely related with time of primary maternal infection during pregnancy. In this study, the results showed that T. gondii infection in early pregnancy was more likely to induce miscarriage in mice than in late pregnancy, which may be related to inflammation of the maternal–fetal interface. Meanwhile, the T. gondii infection-induced-apoptotic rate of Tregs was higher and the expression of programmed death-1 (PD-1) on Tregs was lower in early pregnancy than in late pregnancy. As the level of E2 in mouse serum gradually increased with the development of pregnancy, we proposed that E2 may contribute to the discrepancy of Tregs at different stages of pregnancy. Thus, we investigated in vitro and in vivo effects of E2 in regulating Tregs. We found that E2 in vitro could protect Tregs against apoptosis and upregulate the expression of PD-1 on Tregs in a dose-dependent manner through ERα. Likewise, the simulated mid-pregnancy level of E2 in nonpregnant mice also alleviated the T. gondii infection-induced apoptosis of Tregs and potentiated the PD-1 expression on Tregs. Therefore, in the pathogenesis of T. gondii-induced abnormal pregnancy, E2 helped maintain the immune balance and improve the pregnancy outcome through regulating Tregs. This finding illustrates the intricate working of hormone–immune system interaction in infection-induced abnormal pregnancy.

Association of genetic variants of PD1 with recurrent pregnancy loss

Purpose

Programmed cell death 1 (PD1) and PD ligand 1 (PDL1) are speculated to have an important role in maintaining a normal pregnancy and there are also a few reports of an association between the single-nucleotide polymorphisms (SNPs) of PD1 or PDL1 and diseases in humans. The association was examined between the polymorphisms of PD1,PDL1,CTLA4 and recurrent pregnancy loss (RPL).

Methods

The study group consisted of 243 women with two or more pregnancy losses and 176 parous women. The frequency of three SNPs of PD1, two of PDL1, and four of CTLA4 were compared between the patients and controls. Next, the subsequent live birth rates in the patients with RPL with and without risk alleles were examined.

Results

Two SNPs (rs36084323 and rs3481962) of PD1 were found to occur at significantly higher frequencies in the patient group than in the control group. The subsequent live birth rate of the patients with vs. without the risk alleles of rs36084323 and rs3481962 were 83.3% vs. 83.3% and 81.6% vs. 84.0%, respectively.

Conclusion

Variations of the PD1 gene were identified as risk factors for RPL. However, the presence or absence of the PD1 risk alleles had no predictive effect on the subsequent pregnancy outcome.

Low-dose lymphocyte immunotherapy rebalances the peripheral blood Th1/Th2/Treg paradigm in patients with unexplained recurrent miscarriage

BACKGROUND

The published results regarding lymphocytes immunotherapy for unexplained recurrent miscarriage (uRM) patients are conflicting due to different screening criteria and therapeutic protocols. The objective of the present study is to evaluate the effectiveness of immunotherapy using low-dose lymphocytes in patients with uRM and Th1/Th2/Treg paradigm disorders.

METHODS

Sixty-four uRM patients who received low-dose lymphocytes immunotherapy served as the immunotherapy group, while the other 35 women who did not receive the treatment served as the control group. The proportions of peripheral blood Th1 cells, Th2 cells and Treg cells; and the concentration of TGF-β1 in serum were detected by flow cytometry and enzyme-linked immunosorbent assay (ELISA), respectively, before and after the immunotherapy.

RESULTS

The proportion of Th1 cells was significantly decreased while the proportions of Th2 cells and Treg cells were significantly increased in immunotherapy group patients after treatment. In addition, the concentration of TGF-β1 in serum was significantly higher after immunotherapy than before. Forty-three uRM patients achieved pregnancy after receiving immunotherapy and 5 patients underwent miscarriages in the immunotherapy group (11.6%, 5/43), while 8 of the 23 pregnant patients experienced a miscarriage in the control group (34.8%, 8/23; p < 0.05).

CONCLUSIONS

Low-dose lymphocyte immunotherapy is beneficial for restoring balance in the Th1/Th2/Treg paradigm and improving pregnancy outcome in uRM patients.

TRIAL REGISTRATION

NCT03081325 . ClinicalTrials.gov . Retrospectively registered July 2015.

Correlation between unexplained recurrent spontaneous abortion with CD4+CD25+ regulatory T-cell and killer cell immunoglobulin-like receptor levels

The present study investigated the correlation between unexplained recurrent spontaneous abortion (URSA) with CD4+CD25+ regulatory T-cell (Treg) and killer cell immunoglobulin-like receptor (KIR)-2DL1 levels. A total of 76 URSA patients were enrolled (35 without pregnancy, Group A, and 41 with early abortion, Group B). Additionally, 30 patients who received a regular abortion as planned (Group C) and 30 healthy volunteers (Group D) were selected. Peripheral venous blood and fresh decidual tissue samples were obtained from all the patients, and flow cytometry was performed to detect CD4+CD25+Treg and Foxp3 transcription factor levels. mRNA and protein KIR-2DL1 expression levels were assayed using quantitative PCR and western blot analysis, respectively. No statistically significant differences in peripheral venous blood CD4+CD25+Treg/CD4+ and Foxp3+/CD4+CD25+Treg cell proportions were found among the groups (P>0.05). However, the decidual tissues of Group C presented significantly higher levels of both cell types versus other groups (P<0.05). No statistically significant differences were found in comparisons among Groups A, B, and D (P>0.05). In peripheral venous blood, mRNA and protein KIR-2DL1 expression levels in Group C were significantly higher than those in the other three groups (P<0.05), but again, there were no statistically significant differences among Groups A, B, and D (P>0.05). In decidual tissues, KIR-2DL1 levels were significantly higher in Group C relative to Groups A, B, and D (P<0.05). Decreased CD4+CD25+Treg counts and KIR-2DL1 expression levels were closely associated with the onset of URSA. CD4+CD25+Tregs mainly exert their effects on decidual tissues, while KIR-2DL1 can act on peripheral venous blood and decidual tissues. These may present new targets for early intervention in URSA.

Old game, new players: Linking classical theories to new trends in transplant immunology

The evolutionary emergence of an efficient immune system has a fundamental role in our survival against pathogenic attacks. Nevertheless, this same protective mechanism may also establish a negative consequence in the setting of disorders such as autoimmunity and transplant rejection. In light of the latter, although research has long uncovered main concepts of allogeneic recognition, immune rejection is still the main obstacle to long-term graft survival. Therefore, in order to define effective therapies that prolong graft viability, it is essential that we understand the underlying mediators and mechanisms that participate in transplant rejection. This multifaceted process is characterized by diverse cellular and humoral participants with innate and adaptive functions that can determine the type of rejection or promote graft acceptance. Although a number of mediators of graft recognition have been described in traditional immunology, recent studies indicate that defining rigid roles for certain immune cells and factors may be more complicated than originally conceived. Current research has also targeted specific cells and drugs that regulate immune activation and induce tolerance. This review will give a broad view of the most recent understanding of the allogeneic inflammatory/tolerogenic response and current insights into cellular and drug therapies that modulate immune activation that may prove to be useful in the induction of tolerance in the clinical setting.

Immune regulatory network in successful pregnancy and reproductive failures

Maternal immune system must tolerate semiallogenic fetus to establish and maintain a successful pregnancy. Despite the existence of several strategies of trophoblast to avoid recognition by maternal leukocytes, maternal immune system may react against paternal alloantigenes. Leukocytes are important components in decidua. Not only T helper (Th)1/Th2 balance, but also regulatory T (Treg) cells play an important role in pregnancy. Although the frequency of Tregs is elevated during normal pregnancies, their frequency and function are reduced in reproductive defects such as recurrent miscarriage and preeclampsia. Tregs are not the sole population of suppressive cells in the decidua. It has recently been shown that regulatory B10 (Breg) cells participate in pregnancy through secretion of IL-10 cytokine. Myeloid derived suppressor cells (MDSCs) are immature developing precursors of innate myeloid cells that are increased in pregnant women, implying their possible function in pregnancy. Natural killer T (NKT) cells are also detected in mouse and human decidua. They can also affect the fetomaternal tolerance. In this review, we will discuss on the role of different immune regulatory cells including Treg, γd T cell, Breg, MDSC, and NKT cells in pregnancy outcome.

Human monocytes undergo functional re-programming during differentiation to dendritic cell mediated by human extravillous trophoblasts

Maternal immune adaptation is required for a successful pregnancy to avoid rejection of the fetal–placental unit. Dendritic cells within the decidual microenvironment lock in a tolerogenic profile. However, how these tolerogenic DCs are induced and the underlying mechanisms are largely unknown. In this study, we show that human extravillous trophoblasts redirect the monocyte-to-DC transition and induce regulatory dendritic cells. DCs differentiated from blood monocytes in the presence of human extravillous trophoblast cell line HTR-8/SVneo displayed a DC-SIGN⁺CD14⁺CD1a⁻ phenotype, similar with decidual DCs. HTR8-conditioned DCs were unable to develop a fully mature phenotype in response to LPS, and altered the cytokine secretory profile significantly. Functionally, conditioned DCs poorly induced the proliferation and activation of allogeneic T cells, whereas promoted CD4⁺CD25⁺Foxp3⁺ Treg cells generation. Furthermore, the supernatant from DC and HTR-8/SVneo coculture system contained significant high amount of M-CSF and MCP-1. Using neutralizing antibodies, we discussed the role of M-CSF and MCP-1 during monocyte-to-DCs differentiation mediated by extravillous trophoblasts. Our data indicate that human extravillous trophoblasts play an important role in modulating the monocyte-to-DC differentiation through M-CSF and MCP-1, which facilitate the establishment of a tolerogenic microenvironment at the maternal–fetal interface.

What is wrong with the regulatory T cells and foetomaternal tolerance in women with recurrent miscarriages?

Couples of whom the woman has had a miscarriage have two major concerns: the cause and possible risk of recurrence. Unfortunately, a significant proportion of cases of recurrent miscarriage (RM) remain unexplained despite detailed investigation. Because data suggest that regulatory T cells (Treg) are involved in the maternal acceptance of the allogeneic foetus, RM could possibly be explained by a disturbance of the Treg network. The possible role of Tregs in RM is described in this review, as well as their potential application in diagnostics and therapeutic intervention trials.

Differentiation of ICOS+ and ICOS- recent thymic emigrant regulatory T cells (RTE T regs) during normal pregnancy, pre-eclampsia and HELLP syndrome

Two different subsets of naturally occurring regulatory T cells (nTregs), defined by their expression of the inducible co-stimulatory (ICOS) molecule, are produced by the human thymus. To examine the differentiation of ICOS(+) and ICOS(-) CD45RA(+) CD31(+) recent thymic emigrant (RTE) T regs during normal pregnancy and in the presence of pre-eclampsia or haemolysis elevated liver enzymes low platelet (HELLP)-syndrome, we used six-colour flow cytometric analysis to determine the changes in the composition of the ICOS(+) and ICOS(-) T reg pools with CD45RA(+) CD31(+) RTE T regs, CD45RA(+) CD31(-) mature naive (MN) T regs, CD45RA(-) CD31(+) and CD45RA(-) CD31(-) memory Tregs. With the beginning of pregnancy until term, we observed a strong differentiation of both ICOS(+) and ICOS(-) CD45RA(+) CD31(+) RTE, but not CD45RA(+) CD31(-) MN T regs, into CD45RA(-) CD31(-) memory T regs. At the end of pregnancy, the onset of spontaneous term labour was associated with a significant breakdown of ICOS(+) CD45RA(-) CD31(-) memory T regs. However, in the presence of pre-eclampsia, there was a significantly increased differentiation of ICOS(+) and ICOS(-) CD45RA(+) CD31(+) RTE T regs into CD45RA(-) CD31(+) memory T regs, wherein the lacking differentiation into CD45RA(-) CD31(-) memory T regs was partially replaced by the increased differentiation of ICOS(+) and ICOS(-) CD45RA(+) CD31(-) MN Tregs into CD45RA(-) CD31(-) memory T regs. In patients with HELLP syndrome, this alternatively increased differentiation of CD45RA(-) CD31(-) MN T regs seemed to be exaggerated, and presumably restored the suppressive activity of magnetically isolated ICOS(+) and ICOS(-) T regs, which were shown to be significantly less suppressive in pre-eclampsia patients, but not in HELLP syndrome patients. Hence, our findings propose that the regular differentiation of both ICOS(+) and ICOS(-) CD45RA(+) CD31(+) RTE T regs ensures a healthy pregnancy course, while their disturbed differentiation is associated with the occurrence of pre-eclampsia and HELLP syndrome.