Clinical Significance of Myeloid-Derived Suppressor Cells in Human Renal Transplantation with Acute T Cell-Mediated Rejection

Myeloid-derived suppressor cells (MDSCs) are negative regulators of the immune response and are in part responsible for the inhibition of the T cell-mediated immune response. A recent paper indicated that MDSCs were involved in prolonged allograft survival in animal models of transplantation, but the significance of MDSCs in human renal transplantation is still unknown. In our study, 50 patients with biopsy-proven acute T cell-mediated rejection (ATCMR) were included. The ratio of MDSCs in peripheral blood mononuclear cell (PBMC) was evaluated with FACS, and the patients were divided into the MDSCs high group (MDSCs, >10 %) or the MDSCs low group (MDSCs, <10 %). We compared the allograft function, severity of tissue injury, and long-time survival between the two groups. In the MDSCs high group, allograft function was significantly increased compared with the MDSCs low group. Furthermore, we found that isolated MDSCs from transplant recipients are capable of expanding regulatory T cell (Treg), meanwhile, inhibiting production of IL-17 in vitro. We also found that the ratio between Foxp3⁺ and IL-17-producing CD4⁺ T cells positively correlated with MDSCs frequency in PBMC. In conclusion, we demonstrated a potential role for MDSCs in prolonging allograft survival after ATCMR, and this was associated with higher CD4⁺Foxp3⁺/CD4⁺IL-17⁺ ratio in PBMC.     

Myeloid‐derived suppressor cells mediate tolerance induction in autoimmune disease

In multiple sclerosis (MS) T cells aberrantly recognize self‐peptides of the myelin sheath and attack the central nervous system (CNS). Antigen‐specific peptide immunotherapy, which aims to restore tolerance while avoiding the use of non‐specific immunosuppressive drugs, is a promising approach to combat autoimmune disease, but the cellular mechanisms behind successful therapy remain poorly understood. Myeloid‐derived suppressor cells (MDSCs) have been studied intensively in the field of cancer and to a lesser extent in autoimmunity. Because of their suppressive effect on the immune system in cancer, we hypothesized that the development of MDSCs and their interaction with CD4⁺ T cells could be beneficial for antigen‐specific immunotherapy. Hence, changes in the quantity, phenotype and function of MDSCs during tolerance induction in our model of MS were evaluated. We reveal, for the first time, an involvement of a subset of MDSCs, known as polymorphonuclear (PMN)‐MDSCs, in the process of tolerance induction. PMN‐MDSCs were shown to adopt a more suppressive phenotype during peptide immunotherapy and inhibit CD4⁺ T‐cell proliferation in a cell‐contact‐dependent manner, mediated by arginase‐1. Moreover, increased numbers of tolerogenic PMN‐MDSCs, such as observed over the course of peptide immunotherapy, were demonstrated to provide protection from disease in a model of experimental autoimmune encephalomyelitis.     

Sirolimus vs mycophenolate moftile in Tacrolimus based therapy following induction with Antithymocyte globulin promotes regulatory T cell expansion and inhibits RORγt and T-bet expression in kidney transplantation

BackgroundAccumulating evidence suggests that regulatory T cells (Tregs) have a crucial role in immune tolerance and long-term graft survival. However, the influence of immunosuppressive drugs on the level of Tregs has not been fully understood. Therefore we prospectively compare the effect of two different calcineurin inhibitor (CNI)-based immunosuppression protocols on Tregs frequencies and expression of regulatory and effector T cell-related genes in renal transplant recipients.MethodsThe study included 24 renal transplant recipients who received induction therapy (Antithymocyte globulin) and were on triple immunosuppressive therapy so that one group was on Tacrolimus (Tac), mycophenolate moftile (MMF) and prednisolone (P) whereas another group was on Tac, Sirolimus (SRL) and P. The frequency of circulating Treg cells was analyzed by flow cytometry before and 4 months after transplantation. Also, the mRNA expression of FOXP3, T-bet, GATA3 and RORγt was examined by quantitative RT-PCR before and 4 months after transplantation.ResultsCompared to baseline, the frequency of CD4⁺ CD25⁺ FOXP3⁺ Treg cells was significantly increased in the all patients following transplantation. Patients who received Tac/MMF had significantly higher CD4⁺ CD25⁺ FOXP3⁺ Treg cells compared to patients who received Tac/SRL. There was no a significant difference in the frequency of CD3⁺CD8⁺ CD28^? Tregs between two different calcineurin inhibitor (CNI)-based immunosuppression protocols. FOXP3 mRNA levels in the patients who received Tac/MMF were increased 4 months after transplantation and the expression was significantly higher than patients who received Tac/SRL. On the other hand, T-bet and RORγt expression levels were significantly lower in the Tac/SRL group in comparison to Tac/MMF group. We did not observe any significant difference in GATA3 mRNA level between the two groups.ConclusionsOur results suggest that although Tac/MMF-containing immunosuppressive regimen could significantly increase the frequency of CD4⁺ CD25⁺ FOXP3⁺ Tregs, unlike to Tac/SRL-containing regimen, it could not significantly decrease the expression levels of RORγt and T-bet.     

Role of myeloid-derived suppressor cells in mouse pre-sensitized cardiac transplant model

Harness of sensitized transplantation remains a clinical challenge particularly in parallel with prolonged cold ischemia time (PCI)-mediated injury. Our present study was to test the role of myeloid-derived suppressor cells (MDSCs) in mouse pre-sensitized transplantation. Our findings revealed that CD11b + Gr1^low MDSC was shown to have strong suppressive activity. MDSCs subsets from the tolerated mice exhibited higher suppressive capacities compared with counterparts from naive (untreated) mice. Depletion of Tregs could not affect splenic CD11b + Gr1^-low MDSC frequency, but increase peripheral and intragraft CD11b + Gr1^-low frequency. Intriguingly, boost of Tregs remarkably caused an increase of CD11b + Gr1^-low frequency in the graft, peripheral blood, and spleen. Furthermore, peripheral CD11b + Gr1^-low cells were massively accumulated at the early stage when allogeneic immune response was enhanced. Taken together, MDSCs could prevent grafts from PCI-mediated injury independent on Tregs in the pre-sensitized transplant recipients. Utilization of MDSC subset particularly CD11b + Gr1^-low might provide a novel insight into improving graft outcome under such clinical scenarios.     

Simvastatin induces Foxp3+ T regulatory cells by modulation of transforming growth factor-�� signal transduction

Statins are widely used drugs for the treatment of hypercholesterolaemia. A number of recent studies have suggested that statins also have pleiotropic effects on immune responses and statins have proven to be effective in the treatment of autoimmune diseases in animal models. Foxp3⁺ T regulatory cells are a unique subset of CD4⁺ T cells that mediate immunosuppression. Foxp3⁺ T cells develop in the thymus, but can also be induced in peripheral sites in the presence of transforming growth factor‐β (TGF‐β). We demonstrate here that simvastatin blockade of the mevalonate pathway can mediate induction of mouse Foxp3⁺ T cells and that simvastatin can synergize with low levels of TGF‐β to induce Foxp3⁺ T cells. The effects of simvastatin are secondary to a blockade of protein geranylgeranylation, are mediated at late time‐points after T‐cell activation, and are associated with demethylation of the Foxp3 promoter. One major effect of simvastatin was inhibition of the induction of Smad6 and Smad7, inhibitory Smads that inhibit TGF‐β signalling. Our results suggest that one mechanism responsible for the immunosuppressive effects of statins is the ability to promote the generation of Foxp3⁺ T regulatory cells.     

Myeloid-derived suppressor cells and regulatory T cells share common immunoregulatory pathways-related microRNAs that are dysregulated by acute lymphoblastic leukemia and chemotherapy

BackgroundRelapse remains a critical challenge in children with acute lymphoblastic leukemia (ALL). The emergence of immunoregulatory cells, including myeloid-derived suppressor cells (MDSCs), and T regulatory (T_reg) cells, has been considered one potential mechanism of relapse in children with ALL.AimThis study aimed to address the microRNAs (miRNAs) related to MDSCs and T_reg cells and to explore their targeted immunoregulatory pathways.MethodsAffymetrix microarray was used for global miRNA profiling in B-ALL pediatric patients before, during, and after induction of chemotherapy. Bioinformatics analysis was performed on MDSCs and T_reg cells-related dysregulated miRNAs, and miR-Pathway analysis was performed to explore their targeted immunoregulatory pathways.Results516 miRNAs were dysregulated in ALL patients as compared to the healthy donor. Among them, 13 miRNAs and 8 miRNAs related to MDSCs and T_reg cells, respectively, were common in all patients. Besides, 12 miRNAs were shared between MDSCs and T_reg cells; 4 of them were common in all patients. Four immune-related pathways; TNF, TGF-β, FoxO, and Hippo were found implicated.ConclusionOur pilot study concluded certain miRNAs related to MDSCs and T_reg cells, these miRNAs were linked to immunoregulatory pathways. Our results open avenues for testing those miRNA as molecular biomarkers for the immunosuppressive tumor microenvironment.     

Chemotherapy alters the increased numbers of myeloid-derived suppressor and regulatory T cells in children with acute lymphoblastic leukemia

Introduction: Acute lymphoblastic leukemia (ALL) is the most common cancer diagnosed in children. The precise mechanism behind the relapse in this disease is not clearly known. One possible mechanism could be the accumulation of immunosuppressive cells, including myeloid-derived suppressor cells (MDSCs) and T regulatory cells (T_regs) which we and others have reported to mediate suppression of anti-tumor immune responses.

Aim: In this study, we aimed to analyze the numbers of these cells in a population of B-ALL pediatric patients.

Methods: Peripheral blood samples withdrawn from B-ALL pediatric patients (n?=?45 before, during and after the induction phase of chemotherapy. Using multi parametric flow cytometric analysis. MDSCs were identified as Lin^–HLA-DR^–CD33⁺CD11b⁺; and T_reg cells were defined as CD4⁺CD25⁺CD127^–/low.

Results: Early diagnosed B-ALL patients showed significant increases in the numbers of MDSCs and T_regs as compared to healthy volunteers. During induction of chemotherapy, however, the patients showed higher and lower numbers of MDSCs and T_reg cells, respectively as compared to early diagnosed patients (i.e., before chemotherapy). After induction of chemotherapy, the numbers of MDSCs and T_reg cells showed higher increases and decreases, respectively as compared to the numbers in patients during chemotherapy.

Conclusion: Our results indicate that B-ALL patients harbor high numbers of both MDSCs and T_regs cells. This pilot study opens a new avenue to investigate the mechanism mediating the emergence of these cells on larger number of B-ALL patients at different treatment stages.     

Anti‐psoriatic effect of myeloid‐derived suppressor cells on imiquimod‐induced skin inflammation in mice

Myeloid‐derived suppressor cells (MDSCs) play an important role in controlling the immune response against cancer and in suppression of autoimmunity and allergic inflammation. However, the beneficial effects of MDSCs on the experimental mouse model of psoriasis have not been reported. Therefore, we investigated the anti‐psoriatic effect of MDSCs on IMQ‐induced skin inflammation in mice and explored the mechanisms involved. Our results showed that administration of MDSCs (1 × 10⁶ or 2 × 10⁶ cells) suppressed the development of IMQ‐induced skin inflammation in mice as exemplified by a significant reduction in clinical severity scores and was associated with a reduction of histopathological changes, including inflammatory infiltration, epidermal hyperplasia and hyperkeratosis. The immunosuppressive effect of MDSCs (1 × 10⁶ or 2 × 10⁶ cells) corresponded to the production of Th1 cytokines (TNF‐α, IFN‐γ) and Th17 cytokines (IL‐17A and IL‐23) in the serum and dorsal skin. Administration of MDSCs (1 × 10⁶ or 2 × 10⁶ cells) also inhibited splenomegaly. Moreover, an increased percentage of CD4⁺CD25⁺FoxP3⁺ regulatory T (Treg) cells and decreased percentage of Th1 and Th17 cells were found in mice treated with MDSCs. Taken together, these results imply that MDSCs have immunomodulatory and immunosuppressive effects on disease progression in a murine model of psoriasis and that MDSCs could be used in preventive or therapeutic strategies for the management of autoimmune inflammatory skin disorders, such as psoriasis.     

Regulatory T cells in graft-versus-host disease

Alloreactive T cells present in a bone marrow transplant are responsible for graft-vs-host disease, but their depletion is associated with impaired engraftment, immunosuppression, and loss of the graft-vs-leukemia effect. The subpopulation of CD4⁺CD25⁺ immunoregulatory T cells was first identified based on its crucial role in the control of autoimmune processes, but they also play a role in alloreactive responses. Moreover, these cells could be used to develop innovative strategies in the field of transplantation and particularly to prevent graft-vs-host disease. Indeed, high numbers of CD4⁺CD25⁺ immunoregulatory T cells can modulate graft-vs-host disease if administered at the same time as allogeneic hematopoietic stem cell transplantation in mice. This review discusses various important issues regarding the possible use of CD4⁺CD25⁺ immunoregulatory T cells to modulate alloreactivity in hematopoietic stem cell transplantation.     

Immune regulation by non‐lymphoid cells in transplantation

Regulatory cells play a crucial role in the induction and maintenance of tolerance by controlling T cell as well as B and natural killer (NK) cell‐mediated immunity. In transplantation, CD4⁺CD25⁺forkhead box P3⁺ T regulatory cells are instrumental in the maintenance of immunological tolerance, as are several other T cell subsets such as NK T cells, double negative CD3⁺ T cells, γδ T cells, interleukin‐10‐producing regulatory type 1 cells, transforming growth factor‐β‐producing T helper type 3 cells and CD8⁺CD28^‐ cells. However, not only T cells have immunosuppressive properties, as it is becoming increasingly clear that both T and non‐T regulatory cells co‐operate and form a network of cellular interactions controlling immune responses. Non‐T regulatory cells include tolerogenic dendritic cells, plasmacytoid dendritic cells, mesenchymal stem cells, different types of stem cells, various types of alternatively activated macrophages and myeloid‐derived suppressor cells. Here, we review the mechanism of action of these non‐lymphoid regulatory cells as they relate to the induction or maintenance of tolerance in organ transplantation.     

How immunosuppressive therapy affects T cells from kidney transplanted patients of different age: the role of latent cytomegalovirus infection

The average age of patients receiving renal transplantation is increasing as programmes have been established which support the donation of organs from elderly donors to older recipients. Little is known about the effect of immunosuppressive therapy on the immune system of older patients. In this study, T cell function and the composition of the T cell repertoire were analysed in immunosuppressed renal transplant recipients of different age and cytomegalovirus (CMV) status in comparison to age-and CMV-matched controls. Independent of age and CMV status, the production of interleukin (IL)-2 and interferon (IFN)-γ by T cells was decreased in the patient groups and autologous serum from patients was capable of inhibiting the proliferation of CD3⁺ T cells. CXCR5 expression on T cells was increased in patients versus controls reflecting reduced endogenous IL-2 signalling under immunosuppressive therapy. In CMV-seronegative patients kidney transplantation and immunosuppressive therapy did not induce changes in the CD8⁺ T cell pool, but there was a moderate increase in CD4⁺CD28⁻ effector T cells when compared to age-matched controls. In contrast, latent CMV infection triggered a shift from early to late differentiated CD4⁺ and CD8⁺ T cells in patients and controls. This shift was most pronounced in elderly transplant patients under immunosuppressive therapy. In conclusion, our results demonstrate that immunosuppressive therapy following kidney transplantation is effective in patients older than 65 years. Latent CMV infection, however, accelerates age-related changes in the T cell repertoire in elderly people under immunosuppressive therapy. These patients should therefore be monitored with special care.     

Approaches and challenges in targeting memory T cells in transplant tolerance

Memory T cells are an important cell type in the immune system and are vital to protective immunity against invading pathogens. However, a significant fraction of memory T cells is found to be alloreactive in transplant models, i.e. they can readily attack and dismantle allografts in transplant models. As memory T cells are not as easily amenable as naive T cells, memory T cells constitute a potent barrier to the induction of transplant tolerance. The key issues concerning memory T cells in transplantation are related to the tolerability of alloreactive memory T cells and the effects of commonly used immunosuppressive drugs on the memory response in transplant recipients. The real challenge in the future is to selectively tolerize alloreactive memory T cells but spare those involved in protective immunity following organ transplantation. This review will discuss recent advances in our understating of memory T cells in transplant models, with specific emphasis on the problems and challenges in targeting memory T cells in the induction of transplant tolerance.     

Adaptive transfer of B10 cells: A novel therapy for chronic rejection after solid organ transplantation

Chronic rejection occurs between almost all MHC-mismatched donors and recipients after transplantation. Immunosuppressive agents have been administrated indiscriminately to manage potential rejection, but complications from lifelong immunosuppressive therapy threaten transplant recipients. Recent studies demonstrated that a number of regulatory B cells (B10 cells) negatively regulate T cell mediated immune responses without inducing systemic immune suppression. Therefore, we propose that adaptive transfer of B10 cells suppresses alloreactive CD8⁺ cytotoxic T cell activation induced by allogeneic solid organ transplantation, reduces T cell mediated rejection and prolongs allograft survival.     

Modulation of CD8 T-cell activation events by monocytic and granulocytic myeloid-derived suppressor cells

Myeloid-derived suppressor cells are immature myeloid cells, consisting of a monocytic and a granulocytic fraction, that are known to suppress anti-tumor immune responses. Important targets of the immunosuppressive capacity of MDSC are CD8⁺ T cells, which are crucial cytotoxic effector cells in immunotherapeutic settings. CD8⁺ T-cell activation and differentiation comprises a well-orchestrated series of events, starting from early TCR-mediated signaling and leading to cytokine secretion, the expression of activation markers, proliferation and the differentiation into several subsets of effector and memory cells. In this review, we summarize the available data on how the production of reactive oxygen species, nitric oxide, the arginase-mediated depletion of l-arginine and Cystine depletion by MDSCs interfere with the signaling molecules necessary for normal CTL differentiation and activation.     

Myeloid-Derived Suppressor Cells Protect Mouse Models from Autoimmune Arthritis via Controlling Inflammatory Response

Myeloid-derived suppressor cells (MDSCs) have been reported to participate in immune suppression and autoimmune disorders. However, its role in autoimmune arthritis remains to be determined. We explored whether adoptive transfer of MDSCs in vivo would block joint inflammation and histological damage using collagen-induced arthritis (CIA) and antigen-induced arthritis (AIA) models. CD11b⁺ Gr-1⁺ MDSCs were isolated from the single cells from the spleens of CIA mice on day 41 or AIA mice on day 35. MDSCs (2?×?10⁶) were then transferred to AIA and CIA mice via tail vein before arthritis establishment at indicated time points. Phosphate buffered saline (PBS) was injected as control. Arthritis was evaluated by severity score and histology. The levels of TNF-α, IL-6, IL-17 and IL-10 in the serum and joints were detected by enzyme-linked immunosorbent assay (ELISA). The number of Th17 cells and macrophages in draining lymph nodes and joint tissues was assessed by flow cytometric analysis. Adoptive transfer of MDSCs significantly reduced the clinical score of arthritis, alleviated joint inflammation and histological damage both in AIA and CIA models compared with PBS-treated control groups. The levels of TNF-α, IL-6, IL-17, and IL-10 in the serum and joints were down-regulated by transfer of MDSCs. In addition, adoptive transfer of MDSCs significantly reduced the number of Th17 cells and macrophages in draining lymph nodes and joint tissues. Altogether, we demonstrate that adoptive transfer of MDSCs prevented autoimmune arthritis in mouse models of RA through inhibiting Th17 cells and macrophages. These new findings provide insights into the inhibitory functions of MDSCs and MDSCs may be used as a cell-based biotherapy in RA.     

Transplantation tolerance induced by antigen pretreatment and depleting anti-CD4 antibody depends on CD4+ T cell regulation during the induction phase of the response

Adult mice pretreated with donor-specific transfusion and depleting anti-CD4 antibody 28 days before transplant accept fully allogeneic heart grafts and become specifically tolerant without further treatment. The induction of tolerance in this model is not simply a function of CD4⁺ T cell ablation, but appears to depend on residual CD4⁺ T cells which escape depletion and engage donor alloantigen during a transient period of antibody blockade. To test the hypothesis that these CD4⁺ T cells might be responsible for regulating immune responses toward the graft, mice were reconstituted with naive recipient leukocytes at various times after pretreatment. Reconstitution either shortly after pretreatment or shortly after transplant had little effect on graft survival. However, when pretreated mice were given an additional dose of depleting anti-CD4 antibody at the time of transplant to target putative regulatory cells, naive leukocytes were able to cause acute graft rejection. These data suggest that in clinical transplantation specific T cell regulation might develop following pretreatment with antigen and non-depleting anti-CD4 antibodies. Such an approach could provide donor-specific unresponsiveness prior to transplant without the risks associated with sustained CD4⁺ T cell depletion.     

Rapamycin-based graft-versus-host disease prophylaxis increases the immunosuppressivity of myeloid-derived suppressor cells without affecting T cells and anti-tumor cytotoxicity

The immunosuppressant rapamycin (RAPA) inhibits mammalian target of rapamycin (mTOR) functions and is applied after allogeneic bone marrow transplantation (BMT) to attenuate the development of graft-versus-host disease (GVHD), although the cellular targets of RAPA treatment are not well defined. Allogeneic T cells are the main drivers of GVHD, while immunoregulatory myeloid-derived suppressor cells (MDSCs) were recently identified as potent disease inhibitors. In this study, we analyzed whether RAPA prevents the deleterious effects of allogeneic T cells or supports the immunosuppressive functions of MDSCs in a BMT model with major histocompatibility complex (MHC) classes I and II disparities. RAPA treatment efficiently attenuated clinical and histological GVHD and strongly decreased disease-induced mortality. Although splenocyte numbers increased during RAPA treatment, the ratio of effector T cells to MDSCs was unaltered. However, RAPA treatment induced massive changes in the genomic landscape of MDSCs preferentially up-regulating genes responsible for uptake or signal transduction of lipopeptides and lipoproteins. Most importantly, MDSCs from RAPA-treated mice exhibited increased immunosuppressive potential, which was primarily inducible nitric oxide synthase (iNOS)-dependent. Surprisingly, RAPA treatment had no impact on the genomic landscape of T cells, which was reflected by unchanged expression of activation and exhaustion markers and cytokine profiles in T cells from RAPA-treated and untreated mice. Similarly, T cell cytotoxicity and the graft-versus-tumor effect were maintained as co-transplanted tumor cells were efficiently eradicated, indicating that the immunosuppressant RAPA might be an attractive approach to strengthen the immunosuppressive function of MDSCs without affecting T cell immunity.     

Interferon-Gamma Producing Regulatory T Cells as a Diagnostic and Therapeutic Tool in Organ Transplantation

There is increasing evidence that IFNg plays a major role in both induction of Tregs as well as immunosuppression mediated by IFNg-producing Tregs. The present review focuses on a small subset of iTregs that produces IFNg, comprises only 0.04% of all CD4⁺ T lymphocytes in the blood of healthy individuals, and increases strongly during an immune response. IFNg⁺ Tregs are induced by IFNg and IL12, making them sensors for inflammatory cytokines. They develop rapidly during inflammation and represent the first line of Tregs that suppress initial immune responses. The pool of IFNg⁺ Tregs consists of activated stable immunosuppressive thymus-derived nTregs as well as peripherally proliferating iTregs with in part only transient immunosuppressive function, which limits their diagnostic and therapeutic usefulness in organ transplantation. Apparently, a part of IFNg⁺ Tregs dies during the immune response, whereas others, after efficient immunosuppression with resolution of the immune response, differentiate toward Th1 lymphocytes. Goals of further research are the development of appropriate diagnostic tests for rapid and exact determinination of immunosuppressive IFNg⁺ iTregs, as well as the induction and propagation of stable immunosuppressive IFNg⁺ Tregs that establish and maintain good long-term graft function in transplant recipients.