The impact of inflammatory licensing on heme oxygenase-1-mediated induction of regulatory T cells by human mesenchymal stem cells. Blood. 2011;117:4826-4835. [PMID: 21389316 DOI: 10.1182/blood-2010-12-324038]

Navigating the Immunological Crossroads: Mesenchymal Stem/Stromal Cells as Architects of Inflammatory Harmony in Tissue-Engineered Constructs

In the dynamic landscape of tissue engineering, the integration of tissue-engineered constructs (TECs) faces a dual challenge-initiating beneficial inflammation for regeneration while avoiding the perils of prolonged immune activation. As TECs encounter the immediate reaction of the immune system upon implantation, the unique immunomodulatory properties of mesenchymal stem/stromal cells (MSCs) emerge as key navigators. Harnessing the paracrine effects of MSCs, researchers aim to craft a localized microenvironment that not only enhances TEC integration but also holds therapeutic promise for inflammatory-driven pathologies. This review unravels the latest advancements, applications, obstacles, and future prospects surrounding the strategic alliance between MSCs and TECs, shedding light on the immunological symphony that guides the course of regenerative medicine.

Novel Programmed Death Ligand 1-AKT-engineered Mesenchymal Stem Cells Promote Neuroplasticity to Target Stroke Therapy

Although tissue plasminogen activator (t-PA) and endovascular thrombectomy are well-established treatments for acute ischemic stroke, over half of patients with stroke remain disabled for a long time. Thus, a significant unmet need exists to develop an effective strategy for treating acute stroke. We developed a combination of programmed cell death-ligand 1 (PD-L1) and AKT-modified umbilical cord mesenchymal stem cells (UMSC-PD-L1-AKT) implanted through intravenous (IV) and intracarotid (IA) routes to enhance therapeutic efficacy in a murine stroke model for overcoming the hypoxic environment of the ischemic brain, to prolong stem cell survival, and to attenuate systemic inflammation to protect neuroglial cells from ischemic injury. Higher cellular proliferation and survival upon exposure to toxic agents were observed in UMSC-PD-L1-AKT cells than in UMSCs in vitro. Moreover, increased attenuation of CFSE+ cell proliferation and increased survival of primary cortical cells were verified by the interaction with UMSC-PD-L1-AKT. Consistently, dual-route administration (IV + IA) of UMSC-PD-L1-AKT resulted in a significant reduction in infarction volume and improvement of neurological dysfunction in a stroke model. Furthermore, enhancing CD8+CD122+IL-10+ T-regulatory (Treg) cells and reducing CD11b+CD80+ microglial/macrophages and CD3+CD8+TNF-α+ and CD3+CD8+ IFN-α+ cytotoxic T cells induced an anti-inflammatory microenvironment to protect neuroglial cells in the ischemic brain. Collectively, therapeutic intervention using UMSC-PD-L1-AKT could provide a niche for inducing neuroplastic regeneration in brains after stroke.

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.

Lysis and phenotypic modulation of mesenchymal stromal cells upon blood contact triggers anti-inflammatory skewing of the peripheral innate immune repertoire

BACKGROUND AIMS

Mesenchymal stromal cells (MSCs) are used to treat immune-related disorders, including graft-versus-host disease. Upon intravenous infusion, MSCs trigger the instant blood-mediated inflammatory response, resulting in activation of both complement and coagulation cascades, and are rapidly cleared from circulation. Despite no/minimal engraftment, long-term immunoregulatory properties are evident. The aim of this study was to establish the effects of blood exposure on MSC viability and immunomodulatory functions.

METHODS

Human, bone marrow derived MSCs were exposed to human plasma +/- heat inactivation or whole blood. MSC number, viability and cellular damage was assessed using the JC-1 mitochondrial depolarization assay and annexin V staining. C3c binding and expression of the inhibitory receptors CD46, CD55 and CD59 and complement receptors C3aR and C5aR were evaluated by flow cytometry. MSCs pre-exposed to plasma were cultured with peripheral blood mononuclear cells (PBMCs) and monocyte subsets characterized by flow cytometry. The PBMC and MSC secretome was assessed using enzyme-linked immunosorbent assays against tumor necrosis factor alpha, interleukin (IL)-6 and IL-10. Monocyte recruitment towards the MSC secretome was evaluated using Boyden chambers and screened for chemotactic factors including monocyte chemoattractant protein (MCP)-1. MSC effects on the peripheral immune repertoire was also evaluated in whole blood by flow cytometry.

RESULTS

Plasma induced rapid lysis of 57% of MSCs, which reduced to 1% lysis with heat inactivation plasma. Of those cells that were not lysed, C3c could be seen bound to the surface of the cells, with a significant swelling of the MSCs and induction of cell death. The MSC secretome reduced monocyte recruitment, in part due to a reduction in MCP-1, and downregulated PBMC tumor necrosis factor alpha secretion while increasing IL-6 levels in the co-culture supernatant. A significant decrease in CD14⁺ monocytes was evident after MSC addition to whole blood alongside a significant increase in IL-6 levels, with those remaining monocytes demonstrating an increase in classical and decrease in non-classical subsets. This was accompanied by a significant increase in both mononuclear and polymorphonuclear myeloid-derived suppressor cells.

CONCLUSIONS

This study demonstrates that a significant number of MSCs are rapidly lysed upon contact with blood, with those surviving demonstrating a shift in their phenotype, including a reduction in the secretion of monocyte recruitment factors and an enhanced ability to skew the phenotype of monocytes. Shifts in the innate immune repertoire, towards an immunosuppressive profile, were also evident within whole blood after MSC addition. These findings suggest that exposure to blood components can promote peripheral immunomodulation via multiple mechanisms that persists within the system long after the infused MSCs have been cleared.

Umbilical cord-mesenchymal stem cells induce a memory phenotype in CD4+ T cells

Inflammation is a physiological state where immune cells evoke a response against detrimental insults. Finding a safe and effective treatment for inflammation associated diseases has been a challenge. In this regard, human mesenchymal stem cells (hMSC), exert immunomodulatory effects and have regenerative capacity making it a promising therapeutic option for resolution of acute and chronic inflammation. T cells play a critical role in inflammation and depending on their phenotype, they can stimulate or suppress inflammatory responses. However, the regulatory effects of hMSC on T cells and the underlying mechanisms are not fully elucidated. Most studies focused on activation, proliferation, and differentiation of T cells. Here, we further investigated memory formation and responsiveness of CD4⁺ T cells and their dynamics by immune-profiling and cytokine secretion analysis. Umbilical cord mesenchymal stem cells (UC-MSC) were co-cultured with either αCD3/CD28 beads, activated peripheral blood mononuclear cells (PBMC) or magnetically sorted CD4⁺ T cells. The mechanism of immune modulation of UC-MSC were investigated by comparing different modes of action; transwell, direct cell-cell contact, addition of UC-MSC conditioned medium or blockade of paracrine factor production by UC-MSC. We observed a differential effect of UC-MSC on CD4⁺ T cell activation and proliferation using PBMC or purified CD4⁺ T cell co-cultures. UC-MSC skewed the effector memory T cells into a central memory phenotype in both co-culture conditions. This effect on central memory formation was reversible, since UC-MSC primed central memory cells were still responsive after a second encounter with the same stimuli. The presence of both cell-cell contact and paracrine factors were necessary for the most pronounced immunomodulatory effect of UC-MSC on T cells. We found suggestive evidence for a partial role of IL-6 and TGFβ in the UC-MSC derived immunomodulatory function. Collectively, our data show that UC-MSCs clearly affect T cell activation, proliferation and maturation, depending on co-culture conditions for which both cell-cell contact and paracrine factors are needed.

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.

Intraperitoneally Delivered Umbilical Cord Lining Mesenchymal Stromal Cells Improve Survival and Kidney Function in Murine Lupus via Myeloid Pathway Targeting

To determine the therapeutic efficacy of human umbilical cord lining mesenchymal stromal cells (CL-MSCs) (US Patent number 9,737,568) in lupus-prone MRL/lpr (Fas^lpr) mice and elucidate its working mechanisms. A total of 4 doses of (20-25) × 10⁶ cells/kg of CL-MSCs was given to 16-week-old female Fas^lpr mice by intraperitoneal injection. Three subsequent doses were given on 17 weeks, 18 weeks, and 22 weeks, respectively. Six-week-old Fas^lpr mice were used as disease pre-onset controls. Mice were monitored for 10 weeks. Mouse kidney function was evaluated by examining complement component 3 (C3) deposition, urinary albumin-to-creatinine ratio (ACR), and lupus nephritis (LN) activity and chronicity. Working mechanisms were elucidated by flow cytometry, Luminex/ELISA (detection of anti-dsDNA and isotype antibodies), and RNA sequencing. CL-MSCs improved mice survival and kidney function by reducing LN activity and chronicity and lymphocyte infiltration over 10 weeks. CL-MSCs also reduced urinary ACR, renal complement C3 deposition, anti-dsDNA, and isotype antibodies that include IgA, IgG1, IgG2a, IgG2b, and IgM. Immune and cytokine profiling demonstrated that CL-MSCs dampened inflammation by suppressing splenic neutrophils and monocytes/macrophages, reducing plasma IL-6, IL-12, and CXCL1 and stabilizing plasma interferon-γ and TNF-α. RNA sequencing further showed that CL-MSCs mediated immunomodulation via concerted action of pro-proinflammatory cytokine-induced chemokines and production of nitric oxide in macrophages. CL-MSCs may provide a novel myeloid (neutrophils and monocytes/macrophages)-targeting therapy for SLE.

The different facets of heme-oxygenase 1 in innate and adaptive immunity

Heme oxygenase (HO) enzymes are responsible for the main oxidative step in heme degradation, generating equimolar amounts of free iron, biliverdin and carbon monoxide. HO-1 is induced as a crucial stress response protein, playing protective roles in physiologic and pathological conditions, due to its antioxidant, anti-apoptotic and anti-inflammatory effects. The mechanisms behind HO-1-mediated protection are being explored by different studies, affecting cell fate through multiple ways, such as reduction in intracellular levels of heme and ROS, transcriptional regulation, and through its byproducts generation. In this review we focus on the interplay between HO-1 and immune-related signaling pathways, which culminate in the activation of transcription factors important in immune responses and inflammation. We also discuss the dual interaction of HO-1 and inflammatory mediators that govern resolution and tissue damage. We highlight the dichotomy of HO-1 in innate and adaptive immune cells development and activation in different disease contexts. Finally, we address different known anti-inflammatory pharmaceuticals that are now being described to modulate HO-1, and the possible contribution of HO-1 in their anti-inflammatory effects.

Enhancing Mesenchymal Stromal Cell Potency: Inflammatory Licensing via Mechanotransduction

Mesenchymal stromal cells (MSC) undergo functional maturation upon their migration from bone marrow and introduction to a site of injury. This inflammatory licensing leads to heightened immune regulation via cell-to-cell interaction and the secretion of immunomodulatory molecules, such as anti-inflammatory mediators and antioxidants. Pro-inflammatory cytokines are a recognized catalyst of inflammatory licensing; however, biomechanical forces, such as fluid shear stress, are a second, distinct class of stimuli that incite functional maturation. Here we show mechanotransduction, achieved by exposing MSC to various grades of wall shear stress (WSS) within a scalable conditioning platform, enhances the immunomodulatory potential of MSC independent of classical pro-inflammatory cytokines. A dose-dependent effect of WSS on potency is evidenced by production of prostaglandin E2 (PGE₂) and indoleamine 2,3 dioxygenase 1 (IDO1), as well as suppression of tumor necrosis factor-α (TNF- α) and interferon-γ (IFN-γ) production by activated immune cells. Consistent, reproducible licensing is demonstrated in adipose tissue and bone marrow human derived MSC without significant impact on cell viability, cellular yield, or identity. Transcriptome analysis of WSS-conditioned BM-MSC elucidates the broader phenotypic implications on the differential expression of immunomodulatory factors. These results suggest mechanotransduction as a viable, scalable pre-conditioning alternative to pro-inflammatory cytokines. Enhancing the immunomodulatory capacity of MSC via biomechanical conditioning represents a novel cell therapy manufacturing approach.

Normal mesenchymal stem cells can improve the abnormal function of T cells in psoriasis via upregulating transforming growth factor-β receptor

Psoriasis, a chronic inflammatory skin disease, is a refractory disorder. Previous studies have shown that the imbalance of the T-helper (Th)17/regulatory T cells (Treg) results in the immune imbalance of T cells in psoriatic patients, and that mesenchymal stem cells display an immunosuppressive role by promoting the differentiation of T cells into Treg, leading to a reduction in the proportion of Th17/Treg. Utility of mesenchymal stem cells is becoming a new approach for the treatment of immune disorders. Following co-culture of dermal mesenchymal stromal cells (DMSC) and CD3⁺ T cells with or without transforming growth factor (TGF)-β receptor inhibitor, the biological function and relative signal pathway of CD3⁺ T cells were assessed by flow cytometry, transwell, real-time polymerase chain reaction and western blotting, respectively. Normal DMSC were more potent than psoriatic DMSC in inhibition of CD3⁺ T-cell proliferation, and stimulation of CD3⁺ T-cell apoptosis than psoriasis DMSC. Moreover, normal DMSC decreased the ratio of Th17/Treg, while enhancing the immunosuppressive effect of Tregs on effector T cells. However, TGF-β receptor (TGF-βR) inhibitor attenuated the effect of normal DMSC on CD3⁺ T cells and Th17/Treg ratio. Additionally, the normal DMSC were more potent than the psoriatic DMSC in increasing TGF-β receptors and activation of TGF-β/SMAD pathway in psoriatic CD3⁺ T cells. In conclusion, normal DMSC can partially improve the biological function and immunosuppressive ability of psoriatic CD3⁺ T cells, possibly via upregulating the TGF-β receptors.

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 Cells Alleviate Inflammatory Bowel Disease Via Tr1 Cells

Mesenchymal stem cells (MSCs) have been used to achieve exciting therapeutic outcomes in many animal studies and clinical trials for various autoimmune diseases, including inflammatory bowel disease (IBD). Type 1 regulatory T (Tr1) cells are the main source of interleukin (IL) 10 in the intestine. Whether Tr1 cells are involved during MSC-mediated IBD treatment is unclear. We treated a murine model of 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis with human umbilical cord-derived MSCs (hUCMSCs) and found that the disease severity was alleviated significantly in a dose-dependent manner. hUCMSCs increased the proportion of Tr1 cells and decreased that of T helper (Th)-1 and Th17 cells in the spleen and mesenteric lymph nodes in different stages of colitis. We found that the upregulation of Tr1 cells by hUCMSCs was abrogated after blocking indoleamine-2,3-dioxygenase (IDO), and IDO knockdown in hUCMSCs reversed the increase in Tr1 cell proportions caused by hUCMSCs in colitis. Moreover, hUCMSCs inhibited apoptosis and promoted the proliferation of Tr1 cells. Our results suggest that Tr1 cells play an important role in the amelioration of IBD by MSCs, and they are the target population for the alleviation of IBD by MSCs, providing meaningful references for the study of therapeutic mechanisms of MSCs in other inflammatory diseases.

Human MuStem cells repress T-cell proliferation and cytotoxicity through both paracrine and contact-dependent pathways

Background

Muscular dystrophies (MDs) are inherited diseases in which a dysregulation of the immune response exacerbates disease severity and are characterized by infiltration of various immune cell types leading to muscle inflammation, fiber necrosis and fibrosis. Immunosuppressive properties have been attributed to mesenchymal stem cells (MSCs) that regulate the phenotype and function of different immune cells. However, such properties were poorly considered until now for adult stem cells with myogenic potential and advanced as possible therapeutic candidates for MDs. In the present study, we investigated the immunoregulatory potential of human MuStem (hMuStem) cells, for which we previously demonstrated that they can survive in injured muscle and robustly counteract adverse tissue remodeling.

Methods

The impact of hMuStem cells or their secretome on the proliferative and phenotypic properties of T-cells was explored by co-culture experiments with either peripheral blood mononucleated cells or CD3-sorted T-cells. A comparative study was produced with the bone marrow (BM)-MSCs. The expression profile of immune cell-related markers on hMuStem cells was determined by flow cytometry while their secretory profile was examined by ELISA assays. Finally, the paracrine and cell contact-dependent effects of hMuStem cells on the T-cell-mediated cytotoxic response were analyzed through IFN-γ expression and lysis activity.

Results

Here, we show that hMuStem cells have an immunosuppressive phenotype and can inhibit the proliferation and the cytotoxic response of T-cells as well as promote the generation of regulatory T-cells through direct contact and via soluble factors. These effects are associated, in part, with the production of mediators including heme-oxygenase-1, leukemia inhibitory factor and intracellular cell adhesion molecule-1, all of which are produced at significantly higher levels by hMuStem cells than BM-MSCs. While the production of prostaglandin E2 is involved in the suppression of T-cell proliferation by both hMuStem cells and BM-MSCs, the participation of inducible nitric oxide synthase activity appears to be specific to hMuStem cell-mediated one.

Conclusions

Together, our findings demonstrate that hMuStem cells are potent immunoregulatory cells. Combined with their myogenic potential, the attribution of these properties reinforces the positioning of hMuStem cells as candidate therapeutic agents for the treatment of MDs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02681-3.

Cytological Effects of Serum Isolated from Polytraumatized Patients on Human Bone Marrow-Derived Mesenchymal Stem Cells

Due to their immunomodulatory and regenerative capacity, human bone marrow-derived mesenchymal stem cells (hBMSCs) are promising in the treatment of patients suffering from polytrauma. However, few studies look at the effects of sera from polytraumatized patients on hBMSCs. The aim of this study was to explore changes in hBMSC properties in response to serum from polytrauma patients taken at different time points after the trauma incident. For this, sera from 84 patients with polytrauma (collected between 2010 and 2020 in our department) were used. In order to test the differential influence on hBMSC, sera from the 1^st (D1), 5^th (D5), and 10^th day (D10) after polytrauma were pooled, respectively. As a control, sera from three healthy donors (HS), matched with respect to age and gender to the polytrauma group, were collected. Furthermore, hBMSCs from four healthy donors were used in the experiments. The pooled sera of HS, D1, D5, and D10 were analyzed by multicytokine array for pro-/anti-inflammatory cytokines. Furthermore, the influence of the different sera on hBMSCs with respect to cell proliferation, colony forming unit-fibroblast (CFU-F) assay, cell viability, cytotoxicity, cell migration, and osteogenic and chondrogenic differentiation was analyzed. The results showed that D5 serum significantly reduced hBMSC cell proliferation capacity compared with HS and increased the proportion of dead cells compared with D1. However, the frequency of CFU-F was not reduced in polytrauma groups compared with HS, as well as the other parameters. The serological effect of polytrauma on hBMSCs was related to the time after trauma. It is disadvantageous to use BMSCs in polytraumatized patients at least until the fifth day after polytrauma as obvious cytological changes could be found at that time point. However, it is promising to use hBMSCs to treat polytrauma after five days, combined with the concept of “Damage Control Orthopedics” (DCO).

Effects of immune cells on mesenchymal stem cells during fracture healing

In vertebrates, bone is considered an osteoimmune system which encompasses functions of a locomotive organ, a mineral reservoir, a hormonal organ, a stem cell pool and a cradle for immune cells. This osteoimmune system is based on cooperatively acting bone and immune cells, cohabitating within the bone marrow. They are highly interdependent, a fact that is confounded by shared progenitors, mediators, and signaling pathways. Successful fracture healing requires the participation of all the precursors, immune and bone cells found in the osteoimmune system. Recent evidence demonstrated that changes of the immune cell composition and function may negatively influence bone healing. In this review, first the interplay between different immune cell types and osteoprogenitor cells will be elaborated more closely. The separate paragraphs focus on the specific cell types, starting with the cells of the innate immune response followed by cells of the adaptive immune response, and the complement system as mediator between them. Finally, a brief overview on the challenges of preclinical testing of immune-based therapeutic strategies to support fracture healing will be given.

SDF-1α Facilitates Mesenchymal Stem Cells to Induce Regulatory B Cell Differentiation from Patients with Immune Thrombocytopenia

B cells play a central role in the pathogenesis of immune thrombocytopenia (ITP) by participating in humoral immunity. Meanwhile, regulatory B cells (Bregs), one subset of B cells, express negative regulatory effect on ITP. Mesenchymal stem cells (MSCs) have been demonstrated in the ability to induce immunosuppression, and stromal cell-derived factor-1α (SDF-1α) plays an important role in the migration and survival of MSCs. To investigate the mechanism of SDF-1α in controlling umbilical cord-derived MSCs (UC-MSCs) in inducing regulatory B cell differentiation of patients with ITP, we reconfirmed that SDF-1α promotes the proliferation of MSCs at the low doses of 0.05 μg/mL and 0.1 μg/mL but inhibits the proliferation and promotes the apoptosis of UC-MSCs at the high doses 0.5 μg/mL and 1 μg/mL; when UC-MSCs are cocultured with SDF-1α at 0.1 μg/mL, the decreased proportion of CD19⁺/CD24^hi/CD38^hi cells and IL-10-producing B cells (B 10 cell), considered as the Breg subset from ITP significantly enhanced, and the content of IL-10 in the supernatant is also obviously increased. The proportion of Bregs and the IL-10 secretion could be further promoted by the UC-MSCs treated with 0.1 μg/mL SDF-1α, which could also promote the miRNA-133 expression of UC-MSCs in an exosome-dependent manner; moreover, while the UC-MSCs were transfected with the miR-133 inhibitor, the proportion of induced Bregs decreased obviously when cocultured with peripheral blood mononuclear cells (PBMCs) of ITP. We conclude that UC-MSCs could effectively enhance the decreased proportion of Bregs from ITP; at appropriate concentrations, SDF-1α may promote the proliferating and survival ability of UC-MSCs and improve the production of Bregs induced by UC-MSCs through controlling miRNA-133 expression in the exosomes.

The regulatory effect of hyaluronan on human mesenchymal stem cells' fate modulates their interaction with cancer cells in vitro

Metastatic spread of cancer cells into a pre-metastatic niche is highly dependent on a supporting microenvironment. Human bone marrow-derived mesenchymal stem cells (bmMSCs) contribute to the tumor microenvironment and promote cancer metastasis by inducing epithelial-to-mesenchymal transition and immune evasion. The underlying mechanisms, however, are incompletely understood. The glycosaminoglycan hyaluronan (HA) is a central component of the extracellular matrix and has been shown to harbor pro-metastatic properties. In this study we investigated the highly disseminating breast cancer and glioblastoma multiforme cell lines MDA-MB-321 and U87-MG which strongly differ in their metastatic potential to evaluate the impact of HA on tumor promoting features of bmMSC and their interaction with tumor cells. We show that adipogenic differentiation of bmMSC is regulated by the HA-matrix. This study reveals that MDA-MB-231 cells inhibit this process by the induction of HA-synthesis in bmMSCs and thus preserve the pro-tumorigenic properties of bmMSC. Furthermore, we show that adhesion of MDA-MB-231 cells to bmMSC is facilitated by the tumor cell-induced HA-rich matrix and is mediated by the HA-receptor LAYN. We postulate that invasive breast cancer cells modulate the HA-matrix of bmMSC to adapt the pre-metastatic niche. Thus, the HA-matrix provides a potential novel therapeutic target to prevent cancer metastasis.

Functional heterogeneity of IFN-γ-licensed mesenchymal stromal cell immunosuppressive capacity on biomaterials

Mesenchymal stromal cells (MSCs) are increasingly combined with biomaterials to enhance their therapeutic properties, including their immunosuppressive function. However, clinical trials utilizing MSCs with or without biomaterials have shown limited success, potentially due to their functional heterogeneity across different donors and among different subpopulations of cells. Here, we evaluated the immunosuppressive capacity, as measured by the ability to reduce T-cell proliferation and activation, of interferon-gamma (IFN-γ)-licensed MSCs from multiple donors on fibrin and collagen hydrogels, the two most commonly utilized biomaterials in combination with MSCs in clinical trials worldwide according to ClinicalTrials.gov Variations in the immunosuppressive capacity between IFN-γ-licensed MSC donors on the biomaterials correlated with the magnitude of indoleamine-2,3-dioxygenase activity. Immunosuppressive capacity of the IFN-γ-licensed MSCs depended on the α_V/α₅ integrins when cultured on fibrin and on the α₂/β₁ integrins when cultured on collagen. While all tested MSCs were nearly 100% positive for these integrins, sorted MSCs that expressed higher levels of α_V/α₅ integrins demonstrated greater immunosuppressive capacity with IFN-γ licensing than MSCs that expressed lower levels of these integrins on fibrin. These findings were equivalent for MSCs sorted based on the α₂/β₁ integrins on collagen. These results demonstrate the importance of integrin engagement to IFN-γ licensed MSC immunosuppressive capacity and that IFN-γ-licensed MSC subpopulations of varying immunosuppressive capacity can be identified by the magnitude of integrin expression specific to each biomaterial.

Transcriptional Profile of Cytokines, Regulatory Mediators and TLR in Mesenchymal Stromal Cells after Inflammatory Signaling and Cell-Passaging

Adult human subcutaneous adipose tissue (AT) harbors a rich population of mesenchymal stromal cells (MSCs) that are of interest for tissue repair. For this purpose, it is of utmost importance to determine the response of AT-MSCs to proliferative and inflammatory signals within the damaged tissue. We have characterized the transcriptional profile of cytokines, regulatory mediators and Toll-like receptors (TLR) relevant to the response of MSCs. AT-MSCs constitutively present a distinct profile for each gene and differentially responded to inflammation and cell-passaging. Inflammation leads to an upregulation of IL-6, IL-8, IL-1β, TNFα and CCL5 cytokine expression. Inflammation and cell-passaging increased the expression of HGF, IDO1, PTGS1, PTGS2 and TGFβ. The expression of the TLR pattern was differentially modulated with TLR 1, 2, 3, 4, 9 and 10 being increased, whereas TLR 5 and 6 downregulated. Functional enrichment analysis demonstrated a complex interplay between cytokines, TLR and regulatory mediators central for tissue repair. This profiling highlights that following a combination of inflammatory and proliferative signals, the sensitivity and responsive capacity of AT-MSCs may be significantly modified. Understanding these transcriptional changes may help the development of novel therapeutic approaches.

Adipose-mesenchymal stromal cells suppress experimental Sjögren syndrome by IL-33-driven expansion of ST2+ regulatory T cells

Adipose-derived mesenchymal stromal cells (ADSCs) play important roles in the alleviation of inflammation and autoimmune diseases. Interleukin-33 (IL-33), a member of the IL-1 family, has been shown to regulate innate and adaptive immunity. However, it is still unknown whether ADSCs regulate immune responses via IL-33. We show here that ADSCs produced IL-33 in response to IL-1β stimulation, which depended on TAK1, ERK, and p38 pathways. ADSCs-derived IL-33 drove the proliferation of CD4⁺Foxp3⁺ST2⁺ regulatory T cells (Tregs) and alleviated experimental autoimmune Sjögren syndrome in mice. Importantly, human ADSCs also produced IL-33 in response to IL-1β. Thus, we have revealed a previously unrecognized immunoregulatory function of ADSCs by IL-33 production in experimental autoimmunity, which may have clinical applications for human immunopathology.

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Human and mouse ADSCs express IL-33 in response to IL-β stimulation

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mADSC-derived IL-33 inhibits inflammation in salivary glands in SS model

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mADSC-derived IL-33 expand ST2⁺ Tregs in vitro and in SS model

Regulatory Effect of Mesenchymal Stem Cells on T Cell Phenotypes in Autoimmune Diseases

Research on mesenchymal stem cells (MSCs) starts from the earliest assumption that cells derived from the bone marrow have the ability to repair tissues. Several scientists have since documented the crucial role of bone marrow-derived MSCs (BM-MSCs) in processes such as embryonic bone and cartilage formation, adult fracture and tissue repair, and immunomodulatory activities in therapeutic applications. In addition to BM-MSCs, several sources of MSCs have been reported to possess tissue repair and immunoregulatory abilities, making them potential treatment options for many diseases. Therefore, the therapeutic potential of MSCs in various diseases including autoimmune conditions has been explored. In addition to an imbalance of T cell subsets in most patients with autoimmune diseases, they also exhibit complex disease manifestations, overlapping symptoms among diseases, and difficult treatment. MSCs can regulate T cell subsets to restore their immune homeostasis toward disease resolution in autoimmune conditions. This review summarizes the role of MSCs in relieving autoimmune diseases via the regulation of T cell phenotypes.

Old Friends with Unexploited Perspectives: Current Advances in Mesenchymal Stem Cell-Based Therapies in Asthma

Mesenchymal stem cells (MSCs) have a great regenerative and immunomodulatory potential that was successfully tested in numerous pre-clinical and clinical studies of various degenerative, hematological and inflammatory disorders. Over the last few decades, substantial immunoregulatory effects of MSC treatment were widely observed in different experimental models of asthma. Therefore, it is tempting to speculate that stem cell-based treatment could become an attractive means to better suppress asthmatic airway inflammation, especially in subjects resistant to currently available anti-inflammatory therapies. In this review, we discuss mechanisms accounting for potent immunosuppressive properties of MSCs and the rationale for their use in asthma. We describe in detail an intriguing interplay between MSCs and other crucial players in the immune system as well as lung microenvironment. Finally, we reveal the potential of MSCs in maintaining airway epithelial integrity and alleviating lung remodeling.

Tumor-resident adenosine-producing mesenchymal stem cells as a potential target for cancer treatment

The development of new therapies based on tumor biology is one of the main topics in cancer treatment. In this regard, investigating the microenvironment and cellular composition of the tumor is of particular interest. Mesenchymal stem cells (MSCs) are a major group of cells in the tumor tissue and play a critical role in tumor growth and development. Investigating the mechanisms by which MSCs influence tumor growth and progression is very useful in establishing new therapeutic approaches. MSCs have some immunological capacities, including anti-inflammatory, immune-regulatory, and immune-suppressive abilities, which help the tumor growth in the inflammatory condition. They can suppress the proliferation and activation of CD4 + T cells and direct them toward the regulatory phenotype through the release of some factors such as indoleamine 2,3-dioxygenase, prostaglandin E2, and HO-1, PD-1 ligands (PD-L1 and PD-L2) and promote tolerance and apoptosis. Besides, these cells are able to produce adenosine. Adenosine has a key role in controlling the immune system by signaling through receptors located on the surface of immune cells. It plays a very essential role in tumor growth and progression. In the present review, we investigate and introduce adenosine-producing mesenchymal stem cells as a potential target for cancer treatment.

Perinatal Cells: A Promising COVID-19 Therapy?

The COVID-19 pandemic has become a priority in the health systems of all nations worldwide. In fact, there are currently no specific drugs or preventive treatments such as vaccines. The numerous therapies available today aim to counteract the symptoms caused by the viral infection that in some subjects can evolve causing acute respiratory distress syndromes (ARDS) with consequent admission to intensive care unit. The exacerbated response of the immune system, through cytokine storm, causes extensive damage to the lung tissue, with the formation of edema, fibrotic tissues and susceptibility to opportunistic infections. The inflammatory picture is also aggravated by disseminated intravascular coagulation which worsens the damage not only to the respiratory system, but also to other organs. In this context, perinatal cells represent a valid strategy thanks to their strong immunomodulatory potential, their safety profile, the ability to reduce fibrosis and stimulate reparative processes. Furthermore, perinatal cells exert antibacterial and antiviral actions. This review therefore provides an overview of the characteristics of perinatal cells with a particular focus on the beneficial effects that they could have in patients with COVID-19, and more specifically for their potential use in the treatment of ARDS and sepsis.

Role of mesenchymal stem cell derived extracellular vesicles in autoimmunity: A systematic review

BACKGROUND

Mesenchymal stem cells (MSCs) have been reported to possess immune regulatory effects in innate and adaptive immune reactions. MSCs can mediate intercellular communications by releasing extracellular vesicles (EVs), which deliver functional molecules to targeted cells. MSC derived EVs (MSC-EVs) confer altering effects on many immune cells, including T lymphocytes, B lymphocytes, natural killer cells, dendritic cells, and macrophages. A large number of studies have suggested that MSC-EVs participate in regulating autoimmunity related diseases. This characteristic of MSC-EVs makes them be potential biomarkers for the diagnosis and treatment of autoimmunity related diseases.

AIM

To verify the potential of MSC-EVs for molecular targeted therapy of autoimmunity related diseases.

METHODS

Literature search was conducted in PubMed to retrieve the articles published between 2010 and 2020 in the English language. The keywords, such as “MSCs,” “EVs,” “exosome,” “autoimmunity,” “tumor immunity,” and “transplantation immunity,” and Boolean operator “AND” and “NOT” coalesced admirably to be used for searching studies on the specific molecular mechanisms of MSC-EVs in many immune cell types and many autoimmunity related diseases. Studies that did not investigate the molecular mechanisms of MSC-EVs in the occurrence and development of autoimmune diseases were excluded.

RESULTS

A total of 96 articles were chosen for final reference lists. After analyzing those publications, we found that it had been well documented that MSC-EVs have the ability to induce multiple immune cells, like T lymphocytes, B lymphocytes, natural killer cells, dendritic cells, and macrophages, to regulate immune responses in innate immunity and adaptive immunity. Many validated EVs-delivered molecules have been identified as key biomarkers, such as proteins, lipids, and nucleotides. Some EVs-encapsulated functional molecules can serve as promising therapeutic targets particularly for autoimmune disease.

CONCLUSION

MSC-EVs play an equally important part in the differentiation, activation, and proliferation of immune cells, and they may become potential biomarkers for diagnosis and treatment of autoimmunity related diseases.

In vitro preconditioning of equine adipose mesenchymal stem cells with prostaglandin E2, substance P and their combination changes the cellular protein secretomics and improves their immunomodulatory competence without compromising stemness

Mesenchymal stem cells (MSC) are modern tools in regenerative therapies of humans and animals owed to their immunomodulatory properties, which are activated in a pro-inflammatory environment. Different preconditioning strategies had been devised to enhance the immunomodulatory properties of MSC. In this research, we evaluated the immunological attributes of equine adipose MSC (eAMSC) before and after preconditioning in vitro with prostaglandin E₂ (PGE₂), substance P (SP), their combination and IFNγ. PGE₂/SP was the best combination to keep or enhance the mesodermal lineage differentiation of eAMSC. Alongside with this, preconditioning of eMSC with PGE₂ and SP did not affect expression of stemness MSC surface phenotype: CD90⁺, CD44⁺, MHC class I⁺, MHC class II^- and CD45^-, assessed by cytometry. Both naïve and preconditioned eAMSC expressed genes related with immune properties, such as MHC-I, PTGES, IL6, IL1A, TNFα and IL8 assessed by qPCR. Only TNFα was under expressed in treated cells, while the other markers were either overexpressed or not changed. In no cases MHC-II expression was detected. The antiproliferative effect of preconditioned eAMSC exposed to activated peripheral blood mononuclear cells (PBMC) showed that SP treatment significantly inhibited proliferation of LPS stimulated PBMC. When eAMSC were stimulated with Poly I:C, all the treatments significantly inhibited proliferation of stimulated PBMC (p < 0.05). Direct contact (coculture) between the preconditioned eAMSC and PBMC, induced a shift of significantly more (CD4/CD25/FOXP3)⁺ T-regulatory PBMC than naïve eAMSC. In the experiments of this research, we investigated the secreted proteomic profile of naïve and preconditioned eAMSC, 42 up-regulated and 40 down-regulated proteins were found in the proteomic assay. Our proteomic data revealed profound changes in the secretory pattern of MSC exposed to different treatments, compared to naïve eAMSC as well as among treatments. In overall, compared to naïve cells, the protein profile of preconditioned cells resembled the mesenchymal-epithelial transition (MET). Here we showed that the combined use of PGE₂ and SP provoked in overall the highest expression of anti-inflammatory markers as well as lead to an increased acquisition of a T-regulatory phenotype in preconditioned eAMSC without affecting their "stemness".

Treatment of chronic GvHD with mesenchymal stromal cells induces durable responses: A phase II study

Steroid‐refractory chronic graft‐vs‐host disease (cGvHD) contributes to morbidity after allogeneic hematopoietic stem cell transplantation. Here, we report on 11 patients with severe, refractory cGvHD treated with repeated infusions of allogeneic bone marrow‐derived mesenchymal stromal cells (MSC) over a 6‐ to 12‐month period. Six patients responded to MSC treatment following National Institutes of Health response criteria, accompanied by improvement in GvHD‐related symptoms and quality of life. This response was durable, with systemic immunosuppressive therapy withdrawn from two responders, and a further two free from steroids and tapering calcineurin inhibitors. All responders displayed a distinct immune phenotype characterized by higher levels of naïve T cells and B cells before treatment compared with the nonresponders, and a significantly higher fraction of CD31+ naïve CD4+ T cells. MSC treatment was associated with significant increases in naïve T cells, B cells, and Tregs 7 days after each infusion. Skin biopsies showed resolution of epidermal pathology. CXCL9 and CXCL10 showed differential responses in responder and nonresponder patients. Our data support the use of MSC infusions as treatment for steroid‐refractory cGvHD with durable responses. We propose CXCL9 and CXCL10 as early biomarkers for responsiveness to MSC treatment. Our results highlight the importance of the MSC recipient immune phenotype in promoting treatment response. This trial was registered at www.ClinicalTrials.gov as #NCT01522716.

N-glycosylation controls inflammatory licensing-triggered PD-L1 upregulation in human mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) are characterized by their multipotency, regenerative potential, and immunoregulatory properties. Nowadays, MSCs represent a promising cell-therapeutic option for hyperinflammatory conditions such as graft-vs-host disease following allogeneic hematopoietic stem cell transplantation. A better understanding of their biology is a prerequisite for improving their treatment efficacy. Emerging evidence suggests that immunosuppressive properties are not constitutively active in MSCs. Instead, microenvironmental inflammatory stimuli such as the cytokines interferon (IFN)-γ or tumor necrosis factor (TNF)-α license MSCs to acquire a tolerance-promoting phenotype. The immunological checkpoint molecule programmed death-ligand 1 (PD-L1) is an important regulator of T-cell responses. Binding of PD-L1 to the programmed cell death protein 1 (PD-1) receptor on T-cells suppresses their activation, proliferation, and induces apoptosis. Previous studies have revealed that cell surface expression and secretion of PD-L1 are part of the MSCs' immunomodulatory armamentarium. Here, we report that inflammatory licensing leads to an enhanced PD-L1 cell surface expression and secretion, which are both accompanied by an increased posttranslational protein N-glycosylation. These post-translational modifications have been shown to be critical for key biological processes such as cell trafficking, receptor signaling, and immunohomeostasis. In fact, promoting N-glycosylation in MSCs yielded increased PD-L1 levels. We report for the first time that PD-L1 N-glycosylation plays a decisive role for its transport to the MSCs' cell surface and its subsequent secretion (in response to proinflammatory trigger). Our data offer insights into a novel regulatory mechanism with the potential to be exploited as a means to foster the immunosuppressive potency of human MSCs.

Mesenchymal stromal cells induce regulatory T cells via epigenetic conversion of human conventional CD4 T cells in vitro

Regulatory T cells (Treg) play a critical role in immune tolerance. The scarcity of Treg therapy clinical trials in humans has been largely due to the difficulty in obtaining sufficient Treg numbers. We performed a preclinical investigation on the potential of mesenchymal stromal cells (MSCs) to expand Treg in vitro to support future clinical trials. Human peripheral blood mononuclear cells from healthy donors were cocultured with allogeneic bone marrow‐derived MSCs expanded under xenogeneic‐free conditions. Our data show an increase in the counts and frequency of CD4⁺ CD25^high Foxp3⁺ CD127^low Treg cells (4‐ and 6‐fold, respectively) after a 14‐day coculture. However, natural Treg do not proliferate in coculture with MSCs. When purified conventional CD4 T cells (Tcon) are cocultured with MSCs, only cells that acquire a Treg‐like phenotype proliferate. These MSC‐induced Treg‐like cells also resemble Treg functionally, since they suppress autologous Tcon proliferation. Importantly, the DNA methylation profile of MSC‐induced Treg‐like cells more closely resembles that of natural Treg than of Tcon, indicating that this population is stable. The expression of PD‐1 is higher in Treg‐like cells than in Tcon, whereas the frequency of PDL‐1 increases in MSCs after coculture. TGF‐β levels are also significantly increased MSC cocultures. Overall, our data suggest that Treg enrichment by MSCs results from Tcon conversion into Treg‐like cells, rather than to expansion of natural Treg, possibly through mechanisms involving TGF‐β and/or PD‐1/PDL‐1 expression. This MSC‐induced Treg population closely resembles natural Treg in terms of phenotype, suppressive ability, and methylation profile.

[Mesenchymal stem cell treatment in autoimmune diseases]

Mesenchymal stromal or stem cells (MSC) possess strong immunomodulatory properties. Due to their impressive potential to differentiate into various cell types they are capable of inducing mechanisms of tissue repair. Experimental data have demonstrated impaired MSC function in several rheumatic diseases in vitro; however, the relevance of these phenomena for the pathogenesis of rheumatic disorders has not been convincingly demonstrated. Nevertheless, allogeneic MSC transplantation (MSCT), and possibly autologous MSCT as well, could prove to be an interesting instrument for the treatment of autoimmune rheumatic diseases. The first clinical trials have demonstrated positive effects in systemic lupus erythematosus, systemic sclerosis and Sjogren's syndrome; however, questions regarding the long-term benefits and safety as well as the best source, the optimal cultivation technique and the most effective way of application of MSC are still unanswered.

Mesenchymal stem cells: a promising way in therapies of graft-versus-host disease

It is well acknowledged that allogeneic hematopoietic stem cell transplantation (allo-HSCT) is an effective treatment for numerous malignant blood diseases, which has also been applied to autoimmune diseases for more than a decade. Whereas graft-versus-host disease (GVHD) occurs after allogeneic hematopoietic stem cell transplantation (allo-HSCT) as a common serious complication, seriously affecting the efficacy of transplantation. Mesenchymal stem cells (MSCs) derived from a wealth of sources can easily isolate and expand with low immunogenicity. MSCs also have paracrine and immune regulatory functions, leading to a broad application prospect in treatment and tissue engineering. This review focuses on immunoregulatory function of MSCs, factors affecting mesenchymal stem cells to exert immunosuppressive effects, clinical application of MSCs in GVHD and researches on MSC-derived extracellular vesicles (EVs). The latest research progress on MSC in related fields is reviewed as well. The relevant literature from PubMed databases is reviewed in this article.

Priming with inflammatory cytokines is not a prerequisite to increase immune-suppressive effects and responsiveness of equine amniotic mesenchymal stromal cells

BACKGROUND

Equine amniotic mesenchymal stromal cells (AMSCs) and their conditioned medium (CM) were evaluated for their ability to inhibit in vitro proliferation of peripheral blood mononuclear cells (PBMCs) with and without priming. Additionally, AMSC immunogenicity was assessed by expression of MHCI and MHCII and their ability to counteract the in vitro inflammatory process.

METHODS

Horse PBMC proliferation was induced with phytohemagglutinin. AMSC priming was performed with 10 ng/ml of TNF-α, 100 ng/ml of IFN-γ, and a combination of 5 ng/ml of TNF-α and 50 ng/ml of IFN-γ. The CM generated from naïve unprimed and primed AMSCs was also tested to evaluate its effects on equine endometrial cells in an in vitro inflammatory model induced by LPS. Immunogenicity marker expression (MHCI and II) was evaluated by qRT-PCR and by flow cytometry.

RESULTS

Priming does not increase MHCI and II expression. Furthermore, the inhibition of PBMC proliferation was comparable between naïve and conditioned cells, with the exception of AMSCs primed with both TNF-α and IFN-γ that had a reduced capacity to inhibit T cell proliferation. However, AMSC viability was lower after priming than under other experimental conditions. CM from naïve and primed AMSCs strongly inhibited PBMC proliferation and counteracted the inflammatory process, rescuing about 65% of endometrial cells treated by LPS.

CONCLUSION

AMSCs and their CM have a strong capacity to inhibit PBMC proliferation, and priming is not necessary to improve their immunosuppressive activity or reactivity in an inflammatory in vitro model.

Effects of mesenchymal stromal cells on regulatory T cells: Current understanding and clinical relevance

The immunomodulatory potential of mesenchymal stromal cells (MSCs) and regulatory T cells (T‐reg) is well recognized by translational scientists in the field of regenerative medicine and cellular therapies. A wide range of preclinical studies as well as a limited number of human clinical trials of MSC therapies have not only shown promising safety and efficacy profiles but have also revealed changes in T‐reg frequency and function. However, the mechanisms underlying this potentially important observation are not well understood and, consequently, the optimal strategies for harnessing MSC/T‐reg cross‐talk remain elusive. Cell‐to‐cell contact, production of soluble factors, reprogramming of antigen presenting cells to tolerogenic phenotypes, and induction of extracellular vesicles (“exosomes”) have emerged as possible mechanisms by which MSCs produce an immune‐modulatory milieu for T‐reg expansion. Additionally, these two cell types have the potential to complement each other's immunoregulatory functions, and a combinatorial approach may exert synergistic effects for the treatment of immunological diseases. In this review, we critically assess recent translational research related to the outcomes and mechanistic basis of MSC effects on T‐reg and provide a perspective on the potential for this knowledge base to be further exploited for the treatment of autoimmune disorders and transplants.

Therapeutic Mesenchymal Stromal Cells for Immunotherapy and for Gene and Drug Delivery

Mesenchymal stromal cells (MSCs) possess several fairly unique properties that, when combined, make them ideally suited for cellular-based immunotherapy and as vehicles for gene and drug delivery for a wide range of diseases and disorders. Key among these are: (1) their relative ease of isolation from a variety of tissues; (2) the ability to be expanded in culture without a loss of functionality, a property that varies to some degree with tissue source; (3) they are relatively immune-inert, perhaps obviating the need for precise donor/recipient matching; (4) they possess potent immunomodulatory functions that can be tailored by so-called licensing in vitro and in vivo; (5) the efficiency with which they can be modified with viral-based vectors; and (6) their almost uncanny ability to selectively home to damaged tissues, tumors, and metastases following systemic administration. In this review, we summarize the latest research in the immunological properties of MSCs, their use as immunomodulatory/anti-inflammatory agents, methods for licensing MSCs to customize their immunological profile, and their use as vehicles for transferring both therapeutic genes in genetic disease and drugs and genes designed to destroy tumor cells.

Mechanism and therapeutic effect of umbilical cord mesenchymal stem cells in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a persistent and chronic disease that is characterized by destructive gastrointestinal (GI) inflammation. Researchers are trying to identify and develop new and more effective treatments with no side effects. Acute and chronic mouse models of IBD were established using dextran sulfate sodium (DSS) solution. To evaluate the efficacy and mechanism, umbilical cord mesenchymal stem cells (UCMSCs) were obtained from Kunming (KM) mice and humans. In the chronic IBD study, the survival rates of the normal control, model, mouse UCMSC (mUCMSC) and human UCMSC (hUCMSC) groups were 100%, 40%, 86.7%, and 100%, respectively. The histopathological scores of the normal control, intraperitoneal injection, intravenous treatment, and model groups were 0.5 ± 0.30, 5.9 ± 1.10, 8.7 ± 1.39, and 8.8 ± 1.33 (p = 0.021). UCMSCs promoted the expression of the intestinal tight junction protein occludin, downregulated the protein expression of the autophagy marker LC3A/B in colon tissue, and upregulated the expression of VEGF-A and VEGFR-1 at the injured site. This study provides an experimental model for elucidating the therapeutic effects of UCMSCs in IBD. We provide a theoretical basis and method for the clinical treatment of IBD using UCMSCs.

Immunomodulatory Properties of Mesenchymal Stromal Cells: Still Unresolved "Yin and Yang"

Mesenchymal stromal cells (MSC) are mesodermal elements characterized by the ability to differentiate into several types of cells present mainly in connective tissues. They play a key function in tissue homeostasis and repair. Furthermore, they exert a strong effect on both innate and adaptive immune response. The main current of thought considers MSC as strong inhibitors of the immune system. Indeed, the first description of MSC immunomodulation pointed out their inability to induce alloimmune responses and their veto effects on mixed lymphocyte reactions. This inhibition appears to be mediated both by direct MSC interaction with immune cells and by soluble factors. Unfortunately, evidence to support this notion comes almost exclusively from in vitro experiments. In complex experimental systems, it has been shown that MSC can exert immunosuppressive effects also in vivo, either in murine models or in transplanted patients to avoid the graft versus host disease. However, it is still debated how the small number of administered MSC can regulate efficiently a large number of host effector lymphocytes. In addition, some reports in the literature indicate that MSC can trigger rather than inhibit lymphocyte activation when a very low number of MSC are co-cultured with lymphocytes. This would imply that the ratio between the number of MSC and immune cells is a key point to forecast whether MSC will inhibit or activate the immune system. Herein, we discuss the conflicting results reported on the immunomodulatory effects of MSC to define which features are relevant to understand their behavior and cross-talk with immune cells.

Immune modulation by mesenchymal stem cells

Mesenchymal stem cells (MSCs) can be derived from various adult tissues with multipotent and self‐renewal abilities. The characteristics of presenting no major ethical concerns, having low immunogenicity and possessing immune modulation functions make MSCs promising candidates for stem cell therapies. MSCs could promote inflammation when the immune system is underactivated and restrain inflammation when the immune system is overactivated to avoid self‐overattack. These cells express many immune suppressors to switch them from a pro‐inflammatory phenotype to an anti‐inflammatory phenotype, resulting in immune effector cell suppression and immune suppressor cell activation. We would discuss the mechanisms governing the immune modulation function of these cells in this review, especially the immune‐suppressive effects of MSCs.

Allogeneic chondrogenically differentiated human bone marrow stromal cells do not induce dendritic cell maturation

Bone marrow stromal cell (BMSC)‐mediated endochondral bone formation may be a promising alternative to the current gold standards of autologous bone transplantation, in the development of novel methods for bone repair. Implantation of chondrogenically differentiated BMSCs leads to bone formation in vivo via endochondral ossification. The success of this bone formation in an allogeneic system depends upon the interaction between the implanted constructs and the host immune system. The current study investigated the effect of chondrogenically differentiated human bone marrow stromal cell (hBMSC) pellets on the maturation and function of dendritic cells (DCs) by directly coculturing bone forming chondrogenic hBMSC pellets and immature or lipopolysaccharide (LPS)‐matured DCs in vitro. Allogeneic chondrogenic hBMSC pellets did not affect the expression of CD80, CD86, or HLADR on immature or LPS‐matured DCs following 24, 48, or 72 hr of coculture. Furthermore, they did not induce or inhibit antigen uptake or migration of the DCs over time. IL‐6 was secreted by allogeneic chondrogenic hBMSC pellets in response to LPS‐matured DCs. Overall, this study has demonstrated that maturation of immature DCs was not influenced by allogeneic chondrogenic hBMSC pellets. This suggests that allogeneic chondrogenic hBMSC pellets do not stimulate immunogenic responses from DCs in vitro and are not expected to indirectly activate T cells via DCs. For this reason, allogeneic chondrogenic bone marrow stromal cell pellets are promising candidates for future tissue engineering strategies utilising allogeneic cells for bone repair.

Substantial Overview on Mesenchymal Stem Cell Biological and Physical Properties as an Opportunity in Translational Medicine

Mesenchymal stem cells (MSC) have piqued worldwide interest for their extensive potential to treat a large array of clinical indications, their unique and controversial immunogenic and immune modulatory properties allowing ample discussions and debates for their possible applications. Emerging data demonstrating that the interaction of biomaterials and physical cues with MSC can guide their differentiation into specific cell lineages also provide new interesting insights for further MSC manipulation in different clinical applications. Moreover, recent discoveries of some regulatory molecules and signaling pathways in MSC niche that may regulate cell fate to distinct lineage herald breakthroughs in regenerative medicine. Although the advancement and success in the MSC field had led to an enormous increase in the amount of ongoing clinical trials, we still lack defined clinical therapeutic protocols. This review will explore the exciting opportunities offered by human and animal MSC, describing relevant biological properties of these cells in the light of the novel emerging evidence mentioned above while addressing the limitations and challenges MSC are still facing.

Autophagy inhibition via Becn1 downregulation improves the mesenchymal stem cells antifibrotic potential in experimental liver fibrosis

Liver fibrosis (LF) is the result of a vicious cycle between inflammation-induced chronic hepatocyte injury and persistent activation of hepatic stellate cells (HSCs). Mesenchymal stem cell (MSC)-based therapy may represent a potential remedy for treatment of LF. However, the fate of transplanted MSCs in LF remains largely unknown. In the present study, the fate and antifibrotic effect of MSCs were explored in a LF model induced by CCl₄ in mouse. Additionally, MSCs were stimulated in vitro with LF-associated factors, tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), and transforming growth factor-β1 (TGF-β1), to mimic the LF microenvironment. We unveiled that MSCs exhibited autophagy in response to the LF microenvironment through Becn1 upregulation both in vivo and in vitro. However, autophagy suppression induced by Becn1 knockdown in MSCs resulted in enhanced antifibrotic effects on LF. The improved antifibrotic potential of MSCs may be attributable to their inhibitory effects on T lymphocyte infiltration, HSCs proliferation, as well as production of TNF-α, IFN-γ, and TGF-β1, which may be partially mediated by elevated paracrine secretion of PTGS2/PGE₂ . Thus, autophagy manipulation in MSCs may be a novel strategy to promote their antifibrotic efficacy.

Biological functions of mesenchymal stem cells and clinical implications

Mesenchymal stem cells (MSCs) are isolated from multiple biological tissues-adult bone marrow and adipose tissues and neonatal tissues such as umbilical cord and placenta. In vitro, MSCs show biological features of extensive proliferation ability and multipotency. Moreover, MSCs have trophic, homing/migration and immunosuppression functions that have been demonstrated both in vitro and in vivo. A number of clinical trials are using MSCs for therapeutic interventions in severe degenerative and/or inflammatory diseases, including Crohn's disease and graft-versus-host disease, alone or in combination with other drugs. MSCs are promising for therapeutic applications given the ease in obtaining them, their genetic stability, their poor immunogenicity and their curative properties for tissue repair and immunomodulation. The success of MSC therapy in degenerative and/or inflammatory diseases might depend on the robustness of the biological functions of MSCs, which should be linked to their therapeutic potency. Here, we outline the fundamental and advanced concepts of MSC biological features and underline the biological functions of MSCs in their basic and translational aspects in therapy for degenerative and/or inflammatory diseases.

A novel direct co-culture assay analyzed by multicolor flow cytometry reveals context- and cell type-specific immunomodulatory effects of equine mesenchymal stromal cells

The immunomodulatory potential of multipotent mesenchymal stromal cells (MSC) provides a basis for current and future regenerative therapies. In this study, we established an approach that allows to address the effects of pro-inflammatory stimulation and co-culture with MSC on different specific leukocyte subpopulations. Equine peripheral blood leukocyte recovery was optimized to preserve all leukocyte subpopulations and leukocyte activation regimes were evaluated. Allogeneic labeled equine adipose-derived MSC were then subjected to direct co-culture with either non-stimulated, concanavalin A (ConA)-activated or phosphate 12-myristate 13-acetate and ionomycin (PMA/I)-activated leukocytes. Subsequently, production of the cytokines interferon-γ (IFN- γ), interleukin-1 (IL-1) and tumor necrosis factor-α (TNF-α) and presence of FoxP3 were determined in specific cell populations using multicolor flow cytometry. Prostaglandin E2 (PGE2) was measured in the supernatants. ConA-stimulation induced mild activation of leukocytes, whereas PMA/I-stimulation led to strong activation. In T cells, PMA/I promoted production of all cytokines, with no distinct suppressive effects of MSC. However, increased numbers of CD25/FoxP3-positive cells indicated that MSC supported regulatory T cell differentiation in PMA/I-activated leukocyte cultures. MSC also reduced numbers of cytokine-producing B cells and granulocytes, mostly irrespective of preceding leukocyte activation, and reversed the stimulatory effect of ConA on IFN-γ production in monocytes. Illustrating the possible suppressive mechanisms, higher numbers of MSC produced IL-10 when co-cultured with non-stimulated or ConA-activated leukocytes. This was not observed in co-culture with PMA/I-activated leukocytes. However, PGE2 concentration in the supernatant was highest in the co-culture with PMA/I-activated leukocytes, suggesting that PGE2 could still mediate modulatory effects in strongly inflammatory environment. These context- and cell type-specific modulatory effects observed give insight into the interactions between MSC and different types of immune cells and highlight the roles of IL-10 and PGE2 in MSC-mediated immunomodulation. The approach presented could provide a basis for further functional MSC characterization and the development of potency assays.

Mesenchymal Stromal Cells for Transplant Tolerance

In solid organ transplantation lifelong immunosuppression exposes transplant recipients to life-threatening complications, such as infections and malignancies, and to severe side effects. Cellular therapy with mesenchymal stromal cells (MSC) has recently emerged as a promising strategy to regulate anti-donor immune responses, allowing immunosuppressive drug minimization and tolerance induction. In this review we summarize preclinical data on MSC in solid organ transplant models, focusing on potential mechanisms of action of MSC, including down-regulation of effector T-cell response and activation of regulatory pathways. We will also provide an overview of available data on safety and feasibility of MSC therapy in solid organ transplant patients, highlighting the issues that still need to be addressed before establishing MSC as a safe and effective tolerogenic cell therapy in transplantation.

Similarities in mRNA expression of peripheral blood drug metabolizing enzymes and cancer marker genes with biopsy samples of head and neck cancer patients

Purpose: To develop peripheral blood mRNA expression profiles of drug metabolizing enzymes (DMEs) as a surrogate to monitor tobacco induced head and neck squamous cell carcinoma (HNSCC), attempts were made to investigate (i) similarities in alterations with the cancer marker genes in biopsy samples and (ii) if alterations similar to that seen in biopsy samples are reflected in peripheral blood. Methods: Total RNA from eight soft gingival tissues and eight biopsy samples of HNSCC patients and total DNA and RNA from blood of healthy controls (n = 150) and HNSCC patients (n = 150) was processed for expression and genotyping studies. Blood from patients receiving chemo-radiotherapy was processed for follow-up study. Results: qRT-PCR revealed significant increase in mRNA expression of DMEs in biopsy and blood samples of HNSCC patients when compared to controls. Similar alterations were observed in cancer marker genes in these samples. Patients with variant genotypes of DMEs showed greater magnitude of alterations in mRNA expression when compared to wild type controls. Responders of chemo-radiotherapy showed significant decline in induction of mRNA expression of DMEs and cancer marker genes Conclusions: The data suggest that peripheral blood expression profiles could be used to monitor tobacco-induced HNSCC as well as the treatment response.

Mesenchymal Stem Cells Improve Rheumatoid Arthritis Progression by Controlling Memory T Cell Response

In the last years, mesenchymal stem cell (MSC)-based therapies have become an interesting therapeutic opportunity for the treatment of rheumatoid arthritis (RA) due to their capacity to potently modulate the immune response. RA is a chronic autoimmune inflammatory disorder with an incompletely understood etiology. However, it has been well described that peripheral tolerance defects and the subsequent abnormal infiltration and activation of diverse immune cells into the synovial membrane, are critical for RA development and progression. Moreover, the imbalance between the immune response of pro-inflammatory and anti-inflammatory cells, in particular between memory Th17 and memory regulatory T cells (Treg), respectively, is well admitted to be associated to RA immunopathogenesis. In this context, MSCs, which are able to alter the frequency and function of memory lymphocytes including Th17, follicular helper T (Tfh) cells and gamma delta (γδ) T cells while promoting Treg cell generation, have been proposed as a candidate of choice for RA cell therapy. Indeed, given the plasticity of memory CD4⁺ T cells, it is reasonable to think that MSCs will restore the balance between pro-inflammatory and anti-inflammatory memory T cells populations deregulated in RA leading to prompt their therapeutic function. In the present review, we will discuss the role of memory T cells implicated in RA pathogenesis and the beneficial effects exerted by MSCs on the phenotype and functions of these immune cells abnormally regulated in RA and how this regulation could impact RA progression.

Shaping the Future of Perinatal Cells: Lessons From the Past and Interpretations of the Present

Since their discovery and characterization, mesenchymal stromal cells (MSC) have been a topic of great interest in regenerative medicine. Over the last 10 years, detailed studies investigated the properties of MSC from perinatal tissues and have indicated that these cells may represent important tools for restoring tissue damage or promoting regeneration and repair of the tissue microenvironment. At first, perinatal tissue-derived MSC drew attention due to their potential differentiation capacities suggested by their early embryological origin. It is nowadays accepted that perinatal tissue-derived MSC are promising for a wide range of regenerative medicine applications because of their unique immune modulatory properties, rather than their differentiation ability. As a matter of fact, the activation and function of various cells of the innate and adaptive immune systems are suppressed and modulated by MSC from different perinatal tissues, such as human term placenta. However, the mechanisms by which they act on immune cells to facilitate tissue repair during pathological processes remain to be thoroughly elucidated to develop safe and efficient therapeutic approaches. In addition to immune modulatory ability, several other peculiar characteristics of placenta MSC, less explored and/or more debated, are being investigated. These include an understanding of the anti-microbial properties and the role of placental MSC in tumor progression. Moreover, a thorough investigation on preparation methods, bioactive factors, mechanisms of action of the cell secretome, and the development of potency assays to predict clinical efficacy of placenta MSC and their products, are necessary to provide a solid basis for their clinical application.

Current understanding of the immunosuppressive properties of mesenchymal stromal cells

Several studies have demonstrated the anti-inflammatory potential of mesenchymal stromal cells (MSCs) isolated from bone marrow, adipose tissue, placenta, and other sources. Nevertheless, MSCs may also induce immunosuppression when administered systemically or directly to injured environments, as shown in different preclinical disease models. MSCs express certain receptors, including toll-like receptors and the aryl-hydrocarbon receptor, that are activated by the surrounding environment, thus leading to modulation of their immunosuppressive activity. Once MSCs are activated, they can affect a wide range of immune cells (e.g., neutrophils, monocytes/macrophages, dendritic cells, natural killer cells, T and B lymphocytes), a phenomenon that has been correlated to secretion of several mediators (e.g., indolamine 2,3-dioxygenase, galectins, prostaglandin E₂, nitric oxide, and damage- and pathogen-associated molecular patterns) and stimulation of certain signaling pathways (e.g., protein kinase R, signal transducer and activator of transcription-1, nuclear factor-κB). Additionally, MSC manipulation and culture conditions, as well as the number of passages, duration of cryopreservation, and O₂ content available, can significantly affect the immunosuppressive properties of MSCs. This review sheds light on current knowledge regarding the mechanisms by which MSCs exert immunosuppressive effects both in vitro and in vivo, focusing on the receptors expressed by MSCs, the correlation between soluble factors secreted by MSCs and their immunosuppressive effects, and interactions between MSCs and immune cells.

The Immunomodulatory Properties of Amniotic Cells: The Two Sides of the Coin

Among the many cell types useful in developing therapeutic treatments, human amniotic cells from placenta have been proposed as valid candidates. Both human amniotic epithelial and mesenchymal stromal cells, and the conditioned medium generated from their culture, exert multiple immunosuppressive activities. Indeed, they inhibit T and B cell proliferation, suppress inflammatory properties of monocytes, macrophages, dendritic cells, neutrophils, and natural killer cells, while promoting induction of cells with regulatory functions such as regulatory T cells and anti-inflammatory M2 macrophages. These properties have laid the foundation for their use for the treatment of inflammatory-based diseases, and encouraging results have been obtained in different preclinical disease models where exacerbated inflammation is present. Moreover, an immune-privileged status of amniotic cells has been often highlighted. However, even if long-term engraftment of amniotic cells has been reported into immunocompetent animals, only few cells survive after infusion. Furthermore, amniotic cells have been shown to be able to induce immune responses in vivo and, under specific culture conditions, they can stimulate T cell proliferation in vitro. Although immunosuppressive properties are a widely recognized characteristic of amniotic cells, immunogenic and stimulatory activities appear to be less reported, sporadic events. In order to improve therapeutic outcome, the mechanisms responsible for the suppressive versus stimulatory activity need to be carefully addressed. In this review, both the immunosuppressive and immunostimulatory activity of amniotic cells will be discussed.

Inflammation-induced glycolytic switch controls suppressivity of mesenchymal stem cells via STAT1 glycosylation

Mesenchymal stem cells (MSCs) represent key contributors to tissue homeostasis and promising therapeutics for hyperinflammatory conditions including graft-versus-host disease. Their immunomodulatory effects are controlled by microenvironmental signals. The MSCs' functional response towards inflammatory cues is known as MSC-"licensing" and includes indoleamine 2,3-dioxygenase (IDO) upregulation. MSCs use tryptophan-depleting IDO to suppress T-cells. Increasing evidence suggests that several functions are (co-)determined by the cells' metabolic commitment. MSCs are capable of both, high levels of glycolysis and of oxidative phosphorylation. Although several studies have addressed alterations of the immune regulatory phenotype elicited by inflammatory priming metabolic mechanisms controlling this process remain unknown. We demonstrate that inflammatory MSC-licensing causes metabolic shifts including enhanced glycolysis and increased fatty acid oxidation. Yet, only interfering with glycolysis impacts IDO upregulation and impedes T-cell-suppressivity. We identified the Janus kinase (JAK)/signal transducer and activator of transcription (STAT)1 pathway as a regulator of both glycolysis and IDO, and show that enhanced glucose turnover is linked to abundant STAT1 glycosylation. Inhibiting the responsible O-acetylglucosamine (O-GlcNAc) transferase abolishes STAT1 activity together with IDO upregulation. Our data suggest that STAT1-O-GlcNAcylation increases its stability towards degradation thus sustaining downstream effects. This pathway could represent a target for interventions aiming to enhance the MSCs' immunoregulatory potency.