IL-2 therapy preferentially expands adoptively transferred donor-specific Tregs improving skin allograft survival

Paenibacillus exopolysaccharide alleviates Malassezia-induced skin damage: Enhancing skin barrier function, regulating immune responses, and modulating microbiota

Numerous studies have established a strong association between Malassezia and various skin disorders, including atopic dermatitis. Finding appropriate methods or medications to alleviate Malassezia-induced skin damage is of notable public interest. This study aimed to evaluate the therapeutic effect of the exopolysaccharide EPS1, produced by Paenibacillus polymyxa, on Malassezia restricta-induced skin damage. In vitro assays indicated that EPS1 reduced the expression of pro-inflammatory cytokine genes in TNF-α-induced HaCaT cells. In a murine model, EPS1 was found to mitigate clinical symptoms, reduce epidermal thickness and mast cell infiltration, improve skin barrier function, decrease pro-inflammatory cytokine levels associated with type 17 inflammation, enhance Tregs in the spleen, upregulate the transcription of Treg-related genes in skin lesions, and modulate the skin microbiota. This study is the first to report the alleviating effect of Paenibacillus exopolysaccharide on Malassezia-induced skin inflammation and its impact on the skin microbiota. These findings support the potential of Paenibacillus exopolysaccharides as consumer products and therapeutic agents for managing Malassezia-induced skin damage by improving skin barrier function, modulating immune responses, and influencing skin microbiota.

Cellular strategies to induce immune tolerance after liver transplantation: Clinical perspectives

Liver transplantation (LT) has become the most efficient treatment for pediatric and adult end-stage liver disease and the survival time after transplantation is becoming longer due to the development of surgical techniques and perioperative management. However, long-term side-effects of immunosuppressants, like infection, metabolic disorders and malignant tumor are gaining more attention. Immune tolerance is the status in which LT recipients no longer need to take any immunosuppressants, but the liver function and intrahepatic histology maintain normal. The approaches to achieve immune tolerance after transplantation include spontaneous, operational and induced tolerance. The first two means require no specific intervention but withdrawing immunosuppressant gradually during follow-up. No clinical factors or biomarkers so far could accurately predict who are suitable for immunosuppressant withdraw after transplantation. With the understanding to the underlying mechanisms of immune tolerance, many strategies have been developed to induce tolerance in LT recipients. Cellular strategy is one of the most promising methods for immune tolerance induction, including chimerism induced by hematopoietic stem cells and adoptive transfer of regulatory immune cells. The safety and efficacy of various cell products have been evaluated by prospective preclinical and clinical trials, while obstacles still exist before translating into clinical practice. Here, we will summarize the latest perspectives and concerns on the clinical application of cellular strategies in LT recipients.

Molecular Engineering of Interleukin-2 for Enhanced Therapeutic Activity in Autoimmune Diseases

The interleukin-2 (IL-2) cytokine plays a crucial role in regulating immune responses and maintaining immune homeostasis. Its immunosuppressive effects have been harnessed therapeutically via administration of low cytokine doses. Low-dose IL-2 has shown promise in the treatment of various autoimmune and inflammatory diseases; however, the clinical use of IL-2 is complicated by its toxicity, its pleiotropic effects on both immunostimulatory and immunosuppressive cell subsets, and its short serum half-life, which collectively limit the therapeutic window. As a result, there remains a considerable need for IL-2-based autoimmune disease therapies that can selectively target regulatory T cells with minimal off-target binding to immune effector cells in order to prevent cytokine-mediated toxicities and optimize therapeutic efficacy. In this review, we discuss exciting advances in IL-2 engineering that are empowering the development of novel therapies to treat autoimmune conditions. We describe the structural mechanisms of IL-2 signaling, explore current applications of IL-2-based compounds as immunoregulatory interventions, and detail the progress and challenges associated with clinical adoption of IL-2 therapies. In particular, we focus on protein engineering approaches that have been employed to optimize the regulatory T-cell bias of IL-2, including structure-guided or computational design of cytokine mutants, conjugation to polyethylene glycol, and the development of IL-2 fusion proteins. We also consider future research directions for enhancing the translational potential of engineered IL-2-based therapies. Overall, this review highlights the immense potential to leverage the immunoregulatory properties of IL-2 for targeted treatment of autoimmune and inflammatory diseases.

Promises and Pitfalls of Next-Generation Treg Adoptive Immunotherapy

Regulatory T cells (Tregs) are fundamental to maintaining immune homeostasis by inhibiting immune responses to self-antigens and preventing the excessive activation of the immune system. Their functions extend beyond immune surveillance and subpopulations of tissue-resident Treg cells can also facilitate tissue repair and homeostasis. The unique ability to regulate aberrant immune responses has generated the concept of harnessing Tregs as a new cellular immunotherapy approach for reshaping undesired immune reactions in autoimmune diseases and allo-responses in transplantation to ultimately re-establish tolerance. However, a number of issues limit the broad clinical applicability of Treg adoptive immunotherapy, including the lack of antigen specificity, heterogeneity within the Treg population, poor persistence, functional Treg impairment in disease states, and in vivo plasticity that results in the loss of suppressive function. Although the early-phase clinical trials of Treg cell therapy have shown the feasibility and tolerability of the approach in several conditions, its efficacy has remained questionable. Leveraging the smart tools and platforms that have been successfully developed for primary T cell engineering in cancer, the field has now shifted towards "next-generation" adoptive Treg immunotherapy, where genetically modified Treg products with improved characteristics are being generated, as regards antigen specificity, function, persistence, and immunogenicity. Here, we review the state of the art on Treg adoptive immunotherapy and progress beyond it, while critically evaluating the hurdles and opportunities towards the materialization of Tregs as a living drug therapy for various inflammation states and the broad clinical translation of Treg therapeutics.

Tregs integrate native and CAR-mediated costimulatory signals for control of allograft rejection

Tregs expressing chimeric antigen receptors (CAR-Tregs) are a promising tool to promote transplant tolerance. The relationship between CAR structure and Treg function was studied in xenogeneic, immunodeficient mice, revealing advantages of CD28-encoding CARs. However, these models could underrepresent interactions between CAR-Tregs, antigen-presenting cells (APCs), and donor-specific Abs. We generated Tregs expressing HLA-A2-specific CARs with different costimulatory domains and compared their function in vitro and in vivo using an immunocompetent model of transplantation. In vitro, the CD28-encoding CAR had superior antigen-specific suppression, proliferation, and cytokine production. In contrast, in vivo, Tregs expressing CARs encoding CD28, ICOS, programmed cell death 1, and GITR, but not 4-1BB or OX40, all extended skin allograft survival. To reconcile in vitro and in vivo data, we analyzed effects of a CAR encoding CD3ζ but no costimulatory domain. These data revealed that exogenous costimulation from APCs can compensate for the lack of a CAR-encoded CD28 domain. Thus, Tregs expressing a CAR with or without CD28 are functionally equivalent in vivo, mediating similar extension of skin allograft survival and controlling the generation of anti-HLA-A2 alloantibodies. This study reveals a dimension of CAR-Treg biology and has important implications for the design of CARs for clinical use in Tregs.

Regulatory T cells in autoimmune kidney diseases and transplantation

Regulatory T (Treg) cells that express the transcription factor forkhead box protein P3 (FOXP3) are naturally present in the immune system and have roles in the maintenance of immunological self-tolerance and immune system and tissue homeostasis. Treg cells suppress T cell activation, expansion and effector functions by various mechanisms, particularly by controlling the functions of antigen-presenting cells. They can also contribute to tissue repair by suppressing inflammation and facilitating tissue regeneration, for example, via the production of growth factors and the promotion of stem cell differentiation and proliferation. Monogenic anomalies of Treg cells and genetic variations of Treg cell functional molecules can cause or predispose patients to the development of autoimmune diseases and other inflammatory disorders, including kidney diseases. Treg cells can potentially be utilized or targeted to treat immunological diseases and establish transplantation tolerance, for example, by expanding natural Treg cells in vivo using IL-2 or small molecules or by expanding them in vitro for adoptive Treg cell therapy. Efforts are also being made to convert antigen-specific conventional T cells into Treg cells and to generate chimeric antigen receptor Treg cells from natural Treg cells for adoptive Treg cell therapies with the aim of achieving antigen-specific immune suppression and tolerance in the clinic.

Membrane-bound IL-2 improves the expansion, survival, and phenotype of CAR Tregs and confers resistance to calcineurin inhibitors

Background

Regulatory T cells (Tregs) play an important role in the maintenance of immune homeostasis and the establishment of immune tolerance. Since Tregs do not secrete endogenous IL-2, they are especially dependent on external IL-2. IL-2 deficiency leads to lower Treg numbers, instability of the Treg phenotype and loss of immune regulation. After organ transplantation, patients are treated with calcineurin inhibitors (CNIs), which further limits available IL-2. Application of low-dose IL-2 expands Tregs but also activates NK and CD8+ T cells. It was recently shown that graft-specific Tregs recognizing mismatched MHC I molecules via a chimeric antigen receptor were far more potent than polyclonal Tregs in the regulation of immune responses after solid organ transplantation in a humanized mouse model.

Methods

Therefore, our aim was to enhance the function and stability of transferred CAR-Tregs via expression of membrane-associated IL-2 (mbIL-2).

Results

mbIL-2 promoted higher survival, phenotypic stability, and function among CAR-Tregs than observed in clinical trials. The cells were also more stable under inflammatory conditions. In a preclinical humanized mouse model, we demonstrated that mbIL-2 CAR Tregs survive better in the Treg niche than control CAR Tregs and are even resistant to CNI therapy without affecting other Tregs, thus acting mainly in cis.

Discussion

The functional and phenotypic improvements observed after membrane-attached IL-2 expression in CAR-Tregs will be important step for enhancing CAR-Treg therapies currently being tested in clinical trials for use after kidney and liver transplantation as well as in autoimmune diseases.

The intragraft vascularized bone marrow induces secondary donor-specific mystacial pad allograft tolerance

Introduction

Vascularized bone marrow (VBM) is essential in tolerance induction through chimerism. We hypothesized that the inclusion of VBM contributes to the induction of mystacial pad allotransplantation tolerance.

Method

In this study, 19 VBM, nine mystacial pad, and six sequential VBM and mystacial pad allografts were transplanted from Brown Norway (BN) rats to Lewis (LEW) rats to test our hypothesis. The VBM recipients were divided into antilymphocyte serum (ALS) monotherapy group (two doses of ALS on day 3 pretransplantation and day 1 posttransplantation), immunosuppressant group [a week of 2 mg/kg/day tacrolimus (Tac) and 3 weeks of 3 mg/kg/day rapamycin (RPM)], and combined therapy group. The mystacial pad recipients were divided into VBM and non-VBM transplantation groups, and both groups were treated with an immunosuppression regimen that consists of ALS, Tac, and RPM. For the recipients of sequential VBM and mystacial pad allotransplantations, additional Tac was given 1 week after mystacial pad transplantation. Allograft survival, donor-specific tolerance, and chimerism level were evaluated.

Results

With the administration of ALS and short-term Tac and RPM treatments, VBM recipients demonstrated long-term graft survival (>120 days) with persistent chimerism for 30 days. CD3+ T cells from tolerant rats showed donor-specific hyporesponsiveness and tolerance to donor skin grafts but not to third-party counterparts. Furthermore, mystacial pad graft recipients with VBM transplantation exhibited a higher allograft survival rate than those without VBM transplantation [median survival time (MST) >90 days vs. 70 days, p < 0.05].

Conclusion

This study demonstrated that VBM transplantation is an efficient strategy to induce and maintain donor-specific tolerance for an osseous-free allograft.

Therapeutic Opportunities for Immunoreceptor-Engineered T Cell Therapy for Modulation of Alloimmunity

Achieving immunosuppression-free immune tolerance to an allograft is one of the central goals of transplantation. In this article, we review recent developments in the fields of T cell-based therapies and T cell engineering using chimeric Ag receptors and their potential for effective and targeted immune modulation of T and B cell activity in an effort to eliminate pre-existing alloantibodies (desensitization) and achieve long-term tolerance. Approaches that span preclinical to early clinical studies in transplantation will be reviewed, with specific emphasis on advances in T cell immunotherapy that have shown promise. Lastly, we conclude with a forward-looking discussion of how T cell-based therapies in other fields of medicine can be potentially applied to solid organ transplantation.

Chimeric Antigen Receptor (CAR) Regulatory T-Cells in Solid Organ Transplantation

Solid organ transplantation is the treatment of choice for various end-stage diseases, but requires the continuous need for immunosuppression to prevent allograft rejection. This comes with serious side effects including increased infection rates and development of malignancies. Thus, there is a clinical need to promote transplantation tolerance to prevent organ rejection with minimal or no immunosuppressive treatment. Polyclonal regulatory T-cells (Tregs) are a potential tool to induce transplantation tolerance, but lack specificity and therefore require administration of high doses. Redirecting Tregs towards mismatched donor HLA molecules by modifying these cells with chimeric antigen receptors (CAR) would render Tregs far more effective at preventing allograft rejection. Several studies on HLA-A2 specific CAR Tregs have demonstrated that these cells are highly antigen-specific and show a superior homing capacity to HLA-A2+ allografts compared to polyclonal Tregs. HLA-A2 CAR Tregs have been shown to prolong survival of HLA-A2+ allografts in several pre-clinical humanized mouse models. Although promising, concerns about safety and stability need to be addressed. In this review the current research, obstacles of CAR Treg therapy, and its potential future in solid organ transplantation will be discussed.

Regulatory T-Cell Therapy in Liver Transplantation and Chronic Liver Disease

The constant exposure of the liver to gut derived foreign antigens has resulted in this organ attaining unique immunological characteristics, however it remains susceptible to immune mediated injury. Our understanding of this type of injury, in both the native and transplanted liver, has improved significantly in recent decades. This includes a greater awareness of the tolerance inducing CD4+ CD25+ CD127low T-cell lineage with the transcription factor FoxP3, known as regulatory T-Cells (Tregs). These cells comprise 5-10% of CD4+ T cells and are known to function as an immunological "braking" mechanism, thereby preventing immune mediated tissue damage. Therapies that aim to increase Treg frequency and function have proved beneficial in the setting of both autoimmune diseases and solid organ transplantations. The safety and efficacy of Treg therapy in liver disease is an area of intense research at present and has huge potential. Due to these cells possessing significant plasticity, and the potential for conversion towards a T-helper 1 (Th1) and 17 (Th17) subsets in the hepatic microenvironment, it is pre-requisite to modify the microenvironment to a Treg favourable atmosphere to maintain these cells' function. In addition, implementation of therapies that effectively increase Treg functional activity in the liver may result in the suppression of immune responses and will hinder those that destroy tumour cells. Thus, fine adjustment is crucial to achieve this immunological balance. This review will describe the hepatic microenvironment with relevance to Treg function, and the role these cells have in both native diseased and transplanted livers.

Advances in Liver Transplantation: where are we in the pursuit of transplantation tolerance?

Liver transplantation is the ultimate treatment option for end-stage liver disease. Breakthroughs in surgical practice and immunosuppression have seen considerable advancements in survival after transplantation. However, the intricate management of immunosuppressive regimens, balancing desired immunological quiescence while minimizing toxicity has proven challenging. Diminishing improvements in long-term morbidity and mortality have been inextricably linked with the protracted use of these medications. As such, there is now enormous interest to devise protocols that will allow us to minimize or completely withdraw immunosuppressants after transplantation. Immunosuppression withdrawal trials have proved the reality of tolerance following liver transplantation, however, without intervention will only occur after several years at the risk of potential cumulative immunosuppression-related morbidity. Focus has now been directed at accelerating this phenomenon through tolerance-inducing strategies. In this regard, efforts have seen the use of regulatory cell immunotherapy. Here we focus particularly on regulatory T cells, discussing preclinical data that propagated several clinical trials of adoptive cell therapy in liver transplantation. Furthermore, we describe efforts to further optimize the specificity and survival of regulatory cell therapy guided by concurrent immunomonitoring studies and the development of novel technologies including chimeric antigen receptors and co-administration of low-dose IL-2.

Antigen Specific Regulatory T Cells in Kidney Transplantation and Other Tolerance Settings

Kidney transplantation is the most common solid organ transplant and the best current therapy for end-stage kidney failure. However, with standard immunosuppression, most transplants develop chronic dysfunction or fail, much of which is due to chronic immune injury. Tregs are a subset of T cells involved in limiting immune activation and preventing autoimmune disease. These cells offer the potential to provide tolerance or to allow reduction in immunosuppression in kidney transplants. The importance of Tregs in kidney transplantation has been shown in a number of seminal mouse and animal studies, including those with T cell receptors (TCRs) transgenic Tregs (TCR-Tregs) or Chimeric Antigen Receptor (CAR) Tregs (CAR-Tregs) showing that specificity increases the potency of Treg function. Here we outline the animal and human studies and clinical trials directed at using Tregs in kidney transplantation and other tolerance settings and the various modifications to enhance allo-specific Treg function in vivo and in vitro.

Ex Vivo Expanded Donor Alloreactive Regulatory T Cells Lose Immunoregulatory, Proliferation, and Antiapoptotic Markers After Infusion Into ATG-lymphodepleted, Nonhuman Primate Heart Allograft Recipients

BACKGROUND

Regulatory T cell (Treg) therapy is a promising approach to amelioration of allograft rejection and promotion of organ transplant tolerance. However, the fate of infused Treg, and how this relates to their therapeutic efficacy using different immunosuppressive regimens is poorly understood. Our aim was to analyze the tissue distribution, persistence, replicative activity and phenotypic stability of autologous, donor antigen alloreactive Treg (darTreg) in anti-thymocyte globulin (ATG)-lymphodepleted, heart-allografted cynomolgus monkeys.

METHODS

darTreg were expanded ex vivo from flow-sorted, circulating Treg using activated donor B cells and infused posttransplant into recipients of major histocompatibility complex-mismatched heart allografts. Fluorochrome-labeled darTreg were identified and characterized in peripheral blood, lymphoid, and nonlymphoid tissues and the graft by flow cytometric analysis.

RESULTS

darTreg selectively suppressed autologous T cell responses to donor antigens in vitro. However, following their adoptive transfer after transplantation, graft survival was not prolonged. Early (within 2 wk posttransplant; under ATG, tacrolimus, and anti-IL-6R) or delayed (6-8 wk posttransplant; under rapamycin) darTreg infusion resulted in a rapid decline in transferred darTreg in peripheral blood. Following their early or delayed infusion, labeled cells were evident in lymphoid and nonlymphoid organs and the graft at low percentages (<4% CD4+ T cells). Notably, infused darTreg showed reduced expression of immunoregulatory molecules (Foxp3 and CTLA4), Helios, the proliferative marker Ki67 and antiapoptotic Bcl2, compared with preinfusion darTreg and endogenous CD4+CD25hi Treg.

CONCLUSIONS

Lack of therapeutic efficacy of infused darTreg in lymphodepleted heart graft recipients appears to reflect loss of a regulatory signature and proliferative and survival capacity shortly after infusion.

MiR-146a regulates regulatory T cells to suppress heart transplant rejection in mice

Regulatory T cells (Tregs), which characteristically express forkhead box protein 3 (Foxp3), are essential for the induction of immune tolerance. Here, we investigated microRNA-146a (miR-146a), a miRNA that is widely expressed in Tregs and closely related to their homeostasis and function, with the aim of enhancing the function of Tregs by regulating miR-146a and then suppressing transplant rejection. The effect of the absence of miR-146a on Treg function in the presence or absence of rapamycin was detected in both a mouse heart transplantation model and cell co-cultures in vitro. The absence of miR-146a exerted a mild tissue-protective effect by transiently prolonging allograft survival and reducing the infiltration of CD4⁺ and CD8⁺ T cells into the allografts. Meanwhile, the absence of miR-146a increased Treg expansion but impaired the ability of Tregs to restrict T helper cell type 1 (Th1) responses. A miR-146a deficiency combined with interferon (IFN)-γ blockade repaired the impaired Treg function, further prolonged allograft survival, and alleviated rejection. Importantly, miR-146a regulated Tregs mainly through the IFN-γ/signal transducer and activator of transcription (STAT) 1 pathway, which is implicated in Treg function to inhibit Th1 responses. Our data suggest miR-146a controls a specific aspect of Treg function, and modulation of miR-146a may enhance Treg efficacy in alleviating heart transplant rejection in mice.

Adoptive Transfer of Regulatory Immune Cells in Organ Transplantation

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

Regulatory Cell Therapy in Organ Transplantation: Achievements and Open Questions

The effective development of innovative surgical applications and immunosuppressive agents have improved remarkable advancements in solid organ transplantation. Despite these improvements led to prevent acute rejection and to promote short-term graft survival, the toxicity of long-term immunosuppression regiments has been associated to organ failure or chronic graft rejection. The graft acceptance is determined by the balance between the regulatory and the alloreactive arm of the immune system. Hence, enhance regulatory cells leading to immune tolerance would be the solution to improve long-term allograft survival which, by reducing the overall immunosuppression, will provide transplanted patients with a better quality of life. Regulatory T cells (Tregs), and regulatory myeloid cells (MRCs), including regulatory macrophages and tolerogenic dendritic cells, are promising cell populations for restoring tolerance. Thus, in the last decade efforts have been dedicated to apply regulatory cell-based therapy to improve the successful rate of organ transplantation and to promote allogeneic tolerance. More recently, this approach has been translated into clinical application. The aim of this review is to summarize and discuss results on regulatory cell-based strategies, focusing on Tregs and MRCs, in terms of safety, feasibility, and efficacy in clinical studies of organ transplantation.

Donor-specific chimeric antigen receptor Tregs limit rejection in naive but not sensitized allograft recipients

Cell therapy with autologous donor-specific regulatory T cells (Tregs) is a promising strategy to minimize immunosuppression in transplant recipients. Chimeric antigen receptor (CAR) technology has recently been used successfully to generate donor-specific Tregs and overcome the limitations of enrichment protocols based on repetitive stimulations with alloantigens. However, the ability of CAR-Treg therapy to control alloreactivity in immunocompetent recipients is unknown. We first analyzed the effect of donor-specific CAR Tregs on alloreactivity in naive, immunocompetent mice receiving skin allografts. Tregs expressing an irrelevant or anti-HLA-A2-specific CAR were administered to Bl/6 mice at the time of transplanting an HLA-A2⁺ Bl/6 skin graft. Donor-specific CAR-Tregs, but not irrelevant-CAR Tregs, significantly delayed skin rejection and diminished donor-specific antibodies (DSAs) and frequencies of DSA-secreting B cells. Donor-specific CAR-Treg-treated mice also had a weaker recall DSA response, but normal responses to an irrelevant antigen, demonstrating antigen-specific suppression. When donor-specific CAR Tregs were tested in HLA-A2-sensitized mice, they were unable to delay allograft rejection or diminish DSAs. The finding that donor-specific CAR-Tregs restrain de novo but not memory alloreactivity has important implications for their use as an adoptive cell therapy in transplantation.

Applicability, safety, and biological activity of regulatory T cell therapy in liver transplantation

Regulatory T cells (Tregs) are a lymphocyte subset with intrinsic immunosuppressive properties that can be expanded in large numbers ex vivo and have been shown to prevent allograft rejection and promote tolerance in animal models. To investigate the safety, applicability, and biological activity of autologous Treg adoptive transfer in humans, we conducted an open-label, dose-escalation, Phase I clinical trial in liver transplantation. Patients were enrolled while awaiting liver transplantation or 6-12 months posttransplant. Circulating Tregs were isolated from blood or leukapheresis, expanded under good manufacturing practices (GMP) conditions, and administered intravenously at either 0.5-1 million Tregs/kg or 3-4.5 million Tregs/kg. The primary endpoint was the rate of dose- limiting toxicities occurring within 4 weeks of infusion. The applicability of the clinical protocol was poor unless patient recruitment was deferred until 6-12 months posttransplant. Thus, only 3 of the 17 patients who consented while awaiting liver transplantation were dosed. In contrast, all six patients who consented 6-12 months posttransplant received the cell infusion. Treg transfer was safe, transiently increased the pool of circulating Tregs and reduced anti-donor T cell responses. Our study opens the door to employing Treg immunotherapy to facilitate the reduction or complete discontinuation of immunosuppression following liver transplantation.

Mechanisms of Immune Tolerance in Liver Transplantation-Crosstalk Between Alloreactive T Cells and Liver Cells With Therapeutic Prospects

Liver transplantation (LTx) is currently the most powerful treatment for end-stage liver disease. Although liver allograft is more tolerogenic compared to other solid organs, the majority of LTx recipients still require long-term immune suppression (IS) to control the undesired alloimmune responses, which can lead to severe side effects. Thus, understanding the mechanism of liver transplant tolerance and crosstalk between immune cells, especially alloreactive T cells and liver cells, can shed light on more specific tolerance induction strategies for future clinical translation. In this review, we focus on alloreactive T cell mediated immune responses and their crosstalk with liver sinusoidal endothelial cells (LSECs), hepatocytes, hepatic stellate cells (HSCs), and cholangiocytes in transplant setting. Liver cells mainly serve as antigen presenting cells (APCs) to T cells, but with low expression of co-stimulatory molecules. Crosstalk between them largely depends on the different expression of adhesion molecules and chemokine receptors. Inflammatory cytokines secreted by immune cells further elaborate this crosstalk and regulate the fate of naïve T cells differentiation within the liver graft. On the other hand, regulatory T cells (Tregs) play an essential role in inducing and keeping immune tolerance in LTx. Tregs based adoptive cell therapy provides an excellent therapeutic option for clinical transplant tolerance induction. However, many questions regarding cell therapy still need to be solved. Here we also address the current clinical trials of adoptive Tregs therapy and other tolerance induction strategies in LTx, together with future challenges for clinical translation from bench to bedside.

IL-2 therapy preferentially expands adoptively transferred donor-specific Tregs improving skin allograft survival

Regulatory T cells (Tregs) have unique immunosuppressive properties and are essential to ensure effective immunoregulation. In animal models, Tregs have been shown to prevent autoimmune disorders and establish transplantation tolerance. Therefore, the prospect of harnessing Tregs, either by increasing their frequency or by conferring allospecificity, has prompted a growing interest in the development of immunotherapies. Here, employing a well-established skin transplant model with a single major histocompatibility complex mismatch, we compared the therapeutic efficacy of adoptively transfer Treg with or without donor specificity and the administration of IL-2 to promote in vivo expansion of Treg. We showed that IL-2 treatment preferentially enhances the proliferation of the allospecific Tregs adoptively transferred in an antigen-dependent manner. In addition, donor-specific Tregs significantly increased the expression of regulatory-related marker, such as CTLA4 and inducible costimulator (ICOS), in the skin allograft and draining lymph nodes compared to endogenous and polyclonal transferred Tregs. Importantly, by combining IL-2 with donor-specific Tregs, but not with polyclonal Tregs, a synergistic effect in prolonging skin allograft survival was observed. Altogether, our data suggest that this combination therapy could provide the appropriate conditions to enhance the immunoregulation of alloimmune responses in clinical transplantation.