Thymic regulatory T cells arise via two distinct developmental programs.

The developmental programs that generate a broad repertoire of regulatory T cells (Treg cells) able to respond to both self antigens and non-self antigens remain unclear. Here we found that mature Treg cells were generated through two distinct developmental programs involving CD25+ Treg cell progenitors (CD25+ TregP cells) and Foxp3lo Treg cell progenitors (Foxp3lo TregP cells). CD25+ TregP cells showed higher rates of apoptosis and interacted with thymic self antigens with higher affinity than did Foxp3lo TregP cells, and had a T cell antigen receptor repertoire and transcriptome distinct from that of Foxp3lo TregP cells. The development of both CD25+ TregP cells and Foxp3lo TregP cells was controlled by distinct signaling pathways and enhancers. Transcriptomics and histocytometric data suggested that CD25+ TregP cells and Foxp3lo TregP cells arose by coopting negative-selection programs and positive-selection programs, respectively. Treg cells derived from CD25+ TregP cells, but not those derived from Foxp3lo TregP cells, prevented experimental autoimmune encephalitis. Our findings indicate that Treg cells arise through two distinct developmental programs that are both required for a comprehensive Treg cell repertoire capable of establishing immunotolerance.

Regulatory T cells: exosomes deliver tolerance.

T regulatory (Treg) cells enforce peripheral tolerance through regulation of diverse immune responses in a context-specific manner. Okoye et al. show one way that Treg cells suppress Th1 cell responses is through nonautonomous gene silencing mediated by microRNA-containing exosomes.

Enteric defensins are essential regulators of intestinal microbial ecology.

Antimicrobial peptides are important effectors of innate immunity throughout the plant and animal kingdoms. In the mammalian small intestine, Paneth cell alpha-defensins are antimicrobial peptides that contribute to host defense against enteric pathogens. To determine if alpha-defensins also govern intestinal microbial ecology, we analyzed the intestinal microbiota of mice expressing a human alpha-defensin gene (DEFA5) and in mice lacking an enzyme required for the processing of mouse alpha-defensins. In these complementary models, we detected significant alpha-defensin-dependent changes in microbiota composition, but not in total bacterial numbers. Furthermore, DEFA5-expressing mice had striking losses of segmented filamentous bacteria and fewer interleukin 17 (IL-17)-producing lamina propria T cells. Our data ascribe a new homeostatic role to alpha-defensins in regulating the makeup of the commensal microbiota.

Foxp3: shades of tolerance.

In this issue of Immunity, Darce et al. (2012) and Bettini et al. (2012) demonstrate that seemingly subtle alterations in the interaction of Foxp3 with its transcriptional partners have a ripple effect on the outcome of autoimmune phenotypes, worsening some while ameliorating others.

Regulatory T Cells Control PF4/Heparin Antibody Production in Mice.

Heparin-induced thrombocytopenia is a relatively common drug-induced immune disorder that can have life-threatening consequences for affected patients. Immune complexes consisting of heparin, platelet factor 4 (PF4), and PF4/heparin-reactive Abs are central to the pathogenesis of heparin-induced thrombocytopenia. Regulatory T (Treg) cells are a subpopulation of CD4 T cells that play a key role in regulating immune responses, but their role in controlling PF4/heparin-specific Ab production is unknown. In the studies described in this article, we found that Foxp3-deficient mice lacking functional Treg cells spontaneously produced PF4/heparin-specific Abs. Following transplantation with bone marrow cells from Foxp3-deficient but not wild-type mice, Rag1-deficient recipients also produced PF4/heparin-specific Abs spontaneously. Adoptively transferred Treg cells prevented spontaneous production of PF4/heparin-specific Abs in Foxp3-deficient mice and inhibited PF4/heparin complex-induced production of PF4/heparin-specific IgGs in wild-type mice. Treg cells suppress immune responses mainly through releasing anti-inflammatory cytokines, such as IL-10. IL-10-deficient mice spontaneously produced PF4/heparin-specific Abs. Moreover, bone marrow chimeric mice with CD4 T cell-specific deletion of IL-10 increased PF4/heparin-specific IgG production upon PF4/heparin complex challenge. Short-term IL-10 administration suppresses PF4/heparin-specific IgG production in wild-type mice. Taken together, these findings demonstrate that Treg cells play an important role in suppressing PF4/heparin-specific Ab production.

A requisite role for induced regulatory T cells in tolerance based on expanding antigen receptor diversity.

Although both natural and induced regulatory T (nTreg and iTreg) cells can enforce tolerance, the mechanisms underlying their synergistic actions have not been established. We examined the functions of nTreg and iTreg cells by adoptive transfer immunotherapy of newborn Foxp3-deficient mice. As monotherapy, only nTreg cells prevented disease lethality, but did not suppress chronic inflammation and autoimmunity. Provision of Foxp3-sufficient conventional T cells with nTreg cells reconstituted the iTreg pool and established tolerance. In turn, acute depletion of iTreg cells in rescued mice resulted in weight loss and inflammation. Whereas the transcriptional signatures of nTreg and in vivo-derived iTreg cells were closely matched, there was minimal overlap in their T cell receptor (TCR) repertoires. Thus, iTreg cells are an essential nonredundant regulatory subset that supplements nTreg cells, in part by expanding TCR diversity within regulatory responses.

Blockade of interleukin-27 signaling reduces GVHD in mice by augmenting Treg reconstitution and stabilizing Foxp3 expression.

Reestablishment of competent regulatory pathways has emerged as a strategy to reduce the severity of graft-versus-host disease (GVHD), and recalibrate the effector and regulatory arms of the immune system. However, clinically feasible, cost-effective strategies that do not require extensive ex vivo cellular manipulation have remained elusive. In the current study, we demonstrate that inhibition of the interleukin-27p28 (IL-27p28) signaling pathway through antibody blockade or genetic ablation prevented lethal GVHD in multiple murine transplant models. Moreover, protection from GVHD was attributable to augmented global reconstitution of CD4+ natural regulatory T cells (nTregs), CD4+ induced Tregs (iTregs), and CD8+ iTregs, and was more potent than temporally concordant blockade of IL-6 signaling. Inhibition of IL-27p28 also enhanced the suppressive capacity of adoptively transferred CD4+ nTregs by increasing the stability of Foxp3 expression. Notably, blockade of IL-27p28 signaling reduced T-cell-derived-IL-10 production in conventional T cells; however, there was no corresponding effect in CD4+ or CD8+ Tregs, indicating that IL-27 inhibition had differential effects on IL-10 production and preserved a mechanistic pathway by which Tregs are known to suppress GVHD. Targeting of IL-27 therefore represents a novel strategy for the in vivo expansion of Tregs and subsequent prevention of GVHD without the requirement for ex vivo cellular manipulation, and provides additional support for the critical proinflammatory role that members of the IL-6 and IL-12 cytokine families play in GVHD biology.

Alternatively Activated Macrophages Boost Induced Regulatory T and Th17 Cell Responses during Immunotherapy for Colitis.

Induced regulatory T (iTreg) and Th17 cells promote mucosal homeostasis. We used a T cell transfer model of colitis to compare the capacity of iTreg and Th17 cells to develop in situ following the transfer of naive CD4(+)CD45RB(hi)T cells intoRag1(-/-)C57BL/6 or BALB/c mice, the prototypical Th1/M1- and Th2/M2-prone strains. We found that the frequency and number of Foxp3(+)iTreg cells and Th17 cells were significantly reduced in C57BL/6 mice compared with the BALB/c strain. C57BL/6 mice with colitis were also resistant to natural Treg cell immunotherapy. Pretreatment of C57BL/6Rag1(-/-)mice with IL-4 plus IL-13, or with M2a but not M1 macrophages, dramatically increased the generation of iTreg and Th17 cells. Importantly, M2a transfers, either as a pretreatment or in mice with established colitis, allowed successful immunotherapy with natural Treg cells. M2a macrophages also reduced the generation of pathogenic iTreg cells that lost Foxp3 expression, suggesting that they stabilize the expression of Foxp3. Thus, polarized M2a macrophages drive a directionally concordant expansion of the iTreg-Th17 cell axis and can be exploited as a therapeutic adjuvant in cell-transfer immunotherapy to re-establish mucosal tolerance.

Chronic follicular bronchiolitis requires antigen-specific regulatory T cell control to prevent fatal disease progression.

To study regulatory T (Treg) cell control of chronic autoimmunity in a lymphoreplete host, we created and characterized a new model of autoimmune lung inflammation that targets the medium and small airways. We generated transgenic mice that express a chimeric membrane protein consisting of hen egg lysozyme and a hemoglobin epitope tag under the control of the Clara cell secretory protein promoter, which largely limited transgene expression to the respiratory bronchioles. When Clara cell secretory protein-membrane hen egg lysozyme/hemoglobin transgenic mice were crossed to N3.L2 TCR transgenic mice that recognize the hemoglobin epitope, the bigenic progeny developed dense, pseudo-follicular lymphocytic peribronchiolar infiltrates that resembled the histological pattern of follicular bronchiolitis. Aggregates of activated IFN-γ- and IL-17A-secreting CD4(+) T cells as well as B cells surrounded the airways. Lung pathology was similar in Ifng(-/-) and Il17a(-/-) mice, indicating that either cytokine is sufficient to establish chronic disease. A large number of Ag-specific Treg cells accumulated in the lesions, and Treg cell depletion in the affected mice led to an interstitial spread of the disease that ultimately proved fatal. Thus, Treg cells act to restrain autoimmune responses, resulting in an organized and controlled chronic pathological process rather than a progressive disease.

Mice with an absent stress response are protected against ischemic renal injury.

Inducible heat shock proteins (HSPs), regulated by heat shock factor-1 (HSF-1), protect against renal cell injury in vitro. To determine whether HSPs ameliorate ischemic renal injury in vivo, HSF-1 functional knockout mice (HSF-KO) were compared with wild-type mice following bilateral ischemic renal injury. Following injury, the kidneys of wild-type mice had the expected induction of HSP70 and HSP25; a response absent in the kidneys of HSF-KO mice. Baseline serum creatinine was equivalent between strains. Serum creatinine at 24 h reflow in HSF-KO mice was significantly lower than that in the wild type. Histology showed similar tubule injury in both strains after ischemic renal injury but increased medullary vascular congestion in wild-type compared with HSF-KO mice. Flow cytometry of mononuclear cells isolated from kidneys showed no difference between strains in the number of CD4(+) and CD8(+) T cells in sham-operated animals. At 1 h of reflow, CD4(+) and CD8(+) cells were doubled in the kidneys of wild-type but not HSF-KO mice. Foxp3(+) T-regulatory cells were significantly more abundant in the kidneys of sham-operated HSF-KO than wild-type mice. Suppression of CD25(+)Foxp3(+) cells in HSF-KO kidneys with the anti-CD25 antibody PC61 reversed the protection against ischemic renal injury. Thus, HSF-KO mice are protected from ischemic renal injury by a mechanism that depends on an increase in the T-regulatory cells in the kidney associated with altered T-cell infiltration early in reflow. Hence, stress response activation may contribute to early injury by facilitating T-cell infiltration into ischemic kidney.

CD8+ Foxp3+ regulatory T cells are induced during graft-versus-host disease and mitigate disease severity.

Regulatory T cells (Tregs), in particular CD4(+) Foxp3(+) T cells, have been shown to play an important role in the maintenance of tolerance after allogeneic stem cell transplantation. In the current study, we have identified a population of CD8(+) Foxp3(+) T cells that are induced early during graft-versus-host disease (GVHD), constitute a significant percentage of the entire Treg population, and are present in all major GVHD target organs. These cells expressed many of the same cell surface molecules as found on CD4(+) Tregs and potently suppressed in vitro alloreactive T cell responses. Induction of these cells correlated positively with the degree of MHC disparity between donor and recipient and was significantly greater than that observed for CD4(+)-induced Tregs (iTregs) in nearly all tissue sites. Mice that lacked the ability to make both CD8(+) and CD4(+) iTregs had accelerated GVHD mortality compared with animals that were competent to make both iTreg populations. The absence of both iTreg populations was associated with significantly greater expansion of activated donor T cells and increased numbers of CD4(+) and CD8(+) T cells that secreted IFN-γ and IL-17. The presence of CD8(+) iTregs, however, was sufficient to prevent increased GVHD mortality in the complete absence of CD4(+) Tregs, indicating at least one functional iTreg population was sufficient to prevent an exacerbation in GVHD severity, and that CD8(+) iTregs could compensate for CD4(+) iTregs. These studies define a novel population of CD8(+) Tregs that play a role in mitigating the severity of GVHD after allogeneic stem cell transplantation.

A novel IL-10-independent regulatory role for B cells in suppressing autoimmunity by maintenance of regulatory T cells via GITR ligand.

B cells are important for the regulation of autoimmune responses. In experimental autoimmune encephalomyelitis (EAE), B cells are required for spontaneous recovery in acute models. Production of IL-10 by regulatory B cells has been shown to modulate the severity EAE and other autoimmune diseases. Previously, we suggested that B cells regulated the number of CD4(+)Foxp3(+) T regulatory cells (Treg) in the CNS during EAE. Because Treg suppress autoimmune responses, we asked whether B cells control autoimmunity by maintenance of Treg numbers. B cell deficiency achieved either genetically (µMT) or by depletion with anti-CD20 resulted in a significant reduction in the number of peripheral but not thymic Treg. Adoptive transfer of WT B cells into µMT mice restored both Treg numbers and recovery from EAE. When we investigated the mechanism whereby B cells induce the proliferation of Treg and EAE recovery, we found that glucocorticoid-induced TNF ligand, but not IL-10, expression by B cells was required. Of clinical significance is the finding that anti-CD20 depletion of B cells accelerated spontaneous EAE and colitis. Our results demonstrate that B cells play a major role in immune tolerance required for the prevention of autoimmunity by maintenance of Treg via their expression of glucocorticoid-induced TNFR ligand.

The TCR repertoires of regulatory and conventional T cells specific for the same foreign antigen are distinct.

The relationship between the TCR repertoires of natural regulatory T cells (nTregs) and conventional CD4(+) T cells (Tconv) capable of responding to the same antigenic epitope is unknown. In this study, we used TCRß-chain transgenic mice to generate polyclonal nTreg and Tconv populations specific for a foreign Ag. CD4(+) T cells from immunized 3.L2ß(+/-) TCRα(+/-) Foxp3(EGFP) mice were restimulated in culture to yield nTregs (EGFP(+)) and Tconv (EGFP(-)) defined by their antigenic reactivity. Relative to Tconv, nTreg expansion was delayed, although a higher proportion of viable nTregs had divided after 72 h. Spectratype analysis revealed that both the nTreg and Tconv responses were different and characterized by skewed distributions of CDR3 lengths. CDR3 sequences from nTregs displayed a divergent pattern of Jα usage, minimal CDR3 overlap (3.4%), and less diversity than did CDR3 sequences derived from Tconv. These data indicate that foreign Ag-specific nTregs and Tconv are clonally distinct and that foreign Ag-specific nTreg populations are constrained by a limited TCR repertoire.

IL-10 produced by induced regulatory T cells (iTregs) controls colitis and pathogenic ex-iTregs during immunotherapy.

"Natural" regulatory T cells (nTregs) that express the transcription factor Foxp3 and produce IL-10 are required for systemic immunological tolerance. "Induced" regulatory T cells (iTregs) are nonredundant and essential for tolerance at mucosal surfaces, yet their mechanisms of suppression and stability are unknown. We investigated the role of iTreg-produced IL-10 and iTreg fate in a treatment model of inflammatory bowel disease. Colitis was induced in Rag1(-/-) mice by the adoptive transfer of naive CD4(+) T cells carrying a nonfunctional Foxp3 allele. At the onset of weight loss, mice were treated with both iTregs and nTregs where one marked subset was selectively IL-10 deficient. Body weight assessment, histological scoring, cytokine analysis, and flow cytometry were used to monitor disease activity. Transcriptional profiling and TCR repertoire analysis were used to track cell fate. When nTregs were present but IL-10 deficient, iTreg-produced IL-10 was necessary and sufficient for the treatment of disease, and vice versa. Invariably, ∼85% of the transferred iTregs lost Foxp3 expression (ex-iTregs) but retained a portion of the iTreg transcriptome, which failed to limit their pathogenic potential upon retransfer. TCR repertoire analysis revealed no clonal relationships between iTregs and ex-iTregs, either within mice or between mice treated with the same cells. These data identify a dynamic IL-10-dependent functional reciprocity between regulatory T cell subsets that maintains mucosal tolerance. The niche supporting stable iTregs is limited and readily saturated, which promotes a large population of ex-iTregs with pathogenic potential during immunotherapy.

Corrigendum: Patients with juvenile idiopathic arthritis have decreased clonal diversity in the CD8+ T cell repertoire response to influenza vaccination.

[This corrects the article DOI: 10.3389/fimmu.2024.1306490.].

Patients with juvenile idiopathic arthritis have decreased clonal diversity in the CD8+ T cell repertoire response to influenza vaccination.

Recurrent exposures to a pathogenic antigen remodel the CD8+ T cell compartment and generate a functional memory repertoire that is polyclonal and complex. At the clonotype level, the response to the conserved influenza antigen, M158-66 has been well characterized in healthy individuals, but not in patients receiving immunosuppressive therapy or with aberrant immunity, such as those with juvenile idiopathic arthritis (JIA). Here we show that patients with JIA have a reduced number of M158-66 specific RS/RA clonotypes, indicating decreased clonal richness and, as a result, have lower repertoire diversity. By using a rank-frequency approach to analyze the distribution of the repertoire, we found several characteristics of the JIA T cell repertoire to be akin to repertoires seen in healthy adults, including an amplified RS/RA-specific antigen response, representing greater clonal unevenness. Unlike mature repertoires, however, there is more fluctuation in clonotype distribution, less clonotype stability, and more variable IFNy response of the M158-66 specific RS/RA clonotypes in JIA. This indicates that functional clonal expansion is altered in patients with JIA on immunosuppressive therapies. We propose that the response to the influenza M158-66 epitope described here is a general phenomenon for JIA patients receiving immunosuppressive therapy, and that the changes in clonal richness and unevenness indicate a retarded and uneven generation of a mature immune response.

BATF is Required for Treg Homeostasis and Stability to Prevent Autoimmune Pathology.

Regulatory T (Treg) cells are inevitable to prevent deleterious immune responses to self and commensal microorganisms. Treg function requires continuous expression of the transcription factor (TF) FOXP3 and is divided into two major subsets: resting (rTregs) and activated (aTregs). Continuous T cell receptor (TCR) signaling plays a vital role in the differentiation of aTregs from their resting state, and in their immune homeostasis. The process by which Tregs differentiate, adapt tissue specificity, and maintain stable phenotypic expression at the transcriptional level is still inconclusivei. In this work, the role of BATF is investigated, which is induced in response to TCR stimulation in naïve T cells and during aTreg differentiation. Mice lacking BATF in Tregs developed multiorgan autoimmune pathology. As a transcriptional regulator, BATF is required for Treg differentiation, homeostasis, and stabilization of FOXP3 expression in different lymphoid and non-lymphoid tissues. Epigenetically, BATF showed direct regulation of Treg-specific genes involved in differentiation, maturation, and tissue accumulation. Most importantly, FOXP3 expression and Treg stability require continuous BATF expression in Tregs, as it regulates demethylation and accessibility of the CNS2 region of the Foxp3 locus. Considering its role in Treg stability, BATF should be considered an important therapeutic target in autoimmune disease.

Requirements for growth and IL-10 expression of highly purified human T regulatory cells.

Human regulatory T cells (T(R)) cells have potential for the treatment of a variety of immune mediated diseases but the anergic phenotype of these cells makes them difficult to expand in vitro. We have examined the requirements for growth and cytokine expression from highly purified human T(R) cells, and correlated these findings with the signal transduction events of these cells. We demonstrate that these cells do not proliferate or secrete IL-10 even in the presence of high doses of IL-2. Stimulation with a superagonistic anti-CD28 antibody (clone 9.3) and IL-2 partially reversed the proliferative defect, and this correlated with reversal of the defective calcium mobilization in these cells. Dendritic cells were effective at promoting T(R) cell proliferation, and under these conditions the proliferative capacity of T(R) cells was comparable to conventional CD4 lymphocytes. Blocking TGF-ß activity abrogated IL-10 expression from these cells, while addition of TGF-ß resulted in IL-10 production. These data demonstrate that highly purified populations of T(R) cells are anergic even in the presence of high doses of IL-2. Furthermore, antigen presenting cells provide proper co-stimulation to overcome the anergic phenotype of T(R) cells, and under these conditions they are highly sensitive to IL-2. In addition, these data demonstrate for the first time that TGF-ß is critical to enable human T(R) cells to express IL-10.

1,25-Dihydroxyvitamin D3 acts directly on the T lymphocyte vitamin D receptor to inhibit experimental autoimmune encephalomyelitis.

Multiple sclerosis (MS) is an incurable autoimmune neurodegenerative disease. Environmental factors may be key to MS prevention and treatment. MS prevalence and severity decrease with increasing sunlight exposure and vitamin D(3) supplies, supporting our hypothesis that the sunlight-dependent hormone, 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2) D(3) ), inhibits autoimmune T-cell responses in MS. Moreover, 1,25-(OH)(2) D(3) inhibits and reverses experimental autoimmune encephalomyelitis (EAE), an MS model. Here, we investigated whether 1,25-(OH)(2) D(3) inhibits EAE via the vitamin D receptor (VDR) in T lymphocytes. Using bone marrow chimeric mice with a disrupted VDR only in radio-sensitive hematopoietic cells or radio-resistant non-hematopoietic cells, we found that hematopoietic cell VDR function was necessary for 1,25-(OH)(2) D(3) to inhibit EAE. Furthermore, conditional targeting experiments showed that VDR function in T cells was necessary. Neither 1,25-(OH)(2) D(3) nor T-cell-specific VDR targeting influenced CD4(+) Foxp3(+) T-cell proportions in the periphery or the CNS in these studies. These data support a model wherein 1,25-(OH)(2) D(3) acts directly on pathogenic CD4(+) T cells to inhibit EAE.

Targeting transmembrane-domain-less MOG expression to platelets prevents disease development in experimental autoimmune encephalomyelitis.

Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease of the central nervous system with no cure yet. Here, we report genetic engineering of hematopoietic stem cells (HSCs) to express myelin oligodendrocyte glycoprotein (MOG), specifically in platelets, as a means of intervention to induce immune tolerance in experimental autoimmune encephalomyelitis (EAE), the mouse model of MS. The platelet-specific αIIb promoter was used to drive either a full-length or truncated MOG expression cassette. Platelet-MOG expression was introduced by lentivirus transduction of HSCs followed by transplantation. MOG protein was detected on the cell surface of platelets only in full-length MOG-transduced recipients, but MOG was detected in transmembrane-domain-less MOG1-157-transduced platelets intracellularly. We found that targeting MOG expression to platelets could prevent EAE development and attenuate disease severity, including the loss of bladder control in transduced recipients. Elimination of the transmembrane domains of MOG significantly enhanced the clinical efficacy in preventing the onset and development of the disease and induced CD4+Foxp3+ Treg cells in the EAE model. Together, our data demonstrated that targeting transmembrane domain-deleted MOG expression to platelets is an effective strategy to induce immune tolerance in EAE, which could be a promising approach for the treatment of patients with MS autoimmune disease.