Variation in the HLA-F gene locus with functional impact is associated with pregnancy success and time-to-pregnancy after fertility treatment

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.

Association of human leukocyte antigen-G and -F with recurrent miscarriage and implantation failure: A systematic review and meta-analysis

PROBLEM

The immune system plays an essential role in embryonic implantation and pregnancy, but the molecular details remain controversial. In the past four decades, human leukocyte antigen (HLA)-G and -F have garnered significant attention.

METHOD OF STUDY

MEDLINE, EMBASE, Web of Science, and the Cochrane Trials Registry were searched from their inception dates until December 2022. Studies were selected following PRISMA guidelines. Meta-analyses were used to assess the relationship of soluble HLA-G (sHLA-G) and HLA-G 3'-untranslated region polymorphisms with recurrent miscarriage (RM) and recurrent implantation failure (RIF). Narrative synthesis was conducted to determine the association of RM with other single nucleotide polymorphisms (SNPs) and HLA-G protein in tissues and of RIF with HLA-F. Risk-of-bias was assessed using ROBINS-I. Publication bias was assessed using Egger's and Begg's tests.

RESULTS

Finally, 42 articles were eligible for inclusion in the systematic review (32 in the meta-analysis; 13 in narrative synthesis). We found a significant association between the 14-bp ins/del HLA-G polymorphism and RM risk, but no definitive association with RIF risk. Women with RM had lower blood concentrations of sHLA-G during pregnancy and non-pregnancy than did controls. For women in the RIF group, no significant difference was found.

CONCLUSION

HLA-G protein and gene expression levels may be closely related to RM. The relevance of HLA-G to RIF is still being determined. A narrative synthesis of current studies has shown that HLA-F is likely associated with RIF.

HLA-F transcriptional and protein differential expression according to its genetic polymorphisms

Many specificities single out HLA-F: its structure, expression regulation at cell membrane and function. HLA-F mRNA is detected in the most cell types and the protein is localized in the ER and Golgi apparatus. When expressed at cell surface, HLA-F may be associated to β2-microglobulin and peptide or expressed as an open-conformer molecule. HLA-F reaches the membrane upon activation of different primary cell types and cell-lines. HLA-F has its highest affinity for the KIR3DS1-activating NK receptor, but also binds inhibitory immune receptors. Some studies reported that HLA-F expression is associated with its genotype. Higher HLA-F mRNA expression associated with F*01:01:02, and 3 noncoding SNPs, rs1362126, rs2523405, and rs2523393, located in HLA-F-AS1 or upstream the HLA-F sequence were associated with HLA-F mRNA expression. Given the implication of HLA-F in many clinical setting, and the undisclosed process of its expression regulation, we aim to confirm the effect of the aforementioned SNPs with HLA-F transcriptional and protein expression. We analyzed the distribution, frequency and linkage disequilibrium of these SNPs at worldwide scale in the 1000 Genomes Project samples. Influence on the genotype of each SNP on HLA-F expression was explored using RNAseq data from the 1000 Genomes Project, and using Q-PCR and intracellular cytometry in PBMC from healthy individuals. Our results show that the SNPs under studied displayed remarkably different allelic proportion according to geography and confirm that rs1362126, rs2523405, and rs2523393 displayed the most concordant results, with the highest effect size and a double-dose effect.

Single-cell profiling reveals immune disturbances landscape and HLA-F-mediated immune tolerance at the maternal-fetal interface in preeclampsia

Background

Preeclampsia is a pregnancy-specific disorder that always causes maternal and fetal serious adverse outcome. Disturbances in maternal immune tolerance to embryo at the maternal-fetal interface (MFI) may be associated with preeclampsia onset. Recent studies have revealed the reduced expression pattern of HLA-F at the MFI in preeclampsia, while the mechanism of it mediating maternal fetal immune tolerance has not been revealed.

Methods

Single-cell RNA sequencing on placental decidua was performed to reveal the immune disturbances landscape at the MFI in preeclampsia. Human Jar cells and NK-92MI cells were employed to study the role of HLA-F in trophoblasts and lymphocyte.

Results

A total of 101,250 cells were classified into 22 cell clusters. Disease-related IGFBP1+SPP1+ extracellular villus trophoblast (EVT) was identified in the preeclamptic placental decidua, accompanied by newly discovered immune cellular dysfunction such as reduced ribosomal functions of NK populations and abnormal expression of antigen-presenting molecules in most cell clusters. Certain genes that are characteristic of the intermediate stage of myeloid or EVT cell differentiation were found to have unexplored but important functions in the pathogenesis of preeclampsia; specifically, we detected enhanced cell cross-talk between IGFBP1+SPP1+ EVT2 or SPP1+M1 cells and their receptor cell populations at the MFI of PE patients compared to controls. With respect to HLA-F, mIF staining confirmed its reduced expression in PE samples compared to controls. Over-expression of HLA-F in Jar cells promoted cell proliferation, invasion, and migration while under-expression had the opposite effect. In NK-92MI cells, over-expression of HLA-F increased the secretion of immunoregulation cytokines such as CSF1 and CCL22, and promoted adaptive NKG2C+NK cell transformation.

Conclusions

We revealed the immune disturbance landscape at the MFI in preeclampsia. Our findings regarding cellular heterogeneity and immune cellular dysfunction, as revealed by scRNA-seq, and the function of HLA-F in cells provide new perspectives for further investigation of their roles in the pathogenesis of preeclampsia, and then provide potential new therapeutic target.

HLA-F and LILRB1 Genetic Polymorphisms Associated with Alloimmunisation in Sickle Cell Disease

Red blood cell (RBC) transfusion remains a critical component in caring for the acute and chronic complications of sickle cell disease (SCD). Patient alloimmunisation is the main limitation of transfusion, which can worsen anaemia and lead to delayed haemolytic transfusion reaction or transfusion deadlock. Although biological risk factors have been identified for immunisation, patient alloimmunisation remains difficult to predict. We aimed to characterise genetic alloimmunisation factors to optimise the management of blood products compatible with extended antigen matching to ensure the self-sufficiency of labile blood products. Considering alloimmunisation in other clinical settings, like pregnancy and transplantation, many studies have shown that HLA Ib molecules (HLA-G, -E, and -F) are involved in tolerance mechanism; these molecules are ligands of immune effector cell receptors (LILRB1, LILRB2, and KIR3DS1). Genetic polymorphisms of these ligands and receptors have been linked to their expression levels and their influence on inflammatory and immune response modulation. Our hypothesis was that polymorphisms of HLA Ib genes and of their receptors are associated with alloimmunisation susceptibility in SCD patients. The alloimmunisation profile of thirty-seven adult SCD patients was analysed according to these genetic polymorphisms and transfusion history. Our results suggest that the alloimmunisation of SCD patients is linked to both HLA-F and LILRB1 genetic polymorphisms located in their regulatory region and associated with their protein expression level.

Opposing impacts of HLA-G haplotypes PROMO-G010104-UTR-3 and PROMO-G010101b/c-UTR-4 on risk of recurrent implantation failure

RESEARCH QUESTION

The human leukocyte antigen (HLA) class Ib molecules HLA-F and HLA-G are implicated in pregnancy success, but how do HLA-G and HLA-F genetic polymorphisms impact recurrent implantation failure (RIF)?

DESIGN

Prospective cohort study at a fertility clinic including a cohort of 84 women experiencing RIF and 35 IVF controls to assess the influence of HLA-G haplotypes and diplotypes and HLA-F single nucleotide polymorphisms (SNP) on RIF.

RESULTS

Over-representation trends for HLA-F SNP genotypes rs1362126, rs2523405 and rs2523393, previously linked with a short time-to-pregnancy, were detected in female control groups compared with RIF patients with no identified pathology linked to infertility. The HLA-G promoter haplotype PROMO-G010101b/c linked with the HLA-G 3'-untranslated region (3'UTR) haplotype UTR-4, which previously has been associated with positive IVF outcome and pregnancy success, was less frequent in the RIF group. For RIF patients carrying the UTR-4 haplotype, the odds ratio (OR) was 0.27 (95% CI 0.12-0.66; P = 0.0044, Pc = 0.026). The HLA-G PROMO-G010104-UTR-3 haplotype was associated with an increased risk of RIF. For RIF patients carrying the UTR-3 haplotype, the OR was 5.86 (95% CI 1.52-26.23; P = 0.0115, Pc = 0.069).

CONCLUSIONS

These results show that specific HLA-G haplotypes based on the promoter region and the 3'UTR are either associated with an increased risk of reduced fertility, including the manifestation of RIF, and lower chance of achieving pregnancy, or with a reduced risk of experiencing RIF.

New insights into decidualization: immunological and genetic factors

PURPOSE OF REVIEW

Nowadays, there are many efforts focused on improving embryo quality for assisted reproduction treatments. Nevertheless, there are important maternal aspects, such as decidualization, also essential for pregnancy, often forgotten. With this review, we intend to highlight the main events involved in this endometrial phenomenon, as well as the cells and molecules that have recently been related to it.

RECENT FINDINGS

Decidualization entails a complete transformation of the endometrium, with recent research reaffirming progesterone as its main molecular trigger. Certain immune components and membrane molecules have also been found to play a role in it, notably the killer immunoglobulin-like receptors (KIR) of uterine natural killer (uNK) cells, as well as the human leukocyte antigen (HLA)-F.

SUMMARY

Progesterone directs the cellular changes that take place during decidualization, as well as the recruitment and maturation of uNKs, along with the coordinated action of interleukin-15. Likewise, the role of KIR and HLA-F in this process and in the subsequent development of pregnancy is being highlighted in many studies, with effects on reproductive outcomes related to the different genotypes of these molecules.

Mobilisation of HLA-F on the surface of bronchial epithelial cells and platelets in asthmatic patients

Uncontrolled inflammation of the airways in chronic obstructive lung diseases leads to exacerbation, accelerated lung dysfunction and respiratory insufficiency. Among these diseases, asthma affects 358 million people worldwide. Human bronchial epithelium cells (HBEC) express both anti-inflammatory and activating molecules, and their deregulated expression contribute to immune cell recruitment and activation, especially platelets (PLT) particularly involved in lung tissue inflammation in asthma context. Previous results supported that HLA-G dysregulation in lung tissue is associated with immune cell activation. We investigated here HLA-F expression, reported to be mobilised on immune cell surface upon activation and displaying its highest affinity for the KIR3DS1-activating NK receptor. We explored HLA-F transcriptional expression in HBEC; HLA-F total expression in PBMC and HBEC collected from healthy individuals at rest and upon chemical activation and HLA-F membrane expression in PBMC, HBEC and PLT collected from healthy individuals at rest and upon chemical activation. We compared HLA-F transcriptional expression in HBEC from healthy individuals and asthmatic patients and its surface expression in HBEC and PLT from healthy individuals and asthmatic patients. Our results support that HLA-F is expressed by HBEC and PLT under healthy physiological conditions and is retained in cytoplasm, barely expressed on the surface, as previously reported in immune cells. In both cell types, HLA-F reaches the surface in the inflammatory asthma context whereas no effect is observed at the transcriptional level. Our study suggests that HLA-F surface expression is a ubiquitous post-transcriptional process in activated cells. It may be of therapeutic interest in controlling lung inflammation.

Advances in the study of HLA class Ib in maternal-fetal immune tolerance

The HLA class Ib molecule is an alloantigen that causes transplant rejection on behalf of individual human and plays an important role in maternal-fetal immune tolerance. Early studies on HLA class Ib focused on the mechanism of HLA-G-induced immune escape, but in recent years, studies on the mechanism of HLA-G have deepened and gradually explored the mechanism of HLA-E and HLA-F, which are also HLA class Ib molecules. In the maternal-fetal interface, trophoblast cells express HLA class Ib molecules to protect the fetus from maternal immune cells by binding to inhibitory receptors of decidual immune cells (DICs) and shifting Th1/Th2 balance toward Th2 bias. Further studies on the molecular mechanism of HLA class Ib molecules provide a reference for its application in the field of clinical assisted reproduction.

The current situation and future directions for the study on time-to-pregnancy: a scoping review

Introduction

As problems associated with infertility and population aging increase, there is a growing interest in the factors that cause a decline in human fertility. Time-to-pregnancy (TTP) is a good indicator with which to reflect human fecundability. Here, we present a comprehensive overview of this topic.

Methods

Relevant qualitative and quantitative studies were identified by searching the Web of science and PubMed electronic databases. We included all literature, written in English, from inception to the 10th April 2021 providing the focus was on TTP. We conducted a narrative synthesis using thematic analysis.

Results

Traditional TTP-related study protocols include prospective and retrospective cohorts that provide a wealth of data to reveal potential influences on TTP. Thus far, a variety of factors have been shown to be associated with TTP in couples preparing for pregnancy, including basic demographic characteristics, menstrual status, chronic disease status, environmental endocrine disruptor exposure, and lifestyles. However, there are inevitable epidemiological bias in the existing studies, including recall bias, selection bias and measurement bias. Some methodological advances have brought new opportunities to TTP research, which make it possible to develop precision interventions for population fertility. Future TTP studies should take advantage of artificial intelligence, machine learning, and high-throughput sequencing technologies, and apply medical big data to fully consider and avoid possible bias in the design.

Conclusion

There are many opportunities and future challenges for TTP related studies which would provide a scientific basis for the “precise health management” of the population preparing for pregnancy.

As the problems of infertility and population aging increase, there is a growing interest in the factors that cause a decline in human fertility. Time-to-pregnancy (TTP) is a good indicator with which to reflect human fecundability, and a longer TTP is known to reflect a reduction in fertility. Many original studies, with different designs, have used TTP to explore the factors that might influence fertility, including basic demographic characteristics, chronic disease status, environmental endocrine disruptor exposure, and lifestyles. However, much of the existing evidence is inconsistent and limited by various types of bias. This review provides a synopsis of recent TTP studies, and highlights new opportunities and future challenges.

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.

Human Leukocyte Antigens in Pregnancy and Preeclampsia

Preeclampsia is a pregnancy-induced hypertensive disorder, the pathophysiology of which includes underlying maternal cardiovascular disease, deficient spiral artery remodeling during placenta development, and inflammatory immune responses at the maternal-fetal interface. Human leukocyte antigens (HLA) are major histocompatibility complex molecules essential for the recognition of foreign antigens that is central to immune defense against pathogens and critical determinants for the immune system discriminating between self and non-self tissues, such as in transplantation. Pregnancy represents a naturally existing “transplantation”, where the maternal immune system must be immunologically tolerant to the developing fetus which is 50% allogeneic. It is then unsurprising that HLA also influence normal pregnancy and pregnancy complications including preeclampsia. Here we review the role of classical and non-classical HLA molecules in influencing normal physiologic function during pregnancy and describe the association of HLA with pathophysiology in preeclampsia.

HLA Class I Molecules as Immune Checkpoints for NK Cell Alloreactivity and Anti-Viral Immunity in Kidney Transplantation

Natural killer (NK) cells are innate lymphocytes that can kill diseased- or virally-infected cells, mediate antibody dependent cytotoxicity and produce type I immune-associated cytokines upon activation. NK cells also contribute to the allo-immune response upon kidney transplantation either by promoting allograft rejection through lysis of cells of the transplanted organ or by promoting alloreactive T cells. In addition, they protect against viral infections upon transplantation which may be especially relevant in patients receiving high dose immune suppression. NK cell activation is tightly regulated through the integrated balance of signaling via inhibitory- and activating receptors. HLA class I molecules are critical regulators of NK cell activation through the interaction with inhibitory- as well as activating NK cell receptors, hence, HLA molecules act as critical immune checkpoints for NK cells. In the current review, we evaluate how NK cell alloreactivity and anti-viral immunity are regulated by NK cell receptors belonging to the KIR family and interacting with classical HLA class I molecules, or by NKG2A/C and LILRB1/KIR2DL4 engaging non-classical HLA-E or -G. In addition, we provide an overview of the methods to determine genetic variation in these receptors and their HLA ligands.

Maternal HLA Ib Polymorphisms in Pregnancy Allo-Immunization

During pregnancy the formation of alloreactive anti-human leukocyte antigen (HLA) antibodies are a major cause of acute rejection in organ transplantation and of adverse effects in blood transfusion. The purpose of the study was to identify maternal HLA class Ib genetic factors associated with anti-HLA allo-immunization in pregnancy and the degree of tolerance estimated by IgG4 expression. In total, 86 primiparous women with singleton pregnancies were included in the study. Maternal blood samples and umbilical cord samples were collected at delivery. Clinical data were obtained. Maternal blood serum was screened for HLA class I and II antibodies, identification of Donor Specific Antibody (DSA), activation of complement measured by C1q and IgG4 concentrations. Mothers were genotyped for HLA class Ib (HLA-E, -F and -G). Anti-HLA class I and II antibodies were identified in 24% of the women. The maternal HLA-E*01:06 allele was significantly associated with a higher fraction of anti-HLA I immunization (20.0% vs. 4.8%, p = 0.048). The maternal HLA-G 3’-untranslated region UTR4-HLA-G*01:01:01:05 haplotype and the HLA-F*01:03:01 allele were significantly associated with a low anti-HLA I C1q activation (16.7% vs. 57.1%, p = 0.028; 16.7% vs. 50.0%, p = 0.046; respectively). Both HLA‑G and HLA-F*01:03:01 showed significantly higher levels of IgG4 compared with the other haplotypes. The results support an association of certain HLA class Ib alleles with allo-immunization during pregnancy. Further studies are needed to elucidate the roles of HLA-E*01:06, HLA-F*01:03 and HLA‑G UTR4 in reducing the risk for allo-immunization.

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.