Immunogenicity of allogeneic mesenchymal stem cells

Mesenchymal stem cells (MSCs) inhibit proliferation of allogeneic T cells and express low levels of major histocompatibility complex class I (MHCI), MHCII and vascular adhesion molecule-1 (VCAM-1). We investigated whether their immunosuppressive properties and low immunophenotype protect allogeneic rat MSCs against cytotoxic lysis in vitro and result in a reduced immune response in vivo. Rat MSCs were partially protected against alloantigen-specific cytotoxic T cells in vitro. However, after treatment with IFN-γ and IL-1β, MSCs upregulated MHCI, MHCII and VCAM-1, and cytotoxic lysis was significantly increased. In vivo, allogeneic T cells but not allogeneic MSCs induced upregulation of the activation markers CD25 and CD71 as well as downregulation of CD62L on CD4(+) T cells from recipient rats. However, intravenous injection of allo-MSCs in rats led to the formation of alloantibodies with the capacity to facilitate complement-mediated lysis, although IgM levels were markedly decreased compared with animals that received T cells. The allo-MSC induced immune response was sufficient to lead to significantly reduced survival of subsequently injected allo-MSCs. Interestingly, no increased immunogenicity of IFN-γ stimulated allo-MSCs was observed in vivo. Both the loss of protection against cytotoxic lysis under inflammatory conditions and the induction of complement-activating antibodies will likely impact the utility of allogeneic MSCs for therapeutic applications.     

Immunomodulation by mesenchymal stem cells:Interplay between mesenchymal stem cells and regulatory lymphocytes

Mesenchymal stem cells(MSCs) possess immunomodulatory properties, which confer enormous potential for clinical application. Considerable evidence revealed their efficacy on various animal models of autoimmune diseases, such as multiple sclerosis, systemic lupus erythematosus and uveitis. MSCs elicit their immunomodulatory effects by inhibiting lymphocyte activation and proliferation, forbidding the secretion of proinflammatory cytokines, limiting the function of antigen presenting cells, and inducing regulatory T(Treg) and B(Breg) cells. The induction of Treg and Breg cells is of particular interest since Treg and Breg cells have significant roles in maintaining immune tolerance. Several mechanisms have been proposed regarding to the MSCs-mediated induction of Treg and Breg cells. Accordingly, MSCs induce regulatory lymphocytes through secretion of multiple pleiotropic cytokines, cell-to-cell contact with target cells and modulation of antigen-presenting cells. Here, we summarized how MSCs induce Treg and Breg cells to provoke immunosuppression.     

Substance P enhances mesenchymal stem cells-mediated immune modulation

Since clinical application of MSCs requires long-term ex vivo culture inducing senescence in MSCs and reducing the therapeutic activity of transplanted MSCs, numerous efforts have been attempted to sustain the active state of MSCs. Substance P (SP) is a neuropeptide that functions to activate the cellular physiological responses of MSCs, including proliferation, migration, and secretion of specific cytokines. In this study, we explored the potential of SP to restore the weakened immune modulating activity of MSCs resulting from long-term culture by measuring T cell activity and interleukin-2 (IL-2) secretion of CD4⁺ Jurkat leukemic T cells and primary CD4⁺ T cells. As the number of cell passages increased, the immunosuppressive function of MSCs based on T cell activity decreased. This weakened activity of MSCs could be restored by SP treatment and nullified by co-treatment of an NK1 receptor blocker. Higher levels of transforming growth factor beta 1 (TGF-β1) secretion were noted in the medium of SP-treated late passage MSC cultures, but IL-10 levels did not change. SP-treated MSC-conditioned medium decreased T cell activity and IL-2/Interferon gamma (IFN-g) secretion in T cells even in the activation by lipopolysaccharide (LPS) or CD3/CD28 antibodies, both of which were successfully blocked by inhibiting the TGF beta signaling pathway. This stimulatory effect of SP on late passage MSCs was also confirmed in direct cell–cell contact co-culture of MSCs and CD4⁺ Jurkat T cells. Collectively, our study suggests that SP pretreatment to MSCs may recover the immunosuppressive function of late passage MSCs by potentiating their ability to secrete TGF-β1, which can enhance the therapeutic activity of ex vivo expanded MSCs in long-term culture.     

间充质干细胞诱导分化为胰岛β细胞的研究进展

间充质干细胞是一类具有多向分化潜能的成体干细胞,在体内外不仅可以被诱导分化为中胚层细胞,而且可以分化为内胚层和神经外胚层细胞。间充质干细胞易分离,体外可大量扩增,异体移植不引起免疫排斥反应,在细胞治疗和组织工程中具有广阔的应用前景。经过适当诱导,间充质干细胞可能成为胰岛β细胞的来源之一。就间充质干细胞的生物学性状和优势,以及诱导分化为胰岛β细胞的技术方法和发展趋势进行了综述。     

Mesenchymal stem cells as living anti-inflammatory therapy for COVID-19 related acute respiratory distress syndrome

Coronavirus disease 2019(COVID-19), a pandemic disease caused by the severe acute respiratory syndrome coronavirus 2(SARS-Co V2), is growing at an exponential rate worldwide. Manifestations of this disease are heterogeneous; however, advanced cases often exhibit various acute respiratory distress syndrome-like symptoms, systemic inflammatory reactions, coagulopathy, and organ involvements. A common theme in advanced COVID-19 is unrestrained immune activation, classically referred to as a "cytokine storm", as well as deficiencies in immune regulatory mechanisms such as T regulatory cells. While mesenchymal stem cells(MSCs) themselves are objects of cytokine regulation, they can secrete cytokines to modulate immune cells by inducing antiinflammatory regulatory Treg cells, macrophages and neutrophils; and by reducing the activation of T and B cells, dendritic and nature killer cells. Consequently, they have therapeutic potential for treating severe cases of COVID-19. Here we discuss the unique ability of MSCs, to act as a "living antiinflammatory", which can "rebalance" the cytokine/immune responses to restore equilibrium. We also discuss current MSC trials and present different concepts for optimization of MSC therapy in patients with COVID-19 acute respiratory distress syndrome.     

Human mesenchymal stromal cells transiently increase cytokine production by activated T cells before suppressing T-cell proliferation: effect of interferon-γ and tumor necrosis factor-α stimulation

Background aimsMesenchymal stromal cells (MSCs) suppress T-cell proliferation, especially after activation with inflammatory cytokines. We compared the dynamic action of unprimed and interferon (IFN)-γ plus tumor necrosis factor (TNF)-α–pretreated human bone marrow–derived MSCs on resting or activated T cells.MethodsMSCs were co-cultured with allogeneic peripheral blood mononuclear cells (PBMCs) at high MSC-to-PBMC ratios in the absence or presence of concomitant CD3/CD28-induced T-cell activation. The kinetic effects of MSCs on cytokine production and T-cell proliferation, cell cycle and apoptosis were assessed.ResultsUnprimed MSCs increased the early production of IFN-γ and interleukin (IL)-2 by CD3/CD28-activated PBMCs before suppressing T-cell proliferation. In non-activated PBMC co-cultures, low levels of IL-2 and IL-10 synthesis were observed with MSCs in addition to low levels of CD69 expression by T cells and no T-cell proliferation. MSCs also decreased apoptosis in resting and activated T cells and inhibited the transition of these cells into the sub-G0/G1 and the S phases. With inhibition of indoleamine 2,3 dioxygenase, MSCs increased CD3/CD28-induced T-cell proliferation. After priming with IFN-γ plus TNF-α, MSCs were less potent at increasing cytokine production by CD3/CD28-activated PBMCs and more effective at inhibiting T-cell proliferation but had preserved anti-apoptotic functions.ConclusionsUnprimed MSCs induce a transient increase in IFN-γ and IL-2 synthesis by activated T cells. Pre-treatment of MSCs with IFN-γ plus TNF-α may increase their effectiveness and safety in vivo.     

Immunomodulatory properties of dental tissue-derived mesenchymal stem cells: Implication in disease and tissue regeneration

Mesenchymal stem cells (MSCs) are considered as an attractive tool for tissue regeneration and possess a strong immunomodulatory ability. Dental tissue-derived MSCs can be isolated from different sources, such as the dental pulp, periodontal ligament, deciduous teeth, apical papilla, dental follicles and gingiva. According to numerous in vitro studies, the effect of dental MSCs on immune cells might depend on several factors, such as the experimental setting, MSC tissue source and type of immune cell preparation. Most studies have shown that the immunomodulatory activity of dental MSCs is strongly upregulated by activated immune cells. MSCs exert mostly immunosuppressive effects, leading to the dampening of immune cell activation. Thus, the reciprocal interaction between dental MSCs and immune cells represents an elegant mechanism that potentially contributes to tissue homeostasis and inflammatory disease progression. Although the immunomodulatory potential of dental MSCs has been extensively investigated in vitro, its role in vivo remains obscure. A few studies have reported that the MSCs isolated from inflamed dental tissues have a compromised immunomodulatory ability. Moreover, the expression of some immunomodulatory proteins is enhanced in periodontal disease and even shows some correlation with disease severity. MSC-based immunomodulation may play an essential role in the regeneration of different dental tissues. Therefore, immunomodulation-based strategies may be a very promising tool in regenerative dentistry.     

Adenoviral transduction of mesenchymal stem cells: in vitro responses and in vivo immune responses after cell transplantation

Adult mesenchymal stem cells (MSCs) are non-hematopoietic cells with multi-lineage potential which makes them attractive targets for regenerative medicine applications. However, to date, therapeutic success of MSC-therapy is limited and the genetic modification of MSCs using viral vectors is one option to improve their therapeutic potential. Ex-vivo genetic modification of MSCs using recombinant adenovirus (Ad) could be promising to reduce undesired immune responses as Ad will be removed before cell/tissue transplantation. In this regard, we investigated whether Ad-modification of MSCs alters their immunological properties in vitro and in vivo. We found that Ad-transduction of MSCs does not lead to up-regulation of major histocompatibility complex class I and II and co-stimulatory molecules CD80 and CD86. Moreover, Ad-transduction caused no significant changes in terms of pro-inflammatory cytokine expression, chemokine and chemokine receptor and Toll-like receptor expression. In addition, Ad-modification of MSCs had no affect on their ability to suppress T cell proliferation in vitro. In vivo injection of Ad-transduced MSCs did not change the frequency of various immune cell populations (antigen presenting cells, T helper and cytotoxic T cells, natural killer and natural killer T cells) neither in the blood nor in tissues. Our results indicate that Ad-modification has no major influence on the immunological properties of MSCs and therefore can be considered as a suitable gene vector for therapeutic applications of MSCs.     

Human umbilical cord blood-derived mesenchymal stem cells ameliorate psoriasis-like skin inflammation in mice

Mesenchymal stem cells (MSCs) inhibit the proliferation or activation of lymphocytes, and their inhibitory effects do not require human leukocyte antigen (HLA)-matching because MSCs express low levels of HLA molecules. Therefore, MSCs may be able to regulate immune responses. In this study, we determined whether MSCs could inhibit psoriasis-like skin inflammation in mice. After induction of psoriasis-like skin inflammation using intradermal injection of IL-23 or topical application of imiquimod with or without treatment with MSC, mouse skins were collected, and H&E staining and real-time PCR were performed. IL-23-induced skin inflammation was inhibited when MSCs were injected on day ?1 and day 7. The expression of proinflammatory cytokines such as IL-6, IL-17, and TNF-α was inhibited by MSC injection, and the expression of chemokines such as CCL17, CCL20, and CCL27 was also decreased in mouse skin. We also determined whether MSCs could not only prevent but also treat psoriasis-like skin inflammation in mice. Furthermore, in vitro experiments also showed anti-inflammatory effects of MSCs. Dendritic cells which are co-cultured with MSCs suppressed CD4+ T cell activation and differentiation, which are important for the pathogenesis of psoriasis. These results suggest that MSCs could be useful for treating psoriasis.     

The TLR7 agonist Imiquimod promote the immunogenicity of msenchymal stem cells

Background

Mesenchymal stem cells (MSCs) are considered the best candidate in stem cells therapy due to their multipotent differentiation ability, low expression of co-stimulatory molecules (CD80, CD86, CD34 and HLA-II) and immunosuppression effects on in vivo immune responses. MSCs were now widely used in clinical trials but received no encourage results. The major problem was the fate of engrafted MSCs in vivo could not be defined. Some studies indicated that MSCs could induce immune response and result in the damage and rejection of MSCs. As toll like receptors (TLRs) are important in inducing of immune responses, in this study we study the role of TLR7 in mediating the immune status of MSCs isolated from umbilical cord.

Results

Our results indicated that TLR7 agonist Imiquimod could increase the proliferation of PBMC isolated from healthy human volunteers and release of lactate dehydrogenase (LDH) in supernatant from PBMC-UCMSCs co-culture system. Flow cytometry and quantitative PCR also confirmed the regulated expression of surface co-stimulatory molecules and pro-inflammatory genes (IL-6, IL-8, IL-12, TGF-β and TNF-α). And the down-regulation expression of stem cell markers also confirmed the loss of stemness of UCMSCs. We also found that the osteo-differentiation ability of UCMSCs was enhanced in the presence of Imiquimod.

Conclusion

To our knowledge, this is the first report that activation of TLR7 pathway increases the immunogenicity of UCMSCs. Extensive researches have now been conducted to study whether the change of immune status will be help in tumor rejection based on the tumor-tropism of MSCs.