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

Dawn of CAR-T cell therapy in autoimmune diseases

ABSTRACT

Chimeric antigen receptor (CAR)-T cell therapy has achieved remarkable success in the treatment of hematological malignancies. Based on the immunomodulatory capability of CAR-T cells, efforts have turned toward exploring their potential in treating autoimmune diseases. Bibliometric analysis of 210 records from 128 academic journals published by 372 institutions in 40 countries/regions indicates a growing number of publications on CAR-T therapy for autoimmune diseases, covering a range of subtypes such as systemic lupus erythematosus, multiple sclerosis, among others. CAR-T therapy holds promise in mitigating several shortcomings, including the indiscriminate suppression of the immune system by traditional immunosuppressants, and non-sustaining therapeutic levels of monoclonal antibodies due to inherent pharmacokinetic constraints. By persisting and proliferating in vivo , CAR-T cells can offer a tailored and precise therapeutics. This paper reviewed preclinical experiments and clinical trials involving CAR-T and CAR-related therapies in various autoimmune diseases, incorporating innovations well-studied in the field of hematological tumors, aiming to explore a safe and effective therapeutic option for relapsed/refractory autoimmune diseases.

Regulation of Treg cells by cytokine signaling and co-stimulatory molecules

CD4+CD25+Foxp3+ regulatory T cells (Tregs), a vital component of the immune system, are responsible for maintaining immune homeostasis and preventing excessive immune responses. This review explores the signaling pathways of the cytokines that regulate Treg cells, including transforming growth factor beta (TGF-β), interleukin (IL)-2, IL-10, and IL-35, which foster the differentiation and enhance the immunosuppressive capabilities of Tregs. It also examines how, conversely, signals mediated by IL-6 and tumor necrosis factor -alpha (TNF-α) can undermine Treg suppressive functions or even drive their reprogramming into effector T cells. The B7 family comprises indispensable co-stimulators for T cell activation. Among its members, this review focuses on the capacity of CTLA-4 and PD-1 to regulate the differentiation, function, and survival of Tregs. As Tregs play an essential role in maintaining immune homeostasis, their dysfunction contributes to the pathogenesis of autoimmune diseases. This review delves into the potential of employing Treg-based immunotherapy for the treatment of autoimmune diseases, transplant rejection, and cancer. By shedding light on these topics, this article aims to enhance our understanding of the regulation of Tregs by cytokines and their therapeutic potential for various pathological conditions.

Engineering antigen-presenting cells for immunotherapy of autoimmunity

Autoimmune diseases are burdensome conditions that affect a significant fraction of the global population. The hallmark of autoimmune disease is a host's immune system being licensed to attack its tissues based on specific antigens. There are no cures for autoimmune diseases. The current clinical standard for treating autoimmune diseases is the administration of immunosuppressants, which weaken the immune system and reduce auto-inflammatory responses. However, people living with autoimmune diseases are subject to toxicity, fail to mount a sufficient immune response to protect against pathogens, and are more likely to develop infections. Therefore, there is a concerted effort to develop more effective means of targeting immunomodulatory therapies to antigen-presenting cells, which are involved in modulating the immune responses to specific antigens. In this review, we highlight approaches that are currently in development to target antigen-presenting cells and improve therapeutic outcomes in autoimmune diseases.

Therapeutic induction of antigen-specific immune tolerance

The development of therapeutic approaches for the induction of robust, long-lasting and antigen-specific immune tolerance remains an important unmet clinical need for the management of autoimmunity, allergy, organ transplantation and gene therapy. Recent breakthroughs in our understanding of immune tolerance mechanisms have opened new research avenues and therapeutic opportunities in this area. Here, we review mechanisms of immune tolerance and novel methods for its therapeutic induction.

Immune modulation in transplant medicine: a comprehensive review of cell therapy applications and future directions

Balancing the immune response after solid organ transplantation (SOT) and vascularized composite allotransplantation (VCA) remains an ongoing clinical challenge. While immunosuppressants can effectively reduce acute rejection rates following transplant surgery, some patients still experience recurrent acute rejection episodes, which in turn may progress to chronic rejection. Furthermore, these immunosuppressive regimens are associated with an increased risk of malignancies and metabolic disorders. Despite significant advancements in the field, these IS related side effects persist as clinical hurdles, emphasizing the need for innovative therapeutic strategies to improve transplant survival and longevity. Cellular therapy, a novel therapeutic approach, has emerged as a potential pathway to promote immune tolerance while minimizing systemic side-effects of standard IS regiments. Various cell types, including chimeric antigen receptor T cells (CAR-T), mesenchymal stromal cells (MSCs), regulatory myeloid cells (RMCs) and regulatory T cells (Tregs), offer unique immunomodulatory properties that may help achieve improved outcomes in transplant patients. This review aims to elucidate the role of cellular therapies, particularly MSCs, T cells, Tregs, RMCs, macrophages, and dendritic cells in SOT and VCA. We explore the immunological features of each cell type, their capacity for immune regulation, and the prospective advantages and obstacles linked to their application in transplant patients. An in-depth outline of the current state of the technology may help SOT and VCA providers refine their perioperative treatment strategies while laying the foundation for further trials that investigate cellular therapeutics in transplantation surgery.

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

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

Adoptive cell therapy for solid tumors beyond CAR-T: Current challenges and emerging therapeutic advances

Adoptive cellular immunotherapy using immune cells expressing chimeric antigen receptors (CARs) is a highly specific anti-tumor immunotherapy that has shown promise in the treatment of hematological malignancies. However, there has been a slow progress toward the treatment of solid tumors owing to the complex tumor microenvironment that affects the localization and killing ability of the CAR cells. Solid tumors with a strong immunosuppressive microenvironment and complex vascular system are unaffected by CAR cell infiltration and attack. To improve their efficacy toward solid tumors, CAR cells have been modified and upgraded by "decorating" and "pruning". This review focuses on the structure and function of CARs, the immune cells that can be engineered by CARs and the transformation strategies to overcome solid tumors, with a view to broadening ideas for the better application of CAR cell therapy for the treatment of solid tumors.

Engineered Treg cells: The heir to the throne of immunotherapy

Recently, increased interest in the use of Tregs as adoptive cell therapy for the treatment of autoimmune diseases and transplant rejection had led to several advances in the field. However, Treg cell therapies, while constantly advancing, indiscriminately suppress the immune system without the permanent stabilization of certain diseases. Genetically modified Tregs hold great promise towards solving these problems, but, challenges in identifying the most potent Treg subtype, accompanied by the ambiguity involved in identifying the optimal Treg source, along with its expansion and engineering in a clinical-grade setting remain paramount. This review highlights the recent advances in methodologies for the development of genetically engineered Treg cell-based treatments for autoimmune, inflammatory diseases, and organ rejection. Additionally, it provides a systematized guide to all the recent progress in the field and informs the readers of the feasibility and safety of engineered adoptive Treg cell therapy, with the aim to provide a framework for researchers involved in the development of engineered Tregs.

Chimeric Antigen Receptor (CAR)-Based Cell Therapy for Type 1 Diabetes Mellitus (T1DM); Current Progress and Future Approaches

Type 1 diabetes mellitus (T1DM) is an autoimmune disease that destroys insulin-producing pancreatic β-cells. Insulin replacement therapy is currently the mainstay of treatment for T1DM; however, treatment with insulin does not ameliorate disease progression, as dysregulated immune response and inflammation continue to cause further pancreatic β-cell degradation. Therefore, shifting therapeutic strategies toward immunomodulating approaches could be effective to prevent and reverse disease progression. Different immune-modulatory therapies could be used, e.g., monoclonal-based immunotherapy, mesenchymal stem cell, and immune cell therapy. Since immune-modulatory approaches could have a systemic effect on the immune system and cause toxicity, more specific treatment options should target the immune response against pancreatic β-cells. In this regard, chimeric antigen receptor (CAR)-based immunotherapy could be a promising candidate for modulation of dysregulated immune function in T1DM. CAR-based therapy has previously been approved for a number of hematologic malignancies. Nevertheless, there is renewed interest in CAR T cells' " off-the-shelf " treatment for T1DM. Several pre-clinical studies demonstrated that redirecting antigen-specific CAR T cells, especially regulatory CAR T cells (CAR Tregs), toward the pancreatic β-cells, could prevent diabetes onset and progression in diabetic mice models. Here, we aim to review the current progress of CAR-based immune-cell therapy for T1DM and the corresponding challenges, with a special focus on designing CAR-based immunomodulatory strategies to improve its efficacy in the treatment of T1DM.

Deciphering the developmental trajectory of tissue-resident Foxp3+ regulatory T cells

Foxp3+ TREG cells have been at the focus of intense investigation for their recognized roles in preventing autoimmunity, facilitating tissue recuperation following injury, and orchestrating a tolerance to innocuous non-self-antigens. To perform these critical tasks, TREG cells undergo deep epigenetic, transcriptional, and post-transcriptional changes that allow them to adapt to conditions found in tissues both at steady-state and during inflammation. The path leading TREG cells to express these tissue-specialized phenotypes begins during thymic development, and is further driven by epigenetic and transcriptional modifications following TCR engagement and polarizing signals in the periphery. However, this process is highly regulated and requires TREG cells to adopt strategies to avoid losing their regulatory program altogether. Here, we review the origins of tissue-resident TREG cells, from their thymic and peripheral development to the transcriptional regulators involved in their tissue residency program. In addition, we discuss the distinct signalling pathways that engage the inflammatory adaptation of tissue-resident TREG cells, and how they relate to their ability to recognize tissue and pathogen-derived danger signals.

Immune regulation and therapeutic application of T regulatory cells in liver diseases

CD4+ CD25+ FOXP3+ T regulatory cells (Tregs) are a subset of the immunomodulatory cell population that can inhibit both innate and adaptive immunity by various regulatory mechanisms. In hepatic microenvironment, proliferation, plasticity, migration, and function of Tregs are interrelated to the remaining immune cells and their secreted cytokines and chemokines. In normal conditions, Tregs protect the liver from inflammatory and auto-immune responses, while disruption of this crosstalk between Tregs and other immune cells may result in the progression of chronic liver diseases and the development of hepatic malignancy. In this review, we analyze the deviance of this protective nature of Tregs in response to chronic inflammation and its involvement in inducing liver fibrosis, cirrhosis, and hepatocellular carcinoma. We will also provide a detailed emphasis on the relevance of Tregs as an effective immunotherapeutic option for autoimmune diseases, liver transplantation, and chronic liver diseases including liver cancer.

Human CD4+CD25+ T cells expressing a chimeric antigen receptor against aberrant superoxide dismutase 1 trigger antigen-specific immunomodulation

BACKGROUND AIMS

Amyotrophic lateral sclerosis (ALS) is a fatal disease associated with motor neuron degeneration, accumulation of aggregated misfolded proteins and neuroinflammation in motor regions of the central nervous system (CNS). Clinical trials using regulatory T cells (Tregs) are ongoing because of Tregs' immunomodulatory function, ability to traffic to the CNS, high numbers correlating with slower disease in ALS and disease-modifying activity in ALS mouse models. In the current study, a chimeric antigen receptor (CAR) was developed and characterized in human Tregs to enhance their immunomodulatory activity when in contact with an ALS protein aggregate.

METHODS

A CAR (DG05-28-3z) consisting of a human superoxide dismutase 1 (hSOD1)-binding single-chain variable fragment, CD28 hinge, transmembrane and co-stimulatory domain and CD3ζ signaling domain was created and expressed in human Tregs. Human Tregs were isolated by either magnetic enrichment for CD4+CD25hi cells (Enr-Tregs) or cell sorting for CD4+CD25hiCD127lo cells (FP-Tregs), transduced and expanded for 17 days.

RESULTS

The CAR bound preferentially to the ALS mutant G93A-hSOD1 protein relative to the wild-type hSOD1 protein. The CAR Tregs produced IL-10 when cultured with aggregated G93A-hSOD1 proteins or spinal cord explants from G93A-hSOD1 transgenic mice. Co-culturing DG05-28-3z CAR Tregs with human monocytes/macrophages inhibited production of tumor necrosis factor alpha and reactive oxygen species. Expanded FP-Tregs resulted in more robust Tregs compared with Enr-Tregs. FP-Tregs produced similar IL-10 and less interferon gamma, had lower Treg-specific demethylated region methylation and expressed higher FoxP3 and CD39.

CONCLUSIONS

Taken together, this study demonstrates that gene-modified Tregs can be developed to target an aggregated ALS-relevant protein to elicit CAR-mediated Treg effector functions and provides an approach for generating Treg therapies for ALS with the goal of enhanced disease site-specific immunomodulation.

Beyond FOXP3: a 20-year journey unravelling human regulatory T-cell heterogeneity

The initial idea of a distinct group of T-cells responsible for suppressing immune responses was first postulated half a century ago. However, it is only in the last three decades that we have identified what we now term regulatory T-cells (Tregs), and subsequently elucidated and crystallized our understanding of them. Human Tregs have emerged as essential to immune tolerance and the prevention of autoimmune diseases and are typically contemporaneously characterized by their CD3+CD4+CD25high CD127lowFOXP3+ phenotype. It is important to note that FOXP3+ Tregs exhibit substantial diversity in their origin, phenotypic characteristics, and function. Identifying reliable markers is crucial to the accurate identification, quantification, and assessment of Tregs in health and disease, as well as the enrichment and expansion of viable cells for adoptive cell therapy. In our comprehensive review, we address the contributions of various markers identified in the last two decades since the master transcriptional factor FOXP3 was identified in establishing and enriching purity, lineage stability, tissue homing and suppressive proficiency in CD4+ Tregs. Additionally, our review delves into recent breakthroughs in innovative Treg-based therapies, underscoring the significance of distinct markers in their therapeutic utilization. Understanding Treg subsets holds the key to effectively harnessing human Tregs for immunotherapeutic approaches.

Regulatory T cells in lung disease and transplantation

Pulmonary disease can refer to the disease of the lung itself or the pulmonary manifestations of systemic diseases, which are often connected to the malfunction of the immune system. Regulatory T (Treg) cells have been shown to be important in maintaining immune homeostasis and preventing inflammatory damage, including lung diseases. Given the increasing amount of evidence linking Treg cells to various pulmonary conditions, Treg cells might serve as a therapeutic strategy for the treatment of lung diseases and potentially promote lung transplant tolerance. The most potent and well-defined Treg cells are Foxp3-expressing CD4+ Treg cells, which contribute to the prevention of autoimmune lung diseases and the promotion of lung transplant rejection. The protective mechanisms of Treg cells in lung disease and transplantation involve multiple immune suppression mechanisms. This review summarizes the development, phenotype and function of CD4+Foxp3+ Treg cells. Then, we focus on the therapeutic potential of Treg cells in preventing lung disease and limiting lung transplant rejection. Furthermore, we discussed the possibility of Treg cell utilization in clinical applications. This will provide an overview of current research advances in Treg cells and their relevant application in clinics.

Regulatory T cells in skin regeneration and wound healing

As the body's integumentary system, the skin is vulnerable to injuries. The subsequent wound healing processes aim to restore dermal and epidermal integrity and functionality. To this end, multiple tissue-resident cells and recruited immune cells cooperate to efficiently repair the injured tissue. Such temporally- and spatially-coordinated interplay necessitates tight regulation to prevent collateral damage such as overshooting immune responses and excessive inflammation. In this context, regulatory T cells (Tregs) hold a key role in balancing immune homeostasis and mediating cutaneous wound healing. A comprehensive understanding of Tregs' multifaceted field of activity may help decipher wound pathologies and, ultimately, establish new treatment modalities. Herein, we review the role of Tregs in orchestrating the regeneration of skin adnexa and catalyzing healthy wound repair. Further, we discuss how Tregs operate during fibrosis, keloidosis, and scarring.

Selective reprogramming of regulatory T cells in solid tumors can strongly enhance or inhibit tumor growth

Folate receptor delta (FRδ) has been used as a biomarker for regulatory T cells (Tregs), because its expression is limited to Tregs and ovum. Although FRδ is unable to bind folate, we have used molecular docking software to identify a folate congener that binds FRδ with high affinity and have exploited this FRδ-specific ligand to target attached drugs (imaging agents, immune activators, and immune suppressors) specifically to Tregs in murine tumor xenografts. Analysis of treated tumors demonstrates that targeting of a Toll-like receptor 7 agonist inhibits Treg expression of FOXP3, PD-1, CTLA4, and HELIOS, resulting in 40-80% reduction in tumor growth and repolarization of other tumor-infiltrating immune cells to more inflammatory phenotypes. Targeting of the immunosuppressive drug dexamethasone, in contrast, promotes enhanced tumor growth and shifts the tumor-infiltrating immune cells to more anti-inflammatory phenotypes. Since Tregs comprise <1% of cells in the tumor masses examined, and since the targeted drugs are not internalized by cancer cells, these data demonstrate that Tregs exert a disproportionately large effect on tumor growth. Because the targeted drug did not bind to Tregs or other immune cells in healthy tissues, the data demonstrate that the immunosuppressive properties of Tregs in tumors can be manipulated without causing systemic toxicities associated with global reprogramming of the immune system.

Induced Pluripotent Stem Cell-Derived Chimeric Antigen Receptor T Cells: The Intersection of Stem Cells and Immunotherapy

Chimeric antigen receptor (CAR) T cell therapy is a promising cell-based immunotherapy applicable to various cancers. High cost of production, immune rejection, heterogeneity of cell product, limited cell source, limited expandability, and relatively long production time have created the need to achieve a universal allogeneic CAR-T cell product for "off-the-shelf" application. Since the innovation of induced pluripotent stem cells (iPSCs) by Yamanaka et al., extensive efforts have been made to prepare an unlimited cell source for regenerative medicine, that is, immunotherapy. In the autologous grafting approach, iPSCs prepare the desired cell source for generating autologous CAR-T cells through more accessible and available sources. In addition, generating iPSC-derived CAR-T cells is a promising approach to achieving a suitable source for producing an allogeneic CAR-T cell product. In brief, the first step is reprogramming somatic cells (accessible from peripheral blood, skin, etc.) to iPSCs. In the next step, CAR expression and T cell lineage differentiation should be applied in different arrangements. In addition, in an allogeneic manner, human leukocyte antigen/T cell receptor (TCR) deficiency should be applied in iPSC colonies. The allogeneic iPSC-derived CAR-T cell experiments showed that simultaneous performance of HLA/TCR deficiency, CAR expression, and T cell lineage differentiation could bring the production to the highest efficacy in generating allogeneic iPSC-derived CAR-T cells.

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

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

Challenges and new technologies in adoptive cell therapy

Adoptive cell therapies (ACTs) have existed for decades. From the initial infusion of tumor-infiltrating lymphocytes to the subsequent specific enhanced T cell receptor (TCR)-T and chimeric antigen receptor (CAR)-T cell therapies, many novel strategies for cancer treatment have been developed. Owing to its promising outcomes, CAR-T cell therapy has revolutionized the field of ACTs, particularly for hematologic malignancies. Despite these advances, CAR-T cell therapy still has limitations in both autologous and allogeneic settings, including practicality and toxicity issues. To overcome these challenges, researchers have focused on the application of CAR engineering technology to other types of immune cell engineering. Consequently, several new cell therapies based on CAR technology have been developed, including CAR-NK, CAR-macrophage, CAR-γδT, and CAR-NKT. In this review, we describe the development, advantages, and possible challenges of the aforementioned ACTs and discuss current strategies aimed at maximizing the therapeutic potential of ACTs. We also provide an overview of the various gene transduction strategies employed in immunotherapy given their importance in immune cell engineering. Furthermore, we discuss the possibility that strategies capable of creating a positive feedback immune circuit, as healthy immune systems do, could address the flaw of a single type of ACT, and thus serve as key players in future cancer immunotherapy.

Differential roles of regulatory T cells in acute respiratory infections

Acute respiratory infections trigger an inflammatory immune response with the goal of pathogen clearance; however, overexuberant inflammation causes tissue damage and impairs pulmonary function. CD4+FOXP3+ regulatory T cells (Tregs) interact with cells of both the innate and the adaptive immune system to limit acute pulmonary inflammation and promote its resolution. Tregs also provide tissue protection and coordinate lung tissue repair, facilitating a return to homeostatic pulmonary function. Here, we review Treg-mediated modulation of the host response to respiratory pathogens, focusing on mechanisms underlying how Tregs promote resolution of inflammation and repair of acute lung injury. We also discuss potential strategies to harness and optimize Tregs as a cellular therapy for patients with severe acute respiratory infection and discuss open questions in the field.

Localized immunomodulation technologies to enable cellular and organoid transplantation

Localized immunomodulation technologies are rapidly emerging as a new modality with the potential to revolutionize transplantation of cells and organs. In the past decade, cell-based immunomodulation therapies saw clinical success in the treatment of cancer and autoimmune diseases. In this review, we describe recent advances in engineering solutions for the development of localized immunomodulation techniques focusing on cellular and organoid transplantation. We begin by describing cell transplantation and highlighting notable clinical successes, particularly in the areas of stem cell therapy, chimeric antigen receptor (CAR)-T cell therapy, and islet transplantation. Next, we detail recent preclinical studies centered on genome editing and biomaterials to enhance localized immunomodulation. We close by discussing future opportunities to improve clinical and commercial success using these approaches to facilitate long-term immunomodulation technologies.

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.

Low-dose interleukin-2 treatment increases the proportion of regulatory T cells in patients with rheumatic diseases: A meta-analysis

BACKGROUND

It is now accepted that immune tolerance disorders caused by inadequate Treg cell function or number are important factors in the development and progression of rheumatic diseases. There is increasing evidence that ld IL-2 treatment increases the proportion of Treg cells in patients' peripheral blood, but this conclusion is still controversial. Here, we performed a meta-analysis of reports documenting the proportion of Treg cells and the rate of adverse events in patients with rheumatic disease before and after the administration of ld IL-2 to better understand its effect and safety on Treg cells in the field of rheumatic diseases.

METHODS

We systematically searched PubMed, Embase, Scopus, Cochrane Library, and Web of science databases up to 15th November 2022 and identified studies that reported the proportion of peripheral blood Treg cells before and after ld IL-2 treatment in patients with rheumatic disease. Random-effects model was used to perform a meta-analysis of Treg cell proportions before and after ld IL-2 administration, and a meta-regression analysis was performed to explore heterogeneity. Inconsistency was evaluated using the I-squared index (I²), and publication bias was assessed by examining funnel plot asymmetry using the Egger tests.

RESULTS

Eighteen studies involving 1608 patients were included in the meta-analysis. The proportion of Treg cells in peripheral blood of these patients increased significantly after receiving ld IL-2 treatment [1.07 (95% CI 0.86,1.27), p < 0.001, I² = 67.3%]. Next, Meta-regression was performed for 5 variables including publish year, disease type, trail type and dosage and duration of the medication. The results suggest that these variables do not lead to high heterogeneity. (p = 0.698, 0.267, 0.502, 0.843, 0.560, respectively). And finally, statistical analysis showed no difference in adverse reactions between ld IL-2 group and control group in treatment [1.06 (95% CI 0.86,1.31), p = 0.586, I2 = 53.8%], which is unreliable because the data is so small.

CONCLUSIONS

Ld IL-2 does increase the proportion of peripheral blood Treg cells in patients with rheumatism, and single and cumulative doses must be considered when using ld IL-2. In addition, more studies on the safety of ld IL-2 are urgently needed.

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.

The potential of regulatory T cell-based therapies for alopecia areata

Cytotoxic T lymphocyte has been a concern for the etiopathogenesis of alopecia areata (AA), some recent evidence suggests that the regulatory T (T_reg) cell deficiency is also a contributing factor. In the lesional scalp of AA, T_reg cells residing in the follicles are impaired, leading to dysregulated local immunity and hair follicle (HF) regeneration disorders. New strategies are emerging to modulate T_reg cells' number and function for autoimmune diseases. There is much interest to boost T_reg cells in AA patients to suppress the abnormal autoimmunity of HF and stimulate hair regeneration. With few satisfactory therapeutic regimens available for AA, T_reg cell-based therapies could be the way forward. Specifically, CAR-T_reg cells and novel formulations of low-dose IL-2 are the alternatives.

Regulatory T Cells: Liquid and Living Precision Medicine for the Future of VCA

Transplant rejection remains a challenge especially in the field of vascularized composite allotransplantation (VCA). To blunt the alloreactive immune response' stable levels of maintenance immunosupression are required. However' the need for lifelong immunosuppression poses the risk of severe side effects, such as increased risk of infection, metabolic complications, and malignancies. To balance therapeutic efficacy and medication side effects, immunotolerance promoting immune cells (especially regulatory T cells [Treg]) have become of great scientific interest. This approach leverages immune system mechanisms that usually ensure immunotolerance toward self-antigens and prevent autoimmunopathies. Treg can be bioengineered to express a chimeric antigen receptor or a T-cell receptor. Such bioengineered Treg can target specific antigens and thereby reduce unwanted off-target effects. Treg have demonstrated beneficial clinical effects in solid organ transplantation and promising in vivo data in VCAs. In this review, we summarize the functional, phenotypic, and immunometabolic characteristics of Treg and outline recent advancements and current developments regarding Treg in the field of VCA and solid organ transplantation.

Strategies to enhance CAR-T persistence

Chimeric antigen receptor T (CAR-T) cell therapy has significantly improved the life expectancy for patients with refractory or relapse B cell lymphoma. As for B cell acute lymphoblastic leukemia (B-ALL), although the primary response rate is promising, the high incidence of early relapse has caused modest long-term survival with CAR-T cell alone. One of the main challenges is the limited persistence of CAR-T cells. To further optimize the clinical effects of CAR-T cells, many studies have focused on modifying the CAR structure and regulating CAR-T cell differentiation. In this review, we focus on CAR-T cell persistence and summarize the latest progress and strategies adopted during the in vitro culture stage to optimize CAR-T immunotherapy by improving long-term persistence. Such strategies include choosing a suitable cell source, improving culture conditions, combining CAR-T cells with conventional drugs, and applying genetic manipulations, all of which may improve the survival of patients with hematologic malignancies by reducing the probability of recurrence after CAR-T cell infusion and provide clues for solid tumor CAR-T cell therapy development.

Emerging translational strategies and challenges for enhancing regulatory T cell therapy for graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a curative therapy for many types of cancer. Genetic disparities between donor and host can result in immune-mediated attack of host tissues, known as graft versus host disease (GVHD), a major cause of morbidity and mortality following HSCT. Regulatory CD4+ T cells (Tregs) are a rare cell type crucial for immune system homeostasis, limiting the activation and differentiation of effector T cells (Teff) that are self-reactive or stimulated by foreign antigen exposure. Adoptive cell therapy (ACT) with Treg has demonstrated, first in murine models and now in patients, that prophylactic Treg infusion can also suppress GVHD. While clinical trials have demonstrated Treg reduce severe GVHD occurrence, several impediments remain, including Treg variability and practical need for individualized Treg production for each patient. Additionally, there are challenges in the use of in vitro expansion techniques and in achieving in vivo Treg persistence in context of both immune suppressive drugs and in lymphoreplete patients being treated for GVHD. This review will focus on 3 main translational approaches taken to improve the efficacy of tTreg ACT in GVHD prophylaxis and development of treatment options, following HSCT: genetic modification, manipulating TCR and cytokine signaling, and Treg production protocols. In vitro expansion for Treg ACT presents a multitude of approaches for gene modification to improve efficacy, including: antigen specificity, tissue targeting, deletion of negative regulators/exhaustion markers, resistance to immunosuppressive drugs common in GVHD treatment. Such expansion is particularly important in patients without significant lymphopenia that can drive Treg expansion, enabling a favorable Treg:Teff ratio in vivo. Several potential therapeutics have also been identified that enhance tTreg stability or persistence/expansion following ACT that target specific pathways, including: DNA/histone methylation status, TCR/co-stimulation signaling, and IL-2/STAT5 signaling. Finally, this review will discuss improvements in Treg production related to tissue source, Treg subsets, therapeutic approaches to increase Treg suppression and stability during tTreg expansion, and potential for storing large numbers of Treg from a single production run to be used as an off-the-shelf infusion product capable of treating multiple recipients.

Different subpopulations of regulatory T cells in human autoimmune disease, transplantation, and tumor immunity

CD4⁺CD25⁺ regulatory T cells (Tregs), a subpopulation of naturally CD4⁺ T cells that characteristically express transcription factor Forkhead box P3 (FOXP3), play a pivotal role in the maintenance of immune homeostasis and the prevention of autoimmunity. With the development of biological technology, the understanding of plasticity and stability of Tregs has been further developed. Recent studies have suggested that human Tregs are functionally and phenotypically diverse. The functions and mechanisms of different phenotypes of Tregs in different disease settings, such as tumor microenvironment, autoimmune diseases, and transplantation, have gradually become hot spots of immunology research that arouse extensive attention. Among the complex functions, CD4⁺CD25⁺FOXP3⁺ Tregs possess a potent immunosuppressive capacity and can produce various cytokines, such as IL‐2, IL‐10, and TGF‐β, to regulate immune homeostasis. They can alleviate the progression of diseases by resisting inflammatory immune responses, whereas promoting the poor prognosis of diseases by helping cells evade immune surveillance or suppressing effector T cells activity. Therefore, methods for targeting Tregs to regulate their functions in the immune microenvironment, such as depleting them to strengthen tumor immunity or expanding them to treat immunological diseases, need to be developed. Here, we discuss that different subpopulations of Tregs are essential for the development of immunotherapeutic strategies involving Tregs in human diseases.