Mesenchymal stromal cell-derived CCL2 suppresses plasma cell immunoglobulin production via STAT3 inactivation and PAX5 induction. Blood. 2008;112:4991-4998. [PMID: 18812467 DOI: 10.1182/blood-2008-07-166892]

Exogenous MSC based tissue regeneration: a review of immuno-protection strategies from biomaterial scaffolds

Mesenchymal stem cell (MSC)-based tissue engineering holds great potential for regenerative medicine as a means of replacing damaged or lost tissues to restore their structure and function. However, the efficacy of MSC-based regeneration is frequently limited by the low survival rate and limited survival time of transplanted MSCs. Despite the inherent immune privileges of MSCs, such as low expression of major histocompatibility complex antigens, tolerogenic properties, local immunosuppressive microenvironment creation, and induction of immune tolerance, immune rejection remains a major obstacle to their survival and regenerative potential. Evidence suggests that immune protection strategies can enhance MSC therapeutic efficacy by prolonging their survival and maintaining their biological functions. Among various immune protection strategies, biomaterial-based scaffolds or cell encapsulation systems that mediate the interaction between transplanted MSCs and the host immune system or spatially isolate MSCs from the immune system for a specific time period have shown great promise. In this review, we provide a comprehensive overview of these biomaterial-based immune protection strategies employed for exogenous MSCs, highlighting the crucial role of modulating the immune microenvironment. Each strategy is critically examined, discussing its strengths, limitations, and potential applications in MSC-based tissue engineering. By elucidating the mechanisms behind immune rejection and exploring immune protection strategies, we aim to address the challenges faced by MSC-based tissue engineering and pave the way for enhancing the therapeutic outcomes of MSC therapies. The insights gained from this review will contribute to the development of more effective strategies to protect transplanted MSCs from immune rejection and enable their successful application in regenerative medicine.

Mesenchymal stem cells biological and biotechnological advances: Implications for clinical applications

BACKGROUND

Mesenchymal stem cells (MSCs) are multipotent stem cells that are able to differentiate into multiple lineages including bone, cartilage, muscle and fat. They hold immunomodulatory properties and therapeutic ability to treat multiple diseases, including autoimmune and chronic degenerative diseases. In this article, we reviewed the different biological properties, applications and clinical trials of MSCs. Also, we discussed the basics of manufacturing conditions, quality control, and challenges facing MSCs in the clinical setting.

METHODS

Extensive review of the literature was conducted through the databases PubMed, Google Scholar, and Cochrane. Papers published since 2015 and covering the clinical applications and research of MSC therapy were considered. Furthermore, older papers were considered when referring to pioneering studies in the field.

RESULTS

The most widely studied stem cells in cell therapy and tissue repair are bone marrow-derived mesenchymal stem cells. Adipose tissue-derived stem cells became more common and to a lesser extent other stem cell sources e.g., foreskin derived MSCs. MSCs therapy were also studied in the setting of COVID-19 infections, ischemic strokes, autoimmune diseases, tumor development and graft rejection. Multiple obstacles, still face the standardization and optimization of MSC therapy such as the survival and the immunophenotype and the efficiency of transplanted cells. MSCs used in clinical settings displayed heterogeneity in their function despite their extraction from healthy donors and expression of similar surface markers.

CONCLUSION

Mesenchymal stem cells offer a rising therapeutic promise in various diseases. However, their potential use in clinical applications requires further investigation.

Cause and consequence of heterogeneity in human mesenchymal stem cells: Challenges in clinical application

Human mesenchymal stem cells (hMSCs) are mesoderm-derived adult stem cells with self-proliferation capacity, pluripotent differentiation potency, and excellent histocompatibility. These advantages make hMSCs a promising tool in clinical application. However, the majority of clinical trials using hMSC therapy for diverse human diseases do not achieve expectations, despite the prospective pre-clinical outcomes in animal models. This is partly attributable to the intrinsic heterogeneity of hMSCs. In this review, the cause of heterogeneity in hMSCs is systematically discussed at multiple levels, including isolation methods, cultural conditions, donor-to-donor variation, tissue sources, intra-tissue subpopulations, etc. Additionally, the effect of hMSCs heterogeneity on the contrary role in tumor progression and immunomodulation is also discussed. The attempts to understand the cellular heterogeneity of hMSCs and its consequences are important in supporting and improving therapeutic strategies for hMSCs.

Mesenchymal Stem Cells-Involved Strategies for Rheumatoid Arthritis Therapy

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by chronic inflammation of the joints and bone destruction. Because of systemic administration and poor targeting, traditional anti-rheumatic drugs have unsatisfactory treatment efficacy and strong side effects, including myelosuppression, liver or kidney function damage, and malignant tumors. Consequently, mesenchymal stem cells (MSCs)-involved therapy is proposed for RA therapy as a benefit of their immunosuppressive and tissue-repairing effects. This review summarizes the progress of MSCs-involved RA therapy through suppressing inflammation and promoting tissue regeneration and predicts their potential clinical application.

Temporal dynamics of immune-stromal cell interactions in fracture healing

Bone fracture repair is a complex, multi-step process that involves communication between immune and stromal cells to coordinate the repair and regeneration of damaged tissue. In the US, 10% of all bone fractures do not heal properly without intervention, resulting in non-union. Complications from non-union fractures are physically and financially debilitating. We now appreciate the important role that immune cells play in tissue repair, and the necessity of the inflammatory response in initiating healing after skeletal trauma. The temporal dynamics of immune and stromal cell populations have been well characterized across the stages of fracture healing. Recent studies have begun to untangle the intricate mechanisms driving the immune response during normal or atypical, delayed healing. Various in vivo models of fracture healing, including genetic knockouts, as well as in vitro models of the fracture callus, have been implemented to enable experimental manipulation of the heterogeneous cellular environment. The goals of this review are to (1): summarize our current understanding of immune cell involvement in fracture healing (2); describe state-of-the art approaches to study inflammatory cells in fracture healing, including computational and in vitro models; and (3) identify gaps in our knowledge concerning immune-stromal crosstalk during bone healing.

Stem cell-based therapy for COVID-19

While The World Health Organization (WHO) has announced that COVID-19 is no longer a public health emergency of international concern(PHEIC), the risk of reinfection and new emerging variants still makes it crucial to study and work towards the prevention of COVID-19. Stem cell and stem cell-like derivatives have shown some promising results in clinical trials and preclinical studies as an alternative treatment option for the pulmonary illnesses caused by the COVID-19 and can be used as a potential vaccine. In this review, we will systematically summarize the pathophysiological process and potential mechanisms underlying stem cell-based therapy in COVID-19, and the registered COVID-19 clinical trials, and engineered extracellular vesicle as a potential vaccine for preventing COVID-19.

In Vitro Insights Into the Influence of Marrow Mesodermal/Mesenchymal Progenitor Cells on Acute Myelogenous Leukemia and Myelodysplastic Syndromes

The study of marrow-resident mesodermal progenitors can provide important insight into their role in influencing normal and aberrant hematopoiesis as occurs in acute myelogenous leukemia (AML) and myelodysplastic syndromes (MDS). In addition, the chemokine competency of these cells provides links to the inflammatory milieu of the marrow microenvironment with additional implications for normal and malignant hematopoiesis. While in vivo studies have elucidated the structure and function of the marrow niche in murine genetic models, corollary human studies have not been feasible, and thus the use of culture-adapted mesodermal cells has provided insights into the role these rare endogenous niche cells play in physiologic, malignant, and inflammatory states. This review focuses on culture-adapted human mesenchymal stem/stromal cells (MSCs) as they have been utilized in understanding their influence in AML and MDS as well as on their chemokine-mediated responses to myeloid malignancies, injury, and inflammation. Such studies have intrinsic limitations but have provided mechanistic insights and clues regarding novel druggable targets.

Isolation, culture, and delivery considerations for the use of mesenchymal stem cells in potential therapies for acute liver failure

Acute liver failure (ALF) is a high-mortality syndrome for which liver transplantation is considered the only effective treatment option. A shortage of donor organs, high costs and surgical complications associated with immune rejection constrain the therapeutic effects of liver transplantation. Recently, mesenchymal stem cell (MSC) therapy was recognized as an alternative strategy for liver transplantation. Bone marrow mesenchymal stem cells (BMSCs) have been used in clinical trials of several liver diseases due to their ease of acquisition, strong proliferation ability, multipotent differentiation, homing to the lesion site, low immunogenicity and anti-inflammatory and antifibrotic effects. In this review, we comprehensively summarized the harvest and culture expansion strategies for BMSCs, the development of animal models of ALF of different aetiologies, the critical mechanisms of BMSC therapy for ALF and the challenge of clinical application.

The role of MSCs and CAR-MSCs in cellular immunotherapy

Chimeric antigen receptors (CARs) are widely used by T cells (CAR-T cells), natural killer cells dendritic cells and macrophages, and they are of great importance in cellular immunotherapy. However, the use of CAR-related products faces several challenges, including the poor persistence of cells carrying CARs, cell dysfunction or exhaustion, relapse of disease, immune effector cell-associated neurotoxicity syndrome, cytokine release syndrome, low efficacy against solid tumors and immunosuppression by the tumor microenvironment. Another important cell therapy regimen involves mesenchymal stem cells (MSCs). Recent studies have shown that MSCs can improve the anticancer functions of CAR-related products. CAR-MSCs can overcome the flaws of cellular immunotherapy. Thus, MSCs can be used as a biological vehicle for CARs. In this review, we first discuss the characteristics and immunomodulatory functions of MSCs. Then, the role of MSCs as a source of exosomes, including the characteristics of MSC-derived exosomes and their immunomodulatory functions, is discussed. The role of MSCs in CAR-related products, CAR-related product-derived exosomes and the effect of MSCs on CAR-related products are reviewed. Finally, the use of MSCs as CAR vehicles is discussed. Video Abstract.

Progression of pre-rheumatoid arthritis to clinical disease of joints: Potential role of mesenchymal stem cells

Rheumatoid arthritis (RA) related autoimmunity is developed at mucosal sites due to the interplay between genetic risk factors and environmental triggers. The pre-RA phase that leads to anti-citrullinated protein antibodies, rheumatoid factor, and other autoantibodies spread in the systemic circulation may not affect articular tissue for years until a mysterious second hit triggers the localization of RA-related autoimmunity in joints. Several players in the joint microenvironment mediate the synovial innate and adaptive immunological processes, eventually leading to clinical synovitis. There still exists a gap in the early phase of RA pathogenesis, i.e., the progression of diseases from the systemic circulation to joints. The lack of better understanding of these events results in the inability to answer questions about why only after a certain point of time the disease appears in joints and why in some cases, it simply remains latent and doesn't affect joints at all. In the current review, we focused on the immunomodulatory and regenerative role of mesenchymal stem cells and associated exosomes in RA pathology. We also highlighted the age-related dysregulations in activities of mesenchymal stem cells and how that might trigger homing of systemic autoimmunity to joints.

Mesenchymal Stem Cells in Acquired Aplastic Anemia: The Spectrum from Basic to Clinical Utility

Aplastic anemia (AA), a rare but potentially life-threatening disease, is a paradigm of bone marrow failure syndromes characterized by pancytopenia in the peripheral blood and hypocellularity in the bone marrow. The pathophysiology of acquired idiopathic AA is quite complex. Mesenchymal stem cells (MSCs), an important component of the bone marrow, are crucial in providing the specialized microenvironment for hematopoiesis. MSC dysfunction may result in an insufficient bone marrow and may be associated with the development of AA. In this comprehensive review, we summarized the current understanding about the involvement of MSCs in the pathogenesis of acquired idiopathic AA, along with the clinical application of MSCs for patients with the disease. The pathophysiology of AA, the major properties of MSCs, and results of MSC therapy in preclinical animal models of AA are also described. Several important issues regarding the clinical use of MSCs are discussed finally. With evolving knowledge from basic studies and clinical applications, we anticipate that more patients with the disease can benefit from the therapeutic effects of MSCs in the near future.

Modulation of Mesenchymal Stem Cells-Mediated Adaptive Immune Effectors' Repertoire in the Recovery of Systemic Lupus Erythematosus

The breakdown of self-tolerance of the immune response can lead to autoimmune conditions in which chronic inflammation induces tissue damage. Systemic lupus erythematosus (SLE) is a debilitating multisystemic autoimmune disorder with a high prevalence in women of childbearing age; however, SLE incidence, prevalence, and severity are strongly influenced by ethnicity. Although the mystery of autoimmune diseases remains unsolved, disturbance in the proportion and function of B cell subsets has a major role in SLE's pathogenesis. Additionally, colocalizing hyperactive T helper cell subgroups within inflammatory niches are indispensable. Despite significant advances in standard treatments, nonspecific immunosuppression, the risk of serious infections, and resistance to conventional therapies in some cases have raised the urgent need for new treatment strategies. Without the need to suppress the immune system, mesenchymal stem cells (MSCs), as ''smart" immune modulators, are able to control cellular and humoral auto-aggression responses by participating in precursor cell development. In lupus, due to autologous MSCs disorder, the ability of allogenic engrafted MSCs in tissue regeneration and resetting immune homeostasis with the provision of a new immunocyte repertoire has been considered simultaneously. In Brief The bone marrow mesenchymal stem cells (BM-MSCs) lineage plays a critical role in maintaining the hematopoietic stem-cell microstructure and modulating immunocytes. The impairment of BM-MSCs and their niche partially contribute to the pathogenesis of SLE-like diseases. Allogenic MSC transplantation can reconstruct BM microstructure, possibly contributing to the recovery of immunocyte phenotype restoration of immune homeostasis. In terms of future prospects of MSCs, artificially gained by ex vivo isolation and culture adaptation, the wide variety of potential mediators and mechanisms might be linked to the promotion of the immunomodulatory function of MSCs.

Immunomodulatory Mechanisms of Mesenchymal Stem Cells and Their Potential Clinical Applications

Mesenchymal stem cells (MSCs) are multipotent stem cells with the capacity of self-renewal, homing, and low immunogenicity. These distinct biological characteristics have already shown immense potential in regenerative medicine. MSCs also possess immunomodulatory properties that can maintain immune homeostasis when the immune response is over-activated or under-activated. The secretome of MSCs consists of cytokines, chemokines, signaling molecules, and growth factors, which effectively contribute to the regulation of immune and inflammatory responses. The immunomodulatory effects of MSCs can also be achieved through direct cell contact with microenvironmental factors and immune cells. Furthermore, preconditioned and engineered MSCs can specifically improve the immunomodulation effects in diverse clinical applications. These multifunctional properties of MSCs enable them to be used as a prospective therapeutic strategy to treat immune disorders, including autoimmune diseases and incurable inflammatory diseases. Here we review the recent exploration of immunomodulatory mechanisms of MSCs and briefly discuss the promotion of the genetically engineered MSCs. Additionally, we review the potential clinical applications of MSC-mediated immunomodulation in four types of immune diseases, including systemic lupus erythematosus, Crohn’s disease, graft-versus-host disease, and COVID-19.

Chemokine Assay Matrix Defines the Potency of Human Bone Marrow Mesenchymal Stromal Cells

Potency analysis of mesenchymal stromal cells (MSCs) is required for their use in advanced clinical trials. Assay matrix strategy evaluating more than a single property of MSCs is an emerging strategy in potency analysis. Here we developed an assay matrix approach focusing on the secretory chemokine responses of MSCs using multiplex analytical method. MSCs’ innate fitness in secreting matrix of chemokines is correlated with their metabolic fitness in differential degrees. In addition, innately secreting chemokines are correlated among themselves in a unique pattern. MSC’s matrix chemokine responses to exogenous stimulation of IFNγ and/or TNFα are distinct. However, the combination of IFNγ and TNFα is superior than individual stimulations in eliciting robust and broad matrix chemokine responses of MSCs. Correlation matrix analysis has identified that chemokine responses to IFNγ and/or TNFα display unique correlative secretion patterns. MSC and peripheral blood mononuclear cells coculture analysis has identified the correlation matrix responses of chemokines that predicted immune suppression. In addition, MSC-mediated blocking of T-cell proliferation predominantly correlates with chemokines in an inverse manner. Knockdown of chemokines has demonstrated that MSC-sourced inherent chemokines do not actively play a role in T-cell suppression and thus are the bystander predictors of T-cell suppression. The present analysis of MSC’s matrix chemokine responses can be deployed in the advanced potency analysis of MSCs.

Downregulation of STAT3 in Epstein-Barr Virus-Positive Hodgkin Lymphoma

STAT3 is a transcription factor which is activated via various signaling transduction pathways or Epstein-Barr virus (EBV) infection and plays an oncogenic role in lymphoid malignancies including Hodgkin lymphoma (HL). The tumor cells of HL are derived from germinal center B-cells and transformed by chromosomal rearrangements, aberrant signal transduction, deregulation of developmental transcription factors, and EBV activity. HL cell lines represent useful models to investigate molecular principles and deduced treatment options of this malignancy. Using cell line L-540, we have recently shown that constitutively activated STAT3 drives aberrant expression of hematopoietic NKL homeobox gene HLX. Here, we analyzed HL cell line AM-HLH which is EBV-positive but, nevertheless, HLX-negative. Consistently, AM-HLH expressed decreased levels of STAT3 proteins which were additionally inactivated and located in the cytoplasm. Combined genomic and expression profiling data revealed several amplified and overexpressed gene candidates involved in opposed regulation of STAT3 and EBV. Corresponding knockdown studies demonstrated that IRF4 and NFATC2 inhibited STAT3 expression. MIR155 (activated by STAT3) and SPIB (repressed by HLX) showed reduced and elevated expression levels in AM-HLH, respectively. However, treatment with IL6 or IL27 activated STAT3, elevated expression of HLX and MIR155, and inhibited IRF4. Taken together, this cell line deals with two conflicting oncogenic drivers, namely, JAK2-STAT3 signaling and EBV infection, but is sensitive to switch after cytokine stimulation. Thus, AM-HLH represents a unique cell line model to study the pathogenic roles of STAT3 and EBV and their therapeutic implications in HL.

Mesenchymal Stem Cell Mechanisms of Action and Clinical Effects in Osteoarthritis: A Narrative Review

With the insufficient satisfaction rates and high cost of operative treatment for osteoarthritis (OA), alternatives have been sought. Furthermore, the inability of current medications to arrest disease progression has led to rapidly growing clinical research relating to mesenchymal stem cells (MSCs). The availability and function of MSCs vary according to tissue source. The three primary sources include the placenta, bone marrow, and adipose tissue, all of which offer excellent safety profiles. The primary mechanisms of action are trophic and immunomodulatory effects, which prevent the further degradation of joints. However, the function and degree to which benefits are observed vary significantly based on the exosomes secreted by MSCs. Paracrine and autocrine mechanisms prevent cell apoptosis and tissue fibrosis, initiate angiogenesis, and stimulate mitosis via growth factors. MSCs have even been shown to exhibit antimicrobial effects. Clinical results incorporating clinical scores and objective radiological imaging have been promising, but a lack of standardization in isolating MSCs prevents their incorporation in current guidelines.

Mesenchymal stem cell homing to improve therapeutic efficacy in liver disease

Mesenchymal stem cell (MSC) transplantation, as an alternative strategy to orthotopic liver transplantation, has been evaluated for treating end-stage liver disease. Although the therapeutic mechanism of MSC transplantation remains unclear, accumulating evidence has demonstrated that MSCs can regenerate tissues and self-renew to repair the liver through differentiation into hepatocyte-like cells, immune regulation, and anti-fibrotic mechanisms. Multiple clinical trials have confirmed that MSC transplantation restores liver function and alleviates liver damage. A sufficient number of MSCs must be home to the target tissues after administration for successful application. However, inefficient homing of MSCs after systemic administration is a major limitation in MSC therapy. Here, we review the mechanisms and clinical application status of MSCs in the treatment of liver disease and comprehensively summarize the molecular mechanisms of MSC homing, and various strategies for promoting MSC homing to improve the treatment of liver disease.

Immunomodulatory Activity of Mesenchymal Stem Cells in Lupus Nephritis: Advances and Applications

Lupus nephritis (LN) is a significant cause of various acute and chronic renal diseases, which can eventually lead to end-stage renal disease. The pathogenic mechanisms of LN are characterized by abnormal activation of the immune responses, increased cytokine production, and dysregulation of inflammatory signaling pathways. LN treatment is an important issue in the prevention and treatment of systemic lupus erythematosus. Mesenchymal stem cells (MSCs) have the advantages of immunomodulation, anti-inflammation, and anti-proliferation. These unique properties make MSCs a strong candidate for cell therapy of autoimmune diseases. MSCs can suppress the proliferation of innate and adaptive immune cells, such as natural killer cells (NKs), dendritic cells (DCs), T cells, and B cells. Furthermore, MSCs suppress the functions of various immune cells, such as the cytotoxicity of T cells and NKs, maturation and antibody secretion of B cells, maturation and antigen presentation of DCs, and inhibition of cytokine secretion, such as interleukins (ILs), tumor necrosis factor (TNF), and interferons (IFNs) by a variety of immune cells. MSCs can exert immunomodulatory effects in LN through these immune functions to suppress autoimmunity, improve renal pathology, and restore kidney function in lupus mice and LN patients. Herein, we review the role of immune cells and cytokines in the pathogenesis of LN and the mechanisms involved, as well as the progress of research on the immunomodulatory role of MSCs in LN.

Co-Expression of the B-Cell Key Transcription Factors Blimp-1 and IRF4 Identifies Plasma Cells in the Pig

Antibody-secreting plasma cells (PCs) have remained largely uncharacterized for years in the field of porcine immunology. For an in-depth study of porcine PCs, we identified cross-reactive antibodies against three key transcription factors: PR domain zinc finger protein-1 (Blimp-1), interferon regulatory factor 4 (IRF4), and paired box 5 (Pax5). A distinct Blimp-1⁺IRF4⁺ cell population was found in cells isolated from blood, spleen, lymph nodes, bone marrow, and lung of healthy pigs. These cells showed a downregulation of Pax5 compared to other B cells. Within Blimp-1⁺IRF4⁺ B cells, IgM-, IgG-, and IgA-expressing cells were identified and immunoglobulin-class distribution was clearly different between the anatomical locations, with IgA⁺ PCs dominating in lung tissue and IgM⁺ PCs dominating in the spleen. Expression patterns of Ki-67, MHC-II, CD9, and CD28 were investigated in the different organs. A high expression of Ki-67 was observed in blood, suggesting a plasmablast stage. Blimp-1⁺IRF4⁺ cells showed an overall lower expression of MHC-II compared to regular B cells, confirming a progressive loss in B-cell differentiation toward the PC stage. CD28 showed slightly elevated expression levels in Blimp-1⁺IRF4⁺ cells in most organs, a phenotype that is also described for PCs in mice and humans. This was not seen for CD9. We further developed a FACS-sorting strategy for live porcine PCs for functional assays. CD3^-CD16^-CD172a^– sorted cells with a CD49d^highFSC-A^high phenotype contained Blimp-1⁺IRF4⁺ cells and were capable of spontaneous IgG production, thus confirming PC identity. These results reveal fundamental phenotypes of porcine PCs and will facilitate the study of this specific B-cell subset in the future.

Integrative Single-Cell RNA-Seq and ATAC-Seq Analysis of Mesenchymal Stem/Stromal Cells Derived from Human Placenta

Mesenchymal stem/stromal cells derived from placenta (PMSCs) are an attractive source for regenerative medicine because of their multidifferentiation potential and immunomodulatory capabilities. However, the cellular and molecular heterogeneity of PMSCs has not been fully characterized. Here, we applied single-cell RNA sequencing (scRNA-seq) and assay for transposase-accessible chromatin sequencing (scATAC-seq) techniques to cultured PMSCs from human full-term placenta. Based on the inferred characteristics of cell clusters, we identify several distinct subsets of PMSCs with specific characteristics, including immunomodulatory-potential and highly proliferative cell states. Furthermore, integrative analysis of gene expression and chromatin accessibility showed a clearer chromatin accessibility signature than those at the transcriptional level on immunomodulatory-related genes. Cell cycle gene-related heterogeneity can be more easily distinguished at the transcriptional than the chromatin accessibility level in PMSCs. We further reveal putative subset-specific cis-regulatory elements regulating the expression of immunomodulatory- and proliferation-related genes in the immunomodulatory-potential and proliferative subpopulations, respectively. Moreover, we infer a novel transcription factor PRDM1, which might play a crucial role in maintaining immunomodulatory capability by activating PRDM1-regulon loop. Collectively, our study first provides a comprehensive and integrative view of the transcriptomic and epigenomic features of PMSCs, which paves the way for a deeper understanding of cellular heterogeneity and offers fundamental biological insight of PMSC subset-based cell therapy.

Human Mesenchymal Stem/Stromal Cells in Immune Regulation and Therapy

Studies of mesenchymal stem (or stromal) cells (MSCs) have moved from bedside to bench and back again. The stromal cells or fibroblasts are found in all tissues and participate in building the extracellular matrix (ECM). Bone marrow (BM)-derived MSCs have been studied for more than 50 years and have multiple roles. They function as stem cells and give rise to bone, cartilage, and fat in the BM (these are stem cells); support hematopoiesis (pericytes); and participate in sensing environmental changes and balancing pro- and anti-inflammatory conditions. In disease states, they migrate to sites of injury and release cytokines, hormones, nucleic acids depending on the microenvironment they find. Clinicians have begun to exploit these properties of BM, adipose tissue, and umbilical cord MSCs because they are easy to harvest and expand in culture. In this review, I describe the uses to which MSCs have been put, list ongoing clinical trials by organ system, and outline how MSCs are thought to regulate the innate and adaptive immune systems. I will discuss some of the reasons why clinical applications are still lacking. Much more work will have to be done to find the sources, doses, and culture conditions needed to exploit MSCs optimally and learn their healing potential. They are worth the effort.

UM171A-induced ROS promote antigen cross-presentation of immunogenic peptides by bone marrow-derived mesenchymal stromal cells

Background

Mesenchymal stromal cells (MSCs) have been extensively used in the clinic due to their exquisite tissue repair capacity. However, they also hold promise in the field of cellular vaccination as they can behave as conditional antigen presenting cells in response to interferon (IFN)-gamma treatment under a specific treatment regimen. This suggests that the immune function of MSCs can be pharmacologically modulated. Given the capacity of the agonist pyrimido-indole derivative UM171a to trigger the expression of various antigen presentation-related genes in human hematopoietic progenitor cells, we explored the potential use of UM171a as a means to pharmacologically instill and/or promote antigen presentation by MSCs.

Methods

Besides completing a series of flow-cytometry-based phenotypic analyses, several functional antigen presentation assays were conducted using the SIINFEKL-specific T-cell clone B3Z. Anti-oxidants and electron transport chain inhibitors were also used to decipher UM171a’s mode of action in MSCs. Finally, the potency of UM171a-treated MSCs was evaluated in the context of therapeutic vaccination using immunocompetent C57BL/6 mice with pre-established syngeneic EG.7T-cell lymphoma.

Results

Treatment of MSCs with UM171a triggered potent increase in H2-K^b cell surface levels along with the acquisition of antigen cross-presentation abilities. Mechanistically, such effects occurred in response to UM171a-mediated production of mitochondrial-derived reactive oxygen species as their neutralization using anti-oxidants or Antimycin-A mitigated MSCs’ ability to cross-present antigens. Processing and presentation of the immunogenic ovalbumin-derived SIINFEKL peptide was caused by de novo expression of the Psmb8 gene in response to UM171a-triggered oxidative stress. When evaluated for their anti-tumoral properties in the context of therapeutic vaccination, UM171a-treated MSC administration to immunocompetent mice with pre-established T-cell lymphoma controlled tumor growth resulting in 40% survival without the need of additional supportive therapy and/or standard-of-care.

Conclusions

Altogether, our findings reveal a new immune-related function for UM171a and clearly allude to a direct link between UM171a-mediated ROS induction and antigen cross-presentation by MSCs. The fact that UM171a treatment modulates MSCs to become antigen-presenting cells without the use of IFN-gamma opens-up a new line of investigation to search for additional agents capable of converting immune-suppressive MSCs to a cellular tool easily adaptable to vaccination.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02693-z.

Mesenchymal Stem Cells Enhance Chemotaxis of Activated T Cells through the CCL2-CCR2 Axis In Vitro

Activation and migration of donor T cells to the host target organs are critical mechanisms in the pathogenesis of graft-versus-host disease (GVHD). The role of monocyte chemoattractant protein-1 (MCP-1/CCL2) and its receptor CCR2 in the recruitment of T cells during immune or inflammatory response is also well known. For elucidation of the mechanism of the therapeutic effect of human bone marrow derived-mesenchymal stem cells (MSC) in GVHD, we studied the effect of these cells on migration of activated donor T cells through the CCL2-CCR2 axis in vitro. MSC were expanded from donors' bone marrow mononuclear cells. After co-culturing of IL-2-activated T cells with allogeneic MSC at different ratios, the levels of CCL2 in supernatants were measured by ELISA, and CCR2 expression in CD4⁺/CD8⁺ T cells subsets were detected by flow cytometry. The effect of MSC on the migration of activated T cells in the Transwell system was studied in the absence or presence of CCL2. Our results show that CCL2 levels in supernatants of co-cultures were significantly higher than in MSC monoculture and this increase depended on the number of MSC. MSC inhibited proliferation of T cells, but did not change the percentages of CD4⁺ and CD8⁺ T cells subsets. MSC can up-regulate the CCR2 expression in CD8⁺ subsets rather than in CD4⁺ subsets; MSC enhanced migration of IL-2-activated T cells to CCL2 by increasing the expression of CCR2. The data demonstrate that MSC can enhance chemotaxis of cytokine-activated T cells through the CCL2-CCR2 axis in vitro.

Roles of mesenchymal stromal cells in the head and neck cancer microenvironment

Head and neck cancer (HNC), a common malignancy worldwide, is associated with high morbidity and mortality rates. Squamous cell carcinoma is the most common HNC type, followed by salivary gland carcinomas, head and neck sarcomas, and lymphomas. The microenvironment of HNCs comprises various cells that regulate tumor development. Recent studies have reported that the tumor microenvironment, which modulates cancer progression, regulates cancer treatment response. However, the presence of different types of stromal cells in cancers is a major challenge to elucidate the role of individual cells in tumor progression. The role of mesenchymal stromal cells (MSCs), which are a component of the tumor microenvironment, in HNC is unclear. The major impediment for characterizing the role of MSCs in cancer progression is the lack of MSC-specific markers and their phenotypic similarity with stromal cells. This review aimed to summarize the latest findings on the role of MSCs in the progression of HNC to improve our understanding of HNC pathophysiology.

Immunomodulatory Actions of Mesenchymal Stromal Cells (MSCs) in Osteoarthritis of the Knee

Cellular therapy offers regeneration which curbs osteoarthritis of the knee. Among cellular therapies, mesenchymal stromal cells (MSCs) are readily isolated from various sources as culture expanded and unexpanded cellular population which are used as therapeutic products. Though MSCs possess a unique immunological and regulatory profile through cross-talk between MSCs and immunoregulatory cells (T cells, NK cells, dendritic cells, B cells, neutrophils, monocytes, and macrophages), they provide an immunotolerant environment when transplanted to the site of action. Immunophenotypic profile allows MSCs to escape immune surveillance and promotes their hypoimmunogenic or immune-privileged status. MSCs do not elicit a proliferative response when co-cultured with allogeneic T cells in vitro. MSCs secrete a wide range of anti-inflammatory mediators such as PGE-2, IDO, IL-1Ra, and IL-10. They also stimulate the resilient chondrogenic progenitors and enhance the chondrocyte differentiation by secretion of BMPs and TGFβ1. We highlight the various mechanisms of MSCs during tissue healing signals, their interaction with the immune system, and the impact of their lifespan in the management of osteoarthritis of the knee. A better understanding of the immunobiology of MSC renders them as an efficient therapeutic product for the management of osteoarthritis of the knee.

Therapeutic Potential of Mesenchymal Stromal Cell-Derived Extracellular Vesicles in the Prevention of Organ Injuries Induced by Traumatic Hemorrhagic Shock

Severe trauma is the principal cause of death among young people worldwide. Hemorrhagic shock is the leading cause of death after severe trauma. Traumatic hemorrhagic shock (THS) is a complex phenomenon associating an absolute hypovolemia secondary to a sudden and significant extravascular blood loss, tissue injury, and, eventually, hypoxemia. These phenomena are responsible of secondary injuries such as coagulopathy, endotheliopathy, microcirculation failure, inflammation, and immune activation. Collectively, these dysfunctions lead to secondary organ failures and multi-organ failure (MOF). The development of MOF after severe trauma is one of the leading causes of morbidity and mortality, where immunological dysfunction plays a central role. Damage-associated molecular patterns induce an early and exaggerated activation of innate immunity and a suppression of adaptive immunity. Severe complications are associated with a prolonged and dysregulated immune–inflammatory state. The current challenge in the management of THS patients is preventing organ injury, which currently has no etiological treatment available. Modulating the immune response is a potential therapeutic strategy for preventing the complications of THS. Mesenchymal stromal cells (MSCs) are multipotent cells found in a large number of adult tissues and used in clinical practice as therapeutic agents for immunomodulation and tissue repair. There is growing evidence that their efficiency is mainly attributed to the secretion of a wide range of bioactive molecules and extracellular vesicles (EVs). Indeed, different experimental studies revealed that MSC-derived EVs (MSC-EVs) could modulate local and systemic deleterious immune response. Therefore, these new cell-free therapeutic products, easily stored and available immediately, represent a tremendous opportunity in the emergency context of shock. In this review, the pathophysiological environment of THS and, in particular, the crosstalk between the immune system and organ function are described. The potential therapeutic benefits of MSCs or their EVs in treating THS are discussed based on the current knowledge. Understanding the key mechanisms of immune deregulation leading to organ damage is a crucial element in order to optimize the preparation of EVs and potentiate their therapeutic effect.

Macrophages at the nexus of mesenchymal stromal cell potency: The emerging role of chemokine cooperativity

Pharmacological depletion of macrophages in vivo with liposomal clodronate renders mice unresponsive to adoptive transfer of mesenchymal stromal cells (MSCs) for affecting outcomes of acute inflammatory pathology. This experimental observation identifies host macrophages as necessary in mediating the salutary anti-inflammatory properties of MSCs as a cellular pharmaceutical. This theory is supported by the observation that transfusion of MSCs leads to the prompt phagocytosis of nearly half of lung entrapped MSCs by lung resident macrophages, triggering an interleukin (IL)-10 suppressive efferocytotic response. In addition, non-phagocytosed MSCs with COX2 competency shape the immune milieu by inducing tissue macrophages to express IL-10. Additional experimental evidence identifies MSC-borne IL-6, IDO and TSG-6 as directly involved in macrophage polarization. Along similar lines of functional convergence, implantation of CCL2⁺ MSCs in the extravascular space where interaction with lung resident perivascular macrophages is not operative, also leads to IL-10 polarization of CCR2⁺ macrophages within acute injured tissue far removed from MSC depot. Intriguingly, MSC-derived CCL2 on its own is not sufficient to polarize macrophages and requires heterodimerization with MSC-borne CXCL12 to trigger macrophage IL-10 polarization via CCR2, but not CXCR4. Such chemokine cooperativity opens a new venue for analysis of MSC potency especially considering the rich chemokine secretome of MSC exposed to inflammatory stimulus. As an aggregate, these data highlight a necessary MSC and host macrophage functional dyad that may inform potency attribute analysis of MSCs-including the chemokine interactome-that may be directly linked to in vivo clinical anti-inflammatory and regenerative response.

Genetically Modified Mesenchymal Stromal/Stem Cells: Application in Critical Illness

Critical illnesses including sepsis, acute respiratory distress syndromes, ischemic cardiovascular disorders and acute organ injuries are associated with high mortality, morbidity as well as significant health care system expenses. While these diverse conditions require different specific therapeutic approaches, mesenchymal stem/stromal cell (MSCs) are multipotent cells capable of self-renewal, tri-lineage differentiation with a broad range regenerative and immunomodulatory activities, making them attractive for the treatment of critical illness. The therapeutic effects of MSCs have been extensively investigated in several pre-clinical models of critical illness as well as in phase I and II clinical cell therapy trials with mixed results. Whilst these studies have demonstrated the therapeutic potential for MSC therapy in critical illness, optimization for clinical use is an ongoing challenge. MSCs can be readily genetically modified by application of different techniques and tools leading to overexpress or inhibit genes related to their immunomodulatory or regenerative functions. Here we will review recent approaches designed to enhance the therapeutic potential of MSCs with an emphasis on the technology used to generate genetically modified cells, target genes, target diseases and the implication of genetically modified MSCs in cell therapy for critical illness.

Mesenchymal Stromal Cells from Different Parts of Umbilical Cord: Approach to Comparison & Characteristics

Mesenchymal stromal/stem cells (MSCs) are a unique population of cells that play an important role in the regeneration potential of the body. MSCs exhibit a characteristic phenotype and are capable of modulating the immune response. MSCs can be isolated from various tissues such as: bone marrow, adipose tissue, placenta, umbilical cord and others. The umbilical cord as a source of MSCs, has strong advantages, such as no-risk procedure of tissue retrieval after birth and easiness of the MSCs isolation. As the umbilical cord (UC) is a complex organ and we decided to evaluate, whether the cells derived from different regions of umbilical cord show similar or distinct properties. In this study we characterized and compared MSCs from three regions of the umbilical cord: Wharton's Jelly (WJ), the perivascular space (PRV) and the umbilical membrane (UCM). The analysis was carried out in terms of morphology, phenotype, immunomodulation potential and secretome. Based on the obtained results, we were able to conclude, that MSCs derived from distinct UC regions differ in their properties. According to our result WJ-MSCs have high and stabile proliferation potential and phenotype, when compare with other MSCs and can be treated as a preferable source of cells for medical application.

Taming of Covid-19: potential and emerging application of mesenchymal stem cells

Coronavirus Disease 2019 (COVID-19) caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has turned out to cause a pandemic, with a sky scraping mortality. The virus is thought to cause tissue injury by affecting the renin-angiotensin system. Also, the role of the over-activated immune system is noteworthy, leading to severe tissue injury via the cytokine storms. Thus it would be feasible to modulate the immune system response in order to attenuate the disease severity, as well as treating the patients. Today different medicines are being administered to the patients, but regardless of the efficacy of these treatments, adverse effects are pretty probable. Meanwhile, mesenchymal stem cells (MSCs) prove to be an effective candidate for treating the patients suffering from COVID-19 pneumonia, owing to their immunomodulatory and tissue-regenerative potentials. So far, several experiments have been conducted; transplanting MSCs and results are satisfying with no adverse effects being reported. This paper aims to review the recent findings regarding the novel coronavirus and the conducted experiments to treat patients suffering from COVID-19 pneumonia utilizing MSCs.

Mesenchymal stromal cell-dependent immunoregulation in chemically-induced acute liver failure

Drug-induced liver injury (DILI), which refers to liver damage caused by a drug or its metabolites, has emerged as an important cause of acute liver failure (ALF) in recent years. Chemically-induced ALF in animal models mimics the pathology of DILI in humans; thus, these models are used to study the mechanism of potentially effective treatment strategies. Mesenchymal stromal cells (MSCs) possess immunomodulatory properties, and they alleviate acute liver injury and decrease the mortality of animals with chemically-induced ALF. Here, we summarize some of the existing research on the interaction between MSCs and immune cells, and discuss the possible mechanisms underlying the immuno-modulatory activity of MSCs in chemically-induced ALF. We conclude that MSCs can impact the phenotype and function of macrophages, as well as the differentiation and maturation of dendritic cells, and inhibit the proliferation and activation of T lymphocytes or B lymphocytes. MSCs also have immuno-modulatory effects on the production of cytokines, such as prostaglandin E2 and tumor necrosis factor-alpha-stimulated gene 6, in animal models. Thus, MSCs have significant benefits in the treatment of chemically-induced ALF by interacting with immune cells and they may be applied to DILI in humans in the near future.

Strategies to Potentiate Paracrine Therapeutic Efficacy of Mesenchymal Stem Cells in Inflammatory Diseases

Mesenchymal stem cells (MSCs) have been developed as cell therapeutics for various immune disorders using their immunoregulatory properties mainly exerted by their paracrine functions. However, variation among cells from different donors, as well as rapid clearance after transplantation have impaired the uniform efficacy of MSCs and limited their application. Recently, several strategies to overcome this limitation have been suggested and proven in pre-clinical settings. Therefore, in this review article, we will update the knowledge on bioengineering strategies to improve the immunomodulatory functions of MSCs, including genetic modification and physical engineering.

Mesenchymal stromal cell variables influencing clinical potency: the impact of viability, fitness, route of administration and host predisposition

The International Society for Cell & Gene Therapy mesenchymal stromal cell (MSC) committee has been an interested observer of community interests in all matters related to MSC identity, mechanism of action, potency assessment and etymology, and it has regularly contributed to this conversation through a series of MSC pre-conferences and committee publications dealing with these matters. Arising from these reflections, the authors propose that an overlooked and potentially disruptive perspective is the impact of in vivo persistence on potency that is not predicted by surrogate cellular potency assays performed in vitro and how this translates to in vivo outcomes. Systemic delivery or extravascular implantation at sites removed from the affected organ system seems to be adequate in affecting clinical outcomes in many pre-clinical murine models of acute tissue injury and inflammatory pathology, including the recent European Medicines Agency-approved use of MSCs in Crohn-related fistular disease. The authors further propose that MSC viability and metabolic fitness likely dominate as a potency quality attribute, especially in recipients poised for salutary benefits as defined by emerging predictive biomarkers of response.

CCL2 and CXCL12 Derived from Mesenchymal Stromal Cells Cooperatively Polarize IL-10+ Tissue Macrophages to Mitigate Gut Injury

Mesenchymal stromal cell (MSC)-based therapy for inflammatory diseases involves paracrine and efferocytotic activation of immunosuppressive interleukin-10⁺ (IL-10⁺) macrophages. The paracrine pathway for MSC-mediated IL-10⁺ macrophage functionality and response to tissue injury is not fully understood. In our present study, clodronate pre-treatment of colitic mice confirms the essential role of endogenous macrophages in bone-marrow-derived MSC (BM-MSC)-mediated clinical rescue of dextran sulfate sodium (DSS)-induced colitis. We identify that BM-MSC-secreted chemokine ligand 2 (CCL2) and C-X-C motif chemokine 12 (CXCL12) cooperate as a heterodimer to upregulate IL-10 expression in CCR2⁺ macrophages in vitro and that CCL2 expression by MSC is required for IL-10⁺ polarization of intestinal and peritoneal resident macrophages in vivo. We observe that tissue macrophage IL-10 polarization in vivo is widespread involving extra-intestinal tissues and secondarily leads to bystander IL-10 expression in intestine-resident B and T cells. In conclusion, the BM-MSC-derived chemokine interactome dictates an IL-10⁺-macrophage-amplified anti-inflammatory response in toxic colitis.

Giri et al. show that the chemokines CCL2 and CXCL12, secreted from bone-marrow-derived mesenchymal stromal cells, upregulate IL-10 expression in CCR2⁺ macrophages. These polarized macrophages reduce tissue inflammation in colitis.

Mesenchymal stem cell-based treatment in autoimmune liver diseases: underlying roles, advantages and challenges

Autoimmune liver disease (AILD) is a series of chronic liver diseases with abnormal immune responses, including autoimmune hepatitis (AIH), primary biliary cholangitis (PBC), and primary sclerosing cholangitis (PSC). The treatment options for AILD remain limited, and the adverse side effects of the drugs that are typically used for treatment frequently lead to a low quality of life for AILD patients. Moreover, AILD patients may have a poor prognosis, especially those with an incomplete response to first-line treatment. Mesenchymal stem cells (MSCs) are pluripotent stem cells with low immunogenicity and can be conveniently harvested. MSC-based therapy is emerging as a promising approach for treating liver diseases based on their advantageous characteristics of immunomodulation, anti-fibrosis effects, and differentiation to hepatocytes, and accumulating evidence has revealed the positive effects of MSC therapy in AILD. In this review, we first summarize the mechanisms, safety, and efficacy of MSC treatment for AILD based on work in animal and clinical studies. We also discuss the challenges of MSC therapy in clinical applications. In summary, although promising data from preclinical studies are now available, MSC therapy is currently far for being applied in clinical practice, thus developing MSC therapy in AILD is still challenging and warrants further research.

Cardiac Cell Therapy: Insights into the Mechanisms of Tissue Repair

Stem cell-based cardiac therapies have been extensively studied in recent years. However, the efficacy of cell delivery, engraftment, and differentiation post-transplant remain continuous challenges and represent opportunities to further refine our current strategies. Despite limited long-term cardiac retention, stem cell treatment leads to sustained cardiac benefit following myocardial infarction (MI). This review summarizes the current knowledge on stem cell based cardiac immunomodulation by highlighting the cellular and molecular mechanisms of different immune responses to mesenchymal stem cells (MSCs) and their secretory factors. This review also addresses the clinical evidence in the field.

Thymoproteasome-Expressing Mesenchymal Stromal Cells Confer Protective Anti-Tumor Immunity via Cross-Priming of Endogenous Dendritic Cells

Proteasomes are complex macromolecular structures existing in various forms to regulate a myriad of cellular processes. Besides degrading unwanted or misfolded proteins (proteostasis), distinct immune functions were ascribed for the immunoproteasome and thymoproteasome (TPr) complexes. For instance, antigen degradation during ongoing immune responses mainly relies on immunoproteasome activity, whereas intrathymic CD8 T-cell development requires peptide generation by the TPr complex. Despite these substantial differences, the functional contribution of the TPr to peripheral T-cell immunity remains ill-defined. We herein explored whether the use of mesenchymal stromal cells (MSCs) engineered to exhibit altered proteasomal activity through de novo expression of the TPr complex can be exploited as a novel anti-cancer vaccine capable of triggering potent CD8 T-cell activation. Phenotypic and molecular characterization of MSC-TPr revealed a substantial decrease in MHCI (H2-K^b and H2-D^d) expression along with elevated secretion of various chemokines (CCL2, CCL9, CXCL1, LIX, and CX3CL1). In parallel, transcriptomic analysis pinpointed the limited ability of MSC-TPr to present endogenous antigens, which is consistent with their low expression levels of the peptide-loading proteins TAP, CALR, and PDAI3. Nevertheless, MSC-TPr cross-presented peptides derived from captured soluble proteins. When tested for their protective capacity, MSC-TPr triggered modest anti-tumoral responses despite efficient generation of effector memory CD4 and CD8 T cells. In contrast, clodronate administration prior to vaccination dramatically enhanced the MSC-TPr-induced anti-tumoral immunity clearly highlighting a refractory role mediated by phagocytic cells. Thus, our data elute to a DC cross-priming-dependant pathway in mediating the therapeutic effect of MSC-TPr.

Lymph node stromal CCL2 limits antibody responses

Nonhematopoietic stromal cells in lymph nodes such as fibroblastic reticular cells (FRCs) can support the survival of plasmablasts and plasma cells [together, antibody-forming cells (AFCs)]. However, a regulatory function for the stromal compartment in AFC accumulation has not been appreciated. Here, we show that chemokine ligand 2 (CCL2)-expressing stromal cells limit AFC survival. FRCs express high levels of CCL2 in vessel-rich areas of the T cell zone and the medulla, where AFCs are located. FRC CCL2 is up-regulated during AFC accumulation, and we use lymph node transplantation to show that CCL2 deficiency in BP3⁺ FRCs and lymphatic endothelial cells increases AFC survival without affecting B or germinal center cell numbers. Monocytes are key expressers of the CCL2 receptor CCR2, as monocyte depletion and transfer late in AFC responses increases and decreases AFC accumulation, respectively. Monocytes express reactive oxygen species (ROS) in an NADPH oxidase 2 (NOX2)-dependent manner, and NOX2-deficient monocytes fail to reduce AFC numbers. Stromal CCL2 modulates both monocyte accumulation and ROS production, and is regulated, in part, by manipulations that modulate vascular permeability. Together, our results reveal that the lymph node stromal compartment, by influencing monocyte accumulation and functional phenotype, has a regulatory role in AFC survival. Our results further suggest a role for inflammation-induced vascular activity in tuning the lymph node microenvironment. The understanding of stromal-mediated AFC regulation in vessel-rich environments could potentially be harnessed to control antibody-mediated autoimmunity.

Fostering mesenchymal stem cell therapy to halt cytokine storm in COVID-19

The coronavirus disease 2019 (COVID-19) has been threatening the globe since the end of November 2019. The disease revealed cracks in the health care system as health care providers across the world were left without guidelines on definitive usage of pharmaceutical agents or vaccines. The World Health Organization (WHO) declared COVID-19 as a pandemic on the 11th of March 2020. Individuals with underlying systemic disorders have reported complications, such as cytokine storms, when infected with the virus. As the number of positive cases and the death toll across the globe continue to rise, various researchers have turned to cell based therapy using stem cells to combat COVID-19. The field of stem cells and regenerative medicine has provided a paradigm shift in treating a disease with minimally invasive techniques that provides maximal clinical and functional outcome for patients. With the available evidence of immunomodulatory and immune-privilege actions, mesenchymal stem cells (MSCs) can repair, regenerate and remodulate the native homeostasis of pulmonary parenchyma with improved pulmonary compliance. This article revolves around the usage of novel MSCs therapy for combating COVID-19.

Application of Mesenchymal Stem Cells in Inflammatory and Fibrotic Diseases

Mesenchymal stem cells (MSCs) are multipotent stem cells that can be isolated from various tissues in the adult body. MSCs should be characterized by three criteria for regenerative medicine. MSCs must (1) adhere to plastic surfaces, (2) express specific surface antigens, and (3) differentiate into mesodermal lineages, including chondrocytes, osteoblasts, and adipocytes, in vitro. Interestingly, MSCs have immunomodulatory features and secrete trophic factors and immune receptors that regulate the microenvironment in host tissue. These specific and unique therapeutic properties make MSCs ideal as therapeutic agents in vivo. Specifically, pre-clinical and clinical investigators generated inflammatory and fibrotic diseases models, and then transplantation of MSCs into diseases models for therapeutic effects investigation. In this review, we characterize MSCs from various tissues and describe their applications for treating various inflammation and fibrotic diseases.

Immunomodulation of MSCs and MSC-Derived Extracellular Vesicles in Osteoarthritis

Osteoarthritis (OA) has become recognized as a low-grade inflammatory state. Inflammatory infiltration of the synovium by macrophages, T cells, B cells, and other immune cells is often observed in OA patients and plays a key role in the pathogenesis of OA. Hence, orchestrating the local inflammatory microenvironment and tissue regeneration microenvironment is important for the treatment of OA. Mesenchymal stem cells (MSCs) offer the potential for cartilage regeneration owing to their effective immunomodulatory properties and anti-inflammatory abilities. The paracrine effect, mediated by MSC-derived extracellular vehicles (EVs), has recently been suggested as a mechanism for their therapeutic properties. In this review, we summarize the interactions between MSCs or MSC-derived EVs and OA-related immune cells and discuss their therapeutic effects in OA. Additionally, we discuss the potential of MSC-derived EVs as a novel cell-free therapy approach for the clinical treatment of OA.

The Immune System and Its Contribution to Variability in Regenerative Medicine

The immune system plays a critical role in directing tissue repair and regeneration outcomes. Tissue engineering technologies that are designed to promote new tissue growth will therefore be impacted by immune factors that are present in patients both locally at the site of intervention and systemically. The immune state of patients can be influenced by many factors, including infection, nutrition, and other disease comorbidities. As a result, the immune state is highly variable and may be a source of variability in tissue-engineered products in the clinic, which is not found in preclinical models. In this review, we will summarize key immune cells and evidence of their activity in tissue repair and potential in tissue engineering systems. We also discuss how clinical translation of tissue engineering strategies, in particular stem cells, helped elucidate the importance of the immune system. With increased understanding of the immune system's role in repair and tissue engineering systems, it will likely become a therapeutic target and component of future therapies.

Potential of Extracellular Vesicle-Associated TSG-6 from Adipose Mesenchymal Stromal Cells in Traumatic Brain Injury

Multipotent mesenchymal stromal cells (MSC) represent a promising strategy for a variety of medical applications. Although only a limited number of MSC engraft and survive after in vivo cellular infusion, MSC have shown beneficial effects on immunomodulation and tissue repair. This indicates that the contribution of MSC exists in paracrine signaling, rather than a cell-contact effect of MSC. In this review, we focus on current knowledge about tumor necrosis factor (TNF)-stimulated gene-6 (TSG-6) and mechanisms based on extracellular vesicles (EV) that govern long-lasting immunosuppressive and regenerative activity of MSC. In this context, in particular, we discuss the very robust set of findings by Jha and colleagues, and the opportunity to potentially extend their research focus on EV isolated in concentrated conditioned media (CCM) from adipose tissue derived MSC (ASC). Particularly, the authors showed that ASC-CCM mitigated visual deficits after mild traumatic brain injury in mice. TSG-6 knockdown ASC were, then, used to generate TSG-6-depleted CCM that were not able to replicate the alleviation of abnormalities in injured animals. In light of the presented results, we envision that the infusion of much distilled ASC-CCM could enhance the alleviation of visual abnormalities. In terms of EV research, the advantages of using size-exclusion chromatography are also highlighted because of the enrichment of purer and well-defined EV preparations. Taken together, this could further delineate and boost the benefit of using MSC-based regenerative therapies in the context of forthcoming clinical research testing in diseases that disrupt immune system homeostasis.

Phorbol ester activates human mesenchymal stem cells to inhibit B cells and ameliorate lupus symptoms in MRL.Fas lpr mice

Rationale: Systemic lupus erythematosus (SLE) is a multi-organ autoimmune disease characterized by autoantibody production by hyper-activated B cells. Although mesenchymal stem cells (MSCs) ameliorate lupus symptoms by inhibiting T cells, whether they inhibit B cells has been controversial. Here we address this issue and reveal how to prime MSCs to inhibit B cells and improve the efficacy of MSCs in SLE.

Methods: We examined the effect of MSCs on purified B cells in vitro and the therapeutic efficacy of MSCs in lupus-prone MRL.Fas^lpr mice. We screened chemicals for their ability to activate MSCs to inhibit B cells.

Results: Mouse bone marrow-derived MSCs inhibited mouse B cells in a CXCL12-dependent manner, whereas human bone marrow-derived MSCs (hMSCs) did not inhibit human B (hB) cells. We used a chemical approach to overcome this hurdle and found that phorbol myristate acetate (PMA), phorbol 12,13-dibutyrate, and ingenol-3-angelate rendered hMSCs capable of inhibiting IgM production by hB cells. As to the mechanism, PMA-primed hMSCs attracted hB cells in a CXCL10-dependent manner and induced hB cell apoptosis in a PD-L1-dependent manner. Finally, we showed that PMA-primed hMSCs were better than naïve hMSCs at ameliorating SLE progression in MRL.Fas^lpr mice.

Conclusion: Taken together, our data demonstrate that phorbol esters might be good tool compounds to activate MSCs to inhibit B cells and suggest that our chemical approach might allow for improvements in the therapeutic efficacy of hMSCs in SLE.

Mesenchymal Stem Cells Beyond Regenerative Medicine

Mesenchymal stem cells (MSCs) are competent suitors of cellular therapy due to their therapeutic impact on tissue degeneration and immune-based pathologies. Additionally, their homing and immunomodulatory properties can be exploited in cancer malignancies to transport pharmacological entities, produce anti-neoplastic agents, or induce anti-tumor immunity. Herein, we create a portfolio for MSC properties, showcasing their distinct multiple therapeutic utilities and successes/challenges thereof in both animal studies and clinical trials. We further highlight the promising potential of MSCs not only in cancer management but also in instigating tumor-specific immunity - i.e., cancer vaccination. Finally, we reflect on the possible reasons impeding the clinical advancement of MSC-based cancer vaccines to assist in contriving novel methodologies from which a therapeutic milestone might emanate.

Mesenchymal stromal cell derived CCL2 is required for accelerated wound healing

Mesenchymal stromal cells (MSC) have immunomodulatory effects impacting macrophages, promoting polarisation towards a reparative phenotype. CCL2 is a potent cytokine involved in the recruitment of macrophages. We hypothesised that MSC derived CCL2 may be involved in the MSC therapeutic effect by facilitating macrophage repolarisation. To further delineate this mechanism, MSC isolated from CCL2 deficient mice (MSC-KO) were applied to excisional wounds in wild-type (WT) mice. CCL2 deficiency in MSC completely abrogated the therapeutic response compared to MSC-WT. MSC-KO were unable to repolarise macrophages to the same extent as WT and this was accompanied by a reduced angiogenesis and re-epithelialisation of the wounds at day 10. This study demonstrates that MSC derived CCL2 is required for MSC induced accelerated wound healing. The role of CCL2 in the interaction between MSC and Macrophages has not been previously demonstrated in accelerated wound healing. CCL2 has a potent effect on the ability to reduce the inflammatory response through local recruitment of macrophages. This research highlights CCL2 as a possible target for augmentation of MSC therapy to enhance therapeutic potential.

Hypoxia influences the effects of magnesium degradation products on the interactions between endothelial and mesenchymal stem cells

Biodegradable materials like well-documented Magnesium (Mg) are promising for their biocompatibility and tissue regeneration. Since Mg degradation is reported to be oxygen related, the effects of Mg were hypothesised to be influenced by oxygen. As two vital components of bone marrow, endothelial cells (EC) and mesenchymal stem cells (MSC), their interactions represent high scientific interest for tissue engineering and biodegradable Mg application. Human umbilical cord perivascular (HUCPV) and umbilical vein endothelial cell (HUVEC) were selected as sources of MSC and EC, respectively. Two types of coculture models were established to represent different phases of MSC-EC interaction: (i) where cells were physically separated thanks to a transwell and (ii) where cells were allowed to have heterotypic cellular contacts. Cell migration, gene, cytokines, and proliferation were investigated in HUCPV-HUVEC coculture using DNA, flow cytometry, wound healing assay, semi-quantitative real-time polymerase chain reaction (qRT-PCR), and enzyme-linked immunosorbent assay (ELISA). Mg degradation products increased HUCPV migration in transwell under hypoxia. Oxygen tension changed the gene regulation of migratory, angiogenetic or osteogenic regulators. Under contacting coculture and hypoxia, Mg degradation products remarkably increased cytokines (e.g., c-c motif chemokine ligand 2 and vascular endothelial growth factor) and MSC mineralisation. Mg degradation products decreased and increased the MSC proliferation in transwell and in heterotypic-contact coculture, respectively. In summary, this study indicates the roles of low oxygen and heterotypic contact to effects of Mg materials facilitating HUVEC and HUCPV. STATEMENT OF SIGNIFICANCE.

Thymoquinone promotes mouse mesenchymal stem cells migration in vitro and induces their immunogenicity in vivo

Mesenchymal stem cells (MSCs) have unique potentials, including migration and immunomodulation. Identification of the factors that enhance these activities can improve clinical applications of MSCs. This study aimed to investigate total antioxidant capacity (TAC) and migration potential of mouse MSCs exposed to thymoquinone (TQ) in vitro, and to examine the effect of TQ-treated MSCs on the expression of mouse immune cell markers. The results of total antioxidant capacity and wound healing assays showed that TQ increased the rate of MSCs TAC and migration in a dose- and time-dependent manner. The maximum TAC and migration were detected at 600 and 250 ng/ml of TQ, respectively. Functionally, the real-time PCR data analysis indicated that TQ induced c-Met and Cxcr4 expression and therefore, there may be a correlation between upregulation of these genes and increased MSCs migration. TQ also enhanced the up and down regulating impact of MSCs on Rorγt and Plzf expression and the expression of Tcf4 in mouse immune cells, respectively. Overall, this study declares that TQ increases the TAC of MSCs. It also proposes that TQ may, through activation of c-MET and CXCR4 signalling pathways, promote MSCs migration. TQ may also augment MSCs immunogenicity through its influence on the expression of genes involved in commitment of mouse immune system cells in vivo.