Maternal activating KIRs protect against human reproductive failure mediated by fetal HLA-C2

Subcutaneous G-CSF administration improves IVF outcomes in patients with recurrent implantation failure presenting a KIR/HLA-C mismatch

RESEARCH QUESTION

Despite advances in assisted reproductive technologies, many blastocysts are lost unexpectedly during implantation. Alterations in maternal immune tolerance towards fetal antigens may contribute to adverse IVF outcomes. The purpose of this study is to evaluate whether administering Granulocyte Colony-Stimulating Factor (G-CSF) to couples with a Human Leukocyte Antigen/Killer-Cell Immunoglobulin-Like Receptor (HLA/KIR) mismatch could positively modulate the implantation process in patients with recurrent implantation failure (RIF). A KIR/HLA-C mismatch occurs when the interaction between KIRs and HLA-C causes an inhibition of NK cells, which may result in reduced G-CSF secretion leading to impaired placentation and increased risk of miscarriage, pre-eclampsia and fetal growth restriction.

DESIGN

A retrospective monocentric cohort study conducted at the IVI Clinic in Rome, including women with a history of at least two failed blastocyst transfers. Couples underwent KIR and HLA-C testing. Couples with a KIR/HLA-C mismatch received G-CSF subcutaneously up to week nine of gestation. The mismatch included cases with inhibitory KIR genotypes and HLA-C2C2 females with HLA-C1C1, or C1C2 males or HLA-C1C2 females with male HLA-C2C2. The reproductive outcomes were assessed, and the logistic regression models controlled for potential confounders affecting IVF outcomes.

RESULTS

79 patients with RIF and a KIR/HLA-C mismatch were included in the study. 30 patients were administered G-CSF, and 49 received no treatment. In the univariate analysis, no statistically significant differences were reported in the reproductive outcomes after IVF between the women treated with G-CSF and the control group. However, the logistic regression analysis that controlled for confounding factors showed that patients treated with subcutaneous G-CSF had statistically significant higher ongoing-pregnancy (aOR=3.808) and live-birth (aOR=4.998) rates, and a lower miscarriage rate (aOR=0.057). No statistically significant differences were found in other reproductive outcomes.

CONCLUSION

The use of subcutaneous G-CSF in patients with a KIR/HLA-C mismatch undergoing IVF may reduce miscarriage and improve live-birth rates. G-CSF may modulate NK-mediated immune mechanisms and improve trophoblast invasion and development. Randomized trials are warranted to validate these findings and enhance the chances of successful pregnancies in couples with an immunological mismatch.

High Resolution HLA-A, HLA-B, and HLA-C Allele Frequencies in Romanian Hematopoietic Stem Cell Donors

The HLA genes are associated with various autoimmune pathologies, with the control of the immune response also being significant in organs and cells transplantation. The aim of the study is to identify the HLA-A, HLA-B, and HLA-C alleles frequencies in the analyzed Romanian cohort. We performed HLA typing using next-generation sequencing (NGS) in a Romanian cohort to estimate class I HLA allele frequencies up to a six-digit resolution. A total of 420 voluntary donors from the National Registry of Voluntary Hematopoietic Stem Cell Donors (RNDVCSH) were included in the study for HLA genotyping. Peripheral blood samples were taken and brought to the Fundeni Clinical Institute during 2020-2021. HLA genotyping was performed using the Immucor Mia Fora NGS MFlex kit. A total of 109 different alleles were detected in 420 analyzed samples, out of which 31 were for HLA-A, 49 for HLA-B, and 29 for HLA-C. The most frequent HLA-A alleles were HLA-A*02:01:01 (26.11%), HLA-A*01:01:01 (12.5%), HLA-A*24:02:01 (11.67%), HLA-A*03:01:01 (9.72%), HLA-A*11:01:01, and HLA-A*32:01:01 (each with 8.6%). For the HLA-B locus, the most frequent allele was HLA-B*18:01:01 (11.25%), followed by HLA-B*51:01:01 (10.83%) and HLA-B*08:01:01 (7.78%). The most common HLA-C alleles were HLA-C*07:01:01 (17.36%), HLA-C*04:01:01 (13.47%), and HLA-C*12:03:01 (10.69%). Follow-up studies are ongoing for confirming the detected results.

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.

Multi-Layered Mechanisms of Immunological Tolerance at the Maternal-Fetal Interface

Pregnancy represents an immunological paradox where the maternal immune system must tolerate the semi-allogeneic fetus expressing paternally-derived Ags. Accumulating evidence over decades has revealed that successful pregnancy requires the active development of robust immune tolerance mechanisms. This review outlines the multi-layered processes that establish fetomaternal tolerance, including the physical barrier of the placenta, restricted chemokine-mediated leukocyte trafficking, lack of sufficient alloantigen presentation, the presence of immunosuppressive regulatory T cells and tolerogenic decidual natural killer cells, expression of immune checkpoint molecules, specific glycosylation patterns conferring immune evasion, and unique metabolic/hormonal modulations. Interestingly, many of the strategies that enable fetal tolerance parallel those employed by cancer cells to promote angiogenesis, invasion, and immune escape. As such, further elucidating the mechanistic underpinnings of fetal-maternal tolerance may reciprocally provide insights into developing novel cancer immunotherapies as well as understanding the pathogenesis of gestational complications linked to dysregulated tolerance processes.

Common and rare genetic variants predisposing females to unexplained recurrent pregnancy loss

Recurrent pregnancy loss (RPL) is a major reproductive health issue with multifactorial causes, affecting 2.6% of all pregnancies worldwide. Nearly half of the RPL cases lack clinically identifiable causes (e.g., antiphospholipid syndrome, uterine anomalies, and parental chromosomal abnormalities), referred to as unexplained RPL (uRPL). Here, we perform a genome-wide association study focusing on uRPL in 1,728 cases and 24,315 female controls of Japanese ancestry. We detect significant associations in the major histocompatibility complex (MHC) region at 6p21 (lead variant=rs9263738; P = 1.4 × 10-10; odds ratio [OR] = 1.51 [95% CI: 1.33-1.72]; risk allele frequency = 0.871). The MHC associations are fine-mapped to the classical HLA alleles, HLA-C*12:02, HLA-B*52:01, and HLA-DRB1*15:02 (P = 1.1 × 10-10, 1.5 × 10-10, and 1.2 × 10-9, respectively), which constitute a population-specific common long-range haplotype with a protective effect (P = 2.8 × 10-10; OR = 0.65 [95% CI: 0.57-0.75]; haplotype frequency=0.108). Genome-wide copy-number variation (CNV) calling demonstrates rare predicted loss-of-function (pLoF) variants of the cadherin-11 gene (CDH11) conferring the risk of uRPL (P = 1.3 × 10-4; OR = 3.29 [95% CI: 1.78-5.76]). Our study highlights the importance of reproductive immunology and rare variants in the uRPL etiology.

Australasian recurrent pregnancy loss clinical management guideline 2024, part II

Part II of the Australasian guideline for the investigation and management of recurrent pregnancy loss (RPL) provides evidence-based guidance on the management of RPL provided. The implications of inherited and acquired thrombophilia with respect to RPL and suggestions for clinical management are provided. Autoimmune factors, including human leukocyte antigen, cytokines, antinuclear antibodies and coeliac antibodies, and guidance for management are discussed. Infective, inflammatory and endometrial causes of RPL are discussed in detail. Environmental and lifestyle factors, male factor and unexplained causes are outlined. Levels of evidence and grades of consensus are provided for all evidence-based statements.

Small RNAs in the pathogenesis of preeclampsia

Preeclampsia is a major contributor to maternal and fetal morbidity and mortality. The disorder can be classified into early- and late-onset subtypes, both of which evolve in two stages. The first stage comprises the development of pre-clinical, utero-placental malperfusion. Early and late utero-placental malperfusion have different causes and time courses. Early-onset preeclampsia (20 % of cases) is driven by dysfunctional placentation in the first half of pregnancy. In late-onset preeclampsia (80 % of cases), malperfusion is a consequence of placental compression within the confines of a limited uterine cavity. In both subtypes, the malperfused placenta releases stress signals into the maternal circulation. These stress signals trigger onset of the clinical syndrome (the second stage). Small RNA molecules, which are implicated in cellular stress responses in general, may be involved at different stages. Micro RNAs contribute to abnormal trophoblast invasion, immune dysregulation, angiogenic imbalance, and syncytiotrophoblast-derived extracellular vesicle signalling in preeclampsia. Transfer RNA fragments are placental signals known to be specifically involved in cell stress responses. Disorder-specific differences in small nucleolar RNAs and piwi-interacting RNAs have also been reported. Here, we summarise key small RNA advances in preeclampsia pathogenesis. We propose that existing small RNA classifications are unhelpful and that non-biased assessment of RNA expression, incorporation of non-annotated molecules and consideration of chemical modifications to RNAs may be important in elucidating preeclampsia pathogenesis.

Unveiling the Significance of HLA and KIR Diversity in Underrepresented Populations

Human leukocyte antigen (HLA) molecules and their relationships with natural killer (NK) cells, specifically through their interaction with killer-cell immunoglobulin-like receptors (KIRs), exhibit robust associations with the outcomes of diverse diseases. Moreover, genetic variations in HLA and KIR immune system genes offer limitless depths of complexity. In recent years, a surge of high-powered genome-wide association studies (GWASs) utilizing single nucleotide polymorphism (SNP) arrays has occurred, significantly advancing our understanding of disease pathogenesis. Additionally, advances in HLA reference panels have enabled higher resolution and more reliable imputation, allowing for finer-grained evaluation of the association between sequence variations and disease risk. However, it is essential to note that the majority of these GWASs have focused primarily on populations of Caucasian and Asian origins, neglecting underrepresented populations in Latin America and Africa. This omission not only leads to disparities in health care access but also restricts our knowledge of novel genetic variants involved in disease pathogenesis within these overlooked populations. Since the KIR and HLA haplotypes prevalent in each population are clearly modelled by the specific environment, the aim of this review is to encourage studies investigating HLA/KIR involvement in infection and autoimmune diseases, reproduction, and transplantation in underrepresented populations.

Immunomodulatory Treatment Impact on IVF Outcomes in KIR AA Genotype: Personalized Fertility Insights

Background and Objectives: Recurrent implantation failure (RIF) affects 10% of couples undergoing in vitro fertilization (IVF), spurring exploration into tailored treatments to enhance implantation rates. Maternal immune tolerance towards embryos, particularly killer-cell immunoglobulin-like receptors (KIRs) on natural killer (NK) cells, is a focal point in RIF research. Materials and Methods: This retrospective cohort study, conducted at fertility clinic in Oradea, Romania, involved 65 infertile couples undergoing IVF treatment between January 2022 and December 2023. Couples were divided into two groups: KIR AA (Group A) and KIR Bx (Group B). Results: Factors such as age, type of infertility, oocytes retrieved, embryos produced, pregnancy rates in Group A without and with immunomodulatory treatment were documented. Group A, receiving immunomodulatory treatment, achieved a pregnancy rate of 47.8%, significantly higher than the 23.73% rate without treatment (p = 0.008). Group B had a higher mean patient age than Group A. However, miscarriage rates did not significantly differ between Group A with treatment and Group B (p = 0.2457), suggesting comparable outcomes with immunomodulation. Conclusions: The impact of immunological factors on recurrent implantation failure is being more and more emphasized and warrants the attention of specialists in human reproduction. Uterine natural killers and their function though KIR receptors deserve particular attention as immunomodulatory treatment may improve pregnancy rates in patients with KIR AA haplotype.

Complete Genomic Assembly of Mauritian Cynomolgus Macaque Killer Ig-like Receptor and Natural Killer Group 2 Haplotypes

Mauritian-origin cynomolgus macaques (MCMs) serve as a powerful nonhuman primate model in biomedical research due to their unique genetic homogeneity, which simplifies experimental designs. Despite their extensive use, a comprehensive understanding of crucial immune-regulating gene families, particularly killer Ig-like receptors (KIR) and NK group 2 (NKG2), has been hindered by the lack of detailed genomic reference assemblies. In this study, we employ advanced long-read sequencing techniques to completely assemble eight KIR and seven NKG2 genomic haplotypes, providing an extensive insight into the structural and allelic diversity of these immunoregulatory gene clusters. Leveraging these genomic resources, we prototype a strategy for genotyping KIR and NKG2 using short-read, whole-exome capture data, illustrating the potential for cost-effective multilocus genotyping at colony scale. These results mark a significant enhancement for biomedical research in MCMs and underscore the feasibility of broad-scale genetic investigations.

Preeclampsia epidemiology(ies) and pathophysiology(ies)

Preeclampsia/eclampsia was first described 2000 years ago. Concepts guiding diagnosis have changed over time making longitudinal studies challenging. Similarly, concepts of pathophysiology have evolved from eclampsia as a pregnancy seizure disorder to preeclampsia as a hypertensive and renal disorder to our current concept of a preeclampsia as a pregnancy specific, multisystemic inflammatory disorder. Although preeclampsia is pregnancy specific and many pathophysiologic findings begin to resolve with delivery, its impact extends beyond pregnancy. The risk of cardiovascular and neurological disease is increased after pregnancy in women who have had preeclampsia. The disorder is not a disease, but a syndrome and emerging data indicate multiple pathways to the syndrome. It is likely that our failure to have a major impact on prediction and prevention despite a large increase in understanding is due to the existence of multiple subtypes of preeclampsia. This concept should guide future research.

Pre-eclampsia: Re-visiting pathophysiology, role of immune cells, biomarker identification and recent advances in its management

Pre-eclampsia (PE) is a hypertension condition that occurs exclusively during pregnancy and has the potential to impact nearly all organ systems. It is estimated to complicate approximately 2-8% of pregnancies worldwide. PE is a prominent medical disorder that poses a significant risk to pregnant mothers and their infants. This review commences by giving the most up-to- date concepts about the pathophysiology of PE. The condition involves atypical infiltration of trophoblast cells into the spiral arteries of the decidua and myometrium, resulting in an insufficient establishment of proper blood flow between the uterus and placenta. The aberrant activation of natural killer (NK) cells in both the peripheral blood and the decidua has been identified as one of the contributing factors to the development of PE. The strong evidence for the genetic etiology of PE is provided by the association between maternal killer cell immunoglobulin-like receptor (KIR) and Human Leukocyte Antigen (HLA-C) in trophoblast cells. Recent observations provide evidence that changes in the expression of anti-angiogenic factors in the placenta are the underlying cause of the clinical symptoms associated with the condition. This review also provides a comprehensive overview of the latest advancements in understanding the underlying causes of PE. It specifically highlights the emergence of new diagnostic biomarkers and their potential implications for therapeutic interventions in managing this medical condition.

HLA allele frequency of HLA-A, -B, -C, -DRB1 and -DQB1 in Indian recurrent implantation failure and recurrent pregnancy loss couples - A retrospective study

The maternal-fetal interaction has been hypothesized to involve the human leucocyte antigen (HLA). It has been suggested that excessive HLA antigen sharing between spouses is a mechanism causing maternal hyporesponsiveness to paternal antigens encountered during pregnancy and thus leading to a miscarriage. Participants in this retrospective study are RIF and RPL couples who visited Gunasheela Surgical and Maternity Hospital, Bangalore, India from November 2019 to September 2022. A total of 40 couples with RIF and 195 couples with RPL are included in the study. We observed that the DQB1*02:01:01 allele is associated with an increase in risk of both RIF and RPL, while the C*12:02:01 allele increases risk of only RPL. On the contrary, DQB1*02:02:01 and DQB1*06:03 alleles appear to be protective against both RPL and RIF. In addition, the C*07:02:01 allele was observed to be protective against RPL. In conclusion, C*12:02:01 and DQB1*02:01:01 could play a major role in RPL which is consistent with other studies, while DQB1*02:01:01 is the risk allele in our RIF group. The protective alleles C*07:02:01 in the RPL group, DQB1*02:02:01, and DQB1*06:03 in both RIF and RPL, were discovered for the first time. Allele frequencies will vary in population-based studies depending on the ethnicities of the cohort. Meta-analysis and antibody testing will provide additional insights on whether and how this data can be adopted into clinical practices.

Bibliometric analysis of the global trends in immune-related recurrent pregnancy loss research over the last two decades

PROBLEM

A comprehensive analysis was conducted to explore the scientific output on immune-related recurrent pregnancy loss (RPL) and its key aspects. Despite the lack of clear explanations for most RPL cases, immune factors were found to play a significant role.

METHOD OF STUDY

The study utilized a bibliometric approach, searching the Web of Science Core Collection database for relevant literature published between 2004 and 2023.

RESULTS

The collected dataset consisted of 2228 articles and reviews, revealing a consistent increase in publications and citations over the past two decades. The analysis identified the United States and China as the most productive countries in terms of RPL research. Among the institutions, Fudan University in China emerged as the top contributor, followed by Shanghai Jiaotong University. Kwak-kim J was the most prolific author, while Christiansen Ob had the highest number of co-citations. The top 25 co-cited references on diagnosis, treatment, and mechanisms formed the foundation of knowledge in this field. By examining keyword co-occurrence and co-citations, the study found that antiphospholipid syndrome and natural killer cells were the primary areas of focus in immune-related RPL research. Additionally, three emerging hotspots were identified: chronic endometritis, inflammation, and decidual macrophages. These aspects demonstrated increasing interest and research activity within the field of immune-related RPL.

CONCLUSIONS

Overall, this comprehensive bibliometric analysis provided valuable insights into the patterns, frontiers, and focal points of global scientific output related to immune-related RPL.

Maternal-Fetal Compatibility in Recurrent Pregnancy Loss

Nowadays, recurrent pregnancy loss (RPL) is an undesirable condition suffered by many patients of reproductive age. In this scenario, certain immune cell populations and molecules, involved in maternal-fetal compatibility, have emerged as factors related with the pathogenesis of RPL. Among them, uterine Natural Killer cells (uNKs) appear to be of great relevance. These cells are involved in numerous processes during pregnancy, such as the remodeling of uterine spiral arteries or the control of trophoblast invasion. These functions are regulated by the interactions that these cells establish with the extravillous trophoblast, mainly through their Killer Immunoglobulin-like Receptors (KIRs) and the Human Leukocyte Antigen-C (HLA-C) molecules expressed by the embryo. A high level of polymorphism has been reported for both molecules involved in this interaction, with some of the possible KIR-HLA-C combinations being associated with an increased risk of RPL. However, the complexity of the maternal-fetal interface goes beyond this, as other HLA molecules also appear to be related to this reproductive pathology. In this review, we will discuss the role of uNKs in pregnancy, as well as the polymorphisms and clinical implications of KIR-HLA-C binding. We will also address the involvement of other, different HLA molecules in RPL, and the current advice on the appropriate management of patients with 'immunological mismatch', thus covering the main aspects regarding the involvement of maternal-fetal compatibility in RPL.

HLA-G isoforms, HLA-C allotype and their expressions differ between early abortus and placenta in relation to spontaneous abortions

INTRODUCTION

Spontaneous abortion (SAB) affects approximately 10% of clinically recognized pregnancies. Fetal trophobalst invasion and remodeling of maternal spiral arteries is reported to be dependent on crosstalk between HLA-C/HLA-G expressed on extra villous trophoblast (EVTs)and Killer cell Immunoglobin like receptors (KIRs) of decidual NK (dNK). Immune dysfunction in decidua contributes to early miscarriage.

METHODOLOGY

The study used mother neonate paired cord blood and term placenta samples (n = 46), elective abortus (n = 17,gestational age = 10-12 weeks of pregnancy) and SAB abortus (n = 24, gestational age = 12-15 weeks of pregnancy) for HLA-G, KIR2D and HLA-C. In addition, term placenta was collected from women with history of spontaneous pregnancy loss (n = 24) and women with history of live birth (n = 32). SSP-PCR was used for genotyping, RT-PCR for gene expression, copy number variation (CNVs) and HLA-C allotyping and ELISA for protein expression studies.

RESULTS

Membrane bound HLA-G4 isoform proportion was higher 39.28%, p = 0.02) in term placenta. SAB abortus had higher proportion of HLA-G3 (50%),while elective abortus exhibited higher proportion of soluble isoforms (HLA-G5, = 5.9, HLA-G6 = 5.9%, HLA-G7 = 11.8%). Higher inhibitory KIR2DL1 content and copy numbers with lower HLA-C2 in SAB contrasted with higher copy numbers of KIR2DS1(p = 0.001), KIR2DS1+/2DL1+- HLA-C2 combined genotype in healthy placenta. Elevated KIR2D protein levels (p = 0.001), and concurrently, HLA-C levels were upregulated in healthy placenta.

CONCLUSION

Our data supports lower cognate receptor ligand KIR2DS1+/2DL1+ HLA-C2 together with predominance of HLA-G3 isoform in SAB as confounding factors in spontaneous pregnancy loss. HLA-G isoforms and expression differed between first trimester abortus and term placenta suggesting temporal modulation and marks novelty of the study.

NK cell receptor profiling of endometrial and decidual NK cells reveals pregnancy-induced adaptations

Natural killer (NK) cells, with a unique NK cell receptor phenotype, are abundantly present in the non-pregnant (endometrium) and pregnant (decidua) humanuterine mucosa. It is hypothesized that NK cells in the endometrium are precursors for decidual NK cells present during pregnancy. Microenvironmental changes can alter the phenotype of NK cells, but it is unclear whether decidual NK cell precursors in the endometrium alter their NK cell receptor repertoire under the influence of pregnancy. To examine whether decidual NK cell precursors reveal phenotypic modifications upon pregnancy, we immunophenotyped the NK cell receptor repertoire of both endometrial and early-pregnancy decidual NK cells using flow cytometry. We showed that NK cells in pre-pregnancy endometrium have a different phenotypic composition compared to NK cells in early-pregnancy decidua. The frequency of killer-immunoglobulin-like receptor (KIR expressing NK cells, especially KIR2DS1, KIR2DL2L3S2, and KIR2DL2S2 was significantly lower in decidua, while the frequency of NK cells expressing activating receptors NKG2D, NKp30, NKp46, and CD244 was significantly higher compared to endometrium. Furthermore, co-expression patterns showed a lower frequency of NK cells co-expressing KIR3DL1S1 and KIR2DL2L3S2 in decidua. Our results provide new insights into the adaptations in NK cell receptor repertoire composition that NK cells in the uterine mucosa undergo upon pregnancy.

Centromeric AA motif in KIR as an optimal surrogate marker for precision definition of alloimmune reproductive failure

Throughout pregnancy, the decidua is predominantly populated by NK lymphocytes expressing Killer immunoglobulin-like receptors (KIR) that recognize human leukocyte antigen-C (HLA-C) ligands from trophoblast cells. This study aims to investigate the association of KIR-HLA-C phenotypes in couples facing infertility, particularly recurrent pregnancy loss (RPL) and recurrent implantation failure (RIF), in comparison to a reference population and fertile controls. This observational, non-interventional retrospective case-control study included patients consecutively referred to our Reproductive Immunology Unit from 2015 to 2019. We analyzed the frequencies of KIR and HLA-C genes. As control groups, we analyzed a reference Spanish population for KIR analysis and 29 fertile controls and their male partners for KIR and HLA-C combinations. We studied 397 consecutively referred women with infertility and their male partners. Among women with unexplained RPL (133 women) and RIF (176 women), the centromeric (cen)AA KIR genotype was significantly more prevalent compared to the reference Spanish population (p = 0.001 and 0.02, respectively). Furthermore, cenAA was associated with a 1.51-fold risk of RPL and a 1.2-fold risk of RIF. Conversely, the presence of BB KIR showed a lower risk of reproductive failure compared to non-BB KIR (OR: 0.12, p < 0.001). Women and their partners with HLA-C1C1/C1C1 were significantly less common in the RPL-Group (p < 0.001) and RIF-Group (p = 0.002) compared to the control group. Moreover, the combination of cenAA/C1C1 in women with C1C1 partners was significantly higher in the control group than in the RPL (p = 0.009) and RIF (p = 0.04) groups, associated with a 5-fold increase in successful pregnancy outcomes. In our cohort, the cenAA KIR haplotype proved to be a more accurate biomarker than the classic AA KIR haplotype for assessing the risk of RPL and RIF, and might be particularly useful to identify women at increased risk among the heterogeneous KIR AB or Bx population. The classification of centromeric KIR haplotypes outperforms classical KIR haplotypes, making it a better indicator of potential maternal-fetal KIR-HLA-C mismatch in patients.

Human uterine natural killer cells regulate differentiation of extravillous trophoblast early in pregnancy

In humans, balanced invasion of trophoblast cells into the uterine mucosa, the decidua, is critical for successful pregnancy. Evidence suggests that this process is regulated by uterine natural killer (uNK) cells, but how they influence reproductive outcomes is unclear. Here, we used our trophoblast organoids and primary tissue samples to determine how uNK cells affect placentation. By locating potential interaction axes between trophoblast and uNK cells using single-cell transcriptomics and in vitro modeling of these interactions in organoids, we identify a uNK cell-derived cytokine signal that promotes trophoblast differentiation at the late stage of the invasive pathway. Moreover, it affects transcriptional programs involved in regulating blood flow, nutrients, and inflammatory and adaptive immune responses, as well as gene signatures associated with disorders of pregnancy such as pre-eclampsia. Our findings suggest mechanisms on how optimal immunological interactions between uNK cells and trophoblast enhance reproductive success.

Methods for Co-culture of Primary Human Extravillous Trophoblast Cells and Uterine Natural Killer Cells

During early pregnancy, fetal-derived extravillous trophoblast cells (EVT) from the placenta invade the maternal decidua and inner third of the uterus where they establish fetal tolerance and remodel the uterine spiral arteries, which ensures establishment of a successful pregnancy. Aberrant EVT invasion and spiral artery remodeling is associated with a number of pregnancy complications including miscarriage, preeclampsia, fetal growth restriction, and placenta accrete. During invasion of the maternal tissues, the EVT interact with a number of different cell types including the decidual leukocytes. EVT express HLA-C, HLA-G, HLA-E, and HLA-F and interact with uterine natural killer (uNK) cells through a series of different receptors. Epidemiological evidence suggests that different combinations of HLA-C and killer cell Ig-like receptor (KIR) haplotypes impact pregnancy success. Therefore, there is much interest in the functional consequence of interactions between EVT and uNK cells, and several different methodologies have been used to isolate these different cell types and their co-culture.

Exceptional diversity of KIR and HLA class I in Egypt

Genetically determined variation of killer cell immunoglobulin like receptors (KIR) and their HLA class I ligands affects multiple aspects of human health. Their extreme diversity is generated through complex interplay of natural selection for pathogen resistance and reproductive health, combined with demographic structure and dispersal. Despite significant importance to multiple health conditions of differential effect across populations, the nature and extent of immunogenetic diversity is under-studied for many geographic regions. Here, we describe the first high-resolution analysis of KIR and HLA class I combinatorial diversity in Northern Africa. Analysis of 125 healthy unrelated individuals from Cairo in Egypt yielded 186 KIR alleles arranged in 146 distinct centromeric and 79 distinct telomeric haplotypes. The most frequent haplotypes observed were KIR-A, encoding two inhibitory receptors specific for HLA-C, two that are specific for HLA-A and -B, and no activating receptors. Together with 141 alleles of HLA class I, 75 of which encode a KIR ligand, we identified a mean of six distinct interacting pairs of inhibitory KIR and HLA allotypes per individual. We additionally characterize 16 KIR alleles newly identified in the study population. Our findings place Egyptians as one of the most highly diverse populations worldwide, with important implications for transplant matching and studies of immune-mediated diseases.

Roles of immune microenvironment in the female reproductive maintenance and regulation: novel insights into the crosstalk of immune cells

Female fertility decline is an accumulative consequence caused by complex factors, among them, the disruption of the immune profile in female reproduction stands out as a crucial contributor. Presently, the effects of immune microenvironment (IME) on the female reproductive process have attracted increasing attentions for their dynamic but precisive roles. Immunocytes including macrophages, dendritic cells, T cells, B cells and neutrophils, with diverse subpopulations as well as high plasticity functioned dynamically in the process of female reproduction through indirect intercellular communication via specific cytokine release transduced by molecular signal networks or direct cell-cell contact to maintain the stability of the reproductive process have been unveiled. The immune profile of female reproduction in each stage has also been meticulously unveiled. Especially, the application of single-cell sequencing (scRNA-seq) technology in this process reveals the distribution map of immune cells, which gives a novel insight for the homeostasis of IME and provides a research direction for better exploring the role of immune cells in female reproduction. Here, we provide an all-encompassing overview of the latest advancements in immune modulation within the context of the female reproductive process. Our approach involves structuring our summary in accordance with the physiological sequence encompassing gonadogenesis, folliculogenesis within the ovaries, ovulation through the fallopian tubes, and the subsequent stages of embryo implantation and development within the uterus. Our overarching objective is to construct a comprehensive portrayal of the immune microenvironment (IME), thereby accentuating the pivotal role played by immune cells in governing the intricate female reproductive journey. Additionally, we emphasize the pressing need for heightened attention directed towards strategies that focus on immune interventions within the female reproductive process, with the ultimate aim of enhancing female fertility.

Immunological Aspects of Infertility-The Role of KIR Receptors and HLA-C Antigen

The mechanisms of immune tolerance of a mother against an antigenically foreign fetus without a concomitant loss of defense capabilities against pathogens are the factors underlying the success of a pregnancy. A significant role in human defense is played by killer immunoglobulin-like receptor (KIR) receptors, which regulate the function of the natural killer (NK) cells capable of destroying antigenically foreign cells, virus-infected cells, or tumor-lesioned cells. A special subpopulation of NK cells called uterine NK cells (uNK) is found in the uterus. Disruption of the tolerance process or overactivity of immune-competent cells can lead to immune infertility, a situation in which a woman's immune system attacks her own reproductive cells, making it impossible to conceive or maintain a pregnancy. Since the prominent role of the inflammatory response in infertility, including KIR receptors and NK cells, has been postulated, the process of antigen presentation involving major histocompatibility complex (MHC) molecules (HLA) appears to be crucial for a successful pregnancy. Proper interactions between KIR receptors on female uNK cells and HLA class I molecules, with a predominant role for HLA-C, found on the surface of germ cells, are strategically important during embryo implantation. In addition, maintaining a functional balance between activating and inhibitory KIR receptors is essential for proper placenta formation and embryo implantation in the uterus. A disruption of this balance can lead to complications during pregnancy. The discovery of links between KIR and HLA-C has provided valuable information about the complexity of maternal-fetal immune interactions that determine the success of a pregnancy. The great diversity of maternal KIR and fetal HLA-C ligands is associated with the occurrence of KIR/HLA-C combinations that are more or less favorable for reproductive success.

The novel role of activating receptor KIR2DS5 in preeclampsia

Preeclampsia (PE) is a serious complication of pregnancy. Decidual natural killer (dNK) cells were reported to participate in the remodeling of spiral arteries through producing a group of cytokines, including granulocyte-macrophage colony stimulating factor (GM-CSF). KIR2DS5 is an activating receptor of NK cells that specifically recognizes HLA-C2 on trophoblasts. Currently, there are no reports regarding the precise mechanism of KIR2DS5 in PE. This study included 30 PE patients and 30 healthy pregnant women. We found that the expressions of KIR2DS5 were significantly lower in PE deciduae compared to those of healthy pregnancies. By transfecting knockdown and overexpression lentivirus vectors of KIR2DS5 into dNK cells isolated from deciduae of early pregnancy, we altered the KIR2DS5 expression level in dNK cells. Then, these dNK cells and trophoblast cell lines were co-cultured as trophoblast-dNK cells. In the trophoblast-dNK cells, we examined the influence of KIR2DS5 on the biological manifestations of trophoblasts. As anticipated, overexpression of KIR2DS5 could facilitate cell proliferation, migration, and invasion. Furthermore, increased expression of KIR2DS5 inhibited cell apoptosis and enhanced the progression of cells from theG1 to theS stage. Further mechanistic study demonstrated a positive relationship between KIR2DS5 and GM-CSF in trophoblast-dNK cells. Accordingly, our observations indicated that a decrease in KIR2DS5 could reduce the expression of GM-CSF via the JAK2/STAT5 pathway, resulting in the failure of the activated signal to be transmitted to dNK cells and ultimately leading to the occurrence of PE. KIR2DS5 may be a new contributor for the prediction and diagnosis of PE.

IL-21R-STAT3 signalling initiates a differentiation program in uterine tissue-resident NK cells to support pregnancy

Tissue-resident Natural Killer (trNK) cells are crucial components of local immunity that activate rapidly upon infection. However, under steady state conditions, their responses are tightly controlled to prevent unwanted tissue damage. The mechanisms governing their differentiation and activation are not fully understood. Here, we characterise uterine trNK cells longitudinally during pregnancy by single cell RNA sequencing and find that the combined expression pattern of 4-1BB and CD55 defines their three distinct stages of differentiation in mice. Mechanistically, an IL-21R-STAT3 axis is essential for initiating the trNK cell differentiation. The fully differentiated trNK cells demonstrate enhanced functionality, which is necessary for remodelling spiral arteries in the decidua. We identify an apoptotic program that is specific to the terminal differentiation stage, which may preclude tissue damage by these highly activated trNK cells. In summary, uterine trNK cells become intensely active and effective during pregnancy, but tightly controlled via a differentiation program that also limits potential harm, suggesting an intricate mechanism for harnessing trNK cells in maintaining pregnancy.

Effect of 2-deoxyglucose-mediated inhibition of glycolysis on migration and invasion of HTR-8/SVneo trophoblast cells

The proper invasion of trophoblasts is crucial for embryo implantation and placental development, which is helpful to establish a correct maternal-fetal relationship. Trophoblasts can produce a large amount of lactate through aerobic glycolysis during early pregnancy. Lactate creates a low pH microenvironment around the embryo to help uterine tissue decompose and promote the invasion of trophoblasts. The purpose of this study is to reveal the the potential mechanism of aerobic glycolysis regulating the invasiveness of trophoblasts by investigating the effect of 2-Deoxy-D-glucose (2-DG), a glycolysis inhibitor, on the biological function of HTR-8/SVneo trophoblast cells, the expressions of epithelial mesenchymal transformation (EMT) markers and invasion-related factors. 2-DG could inhibit the aerobic glycolysis of trophoblasts and decrease the activity of trophoblasts in a dose-dependent manner. Moreover, 2-DG inhibited the EMT of HTR-8/SVneo cells, down-regulated the expression of invasion-related factors matrix metalloproteinase 2/9 (MMP2/9) and up-regulated the expression of tissue inhibitor of matrix metalloproteinases 1/2 (TIMP1/2), thus inhibiting cell migration and invasion. This paper provides a foundation in the significance of aerobic glycolysis of trophoblasts in the process of invasion, and also provides ideas and insights for the promotion of embryo implantation.

Immunobiology of pregnancy: from basic science to translational medicine

Embryo implantation failure and spontaneous abortions represent the main causes of infertility in developed countries. Unfortunately, incomplete knowledge of the multiple factors involved in implantation and fetal development keeps the success rate of medically assisted procreation techniques relatively low. According to recent literature, cellular and molecular mechanisms of 'immunogenic tolerance' towards the embryo are crucial to establish an 'anti-inflammatory' state permissive of a healthy pregnancy. In this review we dissect the role played by the immune system in the endometrial-embryo crosstalk, with a particular emphasis towards the fork-head-box-p3 (Foxp3+) CD4+CD25+ regulatory T (Treg) cells and discuss the most recent therapeutic advances in the context of early immune-mediated pregnancy loss.

Is the Development of Ascites in Alcoholic Liver Patients Influenced by Specific KIR/HLA Gene Profiles?

Decompensated cirrhosis is the most common cause of ascites due to hemodynamic and renal alteration by continuous fluid leakage from the hepatic sinusoids and splanchnic capillaries into the interstitial space. Then, fluid leakage exceeds lymphatic return, leading to progressive fluid accumulation directly into the peritoneal cavity. Alcohol consumption is one of the main risks of developing alcoholic cirrhosis (AC), but not all AC patients develop ascites. Avoiding the development of ascites is crucial, given that it deteriorates prognosis and increases the patient mortality patient. The innate immune system plays a crucial role in cirrhosis through natural killer cells, which are abundant in the liver. The aim of this study was to analyze the KIR/HLA-C genetic profile in AC patients with and without ascites to understand this pathology and find predictive clinical susceptibility biomarkers that can help to establish risks and prevent the development of ascites in AC patients. A total of 281 AC patients with and without ascites were analyzed and compared with 319 healthy controls. Genomic DNA was extracted from peripheral blood in all groups. A PCR-SSO assay was performed for KIR/HLA genotyping analysis. A total of 16 activating and inhibitor KIR genes and their corresponding known ligands, epitopes of HLA-C, and their genotypes were analyzed. According to our analysis, C1 epitopes were statistically significantly decreased in AC patients with and without ascites. When comparing AC patients with ascites and healthy controls, a significant decrease in C1 epitope frequency was also observed. A statistically significant decrease was also found when comparing the C1C2 genotype in AC patients without ascites with controls. In conclusion, the absence of KIR2DL2 and KIR3DL1 genes may be a predisposing factor for the development of ascites in AC patients. The KIR2DS2/KIR2DL2 may could be involved in grade I ascites development, and the presence of the C1+ epitope and the homozygous C2C2 genotype may be protective genetic factors against ascites development in AC patients.

Increased cytotoxic natural killer cells in the endometrium alone cannot be considered the immunological cause of recurrent miscarriage

OBJECTIVE

To study the distribution and gene expression of endometrial immune cell populations, especially natural killer (NK) subsets, between assisted reproductive technology patients and healthy donors and explore a possible relationship of these results with patients' killer cell immunoglobulin-like receptor (KIR) genotypes and KIR-human antigen leukocyte-C (HLA-C) binding.

DESIGN

Prospective observational cohort study.

SETTING

Clinic and university laboratories.

PATIENT(S)

Participants included 39 women with recurrent miscarriages who had undergone in vitro fertilization cycles with donated oocytes and 21 healthy oocyte donors with proven fertility.

INTERVENTION(S)

Endometrial biopsy samples were collected from both patients and donors, and the KIR genotypes of the assisted reproductive technology patients were analyzed.

MAIN OUTCOME MEASURE(S)

Endometrial gene expression (cluster of differentiation [CD] antigens and anti-inflammatory and proinflammatory interleukins) and the number and percentage of regulatory T and NK cell populations in patients and donors were determined. Subsequently, the results obtained were categorized in the group of patients by KIR genotype. Killer cell immunoglobulin-like receptor-HLA-C binding was also examined in patients, considering their KIRs.

RESULT(S)

A higher percentage of CD56dimCD16+ NK cells were observed in patients than those in healthy donors. Nevertheless, when categorizing patients by KIR genotype and comparing the KIR AA (35.9%), AB (43.6%), and BB (20.5%) groups, no statistically significant difference was observed in either endometrial gene expression or any of the immune cell populations analyzed. Finally, no differences in binding between KIR and HLA-C molecules were registered among these 3 sets of patients.

CONCLUSION(S)

The reported increase in the number of NK cells with a cytotoxic profile in the endometrium of women with a history of recurrent miscarriages cannot alone explain these events because no relationship is observed between such cellular increase and the KIR genotypes, which individually, and in combination with the different HLA-C alleles, have also been associated, by previous studies, with negative reproductive outcomes.

CLINICAL TRIAL REGISTRATION NUMBER

1405-MAD-025-JG.

Gestational Viral Infections: Role of Host Immune System

Viral infections in pregnancy are major causes of maternal and fetal morbidity and mortality. Infections can develop in the neonate transplacentally, perinatally, or postnatally (from breast milk or other sources) and lead to different clinical manifestations, depending on the viral agent and the gestational age at exposure. Viewing the peculiar tolerogenic status which characterizes pregnancy, viruses could exploit this peculiar immunological status to spread or affect the maternal immune system, adopting several evasion strategies. In fact, both DNA and RNA virus might have a deep impact on both innate and acquired immune systems. For this reason, investigating the interaction with these pathogens and the host's immune system during pregnancy is crucial not only for the development of most effective therapies and diagnosis but mostly for prevention. In this review, we will analyze some of the most important DNA and RNA viruses related to gestational infections.

MHC Class I Ligands of Rhesus Macaque Killer Cell Ig-like Receptors

Definition of MHC class I ligands of rhesus macaque killer cell Ig-like receptors (KIRs) is fundamental to NK cell biology in this species as an animal model for infectious diseases, reproductive biology, and transplantation. To provide a more complete foundation for studying NK cell responses, rhesus macaque KIRs representing common allotypes of lineage II KIR genes were tested for interactions with MHC class I molecules representing diverse Macaca mulatta (Mamu)-A, -B, -E, -F, -I, and -AG alleles. KIR-MHC class I interactions were identified by coincubating reporter cell lines bearing chimeric KIR-CD3ζ receptors with target cells expressing individual MHC class I molecules and were corroborated by staining with KIR IgG-Fc fusion proteins. Ligands for 12 KIRs of previously unknown specificity were identified that fell into three general categories: interactions with multiple Mamu-Bw4 molecules, interactions with Mamu-A-related molecules, including allotypes of Mamu-AG and the hybrid Mamu-B*045:03 molecule, or interactions with Mamu-A1*012:01. Whereas most KIRs found to interact with Mamu-Bw4 are inhibitory, most of the KIRs that interact with Mamu-AG are activating. The KIRs that recognize Mamu-A1*012:01 belong to a phylogenetically distinct group of macaque KIRs with a 3-aa deletion in the D0 domain that is also present in human KIR3DL1/S1 and KIR3DL2. This study more than doubles the number of rhesus macaque KIRs with defined MHC class I ligands and identifies interactions with Mamu-AG, -B*045, and -A1*012. These findings support overlapping, but nonredundant, patterns of ligand recognition that reflect extensive functional diversification of these receptors.

The role of immune cells and mediators in preeclampsia

Preeclampsia is a hypertensive disorder of major concern in pregnancy than can lead to intrauterine growth restriction, placental abruption and stillbirth. The pathophysiology of preeclampsia is multifactorial, including not only kidney dysfunction but also endothelial dysfunction, as the maternal endothelium becomes exposed to placental factors that are released into the circulation and increase systemic levels of vasoconstrictors, oxidative stress, anti-angiogenic factors and inflammatory mediators. Importantly, inflammation can lead to insufficient placental perfusion and low birthweight in offspring. Various innate and adaptive immune cells and mediators have been implicated in the development of preeclampsia, in which oxidative stress is associated with activation of the maternal inflammatory response. Immune cells such as regulatory T cells, macrophages, natural killer cells, and neutrophils are known to have major causative roles in the pathology of preeclampsia, but the contributions of additional immune cells such as B cells, inflammatory cytokines and anti-angiotensin II type 1 receptor autoantibodies are also now recognized. Immunological interventions, therefore, have therapeutic potential in this disease. Here, we provide an overview of the immune responses that are involved in the pathogenesis of preeclampsia, including the role of innate and adaptive immune cells and mediators.

HLA/MHC and KIR characterization in humans and non-human primates using Oxford Nanopore Technologies and Pacific Biosciences sequencing platforms

The gene products of the HLA/MHC and KIR multigene families are important modulators of the immune system and are associated with health and disease. Characterization of the genes encoding these receptors has been integrated into different biomedical applications, including transplantation and reproduction biology, immune therapies and in fundamental research into disease susceptibility or resistance. Conventional short-read sequencing strategies have shown their value in high throughput typing, but are insufficient to uncover the entire complexity of the highly polymorphic HLA/MHC and KIR gene systems. The implementation of single-molecule and real-time sequencing platforms, offered by Pacific Biosciences (PacBio) and Oxford Nanopore Technologies (ONT), revolutionized the fields of genomics and transcriptomics. Using fundamentally distinct principles, these platforms generate long-read data that can unwire the plasticity of the HLA/MHC and KIR genes, including high-resolution characterization of genes, alleles, phased haplotypes, transcription levels and epigenetics modification patterns. These insights might have profound clinical relevance, such as improved matching of donors and patients in clinical transplantation, but could also lift disease association studies to a higher level. Even more, a comprehensive characterization may refine animal models in preclinical studies. In this review, the different HLA/MHC and KIR characterization approaches using PacBio and ONT platforms are described and discussed.

The Influence of Maternal KIR Haplotype on the Reproductive Outcomes after Single Embryo Transfer in IVF Cycles in Patients with Recurrent Pregnancy Loss and Implantation Failure-A Single Center Experience

(1) Background: Recurrent pregnancy loss (RPL) and recurrent implantation failure (RIF) have in common a deficient maternal adaptation to the semi-allogeneic fetus, in which killer immunoglobulin-like receptor (KIR) family expressed by natural killer (NK) cells play an important role. The aim of this study was to evaluate the influence of maternal KIR haplotype on the reproductive outcomes after single embryo transfer in IVF cycles in patients with RPL and RIF. (2) Methods: Patients with RIF and RPL who presented at Origyn Fertility Center from Iasi, Romania, were prospectively enrolled between January 2020 and December 2022. Clinical and paraclinical data was examined. Descriptive statistics and a conditional logistic regression model were used to analyze our data. (3) Results: Patients with a KIR AA haplotype had significantly more chances of miscarriage if they underwent an IVF procedure (aOR: 4.15, 95% CI: 1.39-6.50, p = 0.032) compared with those who spontaneously achieved a pregnancy. Moreover, it appeared that the same haplotype increased the chances of obtaining a pregnancy for patients who underwent an IVF procedure (aOR: 2.57, 95% CI: 0.85-6.75, p = 0.023). (4) Conclusions: Determination of KIR haplotype could be beneficial for patients with RPL or RIF in order to offer an individualized management.

The human placenta shapes the phenotype of decidual macrophages

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

Uterine NK cells underexpress KIR2DL1/S1 and LILRB1 in reproductive failure

A significant proportion of recurrent miscarriage, recurrent implantation failure and infertility are unexplained, and these conditions have been proposed to have an etiology of immunological dysfunction at the maternal-fetal interface. Uterine Natural Killer cells (uNK) comprise three subsets and are the most numerous immune cells found in the uterine mucosa at the time of implantation. They are thought to play an important role in successful pregnancy by regulation of extravillous trophoblast (EVT) invasion and spiral artery remodelling. Here, we examine the frequency, phenotype and function of uNK1-3 from the uterine mucosa of 16 women with unexplained reproductive failure compared to 11 controls with no reproductive problems, during the window of implantation. We report that KIR2DL1/S1 and LILRB1 expression is lower in the reproductive failure group for both uNK (total uNK, uNK 2 and 3) and pNK. We also show that degranulation activity is significantly reduced in total uNK, and that TNF-α production is lower in all uNK subsets in the reproductive failure group. Taken together, our findings suggest that reproductive failure is associated with global reduction in expression of uNK receptors important for interaction with HLA-C and HLA-G on EVT during early pregnancy, leading to reduced uNK activation. This is the first study to examine uNK subsets during the window of implantation in women with reproductive failure and will serve as a platform to focus on particular aspects of phenotype and function of uNK subsets in future studies. Further understanding of uNK dysregulation is important to establish potential diagnostic and therapeutic targets in the population of women with unexplained reproductive failure.

Single cell RNA sequencing research in maternal fetal interface

The maternal-fetal interface is an essential environment for embryonic growth and development, and a successful pregnancy depends on the dynamic balance of the microenvironment at the maternal-fetal interface. Single-cell sequencing, which unlike bulk sequencing that provides averaged data, is a robust method for interpreting the cellular and molecular landscape at single-cell resolution. With the support of single-cell sequencing, the issue of maternal-fetal interface heterogeneity during pregnancy has been more deeply elaborated and understood, which is important for a deeper understanding of physiological and pathological pregnancy. In this paper, we analyze the recent studies of single-cell transcriptomics in the maternal-fetal interface, and provide new directions for understanding and treating various pathological pregnancies.

Recurrent implantation failure: A comprehensive summary from etiology to treatment

Implantation is the first step in human reproduction. Successful implantation depends on the crosstalk between embryo and endometrium. Recurrent implantation failure (RIF) is a clinical phenomenon characterized by a lack of implantation after the transfer of several embryos and disturbs approximately 10% couples undergoing in vitro fertilization and embryo transfer. Despite increasing literature on RIF, there is still no widely accepted definition or standard protocol for the diagnosis and treatment of RIF. Progress in predicting and preventing RIF has been hampered by a lack of widely accepted definitions. Most couples with RIF can become pregnant after clinical intervention. The prognosis for couples with RIF is related to maternal age. RIF can be caused by immunology, thrombophilias, endometrial receptivity, microbiome, anatomical abnormalities, male factors, and embryo aneuploidy. It is important to determine the most possible etiologies, and individualized treatment aimed at the primary cause seems to be an effective method for increasing the implantation rate. Couples with RIF require psychological support and appropriate clinical intervention. Further studies are required to evaluate diagnostic method and he effectiveness of each therapy, and guide clinical treatment.

Postpartum hepatitis and host immunity in pregnant women with chronic HBV infection

In order to develop immune tolerant to the fetal, maternal immune system will have some modification comparing to the time before pregnancy. Immune tolerance starts and develops at the maternal placental interface. In innate immunity, decidual natural killer (dNK) cells, macrophages and dendritic cells play a key role in immue tolerance. In adaptive immunity, a moderate increase of number and immune inhibition function of regulatory T cells (Treg) are essential for immune tolerance. The trophoblast cells and immune cells expressing indoleamine 2,3-dioxygenase (IDO), the trophoblast cells expressing HLA-G, and Th1/Th2 shifting to Th2 dominant and Th17/Treg shifting to Treg domiant are in favor of maternal fetal immune tolerance. Steroids (estrogen and progesterone) and human chorionic gonadotropin (HCG) also participate in immune tolerance by inducing Treg cells or upregulating immunosuppressive cytokines. Most of the patients with chronic HBV infection are in the "HBV immune tolerance period" before pregnancy, and the liver disease is relatively stable during pregnancy. In chronic HBV infection women, after delivery, the relative immunosuppression in vivo is reversed, and Th1 is dominant in Th1/Th2 and Th17 is dominant in Th17/Treg balance. After delivery, the number of Treg decrease and NK cells increase in quantity and cytotoxicity in peripheral blood. Liver NK cells may cause liver inflammation through a non-antigen specific mechanism. After delivery, the number of CD8⁺ T cells will increase and HBV specific T cell response recovers from the disfunction in pregnancy. Under the background of postpartum inflammation, the rapid decrease of cortisol after delivery, and especially the enhancement of HBV specific T cell response induced by HBV DNA and cytokines, are the main reasons for postpartum hepatitis. HBeAg positive, especially HBeAg<700 S/CO, and HBV DNA>3-5Log₁₀IU/ml are risk factors for postpartum hepatitis. Antiviral treatment in late pregnancy can reduce the incidence of mother to child transmission (MTCT) in chronic HBV infection women. Chronic HBV infection women have hepatitis both during pregnancy and more often in 12 weeks postpartum. It is generally agreed that postpartum hepatitis is mild symptoms and self-limited. Delaying drug withdrawal to 48 weeks can increase the seroconversion rate of HBeAg in delivery women with elevated alanine aminotransferase (ALT) in pregnancy.

Circulating Non-coding RNAs and Exosomes: Liquid Biopsies for Monitoring Preeclampsia

Preeclampsia (PE) remains a leading cause of maternal and fetal mortality, due to ineffective treatment and diagnostic strategies, compounded by the lack of clarity on the etiology of the disorder. The early prediction or accurate diagnosis of PE is a concern of researchers. Liquid biopsy can be analyzed for cell-free nucleic acids and exosomes. Because circulating non-coding RNAs (ncRNAs) and peripheral blood exosomes can be detected in the peripheral blood of women in early pregnancy, these vesicles and their contents have become the focus of research on early predictive and diagnostic biomarkers for preeclampsia. In this review, we focus on recent studies addressing the roles of circulating ncRNAs and exosomes in PE, with particular attention paid to the potential application value of placenta-derived exosomes and circulating ncRNAs as PE-specific biomarkers.

Effectiveness of Scutellaria baicalensis Georgi root in pregnancy-related diseases: A review

The root of Scutellaria baicalensis Georgi, also called Huangqin, is frequently used in traditional Chinese medicine. In ancient China, S. baicalensis root was used to clear heat, protect the fetus, and avoid a miscarriage for thousands of years. In modern times, pregnancy-related diseases can seriously affect maternal and fetal health, but few systematic studies have explored the mechanisms and potential targets of S. baicalensis root in the treatment of pregnancy-related diseases. Flavonoids (baicalein, wogonin and oroxylin A) and flavonoid glycosides (baicalin and wogonoside) are the main chemical components in the root of S. baicalensis. This study presents the current understanding of the major chemical components in the root of S. baicalensis, focusing on their traditional uses, potential therapeutic effects and ethnopharmacological relevance to pregnancy-related disorders. The mechanisms, potential targets and experimental models of S. baicalensis root for ameliorating pregnancy-related diseases, such as recurrent spontaneous abortion, preeclampsia, preterm birth, fetal growth restriction and gestational diabetes mellitus, are highlighted.

The central role of natural killer cells in preeclampsia

Preeclampsia (PE) is a disease that is unique to pregnancy and affects multiple systems. It can lead to maternal and perinatal mortality. The precise etiology of PE is unclear. Patients with PE may have systemic or local immune abnormalities. A group of researchers has proposed that the immune communication between the fetus and mother is primarily moderated by natural killer (NK) cells as opposed to T cells, since NK cells are the most abundant immune cells in the uterus. This review examines the immunological roles of NK cells in the pathogenesis of PE. Our aim is to provide obstetricians with a comprehensive and updated research progress report on NK cells in PE patients. It has been reported that decidual NK (dNK) cells contribute to the process of uterine spiral artery remodeling and can modulate trophoblast invasion. Additionally, dNK cells can stimulate fetal growth and regulate delivery. It appears that the count or proportion of circulating NK cells is elevated in patients with or at risk for PE. Changes in the number or function of dNK cells may be the cause of PE. The Th1/Th2 equilibrium in PE has gradually shifted to an NK1/NK2 equilibrium based on cytokine production. An improper combination of killer cell immunoglobulin-like receptor (KIR) and human leukocyte antigen (HLA)-C may lead to insufficient activation of dNK cells, thereby causing PE. In the etiology of PE, NK cells appear to exert a central effect in both peripheral blood and the maternal-fetal interface. To maintain immune equilibrium both locally and systemically, it is necessary to take therapeutic measures directed at NK cells.

Isolation of single cells from human uterus in the third trimester of pregnancy: myometrium, decidua, amnion and chorion

During pregnancy, interactions between uterine immune cells and cells of the surrounding reproductive tissues are thought to be vital for regulating labour. The mechanism that specifically initiates spontaneous labour has not been determined, but distinct changes in uterine immune cell populations and their activation status have been observed during labour at term gestation. To understand the regulation of human labour by the immune system, the ability to isolate both immune cells and non-immune cells from the uterus is required. Here, we describe protocols developed in our laboratory to isolate single cells from uterine tissues, which preserve both immune and non-immune cell populations for further analysis. We provide detailed methods for isolating immune and non-immune cells from human myometrium, chorion, amnion and decidua, together with representative flow cytometry analysis of isolated cell populations present. The protocols can be completed in tandem and take approximately 4-5 h, resulting in single-cell suspensions that contain viable leucocytes, and non-immune cells in sufficient numbers for single-cell analysis approaches such as flow cytometry and single cell RNA sequencing (scRNAseq).

Integrative analyses of maternal plasma cell-free DNA nucleosome footprint differences reveal chromosomal aneuploidy fetuses gene expression profile

Background

Chromosomal aneuploidy is the most common birth defect. However, the developmental mechanism and gene expression profile of fetuses with chromosomal aneuploidy are relatively unknown, and the maternal immune changes induced by fetal aneuploidy remain unclear. The inability to obtain the placenta multiple times in real-time is a bottleneck in research on aneuploid pregnancies. Plasma cell-free DNA (cfDNA) carries the gene expression profile information of its source cells and may be used to evaluate the development of fetuses with aneuploidy and the immune changes induced in the mother owing to fetal aneuploidy.

Methods

Here, we carried out whole-genome sequencing of the plasma cfDNA of 101 pregnant women carrying a fetus with trisomy (trisomy 21, n = 42; trisomy 18, n = 28; trisomy 13, n = 31) based on non-invasive prenatal testing (NIPT) screening and 140 normal pregnant women to identify differential genes according to the cfDNA nucleosome profile in the region around the transcription start sites (TSSs).

Results

The plasma cfDNA promoter profiles were found to differ between aneuploid and euploid pregnancies. A total of 158 genes with significant differences were identified, of which 43 genes were upregulated and 98 genes were downregulated. Functional enrichment and signaling pathway analysis were performed based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases found that these signal pathways were mainly related to the coordination of developmental signals during embryonic development, the control of cell growth and development, regulation of neuronal survival, and immune regulation, such as the MAPK, Hippo, TGF-β, and Rap1 signaling pathways, which play important roles in the development of embryonic tissues and organs. Furthermore, based on the results of differential gene analysis, a total of 14 immune-related genes with significant differences from the ImmPort database were collected and analyzed. These significantly different immune genes were mainly associated with the maintenance of embryonic homeostasis and normal development.

Conclusions

These results suggest that the distribution characteristics of cfDNA nucleosomes in maternal plasma can be used to reflect the status of fetal development and changes of the immune responses in trisomic pregnancies. Overall, our findings may provide research ideas for non-invasive detection of the physiological and pathological states of other diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03735-7.

Maternal selection of human embryos in early gestation: Insights from recurrent miscarriage

Compared to most mammals, human pregnancy is unusual in that it involves chromosomally diverse embryos, cyclical breakdown and regeneration of the uterine mucosa, and intimate integration of fetal and maternal cells at the uteroplacental interface. Not surprisingly, pregnancy often falters in early gestation. Whether these losses result in clinical miscarriages depends on the origins and impacts of chromosomal errors on fetal development and the ability of the decidualizing endometrium to engage in embryo biosensing and selection. Aneuploidy originating in oocytes during meiosis drives the age-related risk of miscarriage. By contrast, the frequency of endometrial cycles with an impaired decidual response may account for the stepwise increase in miscarriage rates with each pregnancy loss independently of maternal age. Additional physiological mechanisms operate in early gestation to ensure that most failing pregnancies are lost before vascular maternal-fetal connections are established by the end of the first trimester. Here, we summarise how investigations into the mechanisms that cause miscarriage led to new insights into the processes that govern maternal selection of human embryos in early gestation.

ERAP/HLA-C and KIR Genetic Profile in Couples with Recurrent Implantation Failure

Proper embryo implantation depends on the tolerance of the maternal immune system to the fetus and its foreign paternal antigens. During implantation and early pregnancy, the dominant leukocytes in the uterus are uterine NK cells, expressing killer immunoglobulin-like receptors (KIR). KIRs recognize human leukocyte antigens (HLA-C) on the human trophoblast inherited from the father and mother. The antigenic peptides presented by the HLA are formed via their cleavage by endoplasmic reticulum aminopeptidases ERAP1 and ERAP2. The aim of this study was to assess the association of combined KIR genes and their HLA-C ligands, as well as ERAP1 and ERAP2 polymorphisms with recurrent implantation failure after in vitro fertilization (RIF). We tested 491 couples who underwent in vitro fertilization (IVF) and 322 fertile couples. Genotype CC rs27044 ERAP1 in female with a male’s HLA-C1C1 or HLA-C1C2 protected from RIF (p/pcorr. = 0.005/0.044, OR = 0.343; p/pcorr. = 0.003/0.027, OR = 0.442, respectively). Genotype TT rs30187 ERAP1 in female with a male’s HLA-C1C2 genotype increased the risk of RIF. Summarizing, in the combination of female ERAP1 and an HLA-C partner, the rs30187 C>T and rs27044 C>G polymorphisms play an important role in implantation failure.

Single-Cell Immunobiology of the Maternal-Fetal Interface

Pregnancy success requires constant dialogue between the mother and developing conceptus. Such crosstalk is facilitated through complex interactions between maternal and fetal cells at distinct tissue sites, collectively termed the "maternal-fetal interface." The emergence of single-cell technologies has enabled a deeper understanding of the unique processes taking place at the maternal-fetal interface as well as the discovery of novel pathways and immune and nonimmune cell types. Single-cell approaches have also been applied to decipher the cellular dynamics throughout pregnancy, in parturition, and in obstetrical syndromes such as recurrent spontaneous abortion, preeclampsia, and preterm labor. Furthermore, single-cell technologies have been used during the recent COVID-19 pandemic to evaluate placental viral cell entry and the impact of SARS-CoV-2 infection on maternal and fetal immunity. In this brief review, we summarize the current knowledge of cellular immunobiology in pregnancy and its complications that has been generated through single-cell investigations of the maternal-fetal interface.

Genetic variation in placental insufficiency: What have we learned over time?

Genetic variation shapes placental development and function, which has long been known to impact fetal growth and pregnancy outcomes such as miscarriage or maternal pre-eclampsia. Early epidemiology studies provided evidence of a strong heritable component to these conditions with both maternal and fetal-placental genetic factors contributing. Subsequently, cytogenetic studies of the placenta and the advent of prenatal diagnosis to detect chromosomal abnormalities provided direct evidence of the importance of spontaneously arising genetic variation in the placenta, such as trisomy and uniparental disomy, drawing inferences that remain relevant to this day. Candidate gene approaches highlighted the role of genetic variation in genes influencing immune interactions at the maternal-fetal interface and angiogenic factors. More recently, the emergence of molecular techniques and in particular high-throughput technologies such as Single-Nucleotide Polymorphism (SNP) arrays, has facilitated the discovery of copy number variation and study of SNP associations with conditions related to placental insufficiency. This review integrates past and more recent knowledge to provide important insights into the role of placental function on fetal and perinatal health, as well as into the mechanisms leading to genetic variation during development.

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.

[HLA-C KIR interactions and placental defects: Implications in ART pregnancy issues]

OBJECTIVE

The aim of this review is to update data concerning the impact of HLA-C KIR system on placental disorders and assess the involvement on ART clinical outcomes.

METHOD

Ensuring the maintenance of human pregnancy requires the set up of immunological tolerance to prevent foetus rejection. This phenomenon involves different actors of the immune system: among them, uterine NK cells (uNK) hold specific KIR (killer-cell immunoglobulin-like) receptors linking to HLA molecules on the surface of trophoblastic cells at implantation. Many studies provided evidence that the specific interaction between maternal KIR and foetal HLA-C could influence the process of placentation; according to the KIR haplotype and the type of HLA-C, the interaction could be detrimental for placental function. We reviewed the latest data available regarding HLA-C KIR interactions and ART outcomes.

RESULTS

The available results highlight a significant increase of preeclampsia risk and recurrent miscarriages when the maternal inhibitory haplotype KIR AA is present, this risk is all the more enhanced when the interaction occurs with foetal HLA-C2. Recent data suggest the consequences of this detrimental interaction in case of DET (double embryo transfer) or use of donor's oocytes in ART practice. On the other hand, maternal KIR AB or BB haplotypes haven't been related to an additional obstetrical risk, as well as the foetal HLA-C1 homozygous allotype.

CONCLUSION

Despite the existence of many confoundings in current literature on the subject, interaction between maternal KIR and foetal HLA-C represent a promising target lead to broaden the spectrum of placental defects etiologies, especially in the reproductive health area.