Implications of uterine NK cells and regulatory T cells in the endometrium of infertile women

Innate and adaptive immune dysregulation in women with recurrent implantation failure

Recurrent implantation failure (RIF) is a condition where a woman fails to obtain pregnancy after multiple embryo transfer cycles, even with superior-quality blastocysts. There are various factors that can contribute to RIF, including immunologic disturbances. The immune system is extremely important during pregnancy. Immune cells such as T cells, B cells, natural killer (NK) cells, and macrophages (MQ) are present in the female reproductive tract and are accountable for regulating the immune response to invading pathogens and maintaining tissue homeostasis. Dysregulation of these immune cells can lead to inflammation, which can impair fertility. One of the most common immunological disturbances observed in RIF is an altered Th1/Th2 ratio, along with changes in NK cell and macrophage numbers. In addition, the presence of some antibodies, such as anti-ovarian antibodies, can also contribute to RIF. Interleukins have been implicated in the development of an inflammatory response that can interfere with successful embryo implantation. As a result, a comprehensive understanding of immunological compartments in RIF women could assist us in determining the immunological origins of this disease. We will discuss immunological factors that might contribute to RIF etiology, including cellular and molecular components.

Dominant immune cells in pregnancy and pregnancy complications: T helper cells (TH1/TH2, TH17/Treg cells), NK cells, MDSCs, and the immune checkpoints

Pregnancy problems including recurrent pregnancy loss, repeated implantation failure and pre-eclampsia  are common problems in the reproductive ages. Different reasons such as genetic, immunological, and environmental agents and also infections could develop these complications. In those cases in which the cause of the abortion is diagnosed, the chance of a successful pregnancy is increased by eliminating defective factors. However, in patients with unknown causes, there may be an imbalance in immune cells pattern. As a matter of fact, an inappropriate immune response is often associated with a failed pregnancy. Hence, the focus of treatment is to increase tolerance, not to suppress maternal immune system. These findings are linked to an elevated number of Treg cells and immune checkpoints through normal pregnancy. The present review discusses the balance of myeloid-derived suppressor cells, natural killer cells, T cells, and immune checkpoints, and also targeting them to maintain pregnancy and prevent associated complications.

Immunomodulation for unexplained recurrent implantation failure: where are we now?

In brief

Immune dysfunction may contribute to or cause recurrent implantation failure. This article summarizes normal and pathologic immune responses at implantation and critically appraises currently used immunomodulatory therapies.

Abstract

Recurrent implantation failure (RIF) may be defined as the absence of pregnancy despite the transfer of ≥3 good-quality blastocysts and is unexplained in up to 50% of cases. There are currently no effective treatments for patients with unexplained RIF. Since the maternal immune system is intricately involved in mediating endometrial receptivity and embryo implantation, both insufficient and excessive endometrial inflammatory responses during the window of implantation are proposed to lead to implantation failure. Recent strategies to improve conception rates in RIF patients have focused on modulating maternal immune responses at implantation, through either promoting or suppressing inflammation. Unfortunately, there are no validated, readily available diagnostic tests to confirm immune-mediated RIF. As such, immune therapies are often started empirically without robust evidence as to their efficacy. Like other chronic diseases, patient selection for immunomodulatory therapy is crucial, and personalized medicine for RIF patients is emerging. As the literature on the subject is heterogenous and rapidly evolving, we aim to summarize the potential efficacy, mechanisms of actions and side effects of select therapies for the practicing clinician.

Populations of NK Cells and Regulatory T Cells in the Endometrium of Cycling Mares-A Preliminary Study

Endometrial immune cells are essential to support uterine functions across the estrous cycle and in preparation for pregnancy. It has been acknowledged that changes in phenotype and/or numbers of lymphocytes, such as regulatory T cells (Tregs) and NK cells, might result in lower fertility in women and mice. Little is known about equine endometrial immune cells across the estrous cycle. Here, we compared the populations of endometrial Tregs and NK cells in estrus and diestrus in mares. Endometrial biopsy and blood samples were taken in estrus and diestrus from 11 mares ages 4-12 years. Flow cytometry with anti-CD4, -CD25 and -FOXP3 and anti-NKp46 and -CD3 antibodies was used to determine the populations of Tregs and NK cells, respectively. The concentration of progesterone was measured with chemiluminescence immunoassay. The results were analyzed with paired Student t tests. The mean percentage of endometrial CD4⁺FOXP3⁺ Tregs was 13.7 ± 6.2% in diestrus and 14.5 ± 5.9% in estrus, while the mean percentage of endometrial CD4⁺FOXP3⁺CD25⁺ Tregs changed from 3.6 ± 2.1% in diestrus to 2 ± 2% in estrus (p = 0.0947). The mean proportion of CD3^-NKp46⁺ lymphocytes in the endometrium was not significantly different, with 6 ± 1% in estrus and 6.5 ± 1.4% in diestrus. There was a large variation in the percentage of NK cells between mares of 2.1-12.7%. This study showed, for the first time, the presence of CD4⁺FOXP3⁺CD25⁺ Tregs and CD3^-NKp46⁺ NK cells in the endometrium of non-pregnant cycling mares. The percentage of Tregs, and to a greater extent NK cells, showed large fluctuations between mares. Both Tregs and NK cells might be important for the preparation of the endometrium for semen deposition and pregnancy; however, further research is required.

Functional prominence of natural killer cells and natural killer T cells in pregnancy and infertility: A comprehensive review and update

During pregnancy, complicated connections are formed between a mother and a fetus. In a successful pregnancy, the maternal-fetal interface is affected by dynamic changes, and the fetus is protected against the mother's immune system. Natural killer (NK) cells are one of the immune system cells in the female reproductive system that play an essential role in the physiology of pregnancy. NK cells not only exist in peripheral blood (PB) but also can exist in the decidua. Studies have suggested multiple roles for these cells, including decidualization, control of trophoblast growth and invasion, embryo acceptance and maintenance by the mother, and facilitation of placental development during pregnancy. Natural killer T (NKT) cells are another group of NK cells that play a crucial role in the maintenance of pregnancy and regulation of the immune system during pregnancy. Studies show that NK and NKT cells are not only effective in maintaining pregnancy but also can be involved in infertility-related diseases. This review focuses on NK and NKT cells biology and provides a detailed description of the functions of these cells in implantation, placentation, and immune tolerance during pregnancy and their role in pregnancy complications.

Neutrophil-to-lymphocyte ratio is a predictor of biochemical miscarriage following artificial frozen embryo transfer cycles

The aim of this study is to examine the relationship between complete blood count (CBC) inflammatory markers and pregnancy outcome following artificial frozen embryo transfer cycles (AC-FET). This was a retrospective cohort study including 183 patients undergoing an AC-FET. The inflammatory markers including white blood cell count (WCC), neutrophil and lymphocyte count, neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) were compared between cycles with and without clinical pregnancies. Furthermore, these markers were compared between pregnancies with and without biochemical and clinical miscarriages. NLR was significantly higher in cycles with biochemical miscarriages (p = 0.009). Receiver operating curve analysis was performed to assess the role of NLR in predicting biochemical pregnancy. The area under the curve was 0.714 (95% confidence interval; 0.578-0.850, p = 0.009). The optimal cut-off value for NLR that was associated with biochemical miscarriage was 2.48 with 63% sensitivity and 75% specificity. A logistic regression analysis was performed with biochemical miscarriage as the dependent variable. An NLR value below 2.48 was an independent variable to affect biochemical miscarriage (OR: 0.2, 95% CI 0.05-0.92, p = 0.030). NLR emerged as a reliable predictor of biochemical miscarriage in AC-FET.Impact StatementWhat is already known on this subject? NLR and PLR are novel markers of inflammation. They are related to various gynecological and obstetric conditions including spontaneous abortion, preeclampsia. These markers are also associated with assisted reproductive technology success in fresh cycles.What the results of this study add? This is the first study to investigate the association of these markers with FET cycles. Our results have shown that cycles that ended in biochemical miscarriage had a significantly higher NLR compared with cycles continuing as a clinical pregnancy. An NLR value above 2.48 was predictive of biochemical miscarriage following AC-FET.What the implications are of these findings for clinical practice and/or further research? A high NLR level might have a significant value for the identification of patients at risk of biochemical miscarriage. Future research should assess the impact of anti-inflammatory agents on pregnancy outcomes in patient populations where systemic inflammation is documented by CBC inflammatory markers.

Endometrial HLA-F expression is influenced by genotypes and correlates differently with immune cell infiltration in IVF and recurrent implantation failure patients

STUDY QUESTION

Is human leukocyte antigen (HLA)-F protein expressed in mid-secretory endometrium, and are its expression levels influenced by HLA-F gene polymorphisms and correlated with the abundance of uterine natural killer (uNK) cells and anti-inflammatory M2 macrophages?

SUMMARY ANSWER

HLA-F protein is expressed in mid-secretory endometrium, and levels are correlated with immune cell infiltration, plasma progesterone concentrations and HLA-F single-nucleotide polymorphisms (SNPs), however, women experiencing recurrent implantation failure (RIF) show differences when compared to women attending their first IVF treatment.

WHAT IS KNOWN ALREADY

The immunomodulatory HLA class Ib molecules HLA-G and HLA-F are expressed on the extravillous trophoblast cells and interact with receptors on maternal immune cells. Little is known regarding HLA-F expression in endometrial stroma and HLA-F function; furthermore, HLA-F and HLA-G SNP genotypes and haplotypes have been correlated with differences in time-to-pregnancy.

STUDY DESIGN, SIZE, DURATION

Primary endometrial stromal cell (ESC) cultures (n = 5) were established from endometrial biopsies from women attending IVF treatment at a fertility clinic. Basic HLA-F and HLA-G protein expression by the ESCs were investigated. A prospective controlled cohort study was performed including 85 women with a history of RIF and 36 control women beginning their first fertility treatment and with no history of RIF. In some analyses, the RIF group was divided into unknown cause, male infertility, female infertility, and both female and male infertility. Endometrial biopsies and blood samples were obtained the day equivalent to embryo transfer in a hormone-substituted cycle.

PARTICIPANTS/MATERIALS, SETTING, METHODS

HLA protein expression by ESCs was characterized using flow cytometry and western blot. In the cohort study, the specific immune markers HLA-F and HLA-G, CD56 and CD16 (NK cells), CD163 (M2 macrophages), FOXP3 (regulatory T cells) and CD138 (plasma cells) were analysed by immunohistochemistry and a digital image analysis system in endometrial biopsies. Endometrial receptivity was assessed by an endometrial receptivity array test (the ERA® test). Endometrial biopsies were examined according to modified Noyes' criteria. SNPs at the HLA-F gene and HLA-G haplotypes were determined.

MAIN RESULTS AND THE ROLE OF CHANCE

HLA-F protein is expressed in the endometrium at the time of implantation. Furthermore, the HLA-F protein levels were different according to the womeńs HLA-F SNP genotypes and diplotypes, which have previously been correlated with differences in time-to-pregnancy. Endometrial HLA-F was positively correlated with anti-inflammatory CD163+ M2 macrophage infiltration and CD56+ uNK cell abundance for the entire cohort. However, this was not the case for CD56+ in the female infertility RIF subgroup. HLA-F levels in the endometrial stroma were negatively correlated with plasma progesterone concentrations in the RIF subgroup with known female infertility. Conversely, HLA-F and progesterone were positively correlated in the RIF subgroup with infertility of the male partner and no infertility diagnosis of the woman indicating interconnections between progesterone, HLA-F and immune cell infiltration. Glandular sHLA-G expression was also positively correlated with uNK cell abundance in the RIF subgroup with no female infertility but negatively correlated in the RIF subgroup with a female infertility diagnosis.

LARGE SCALE DATA

Immunohistochemistry analyses of endometrial biopsies and DNA sequencing of HLA genes. Data will be shared upon reasonable request to the corresponding author.

LIMITATIONS, REASONS FOR CAUTION

The control group of women attending their first IVF treatment had an anticipated good prognosis but was not proven fertile. A significant age difference between the RIF group and the IVF group reflects the longer treatment period for women with a history of RIF. The standardization of hormonal endometrial preparation, which allowed consistent timing of endometrial and blood sampling, might be a strength because a more uniform hormonal background may more clearly show an influence on the immune marker profile and HLA class Ib levels in the endometrium by other factors, for example genetic polymorphisms. However, the immune marker profile might be different during a normal cycle.

WIDER IMPLICATIONS OF THE FINDINGS

The findings further highlight the importance of HLA-F and HLA-G at the implantation site and in early pregnancy for pregnancy success. Diagnostic measures and modulation of the complex interactions between HLA class Ib molecules, maternal immune cells and hormonal factors may have potential to improve fertility treatment.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Region Zealand Health Sciences Research Foundation and the Zealand University Hospital through the ReproHealth Research Consortium ZUH. The authors declared there are no conflicts of interest.

Proteomic alteration of endometrial tissues during secretion in polycystic ovary syndrome may affect endometrial receptivity

Embryo implantation is a complex developmental process that requires coordinated interactions among the embryo, endometrium, and the microenvironment of endometrium factors. Even though the impaired endometrial receptivity of patients with polycystic ovary syndrome (PCOS) is known, understanding of endometrial receptivity is limited. A proteomics study in three patients with PCOS and 3 fertile women was performed to understand the impaired endometrial receptivity in patients with PCOS during luteal phases. Through isobaric tags for relative and absolute quantitation (iTRAQ) analyses, we identified 232 unique proteins involved in the metabolism, inflammation, and cell adhesion molecules. Finally, our results suggested that energy metabolism can affect embryo implantation, whereas inflammation and cell adhesion molecules can affect both endometrial conversion and receptivity. Our results showed that endometrial receptive damage in patients with PCOS is not a single factor. It is caused by many proteins, pathways, systems, and abnormalities, which interact with each other and make endometrial receptive research more difficult.

KIR Receptors as Key Regulators of NK Cells Activity in Health and Disease

Natural killer (NK) cells are part of the cellular immune response. They target mainly cancer and virally infected cells. To a high extent cytotoxic activity of NK cells is regulated inter alia by signals from killer immunoglobulin-like receptors (KIR). The major histocompatibility complex (MHC) class I molecules are important ligands for KIR receptors. Binding of ligands (such as MHC I) to the KIR receptors has the important role in solid organ or hematopoietic cell transplantation. Of note, the understanding of the relationship between KIR and MHC receptors may contribute to the improvement of transplant results. Donor-recipient matching, which also includes the KIR typing, may improve monitoring, individualize the treatment and allow for predicting possible effects after transplantation, such as the graft-versus-leukemia effect (GvL) or viral re-infection. There are also less evident implications of KIR/MHC matching, such as with pregnancy and cancer. In this review, we present the most relevant literature reports on the importance of the KIR/MHC relationship on NK cell activity and hematopoietic stem cell transplantation (HSCT)/solid organ transplantation (SOT) effects, the risk of allograft rejection, protection against post-transplant cytomegalovirus (CMV) infection, pregnancy complications, cancer and adoptive therapy with NK cells.

Immunomodulatory Factors in Primary Endometrial Cell Cultures Isolated from Cancer and Noncancerous Human Tissue-Focus on RAGE and IDO1

Background: Immune modulatory factors like indoleamine 2,3-dioxygenase 1 (IDO1) generating kynurenine (Kyn) and receptor for advanced glycation end-products (RAGE) contribute to endometrial and cancer microenvironment. Using adequate experimental models is needed to learn about the significance of these molecular factors in endometrial biology. In this paper we study IDO1 activity and RAGE expression in the in vitro cultured primary human endometrial cells derived from cancerous and noncancerous tissue. Methods: The generated primary cell cultures from cancer and noncancerous endometrial tissues were characterized using immunofluorescence and Western Blot for expression of endometrial and cancer markers. IDO1 activity was studied by Kyn quantification with High Performance Liquid Chromatography with Diode Array Detector. Results: The primary cultures of endometrial cells were obtained with 80% success rate and no major genetic aberrations. The cells retained in vitro expression of markers (mucin MUC1 and HER2) or immunomodulatory factors (RAGE and IDO1). Increased Kyn secretion was associated with cancer endometrial cell culture in contrast to the control one. Conclusions: Primary endometrial cells express immune modulatory factors RAGE and IDO1 in vitro associated with cancer phenotype of endometrium.

Conventional microscopy versus digital image analysis for histopathologic evaluation of immune cells in the endometrium

In the search for a reliable biomarker able to diagnose immunological causes of infertility, uterine immune cells have been widely investigated. As a result, heterogeneous methods and cutoff values of what constitutes an aberrant number of immune cells have been reported, and a standardized method for quantification is needed. The objective of this study was to compare methods for quantification of immune cells visualized with immunohistochemistry in the endometrium of women in fertility treatment. Evaluation of the density of CD56⁺, CD16⁺ and CD163⁺ cells by conventional microscopy on a semiquantitative scale (low, medium and high) was compared to a continuous count using digital image analysis (DIA) reported as percentage positive cells out of the total number of stromal cells and number of positive cells per mm², respectively. We previously reported the CD56/CD16 ratio as a possible prognostic marker, and therefore the ratios of CD56/CD16 were compared using two different methods for selecting fields for counting with DIA: one method using principles of systematic random sampling, where glands were excluded, and one method analyzing large parts of the tissue including glands. A significant association between conventional microscopy and DIA was found when the semiquantitative scale was compared to medians of positive cells in CD56, CD16 and CD163, respectively, p < 0.001. A systematic significant difference in the ratios of CD56/CD16 was found when comparing the two methods for field selection, p < 0.001. To determine the possible use of these methods, more knowledge of the correlation to clinical outcome is warranted.

Do endometrial natural killer and regulatory T cells differ in infertile and clinical pregnancy patients? An analysis in patients undergoing frozen embryo transfer cycles

PROBLEM

Clinical significance of endometrial and peripheral blood natural killer (NK) and regulatory T cells (Tregs) during frozen embryo transfer (FET) cycles has not been well characterized.

DESIGN

Retrospective cohort study.

METHOD OF STUDY

Endometrial tissue was collected from infertility patients prior to a frozen embryo transfer cycle as part of an endometrial receptivity analysis (ERA^® ) biopsy or endometrial scratch test. Uterine NK (uNK) and Treg cell density was compared based on pregnancy status in the subsequent frozen embryo transfer cycle. Peripheral blood was also collected from a separate cohort of patients undergoing frozen embryo transfer. Treg cell density was compared by the presence or the absence of a clinical pregnancy in each phase of the cycle.

RESULTS

In the 33 luteal phase biopsies there were more endometrial Tregs, similar uNK and a trend toward lower CD16⁺ uNK cells in women with a future ongoing clinical pregnancy compared to non-pregnant women. There were no differences in uNK and Treg density in natural scratch cycles vs programmed cycles or in non-receptive vs receptive endometrium (ERA^® cycles). In the peripheral blood analysis, the pregnant group had higher peripheral blood Tregs on the day of serum β-hCG time point when compared to the non-pregnant group.

CONCLUSION

Higher levels of endometrial Tregs and lower levels of CD16⁺ uNK cells are positive prognostic factors for infertile women prior to frozen embryo transfer. Our work on phenotypic and proportional analyses of endometrial immune cells may complement the ERA^® in predicting improved pregnancy rates in patients with implantation failure.

Endometrial function in women with polycystic ovary syndrome: a comprehensive review

BACKGROUND

Polycystic ovary syndrome (PCOS) is the most common cause of anovulatory infertility. An endometrial component has been suggested to contribute to subfertility and poor reproductive outcomes in affected women.

OBJECTIVE AND RATIONALE

The aim of this review was to determine whether there is sufficient evidence to support that endometrial function is altered in women with PCOS, whether clinical features of PCOS affect the endometrium, and whether there are evidence-based interventions to improve endometrial dysfunction in PCOS women.

SEARCH METHODS

An extensive literature search was performed from 1970 up to July 2020 using PubMed and Web of Science without language restriction. The search included all titles and abstracts assessing a relationship between PCOS and endometrial function, the role played by clinical and biochemical/hormonal factors related to PCOS and endometrial function, and the potential interventions aimed to improve endometrial function in women with PCOS. All published papers were included if considered relevant. Studies having a specific topic/hypothesis regarding endometrial cancer/hyperplasia in women with PCOS were excluded from the analysis.

OUTCOMES

Experimental and clinical data suggest that the endometrium differs in women with PCOS when compared to healthy controls. Clinical characteristics related to the syndrome, alone and/or in combination, may contribute to dysregulation of endometrial expression of sex hormone receptors and co-receptors, increase endometrial insulin-resistance with impaired glucose transport and utilization, and result in chronic low-grade inflammation, immune dysfunction, altered uterine vascularity, abnormal endometrial gene expression and cellular abnormalities in women with PCOS. Among several interventions to improve endometrial function in women with PCOS, to date, only lifestyle modification, metformin and bariatric surgery have the highest scientific evidence for clinical benefit.

WIDER IMPLICATIONS

Endometrial dysfunction and abnormal trophoblast invasion and placentation in PCOS women can predispose to miscarriage and pregnancy complications. Thus, patients and their health care providers should advise about these risks. Although currently no intervention can be universally recommended to reverse endometrial dysfunction in PCOS women, lifestyle modifications and metformin may improve underlying endometrial dysfunction and pregnancy outcomes in obese and/or insulin resistant patients. Bariatric surgery has shown its efficacy in severely obese PCOS patients, but a careful evaluation of the benefit/risk ratio is warranted. Large scale randomized controlled clinical trials should address these possibilities.

PlGF Immunological Impact during Pregnancy

During pregnancy, the mother’s immune system has to tolerate the persistence of paternal alloantigens without affecting the anti-infectious immune response. Consequently, several mechanisms aimed at preventing allograft rejection, occur during a pregnancy. In fact, the early stages of pregnancy are characterized by the correct balance between inflammation and immune tolerance, in which proinflammatory cytokines contribute to both the remodeling of tissues and to neo-angiogenesis, thus, favoring the correct embryo implantation. In addition to the creation of a microenvironment able to support both immunological privilege and angiogenesis, the trophoblast invades normal tissues by sharing the same behavior of invasive tumors. Next, the activation of an immunosuppressive phase, characterized by an increase in the number of regulatory T (Treg) cells prevents excessive inflammation and avoids fetal immuno-mediated rejection. When these changes do not occur or occur incompletely, early pregnancy failure follows. All these events are characterized by an increase in different growth factors and cytokines, among which one of the most important is the angiogenic growth factor, namely placental growth factor (PlGF). PlGF is initially isolated from the human placenta. It is upregulated during both pregnancy and inflammation. In this review, we summarize current knowledge on the immunomodulatory effects of PlGF during pregnancy, warranting that both innate and adaptive immune cells properly support the early events of implantation and placental development. Furthermore, we highlight how an alteration of the immune response, associated with PlGF imbalance, can induce a hypertensive state and lead to the pre-eclampsia (PE).

Cytokine imbalance at materno-embryonic interface as a potential immune mechanism for recurrent pregnancy loss

Recurrent pregnancy loss (RPL) is a prominent reproductive disease that distresses about 2%-5% of couples. RPL is the loss of two or more successive spontaneous pregnancies prior to the 20th week of embryo development. The commencement of pregnancy necessitates implantation of the embryo into responsive maternal decidua synchronized with the process of placentation, decidual and myometrial trophoblast incursion as well as refashioning of spiral blood arteries of uterus. The collapse of any of the processes fundamental for pregnancy success may result into an array of pregnancy problems including spontaneous pregnancy loss. Endometrium of human female manufactures an extensive range of cytokines during the proliferative and secretory stage of the menstrual cycle. These endometrial cytokines are thought as major players for making the uterus ready for embryo implantation and placental development during pregnancy. Decidual cytokines regulate the invasion of trophoblast and remodeling of spiral arteries as well as take part in immune suppression to accomplish the pregnancy. Deterrence of maternal rejection of embryo needs a regulated milieu, which takes place essentially at the embryo-maternal interface and the tissues of the uterus. The reasons of RPL remain anonymous in a large number of cases that lead to difficulties in management and severe trauma in couples. Cytokine modulatory therapies have been shown promising for preventing RPL. Further study of novel factors is wanted to establish more effective RPL treatment protocols. The present study aims to review the outcome of cytokine breach at materno-embryonic interface and the efficacy of cytokine modulatory therapies in RPL.

Are different markers of endometrial receptivity telling us different things about endometrial function?

PROBLEM

To what extent do endocrine, immunological, gene expression and histological markers of endometrial receptivity correlate?

METHOD OF STUDY

Between November 2017 and September 2019, 121 women referred to a University Hospitals Fertility Clinic consented to inclusion in this cohort study. The women underwent timed endometrial biopsy followed by blood samples in a hormone-substituted cycle. Of these, 37 women had just started IVF treatment, and the remaining 84 had experienced recurrent implantation failure following IVF/ICSI. The hormone-substituted cycle consisted of initiation with oral oestradiol followed by addition of vaginal progesterone treatment for five full days. Endometrial biopsies were subject to histological examination, immune cell markers by immunohistochemistry (CD56⁺ , CD16⁺ , CD163⁺ , FoxP3) and gene expression microarray analyses with the endometrial receptivity array (ERA^® ) test (Igenomix). Plasma progesterone and oestradiol were measured on the day of biopsy.

RESULTS

CD56⁺ uterine natural killer (uNK) cell counts correlate with transcriptional markers of endometrial receptivity assessed by the ERA test. Endometrial maturation, receptivity and immunological markers were not correlated with mid-luteal blood plasma progesterone level. Mid-luteal serum oestradiol level correlated with markers of endometrial maturation and receptivity. The tests were carried out during a standard hormone substitution cycle, and the findings may not apply in the natural cycle.

CONCLUSION

CD56⁺ uNK cell counts and endometrial receptivity assessed by the ERA test appear to be linked. Mid-luteal progesterone levels were not correlated to the tested markers of endometrial receptivity. In contrast, mid-luteal oestradiol level was inversely related to markers of endometrial receptivity and maturation.

Immune cells in normal pregnancy and gestational trophoblastic diseases

A healthy pregnancy requires the development of maternal-fetal immune tolerance against the semi-allogeneic fetus. The interactions between the trophoblastic cells and the maternal immune cells (p.e., natural killer cells, T cells, macrophages, dendritic cells and B-cells) are important for the development of the maternal-fetal immune tolerance and the placental growth and function. These interactions are mediated by cell to cell contact and secreted molecules such as cytokines, chemokines, angiogenic factors and growth factors. The maternal immune cells are present in normal non-pregnant and pregnant endometrium and there are several lines of evidence based on immunohistochemical and RNA sequencing data that the decidual immune cells and immune-related pathways display alterations in GTD, which may have pathogenetic and clinical significance. The present review focuses on the usefulness of the immunohistochemical analysis which provides multiparametric in situ information regarding the numbers, the immunophenotypes and the immunotopographical distributions of the decidual immune cells in tissue sections from normal pregnancy and GTD. We also discuss the significance of the immunohistochemical information in order to gain insight in the putative mechanisms explaining the alterations of the decidual immune cells in GTD and the potential implications of these alterations in the pathogenesis and the clinical behavior of GTD.

Novel predictive and therapeutic options for better pregnancy outcome in frozen embryo transfer cycles

Since 1978, in the first decades of in vitro fertilization (IVF), the use of ovarian hyperstimulation allowed for the development and transfer of multiple embryos. As IVF technology improved, the number of multiple pregnancies increased, which led to gradual reduction in the number of embryos that were transferred. Embryo freezing (vitrification) was recommended to allow subsequent transfer if the fresh cycle was unsuccessful. However, experimentation has continued to improve pregnancy outcomes. We discuss here the significance of frozen embryo transfer cycle and the impact of uterine and peripheral immunity dominated by NK cells and regulatory T cells and human chorionic gonadotropin on pregnancy outcome in this innovative mode of IVF therapy.

Immunophenotypic Profiles in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) a long-known endocrinopathy and one of the most common endocrine-reproductive-metabolic disorders in women, which can lead to infertility. Although the precise etiology remains unclear, PCOS is considered as a complex genetic trait, with a high degree of heterogeneity. Besides, hormones and immune cells, including both innate and adaptive immune cells, are reportedly a cross talk in PCOS. Chronic low-grade inflammation increases autoimmune disease risk. This proinflammatory condition may, in turn, affect vital physiological processes that ultimately cause infertility, such as ovulation failure and embryo implantation. Here, we review the accumulating evidence linking PCOS with inflammatory status providing an overview of the underlying hormone-mediated dysregulation of immune cells. We mainly focus on the correlational evidence of associations between immune status in women and the increased prevalence of PCOS, along with the specific changes in immune responses. Further recognition and exploration of these interactions may help elucidate PCOS pathophysiology and highlight targets for its treatment and prevention.

Increase in FoxP3, CD56 immune cells and decrease in glands PGRMC1 expression in the endometrium are associated with recurrent miscarriages

OBJECTIVE

Recurrent miscarriage (RM) is a multifactorial condition that involves frequent uterine anatomical abnormalities, parental karyotype abnormalities, and clotting disorders. We investigate the potential roles of endometrium FoxP3⁺ Tregs and CD56+ cells (uNK cells) and endometrial expression of PGRMC1 in the development of recurrent miscarriage.

STUDY DESIGN

This prospective study included 102 out of 286 cases of SA patients. The cases were divided into groups with RM (+RM) and without RM (-RM). Immunohistochemistry staining was made using primary antibodies to FoxP3, CD56, and PGRMC1 in both groups. Morphometry analyses were carried out in 10 non-overlapping high power fields. Mann-Whitney U test, Fisher two-tail test, correlation analysis and relative risk (RR) were evaluated. A p < 0.05 was considered statistically significant.

RESULTS

An increased presence of CD56-positive (p < 0.001) and FoxP3⁺ Treg (p = 0.0005) cells was found in the endometrium, with a reduction in PGRMC1 expression compared with -RM group (p = 0.004). A positive correlation was shown between the number of CD56-positive cells and FoxP3⁺ cells (r = 0.55), and an inverse correlation with PGRMC1 (r =  -0.35) in the + RM group. A similar observation was found in the -RM group, with a positive correlation of uNK cell number with the number of pregnancies (p < 0.001; r = 0.34). Endometrial infiltration of CD56-positive (p < 0.0001) and FoxP3⁺ (p < 0.0001) cells revealed an increased relative risk of RM. This increased risk was also revealed in SA with a loss of PGRMC1 expression (p < 0.0001).

CONCLUSION

Our prospective study suggests, for the first time, that increased endometrial infiltration of uNK, FoxP3⁺ Treg cells and a decreased PGRMC1 expression may play potential roles in the development of RM.

Endometrial Immune Dysfunction in Recurrent Pregnancy Loss

Recurrent pregnancy loss (RPL) represents an unresolved problem for contemporary gynecology and obstetrics. In fact, it is not only a relevant complication of pregnancy, but is also a significant reproductive disorder affecting around 5% of couples desiring a child. The current knowledge on RPL is largely incomplete, since nearly 50% of RPL cases are still classified as unexplained. Emerging evidence indicates that the endometrium is a key tissue involved in the correct immunologic dialogue between the mother and the conceptus, which is a condition essential for the proper establishment and maintenance of a successful pregnancy. The immunologic events occurring at the maternal-fetal interface within the endometrium in early pregnancy are extremely complex and involve a large array of immune cells and molecules with immunoregulatory properties. A growing body of experimental studies suggests that endometrial immune dysregulation could be responsible for several, if not many, cases of RPL of unknown origin. The present article reviews the major immunologic pathways, cells, and molecular determinants involved in the endometrial dysfunction observed with specific application to RPL.

HHV-6A infection of endometrial epithelial cells affects immune profile and trophoblast invasion

PROBLEM

We first reported human herpesvirus (HHV)-6A DNA presence in 43% of endometrial cells from women with idiopathic infertility, whereas no fertile control women harbored the virus. We investigated the effect of HHV-6A infection on the immunological status of the endometrium.

METHOD OF STUDY

Endometrial biopsies, uterine flushing, and whole blood samples were collected from 67 idiopathic infertile women (mid-secretory phase). We analyzed the endometrial immunological status evaluating: (a) the effect of HHV-6A infection on endometrial immune profile analyzing the ratio of interleukin (IL)-15/ fibroblast growth factor-inducible 14 (Fn-14) and IL-18/ TNF-related weak inducer of apoptosis (TWEAK) mRNA as a biomarker of endometrial (e)natural killer activation/maturation, angiogenesis, and Th1/Th2 balance; (b) endometrial receptivity to trophoblasts in endometrial 3D in vitro model; (c) natural killer (NK) cells and T cells percentage and subpopulations by flow cytometry.

RESULTS

We confirmed the presence of HHV-6A infection in a 40% of idiopathic infertile women, characterized by an immune profile reflecting eNK cell cytotoxic activation and a decrease in CD4+ CD25+ CD127dim/^- regulatory T cells. The co-culture of endometrial epithelial cells with spheroids generated from the extravillous trophoblast-derived cell line JEG3 showed a twofold expansion of spheroids on endometrial epithelial-stromal cells (ESC) culture surface from HHV-6A negative women while no expansion was observed on the surface of ESC from HHV-6A positive women.

CONCLUSION

The identification of an effect of HHV-6A infection on endometrial immune status opens new perspectives in idiopathic infertile women care management. In addition, it would be possible to select antiviral therapies as novel, non-hormonal therapeutic approaches to those idiopathic infertile women characterized by the presence of endometrial HHV-6A infection, to increase their pregnancy rate.

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.