The identification of endometrial immune cell densities and clustering analysis in the mid-luteal phase as predictor for pregnancy outcomes after IVF-ET treatment

Immune system cells modulation in patients with reproductive issues: A systematic review approach

The aim of this study was to carry out a systematic literature review to investigate the main immune cells responsible for implantation failures. We selected papers from PubMed, Embase and Virtual Health Library databases. Eligible articles included publications between January 1, 2010 and April 24, 2022. Inclusion criteria were: observational and case-control studies; and the exclusion criteria were: review papers, letters to the editor, abstracts, animal studies and case reports. We extracted the following information: day of collection, number of patients, control group, age of patients, type of sample used, immune cells and cytokines. As main findings in our mapping, we found that in peripheral blood, CD3+, CD4+, CD8+, CD16+, CD56+, CD57+, CD69+, CD154+, CD158a+, NKp46 cells were increased and the CD4+, CD45+, Foxp3 and NKp46 markers were reduced. From the endometrial biopsies, there was an increase in CD3+, CD4+, CD5+, CD8+, CD16+, CD25+, CD45+, CD56+, CD57+, CD68+, CD127+ and a reduction in CD45+, CD56+, NKp46 and FoxP3 cells. Cytokines found increased in peripheral blood included IL-6, IL-10, IL-17, INF-γ, TGF-ß, TNF-α; while IL-4, IL-6, IL-10, IL-35, FoxP3, TGF-ß, SOCS3 were reduced. As for the biopsies, there was an increase in IL-2, IL-6, IL-17, IL-22, IL-23, INF-A1, INF-B1, INF-γ, TNF-R and a reduction in IL-6, IL-10, INF-γ, TGFß, TNF-α. We concluded that immune cells can be modulated during pregnancy failure, but further studies are needed to elucidate the modulating effect of the immune system on the endometrium of these patients.

The Neglected Uterine NK Cells/Hamperl Cells/Endometrial Stromal Granular Cell, or K Cells: A Narrative Review from History through Histology and to Medical Education

Reproductive immunology is at the forefront of research interests, aiming to better understand the mechanisms of immune regulation during gestation. The relationship between the immune system and the implanting embryo is profound because the embryo is semi-allogenic but not targeted by the maternal immune system, as expected in graft-versus-host reactions. The most prominent cell population at the maternal-fetal interface is the population of uterine natural killer (uNK) cells. Uterine NK cells are two-faced immunologically active cells, bearing comparison with Janus, the ancient Roman god of beginnings and endings. Their first face can be seen as natural killer cells, namely lymphocytes, which are critical for host defense against viruses and tumors. Even though uNK cells contain cytolytic molecules, their cytotoxic effect is not applied to classical target cells in vivo, playing a permissive rather than a defensive role. Their second face is crucial in maintaining physiological gestation-uNK cells show critical immunomodulatory functions with the potential to control embryo implantation and trophoblast invasion, regulate placental vascular remodeling, and promote embryonic/fetal growth. Therefore, we believe that their current designation "natural killer cells" (the first "cytotoxic" Janus's face) is misleading and inappropriate, considering their principal function is supporting and maintaining pregnancy. In this narrative review, we will focus on three lesser-known areas of knowledge about uNK cells. First, from the point of view of histology, we will comprehensively map the history of the discovery of these cells, as well as the current histological possibilities of their identification within the endometrium. To be brief, the discovery of uNK cells is generally attributed to Herwig Hamperl, one of the most influential and prominent representatives of German pathology in the 20th century, and his co-worker, Gisela Hellweg. Secondly, we will discuss the interesting aspect of terminology, since uNK cells are probably one of the human cells with the highest number of synonymous names, leading to significant discrepancies in their descriptions in scientific literature. From the first description of this cell type, they were referred to as endometrial granulocytes, granular endometrial stromal cells, or large granular lymphocytes until the end of the 1980s and the beginning of the 1990s of the last century, when the first publications appeared where the name "uterine NK cells" was used. The third area of present review is medical teaching of histology and clinical embryology. We can confirm that uNK cells are, in most textbooks, overlooked and almost forgotten cells despite their enormous importance. In the present narrative review, we summarize the lesser-known historical and terminological facts about uNK cells. We can state that within the textbooks of histology and embryology, this important cell population is still "overlooked and neglected" and is not given the same importance as in fields of clinical research and clinical practice.

Endometrial immune cell ratios and implantation success in patients with recurrent implantation failure

The objective of this study was to compare the endometrial immune cells quantities and ratios during the mid-luteal phase between women with recurrent implantation failure (RIF) with successful and unsuccessful embryo implantation. For this purpose, endometrial biopsies from 116 women aged between 29 and 46 with history of RIF undergoing Assisted Reproductive Technology (ART) without endometrial pathologies were immunohistochemically stained for CD3 + T-cells, CD4 + T-helpers, CD8 + T-killers, CD14 + monocytes, CD68 + macrophages, CD56 + NK cells and CD79α+ B-cells. Endometrial immune cells quantities and ratios were compared based on the embryo implantation outcome in the subsequent embryo transfer cycle. Spearman correlation analysis and Mann-Whitney U test were used to analyse the obtained data. Patients who experienced successful implantation at the subsequent cycle had significantly lower percentage of CD3 + T cells, and higher ratios of CD4 + /CD8 + , CD4 + /CD3 + and CD68 + /CD3 + than the patients who experienced another failure in implantation. In addition, the ratios of CD3 + /CD14 + , CD79α+ /CD14 + and CD56 + /CD14 + were significantly lower in the successful implantation group than that in the unsuccessful one. A cut off value of CD68 + /CD3 + ratio higher than 0.85 (AUC 0.67, 95% CI 0.56-0.79), CD4 + /CD3 + ratio higher than 0.19 (AUC 0.67, 95% CI 0.56-0.79) and CD4 + /CD8 + ratio higher than 0.43 (AUC 0.62, 95% CI 0.50-0.73) could be predictive factors for successful implantation in RIF patients. Knowledge on the immune cell composition could assist in the evaluation of the endometrial receptivity in RIF patients.

Myeloid-derived suppressor cells: A new emerging player in endometriosis

Endometriosis is a common gynecological disorder defined by the presence of endometrial tissue outside the uterus. This is commonly associated with chronic pelvic pain, infertility, and dysmenorrhea, which occurs in approximately 10% of women of reproductive age. Although the exact mechanism remains uncertain, it has been widely accepted to be an estrogen-dependent and inflammatory disease. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of immune cells with immunosuppressive capacity and non-immunological functions. They have been found to be aggressively involved in the pathologies of various disorders. In regards to tumors, the functions of MDSCs have been profoundly shown to inhibit tumor immune response and to promote angiogenesis, tumor metastasis, fibrosis, and epithelial-mesenchymal transition (EMT). In recent years, the elevation of MDSCs in endometriosis was reported by several studies that provoke the assumption that MDSCs might exert similar roles to promote the development of endometriosis. Such that, precision treatments targeting MDSCs might be a promising direction for future study. Herein, we will review the research progress of MDSCs in endometriosis and its potential relevance to the pathogenesis, progression, and therapeutics strategy of endometriosis.

Three-Dimensional Culture for In Vitro Folliculogenesis in the Aspect of Methods and Materials

In vitro ovarian follicle culture is a reproduction technique used to obtain fertilizable oocytes, for overcoming fertility issues due to premature ovarian failure. This requires the establishment of an in vitro culture model that is capable of better simulating the in vivo ovarian growth environment. Two-dimensional (2D) culture systems have been successfully set up in rodent models. However, they are not suitable for larger animal models as the follicles of larger animals cultured in 2D culture systems often lose their shape due to dysfunction in the gap junctions. Three-dimensional (3D) culture systems are more suitable for maintaining follicle architecture, and therefore are proposed for the successful in vitro culturing of follicles in various animal models. The role of different methods, scaffolds, and suspension cultures in supporting follicle development has been studied to provide direction for improving in vitro follicle culture technologies. The three major strategies for in vitro 3D follicle cultures are discussed in this article. First, the in vitro culture systems, such as microfluidics, hanging drop, hydrogels, and 3D-printing, are reviewed. We have focused on the 3D hydrogel system as it uses different materials for supporting follicular growth and oocyte maturation in several animal models and in humans. We have also discussed the criteria used for biomaterial evaluations such as solid concentration, elasticity, and rigidity. In addition, future research directions for advancing in vitro 3D follicle culture system are discussed. Impact statement A new frontier in assisted reproductive technology is in vitro tissue or follicle culture, particularly for fertility preservation. The in vitro three-dimensional (3D) culture technique enhances follicular development and provides mature oocytes, overcoming the limitations of traditional in vitro two-dimensional cultures. Polymer biomaterials have good compatibility and retain the physiological structure of follicles in the 3D culture system. Utilizing hybrid in vitro culture materials by merging matrix, hydrogel, and unique patterned materials may facilitate follicular growth in the future.