C-C Chemokine Receptor Type 2-Dependent Migration of Myeloid-Derived Suppressor Cells in Protection of Islet Transplants

Cannabidiol alleviates suture-induced corneal pathological angiogenesis and inflammation by inducing myeloid-derived suppressor cells

BACKGROUND

Currently, no perfect treatment for neovascularization and lymphangiogenesis exist, and each treatment method has its complications and side effects. This study aimed to investigate the anti-angiogenic and anti-inflammatory effects of cannabidiol and its mechanism of action.

METHOD

An in vivo corneal neovascularization (CNV) model was established using the suture method to investigate the inhibitory effects of CBD on suture-induced corneal inflammation, pathological blood vessel formation, and lymphangiogenesis. Additionally, the impact of CBD on immune cells was studied. In vitro methodologies, including cell sorting and co-culture, were employed to elucidate its mechanism of action.

RESULTS

Compared with the CNV group, CBD can inhibit CNV, lymphangiogenesis, and inflammation induced via the suture method. In addition, CBD specifically induced CD45+CD11b+Gr-1+ cell upregulation, which significantly inhibited the proliferation of CD4+ T lymphocytes in vitro and exhibited a CD31+ phenotype, proving that they were myeloid-derived suppressor cells (MDSCs). We administered anti-Gr-1 to mice to eliminate MDSCs in vivo and found that anti-Gr-1 partially reversed the anti-inflammatory and angiogenic effects of CBD. Furthermore, we found that compared with MDSCs in the normal group, CBD-induced MDSCs overexpress peroxisome proliferator-activated receptor-gamma (PPAR-γ). Administering PPAR-γ inhibitor in mice almost reversed the induction of MDSCs by CBD, demonstrating the role of PPAR-γ in the function of CBD.

CONCLUSION

This study indicates that CBD may induce MDSCs upregulation by activating the nuclear receptor PPAR-γ, exerting anti-inflammatory, antiangiogenic, and lymphangiogenic effects, and revealing potential therapeutic targets for corneal neovascularization and lymphangiogenesis.

Rapamycin antagonizes angiogenesis and lymphangiogenesis through myeloid-derived suppressor cells in corneal transplantation

Rapamycin is an immunosuppressive drug that is widely used in the postsurgery management of transplantation. To date, the mechanism by which rapamycin reduces posttransplant neovascularization has not been fully understood. Given the original avascularity and immune privilege of the cornea, corneal transplantation is considered as an ideal model to investigate neovascularization and its effects on allograft rejection. Previously, we found that myeloid-derived suppressor cells (MDSC) prolong corneal allograft survival through suppression of angiogenesis and lymphangiogenesis. Here, we show that depletion of MDSC abolished rapamycin-mediated suppression of neovascularization and elongation of corneal allograft survival. RNA-sequencing analysis revealed that rapamycin dramatically enhanced the expression of arginase 1 (Arg1). Furthermore, an Arg1 inhibitor also completely abolished the rapamycin-mediated beneficial effects after corneal transplantation. Taken together, these findings indicate that MDSC and elevated Arg1 activity are essential for the immunosuppressive and antiangiogenic functions of rapamycin.

Here, There, and Everywhere: Myeloid-Derived Suppressor Cells in Immunology

Myeloid-derived suppressor cells (MDSCs) were initially identified in humans and mice with cancer where they profoundly suppress T cell- and NK cell-mediated antitumor immunity. Inflammation is a central feature of many pathologies and normal physiological conditions and is the dominant driving force for the accumulation and function of MDSCs. Therefore, MDSCs are present in conditions where inflammation is present. Although MDSCs are detrimental in cancer and conditions where cellular immunity is desirable, they are beneficial in settings where cellular immunity is hyperactive. Because MDSCs can be generated ex vivo, they are being exploited as therapeutic agents to reduce damaging cellular immunity. In this review, we discuss the detrimental and beneficial roles of MDSCs in disease settings such as bacterial, viral, and parasitic infections, sepsis, obesity, trauma, stress, autoimmunity, transplantation and graft-versus-host disease, and normal physiological settings, including pregnancy and neonates as well as aging. The impact of MDSCs on vaccination is also discussed.

Leverage biomaterials to modulate immunity for type 1 diabetes

The pathogeny of type 1 diabetes (T1D) is mainly provoked by the β-cell loss due to the autoimmune attack. Critically, autoreactive T cells firsthand attack β-cell in islet, that results in the deficiency of insulin in bloodstream and ultimately leads to hyperglycemia. Hence, modulating immunity to conserve residual β-cell is a desirable way to treat new-onset T1D. However, systemic immunosuppression makes patients at risk of organ damage, infection, even cancers. Biomaterials can be leveraged to achieve targeted immunomodulation, which can reduce the toxic side effects of immunosuppressants. In this review, we discuss the recent advances in harness of biomaterials to immunomodulate immunity for T1D. We investigate nanotechnology in targeting delivery of immunosuppressant, biological macromolecule for β-cell specific autoreactive T cell regulation. We also explore the biomaterials for developing vaccines and facilitate immunosuppressive cells to restore immune tolerance in pancreas.

Emerging local immunomodulatory strategies to circumvent systemic immunosuppression in cell transplantation

INTRODUCTION

Cell transplantation is a promising curative therapeutic strategy whereby impaired organ functions can be restored without the need for whole organ transplantation. A key challenge in allotransplantation is the requirement for life-long systemic immunosuppression to prevent rejection, which is associated with serious adverse effects such as increased risk of opportunistic infections and the development of neoplasms. This challenge underscores the urgent need for novel strategies to prevent graft rejection while abrogating toxicity-associated adverse events.

AREAS COVERED

We review recent advances in immunoengineering strategies for localized immunomodulation that aim to support allograft function and provide immune tolerance in a safe and effective manner.

EXPERT OPINION

Immunoengineering strategies are tailored approaches for achieving immunomodulation of the transplant microenvironment. Biomaterials can be adapted for localized and controlled release of immunomodulatory agents, decreasing the effective dose threshold and frequency of administration. The future of transplant rejection management lies in the shift from systemic to local immunomodulation with suppression of effector and activation of regulatory T cells, to promote immune tolerance.

Infection-Derived Monocytic MDSCs Require TGF-β to Suppress Filarial-Specific IFN-γ But Not IL-13 Release by Filarial-Specific CD4+ T Cells In Vitro

Lymphatic filariasis (LF) remains a major health problem with severe economic repercussions in endemic communities of Sub-saharan Africa, South-East Asia and South America. The rodent-specific nematode Litomosoides sigmodontis (Ls) is used to study the immunomodulatory potential of filariae and research has elucidated pathways involving regulatory T cells (Tregs), IL-10 producing cells and alternatively activated macrophages (AAMs) and that CD4+ T cells play a paramount role during infection. Myeloid-derived suppressor cells (MDSCs) have been identified and characterised in man in cancer and other pathologies. The hallmark of MDSC populations is the suppression of T and B cell responses using various mechanisms, which are mostly specific to the pathology or setting. However, until now, it remains unclear whether they play a role in filarial-specific responses. We report here that monocytic MDSCs (Mo-MDSCs, CD11b+Ly6C+Ly6G-) and polymorphonuclear MDSCs (PMN-MDSCs, CD11b+Ly6Cint/loLy6G+) expanded in the thoracic cavity (TC, the site of infection) and correlated positively with filarial life-stages in Ls-infected BALB/c mice. In vitro, only infection-derived Mo-MDSCs showed a suppressive nature by preventing IL-13 and IFN-γ secretion from filarial-specific CD4+ T cells upon co-culture with soluble worm extract. This suppression was not mediated by IL-10, IL-6 or TNF-α, and did not require cell-contact, nitric oxide (NO), IL-4/IL-5 signalling pathways or CCR2. Interestingly, neutralizing TGF-β significantly rescued IFN-γ but not IL-13 production by filarial-specific CD4+ T cells. In comparison to naive cells, PCR array data showed an overall down-regulation of inflammatory pathways in both infection-derived Mo-MDSCs and PMN-MDSCs. In conclusion, these primary data sets show activity and expansion of MDSCs during Ls infection adding this regulatory cell type to the complex milieu of host responses during chronic helminth infections.

Specific Blood Cells Derived from Pluripotent Stem Cells: An Emerging Field with Great Potential in Clinical Cell Therapy

Widely known for self-renewal and multilineage differentiation, stem cells can be differentiated into all specialized tissues and cells in the body. In the past few years, a number of researchers have focused on deriving hematopoietic stem cells (HSCs) from pluripotent stem cells (PSCs) as alternative sources for clinic. Existing findings demonstrated that it is feasible to obtain HSCs and certain mature blood lineages from PSCs, except for several issues to be addressed. This short review outlines the technologies used for hematopoietic differentiation in recent years. In addition, the therapeutic value of PSCs as a potential source of various blood cells is also discussed as well as its challenges and directions in future clinical applications.

Analysis of therapeutic potential of monocytic myeloid-derived suppressor cells in cardiac allotransplantation

BACKGROUND

Myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Tregs) are attractive immune cells to induce immune tolerance. To explore a strategy for improving the efficacy of MDSC therapies, we examined the impact of adoptive transfer of several types of MDSCs on graft rejection in a murine heart transplantation model.

METHODS

We analyzed the effects of induced syngeneic and allogeneic bone marrow-derived MDSCs (BM-MDSCs) on graft survival and suppressive capacity. We also compared the ability of syngeneic monocytic MDSCs (Mo-MDSCs) and polymorphonuclear MDSCs (PMN-MDSCs) to inhibit graft rejection and investigated the suppression mechanisms.

RESULTS

Both syngeneic and allogeneic donor- or allogeneic third-party-derived BM-MDSCs prolonged graft survival, although syngeneic BM-MDSCs inhibited anti-donor immune responses most effectively in vitro. Syngeneic Mo-MDSCs, rather than PMN-MDSCs, were responsible for immune suppression through downregulating inducible nitric oxide synthase (iNOS) and expanded naturally occurring thymic originated Treg (nTreg) in vitro. Adoptive transfer of Mo-MDSCs, but not PMN-MDSCs, prolonged graft survival and increased Treg infiltration into the graft heart.

CONCLUSION

Recipient-derived Mo-MDSCs are most effective in prolonging graft survival via inhibiting T cell response and nTreg infiltration.

Adoptive Transfer of Regulatory Immune Cells in Organ Transplantation

Chronic graft rejection remains a significant barrier to solid organ transplantation as a treatment for end-organ failure. Patients receiving organ transplants typically require systemic immunosuppression in the form of pharmacological immunosuppressants for the duration of their lives, leaving these patients vulnerable to opportunistic infections, malignancies, and other use-restricting side-effects. In recent years, a substantial amount of research has focused on the use of cell-based therapies for the induction of graft tolerance. Inducing or adoptively transferring regulatory cell types, including regulatory T cells, myeloid-derived suppressor cells, and IL-10 secreting B cells, has the potential to produce graft-specific tolerance in transplant recipients. Significant progress has been made in the optimization of these cell-based therapeutic strategies as our understanding of their underlying mechanisms increases and new immunoengineering technologies become more widely available. Still, many questions remain to be answered regarding optimal cell types to use, appropriate dosage and timing, and adjuvant therapies. In this review, we summarize what is known about the cellular mechanisms that underly the current cell-based therapies being developed for the prevention of allograft rejection, the different strategies being explored to optimize these therapies, and all of the completed and ongoing clinical trials involving these therapies.

Myeloid-derived suppressor cells as cellular immunotherapy in transplantation and autoimmune diseases

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells, which have been characterized for their immunosuppressive capacity through multiple mechanisms. These cells have been extensively studied in the field of tumor immunity. Emerging evidence has highlighted its essential role in maintaining immune tolerance in transplantation and autoimmunity. Because of their robust immune inhibitory activities, there has been growing interest in MDSC-based cellular therapy. Various pre-clinical studies have demonstrated that the adoptive transfer of MDCS represented a promising therapeutic strategy for immune-related disorders. In this review, we summarize relevant studies of MDSC-based cell therapy in transplantation and autoimmune diseases and discuss the challenges and future directions for clinical application of MDSC-based cell therapy.

Myeloid-derived suppressor cells improve corneal graft survival through suppressing angiogenesis and lymphangiogenesis

Myeloid-derived suppressor cells (MDSC) are one of the major negative regulators of immune responses during many pathological conditions such as cancer and transplantation. Emerging evidence indicates that MDSC also contribute to tumor progression through their pro-angiogenic activity in addition to immunosuppressive function. However, virtually nothing is known about the role of MDSC in the regulation of neovascularization after transplantation. Here we showed that antibody-mediated depletion of MDSC in mice led to robust growth of blood and lymphatic neovessels and rapid allograft rejection after corneal penetrating keratoplasty. In contrast, adoptive transfer of ex vivo generated MDSC from cytokine-treated bone marrow cells (evMDSC) suppressed neovascularization and prolonged corneal allograft survival in an inducible nitric oxide synthase (iNOS)-dependent manner. Mechanistically, compared to naïve MDSC control, evMDSC have increased expression of an anti-angiogenic factor thrombospondin 1 (Tsp-1) and decreased expression of two critical pro-angiogenic factors, vascular endothelial growth factor A (VEGF-A), and VEGF-C. These findings demonstrate MDSC as a critical anti-angiogenic regulator during transplantation. Our study also indicates that evMDSC are a valuable candidate agent for development of novel cell therapy to improve allograft survival after transplantation.

Recent advances in myeloid-derived suppressor cell biology

In recent years, studying the role of myeloid-derived suppressor cells (MDSCs) in many pathological inflammatory conditions has become a very active research area. Although the role of MDSCs in cancer is relatively well established, their role in non-cancerous pathological conditions remains in its infancy resulting in much confusion. Our objectives in this review are to address some recent advances in MDSC research in order to minimize such confusion and to provide an insight into their function in the context of other diseases. The following topics will be specifically focused upon: (1) definition and characterization of MDSCs; (2) whether all MDSC populations consist of immature cells; (3) technical issues in MDSC isolation, estimation and characterization; (4) the origin of MDSCs and their anatomical distribution in health and disease; (5) mediators of MDSC expansion and accumulation; (6) factors that determine the expansion of one MDSC population over the other; (7) the Yin and Yang roles of MDSCs. Moreover, the functions of MDSCs will be addressed throughout the text.

Myeloid-derived suppressor cells expand after transplantation and their augmentation increases graft survival

Myeloid-derived suppressor cells (MDSCs) expand in an inflammatory microenvironment such as cancer and autoimmunity. To study if transplantation induces MDSCs and these cells regulate allograft survival, C57BL/6 donor hearts were transplanted into BALB/c recipients and endogenous MDSCs were characterized. The effects of adoptive transfer of transplant (tx), tumor (tm), and granulocyte-colony stimulating factor (g-csf)-expanded MDSCs or depletion of MDSC were assessed. MDSCs expanded after transplantation (1.7-4.6-fold) in the absence of immunosuppression, homed to allografts, and suppressed proliferation of CD4 T cells in vitro. Tx-MDSCs differed phenotypically from tm-MDSCs and g-csf-MDSCs. Among various surface markers, Rae-1 expression was notably low and TGF-β receptor II was high in tx-MDSCs when compared to tm-MDSCs and g-csf-MDSCs. Adoptive transfer of these three MDSCs led to differential graft survival: control (6 days), tx-MDSCs (7.5 days), tm-MDSCs (9.5 days), and g-csf-MDSCs (19.5 days). In combination with anti-CD154 mAb, MDSCs synergistically extended graft survival from 40 days (anti-CD154 alone) to 86 days with tm-MDSCs and 132 days with g-csf-MDSCs. Early MDSC depletion (day 0 or 20), however, abrogated graft survival, but late depletion (day 25) did not. In conclusion, MDSCs expanded following transplantation, migrated to cardiac allografts, prolonged graft survival, and were synergistic with anti-CD154 mAb.

Myeloid-derived suppressor cells in transplantation tolerance induction

Myeloid-derived suppressor cells (MDSCs) are a group of heterogeneous cells derived from bone marrow. These cells are developed from immature myeloid cells and have strong negative immunomodulatory effects. In the context of pathology (such as tumor, autoimmune disease, trauma, and burns), MDSCs accumulate around tumor and inflammatory tissues, where their main role is to inhibit the function of effector T cells and promote the recruitment of regulatory T cells. MDSCs can be used in organ transplantation to regulate the immune responses that participate in rejection of the transplanted organ. This effect is achieved by increasing the production of MDSCs in vivo or transfusion of MDSCs induced in vitro to establish immune tolerance and prolong the survival of the graft. In this review, we discuss the efficacy of MDSCs in a variety of transplantation studies as well as the induction of immune tolerance to prevent transplant rejection through the use of common clinical immunosuppressants combined with MDSCs.

Impact of infection on transplantation tolerance

Allograft tolerance is the ultimate goal of organ transplantation. Current strategies for tolerance induction mainly focus on inhibiting alloreactive T cells while promoting regulatory immune cells. Pathogenic infections may have direct impact on both effector and regulatory cell populations, therefore can alter host susceptibility to transplantation tolerance induction as well as impair the quality and stability of tolerance once induced. In this review, we will discuss existing data demonstrating the effect of infections on transplantation tolerance, with particular emphasis on the role of the stage of infection (acute, chronic, or latent) and the stage of tolerance (induction or maintenance) in this infection-tolerance interaction. While the deleterious effect of acute infection on tolerance is mainly driven by proinflammatory cytokines induced shortly after the infection, chronic infection may generate exhausted T cells that could in fact facilitate transplantation tolerance. In addition to pathogenic infections, commensal intestinal microbiota also has numerous significant immunomodulatory effects that can shape the host alloimmunity following transplantation. A comprehensive understanding of these mechanisms is crucial for the development of therapeutic strategies for robustly inducing and stably maintaining transplantation tolerance while preserving host anti-pathogen immunity in clinically relevant scenarios.

Preliminary assessment of the feasibility of autologous myeloid-derived suppressor cell infusion in non-human primate kidney transplantation

Myeloid-derived suppressor cells (MDSC) are a heterogenous population of immunosuppressive myeloid cells now considered important immune regulatory cells in diverse clinical conditions, including cancer, chronic inflammatory disorders and transplantation. In rodents, MDSC administration can inhibit graft-versus-host disease lethality and enhance organ or pancreatic islet allograft survival. There is also evidence, however, that under systemic inflammatory conditions, adoptively-transferred MDSC can rapidly lose their suppressive function. To our knowledge, there are no reports of autologous MDSC administration to either human or clinically-relevant non-human primate (NHP) transplant recipients. Monocytic (m) MDSC have been shown to be more potent suppressors of T cell responses than other subsets of MDSC. Following their characterization in rhesus macaques, we have conducted a preliminary analysis of the feasibility and preliminary efficacy of purified mMDSC infusion into MHC-mismatched rhesus kidney allograft recipients. The graft recipients were treated with rapamycin and the high affinity variant of the T cell co-stimulation blocking agent cytotoxic T lymphocyte antigen 4 Ig (Belatacept) that targets the B7-CD28 pathway. Graft survival and histology were not affected by infusions of autologous, leukapheresis product-derived mMDSC on days 7 and 14 post-transplant (cumulative totals of 3.19 and 1.98 × 106 cells/kg in n = 2 recipients) compared with control monkeys that did not receive MDSC (n = 2). Sequential analyses of effector T cell populations revealed no differences between the groups. While these initial findings do not provide evidence of efficacy under the conditions adopted, further studies in NHP, designed to ascertain the appropriate mMDSC source and dose, timing and anti-inflammatory/immunosuppressive agent support are likely to prove instructive regarding the therapeutic potential of MDSC in organ transplantation.

Tolerogenic Role of Myeloid Suppressor Cells in Organ Transplantation

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature cells of myeloid origin with a specific immune inhibitory function that negatively regulates the adaptive immune response. Since MDSC participate in the promotion of tolerance in the context of organ transplantation, therapeutic strategies that regulate the induction and development of MDSC have been the center of scientist attention. Here we review literature regarding induction of MDSC with demonstrated suppressive function among different types of allografts and their mechanism of action. While manipulation of MDSC represents a potential therapeutic approach for the promotion of donor specific tolerance in solid organ transplantation, further characterization of their specific phenotype, which distinguishes MDSC from non-suppressive myeloid cells, and detailed evaluation of the inhibitory mechanism that determines their suppressive function, is necessary for the realistic application of MDSC as biomarkers in health and disease and their potential use as immune cell therapy in organ transplantation.

Roles of Myeloid-Derived Suppressor Cell Subpopulations in Autoimmune Arthritis

Emerging evidence suggests the promise of the use of myeloid-derived suppressor cells (MDSCs) in inflammatory disorders based on their unique immune-intervention properties. However, the roles of MDSCs in autoimmune arthritis are not completely understood. Indeed, their immunosuppressive functions in arthritic conditions remain controversial, with heterogeneity among MDSCs and differential effects among subpopulations receiving much attention. As a result, it is necessary to determine the roles of MDSC subpopulations in autoimmune arthritis to clarify their diagnostic and therapeutic potential. Interestingly, in the inflammation niche of autoimmune arthritis, each MDSC subpopulation can exhibit both alternatives of a given characteristic. Moreover, polymorphonuclear MDSCs (PMN-MDSCs) are likely to be more suppressive and stable compared with monocytic MDSCs (MO-MDSCs). Although various important cytokines associated with the differentiation of MDSCs or MDSC subpopulations from immature myeloid precursors, such as granulocyte colony-stimulating factor (G-CSF), have been largely applied in external inductive systems, their roles are not entirely clear. Moreover, MDSC-based clinical treatments in rheumatoid arthritis (RA) continue to represent a significant challenge, as also reported for other autoimmune diseases. In this review, we describe the effects and actions of MDSC subpopulations on the development of autoimmune arthritis and analyze several types of MDSC-based therapeutic strategies to provide comprehensive information regarding immune networks and a foundation for more effective protocols for autoimmune arthritis.

Myeloid-Derived Suppressor Cells and Their Potential Application in Transplantation

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immunosuppressive cells of the myeloid lineage upregulated by mediators of inflammation, such as IL-2, granulocyte colony-stimulating factor, and S100A8/A9. These cells have been studied extensively by tumor biologists. Because of their robust immunosuppressive potential, MDSCs have stirred recent interest among transplant immunologists as well. MDSCs inhibit T-cell responses through, among other mechanisms, the activity of arginase-1 and inducible nitric oxide synthase, and the expansion of T regulatory cells. In the context of transplantation, MDSCs have been studied in several animal models, and to a lesser degree in humans. Here, we will review the immunosuppressive qualities of this important cell type and discuss the relevant studies of MDSCs in transplantation. It may be possible to exploit the immunosuppressive capacity of MDSCs for the benefit of transplant patients.

Rapamycin Nano-Micelle Ophthalmic Solution Reduces Corneal Allograft Rejection by Potentiating Myeloid-Derived Suppressor Cells' Function

Allograft rejection is the major cause of corneal allograft failure. Rapamycin (RAPA) has been reported as an effective and novel immunosuppressive agent for patients undergoing corneal transplantation. However, its high water insolubility and low bioavailability have strongly constrained its clinical application. In this study, we successfully developed a RAPA nano-micelle ophthalmic solution and found that corneal allograft survival in recipients treated with RAPA nano-micelle ophthalmic solution was significantly prolonged for more than 2 months, with less inflammatory infiltration, decreased production of pro-inflammatory factors, and elevated recruitment of myeloid-derived suppressor cells (MDSCs). MDSCs from mice treated with RAPA nano-micelle ophthalmic solution could significantly inhibit the proliferation of CD4⁺T cells through increased expressions of inducible nitric oxidase (iNOS) and arginase-1 (Arg-1). The activity blockade of Arg-1 and iNOS pharmacologically reversed their immunosuppressive ability. Moreover, the effects of RAPA were antagonized by the administration of anti-Gr-1 antibody or by inhibiting the activity of iNOS pharmacologically. In addition, RAPA nano-micelle also effectively alleviated allograft rejection in high-risk rabbit penetrating keratoplasty (PKP) models with corneal vascularization. Collectively, our results demonstrate that RAPA nano-micelle ophthalmic solution could improve the immunosuppressive activity of MDSCs through elevated expression of Arg-1 and iNOS, which highlights the possible therapeutic applications of RAPA against corneal allograft rejection.

Myeloid-derived suppressor cells increase and inhibit donor-reactive T cell responses to graft intestinal epithelium in intestinal transplant patients

Recent advances in immunosuppressive regimens have decreased acute cellular rejection (ACR) rates and improved intestinal and multivisceral transplant (ITx) recipient survival. We investigated the role of myeloid-derived suppressor cells (MDSCs) in ITx. We identified MDSCs as CD33⁺ CD11b⁺ lineage(CD3/CD56/CD19)^- HLA-DR^-/low cells with 3 subsets, CD14^- CD15^- (e-MDSCs), CD14⁺ CD15^- (M-MDSCs), and CD14^- CD15⁺ (PMN-MDSCs), in peripheral blood mononuclear cells (PBMCs) and mononuclear cells in the grafted intestinal mucosa. Total MDSC numbers increased in PBMCs after ITx; among MDSC subsets, M-MDSC numbers were maintained at a high level after 2 months post ITx. The MDSC numbers decreased in ITx recipients with ACR. MDSC numbers were positively correlated with serum interleukin (IL)-6 levels and the glucocorticoid administration index. IL-6 and methylprednisolone enhanced the differentiation of bone marrow cells to MDSCs in vitro. M-MDSCs and e-MDSCs expressed CCR1, -2, and -3; e-MDSCs and PMN-MDSCs expressed CXCR2; and intestinal grafts expressed the corresponding chemokine ligands after ITx. Of note, the percentage of MDSCs among intestinal mucosal CD45⁺ cells increased after ITx. A novel in vitro assay demonstrated that MDSCs suppressed donor-reactive T cell-mediated destruction of donor intestinal epithelial organoids. Taken together, our results suggest that MDSCs accumulate in the recipient PBMCs and the grafted intestinal mucosa in ITx, and may regulate ACR.