Adoptive therapy with redirected primary regulatory T cells results in antigen-specific suppression of arthritis

Targeted Therapy of Multiple Sclerosis: A Case for Antigen-Specific Tregs

Multiple sclerosis is an autoinflammatory condition that results in damage to myelinated neurons in affected patients. While disease-modifying treatments have been successful in slowing the progression of relapsing-remitting disease, most patients still progress to secondary progressive disease that is largely unresponsive to disease-modifying treatments. Similarly, there is currently no effective treatment for patients with primary progressive MS. Innate and adaptive immune cells in the CNS play a critical role in initiating an autoimmune attack and in maintaining the chronic inflammation that drives disease progression. In this review, we will focus on recent insights into the role of T cells with regulatory function in suppressing the progression of MS, and, more importantly, in promoting the remyelination and repair of MS lesions in the CNS. We will discuss the exciting potential to genetically reprogram regulatory T cells to achieve immune suppression and enhance repair locally at sites of tissue damage, while retaining a fully competent immune system outside the CNS. In the future, reprogramed regulatory T cells with defined specificity and function may provide life medicines that can persist in patients and achieve lasting disease suppression after one cycle of treatment.

Exploring the therapeutic potential of regulatory T cell in rheumatoid arthritis: Insights into subsets, markers, and signaling pathways

Rheumatoid arthritis (RA) is a complex autoimmune inflammatory rheumatic disease characterized by an imbalance between immunological reactivity and immune tolerance. Regulatory T cells (Tregs), which play a crucial role in controlling ongoing autoimmunity and maintaining peripheral tolerance, have shown great potential for the treatment of autoimmune inflammatory rheumatic diseases such as RA. This review aims to provide an updated summary of the latest insights into Treg-targeting techniques in RA. We focus on current therapeutic strategies for targeting Tregs based on discussing their subsets, surface markers, suppressive function, and signaling pathways in RA.

From islet transplantation to beta-cell regeneration: an update on beta-cell-based therapeutic approaches in type 1 diabetes

INTRODUCTION

Type 1 diabetes (T1D) mellitus is an autoimmune disease in which immune cells, predominantly effector T cells, destroy insulin-secreting beta-cells. Beta-cell destruction led to various consequences ranging from retinopathy and nephropathy to neuropathy. Different strategies have been developed to achieve normoglycemia, including exogenous glucose compensation, whole pancreas transplantation, islet transplantation, and beta-cell replacement.

AREAS COVERED

The last two decades of experience have shown that indigenous glucose compensation through beta-cell regeneration and protection is a peerless method for T1D therapy. Tremendous studies have tried to find an unlimited source for beta-cell regeneration, on the one hand, and beta-cell protection against immune attack, on the other hand. Recent advances in stem cell technology, gene editing methods, and immune modulation approaches provide a unique opportunity for both beta-cell regeneration and protection.

EXPERT OPINION

Pluripotent stem cell differentiation into the beta-cell is considered an unlimited source for beta-cell regeneration. Devising engineered pancreas-specific regulatory T cells using Chimeric Antigen Receptor (CAR) technology potentiates an effective immune tolerance induction for beta-cell protection. Beta-cell regeneration using pluripotent stem cells and beta-cell protection using pancreas-specific engineered regulatory T cells promises to develop a curative protocol in T1D.

Niche-specific control of tissue function by regulatory T cells-Current challenges and perspectives for targeting metabolic disease

Tissue regulatory T cells (Tregs) exert pivotal functions in both immune and metabolic regulation, maintaining local tissue homeostasis, integrity, and function. Accordingly, Tregs play a crucial role in controlling obesity-induced inflammation and supporting efficient muscle function and repair. Depending on the tissue context, Tregs are characterized by unique transcriptomes, growth, and survival factors and T cell receptor (TCR) repertoires. This functional specialization offers the potential to selectively target context-specific Treg populations, tailoring therapeutic strategies to specific niches, thereby minimizing potential side effects. Here, we discuss challenges and perspectives for niche-specific Treg targeting, which holds promise for highly efficient and precise medical interventions to combat metabolic disease.

Translation of cell therapies to treat autoimmune disorders

Autoimmune diseases are a diverse and complex set of chronic disorders with a substantial impact on patient quality of life and a significant global healthcare burden. Current approaches to autoimmune disease treatment comprise broadly acting immunosuppressive drugs that lack disease specificity, possess limited efficacy, and confer undesirable side effects. Additionally, there are limited treatments available to restore organs and tissues damaged during the course of autoimmune disease progression. Cell therapies are an emergent area of therapeutics with the potential to address both autoimmune disease immune dysfunction as well as autoimmune disease-damaged tissue and organ systems. In this review, we discuss the pathogenesis of common autoimmune disorders and the state-of-the-art in cell therapy approaches to (1) regenerate or replace autoimmune disease-damaged tissue and (2) eliminate pathological immune responses in autoimmunity. Finally, we discuss critical considerations for the translation of cell products to the clinic.

Chimeric antigen receptor Treg therapy in transplantation

In the quest for more precise and effective organ transplantation therapies, chimeric antigen receptor (CAR) regulatory T cell (Treg) therapies represent a potential cutting-edge advance. This review comprehensively analyses CAR Tregs and how they may address important drawbacks of polyclonal Tregs and conventional immunosuppressants. We examine a growing body of preclinical findings of CAR Treg therapy in transplantation, discuss CAR Treg design specifics, and explore established and attractive new targets in transplantation. In addition, we explore present impediments where future studies will be necessary to determine the efficacy of CAR Tregs in reshaping alloimmune responses and transplant microenvironments to reduce reliance on chemical immunosuppressants. Overall, ongoing studies and trials are crucial for understanding the full scope of CAR Treg therapy in transplantation.

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.

Eras of designer Tregs: Harnessing synthetic biology for immune suppression

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

Regulating the regulatory T cells as cell therapies in autoimmunity and cancer

Regulatory T cells (Tregs), possess a pivotal function in the maintenance of immune homeostasis. The dysregulated activity of Tregs has been associated with the onset of autoimmune diseases and cancer. Hence, Tregs are promising targets for interventions aimed at steering the immune response toward the desired path, either by augmenting the immune system to eliminate infected and cancerous cells or by dampening it to curtail the damage to self-tissues in autoimmune disorders. The activation of Tregs has been observed to have a potent immunosuppressive effect against T cells that respond to self-antigens, thus safeguarding our body against autoimmunity. Therefore, promoting Treg cell stability presents a promising strategy for preventing or managing chronic inflammation that results from various autoimmune diseases. On the other hand, Tregs have been found to be overactivated in several forms of cancer, and their role as immune response regulators with immunosuppressive properties poses a significant impediment to the successful implementation of cancer immunotherapy. However, the targeting of Tregs in a systemic manner may lead to the onset of severe inflammation and autoimmune toxicity. It is imperative to develop more selective methods for targeting the function of Tregs in tumors. In this review, our objective is to elucidate the function of Tregs in tumors and autoimmunity while also delving into numerous therapeutic strategies for reprogramming their function. Our focus is on reprogramming Tregs in a highly activated phenotype driven by the activation of key surface receptors and metabolic reprogramming. Furthermore, we examine Treg-based therapies in autoimmunity, with a specific emphasis on Chimeric Antigen Receptor (CAR)-Treg therapy and T-cell receptor (TCR)-Treg therapy. Finally, we discuss key challenges and the future steps in reprogramming Tregs that could lead to the development of novel and effective cancer immunotherapies.

Immunomodulation for Tissue Repair and Regeneration

Various immune cells participate in repair and regeneration following tissue injury or damage, orchestrating tissue inflammation and regeneration processes. A deeper understanding of the immune system's involvement in tissue repair and regeneration is critical for the development of successful reparatory and regenerative strategies. Here we review recent technologies that facilitate cell-based and biomaterial-based modulation of the immune systems for tissue repair and regeneration. First, we summarize the roles of various types of immune cells in tissue repair. Second, we review the principle, examples, and limitations of regulatory T (Treg) cell-based therapy, a representative cell-based immunotherapy. Finally, we discuss biomaterial-based immunotherapy strategies that aim to modulate immune cells using various biomaterials for tissue repair and regeneration.

New cell sources for CAR-based immunotherapy

Chimeric antigen receptor (CAR) T cell therapy, in which a patient's own T lymphocytes are engineered to recognize and kill cancer cells, has achieved striking success in some hematological malignancies in preclinical and clinical trials, resulting in six FDA-approved CAR-T products currently available in the market. Despite impressive clinical outcomes, concerns about treatment failure associated with low efficacy or high cytotoxicity of CAR-T cells remain. While the main focus has been on improving CAR-T cells, exploring alternative cellular sources for CAR generation has garnered growing interest. In the current review, we comprehensively evaluated other cell sources rather than conventional T cells for CAR generation.

Enhancing Regulatory T Cells to Treat Inflammatory and Autoimmune Diseases

Regulatory T cells (Tregs) control immune responses and are essential to maintain immune homeostasis and self-tolerance. Hence, it is no coincidence that autoimmune and chronic inflammatory disorders are associated with defects in Tregs. These diseases have currently no cure and are treated with palliative drugs such as immunosuppressant and immunomodulatory agents. Thereby, there is a great interest in developing medical interventions against these diseases based on enhancing Treg cell function and numbers. Here, we give an overview of Treg cell ontogeny and function, paying particular attention to mucosal Tregs. We review some notable approaches to enhance immunomodulation by Tregs with therapeutic purposes including adoptive Treg cell transfer therapy and discuss relevant clinical trials for inflammatory bowel disease. We next introduce ways to expand mucosal Tregs in vivo using microbiota and dietary products that have been the focus of clinical trials in various autoimmune and chronic-inflammatory diseases.

Engineered Treg cells as putative therapeutics against inflammatory diseases and beyond

Regulatory T (Treg) cells ensure tolerance against self-antigens, limit excessive inflammation, and support tissue repair processes. Therefore, Treg cells are currently attractive candidates for the treatment of certain inflammatory diseases, autoimmune disorders, or transplant rejection. Early clinical trials have proved the safety and efficacy of certain Treg cell therapies in inflammatory diseases. We summarize recent advances in engineering Treg cells, including the concept of biosensors for inflammation. We assess Treg cell engineering possibilities for novel functional units, including Treg cell modifications influencing stability, migration, and tissue adaptation. Finally, we outline perspectives of engineered Treg cells going beyond inflammatory diseases by using custom-designed receptors and read-out systems, aiming to use Treg cells as in vivo diagnostic tools and drug delivery vehicles.

Regulatory T Cells (Tregs) and COVID-19: Unveiling the Mechanisms, and Therapeutic Potentialities with a Special Focus on Long COVID

The COVID-19 pandemic has caused havoc all around the world. The causative agent of COVID-19 is the novel form of the coronavirus (CoV) named SARS-CoV-2, which results in immune system disruption, increased inflammation, and acute respiratory distress syndrome (ARDS). T cells have been important components of the immune system, which decide the fate of the COVID-19 disease. Recent studies have reported an important subset of T cells known as regulatory T cells (Tregs), which possess immunosuppressive and immunoregulatory properties and play a crucial role in the prognosis of COVID-19 disease. Recent studies have shown that COVID-19 patients have considerably fewer Tregs than the general population. Such a decrement may have an impact on COVID-19 patients in a number of ways, including diminishing the effect of inflammatory inhibition, creating an inequality in the Treg/Th17 percentage, and raising the chance of respiratory failure. Having fewer Tregs may enhance the likelihood of long COVID development in addition to contributing to the disease's poor prognosis. Additionally, tissue-resident Tregs provide tissue repair in addition to immunosuppressive and immunoregulatory activities, which may aid in the recovery of COVID-19 patients. The severity of the illness is also linked to abnormalities in the Tregs' phenotype, such as reduced expression of FoxP3 and other immunosuppressive cytokines, including IL-10 and TGF-beta. Hence, in this review, we summarize the immunosuppressive mechanisms and their possible roles in the prognosis of COVID-19 disease. Furthermore, the perturbations in Tregs have been associated with disease severity. The roles of Tregs are also explained in the long COVID. This review also discusses the potential therapeutic roles of Tregs in the management of patients with COVID-19.

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.

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.

T cell Repertoire Profiling and the Mechanism by which HLA-B27 Causes Ankylosing Spondylitis

Purpose of Review

Ankylosing spondylitis (AS) is strongly associated with the HLA-B27 gene. The canonical function of HLA-B27 is to present antigenic peptides to CD8 lymphocytes, leading to adaptive immune responses. The ‘arthritogenic peptide’ theory as to the mechanism by which HLA-B27 induces ankylosing spondylitis proposes that HLA-B27 presents peptides derived from exogenous sources such as bacteria to CD8 lymphocytes, which subsequently cross-react with antigens at the site of inflammation of the disease, causing inflammation. This review describes findings of studies in AS involving profiling of T cell expansions and discusses future research opportunities based on these findings.

Recent Findings

Consistent with this theory, there is an expanding body of data showing that expansion of a restricted pool of CD8 lymphocytes is found in most AS patients yet only in a small proportion of healthy HLA-B27 carriers.

Summary

These exciting findings strongly support the theory that AS is driven by presentation of antigenic peptides to the adaptive immune system by HLA-B27. They point to new potential approaches to identify the exogenous and endogenous antigens involved and to potential therapies for the disease.

Pancreatic islet-specific engineered Tregs exhibit robust antigen-specific and bystander immune suppression in type 1 diabetes models

Adoptive transfer of regulatory T cells (T_regs) is therapeutic in type 1 diabetes (T1D) mouse models. T_regs that are specific for pancreatic islets are more potent than polyclonal T_regs in preventing disease. However, the frequency of antigen-specific natural T_regs is extremely low, and ex vivo expansion may destabilize T_regs, leading to an effector phenotype. Here, we generated durable, antigen-specific engineered T_regs (EngT_regs) from primary human CD4⁺ T cells by combining FOXP3 homology-directed repair editing and lentiviral T cell receptor (TCR) delivery. Using TCRs derived from clonally expanded CD4⁺ T cells isolated from patients with T1D, we generated islet-specific EngT_regs that suppressed effector T cell (T_eff) proliferation and cytokine production. EngT_regs suppressed T_effs recognizing the same islet antigen in addition to bystander T_effs recognizing other islet antigens through production of soluble mediators and both direct and indirect mechanisms. Adoptively transferred murine islet-specific EngT_regs homed to the pancreas and blocked diabetes triggered by islet-specific T_effs or diabetogenic polyclonal T_effs in recipient mice. These data demonstrate the potential of antigen-specific EngT_regs as a targeted therapy for preventing T1D.

Forced Fox-P3 expression can improve the safety and antigen-specific function of engineered regulatory T cells

Regulatory T cells (Treg) are potent inhibitors of autoreactive T cells. The intracellular transcription factor FoxP3 controls the expression levels of a diverse set of genes and plays a critical role in programming functional Tregs. Although, antigen-specific Tregs are more potent than polyclonal Tregs in treating ongoing autoimmunity, phenotype plasticity associated with loss of FoxP3 expression in Tregs can lead to the conversion into antigen-specific effector T cells which might exacerbate autoimmune pathology. In this study, we designed a retroviral vector driving the expression of FoxP3 and a human HLA-DR-restricted TCR from the same promoter. Transduction of purified human Tregs revealed that all TCR-positive cells had elevated levels of FoxP3 expression, increased CD25 and CTLA4 expression and potent suppressive function. Elevated FoxP3 expression did not impair the in vitro expansion of engineered Tregs. Adoptive transfer into HLA-DR transgenic mice revealed that FoxP3+TCR engineered Tregs showed long-term persistence with stable FoxP3 and TCR expression. In contrast, adoptive transfer of Tregs engineered with TCR only resulted in the accumulation of TCR-positive, FoxP3-negative T cells which displayed antigen-specific effector function when stimulated with the TCR-recognised peptides. Our data indicate that forced expression of FoxP3 can prevent accumulation of antigen-specific effector T cells without impairing the engraftment and persistence of engineered Tregs.

The Dynamic Role of FOXP3+ Tregs and Their Potential Therapeutic Applications During SARS-CoV-2 Infection

Coronavirus disease 2019 (COVID-19) has been raging all around the world since the beginning of 2020, and leads to acute respiratory distress syndrome (ARDS) with strong cytokine storm which contributes to widespread tissue damage and even death in severe patients. Over-activated immune response becomes one of the characteristics of severe COVID-19 patients. Regulatory T cells (Treg) play an essential role in maintaining the immune homeostasis, which restrain excessive inflammation response. So FOXP3+ Tregs might participate in the suppression of inflammation caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Besides suppressive function, tissue resident Tregs are also responsible for tissue repair. In this review, we mainly summarize the latest research focusing on the change of FOXP3+ Tregs in the COVID-19 patients, discuss the relationship between disease severity and number change of Tregs and speculate the potential role of FOXP3+ Tregs during SARS-CoV-2 infection. Furthermore, we introduce some potential Treg-based therapies to improve patients’ outcomes, which include small molecular drugs, antibody drugs, CAR-Treg and cytokine treatment. We hope to reduce tissue damage of severe COVID-19 patients and offer better prognosis through Treg-based therapy.

Current Strategies to Modulate Regulatory T Cell Activity in Allergic Inflammation

Over the past decades, atopic diseases, including allergic rhinitis, asthma, atopic dermatitis, and food allergy, increased strongly worldwide, reaching up to 50% in industrialized countries. These diseases are characterized by a dominating type 2 immune response and reduced numbers of allergen-specific regulatory T (Treg) cells. Conventional allergen-specific immunotherapy is able to tip the balance towards immunoregulation. However, in mouse models of allergy adaptive transfer of Treg cells did not always lead to convincing beneficial results, partially because of limited stability of their regulatory phenotype activity. Besides genetic predisposition, it has become evident that environmental factors like a westernized lifestyle linked to modern sanitized living, the early use of antibiotics, and the consumption of unhealthy foods leads to epithelial barrier defects and dysbiotic microbiota, thereby preventing immune tolerance and favoring the development of allergic diseases. Epigenetic modification of Treg cells has been described as one important mechanism in this context. In this review, we summarize how environmental factors affect the number and function of Treg cells in allergic inflammation and how this knowledge can be exploited in future allergy prevention strategies as well as novel therapeutic approaches.

Cell-based therapies for rheumatoid arthritis: opportunities and challenges

Rheumatoid arthritis (RA) is the most common immune-mediated inflammatory disease characterized by chronic synovitis that hardly resolves spontaneously. The current treatment of RA consists of nonsteroidal anti-inflammatory drugs (NSAIDs), glucocorticoids, conventional disease-modifying antirheumatic drugs (cDMARDs), biologic and targeted synthetic DMARDs. Although the treat-to-target strategy has been intensively applied in the past decade, clinical unmet needs still exist since a substantial proportion of patients are refractory or even develop severe adverse effects to current therapies. In recent years, with the deeper understanding of immunopathogenesis of the disease, cell-based therapies have exhibited effective and promising interventions to RA. Several cell-based therapies, such as mesenchymal stem cells (MSC), adoptive transfer of regulatory T cells (Treg), and chimeric antigen receptor (CAR)-T cell therapy as well as their beneficial effects have been documented and verified so far. In this review, we summarize the current evidence and discuss the prospect as well as challenges for these three types of cellular therapies in RA.

Emerging therapeutic potential of regulatory T (Treg) cells for rheumatoid arthritis: New insights and challenges

Rheumatoid arthritis (RA) is an autoimmune-related disorder characterized by chronic inflammation. Although the etiopathogenesis of RA still remains to be clarified, it is supposed that the breakdown of immune self-tolerance may contribute to the development of RA. Thus, restoring of immune tolerance at the site of inflammation is the ultimate goal of RA treatment. Regulatory T cells (Treg cells) are the main suppressive cells that maintain tolerance and inhibit immunity against auto-antigen. Of note, recent studies demonstrated the efficacy of adoptive transfer of Treg cells in the modulation of the unwanted immune response, which makes them an ideal candidate to maintain immune homeostasis and restore antigen-specific tolerance in the case of RA and other autoimmune diseases. This review intends to submit recent finding of Treg cells-based therapies in RA with a focus on strategies applied to improve the therapeutic value of Treg cells to restore immune tolerance.

CAR-T Regulatory (CAR-Treg) Cells: Engineering and Applications

Regulatory T cells are critical for maintaining immune tolerance. Recent studies have confirmed their therapeutic suppressive potential to modulate immune responses in organ transplant and autoimmune diseases. However, the unknown and nonspecific antigen recognition of polyclonal Tregs has impaired their therapeutic potency in initial clinical findings. To address this limitation, antigen specificity can be conferred to Tregs by engineering the expression of transgenic T-cell receptor (TCR) or chimeric antigen receptor (CAR). In contrast to TCR Tregs, CAR Tregs are major histocompatibility complex (MHC) independent and less dependent on interleukin-2 (IL-2). Furthermore, CAR Tregs maintain Treg phenotype and function, home to the target tissue and show enhanced suppressive efficacy compared to polyclonal Tregs. Additional development of engineered CAR Tregs is needed to increase Tregs’ suppressive function and stability, prevent CAR Treg exhaustion, and assess their safety profile. Further understanding of Tregs therapeutic potential will be necessary before moving to broader clinical applications. Here, we summarize recent studies utilizing CAR Tregs in modulating immune responses in autoimmune diseases, transplantation, and gene therapy and future clinical applications.

Emerging strategies for treating autoimmune disorders with genetically modified Treg cells

Gene editing of living cells is a cornerstone of present-day medical research that has enabled scientists to address fundamental biologic questions and identify novel strategies to treat diseases. The ability to manipulate adoptive cell therapy products has revolutionized cancer immunotherapy and promises similar results for the treatment of autoimmune diseases, inflammatory disorders, and transplant rejection. Clinical trials have recently deemed polyclonal regulatory T (Treg) cell therapy to be a safe therapeutic option, but questions remain regarding the efficacy of this approach. In this review, we discuss how gene editing technologies are being applied to transform the future of Treg cell therapy, focusing on the preclinical strategies that are currently being investigated to enhance the efficacy, function, and survival of human Treg cells. We explore approaches that may be used to generate immunoregulatory cells ex vivo, detail emerging strategies that are being used to modify these cells (such as using chimeric antigen receptors to confer antigen specificity), and outline concepts that have been explored to repurpose conventional T cells to target and destroy autoreactive and alloreactive lymphocytes. We also describe the key hurdles that currently hinder the clinical adoption of Treg cell therapy and propose potential future avenues of research for this field.

Recent Advances in Cell Therapeutics for Systemic Autoimmune Diseases

Systemic autoimmune diseases arise from loss of self-tolerance and immune homeostasis between effector and regulator functions. There are many therapeutic modalities for autoimmune diseases ranging from conventional disease-modifying anti-rheumatic drugs and immunosuppressants exerting nonspecific immune suppression to targeted agents including biologic agents and small molecule inhibitors aiming at specific cytokines and intracellular signal pathways. However, such current therapeutic strategies can rarely induce recovery of immune tolerance in autoimmune disease patients. To overcome limitations of conventional treatment modalities, novel approaches using specific cell populations with immune-regulatory properties have been attempted to attenuate autoimmunity. Recently progressed biotechnologies enable sufficient in vitro expansion and proper manipulation of such ‘tolerogenic’ cell populations to be considered for clinical application. We introduce 3 representative cell types with immunosuppressive features, including mesenchymal stromal cells, Tregs, and myeloid-derived suppressor cells. Their cellular definitions, characteristics, mechanisms of immune regulation, and recent data about preclinical and clinical studies in systemic autoimmune diseases are reviewed here. Challenges and limitations of each cell therapy are also addressed.

CAR Treg: A new approach in the treatment of autoimmune diseases

Regulatory T cells (Tregs) have the role of regulating self-tolerance, and suppressing immune responses. Defects in Treg function and number can lead to in loss of tolerance or autoimmune disease. To treat or control autoimmune diseases, one of the options is to develop immune tolerance for Tregs cell therapy, which includes promotion and activation. Recently, cell-based treatment as a promising approach to increase cells function and number has been developed. Cell therapy by chimeric T antigen receptor (CAR-T) cells has shown significant efficacy in the treatment of leukemia, which has led researchers to use CAR-T cells in other diseases like autoimmune diseases. Here, we describe the existing treatments for autoimmune diseases and the available treatments based on Treg, their benefits and restrictions for implementation in clinical trials. We also discussed potential solutions to overcome these limitations. It seems novel designs of CARs to be new hope for autoimmune diseases and expected to be a potential cure option in a wide array of disease in the future. Therefore, it is very important to address this issue and increase information about it.

CRISPR/Cas9-mediated TGFβRII disruption enhances anti-tumor efficacy of human chimeric antigen receptor T cells in vitro

BACKGROUND

CAR T-cell therapy has been recently unveiled as one of the most promising cancer therapies in hematological malignancies. However, solid tumors mount a profound line of defense to escape immunosurveillance by CAR T-cells. Among them, cytokines with an inhibitory impact on the immune system such as IL-10 and TGFβ are of great importance: TGFβ is a pleiotropic cytokine, which potently suppresses the immune system and is secreted by a couple of TME resident and tumor cells.

METHODS

In this study, we hypothesized that knocking out the TGFβ receptor II gene, could improve CAR T-cell functions in vitro and in vivo. Hereby, we used the CRISPR/Cas9 system, to knockout the TGFβRII gene in T-cells and could monitor the efficient gene knock out by genome analysis techniques. Next, Mesothelin or Claudin 6 specific CAR constructs were overexpressed via IVT-RNA electroporation or retroviral transduction and the poly-functionality of these TGFβRII KO CAR T-cells in terms of proliferation, cytokine secretion and cytotoxicity were assessed and compared with parental CAR T-cells.

RESULTS

Our experiments demonstrated that TGFβRII KO CAR T-cells fully retained their capabilities in killing tumor antigen positive target cells and more intriguingly, could resist the anti-proliferative effect of exogenous TGFβ in vitro outperforming wild type CAR T-cells. Noteworthy, no antigen or growth factor-independent proliferation of these TGFβRII KO CAR T-cells has been recorded. TGFβRII KO CAR T-cells also resisted the suppressive effect of induced regulatory T-cells in vitro to a larger extent. Repetitive antigen stimulation demonstrated that these TGFβRII KO CAR T-cells will experience less activation induced exhaustion in comparison to the WT counterpart.

CONCLUSION

The TGFβRII KO approach may become an indispensable tool in immunotherapy of solid tumors, as it may surmount one of the key negative regulatory signaling pathways in T-cells.

A reasoned approach to the treatment of autoimmune hepatitis

Autoimmune hepatitis (AIH) is a chronic inflammatory liver disease affecting all ages, characterised by elevated transaminase and immunoglobulin G levels, positive autoantibodies, interface hepatitis on histology and good response to immunosuppressive treatment. If untreated, it has a poor prognosis. The aim of this review is to analyse AIH therapeutic interventions with reference to our knowledge of the pathogenesis of AIH. Standard treatment, based on steroids and azathioprine, leads to disease remission in 80-90% of patients. Alternative first-line treatment with budesonide is effective in adults, but less so in the juvenile form of AIH; first-line treatment with ciclosporin does not provide convincing advantages compared to standard treatment. Second-line treatments are needed for patients not responding or intolerant to first-line standard management. Mycophenolate mofetil is the most widely used second-line drug, and has good efficacy particularly for patients intolerant to azathioprine, but is teratogenic. Only few and heterogeneous data on calcineurin inhibitors and m-TOR inhibitors are available. Biologicals, including anti-tumour necrosis factor- α and anti-CD20 monoclonal antibodies, have given ambivalent results and may have severe side-effects. Clinical trials with new therapeutic options aiming at targeting B lymphocytes and proinflammatory cytokines, or expanding regulatory T cells to restore tolerance are ongoing.

Neutralization of IL-17 and treatment with IL-2 protects septic arthritis by regulating free radical production and antioxidant enzymes in Th17 and Tregs: An immunomodulatory TLR2 versus TNFR response

Septic arthritis is a destructive joint disease caused by Staphylococcus aureus. Synovial inflammation involved Th17 proliferation and down regulation of Treg population, thus resolution of inflammation targeting IL-17 may be important to control arthritis. Endogenous inhibition of IL-17 to regulate arthritic inflammation correlating with Th17/Treg cells TLR2 and TNFRs are not done. The role of SOD, CAT and GRx in relation to ROS production during arthritis along with expression of TLR2, TNFR1/TNFR2 in Th17/Treg cells of mice treated with IL-17A Ab/ IL-2 were studied. Increased ROS, reduced antioxidant enzyme activity was found in Th17 cells of SA infected mice whereas Treg cells of IL-17A Ab/ IL-2 treated group showed opposite effects. Neutralization of IL-17 after arthritis cause decreased TNFR1 and increased TNFR2 expression in Treg cells. Thus, neutralization of IL-17 or IL-2 treatment regulates septic arthritis by enhancing anti-inflammatory properties of Treg via antioxidant balance and modulating TLR2/TNFR response.

Regulatory T Cell Therapy of Graft-versus-Host Disease: Advances and Challenges

Graft-versus-host disease (GVHD) is the leading cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Immunomodulation using regulatory T cells (Tregs) offers an exciting option to prevent and/or treat GVHD as these cells naturally function to maintain immune homeostasis, can induce tolerance following HSCT, and have a tissue reparative function. Studies to date have established a clinical safety profile for polyclonal Tregs. Functional enhancement through genetic engineering offers the possibility of improved potency, specificity, and persistence. In this review, we provide the most up to date preclinical and clinical data on Treg cell therapy with a particular focus on GVHD. We discuss the different Treg subtypes and highlight the pharmacological and genetic approaches under investigation to enhance the application of Tregs in allo-HSCT. Lastly, we discuss the remaining challenges for optimal clinical translation and provide insights as to future directions of the field.

Transcriptional and posttranslational regulation of Th17/Treg balance in health and disease

Regulatory T (Treg) cells and T helper type 17 (Th17) cells play important roles in adaptive immune responses, antagonizing each other in immune disorders. Th17/Treg balance is critical to maintaining the immune homeostasis of human bodies and is tightly regulated under healthy conditions. The transcription factors that are required for driving Th17 and Treg cell lineages differentiation respectively, RORγt and FOXP3 are tightly regulated under different tissue microenvironment, especially the transcriptional induction, posttranslational modifications, and dynamic enzymatic cofactors binding. The imbalance caused by alteration of the quantity or properties of RORγt⁺ Th17 or FOXP3⁺ Treg can contribute to inflammatory disorders in humans. Restoring Th17/Treg balance by modifying the enzymatic activities of RORγt and FOXP3 binding partners may be therapeutically applied to treat severe immune disorders. In this review, we focus on the transcriptional and posttranslational regulations of Th17/Treg balance, immune disorders caused by Th17/Treg imbalance, and new therapeutic strategies for restoring immune homeostasis.

Expansion of tumor-associated Treg cells upon disruption of a CTLA-4-dependent feedback loop

Foxp3+ T regulatory (Treg) cells promote immunological tumor tolerance, but how their immune-suppressive function is regulated in the tumor microenvironment (TME) remains unknown. Here, we used intravital microscopy to characterize the cellular interactions that provide tumor-infiltrating Treg cells with critical activation signals. We found that the polyclonal Treg cell repertoire is pre-enriched to recognize antigens presented by tumor-associated conventional dendritic cells (cDCs). Unstable cDC contacts sufficed to sustain Treg cell function, whereas T helper cells were activated during stable interactions. Contact instability resulted from CTLA-4-dependent downregulation of co-stimulatory B7-family proteins on cDCs, mediated by Treg cells themselves. CTLA-4-blockade triggered CD28-dependent Treg cell hyper-proliferation in the TME, and concomitant Treg cell inactivation was required to achieve tumor rejection. Therefore, Treg cells self-regulate through a CTLA-4- and CD28-dependent feedback loop that adjusts their population size to the amount of local co-stimulation. Its disruption through CTLA-4-blockade may off-set therapeutic benefits in cancer patients.

T cell receptor revision and immune repertoire changes in autoimmune diseases

Autoimmune disease (AID) is a condition in which the immune system breaks down and starts to attack the body. Some common AIDs include systemic lupus erythematosus, rheumatoid arthritis, type 1 diabetes mellitus and so forth. The changes in T-cell receptor (TCR) repertoire have been found in several autoimmune diseases, and may be responsible for the breakdown of peripheral immune tolerance. In this review, we discussed the processes of TCR revision in peripheral immune environment, the changes in TCR repertoire that occurred in various AIDs, and the specifically expanded T cell clones. We hope our discussion can provide insights for the future studies, helping with the discovery of disease biomarkers and expanding the strategies of immune-targeted therapy. HighlightsRestricted TCR repertoire and biased TCR-usage are found in a variety of AIDs.TCR repertoire shows tissue specificity in a variety of AID diseases.The relationship between TCR repertoire diversity and disease activity is still controversial in AIDs.Dominant TCR clonotypes may help to discover new disease biomarkers and expand the strategies of immune-targeted therapy.

Improving the Efficacy of Regulatory T Cell Therapy

Autoimmunity is caused by an unbalanced immune system, giving rise to a variety of organ-specific to system disorders. Patients with autoimmune diseases are commonly treated with broad-acting immunomodulatory drugs, with the risk of severe side effects. Regulatory T cells (Tregs) have the inherent capacity to induce peripheral tolerance as well as tissue regeneration and are therefore a prime candidate to use as cell therapy in patients with autoimmune disorders. (Pre)clinical studies using Treg therapy have already established safety and feasibility, and some show clinical benefits. However, Tregs are known to be functionally impaired in autoimmune diseases. Therefore, ex vivo manipulation to boost and stably maintain their suppressive function is necessary when considering autologous transplantation. Similar to autoimmunity, severe coronavirus disease 2019 (COVID-19) is characterized by an exaggerated immune reaction and altered Treg responses. In light of this, Treg-based therapies are currently under investigation to treat severe COVID-19. This review provides a detailed overview of the current progress and clinical challenges of Treg therapy for autoimmune and hyperinflammatory diseases, with a focus on recent successes of ex vivo Treg manipulation.

Function, Failure, and the Future Potential of Tregs in Type 1 Diabetes

Critical insights into the etiology of type 1 diabetes (T1D) came from genome-wide association studies that unequivocally connected genetic susceptibility to immune cell function. At the top of the susceptibility are genes involved in regulatory T-cell (Treg) function and development. The advances in epigenetic and transcriptional analyses have provided increasing evidence for Treg dysfunction in T1D. These are well supported by functional studies in mouse models and analysis of peripheral blood during T1D. For these reasons, Treg-based therapies are at the forefront of research and development and have a tangible probability to deliver a long-sought-after successful immune-targeted treatment for T1D. The current challenge in the field is whether we can directly assess Treg function at the tissue site or make informative interpretations based on peripheral data. Future studies focused on Treg function in pancreatic lymph nodes and pancreas could provide key insight into the ultimate mechanisms underlying Treg failure in T1D. In this Perspective we will provide an overview of current literature regarding Treg development and function in T1D and how this knowledge has been applied to Treg therapies.

Antigen-Specific Regulatory T Cell Therapy in Autoimmune Diseases and Transplantation

Regulatory T (Treg) cells are a heterogenous population of immunosuppressive T cells whose therapeutic potential for the treatment of autoimmune diseases and graft rejection is currently being explored. While clinical trial results thus far support the safety and efficacy of adoptive therapies using polyclonal Treg cells, some studies suggest that antigen-specific Treg cells are more potent in regulating and improving immune tolerance in a disease-specific manner. Hence, several approaches to generate and/or expand antigen-specific Treg cells in vitro or in vivo are currently under investigation. However, antigen-specific Treg cell therapies face additional challenges that require further consideration, including the identification of disease-relevant antigens as well as the in vivo stability and migratory behavior of Treg cells following transfer. In this review, we discuss these approaches and the potential limitations and describe prospective strategies to enhance the efficacy of antigen-specific Treg cell treatments in autoimmunity and transplantation.

Emerging Therapeutics for Immune Tolerance: Tolerogenic Vaccines, T cell Therapy, and IL-2 Therapy

Autoimmune diseases affect roughly 5-10% of the total population, with women affected more than men. The standard treatment for autoimmune or autoinflammatory diseases had long been immunosuppressive agents until the advent of immunomodulatory biologic drugs, which aimed at blocking inflammatory mediators, including proinflammatory cytokines. At the frontier of these biologic drugs are TNF-α blockers. These therapies inhibit the proinflammatory action of TNF-α in common autoimmune diseases such as rheumatoid arthritis, psoriasis, ulcerative colitis, and Crohn's disease. TNF-α blockade quickly became the "standard of care" for these autoimmune diseases due to their effectiveness in controlling disease and decreasing patient's adverse risk profiles compared to broad-spectrum immunosuppressive agents. However, anti-TNF-α therapies have limitations, including known adverse safety risk, loss of therapeutic efficacy due to drug resistance, and lack of efficacy in numerous autoimmune diseases, including multiple sclerosis. The next wave of truly transformative therapeutics should aspire to provide a cure by selectively suppressing pathogenic autoantigen-specific immune responses while leaving the rest of the immune system intact to control infectious diseases and malignancies. In this review, we will focus on three main areas of active research in immune tolerance. First, tolerogenic vaccines aiming at robust, lasting autoantigen-specific immune tolerance. Second, T cell therapies using Tregs (either polyclonal, antigen-specific, or genetically engineered to express chimeric antigen receptors) to establish active dominant immune tolerance or T cells (engineered to express chimeric antigen receptors) to delete pathogenic immune cells. Third, IL-2 therapies aiming at expanding immunosuppressive regulatory T cells in vivo.

Separating the wheat from the chaff: Making sense of Treg heterogeneity for better adoptive cellular therapy

Regulatory T (Treg) cells are essential for immunological tolerance and can be used to suppress unwanted or excessive immune responses through adoptive cellular therapy. It is increasingly clear that many subsets of Treg cells exist, which have different functions and reside in different locations. Treg cell therapies may benefit from tailoring the selected subset to the tissue that must be protected as well as to characteristics of the immune response that must be suppressed, but little attention is given to this topic in current therapies. Here, we will discuss how three major axes of heterogeneity can be discerned among the Treg cell population, which determine function and lineage fidelity. A first axis relates to the developmental route, as Treg cells can be generated from immature T cells in the thymus or from already mature Tconv cells in the immunological periphery. Heterogeneity furthermore stems from activation history (naïve or effector) and location (lymphoid or peripheral tissues). Each of these axes bestows specific properties on Treg cells, which are further refined by additional processes leading to yet further variation. A critical aspect impacting on Treg cell heterogeneity is TCR specificity, which determines when and where Treg cells are generated as well as where they exhibit their effector functions. We will discuss the implications of this heterogeneity and the role of the TCR for the design of next generation adoptive cellular therapy with Treg cells.

Super-Treg: Toward a New Era of Adoptive Treg Therapy Enabled by Genetic Modifications

Regulatory Tcells (Treg) are essential components of peripheral immune homeostasis. Adoptive Treg cell therapy has shown efficacy in a variety of immune-mediated diseases in preclinical studies and is now moving from phase I/IIa to larger phase II studies aiming to demonstrate efficacy. However, hurdles such as in vivo stability and efficacy remain to be addressed. Nevertheless, preclinical models have shown that Treg function and specificity can be increased by pharmacological substances or gene modifications, and even that conventional T cells can be converted to Treg potentially providing new sources of Treg and facilitating Treg cell therapy. The exponential growth in genetic engineering techniques and their application to T cells coupled to a large body of knowledge on Treg open numerous opportunities to generate Treg with "superpowers". This review summarizes the genetic engineering techniques available and their applications for the next-generation of Super-Treg with increased function, stability, redirected specificity and survival.

Immune modulation via T regulatory cell enhancement: Disease-modifying therapies for autoimmunity and their potential for chronic allergic and inflammatory diseases-An EAACI position paper of the Task Force on Immunopharmacology (TIPCO)

Therapeutic advances using targeted biologicals and small-molecule drugs have achieved significant success in the treatment of chronic allergic, autoimmune, and inflammatory diseases particularly for some patients with severe, treatment-resistant forms. This has been aided by improved identification of disease phenotypes. Despite these achievements, not all severe forms of chronic inflammatory and autoimmune diseases are successfully targeted, and current treatment options, besides allergen immunotherapy for selected allergic diseases, fail to change the disease course. T cell-based therapies aim to cure diseases through the selective induction of appropriate immune responses following the delivery of engineered, specific cytotoxic, or regulatory T cells (Tregs). Adoptive cell therapies (ACT) with genetically engineered T cells have revolutionized the oncology field, bringing curative treatment for leukemia and lymphoma, while therapies exploiting the suppressive functions of Tregs have been developed in nononcological settings, such as in transplantation and autoimmune diseases. ACT with Tregs are also being considered in nononcological settings such as cardiovascular disease, obesity, and chronic inflammatory disorders. After describing the general features of T cell-based approaches and current applications in autoimmune diseases, this position paper reviews the experimental models testing or supporting T cell-based approaches, especially Treg-based approaches, in severe IgE-mediated responses and chronic respiratory airway diseases, such as severe asthma and COPD. Along with an assessment of challenges and unmet needs facing the application of ACT in these settings, this article underscores the potential of ACT to offer curative options for patients with severe or treatment-resistant forms of these immune-driven disorders.

A method for expansion and retroviral transduction of mouse regulatory T cells

Adoptive cell therapy with genetically modified regulatory T cells (Tregs) is under clinical investigation for the treatment of transplant rejection and various autoimmune conditions. A limitation of modelling this approach in mice is the lack of optimized protocols for expanding and transducing mouse Tregs. Here we describe a protocol for purifying, expanding and retrovirally transducing mouse Tregs with a vector encoding a chimeric antigen receptor as a model transgene. We found that isolation of Tregs from C57Bl/6J Foxp3EGFP mice solely based on eGFP expression resulted in sufficiently pure cells; co-sorting of CD25hi cells was not essential. Although expansion with rapamycin reduced Treg expansion, it promoted maximal in vitro suppressive activity. Retroviral transduction of Tregs following 2 days of stimulation with anti-CD3/CD28 beads achieved a transduction efficiency of ~40% and did not impair their suppressive capacity. When injected into a conventional T cell (Tconv)-transfer-induced colitis model, transduced Tregs inhibited colitis progression at ratios as low as 1 Treg to 100 Tconvs, and maintained Foxp3 and transgene expression throughout an 8-week period. This method facilitates the study of transduced Tregs in animal models and will enable the study of genetically engineered Treg therapy for a variety of inflammatory diseases.

Regulatory T cell heterogeneity and therapy in autoimmune diseases

Regulatory T (Treg) cells are a group of CD4⁺ T cell with high expression of CD25 and cell linage specific transcription factor forkhead box P3 (Foxp3) and play a vital role in maintaining immune homeostasis. In the last two decades, researchers have shown that Treg cells involved in the occurrence, development and prognosis of many diseases, especially in autoimmune diseases. Treg targeted therapies, such as low-dose interleukin-2 (IL-2) treatment and Treg infusion therapy, which are aimed at restoring the number or function of Treg cells, have become a hot topic in clinical trials of these diseases. It is believed that Treg cells are heterogeneous. Different subsets of Treg cells have various functions and play different parts in immunomodulatory. Gaining insights into Treg heterogeneity will help us further understand the function of Treg cells and provide news ideas for the selective therapeutic manipulation of Treg cells. In this review, we mainly summarize the heterogeneity of Treg cells and their potential therapeutic value in autoimmune diseases.

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

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

Conventional T cell therapies pave the way for novel Treg therapeutics

Approaches to harness the immune system to alleviate disease have become remarkably sophisticated since the crude, yet impressively-effective, attempts using live bacteria in the late 1800s. Recent evidence that engineered T cell therapy can deliver durable results in patients with cancer has spurred frenzied development in the field of T cell therapy. The myriad approaches include an innumerable variety of synthetic transgenes, multiplex gene-editing, and broader application to diseases beyond cancer. In this article, we review the preclinical studies and over a decade of clinical experience with engineered conventional T cells that have paved the way for translating engineered regulatory T cell therapies.

Regulatory T cell therapy: Current and future design perspectives

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

The Future of Regulatory T Cell Therapy: Promises and Challenges of Implementing CAR Technology

Cell therapy with polyclonal regulatory T cells (Tregs) has been translated into the clinic and is currently being tested in transplant recipients and patients suffering from autoimmune diseases. Moreover, building on animal models, it has been widely reported that antigen-specific Tregs are functionally superior to polyclonal Tregs. Among various options to confer target specificity to Tregs, genetic engineering is a particularly timely one as has been demonstrated in the treatment of hematological malignancies where it is in routine clinical use. Genetic engineering can be exploited to express chimeric antigen receptors (CAR) in Tregs, and this has been successfully demonstrated to be robust in preclinical studies across various animal disease models. However, there are several caveats and a number of strategies should be considered to further improve on targeting, efficacy and to understand the in vivo distribution and fate of CAR-Tregs. Here, we review the differing approaches to confer antigen specificity to Tregs with emphasis on CAR-Tregs. This includes an overview and discussion of the various approaches to improve CAR-Treg specificity and therapeutic efficacy as well as addressing potential safety concerns. We also discuss different imaging approaches to understand the in vivo biodistribution of administered Tregs. Preclinical research as well as suitability of methodologies for clinical translation are discussed.

Characterization of regulatory T cell expansion for manufacturing cellular immunotherapies

Regulatory T cells (T_regs) are critical mediators of peripheral immune tolerance. T_regs suppress immune activation against self-antigens and are the focus of cell-based therapies for autoimmune diseases. However, T_regs circulate at a very low frequency in blood, limiting the number of cells that can be isolated by leukapheresis. To effectively expand T_regsex vivo for cell therapy, we report the metabolic modulation of T cells using mono-(6-amino-6-deoxy)-β-cyclodextrin (βCD-NH₂) encapsulated rapamycin (Rapa). Encapsulating Rapa in β-cyclodextrin increased its aqueous solubility ∼154-fold and maintained bioactivity for at least 30 days. βCD-NH₂-Rapa complexes (CRCs) enriched the fraction of CD4⁺CD25⁺FoxP3⁺ mouse T (mT) cells and human T (hT) cells up to 6-fold and up to 2-fold respectively and suppressed the overall expansion of effector T cells by 5-fold in both species. Combining CRCs and transforming growth factor beta-1 (TGF-β1) synergistically promoted the expansion of CD4⁺CD25⁺FoxP3⁺ T cells. CRCs significantly reduced the fraction of pro-inflammatory interferon-gamma (IFN-γ) expressing CD4⁺ T cells, suppressing this Th1-associated cytokine while enhancing the fraction of IFN-γ^- tumor necrosis factor-alpha (TNF-α) expressing CD4⁺ T cells. We developed a model using kinetic rate equations to describe the influence of the initial fraction of naïve T cells on the enrichment of T_regsin vitro. The model related the differences in the expansion kinetics of mT and hT cells to their susceptibility for immunophenotypic modulation. CRCs may be an effective and potent means for phenotypic modulation of T cells and the enrichment of T_regsin vitro. Our findings contribute to the development of experimental and analytical techniques for manufacturing T_reg based immunotherapies.