Advances in mesenchymal stem cell-based therapies for recurrent spontaneous abortion

Abstract

Young women’s physical and mental health is seriously impacted by recurrent spontaneous abortion (RSA), a prevalent obstetric complication that is becoming more commonplace worldwide. Therefore, a thorough investigation into the pathophysiology of RSA and the development of novel therapeutic strategies are imperative. Recent developments suggest that mesenchymal stem cell (MSC)-based therapies may be viable for addressing RSA. Through a variety of mechanisms, the immunological circumstances at the maternal-fetal contact can be altered, including regulating immune cell homeostasis, enhancing immune tolerance, alleviating inflammatory responses, promoting angiogenic processes, and promoting tissue regeneration. MSCs exhibit a remarkable capacity for multi-differentiation that could enhance pregnancy outcomes. This article provides compelling studies supporting the efficacy of MSC-based therapies in improving pregnancy outcomes in women with RSA.

Key Words: Mesenchymal stem cells; Therapy; Recurrent spontaneous abortion; Mechanism; Immune; Maternal-fetal; Outcome; Treatment

Core Tip: The reproductive health of women of childbearing age is significantly impacted by recurrent spontaneous abortion. Although there are several therapeutic options available today, the curative efficacy is unsatisfactory. By controlling immunological factors, mesenchymal stem cell therapy is one possible treatment option that can enhance pregnancy outcomes. Mesenchymal stem cell treatment and its associated mechanisms are briefly explained in this article.

INTRODUCTION

The American College of Obstetrics and Gynecology defines recurrent spontaneous abortion (RSA) as the failure of three or more successive pregnancies before 20 weeks of conception with the same sexual partner[1]. Due to varying definitions, the mean occurrence of RSA is between 1% and 4%[2]. In addition to affecting women’s health[3], RSA also causes psychological distress and places economic and emotional strain on the entire family[4-6]. There are numerous causes of RSA, including immunological disorders, chromosomal abnormalities, endometrial dysfunction, and uterine malformations[6,7]. Mesenchymal stem cell (MSC) therapy, hydrogels, or synthetic biosimilars containing MSCs have been shown by Rodríguez-Eguren et al[8] to stimulate tissue healing, vascular growth, and endometrial proliferation. These actions may aid in the restoration of endometrial function and, eventually, fertility[8]. Accurate personalized treatment is still challenging, as the exact cause of RSA is unknown and requires more research[9].

Because of their ability to proliferate, self-renew, and differentiate either unidirectionally or multidirectionally, stem cells may be used for wound repair, tissue regeneration, restoration of organ and tissue function and maintenance of the normal state of the body[10,11]. Stem cell therapy is one type of immunotherapy that may be used for the treatment of RSA[6]. Depending upon the source they originate from, stem cells can be classified as either adult or embryonic. Due to their rich sources, ease of separation and culture, and minimal immunogenicity, stem cells are regarded as an effective therapeutic approach. At present, an increasing number of studies have demonstrated that MSC therapy can enhance pregnancy outcome in RSA and preserve the immunological tolerance of the maternal-fetal interface[12-14].

To provide specific treatment for RSA, it is necessary to determine the pertinent mechanisms of MSCs from various origins in the management of RSA. This will have a definite effect on unexplained RSA. Understanding the mechanism of RSA aids in the advancement of MSC research and can provide a basis for the clinical use of MSCs in RSA treatment.

MSCS AND CLASSIFICATION BASED ON THEIR ORIGIN

MSCs are multifunctional adult stem cells that can be generated from a variety of organs, including bone marrow, fat, umbilical cord, umbilical cord blood, skeletal muscle, dental pulp, placenta, amniotic fluid, and amniotic membrane[15-17] (Figure 1). MSCs could enhance the results of pregnancies by modifying the immunological milieu at the maternal-fetal interaction through various mechanisms, including regulating immune cell homeostasis, enhancing immune tolerance, alleviating inflammatory responses, promoting angiogenic processes, and promoting tissue regeneration (Figure 2). We performed a systematic search of full-text articles available in PubMed to identify original peer-reviewed studies published in English. The search terms included: “Stem cell”, “mesenchymal stem cell”, “abortion”, “miscarriage”, and “recurrent spontaneous abortion”. Preclinical and clinical studies were included. According to the literature review, there are currently five origins of MSCs that satisfy the requirements: Bone marrow, adipose, umbilical cord, amniotic, and decidual.

Figure 1 Origin and differentiation of mesenchymal stem cells. The figure was created by BioRender (Supplementary material). MSC: Mesenchymal stem cell.

Figure 2 Action mechanisms of the mentioned mesenchymal stem cells for preventing recurrent spontaneous abortion. The figure was created by BioRender (Supplementary material). MSC: Mesenchymal stem cell; Th1: T helper type 1; Th2: T helper type 2; NF-κB: Nuclear factor kappa B; TLR-4: Toll-like receptor 4; STAT-1: Signal transducer and activator of transcription 1; Nrf2: Nuclear factor erythroid-2-related factor 2; IFN: Interferon; TNF: Tumor necrosis factor; IL: Interleukin; HMOX-1: Heme oxygenase-1.

Bone marrow MSCs

The adult stem cells most frequently utilized in therapeutic research to date are bone marrow derived MSCs (BMSCs), which have minimal immunogenicity. Multiple disorders affecting the reproductive system have been treated with these cells[18,19]. Numerous animal studies have been conducted to investigate the mechanism by which BMSCs could treat RSA. Although BMSCs do not affect CD4+ T cells and macrophages in the entire body, they can decrease the rate of embryo absorption in mice and act locally on CD4+ T cells and macrophages at the interaction site between mother and fetus[20]. At the site of BMSC injection, the secretion of interleukin (IL)-4 and IL-10 increased while tumor necrosis factor (TNF)-α and interferon (IFN)-γ secretion was inhibited. This indicated that BMSCs improve the outcome of pregnancy by suppressing the T helper type 1 (Th1) immunological response, encouraging the Th2 immunological response, and making the Th2 immune response a key player in the interaction between the mother and the fetus[21]. Following BMSC injection, M1-type macrophages transformed into M2-type macrophages, which increased IL-10 release and decreased IL-12 secretion, shifting the macrophage balance to an anti-inflammatory state[22,23]. Additionally, by interacting with M1-type macrophages, BMSCs can alleviate abortion by immunosuppressing TNF-stimulating gene-6 and promoting its paracrine function[24-26]. In one study, exosomes were extracted from BMSC culture medium and injected into the uterine horn. These exosomes induced macrophages to polarize to M2-type in addition to transporting miR-101 to T cells to boost the Th2 immune response. At the interaction site between mother and fetus, exosomes regulate T cell and macrophage activity, which decreases the rate of embryo absorption[27,28].

Adipose-derived MSCs

Adipose-derived MSCs (ADMSCs) are less invasive than BMSCs, have high proliferative capacity, and release a range of growth factors[29]. The primary way that ADMSCs modulate the immune system is by controlling the equilibrium between Th1 and Th2 inflammatory agents both locally and systemically. ADMSC therapy has an immunomodulatory effect by downregulating IFN-γ and TNF-α gene expression and upregulating the production of transforming growth factor-β and IL-10 in the decidua, thereby reducing the rate of embryo absorption and protecting the fetus[30]. Salek Farrokhi et al[31] discovered that the identical alterations took place in the spleen of mice and that ADMSCs might reduce the immunological rejection of paternal antigens by the spleen. Rezaei Kahmini et al[32] discovered that ADMSCs improve the tolerance environment of the maternal-fetal interaction by reducing CD49b+ natural killer (NK) cell infiltration into the interface and modifying the NK cell cytokine spectrum from an inflammatory to a tolerance spectrum. ADMSCs prevented excessive complement C3 activation and deposition during pregnancy and enhanced angiogenic equilibrium at the interaction site between mother and fetus, which benefited the fetus and enhanced intrauterine pregnancy[33]. By examining the data from relevant studies on the use of ADMSCs to treat abortion, Zhao et al[34] validated the aforementioned perspective, which was crucial in supporting the ensuing clinical data translation.

Wharton’s jelly-derived MSCs

Human umbilical cord-derived MSCs, known as Wharton’s jelly-derived MSCs (WJMSCs), are capable of tissue healing and immunoregulation[35,36]. They are regarded as the perfect stem cell type in regenerative medicine due to their lack of intrusion[37]. Chen et al[38] discovered that injection of WJMSCs improved early abortion by increasing IL-10 expression in the mouse placenta and decreasing IFN-γ and IL-17 expression. WJMSCs decreased the rate of embryo absorption by increasing the production of Th2 immune indicators through the Janus kinase/signal transducer and activator of transcription pathway, as confirmed by Ding et al[39]. The connection between decidual tissues in the abortion model, particularly that between stromal cells and NK cells, was found to be suppressed using single cell sequencing. Treatment with WJMSCs may improve RSA at the single cell scale by partially repairing barriers between decidual tissues[40]. The precise mechanism of WJMSCs requires further investigation, as there has been little preclinical research on their use in treating RSA.

Amniotic MSCs

Amniotic membrane is simple to obtain, is noninvasive, has almost no ethical limitations, and has therapeutic potential in the field of regenerative medicine. After repeated passage and growth, amniotic MSCs (AMSCs), which have a high initial order of magnitude and minimal immunogenicity, can maintain good proliferation and differentiation potential[41-43]. By suppressing proinflammatory cytokines and stimulating anti-inflammatory molecule release, AMSCs may decrease intrauterine adhesion and promote early miscarriage. By controlling the population of regulatory T cells, AMSCs may additionally improve the number of glands, decrease areas of ovarian fibrosis, and encourage endometrial regeneration[44]. Research has verified that human AMSCs enhanced angiogenesis, facilitated macrophages to polarize into M2-type macrophages, reduced the rate of embryo absorption and inflammatory cell infiltration, and markedly increased IL-10 and transforming growth factor-β expression while decreasing that of IL-1β and IL-6[45]. In order to cure disorders of the reproductive system, AMSCs can stimulate follicular creation, endometrial regeneration, gland development, and the restoration of hormone levels (such as anti-Müllerian hormone and estradiol)[46]. Even though these studies offer a theoretical framework for treating abortion, more investigation is required to validate these findings and determine how to use them in a clinical setting.

Decidual MSCs

With the patient’s consent, decidual tissue is extracted from samples of induced abortions between 6 and 8 weeks of pregnancy. This tissue is a promising candidate for treatment in regenerative medicine and has good angiogenesis, anti-inflammatory, and antiapoptotic properties[47,48]. Although there are currently limited investigations on decidual MSCs (DMSCs), related research has shown that like MSCs from other origins, DMSCs can play a role in immunomodulation. DMSCs have been shown to boost the proportion of regulatory T cells and suppress apoptosis and proliferation, both of which are beneficial for preserving immunological resistance at the junction between the mother and the fetus. Nevertheless, the study also discovered that spontaneous abortion had a better immunoregulatory impact than RSA following DMSC administration[49]. To ensure successful pregnancy in the future, a customized diagnosis and treatment plan should be developed, as DMSCs have distinct immunomodulatory effects on spontaneous abortion and RSA.

CONCLUSION

Immunology is essential for preserving the immunological tolerance of the maternal-fetal interface and preventing pathogen invasion, which can preserve the equilibrium of immune cells, cytokines, and autoantibodies. The majority of RSAs are caused by bodily imbalances. Thus, controlling the immunological response to RSA may be a successful therapeutic approach. At present, immune regulation methods primarily include intravenous immunoglobulin, paternal lymphocyte immunization, granulocyte colony stimulating factor and MSC therapy[6]. MSC therapy is an effective immune regulation method.

MSCs’ low immunogenicity, repeatability, and immunomodulatory action make them promising for use in regenerative therapy. In addition to improving pregnancy outcome in RSA, MSCs can be utilized as regenerative materials in other medical specialties, including neurology, orthopedics, and cardiovascular medicine[50]. Although MSCs in tissue engineering have advanced due to the use of biocompatible scaffolds, 3D culture systems, and organ-like architectures, there are still technical obstacles to overcome[51].

Although there is some evidence that MSCs are a viable and successful treatment for RSA, clinical implementation of this treatment is still in its infancy. The precise techniques and procedures of MSC treatment are still being investigated. Through uterine horn or intraperitoneal injection, MSCs are primarily extracted from the bone marrow, fat, umbilical cord, amniotic membrane, and decidua. They are involved in immune cell balance regulation, immune tolerance enhancement, inflammation inhibition, angiogenesis promotion, and tissue regeneration[12] (Table 1). Abortion safety with stem cell therapy remains a prominent concern. After stem cell transplantation, there remains a risk of immunological rejection, carcinogenicity, and other negative outcomes[52,53]. The study of MSC exosomes has recently attracted a lot of interest. According to research by Xiang et al[27], BMSC exosomes can carry miR-101, decreasing the rate of embryo absorption and preserving immunological tolerance. Researchers also need to investigate the unclear mechanism of additional MSC exosomes in the treatment of RSA. Hormone levels may be impacted by MSC treatment, for instance, by preventing iron death and preserving apoptosis, MSCs and their exosome vesicles can alleviate polycystic ovarian syndrome and premature ovarian failure. Therefore, more research is required to determine whether MSCs can alter hormone levels and whether MSCs have an impact on hormone homeostasis[54,55]. More preclinical research is required before clinical trials are initiated on the assumption of safety and efficacy. The research of MSCs in RSA therapy is still at the animal experimental stage. Although MSC treatment now has certain restrictions and challenges, its regeneration potential and therapeutic impact cannot be disregarded. In order to advance treatment to the clinic as soon as possible, a number of animal studies and preclinical research are still required to determine how MSC therapy can safely and efficiently improve RSA outcomes.

Table 1 Mechanisms of mesenchymal stem cells improving recurrent spontaneous abortion.

Origin	Mechanism	Ref.
Bone marrow	Act locally on CD4+ T cells and macrophages at the maternal-fetal interface	Meng et al[20]
	Inhibit the Th1 immune response and promote the Th2 immune response	Aggarwal and Pittenger[21]
	Promote macrophage polarization to M2-type	Maggini et al[23]
	Immunosuppress TNF-stimulating gene-6	Vallés et al[25]
	Promote paracrine function	Li et al[26]
	Exosomes regulate T cells and macrophages activity	Xiang et al[27]
Adipose	Control the balance of Th1 and Th2 cytokines	Sadighi-Moghaddam et al[30]
	Decrease immunological rejection of paternal antigens by the spleen	Salek Farrokhi et al[31]
	Reduce the infiltration of CD49b+ NK cells into the interface	Rezaei Kahmini et al[32]
	Enhance the balance of angiogenesis	Shahgaldi et al[33]
Wharton’s jelly	Increase expression of Th2 immune factors	Chen et al[38], Ding et al[39]
	Suppress stromal cells and NK cells	Jin et al[40]
Amniotic membrane	Suppress proinflammatory cytokines and control the population of Treg cells	Gan et al[44]
	Enhance angiogenesis and macrophage polarization	Xiao et al[45]
	Stimulate endometrial regeneration and restore the hormone levels	Naeem et al[46]
Decidual	Stimulate angiogenesis	Chen et al[47]
	Increase the proportion of Treg cells and suppress apoptosis and proliferation	Büyükbayrak et al[49]

Th2: T helper type 2; TNF: Tumor necrosis factor; Th1: T helper type 1; NK: Natural killer; Treg: Regulatory T.