Therapeutic plasticity of stem cells and allograft tolerance

Therapeutic effect of bone marrow mesenchymal stem cells in a rat model of carbon tetrachloride induced liver fibrosis

Background

Liver fibrosis is a major medical problem with high mortality and morbidity rates where the formation of regenerative nodules and cirrhosis leads to loss of liver function and may result in the development of hepatocellular carcinoma. bone marrow mesenchymal stem cells (BM-MSCs) have drawn attention as a novel approach for treatment of liver fibrosis. This study aimed to evaluate the therapeutic effect of BM-MSCs on the liver structure in carbon tetrachloride (CCl₄) induced liver fibrosis in male rats relative to resveratrol and Silybum marianum as standard drugs derived from herbal plants.

Methods

Fifty adult male albino rats (Sprague Dawley strain; 180–220 g mean body weight) were purchased from the Laboratory Animal Unit in the Nile Center of Experimental Research, Mansoura, Egypt. Liver function were determined, isolation and preparation of BM- MSCs and detection of cell-surface markers by flow cytometry.

Results

Animals exposed to CCl₄ developed liver injury characterized by significant increase of liver enzymes, malondialdehyde (MDA), tumor necrosis factor alpha (TNFα), and CYP450, inhibition of antioxidant enzymes, and decreased albumin. Treatment with stem cells enhanced liver state more effectively than resveratrol and S. marianum. It significantly decreased AST, ALT, ALP, MDA, TNF-α, and CYP450 and increased albumin, SOD, GSH, GST, and CAT. Histopathological study and atomic force microscope results confirmed the therapeutic effects of MSCs.

Conclusions

BM-MSCs could restore liver structure and function in CCL₄ induced liver fibrosis rat model, ameliorating the toxicity of CCl₄ and improving liver function tests.

Healing the Broken Heart; The Immunomodulatory Effects of Stem Cell Therapy

Cardiovascular Disease (CVD) is a leading cause of mortality within the United States. Current treatments being administered to patients who suffered a myocardial infarction (MI) have increased patient survival, but do not facilitate the replacement of damaged myocardium. Recent studies demonstrate that stem cell-based therapies promote myocardial repair; however, the poor engraftment of the transferred stem cell populations within the infarcted myocardium is a major limitation, regardless of the cell type. One explanation for poor cell retention is attributed to the harsh inflammatory response mounted following MI. The inflammatory response coupled to cardiac repair processes is divided into two distinct phases. The first phase is initiated during ischemic injury when necrosed myocardium releases Danger Associated Molecular Patterns (DAMPs) and chemokines/cytokines to induce the activation and recruitment of neutrophils and pro-inflammatory M1 macrophages (MΦs); in turn, facilitating necrotic tissue clearance. During the second phase, a shift from the M1 inflammatory functional phenotype to the M2 anti-inflammatory and pro-reparative functional phenotype, permits the resolution of inflammation and the establishment of tissue repair. T-regulatory cells (Tregs) are also influential in mediating the establishment of the pro-reparative phase by directly regulating M1 to M2 MΦ differentiation. Current studies suggest CD4+ T-lymphocyte populations become activated when presented with autoantigens released from the injured myocardium. The identity of the cardiac autoantigens or paracrine signaling molecules released from the ischemic tissue that directly mediate the phenotypic plasticity of T-lymphocyte populations in the post-MI heart are just beginning to be elucidated. Stem cells are enriched centers that contain a diverse paracrine secretome that can directly regulate responses within neighboring cell populations. Previous studies identify that stem cell mediated paracrine signaling can influence the phenotype and function of immune cell populations in vitro, but how stem cells directly mediate the inflammatory microenvironment of the ischemic heart is poorly characterized and is a topic of extensive investigation. In this review, we summarize the complex literature that details the inflammatory microenvironment of the ischemic heart and provide novel insights regarding how paracrine mediated signaling produced by stem cell-based therapies can regulate immune cell subsets to facilitate pro-reparative myocardial wound healing.

Total Body Irradiation and Risk of Diabetes Mellitus; A Meta-Analysis

Objective: Hematopoietic stem cell transplant (HSCT) has recently emerged as a cure for previously “incurable” diseases and is being explored and attempted in many other fields including congenital and acquired non-malignant diseases. However, the long-term side effect associated with HSCT especially Total Body Irradiation (TBI) is still understudied. Therefore, we attempted to establish association between TBI and risk of developing Diabetes Mellitus (DM) or impaired glucose metabolism (IGM). Methods: We searched for titles of articles in MEDLINE (PubMed), EMBASE, and Cochrane library in August 2018 that evaluated the association between TBI in the setting of HSCT and DM or IGM. We conducted a random effect meta-analysis of 11 studies involving a total of 13,191 participants and reported the pooled MD (mean difference) for the development of DM/IGM after TBI as part of the conditioning regimen for HSCT. Results: We found a significant increase in the risk of developing DM/IGM after TBI is used as part of the conditioning regimen compared to other types of conditioning regimen with the pooled MD being 5.42, 95% Confidence Interval (CI) 2.51-11.71, I2=92.4%. Conclusion: TBI as a conditioning regimen in the setting of HSCT significantly increases the risk of developing DM/IGM. Therefore, we recommend close monitoring and screening for diabetes mellitus in patients who underwent TBI before HSCT.

Equine Mesenchymal Stem Cells: Properties, Sources, Characterization, and Potential Therapeutic Applications

Properties like sustained multiplication and self-renewal, and homing and multilineage differentiation to undertake repair of the damaged tissues make stem cells the lifeline for any living system. Therefore, stem cell therapy is regarded to carry immense therapeutic potential. Though the dearth of understanding about the basic biological properties and pathways involved in therapeutic benefits currently limit the application of stem cells in humans as well as animals, there are innumerable reports that suggest clinical benefits of stem cell therapy in equine. Among various stem cell sources, currently adult mesenchymal stem cells (MSCs) are preferred for therapeutic application in horse owing to their easy availability, capacity to modulate inflammation, and promote healing. Also the cells carry very limited teratogenic risk compared to the pluripotent stem cells. Mesenchymal stem cells were earlier considered mainly for musculoskeletal tissues, but now may also be utilized in other diverse clinical problems in horse, and the results may be extrapolated even for human medicine. The current review highlights biological properties, sources, mechanisms, and potential therapeutic applications of stem cells in equine practice.

Tissue Engineering in Osteoarthritis: Current Status and Prospect of Mesenchymal Stem Cell Therapy

Osteoarthritis (OA) is the most common form of arthritis. Over the last 20 years, attempts have been made to regenerate articular cartilage to overcome the limitations of conventional treatments. As OA is generally associated with larger and diffuse involvement of articular surfaces and alteration of joint homeostasis, a tissue engineering approach for cartilage regeneration is more difficult than in simple chondral defects. Autologous and allogeneic mesenchymal stem cells (MSCs) have rapidly emerged as investigational products for cartilage regeneration. This review outlines points to consider in MSC-based approaches for OA treatment, including allogeneic MSCs, sources of MSCs, dosages, feasibility of multiple injections, indication according to severity of OA lesion and patient age, and issues regarding implantation versus injection. We introduce possible mechanisms of action of implanted or injected MSCs as well as the immunological aspects of MSC therapy and provide a summary of clinical trials of MSCs in the treatment of OA. Given current knowledge, it is too early to draw conclusions on the ultimate effectiveness of intra-articular application of MSCs in terms of regenerative effects. Further radiological and histological data will be needed, with a larger pool of patients, before this question can be answered.

BMSCs and miR-124a ameliorated diabetic nephropathy via inhibiting notch signalling pathway

BMSCs are important in replacement therapy of diabetic nephropathy (DN). MiR‐124a exerts effect on the differentiation capability of pancreatic progenitor cells. The objective of this study was to explore the molecular mechanisms, the functions of miR‐124a and bone marrow mesenchymal stem cells (BMSCs) in the treatment of DN. Characterizations of BMSCs were identified using the inverted microscope and flow cytometer. The differentiations of BMSCs were analysed by immunofluorescence assay and DTZ staining. The expression levels of islet cell‐specific transcription factors, apoptosis‐related genes, podocytes‐related genes and Notch signalling components were detected using quantitative real‐time reverse transcription PCR (qRT‐PCR) and Western blot assays. The production of insulin secretion was detected by adopting radioimmunoassay. Cell proliferation and apoptosis abilities were detected by CCK‐8, flow cytometry and TUNEL assays. We found that BMSCs was induced into islet‐like cells and that miR‐124a could promote the BMSCs to differentiate into islet‐like cells. BMSCs in combination with miR‐124a regulated islet cell‐specific transcription factors, apoptosis‐related genes, podocytes‐related genes as well as the activity of Notch signalling pathway. However, BMSCs in combination with miR‐124a relieved renal lesion caused by DN and decreased podocyte apoptosis caused by HG. The protective effect of BMSCs in combination with miR‐124a was closely related to the inactivation of Notch signalling pathway. MSCs in combination with miR‐124a protected kidney tissue from impairment and inhibited nephrocyte apoptosis in DN.

Role of Human Wharton's Jelly Derived Mesenchymal Stem Cells (WJ-MSCs) for Rescue of d-Galactosamine Induced Acute Liver Injury in Mice

BACKGROUND/AIM

Mesenchymal stem cells (MSCs) are multipotent precursor cells having self-renewal ability making them a candidate for use in regenerative medicine. Acute liver injury results in sudden loss of hepatic function leading to organ failure. Liver transplantation is often required to salvage patients with acute liver failure. Due to shortage of organs, identification of alternate method is the need of the hour. In view of this, an attempt has been made to check the regenerative ability of WJ-MSCs (wharton's jelly derived MSC) in mice models for acute liver injury.

METHODS

Swiss albino mice weighing 25 ± 5 g were used in this study. The control mice (Group I), was given saline. Group II mice received d-Galactosamine (d-GalN-800 mg/kg; i.p). Group III mice similar with Group II, received WJ-MSCs (5 × 105 cells/0.5 ml DMEM) through tail vein, 24 h after d-GalN administration and Group IV mice received MSC alone.

RESULTS

Parameters, indicative of hepatotoxicity and oxidative stress were analyzed. A two-fold elevation in the marker enzymes of liver toxicity such as aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (SAP), and total serum bilirubin (TBIL) confirms hepatocellular injury, while a greater than four-fold increase in malondialdehyde (MDA) formation, along with around 40% fall in superoxide-dis-mutase (SOD) activity was indicative of oxidative stress and loss of hepatocellular membrane integrity induced by d-GalN. The above biochemical and pathological changes were significantly restored in mice that received WJ-MSCs indicating hepatoprotective and probable regenerative property.

CONCLUSION

The present study showed that WJ-MSC treatment is able to rescue/ameliorate the hepatotoxicity induced by d-GalN in mice.

Human Mesenchymal Stromal Cell Sheet Enhances Allograft Repair in a Mouse Model

To determine whether cell sheets generated with long-term passaged (P10) aging human mesenchymal stromal cells (MSCs) could be used for bone tissue regeneration as tissue engineered periosteum in a femoral allograft mouse model similar to fresh passaged (P3) young MSCs. At 3 weeks after transplantation of MSC sheets, results showed more bony callus formed between allograft and host bone ends in both young P3 MSC and aged P10 MSC sheet-wrapped groups when compared to allograft alone. At 6 weeks, while both MSC sheet-wrapped allografts showed more bony callus formation when compared to allograft alone groups, the bony callus size in aged P10 MSC sheet groups was significantly less than young P3 MSC sheet groups. Biomechanical testing confirmed that P3 MSC sheet-grafted femurs had the highest biomechanical strength in the three groups. Histology sections showed that the area of the chondriod callus in the aged P10 MSC sheet groups was significantly larger than in P3 MSC sheet groups. Finally, a significant increase of chondro-osteoclast activity was observed in the P3 MSC sheet-grafted femur. Our data demonstrates that extensive long-term culture-induced MSC aging impaired their osteogenic ability and subsequent bony callus formation, and could be used to induce cartilaginous callus formation.

Amnion-derived stem cell transplantation: A novel treatment for neurological disorders

In this review, we evaluated the literature reporting the use of amniotic stem cells (ASCs) in regenerative medicine for the treatment of neurological disorders. There is an increasing amount of evidence that indicates the exacerbation of the primary injury by inflammation in neurological disorders characterized by rampant inflammation, thereby increasing damage to the central nervous system (CNS). To address this, we focus on the amnion cells' anti-inflammatory properties, which make their transplantation a promising treatment for these disorders. In addition, we offered insights into new applications of the ASC in the fields of regenerative medicine and tissue engineering.

Immunomodulation in stem cell differentiation into neurons and brain repair

Immunomodulators regulate stem cell activity at all stages of development as well as during adulthood. Embryonic stem cell (ESC) proliferation as well as neurogenic processes during embryonic development are controlled by factors of the immune system. We review here immunophenotypic expression patterns of  different stem cell types, including ESC, neural (NSC) and tissue-specific mesenchymal stem cells (MSC), and focus on immunodulatory properties of these cells. Immune and inflammatory responses, involving actions of cytokines as well as toll-like receptor (TLR) signaling are known to affect the differentiation capacity of NSC and MSC. Secretion of pro- and anti-inflammatory messengers by MSC have been observed as the consequence of TLR and cytokine activation and promotion of differentiation into specified phenotypes. As result of augmented differentiation capacity, stem cells secrete angiogenic factors including vascular endothelial growth factor, resulting in multifactorial actions in tissue repair. Immunoregulatory properties of tissue specific adult stem cells are put into the context of possible clinical applications.

Mesenchymal stem cell therapy for osteoarthritis

The versatility of mesenchymal stem cells (MSCs) as a treatment modality has landed it another repair target: osteoarthritis, a crippling cartilage disease that frequently afflicts the aged population. Through many studies, this newly discovered method has been shown to significantly alleviate the pain experienced by osteoarthritic patients. Notwithstanding the effectiveness of MSCs in this regard, varying degrees of success rates have also been reported, which is probably attributable to the different approaches adopted in harnessing MSCs' therapeutic value. Accordingly, it is pertinent to understand the contributory factors like MSC type, dosage, size of osteoarthritic lesion, MSC carrier, and mode of infusion, which would be briefly discussed in this review.

The immune response of stem cells in subretinal transplantation

Stem cell transplantation is a potential curative treatment for degenerative diseases of the retina. Among cell injection sites, the subretinal space (SRS) is particularly advantageous as it is maintained as an immune privileged site by the retinal pigment epithelium (RPE) layer. Thus, the success of subretinal transplantation depends on maintenance of RPE integrity. Moreover, both embryonic stem cells (ESCs) and mesenchymal stem cells (MSCs) have negligible immunogenicity and in fact are immunosuppressive. Indeed, many studies have demonstrated that immunosuppressive drugs are not necessary for subretinal transplantation of stem cells if the blood-retinal barrier is not breached during surgery. The immunogenicity of induced pluripotent stem cells (iPSCs) appears more complex, and requires careful study before clinical application. Despite low rates of graft rejection in animal models, survival rates for ESCs, MSCs, and iPSCs in retina are generally poor, possibly due to resident microglia activated by cell transplantation. To improve graft survival in SRS transplantation, damage to the blood-retinal barrier must be minimized using appropriate surgical techniques. In addition, agents that inhibit microglial activation may be required. Finally, immunosuppressants may be required, at least temporarily, until the blood-retinal barrier heals. We review surgical methods and drug regimens to enhance the likelihood of graft survival after SRS transplantation.

Suppression of graft-versus-host disease and retention of graft-versus-tumour reaction by murine genetically engineered dendritic cells following bone marrow transplantation

The effect of infusion of lentiviral vector‑mediated, genetically engineered dendritic cells (DCs) following allogeneic bone marrow transplantation (allo‑BMT) on graft‑versus‑host disease (GVHD) and graft‑versus‑leukemia (GVL) was investigated in a mouse model. Lentivirus‑mediated expression of soluble tumor necrosis factor receptor 1 (sTNFR1) converted immature DCs (imDCs) from BABL/c mice into engineered DCs in vitro. An EL4 leukemia allo‑BMT model of BABL/c to C57BL/6 mice was established. Engineered DCs with donor bone marrow cells and splenocytes were subsequently transplanted into myeloablatively irradiated recipients. The average survival duration in the sTNFR1‑ and pXZ9‑imDC groups was significantly prolonged compared with that of the allo‑BMT group (P<0.05). Mild histological changes in GVHD or leukemia were observed in the recipients in the sTNFR1‑imDC group and clinical GVHD scores in this group were significantly decreased compared with those of the transplantation and pXZ9‑imDC groups. Serum interferon‑γ levels were decreased in the pXZ9‑imDC and sTNFR1‑imDC groups compared with those in the allo‑BMT group (P<0.05), with the reduction being more significant in the sTNFR1‑imDC group (P<0.05). Serum interleukin‑4 expression levels were decreased in the allo‑BMT group, but gradually increased in the pXZ9‑imDC and sTNFR1‑imDC groups (P<0.05). Co‑injection of donor genetically‑engineered imDCs was able to efficiently protect recipient mice from lethal GVHD while preserving GVL effects during allo‑BMT.

Effect of bone marrow mesenchymal stem cell transplantation on expression of Caspase1 and IL-18 in rats with acute hepatic liver failure

AIM: To investigate the effect of bone marrow mesenchymal stem cell (BMSC) transplantation in the treatment of acute liver failure (ALF) in rats and optimize the administration route.

METHODS: D-galactosamine (D-GalN)/lipopolysaccharide (LPS) were used to make a rat model of experimental ALF. Seventy-two rats were randomly divided into an ALF group, a tail vein group, and a portal vein transplantation group. At different time points (24, 72, 120, and 168 h) after BMSC transplantation, serum ALT and AST were detected. TUNEL assay was applied to detect hepatocyte apoptosis. Immunohistochemistry and Western blot were performed to detect the expression of Caspase1 and IL-18 proteins in liver tissue.

RESULTS: Serum levels of ALT and AST in the ALF group were gradually increased with the progression of the disease. Compared with the ALF group, significant improvement of liver function parameters and histological findings was observed in the transplantation group 120 and 168 h after transplantation (P < 0.05 for both). The apoptosis indexes in the tail vein group and portal vein transplantation group (120 h: 28.17% ± 17.08%, 20.67% ± 12.68%; 168 h: 19.67 % ± 11.82%, 13.00 % ± 6.84% ) were significantly lower than those in the ALF group (P < 0.01 for all). The expression levels of Caspase1 and IL-18 proteins in the two transplantation groups were decreased significantly at 120 and 168 h compared with the ALF group (P < 0.05 for both). Both administration routes had a therapeutic effect against ALF in rats, but no significant difference was observed between them.

CONCLUSION: BMSCs can improve the liver function, inhibit hepatic apoptosis and reduce the levels of Caspase1 and IL-18 proteins in ALF rats. Caspase1 and IL-18 play an important role in the pathogenesis of ALF and are expected to be predictors of ALF and future therapeutic targets.

The role of bone marrow mesenchymal stem cells in the treatment of acute liver failure

Objective. This study is to investigate the effects of bone marrow mesenchymal stem cell (BMSC) transplantation on acute liver failure (ALF). Methods. BMSCs were separated from rat bone marrow, cultured, and identified by flow cytometry. Rat model with ALF was established by injecting D-galactosamine and lipopolysaccharide. Rats were randomly divided into the control group and BMSC transplantation group. The serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were measured at 24 h, 120 h, and 168 h after BMSC transplantation. Apoptosis was detected by TUNEL assay. The expression of VEGF and AFP proteins was detected by immunofluorescence. Caspase-1 and IL-18 proteins and mRNA were detected by immunohistochemistry and RT-PCR. Results. Compared with the control group, levels of ALT, AST, caspase-1 and IL-18 proteins, and mRNA in the transplantation group were significantly lower at 120 h and 168 h after BMSCs transplantation. Apoptosis was inhibited by BMSCs transplantation. The VEGF protein levels were increased with the improvement of liver function, and the AFP protein levels were increased with the deterioration of the liver function after BMSCs transplantation. Conclusions. BMSCs transplantation can improve liver function and inhibit hepatocyte apoptosis as well as promote hepatocyte proliferation in rat model with ALF.

Functional regeneration of laryngeal muscle using bone marrow-derived stromal cells

OBJECTIVES/HYPOTHESIS

To investigate the functional efficiency of skeletal muscles regenerated by transplantation of bone marrow-derived stromal cells (BSCs) or induced-muscle progenitor cells (IMCs) as assessed in the canine posterior cricoarytenoid (PCA) muscle injury model.

STUDY DESIGN

Prospective animal experiment with control.

METHODS

We performed BSC/IMC transplantation into injured canine PCA muscles. We investigated the capability of auto- and allo-BSC/IMC transplantation using a gelatin sponge scaffold to promote functional regeneration of PCA muscles. Transplantation was assessed by fiberscopic analysis of vocal fold movement. We also examined the histologic changes of the transplanted regions. As a control, a gelatin sponge scaffold without additional cells was transplanted into the injured area.

RESULTS

Auto-BSC/IMC transplantation effectively restored vocal fold movement, whereas scaffold alone or allo-BSC/IMC transplantation did not. Histologic examination revealed that (in cases of good recovery) muscle regeneration occurred in the area of cell transplantation, and scar formation without muscle regeneration was observed under control conditions. The dogs with autologous transplantation of BSC had faster functional recovery than did dogs treated with autologous transplantation of IMC.

CONCLUSIONS

Functional efficiency was shown in skeletal muscles regenerated using BSCs and IMPs. Motor function recovery was observed using autologous transplantation of BSCs and IMCs. Minimal functional recovery was observed using allogeneic transplantation of these cells.

Mesenchymal stem cell transfusion for desensitization of positive lymphocyte cross-match before kidney transplantation: outcome of 3 cases

OBJECTIVES

Donor specific antibodies (DSA) and a positive cross-match are contraindications for kidney transplantation. Trials of allograft transplantation across the HLA barrier have employed desensitization strategies, including the use of plasmapheresis, intravenous immunoglobulins, anti-B-cell monoclonal antibodies and splenectomy, associated with high-intensity immunosuppressive regimens. Our case 1 report suffered from repeatedly positive lymphocyte cross match after 1st renal transplantation. Graft nephrectomy could not correct the state of sensitization. Splenectomy was done in a trial to get rid of the antibody producing clone. Furthermore plasmapheresis with low dose IVIG could not as well revert the state of sensitization for the patient.

MATERIAL AND METHODS

About 50 millions donor specific MSCs were injected to the patient.

RESULTS

MSCs transfusion proved to be the only procedure which could achieve successful desensitization before performing the second transplantation owing to their immunosuppressive properties.

CONCLUSION

This case indicates that DS-MSCs is a potential option for anti-HLA desensitization. In cases 2 and 3 IV DS-MSCs transfusion was selected from the start as a successful line of treatment for pre renal transplantation desensitization to save other unnecessary lines of treatment that were tried in case 1.

Strategy for the creation of clinical grade hESC line banks that HLA-match a target population

Here, we describe a pre-derivation embryo haplotyping strategy that we developed in order to maximize the efficiency and minimize the costs of establishing banks of clinical grade hESC lines in which human leukocyte antigen (HLA) haplotypes match a significant proportion of the population. Using whole genome amplification followed by medium resolution HLA typing using PCR amplification with sequence-specific primers (PCR-SSP), we have typed the parents, embryos and hESC lines from three families as well as our eight clinical grade hESC lines and shown that this technical approach is rapid, reliable and accurate. By employing this pre-derivation strategy where, based on HLA match, embryos are selected for a GMP route on day 3-4 of development, we would have drastically reduced our cGMP laboratory running costs.

Permanent CNI treatment for prevention of renal allograft rejection in sensitized hosts can be replaced by regulatory T cells

Recent data suggest that donor-specific memory T cells (T(mem)) are an independent risk factor for rejection and poor graft function in patients and a major challenge for immunosuppression minimizing strategies. Many tolerance induction protocols successfully proven in small animal models e.g. costimulatory blockade, T cell depletion failed in patients. Consequently, there is a need for more predictive transplant models to evaluate novel promising strategies, such as adoptive transfer of regulatory T cells (Treg). We established a clinically more relevant, life-supporting rat kidney transplant model using a high responder (DA to LEW) recipients that received donor-specific CD4(+)/ 8(+) GFP(+) T(mem) before transplantation to achieve similar pre-transplant frequencies of donor-specific T(mem) as seen in many patients. T cell depletion alone induced long-term graft survival in naïve recipients but could not prevent acute rejection in T(mem)(+) rats, like in patients. Only if T cell depletion was combined with permanent CNI-treatment, the intragraft inflammation, and acute/chronic allograft rejection could be controlled long-term. Remarkably, combining 10 days CNI treatment and adoptive transfer of Tregs (day 3) but not Treg alone also induced long-term graft survival and an intragraft tolerance profile (e.g. high TOAG-1) in T(mem)(+) rats. Our model allows evaluation of novel therapies under clinically relevant conditions.

Developing immunologic tolerance for transplantation at the fetal stage

Given the shortage of human organs for transplantation, the waiting lists are increasing annually and consequently so is the time and deaths during the wait. As most immune suppression therapy is not antigen specific and the risk of infection tends to increase, scientists are looking for new options for immunosuppression or immunotolerance. Tolerance induction would avoid the complications caused by immunosupressive drugs. As such, taking into account the experience with autoimmune diseases, one strategy could be immune modulation-induced changes in T-cell cytokine secretion or antigen therapy; however, most clinical trials have failed. Gene transfer of MHC genes across species may be used to induce tolerance to xenogenic solid organs. Other options are induction of central tolerance by the establishment of mixed chimerism through hematopoietic stem cell transplantation and the induction of 'operational tolerance' through immunodeviation involving dendritic or Tregs. I propose that, as the recognition and tolerance of proteins takes place in the thymus, this organ should be the main target for immunotolerance research protocols even as early as during the fetal development.

Therapeutic implications of mesenchymal stem cells in liver injury

Mesenchymal stem cells (MSCs), represent an attractive tool for the establishment of a successful stem-cell-based therapy of liver diseases. A number of different mechanisms contribute to the therapeutic effects exerted by MSCs, since these cells can differentiate into functional hepatic cells and can also produce a series of growth factors and cytokines able to suppress inflammatory responses, reduce hepatocyte apoptosis, regress liver fibrosis, and enhance hepatocyte functionality. To date, the infusion of MSCs or MSC-conditioned medium has shown encouraging results in the treatment of fulminant hepatic failure and in end-stage liver disease in experimental settings. However, some issues under debate hamper the use of MSCs in clinical trials. This paper summarizes the biological relevance of MSCs and the potential benefits and risks that can result from translating the MSC research to the treatment of liver diseases.

The effects of TLR activation on T-cell development and differentiation

Invading pathogens have unique molecular signatures that are recognized by Toll-like receptors (TLRs) resulting in either activation of antigen-presenting cells (APCs) and/or costimulation of T cells inducing both innate and adaptive immunity. TLRs are also involved in T-cell development and can reprogram Treg cells to become helper cells. T cells consist of various subsets, that is, Th1, Th2, Th17, T follicular helper (Tfh), cytotoxic T lymphocytes (CTLs), regulatory T cells (Treg) and these originate from thymic progenitor thymocytes. T-cell receptor (TCR) activation in distinct T-cell subsets with different TLRs results in differing outcomes, for example, activation of TLR4 expressed in T cells promotes suppressive function of regulatory T cells (Treg), while activation of TLR6 expressed in T cells abrogates Treg function. The current state of knowledge of regarding TLR-mediated T-cell development and differentiation is reviewed.

Therapeutic implications of mesenchymal stem cells in liver injury

Mesenchymal stem cells (MSCs), represent an attractive tool for the establishment of a successful stem-cell-based therapy of liver diseases. A number of different mechanisms contribute to the therapeutic effects exerted by MSCs, since these cells can differentiate into functional hepatic cells and can also produce a series of growth factors and cytokines able to suppress inflammatory responses, reduce hepatocyte apoptosis, regress liver fibrosis, and enhance hepatocyte functionality. To date, the infusion of MSCs or MSC-conditioned medium has shown encouraging results in the treatment of fulminant hepatic failure and in end-stage liver disease in experimental settings. However, some issues under debate hamper the use of MSCs in clinical trials. This paper summarizes the biological relevance of MSCs and the potential benefits and risks that can result from translating the MSC research to the treatment of liver diseases.