Preclinical assessment of antigen-specific chimeric antigen receptor regulatory T cells for use in solid organ transplantation

MOG-specific CAR Tregs: a novel approach to treat multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease affecting the central nervous system (CNS) with the immune system attacking myelin sheaths leading to neuronal death. While several disease-modifying therapies are available to treat MS, these therapies are not universally effective and do not stop disease progression. More personalized long-term treatment options that target specific aspects of the disease, such as reducing relapse frequency, delaying disability accumulation, and addressing symptoms that impact daily functioning, as well as therapies that can promote neuroprotection and repair are needed. Chimeric Antigen Receptor (CAR) Tcell therapies have revolutionized cancer treatment by intravenously (IV) administering a defined dose of T cells with high specificity provided by the CAR. An autologous CAR T cell therapy using suppressive regulatory T cells (Tregs) inducing long-lasting tolerance would be the ideal treatment for patients. Hence, we expanded the application of CAR-T cells by introducing a CAR into Tregs to treat MS patients. We developed a myelin oligodendrocyte glycoprotein (MOG)-specific CAR Treg cell therapy for patients with MS. MOG is expressed on the outer membrane of the myelin sheath, the insulating layer the forms around nerves, making it an ideal target for CAR Treg therapy. Our lead candidate is a 2nd generation CAR, composed of an anti-MOG scFv screened from a large human library. In vitro, we demonstrated CAR-dependent functionality and showed efficacy in vivo using a passive EAE mouse model. Additionally, the MOG-CAR Tregs have very low tonic signaling with a desirable signal-to-noise ratio resulting in a highly potent CAR. In summary our data suggest that MOG-CAR Tregs are a promising MS treatment option with the potential to induce long-lasting tolerance in patients.

Efficacy and limitations of combined A2.CAR Treg and anti-CD154 therapy in a mouse model of haplo-mismatched heart transplantation

The ability to induce allograft specific tolerance would reduce the need for daily pharmacological immunosuppression, improve post-transplant quality of life and transplant outcomes. Adoptive cell therapy with regulatory T cells expressing donor-specific Chimeric Antigen Receptors (CAR-Tregs) is a promising strategy, but monotherapy has not resulted in prolonged survival of grafts with multiple MHC mismatches. We used a clinically-relevant, haplo-mismatched model of heart transplantation in immune-competent C57BL/6 recipients to test the ability of HLA-A2-specific (A2) CAR Tregs to synergize with CD154 blockade to enhance graft survival. We found that in combination with a single low dose of anti-CD154, A2.CAR Tregs significantly prolonged heart allograft survival. Through use of grafts expressing the 2W-OVA transgene, tetramer tracking of 2W- and OVA-specific cells revealed that in mice with accepted grafts, the effects of A2.CAR Tregs included inhibition of endogenous donor-specific CD4 + and CD8 + T cell expansion, and B cell and antibody responses. Moreover, within the 2W-specific CD4 + T cell population, there was a significant increase in the proportion of FoxP3 pos cells, suggestive of infectious tolerance. In mice where CD154 blockade and A2.CAR Tregs failed to prolong graft survival, there was preferential expansion of FoxP3 neg A2.CAR T cells within the rejecting allograft. Thus, this study provides the first evidence for a synergistic effect between CAR Tregs and CD40-pathway blockade and supports the further refinement of this strategy as a promising future direction towards the goal of transplantation tolerance.

IL23R-specific CAR Tregs for the treatment of Crohn's disease

BACKGROUND AND AIMS

Regulatory T cells (Tregs) are key regulators in maintaining tissue homeostasis. Disrupted immune homeostasis is associated with Crohn's disease (CD) pathogenesis. Thus, Treg therapy represents a promising long-acting treatment to restore immune balance in the diseased intestine. CAR (Chimeric Antigen Receptor) T-cell therapy has revolutionized cancer treatment. This innovative approach also provides the opportunity to improve therapy for CD. By targeting a disease-relevant protein, Interleukin-23 receptor (IL23R), we engineered Tregs expressing IL23R-CAR for treating active CD.

METHODS

Intestinal IL23R expression from active CD was verified by immunohistochemical analysis. Phenotypic and functional characteristics of IL23R-CAR Tregs were assessed using in vitro assays and their migration capacity was monitored in a xenograft tumor model. Transcriptomic and proteomic analyses were performed to associate molecular profiles with IL23R-CAR Treg activation against colon biopsy-derived cells from active CD patients.

RESULTS

Our study showed that IL23R-CAR displayed negligible tonic signalling and strong signal-to-noise ratio. IL23R-CAR Tregs maintained regulatory phenotype during in vitro expansion, even when chronically exposed to proinflammatory cytokines and target antigen. IL23R engagement on IL23R-CAR Tregs triggered CAR-specific activation and significantly enhanced their suppressive activity. Also, IL23R-CAR Tregs migrated to IL23R-expressing tissue in humanized mice. Finally, IL23R-CAR Tregs elicited a specific activation against colon biopsy-derived cells from active CD, suggesting an efficient CAR engagement in active CD. Molecular profiling of CD patient biopsies also revealed transcriptomic and proteomic patterns associated with IL23R-CAR activation.

CONCLUSIONS

Overall, our results demonstrate that IL23R-CAR Tregs represent a promising therapy for active CD.

Effector memory-type regulatory T cells display phenotypic and functional instability

Regulatory T cells (Treg cells) hold promise for sustainable therapy of immune disorders. Recent advancements in chimeric antigen receptor development and genome editing aim to enhance the specificity and function of Treg cells. However, impurities and functional instability pose challenges for the development of safe gene-edited Treg cell products. Here, we examined different Treg cell subsets regarding their fate, epigenomic stability, transcriptomes, T cell receptor repertoires, and function ex vivo and after manufacturing. Each Treg cell subset displayed distinct features, including lineage stability, epigenomics, surface markers, T cell receptor diversity, and transcriptomics. Earlier-differentiated memory Treg cell populations, including a hitherto unidentified naïve-like memory Treg cell subset, outperformed late-differentiated effector memory-like Treg cells in regulatory function, proliferative capacity, and epigenomic stability. High yields of stable, functional Treg cell products could be achieved by depleting the small effector memory-like Treg cell subset before manufacturing. Considering Treg cell subset composition appears critical to maintain lineage stability in the final cell product.

The future of liver transplantation

Over the last 50 years, liver transplantation has evolved into a procedure routinely performed in many countries worldwide. Those able to access this therapy frequently experience a miraculous risk-benefit ratio, particularly if they face the imminently life-threatening disease. Over the decades, the success of liver transplantation, with dramatic improvements in early posttransplant survival, has aggressively driven demand. However, despite the emergence of living donors to augment deceased donors as a source of organs, supply has lagged far behind demand. As a result, rationing has been an unfortunate focus in recent decades. Recent shifts in the epidemiology of liver disease combined with transformative innovations in liver preservation suggest that the underlying premise of organ shortage may erode in the foreseeable future. The focus will sharpen on improving equitable access while mitigating constraints related to workforce training, infrastructure for organ recovery and rehabilitation, and their associated costs. Research efforts in liver preservation will undoubtedly blossom with the aim of optimizing both the timing and conditions of transplantation. Coupled with advances in genetic engineering, regenerative biology, and cellular therapies, the portfolio of innovation, both broad and deep, offers the promise that, in the future, liver transplantation will not only be broadly available to those in need but also represent a highly durable life-saving therapy.

Posttransplant complications: molecular mechanisms and therapeutic interventions

Posttransplantation complications pose a major challenge to the long-term survival and quality of life of organ transplant recipients. These complications encompass immune-mediated complications, infectious complications, metabolic complications, and malignancies, with each type influenced by various risk factors and pathological mechanisms. The molecular mechanisms underlying posttransplantation complications involve a complex interplay of immunological, metabolic, and oncogenic processes, including innate and adaptive immune activation, immunosuppressant side effects, and viral reactivation. Here, we provide a comprehensive overview of the clinical features, risk factors, and molecular mechanisms of major posttransplantation complications. We systematically summarize the current understanding of the immunological basis of allograft rejection and graft-versus-host disease, the metabolic dysregulation associated with immunosuppressive agents, and the role of oncogenic viruses in posttransplantation malignancies. Furthermore, we discuss potential prevention and intervention strategies based on these mechanistic insights, highlighting the importance of optimizing immunosuppressive regimens, enhancing infection prophylaxis, and implementing targeted therapies. We also emphasize the need for future research to develop individualized complication control strategies under the guidance of precision medicine, ultimately improving the prognosis and quality of life of transplant recipients.

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

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

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.

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.

Production of therapeutic levels of human FIX-R338L by engineered B cells using GMP-compatible medium

B cells can differentiate into plasmablast and plasma cells, capable of producing antibodies for decades. Gene editing using zinc-finger nucleases (ZFN) enables the engineering of B cells capable of secreting sustained and high levels of therapeutic proteins. In this study, we established an advanced in vitro good manufacturing practice-compatible culturing system characterized by robust and consistent expansion rate, high viability, and efficient B cell differentiation. Using this process, an optimized B cell editing protocol was developed by combining ZFN/adeno-associated virus 6 technology to achieve site-specific insertion of the human factor IX R338L Padua into the silent TRAC locus. In vitro analysis revealed high levels of secreted human immunoglobulins and human factor IX-Padua. Following intravenous infusion in a mouse model, human plasma cells were detected in spleen and bone marrow, indicating successful and potentially long-term engraftment in vivo. Moreover, high levels of human immunoglobin and therapeutic levels of human factor IX-Padua were detected in mouse plasma, correlating with 15% of normal human factor IX activity. These data suggest that the proposed process promotes the production of functional and differentiated engineered B cells. In conclusion, this study represents an important step toward the development of a manufacturing platform for potential B cell-derived therapeutic products.

Comparing the Benefits and Drawbacks of Stem Cell Therapy Based on the Cell Origin or Manipulation Process: Addressing Immunogenicity

Mesenchymal stem cells (MSCs) are effective in treating autoimmune diseases and managing various conditions, such as engraftment of allogeneic islets. Additionally, autologous and HLA-matched allogeneic MSCs can aid in the engraftment of human allogeneic kidneys with or without low doses of tacrolimus, respectively. However, HLA alloantigens are problematic because cell therapy uses more HLA-mismatched allogeneic cells than autologous for convenience and standardization. In particular, HLA-mismatched MSCs showed increased Ag-specific T/B cells and reduced viability faster than HLA-matched MSCs. In CRISPR/Cas9-based cell therapy, Cas9 induce T cell activation in the recipient's immune system. Interestingly, despite their immunogenicity being limited to the cells with foreign Ags, the accumulation of HLA alloantigen-sensitized T/B cells may lead to allograft rejection, suggesting that alloantigens may have a greater scope of adverse effects than foreign Ags. To avoid alloantigen recognition, the β2-microglobulin knockout (B2MKO) system, eliminating class-I MHC, was able to avoid rejection by alloreactive CD8 T cells compared to controls. Moreover, universal donor cells in which both B2M and Class II MHC transactivator (CIITA) were knocked out was more effective in avoiding immune rejection than single KO. However, B2MKO and CIITA KO system remain to be controlled and validated for adverse effects such as the development of tumorigenicity due to deficient Ag recognition by CD8 T and CD4 T cells, respectively. Overall, better HLA-matching or depletion of HLA alloantigens prior to cell therapy can reduce repetitive transplantation through the long-term survival of allogeneic cell therapy, which may be especially important for patients seeking allogeneic transplantation.

CAR T cells for treating autoimmune diseases

Autoimmune disorders occur when immune cells go wrong and attack the body's own tissues. Currently, autoimmune disorders are largely treated by broad immunosuppressive agents and blocking antibodies, which can manage the diseases but often are not curative. Thus, there is an urgent need for advanced therapies for patients suffering from severe and refractory autoimmune diseases, and researchers have considered cell therapy as potentially curative approach for several decades. In the wake of its success in cancer therapy, adoptive transfer of engineered T cells modified with chimeric antigen receptors (CAR) for target recognition could now become a therapeutic option for some autoimmune diseases. Here, we review the ongoing developments with CAR T cells in the field of autoimmune disorders. We will cover first clinical results of applying anti-CD19 and anti-B cell maturation antigen CAR T cells for B cell elimination in systemic lupus erythematosus, refractory antisynthetase syndrome and myasthenia gravis, respectively. Furthermore, in preclinical models, researchers have also developed chimeric autoantibody receptor T cells that can eliminate individual B cell clones producing specific autoantibodies, and regulatory CAR T cells that do not eliminate autoreactive immune cells but dampen their wrong activation. Finally, we will address safety and manufacturing aspects for CAR T cells and discuss mRNA technologies and automation concepts for ensuring the future availability of safe and efficient CAR T cell products.

Immune Privileges as a Result of Mutual Regulation of Immune and Stem Systems

Immune privileges of cancer stem cells is a well-known and widely studied problem, as presence of such cells in tumors is associated with refractoriness, recurrence, and metastasis. Accumulating evidence also suggests presence of immune privileges in non-pathological stem cells in addition to their other defense mechanisms against damaging factors. This similarity between pathological and normal stem cells raises the question of why stem cells have such a potentially dangerous property. Regulation of vital processes of autoimmunity control and regeneration realized through interactions between immune cells, stem cells, and their microenvironment are reviewed in this work as causes of formation of the stem cell immune privilege. Deep mutual integration between regulations of stem and immune cells is noted. Considering diversity and complexity of mutual regulation of stem cells, their microenvironment, and immune system, I suggest the term "stem system".

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.

CAR-T cells and CAR-Tregs targeting conventional type-1 dendritic cell suppress experimental autoimmune encephalomyelitis

Conventional type 1 dendritic cells (DC1) contribute to the development of pathogenic T helper type 1 (Th1) cells in part via the production of the proinflammatory cytokine interleukin-12. Thus, depletion of DC1 has the potential to dampen autoimmune responses. Here, we developed X-C motif chemokine receptor 1 (XCR1)-specific chimeric antigen receptor (CAR)-T cells and CAR-Tregs that specifically targeted DC1. XCR1 CAR-T cells were successfully generated as CD4+ and CD8+ T cells, expressed XCR1 CAR efficiently, and induced XCR1-dependent activation, cytokine production and proliferation. XCR1 CAR-T cells selectively depleted DC1 when transferred into RAG2-/- mice with a compensatory increase in conventional type 2 DC (DC2) and plasmacytoid DC (pDC). XCR1 CAR-T cell-mediated depletion of DC1 modestly suppressed the onset of Th1-driven experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. Diphtheria toxin-mediated DC1 depletion in XCR1-diphtheria toxin receptor mice also suppressed EAE, suggesting that DC1 depletion was responsible for EAE suppression. XCR1 CAR-Tregs were successfully generated and suppressed effector T cells in the presence of XCR1+ cells. Therapeutic treatment with XCR1 CAR-Tregs suppressed Th1-driven EAE. Therefore, we conclude that depletion of DC1 with XCR1 CAR-T cells or immune suppression with XCR1 CAR-Tregs can modestly suppress Th1-driven EAE.

T cells in health and disease

T cells are crucial for immune functions to maintain health and prevent disease. T cell development occurs in a stepwise process in the thymus and mainly generates CD4+ and CD8+ T cell subsets. Upon antigen stimulation, naïve T cells differentiate into CD4+ helper and CD8+ cytotoxic effector and memory cells, mediating direct killing, diverse immune regulatory function, and long-term protection. In response to acute and chronic infections and tumors, T cells adopt distinct differentiation trajectories and develop into a range of heterogeneous populations with various phenotype, differentiation potential, and functionality under precise and elaborate regulations of transcriptional and epigenetic programs. Abnormal T-cell immunity can initiate and promote the pathogenesis of autoimmune diseases. In this review, we summarize the current understanding of T cell development, CD4+ and CD8+ T cell classification, and differentiation in physiological settings. We further elaborate the heterogeneity, differentiation, functionality, and regulation network of CD4+ and CD8+ T cells in infectious disease, chronic infection and tumor, and autoimmune disease, highlighting the exhausted CD8+ T cell differentiation trajectory, CD4+ T cell helper function, T cell contributions to immunotherapy and autoimmune pathogenesis. We also discuss the development and function of γδ T cells in tissue surveillance, infection, and tumor immunity. Finally, we summarized current T-cell-based immunotherapies in both cancer and autoimmune diseases, with an emphasis on their clinical applications. A better understanding of T cell immunity provides insight into developing novel prophylactic and therapeutic strategies in human diseases.

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.

Manufacturing next-generation regulatory T-cell therapies

Regulatory T-cell (Treg) therapy has shown promise in treating autoimmune diseases, transplant rejection, or graft-versus-host disease in early clinical trials. These trials have demonstrated that cell therapy using polyclonal Tregs is feasible and safe, however, the field has been limited by the lack of polyclonal cell specificity and consequent large cell numbers required, and the difficulty in generating autologous products for some patients. Thus, the field is moving toward 'next generation' Treg cell therapies that include genetic modification strategies to engineer specificity and/or modify function, as well as methods to generate Tregs in vitro. In this review, we describe how genetic modification of Tregs using viral transduction or gene editing may be incorporated into Treg manufacturing protocols. We also describe how Tregs may be generated via FOXP3 gene editing or overexpression, or by differentiation from pluripotent stem cells. The application of these various types of engineered Tregs is discussed.