Type 1 regulatory T cell-mediated tolerance in health and disease

Antigen-specific immunotherapies for autoimmune disease

Antigen-specific therapies have a long history in the treatment of allergy but have not been successful in autoimmunity. However, in the past 20 years, advances in the definition of the self-antigens that promote autoimmunity and the growing understanding of the mechanisms that maintain tolerance in health but fail in autoimmunity have led to antigen-specific approaches being considered for the treatment of autoimmune diseases. The core goal of each antigen-specific treatment approach is to remove the immune response that promotes autoimmunity whilst sparing protective responses. Approaches to antigen-specific therapy range from targeted deletion of autoreactive lymphocytes to tolerization of autoreactive T cells and active inhibition of autoimmune responses. Technologies such as vaccines, nanoparticles, cell-based therapies and gene editing are being harnessed to achieve these goals. Remaining challenges include the selection of the best antigen to target, modality and timing of administration of these therapies and the disease in which the therapies are used; overcoming these challenges will be vital to move antigen-specific therapies forward. Once established, antigen-specific therapy has the potential to be applied broadly in the area of autoimmunity.

Harnessing the biology of regulatory T cells to treat disease

Regulatory T (Treg) cells are a suppressive subset of CD4+ T cells that maintain immune homeostasis and restrain inflammation. Three decades after their discovery, the promise of strategies to harness Treg cells for therapy has never been stronger. Multiple clinical trials seeking to enhance endogenous Treg cells or deliver them as a cell-based therapy have been performed and hint at signs of success, as well as to important limitations and unanswered questions. Strategies to deplete Treg cells in cancer are also in active clinical testing. Furthermore, multi-dimensional methods to interrogate the biology of Treg cells are leading to a refined understanding of Treg cell biology and new approaches to harness tissue-specific functions for therapy. A new generation of Treg cell clinical trials is now being fuelled by advances in nanomedicine and synthetic biology, seeking more precise ways to tailor Treg cell function. This Review will discuss recent advances in our understanding of human Treg cell biology, with a focus on mechanisms of action and strategies to assess outcomes of Treg cell-targeted therapies. It highlights results from recent clinical trials aiming to enhance or inhibit Treg cell activity in a variety of diseases, including allergy, transplantation, autoimmunity and cancer, and discusses ongoing strategies to refine these approaches.

From promise to practice: CAR T and Treg cell therapies in autoimmunity and other immune-mediated diseases

Autoimmune diseases, characterized by the immune system's attack on the body's own tissues, affect millions of people worldwide. Current treatments, which primarily rely on broad immunosuppression and symptom management, are often associated with significant adverse effects and necessitate lifelong therapy. This review explores the next generation of therapies for immune-mediated diseases, including chimeric antigen receptor (CAR) T cell and regulatory T cell (Treg)-based approaches, which offer the prospect of targeted, durable disease remission. Notably, we highlight the emergence of CD19-targeted CAR T cell therapies, and their ability to drive sustained remission in B cell-mediated autoimmune diseases, suggesting a possible paradigm shift. Further, we discuss the therapeutic potential of Type 1 and FOXP3+ Treg and CAR-Treg cells, which aim to achieve localized immune modulation by targeting their activity to specific tissues or cell types, thereby minimizing the risk of generalized immunosuppression. By examining the latest advances in this rapidly evolving field, we underscore the potential of these innovative cell therapies to address the unmet need for long-term remission and potential tolerance induction in individuals with autoimmune and immune-mediated diseases.

Regulation of inflammation by Interleukin-10 in the intestinal and respiratory mucosa

Intricate immune regulation is required at mucosal surfaces to allow tolerance to microbiota and harmless allergens and to prevent overexuberant inflammatory responses to pathogens. The cytokine Interleukin-10 (IL-10) is a key mediator of mucosal immune regulation. While IL-10 can be produced by virtually all cells of the immune system, many of its in vivo functions depend upon its production by regulatory or effector T cell populations and its signalling to macrophages, dendritic cells and specific T cell subsets. In this review, we discuss our current understanding of the role of IL-10 in regulation of immune responses, with a focus on its context-specific roles in intestinal homeostasis, respiratory infection and asthma. We highlight the importance of appropriate production and function of IL-10 for balancing pathogen clearance, control of microbiota and host tissue damage, and that precise modulation of IL-10 functions in vivo could present therapeutic opportunities.

Chimeric antigen receptor T cell therapy for autoimmune disease

Infusion of T cells engineered to express chimeric antigen receptors (CARs) that target B cells has proven to be a successful treatment for B cell malignancies. This success inspired the development of CAR T cells to selectively deplete or modulate the aberrant immune responses that underlie autoimmune disease. Promising results are emerging from clinical trials of CAR T cells targeting the B cell protein CD19 in patients with B cell-driven autoimmune diseases. Further approaches are being designed to extend the application and improve safety of CAR T cell therapy in the setting of autoimmunity, including the use of chimeric autoantibody receptors to selectively deplete autoantigen-specific B cells and the use of regulatory T cells engineered to express antigen-specific CARs for targeted immune modulation. Here, we highlight important considerations, such as optimal target cell populations, CAR construct design, acceptable toxicities and potential for lasting immune reset, that will inform the eventual safe adoption of CAR T cell therapy for the treatment of autoimmune diseases.

The expanding universe of type I regulatory T cell biology: a new role in cancer immunotherapy

In this article, we discuss new findings which suggest that type I regulatory T (Tr1) cells can interfere with cancer vaccine efficacy in mice by exerting strong regulatory control over antitumor immune responses.

Molecular Hydrogen Therapy in Aneurysmal SAH With RA and Newly-diagnosed SLE, Complicated With Acute Ischemic Infarction: A Case Report of Improved Immune Markers Including Tr1 Cells, Breg Cells and TIM3 Expression on Tc Cells

BACKGROUND/AIM

Most nontraumatic subarachnoid hemorrhages (SAHs) are caused by ruptured saccular aneurysms, often resulting in a devastating clinical event characterized by high mortality and significant morbidity among survivors. Numerous studies have confirmed the neuroprotective effects of the molecular hydrogen due to its unique biological properties.

CASE REPORT

We present the case of a 44-year-old female with aneurysmal SAH with rheumatoid arthritis (RA) and newly diagnosed systemic lupus erythematosus (SLE), complicated by acute ischemic infarction. Despite surgical, pharmacological and non-pharmacological interventions, including embolization of the aneurysm, immunosuppressant, non-vitamin K antagonist oral anticoagulant (NOAC), and plasmapheresis, loss of consciousness continued. The patient began daily treatment with hydrogen capsules, resulting in increased in Treg cells, Breg cells, increased TIM3+ expression on Tc cells, and the conversion of anti-dsDNA from positive to negative. Her clinical symptoms stabilized without adverse effects.

CONCLUSION

This case highlights the potential benefits of molecular hydrogen therapy in managing aneurysmal SAH with underlying autoimmune disease, warranting further research.

CAR Treg synergy with anti-CD154 mediates infectious tolerance to dictate heart transplant outcomes

Successful allograft specific tolerance induction would eliminate the need for daily immunosuppression and improve post-transplant quality of life. Adoptive cell therapy with regulatory T cells expressing donor-specific Chimeric Antigen Receptors (CAR-Tregs) is a promising strategy, but as monotherapy, cannot prolong the survival with allografts with multiple MHC mismatches. Using an HLA-A2-transgenic haplo-mismatched heart transplantation model in immunocompetent C57Bl/6 recipients, we show that HLA-A2-specific (A2) CAR Tregs was able to synergize with low dose of anti-CD154 to enhance graft survival. Using haplo-mismatched grafts expressing the 2W-OVA transgene and tetramer-based tracking of 2W- and OVA-specific T cells, we showed that in mice with accepted grafts, A2.CAR Tregs inhibited endogenous non-A2 donor- specific T cell, B cell and antibody responses, and promoted a significant increase in endogenous FoxP3 + Tregs with indirect donor-specificity. By contrast, in mice where A2.CAR Tregs failed to prolong graft survival, FoxP3 neg A2.CAR T cells preferentially accumulated in rejecting allografts and endogenous donor-specific responses were not controlled. This study therefore provides the first evidence for synergy between A2.CAR Tregs and CD154 blockade to promote infectious tolerance in immunocompetent recipients of haplo-mismatched heart grafts and defines features of A2.CAR Tregs when they fail to reshape host immunity towards allograft tolerance.

Mitigation of checkpoint inhibitor-induced autoimmune hemolytic anemia through modulation of purinergic signaling

ABSTRACT

Immune checkpoint inhibitors (ICPis) have revolutionized cancer immunotherapy but also can induce autoimmune hemolytic anemia (AIHA), a severe disease with high mortality. However, the cellular and molecular mechanism(s) of AIHA secondary to ICPi therapy (ICPi-AIHA) are unclear, other than being initiated through decreased checkpoint inhibition. Herein, we report ICPi-AIHA in a novel mouse model that shows similar characteristics of known human ICPi-AIHA (eg, autoantibodies, hemolysis, and increased mortality). During ICPi-AIHA, there is the simultaneous reduction of 2 regulatory T-cell populations (FoxP3+ and Tr1 [type 1 regulatory cells]) and an increase in inflammatory T helper cell 17 (TH17). Moreover, a novel CD39+CD73-FoxP3-CD25- CD4+ T-cell subset (ie, CD39 single positive [CD39SP]) emerges, and early increases in CD39SP predict AIHA development; CD39 is an ectonuclease that breaks down adenosine triphosphate (ATP). Additionally, we found that boosting ATPase activity by injecting recombinant apyrase mitigates AIHA development and significant CD39SP reductions, both suggesting a functional role for CD39 and demonstrating a novel therapeutic approach. Importantly, CD39SP are detectable in multiple mouse models developing AIHA and in patients with AIHA, demonstrating applicability to idiopathic and secondary AIHA. Highlighting broader autoimmunity relevance, ICPi-treated NZB mice experienced accelerated onset and severity of lupus, including AIHA. Moreover, ICPi treatment of healthy B6 animals led to detectable CD39SP and development of autoantibodies against multiple autoantigens including those on red blood cells and platelets. Together, our findings provide further insight into the cellular and molecular mechanisms of ICPi-AIHA, leading to novel diagnostic and therapeutic approaches with translational potential for use in humans being treated with ICPi.

Regulatory T cells as a therapeutic target in acute myocardial infarction

Acute myocardial infarction (AMI), mainly triggered by vascular occlusion or thrombosis, is the most prevalent cause of morbidity and mortality among all cardiovascular diseases. The devastating consequences of AMI are further aggravated by the intricate cellular processes involved in inflammation. In the past two decades, many studies have reported that regulatory T cells (Tregs), as the main immunoregulatory cells, play a crucial role in AMI progression. This review offers a comprehensive insight into the intricate relationship between Tregs and AMI development. Moreover, it explores emerging therapeutic strategies that focus on Tregs and their exosomes. Furthermore, we underscore the importance of employing noninvasive in vivo imaging techniques to advance the clinical applications of Tregs-based treatments in AMI. Although further research is essential to fully elucidate the molecular mechanisms underlying the effects of Tregs, therapies tailored to these cells hold immense potential for the treatment of patients with AMI.

Re-establishing immune tolerance in multiple sclerosis: focusing on novel mechanisms of mesenchymal stem cell regulation of Th17/Treg balance

The T-helper 17 (Th17) cell and regulatory T cell (Treg) axis plays a crucial role in the development of multiple sclerosis (MS), which is regarded as an immune imbalance between pro-inflammatory cytokines and the maintenance of immune tolerance. Mesenchymal stem cell (MSC)-mediated therapies have received increasing attention in MS research. In MS and its animal model experimental autoimmune encephalomyelitis, MSC injection was shown to alter the differentiation of CD4+T cells. This alteration occurred by inducing anergy and reduction in the number of Th17 cells, stimulating the polarization of antigen-specific Treg to reverse the imbalance of the Th17/Treg axis, reducing the inflammatory cascade response and demyelination, and restoring an overall state of immune tolerance. In this review, we summarize the mechanisms by which MSCs regulate the balance between Th17 cells and Tregs, including extracellular vesicles, mitochondrial transfer, metabolic reprogramming, and autophagy. We aimed to identify new targets for MS treatment using cellular therapy by analyzing MSC-mediated Th17-to-Treg polarization.

The Increased Frequency of Type 1 Regulatory T (Tr1) Cells and the Altered Expression of Aryl Hydrocarbon Receptor (AHR) and Interferon Regulatory Factor-4 (IRF4) Genes in Type 1 Diabetes: A Case-Control Study

Background and aim Type 1 diabetes is an autoimmune disorder characterized by the destruction of pancreatic beta cells, leading to insulin deficiency and hyperglycemia. Regulatory T cells (Tregs), particularly type 1 regulatory T (Tr1) cells, play a crucial role in modulating autoimmune responses. Therefore, this study aimed to evaluate the frequency of Tr1 cells and their association with aryl hydrocarbon receptor (AHR) and interferon regulatory factor-4 (IRF4) gene expression levels in type 1 diabetes mellitus (T1DM) compared to the healthy controls. Method A case-control study design was used. The case group included patients diagnosed with T1DM, while the control group consisted of healthy individuals, matched for age and sex. Blood samples were collected, and peripheral blood mononuclear cells (PBMCs) were isolated. Serum interleukin 10 (IL-10) and interleukin 21 (IL-21) levels were measured using enzyme-linked immunosorbent assay (ELISA). The gene expression of AHR and IRF4 was analyzed using quantitative real-time polymerase chain reaction (qPCR), and Tr1 cell populations were determined using flow cytometry. Data were summarized with mean and standard error of the mean (SEM) for quantitative variables. Independent sample t-test, chi-square test, and the Mann-Whitney U test were used to compare groups. Statistical analyses were performed using SPSS version 25 (IBM SPSS Statistics, Armonk, NY), with significance levels set at p < 0.05. Figures were created using GraphPad Prism (GraphPad Software, San Diego, CA). Results A total of 45 cases were enrolled in the study, with 30 T1DM patients and 15 healthy controls. The mean IL-10 concentration was significantly higher in the patients (10.4 ± 1.1 pg/mL) compared to the healthy controls (5.1 ± 0.7 pg/mL), with a p-value of 0.001. There was no significant difference in IL-21 levels between the patients (76.1 ± 9.0 pg/mL) and healthy controls (88.2 ± 17.5 pg/mL), indicated by a p-value of 0.480. AHR gene expression was significantly lower in patients, with a p-value of 0.037. Although IRF4 gene expression was higher in patients, the difference was not statistically significant (p = 0.449). Tr1 cell frequency was significantly higher in T1DM patients (1.45% of cluster of differentiation 4+ {CD4+} T cells) compared to the healthy controls (0.40% of CD4+ T cells), with a p-value of 0.045. Conclusions The study demonstrated that T1DM is associated with higher IL-10 levels, decreased AHR gene expression, and a higher frequency of Tr1 cells. Policymakers should focus on developing targeted immunomodulatory therapies to address these immunological abnormalities. Healthcare providers should prioritize monitoring cytokine levels and gene expression in T1DM patients to tailor treatment plans effectively. Further research is needed to explore the therapeutic potential of modulating Tr1 cells and their related pathways in T1DM management.

Biomaterial-enhanced treg cell immunotherapy: A promising approach for transplant medicine and autoimmune disease treatment

Regulatory T cells (Tregs) are crucial for preserving tolerance in the body, rendering Treg immunotherapy a promising treatment option for both organ transplants and autoimmune diseases. Presently, organ transplant recipients must undergo lifelong immunosuppression to prevent allograft rejection, while autoimmune disorders lack definitive cures. In the last years, there has been notable advancement in comprehending the biology of both antigen-specific and polyclonal Tregs. Clinical trials involving Tregs have demonstrated their safety and effectiveness. To maximize the efficacy of Treg immunotherapy, it is essential for these cells to migrate to specific target tissues, maintain stability within local organs, bolster their suppressive capabilities, and ensure their intended function's longevity. In pursuit of these goals, the utilization of biomaterials emerges as an attractive supportive strategy for Treg immunotherapy in addressing these challenges. As a result, the prospect of employing biomaterial-enhanced Treg immunotherapy holds tremendous promise as a treatment option for organ transplant recipients and individuals grappling with autoimmune diseases in the near future. This paper introduces strategies based on biomaterial-assisted Treg immunotherapy to enhance transplant medicine and autoimmune treatments.

Direct exposure to CpG and specific antigens mitigate airway allergy through modulating dendritic cell properties

BACKGROUND

CpG oligodeoxynucleotide (CpG-ODN; CpG, in short) has been employed as an adjuvant in allergen specific immunotherapy (AIT) to treat allergic diseases. The underlying mechanism needs to be further explained. The aim of this study is to examine the mechanism by which CpG and dust mite extracts (DME, a specific antigen) alleviate experimental airway allergy.

METHODS

DME was used as the specific allergen to establish an airway allergy mouse model. The mice were directly exposed to DME and CpG through nasal instillations (the CpG.DME therapy). The response of DCs and allergic responses in the airways were assessed using immunological approaches.

RESULTS

The airway allergy reaction was effectively suppressed by CpG.DME therapy. The administration of CpG or DME alone did not have any significant suppressive effects on the airway allergic response. Direct exposure to CpG.DME induced type 1 DCs (DC1s) and plasmacytoid DCs (pDCs), while CpG alone induced DC1s and DME alone induced DC2s in the airway tissues. Both DC1s and pDCs were required for the induction of type 1 regulatory T cells in the airway tissues by CpG.DME therapy. Depletion of either pDCs or DC1s abolished the induction of Tr1 cells, and abolished the suppressive effects on airway allergic response by the CpG.DME therapy.

CONCLUSIONS

Direct exposure to CpG.DME induces DC1s and pDCs in the airway tissues. DC1s in synergy with pDCs induce type 1 regulatory T cells. The CpG.DME therapy is effective in suppressing allergic responses in mice with airway allergy.

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.

Lineage origin and transcriptional control of autoantigen-specific T-regulatory type 1 cells

T Regulatory type-1 (TR1) cells represent an immunosuppressive T cell subset, discovered over 25 years ago, that produces high levels of interleukin-10 (IL-10) but, unlike its FoxP3+ T regulatory (Treg) cell counterpart, does not express FoxP3 or CD25. Experimental evidence generated over the last few years has exposed a promising role for TR1 cells as targets of therapeutic intervention in immune-mediated diseases. The discovery of cell surface markers capable of distinguishing these cells from related T cell types and the application of next generation sequencing techniques to defining their transcriptional make-up have enabled a more accurate description of this T cell population. However, the developmental biology of TR1 cells has long remained elusive, in particular the identity of the cell type(s) giving rise to bona fide TR1 cells in vivo. Here, we review the fundamental phenotypic, transcriptional and functional properties of this T cell subset, and summarize recent lines of evidence shedding light into its ontogeny.

Role of Regulatory T Cells and Their Potential Therapeutic Applications in Celiac Disease

Celiac disease (CeD) is a T-cell-mediated immune disease, in which gluten-derived peptides activate lamina propria effector CD4+ T cells. While this effector T cell subset produces proinflammatory cytokines, which cause substantial tissue injury in vivo, additional subsets of T cells exist with regulatory functions (Treg). These subsets include CD4+ type 1 regulatory T cells (Tr1) and CD4+ CD25+ T cells expressing the master transcription factor forkhead box P3 (Foxp3) that may have important implications in disease pathogenesis. In this review, we provide an overview of the current knowledge about the effects of immunomodulating cytokines on CeD inflammatory status. Moreover, we outline the main Treg cell populations found in CeD and how their regulatory activity could be influenced by the intestinal microenvironment. Finally, we discuss the Treg therapeutic potential for the development of alternative strategies to the gluten-free diet (GFD).

Pathogenesis and novel therapeutics of regulatory T cell subsets and interleukin-2 therapy in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a heterogeneous multisystem inflammatory disease with wide variability in clinical manifestations. Natural arising CD4+ regulatory T cells (Tregs) play a critical role in maintaining peripheral tolerance by suppressing inflammation and preventing autoimmune responses in SLE. Additionally, CD8+ regulatory T cells, type 1 regulatory T cells (Tr1), and B regulatory cells also have a less well-defined role in the pathogenesis of SLE. Elucidation of the roles of various Treg subsets dedicated to immune homeostasis will provide a novel therapeutic approach that governs immune tolerance for the remission of active lupus. Diminished interleukin (IL)-2 production is associated with a depleted Treg cell population, and its reversibility by IL-2 therapy provides important reasons for the treatment of lupus. This review focuses on the pathogenesis and new therapeutics of human Treg subsets and low-dose IL-2 therapy in clinical benefits with SLE.

Using Treg, Tr1, and Breg Expression Levels to Predict Clinical Responses to csDMARD Treatment in Drug-naive Patients With Rheumatoid Arthritis

BACKGROUND/AIM

Regulatory T cells (Treg) play a crucial role in maintaining immune tolerance and preventing autoimmune diseases. Recent data also indicate that type 1 regulatory T (Tr1) and regulatory B (Breg) cells play an inhibitory (i.e., protective) role in autoimmune diseases. Conventional synthetic disease-modifying antirheumatic drugs (csDMARD) are a first-line therapy for rheumatoid arthritis (RA), and our aim was to predict clinical responses of this treatment using immunophenotyping.

MATERIALS AND METHODS

We first detected the presence of immune cells in fresh blood from 16 healthy controls (HC) and 26 patients with RA (14 drug-naive and 12 csDMARD-experienced). Then, we recorded immunophenotypic changes in 14 drug-naive RA (naive RA) patients prior to csDMARD treatment (i.e., day 0) and after receiving treatment for 6 months. The observed changes were also compared with other clinical indicators, including the presence of anti-citrullinated peptide antibodies (anti-CCP), rheumatoid factor (RF) levels, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) levels.

RESULTS

Naive RA patients had significantly lower Tregs than HC and csDMARD-experienced patients (both p<0.0001) and the number of Tregs correlated with the diagnosis of RA and therapeutic efficacy of csDMARD treatment. Furthermore, lower baseline levels of Treg, memory Treg, Tr1, and higher PD-1+ Marginal B, Breg cells were significantly associated with decreased development of the 28-joint Disease Activity Score (DAS28) (all p<0.05), revealing better medical response. Multiple regression and principal component analysis identified Treg, Tr1, and Breg as potential predictors of csDMARD responses (Area under curve: 0.9; Accuracy: 92.86%). Furthermore, elevated Treg, Tr1, and Breg cells were associated with decreased DAS28, ESR, and CRP (all p<0.05); changes in Treg and Breg cell expression were also more pronounced among double negative anti-CCP and RF in RA patients with better outcomes (p<0.05).

CONCLUSION

Immunophenotyping can be an adjunct clinical tool to identify patients who are poor candidates for csDMARD therapy. Alternative therapeutic interventions in the early stages of disease should be formulated for these patients.

Cytotoxic CD4 T cells in the mucosa and in cancer

CD4 T cells were initially described as helper cells that promote either the cellular immune response (Th1 cells) or the humoral immune response (Th2 cells). Since then, a plethora of functionally distinct helper and regulatory CD4 T cell subsets have been described. CD4 T cells with cytotoxic function were first described in the setting of viral infections and autoimmunity, and more recently in cancer and gut dysbiosis. Regulatory CD4 T cell subsets such as Tregs and T-regulatory type 1 (Tr1) cells have also been shown to have cytotoxic potential. Indeed, Tr1 cells have been shown to be important for maintenance of stem cell niches in the bone marrow and the gut. This review will provide an overview of cytotoxic CD4 T cell development, and discuss the role of inflammatory and Tr1-like cytotoxic CD4 T cells in maintenance of intestinal stem cells and in anti-cancer immune responses.

Toward a general model of CD4+ T cell subset specification and memory cell formation

In the past few decades, a number of transformative discoveries have been made regarding memory CD8+ T cell biology; meanwhile, the CD4+ T cell field has lagged behind this progress. This perspective focuses on CD4+ helper T (Th) cell subset specification and memory cell formation. Here, we argue that the sheer number of Th effector and memory cell subsets and a focus on their differences have been a barrier to a general model of CD4+ memory T cell formation that applies to all immune responses. We highlight a bifurcation model that relies on an IL-2 signal-dependent switch as an explanation for the balanced production of diverse Th memory cells that participate in cell-mediated or humoral immunity in most contexts.