Activation of CD4+CD25+ regulatory T cell suppressor function by analogs of the selecting peptide

Preceding Viral Infections Do Not Imprint Long-Term Changes in Regulatory T Cell Function

Regulatory T cells (T_regs) maintain peripheral self-tolerance and limit immune mediated pathology. Like effector T cells, T_regs can specialize in T_H1-dominated immune responses and co-express T-bet together with Foxp3. This allows for expression of CXCR3 and efficient homing to sites of T_H1 responses. However, whether such functional specialization is paralleled by memory generation among T_regs is unknown. In this study, we investigated the ability of polyclonal T_regs to form functional memory in response to viral infection. Using adoptive transfer models to compare infection-experienced T_regs generated upon acute Lymphocytic Choriomeningitis Virus (LCMV) WE and Vaccinia Virus (VV) infections with naive T_regs, we observed no differences in their phenotype or their in vivo maintenance. When comparing functional properties of infection-experienced and naive T_regs, we found no differences in in vitro suppressive capacity nor in their ability to limit the effector response upon homologous, systemic or local re-challenge in vivo. Our results suggest that no functional T_reg memory is generated in the context of systemic LCMV or VV infection, but we cannot rule out the possibility that the generation of T_reg memory may be possible in other contexts.

Human leukocyte Antigen-DM polymorphisms in autoimmune diseases

Classical MHC class II (MHCII) proteins present peptides for CD4⁺ T-cell surveillance and are by far the most prominent risk factor for a number of autoimmune disorders. To date, many studies have shown that this link between particular MHCII alleles and disease depends on the MHCII's particular ability to bind and present certain peptides in specific physiological contexts. However, less attention has been paid to the non-classical MHCII molecule human leucocyte antigen-DM, which catalyses peptide exchange on classical MHCII proteins acting as a peptide editor. DM function impacts the presentation of both antigenic peptides in the periphery and key self-peptides during T-cell development in the thymus. In this way, DM activity directly influences the response to pathogens, as well as mechanisms of self-tolerance acquisition. While decreased DM editing of particular MHCII proteins has been proposed to be related to autoimmune disorders, no experimental evidence for different DM catalytic properties had been reported until recently. Biochemical and structural investigations, together with new animal models of loss of DM activity, have provided an attractive foundation for identifying different catalytic efficiencies for DM allotypes. Here, we revisit the current knowledge of DM function and discuss how DM function may impart autoimmunity at the organism level.

Higher Sensitivity of Foxp3+ Treg Compared to Foxp3- Conventional T Cells to TCR-Independent Signals for CD69 Induction

T lymphocytes elicit specific responses after recognizing cognate antigen. However, antigen-experienced T cells can also respond to non-cognate stimuli, such as cytokines. CD4⁺ Foxp3⁺ regulatory T cells (Treg) exhibit an antigen-experienced-like phenotype. Treg can regulate T cell responses in an antigen-specific or bystander way, and it is still unclear as to which extent they rely on T cell receptor (TCR) signals. The study of the antigen response of Treg has been hampered by the lack of downstream readouts for TCR stimuli. Here we assess the effects of TCR signals on the expression of a classical marker of early T cell activation, CD69. Although it can be induced following cytokine exposure, CD69 is commonly used as a readout for antigen response on T cells. We established that upon in vitro TCR stimulation CD69 induction on Foxp3⁺ Treg cells was more dependent on signaling via soluble factors than on TCR activation. By contrast, expression of the activation marker Nur77 was only induced after TCR stimulation. Our data suggest that Treg are more sensitive to TCR-independent signals than Foxp3^- cells, which could contribute to their bystander activity.

Engineered antigen-specific human regulatory T cells: immunosuppression of FVIII-specific T- and B-cell responses

Expansion of human regulatory T cells (Tregs) for clinical applications offers great promise for the treatment of undesirable immune responses in autoimmunity, transplantation, allergy, and antidrug antibody responses, including inhibitor responses in hemophilia A patients. However, polyclonal Tregs are nonspecific and therefore could potentially cause global immunosuppression. To avoid this undesirable outcome, the generation of antigen-specific Tregs would be advantageous. Herein, we report the production and properties of engineered antigen-specific Tregs, created by transduction of a recombinant T-cell receptor obtained from a hemophilia A subject's T-cell clone, into expanded human FoxP3(+) Tregs. Such engineered factor VIII (FVIII)-specific Tregs efficiently suppressed the proliferation and cytokine production of FVIII-specific T-effector cells. Moreover, studies with an HLA-transgenic, FVIII-deficient mouse model demonstrated that antibody production from FVIII-primed spleen cells in vitro were profoundly inhibited in the presence of these FVIII-specific Tregs, suggesting potential utility to treat anti-FVIII inhibitory antibody formation in hemophilia A patients.

Epigenetic modification of FOXP3 in patients with chronic HIV infection

OBJECTIVES

HIV-1 modulates host cell epigenetic machinery to control its own replication and induce immune suppression. HIV-1 infection leads to activation of T regulatory cell (T(reg)), but the mechanism underlying this immune modulation is unclear. T(reg) plays a prominent role in gut-mucosal immune tolerance by restraining excessive effector T-cell responses, a mechanism that is known to be disturbed in chronic HIV-1 infection. DNA methylation plays a major role in T(reg) lineage commitment and immune homeostasis, which may be regulated by HIV. To investigate the mechanisms of aberrant methylation of the T(reg) marker FOXP3 in HIV-1 infection, we evaluated the expression pattern of methylation-related enzymes and its correlation to FOXP3 methylation.

METHODS

FOXP3 promoter methylation in the colon mucosa and peripheral blood from HIV-infected patients and control subjects was measured using Pyrosequencing. Gene expression pattern of DNA methylation enzymes in the colon mucosa was investigated by Microarray and quantitative reverse transcriptase-polymerase chain reaction analysis in the same subjects.

RESULTS

FOXP3 promoter was significantly (P ≤ 0.0001) demethylated in HIV-infected patients compared with control subjects in both tissues. Expression of DNA methyltransferase 1 (DNAMT1), DNA methyltransferase 1-associated protein 1(DMAP1), methyltransferase-like 7B (METTL7B), and methyltransferase-like 10 (METTL10) were significantly down regulated in HIV-infected patients compared with controls and had a significant positive correlation to FOXP3 promoter methylation.

CONCLUSIONS

We present evidence suggesting that altered methylation pattern of FOXP3 and accordingly higher T(reg) frequency in gut mucosa of HIV-infected patients may be because of aberrant methylation processing in HIV.

Regulation of interferon gamma signaling by suppressors of cytokine signaling and regulatory T cells

Regulatory T cells (Tregs) play an indispensable role in the prevention of autoimmune disease, as interferon gamma (IFNγ) mediated, lethal auto-immunity occurs (in both mice and humans) in their absence. In addition, Tregs have been implicated in preventing the onset of autoimmune and auto-inflammatory conditions associated with aberrant IFNγ signaling such as type 1 diabetes, lupus, and lipopolysaccharide (LPS) mediated endotoxemia. Notably, suppressor of cytokine signaling-1 deficient (SOCS1^−/−) mice also succumb to a lethal auto-inflammatory disease, dominated by excessive IFNγ signaling and bearing similar disease course kinetics to Treg deficient mice. Moreover SOCS1 deficiency has been implicated in lupus progression, and increased susceptibility to LPS mediated endotoxemia. Although it has been established that Tregs and SOCS1 play a critical role in the regulation of IFNγ signaling, and the prevention of lethal auto-inflammatory disease, the role of Treg/SOCS1 cross-talk in the regulation of IFNγ signaling has been essentially unexplored. This is especially pertinent as recent publications have implicated a role of SOCS1 in the stability of peripheral Tregs. This review will examine the emerging research findings implicating a critical role of the intersection of the SOCS1 and Treg regulatory pathways in the control of IFN gamma signaling and immune system function.

Human Treg responses allow sustained recombinant adeno-associated virus-mediated transgene expression

Recombinant adeno-associated virus (rAAV) vectors have shown promise for the treatment of several diseases; however, immune-mediated elimination of transduced cells has been suggested to limit and account for a loss of efficacy. To determine whether rAAV vector expression can persist long term, we administered rAAV vectors expressing normal, M-type α-1 antitrypsin (M-AAT) to AAT-deficient subjects at various doses by multiple i.m. injections. M-specific AAT expression was observed in all subjects in a dose-dependent manner and was sustained for more than 1 year in the absence of immune suppression. Muscle biopsies at 1 year had sustained AAT expression and a reduction of inflammatory cells compared with 3 month biopsies. Deep sequencing of the TCR Vβ region from muscle biopsies demonstrated a limited number of T cell clones that emerged at 3 months after vector administration and persisted for 1 year. In situ immunophenotyping revealed a substantial Treg population in muscle biopsy samples containing AAT-expressing myofibers. Approximately 10% of all T cells in muscle were natural Tregs, which were activated in response to AAV capsid. These results suggest that i.m. delivery of rAAV type 1-AAT (rAAV1-AAT) induces a T regulatory response that allows ongoing transgene expression and indicates that immunomodulatory treatments may not be necessary for rAAV-mediated gene therapy.

Autologous regulatory T cells for the treatment of type 1 diabetes

The immune system is tasked with defending the host from a wide array of pathogens and environmental insults. When uncontrolled, this endeavor may lead to off-target reactivity to self-tissues resulting in multiple autoimmune diseases including type 1 diabetes (T1D). This multifactorial disease process involves over 40 susceptibility genes and is influenced by poorly characterized environmental factors. While many questions regarding the pathogenesis of the disease process remain, it has become increasingly clear that the progression to disease results from a breakdown in the processes that maintain peripheral immune tolerance. The end result of this process is localized tissue inflammation, islet dysfunction, and ultimately the destruction of pancreatic β cells due to concomitant defects in innate and adaptive immune responses. A number of immunomodulatory intervention trials have now been conducted in patients at risk for or with recent onset T1D, often with the goal of restoring immune tolerance by inducing regulatory T cells (Tregs). Unfortunately, many of these trials have fallen short of inducing persistent immune regulation. This shortfall has led to additional efforts to more directly shift the balance from destructive effector T cell (Teff) responses to favor Tregs, including the use of autologous Treg cell therapy. In this review we will discuss key concepts related to the use of autologous Treg cell therapy for the treatment of T1D. Among these topics, we will discuss the notions of genetic control of Treg activity, Treg cellular plasticity, and requirements for antigen-specificity.

How specificity for self-peptides shapes the development and function of regulatory T cells

The cataclysmic disease that develops in mice and humans lacking CD4+ T cells expressing the transcription factor Foxp3 has provided abundant evidence that Foxp3+CD4+ Tregs are required to suppress a latent autoreactivity of the immune system. There is also evidence for the existence of tissue-specific Tregs that can act to suppress regional autoimmune responses, suggesting that Tregs exert their effects, in part, through responding to self-peptides. However, how the immune system generates a repertoire of Tregs that is designed to recognize and direct regulatory function to self-peptides is incompletely understood. This review describes studies aimed at determining how T cell recognition of self-peptide(s) directs Treg formation in the thymus, including discussion of a modified "avidity" model of thymocyte development. Studies aimed at determining how TCR specificity contributes to the ability of Tregs to suppress autoimmune diseases are also discussed.

Mammalian target of rapamycin inhibition and alloantigen-specific regulatory T cells synergize to promote long-term graft survival in immunocompetent recipients

Minimization of immunosuppression and donor-specific tolerance to MHC-mismatched organ grafts are important clinical goals. The therapeutic potential of regulatory T cells (Tregs) has been demonstrated, but conditions for optimizing their in vivo function posttransplant in nonlymphocyte-depleted hosts remain undefined. In this study, we address mechanisms through which inhibition of the mammalian target of rapamycin (Rapa) synergizes with alloantigen-specific Treg (AAsTreg) to permit long-term, donor-specific heart graft survival in immunocompetent hosts. Crucially, immature allogeneic dendritic cells allowed AAsTreg selection in vitro, with minimal expansion of unwanted (Th17) cells. The rendered Treg potently inhibited T cell proliferation in an Ag-specific manner. However, these AAsTreg remained unable to control T cells stimulated by allogeneic mature dendritic cells, a phenomenon dependent on the release of proinflammatory cytokines. In vivo, Rapa administration reduced danger-associated IL-6 production, T cell proliferation, and graft infiltration. Based on these observations, AAsTreg were administered posttransplant (day 7) in combination with a short course of Rapa and rendered >80% long-term (>150 d) graft survival, a result superior to that achieved with polyclonal Treg. Moreover, graft protection was alloantigen-specific. Significantly, long-term graft survival was associated with alloreactive T cell anergy. These findings delineate combination of transient mammalian target of Rapa inhibition with appropriate AAsTreg selection as an effective approach to promote long-term organ graft survival.

Regulatory T-cell counter-regulation by innate immunity is a barrier to transplantation tolerance

Innate immune signals foster adaptive immunity through activation of antigen-presenting cells. Recent in vitro evidence suggests that innate signaling may also contribute to immunity by countering the effects of regulatory T cells (T-regs), counter-regulation. We present in vivo evidence using a transgenic skin allograft model that the function of T-regs is lost in the setting of acute skin transplantation but remains intact when grafts were transplanted 1 month prior to allow surgery-induced inflammation to abate. Our findings identify T-reg counter-regulation as a naturally occurring process that accompanies transplantation and an important barrier to T-reg-mediated tolerance. Our finding further highlights the central role of regulatory cell deactivation in the initiation of the immune response.

Systemic targeting of CpG-ODN to the tumor microenvironment with anti-neu-CpG hybrid molecule and T regulatory cell depletion induces memory responses in BALB-neuT tolerant mice

We have shown that neu transgenic mice are immunotolerant and that immunizations with dendritic cells (DC) pulsed with neu-derived antigens were not able to control tumor growth in these animals. We tested whether, by modulating the tumor microenvironment with Toll-like receptor ligands, it could be possible to induce the activation of antitumor responses in neu mice. Our results indicate that only intratumoral (i.t.) injections of CpG-ODN induce an antitumor response in neu mice. To target the CpG-ODN to the tumor site anywhere within the body, we chemically conjugated an anti-Her-2/neu monoclonal antibody (mAb) with CpG-ODN. The anti-neu-CpG hybrid molecule retained its ability to bind to Her-2/neu(+) tumors, activate DCs, and induce antitumor responses. Our results indicated that injections of anti-neu-CpG induced the rejection of primary tumors in 100% of BALB/c mice and only in approximately 30% of BALB-neuT mice. After challenging the BALB/c and BALB-neuT mice, we observed that BALB/c mice developed a protective memory response; in contrast, BALB-neuT mice succumbed to the challenge. After injections of anti-neu-CpG, T regulatory cells (T-reg) were drastically reduced at the tumor site, but a large number were still present in the lymphoid organs. When BALB-neuT mice were treated with anti-neu-CpG plus anti-GITR mAb, but not with anti-CD25 mAb, 100% of the BALB-neuT mice rejected the primary tumor and developed a protective memory response indicating the critical role of T-regs in regulating the repertoire against self antigens. Taken together, these results indicate that CpG-ODN-targeted therapy and depletion of T-regs optimally activate a primary response and generate a protective memory response against self-tumor antigens.

What roles do regulatory T cells play in the control of the adaptive immune response?

The immune system, like many systems responsive to specific stimuli, requires feedback regulation. The key regulatory element determining antigen-specific responsiveness is the effector T helper. As the response tends to overshoot, a feedback control of the magnitude of the response is critical to avoid immunopathology. This is the proposed role of the effector T suppressor (T(s)). The reasons for this interpretation of the data are discussed as are the reasons that the competing postulate is ruled out, namely that T(s) function in determining the self-non-self-discrimination. The regulatory T cell family consists of two lineages, T helpers and T(s). Differentiated derivatives of the T helper lineage drive the expression and amplification of specific classes of defensive effector cells. T(s) feedback to limit the magnitude of the process so that debilitating immunopathology is acceptably infrequent.

The role of regulatory T cells in chronic and acute viral infections

Regulatory T cells, a subset of CD4(+) T lymphocytes, play a pivotal role in the maintenance of the balance between the tissue-damaging and protective effects of the immune response. These cells have immunosuppressive function and have been intensely studied in the context of autoimmunity, cancer, allergies, asthma, and infectious diseases. Their role in chronic and persistent viral infections is well appreciated. In acute viral infections, the function of these cells is still unclear. The host and pathogen factors that control the generation and activity of regulatory T cells and the role of these cells in modulating expansion, contraction, and development of immune memory in acute respiratory virus infection need to be further elucidated.

CD4+CD25+ regulatory T cell repertoire formation shaped by differential presentation of peptides from a self-antigen

We have used TCR transgenic mice directed to different MHC class II-restricted determinants from the influenza virus hemagglutinin (HA) to analyze how specificity for self-peptides can shape CD4+CD25+ regulatory T (Treg) cell formation. We show that substantial increases in the number of CD4+CD25+ Treg cells can occur when an autoreactive TCR directed to a major I-E(d)-restricted determinant from HA develops in mice expressing HA as a self-Ag, and that the efficiency of this process is largely unaffected by the ability to coexpress additional TCR alpha-chains. This increased formation of CD4+CD25+ Treg cells in the presence of the self-peptide argues against models that postulate selective survival rather than induced formation as mechanisms of CD4+CD25+ Treg cell formation. In contrast, T cells bearing a TCR directed to a major I-A(d)-restricted determinant from HA underwent little or no selection to become CD4+CD25+ Treg cells in mice expressing HA as a self-Ag, correlating with inefficient processing and presentation of the peptide from the neo-self-HA polypeptide. These findings show that interactions with a self-peptide can induce thymocytes to differentiate along a pathway to become CD4+CD25+ Treg cells, and that peptide editing by DM molecules may help bias the CD4+CD25+ Treg cell repertoire away from self-peptides that associate weakly with MHC class II molecules.

Regulatory T cell-like responses in deer mice persistently infected with Sin Nombre virus

Hantavirus cardiopulmonary syndrome is a zoonotic illness associated with a systemic inflammatory immune response, capillary leak, noncardiogenic pulmonary edema, and shock in humans. Cytokines, including TNF, IFN-gamma, and lymphotoxin, are thought to contribute to its pathogenesis. In contrast, infected rodent reservoirs of hantaviruses experience few or no pathologic changes and the host rodent can remain persistently infected for life. Generally, it is unknown why such dichotomous immune responses occur between humans and reservoir hosts. Thus, we examined CD4(+) T cell responses from one such reservoir, the deer mouse (Peromyscus maniculatus), infected with Sin Nombre virus. Proliferation responses to viral nucleocapsid antigen were relatively weak in T cells isolated from deer mice, regardless of acute or persistent infection. The T cells from acutely infected deer mice synthesized a broad spectrum of cytokines, including IFN-gamma, IL-4, IL-5, and TGF-beta(1), but not TNF, lymphotoxin, or IL-17. However, in T cells from persistently infected deer mice, only TGF-beta(1) was expressed by all lines, whereas some expressed reduced levels of IFN-gamma or IL-5. The Forkhead box P3 transcription factor, a marker of some regulatory T cells, was expressed by most of these cells. Collectively, these data suggest that TGF-beta(1)-expressing regulatory T cells may play an important role in limiting immunopathology in the natural reservoir host, but this response may interfere with viral clearance. Such a response may have arisen as a mutually beneficial coadaptive evolutionary event between hantaviruses and their rodent reservoirs, so as to limit disease while also allowing the virus to persist.

Nonself-antigens are the cognate specificities of Foxp3+ regulatory T cells

The majority of regulatory Foxp3+CD4+ T cells naturally arises in the thymus. It has been proposed that T cell receptors (TCRs) on these cells recognize self-MHC class II-peptide complexes with high or higher affinity and that their specificities mirror specificities of autoreactive T cells. Here, we analyzed hundreds of TCRs derived from regulatory or nonregulatory T cells and found little evidence that the former population preferably recognizes self-antigens as agonists. Instead, these cells recognized foreign MHC-peptide complexes as often as nonregulatory T cells. Our results show that high-affinity, autoreactive TCRs are rare on all CD4+ T cells and suggest that selecting self-peptide is different from the peptide that activates the same regulatory T cells in the periphery.