Ex vivo-expanded human regulatory T cells prevent the rejection of skin allografts in a humanized mouse model

T Cell Development and Responses in Human Immune System Mice

Human Immune System (HIS) mice constructed with mature human immune cells or with human hematopoietic stem cells and thymic tissue have provided an important tool for human immunological research. In this article, we first review the different types of HIS mice based on human tissues transplanted and sources of the tissues. We then focus on knowledge of human T cell development and responses obtained using HIS mouse models. These areas include the development of human T cell subsets, with a focus on αβ conventional T cells and regulatory T cells, and human T cell responses in the settings of infection, transplantation rejection and tolerance, autoimmune disease, cancer immunotherapy, and regulatory T cell therapy. We also discuss the limitations and potential future applications of HIS mouse models.

Gene editing of CD3 epsilon to redirect regulatory T cells for adoptive T cell transfer

Adoptive transfer of antigen-specific regulatory T cells (Tregs) is a promising strategy to combat immunopathologies in transplantation and autoimmune diseases. However, their low frequency in peripheral blood poses challenges for both manufacturing and clinical application. Chimeric antigen receptors have been used to redirect the specificity of Tregs, using retroviral vectors. However, retroviral gene transfer is costly, time consuming, and raises safety issues. Here, we explored non-viral CRISPR-Cas12a gene editing to redirect Tregs, using human leukocyte antigen (HLA)-A2-specific constructs for proof-of-concept studies in transplantation models. Knock-in of an antigen-binding domain into the N terminus of CD3 epsilon (CD3ε) gene generates Tregs expressing a chimeric CD3ε-T cell receptor fusion construct (TRuC) protein that integrates into the endogenous TCR/CD3 complex. These CD3ε-TRuC Tregs exhibit potent antigen-dependent activation while maintaining responsiveness to TCR/CD3 stimulation. This enables preferential enrichment of TRuC-redirected Tregs over CD3ε knockout Tregs via repetitive CD3/CD28 stimulation in a good manufacturing practice-compatible expansion system. CD3ε-TRuC Tregs retained their phenotypic, epigenetic, and functional identity. In a humanized mouse model, HLA-A2-specific CD3ε-TRuC Tregs demonstrate superior protection of allogeneic HLA-A2+ skin grafts from rejection compared with polyclonal Tregs. This approach provides a pathway for developing clinical-grade CD3ε-TRuC-based Treg cell products for transplantation immunotherapy and other immunopathologies.

Protocol for a first-in-human feasibility study of T regulatory cells (TR004) for inflammatory bowel disease using (ex vivo) Treg expansion (TRIBUTE)

INTRODUCTION

Crohn's disease (CD) is a chronic, immune-mediated inflammatory bowel disease (IBD), presenting with symptoms of abdominal pain and bleeding from the gastrointestinal tract. There is no known cure. In vitro-expanded 'thymus-derived' regulatory T cells (tTreg) have shown promise in preclinical models of IBD, leading to interest in their use as a potential therapy in CD. We present a study protocol for a first-in-human study of Tregs for IBD using ex vivo Treg expansion. This study will explore the preliminary safety and tolerability of a single dose of Treg immunotherapy and will inform the design of a subsequent larger trial.

METHODS AND ANALYSIS

Four patients will be recruited from gastroenterology clinics at Guy's and St Thomas' NHS Foundation Trust. Eligible participants are those who are at least 18 years old, have a diagnosis of active moderate to severe CD and have failed to respond to or tolerate at least two prior lines of standard medication. Participants receive a single dose of autologous ex vivo-expanded Tregs and will be followed up to week 21 to collect safety and exploratory efficacy data. Additional safety monitoring will occur at 1 and 2 years post-dose. The primary endpoint is defined as the occurrence of dose-limiting toxicity occurring within 5 weeks post-infusion.

ETHICS AND DISSEMINATION

The study protocol and related documents have been approved by a NHS Research Ethics Committee, the Health Research Authority and the Medicines and Healthcare products Regulatory Agency for Clinical Trial Authorisation. It is intended that the results of the trial will be presented at international conferences and will be submitted for publication in a peer-reviewed scientific journal.

TRIAL REGISTRATION NUMBER

NCT03185000.

Humanized Mouse Models of Bacterial Infections

Bacterial infections continue to represent a significant healthcare burden worldwide, causing considerable mortality and morbidity every year. The emergence of multidrug-resistant bacterial strains continues to rise, posing serious risks to controlling global disease outbreaks. To develop novel and more effective treatment and vaccination programs, there is a need for clinically relevant small animal models. Since multiple bacterial species have human-specific tropism for numerous virulence factors and toxins, conventional mouse models do not fully represent human disease. Several human disease characteristic phenotypes, such as lung granulomas in the case of Mycobacterium tuberculosis infections, are absent in standard mouse models. Alternatively, certain pathogens, such as Salmonella enterica serovar typhi and Staphylococcus aureus, can be well tolerated in mice and cleared quickly. To address this, multiple groups have developed humanized mouse models and observed enhanced susceptibility to infection and a more faithful recapitulation of human disease. In the last two decades, multiple humanized mouse models have been developed to attempt to recapitulate the human immune system in a small animal model. In this review, we first discuss the history of immunodeficient mice that has enabled the engraftment of human tissue and the engraftment methods currently used in the field. We then highlight how humanized mouse models successfully uncovered critical human immune responses to various bacterial infections, including Salmonella enterica serovar Typhi, Mycobacterium tuberculosis, and Staphylococcus aureus.

Clinical grade multiparametric cell sorting and gene-marking of regulatory T cells

BACKGROUND AIMS

Regulatory T cells (Tregs) are the main mediators of peripheral tolerance. Treg-directed therapy has shown promising results in preclinical studies of diverse immunopathologies. At present, the clinical applicability of adoptive Treg transfer is limited by difficulties in generating Tregs at sufficient cell dose and purity.

METHODS

We developed a Good Manufacturing Practice (GMP) compliant method based on closed-system multiparametric Fluorescence-Activated Cell Sorting (FACS) to purify Tregs, which are then expanded in vitro and gene-marked with a clinical grade retroviral vector to enable in vivo fate tracking. Following small-scale optimization, we conducted four clinical-scale processing runs.

RESULTS

We showed that Tregs could be enriched to 87- 92% purity following FACS-sorting, and expanded and transduced to yield clinically relevant cell dose of 136-732×106 gene-marked cells, sufficient for a cell dose of at least 2 × 106 cells/kg. The expanded Tregs were highly demethylated in the FOXP3 Treg-specific demethylated region (TSDR), consistent with bona fide natural Tregs. They were suppressive in vitro, but a small percentage could secrete proinflammatory cytokines, including interferon-γ and interleukin-17A.

CONCLUSIONS

This study demonstrated the feasibility of isolating, expanding and gene-marking Tregs in clinical scale, thus paving the way for future phase I trials that will advance knowledge about the in vivo fate of transferred Tregs and its relationship with concomitant Treg-directed pharmacotherapy and clinical response.

Antibody-Suppressor CXCR5+CD8+ T Cells Are More Potent Regulators of Humoral Alloimmunity after Kidney Transplant in Mice Compared to CD4+ Regulatory T Cells

Adoptive cell therapy (ACT), especially with CD4+ regulatory T cells (CD4+ Tregs), is an emerging therapeutic strategy to minimize immunosuppression and promote long-term allograft acceptance, although much research remains to realize its potential. In this study, we investigated the potency of novel Ab-suppressor CXCR5+CD8+ T cells (CD8+ TAb-supp) in comparison with conventional CD25highFoxp3+CD4+ Tregs for suppression of humoral alloimmunity in a murine kidney transplant (KTx) model of Ab-mediated rejection (AMR). We examined quantity of peripheral blood, splenic and graft-infiltrating CD8+ TAb-supp, and CD4+ Tregs in KTx recipients and found that high alloantibody-producing CCR5 knockout KTx recipients have significantly fewer post-transplant peripheral blood and splenic CD8+ TAb-supp, as well as fewer splenic and graft-infiltrating CD4+ Tregs compared with wild-type KTx recipients. ACT with alloprimed CXCR5+CD8+ T cells reduced alloantibody titer, splenic alloprimed germinal center (GC) B cell quantity, and improved AMR histology in CCR5 knockout KTx recipients. ACT with alloprimed CD4+ Treg cells improved AMR histology without significantly inhibiting alloantibody production or the quantity of splenic alloprimed GC B cells. Studies with TCR transgenic mice confirmed Ag specificity of CD8+ TAb-supp-mediated effector function. In wild-type recipients, CD8 depletion significantly increased alloantibody titer, GC B cells, and severity of AMR pathology compared with isotype-treated controls. Anti-CD25 mAb treatment also resulted in increased but less pronounced effect on alloantibody titer, quantity of GC B cells, and AMR pathology than CD8 depletion. To our knowledge, this is the first report that CD8+ TAb-supp cells are more potent regulators of humoral alloimmunity than CD4+ Treg cells.

CXCR5 + CD8 + T Cell-mediated Suppression of Humoral Alloimmunity and AMR in Mice Is Optimized With mTOR and Impaired With Calcineurin Inhibition

BACKGROUND

Adoptive cellular therapy (ACT) with antibody-suppressor CXCR5 + CD8 + T cells (CD8 + T Ab-supp ) inhibits alloantibody production, antibody-mediated rejection (AMR), and prolongs graft survival in multiple transplant mouse models. However, it is not known how conventional immunosuppressive agents impact the efficacy of CD8 + T Ab-supp ACT.

METHODS

We investigated the efficacy of CD8 + T Ab-supp cell ACT when combined with calcineurin inhibitor (CNi) or mammalian target of rapamycin inhibitor (mTORi) in a murine model of kidney transplant.

RESULTS

ACT-mediated decrease in germinal center B cells, posttransplant alloantibody titer, and amelioration of AMR in high alloantibody-producing CCR5 knockout kidney transplant recipients were impaired when ACT was combined with CNi and enhanced when combined with mTORi. CNi (but not mTORi) reduced ACT-mediated in vivo cytotoxicity of IgG + B cells and was associated with increased quantity of germinal center B cells. Neither CNi nor mTORi treatment impacted the expression of cytotoxic effector molecules (FasL, Lamp1, perforin, granzyme B) by CD8 + T Ab-supp after ACT. Concurrent treatment with CNi (but not mTORi) reduced in vivo proliferation of CD8 + T Ab-supp after ACT. The increase in quantity of splenic CD44 + CXCR5 + CD8 + T cells that occurs after ACT was reduced by concurrent treatment with CNi but not by concurrent treatment with mTORi (dose-dependent).

CONCLUSIONS

Impaired efficacy of ACT by CNi is attributed to reduced persistence and/or expansion of CD8 + T Ab-supp cells after ACT. In contrast, concurrent immunosuppression with mTORi preserves CD8 + T Ab-supp cells quantity, in vivo proliferation, and in vivo cytotoxic effector function after ACT and enhances suppression of humoral alloimmunity and AMR.

Clinical Manufacturing of Regulatory T Cell Products For Adoptive Cell Therapy and Strategies to Improve Therapeutic Efficacy

Based on successes in preclinical animal transplant models, adoptive cell therapy (ACT) with regulatory T cells (Tregs) is a promising modality to induce allograft tolerance or reduce the use of immunosuppressive drugs to prevent rejection. Extensive work has been done in optimizing the best approach to manufacture Treg cell products for testing in transplant recipients. Collectively, clinical evaluations have demonstrated that large numbers of Tregs can be expanded ex vivo and infused safely. However, these trials have failed to induce robust drug-free tolerance and/or significantly reduce the level of immunosuppression needed to prevent solid organ transplant (SOTx) rejection. Improving Treg therapy effectiveness may require increasing Treg persistence or orchestrating Treg migration to secondary lymphatic tissues or places of inflammation. In this review, we describe current clinical Treg manufacturing methods used for clinical trials. We also highlight current strategies being implemented to improve delivered Treg ACT persistence and migration in preclinical studies.

Hematopoietic cell-based and non-hematopoietic cell-based strategies for immune tolerance induction in living-donor renal transplantation: A systematic review

INTRODUCTION

Despite its use to prevent acute rejection, lifelong immunosuppression can adversely impact long-term patient and graft outcomes. In theory, immunosuppression withdrawal is the ultimate goal of kidney transplantation, and is made possible by the induction of immunological tolerance. The purpose of this paper is to review the safety and efficacy of immune tolerance induction strategies in living-donor kidney transplantation, both chimerism-based and non-chimerism-based. The impact of these strategies on transplant outcomes, including acute rejection, allograft function and survival, cost, and immune monitoring, will also be discussed.

MATERIALS AND METHODS

Databases such as PubMed, Scopus, and Web of Science, as well as additional online resources such as EBSCO, were exhaustively searched. Adult living-donor kidney transplant recipients who developed chimerism-based tolerance after concurrent bone marrow or hematopoietic stem cell transplantation or those who received non-chimerism-based, non-hematopoietic cell therapy using mesenchymal stromal cells, dendritic cells, or regulatory T cells were studied between 2000 and 2021. Individual sources of evidence were evaluated critically, and the strength of evidence and risk of bias for each outcome of the transplant tolerance study were assessed.

RESULTS

From 28,173 citations, 245 studies were retrieved after suitable exclusion and duplicate removal. Of these, 22 studies (2 RCTs, 11 cohort studies, 6 case-control studies, and 3 case reports) explicitly related to both interventions (chimerism- and non-chimerism-based immune tolerance) were used in the final review process and were critically appraised. According to the findings, chimerism-based strategies fostered immunotolerance, allowing for the safe withdrawal of immunosuppressive medications. Cell-based therapy, on the other hand, frequently did not induce tolerance except for minimising immunosuppression. As a result, the rejection rates, renal allograft function, and survival rates could not be directly compared between these two groups. While chimerism-based tolerance protocols posed safety concerns due to myelosuppression, including infections and graft-versus-host disease, cell-based strategies lacked these adverse effects and were largely safe. There was a lack of direct comparisons between HLA-identical and HLA-disparate recipients, and the cost implications were not examined in several of the retrieved studies. Most studies reported successful immunosuppressive weaning lasting at least 3 years (ranging up to 11.4 years in some studies), particularly with chimerism-based therapy, while only a few investigators used immune surveillance techniques. The studies reviewed were often limited by selection, classification, ascertainment, performance, and attrition bias.

CONCLUSIONS

This review demonstrates that chimerism-based hematopoietic strategies induce immune tolerance, and a substantial number of patients are successfully weaned off immunosuppression. Despite the risk of complications associated with myelosuppression. Non-chimerism-based, non-hematopoietic cell protocols, on the other hand, have been proven to facilitate immunosuppression minimization but seldom elicit immunological tolerance. However, the results of this review must be interpreted with caution because of the non-randomised study design, potential confounding, and small sample size of the included studies. Further validation and refinement of tolerogenic protocols in accordance with local practice preferences is also warranted, with an emphasis on patient selection, cost ramifications, and immunological surveillance based on reliable tolerance assays.

Blank Spots in the Map of Human Skin: The Challenge for Xenotransplantation

Most of the knowledge about human skin homeostasis, development, wound healing, and diseases has been accumulated from human skin biopsy analysis by transferring from animal models and using different culture systems. Human-to-mouse xenografting is one of the fundamental approaches that allows the skin to be studied in vivo and evaluate the ongoing physiological processes in real time. Humanized animals permit the actual techniques for tracing cell fate, clonal analysis, genetic modifications, and drug discovery that could never be employed in humans. This review recapitulates the novel facts about mouse skin self-renewing, regeneration, and pathology, raises issues regarding the gaps in our understanding of the same options in human skin, and postulates the challenges for human skin xenografting.

Innate immune cellular therapeutics in transplantation

Successful organ transplantation provides an opportunity to extend the lives of patients with end-stage organ failure. Selectively suppressing the donor-specific alloimmune response, however, remains challenging without the continuous use of non-specific immunosuppressive medications, which have multiple adverse effects including elevated risks of infection, chronic kidney injury, cardiovascular disease, and cancer. Efforts to promote allograft tolerance have focused on manipulating the adaptive immune response, but long-term allograft survival rates remain disappointing. In recent years, the innate immune system has become an attractive therapeutic target for the prevention and treatment of transplant organ rejection. Indeed, contemporary studies demonstrate that innate immune cells participate in both the initial alloimmune response and chronic allograft rejection and undergo non-permanent functional reprogramming in a phenomenon termed "trained immunity." Several types of innate immune cells are currently under investigation as potential therapeutics in transplantation, including myeloid-derived suppressor cells, dendritic cells, regulatory macrophages, natural killer cells, and innate lymphoid cells. In this review, we discuss the features and functions of these cell types, with a focus on their role in the alloimmune response. We examine their potential application as therapeutics to prevent or treat allograft rejection, as well as challenges in their clinical translation and future directions for investigation.

Regulatory T-cell therapy approaches

Regulatory T cells (Tregs) have enormous therapeutic potential to treat a variety of immunopathologies characterized by aberrant immune activation. Adoptive transfer of ex vivo expanded autologous Tregs continues to progress through mid- to late-phase clinical trials in several disease spaces and has generated promising preliminary safety and efficacy signals to date. However, the practicalities of this strategy outside of the clinical trial setting remain challenging. Here, we review the current landscape of regulatory T-cell therapy, considering emergent approaches and technologies presenting novel ways to engage Tregs, and reflect on the progress necessary to deliver their therapeutic potential to patients.

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.

Clinical adoptive regulatory T Cell therapy: State of the art, challenges, and prospective

Rejection of solid organ transplant and graft versus host disease (GvHD) continue to be challenging in post transplantation management. The introduction of calcineurin inhibitors dramatically improved recipients' short-term prognosis. However, long-term clinical outlook remains poor, moreover, the lifelong dependency on these toxic drugs leads to chronic deterioration of graft function, in particular the renal function, infections and de-novo malignancies. These observations led investigators to identify alternative therapeutic options to promote long-term graft survival, which could be used concomitantly, but preferably, replace pharmacologic immunosuppression as standard of care. Adoptive T cell (ATC) therapy has evolved as one of the most promising approaches in regenerative medicine in the recent years. A range of cell types with disparate immunoregulatory and regenerative properties are actively being investigated as potential therapeutic agents for specific transplant rejection, autoimmunity or injury-related indications. A significant body of data from preclinical models pointed to efficacy of cellular therapies. Significantly, early clinical trial observations have confirmed safety and tolerability, and yielded promising data in support of efficacy of the cellular therapeutics. The first class of these therapeutic agents commonly referred to as advanced therapy medicinal products have been approved and are now available for clinical use. Specifically, clinical trials have supported the utility of CD4⁺CD25+FOXP3+ regulatory T cells (Tregs) to minimize unwanted or overshooting immune responses and reduce the level of pharmacological immunosuppression in transplant recipients. Tregs are recognized as the principal orchestrators of maintaining peripheral tolerance, thereby blocking excessive immune responses and prevent autoimmunity. Here, we summarize rationale for the adoptive Treg therapy, challenges in manufacturing and clinical experiences with this novel living drug and outline future perspectives of its use in transplantation.

Barriers to Treg therapy in Europe: From production to regulation

There has been an increased interest in cell based therapies for a range of medical conditions in the last decade. This explosion in novel therapeutics research has led to the development of legislation specifically focused on cell and gene based therapies. In Europe, the European medicines agency (EMA) designates any medicines for human use which are based on genes, tissues, or cells as advanced therapy medicinal products or advanced therapy medicinal products (ATMPs). In this article we discuss the hurdles to widespread adoption of ATMPs in Europe, with a focus on regulatory T cells (Tregs). There are numerous barriers which must be overcome before mainstream adoption of Treg therapy becomes a reality. The source of the cells, whether to use autologous or allogenic cells, and the methods through which they are isolated and expanded, must all meet strict good manufacturing practice (GMP) standards to allow use of the products in humans. GMP compliance is costly, with the equipment and reagents providing a significant cost barrier and requiring specialized facilities and personnel. Conforming to the regulations set centrally by the EMA is difficult, and the different interpretations of the regulations across the various member states further complicates the regulatory approval process. The end products then require a complex and robust distribution network to ensure timely delivery of potentially life saving treatments to patients. In a European market whose logistics networks have been hammered by COVID and Brexit, ensuring rapid and reliable delivery systems is a more complex task than ever. In this article we will examine the impact of these barriers on the development and adoption of Tregs in Europe, and potential approaches which could facilitate more widespread use of Tregs, instead of its current concentration in a few very specialized centers.

Nanoparticle delivery of CD40 siRNA suppresses alloimmune responses by inhibiting activation and differentiation of DCs and macrophages

CD40 is an important costimulatory molecule expressed on antigen-presenting cells (APCs) and plays a critical role for APC activation, offering a promising therapeutic target for preventing allograft rejection. Here, we developed a biodegradable nanoparticle small interfering RNA delivery system (siCD40/NPs) to effectively deliver CD40 siRNA (siCD40) into hematopoietic stem cells (HSCs), myeloid progenitors, and mature dendritic cells (DCs) and macrophages. Injection of siCD40/NPs not only down-regulated CD40 expression in DCs and macrophages but also inhibited the differentiation of HSCs and/or myeloid progenitors into functional DCs and macrophages. Furthermore, siCD40/NPs treatment significantly prolonged allograft survival in mouse models of skin allotransplantation. In addition to reiteration of the role of CD40 in APC activation, our findings highlight a previously unappreciated role of CD40 in DC and macrophage differentiation from their progenitors. Furthermore, our results support the effectiveness of siCD40/NPs in suppressing alloimmune responses, providing a potential means of facilitating tolerance induction and preventing allotransplant rejection.

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.

Assessment of Angiogenesis and Cell Survivability of an Inkjet Bioprinted Biological Implant in an Animal Model

The rapidly growing field of tissue engineering hopes to soon address the shortage of transplantable tissues, allowing for precise control and fabrication that could be made for each specific patient. The protocols currently in place to print large-scale tissues have yet to address the main challenge of nutritional deficiencies in the central areas of the engineered tissue, causing necrosis deep within and rendering it ineffective. Bioprinted microvasculature has been proposed to encourage angiogenesis and facilitate the mobility of oxygen and nutrients throughout the engineered tissue. An implant made via an inkjet printing process containing human microvascular endothelial cells was placed in both B17-SCID and NSG-SGM3 animal models to determine the rate of angiogenesis and degree of cell survival. The implantable tissues were made using a combination of alginate and gelatin type B; all implants were printed via previously published procedures using a modified HP inkjet printer. Histopathological results show a dramatic increase in the average microvasculature formation for mice that received the printed constructs within the implant area when compared to the manual and control implants, indicating inkjet bioprinting technology can be effectively used for vascularization of engineered tissues.

Ex vivo-expanded human CD19+TIM-1+ regulatory B cells suppress immune responses in vivo and are dependent upon the TIM-1/STAT3 axis

Regulatory B cells (Breg) are a heterogenous population with immune-modulating functions. The rarity of human IL-10⁺ Breg makes translational studies difficult. Here we report ex vivo expansion of human B cells with in vivo regulatory function (expBreg). CD154-stimulation of human CD19⁺ B cells drives >900-fold expansion of IL-10⁺ B cells that is maintained in culture for 14 days. Whilst expBreg-mediated suppressive function is partially dependent on IL-10 expression, CRISPR-mediated gene deletions demonstrate predominant roles for TIM-1 and CD154. TIM-1 regulates STAT3 signalling and modulates downstream suppressive function. In a clinically relevant humanised mouse model of skin transplantation, expBreg prolongs human allograft survival. Meanwhile, CD19⁺CD73^-CD25⁺CD71⁺TIM-1⁺CD154⁺ Breg cells are enriched in the peripheral blood of human donors with cutaneous squamous cell carcinoma (SCC). TIM-1⁺ and pSTAT3⁺ B cells are also identified in B cell clusters within histological sections of human cutaneous SCC tumours. Our findings thus provide insights on Breg homoeostasis and present possible targets for Breg-related therapies.

Intermittent Exposure of Hypercapnia Suppresses Allograft Rejection via Induction of Treg Differentiation and Inhibition of Neutrophil Accumulation

Background: In the management of major burn wounds, allogeneic skin transplantation is a critical procedure to improve wound repair. Our previous works found that intermittent exposure to carbon dioxide leads to permissive hypercapnia (HCA) and prolongs skin allograft survival. However, the modulatory effects of HCA exposure on the immune system are not well understood. Objectives: Our purpose was to investigate how intermittent exposure to HCA can effectively reduce the immune reaction to allogeneic skin graft rejection. Methods: A fully major histocompatibility complex-incompatible skin transplant from BALB/c to C57BL/6 mice model was utilized. Immune cells from splenic and draining lymph nodes were analyzed by flow cytometry. Serum proinflammatory cytokines were analyzed by ELISA. Results: Serum levels of IFN-γ, IL-2, IL-6, and TNF-α were significantly decreased in the HCA group. Additionally, the percentage of CD8+ cells in draining lymph nodes was significantly lower in HCA than in the control group. Moreover, the generation rate of FoxP3+ regulatory T cells (Tregs) from spleen naïve CD4+ T cells was increased by intermittent exposure to carbon dioxide. The infiltrated neutrophils were also eliminated by HCA. Taken together, we concluded that intermittent hypercapnia exposure could effectively suppress skin rejection by stimulating Treg cell generation and suppressing immune reactions.

A New Generation of Cell Therapies Employing Regulatory T Cells (Treg) to Induce Immune Tolerance in Pediatric Transplantation

Kidney transplantation is the most common solid organ transplant and the preferred treatment for pediatric patients with end-stage renal disease, but it is still not a definitive solution due to immune graft rejection. Regulatory T cells (Treg) and their control over effector T cells is a crucial and intrinsic tolerance mechanism in limiting excessive immune responses. In the case of transplants, Treg are important for the survival of the transplanted organ, and their dysregulation could increase the risk of rejection in transplanted children. Chronic immunosuppression to prevent rejection, for which Treg are especially sensitive, have a detrimental effect on Treg counts, decreasing the Treg/T-effector balance. Cell therapy with Treg cells is a promising approach to restore this imbalance, promoting tolerance and thus increasing graft survival. However, the strategies used to date that employ peripheral blood as a Treg source have shown limited efficacy. Moreover, it is not possible to use this approach in pediatric patients due to the limited volume of blood that can be extracted from children. Here, we outline our innovative strategy that employs the thymus removed during pediatric cardiac surgeries as a source of therapeutic Treg that could make this therapy accessible to transplanted children. The advantageous properties and the massive amount of Treg cells obtained from pediatric thymic tissue (thyTreg) opens a new possibility for Treg therapies to prevent rejection in pediatric kidney transplants. We are recruiting patients in a clinical trial to prevent rejection in heart-transplanted children through the infusion of autologous thyTreg cells (NCT04924491). If its efficacy is confirmed, thyTreg therapy may establish a new paradigm in preventing organ rejection in pediatric transplants, and their allogeneic use would extend its application to other solid organ transplantation.

Towards regulatory cellular therapies in solid organ transplantation

Organ transplantation is a modern medical success story. However, since its inception it has been limited by the need for pharmacological immunosuppression. Regulatory cellular therapies offer an attractive solution to these challenges by controlling transplant alloresponses through multiple parallel suppressive mechanisms. A number of cell types have seen an accelerated development into human trials and are now on the threshold of a long-awaited breakthrough in personalized transplant therapeutics. Here we assess recent developments with a focus on the most likely candidates, some of which have already facilitated successful immunosuppression withdrawal in early clinical trials. We propose that this may constitute a promising approach in clinical transplantation but also evaluate outstanding issues in the field, providing cause for cautious optimism.

FK506-loaded PLGA nanoparticles improve long-term survival of a vascularized composite allograft in a murine model

Background

The side effects of life-long administration of FK506 limit the clinical practice of vascularized composite allografts (VCAs). This study aimed to evaluate the feasibility of FK506-loaded poly (lactic-co-glycolic acid) (PLGA) nanoparticles (FK506 NPs) for prolonging the long-term survival of VCAs and reducing the side effects of FK506.

Methods

PLGA nanoparticles loaded with FK506 were prepared by the solvent evaporation method. The characterization of FK506 NPs was evaluated by electron microscopy. To confirm the function and safety of FK506 NPs, these particles were administrated into rats by intraperitoneal injection. The survival time of the allograft, systemic concentration of FK506, anti-rejection activity, and side-effect of FK506 NPs were evaluated in a Brown Norway (BN)-to-Sprague Dawley (SD) epigastric VCA transplantation model.

Results

Compared with the nontreatment, PLGA control and FK506 groups, the median survival times (MST) of the FK506 NP groups were significantly prolonged. The FK506 NPs could maintain therapeutic drug concentration for 60 days. Moreover, cytokine concentrations, flow cytometry of regulatory T cells (Tregs) and histopathology of allografts revealed significantly prolonged immunosuppression by FK506 NPs. FK506 NPs also ameliorated FK506 nephrotoxicity.

Conclusions

FK506 NPs prolong the survival time of VCAs in a murine model with minimal nephrotoxicity, and provide a potential clinical strategy for ameliorating long-term side effects of immunosuppressive therapy.

Therapeutically expanded human regulatory T-cells are super-suppressive due to HIF1A induced expression of CD73

The adoptive transfer of regulatory T-cells (Tregs) is a promising therapeutic approach in transplantation and autoimmunity. However, because large cell numbers are needed to achieve a therapeutic effect, in vitro expansion is required. By comparing their function, phenotype and transcriptomic profile against ex vivo Tregs, we demonstrate that expanded human Tregs switch their metabolism to aerobic glycolysis and show enhanced suppressive function through hypoxia-inducible factor 1-alpha (HIF1A) driven acquisition of CD73 expression. In conjunction with CD39, CD73 expression enables expanded Tregs to convert ATP to immunosuppressive adenosine. We conclude that for maximum therapeutic benefit, Treg expansion protocols should be optimised for CD39/CD73 co-expression.

The intestinal flora of patients with GHPA affects the growth and the expression of PD-L1 of tumor

Context

Pituitary adenoma (PA) is a common intracranial tumor. The evidence indicates that the tumor immune microenvironment (TIME) is associated with PA and that the intestinal flora influences other tumors' growth through interacting with the TIME. However, how the intestinal microbial flora contributes to the development of PA through the immune response is unknown.

Objective and methods

Here we used high-throughput Illumina MiSeq sequencing targeting the V3−V4 region of the 16S ribosomal RNA gene to investigate the intestinal flora of patients with growth hormone-secreting pituitary adenoma (GHPA), nonfunctional pituitary adenoma (NFPA), and healthy controls. We determined their effects on tumor growth and the TIME. Fecal microbiota transplantation (FMT) was performed after adoptive transfer via peripheral blood mononuclear cells to tumor-bearing nude mice, which allowed the study of the immune response.

Result

We discovered differences in the structures and quantities of intestinal flora between patients with GHPA, patients with NFPA, and healthy controls. After FMT, the intestinal flora of GHPA patients promoted the growth of tumors in mouse models. The number of programmed cell death ligand 1 (PD-L1)-positive cells increased in tumor tissues as well as the extent of infiltration of CD8⁺ cells. Increased numbers of CD3⁺CD8⁺ cells and increased levels of sPD-L1 were detected in peripheral blood.

Conclusion

These findings indicated that the intestinal flora of patients with GHPA promoted tumor growth and that the immune system may mediate this change.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00262-021-03080-6.

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.

Mouse Models for Human Skin Transplantation: A Systematic Review

Immunodeficient mouse models with human skin xenografts have been developed in the past decades to study different conditions of the skin. Features such as follow-up period and size of the graft are of different relevance depending on the purpose of an investigation. The aim of this study is to analyze the different mouse models grafted with human skin. A systematic review of the literature was performed in line with the PRISMA statement using MEDLINE/PubMed databases from January 1970 to June 2020. Articles describing human skin grafted onto mice were included. Animal models other than mice, skin substitutes, bioengineered skin, postmortem or fetal skin, and duplicated studies were excluded. The mouse strain, origin of human skin, graft dimensions, follow-up of the skin graft, and goals of the study were analyzed. Ninety-one models were included in the final review. Five different applications were found: physiology of the skin (25 models, mean human skin graft size 1.43 cm2 and follow-up 72.92 days), immunology and graft rejection (17 models, mean human skin graft size 1.34 cm2 and follow-up 86 days), carcinogenesis (9 models, mean human skin graft size 1.98 cm2 and follow-up 253 days), skin diseases (25 models, mean human skin graft size 1.55 cm2 and follow-up 86.48 days), and would healing/scars (15 models, mean human skin graft size 2.54 cm2 and follow-up 129 days). The follow-up period was longer in carcinogenesis models (253 ± 233.73 days), and the skin graft size was bigger in wound healing applications (2.54 ± 3.08 cm2). Depending on the research application, different models are suggested. Careful consideration regarding graft size, follow-up, immunosuppression, and costs should be analyzed and compared before choosing any of these mouse models. To our knowledge, this is the first systematic review of mouse models with human skin transplantation.

T- and B-cell therapy in solid organ transplantation: current evidence and future expectations

Cell therapy has emerged as an attractive therapeutic option in organ transplantation. During the last decade, the therapeutic potency of Treg immunotherapy has been shown in various preclinical animal models and safety was demonstrated in first clinical trials. However, there are still critical open questions regarding specificity, survival, and migration to the target tissue so the best Treg population for infusion into patients is still under debate. Recent advances in CAR technology hold the promise for Treg-functional superiority. Another exciting strategy is the generation of B-cell antibody receptor (BAR) Treg/cytotoxic T cells to specifically regulate or deplete alloreactive memory B cells. Finally, B cells are also capable of immune regulation, making them promising candidates for immunomodulatory therapeutic strategies. This article summarizes available literature on cell-based innovative therapeutic approaches aiming at modulating alloimmune response for transplantation. Crucial areas of investigation that need a joined effort of the transplant community for moving the field toward successful achievement of tolerance are highlighted.

Cell therapy in transplantation: A comprehensive review of the current applications of cell therapy in transplant patients with the focus on Tregs, CAR Tregs, and Mesenchymal stem cells

Organ transplantation is a practical treatment for patients with end-stage organ failure. Despite the advances in short-term graft survival, long-term graft survival remains the main challenge considering the increased mortality and morbidity associated with chronic rejection and the toxicity of immunosuppressive drugs. Since a novel therapeutic strategy to induce allograft tolerance seems urgent, focusing on developing novel and safe approaches to prolong graft survival is one of the main goals of transplant investigators. Researchers in the field of organ transplantation are interested in suppressing or optimizing the immune responses by focusing on immune cells including mesenchymal stem cells (MSCs), polyclonal regulatory Tcells (Tregs), and antigen-specific Tregs engineered with chimeric antigen receptors (CAR Tregs). We review the mechanistic pathways, phenotypic and functional characteristics of these cells, and their promising application in organ transplantation.

Modeling human tumor-immune environments in vivo for the preclinical assessment of immunotherapies

Despite the significant contributions of immunocompetent mouse models to the development and assessment of cancer immunotherapies, they inadequately represent the genetic and biological complexity of corresponding human cancers. Immunocompromised mice reconstituted with a human immune system (HIS) and engrafted with patient-derived tumor xenografts are a promising novel preclinical model for the study of human tumor-immune interactions. Whilst overcoming limitations of immunocompetent models, HIS-tumor models often rely on reconstitution with allogeneic immune cells, making it difficult to distinguish between anti-tumor and alloantigen responses. Models that comprise of autologous human tumor and human immune cells provide a platform that is more representative of the patient immune-tumor interaction. However, limited access to autologous tissues, short experimental windows, and poor retention of tumor microenvironment and tumor infiltrating lymphocyte components are major challenges affecting the establishment and application of autologous models. This review outlines existing preclinical murine models for the study of immuno-oncology, and highlights innovations that can be applied to improve the feasibility and efficacy of autologous models.

Feasibility, long-term safety, and immune monitoring of regulatory T cell therapy in living donor kidney transplant recipients

Short-term outcomes in kidney transplantation are marred by progressive transplant failure and mortality secondary to immunosuppression toxicity. Immune modulation with autologous polyclonal regulatory T cell (Treg) therapy may facilitate immunosuppression reduction promoting better long-term clinical outcomes. In a Phase I clinical trial, 12 kidney transplant recipients received 1-10 × 10⁶ Treg per kg at Day +5 posttransplantation in lieu of induction immunosuppression (Treg Therapy cohort). Nineteen patients received standard immunosuppression (Reference cohort). Primary outcomes were rejection-free and patient survival. Patient and transplant survival was 100%; acute rejection-free survival was 100% in the Treg Therapy versus 78.9% in the reference cohort at 48 months posttransplant. Treg therapy revealed no excess safety concerns. Four patients in the Treg Therapy cohort had mycophenolate mofetil withdrawn successfully and remain on tacrolimus monotherapy. Treg infusion resulted in a long-lasting dose-dependent increase in peripheral blood Tregs together with an increase in marginal zone B cell numbers. We identified a pretransplantation immune phenotype suggesting a high risk of unsuccessful ex-vivo Treg expansion. Autologous Treg therapy is feasible, safe, and is potentially associated with a lower rejection rate than standard immunosuppression. Treg therapy may provide an exciting opportunity to minimize immunosuppression therapy and improve long-term outcomes.

Development of LT-HSC-Reconstituted Non-Irradiated NBSGW Mice for the Study of Human Hematopoiesis In Vivo

Humanized immune system (HIS) mouse models are useful tools for the in vivo investigation of human hematopoiesis. However, the majority of HIS models currently in use are biased towards lymphocyte development and fail to support long-term multilineage leucocytes and erythrocytes. Those that achieve successful multilineage reconstitution often require preconditioning steps which are expensive, cause animal morbidity, are technically demanding, and poorly reproducible. In this study, we address this challenge by using HSPC-NBSGW mice, in which NOD,B6.SCID IL-2rγ-/-KitW41/W41 (NBSGW) mice are engrafted with human CD133+ hematopoietic stem and progenitor cells (HSPCs) without the need for preconditioning by sublethal irradiation. These HSPCs are enriched in long-term hematopoietic stem cells (LT-HSCs), while NBSGW mice are permissive to human hematopoietic stem cell (HSC) engraftment, thus reducing the cell number required for successful HIS development. B cells reconstitute with the greatest efficiency, including mature B cells capable of class-switching following allogeneic stimulation and, within lymphoid organs and peripheral blood, T cells at a spectrum of stages of maturation. In the thymus, human thymocytes are identified at all major stages of development. Phenotypically distinct subsets of myeloid cells, including dendritic cells and mature monocytes, engraft to a variable degree in the bone marrow and spleen, and circulate in peripheral blood. Finally, we observe human erythrocytes which persist in the periphery at high levels following macrophage clearance. The HSPC-NBSGW model therefore provides a useful platform for the study of human hematological and immunological processes and pathologies.

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 T Cells for the Induction of Transplantation Tolerance

Organ transplantation is the optimal treatment for terminal and irreversible organ failure. Achieving transplantation tolerance has long been the ultimate goal in the field of transplantation. Regulatory T cell (Treg)-based therapy is a promising novel approach for inducing donor organ-specific tolerance. Tregs play critical roles in the maintenance of immune homeostasis and self-tolerance, by promoting transplantation tolerance through a variety of mechanisms on different target cells, including anti-inflammatory cytokine production, induction of apoptosis, disruption of metabolic pathways, and mutual interaction with dendritic cells. The continued success of Treg-based therapy in the clinical setting is critically dependent on preclinical studies that support its translational potential. However, although some initial clinical trials of adoptive Treg therapy have successively demonstrated safety and efficacy for immunosuppressant minimization and transplantation tolerance induction, most Treg-based hematopoietic stem cell and solid organ clinical trials are still in their infancy. These clinical trials have not only focused on safety and efficacy but also included optimization and standardization protocols of good manufacturing practice regarding cell isolation, expansion, dosing, timing, specificity, quality control, concomitant immunosuppressants, and post-administration monitoring. We herein report a brief introduction of Tregs, including their phenotypic and functional characterization, and focus on the clinical translation of Treg-based therapeutic applications in the setting of transplantation.

Humanization of Immunodeficient Animals for the Modeling of Transplantation, Graft Versus Host Disease, and Regenerative Medicine

The humanization of animals is a powerful tool for the exploration of human disease pathogenesis in biomedical research, as well as for the development of therapeutic interventions with enhanced translational potential. Humanized models enable us to overcome biologic differences that exist between humans and other species, while giving us a platform to study human processes in vivo. To become humanized, an immune-deficient recipient is engrafted with cells, tissues, or organoids. The mouse is the most well studied of these hosts, with a variety of immunodeficient strains available for various specific uses. More recently, efforts have turned to the humanization of other animal species such as the rat, which offers some technical and immunologic advantages over mice. These advances, together with ongoing developments in the incorporation of human transgenes and additional mutations in humanized mouse models, have expanded our opportunities to replicate aspects of human allotransplantation and to assist in the development of immunotherapies. In this review, the immune and tissue humanization of various species is presented with an emphasis on their potential for use as models for allotransplantation, graft versus host disease, and regenerative medicine.

Exosomes from donor-derived adipose mesenchymal stem cells prolong the survival of vascularized composite allografts

Donor-derived adipose-derived mesenchymal stem cells (ADMSCs) dampen the alloimmune response and exosomes are reported to have biological activity similar to their parent cells. Here, we investigated the roles of exosomes from donor-derived ADMSCs (ADMSC-exo) in vascularized composite allotransplantation (VCA). Brown Norway-to-Lewis rat hindlimb transplantations were intravenously treated with either exosome from donor-derived ADMSCs or phosphate-buffered saline, combined with a short course of immunosuppression. We established that the treatment with ADMSC-exo prolongs the survival time of VCA grafts. Skin and muscle samples from ADMSC-exo-treated animals showed no histological signs of rejection, but samples from controls showed rejection of degree III. Comparing to the control group, a significant increase of donor cell chimerism, Tr1 and Treg, while a decrease of CD4⁺ T and Th1 cells were observed in the ADMSC-exo-treated group. Our findings imply that ADMSC-exo may be a valuable and safe treatment for extending VCA graft survival.

Adoptive transfer of Tregs: A novel strategy for cell-based immunotherapy in spontaneous abortion: Lessons from experimental models

Since half of the genes are inherited from the paternal side, the maternal immune system has to tolerate the presence of foreign paternal antigens. Regulatory T cells facilitate the development and maintenance of peripheral tissue tolerance of the fetus during pregnancy. Reduction in regulatory T cells is associated with complications of pregnancy, including spontaneous abortion. Recent studies in mouse models have shown that the adoptive transfer of Tregs can prevent spontaneous abortion in mouse models through improving maternal tolerance. Thus, adoptive cell therapy using autologous Tregs could potentially be a novel therapeutic approach for cell-based immunotherapy in women with unexplained spontaneous abortion. Besides, strategies for activating and expanding antigen-specific Tregs ex vivo and in vivo based on pharmacological agents can pave the foundation for an approach incorporating immunotherapy and pharmacotherapy. This review aims to elaborate on the current understanding of the therapeutic potential of the adoptive transfer of Tregs in the treatment of spontaneous abortion disease.

Rapamycin and abundant TCR stimulation are required for the generation of stable human induced regulatory T cells

OBJECTIVES

Regulatory T cells (Tregs) are a vital sub-population of CD4+ T cells with major roles in immune tolerance and homeostasis. Given such properties, the use of regulatory T cells for immunotherapies has been extensively investigated, with a focus on adoptive transfer of ex vivo expanded natural Tregs (nTregs). For immunotherapies, induced Tregs (iTregs), generated in vitro from naïve CD4+ T cells, provide an attractive alternative, given the ease of generating cell numbers required for clinical dosage. While the combination of TGF-β, ATRA and rapamycin has been shown to generate highly suppressive iTregs, the challenge for therapeutic iTreg generation has been their instability. Here, we investigate the impact of rapamycin concentrations and α-CD3/CD28 bead ratios on human iTreg stability.

METHODS

We assess iTregs generated with various concentrations of rapamycin and differing ratios of α-CD3/CD28 beads for their differentiation, stability, expression of Treg signature molecules and T helper effector cytokines, and Treg-specific demethylation region (TSDR) status.

RESULTS

iTregs generated in the presence of TGF-β, ATRA, rapamycin and a higher ratio of α-CD3/CD28 beads were highly suppressive and stable upon in vitro re-stimulation. These iTregs exhibited a similar expression profile of Treg signature molecules and T helper effector cytokines to nTregs, in the absence of TSDR demethylation.

CONCLUSION

This work establishes a method to generate human iTregs which maintain stable phenotype and function upon in vitro re-stimulation. Further validation in pre-clinical models will be needed to ensure its suitability for applications in adoptive transfer.

Skin Immunology and Rejection in VCA and Organ Transplantation

Purpose of Review

Skin provides a window into the health of an individual. Using transplanted skin as a monitor can provide a powerful tool for surveillance of rejection in a transplant. The purpose of this review is to provide relevant background to the role of skin in vascularized transplantation medicine.

Recent Findings

Discrete populations of T memory cells provide distributed immune protection in skin, and cycle between skin, lymph nodes, and blood. Skin-resident TREGcells proliferate in response to inflammation and contribute to long-term VCA survival in small animal models. Early clinical studies show sentinel flap rejection to correlate well with facial VCA skin rejection, and abdominal wall rejection demonstrates concordance with visceral rejection, but further studies are required.

Summary

This review focuses on the immunology of skin, skin rejection in vascularized composite allografts, and the recent advances in monitoring the health of transplanted tissues using distant “sentinel” flaps.

IL-10 producing type 2 innate lymphoid cells prolong islet allograft survival

Type 2 innate lymphoid cells (ILC2s) are a subset of ILCs with critical roles in immunoregulation. However, the possible role of ILC2s as immunotherapy against allograft rejection remains unclear. Here, we show that IL‐33 significantly prolonged islet allograft survival. IL‐33‐treated mice had elevated numbers of ILC2s and regulatory T cells (Tregs). Depletion of Tregs partially abolished the protective effect of IL‐33 on allograft survival, and additional ILC2 depletion in Treg‐depleted DEREG mice completely abolished the protective effects of IL‐33, indicating that ILC2s play critical roles in IL‐33‐mediated islet graft protection. Two subsets of ILC2s were identified in islet allografts of IL‐33‐treated mice: IL‐10 producing ILC2s (ILC2¹⁰) and non‐IL‐10 producing ILC2s (non‐ILC¹⁰). Intravenous transfer of ILC2¹⁰ cells, but not non‐ILC¹⁰, prolonged islet allograft survival in an IL‐10‐dependent manner. Locally transferred ILC2¹⁰ cells led to long‐term islet graft survival, suggesting that ILC2¹⁰ cells are required within the allograft for maximal suppressive effect and graft protection. This study has uncovered a major protective role of ILC2¹⁰ in islet transplantation which could be potentiated as a therapeutic strategy.

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.

Distinct metabolic pathways mediate regulatory T cell differentiation and function

Investigation of the cellular metabolic pathways of immune cells, or immunometabolism, is a field of increasing interest. An understanding of immunometabolism provides routes to modifying T cell function for therapeutic purposes. Here, we review immunometabolism with a specific focus on regulatory T cells (Tregs). While T cells are known to switch their metabolic profile from oxidative phosphorylation to aerobic glycolysis upon activation, in vitro-induced Tregs display alternate metabolic characteristics which may be related to their specialised suppressive function. Recent data suggest that the preferential pathways employed by Tregs differ in vivo and ex vivo. Metabolic 'harshness', particularly the deterioration of glycolysis, positively affects Treg differentiation and function, while negatively correlating with Treg clonal expansion and migratory capacity. These context-dependent findings provide new insights into the behaviour of Tregs with implications for both tumour immunology and autoimmunity. This review examines the field in detail, offering an overview of our current understanding of Treg immunometabolism.

The Effects of an IL-21 Receptor Antagonist on the Alloimmune Response in a Humanized Mouse Skin Transplant Model

BACKGROUND

Interleukin 21 (IL-21) is involved in regulating the expansion and effector function of a broad range of leukocytes, including T cells and B cells. In transplantation, the exact role of IL-21 in the process of allograft rejection is unknown. To further explore this, the aim of this study is to test the effect of an IL-21 receptor (IL-21R) blocking antibody on the early phase of allograft rejection in a humanized skin transplantation model in mice reconstituted with human T and B cells.

METHODS

Immunodeficient Balb/c IL2rγRag2 mice were transplanted with human skin followed by adoptive transfer of human allogeneic splenocytes. Control animals were treated with a phosphate buffered saline vehicle while the other group was treated with a humanized anti-IL-21R antibody (αIL-21R).

RESULTS

In the phosphate buffered saline-treated animals, human skin allografts were infiltrated with lymphocytes and developed a thickened epidermis with increased expression of the inflammatory markers Keratin 17 (Ker17) and Ki67. In mice treated with αIL-21R, these signs of allograft reactivity were significantly reduced. Concordantly, STAT3 phosphorylation was inhibited in this group. Of note, treatment with αIL-21R attenuated the process of T and B cell reconstitution after adoptive cellular transfer.

CONCLUSIONS

These findings demonstrate that blockade of IL-21 signaling can delay allograft rejection in a humanized skin transplantation model.

Successful Regulatory T Cell-Based Therapy Relies on Inhibition of T Cell Effector Function and Enrichment of FOXP3+ Cells in a Humanized Mouse Model of Skin Inflammation

Background

Recent clinical trials using regulatory T cells (Treg) support the therapeutic potential of Treg-based therapy in transplantation and autoinflammatory diseases. Despite these clinical successes, the effect of Treg on inflamed tissues, as well as their impact on immune effector function in vivo, is poorly understood. Therefore, we here evaluated the effect of human Treg injection on cutaneous inflammatory processes in vivo using a humanized mouse model of human skin inflammation (huPBL-SCID-huSkin).

Methods

SCID beige mice were transplanted with human skin followed by intraperitoneal (IP) injection of 20‐40 × 10⁶ allogeneic human PBMCs. This typically results in human skin inflammation as indicated by epidermal thickening (hyperkeratosis) and changes in dermal inflammatory markers such as the antimicrobial peptide hBD2 and epidermal barrier cytokeratins K10 and K16, as well as T cell infiltration in the dermis. Ex vivo-expanded human Treg were infused intraperitoneally. Human cutaneous inflammation and systemic immune responses were analysed by immunohistochemistry and flow cytometry.

Results

We confirmed that human Treg injection inhibits skin inflammation and the influx of effector T cells. As a novel finding, we demonstrate that human Treg injection led to a reduction of IL-17-secreting cells while promoting a relative increase in immunosuppressive FOXP3+ Treg in the human skin, indicating active immune regulation in controlling the local proinflammatory response. Consistent with the local control (skin), systemically (splenocytes), we observed that Treg injection led to lower frequencies of IFNγ and IL-17A-expressing human T cells, while a trend towards enrichment of FOXP3+ Treg was observed.

Conclusion

Taken together, we demonstrate that inhibition of skin inflammation by Treg infusion, next to a reduction of infiltrating effector T cells, is mediated by restoring both the local and systemic balance between cytokine-producing effector T cells and immunoregulatory T cells. This work furthers our understanding of Treg-based immunotherapy.

IL-2 enhances ex vivo-expanded regulatory T-cell persistence after adoptive transfer

As regulatory T cell (Treg) adoptive therapy continues to develop clinically, there is a need to determine which immunomodulatory agents pair most compatibly with Tregs to enable persistence and stabilize suppressor function. Prior work has shown that mechanistic target of rapamycin inhibition can increase the stability of thymic Tregs. In this study, we investigated the transcriptomic signatures of ex vivo-expanded Tregs after adoptive transfer in the setting of clinically relevant immunosuppression using a nonhuman primate (NHP) model as a prelude to future transplant studies. Here, we found that adding interleukin-2 (IL-2) to rapamycin in vivo supported a logarithmic increase in the half-life of adoptively transferred carboxyfluorescein diacetate succinimidyl ester-labeled, autologous NHP Tregs, effectively doubling the number of cells in the peripheral blood Treg compartment compared with Treg infusion when rapamycin was given alone. Using single-cell transcriptomics, we found that transferred ex vivo-expanded Tregs initially exhibit a gene expression signature consistent with an activated state. Moreover, those cells with the highest levels of activation also expressed genes associated with p53-mediated apoptosis. In contrast, transferred Tregs interrogated at day +20 posttransfer demonstrated a gene signature more similar to published profiles of resting Tregs. Together, these preclinical data further support combining IL-2 and rapamycin in vivo as adjunctive therapy for ex vivo-expanded adoptively transferred Tregs and suggest that the activation status of ex vivo-expanded Tregs is critical to their persistence.

Novel immunological approach to asses donor reactivity of transplant recipients using a humanized mouse model

In organ transplantation, a reproducible and robust immune-monitoring assay has not been established to determine individually tailored immunosuppressants (IS). We applied humanized mice reconstituted with human (hu-) peripheral blood mononuclear cells (PBMCs) obtained from living donor liver transplant recipients to evaluate their immune status. Engraftment of 2.5 × 10⁶ hu-PBMCs from healthy volunteers and recipients in the NSG mice was achieved successfully. The reconstituted lymphocytes consisted mainly of hu-CD3⁺ lymphocytes with predominant CD45RA^-CD62L^lo T_EM and CCR6^-CXCR3⁺CD4⁺ Th1 cells in hu-PBMC-NSG mice. Interestingly, T cell allo-reactivity of hu-PBMC-NSG mice was amplified significantly compared with that of freshly isolated PBMCs (p < 0.05). Furthermore, magnified hu-T cell responses to donor antigens (Ag) were observed in 2/10 immunosuppressed recipients with multiple acute rejection (AR) experiences, suggesting that the immunological assay in hu-PBMC-NSG mice revealed hidden risks of allograft rejection by IS. Furthermore, donor Ag-specific hyporesponsiveness was maintained in recipients who had been completely weaned off IS (n = 4), despite homeostatic proliferation of hu-T cells in the hu-PBMC-NSG mice. The immunological assay in humanized mice provides a new tool to assess recipient immunity in the absence of IS and explore the underlying mechanisms to maintaining operational tolerance.

2019 ATVB Plenary Lecture: Interleukin-2 Therapy in Cardiovascular Disease: The Potential to Regulate Innate and Adaptive Immunity

Regulatory T cells and type-2 innate lymphoid cells represent 2 subsets of immune cells, which have been shown in preclinical models to be important in atherosclerosis and myocardial repair. Regulatory T cells play a crucial role in immune homeostasis and tolerance via their interactions with effector T cells, dendritic cells, and monocytes/macrophages. They also utilize and secrete inhibitory cytokines, including interleukin 10 and transforming growth factor β, to regulate or suppress pathogenic immune responses. Type-2 innate lymphoid cells have an important role in type-2 immune responses and tissue repair through secreting interleukins 5 and 13, as well as a variety of biological mediators and growth factors. Intriguingly, interleukin-2 has emerged as a common cytokine, which can be harnessed to upregulate both cell types, and also has important translational consequences as clinical trials are ongoing for its use in cardiovascular disease. Here, we briefly review the biology of these regulatory immune cell types, discuss the preclinical and clinical evidence for their functions in cardiovascular disease, examine the prospects for clinical translation and current ongoing trials, and finally, postulate how overlap in the mechanisms of upregulation may be leveraged in future treatments for patients.

Generation and functional assessment of nonhuman primate regulatory dendritic cells and their therapeutic efficacy in renal transplantation

Nonhuman primates (NHP) are important pre-clinical models for evaluation of the safety and efficacy of the most promising potential therapeutic advances in organ transplantation based on rodent studies. Although rare, dendritic cells (DC) play important roles in preservation of self tolerance and DC with immunoregulatory properties (regulatory DC; DCreg) can promote transplant tolerance in rodents when adoptively transferred to allograft recipients. NHP DCreg can be generated ex vivo from bone marrow precursors or blood monocytes of cynomolgus or rhesus macaques or baboons. NHP DCreg generated in the presence of anti-inflammatory factors that confer stability and resistance to maturation, subvert alloreactive T cell responses. When infused into rhesus renal allograft recipients before transplant, they safely prolong MHC mis-matched graft survival, associated with attenuation of anti-donor immune reactivity. In this concise review we describe the properties of NHP DCreg and discuss their influence on T cell responses, alloimmunity and organ transplant survival.

Distinct Regulatory and Effector T Cell Metabolic Demands during Graft-Versus-Host Disease

Despite graft-versus-host disease (GVHD) prophylactic agents, the success and wider utilization of allogeneic hematopoietic stem cell transplantation (allo-HSCT) is limited by GVHD. Increasing donor graft regulatory T cell (Treg):effector T cell (Teff) ratios can substantially reduce GVHD in cancer patients, but pre-HSCT conditioning regimens and GVHD create a challenging inflammatory environment for Treg stability, persistence, and function. Metabolism plays a crucial role in T cell and Treg differentiation, and development of effector function. Although glycolysis is a main driver of allogeneic T cell-driven GVHD, oxidative phosphorylation is a main driver of Treg suppressor function. This review focuses on recent advances in our understanding of Treg metabolism in the context of GVHD, and discusses potential therapeutic applications of Tregs in the prevention or treatment of GVHD in cancer patients.