In vitro-expanded human CD4(+)CD25(+) T-regulatory cells can markedly inhibit allogeneic dendritic cell-stimulated MLR cultures

The potential therapeutic role of IL-35 in pathophysiological processes in type 1 diabetes mellitus

A chronic autoimmune condition known as type 1 diabetes mellitus (T1DM) has characteristics marked by a gradual immune-mediated deterioration of the β-cells that produce insulin and causes overt hyperglycemia. it affects more than 1.2 million kids and teenagers (0-19 years old). In both, the initiation and elimination phases of T1DM, cytokine-mediated immunity is crucial in controlling inflammation. T regulatory (Treg) cells, a crucial anti-inflammatory CD4+ T cell subset, secretes interleukin-35 (IL-35). The IL-35 has immunomodulatory properties by inhibiting pro-inflammatory cells and cytokines, increasing the secretion of interleukin-10 (IL-10) as well as transforming Growth Factor- β (TGF-β), along with stimulating the Treg and B regulatory (Breg) cells. IL-35, it is a possible target for cutting-edge therapies for cancers, inflammatory, infectious, and autoimmune diseases, including TIDM. Unanswered questions surround IL-35's function in T1DM. Increasing data suggests Treg cells play a crucial role in avoiding autoimmune T1DM. Throughout this review, we will explain the biological impacts of IL-35 and highlight the most recently progresses in the roles of IL-35 in treatment of T1DM; the knowledge gathered from these findings might lead to the development of new T1DM treatments. This review demonstrates the potential of IL-35 as an effective autoimmune diabetes inhibitor and points to its potential therapeutic value in T1DM clinical trials.

Therapy with regulatory T-cell infusion in autoimmune diseases and organ transplantation: A review of the strengths and limitations

In the last decade, cell therapies have revolutionized the treatment of some diseases, earning the definition of being the "third pillar" of therapeutics. In particular, the infusion of regulatory T cells (Tregs) is explored for the prevention and control of autoimmune reactions and acute/chronic allograft rejection. Such an approach represents a promising new treatment for autoimmune diseases to recover an immunotolerance against autoantigens, and to prevent an immune response to alloantigens. The efficacy of the in vitro expanded polyclonal and antigen-specific Treg infusion in the treatment of a large number of autoimmune diseases has been extensively demonstrated in mouse models. Similarly, experimental work documented the efficacy of Treg infusions to prevent acute and chronic allograft rejections. The Treg therapy has shown encouraging results in the control of type 1 diabetes (T1D) as well as Crohn's disease, systemic lupus erythematosus, autoimmune hepatitis and delaying graft rejection in clinical trials. However, the best method for Treg expansion and the advantages and pitfalls with the different types of Tregs are not fully understood in terms of how these therapeutic treatments can be applied in the clinical setting. This review provides an up-to-date overview of Treg infusion-based treatments in autoimmune diseases and allograft transplantation, the current technical challenges, and the highlights and disadvantages of this therapeutic approaches."

Alpha-Synuclein-Specific Regulatory T Cells Ameliorate Parkinson's Disease Progression in Mice

Parkinson's disease (PD) is a long-term neurodegenerative disease characterized by dopaminergic neuronal loss and the aggregation of alpha-synuclein (α-syn) in the brain. Cell therapy using regulatory T cells (Tregs) has therapeutic potential on PD progression in a mouse model; however, several challenges were associated with its applications. Here, we propose a strategy for α-syn specific Treg expansion (α-syn Treg). We presented α-syn to T cells via dendritic cells. This method increased the mobility of Tregs towards the site of abundant α-syn in vitro (p < 0.01; α-syn Tregs versus polyclonal Tregs (poly Tregs)) and in vivo. Consequently, α-syn Tregs showed noteworthy neuroprotective effects against motor function deficits (p < 0.05, p < 0.01; α-syn Tregs versus poly Tregs), dopaminergic neuronal loss (p < 0.001; α-syn Tregs versus poly Tregs), and α-syn accumulation (p < 0.05; α-syn Tregs versus poly Tregs) in MPTP-induced PD mice. Furthermore, the adoptive transfer of α-syn Tregs exerted immunosuppressive effects on activated microglia, especially pro-inflammatory microglia, in PD mice. Our findings suggest that α-syn presentation may provide a significant improvement in neuroprotective activities of Tregs and suggest the effective clinical application of Treg therapy in PD.

Umbilical cord blood and peripheral blood-derived regulatory T cells therapy: Progress in type 1 diabetes

Regulatory T cells (Tregs) are key regulators for the inflammatory response and play a role in maintaining the immune tolerance. Type 1 diabetes (T1D) is a relatively common autoimmune disease that results from the loss of immune tolerance to β-cell-associated antigens. Preclinical models have demonstrated the safety and efficacy of Tregs given in transplant rejection and autoimmune diseases such as T1D. Adoptive transfer of Tregs has been utilized in clinical trials for over a decade. However, the achievement of the adoptive transfer of Tregs therapy in clinical application remains challenging. In this review, we highlight the characterization of Tregs and compare the differences between umbilical cord blood and adult peripheral blood-derived Tregs. Additionally, we summarize conditional modifications in the expansion of Tregs in clinical trials, especially for the treatment of T1D. Finally, we discuss the existing technical challenges for Tregs in clinical trials for the treatment of T1D.

In vitro treatment of murine splenocytes with extracellular vesicles derived from mesenchymal stem cells altered the mRNA levels of the master regulator genes of T helper cell subsets

INTRODUCTION

The purpose of the current study was to evaluate the effect of mesenchymal stem cells-derived extracellular vesicles (MSC-EVs) on the production of cytokines and expression of genes, which are corresponded to the subsets of T helper cells.

MATERIALS AND METHODS

The supernatant of the second passage of MSCs that had been isolated from C57BL/6 mice abdominal adipose tissue was used to collect the MSC-EV. Splenocytes of healthy mice were activated using anti-CD3 and anti-CD28 antibodies and simultaneously were treated using the MSC-EVs. The proliferation rate of lymphocytes and the frequency of regulatory T cells were measured using flow cytometry. In addition, the expressions of T helper cell subset-specific transcription factors were evaluated using a real-time PCR assay. To appraise the effects of MSC-EV on splenocytes, the levels of IFN-γ, IL-17A, IL-10, and TGF-β were measured using ELISA.

RESULTS

The results showed that the treatment of the CD3/CD28-activated splenocytes with MSC-EV did not statistically change the proliferation of CD3⁺ splenocytes. However, after the treatment, the mRNA levels of Foxp3 and Elf4 as well as the frequency of regulatory T cells was significantly higher when compared to the control group. The expression levels of Gata3, Rorc, and Tbx21 were down-regulated while, the corresponding cytokines levels did not alter.

CONCLUSION

The results revealed that the in vitro treatment of MSC-EV was associated with the increase in the frequency of CD4⁺CD25⁺FOXP3⁺ T cells and upregulation of Foxp3 mRNA level.

CARs: a new approach for the treatment of autoimmune diseases

The development of chimeric antigen receptor (CAR)-based therapeutic interventions represented a breakthrough in cancer treatment. Following the success of the CAR-T-cell strategy, this novel therapeutic approach has been applied to other diseases, including autoimmune diseases. Using CAR-T cells to deplete pathological immune cells (i.e., B cells, autoreactive B or T cells, and accessory antigen-presenting cells (APCs)) has resulted in favorable outcomes in diseases characterized by excessive autoantibody levels or hyperactive lymphocyte cell numbers. The importance of immunosuppressive regulatory T cells (Tregs) in restoring immune tolerance has been well established, and CAR-Tregs have shown promising therapeutic potential in treating autoimmune diseases. Moreover, prior experience from the cancer field has provided sufficient paradigms for understanding how to optimize the structure and function of CARs to improve their function, persistence, stability and safety. In this review, we describe the potential application of CAR-T cells and CAR-Tregs in the treatment of autoimmune diseases, and we summarize the currently available strategies of gene editing and synthetic biological tools that have improved the practical application of CAR-based therapies.

LAG-3xPD-L1 bispecific antibody potentiates antitumor responses of T cells through dendritic cell activation

Several preclinical studies demonstrate that antitumor efficacy of programmed cell death-1 (PD-1)/programmed death-ligand 1 (PD-L1) blockade can be improved by combination with other checkpoint inhibitors. Lymphocyte-activation gene 3 (LAG-3) is an inhibitory checkpoint receptor involved in T cell exhaustion and tumor immune escape. Here, we describe ABL501, a bispecific antibody targeting LAG-3 and PD-L1 in modulating immune cell responses against tumors. ABL501 that efficiently inhibits both LAG-3 and PD-L1 pathways enhances the activation of effector CD4+ and CD8+ T cells with a higher degree than a combination of single anti-LAG-3 and anti-PD-L1. The augmented effector T cell responses by ABL501 resulted in mitigating regulatory-T-cell-mediated immunosuppression. Mechanistically, the simultaneous binding of ABL501 to LAG-3 and PD-L1 promotes dendritic cell (DC) activation and tumor cell conjugation with T cells that subsequently mounts effective CD8+ T cell responses. ABL501 demonstrates its potent in vivo antitumor efficacy in a humanized xenograft model and with knockin mice expressing human orthologs. The immune profiling analysis of peripheral blood reveals an increased abundance of LAG-3hiPD-1hi memory CD4+ T cell subset in relapsed cholangiocarcinoma patients after gemcitabine plus cisplatin therapy, which are more responsive to ABL501. This study supports the clinical evaluation of ABL501 as a novel cancer immunotherapeutic, and a first-in-human trial has started (NCT05101109).

T Cell Subsets in Graft Versus Host Disease and Graft Versus Tumor

Allogeneic hematopoietic cell transplantation (allo-HCT) is an essential therapeutic modality for patients with hematological malignancies and other blood disorders. Unfortunately, acute graft-versus-host disease (aGVHD) remains a major source of morbidity and mortality following allo-HCT, which limits its use in a broader spectrum of patients. Chronic graft-versus-host disease (cGVHD) also remains the most common long-term complication of allo-HCT, occurring in reportedly 30-70% of patients surviving more than 100 days. Chronic GVHD is also the leading cause of non-relapse mortality (NRM) occurring more than 2 years after HCT for malignant disease. Graft versus tumor (GVT) is a major component of the overall beneficial effects of allogeneic HCT in the treatment of hematological malignancies. Better understanding of GVHD pathogenesis is important to identify new therapeutic targets for GVHD prevention and therapy. Emerging data suggest opposing roles for different T cell subsets, e.g., IFN-γ producing CD4+ and CD8+ T cells (Th1 and Tc1), IL-4 producing T cells (Th2 and Tc2), IL-17 producing T cells (Th17 and Tc17), IL-9 producing T cells (Th9 and Tc9), IL-22 producing T cells (Th22), T follicular helper cells (Tfh), regulatory T-cells (Treg) and tissue resident memory T cells (Trm) in GVHD and GVT etiology. In this review, we first summarize the general description of the cytokine signals that promote the differentiation of T cell subsets and the roles of these T cell subsets in the pathogenesis of GVHD. Next, we extensively explore preclinical findings of T cell subsets in both GVHD/GVT animal models and humans. Finally, we address recent findings about the roles of T-cell subsets in clinical GVHD and current strategies to modulate T-cell differentiation for treating and preventing GVHD in patients. Further exploring and outlining the immune biology of T-cell differentiation in GVHD that will provide more therapeutic options for maintaining success of allo-HCT.

A Clinical Trial With Adoptive Transfer of Ex Vivo-induced, Donor-specific Immune-regulatory Cells in Kidney Transplantation-A Second Report

BACKGROUND

Although the outcome of kidney transplantation (KTx) has improved, various adverse effects of immunosuppressants and chronic rejection aggravate the long-term prognosis of patients. Therefore, the induction of immune tolerance may be an effective therapeutic strategy.

METHODS

A clinical trial aiming at immune tolerance induction was conducted in kidney transplant recipients from HLA mismatched living donors by infusing autologous donor-specific regulatory T cells (Treg). To obtain Treg, recipient's peripheral blood mononuclear cells were cocultured with irradiated donor cells in the presence of anti-CD80/CD86 monoclonal antibody for 2 weeks. For preconditioning, splenectomy + cyclophosphamide (CP) was employed in the first series (group A; n = 9). In group B, splenectomy was substituted by preadministration of rituximab (group B; n = 3). In the latest cases, rituximab + rabbit antithymocyte globulin was administered instead of cyclophosphamide (group C; n = 4). Twelve days after KTx, the cultured cells were intravenously infused, and immunosuppressants were gradually tapered thereafter.

RESULTS

Although mixed lymphocyte reaction was remarkably suppressed in a donor-specific fashion, 6 out of 9 patients from group A, 1 out of 3 from group B, and 1 out of 4 from group C developed acute rejection within 1 year after KTx. Complete cessation of immunosuppression was not achieved, and a small dose of immunosuppressants was continued.

CONCLUSIONS

The adoptive transfer of autologous ex vivo-expanded Treg is 1 of the options to possibly induce alloimmune hyporesponsiveness. However, in the present study, further regimen optimization is still required and should be the focus of future investigations.

An Efficient Culture Method of CD3-Positive T Cells from Human Cryopreserved Buffy Coat Specimens

Context: In the National Cerebral and Cardiovascular Center (NCVC) Biobank, buffy coats have been collected from patients and stored with cryoprotective agents as a possible source for viable blood cells, using cost-efficient methods for storage. However, whether viable cells for in vitro studies can be recovered from these biospecimens has not been verified. Objective: To investigate whether T cells can be collected and expanded as viable cells from cryopreserved human buffy coats. Design: After thawing of cryopreserved buffy coat specimens, CD3-positive cells were isolated from the cell suspension using a leukocyte separation filter coated with an anti-CD3 antibody, and the filter-attached cells were cultured in T cell culture medium. To analyze the characteristics of these cultured cells, histocytological analyses of Giemsa staining, immunocytochemical (ICC) staining for CD3, and flow cytometry for CD3 in live cells were conducted. Results: A few days after starting cell culture, cell clusters were observed, and they gradually grew in size. Using Giemsa staining, the expanded cells were found to be ∼15 μm in diameter, having round nuclei, a high nucleus/cytoplasm ratio, and cytoplasm stained light blue, which is characteristic of lymphocytes. From ICC staining, these cells were CD3 positive, a pan-T cell marker among lymphocytes. Furthermore, CD3 immunoreactivity in live cells was detected in a flow cytometry assay, though that for CD19 was not detected, which is a marker of pan-B cells. Conclusions: These results suggest that T cells can be expanded from buffy coats cryopreserved at -180°C as an adequate method of NCVC Biobank, highlighting these biospecimens as a possible useful source for future in vitro studies.

Regulating the regulators: Is introduction of an antigen-specific approach in regulatory T cells the next step to treat autoimmunity?

In autoimmunity, the important and fragile balance between immunity and tolerance is disturbed, resulting in abnormal immune responses to the body's own tissues and cells. CD4⁺CD25^hiFoxP3⁺ regulatory T cells (Tregs) induce peripheral tolerance in vivo by means of direct cell-cell contact and release of soluble factors, or indirectly through antigen-presenting cells (APC), thereby controlling auto-reactive effector T cells. Based on these unique capacities of Tregs, preclinical studies delivered proof-of-principle for the clinical use of Tregs for the treatment of autoimmune diseases. To date, the first clinical trials using ex vivo expanded polyclonal Tregs have been completed. These pioneering studies demonstrate the feasibility of generating large numbers of polyclonal Tregs in a good manufacturing practices (GMP)-compliant manner, and that infusion of Tregs is well tolerated by patients with no evidence of general immunosuppression. Nonetheless, only modest clinical results were observed, arguing that a more antigen-specific approach might be needed to foster a durable patient-specific clinical cell therapy without the risk for general immunosuppression. In this review, we discuss current knowledge, applications and future goals of adoptive immune-modulatory Treg therapy for the treatment of autoimmune disease and transplant rejection. We describe the key advances and prospects of the potential use of T cell receptor (TCR)- and chimeric antigen receptor (CAR)-engineered Tregs in future clinical applications. These approaches could deliver the long-awaited breakthrough in stopping undesired autoimmune responses and transplant rejections.

Regulatory T cell therapy: Current and future design perspectives

Regulatory T cells (Tregs) maintain immune equilibrium by suppressing immune responses through various multistep contact dependent and independent mechanisms. Cellular therapy using polyclonal Tregs in transplantation and autoimmune diseases has shown promise in preclinical models and clinical trials. Although novel approaches have been developed to improve specificity and efficacy of antigen specific Treg based therapies, widespread application is currently restricted. To date, design-based approaches to improve the potency and persistence of engineered chimeric antigen receptor (CAR) Tregs are limited. Here, we describe currently available Treg based therapies, their advantages and limitations for implementation in clinical studies. We also examine various strategies for improving CAR T cell design that can potentially be applied to CAR Tregs, such as identifying co-stimulatory signalling domains that enhance suppressive ability, determining optimal scFv affinity/avidity, and co-expression of accessory molecules. Finally, we discuss the importance of tailoring CAR Treg design to suit the individual disease.

Dendritic Cells and T Cells, Partners in Atherogenesis and the Translating Road Ahead

Atherosclerosis is a chronic process associated with arterial inflammation, the accumulation of lipids, plaque formation in vessel walls, and thrombosis with late mortal complications such as myocardial infarction and ischemic stroke. Immune and inflammatory responses have significant effects on every phase of atherosclerosis. Increasing evidence has shown that both innate and adaptive “arms” of the immune system play important roles in regulating the progression of atherosclerosis. Accumulating evidence suggests that a unique type of innate immune cell, termed dendritic cells (DCs), play an important role as central instigators, whereas adaptive immune cells, called T lymphocytes, are crucial as active executors of the DC immunity in atherogenesis. These two important immune cell types work in pairs to establish pro-atherogenic or atheroprotective immune responses in vascular tissues. Therefore, understanding the role of DCs and T cells in atherosclerosis is extremely important. Here, in this review, we will present a complete overview, based on existing knowledge of these two cell types in the atherosclerotic microenvironment, and discuss some of the novel means of targeting DCs and T cells as therapeutic tactics for the treatment of atherosclerosis.

Therapeutic use of regulatory T cells for graft-versus-host disease

Regulatory T cells (Treg cells) represent a CD4+ T-cell lineage that plays a critical role in restraining immune responses to self and foreign antigens and associated inflammation. Due to the suppressive function of Treg cells, inhibition or ablation of these cells can be used to boost the immunity against malignant cells. On the other hand, augmenting the activity of Treg cells can be employed for the treatment of inflammatory or autoimmune diseases and allogeneic conflicts associated with transplantation. Graft-versus-host disease (GvHD) is a leading cause of morbidity and mortality after haematopoietic stem cell transplantation (HSCT). In this review, we describe basic biological properties of Treg cells and their role in GvHD. We focus on the application of adoptive transfer of Treg cells and the therapeutic modulation of their activity for the prevention and treatment of GvHD in pre-clinical models and in clinical settings. We also discuss the main obstacles to applying Treg cell-based therapies for GvHD in clinical practice.

HLA-Class II Artificial Antigen Presenting Cells in CD4+ T Cell-Based Immunotherapy

CD4+ T cells differentiate into various T helper subsets characterized by distinct cytokine secreting profiles that confer them effector functions adapted to a variety of infectious or endogenous threats. Regulatory CD4+ T cells are another specialized subset that plays a fundamental role in the maintenance of immune tolerance to self-antigens. Manipulating effector or regulatory CD4+ T cells responses is a promising immunotherapy strategy for, respectively, chronical viral infections and cancer, or severe autoimmune diseases and transplantation. Adoptive cell therapy (ACT) is an emerging approach that necessitates defining robust and efficient methods for the in vitro expansion of antigen-specific T cells then infused into patients. To address this challenge, artificial antigen presenting cells (AAPCs) have been developed. They constitute a reliable and easily usable platform to stimulate and amplify antigen-specific CD4+ T cells. Here, we review the recent advances in understanding the functions of CD4+ T cells in immunity and in immune tolerance, and their use for ACT. We also describe the characteristics of different AAPC models and the way to improve their stimulating functions. Finally, we discuss the potential interest of these AAPCs, both as fundamental tools to decipher CD4+ T cell responses and as reagents to generate clinical grade antigen-specific CD4+ T cells for immunotherapy.

Depleting T regulatory cells by targeting intracellular Foxp3 with a TCR mimic antibody

Depletion of T regulatory cells (Tregs) in the tumor microenvironment is a promising cancer immunotherapy strategy. Current approaches for depleting Tregs are limited by lack of specificity and concurrent depletion of anti-tumor effector T cells. The transcription factor forkhead box p3 (Foxp3) plays a central role in the development and function of Tregs and is an ideal target in Tregs, but Foxp3 is an intracellular, undruggable protein to date. We have generated a T cell receptor mimic antibody, "Foxp3-#32," recognizing a Foxp3-derived epitope in the context of HLA-A*02:01. The mAb Foxp3-#32 selectively recognizes CD4 + CD25 + CD127low and Foxp3 + Tregs also expressing HLA-A*02:01 and depletes these cells via antibody-mediated cellular cytotoxicity. Foxp3-#32 mAb depleted Tregs in xenografts of PBMCs from a healthy donor and ascites fluid from a cancer patient. A TCRm mAb targeting intracellular Foxp3 epitope represents an approach to deplete Tregs.

Automated Clinical Grade Expansion of Regulatory T Cells in a Fully Closed System

Adoptive transfer of T regulatory cells (Treg) has been successfully exploited in the context of graft-versus-host disease, transplantation, and autoimmune disease. For the majority of applications, clinical administration of Treg requires laborious ex vivo expansion and typically involves open handling for culture feeds and repetitive sampling. Here we show results from our approach to translate manual Treg manufacturing to the fully closed automated CliniMACS Prodigy® system reducing contamination risk, hands-on time, and quality variation from human intervention. Polyclonal Treg were isolated from total nucleated cells obtained through leukapheresis of healthy donors by CD8⁺ cell depletion and subsequent CD25^high enrichment. Treg were expanded with the CliniMACS Prodigy® device using clinical-grade cell culture medium, rapamycin, IL-2, and αCD3/αCD28 beads for 13–14 days. We successfully integrated expansion bead removal and final formulation into the automated procedure, finalizing the process with a ready to use product for bedside transfusion. Automated Treg expansion was conducted in parallel to an established manual manufacturing process using G-Rex cell culture flasks. We could prove similar expansion kinetics leading to a cell yield of up to 2.12 × 10⁹ cells with the CliniMACS Prodigy® and comparable product phenotype of >90% CD4⁺CD25^highCD127^lowFOXP3⁺ cells that had similar in vitro immunosuppressive function. Efficiency of expansion bead depletion was comparable to the CliniMACS® Plus system and the final ready-to-infuse product had phenotype stability and high vitality after overnight storage. We anticipate this newly developed closed system expansion approach to be a starting point for the development of enhanced throughput clinical scale Treg manufacture, and for safe automated generation of antigen-specific Treg grafted with a chimeric antigen receptor (CAR Treg).

Harnessing the power of regulatory T-cells to control autoimmune diabetes: overview and perspective

Type 1 diabetes (T1D) is a T-cell-mediated autoimmune disease resulting in islet β-cell destruction, hypoinsulinaemia and severely altered glucose homeostasis. Although the mechanisms that initiate T1D still remain elusive, a breakdown of immune tolerance between effector T-cells (T_eff ) and regulatory T-cells (T_reg ) is considered to be the crucial component leading to autoimmunity. As such, strategies have been developed to boost the number and/or function of T_reg in the hope of specifically hampering the pathogenic T_eff activity. In this review, we will summarize the current understanding of biomarkers and functions of both forkhead box protein 3 (FoxP3)⁺ T_reg and type 1 regulatory T (Tr1) cells in health and in T1D, examine the outcome of experimental therapies in both animal models and humans via manipulation of T_reg responses and also provide an outlook on the potential of T_reg -based immunotherapies in the prevention and treatment of this disease. Discussed immunotherapies include adoptive transfer of ex-vivo expanded FoxP3⁺ T_reg , manipulation of T_reg cells via the interleukin (IL)-2/IL-2R pathway and induction of T_reg by tolerogenic peptides, tolerogenic dendritic cells or altered gut microbiota.

Regulatory T cells: tolerance induction in solid organ transplantation

The concept of regulatory T cell (T_reg ) therapy in transplantation is now a reality. Significant advances in science and technology have enabled us to isolate human T_regs , expand them to clinically relevant numbers and infuse them into human transplant recipients. With several Phase I/II trials under way investigating T_reg safety and efficacy it is now more crucial than ever to understand their complex biology. However, our journey is by no means complete; results from these trials will undoubtedly provoke both further knowledge and enquiry which, alongside evolving science, will continue to drive the optimization of T_reg therapy in the pursuit of transplantation tolerance. In this review we will summarize current knowledge of T_reg biology, explore novel technologies in the setting of T_reg immunotherapy and address key prerequisites surrounding the clinical application of T_regs in transplantation.

CD25 Blockade Delays Regulatory T Cell Reconstitution and Does Not Prevent Graft-versus-Host Disease After Allogeneic Hematopoietic Cell Transplantation

Daclizumab, a humanized monoclonal antibody, binds CD25 and blocks formation of the IL-2 receptor on T cells. A study of daclizumab as acute graft-versus-host disease (GVHD) prophylaxis after unrelated bone marrow transplantation was conducted before the importance of CD25⁺FOXP3⁺ regulatory T cells (Tregs) was recognized. Tregs can abrogate the onset of GVHD. The relation between Tregs and a graft-versus-malignancy effect is not fully understood. An international, multicenter, double-blind clinical trial randomized 210 adult or pediatric patients to receive 5 weekly doses of daclizumab at 0.3 mg/kg (n = 69) or 1.2 mg/kg (n = 76) or placebo (n = 65) after unrelated marrow transplantation for treatment of hematologic malignancies or severe aplastic anemia. The risk of acute GVHD did not differ among the groups (P = .68). Long-term follow-up of clinical outcomes and correlative analysis of peripheral blood T cell phenotype suggested that the patients treated with daclizumab had an increased risk of chronic GVHD (hazard ratio [HR], 1.49; 95% confidence interval [CI], 1.0 to 2.3; P = .08) and a decreased risk of relapse (HR, 0.57; 95% CI, 0.3 to 1.0; P = .05), but similar survival (HR, 0.89; 95% CI, 0.6 to 1.3; P = .53). T cells from a subset of patients (n = 107) were analyzed by flow cytometry. Compared with placebo, treatment with daclizumab decreased the proportion of Tregs among CD4 T cells at days 11-35 and increased the proportion of central memory cells among CD4 T cells at 1 year. Prophylactic administration of daclizumab does not prevent acute GVHD, but may increase the risk of chronic GVHD and decrease the risk of relapse. By delaying Treg reconstitution and promoting immunologic memory, anti-CD25 therapy may augment alloreactivity and antitumor immunity.

Platelet microparticles inhibit IL-17 production by regulatory T cells through P-selectin

Self-tolerance and immune homeostasis are orchestrated by FOXP3(+)regulatory T cells (Tregs). Recent data have revealed that upon stimulation, Tregs may exhibit plasticity toward a proinflammatory phenotype, producing interleukin 17 (IL-17) and/or interferon γ (IFN-γ). Such deregulation of Tregs may contribute to the perpetuation of inflammatory processes, including graft-versus-host disease. Thus, it is important to identify immunomodulatory factors influencing Treg stability. Platelet-derived microparticles (PMPs) are involved in hemostasis and vascular health and have recently been shown to be intimately involved in (pathogenic) immune responses. Therefore, we investigated whether PMPs have the ability to affect Treg plasticity. PMPs were cocultured with healthy donor peripheral blood-derived Tregs that were stimulated with anti-CD3/CD28 monoclonal antibodies in the presence of IL-2, IL-15, and IL-1β. PMPs prevented the differentiation of peripheral blood-derived Tregs into IL-17- and IFN-γ-producing cells, even in the presence of the IL-17-driving proinflammatory cytokine IL-1β. The mechanism of action by which PMPs prevent Treg plasticity consisted of rapid and selective P-selectin-dependent binding of PMPs to a CCR6(+)HLA-DR(+)memory-like Treg subset and their ability to inhibit Treg proliferation, in part through CXCR3 engagement. The findings that ~8% of Tregs in the circulation of healthy individuals are CD41(+)P-selectin(+)and that distinct binding of patient plasma PMPs to Tregs was observed support in vivo relevance. These findings open the exciting possibility that PMPs actively regulate the immune response at sites of (vascular) inflammation, where they are known to accumulate and interact with leukocytes, consolidating the (vascular) healing process.

Biased signaling pathways via CXCR3 control the development and function of CD4+ T cell subsets

Structurally related chemotactic cytokines (chemokines) regulate cell trafficking through interactions with 7-transmembrane domain, G protein-coupled receptors. Biased signaling or functional selectivity is a concept that describes a situation where a 7-transmembrane domain receptor preferentially activates one of several available cellular signaling pathways. It can be divided into 3 distinct cases: ligand bias, receptor bias, and tissue or cell bias. Many studies, including those coming from our lab, have shown that only a limited number of chemokines are key drivers of inflammation. We have referred to them as "driver chemokines." They include the CXCR3 ligands CXCL9 and CXCL10, the CCR2 ligand CCL2, all 3 CCR5 ligands, and the CCR9 ligand CCL25. As for CXCR3, despite the proinflammatory nature of CXCL10 and CXCL9, transgenic mice lacking CXCR3 display an aggravated manifestation of different autoimmune disease, including Type I diabetes and experimental autoimmune encephalomyelitis. Recently, we showed that whereas CXCL9 and CXCL10 induce effector Th1/Th17 cells to promote inflammation, CXCL11, with a relatively higher binding affinity to CXCR3, drives the development of the forkhead box P3-negative IL-10(high) T regulatory 1 cell subset and hence, dampens inflammation. We also showed that CXCL9/CXCL10 activates a different signaling cascade than CXCL11, despite binding to the same receptor, CXCR3, which results in these diverse biologic activities. This provides new evidence for the role of biased signaling in regulating biologic activities, in which CXCL11 induces ligand bias at CXCR3 and receptor-biased signaling via atypical chemokine receptor 3.

Neonatal regulatory T cells have reduced capacity to suppress dendritic cell function

Regulatory T cells (Treg cells) limit contact between dendritic cells (DCs) and conventional T cells (Tcons), decreasing the formation of aggregates as well as down-modulating the expression of co-stimulatory molecules by DCs, thus decreasing DC immunogenicity and abrogating T-cell activation. Despite the importance of this Treg-cell function, the capacity of Treg cells from term and preterm neonates to suppress DCs, and the suppressive mechanisms they use, are still undefined. We found that, relative to adult Treg cells, activated Treg cells from human neonates expressed lower FOXP3 and CTLA-4, but contained higher levels of cAMP. We developed an in vitro model in which Treg function was measured at a physiological ratio of 1 Treg for 10 Tcon and 1 monocyte-derived DC, as Treg target. Term and preterm Treg cells failed to suppress the formation of DC-Tcon aggregates, in contrast to naïve and memory Treg cells from adults. However, neonatal Treg cells diminished DC and Tcon activation as well as actin polymerization at the immunological synapses. In addition, CTLA-4 and cAMP were the main suppressive molecules used by neonatal Treg. Altogether, both preterm and term neonatal Treg cells appear less functional than adult Treg cells, and this defect is consistent with the general impairment of CD4 cell function in newborns.

Sequential monitoring and stability of ex vivo-expanded autologous and nonautologous regulatory T cells following infusion in nonhuman primates

Ex vivo-expanded cynomolgus monkey CD4(+)CD25(+)CD127(-) regulatory T cells (Treg) maintained Foxp3 demethylation status at the Treg-specific demethylation region, and potently suppressed T cell proliferation through three rounds of expansion. When carboxyfluorescein succinimidyl ester- or violet proliferation dye 450-labeled autologous (auto) and nonautologous (non-auto)-expanded Treg were infused into monkeys, the number of labeled auto-Treg in peripheral blood declined rapidly during the first week, but persisted at low levels in both normal and anti-thymocyte globulin plus rapamycin-treated (immunosuppressed; IS) animals for at least 3 weeks. By contrast, MHC-mismatched non-auto-Treg could not be detected in normal monkey blood or in blood of two out of the three IS monkeys by day 6 postinfusion. They were also more difficult to detect than auto-Treg in peripheral lymphoid tissue. Both auto- and non-auto-Treg maintained Ki67 expression early after infusion. Sequential monitoring revealed that adoptively transferred auto-Treg maintained similarly high levels of Foxp3 and CD25 and low CD127 compared with endogenous Treg, although Foxp3 staining diminished over time in these nontransplanted recipients. Thus, infused ex vivo-expanded auto-Treg persist longer than MHC-mismatched non-auto-Treg in blood of nonhuman primates and can be detected in secondary lymphoid tissue. Host lymphodepletion and rapamycin administration did not consistently prolong the persistence of non-auto-Treg in these sites.

Cell therapy to induce allograft tolerance: time to switch to plan B?

Organ transplantation is widely acknowledged as the best option for end stage failure of vital organs. Long-term graft survival is however limited by graft rejection, a destructive process resulting from the response of recipient’s immune system against donor-specific alloantigens. Prevention of rejection currently relies exclusively on immunosuppressive drugs that lack antigen specificity and therefore increase the risk for infections and cancers. Induction of donor-specific tolerance would provide indefinite graft survival without morbidity and therefore represents the grail of transplant immunologists. Progresses in the comprehension of immunoregulatory mechanisms over the last decades have paved the way for cell therapies to induce allograft tolerance. The first part of the present article reviews the promising results obtained in experimental models with adoptive transfer of ex vivo-expanded regulatory CD4+ T cells (CD4+ Tregs) and discuss which source and specificity should be preferred for transferred CD4+ Tregs. Interestingly, B cells have recently emerged as potent regulatory cells, able to establish a privileged crosstalk with CD4+ T cells. The second part of the present article reviews the evidences demonstrating the crucial role of regulatory B cells in transplantation tolerance. We propose the possibility to harness B cell regulatory functions to improve cell-based therapies aiming at inducing allograft tolerance.

Alloreactive regulatory T cells generated with retinoic acid prevent skin allograft rejection

CD4(+) CD25(+) Foxp3(+) regulatory T (Treg) cells mediate immunological self-tolerance and suppress immune responses. Retinoic acid (RA), a natural metabolite of vitamin A, has been reported to enhance the differentiation of Treg cells in the presence of TGF-β. In this study, we show that the co-culture of naive T cells from C57BL/6 mice with allogeneic antigen-presenting cells (APCs) from BALB/c mice in the presence of TGF-β, RA, and IL-2 resulted in a striking enrichment of Foxp3(+) T cells. These RA in vitro-induced regulatory T (RA-iTreg) cells did not secrete Th1-, Th2-, or Th17-related cytokines, showed a nonbiased homing potential, and expressed several cell surface molecules related to Treg-cell suppressive potential. Accordingly, these RA-iTreg cells suppressed T-cell proliferation and inhibited cytokine production by T cells in in vitro assays. Moreover, following adoptive transfer, RA-iTreg cells maintained Foxp3 expression and their suppressive capacity. Finally, RA-iTreg cells showed alloantigen-specific immunosuppressive capacity in a skin allograft model in immunodeficient mice. Altogether, these data indicate that functional and stable allogeneic-specific Treg cells may be generated using TGF-β, RA, and IL-2. Thus, RA-iTreg cells may have a potential use in the development of more effective cellular therapies in clinical transplantation.

Treating atherosclerosis with regulatory T cells

Regulatory T cells (Tregs) play an important role in the regulation of T-cell-mediated immune responses through suppression of T-cell proliferation and secretion of inhibitory cytokines, such as interleukin-10 and transforming growth factor-β. Impaired Treg numbers and function have been associated with numerous diseases, and an imbalance between proinflammatory/proatherogenic cells and Tregs promotes atherosclerotic disease. Restoration of this balance by inducing Tregs has great therapeutic potential to prevent cardiovascular disease. In addition to suppressing differentiation and function of effector T cells, Tregs have been shown to induce anti-inflammatory macrophages, inhibit foam cell formation and to influence cholesterol metabolism. Furthermore, Tregs suppress immune responses of endothelial cells and innate lymphoid cells. In this review, we focus on the recent knowledge on Treg subsets, their activity and function in atherosclerosis, and discuss promising strategies to use Tregs as a therapeutic tool to prevent cardiovascular disease.

Thymus-deriving natural regulatory T cell generation in vitro: role of the source of activation signals

In this research we have examined different sources of activation signals in order to optimize culture conditions for in vitro generation of thymus-deriving natural regulatory T cells (nTregs). We have established a novel model using JAWS II dendritic cell line of immature phenotype and compared it to commonly used methods for the generation of Tregs from peripheral lymphoid organs or blood T cells. In our model the first activation signal is provided by anti-CD3 monoclonal antibodies while the second is delivered by costimulatory molecules expressed on JAWS II cells. The presence of JAWS II cells co-cultured in vitro with unsorted thymocytes directly isolated from the thymus gland creates environment favoring SP CD4+ differentiation, provides the apoptotic cells clearance, maintains the survival of thymocytes and facilitate nTreg generation. Moreover the usage of immature dendritic cells stimuli enables to conduct research on agents affecting nTreg survival, proliferation and development in conditions of cell-to-cell contact of undifferentiated thymocytes with dendritic cells.

Treatment of graft-versus-host disease with naturally occurring T regulatory cells

A significant body of evidence suggests that treatment with naturally occurring CD4⁺CD25⁺ T regulatory cells (Tregs) is an appropriate therapy for graft-versus-host disease (GvHD). GvHD is a major complication of bone marrow transplantation in which the transplanted immune system recognizes recipient tissues as a non-self and destroys them. In many cases, this condition significantly deteriorates the quality of life of the affected patients. It is also one of the most important causes of death after bone marrow transplantation. Tregs constitute a population responsible for dominant tolerance to self-tissues in the immune system. These cells prevent autoimmune and allergic reactions and decrease the risk of rejection of allotransplants. For these reasons, Tregs are considered as a cellular drug in GvHD. The results of the first clinical trials with these cells are already available. In this review we present important experimental facts which led to the clinical use of Tregs. We then critically evaluate specific requirements for Treg therapy in GvHD and therapies with Tregs currently under clinical investigation, including our experience and future perspectives on this kind of cellular treatment.

Dual function of CD70 in viral infection: modulator of early cytokine responses and activator of adaptive responses

The role of the TNF family member CD70 in adaptive T cell responses has been intensively studied, but its function in innate responses is still under investigation. In this study, we show that CD70 inhibits the early innate response to murine CMV (MCMV) but is essential for the optimal generation of virus-specific CD8 T cells. CD70(-/-) mice reacted to MCMV infection with a robust type I IFN and proinflammatory cytokine response. This response was sufficient for initial control of MCMV, although at later time points, CD70(-/-) mice became more susceptible to MCMV infection. The heightened cytokine response during the early phase of MCMV infection in CD70(-/-) mice was paralleled by a reduction in regulatory T cells (Treg). Treg from naive CD70(-/-) mice were not as efficient at suppressing T cell proliferation compared with Treg from naive wild-type mice, and depletion of Treg during MCMV infection in Foxp3-diphtheria toxin receptor mice or in wild-type mice recapitulated the phenotype observed in CD70(-/-) mice. Our study demonstrates that although CD70 is required for the activation of the antiviral adaptive response, it has a regulatory role in early cytokine responses to viruses such as MCMV, possibly through maintenance of Treg survival and function.

Adoptive immunotherapy for cancer or viruses

Adoptive immunotherapy, or the infusion of lymphocytes, is a promising approach for the treatment of cancer and certain chronic viral infections. The application of the principles of synthetic biology to enhance T cell function has resulted in substantial increases in clinical efficacy. The primary challenge to the field is to identify tumor-specific targets to avoid off-tumor, on-target toxicity. Given recent advances in efficacy in numerous pilot trials, the next steps in clinical development will require multicenter trials to establish adoptive immunotherapy as a mainstream technology.

Ex vivo expanded human regulatory T cells can prolong survival of a human islet allograft in a humanized mouse model

BACKGROUND

Human regulatory T cells (Treg) offer an attractive adjunctive therapy to reduce current reliance on lifelong, nonspecific immunosuppression after transplantation. Here, we evaluated the ability of ex vivo expanded human Treg to prevent the rejection of islets of Langerhans in a humanized mouse model and examined the mechanisms involved.

METHODS

We engrafted human pancreatic islets of Langerhans into the renal subcapsular space of immunodeficient BALB/c.rag2(-/-).cγ(-/-) mice, previously rendered diabetic via injection of the β-cell toxin streptozocin. After the establishment of stable euglycemia, mice were reconstituted with allogeneic human peripheral blood mononuclear cells (PBMC) and the resultant alloreactive response studied. Ex vivo expanded CD25high CD4+ human Treg, which expressed FoxP3, CTLA-4, and CD62L and remained CD127low, were then cotransferred together with human PBMC and islet allografts and monitored for evidence of rejection.

RESULTS

Human islets transplanted into diabetic immunodeficient mice reversed diabetes but were rejected rapidly after the mice were reconstituted with allogeneic human PBMC. Cotransfer of purified, ex vivo expanded human Treg prolonged islet allograft survival resulting in the accumulation of Treg in the peripheral lymphoid tissue and suppression of proliferation and interferon-γ production by T cells. In vitro, Treg suppressed activation of signal transducers and activators of transcription and inhibited the effector differentiation of responder T cells.

CONCLUSIONS

Ex vivo expanded Treg retain regulatory activity in vivo, can protect a human islet allograft from rejection by suppressing signal transducers and activators of transcription activation and inhibiting T-cell differentiation, and have clinical potential as an adjunctive cellular therapy.

Human regulatory T cells against minor histocompatibility antigens: ex vivo expansion for prevention of graft-versus-host disease

Alloreactive donor T cells against host minor histocompatibility antigens (mHAs) cause graft-versus-host disease (GVHD) after marrow transplantation from HLA-identical siblings. We sought to identify and expand regulatory CD4 T cells (Tregs) specific for human mHAs in numbers and potency adequate for clinical testing. Purified Tregs from normal donors were stimulated by dendritic cells (DCs) from their HLA-matched siblings in the presence of interleukin 2, interleukin 15, and rapamycin. Male-specific Treg clones against H-Y antigens DBY, UTY, or DFFRY-2 suppressed conventional CD4 T cell (Tconv) response to the specific antigen. In the blood of 16 donors, we found a 24-fold (range, 8-fold to 39-fold) excess Tconvs over Tregs reactive against sibling mHAs. We expanded mHA-specific Tregs from 4 blood samples and 4 leukaphereses by 155- to 405-fold. Cultured Tregs produced allospecific suppression, maintained demethylation of the Treg-specific Foxp3 gene promoter, Foxp3 expression, and transforming growth factor β production. The rare CD4 T conv and CD8 T cells in the end product were anergic. This is the first report of detection and expansion of potent mHA-specific Tregs from HLA-matched siblings in sufficient numbers for application in human transplant trials.

Natural CD8⁺25⁺ regulatory T cell-secreted exosomes capable of suppressing cytotoxic T lymphocyte-mediated immunity against B16 melanoma

Natural CD4(+)25(+) and CD8(+)25(+) regulatory T (Tr) cells have been shown to inhibit autoimmune diseases. Immune cells secrete exosomes (EXOs), which are crucial for immune regulation. However, immunomodulatory effect of natural Tr cell-secreted EXOs is unknown. In this study, we purified natural CD8(+)25(+) Tr cells from C57BL/6 mouse naive CD8(+) T cells, and in vitro amplified them with CD3/CD28 beads. EXOs (EXO(Tr)) were purified from Tr cell's culture supernatants by differential ultracentrifugation and analyzed by electron microscopy, Western blot and flow cytometry. Our data showed that EXO(Tr) had a "saucer" or round shape with 50-100 nm in diameter, contained EXO-associated markers LAMP-1 and CD9, and expressed natural Tr cell markers CD25 and GITR. To assess immunomodulatory effect, we i.v. immunized C57BL/6 mice with ovalbumin (OVA)-pulsed DCs (DC(OVA)) plus Tr cells or EXO(Tr), and then assessed OVA-specific CD8(+) T cell responses using PE-H-2K(b)/OVA tetramer and FITC-anti-CD8 antibody staining by flow cytometry and antitumor immunity in immunized mice with challenge of OVA-expressing BL6-10OVA melanoma cells. We demonstrated that DC(OVA)-stimulated CD8(+) T cell responses and protective antitumor immunity significantly dropped from 2.52% to 1.08% and 1.81% (p<0.05), and from 8/8 to 2/8 and 5/8 mice DC(OVA) (p<0.05) in immunized mice with co-injection of Tr cells and EXO(Tr), respectively. Our results indicate that natural CD8(+)25(+) Tr cell-released EXOs, alike CD8(+)25(+) Tr cells, can inhibit CD8(+) T cell responses and antitumor immunity. Therefore, EXOs derived from natural CD4(+)25(+) and CD8(+)25(+) Tr cells may become an alternative for immunotherapy of autoimmune diseases.

Promoting transplantation tolerance; adoptive regulatory T cell therapy

Transplantation is a successful treatment for end-stage organ failure. Despite improvements in short-term outcome, long-term survival remains suboptimal because of the morbidity and mortality associated with long-term use of immunosuppression. There is, therefore, a pressing need to devise protocols that induce tolerance in order to minimize or completely withdraw immunosuppression in transplant recipients. In this review we will discuss how regulatory T cells (T(regs)) came to be recognized as an attractive way to promote transplantation tolerance. We will summarize the preclinical data, supporting the importance of these cells in the induction and maintenance of immune tolerance and that provide the rationale for the isolation and expansion of these cells for cellular therapy. We will also describe the data from the first clinical trials, using T(regs) to inhibit graft-versus-host disease (GVHD) after haematopoietic stem cell transplantation and will address both the challenges and opportunities in human T(reg) cell therapy.

Clinical operational tolerance in liver transplantation: state-of-the-art perspective and future prospects

BACKGROUND

Liver transplantation is the definite treatment for end-stage liver diseases with satisfactory results. However, untoward effects of life-long immunosuppression prevent the development of alternative strategies to achieve better long-term outcome. Achieving clinical operational tolerance is the ultimate goal.

DATA SOURCES

A PubMed and Google Scholar search using terms: "immune tolerance", "liver transplantation", "clinical trial", "operational tolerance" and "immunosuppression withdrawal" was performed, and relevant articles published in English in the past decade were reviewed. Full-text publications relevant to the field were selected and relevant articles from reference lists were also included. Priority was given to those articles which are relevant to the review.

RESULTS

Because of the inherent tolerogenic property, around 20%-30% of liver transplantation recipients develop spontaneous operational tolerance after immunosuppression withdrawal, and the percentage may be even higher in pediatric living donor liver transplantation recipients. Several natural killer and gammadeltaT cell related markers have been identified to be associated with the tolerant state in liver transplantation patients. Despite the progress, clinical operational tolerance is still rare in liver transplantation. Reprogramming the recipient immune system by creating chimerism and regulatory cell therapies is among newer promising means to achieve clinical liver transplantation tolerance in the future.

CONCLUSION

Although clinical operational tolerance is still rare in liver transplantation recipients, ongoing basic research and collaborative clinical trials may help to decipher the mystery of transplantation tolerance and extend the potential benefits of drug withdrawal to an increasing number of patients in a more predictable fashion.

Interleukin 15 provides relief to CTLs from regulatory T cell-mediated inhibition: implications for adoptive T cell-based therapies for lymphoma

PURPOSE

Systemic administration of recombinant interleukin (IL)-2 is used to support the expansion and persistence of adoptively transferred antigen-specific CTLs in patients with cancer. However, IL-2 also expands regulatory T cells (Treg) that in turn impair the antitumor activity of CTLs. As recombinant IL-15 is approaching clinical applications, we assessed the effects of this cytokine on the proliferation and antitumor activity of CTLs in the presence of Tregs. We used the model of adoptive transfer of Epstein-Barr virus (EBV)-CTLs, as these cells induce responses in patients with EBV-associated Hodgkin lymphoma, and Tregs are frequently abundant in these patients.

EXPERIMENTAL DESIGN

Tregs were isolated from the peripheral blood of healthy donors and patients with Hodgkin lymphoma or from Hodgkin lymphoma tumors and assessed for their ability to inhibit the proliferation and antitumor activity of EBV-CTLs in the presence of IL-15 or IL-2. Specific molecular pathways activated by IL-15 were also explored.

RESULTS

We found that in the presence of Tregs, IL-15, but not IL-2, promoted the proliferation, effector function, and resistance to apoptosis of effectors T cells and EBV-CTLs. IL-15 did not reverse or block Tregs but instead preferentially supported the proliferation of CTLs and effector T cells as compared with Tregs.

CONCLUSIONS

IL-15 selectively favors the survival, proliferation, and effector function of antigen-specific CTLs in the presence of Tregs, and thus IL-15, unlike IL-2, would have a significant impact in sustaining expansion and persistence of adoptively transferred CTLs in patients with cancer, including those infused with EBV-CTLs for treatment of EBV-associated malignancies.

New ways to separate graft-versus-host disease and graft-versus-tumour effects after allogeneic haematopoietic stem cell transplantation

A major challenge to transplant immunologists and physicians remains the separation of harmful graft-versus-host disease (GvHD) and beneficial graft-versus-tumour (GvT) effects after allogeneic haematopoietic stem cell transplantation. Recent advances in our understanding of the allogeneic immune response provide potential new opportunities to achieve this goal. Three potential new approaches that capitalize on this new knowledge are considered in depth; the manipulation of organ-specific cytokines and other pro-inflammatory signals, the selective manipulation of donor effector T cell migration, and the development of cell-mediated immunosuppressive strategies using donor-derived regulatory T cells. These new approaches could provide strategies for local control of allogeneic immune responses, a new paradigm to separate GvHD and GvT effects. Although these strategies are currently in their infancy and have challenges to successful translation to clinical practice, all have exciting potential for the future.

IL-7 abrogates suppressive activity of human CD4+CD25+FOXP3+ regulatory T cells and allows expansion of alloreactive and autoreactive T cells

CD4(+)CD25(+)FOXP3(+) regulatory T cells (Tregs) control the activation and expansion of alloreactive and autoreactive T cell clones. Because uncontrolled activation and expansion of autoreactive T cells occur in an IL-7-rich environment, we explored the possibility that IL-7 may affect the function of Treg. We show that the functional high-affinity IL-7R is expressed on both naive and memory Tregs, and exposure to IL-7 results in STAT-5 phosphorylation. Naive, but not memory, Tregs proliferated greatly and acquired a memory phenotype in the setting of a suppression assay when IL-7 was present. Importantly, the presence of IL-7 abrogated the capacity of Tregs to suppress proliferation of conventional T cells in response to TCR activators, including alloantigens and autoantigens. Removal of IL-7 restored the suppressive function of Tregs. Preblocking of the IL-7R on the Tregs also restored suppressor function, indicating that IL-7 directly affected Treg function. Thus, prolonged periods of homeostatic expansion can temporarily release natural regulatory brakes on T cells, thereby providing an additional mechanism for activating and expanding alloreactive and autoreactive T cells.

Ex Vivo Alloanergization with Belatacept: A Strategy to Selectively Modulate Alloresponses after Transplantation

Ex vivo alloanergization of human immune cells, via allostimulation in the presence of costimulatory blockade with either a combination of anti-B7.1 and anti-B7.2 antibodies or first-generation cytotoxic T-lymphocyte antigen 4-immunoglobulin (CTLA4-Ig), induces alloantigen-specific hyporesponsiveness and expands alloantigen-specific regulatory T cells (Treg). We have successfully used this approach in the clinical setting of haploidentical hematopoietic stem cell transplantation. Recently, the in vivo use of a new second-generation CTLA4-Ig, belatacept, has shown promise in controlling alloresponses after transplantation of both human kidneys and islet cells. We therefore compared the efficiency of first- and second-generation CTLA4-Ig in alloanergizing human peripheral blood mononuclear cells (PBMCs) and investigated whether ex vivo alloanergization with belatacept could be used to engineer an alloantigen-specific immunoregulatory population of autologous cells suitable for administration to recipients of cellular or solid organ transplant recipients. Alloanergization of HLA-mismatched human PBMCs with belatacept resulted in a greater reduction in subsequent alloresponses than alloanergization with first generation CTLA4-Ig. Moreover, subsequent ex vivo re-exposure of alloanergized cells to alloantigen in the absence of belatacept resulted in a significant expansion of Tregs with enhanced alloantigen-specific suppressive function. Alloanergized PBMCs retained functional Epstein-Barr virus (EBV)-specific T-cell responses, and expanded Tregs did not suppress EBV-specific proliferation of autologous cells. These results suggest that ex vivo alloanergization with belatacept provides a platform to engineer populations of recipient Treg with specificity for donor alloantigens but without nonspecific suppressive capacity. The potential advantages of such cells for solid organ transplantation include ( 1 ) reduction of the need for nonspecific immunosuppression, ( 2 ) retention of pathogen-specific immunity, and ( 3 ) control of graft rejection, if used as an intervention.