The low cytotoxic activity of peripheral blood NK cells may relate to unexplained recurrent miscarriage

From genes to reproductive health: Immune cell influences on abortion

BACKGROUND

The relationship between dysregulation of the immune system and reproductive health, particularly in the context of abortion, is an area of critical research. Identifying the immunological factors that contribute to abortion could provide valuable insights into its prevention and management.

METHODS

This study used bidirectional two-sample Mendelian Randomization (MR) approach to evaluate the causal link between 731 immune cell features and the risk of abortion. The study analyzed GWAS data from 257,561 Europeans, including 7,069 cases and 250,492 controls, by utilizing genetic variation as instrumental variables. The immune phenotypes included several cell types, including B cells, T cells, TBNK cells, Treg cells, and monocytes. These were analyzed using the 'TwoSampleMR' package in R software.

RESULTS

The study identified 34 immune phenotypes that have a significant causal relationship with abortion risk. Notably, Results from the B cell group showed a positive correlation between abortion and certain phenotypes, including Unsw mem %B cell, PB/PC %B cell, IgD+ CD24+ %B cell and Naive-mature B cell %lymphocyte. In the T cell group, certain maturation stages such as Naive CD8br %T cell and CD4 on CD45RA+ CD4+ exhibited negative causal links, whereas CCR7 on naive CD8br showed a positive association. The group of Treg cells showed both positive and negative causal relationships with abortion, highlighting the complexity of immune regulation in reproductive health.

CONCLUSIONS

This study reflects the causal relationship between different subtypes of different immune cells and abortion. The results underscore the importance of the immune system in reproductive health and suggest potential therapeutic interventions targeting these immunological pathways.

Unexplained Recurrent Pregnancy Loss: Clinical Application of Immunophenotyping

PROBLEM

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

METHODS

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

DISCUSSION AND CONCLUSION

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

Intravenous immunoglobulin improves live birth rates in patients with unexplained recurrent pregnancy loss

This real-world study aimed to assess the clinical efficacy and safety of intravenous immunoglobulin (IVIG) in treating unexplained recurrent pregnancy loss (uRPL) patients. A total of 238 patients with uRPL were enrolled in this retrospective study. According to the treatment, patients were assigned into treatment group (n=184, receiving IVIG+low molecular weight heparin [LMWH]) and control group (n=54, only LMWH). The primary outcome was the live birth rates (LBR) after 24 weeks of gestation. In addition, we performed subgroup analyses to assess the LBR in uRPL patients with age (≥30 years or <30 years), body mass index (BMI, 18-24 kg/m2 or ≥24 kg/m2), number of previous pregnancy losses (2 or ≥3), gestational week of first medication, and IVIG medication regimen during pregnancy. The LBR showed a significant increase after IVIG treatment compared to the control group (77.7 % vs. 53.7 %, P=0.001). Multivariable logistic regression indicated that IVIG was associated with increased LBR (aOR=4.383, 95 %CI 2.024-9.489). Besides, we observed a significantly lower incidence of decreased platelet count (1.6 % vs. 7.4 %, P=0.049) in the treatment group. Subgroup analyses showed that IVIG treatment was associated with improved LBR in uRPL patients with age of <30 years (aOR=4.012, 95 %CI 1.428-11.266), previous pregnancy losses ≥3 times (aOR=17.327, 95 %CI 2.525-118.921), and BMI of 18-24 kg/m2 (aOR=8.914, 95 %CI 2.985-26.618). IVIG treatment significantly improves the LBR in uRPL patients. These findings from real-world data provide evidence for the safety and efficacy of IVIG as a viable treatment for uRPL patients in clinical practice.

Decrease in peripheral natural killer cell level during early pregnancy predicts live birth among women with unexplained recurrent pregnancy loss: a prospective cohort study

BACKGROUND

Previous studies have suggested that trophoblast cells inhibit the proliferation of peripheral natural killer cells and that the level of peripheral natural killer cells decrease in the middle and late pregnancy stage among healthy women. The change in peripheral natural killer cell level during early pregnancy and the relationship between the change in peripheral natural killer cell level and pregnancy outcomes among women with unexplained recurrent pregnancy loss have not been sufficiently explored.

OBJECTIVE

This study aimed to characterize the level of prepregnancy peripheral natural killer cells in comparison with those in early pregnancy among women with unexplained recurrent pregnancy loss and to determine if the change in the level of peripheral natural killer cells from prepregnancy to early pregnancy can predict pregnancy outcomes.

STUDY DESIGN

In this prospective cohort study, 1758 women with recurrent pregnancy loss were recruited between January 2017 and December 2021 among whom 252 women with unexplained recurrent pregnancy loss had prepregnancy and early pregnancy (4-6 weeks gestation) peripheral natural killer cell measurements. These 252 women were divided into 2 groups, namely those with a lower gestational peripheral natural killer cell level (group 1) when compared with prepregnancy levels and those who did not (group 2). The respective outcomes of these groups in terms of live birth and pregnancy loss were comparatively analyzed using chi-square and Student's t tests. Candidate factors that could influence live birth were selected using the Akaike information criterion. The participates were then randomly divided into training and testing groups. A multivariable logistic regression analysis was performed and a nomogram was created to assess the possibility of live birth. The predictive accuracy was determined by the area under the receiver operating characteristic curve and validated by plotting the predicted probabilities and the observed probabilities. A Hosmer-Lemeshow test was used to assess the goodness of fit.

RESULTS

When early gestational peripheral natural killer cell levels were compared with prepregnancy peripheral natural killer cell levels, 61.5% (154) of women had a comparatively lower early-gestational peripheral natural killer cell level and 38.9% (98) of women had an increase or no change in the peripheral natural killer cell level. The live birth rate in group 1 was 89.0% (137/154), which was significantly higher than the rate of 49.0% (48/98) in group 2 (P<.001). A decrease in the peripheral natural killer cell level (odds ratio, 1.36; 95% confidence interval, 1.22-1.55; P<.001) and the anti-Muellerian hormone level (odds ratio, 1.41; 95% confidence interval, 1.14-1.81; P=.003) were important predicting factors for a higher live birth rate. Female body mass index (odds ratio, 0.97; 95% confidence interval, 0.82-1.15; P=.763) and parity (odds ratio, 1.61; 95% confidence interval, 0.71-4.12; P=.287) also were predicting factors. Furthermore, the area under the receiver operating characteristic curve of the model to diagnose of live birth was 0.853 with a sensitivity of 81.6% and a specificity of 78.0% using the training data set. And the Hosmer-Lemeshow test showed that the model was a good fit (p=6.068).

CONCLUSION

We report a comparative decrease in the peripheral natural killer cell levels in early gestation when compared with prepregnancy cell levels in more than 60% of women with unexplained recurrent pregnancy loss at 4 to 6 weeks of gestation. When compared with prepregnancy peripheral natural killer cell levels, a decrease in the peripheral natural killer cell level during early pregnancy might be a useful predictor of the live birth rate among women with unexplained recurrent pregnancy loss.

Exploring Natural Killer Cell Testing in Embryo Implantation and Reproductive Failure: An Overview of Techniques and Controversies

The blastocyst nidation is the most crucial stage to a successful pregnancy, as the white cells work to promote a favorable endometrial microenvironment for this process. Intriguingly, this implantation window lasts, on average, 6 days in most regular women, and its quality is affected by many pathological conditions. Since the grounds of reproductive failure in healthy couples are still uncharted, studies have widely suggested a potential hostile role of the immune system in the equilibrium of the maternal-fetal interface. In recent years, natural killer cells have been the highlight as they represent the greatest lymphocyte in the uterus and have immune surveillance through cytotoxicity during the implantation window. This review explored the main techniques used for natural killer (NK) cell testing in the implantation window over the last 13 years on the PubMed® database. Of 2167 published articles potentially relevant for the review, only thirty-three were about cell evaluation in healthy women, met the inclusion criteria, and had their methodology critically analyzed. Here, we bring a summary from the study group and sample collection to evidence comments about their findings and correlations. Meanwhile, we also summarize the current relationship between NK cells and endometrial receptivity with reproductive failure to help enhance the possibilities for future research. In conclusion, our overview points out that restricted and unstandardized methods support the controversy between the NK population and unsuccessful embryo implantation, which is an obstacle to studying why healthy eggs do not thrive and finding a solution for one of the most controversial topics in human reproduction.

Natural killer cell profiles in recurrent pregnancy loss: Increased expression and positive associations with TACTILE and LILRB1

PROBLEM

NK cells are important for healthy pregnancy and aberrant phenotypes or effector functions have been associated with RPL. We compared expression of a broad panel of NK cell receptors, including immune checkpoint receptors, and investigated their clinical association with RPL as this might improve patient stratification and prediction of RPL.

METHOD OF STUDY

Peripheral blood mononuclear cells were isolated from 52 women with RPL and from 2 women with an uncomplicated pregnancy for flowcytometric analysis and plasma was used to determine anti-CMV IgG antibodies.

RESULTS

Between RPL and controls, we observed no difference in frequencies of T-, NKT or NK cells, in CD56dimCD16+ or CD56brightCD16- NK cell subsets or in the expression of KIRs, NKG2A, NKG2C, NKG2D, NKp30, NKp44, NKp46 or DNAM1. NK cells from women with RPL had a higher expression of LILRB1 and TACTILE and this was associated with the number of losses. The immune checkpoint receptors PD1, TIM3 and LAG3 were not expressed on peripheral blood NK cells. In RPL patients, there was a large variation in NKG2C expression and higher levels could be explained by CMV seropositivity.

CONCLUSION

Our study identified LILRB1 and TACTILE as NK cell receptors associated with RPL. Moreover, we provide first support for the potential role of CMV in RPL via its impact on the NK cell compartment. Thereby our study could guide future studies to confirm the clinical association of LILRB1, TACTILE and NKG2C with RPL in a larger cohort and to explore their functional relevance in reproductive success.

Uterine Natural Killer Cells: A Rising Star in Human Pregnancy Regulation

Uterine natural killer (uNK) cells are an immune subset located in the uterus. uNK cells have distinct tissue-specific characteristics compared to their counterparts in peripheral blood and lymphoid organs. Based on their location and the pregnancy status of the host, uNK cells are classified as endometrial NK (eNK) cells or decidua NK (dNK) cells. uNK cells are important in protecting the host from pathogen invasion and contribute to a series of physiological processes that affect successful pregnancy, including uterine spiral artery remodeling, fetal development, and immunity tolerance. Abnormal alterations in uNK cell numbers and/or impaired function may cause pregnancy complications, such as recurrent miscarriage, preeclampsia, or even infertility. In this review, we introduce recent advances in human uNK cell research under normal physiological or pathological conditions, and summarize their unique influences on the process of pregnancy complications or uterine diseases. Finally, we propose the potential clinical use of uNK cells as a novel cellular immunotherapeutic approach for reproductive disorders.

Decidualization-derived cAMP promotes decidual NK cells to be angiogenic phenotype

BACKGROUND

During early pregnancy, a large number of CD56^bright natural killer cells (NKs) are accumulated in the decidua; unlike peripheral and cord blood NK cells (pNK and cNK), these decidual NK cells (dNK) display a great capacity to secrete a series of angiogenic/vascular factors, which are essential for placental development. However, the mechanism underlying the formation of dNK cells with an angiogenic phenotype remains unclear.

METHODS

First, we compared the difference between dNK and cNK/pNK cells in terms of the expression of CD56 and VEGF, and the regulation of the tube formation. The effect of cAMP on the differentiation of NK cells was evaluated by its analog and inhibitor stimulation. We further analyzed the differences in the phenotype of dNK cells and the expression of VEGF in dNK cells from normal pregnancies and miscarriages.

RESULTS

Different from cNK and pNK, dNK cells displayed high expression of CD56 and VEGF. And dNK cells showed a higher capacity of inducing tube formation of HUVEC by trophoblast. Meanwhile, we observed that cAMP-analogue increased the percentage of CD56^bright NK population in cNK cells with up-regulated VEGF secretion and tube formation of HUVEC by trophoblast, which could be inhibited by pretreatment with VEGFR neutralizing antibody. Similar changes occurred when co-culturing cNK cells with DSCs but not ESCs. Interestingly, the inhibitor of cAMP signaling (Metadoxine, META) could significantly inhibit the upregulation of VEGF in cNK cells by DSCs. Furthermore, DSCs could secret much more cAMP than ESCs. Notably, decreased CD56^bright NK population and VEGF secretion by dNK were related to pregnancy loss.

CONCLUSIONS

These findings suggest that dNK cells display an angiogenic phenotype that can be induced by decidualized cAMP signaling. Our study indicates the significance of decidualization-derived cAMP in regulating angiogenesis of decidual NKs and reveals complex crosstalk between different cell types in a critical period during early pregnancy.

NKG2D Natural Killer Cell Receptor-A Short Description and Potential Clinical Applications

Natural Killer (NK) cells are natural cytotoxic, effector cells of the innate immune system. They can recognize transformed or infected cells. NK cells are armed with a set of activating and inhibitory receptors which are able to bind to their ligands on target cells. The right balance between expression and activation of those receptors is fundamental for the proper functionality of NK cells. One of the best known activating receptors is NKG2D, a member of the CD94/NKG2 family. Due to a specific NKG2D binding with its eight different ligands, which are overexpressed in transformed, infected and stressed cells, NK cells are able to recognize and attack their targets. The NKG2D receptor has an enormous significance in various, autoimmune diseases, viral and bacterial infections as well as for transplantation outcomes and complications. This review focuses on the NKG2D receptor, the mechanism of its action, clinical relevance of its gene polymorphisms and a potential application in various clinical settings.