Induction of allopeptide-specific human CD4+CD25+ regulatory T cells ex vivo

Polyclonally Derived Alloantigen-Specific T Regulatory Cells Exhibit Target-Specific Suppression and Capture MHC Class II from Dendritic Cells

Foxp3+ T regulatory (Treg) cells prevent allograft rejection and graft-versus-host disease. Although polyclonal Tregs have been used both in animal models and in humans, the fine specificity of their suppressive function is poorly defined. We have generated mouse recipient-derived alloantigen-specific Tregs in vitro and explored the fine specificity of their suppressive function and their mechanism of action in vitro and in vivo. In vitro, when alloantigen and peptide Ag were both presented on the same dendritic cell, both responses were suppressed by iTregs specific either for the alloantigen or for the peptide Ag. In vivo, iTreg suppression was limited to the cognate Ag, and no bystander suppression was observed when both allo-antigen and peptide Ag were present on the same dendritic cell. In vitro, alloantigen-specific Tregs captured cognate MHC but failed to capture noncognate MHC. Our results demonstrate that a polyclonal population of iTregs generated from naive T cells can mediate highly specific function in vivo and support the view that Treg therapy, even with unselected polyclonal populations, is likely to be target antigen-specific and that bystander responses to self-antigens or to infectious agents are unlikely.

Development and evaluation of a human CD47/HER2 bispecific antibody for Trastuzumab-resistant breast cancer immunotherapy

The treatment for trastuzumab-resistant breast cancer (BC) remains a challenge in clinical settings. It was known that CD47 is preferentially upregulated in HER2+ BC cells, which is correlated with drug resistance to trastuzumab. Here, we developed a novel anti-CD47/HER2 bispecific antibody (BsAb) against trastuzumab-resistant BC, named IMM2902. IMM2902 demonstrated high binding affinity, blocking activity, antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and internalization degradation effects against both trastuzumab-sensitive and trastuzumab-resistant BC cells in vitro. The in vivo experimental data indicated that IMM2902 was more effective than their respective controls in inhibiting tumor growth in a trastuzumab-sensitive BT474 mouse model, a trastuzumab-resistant HCC1954 mouse model, two trastuzumab-resistant patient-derived xenograft (PDX) mouse models and a cord blood (CB)-humanized HCC1954 mouse model. Through spatial transcriptome assays, multiplex immunofluorescence (mIFC) and in vitro assays, our findings provided evidence that IMM2902 effectively stimulates macrophages to generate C-X-C motif chemokine ligand (CXCL) 9 and CXCL10, thereby facilitating the recruitment of T cells and NK cells to the tumor site. Moreover, IMM2902 demonstrated a high safety profile regarding anemia and non-specific cytokines release. Collectively, our results highlighted a novel therapeutic approach for the treatment of HER2+ BCs and this approach exhibits significant anti-tumor efficacy without causing off-target toxicity in trastuzumab-resistant BC cells.

Genetic engineering of regulatory T cells for treatment of autoimmune disorders including type 1 diabetes

Suppression of pathogenic immune responses is a major goal in the prevention and treatment of type 1 diabetes. Adoptive cell therapy using regulatory T cells (Tregs), a naturally suppressive immune subset that is often dysfunctional in type 1 diabetes, is a promising approach to achieving localised and specific immune suppression in the pancreas or site of islet transplant. However, clinical trials testing administration of polyclonal Tregs in recent-onset type 1 diabetes have observed limited efficacy despite an excellent safety profile. Several barriers to efficacy have been identified, including lack of antigen specificity, low cell persistence post-administration and difficulty in generating sufficient cell numbers. Fortunately, the emergence of advanced gene editing techniques has opened the door to new strategies to engineer Tregs with improved specificity and function. These strategies include the engineering of FOXP3 expression to produce a larger source of suppressive cells for infusion, expressing T cell receptors or chimeric antigen receptors to generate antigen-specific Tregs and improving Treg survival by targeting cytokine pathways. Although these approaches are being applied in a variety of autoimmune and transplant contexts, type 1 diabetes presents unique opportunities and challenges for the genetic engineering of Tregs for adoptive cell therapy. Here we discuss the role of Tregs in type 1 diabetes pathogenesis and the application of Treg engineering in the context of type 1 diabetes.

Eras of designer Tregs: Harnessing synthetic biology for immune suppression

Since their discovery, CD4+ CD25hi FOXP3hi regulatory T cells (Tregs) have been firmly established as a critical cell type for regulating immune homeostasis through a plethora of mechanisms. Due to their immunoregulatory power, delivery of polyclonal Tregs has been explored as a therapy to dampen inflammation in the settings of transplantation and autoimmunity. Evidence shows that Treg therapy is safe and well-tolerated, but efficacy remains undefined and could be limited by poor persistence in vivo and lack of antigen specificity. With the advent of new genetic engineering tools, it is now possible to create bespoke "designer" Tregs that not only overcome possible limitations of polyclonal Tregs but also introduce new features. Here, we review the development of designer Tregs through the perspective of three 'eras': (1) the era of FOXP3 engineering, in which breakthroughs in the biological understanding of this transcription factor enabled the conversion of conventional T cells to Tregs; (2) the antigen-specificity era, in which transgenic T-cell receptors and chimeric antigen receptors were introduced to create more potent and directed Treg therapies; and (3) the current era, which is harnessing advanced genome-editing techniques to introduce and refine existing and new engineering approaches. The year 2022 marked the entry of "designer" Tregs into the clinic, with exciting potential for application and efficacy in a wide variety of immune-mediated diseases.

The potential for Treg-enhancing therapies in transplantation

Since the discovery of regulatory T cells (Tregs) as crucial regulators of immune tolerance against self-antigens, these cells have become a promising tool for the induction of donor-specific tolerance in transplantation medicine. The therapeutic potential of increasing in vivoTreg numbers for a favorable Treg to Teff cell ratio has already been demonstrated in several sophisticated pre-clinical models and clinical pilot trials. In addition to improving cell quantity, enhancing Treg function utilizing engineering techniques led to encouraging results in models of autoimmunity and transplantation. Here we aim to discuss the most promising approaches for Treg-enhancing therapies, starting with adoptive transfer approaches and ex vivoexpansion cultures (polyclonal vs. antigen specific), followed by selective in vivostimulation methods. Furthermore, we address next generation concepts for Treg function enhancement (CARs, TRUCKs, BARs) as well as the advantages and caveats inherit to each approach. Finally, this review will discuss the clinical experience with Treg therapy in ongoing and already published clinical trials; however, data on long-term results and efficacy are still very limited and many questions that might complicate clinical translation remain open. Here, we discuss the hurdles for clinical translation and elaborate on current Treg-based therapeutic options as well as their potencies for improving long-term graft survival in transplantation.

Strategies to Use Nanoparticles to Generate CD4 and CD8 Regulatory T Cells for the Treatment of SLE and Other Autoimmune Diseases

Autoimmune diseases are disorders of immune regulation where the mechanisms responsible for self-tolerance break down and pathologic T cells overcome the protective effects of T regulatory cells (Tregs) that normally control them. The result can be the initiation of chronic inflammatory diseases. Systemic lupus erythematosus (SLE) and other autoimmune diseases are generally treated with pharmacologic or biological agents that have broad suppressive effects. These agents can halt disease progression, yet rarely cure while carrying serious adverse side effects. Recently, nanoparticles have been engineered to correct homeostatic regulatory defects and regenerate therapeutic antigen-specific Tregs. Some approaches have used nanoparticles targeted to antigen presenting cells to switch their support from pathogenic T cells to protective Tregs. Others have used nanoparticles targeted directly to T cells for the induction and expansion of CD4+ and CD8+ Tregs. Some of these T cell targeted nanoparticles have been formulated to act as tolerogenic artificial antigen presenting cells. This article discusses the properties of these various nanoparticle formulations and the strategies to use them in the treatment of autoimmune diseases. The restoration and maintenance of Treg predominance over effector cells should promote long-term autoimmune disease remission and ultimately prevent them in susceptible individuals.

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.

Identification, selection, and expansion of non-gene modified alloantigen-reactive Tregs for clinical therapeutic use

Transplantation is limited by the need for life-long pharmacological immunosuppression, which carries significant morbidity and mortality. Regulatory T cell (Treg) therapy holds significant promise as a strategy to facilitate immunosuppression minimization. Polyclonal Treg therapy has been assessed in a number of Phase I/II clinical trials in both solid organ and hematopoietic transplantation. Attention is now shifting towards the production of alloantigen-reactive Tregs (arTregs) through co-culture with donor antigen. These allospecific cells harbour potent suppressive function and yet their specificity implies a theoretical reduction in off-target effects. This review will cover the progress in the development of arTregs including their potential application for clinical use in transplantation, the knowledge gained so far from clinical trials of Tregs in transplant patients, and future directions for Treg therapy.

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.

Clinical Grade Regulatory CD4+ T Cells (Tregs): Moving Toward Cellular-Based Immunomodulatory Therapies

Regulatory T cells (Tregs) are CD4⁺ T cells that are key players of immune tolerance. They are powerful suppressor cells, able to impact the function of numerous immune cells, including key effectors of inflammation such as effector T cells. For this reason, Tregs are an ideal candidate for the development of cell therapy approaches to modulate immune responses. Treg therapy has shown promising results so far, providing key knowledge on the conditions in which these cells can provide protection and demonstrating that they could be an alternative to current pharmacological immunosuppressive therapies. However, a more comprehensive understanding of their characteristics, isolation, activation, and expansion is needed to be able design cost effective therapies. Here, we review the practicalities of making Tregs a viable cell therapy, in particular, discussing the challenges faced in isolating and manufacturing Tregs and defining what are the most appropriate applications for this new therapy.

Cell Therapy in Kidney Transplantation: Focus on Regulatory T Cells

Renal transplantation is the renal replacement modality of choice for suitable candidates with advanced CKD or ESRD. Prevention of rejection, however, requires treatment with nonspecific pharmacologic immunosuppressants that carry both systemic and nephrologic toxicities. Use of a patient's own suppressive regulatory T cells (Tregs) is an attractive biologic approach to reduce this burden. Here, we review the immunologic underpinnings of Treg therapy and technical challenges to developing successful cell therapy. These issues include the selection of appropriate Treg subsets, ex vivo Treg expansion approaches, how many Tregs to administer and when, and how to care for patients after Treg administration.

Restoring immune tolerance in neuromyelitis optica: Part II

Neuromyelitis optica spectrum disorder (NMO/SD) and its clinical variants have at their core the loss of immune tolerance to aquaporin-4 and perhaps other autoantigens. The characteristic phenotype is disruption of astrocyte function and demyelination of spinal cord, optic nerves, and particular brain regions. In this second of a 2-part article, we present further perspectives regarding the pathogenesis of NMO/SD and how this disease might be amenable to emerging technologies aimed at restoring immune tolerance to disease-implicated self-antigens. NMO/SD appears to be particularly well-suited for these strategies since aquaporin-4 has already been identified as the dominant autoantigen. The recent technical advances in reintroducing immune tolerance in experimental models of disease as well as in humans should encourage quantum leaps in this area that may prove productive for novel therapy. In this part of the article series, the potential for regulatory T and B cells is brought into focus, as are new approaches to oral tolerization. Finally, a roadmap is provided to help identify potential issues in clinical development and guide applications in tolerization therapy to solving NMO/SD through the use of emerging technologies. Each of these perspectives is intended to shine new light on potential cures for NMO/SD and other autoimmune diseases, while sparing normal host defense mechanisms.

Transplantation Tolerance Induction: Cell Therapies and Their Mechanisms

Cell-based therapies have been studied extensively in the context of transplantation tolerance induction. The most successful protocols have relied on transfusion of bone marrow prior to the transplantation of a renal allograft. However, it is not clear that stem cells found in bone marrow are required in order to render a transplant candidate immunologically tolerant. Accordingly, mesenchymal stem cells, regulatory myeloid cells, T regulatory cells, and other cell types are being tested as possible routes to tolerance induction, in the absence of donor-derived stem cells. Early data with each of these cell types have been encouraging. However, the induction regimen capable of achieving consistent tolerance, while avoiding unwanted sided effects, and which is scalable to the human patient, has yet to be identified. Here, we present the status of investigations of various tolerogenic cell types and the mechanistic rationale for their use in tolerance induction protocols.

Regulatory T Cells: Serious Contenders in the Promise for Immunological Tolerance in Transplantation

Regulatory T cells (Tregs) play an important role in immunoregulation and have been shown in animal models to promote transplantation tolerance and curb autoimmunity following their adoptive transfer. The safety and potential therapeutic efficacy of these cells has already been reported in Phase I trials of bone-marrow transplantation and type I diabetes, the success of which has motivated the broadened application of these cells in solid-organ transplantation. Despite major advances in the clinical translation of these cells, there are still key questions to be addressed to ensure that Tregs attest their reputation as ideal candidates for tolerance induction. In this review, we will discuss the unique traits of Tregs that have attracted such fame in the arena of tolerance induction. We will outline the protocols used for their ex vivo expansion and discuss the future directions of Treg cell therapy. In this regard, we will review the concept of Treg heterogeneity, the desire to isolate and expand a functionally superior Treg population and report on the effect of differing culture conditions. The relevance of Treg migratory capacity will also be discussed together with methods of in vivo visualization of the infused cells. Moreover, we will highlight key advances in the identification and expansion of antigen-specific Tregs and discuss their significance for cell therapy application. We will also summarize the clinical parameters that are of importance, alongside cell manufacture, from the choice of immunosuppression regimens to the number of injections in order to direct the success of future efficacy trials of Treg cell therapy. Years of research in the field of tolerance have seen an accumulation of knowledge and expertise in the field of Treg biology. This perpetual progression has been the driving force behind the many successes to date and has put us now within touching distance of our ultimate success, immunological tolerance.

Effect of cell density and HLA-DR incompatibility on T-cell proliferation and forkhead box P3 expression in human mixed lymphocyte reaction

BACKGROUND

The proliferation rates of human T cells in vitro are affected by some factors such as initial T-cell number, dose of stimulating cells, and duration of culture. The transcription factor forkhead box P3 (FoxP3) has been used to identify regulatory T cells in humans and is thought to correlate with tolerance to allogeneic organ transplant. Thus, it is important to optimize conditions to expand FoxP3 cell proliferation to improve engraftment of allogeneic organ transplants.

METHODS

We studied proliferative responses and FoxP3 expression in divided T cells with the use of flow cytometric analysis of Ki-67 in culture of different concentrations of responding cells (6 × 10(6), 4 × 10(6), 2 × 10(6), 1 × 10(6), and 0.5 × 10(6)cells/mL), different types of stimulating cells (lymphocytes and low density cells), and different numbers of HLA mismatches.

RESULTS

The proportion of CD3(+) cells, CD4(+)CD25(+) cells, and CD4(+)CD25(+)FoxP3(+) cells among mononuclear cells were highest at initial cell concentration of 2 × 10(6) responder cells/mL with lymphocytes as stimulators at day-5 mixed lymphocyte reaction (MLR). They were highest at a concentration of 4 × 10(6) responder cells/mL with low density cells as stimulators. The recovery (%), proportion of CD3(+) cells, CD4(+)CD25(+) cells, and CD4(+)CD25(+)FoxP3(+) cells with 2 HLA-DR incompatibility were significantly higher than those of 1 HLA-DR incompatibility at day-5 MLR.

CONCLUSIONS

Initial cell concentration and HLA-DR incompatibility can affect the generation of FoxP3+ T cells in human MLR. These factors could be considered for efficient generation of Tregs for clinical trials in the future.

The therapeutic potential of regulatory T cells for the treatment of autoimmune disease

INTRODUCTION

Immune tolerance remains the holy grail of therapeutic immunology in the fields of organ and tissue transplant rejection, autoimmune diseases, and allergy and asthma. We have learned that FoxP3(+)CD4(+) regulatory T cells play a vital role in both the induction and maintenance of self-tolerance.

AREAS COVERED

In this opinion piece, we highlight regulatory T cells (Treg) cell biology and novel immune treatments to take advantage of these cells as potent therapeutics. We discuss the potential to utilize Treg and Treg-friendly therapies to replace current general immunosuppressives and induce tolerance as a path towards a drug-free existence without associated toxicities.

EXPERT OPINION

Finally, we opine on the fact that biomedicine sits on the cusp of a new revolution: the use of human cells as versatile therapeutic engines. We highlight the challenges and opportunities associated with the development of a foundational cellular engineering science that provides a systematic framework for safely and predictably regulating cellular behaviors. Although Treg therapy has become a legitimate clinical treatment, development of the therapy will require a better understanding of the underlying Treg biology, manufacturing advances to promote cost effectiveness and combinations with other drugs to alter the pathogenicity/regulatory balance.

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.

Regulatory T-cell therapy in transplantation: moving to the clinic

Regulatory T cells (Tregs) are essential to transplantation tolerance and their therapeutic efficacy is well documented in animal models. Moreover, human Tregs can be identified, isolated, and expanded in short-term ex vivo cultures so that a therapeutic product can be manufactured at relevant doses. Treg therapy is being planned at multiple transplant centers around the world. In this article, we review topics critical to effective implementation of Treg therapy in transplantation. We will address issues such as Treg dose, antigen specificity, and adjunct therapies required for transplant tolerance induction. We will summarize technical advances in Treg manufacturing and provide guidelines for identity and purity assurance of Treg products. Clinical trial designs and Treg manufacturing plans that incorporate the most up-to-date scientific understanding in Treg biology will be essential for harnessing the tolerogenic potential of Treg therapy in transplantation.

Protection of islet grafts through transforming growth factor-β-induced tolerogenic dendritic cells

In type 1 diabetes, the insulin-producing β-cells are destroyed by the immune system. One way of restoring glucose control is to transplant β-cells from a donor. Although this procedure may restore endogenous insulin production, immunosuppressive treatment is needed to prevent the recipient from rejecting the donor-derived islets. We investigated the possibilities of transient expression of the immunosuppressive cytokine transforming growth factor (TGF)-β within islets to achieve long-term graft tolerance. We found that brief expression of TGF-β prevented rejection of syngeneic islets, that there was reduction of dendritic cell (DC) activation in the graft, and that there was reduced reactivation of T cells in the graft-draining lymph nodes. In vitro exposure of bone marrow-derived DCs to TGF-β reduced expression of costimulatory molecules CD80 and CD86, as well as production of proinflammatory cytokines such as interleukin-12 p70 in DCs, but did not alter levels of major histocompatibility complex classes I and II. Furthermore, the capacity of TGF-β-treated bone marrow-derived DCs to activate both CD4(+) and CD8(+) T cells was reduced. Adding TGF-β-conditioned tolerogenic DCs to the grafted islets led to long-term survival of the graft, demonstrating that TGF-β-induced tolerogenic DCs can provide an effective means to restore immune tolerance in an already established autoimmune disease.

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.

Regulatory T cells in the immunodiagnosis and outcome of kidney allograft rejection

Acute rejection (AR) is responsible for up to 12% of graft loss with the highest risk generally occurring during the first six months after transplantation. AR may be broadly classified into humoral as well as cellular rejection. Cellular rejection develops when donor alloantigens, presented by antigen-presenting cells (APCs) through class I or class II HLA molecules, activate the immune response against the allograft, resulting in activation of naive T cells that differentiate into subsets including cytotoxic CD8⁺ and helper CD4⁺ T cells type 1 (TH1) and TH2 cells or into cytoprotective immunoregulatory T cells (Tregs). The immune reaction directed against a renal allograft has been suggested to be characterized by two major components: a destructive one, mediated by CD4⁺ helper and CD8⁺ cytotoxic T cells, and a protective response, mediated by Tregs. The balance between these two opposite immune responses can significantly affect the graft survival. Many studies have been performed in order to define the role of Tregs either in the immunodiagnosis of transplant rejection or as predictor of the clinical outcome. However, information available from the literature shows a contradictory picture that deserves further investigation.

Tregs: application for solid-organ transplantation

PURPOSE OF REVIEW

Transfer of human regulatory T cells (Tregs) has become an attractive therapeutic alternative to improve the long-term outcome in transplantation and thus reduce the side-effects of conventional immunosuppressive drugs. Here, we summarize the recent findings on human Treg subsets, their phenotype and in-vivo function.

RECENT FINDINGS

In the last 2 years, it has become apparent that several Treg subsets exist that specifically regulate Th1-driven, Th2-driven, or Th17-driven immune responses; these subsets are very unstable and rapidly change their phenotype, for example, there is loss of Foxp3 expression upon extensive ex-vivo expansion and only the administration of rapamycin has been shown to be able to interfere reproducibly. New humanized mouse models incorporating human solid-organ grafts have been developed, which have been used to test the human Treg in-vivo function, and the first human Treg-cell products have been tested for safety and efficacy in stem cell transplantation.

SUMMARY

With the recent findings, we have gained a better understanding of Treg heterogeneity, plasticity and function. Using the outcomes of clinical trials in stem cell transplantation, we have learned that adoptive therapy of Tregs is well tolerated and we are now awaiting the first result in solid-organ transplantation from the 'ONE Study'.

[Use of regulatory T cells in cellular therapies in autoimmune diseases]

Self tolerance is dependent on regulatory T cells (Treg) which suppress effector T cells, avoiding autoimmunity. Functional and quantitative deficits of Treg have been reported in autoimmune diseases. A new therapeutic approach consisting in Treg adoptive transfer has proved to be efficient and safe in murine models. Two populations seem to be available for a clinical application: CD4(+)CD25(+)Foxp3(+) natural Treg derived from the thymus and induced regulatory T cells. First clinical trials have been applied to patients with autoimmune diseases. Classical treatments of autoimmune diseases are usually non-curative and require long-term administration. Treg cellular therapy may have a long-term effect and offers an alternative attractive approach.

Pathways of major histocompatibility complex allorecognition

PURPOSE OF REVIEW

Here, we review the pathways of allorecognition and their potential relevance to the balance between regulatory and effector responses following transplantation.

RECENT FINDINGS

Transplantation between nonidentical members of the same species elicits an immune response that manifests as graft rejection or persistence. Presentation of foreign antigen to recipient T cells can occur via three nonmutually exclusive routes, the direct, indirect and semi-direct pathways. Allospecific T cells can have effector or regulatory functions, and the relative proportions of the two populations activated following alloantigen presentation are two of the factors that determine the clinical outcome. Regulatory T cells have been the subject of significant research, and there is now greater understanding of their recruitment and function in the context of allorecognition.

SUMMARY

A greater understanding of the mechanisms underlying allorecognition may be fundamental to appreciating how these different populations are recruited and could in turn inform novel strategies for immunomodulation.

Therapeutic potential of induced and natural FoxP3(+) regulatory T cells for the treatment of Graft-versus-host disease

Graft-versus-host disease (GvHD) remains a major complication after allogeneic hematopoietic stem-cell-transplantation. Present GvHD prophylaxis and treatment is still based on unspecific immunosuppressive drug therapy. Over the last decade, the potential of cell-based therapies involving the infusion of regulatory T cells has emerged as a feasible alternative approach for the treatment and prevention of GvHD. Here we review current efforts to translate data obtained in rodent models into clinical trials. Special emphasis is placed on the variety of strategies to generate sufficient numbers of alloantigen-specific regulatory T cells for adoptive cell therapy. This can be achieved either by expansion or by induction of a regulatory phenotype in naive T cells. Stability of the immunosuppressive phenotype of transferred regulatory T cells even in the highly inflammatory environment of acute GvHD will be thereby a critical parameter for actual therapeutic application.

Antigen-specific T-regulatory cells can extend skin graft survival time in mice

This study investigated the effects of donor antigen-specific CD4(+)CD25(+) T-regulatory cells (Tregs) on skin allografts in mice. An allogeneic skin transplant model was established using donor C57BL/6 or DBA and recipient BALB/c mice. Recipients were divided into 4 groups: control group without intervention (CON; C57BL/6 to BALB/c), rapamycin gavage group (RAP; C57BL/6 to BALB/c), CD4(+)CD25(+) Tregs-treated group (TRE; C57BL/6 to BALB/c), in which recipients received transfusions of CD4(+)CD25(+) Tregs stimulated with C57BL/6-derived immature dendritic cells, and the third-party donor group (DBA; DBA to BALB/c) in which recipients received transfusions of BALB/c CD4(+)CD25(+) Tregs stimulated with C57BL/6-derived immature dendritic cells. Mean (SD) survival time of the skin allografts in the TRE group was 17.0 (3.4) days, significantly longer than in the other groups: CON, 6.9 (1.9) days; RAP, 10.3 (3.0) days; and DBA, 10.8 (3.6) days. The TRE group demonstrated a significantly greater expression of transforming growth factor-β and interleukin (IL)-10. Donor antigen-specific CD4(+)CD25(+) Tregs effectively extend skin allograft survival in mice.

Isolation, expansion and functional assessment of CD4+CD25+FoxP3+ regulatory T cells and Tr1 cells from uremic patients awaiting kidney transplantation

BACKGROUND

The immunosuppressive properties of regulatory T cells have emerged as an attractive tool for the development of immunotherapies in various disease contexts, e.g. to treat transplantation induced immune reactions. This paper focuses on the process of obtaining and functionally characterizing CD4+CD25+FoxP3+ regulatory T cells and Tr1 cells from uremic patients awaiting kidney transplantation.

METHODS

From October 2010 to March 2011 uremic patients awaiting living donor kidney transplantation, and their corresponding kidney donors, were enrolled in the study. A total of seven pairs were included. Isolation of CD4+CD25+FoxP3+ regulatory T cells was performed by magnetic activated cell sorting of peripheral blood mononuclear cells obtained from the uremic patients. Donor specific Tr1 cells were differentiated by repetitive stimulation of immature CD4+ T cells with immature dendritic cells, with the T cells coming from the future kidney recipients and the dendritic cells from the corresponding kidney donors. Cells were then expanded and functionally characterized by the one-way mixed leukocyte reaction and assessment of IL-10 production. Phenotypic analysis was performed by flow cytometry.

RESULTS

The fraction of CD4+CD25+FoxP3+ regulatory T cells after expansion varied from 39.1 to 50.4% and the cells retained their ability to substantially suppress the mixed leukocyte reaction in all but one patient (3.8-19.2% of the baseline stimulated leukocyte activity, p<0.05). Tr1 cells were successfully differentiated from all but one patient and produced high levels of IL-10 when stimulated with immature dendritic cells (1,275-11,038% of the baseline IL-10 secretion, p<0.05).

CONCLUSION

It is practically feasible to obtain and subsequently expand CD4+CD25+FoxP3+ regulatory T cells and Tr1 cells from uremic patients without loss of function as assessed by in vitro analyses. This forms a base for adoptive regulatory T cell therapy in the setting of living donor kidney transplantation.

Regulatory T cell therapy for the induction of clinical organ transplantation tolerance

The pursuit of transplantation tolerance is the holygrail in clinical organ transplantation. It has been established that regulatory T cells (Tregs) can confer donor-specific tolerance in mouse models of transplantation. However, this is crucially dependent on the strain combination, the organ transplanted and most importantly, the ratio of Tregs to alloreactive effector T cells. The ex vivo expansion of Tregs is one solution to increase the number of alloantigen specific cells capable of suppressing the alloresponse. Indeed, ex vivo expanded, alloantigen specific murine Tregs are shown to preferentially migrate to, and proliferate in, the graft and draining lymph node. In human transplantation it has been proposed that depletion of the majority of direct pathway alloreactive T cells will be required to tip the balance in favour of regulation. Ex vivo expansion of alloantigen specific, indirect pathway human Tregs, which can cross regulate the residual direct pathway has been established. Rapid expansion of these cells is possible, whilst they retain antigen specificity, suppressive properties and favourable homing markers. Furthermore, considerable progress has been made to define which immunosuppressive drugs favour the expansion and function of Tregs. Currently a series of clinical trials of adoptive Treg therapy in combination with depletion of alloreactive T cells and short term immunosuppression are underway for human transplantation with the aim of minimizing immunosuppressive drugs and completely withdrawal.

Tolerogenic dendritic cells and their role in transplantation

The pursuit of clinical transplant tolerance has led to enhanced understanding of mechanisms underlying immune regulation, including the characterization of immune regulatory cells, in particular antigen-presenting cells (APC) and regulatory T cells (Treg), that may play key roles in promoting operational tolerance. Dendritic cells (DC) are highly efficient APC that have been studied extensively in rodents and humans, and more recently in non-human primates. Owing to their ability to regulate both innate and adaptive immune responses, DC are considered to play crucial roles in directing the alloimmune response towards transplant tolerance or rejection. Mechanisms via which they can promote central and peripheral tolerance include clonal deletion, the induction of Treg, and inhibition of memory T cell responses. These properties have led to the use of tolerogenic DC as a therapeutic strategy to promote organ transplant tolerance. In rodents, infusion of donor- or recipient-derived tolerogenic DC can extensively prolong donor-specific allograft survival, in association with regulation of the host T cell response. In clinical transplantation, progress has been made in monitoring DC in relation to graft outcome, including studies in operational liver transplant tolerance. Although clinical trials involving immunotherapeutic DC for patients with cancer are ongoing, implementation of human DC therapy in clinical transplantation will require assessment of various critical issues. These include cell isolation and purification techniques, source, route and timing of administration, and combination immunosuppressive therapy. With ongoing non-human primate studies focused on DC therapy, these logistics can be investigated seeking the optimal approaches. The scientific rationale for implementation of tolerogenic DC therapy to promote clinical transplant tolerance is strong. Evaluation of technical and therapeutic logistic issues is an important next step prior to the application of tolerogenic DC in clinical organ transplantation.

Foxp3 expression in liver correlates with the degree but not the cause of inflammation

Patients with chronic viral hepatitis display increased expression of Foxp3 in liver, suggesting that Tregs expansion contributes to persistent infection. The purpose of this study was to elucidate whether the expression of Foxp3 relates not to the viral infection but to the resulting liver inflammation. Liver biopsies obtained from 69 individuals (26 chronic HBV hepatitis, 14 chronic HCV hepatitis, 11 nonalcoholic fatty liver disease, 8 autoimmune diseases, 2 methotrexate-related toxicity, and 8 controls) were examined, by qRT-PCR, for the mRNA expression of Foxp3, IL-10, TGF-β1, Fas, FasL, TRAIL, caspase-3, TNF-α, IFN-γ, and IL-1β. Significant increase of Foxp3 was observed in all disease groups compared to controls, which was positively correlated with the intensity of inflammation. The expression of the apoptosis mediators Fas, FasL, and TRAIL, but not of IL-10 and TGF-β1, was also significantly elevated. Our findings indicate that, independently of the initial inducer, liver inflammation is correlated with elevated expression of apoptosis mediators and is followed by local Treg accumulation. Further research towards the elucidation of the underlying casual relationships is required, in order to clarify whether our results signify the existence of a uniform Treg-mediated regulatory mechanism of apoptosis-induced inflammation.

Immunotherapy with regulatory T cells in transplantation

Regulatory T cell (Treg)-based immunotherapy is of great interest to induce tolerance in clinical transplantation settings. In fact, the first clinical trials of Treg infusion after stem cell transplantation have recently begun. However, many important issues regarding human Treg immunotherapy are still to be resolved. In this review, we provide a short update on Tregs and elaborate on various strategies for Treg-based immunotherapy. First, infusion of ex vivo-selected naturally occurring Tregs is addressed, with emphasis on Treg isolation, expansion, antigen specificity, homing and stability. Next, the potential of ex vivo-induced Treg transfusion strategies is discussed. Finally, therapies aimed at in vivo increase of Treg numbers or function are addressed. In addition, we summarize the current knowledge on effects of immunosuppressive drugs on Tregs. In the following years, we expect exciting new data regarding the clinical application of Treg immunotherapy in transplantation to be released.

T-cell alloimmunity and chronic allograft dysfunction

Solid organ transplantation is the standard treatment to improve both the quality of life and survival in patients with various end-stage organ diseases. The primary barrier against successful transplantation is recipient alloimmunity and the need to be maintained on immunosuppressive therapies with associated side effects. Despite such treatments in renal transplantation, after death with a functioning graft, chronic allograft dysfunction (CAD) is the most common cause of late allograft loss. Recipient recognition of donor histocompatibility antigens, via direct, indirect, and semidirect pathways, is critically dependent on the antigen-presenting cell (APC) and elicits effector responses dominated by recipient T cells. In allograft rejection, the engagement of recipient and donor cells results in recruitment of T-helper (Th) cells of the Th1 and Th17 lineage to the graft. In cases in which the alloresponse is dominated by regulatory T cells (Tregs), rejection can be prevented and the allograft tolerated with minimum or no immunosuppression. Here, we review the pathways of allorecognition that underlie CAD and the T-cell effector phenotypes elicited as part of the alloresponse. Future therapies including depletion of donor-reactive lymphocytes, costimulation blockade, negative vaccination using dendritic cell subtypes, and Treg therapy are inferred from an understanding of these mechanisms of allograft rejection.

Adoptive transfer of CD4+CD25+ regulatory cells combined with low-dose sirolimus and anti-thymocyte globulin delays acute rejection of renal allografts in Cynomolgus monkeys

Although donor alloantigen specific Treg cells play an important role in transplant tolerance, therapeutic applications are limited by their low frequency. In this study, isolated Tregs from Cynomolgus monkeys were efficiently expanded by a co-culture system, and maintained suppressive function on the proliferation of CD4(+) effector cells in vitro. Adoptive transfer of expanded donor alloantigen specific Tregs without any immunosuppressants could prolong survival of MHC-mismatched allografts in Cynomolgus monkeys. To reach the feasibility of clinical transplantation, our objectives focused on whether exposure of monkey Tregs to immunosuppressants could preserve suppressive function in vitro and in vivo. The results showed that low-dose sirolimus selectively expanded Tregs, increased the expression of CD25(bright) and Foxp3 markers, and suppressed TCR- or allo-antigens induced CD4(+) T cell proliferation in vitro. In vivo, after pre-treated with anti-thymocyte globulin (ATG) for consecutive 3days, a 14-day therapy of adoptive infusion of donor alloantigen-specific Tregs combined with low-dose sirolimus delayed acute rejection of renal allografts in Cynomolgus monkeys, showing an MST of 48.5days as compared with those of untreated and sirolimus-treated monkeys (7days and 22days). The frequencies of CD4(+)CD25(bright) T cells were significantly elevated in mesenteric lymph nodes vs. those in inguino lymph nodes and peripheral blood. In summary, expanded donor alloantigen specific Tregs exposed to sirolimus can preserve inhibition in vitro and in vivo. Tregs are more resistant to sirolimus than other T cells. Expanded donor alloantigen specific Tregs combined with sirolimus and ATG prolongs renal allograft survival in monkeys, suggesting that sirolimus might be one of the best synergists for Tregs therapy.

Adoptive regulatory T cell therapy: challenges in clinical transplantation

PURPOSE OF REVIEW

The identification and characterisation of regulatory T cells (Tregs) has recently opened up exciting opportunities for Treg cell therapy in transplantation. In this review, we outline the basic biology of Tregs and discuss recent advances and challenges for the identification, isolation and expansion of these cells for cell therapy.

RECENT FINDINGS

Tregs of thymic origin have been shown to be key regulators of immune responses in mice and humans, preventing autoimmunity, graft-versus-host disease and organ graft rejection in the transplantation setting. To date, a variety of different methods to isolate and expand Tregs ex vivo have been advocated. Although promising, relatively few clinical trials of human Treg cell infusion have been initiated.

SUMMARY

Many key questions about Treg cell therapy still remain and here we provide an in-depth analysis and highlight the challenges and opportunities for immune intervention with Treg-based therapeutics in clinical transplantation.

Dendritic cells and regulation of alloimmune responses: relevance to outcome and therapy of organ transplantation

Dendritic cells are uniquely well-equipped for antigen capture, processing and presentation. They are highly-efficient antigen-presenting cells that induce and regulate T-cell reactivity. Due to their inherent tolerogenicity, immature dendritic cells offer considerable potential as candidate cellular vaccines for negative regulation of immune reactivity/promotion of tolerance. Both classic myeloid and, more recently, characterized plasmacytoid dendritic cells, exhibit tolerogenic properties. Manipulation of dendritic cells differentiation/ maturation in the laboratory using cytokines, pharmacologic agents or genetic engineering approaches can render stably immature dendritic cells that promote organ transplant tolerance in rodents. There are also indications from human studies of the ability of dendritic cells to promote T-cell tolerance and induce T-regulatory cells, with potential for therapeutic application in organ transplantation. In addition, recent clinical observations suggest that modulation of dendritic cell function (e.g., by immunosuppressive drugs) affects the outcome of transplantation. The challenge confronting applied dendritic cell biology is the identification of optimal strategies and therapeutic regimens to allow the potential of these powerful immune regulatory cells to be realized in the clinic.

Regulatory T cells in transplantation: does extracellular adenosine triphosphate metabolism through CD39 play a crucial role?

Despite tremendous improvements in short-term renal allograft survival, many patients still have chronic rejection or side effects of nonspecific immunosuppression. The discovery of Foxp3(+) regulatory T cells (Tregs) has revolutionized the concepts in immunoregulation and offers perspectives for overcoming rejection. Recently, a subset of Foxp3(+)CD39(+) effector/memory-like Tregs (T(REM)) was identified. The role of CD39(+) Tregs in immunoregulation is supported by the occurrence of alopecia areata and experimental autoimmune encephalomyelitis in CD39-deficient mice and by the failure of CD39(-) Tregs to suppress contact hypersensitivity. In humans, CD39 polymorphisms have been associated with diabetes and nephropathy, and multiple sclerosis patients have reduced numbers of blood CD39(+) Tregs. Preliminary experiments in a murine transplantation model showed that CD39(+) Tregs can determine allograft outcome. CD39 degrades the extracellular adenosine triphosphate (ATP) released during tissue injury, which otherwise would trigger inflammation. Currently, our groups are assessing the role of CD39(+) Tregs and extracellular ATP metabolism in clinical transplantation and whether tolerogenic Treg profiles possess immunopredictive value, envisioning the development of clinical trials using CD39(+) Treg-based vaccination for autoimmunity or transplantation. This is a comprehensive review on the fundamentals of Treg biology, the potential role of ATP metabolism in immunoregulation, and the potential use of Treg-based immunotherapy in transplantation.

Rhesus monkey immature monocyte-derived dendritic cells generate alloantigen-specific regulatory T cells from circulating CD4+CD127-/lo T cells

BACKGROUND

Generation of non-human primate regulatory T cells (Treg) with alloantigen (alloAg) specificity would allow their testing in preclinical transplant models. Low recovery of Treg from peripheral blood limits their potential utility. In small animals and humans, conventional myeloid dendritic cells (DC) have been shown to select or induce alloAg-specific Treg.

METHODS

We combined enrichment of rhesus macaque blood CD4 Treg based on IL-7Ralpha (CD127) expression with their stimulation in mixed leukocyte cultures with immature, allogeneic control or vitamin (Vit) D3/IL-10-conditioned monocyte-derived DC. After co-culture in IL-2 and IL-15 for up to 14 days, the ability of the resulting T cells to suppress alloreactive effector T-cell proliferation was assessed.

RESULTS

CD4CD127 T cells represented approximately 7% of normal rhesus circulating CD4 T cells and were enriched for forkhead box P3 (Foxp3) cells. When stimulated with control allogeneic DC, they exhibited much inferior proliferative responses compared with bulk CD4 or CD4CD127 cells. This anergic state was reversed by exogenous IL-2 and IL-15. After 10 to 14 days culture of CD4CD127 T cells with immature allogeneic DC, particularly maturation-resistant VitD3/IL-10 DC, the frequency of Foxp3 T cells was increased. The cultured cells markedly inhibited CD4 effector T-cell proliferation in a dose-related and donor alloAg-specific manner.

CONCLUSION

Stimulation of rhesus CD4CD127 T cells with immature and especially maturation-resistant allogeneic DC, generated highly-suppressive, alloAg-specific Treg. Without resorting to a more purified starting population, this approach may have therapeutic utility in clinically relevant transplant models.

The human "Treg MLR": immune monitoring for FOXP3+ T regulatory cell generation

BACKGROUND

Controversy exists about the conditions effecting the development of forkhead/winghead helix transcription factor P3 (FOXP3) expressing T cells and their relevance in transplant recipients.

METHODS

We generated carboxy-fluorescein diacetate succinimidyl ester-labeled CD4+CD25 high FOXP3+ cells in mixed lymphocyte reactions (MLRs) ("the Treg MLR"), with varying human leukocyte antigen (HLA) disparities and cell components. Five color flow cytometry and H-thymidine uptakes were the readouts.

RESULTS

(1) Despite lower stimulation indices (SIs) than two DR-mismatched MLRs, 2 DR-matched MLRs generated more than twofold higher percentages when gating on proliferating CD4+CD25 high FOXP3+ cells; (2) Even with low numbers of proliferating cells, autologous and HLA identical MLRs generated the highest FOXP3+:FOXP3- cell ratios; (3) Elimination of either non-CD3+ responding cells (resulting in "direct presentation" only) or responding CD25+ (Treg generating) cells increased the SI but inhibited proliferating CD4+CD25 high FOXP3+ cell development; (4) MLR-generated CD4+CD25 high FOXP3+ cells added as third components specifically inhibited the same freshly set MLR SI and caused recruitment of new CD4+CD25 high FOXP3+ cells. As an example of the "Treg MLR" immune monitoring potential, addition of third component peripheral blood mononuclear cell containing high percentages of CD4+CD25 high FOXP3+ cells from an HLA identical kidney transplant recipient (in a tolerance protocol) caused donor-specific Treg MLR inhibition or recruitment. This was similar to the third component MLR Tregs generated entirely in vitro.

CONCLUSION

In the Treg MLR, the generation of CD4+CD25 high FOXP3+ cells is more pronounced in the context of self-recognition (HLA matching, indirect presentation). These cells can be assayed for MLR inhibitory and Treg recruitment functions, so as to immunologically monitor the allospecific regulation after transplantation.

Successful reduction of immunosuppression in older renal transplant recipients who exhibit donor-specific regulation

BACKGROUND

We hypothesized that T-regulatory cells specific for donor alloantigens would protect a renal transplant during partial withdrawal of immunosuppression.

METHODS

To test this hypothesis, 32 renal transplant recipients aged 55 years and older with excellent renal function were tested for donor-specific regulation (DSR) by trans-vivo delayed type hypersensitivity assay at the time of enrollment (T=0) and 6 months later (T=6). Twenty-two patients had prednisone withdrawn during a 3-month period, whereas 10 controls were maintained on triple therapy (prednisone, cyclosporine, and mycophenolate).

RESULTS

Of 22 patients in the steroid withdrawal group, 10 were DSR+ and 12 were DSR- at the time of enrollment (T=0). None of the DSR+ patients experienced acute rejection, nor did any have donor-specific human leukocyte antigen (HLA) antibody during or after withdrawal. Of 12 DSR- patients, three developed acute rejection, which were reversed with bolus steroid treatment, and four were donor-specific antibody+ at T=0 or T=6. Two years later, 80% (8 of 10) of DSR+ patients in the withdrawal group remain steroid free while maintaining excellent renal function, as compared with only 58% (7 of 12) DSR- patients. Patient survival at 4 years was similar for DSR+ (9 of 10) and DSR- (11 of 12) patients in the withdrawal group. Patients maintained on triple therapy remained rejection free during the 4-year follow-up regardless of initial DSR status, with patient survival rate of 70% (7 of 10).

CONCLUSIONS

DSR before steroid withdrawal may identify a subset of transplant patients who could benefit from reduction of immunosuppression without elevated risk of rejection or deteriorating renal function.

Superantigen-activated regulatory T cells inhibit the migration of innate immune cells and the differentiation of naive T cells

Regulatory T cells can be used as tools to suppress pathogenic T cells in autoimmunity, graft-vs-host-disease, and transplantation. But even when high numbers of Ag-specific regulatory T cells are available, it is still possible under certain in vivo and in vitro conditions for effector T cells to escape effective control. Current reports suggest that the degree of suppression is modulated by the inflammatory milieu, which can induce resistance to suppression in effector T cells or subvert the inhibitory function of the regulatory T cells. Cells of the innate immune system integrate early signals of injury and infection and have a major impact on the ensuing inflammation. Hence, the modification of these initial events can be key to allowing suppression to dominate. The approach we took here was to test whether the in vivo preactivation of endogenous regulatory T cells with a superantigen could enhance their suppressive potency. We provide evidence that this not only proved effective in expanding the pool of preactivated regulatory T cells but also in preventing the migration of NK cells and granulocytes upon sensitization with matured dendritic cells. The attenuation of innate immune activation was accompanied by linked suppression of adoptively transferred OVA-specific T cells when APC coexpressing OVA and the superantigen were injected. These data suggest that the preactivation of regulatory T cells is a promising approach to increase their potency.

Indefinite mouse heart allograft survival in recipient treated with CD4(+)CD25(+) regulatory T cells with indirect allospecificity and short term immunosuppression

CD4(+)CD25(+) regulatory T cells (Tregs) play a crucial role in controlling immune responses. It is an appealing strategy to harness Tregs for adoptive cell therapy to induce tolerance to allografts. Several approaches have been developed to expand antigen-specific Tregs. Despite the large body of experimental data from murine studies demonstrating the great potential of these cells for clinical application, Treg adoptive transfer therapy was used in immunodeficient animals or in strain combinations with limited histiocompatibility. The aim of this study was to investigate whether Treg lines can protect from allograft rejection in a fully MHC-mismatched strain combination and whether the presence of Tregs with indirect allospecificity offered an advantage compared to self-reactive Tregs. Treg lines with self-specificity or with indirect allospecificity were generated by stimulating BL/6 CD4(+)CD25(+) T cells with autologous immature DCs either unpulsed or pulsed with K(d) peptide. The Treg lines were injected into recipient mice in combination with temporary depletion of CD8(+) T cells and a short course of Rapamycin. The data demonstrate that Treg lines with indirect allospecificity can be generated and most importantly they can induce indefinite survival of BALB/c hearts transplanted into BL/6 recipients when combined with short term immunosuppression. However, the Treg lines with self-specificity were only slightly less effective. The data presented in this study demonstrate the potential of ex vivo expanded Treg lines for adoptive cell therapy to promote transplantation tolerance.

Direct expansion of human allospecific FoxP3+CD4+ regulatory T cells with allogeneic B cells for therapeutic application

Compelling evidence from animal studies has demonstrated that allospecific FoxP3(+)CD4(+) regulatory T (Treg) cells expanded ex vivo can be used as effective therapeutic tools in the treatment of allograft rejection and graft-vs-host disease. Despite the promising results from animal studies, there remain major barriers to developing Treg cell-based immunotherapy in humans. Currently, no effective approach has been established for selective expansion of human allospecific Treg cells ex vivo. Additionally, the very low frequency of Treg cells present in human peripheral blood could pose a formidable challenge to obtaining a sufficient number of Treg cells from a single donor for ex vivo expansion for therapeutic utilization. Extending our recent finding that mouse B cells preferentially induce expansion of alloreactive Treg cells, we report herein that human Treg cells can be expanded ex vivo with allogeneic B cells. The expanded Treg cells express very high levels of FoxP3, maintain anergic phenotype, and are potent suppressors capable of inhibiting the alloproliferation of third-party responder T cells at very low Treg-to-T effector cell ratio in an alloantigen-specific manner. The alloantigen specificity demonstrated by B cell-expanded Treg cells is not determined by the HLA haplotypes of the Treg cells, but it is induced and determined by the haplotype of the B cells used to expand them. Our findings represent a significant advance in the development of Treg cell-based immunotherapy in humans and raise the possibility of using third-party Treg cells for therapeutic applications.