Human regulatory T-cell development is dictated by Interleukin-2 and -15 expressed in a non-overlapping pattern in the thymus

The distinctive signature of regulatory CD4 T cells committed in the human thymus

Thymically committed regulatory CD4 T cells (tTregs) are essential for immune homeostasis and self-tolerance. We established the human tTreg Expression Signature by comparing genome-wide transcriptomic profiles between tTregs and their conventional counterparts (tTconvs). We further exploited the high sequencing depth of our bulk RNA-seq data to identify a subset of 250 genes significantly expressed in human tTregs and with neglectable expression in tTconvs, defined as below the levels of expression of IL2RA, that we named thymic Treg "private" genes. Notably, pathways related to cell motility, inflammation, and T-cell effector specification were overrepresented within the tTreg private genes. We found that 163 of these genes were significantly less expressed in circulating naïve and memory Tregs when compared to peripheral data generated in parallel. This result suggested a higher activity for most of the "private" genes in the thymus when compared to the peripheral compartments. Altogether, we provide a unique resource to inform future studies, such as for improving annotation in single-cell and spatial transcriptional data, or help in designing human studies to validate putative biomarkers for thymically committed Tregs, a priority in the field.

A backbone-based flow cytometry approach to decipher regulatory T cell trajectories in the human thymus

Thymus-committed regulatory T cells (Tregs) are essential for immune homeostasis. Recent findings stress their heterogeneity, suggesting possible alternate routes for thymic Treg development with unique features in humans, namely the clear evidence of Treg commitment at the double-positive (DP) stage and the presence of a significant population of CD8 single-positive (SP) FOXP3pos Tregs. Here, we present a dedicated analysis strategy to a spectral flow cytometry-based study of thymus from children and aged adults (≥ 74-years-old), to further elucidate Treg development and heterogeneity in the human thymus. We applied an unsupervised analysis pipeline to data generated from 6 high-dimensional panels, taking advantage of a common backbone of 11 markers, and we were able to map thymocytes along T cell maturation stages. Generating UMAP and FlowSOM cluster coordinates from the backbone, we projected all other markers onto these, characterizing clusters with the information of all markers. Focusing this analysis on events inside a putative total Treg gate, we could portray rarer subsets of human thymic Tregs and investigate their trajectories using pseudotime analysis. We uncover clusters within human DP thymocytes uniquely expressing FOXP3 or CD25, a DP-branching trajectory towards a CD103posCD8SP Tregs endpoint, and define trajectories towards CD4SP Tregs, including towards a cluster of CXCR3posCD4SP Tregs, that may consist of thymic resident or recirculating Tregs, and do not expand in the elderly. Our flow cytometry approach separates Treg populations with likely distinct functions and facilitates the design of future studies to unravel the complexity of human regulatory T cells.

Decoding mutational hotspots in human disease through the gene modules governing thymic regulatory T cells

Computational strategies to extract meaningful biological information from multiomics data are in great demand for effective clinical use, particularly in complex immune-mediated disorders. Regulatory T cells (Tregs) are essential for immune homeostasis and self-tolerance, controlling inflammatory and autoimmune processes in many diseases with a multigenic basis. Here, we quantify the Transcription Factor (TF) differential occupancy landscape to uncover the Gene Regulatory Modules governing lineage-committed Tregs in the human thymus, and show that it can be used as a tool to prioritise variants in complex diseases. We combined RNA-seq and ATAC-seq and generated a matrix of differential TF binding to genes differentially expressed in Tregs, in contrast to their counterpart conventional CD4 single-positive thymocytes. The gene loci of both established and novel genetic interactions uncovered by the Gene Regulatory Modules were significantly enriched in rare variants carried by patients with common variable immunodeficiency, here used as a model of polygenic-based disease with severe inflammatory and autoimmune manifestations. The Gene Regulatory Modules controlling the Treg signature can, therefore, be a valuable resource for variant classification, and to uncover new therapeutic targets. Overall, our strategy can also be applied in other biological processes of interest to decipher mutational hotspots in individual genomes.

Engineering antigen-presenting cells for immunotherapy of autoimmunity

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

IL-2 and IL-15 drive intrathymic development of distinct periphery-seeding CD4+Foxp3+ regulatory T lymphocytes

Development of Foxp3-expressing regulatory T-lymphocytes (Treg) in the thymus is controlled by signals delivered in T-cell precursors via the TCR, co-stimulatory receptors, and cytokine receptors. In absence of IL-2, IL-15 or their receptors, fewer Treg apparently develop in the thymus. However, it was recently shown that a substantial part of thymic Treg are cells that had recirculated from the periphery back to the thymus, troubling interpretation of these results. We therefore reassessed the involvement of IL-2 and IL-15 in the development of Treg, taking into account Treg-recirculation. At the age of three weeks, when in wt and IL-15-deficient (but not in IL-2-deficient) mice substantial amounts of recirculating Treg are present in the thymus, we found similarly reduced proportions of newly developed Treg in absence of IL-2 or IL-15, and in absence of both cytokines even less Treg developed. In neonates, when practically no recirculating Treg were found in the thymus, the absence of IL-2 led to substantially more reduced Treg-development than deficiency in IL-15. IL-2 but not IL-15 modulated the CD25, GITR, OX40, and CD73-phenotypes of the thymus-egress-competent and periphery-seeding Treg-population. Interestingly, IL-2 and IL-15 also modulated the TCR-repertoire expressed by developing Treg. Upon transfer into Treg-less Foxp3^sf mice, newly developed Treg from IL-2- (and to a much lesser extent IL-15-) deficient mice suppressed immunopathology less efficiently than wt Treg. Taken together, our results firmly establish important non-redundant quantitative and qualitative roles for IL-2 and, to a lesser extent, IL-15 in intrathymic Treg-development.

Instructive Cues of Thymic T Cell Selection

A high diversity of αβ T cell receptors (TCRs), capable of recognizing virtually any pathogen but also self-antigens, is generated during T cell development in the thymus. Nevertheless, a strict developmental program supports the selection of a self-tolerant T cell repertoire capable of responding to foreign antigens. The steps of T cell selection are controlled by cortical and medullary stromal niches, mainly composed of thymic epithelial cells and dendritic cells. The integration of important cues provided by these specialized niches, including (a) the TCR signal strength induced by the recognition of self-peptide-MHC complexes, (b) costimulatory signals, and (c) cytokine signals, critically controls T cell repertoire selection. This review discusses our current understanding of the signals that coordinate positive selection, negative selection, and agonist selection of Foxp3⁺ regulatory T cells. It also highlights recent advances that have unraveled the functional diversity of thymic antigen-presenting cell subsets implicated in T cell selection.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (third edition)

The third edition of Flow Cytometry Guidelines provides the key aspects to consider when performing flow cytometry experiments and includes comprehensive sections describing phenotypes and functional assays of all major human and murine immune cell subsets. Notably, the Guidelines contain helpful tables highlighting phenotypes and key differences between human and murine cells. Another useful feature of this edition is the flow cytometry analysis of clinical samples with examples of flow cytometry applications in the context of autoimmune diseases, cancers as well as acute and chronic infectious diseases. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid. All sections are written and peer-reviewed by leading flow cytometry experts and immunologists, making this edition an essential and state-of-the-art handbook for basic and clinical researchers.

The Multifaceted Roles of B Cells in the Thymus: From Immune Tolerance to Autoimmunity

The thymus is home to a significant number of resident B cells which possess several unique characteristics regarding their origin, phenotype and function. Evidence shows that they originate both from precursors that mature intrathymically and as the entry of recirculating mature B cells. Under steady-state conditions they exhibit hallmark signatures of activated B cells, undergo immunoglobulin class-switch, and express the Aire transcription factor. These features are imprinted within the thymus and enable B cells to act as specialized antigen-presenting cells in the thymic medulla that contribute negative selection of self-reactive T cells. Though, most studies have focused on B cells located in the medulla, a second contingent of B cells is also present in non-epithelial perivascular spaces of the thymus. This latter group of B cells, which includes memory B cells and plasma cells, is not readily detected in the thymus of infants or young mice but gradually accumulates during normal aging. Remarkably, in many autoimmune diseases the thymus suffers severe structural atrophy and infiltration of B cells in the perivascular spaces, which organize into follicles similar to those typically found in secondary lymphoid organs. This review provides an overview of the pathways involved in thymic B cell origin and presents an integrated view of both thymic medullary and perivascular B cells and their respective physiological and pathological roles in central tolerance and autoimmune diseases.

Novel Combination of Surface Markers for the Reliable and Comprehensive Identification of Human Thymic Epithelial Cells by Flow Cytometry: Quantitation and Transcriptional Characterization of Thymic Stroma in a Pediatric Cohort

Thymic epithelial cells (TECs) are essential in supporting the development of mature T cells from hematopoietic progenitor cells and facilitate their lineage-commitment, proliferation, T-cell receptor repertoire selection and maturation. While animal model systems have greatly aided in elucidating the contribution of stromal cells to these intricate processes, human tissue has been more difficult to study, partly due to a lack of suitable surface markers comprehensively defining human TECs. Here, we conducted a flow cytometry based surface marker screen to reliably identify and quantify human TECs and delineate medullary from cortical subsets. These findings were validated by transcriptomic and histologic means. The combination of EpCAM, podoplanin (pdpn), CD49f and CD200 comprehensively identified human TECs and not only allowed their reliable distinction in medullary and cortical subsets but also their detailed quantitation. Transcriptomic profiling of each subset in comparison to fibroblasts and endothelial cells confirmed the identity of the different stromal cell subsets sorted according to the proposed strategy. Our dataset not only demonstrated transcriptional similarities between TEC and cells of mesenchymal origin but furthermore revealed a subset-specific distribution of a specific set of extracellular matrix-related genes in TECs. This indicates that TECs significantly contribute to the distinct compartmentalization - and thus function - of the human thymus. We applied the strategy to quantify TEC subsets in 31 immunologically healthy children, which revealed sex-specific differences of TEC composition early in life. As the distribution of mature CD4- or CD8-single-positive thymocytes was correspondingly altered, the composition of the thymic epithelial compartment may directly impact on the CD4-CD8-lineage choice of thymocytes. We prove that the plain, reliable strategy proposed here to comprehensively identify human TEC subpopulations by flow cytometry based on surface marker expression is suitable to determine their frequency and phenotype in health and disease and allows sorting of live cells for downstream analysis. Its use reaches from a reliable diagnostic tool for thymic biopsies to improved phenotypic characterization of thymic grafts intended for therapeutic use.

Ectopic FOXP3 Expression in Combination with TGF-β1 and IL-2 Stimulation Generates Limited Suppressive Function in Human Primary Activated Thymocytes Ex Vivo

Regulatory T cells (Tregs), which are characterized by the expression of the transcription factor forkhead box P3 (FOXP3), are the main immune cells that induce tolerance and are regulators of immune homeostasis. Natural Treg cells (nTregs), described as CD4⁺CD25⁺FOXP3⁺, are generated in the thymus via activation and cytokine signaling. Transforming growth factor beta type 1 (TGF-β1) is pivotal to the generation of the nTreg lineage, its maintenance in the thymus, and to generating induced Treg cells (iTregs) in the periphery or in vitro arising from conventional T cells (Tconvs). Here, we tested whether TGF-β1 treatment, associated with interleukin-2 (IL-2) and CD3/CD28 stimulation, could generate functional Treg-like cells from human thymocytes in vitro, as it does from Tconvs. Additionally, we genetically manipulated the cells for ectopic FOXP3 expression, along with the TGF-β1 treatment. We demonstrated that TGF-β1 and ectopic FOXP3, combined with IL-2 and through CD3/CD28 activation, transformed human thymocytes into cells that expressed high levels of Treg-associated markers. However, these cells also presented a lack of homogeneous suppressive function and an unstable proinflammatory cytokine profile. Therefore, thymocyte-derived cells, activated with the same stimuli as Tconvs, were not an appropriate alternative for inducing cells with a Treg-like phenotype and function.

Specific antigen-guiding exosomes inhibit food allergies by inducing regulatory T cells

The therapies for food allergy (FA) need to be improved. The generation of inducible regulatory T cells (Tregs) can support immune tolerance in the body. This study aims to suppress experimental FA by inducing Tregs through the employment of modified exosomes (mExosomes). In this study, mExosomes were prepared by incubating dendritic cells with interleukin (IL)-2 and ovalbumin (OVA, used as a specific antigen) in the culture. Exosomes were purified from culture supernatant and used as the mExosomes. A murine FA model was developed to test the effects of mExosomes on the generation of Tregs in the mouse intestinal tissues and inhibiting FA. The results showed that mExosomes, which carried IL-2 and a complex of OVA peptide-major histocompatibility complex class II on the surface of exosomes, bound to OVA-specific CD4⁺ T cells and induced CD4⁺ T cells to differentiate into Tregs. In the FA mouse intestinal tissues, we found low IL-2 levels that were positively correlated with the number of Tregs. Depletion of IL-2 in mice prevented the generation of Tregs. The levels of peroxisome proliferator-activated receptor-γ were increased in the FA intestinal tissues with inhibited IL-2 production. Administration of mExosomes induced Tregs in the intestinal tissues and efficiently suppressed FA in mice. We conclude that the mExosomes can suppress FA in mice through inducing Tregs. The data suggest that the mExosomes have translational potential in the treatment of FA and other allergic disorders.

Epigenetic and transcriptional analysis supports human regulatory T cell commitment at the CD4+CD8+ thymocyte stage

The natural CD25+ FOXP3+ regulatory T cell (Treg) population is generated as a distinct lineage in the thymus, but the details of Treg development in humans remain unclear, and the timing of Treg commitment is also contested. Here we have analyzed the emergence of CD25+ cells at the CD4+CD8+ double positive (DP) stage in the human thymus. We show that these cells share T cell receptor repertoire with CD25+ CD4 single-positive thymocytes, believed to be committed Tregs. They already have a fully demethylated FOXP3 enhancer region and thus display stable expression of FOXP3 and the associated Treg phenotype. Transcriptome analysis also grouped the DP CD25+ and CD4 CD25+ thymocytes apart from the CD25- subsets. Together with earlier studies, our data are consistent with human Treg commitment already at the DP thymocyte stage. We suggest that the most important antigens and signals necessary for human Treg differentiation may be found in the thymic cortex.

Cryopreservation timing is a critical process parameter in a thymic regulatory T-cell therapy manufacturing protocol

Regulatory T cells (Tregs) are a promising therapy for several immune-mediated conditions but manufacturing a homogeneous and consistent product, especially one that includes cryopreservation, has been challenging. Discarded pediatric thymuses are an excellent source of therapeutic Tregs with advantages including cell quantity, homogeneity and stability. Here we report systematic testing of activation reagents, cell culture media, restimulation timing and cryopreservation to develop a Good Manufacturing Practice (GMP)-compatible method to expand and cryopreserve Tregs. By comparing activation reagents, including soluble antibody tetramers, antibody-conjugated beads and artificial antigen-presenting cells (aAPCs) and different media, we found that the combination of Dynabeads Treg Xpander and ImmunoCult-XF medium preserved FOXP3 expression and suppressive function and resulted in expansion that was comparable with a single stimulation with aAPCs. Cryopreservation tests revealed a critical timing effect: only cells cryopreserved 1-3 days, but not >3 days, after restimulation maintained high viability and FOXP3 expression upon thawing. Restimulation timing was a less critical process parameter than the time between restimulation and cryopreservation. This systematic testing of key variables provides increased certainty regarding methods for in vitro expansion and cryopreservation of Tregs. The ability to cryopreserve expanded Tregs will have broad-ranging applications including enabling centralized manufacturing and long-term storage of cell products.

Restoring self-tolerance in autoimmune diseases by enhancing regulatory T-cells

Self-tolerance, the state of unresponsiveness to self-tissues/antigens, is maintained through central and peripheral tolerance mechanisms, and a breach of these mechanisms leads to autoimmune diseases. Foxp3 + T-regulatory cells (Tregs) play an essential role in suppressing autoimmune response directed against self-antigens and thereby regulate self-tolerance. Natural Tregs are differentiated in the thymus on the basis of their higher TCR-affinity to self-antigens and migrate to the periphery where they maintain peripheral tolerance. In addition, extra-thymic differentiation of induced Tregs can occur in the periphery which can control abrupt immune responses under inflammatory conditions. A defect in Treg cell numbers and/or function is found to be associated with the development of autoimmune disease in several experimental models and human autoimmune diseases. Moreover, augmentation of Tregs has been shown to be beneficial in treating autoimmunity in preclinical models, and Treg based cellular therapy has shown initial promise in clinical trials. However, emerging studies have identified an unstable subpopulation of Tregs which expresses pro-inflammatory cytokines under both homeostatic and autoimmune conditions, as well as in ex vivo cultures. In addition, clinical translation of Treg cellular therapy is impeded by limitations such as lack of easier methods for selective expansion of Tregs and higher cost associated with GMP-facilities required for cell sorting, ex vivo expansion and infusion of ex vivo expanded Tregs. Here, we discuss the recent advances in molecular mechanisms regulating Treg differentiation, Foxp3 expression and lineage stability, the role of Tregs in the prevention of various autoimmune diseases, and critically review their clinical utility for treating human autoimmune diseases.

Common gamma chain cytokines promote regulatory T cell development and survival at the CD4+ CD8+ stage in the human thymus

Thymic commitment of human FOXP3+ regulatory T cells begins at the double-positive (DP) CD4+  CD8+ stage. In the current study, we show that interleukin-2 promotes the development of FOXP3+ thymocytes and enhances their survival at the DP phase. IL-2 increases the frequency of FOXP3+ cells and promotes the Treg phenotype after TCR-mediated positive selection at the most mature DP stage. However, it has no effect on FOXP3+ cells at the earlier maturation steps before positive selection. DP FOXP3+ thymocytes are highly susceptible to cell death but IL-2 promotes their survival. The anti-apoptotic protein BCL-2 (B Cell Lymphoma 2) is also upregulated by IL-2 at the most mature DP stage. In addition to IL-2, we identify IL-15 to have a significant role in the upregulating FOXP3 and survival of Tregs at the DP phase. IL-7 also increases the expression of BCL-2 in the DP FOXP3+ thymocytes. Our results indicate that common gamma chain cytokines IL-2, IL-7 and IL-15 promote the development of regulatory T cells at the most mature DP stage after TCR-mediated positive selection through suppressing cell death.

IL-2 and IL-15 dependent thymic development of Foxp3-expressing regulatory T lymphocytes

Immunosuppressive regulatory T lymphocytes (Treg) expressing the transcription factor Foxp3 play a vital role in the maintenance of tolerance of the immune-system to self and innocuous non-self. Most Treg that are critical for the maintenance of tolerance to self, develop as an independent T-cell lineage from common T cell precursors in the thymus. In this organ, their differentiation requires signals from the T cell receptor for antigen, from co-stimulatory molecules, as well as from cytokine-receptors. Here we focus on the cytokines implicated in thymic development of Treg, with a particular emphasis on the roles of interleukin-2 (IL-2) and IL-15. The more recently appreciated involvement of TGF-β in thymic Treg development is also briefly discussed. Finally, we discuss how cytokine-dependence of Treg development allows for temporal, quantitative, and potentially qualitative modulation of this process.

Critical role of OX40 signaling in the TCR-independent phase of human and murine thymic Treg generation

Regulatory T cells (Tregs) play a pivotal role in immune-tolerance, and loss of Treg function can lead to the development of autoimmunity. Natural Tregs generated in the thymus substantially contribute to the Treg pool in the periphery, where they suppress self-reactive effector T cells (Teff) responses. Recently, we showed that OX40L (TNFSF4) is able to drive selective proliferation of peripheral Tregs independent of canonical antigen presentation (CAP-independent) in the presence of low-dose IL-2. Therefore, we hypothesized that OX40 signaling might be integral to the TCR-independent phase of murine and human thymic Treg (tTreg) development. Development of tTregs is a two-step process: Strong T-cell receptor (TCR) signals in combination with co-signals from the TNFRSF members facilitate tTreg precursor selection, followed by a TCR-independent phase of tTreg development in which their maturation is driven by IL-2. Therefore, we investigated whether OX40 signaling could also play a critical role in the TCR-independent phase of tTreg development. OX40^-/- mice had significantly reduced numbers of CD25^-Foxp3^low tTreg precursors and CD25⁺Foxp3⁺ mature tTregs, while OX40L treatment of WT mice induced significant proliferation of these cell subsets. Relative to tTeff cells, OX40 was expressed at higher levels in both murine and human tTreg precursors and mature tTregs. In ex vivo cultures, OX40L increased tTreg maturation and induced CAP-independent proliferation of both murine and human tTregs, which was mediated through the activation of AKT-mTOR signaling. These novel findings show an evolutionarily conserved role for OX40 signaling in tTreg development and proliferation, and might enable the development of novel strategies to increase Tregs and suppress autoimmunity.

Unraveling Natural Killer T-Cells Development

Natural killer T-cells are a subset of innate-like T-cells with the ability to bridge innate and adaptive immunity. There is great interest in harnessing these cells to improve tumor therapy; however, greater understanding of invariant NKT (iNKT) cell biology is needed. The first step is to learn more about NKT development within the thymus. Recent studies suggest lineage separation of murine iNKT cells into iNKT1, iNKT2, and iNKT17 cells instead of shared developmental stages. This review will focus on these new studies and will discuss the evidence for lineage separation in contrast to shared developmental stages. The author will also highlight the classifications of murine iNKT cells according to identified transcription factors and cytokine production, and will discuss transcriptional and posttranscriptional regulations, and the role of mammalian target of rapamycin. Finally, the importance of these findings for human cancer therapy will be briefly discussed.

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.

Two separate effects contribute to regulatory T cell defect in systemic lupus erythematosus patients and their unaffected relatives

Forkhead box P3 (FoxP3)⁺ regulatory T cells (T_regs) are functionally deficient in systemic lupus erythematosus (SLE), characterized by reduced surface CD25 [the interleukin (IL)‐2 receptor alpha chain]. Low‐dose IL‐2 therapy is a promising current approach to correct this defect. To elucidate the origins of the SLE T_reg phenotype, we studied its role through developmentally defined regulatory T cell (T_reg) subsets in 45 SLE patients, 103 SLE‐unaffected first‐degree relatives and 61 unrelated healthy control subjects, and genetic association with the CD25‐encoding IL2RA locus. We identified two separate, uncorrelated effects contributing to T_reg CD25. (1) SLE patients and unaffected relatives remarkably shared CD25 reduction versus controls, particularly in the developmentally earliest CD4⁺FoxP3⁺CD45RO^–CD31⁺ recent thymic emigrant T_regs. This first component effect influenced the proportions of circulating CD4⁺FoxP3^highCD45RO⁺ activated T_regs. (2) In contrast, patients and unaffected relatives differed sharply in their activated T_reg CD25 state: while relatives as control subjects up‐regulated CD25 strongly in these cells during differentiation from naive T_regs, SLE patients specifically failed to do so. This CD25 up‐regulation depended upon IL2RA genetic variation and was related functionally to the proliferation of activated T_regs, but not to their circulating numbers. Both effects were found related to T cell IL‐2 production. Our results point to (1) a heritable, intrathymic mechanism responsible for reduced CD25 on early T_regs and decreased activation capacity in an extended risk population, which can be compensated by (2) functionally independent CD25 up‐regulation upon peripheral T_reg activation that is selectively deficient in patients. We expect that T_reg‐directed therapies can be monitored more effectively when taking this distinction into account.

Interleukin-7 promotes human regulatory T cell development at the CD4+CD8+ double-positive thymocyte stage

Although mature human FOXP3(+) regulatory T cells are CD127 (IL-7Rα) negative, CD4(+)CD8(+) FOXP3(+) thymocytes express relatively high levels of CD127 and are responsive to IL-7. However, the role of IL-7 in human regulatory T cell development is poorly known. We show that at the CD4(+)CD8(+) stage, FOXP3(+) thymocytes are highly susceptible to apoptosis, and IL-7 selectively rescues them from death, leading to an increased frequency of FOXP3(+) cells. IL-7 also promotes the development of regulatory T cell phenotype by inducing up-regulation of FOXP3(+) and CTLA-4 expression. In contrast, IL-7 does not enhance proliferation of FOXP3(+)thymocytes or induce demethylation of FOXP3(+) regulatory T cell-specific demethylated region. After the CD4(+)CD8(+) stage, the FOXP3(+) thymocytes down-regulate CD127 expression but despite very low levels of CD127, remain responsive to IL-7. These results suggest that IL-7 affects human regulatory T cell development in the thymus by at least 2 distinct mechanisms: suppression of apoptosis and up-regulation of FOXP3(+) expression.

Bee venom enhances the differentiation of human regulatory T cells

Venom-specific immunotherapy (VIT) is well recognized by its efficacy, and compelling evidence implicates regulatory T cells (Tregs) in the underlying tolerogenic mechanisms. Additionally, hymenoptera venom has for a long time been claimed to modulate immunity. Here, we investigated the putative role of bee venom (Bv) in human FOXP3-expressing Treg homeostasis and differentiation, irrespective of the donors' allergic status. We found that Bv significantly enhanced the differentiation of FOXP3-expressing cells both from conventional naïve CD4 T cells and mature CD4 thymocytes, a property that may contribute to the VIT's capacity to expand circulating Tregs in allergic individuals. We expect that our data enlightening the Treg-mediated immunomodulatory properties of Bv regardless of TCR specificity, to have application in other allergies, as well as in other clinical settings, such as autoimmunity and transplantation.

Regulatory T-Cell Development in the Human Thymus

The thymus generates a lineage-committed subset of regulatory T-cells (Tregs), best identified by the expression of the transcription factor FOXP3. The development of thymus-derived Tregs is known to require high-avidity interaction with MHC-self peptides leading to the generation of self-reactive Tregs fundamental for the maintenance of self-tolerance. Notwithstanding their crucial role in the control of immune responses, human thymic Treg differentiation remains poorly understood. In this mini-review, we will focus on the developmental stages at which Treg lineage commitment occurs, and their spatial localization in the human thymus, reviewing the molecular requirements, including T-cell receptor and cytokine signaling, as well as the cellular interactions involved. An overview of the impact of described thymic defects on the Treg compartment will be provided, illustrating the importance of these in vivo models to investigate human Treg development.

Therapeutic effect of Zhuang herb Hanyitai on duck hepatitis B

AIM: To investigate the therapeutic effect of Zhuang herb Hanyitai on liver function, viral replication, immune regulation and liver inflammation in a duck model infected by duck hepatitis B virus (DHBV).

METHODS: Duck hepatitis B was induced by intraperitoneal injection of DHBV positive serum into one-day-old Guangxi sheldrakes. On the day before treatment (T0), 7 d (T7) and 14 d (T14) during treatment, and 3 d (P3) after treatment, jugular blood and liver tissue samples were collected to detect aspartate aminotransferase (ALT), alanine aminotransferase (AST), interleukin-2 (IL-2), DHBV DNA, and liver pathology.

RESULTS: In the model group, ALT, AST and IL-2 levels were significantly increased after DHBV infection for one week and two weeks (P = 0.028, 0.036; P = 0.005, 0.04; P = 0.045), the amount of virus was relatively stable, and severe fatty degeneration was observed in liver tissues. In the lamivudine group, ALT and IL-2 levels were significantly decreased after treatment for one week and two weeks (P = 0.001, 0.042; P = 0.023), AST level showed no significant changes, the replication of virus was significantly inhibited (P = 0.034; 0.007), without rebounding after medication withdrawal for three days (P = 0.013), and liver tissue pathology showed moderate liver steatosis. In the high dose Hanyitai group, ALT, AST, and IL-2 levels were significantly reduced after treatment for one week and two weeks (P = 0.047, 0.035; P = 0.007, 0.003; P = 0.026, 0.049), the replication of virus was inhibited significantly as the lamivudine group (P = 0.025; P = 0.012; P = 0.011), and liver tissue pathology displayed moderate liver steatosis. In the usual dose Hanyitai group, ALT, AST, and IL-2 levels were significantly reduced after treatment for one week and two weeks (P = 0.015; P = 0.038; P = 0.024, 0.004), but at T14, ALT and AST level rebounded, the replication of virus was inhibited moderately, and moderate or severe steatosis was noted.

CONCLUSION: Hanyitai can reduce transaminase levels, inhibit DHBV DNA replication, and reduce IL-2 secretion in a dose-dependent manner. Hanyitai could protect liver cells, relieve hepatic steatosis, and reduce acute immunological liver injury.