Mouse mesenchymal stem cells suppress antigen-specific TH cell immunity independent of indoleamine 2,3-dioxygenase 1 (IDO1)

The Immunomodulatory Properties of Mesenchymal Stem Cells Play a Critical Role in Inducing Immune Tolerance after Liver Transplantation

Although liver transplantation is considered to be the best choice for patients with end-stage liver diseases, postoperative immune rejection still cannot be overlooked. Patients with liver transplantation have to take immunosuppressive drugs for a long time or even their entire lives, in which heavy economic burden and side effects caused by the drugs have become the major impediment for liver transplantation. There is a growing body of evidences indicating that mesenchymal stem cell (MSC) transplantation, a promising tool in regenerative medicine, can be used as an effective way to induce immune tolerance after liver transplantation based on their huge expansion potential and unique immunomodulatory properties. MSCs have been reported to inhibit innate immunity and adaptive immunity to induce a tolerogenic microenvironment. In in vitro studies, transplanted MSCs show plasticity in immune regulation by altering their viability, migration, differentiation, and secretion in the interactions with the surrounding host microenvironment. In this review, we aim to provide an overview of the current understanding of immunomodulatory properties of MSCs in liver transplantation, to elucidate the potential mechanisms behind MSCs regulating immune response, especially in vivo and the influence of the microenvironment, and ultimately to discuss the feasible strategies to improve the clinical prognosis of liver transplantation. Only after exhaustive understanding of potential mechanisms of the MSC immunomodulation can we improve the safety and effectiveness of MSC treatment and achieve better therapeutic effects.

The protective effect of 1-methyltryptophan isomers in renal ischemia-reperfusion injury is not exclusively dependent on indolamine 2,3-dioxygenase inhibition

BACKGROUND AND PURPOSE

Indolamine 2,3-dioxygenase (IDO), an enzyme that catalyses the metabolism of tryptophan, may play a detrimental role in ischemia-reperfusion injury (IRI). IDO can be inhibited by 1-methyl-tryptophan, which exists in a D (D-MT) or L (L-MT) isomer. These forms show different pharmacological effects besides IDO inhibition. Therefore, we sought to investigate whether these isomers can play a protective role in renal IRI, either IDO-dependent or independent.

EXPERIMENTAL APPROACH

We studied the effect of both isomers in a rat renal IRI model with a focus on IDO-dependent and independent effects.

KEY RESULTS

Both MT isomers reduced creatinine and BUN levels, with D-MT having a faster onset of action but shorter duration and L-MT a slower onset but longer duration (24 h and 48 h vs 48 h and 96 h reperfusion time). Interestingly, this effect was not exclusively dependent on IDO inhibition, but rather from decreased TLR4 signalling, mimicking changes in renal function. Additionally, L-MT increased the overall survival of rats. Moreover, both MT isomers interfered with TGF-β signalling and epithelial-mesenchymal transition. In order to study the effect of isomers in all mechanisms involved in IRI, a series of in vitro experiments was performed. The isomers affected signalling pathways in NK cells and tubular epithelial cells, as well as in dendritic cells and T cells.

CONCLUSION AND IMPLICATIONS

This study shows that both MT isomers have a renoprotective effect after ischemia-reperfusion injury, mostly independent of IDO inhibition, involving mutually different mechanisms. We bring novel findings in the pharmacological properties and mechanism of action of MT isomers, which could become a novel therapeutic target of renal IRI.

Mesenchymal stem cells in experimental autoimmune encephalomyelitis model of multiple sclerosis: A systematic review and meta-analysis

BACKGROUND/AIMS

Mesenchymal stem cells (MSCs) transplantation has been considered a possible therapeutic method for Multiple Sclerosis (MS). However, no quantitative data synthesis of MSCs therapy for MS exists. We conducted a systematic review and meta-analysis to evaluate the effects of MSCs in experimental autoimmune encephalomyelitis (EAE) animal model of MS.

METHODS

We identified eligible studies published from January 1980 to January 2017 by searching four electronic databases (PubMed, MEDLINE, Embase and Web of Science). The outcome was the effects of MSCs on clinical performance evaluated by the EAE clinical score.

RESULTS

36 preclinical studies including 675 animals in MSCs treatment group, and 693 animals in control group were included in this meta-analysis. We found that MSCs transplantation significantly ameliorated the symptoms and delayed the disease progression (SMD = -1.25, 95% CI: -1.45 to -1.05, P < 0.001). However, no significant differences in effect sizes were unveiled relative to clinical score standard (P = 0.35), type of MSCs (P = 0.35), source of MSCs (P = 0.06), MSCs dose (P = 0.44), delivery methods (P = 0.31) and follow up period (P = 0.73).

CONCLUSIONS

The current study showed that MSCs transplantation could ameliorate clinical performance in EAE animal model of MS. These findings support the further studies translate MSCs to treat MS in humans.

The therapeutic potential of targeting tryptophan catabolism in cancer

Based on its effects on both tumour cell intrinsic malignant properties as well as anti-tumour immune responses, tryptophan catabolism has emerged as an important metabolic regulator of cancer progression. Three enzymes, indoleamine-2,3-dioxygenase 1 and 2 (IDO1/2) and tryptophan-2,3-dioxygenase (TDO2), catalyse the first step of the degradation of the essential amino acid tryptophan (Trp) to kynurenine (Kyn). The notion of inhibiting IDO1 using small-molecule inhibitors elicited high hopes of a positive impact in the field of immuno-oncology, by restoring anti-tumour immune responses and synergising with other immunotherapies such as immune checkpoint inhibition. However, clinical trials with IDO1 inhibitors have yielded disappointing results, hence raising many questions. This review will discuss strategies to target Trp-degrading enzymes and possible down-stream consequences of their inhibition. We aim to provide comprehensive background information on Trp catabolic enzymes as targets in immuno-oncology and their current state of development. Details of the clinical trials with IDO1 inhibitors, including patient stratification, possible effects of the inhibitors themselves, effects of pre-treatments and the therapies the inhibitors were combined with, are discussed and mechanisms proposed that might have compensated for IDO1 inhibition. Finally, alternative approaches are suggested to circumvent these problems.

Tryptophan metabolism as a common therapeutic target in cancer, neurodegeneration and beyond

L-Tryptophan (Trp) metabolism through the kynurenine pathway (KP) is involved in the regulation of immunity, neuronal function and intestinal homeostasis. Imbalances in Trp metabolism in disorders ranging from cancer to neurodegenerative disease have stimulated interest in therapeutically targeting the KP, particularly the main rate-limiting enzymes indoleamine-2,3-dioxygenase 1 (IDO1), IDO2 and tryptophan-2,3-dioxygenase (TDO) as well as kynurenine monooxygenase (KMO). However, although small-molecule IDO1 inhibitors showed promise in early-stage cancer immunotherapy clinical trials, a phase III trial was negative. This Review summarizes the physiological and pathophysiological roles of Trp metabolism, highlighting the vast opportunities and challenges for drug development in multiple diseases.

Tryptophan-2,3-Dioxygenase (TDO) deficiency is associated with subclinical neuroprotection in a mouse model of multiple sclerosis

The catabolism of tryptophan to immunosuppressive and neuroactive kynurenines is a key metabolic pathway regulating immune responses and neurotoxicity. The rate-limiting step is controlled by indoleamine-2,3-dioxygenase (IDO) and tryptophan-2,3-dioxygenase (TDO). IDO is expressed in antigen presenting cells during immune reactions, hepatic TDO regulates blood homeostasis of tryptophan and neuronal TDO influences neurogenesis. While the role of IDO has been described in multiple immunological settings, little is known about TDO’s effects on the immune system. TDO-deficiency is neuroprotective in C. elegans and Drosophila by increasing tryptophan and specific kynurenines. Here we have determined the role of TDO in autoimmunity and neurodegeneration in experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis. We created reporter-TDO mice for in vivo imaging to show that hepatic but not CNS TDO expression is activated during EAE. TDO deficiency did not influence myelin-specific T cells, leukocyte infiltration into the CNS, demyelination and disease activity. TDO-deficiency protected from neuronal loss in the spinal cord but not in the optic nerves. While this protection did not translate to an improved overt clinical outcome, our data suggest that spatially distinct neuroprotection is conserved in mammals and support TDO as a potential target for treatment of diseases associated with neurodegeneration.

Modulation of host immune responses following non-hematopoietic stem cell transplantation: Translational implications in progressive multiple sclerosis

There exists an urgent need for effective treatments for those patients suffering from chronic/progressive multiple sclerosis (MS). Accordingly, it has become readily apparent that different classes of stem cell-based therapies must be explored at both the basic science and clinical levels. Herein, we provide an overview of the basic mechanisms underlying the pre-clinical benefits of exogenously delivered non-hematopoietic stem cells (nHSCs) in animal models of MS. Further, we highlight a number of early clinical trials in which nHSCs have been used to treat MS. Finally, we identify a series of challenges that must be met and ultimately overcome if such promising therapeutics are to be advanced from the bench to the bedside.

Human mesenchymal stem cells (MSCs) for treatment towards immune- and inflammation-mediated diseases: review of current clinical trials

Human mesenchymal stem cells (MSCs) are multilineage somatic progenitor/stem cells that have been shown to possess immunomodulatory properties in recent years. Initially met with much skepticism, MSC immunomodulation has now been well reproduced across tissue sources and species to be clinically relevant. This has opened up the use of these versatile cells for application as 3rd party/allogeneic use in cell replacement/tissue regeneration, as well as for immune- and inflammation-mediated disease entities. Most surprisingly, use of MSCs for in immune-/inflammation-mediated diseases appears to yield more efficacy than for regenerative medicine, since engraftment of the exogenous cell does not appear necessary. In this review, we focus on this non-traditional clinical use of a tissue-specific stem cell, and highlight important findings and trends in this exciting area of stem cell therapy.

Overexpression of Glutamate Decarboxylase in Mesenchymal Stem Cells Enhances Their Immunosuppressive Properties and Increases GABA and Nitric Oxide Levels

The neurotransmitter GABA has been recently identified as a potent immunosuppressive agent that targets both innate and adaptive immune systems and prevents disease progression of several autoimmunity models. Mesenchymal stem cells (MSCs) are self-renewing progenitor cells that differentiate into various cell types under specific conditions, including neurons. In addition, MSC possess strong immunosuppressive capabilities. Upon cytokine priming, undifferentiated MSC suppress T-cell proliferation via cell-to-cell contact mechanisms and the secretion of soluble factors like nitric oxide, prostaglandin E2 and IDO. Although MSC and MSC-derived neuron-like cells express some GABAergic markers in vitro, the role for GABAergic signaling in MSC-mediated immunosuppression remains completely unexplored. Here, we demonstrate that pro-inflammatory cytokines selectively regulate GAD-67 expression in murine bone marrow-MSC. However, expression of GAD-65 is required for maximal GABA release by MSC. Gain of function experiments using GAD-67 and GAD-65 co-expression demonstrates that GAD increases immunosuppressive function in the absence of pro-inflammatory licensing. Moreover, GAD expression in MSC evokes an increase in both GABA and NO levels in the supernatants of co-cultured MSC with activated splenocytes. Notably, the increase in NO levels by GAD expression was not observed in cultures of isolated MSC expressing GAD, suggesting crosstalk between these two pathways in the setting of immunosuppression. These results indicate that GAD expression increases MSC-mediated immunosuppression via secretion of immunosuppressive agents. Our findings may help reconsider GABAergic activation in MSC for immunological disorders.

The Synergistic Local Immunosuppressive Effects of Neural Stem Cells Expressing Indoleamine 2,3-Dioxygenase (IDO) in an Experimental Autoimmune Encephalomyelitis (EAE) Animal Model

Neurodegenerative diseases provoke robust immunological reactions in the central nervous system (CNS), which further deteriorate the neural tissue damage. We hypothesized that the expression levels of indoleamine 2,3-dioxygenase (IDO), an enzyme that has potent immune suppressive activities, in neural stem cells (NSCs) would have synergistic therapeutic effects against neurodegenerative diseases, since NSCs themselves have low IDO expression. In this study, the synergistic immune suppressive effects of rat fetal NSCs expressing IDO (rfNSCs-IDO) were validated by mixed leukocyte reaction (MLR) in vitro and an experimental autoimmune encephalomyelitis (EAE) animal model in vivo. rfNSCs-IDO showed significantly more suppressive effects on T cell proliferation in the MLR compared to control rfNSCs (rfNSCs-Cont). Importantly, IDO inhibition using 1-methyl-DL-tryptophan (1-MT), an IDO inhibitor, reversed the synergistic effects, confirming IDO-specific effects in rfNSCs-IDO. In the EAE animal model, systemic rfNSCs-IDO injections resulted in significant local immune suppression in the cervical lymph nodes and CNS, evidenced by a reduction in the number of activated T lymphocytes and an increase in regulatory T cell numbers, which induced significantly fewer clinical symptoms and faster recovery. In contrast, rfNSCs-Cont failed to reduce symptoms in the EAE animal models, although they showed local immune suppression, which was significantly less than that in rfNSCs-IDO. Taken together, IDO expression in NSCs synergistically potentiates the immune suppression activities of NSCs and could be applicable for the development of therapeutic modalities against various neurodegenerative diseases.

Mesenchymal stem cells do not exert direct beneficial effects on CNS remyelination in the absence of the peripheral immune system

Remyelination is the natural repair mechanism in demyelinating disorders such as multiple sclerosis (MS) and it was proposed that it might protect from axonal loss. For unknown reasons, remyelination is often incomplete or fails in MS lesions and therapeutic treatments to enhance remyelination are not available. Recently, the transplantation of exogenous mesenchymal stem cells (MSC) has emerged as a promising tool to enhance repair processes. This included the animal model experimental autoimmune encephalomyelitis (EAE), a commonly used model for the autoimmune mechanisms of MS. However, in EAE it is not clear if the beneficial effect of MSC derives from a direct influence on brain resident cells or if this is an indirect phenomenon via modulation of the peripheral immune system. The aim of this study was to determine potential regenerative functions of MSC in the toxic cuprizone model of demyelination that allows studying direct effects on de- and remyelination without the influence of the peripheral immune system. MSC from three different species (human, murine, canine) were transplanted either intraventricularly into the cerebrospinal fluid or directly into the lesion of the corpus callosum at two time points: at the onset of oligodendrocyte progenitor cell (OPC) proliferation or the peak of OPC proliferation during cuprizone induced demyelination. Our results show that MSC did not exert any regenerative effects after cuprizone induced demyelination and oligodendrocyte loss. During remyelination, MSC did not influence the dynamics of OPC proliferation and myelin formation. In conclusion, MSC did not exert direct regenerative functions in a mouse model where peripheral immune cells and especially T lymphocytes do not play a role. We thus suggest that the peripheral immune system is required for MSC to exert their effects and this is independent from a direct influence of the central nervous system.

The Role of Indoleamine 2, 3-Dioxygenase in Immune Suppression and Autoimmunity

Indoleamine 2, 3-dioxygenase (IDO) is the first and rate limiting catabolic enzyme in the degradation pathway of the essential amino acid tryptophan. By cleaving the aromatic indole ring of tryptophan, IDO initiates the production of a variety of tryptophan degradation products called "kynurenines" that are known to exert important immuno-regulatory functions. Because tryptophan must be supplied in the diet, regulation of tryptophan catabolism may exert profound effects by activating or inhibiting metabolism and immune responses. Important for survival, the regulation of IDO biosynthesis and its activity in cells of the immune system can critically alter their responses to immunological insults, such as infection, autoimmunity and cancer. In this review, we assess how IDO-mediated catabolism of tryptophan can modulate the immune system to arrest inflammation, suppress immunity to cancer and inhibit allergy, autoimmunity and the rejection of transplanted tissues. Finally, we examine how vaccines may enhance immune suppression of autoimmunity through the upregulation of IDO biosynthesis in human dendritic cells.

Bone Marrow Mesenchymal Stem Cells Alleviate Extracellular Kynurenine Levels, as Detected by High-Performance Liquid Chromatography

Endothelial cell dysfunction plays an important role in the occurrence and development of sepsis, which is a consequence of the interaction between coagulation and inflammation. Kynurenine (KYN) is an endothelium-derived relaxing factor that makes a large contribution to sepsis pathophysiology. In this study, we investigated the influence of bone marrow mesenchymal stem cells (BMSCs) on KYN production by cultured endothelial cells. KYN and tryptophan (TRP) concentrations in cell supernatants were simultaneously measured with a high-performance liquid chromatography (HPLC) system equipped with a fluorescence detector (FLD) and an ultraviolet detector (UVD). Our results revealed that lipopolysaccharide-stimulated endothelial cells produced more KYN, which was accompanied by a parallel decrease in TRP. When co-cultured with BMSCs, KYN and TRP production were significantly decreased compared to lipopolysaccharide (LPS)-induction alone. Our results suggest that BMSCs can attenuate endothelial cell damage by decreasing KYN as detected with HPLC. This method is the first to be capable of capturing functional changes in the cells and is simple, fast, and suitable for cellular level research purposes.

Enhanced medial collateral ligament healing using mesenchymal stem cells: dosage effects on cellular response and cytokine profile

Mesenchymal stem cells (MSCs) have potential therapeutic applications for musculoskeletal injuries due to their ability to differentiate into several tissue cell types and modulate immune and inflammatory responses. These immune-modulatory properties were examined in vivo during early stage rat medial collateral ligament healing. Two different cell doses (low dose 1 × 10(6) or high dose 4 × 10(6) MSCs) were administered at the time of injury and compared with normal ligament healing at days 5 and 14 post-injury. At both times, the high dose MSC group demonstrated a significant decrease in M2 macrophages compared to controls. At day 14, fewer M1 macrophages were detected in the low dose group compared to the high dose group. These results, along with significant changes in procollagen I, proliferating cells, and endothelialization suggest that MSCs can alter the cellular response during healing in a dose-dependent manner. The higher dose ligaments also had increased expression of several pro-inflammatory cytokines at day 5 (IL-1β, IFNγ, IL-2) and increased expression of IL-12 at day 14. Mechanical testing at day 14 revealed increased failure strength and stiffness in low dose ligaments compared to controls. Based on these improved mechanical properties, MSCs enhanced functional healing when applied at a lower dose. Different doses of MSCs uniquely affected the cellular response and cytokine expression in healing ligaments. Interestingly, the lower dose of cells proved to be most effective in improving functional properties.

Cord blood mesenchymal stem cells suppress DC-T Cell proliferation via prostaglandin B2

Immune suppression is a very stable property of multipotent stromal cells also known as mesenchymal stem cells (MSCs). All cell lines tested showed robust immune suppression not affected by a long culture history. Several mechanisms were described to account for this capability. Since several of the described mechanisms were not causing the immune suppression, the expression pattern of cord-blood-derived MSCs by microarray experiments was determined. Dendritic cells cocultured with cord blood MSCs were compared with cord blood MSCs. Putative immune suppressive candidates were tested to explain this inhibition. We find that cord blood MSCs themselves are hardly immunogenic as tested with allogeneic T-cells. Dendritic cells cocultured with second-party T-cells evoked abundant proliferation that was inhibited by third-party cord blood MSCs. Optimal inhibition was seen with one cord blood MSC for every dendritic cell. Blocking human leukocyte antigen G only saw partial recovery of proliferation. Several cytokines, gangliosides, enzymes like arginase, NO synthase, and indole amine 2,3-dioxygenase as well as the induction of Treg were not involved in the inhibition. The inhibiting moiety was identified as prostaglandin B2 by lipid metabolite analysis of the culture supernatant and confirmed with purified prostaglandin B2.

Transplantation of autologous adipose stem cells lacks therapeutic efficacy in the experimental autoimmune encephalomyelitis model. PLoS One. 2014;9:e85007. [PMID: 24465465 PMCID: PMC3897387 DOI: 10.1371/journal.pone.0085007]

Multiple sclerosis (MS), characterized by chronic inflammation, demyelination, and axonal damage, is a complicated neurological disease of the human central nervous system. Recent interest in adipose stromal/stem cell (ASCs) for the treatment of CNS diseases has promoted further investigation in order to identify the most suitable ASCs. To investigate whether MS affects the biologic properties of ASCs and whether autologous ASCs from MS-affected sources could serve as an effective source for stem cell therapy, cells were isolated from subcutaneous inguinal fat pads of mice with established experimental autoimmune encephalomyelitis (EAE), a murine model of MS. ASCs from EAE mice and their syngeneic wild-type mice were cultured, expanded, and characterized for their cell morphology, surface antigen expression, osteogenic and adipogenic differentiation, colony forming units, and inflammatory cytokine and chemokine levels in vitro. Furthermore, the therapeutic efficacy of the cells was assessed in vivo by transplantation into EAE mice. The results indicated that the ASCs from EAE mice displayed a normal phenotype, typical MSC surface antigen expression, and in vitro osteogenic and adipogenic differentiation capacity, while their osteogenic differentiation capacity was reduced in comparison with their unafflicted control mice. The ASCs from EAE mice also demonstrated increased expression of pro-inflammatory cytokines and chemokines, specifically an elevation in the expression of monocyte chemoattractant protein-1 and keratin chemoattractant. In vivo, infusion of wild type ASCs significantly ameliorate the disease course, autoimmune mediated demyelination and cell infiltration through the regulation of the inflammatory responses, however, mice treated with autologous ASCs showed no therapeutic improvement on the disease progression.

Immature mesenchymal stem cell-like pericytes as mediators of immunosuppression in human malignant glioma

Malignant gliomas are primary brain tumors characterized by profound local immunosuppression. While the remarkable plasticity of perivascular cells - resembling mesenchymal stem cells (MSC) - in malignant gliomas and their contribution to angiogenesis is increasingly recognized, their role as potential mediators of immunosuppression is unknown. Here we demonstrate that FACS-sorted malignant glioma-derived pericytes (HMGP) were characterized by the expression of CD90, CD248, and platelet-derived growth factor receptor-β (PDGFR-β). HMGP shared this expression profile with human brain vascular pericytes (HBVP) and human MSC (HMSC) but not human cerebral microvascular endothelial cells (HCMEC). CD90+PDGFR-β+perivascular cells distinct from CD31+ endothelial cells accumulated in human gliomas with increasing degree of malignancy and negatively correlated with the presence of blood vessel-associated leukocytes and CD8+ T cells. Cultured CD90+PDGFR-β+HBVP were equally capable of suppressing allogeneic or mitogen-activated T cell responses as human MSC. HMGP, HBVP and HMSC expressed prostaglandin E synthase (PGES), inducible nitric oxide synthase (iNOS), human leukocyte antigen-G (HLA-G), hepatocyte growth factor (HGF) and transforming growth factor-β (TGF-β). These factors but not indoleamine 2,3-dioxygenase-mediated conversion of tryptophan to kynurenine functionally contributed to immunosuppression of immature pericytes. Our data provide evidence that human cerebral CD90+ perivascular cells possess T cell inhibitory capability comparable to human MSC and suggest that these cells, besides their critical role in tumor vascularization, also promote local immunosuppression in malignant gliomas and possibly other brain diseases.

The kynurenine pathway in stem cell biology

The kynurenine pathway (KP) is the main catabolic pathway of the essential amino acid tryptophan. The KP has been identified to play a critical role in regulating immune responses in a variety of experimental settings. It is also known to be involved in several neuroinflammatory diseases including Huntington's disease, amyotrophic lateral sclerosis, and Alzheimer's disease. This review considers the current understanding of the role of the KP in stem cell biology. Both of these fundamental areas of cell biology have independently been the focus of a burgeoning research interest in recent years. A systematic review of how the two interact has not yet been conducted. Several inflammatory and infectious diseases in which the KP has been implicated include those for which stem cell therapies are being actively explored at a clinical level. Therefore, it is highly relevant to consider the evidence showing that the KP influences stem cell biology and impacts the functional behavior of progenitor cells.

Mesenchymal stem cells in tissue repair

The advent of mesenchymal stem cell (MSC)-based therapies for clinical therapeutics has been an exciting and new innovation for the treatment of a variety of diseases associated with inflammation, tissue damage, and subsequent regeneration and repair. Application-based ability to measure MSC potency and fate of the cells post-MSC therapy are the variables that confound the use of MSCs therapeutics in human diseases. An evaluation of MSC function and applications with attention to detail in the preparation as well as quality control and quality assurance are only as good as the assays that are developed. In vivo measures of efficacy and potency require an appreciation of the overall pathophysiology of the model and standardization of outcome measures. The new concepts of how MSC’s participate in the tissue regeneration and wound repair process and further, how this is impacted by estimates of efficacy and potency are important new topics. In this regard, this chapter will review some of the in vitro and in vivo assays for MSC function and activity and their application to the clinical arena.

Administration of murine stromal vascular fraction ameliorates chronic experimental autoimmune encephalomyelitis

Administration of adipose-derived stromal/stem cells (ASCs) represents a promising therapeutic approach for autoimmune diseases since they have been shown to have immunomodulatory properties. The uncultured, nonexpanded counterpart of ASCs, the stromal vascular fraction (SVF), is composed of a heterogeneous mixture of cells. Although administration of ex vivo culture-expanded ASCs has been used to study immunomodulatory mechanisms in multiple models of autoimmune diseases, less is known about SVF-based therapy. The ability of murine SVF cells to treat myelin oligodendrocyte glycoprotein35-55-induced experimental autoimmune encephalitis (EAE) was compared with that of culture-expanded ASCs in C57Bl/6J mice. A total of 1 × 10(6) SVF cells or ASCs were administered intraperitoneally concomitantly with the induction of disease. The data indicate that intraperitoneal administration of ASCs significantly ameliorated the severity of disease course. They also demonstrate, for the first time, that the SVF effectively inhibited disease severity and was statistically more effective than ASCs. Both cell therapies also demonstrated a reduction in tissue damage, a decrease in inflammatory infiltrates, and a reduction in sera levels of interferon-γ and interleukin-12. Based on these data, SVF cells effectively inhibited EAE disease progression more than culture-expanded ASCs.

How stem cells speak with host immune cells in inflammatory brain diseases

Advances in stem cell biology have raised great expectations that diseases and injuries of the central nervous system (CNS) may be ameliorated by the development of non-hematopoietic stem cell medicines. Yet, the application of adult stem cells as CNS therapeutics is challenging and the interpretation of some of the outcomes ambiguous. In fact, the initial idea that stem cell transplants work only via structural cell replacement has been challenged by the observation of consistent cellular signaling between the graft and the host. Cellular signaling is the foundation of coordinated actions and flexible responses, and arises via networks of exchanging and interacting molecules that transmit patterns of information between cells. Sustained stem cell graft-to-host communication leads to remarkable trophic effects on endogenous brain cells and beneficial modulatory actions on innate and adaptive immune responses in vivo, ultimately promoting the healing of the injured CNS. Among a number of adult stem cell types, mesenchymal stem cells (MSCs) and neural stem/precursor cells (NPCs) are being extensively investigated for their ability to signal to the immune system upon transplantation in experimental CNS diseases. Here, we focus on the main cellular signaling pathways that grafted MSCs and NPCs use to establish a therapeutically relevant cross talk with host immune cells, while examining the role of inflammation in regulating some of the bidirectionality of these communications. We propose that the identification of the players involved in stem cell signaling might contribute to the development of innovative, high clinical impact therapeutics for inflammatory CNS diseases.

Towards clinical application of mesenchymal stem cells for treatment of neurological diseases of the central nervous system

The diagnosis of a neurological disease of the central nervous system (CNS) is often associated with the anticipation of an irreversible and untreatable disability. This is the case also of multiple sclerosis (MS) where approved treatments effectively modulate the autoimmune attack to myelin antigens, but poorly affect neurodegeneration and do not promote tissue repair. Thus, stem cell-based therapies are increasingly being considered a possible strategy for diseases of the CNS. Mesenchymal stem cells (MSC), the safety of which has been demonstrated in the last 20 years through clinical trials and case studies, are of particular interest in view not only of their neuroprotective, but also of their immunomodulatory properties. Here, we review the therapeutic features of MSC that make them relevant in the treatment of CNS illnesses and discuss the pioneer clinical experience with MSC-based therapy in neurological diseases.

In vitro assessment of mesenchymal stem cells immunosuppressive potential in multiple sclerosis patients

Mesenchymal stem cells (MSC) are promising for multiple sclerosis (MS) treatment. However, clinical results remain controversial, and no criteria are available for predicting the efficiency of MSC therapy. Using an in vitro model of lymphocytes and MSC cocultivation we revealed that the Index of MSC Suppression of myelin-induced memory T cells proliferation was stronger than that of PHA-stimulated proliferation and inversely correlated with patients'EDSS score. In vitro expression of CD119 (IFNGR1) in mitogen/myelin-stimulated T cells increased in the presence of MSC being inversely correlated with T-lymphocytes proliferation. The Index of MSC Suppression and CD119 expression in T-lymphocytes may be useful when assessing MSC immunosuppressive potential in MS patients.

Antimicrobial effects of murine mesenchymal stromal cells directed against Toxoplasma gondii and Neospora caninum: role of immunity-related GTPases (IRGs) and guanylate-binding proteins (GBPs)

Mesenchymal stromal cells (MSCs) have a multilineage differentiation potential and provide immunosuppressive and antimicrobial functions. Murine as well as human MSCs restrict the proliferation of T cells. However, species-specific differences in the underlying molecular mechanisms have been described. Here, we analyzed the antiparasitic effector mechanisms active in murine MSCs. Murine MSCs, in contrast to human MSCs, could not restrict the growth of a highly virulent strain of Toxoplasma gondii (BK) after stimulation with IFN-γ. However, the growth of a type II strain of T. gondii (ME49) was strongly inhibited by IFN-γ-activated murine MSCs. Immunity-related GTPases (IRGs) as well as guanylate-binding proteins (GBPs) contributed to this antiparasitic effect. Further analysis showed that IFN-γ-activated mMSCs also inhibit the growth of Neospora caninum, a parasite belonging to the apicomplexan group as well. Detailed studies with murine IFN-γ-activated MSC indicated an involvement in IRGs like Irga6, Irgb6 and Irgd in the inhibition of N. caninum. Additional data showed that, furthermore, GBPs like mGBP1 and mGBP2 could have played a role in the anti-N. caninum effect of murine MSCs. These data underline that MSCs, in addition to their regenerative and immunosuppressive activity, function as antiparasitic effector cells as well. However, IRGs are not present in the human genome, indicating a species-specific difference in anti-T. gondii and anti-N. caninum effect between human and murine MSCs.

Antimicrobial effects of murine mesenchymal stromal cells directed against Toxoplasma gondii and Neospora caninum: role of immunity-related GTPases (IRGs) and guanylate-binding proteins (GBPs). Med Microbiol Immunol. 2013;202:197-206. [PMID: 23269418 DOI: 10.1007/s00430-012-0281]

Mesenchymal stromal cells (MSCs) have a multilineage differentiation potential and provide immunosuppressive and antimicrobial functions. Murine as well as human MSCs restrict the proliferation of T cells. However, species-specific differences in the underlying molecular mechanisms have been described. Here, we analyzed the antiparasitic effector mechanisms active in murine MSCs. Murine MSCs, in contrast to human MSCs, could not restrict the growth of a highly virulent strain of Toxoplasma gondii (BK) after stimulation with IFN-γ. However, the growth of a type II strain of T. gondii (ME49) was strongly inhibited by IFN-γ-activated murine MSCs. Immunity-related GTPases (IRGs) as well as guanylate-binding proteins (GBPs) contributed to this antiparasitic effect. Further analysis showed that IFN-γ-activated mMSCs also inhibit the growth of Neospora caninum, a parasite belonging to the apicomplexan group as well. Detailed studies with murine IFN-γ-activated MSC indicated an involvement in IRGs like Irga6, Irgb6 and Irgd in the inhibition of N. caninum. Additional data showed that, furthermore, GBPs like mGBP1 and mGBP2 could have played a role in the anti-N. caninum effect of murine MSCs. These data underline that MSCs, in addition to their regenerative and immunosuppressive activity, function as antiparasitic effector cells as well. However, IRGs are not present in the human genome, indicating a species-specific difference in anti-T. gondii and anti-N. caninum effect between human and murine MSCs.

Stem cells in autoimmune diseases: Implications for pathogenesis and future trends in therapy

In this review we report the recent progresses, available in the literature, concerning the biology and the potential therapeutic role of both mesenchymal stem cells (MSCs) and hematopoietic stem cells in autoimmune diseases. Mesenchymal stem cells (MSCs) are responsible for the normal turnover and maintenance of adult mesenchymal tissues and their pleiotropic nature allows them to sense and respond to an event in the local environment, be it injury or inflammation. Recently, MSCs have been shown to have immune-modulatory properties and immunosuppressive capacities, acting on different immune cells both in vitro and in vivo, in addition to an immunologically privileged phenotype. Moreover, several works suggest that MSCs are defective in autoimmune diseases. These aspects are now considered the most intriguing aspect of their biology, introducing the possibility that these cells might be used as effective therapy in autoimmune diseases. Autoimmune diseases represent a failure of normal immune regulatory processes as they are characterized by activation and expansion of immune cell subsets in response to non-pathogenic stimuli. As autoimmune diseases can be transferred, or alternatively, cured, by stem cell transplantation, a defect in the hemopoietic stem cell as a cause of autoimmune diseases may be postulated. The rationale for autologous hematopoietic stem cell transplantation (HSCT) in autoimmune diseases is the ablation of an aberrant or self-reactive immune system by chemotherapy and regeneration of a new and hopefully self-tolerant immune system from hematopoietic stem cells. In the past 15years, more than 1500 patients worldwide have received HSCT, mostly autologous, as treatment for a severe autoimmune disease and the majority were affected by multiple sclerosis, systemic sclerosis, systemic lupus erythematosus, rheumatoid arthritis, juvenile idiopathic arthritis and idiopathic cytopenic purpura.

Stem cell therapy for multiple sclerosis: preclinical evidence beyond all doubt?

Stem cell transplantation holds great promise for restoration of neural function in various neurodegenerative disorders, including multiple sclerosis (MS). However, many questions remain regarding the true efficacy and precise mode of action of stem cell-based therapeutic approaches. Therefore, in this article, we will first discuss the ideal route and/or timing of stem cell-based therapies for experimental autoimmune encephalomyelitis (EAE), the most used preclinical animal model for MS. Next, we will provide an overview of the proposed mechanisms that contribute to the beneficial effects of stem cell transplantation observed during the treatment of rodent EAE. Reviews of current and past literature clearly demonstrate conceptual changes in the development of stem cell-based approaches for EAE/MS, leading to the identification of several major challenges to be tackled before (stem) cell therapy for rodent EAE can be safely and successfully translated to human therapy for MS.

High-throughput screening of stem cell therapy for globoid cell leukodystrophy using automated neurophenotyping of twitcher mice

Globoid cell leukodystrophy (Krabbe's disease) is an autosomal recessive neurodegenerative disorder that results from the deficiency of galactosylceramidase, a lysosomal enzyme involved in active myelination. Due to the progressive, lethal nature of this disease and the limited treatment options available, multiple laboratories are currently exploring novel therapies using the mouse model of globoid cell leukodystrophy. In order to establish a protocol for motor function assessment of the twitcher mouse, this study tested the capability of an automated system to detect phenotypic differences across mouse genotypes and/or treatment groups. The sensitivity of this system as a screening tool for the assessment of therapeutic interventions was determined by the administration of murine bone marrow-derived stem cells into twitcher mice via intraperitoneal injection. Animal behavior was analyzed using the Noldus EthoVision XT7 software. Novel biomarkers, including abnormal locomotion (e.g., velocity, moving duration, distance traveled, turn angle) and observed behaviors (e.g., rearing activity, number of defecation boli), were established for the twitcher mouse. These parameters were monitored across all mouse groups, and the automated system detected improved locomotion in the treated twitcher mice based on the correction of angular velocity, turn angle, moving duration, and exploratory behavior, such as thigmotaxis. Further supporting these findings, the treated mice showed improved lifespan, gait, wire hang ability, twitching severity and frequency, and sciatic nerve histopathology. Taken together, these data demonstrate the utility of computer-based neurophenotyping for motor function assessment of twitcher mice and support its utility for detecting the efficacy of stem cell-based therapy for neurodegenerative disorders.

Toll-like receptors as modulators of mesenchymal stem cells

Mesenchymal stem cells (MSCs) have differentiation and immunomodulatory properties that make them interesting tools for the treatment of degenerative disorders, allograft rejection, or inflammatory and autoimmune diseases. Biological properties of MSCs can be modulated by the inflammatory microenvironment they face at the sites of injury or inflammation. Indeed, MSCs do not constitutively exert their immunomodulating properties but have to be primed by inflammatory mediators released from immune cells and inflamed tissue. A polarization process, mediated by Toll-like receptors (TLRs), toward either an anti-inflammatory or a pro-inflammatory phenotype has been described for MSCs. TLRs have been linked to allograft rejection and the perpetuation of chronic inflammatory diseases (e.g., Crohn’s disease, rheumatoid arthritis) through the recognition of conserved pathogen-derived components or endogenous ligands (danger signals) produced upon injury. Interest in understanding the effects of TLR activation on MSCs has greatly increased in the last few years since MSCs will likely encounter TLR ligands at sites of injury, and it has been proven that the activation of TLRs in MSCs can modulate their function and therapeutic effect.

Harnessing the therapeutic potential of mesenchymal stem cells in multiple sclerosis

Phase I clinical trials exploring the use of autologous mesenchymal stem cell (MSC) therapy for the treatment of multiple sclerosis (MS) have begun in a number of centers across the world. MS is a complex and chronic immune-mediated and neurodegenerative disease influenced by genetic susceptibility and environmental risk factors. The ideal treatment for MS would involve both attenuation of detrimental inflammatory responses, and induction of a degree of tissue protection/regeneration within the CNS. Preclinical studies have demonstrated that both human-derived and murine-derived MSCs are able to improve outcomes in the animal model of MS, experimental autoimmune encephalomyelitis. How MSCs ameliorate experimental autoimmune encephalomyelitis is being intensely investigated. One of the major mechanisms of action of MSC therapy is to inhibit various components of the immune system that contribute to tissue destruction. Emerging evidence now supports the idea that MSCs can access the CNS where they can provide protection against tissue damage, and may facilitate tissue regeneration through the production of growth factors. The prospect of cell-based therapy using MSCs has several advantages, including the relative ease with which they can be extracted from autologous bone marrow or adipose tissue and expanded in vitro to reach the purity and numbers required for transplantation, and the fact that MSC therapy has already been used in other human disease settings, such as graft-versus-host and cardiac disease, with initial reports indicating a good safety profile. This article will focus on the theoretical and practical issues relevant to considerations of MSC therapy in the context of MS.

The therapeutic effect of mesenchymal stem cell transplantation in experimental autoimmune encephalomyelitis is mediated by peripheral and central mechanisms

Stem cells are currently seen as a treatment for tissue regeneration in neurological diseases such as multiple sclerosis, anticipating that they integrate and differentiate into neural cells. Mesenchymal stem cells (MSCs), a subset of adult progenitor cells, differentiate into cells of the mesodermal lineage but also, under certain experimental circumstances, into cells of the neuronal and glial lineage. Their clinical development, however, has been significantly boosted by the demonstration that MSCs display significant therapeutic plasticity mainly occurring through bystander mechanisms. These features have been exploited in the effective treatment of experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis where the inhibition of the autoimmune response resulted in a significant amelioration of disease and decrease of demyelination, immune infiltrates and axonal loss. Surprisingly, these effects do not require MSCs to engraft in the central nervous system but depend on the cells' ability to inhibit pathogenic immune responses both in the periphery and inside the central nervous system and to release neuroprotective and pro-oligodendrogenic molecules favoring tissue repair. These results paved the road for the utilization of MSCs for the treatment of multiple sclerosis.

In vitro differentiation of bone marrow stromal cells into oligodendrocyte-like cells using triiodothyronine as inducer

An in vitro technique was devised to induced autologous adult stem cells into oligodendrocyte-like cells. In this study, a protocol was developed for the induction of bone marrow stromal cells (BMSCs) into oligodendrocyte-like cells. BMSCs were incubated in one of these three pre-inducers: dimethyl sulfoxide (DMSO), β-mercaptoethanol (βME) or biotylated hydroxyanisol (BHA), each followed by retinoic acid (RA) treatment. The percentage of viable cells in BHA-RA preinduced cells was significantly lower than the others. The results showed that the preinduced cells were immunoreactive for nestin and NF-68; among the mentioned protocols, the immunoreactivity yielded by following the DMSO-RA protocol was significantly higher than the others. Moreover, no significant immunoreactivity was observed for preinduced cells to O4, O1, MBP (myelin basic protein), S100, and GFAP (glial fibrillary acidic protein). The cells were immunoreactive to oligo-2. Two phases of induction were done: the first was a combination of basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF) and heregulin (HRG), followed by either triiodothyronine (T3) or Forskolin (FSK) as the second phase. The conclusion is that the trans-differentiation of BMSCs by DMSO followed by RA (preinduction stage) then bFGF-PDGF-HRG followed by T3 (10 ng/ml) (induction stage) can be a potential source for oligodendrocyte-like cells preparation.

Stem cells and cell therapies in lung biology and lung diseases

The University of Vermont College of Medicine and the Vermont Lung Center, with support of the National Heart, Lung, and Blood Institute (NHLBI), the Alpha-1 Foundation, the American Thoracic Society, the Emory Center for Respiratory Health,the Lymphangioleiomyomatosis (LAM) Treatment Alliance,and the Pulmonary Fibrosis Foundation, convened a workshop,‘‘Stem Cells and Cell Therapies in Lung Biology and Lung Diseases,’’ held July 26-29, 2009 at the University of Vermont,to review the current understanding of the role of stem and progenitor cells in lung repair after injury and to review the current status of cell therapy approaches for lung diseases. These are rapidly expanding areas of study that provide further insight into and challenge traditional views of the mechanisms of lung repair after injury and pathogenesis of several lung diseases. The goals of the conference were to summarize the current state of the field, discuss and debate current controversies, and identify future research directions and opportunities for both basic and translational research in cell-based therapies for lung diseases.

The indoleamine-2,3-dioxygenase (IDO) inhibitor 1-methyl-D-tryptophan upregulates IDO1 in human cancer cells

1-methyl-D-tryptophan (1-D-MT) is currently being used in clinical trials in patients with relapsed or refractory solid tumors with the aim of inhibiting indoleamine-2,3-dioxygenase (IDO)-mediated tumor immune escape. IDO is expressed in tumors and tumor-draining lymph nodes and degrades tryptophan (trp) to create an immunsuppressive micromilieu both by depleting trp and by accumulating immunosuppressive metabolites of the kynurenine (kyn) pathway. Here we show that proliferation of alloreactive T-cells cocultured with IDO1-positive human cancer cells paradoxically was inhibited by 1-D-MT. Surprisingly incubation with 1-D-MT increased kyn production of human cancer cells. Cell-free assays revealed that 1-D-MT did not alter IDO1 enzymatic activity. Instead, 1-D-MT induced IDO1 mRNA and protein expression through pathways involving p38 MAPK and JNK signalling. Treatment of cancer patients with 1-D-MT has transcriptional effects that may promote rather than suppress anti-tumor immune escape by increasing IDO1 in the cancer cells. These off-target effects should be carefully analyzed in the ongoing clinical trials with 1-D-MT.

Mesenchymal stem cells: mechanisms of inflammation

In adults, human mesenchymal stem cells (hMSCs) are found in vivo at low frequency and are defined by their capacity to differentiate into bone, cartilage, and adipose tissue, depending on the stimuli and culture conditions under which they are expanded. Although MSCs were initially hypothesized to be the panacea for regenerating tissues, MSCs appear to be more important in therapeutics to regulate the immune response invoked in settings such as tissue injury, transplantation, and autoimmunity. MSCs have been used therapeutically in clinical trials and subsequently in practice to treat graft-versus-host disease following bone marrow transplantation. Reports of successful immune modulation suggest efficacy in a wide range of autoimmune conditions, such as demyelinating neurological disease (multiple sclerosis), systemic lupus erythematosus, and Crohn's disease, among others. This review provides background information about hMSCs and also describes their putative mechanisms of action in inflammation. We provide a summary of ongoing clinical trials to allow (a) full comprehension of the range of diseases in which hMSC therapy may be beneficial and (b) identification of gaps in our knowledge about the mechanisms of action of therapeutic MSCs in disease.

Why should mesenchymal stem cells (MSCs) cure autoimmune diseases?

The adult stem/progenitor cells from bone marrow and other tissues referred to as mesenchymal stem cells or multipotent mesenchymal stromal cells (MSCs) display a significant therapeutic plasticity as reflected by their ability to enhance tissue repair and influence the immune response both in vitro and in vivo. In this review we will focus on the paradigmatic preclinical experience achieved testing MSCs in experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis. We will emphasize how the paradigm changed over time from the original prediction that MSCs would enhance tissue repair through their transdifferentiation into somatic cells to the current paradigm that they can produce therapeutic benefits without engraftment into the injured tissues. The data will be reviewed in terms of the potentials of MSCs for therapy of autoimmune diseases.