Review of Clinical and Therapeutic Applications of Cellular Therapy and Endometrial Regeneration

Review of Clinical and Therapeutic Applications of Cellular Therapy and Endometrial Regeneration

Nahla Kazim *, Varsha Ojha’s1, Dr Archana Singh2

 

1.Specialist Obstetrician and Gynecologist, Prime Hospital, Dubai.

2. Specialist Gynecologist, IVF specialist, Indra IVF, Jodhpur, India.

 

*Correspondence to:   Nahla Kazim, Dr Nahla Kazim MD, MSc, PhD (UAE)., Consultant/ Reproductive Medicine and Infertility. Director of Fertility Preservation (Bourn Hall Fertility Clinic, UAE, Adjunct Associate Professor (UAE University).

Copyright                             

© 2024 Nahla Kazim. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Received: 17 Sept 2024

Published: 21 Sept 2024

DOI:https://doi.org/10.5281/zenodo.13892754

 

ABSTRACT

One of the challenges of current reproductive medicine is the treatment of implantation failure. In many cases the reason for this failure is unknown. Other times, is due to the presence of uterine adhesions or insufficient endometrial thickening. Nowadays, the discovery of an endometrial lineage of adult stem cells have made great progress in cell therapy. These cells are able to regenerate after each menstruation and represent an alternative to other tissues mesenchymal stem cells, such as bone marrow, embryonic cells or umbilical cord. They constitute a non- invasive solution to this common problem. The application of these therapies in human beings is still at an experimental phase. Effectiveness and safety have to be clarified in women undergoing assisted reproductive treatments. Furthermore, therapeutic applications in regenerative medicine need to be investigated.

Keywords: cell therapy, endometrial regeneration, endometrial stem cells, uterine adhesions, endometrial thinning.

Review of Clinical and Therapeutic Applications of Cellular Therapy and Endometrial Regeneration

Introduction

The endometrium is a very dynamic tissue, where its rupture and repair occur simultaneously, under a carefully controlled balance in each cycle menstrual cycle during a woman's reproductive life (about 400 cycles). sin is repaired scarring (a fact that occurs only in fetal wounds and some adult mucous membranes) and then Regenerating the precise thickness (approximately 8 mm) with the functionality adequate to allow implantation and placentation of a pregnancy. It is believed that the Human endometrium possesses endogenous and exogenous sources of stem cells that are key to understand its extraordinary regenerative capacity. Yet every day we see changes in endometrial receptivity or uterine adhesions that alter this repair

The endometrium is made up of two layers, the functional layer and the basal layer. The first of them it is formed by numerous adjoining glands and the luminal epithelium; is the one that is lost during menstruation, this is regulated by ovarian hormones. It is in the basal layer where you will be able to find glands, stromal cells and vascularization that will provide most of the essential stem cells for the regeneration of functionality endometrial after menstruation, as well as immune cells involved in this process(1). This layer will not be affected by hormonal changes. Menstruation begins after hormonal fall, mediated by endocrine signals and paracrines in the endometrium. During this phase, the functional layer is removed and a posterior endometrial re-epithelialization(2). Reepithelialization begins at 36 hours approximately after the onset of bleeding, and requires about 48 hours to complete(3). Endometrial repair does not involve any scar formation as can occur in other organs, and this may be due to the basal layer at all times. When this layer is damaged or lost, scarring occurs, which is what will cause endometrial pathology(4). For the next 10 days or so after the menstrual phase, the thickness endometrial and the entire cohort of cellular structures, including glands, stroma, vascularization and extracellular matrix, is regenerated by massive cell destruction in the functional layer. This phase is known as proliferative.

 

Stem/progenitor cells as a form of endometrial regeneration

Somatic stem cells are undifferentiated cells capable of maintaining their own self-renewal mechanisms. They have a high proliferative and differentiation potential in one or more more specialized cell lines(5). In 1989, the concept of somatic or progenitor stem cells was proposed, existing in the basal layer of the endometrium, being responsible for its cyclical growth(6). A From this moment on, different stem cells involved in the endometrial regeneration(7). Stem cells occupy specific niches that allow their differentiation depending on the microenvironment in which they are found. For example, Endometrial stem cells reside predominantly in the basal layer, whereas endometrial stem cells mesenchymal stem cells are also present in the functional layer.

 

Among the pathologies that can affect the endometrium are:

Asherman's syndrome (AS) or intrauterine adhesions

This syndrome is a condition caused by severe damage to the basal layer of the endometrium, the cavity being partially replaced by a layer of cells fibrotic that can lead to infertility, recurrent abortions, hypomenorrhea, pain pelvic or menopause. It appears after procedures such as curettage. It is described even in 39% of women with recurrent abortions(8). Among the possible treatments: lysis of intrauterine adhesions with hysteroscopy, use of intrauterine balloons, IUD, or estrogen therapy. As a new alternative, regeneration of the endometrial basal layer with stem cell therapies(8,9).

 

?Endometrial thinning

A good marker of receptivity is endometrial thickness. It is considered slim when it has a thickness of less than 7 mm prior to transfer(10). The pathophysiology of why the thinned endometrium reduces the probability of pregnancy is still today uncertain. Several explanatory hypotheses are proposed; one of them proposes the proximity to the layer basal, rich in reactive oxygen species (ROS), detrimental to the development of the embryo(11). Another theory is the malfunction of endometrial stem cells that would render him incompetent. The main consequence of the persistence of a Endometrial thinning is the decrease in the rate of implantation and the increase in the abortion rate in these patients(12).

The prevalence of this finding is around 5% in women under 40 years, reaching up to 25% in women over 40 years of age with natural cycles(13). Aspirin and estrogen therapy are two of the treatments used currently to improve endometrial thickness as well as Asherman's syndrome(14). A Despite this, a recurrence of adhesions has been described despite treatment of up to 66%(15). Consequently, many researchers have sought to identify new ways therapies capable of improving endometrial receptivity and endometrial growth.

Recently, cell therapy has been proposed as an ideal alternative for regeneration of the endometrium, including the use of stem cells, platelet-rich plasma and growth factors as therapeutic agents. Since cell therapy is personalized, dynamic, interactive and specific, could be a strategy in the future(16).

 

Materials and Methods

An electronic review of the literature of articles published in English has been carried out. Regarding the types and use of stem cells in the field of reproductive pathology, carried out in May 2022. The online databases used have been PubMed performing bibliographic searches with the following terms 'stem cell therapy', ‘menstrual cycle`, endometrial regeneration`, ´Asherman syndrome`, ‘weight loss endometrial` and ´uterine adhesions`.

Titles were screened and relevant articles and cited references were analyzed. Considering abstracts, case reports, original articles and meta-analyses on the use of stem cells and their involvement in endometrial regeneration and impact on the reproduction. It should be noted that today most of the works published in the In this regard, they have a very small sample size or are studies on animal populations.

 

Results

Repeated curettage, abortions or infections can damage stem cells endometrial. Although these cells can live without estrogen, the cellular niches in the found require this hormone(8,17). The application of stem cell therapy could give us an effective therapeutic approach for patients who are suffering from infertility.

 

Mesenchymal cells (MSCs)

They are a type of multipotent adult stem cells from various tissues such as bone marrow, umbilical cord, menstrual blood, endometrial tissue, or adipose tissue. They have self-renewal capacity and differentiation potential. It is well known that the therapeutic effects of MSCs are due to their immunomodulatory function and their effect anti-inflammatory through the regulation of lymphocytes in numerous diseases.

They balance the activity of Th1 and Th2, inhibit the proliferation of NK cells and prevent activation of dendritic cells. They also stimulate the secretion of cytokines by activating the innate immune system(18). Endometrial mesenchymal cells (eMSCs) can be isolated from women of all ages, and used autologous(19). They can be obtained from the menstrual flow and in postmenopausal patients after a period with hormone replacement therapy(20). There are it should be noted that women who may require endometrial regeneration may have irregular or abnormal menstruation In these cases, we can consider the use of eMSCs donated, thanks to the low immunogenicity they present due to the low expression of the antigen HLA-ABC and HLA- DR negative(21).

Umbilical cord mesenchymal cells (UC-MSCs) have also been studied as an alternative in the treatment of endometrial alterations thanks to its capabilities immunomodulatory. Works such as that of Cao et al of 2018, successfully report the increase in endometrial thickness and decrease in intrauterine adhesions after the application of UC-MSCs(22). We can also find studies applied to endometrial regeneration referring to mesenchymal stromal cells derived from adipose tissue (ADSCs)(9). On the other hand, new studies are focusing on investigating exosomes secreted by these cells. These exosomes present paracrine activity that repairs the damage tissue, being superior in biological stability and less immunogenicity compared to MSCs(23).

?Bone marrow derived stem cells (BMDSCs)

Within the stem cells we find the BMDSC. They are an exogenous source of cells mother and are capable of repopulating various nonhematopoietic tissues. In 2004, the group of Taylor first reported the recruitment of BMDSCs in the human uterus after bone marrow transplant(24). These types of stem cells are capable of migrating through different organs, regenerating and repairing tissues including the reproductive tract(25). In situations of uterine ischemia, stem cells are recruited from the bone marrow in the uterus. Despite this, it has not been observed that they are involved in the monthly regeneration of the endometrium(26). However, the cell extraction process, the risk of complications and the decreased age-dependent turnover, have limited its use as well as trials clinical.

 

Endometrial stem cells (EndoSCs)

EndoSCs include epithelial, stromal, and endothelial cells, and all can contribute to rapid endometrial regeneration(27). The EndoSCs reside in the endometrium allowing their regeneration together with the cells derived from bone marrow. A randomized trial in mice comparing BMDSC with EndoSC for regeneration of the endometrium(28). In this study, cells endometrial scavengers were less effective than BMDSCs in repopulating the endometrium. Based on these findings, it is hypothesized that endogenous EndoSCs differ partially while BMDSCs are still multipotent and could probably differentiate into early precursor cells that can completely replace all the endometrial cells.

 

Menstrual blood-derived stem cells (MenSC)

They are also known as the cells that allow endometrial regeneration, but phenotypically different from endometrial stem cells. Among its effects on tissue is found: differentiation, immunomodulation and paracrine signals. It has also been described that they have an important effect on the inhibition of fibrosis.

 

Myometrial stem cells (MyoSCs)

Myometrial stem cells have been shown to be capable of generating myometrium after in utero transplantation in immunodeficient mice(29). Considering that the eventual formation of the uterus is the result of the proliferation of cells mesenchymal, the internal mesenchyme would correspond to the endometrial stroma of the uterus adult, while the external mesenchyme would give rise to the adult myometrium. The existence of MyoSCs are evidenced in tissue growth during pregnancy. The cells are also capable of reconstructing myometrial tissue in vivo in animal xenograft models, which corroborates the validity of CD49f/CD34 and STRO-1/CD44 as potential markers of MyoSC, although its biological importance remains unclear(30). Therefore, considering that the Uterine leiomyomas are monoclonal tumors, it is possible that dysregulation of MyoSCs or from these committed cells that acquire tumor-like characteristics, cells tumor-initiating tumor cells (TICs), may be responsible for this benign condition. Unfortunately, the great plasticity of stem cells also offers an opportunity for cell reprogramming aberrantly through epigenetic mechanisms, such as DNA methylation, histone modification, or miRNA regulation, which promotes susceptibility to disease later in adulthood.

 

Human Amniotic Epithelial Cells (hAEC)

As a potential source of stem cells, hAECs are isolated from the amniotic membrane, which is in contact with the amniotic fluid and is the layer closest to the fetus. They improve the proliferative cell nuclear antigen (PCNA), which is responsible for the duplication of the DNA is precise, being more abundant in the proliferative phase and in the menstrual period. In addition, it promotes endometrial expression of vascular endothelial growth factor (VEGF). It has been seen in murine models that hAECs were capable of increasing the expression of estrogen receptors in the damaged murine endometrium by repairing the damage(31). to day of Today, there are no clínical studies examining the effect of hAEC in humans for the prevention of AS treatment.

 

Cell niches.

Stem cells reside in specialized microenvironments, also called cell niches. stem cells, which regulate their cell division and fate. Since then, the niche has redefined as a dynamic system in which stem cells interact with differentcomponents of the microenvironment, such as other differentiated cells, secreted factors (chemokines, hormones, growth factor receptors), extracellular matrix (ECM) (collagen fibers, fibronectin), physical factors, hypoxia/metabolism and the general environment (inflammation, scarring, rich in hormones)(32).

An essential aspect of grafting is incorporation into the niche, a supportive environment where appropriate paracrine signals maintain the undifferentiated and multipotent state. this niche is perivascular, hence the incorporation is more effective intravenously and not within the endometrium.

 

Platelet Rich Plasma (PRP)

Starting in the 1970s, autologous PRP began to be used due to safety that it generates thanks to its origin from the patient's autologous blood. It has been described capacity for tissue regeneration, angiogenesis, remodeling of the extracellular matrix, differentiation, proliferation and recruitment of stem cells(33). PRP treatment could restore the damaged endometrium. It has been reported that this treatment can thicken the endometrium and increase the rate of pregnancy and live birth, although it is not clear if These results are directly related to the intrauterine administration of PRP(34).

Growth factors (GFs)

Growth factors have the potential to stimulate differentiation and cell proliferation(35). This capacity has meant that in recent years it has been considered as a line of research the use of these agents in endometrial regeneration. Also, the the role of growth factors as participants in the implantation process has been reflected in numerous works(36).

 

Discussion

In recent years, these cell therapies have begun to be applied to endometrium with pathologies that affect reproduction. Sources such as BMDSCs, menSCs and ADSCs, have been applied for endometrial regeneration in patients with Asherman's syndrome(9). Authors such as Zhao et al. and Gan et al. they have corroborated the immunomodulatory role of stem cells by injecting stem cells mesenchymal cells in the uterine cavity of mice, observing an increase in the expression of cytokeratins, vimentin, alpha and B3 integrin; an increase in anti-inflammatory cytokines and a decrease in the expression of proinflammatory cytokines (IL 1 and TNF alpha)(37).

The prospective study carried out by Santamaría et al. with 16 patients, administered by catheterization to the spiral arterioles a pool of BMSC CD133+, monitoring of these patients observed an increase in endometrial thickness both in thin endometria as in patients with Asherman's Syndrome(38).

Previously, studies on the murine population have been described. Zhao et al. Demonstrated in 2015 not only the effects of BMSCs on the endometrium in terms of regeneration and endometrial receptivity. Induced endometrial thinning after ethanol infusión intrauterine in rats. BMDSCs were transplanted directly intrauterine and saline in the control group. Observing a significant endometrial thickening with respect to the group control, as well as an attenuation of proinflammatory cytokines, and an increase in cytokines anti- inflammatory and markers of endometrial regeneration (cytokeratin, vimentin)(39).

Observational studies in patients who have undergone bone marrow transplantation suggest that bone marrow-derived stem cells (CD45+) can differentiate into epithelial and stromal endometrial cells contributing to regeneration endometrium(25,40). Ong et al. in their work with mice on this cell population have described, that there may have been confusion in the selection of these cell lines due to that present markers similar to macrophage colonies (CD45+)(41). This work has implied that there is currently no consensus on bone marrow-derived stem cells bone and its endometrial involvement(42,43).

The potential effect of MenSCs as cell therapy includes the decrease of uterine adhesions, but the molecular mechanism by which this occurs remains to be seen elucidate. Zhu et al. in 2019 study these pathways of action in vitro, concluding that MenSCs they inhibit the activation of myofibroblasts, which allows a more rapid proliferation of myofibroblasts EndoSCs(44). Another study, in this case carried out on 7 infertile patients with AS, isolated and cultured MenSCs from the menstrual blood of each patient, transplanting it subsequently and a significant endometrial thickness increase >7 mm was observed in 5 women; 4 underwent cryotransfer and 2 became pregnant. One of the patients had a spontaneous pregnancy after the second transplantation of MenSCs(45).

One of the studies carried out in humans injected ADSCs at the endometrial level autologous in 25 patients with a thinned endometrium who had failed the reproductive cycles. The result showed an increase in endometrial thickness in 80% of the patients, with 13 pregnancies and 9 healthy newborns(46). The work published in 2020 by a group from Korea, consisted of the study of six infertile women with severe AS diagnosed by hysteroscopy. Through liposuction, in these patients the fraction of autologous adipose tissue- derived vascular stroma, containing ADSCs, and its subsequent intrauterine transplant followed by hormonal treatment with estrogens. Of the 5 patients who continued in the study, all of them increased their menstrual flow. It was observed a Significant endometrial thickness increase from 3 +/- 1 mm to 6.9 +/-2.9 mm after treatment. All 5 patients underwent embryo transfer, although only one of them they became pregnant, resulting in an abortion at 9 weeks of gestation(47).

Endometrial regeneration using platelet-rich plasma has also been documented(48). It has the ability to promote cell migration and proliferation mesenchymal stem cells that subsequently differentiate into endometrial cells. A randomized and controlled study has observed a regeneration of the endometrium as well as a decrease in fibrosis in murine models (n=6) with damaged endometria, after administration of autologous PRP(49). These findings have also been described in other Works such as that of Kim et al(50). The study of PRP on human endometrium has also been hopeful, Wang et al. describe how after the intrauterine infusion of PRP the growth and migration of endometrial mesenchymal cells, enhancing expansión endometrial and an increase in the pregnancy rate of 60%(51).

The administration of granulocyte colony-stimulating factors (G-CSF) has been shown to be effective in non- hematopoietic cells such as the endometrium, allowing its growth(52). The prospective study after the administration of G-CSF between 6-8 hours before the trigger with HCG has been shown to increase endometrial thickness, improving the pregnancy rate(52). Kunicki et al. showed an increase in endometrial thickness after administration of G-CSF in women with previous IVF cycles with abnormal endometrium suitable(53). Other groups have described a decreased cancellation rate in cycles cryotransfer after administration of G-CSF in patients with an endometrium thinned, but they do not show an increase in the rate of implantation and pregnancy(54).

Barad et al. led a randomized controlled study with up to 141 patients showing that G-CSF would improve endometrial thickness in patients with endometrial disease, not in those without endometrial pathology(55). Most papers describe a dose of 300 micrograms administered intrauterinely. In 2019, Banerjee et al. performed this infusion via subcutaneous, objectifying the improvement in the clinical pregnancy rate (55% vs 24% in the group control, p<0.001)(56).

 

Future Perspectives

Today, we find some obstacles to implement these therapies in our daily clinical practice. Determine the route of administration as well as the appropriate time of cycle are two of the factors involved. For this, the cell type should be taken into account transplanted, and how the activity of immune cells is modified during the cycle(25,57). Some engineering tools are currently being developed for the adequate administration and cell transplantation, including cell membranes or layers(58).

Before the development of these therapies, it will be important to elucidate the possible effect that have due to their proliferative capacity, which can contribute to the development of endometriosis or in the formation of endometrial carcinomas if the ectopic endometrial tissue grows(25).

 

Conclusions

There are numerous lines of research on cellular sources for regeneration endometrial, but the molecular mechanisms are still to be determined due to the endometrial tissue dynamics; It will be these lines of research that facilitate the application of the different cell lineages as therapies in reproduction. Most of the therapies described are based on animal models, so it is It is difficult to obtain a conclusion on the effectiveness of these therapies in humans, especially regarding the increase in the rate of live births at the present time.

 

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