A peripheral circulating compartment of natural naive CD4 Tregs

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.

Accumulation of immune-suppressive CD4 + T cells in aging - tempering inflammaging at the expense of immunity

The 'immune risk profile' has been shown to predict mortality in the elderly, highlighting the need to better understand age-related immune dysfunction. While aging leads to many defects affecting all arms of the immune system, this review is focused on the accrual of immuno-suppressive CD4 + T cell populations, including FoxP3 + regulatory T cells, and subsets of IL-10-producing T follicular helper cells. New data suggest that such accumulations constitute feedback mechanisms to temper the ongoing progressive low-grade inflammation that develops with age, the so-called "inflammaging", and by doing so, how they have the potential to promote healthier aging. However, they also impair effector immune responses, notably to infections, or vaccines. These studies also reinforce the idea that the aged immune system should not be considered as a poorly functional version of the young one, but more as a dynamic system in which CD4 + T cells, and other immune/non-immune subsets, differentiate, interact with their milieu and function differently than in young hosts. A better understanding of these unique interactions is thus needed to improve effector immune responses in the elderly, while keeping inflammaging under control.

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.

Molecular Markers of Blood Cell Populations Can Help Estimate Aging of the Immune System

Aging of the immune system involves functional changes in individual cell populations, in hematopoietic tissues and at the systemic level. They are mediated by factors produced by circulating cells, niche cells, and at the systemic level. Age-related alterations in the microenvironment of the bone marrow and thymus cause a decrease in the production of naive immune cells and functional immunodeficiencies. Another result of aging and reduced tissue immune surveillance is the accumulation of senescent cells. Some viral infections deplete adaptive immune cells, increasing the risk of autoimmune and immunodeficiency conditions, leading to a general degradation in the specificity and effectiveness of the immune system in old age. During the COVID-19 pandemic, the state-of-the-art application of mass spectrometry, multichannel flow cytometry, and single-cell genetic analysis have provided vast data on the mechanisms of aging of the immune system. These data require systematic analysis and functional verification. In addition, the prediction of age-related complications is a priority task of modern medicine in the context of the increase in the aged population and the risk of premature death during epidemics. In this review, based on the latest data, we discuss the mechanisms of immune aging and highlight some cellular markers as indicators of age-related immune disbalance that increase the risk of senile diseases and infectious complications.

Human Regulatory T Cells: Understanding the Role of Tregs in Select Autoimmune Skin Diseases and Post-Transplant Nonmelanoma Skin Cancers

Regulatory T cells (Tregs) play an important role in maintaining immune tolerance and homeostasis by modulating how the immune system is activated. Several studies have documented the critical role of Tregs in suppressing the functions of effector T cells and antigen-presenting cells. Under certain conditions, Tregs can lose their suppressive capability, leading to a compromised immune system. For example, mutations in the Treg transcription factor, Forkhead box P3 (FOXP3), can drive the development of autoimmune diseases in multiple organs within the body. Furthermore, mutations leading to a reduction in the numbers of Tregs or a change in their function facilitate autoimmunity, whereas an overabundance can inhibit anti-tumor and anti-pathogen immunity. This review discusses the characteristics of Tregs and their mechanism of action in select autoimmune skin diseases, transplantation, and skin cancer. We also examine the potential of Tregs-based cellular therapies in autoimmunity.

The impact of HIV infection on the frequencies, function, spatial localization and heterogeneity of T follicular regulatory cells (TFRs) within human lymph nodes

BACKGROUND

HIV eradication efforts have been unsuccessful partly due to virus persistence in immune sanctuary sites such as germinal centres within lymph node (LN) tissues. Recent evidence suggests that LNs harbour a novel subset of regulatory T cells, termed follicular regulatory T cells (TFRs), but their role in HIV pathogenesis is not fully elucidated.

RESULTS

Paired excisional LN and peripheral blood samples obtained from 20 HIV-uninfected and 31 HIV-infected treated and 7 chronic untreated, were used to determine if and how HIV infection modulate frequencies, function and spatial localization of TFRs within LN tissues. Imaging studies showed that most TFRs are localized in extra-follicular regions. Co-culture assays showed TFRs suppression of TFH help to B cells. Importantly, epigenetic and transcriptional studies identified DPP4 and FCRL3 as novel phenotypic markers that define four functionally distinct TFR subpopulations in human LNs regardless of HIV status. Imaging studies confirmed the regulatory phenotype of DPP4+TFRs.

CONCLUSION

Together these studies describe TFRs dynamic changes during HIV infection and reveal previously underappreciated TFR heterogeneity within human LNs.

Reduced Bordetella pertussis-specific CD4+ T-Cell Responses at Older Age

Pertussis, a human-specific respiratory infectious disease caused by the Gram-negative bacterium Bordetella pertussis (Bp), remains endemic with epidemic years despite high vaccination coverage. Whereas pertussis vaccines and natural infection with Bp confer immune protection, the duration of protection varies and is not lifelong. Recent evidence indicates a considerable underestimation of the pertussis burden among older adults. Whereas the impact of increasing age on Bp-specific humoral immunity has been demonstrated, little is known on immunosenescence of CD4⁺ T-cell responses in the context of Bp. Here, we aimed to address whether increasing age impacts responsiveness of the Bp-specific CD4⁺ T-cells in the memory pool following a clinically symptomatic pertussis infection in whole cell vaccine-primed pediatric and adult cases. Cytokine and proliferative responses and phenotypical profiles of CD4⁺ T cells specific for Bp antigens at an early and late convalescent timepoint were compared. Responses of various Th cytokines, including IFNγ, were significantly lower in older adults at early and late timepoints post diagnosis. In addition, we found lower frequencies of Bp-specific proliferated CD4⁺ T cells in older adults, in the absence of differences in replication profile. Phenotyping of Bp-specific CD4⁺ T cells suggested reduced expression of activation markers rather than increased expression of co-inhibitory markers. Altogether, our findings show that the magnitude and functionality of the Bp-specific memory CD4⁺ T-cell pool decrease at older age. Declined CD4⁺ T-cell responsiveness to Bp is suggested to contribute to the burden of pertussis in older adults.

Effect of switching glatiramer acetate formulation from 20 mg daily to 40 mg three times weekly on immune function in multiple sclerosis

Background

Many RRMS patients who had been treated for over 20 years with GA 20 mg/ml daily (GA20) switched to 40 mg/ml three times-a-week (GA40) to reduce injection-related adverse events. Although GA40 is as effective as GA20 in reducing annualized relapse rate and MRI activity, it remains unknown how switching to GA40 from GA20 affects the development of pathogenic and regulatory immune cells.

Objective

To investigate the difference in immunological parameters in response to GA20 and GA40 treatments.

Methods

We analyzed five pro-inflammatory cytokines (IL-1β, IL-23, IL-12, IL-18, TNF-α), and three anti-inflammatory/regulatory cytokines (IL-10, IL-13, and IL-27) in serum. In addition, we analyzed six cytokines (IFN-γ, IL-17A, GM-CSF, IL-10, IL-6, and IL-27) in cultured PBMC supernatants. The development of Th1, Th17, Foxp3 Tregs, M1-like, and M2-like macrophages were examined by flow cytometry. Samples were analyzed before and 12 months post switching to GA40 or GA20.

Results

Pro- and anti-inflammatory cytokines were comparable between the GA40 and GA20 groups. Development of Th1, Th17, M1-like macrophages, M2-like macrophages, and Foxp3 Tregs was also comparable between the two groups.

Conclusions

The immunological parameters measured in RRMS patients treated with GA40 three times weekly are largely comparable to those given daily GA20 treatment.

Surface Phenotype Changes and Increased Response to Oxidative Stress in CD4+CD25high T Cells

Conversion of CD4⁺CD25⁺FOXP3⁺ T regulatory cells (T_regs) from the immature (CD45RA⁺) to mature (CD45RO⁺) phenotype has been shown during development and allergic reactions. The relative frequencies of these T_reg phenotypes and their responses to oxidative stress during development and allergic inflammation were analysed in samples from paediatric and adult subjects. The FOXP3^lowCD45RA⁺ population was dominant in early childhood, while the percentage of FOXP3^highCD45RO⁺ cells began increasing in the first year of life. These phenotypic changes were observed in subjects with and without asthma. Further, there was a significant increase in phosphorylated ERK1/2 (pERK1/2) protein in hydrogen peroxide (H₂O₂)-treated CD4⁺CD25^high cells in adults with asthma compared with those without asthma. Increased pERK1/2 levels corresponded with increased Ca²⁺ response to T cell receptor stimulation. mRNA expression of peroxiredoxins declined in T_regs from adults with asthma. Finally, CD4⁺CD25^high cells from paediatric subjects were more sensitive to oxidative stress than those from adults in vitro. The differential T_reg sensitivity to oxidative stress observed in children and adults was likely dependent on phenotypic CD45 isoform switching. Increased sensitivity of T_reg cells from adults with asthma to H₂O₂ resulted from a reduction of peroxiredoxin-2, -3, -4 and increased pERK1/2 via impaired Ca²⁺ response in these cells.

Targeting regulatory T cells for immunotherapy in melanoma

Regulatory T cells (Tregs) are essential in the maintenance of immunity, and they are also a key to immune suppressive microenvironment in solid tumors. Many studies have revealed the biology of Tregs in various human pathologies. Here we review recent understandings of the immunophenotypes and suppressive functions of Tregs in melanoma, including Treg recruitment and expansion in a tumor. Tregs are frequently accumulated in melanoma and the ratio of CD8+ T cells versus Tregs in the melanoma is predictive for patient survival. Hence, depletion of Tregs is a promising strategy for the enhancement of anti-melanoma immunity. Many recent studies are aimed to target Tregs in melanoma. Distinguishing Tregs from other immune cells and understanding the function of different subsets of Tregs may contribute to better therapeutic efficacy. Depletion of functional Tregs from the tumor microenvironment has been tested to induce clinically relevant immune responses against melanomas. However, the lack of Treg specific therapeutic antibodies or Treg specific depleting strategies is a big hurdle that is yet to be overcome. Additional studies to fine-tune currently available therapies and more agents that specifically and selectively target tumor infiltrating Tregs in melanoma are urgently needed.

FOXP3+ regulatory T cells and age-related diseases

Regulatory T (Treg) cells are critical for the maintenance of immune homeostasis. Dysregulation of Treg cells has been implicated in the pathogenesis of autoimmunity and chronic inflammation, while aging is characterized by an accumulation of inflammatory markers in the peripheral blood, a phenomenon known as 'inflammaging'. The relationship between Treg cells and age-related diseases remains to be further studied. Increasing evidence revealed that Treg cells' dysfunction occurs in aged patients, suggesting that immune therapies targeting Treg cells may be a promising approach to treat diseases such as cancers and autoimmune diseases. Furthermore, drugs targeting Treg cells show encouraging results and contribute to CD8⁺ T-cell-mediated cytotoxic killing of tumor and infected cells. In general, a better understanding of Treg cell function may help us to develop new immune therapies against aging. In this review, we discuss potential therapeutic strategies to modify immune responses of relevance for aging to prevent and treat age-related diseases, as well as the challenges posed by the translation of novel immune therapies into clinical practice.

Mature Dendritic Cells May Promote High-Avidity Tuning of Vaccine T Cell Responses

Therapeutic vaccines can elicit tumor-specific cytotoxic T lymphocytes (CTLs), but durable reductions in tumor burden require vaccines that stimulate high-avidity CTLs. Recent advances in immunotherapy responses have led to renewed interest in vaccine approaches, including dendritic cell vaccine strategies. However, dendritic cell requirements for vaccines that generate potent anti-tumor T-cell responses are unclear. Here we use mathematical modeling to show that, counterintuitively, increasing levels of immature dendritic cells may lead to selective expansion of high-avidity CTLs. This finding is in contrast with traditional dendritic cell vaccine approaches that have sought to harness ex vivo generated mature dendritic cells. We show that the injection of vaccine antigens in the context of increased numbers of immature dendritic cells results in a decreased overall peptide:MHC complex load that favors high-avidity CTL activation and expansion. Overall, our results provide a firm basis for further development of this approach, both alone and in combination with other immunotherapies such as checkpoint blockade.

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

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

Dynamics of effector and naïve Regulatory T cells throughout pregnancy

Regulatory T (Treg) cells are a specialized subset of T cells possessing immunosuppressive functions indispensable for the maintenance of self-tolerance and pregnancy. However, how functional Treg cells dynamically change and are engaged in feto-maternal tolerance during human pregnancy is still unclear. Recent studies have shown that functionally distinct and immunosuppressive subsets of Treg cells, i.e., effector Treg (eTreg) and naïve Treg (nTreg) cells, can be delineated by combinations of molecular markers and that their proportions differ in normal and disease states. In this study, we examined how the proportion of eTreg and nTreg cells in peripheral blood changes in the 1^st, 2^nd, and 3^rd trimesters of pregnancy and the postpartum period. During the 2^nd trimester the proportion of eTreg cells was reduced while nTreg cells was increased. This pattern was maintained throughout the 3^rd trimester of pregnancy. The kinetics of eTreg reduction highly correlated with migration of eTreg cells into feto-maternal interface while stable nTreg proportion paralleled with their expression of the anti-apoptotic molecule Bcl-2 and production of thymic emigrant naïve Treg cells. These results suggest that further studies on divergence of functional Treg proportions will be helpful for predicting instability of pregnancy.

Treg cell-based therapies: challenges and perspectives

Cellular therapies using regulatory T (Treg) cells are currently undergoing clinical trials for the treatment of autoimmune diseases, transplant rejection and graft-versus-host disease. In this Review, we discuss the biology of Treg cells and describe new efforts in Treg cell engineering to enhance specificity, stability, functional activity and delivery. Finally, we envision that the success of Treg cell therapy in autoimmunity and transplantation will encourage the clinical use of adoptive Treg cell therapy for non-immune diseases, such as neurological disorders and tissue repair.

Regulatory T Cells and Human Disease

Naturally occurring CD4⁺ regulatory T cells (Tregs), which specifically express the transcription factor FoxP3 in the nucleus and CD25 and CTLA-4 on the cell surface, are a functionally distinct T cell subpopulation actively engaged in the maintenance of immunological self-tolerance and homeostasis. Recent studies have facilitated our understanding of the cellular and molecular basis of their generation, function, phenotypic and functional stability, and adaptability. It is under investigation in humans how functional or numerical Treg anomalies, whether genetically determined or environmentally induced, contribute to immunological diseases such as autoimmune diseases. Also being addressed is how Tregs can be targeted to control physiological and pathological immune responses, for example, by depleting them to enhance tumor immunity or by expanding them to treat immunological diseases. This review discusses our current understanding of Treg immunobiology in normal and disease states, with a perspective on the realization of Treg-targeting therapies in the clinic.

Molecular Mechanisms Controlling Foxp3 Expression in Health and Autoimmunity: From Epigenetic to Post-translational Regulation

The discovery of the transcription factor Forkhead box-p3 (Foxp3) has shed fundamental insights into the understanding of the molecular determinants leading to generation and maintenance of T regulatory (Treg) cells, a cell population with a key immunoregulatory role. Work over the past few years has shown that fine-tuned transcriptional and epigenetic events are required to ensure stable expression of Foxp3 in Treg cells. The equilibrium between phenotypic plasticity and stability of Treg cells is controlled at the molecular level by networks of transcription factors that bind regulatory sequences, such as enhancers and promoters, to regulate Foxp3 expression. Recent reports have suggested that specific modifications of DNA and histones are required for the establishment of the chromatin structure in conventional CD4⁺ T (Tconv) cells for their future differentiation into the Treg cell lineage. In this review, we discuss the molecular events that control Foxp3 gene expression and address the associated alterations observed in human diseases. Also, we explore how Foxp3 influences the gene expression programs in Treg cells and how unique properties of Treg cell subsets are defined by other transcription factors.

TNFα-Signaling Modulates the Kinase Activity of Human Effector Treg and Regulates IL-17A Expression

Maintenance of regulatory T cells CD4⁺CD25^highFOXP3⁺ (Treg) stability is vital for proper Treg function and controlling the immune equilibrium. Treg cells are heterogeneous and can reveal plasticity, exemplified by their potential to express IL-17A. TNFα-TNFR2 signaling controls IL-17A expression in conventional T cells via the anti-inflammatory ubiquitin-editing and kinase activity regulating enzyme TNFAIP3/A20 (tumor necrosis factor-alpha-induced protein 3). To obtain a molecular understanding of TNFα signaling on IL-17 expression in the human effector (_effTreg, CD25^highCD45RA⁻) Treg subset, we here studied the kinome activity regulation by TNFα signaling. Using FACS-sorted naïve (_naïveTreg, CD25^highCD45RA⁺) and _effTreg subsets, we demonstrated a reciprocal relationship between TNFα and IL-17A expression; _effTreg (TNFα^low/IL-17A^high) and _naïveTreg (TNFα^high/IL-17A^low). In _effTreg, TNFα-TNFR2 signaling prevented IL-17A expression, whereas inhibition of TNFα signaling by clinically applied anti-TNF antibodies led to increased IL-17A expression. Inhibition of TNFα signaling led to reduced TNFAIP3 expression, which, by using siRNA inhibition of TNFAIP3, appeared causally linked to increased IL-17A expression in _effTreg. Kinome activity screening of CD3/CD28-activated _effTreg revealed that anti-TNF-mediated neutralization led to increased kinase activity. STRING association analysis revealed that the TNF suppression _effTreg kinase activity network was strongly associated with kinases involved in TCR, JAK, MAPK, and PKC pathway signaling. Small-molecule-based inhibition of TCR and JAK pathways prevented the IL-17 expression in _effTreg. Together, these findings stress the importance of TNF-TNFR2 in regulating the kinase architecture of antigen-activated _effTreg and controlling IL-17 expression of the human Treg. These findings might be relevant for optimizing anti-TNF-based therapy and may aid in preventing Treg plasticity in case of Treg-based cell therapy.

One, No One, and One Hundred Thousand: T Regulatory Cells' Multiple Identities in Neuroimmunity

As the Nobel laureate Luigi Pirandello wrote in his novels, identities can be evanescent. Although a quarter of a century has passed since regulatory T cells (Treg) were first described, new studies continue to reveal surprising and contradictory features of this lymphocyte subset. Treg cells are the core of the immunological workforce engaged in the restraint of autoimmune or inflammatory reactions, and their characterization has revealed substantial heterogeneity and complexity in the phenotype and gene expression profiles, proving them to be a most versatile and adaptive cell type, as exemplified by their plasticity in fine-tuning immune responses. Defects in Treg function are associated with several autoimmune diseases, including multiple sclerosis, which is caused by an inappropriate immune reaction toward brain components; conversely, the beneficial effects of immunomodulating therapies on disease progression have been shown to partly act upon the biology of these cells. Both in animals and in humans the pool of circulating Treg cells is a mixture of natural (nTregs) and peripherally-induced Treg (pTregs). Particularly in humans, circulating Treg cells can be phenotypically subdivided into different subpopulations, which so far are not well-characterized, particularly in the context of autoimmunity. Recently, Treg cells have been rediscovered as mediators of tissue healing, and have also shown to be involved in organ homeostasis. Moreover, stability of the Treg lineage has recently been addressed by several conflicting reports, and immune-suppressive abilities of these cells have been shown to be dynamically regulated, particularly in inflammatory conditions, adding further levels of complexity to the study of this cell subset. Finally, Treg cells exert their suppressive function through different mechanisms, some of which—such as their ectoenzymatic activity—are particularly relevant in CNS autoimmunity. Here, we will review the phenotypically and functionally discernible Treg cell subpopulations in health and in multiple sclerosis, touching also upon the effects on this cell type of immunomodulatory drugs used for the treatment of this disease.

BAFF gene silencing attenuates allergic airway inflammation by promoting the generation of Tregs via activating pro-Treg cytokines

AIMS

Allergic airway inflammation is one of the major pathological events involved in asthma, and dysregulation of regulatory T cells (Treg) plays a crucial role in the development of allergic airway inflammation. Here, we attempted to investigate the regulatory effects of B cell-activating factor (BAFF) on Tregs in allergic airway inflammation.

MAIN METHODS

BAFF expression was analyzed by ELISA, quantitative reverse transcription PCR (RT-PCR) and Western blot assays. The levels of IL-4, TGF-β, IL-2, and IL-10 were tested using ELISA kits. Flow cytometry was conducted to analyze the populations of CTLA4⁺ Foxp3⁺ Tregs.

KEY FINDINGS

BAFF was found to be aberrantly expressed in sputum and lungs in patients with asthma as well as OVA sensitized mice. BAFF silencing by lentiviral BAFF shRNA reduced the number of eosinophils and levels of IL-4 in the BAL fluid, as well as the Fizz1 expression in the lungs of OVA mice. Additionally, the population of CTLA4⁺ Foxp3⁺ Tregs were significantly decreased in OVA mice and had a negative correlation to BAFF levels in asthmatic patients and OVA mice. BAFF silencing in vivo increased levels of CTLA4⁺ Foxp3⁺ Tregs and the secretion of IL-10, and improved the regulatory phenotype and suppressor function of Tregs in vitro. Furthermore, BAFF can affect Tregs generation by regulating the production of the pro-Treg cytokines IL-2 and TGF-β.

SIGNIFICANCE

BAFF has an inhibitory effect on the generation and suppressor function of Tregs by affecting pro-Tregs cytokines, thereby contributing to the development of allergic airway inflammation.

Inflammaging and Oxidative Stress in Human Diseases: From Molecular Mechanisms to Novel Treatments

It has been proposed that a chronic state of inflammation correlated with aging known as inflammaging, is implicated in multiple disease states commonly observed in the elderly population. Inflammaging is associated with over-abundance of reactive oxygen species in the cell, which can lead to oxidation and damage of cellular components, increased inflammation, and activation of cell death pathways. This review focuses on inflammaging and its contribution to various age-related diseases such as cardiovascular disease, cancer, neurodegenerative diseases, chronic obstructive pulmonary disease, diabetes, and rheumatoid arthritis. Recently published mechanistic details of the roles of reactive oxygen species in inflammaging and various diseases will also be discussed. Advancements in potential treatments to ameliorate inflammaging, oxidative stress, and consequently, reduce the morbidity of multiple disease states will be explored.

Human FOXP3+ Regulatory T Cell Heterogeneity and Function in Autoimmunity and Cancer

Regulatory T (Treg) cells expressing the transcription factor Foxp3 have a critical role in the maintenance of immune homeostasis and prevention of autoimmunity. Recent advances in single cell analyses have revealed a range of Treg cell activation and differentiation states in different human pathologies. Here we review recent progress in the understanding of human Treg cell heterogeneity and function. We discuss these findings within the context of concepts in Treg cell development and function derived from preclinical models and insight from approaches targeting Treg cells in clinical settings. Distinguishing functional Treg cells from other T cells and understanding the context-dependent function(s) of different Treg subsets will be crucial to the development of strategies toward the selective therapeutic manipulation of Treg cells in autoimmunity and cancer.

Examining Peripheral and Tumor Cellular Immunome in Patients With Cancer

Immunotherapies are rapidly being integrated into standard of care (SOC) therapy in conjunction with surgery, chemotherapy, and radiotherapy for many cancers and a large number of clinical studies continue to explore immunotherapy alone and as part of combination therapies in patients with cancer. It is evident that clinical effectiveness of immunotherapy is limited to a subset of patients and improving immunotherapy related outcomes remains a major scientific and clinical effort. Understanding the immune cell subset phenotype and activation/functional status (cellular immunome) prior to and post therapy is therefore critical to develop biomarkers that (1) will predict if a patient will respond to immunotherapy and (2) are a result of immunotherapy. In this study, we investigated local (tumor) and peripheral (blood) cellular immunome of patients with melanoma, breast cancer, and brain cancer using a rapid and reliable standardized, multiparameter flow cytometry assay. We used this approach to monitor changes in the peripheral cellular immunome in women with breast cancer undergoing SOC therapy. Our analysis is unique because it is conducted using matched fresh tumor tissue and blood from patients in real-time, within 2–3 h of sample acquisition, and provides insight into the innate and adaptive immune cell profile in blood and tumor. Specific to blood, this approach involves no manipulation and evaluates all immune subsets such as T cells, B cells, natural killer (NK) cells, monocytes, dendritic cells (DCs), neutrophils, eosinophils, and basophils using 0.5 ml of blood. Analysis of the corresponding tumor provides much needed insight into the phenotype and activation status of immune cells, especially T and B cells, in the tumor microenvironment vs. the periphery. This analysis will be used to assess baseline and therapy-mediated changes in local and peripheral cellular immunome in patients with glioblastoma, breast cancer, and melanoma in planned immunotherapy clinical studies.

Different phenotypes of CD4+CD25+Foxp3+ regulatory T cells in recipients post liver transplantation

CD4⁺ regulatory T cells (Tregs) play an important role in inducing immune tolerance in organ transplantation, which can be divided into CD45RA⁺Tregs (resting Tregs, rTregs) and CD45RO⁺Tregs (activated Tregs, aTregs). Currently, the expressions and phenotypic changes of Tregs in recipients after liver transplantation (LT) is unknown. We therefore investigated the expression and transformation of rTregs and aTregs in 83 cases of recipients with normal status post-LT. The percentages of CD45RA, CD45RO, CD31 in CD4⁺Tregs were detected by flow cytometry and the effective factors were analyzed. In LT recipients, the percentage of CD45RO⁺Tregs in CD4⁺Tregs was higher than that of CD45RA⁺Tregs. There was significant difference in the ratio of positive Foxp3 between CD45RA⁺Tregs and CD45RO⁺Tregs. Percentage of CD45RA⁺Tregs was higher in pediatric group than that in adult group, whereas percentage of CD45RO⁺Tregs was lower in the pediatric group. However, it was different only in CD45RO⁺Tregs in various survival periods post-LT. In conclusion, Tregs pool in human was heterogeneous post-LT and contained different subsets in phenotypes. Upon stimulation by donor graft, percentages of CD4⁺Tregs and CD45RO⁺Tregs were increased post-LT and most of rTregs was transformed into aTregs in peripheral blood, and rTregs and aTregs were both related to recipients' ages.

Characterization of Regulatory T Cells in Preterm and Term Infants

Our study aimed to study regulatory T cells (Tregs) and their expression of CD45RA, HLA-DR, and CD39 in preterm and full-term infants. In an observational study, we used a three-color flow cytometry for determination of Tregs and their expression of CD45RA, HLA-DR, and CD39 in preterm and full-term infants. The percentages of CD4⁺CD25^+highFoxp3⁺, CD39⁺ Tregs, HLA-DR⁺ Tregs and the expression of Foxp3⁺ in CD4⁺CD25^+highFoxp3 Tregs cells were significantly lower in neonates when compared to healthy adult controls. The levels of naïve resting Tregs (CD45RA⁺Tregs) were significantly higher in neonates than controls. The percentages of CD4⁺CD25^+highFoxp3⁺Tregs, total CD4⁺CD25⁺ and CD4⁺CD25^+high were significantly higher in preterm infants when compared to the full-term group. Moreover, CD45RA⁺Tregs were significantly higher in preterm than in term infants. We found significant inverse correlations between the gestational age and the levels of both Tregs (r = - 0.395, p = 0.017) and CD45RA⁺Tregs (r = - 0.422, p = 0.010). Relative to full-term, the frequencies, and phenotypes of Tregs were affected by prematurity. A larger longitudinal study with a sufficient number of newborns is needed to investigate the Treg pool of term and preterm infants thoroughly and to explore the association between the Treg pool and clinical variables.

Human naïve regulatory T-cells feature high steady-state turnover and are maintained by IL-7

Naïve FoxP3-expressing regulatory T-cells (Tregs) are essential to control immune responses via continuous replenishment of the activated-Treg pool with thymus-committed suppressor cells. The mechanisms underlying naïve-Treg maintenance throughout life in face of the age-associated thymic involution remain unclear. We found that in adults thymectomized early in infancy the naïve-Treg pool is remarkably well preserved, in contrast to conventional naïve CD4 T-cells. Naïve-Tregs featured high levels of cycling and pro-survival markers, even in healthy individuals, and contrasted with other circulating naïve/memory CD4 T-cell subsets in terms of their strong γc-cytokine-dependent signaling, particularly in response to IL-7. Accordingly, ex-vivo stimulation of naïve-Tregs with IL-7 induced robust cytokine-dependent signaling, Bcl-2 expression, and phosphatidylinositol 3-kinase (PI3K)-dependent proliferation, whilst preserving naïve phenotype and suppressive capacity. Altogether, our data strongly implicate IL-7 in the thymus-independent long-term survival of functional naïve-Tregs, and highlight the potential of targeting the IL-7 pathway to modulate Tregs in different clinical settings.

DNA damage, metabolism and aging in pro-inflammatory T cells: Rheumatoid arthritis as a model system

The aging process is the major driver of morbidity and mortality, steeply increasing the risk to succumb to cancer, cardiovascular disease, infection and neurodegeneration. Inflammation is a common denominator in age-related pathologies, identifying the immune system as a gatekeeper in aging overall. Among immune cells, T cells are long-lived and exposed to intense replication pressure, making them sensitive to aging-related abnormalities. In successful T cell aging, numbers of naïve cells, repertoire diversity and activation thresholds are preserved as long as possible; in maladaptive T cell aging, protective T cell functions decline and pro-inflammatory effector cells are enriched. Here, we review in the model system of rheumatoid arthritis (RA) how maladaptive T cell aging renders the host susceptible to chronic, tissue-damaging inflammation. In T cells from RA patients, known to be about 20years pre-aged, three interconnected functional domains are altered: DNA damage repair, metabolic activity generating energy and biosynthetic precursor molecules, and shaping of plasma membranes to promote T cell motility. In each of these domains, key molecules and pathways have now been identified, including the glycolytic enzymes PFKFB3 and G6PD; the DNA repair molecules ATM, DNA-PKcs and MRE11A; and the podosome marker protein TKS5. Some of these molecules may help in defining targetable pathways to slow the T cell aging process.

Successful and Maladaptive T Cell Aging

Throughout life, the T cell system adapts to shifting resources and demands, resulting in a fundamentally restructured immune system in older individuals. Here we review the cellular and molecular features of an aged immune system and discuss the trade-offs inherent to these adaptive mechanisms. Processes include homeostatic proliferation that maintains compartment size at the expense of partial loss in stemness and incomplete differentiation and the activation of negative regulatory programs, which constrain effector T cell expansion and prevent increasing oligoclonality but also interfere with memory cell generation. We propose that immune failure occurs when adaptive strategies developed by the aging T cell system fail and also discuss how, in some settings, the programs associated with T cell aging culminates in a maladaptive response that directly contributes to chronic inflammatory disease.

Exacerbation of Endometriosis Due To Regulatory T-Cell Dysfunction

CONTEXT

Endometriosis is a chronic inflammatory disease associated with altered immune response to endometrial cells facilitating the implantation and proliferation of ectopic endometrial tissues. Although regulatory T (Treg) cells play a key role in T cell-mediated immune response and development of immune disorders, their significance in endometriosis remains to be elucidated. Recently, CD4+CD45RA- forkhead box protein 3 (Foxp3)hi T cells, activated Treg cells, have been identified as a functionally true suppressive population of Treg cells.

OBJECTIVE

To investigate the role of Treg cells in endometriosis.

DESIGN

Three Treg cell fractions (resting Treg cells, activated Treg cells, and non-Treg cells) were examined using flow cytometry in the endometrioma, endometrium, peritoneal fluid, and peripheral blood obtained from women with (n = 27) and without (n = 28) endometriosis. A mouse model of endometriosis was made in Foxp3tm3Ayr/J (Foxp3DTR) C57BL/6 Treg cell-depleted mice (n = 28).

RESULTS

In women with endometrioma, the proportion of activated Treg cells in the endometrioma and the endometrium, but not in the peritoneal fluid or peripheral blood, was significantly decreased compared with that in women without endometriosis. In Foxp3DTR/diphtheria toxin mice, the number and weight of endometriotic lesions, inflammatory cytokine levels and angiogenetic factors were significantly increased compared with those in control mice.

CONCLUSIONS

Treg cell deficiency exaggerates local inflammation and angiogenesis and simultaneously facilitates the attachment and growth of endometrial implants. The findings provide an insight into dysregulated immune response for the pathogenesis and development.

Human blood Tfr cells are indicators of ongoing humoral activity not fully licensed with suppressive function

Germinal center (GC) responses are controlled by T follicular helper (Tfh) and T follicular regulatory (Tfr) cells and are crucial for the generation of high-affinity antibodies. Although the biology of human circulating and tissue Tfh cells has been established, the relationship between blood and tissue Tfr cells defined as CXCR5+Foxp3+ T cells remains elusive. We found that blood Tfr cells are increased in Sjögren syndrome, an autoimmune disease with ongoing GC reactions, especially in patients with high autoantibody titers, as well as in healthy individuals upon influenza vaccination. Although blood Tfr cells correlated with humoral responses, they lack full B cell-suppressive capacity, despite being able to suppress T cell proliferation. Blood Tfr cells have a naïve-like phenotype, although they are absent from human thymus or cord blood. We found that these cells were generated in peripheral lymphoid tissues before T-B interaction, as they are maintained in B cell-deficient patients. Therefore, blood CXCR5+Foxp3+ T cells in human pathology indicate ongoing humoral activity but are not fully competent circulating Tfr cells.

Stabilizing human regulatory T cells for tolerance inducing immunotherapy

Many autoimmune diseases develop as a consequence of an altered balance between autoreactive immune cells and suppressive FOXP3⁺ Treg. Restoring this balance through amplification of Treg represents a promising strategy to treat disease. However, FOXP3⁺ Treg might become unstable especially under certain inflammatory conditions, and might transform into proinflammatory cytokine-producing cells. The issue of heterogeneity and instability of Treg has caused considerable debate in the field and has important implications for Treg-based immunotherapy. In this review, we discuss how Treg stability is defined and what the molecular mechanisms underlying the maintenance of FOXP3 expression and the regulation of Treg stability are. Also, we elaborate on current strategies used to stabilize human Treg for clinical purposes. This review focuses on human Treg, but considering that cell-intrinsic mechanisms to regulate Treg stability in mice and in humans might be similar, data derived from mice studies are also discussed in this paper.

Regulatory T cell frequencies and phenotypes following anti-viral vaccination

Regulatory T cells (Treg) function in the prevention of excessive inflammation and maintenance of immunological homeostasis. However, these cells may also interfere with resolution of infections or with immune reactions following vaccination. Effects of Treg on vaccine responses are nowadays investigated, but the impact of vaccination on Treg homeostasis is still largely unknown. This may be a relevant safety aspect, since loss of tolerance through reduced Treg may trigger autoimmunity. In exploratory clinical trials, healthy adults were vaccinated with an influenza subunit vaccine plus or minus the adjuvant MF59®, an adjuvanted hepatitis B subunit vaccine or a live attenuated yellow fever vaccine. Frequencies and phenotypes of resting (rTreg) and activated (aTreg) subpopulations of circulating CD4+ Treg were determined and compared to placebo immunization. Vaccination with influenza vaccines did not result in significant changes in Treg frequencies and phenotypes. Vaccination with the hepatitis B vaccine led to slightly increased frequencies of both rTreg and aTreg subpopulations and a decrease in expression of functionality marker CD39 on aTreg. The live attenuated vaccine resulted in a decrease in rTreg frequency, and an increase in expression of activation marker CD25 on both subpopulations, possibly indicating a conversion from resting to migratory aTreg due to vaccine virus replication. To study the more local effects of vaccination on Treg in lymphoid organs, we immunized mice and analyzed the CD4+ Treg frequency and phenotype in draining lymph nodes and spleen. Vaccination resulted in a transient local decrease in Treg frequency in lymph nodes, followed by a systemic Treg increase in the spleen. Taken together, we showed that vaccination with vaccines with an already established safe profile have only minimal impact on frequencies and characteristics of Treg over time. These findings may serve as a bench-mark of inter-individual variation of Treg frequencies and phenotypes following vaccination.

T-regulatory cells exhibit a biphasic response to prolonged endurance exercise in humans

Purpose

T-regulatory cells (Tregs) are a sub-population of lymphocytes that act to suppress aberrant immune responses. We investigated changes in the numbers of naïve and terminally differentiated Tregs in the peripheral blood to establish their role in the immuno-suppressive response to prolonged exercise.

Methods

Blood was drawn from seventeen experienced runners (age 40 ± 12 years; height 1.75 ± 0.08 m; mass 71.4 ± 10.8 kg) before, ~1 h after (POST-1h), and on the day following the marathon (POST-1d). Tregs (CD3⁺CD4⁺Foxp3⁺CD25⁺⁺CD127⁻) were analysed in peripheral blood mononuclear cells using flow cytometry. The markers CD45RA and HLA-DR were included to define naïve and terminally differentiated Tregs, respectively.

Results

The absolute number of Tregs decreased (27%) POST-1h marathon (P < 0.001) but increased (21%) at POST-1d (P < 0.01). Naïve CD45RA⁺ Tregs fell by 39% POST-1h (P < 0.01) but were unaffected POST-1d (P > 0.05). In contrast, an increased number of Tregs expressing HLA-DR was observed at POST-1d (P < 0.01). Interleukin (IL)-1β, IL-6, IL-8 and IL-10 levels in the serum all increased POST-1h (P > 0.05) but returned to pre-exercise levels POST-1d. The suppressive cytokine, transforming growth factor-beta, was unaffected by the marathon (P > 0.05).

Conclusions

These results suggest that Tregs do not play a major role in immune suppression in the early hours of recovery from a marathon. However, terminally differentiated HLA-DR⁺ Tregs are mobilized the following day, which could represent a compensatory attempt by the host to restore immune homeostasis and limit excessive cell damage.

Early Immune Regulatory Changes in a Primary Controlled Human Plasmodium vivax Infection: CD1c+ Myeloid Dendritic Cell Maturation Arrest, Induction of the Kynurenine Pathway, and Regulatory T Cell Activation

Plasmodium vivax malaria remains a major public health problem. The requirements for acquisition of protective immunity to the species are not clear. Dendritic cells (DC) are essential for immune cell priming but also perform immune regulatory functions, along with regulatory T cells (Treg). An important function of DC involves activation of the kynurenine pathway via indoleamine 2,3-dioxygenase (IDO). Using a controlled human experimental infection study with blood-stage P. vivax, we characterized plasmacytoid DC (pDC) and myeloid DC (mDC) subset maturation, CD4⁺ CD25⁺ CD127^lo Treg activation, and IDO activity. Blood samples were collected from six healthy adults preinoculation, at peak parasitemia (day 14; ∼31,400 parasites/ml), and 24 and 48 h after antimalarial treatment. CD1c⁺ and CD141⁺ mDC and pDC numbers markedly declined at peak parasitemia, while CD16⁺ mDC numbers appeared less affected. HLA-DR expression was selectively reduced on CD1c⁺ mDC, increased on CD16⁺ mDC, and was unaltered on pDC. Plasma IFN-γ increased significantly and was correlated with an increased kynurenine/tryptophan (KT) ratio, a measure of IDO activity. At peak parasitemia, Treg presented an activated CD4⁺ CD25⁺ CD127^lo CD45RA^- phenotype and upregulated TNFR2 expression. In a mixed-effects model, the KT ratio was positively associated with an increase in activated Treg. Our data demonstrate that a primary P. vivax infection exerts immune modulatory effects by impairing HLA-DR expression on CD1c⁺ mDC while activating CD16⁺ mDC. Induction of the kynurenine pathway and increased Treg activation, together with skewed mDC maturation, suggest P. vivax promotes an immunosuppressive environment, likely impairing the development of a protective host immune response.

Novel Senescent Regulatory T-Cell Subset with Impaired Suppressive Function in Rheumatoid Arthritis

Objective

Premature senescence of lymphocytes is a hallmark of inflammatory rheumatic diseases such as rheumatoid arthritis (RA). Early T-cell aging affects conventional T-cells but is presumably not limited to this cell population; rather it might also occur in the regulatory T-cells (Tregs) compartment. In RA, Tregs fail to halt aberrant immune reactions and disease progression. Whether this is associated with early Treg senescence leading to phenotypic and functional changes of this subset is elusive so far.

Methods

Eighty-four RA patients and 75 healthy controls were prospectively enrolled into the study. Flow cytometry, magnetic-associated cell sorting, and cell culture experiments were performed for phenotypic and functional analyses of Treg subsets. T-cell receptor excision circle (TREC) levels and telomere lengths were determined using RT-PCR.

Results

In this paper, we describe the novel CD4⁺FoxP3⁺CD28⁻ T-cell subset (CD28⁻ Treg-like cells) in RA patients revealing features of both Tregs and senescent T-cells: Treg surface/intracellular markers such as CD25, CTLA-4, and PD-1 as well as FOXP3 were all expressed by CD28⁻ Treg-like cells, and they yielded signs of premature senescence including reduced TREC levels and an accumulation of γH2AX. CD28⁻ Treg-like could be generated in vitro by stimulation of (CD28⁺) Tregs with TNF-α. CD28⁻ Treg-like cells insufficiently suppressed the proliferation of effector T-cells and yielded a pro-inflammatory cytokine profile.

Conclusion

In conclusion, we describe a novel T-cell subset with features of Tregs and senescent non-Tregs. These cells may be linked to an aberrant balance between regulatory and effector functions in RA.

Single CD28 stimulation induces stable and polyclonal expansion of human regulatory T cells

CD4+FOXP3+ Treg are essential for immune tolerance. Phase-1 clinical trials of Treg-therapy to treat graft-versus-host-disease reported safety and potential therapeutic efficacy. Treg-based trials have started in organ-transplant patients. However, efficient ex vivo expansion of a stable Treg population remains a challenge and exploring novel ways for Treg expansion is a pre-requisite for successful immunotherapy. Based on the recent finding that CD28-signaling is crucial for survival and proliferation of mouse Treg, we studied single-CD28 stimulation of human Treg, without T cell receptor stimulation. Single-CD28 stimulation of human Treg in the presence of recombinant human IL-2(rhIL-2), as compared to CD3/CD28/rhIL-2 stimulation, led to higher expression levels of FOXP3. Although the single-CD28 expanded Treg population was equally suppressive to CD3/CD28 expanded Treg, pro-inflammatory cytokine (IL-17A/IFNγ) production was strongly inhibited, indicating that single-CD28 stimulation promotes Treg stability. As single-CD28 stimulation led to limited expansion rates, we examined a CD28-superagonist antibody and demonstrate a significant increased Treg expansion that was more efficient than standard anti-CD3/CD28-bead stimulation. CD28-superagonist stimulation drove both naïve and memory Treg proliferation. CD28-superagonist induction of stable Treg appeared both PI3K and mTOR dependent. Regarding efficient and stable expansion of Treg for adoptive Treg-based immunotherapy, application of CD28-superagonist stimulation is of interest.

Healthy Preterm Newborns Show an Increased Frequency of CD4(+) CD25(high) CD127(low) FOXP3(+) Regulatory T Cells with a Naive Phenotype and High Expression of Gut-Homing Receptors

Treg cells are crucial to prevent immune dysregulation, but little is known about the frequency of these cells in neonates, particularly in very/moderate and late preterm newborns studied as separate groups. The CD4(+) CD25(hi) CD127(lo) FOXP3(+) Treg population was phenotypically characterized to assess maturation markers and gut-homing integrins by flow cytometry in the cord blood of healthy preterm newborns born at 30-33(6/7) gestation weeks (Group 1), at 34-36(6/7) gestation weeks (Group 2) and term newborns born at 37-41 gestation weeks (Group 3), compared to healthy adults. An inverse correlation of the Treg percentage and gestational age was found, with significantly higher frequencies in Group 1 compared to Groups 2 and 3 and in Group 2 compared to Group 3, and significantly higher Treg frequencies and numbers in the neonates compared to the adults. All of the newborns exhibited increased Treg frequencies with a naive phenotype compared to adults. Cytotoxic T-lymphocyte-associated protein 4 CTLA-4 expression in the naive Treg was decreased in both preterm groups compared with those from term newborns and adults, and in the memory Treg from Group 1 compared with the other groups. The frequencies of Treg expressing α4β7 and α4β1 integrins were higher in both preterm groups, but significantly different only in Group 1, when compared with those from the term newborns and the adults. In conclusion, although a high frequency of Treg is present in newborns, an immature phenotype with a higher expression of CD45RA and α4β7/α4β1 and a lower expression of CTLA-4 is found, particularly in the very preterm group.

Prognostic value of circulating regulatory T cell subsets in untreated non-small cell lung cancer patients

The role of the different circulating regulatory T-cells (Treg) subsets, as well as their correlation with clinical outcome of non-small cell lung cancer (NSCLC) patients is poorly understood. Peripheral blood from 156 stage III/IV chemotherapy-naive NSCLC patients and 31 healthy donors (HD) was analyzed with flow cytometry for the presence and functionality of CD4⁺ Treg subsets (naive, effector and terminal effector). Their frequencies were correlated with the clinical outcome. All CD4⁺ Treg subsets exhibited highly suppressive activity by TGF-β and IL-10 production. The percentages of naive Treg were found elevated in NSCLC patients compared to HD and were associated with poor clinical outcome, whereas the percentage of terminal effector Treg was lower compared to HD and higher levels were correlated with improved clinical response. At baseline, normal levels of naive and effector Treg were associated with longer overall survival (OS) compared to high levels, while the high frequency of the terminal effector Treg was correlated with longer Progression-Free Survival and OS. It is demonstrated, for first time, that particular CD4⁺ Treg subtypes are elevated in NSCLC patients and their levels are associated to the clinical outcome. The blocking of their migration to the tumor site may be an effective therapeutic strategy.

Adoptive Cell Therapy with Tregs to Improve Transplant Outcomes: The Promise and the Stumbling Blocks

The contribution of regulatory T cells (Treg) to the induction and maintenance of tolerance is well-recognized in rodents and may contribute to long-term human organ allograft survival. The therapeutic efficacy of adoptively-transferred Treg in promoting tolerance to organ allografts is well-recognized in mouse models. Early phase 1/2 clinical studies of Treg therapy have been conducted in patients with type-1 (autoimmune) diabetes and refractory Crohn's disease, and for inhibition of graft-versus-host disease following bone marrow transplantation with proven safety. The feasibility of adoptive Treg therapy in the clinic is subject to various parameters, including optimal cell source, isolation procedure, expansion, target dose, time of infusion, as well as generation of a GMP-cell product. Several phase 1/2 Treg dose-escalation studies are underway in organ transplantation. Recent evidence suggests that additional factors are critical to ensure Treg safety and efficacy in allograft recipients, including Treg characterization, stability, longevity, trafficking, concomitant immunosuppression, and donor antigen specificity. Accordingly, Treg therapy in the context of organ transplantation may prove more challenging in comparison to other prospective clinical settings of Treg immunotherapy, such as type-1 diabetes.

Low-dose IL-2 selectively activates subsets of CD4+ Tregs and NK cells

CD4⁺ regulatory T cells (CD4Tregs) play a critical role in the maintenance of immune tolerance and prevention of chronic graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation. IL-2 supports the proliferation and survival of CD4Tregs and previous studies have demonstrated that IL-2 induces selective expansion of CD4Tregs and improves clinical manifestations of chronic GVHD. However, mechanisms for selective activation of CD4Tregs and the effects of low-dose IL-2 on other immune cells are not well understood. Using mass cytometry, we demonstrate that low concentrations of IL-2 selectively induce STAT5 phosphorylation in Helios⁺ CD4Tregs and CD56^brightCD16^- NK cells in vitro. Preferential activation and expansion of Helios⁺ CD4Tregs and CD56^brightCD16^- NK cells was also demonstrated in patients with chronic GVHD receiving low-dose IL-2. With prolonged IL-2 treatment for 48 weeks, phenotypic changes were also observed in Helios^- CD4Tregs. The effects of low-dose IL-2 therapy on conventional CD4⁺ T cells and CD8⁺ T cells were limited to increased expression of PD-1 on effector memory T cells. These studies reveal the selective effects of low-dose IL-2 therapy on Helios⁺ CD4Tregs and CD56^bright NK cells that constitutively express high-affinity IL-2 receptors as well as the indirect effects of prolonged exposure to low concentrations of IL-2 in vivo.

Context- and Tissue-Specific Regulation of Immunity and Tolerance by Regulatory T Cells

The immune system has evolved to defend the organism against an almost infinite number of pathogens in a locally confined and antigen-specific manner while at the same time preserving tolerance to harmless antigens and self. Regulatory T (Treg) cells essentially contribute to an immunoregulatory network preventing excessive immune responses and immunopathology. There is emerging evidence that Treg cells not only operate in secondary lymphoid tissue but also regulate immune responses directly at the site of inflammation. Hence, the classification of Treg cells might need to be further extended by Treg cell subsets that are functionally and phenotypically polarized by their residency. In this review, we discuss recent findings on these tissue-resident Treg cell subsets and how these cells may operate in a tissue- and context-dependent manner.

Mechanisms of T cell organotropism

Protective immunity relies upon T cell differentiation and subsequent migration to target tissues. Similarly, immune homeostasis requires the localization of regulatory T cells (Tregs) to the sites where immunity takes place. While naïve T lymphocytes recirculate predominantly in secondary lymphoid tissue, primed T cells and activated Tregs must traffic to the antigen rich non-lymphoid tissue to exert effector and regulatory responses, respectively. Following priming in draining lymph nodes, T cells acquire the 'homing receptors' to facilitate their access to specific tissues and organs. An additional level of topographic specificity is provided by T cells receptor recognition of antigen displayed by the endothelium. Furthermore, co-stimulatory signals (such as those induced by CD28) have been shown not only to regulate T cell activation and differentiation, but also to orchestrate the anatomy of the ensuing T cell response. We here review the molecular mechanisms supporting trafficking of both effector and regulatory T cells to specific antigen-rich tissues.

Ex-vivo characterization of regulatory T cells in pulmonary tuberculosis patients, latently infected persons, and healthy endemic controls

BACKGROUND

Regulatory T cells (Treg) are an essential arm of adaptive immunity not only in tolerance and autoimmunity but also in infectious diseases. In Tuberculosis (TB), it has been suggested that the frequency of Tregs is higher in the blood of TB patients when compared to healthy controls with subsequent decline after treatment. However, with the discovery that FOXP3, the hallmark marker of Tregs, is not exclusive to Tregs and the lack of specific markers for Tregs, it has been a challenge to fully understand the role of Tregs in TB.

METHOD

We isolated PBMC from smear positive TB patients (TB, N = 13) before and after treatment, latent TB infected participants (LTBI, N = 8), and healthy endemic controls (EC, N = 9) and evaluated the frequency of different populations of Tregs and expression of FOXP3 by flowcytometry using six markers.

RESULTS

The findings in this study showed that the association of Treg frequency with TB disease depends on the phenotypic markers used. While the frequency of CD4(+)CD25(+/hi) T cells was higher in TB patients compared to LTBI individuals, there was no difference in the frequency of CD4(+)CD25(+)FOXP3(+)CD127(lo) Treg among TB, LTBI, or EC. However, delineation of Tregs into active and naïve subsets revealed a significant increase in FOXP3 expression in active primed Tregs (CD4(+)CD25(+)FOXP3(+)CD127(lo)CD45RO(+)Ki-67(+)) of TB patients compared to LTBI and EC; and a significantly higher frequency of resting primed (CD45RO(+)Ki-67(-)) Treg in QuantiFERON negative EC compared to TB patients. After treatment completion, there was a significant decline in the frequency of active primed Treg, median (IQR) from 12.4% (9.5-21.9) of Tregs to 9.3% (7.0-12.2); P = 0.003 Wilcoxon signed rank test. We conclude that Treg subsets may be differentially regulated and expressed in TB disease, cure, and infection.

Utility of CD127 combined with FOXP3 for identification of operational tolerance after liver transplantation

Loss of cell surface expression of CD127 on CD4(+)CD25(++) regulatory T-cells (Tregs) may be a useful marker to efficiently isolate Tregs. As FOXP3 was specifically used to identify Tregs, combining these two markers could give better identification for patient with operational tolerance (OT) after liver transplantation. To testify this mixed lymphocyte reaction (MLR), the function of circulating CD4(+)CD25(++)CD127(dim) cells (CD127(dim) cells) was examined in immunosuppression (IS)-free pediatric recipients after liver transplantation (LTx) (group operational tolerance: OT) (Gr-tol n=25) compared to recipients who could not stop IS due to clinically overt rejection (group intolerance) (Gr-intol n=18), recipients who were weaning IS (Gr-weaning n=11) and age-matched healthy volunteers (Gr-vol n=11). In addition, the frequencies of CD127(dim) cells vs CD4(+)CD25(++)CD127(dim)FOXP3(+) (CD127(dim)FOXP3(+)) cells were compared in these four groups by FACS analyses. Our results showed that The proliferation of CD4 cells to donor antigens was reduced compared to third-party antigens only in Gr-tol (P=0.022) but not in other groups (P=NS). Depletion of CD127(dim) cells resulted in a donor antigen-specific abrogation of this MLR hyporesponsiveness in Gr-tol (P<0.001) but not other groups (P=NS). This implied that CD127 efficiently isolated donor antigen-specific Tregs. The frequencies of CD127(dim) cells were significantly lower in Gr-intol (5.2%±1.9%) compared to those in Gr-tol (7.8%±1.8%) (P<0.001) as were the frequencies of CD127(dim) FOXP3(+) cells (Gr-tol: 5.4%±1.7% vs Gr-intol: 2.9%±1.0%, P<0.001). Of interest, there were fewer CD127(dim)FOXP3(+) cells in Gr-intol (2.9%±1%) than in Gr-weaning (5.1%±1.8%) (P=0.002), but no difference in CD127(dim) cells (Gr-intol: 5.2%±1.9% vs Gr-weaning: 6.7%±2.0%) (NS). Thus, combining FOXP3 with CD127 for phenotype analysis demonstrated an unequivocal difference between Gr-intol and Gr-weaning that was not detected by CD127 alone. In conclusion CD127 was a useful surface marker to isolate donor-antigen-specific-Tregs in OT after LTx. The additive effect of its combination with FOXP3 is important in phenotypical Treg analyses of OT patients.

Regulatory T Cells in Melanoma Revisited by a Computational Clustering of FOXP3+ T Cell Subpopulations

CD4⁺ T cells that express the transcription factor FOXP3 (FOXP3⁺ T cells) are commonly regarded as immunosuppressive regulatory T cells (Tregs). FOXP3⁺ T cells are reported to be increased in tumor-bearing patients or animals and are considered to suppress antitumor immunity, but the evidence is often contradictory. In addition, accumulating evidence indicates that FOXP3 is induced by antigenic stimulation and that some non-Treg FOXP3⁺ T cells, especially memory-phenotype FOXP3^low cells, produce proinflammatory cytokines. Accordingly, the subclassification of FOXP3⁺ T cells is fundamental for revealing the significance of FOXP3⁺ T cells in tumor immunity, but the arbitrariness and complexity of manual gating have complicated the issue. In this article, we report a computational method to automatically identify and classify FOXP3⁺ T cells into subsets using clustering algorithms. By analyzing flow cytometric data of melanoma patients, the proposed method showed that the FOXP3⁺ subpopulation that had relatively high FOXP3, CD45RO, and CD25 expressions was increased in melanoma patients, whereas manual gating did not produce significant results on the FOXP3⁺ subpopulations. Interestingly, the computationally identified FOXP3⁺ subpopulation included not only classical FOXP3^high Tregs, but also memory-phenotype FOXP3^low cells by manual gating. Furthermore, the proposed method successfully analyzed an independent data set, showing that the same FOXP3⁺ subpopulation was increased in melanoma patients, validating the method. Collectively, the proposed method successfully captured an important feature of melanoma without relying on the existing criteria of FOXP3⁺ T cells, revealing a hidden association between the T cell profile and melanoma, and providing new insights into FOXP3⁺ T cells and Tregs.

Treg activation defect in type 1 diabetes: correction with TNFR2 agonism

Activated T-regulatory cells (aTregs) prevent or halt various forms of autoimmunity. We show that type 1 diabetics (T1D) have a Treg activation defect through an increase in resting Tregs (rTregs, CD4⁺CD25⁺Foxp3⁺CD45RA) and decrease in aTregs (CD4⁺CD25⁺Foxp3⁺CD45RO) (n= 55 T1D, n=45 controls, P=0.01). The activation defect persists life long in T1D subjects (T1D=45, controls=45, P=0.01, P=0.04). Lower numbers of aTregs had clinical significance because they were associated with a trend for less residual C-peptide secretion from the pancreas (P=0.08), and poorer HbA1C control (P=0.03). In humans, the tumor necrosis factor receptor 2 (TNFR2) is obligatory for Treg induction, maintenance and expansion of aTregs. TNFR2 agonism is a method for stimulating Treg conversion from resting to activated. Using two separate in vitro expansion protocols, TNFR2 agonism corrected the T1D activation defect by triggering conversion of rTregs into aTregs (n=54 T1D, P<0.001). TNFR2 agonism was superior to standard protocols and TNF in proliferating Tregs. In T1D, TNFR2 agonist-expanded Tregs were homogeneous and functionally potent by virtue of suppressing autologous cytotoxic T cells in a dose-dependent manner comparable to controls. Targeting the TNFR2 receptor for Treg expansion in vitro demonstrates a means to correct the activation defect in T1D.

Establishment and Maintenance of the Human Naïve CD4+ T-Cell Compartment

The naïve CD4⁺ T-cell compartment is considered essential to guarantee immune competence throughout life. Its replenishment with naïve cells with broad diverse receptor repertoire, albeit with reduced self-reactivity, is ensured by the thymus. Nevertheless, cumulative data support a major requirement of post-thymic proliferation both for the establishment of the human peripheral naïve compartment during the accelerated somatic growth of childhood, as well as for its lifelong maintenance. Additionally, a dynamic equilibrium is operating at the cell level to fine-tune the T-cell receptor threshold to activation and survival cues, in order to counteract the continuous naïve cell loss by death or conversion into memory/effector cells. The main players in these processes are low-affinity self-peptide/MHC and cytokines, particularly IL-7. Moreover, although naïve CD4⁺ T-cells are usually seen as a homogeneous population regarding stage of maturation and cell differentiation, increasing evidence points to a variety of phenotypic and functional subsets with distinct homeostatic requirements. The paradigm of cells committed to a distinct lineage in the thymus are the naïve regulatory T-cells, but other functional subpopulations have been identified based on their time span after thymic egress, phenotypic markers, such as CD31, or cytokine production, namely IL-8. Understanding the regulation of these processes is of utmost importance to promote immune reconstitution in several clinical settings, namely transplantation, persistent infections, and aging. In this mini review, we provide an overview of the mechanisms underlying human naïve CD4⁺ T-cell homeostasis, combining clinical data, experimental studies, and modeling approaches.

Early-life compartmentalization of human T cell differentiation and regulatory function in mucosal and lymphoid tissues

It is unclear how the immune response in early life becomes appropriately stimulated to provide protection while also avoiding excessive activation as a result of diverse new antigens. T cells are integral to adaptive immunity; mouse studies indicate that tissue localization of T cell subsets is important for both protective immunity and immunoregulation. In humans, however, the early development and function of T cells in tissues remain unexplored. We present here an analysis of lymphoid and mucosal tissue T cells derived from pediatric organ donors in the first two years of life, as compared to adult organ donors, revealing early compartmentalization of T cell differentiation and regulation. Whereas adult tissues contain a predominance of memory T cells, in pediatric blood and tissues the main subset consists of naive recent thymic emigrants, with effector memory T cells (T(EM)) found only in the lungs and small intestine. Additionally, regulatory T (T(reg)) cells comprise a high proportion (30-40%) of CD4(+) T cells in pediatric tissues but are present at much lower frequencies (1-10%) in adult tissues. Pediatric tissue T(reg) cells suppress endogenous T cell activation, and early T cell functionality is confined to the mucosal sites that have the lowest T(reg):T(EM) cell ratios, which suggests control in situ of immune responses in early life.

FOXP3+ Tregs: heterogeneous phenotypes and conflicting impacts on survival outcomes in patients with colorectal cancer

The tumor microenvironment composites a mixture of immune lymphoid cells, myeloid cells, stromal cells with complex cytokines, as well as numerous lymphovascular vessels. Colorectal cancer (CRC) is a common malignancy and one of the leading causes of tumor-related death in the United States and worldwide. The immune status in the tumor microenvironment contributes to the survival of a patient with CRC. Regulatory T cells (Tregs) are considered a key factor in immune escape and immunotherapy failure among cancer patients. The transcription factor forkhead box P3 (FOXP3) is a crucial intracellular marker and also a key developmental and functional factor for CD4+CD25+ Tregs. Tregs are correlated with survival in various human neoplasms, and elevated proportions of Tregs are usually associated with unfavorable clinical outcomes. However, the role of Tregs in CRC remains controversial. High densities of tumor-infiltrating Tregs in CRC patients are reported to be correlated with worse or better outcomes. And Tregs may not be predictive of prognosis after resection of the primary tumor. The exact explanations for these discordant results remain unclear. The heterogeneous instincts of cell phenotype, gene expression, and functional activities of Tregs may partly contribute this contrasting result. Furthermore, the lack of a robust marker for identifying Tregs or due to the different techniques applied is also account. The Treg-specific demethylated region (TSDR) was recently reported to be a specific epigenetic marker for natural Tregs (nTregs), which can stably express FOXP3. The FOXP3-TSDR demethylation assay may be an promising technique for CRC-related nTregs studies.

Translating Treg Therapy in Humanized Mice

Regulatory T cells (Treg) control immune cell function as well as non-immunological processes. Their far-reaching regulatory activities suggest their functional manipulation as a means to sustainably and causally intervene with the course of diseases. Preclinical tools and strategies are however needed to further test and develop interventional strategies outside the human body. “Humanized” mouse models consisting of mice engrafted with human immune cells and tissues provide new tools to analyze human Treg ontogeny, immunobiology, and therapy. Here, we summarize the current state of humanized mouse models as a means to study human Treg function at the molecular level and to design strategies to harness these cells for therapeutic purposes.