CD8+ T cell-mediated suppression of autoimmunity in a murine lupus model of peptide-induced immune tolerance depends on Foxp3 expression

Research progress on CD8+ T cell immune regulation in allogenic transplantation

With advances in tissue typing, organ preservation techniques, and clinical surgery, organ transplantation has gained popularity as a treatment option for various end-stage diseases. Allogeneic transplantation has been widely adopted and extensively researched in clinical practice. Despite significant breakthroughs and progress in immunosuppression, this procedure is still associated with several adverse reactions and complications. Therefore, there is a continuing need to explore new immunological approaches to provide fresh insights and guidance for clinical transplantation. CD8+ T cells, traditionally known for their cytotoxic function and their ability to recognize transplanted organs as "non-self" entities, display cytotoxicity. However, recent studies have unveiled that CD8+ T cells have various subtypes and functions that extend beyond conventional cytotoxicity. These CD8+ T cell subtypes include Effector CD8+ T cells, Memory CD8+ T cells, and CD8Treg cells. This review examines the immune regulatory mechanisms of CD8+ T cells in allogeneic transplantation and discusses the potential applications of CD8+ T cells in treating tumors in transplant recipients who are receiving immunosuppressive therapy. These findings offer theoretical guidance for reducing post-transplant rejection reactions and improving adverse prognoses, offering new hope for improved clinical survival rate.

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

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

Bischoff D, S Singh S, H. Hahn B. Peptide-based immunotherapy in lupus: Where are we now?

In autoimmune rheumatic diseases, immune hyperactivity and chronic inflammation associate with immune dysregulation and the breakdown of immune self-tolerance. A continued, unresolved imbalance between effector and regulatory immune responses further exacerbates inflammation that ultimately causes tissue and organ damage. Many treatment modalities have been developed to restore the immune tolerance and immmunoregulatory balance in autoimmune rheumatic diseases, including the use of peptide-based therapeutics or the use of nanoparticles-based nanotechnology. This review summarizes the state-of-the-art therapeutic use of peptide-based therapies in autoimmune rheumatic diseases, with a specific focus on lupus.

Selective CD28 blockade impacts T cell differentiation during homeostatic reconstitution following lymphodepletion

Introduction

Costimulation blockade targeting the CD28 pathway provides improved long-term renal allograft survival compared to calcineurin inhibitors but may be limited as CTLA-4-Ig (abatacept, belatacept) blocks both CD28 costimulation and CTLA-4 coinhibition. Directly targeting CD28 while leaving CTLA-4 intact may provide a mechanistic advantage. Fc-silent non-crosslinking CD28 antagonizing domain antibodies (dAb) are currently in clinical trials for renal transplantation. Given the current standard of care in renal transplantation at most US centers, it is likely that lymphodepletion via thymoglobulin induction therapy could be used in patients treated with CD28 antagonists. Thus, we investigated the impact of T cell depletion (TCD) on T cell phenotype following homeostatic reconstitution in a murine model of skin transplantation treated with anti-CD28dAb.

Methods

Skin from BALB/cJ donors was grafted onto C56BL/6 recipients which were treated with or without 0.2mg anti-CD4 and 10μg anti-CD8 one day prior to transplant and with or without 100μg anti-CD28dAb on days 0, 2, 4, 6, and weekly thereafter. Mice were euthanized six weeks post-transplant and lymphoid cells were analyzed by flow cytometry.

Results

Anti-CD28dAb reversed lymphopenia-induced differentiation of memory CD4+ T cells in the spleen and lymph node compared to TCD alone. Mice treated with TCD+anti-CD28dAb exhibited significantly improved skin graft survival compared to anti-CD28dAb alone, which was also improved compared to no treatment. In addition, the expression of CD69 was reduced on CD4+ and CD8+ T cells in the spleen and lymph node from mice that received TCD+anti-CD28dAb compared to TCD alone. While a reduced frequency of CD4+FoxP3+ T cells was observed in anti-CD28dAb treated mice relative to untreated controls, this was balanced by an increased frequency of CD8+Foxp3+ T cells that was observed in the blood and kidney of mice given TCD+anti-CD28dAb compared to TCD alone.

Discussion

These data demonstrate that CD28 signaling impacts the differentiation of both CD4+ and CD8+ T cells during homeostatic reconstitution following lymphodepletion, resulting in a shift towards fewer activated memory T cells and more CD8+FoxP3+ T cells, a profile that may underpin the observed prolongation in allograft survival.

Nature vs. nurture: FOXP3, genetics, and tissue environment shape Treg function

The importance of regulatory T cells (Tregs) in preventing autoimmunity has been well established; however, the precise alterations in Treg function in autoimmune individuals and how underlying genetic associations impact the development and function of Tregs is still not well understood. Polygenetic susceptibly is a key driving factor in the development of autoimmunity, and many of the pathways implicated in genetic association studies point to a potential alteration or defect in regulatory T cell function. In this review transcriptomic control of Treg development and function is highlighted with a focus on how these pathways are altered during autoimmunity. In combination, observations from autoimmune mouse models and human patients now provide insights into epigenetic control of Treg function and stability. How tissue microenvironment influences Treg function, lineage stability, and functional plasticity is also explored. In conclusion, the current efficacy and future direction of Treg-based therapies for Type 1 Diabetes and other autoimmune diseases is discussed. In total, this review examines Treg function with focuses on genetic, epigenetic, and environmental mechanisms and how Treg functions are altered within the context of autoimmunity.

Identification and Contribution of Inflammation-Induced Novel MicroRNA in the Pathogenesis of Systemic Lupus Erythematosus

Recently microRNAs (miRNAs) have been recognized as powerful regulators of many genes and pathways involved in the pathogenesis of inflammatory diseases including Systemic Lupus Erythematosus (SLE). SLE is an autoimmune disease characterized by production of various autoantibodies, inflammatory immune cells, and dysregulation of epigenetic changes. Several candidate miRNAs regulating inflammation and autoimmunity in SLE are described. In this study, we found significant increases in the expression of miR21, miR25, and miR186 in peripheral blood mononuclear cells (PBMCs) of SLE patients compared to healthy controls. However, miR146a was significantly decreased in SLE patients compared to healthy controls and was negatively correlated with plasma estradiol levels and with SLE disease activity scores (SLEDAI). We also found that protein levels of IL-12 and IL-21 were significantly increased in SLE patients as compared to healthy controls. Further, our data shows that protein levels of IL-12 were positively correlated with miR21 expression and protein levels of IL-21 positively correlated with miR25 and miR186 expression in SLE patients. In addition, we found that levels of miR21, miR25, and miR186 positively correlated with SLEDAI and miR146a was negatively correlated in SLE patients. Thus, our data shows a dynamic interplay between disease pathogenesis and miRNA expression. This study has translational potential and may identify novel therapeutic targets in patients with SLE.

Cytolytic CD4+ and CD8+ Regulatory T-Cells and Implications for Developing Immunotherapies to Combat Graft-Versus-Host Disease

Regulatory T-cells (Treg) are critical for the maintenance of immune homeostasis and tolerance induction. While the immunosuppressive mechanisms of Treg have been extensively investigated for decades, the mechanisms responsible for Treg cytotoxicity and their therapeutic potential in regulating immune responses have been incompletely explored and exploited. Conventional cytotoxic T effector cells (Teffs) are known to be important for adaptive immune responses, particularly in the settings of viral infections and cancer. CD4+ and CD8+ Treg subsets may also share similar cytotoxic properties with conventional Teffs. Cytotoxic effector Treg (cyTreg) are a heterogeneous population in the periphery that retain the capacity to suppress T-cell proliferation and activation, induce cellular apoptosis, and migrate to tissues to ensure immune homeostasis. The latter can occur through several cytolytic mechanisms, including the Granzyme/Perforin and Fas/FasL signaling pathways. This review focuses on the current knowledge and recent advances in our understanding of cyTreg and their potential application in the treatment of human disease, particularly Graft-versus-Host Disease (GVHD).

Cellular and Molecular Phenotypes of pConsensus Peptide (pCons) Induced CD8+ and CD4+ Regulatory T Cells in Lupus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease with widespread inflammation, immune dysregulation, and is associated with the generation of destructive anti-DNA autoantibodies. We have shown previously the immune modulatory properties of pCons peptide in the induction of both CD4⁺ and CD8⁺ regulatory T cells which can in turn suppress development of the autoimmune disease in (NZB/NZW) F1 (BWF1) mice, an established model of lupus. In the present study, we add novel protein information and further demonstrate the molecular and cellular phenotypes of pCons-induced CD4⁺ and CD8⁺ T_reg subsets. Flow cytometry analyses revealed that pCons induced CD8⁺ T_reg cells with the following cell surface molecules: CD25^highCD28^{high and low} subsets (shown earlier), CD62L^high, CD122^low, PD1^low, CTLA4^low, CCR7^low and 41BB^high. Quantitative real-time PCR (qRT-PCR) gene expression analyses revealed that pCons-induced CD8⁺ T_reg cells downregulated the following several genes: Regulator of G protein signaling (RGS2), RGS16, RGS17, BAX, GPT2, PDE3b, GADD45β and programmed cell death 1 (PD1). Further, we confirmed the down regulation of these genes by Western blot analyses at the protein level. To our translational significance, we showed herein that pCons significantly increased the percentage of CD8⁺FoxP3⁺ T cells and further increased the mean fluorescence intensity (MFI) of FoxP3 when healthy peripheral blood mononuclear cells (PBMCs) are treated with pCons (10 μg/ml, for 24-48 hours). In addition, we found that pCons reduced apoptosis in CD4⁺ and CD8⁺ T cells and B220⁺ B cells of BWF1 lupus mice. These data suggest that pCons stimulates cellular, immunological, and molecular changes in regulatory T cells which in turn protect against SLE autoimmunity.

Interferon Genes Are Influenced by 17β-Estradiol in SLE

Recent evidence suggests the existence of a nexus between inflammatory pathways and the female sex hormone 17β-estradiol, resulting in increased interferon-stimulated genes (ISGs), autoantibodies, and dysregulation of immune cells in SLE. However, the molecular mechanisms and the effect of estradiol on candidate target genes and their pathways remains poorly understood. Our previous work suggests that female SLE patients have increased estradiol levels compared to healthy controls. In the present study, we explored the effects of 17β-estradiol treatment on expression of IFN (interferons)-stimulated genes and pro-inflammatory cytokines/chemokines. We found significantly increased (5-10-fold) expression of IFN-regulated genes in healthy females. Furthermore, we found significantly increased plasma levels of IL-6, IL-12, IL-17, IL-18, stem cell factor (SCF), and IL-21/IL-23 in SLE patients compared to healthy controls, and those levels positively correlated with the plasma levels of 17β-estradiol. In addition, levels of IL-21 positively correlated with the SLE disease activity index (SLEDAI) score of SLE patients. In vitro treatment of PBMCs from either SLE patients or healthy controls with 17β-estradiol at physiological concentration (~50 pg/ml) also significantly increased secretion of many pro-inflammatory cytokines and chemokines (IL-6, IL-12, IL-17, IL-8, IFN-γ; MIP1α, and MIP1β) in both groups. Further our data revealed that 17β-estradiol significantly increased the percentage of CD3⁺CD69⁺ and CD3⁺IFNγ⁺ T cells; whereas, simultaneous addition of 17β-estradiol and an ERα inhibitor prevented this effect. Collectively, our findings indicate that 17β-estradiol participates in the induction of pro-inflammatory cytokines and chemokines and further influences interferon genes and pathways.

Harnessing CD8+CD28- Regulatory T Cells as a Tool to Treat Autoimmune Disease

T regulatory cell therapy presents a novel therapeutic strategy for patients with autoimmune diseases or who are undergoing transplantation. At present, the CD4+ Treg population has been extensively characterized, as a result of defined phenotypic and functional readouts. In this review article, we discuss the development and biology of CD8+ Tregs and their role in murine and human disease indications. A subset of CD8+ Tregs that lack the surface expression of CD28 (CD8+CD28- Treg) has proved efficacious in preclinical models. CD8+CD28- Tregs are present in healthy individuals, but their impaired functionality in disease renders them less effective in mediating immunosuppression. We primarily focus on harnessing CD8+ Treg cell therapy in the clinic to support current treatment for patients with autoimmune or inflammatory conditions.

CD8+ T regulatory cells in lupus

T regulatory cells (Tregs) have a key role in the maintenance of immune homeostasis and the regulation of immune tolerance by preventing the inflammation and suppressing the autoimmune responses. Numerical and functional deficits of these cells have been reported in systemic lupus erythematosus (SLE) patients and mouse models of SLE, where their imbalance and dysregulated activities have been reported to significantly influence the disease pathogenesis, progression and outcomes. Most studies in SLE have focused on CD4+ Tregs and it has become clear that a critical role in the control of immune tolerance after the breakdown of self-tolerance is provided by CD8+ Tregs. Here we review the role, cellular and molecular phenotypes, and mechanisms of action of CD8+ Tregs in SLE, including ways to induce these cells for immunotherapeutic modulation in SLE.

The role of CD8+ T-cell systemic lupus erythematosus pathogenesis: an update

PURPOSE OF REVIEW

Systemic lupus erythematosus (SLE) is a serious autoimmune disease with a wide range of organ involvement. In addition to aberrant B-cell responses leading to autoantibody production, T-cell abnormalities are important in the induction of autoimmunity and the ensuing downstream organ damage. In this article, we present an update on how subsets of CD8+ T cells contribute to SLE pathogenesis.

RECENT FINDINGS

Reduced cytolytic function of CD8+ T cells not only promotes systemic autoimmunity but also accounts for the increased risk of infections. Additional information suggests that effector functions of tissue CD8+ T cells contribute to organ damage. The phenotypic changes in tissue CD8+ T cells likely arise from exposure to tissue microenvironment and crosstalk with tissue resident cells. Research on pathogenic IL-17-producing double negative T cells also suggests their origin from autoreactive CD8+ T cells, which also contribute to the induction and maintenance of systemic autoimmunity.

SUMMARY

Reduced CD8+ T-cell effector function illustrates their role in peripheral tolerance in the control of autoimmunity and to the increased risk of infections. Inflammatory cytokine producing double negative T cells and functional defects of regulatory CD8+ T cell both contribute to SLE pathogenesis. Further in depth research on these phenotypic changes are warranted for the development of new therapeutics for people with SLE.

Effects of Peptide-Induced Immune Tolerance on Murine Lupus

The regulation of autoimmunity and the molecular mechanisms by which different immune cells, including T cells, polymorphonuclear leukocytes (PMN-granulocytes), and B cells suppress autoimmune diseases is complex. We have shown previously that BWF1 lupus mice are protected from autoimmunity after i.v. injection or oral administration of tolerogenic doses of pCons, an artificial synthetic peptide based on sequences containing MHC class I and MHC class II determinants in the VH region of a J558-encoded BWF1 anti-DNA Ab. Several T cell subsets can transfer this tolerance. In this study, we determined the potential roles of granulocytes, B cells and regulatory T cells altered by pCons treatment in the BWF1 (NZB/NZW) mouse model of lupus. Immunophenotyping studies indicated that pCons treatment of BWF1 mice significantly increased CD4⁺FoxP3⁺ T cells, reduced the percent of B cells expressing CD19⁺CD5⁺ but increased the percent of CD19⁺CD1d⁺ regulatory B cells and increased the ability of the whole B cell population to suppress IgG anti-DNA production in vitro. pCons treatment significantly decreased the expression of CTLA-4 (cytotoxic T-lymphocyte-associated protein-4) in CD8⁺ T cells. In addition, peptide administration modified granulocytes so they became suppressive. We co-cultured sorted naïve B cells from mice making anti-DNA Ab (supported by addition of sorted naive CD4⁺ and CD8⁺ T cells from young auto-antibody-negative BWF1 mice) with sorted B cells or granulocytes from tolerized mice. Both tolerized granulocytes and tolerized B cells significantly suppressed the production of anti-DNA in vitro. In granulocytes from tolerized mice compared to saline-treated littermate controls, real-time PCR analysis indicated that expression of interferon-induced TNFAIP2 increased more than 2-fold while Ptdss2 and GATA1 mRNA were up-regulated more than 10-fold. In contrast, expression of these genes was significantly down-regulated in tolerized B cells. Further, another IFN-induced protein, Bcl2, was reduced in tolerized B cells as determined by Western blot analyses. In contrast, expression of FoxP3 was significantly increased in tolerized B cells. Together, these data suggest that B cells and granulocytes are altered toward suppressive functions by in vivo tolerization of BWF1 mice with pCons and it is possible these cell types participate in the clinical benefits seen in vivo.

Sex Hormones and Gender Influence the Expression of Markers of Regulatory T Cells in SLE Patients

Regulatory T cells have been implicated in the regulation and maintenance of immune homeostasis. Whether gender and sex hormones differentially influence the expression and function of regulatory T cell phenotype and their influence on FoxP3 expression remains obscure. We provide evidence in this study that the number and percent of human regulatory T cells (T_regs) expressing CD4⁺ and CD8⁺ are significantly reduced in healthy females compared to healthy males. In addition, both CD4⁺CD25^+hi and CD8⁺CD25^+hi subsets in healthy males have a 2-3 fold increase in FoxP3 mRNA expression compared to healthy females. Female SLE patients, compared to healthy women, have elevated plasma levels of estradiol and decreased levels of testosterone. Higher levels of testosterone correlate with higher expression of FoxP3 in CD4⁺CD25^hiCD127^low putative T_regs in women with SLE. Incubation of CD4⁺ regulatory T cells with 17β-estradiol at physiological levels generally decreased FoxP3 expression in females with SLE. These data suggest that females may be more susceptible than males to SLE and other autoimmune diseases in part because they have fewer T_regs and reduced FoxP3 expression within those cells due to normal E2 levels which suppress FoxP3 expression. In addition, low levels of plasma testosterone in women may further reduce the ability of the T_regs to express FoxP3. These data suggest that gender and sex hormones can influence susceptibility to SLE via effects on regulatory T cells and FoxP3 expression.

CD8+ Tregs revisited: A heterogeneous population with different phenotypes and properties

Regulatory T cells (Tregs) play a key role in the peripheral self-tolerance and preventing autoimmunity. While classical CD4⁺ Foxp3⁺ Tregs are well established, their CD8⁺ counterparts are still controversial in many aspects including their phenotypic identity and their mechanisms of suppression. Because of these controversies and because of only a limited number of studies documenting the immunoregulatory function of CD8⁺ Tregs in vivo, the concept of CD8⁺ Tregs is still not unanimously accepted. We propose that any T-cell subset considered as true regulatory must be distinguishable from other cell types and must suppress in vivo immune responses via a known mechanism. In this article, we revisit the concept of CD8⁺ Tregs by focusing on the characterization of individual CD8⁺ T-cell subsets with proposed regulatory capacity separately. Therefore, we review the phenotype and function of CD8⁺ FOXP3⁺ T cells, CD8⁺ CD122⁺ T cells, CD8⁺ CD28^low/- T cells, CD8⁺ CD45RC^low T cells, T cells expressing CD8αα homodimer and Qa-1-restricted CD8⁺ T cells to show whether there is sufficient evidence to establish these subsets as bona fide Tregs. Based on the intrinsic ability of CD8⁺ Treg subsets to promote immune tolerance in animal models, we elaborate on their potential use in clinics.

CD8+ T cells: The past and future of immune regulation

Regulation of the adaptive immune response is critical for health. Regulatory activity can be found in multiple components of the immune system, however, the focus on particular components of the immune regulatory network has left many aspects of this critical immune component understudied. Here we review the evidence for activities of CD8+ T cells in immune homeostasis and regulation of autoimmune reactivity. The heterogeneous nature of identified CD8+ cell types are examined, and common phenotypes associated with functional activities are defined. The varying types of antigen signal crucial for CD8+ T cell regulatory activity are identified and the implications of these activation pathways for control of adaptive responses is considered. Finally, the promising capacity for transgenic antigen receptor directed cytotoxicity as a mechanism for modulation of autoimmunity is detailed.

Peptide-Based Vaccination Therapy for Rheumatic Diseases

Rheumatic diseases are extremely heterogeneous diseases with substantial risks of morbidity and mortality, and there is a pressing need in developing more safe and cost-effective treatment strategies. Peptide-based vaccination is a highly desirable strategy in treating noninfection diseases, such as cancer and autoimmune diseases, and has gained increasing attentions. This review is aimed at providing a brief overview of the recent advances in peptide-based vaccination therapy for rheumatic diseases. Tremendous efforts have been made to develop effective peptide-based vaccinations against rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), while studies in other rheumatic diseases are still limited. Peptide-based active vaccination against pathogenic cytokines such as TNF-α and interferon-α (IFN-α) is shown to be promising in treating RA or SLE. Moreover, peptide-based tolerogenic vaccinations also have encouraging results in treating RA or SLE. However, most studies available now have been mainly based on animal models, while evidence from clinical studies is still lacking. The translation of these advances from experimental studies into clinical therapy remains impeded by some obstacles such as species difference in immunity, disease heterogeneity, and lack of safe delivery carriers or adjuvants. Nevertheless, advances in high-throughput technology, bioinformatics, and nanotechnology may help overcome these impediments and facilitate the successful development of peptide-based vaccination therapy for rheumatic diseases.

Future prospects for CD8+ regulatory T cells in immune tolerance

CD8⁺ Tregs have been long described and significant progresses have been made about their phenotype, their functional mechanisms, and their suppressive ability compared to conventional CD4⁺ Tregs. They are now at the dawn of their clinical use. In this review, we will summarize their phenotypic characteristics, their mechanisms of action, the similarities, differences and synergies between CD8⁺ and CD4⁺ Tregs, and we will discuss the biology, development and induction of CD8⁺ Tregs, their manufacturing for clinical use, considering open questions/uncertainties and future technically accessible improvements notably through genetic modifications.

Suppression of Murine Lupus by CD4+ and CD8+ Treg Cells Induced by T Cell-Targeted Nanoparticles Loaded With Interleukin-2 and Transforming Growth Factor β

OBJECTIVE

To develop a nanoparticle (NP) platform that can expand both CD4+ and CD8+ Treg cells in vivo for the suppression of autoimmune responses in systemic lupus erythematosus (SLE).

METHODS

Poly(lactic-co-glycolic acid) (PLGA) NPs encapsulating interleukin-2 (IL-2) and transforming growth factor β (TGFβ) were coated with anti-CD2/CD4 antibodies and administered to mice with lupus-like disease induced by the transfer of DBA/2 T cells into (C57BL/6 × DBA/2)F₁ (BDF1) mice. The peripheral frequency of Treg cells was monitored ex vivo by flow cytometry. Disease progression was assessed by measuring serum anti-double-stranded DNA antibody levels by enzyme-linked immunosorbent assay. Kidney disease was defined as the presence of proteinuria or renal histopathologic features.

RESULTS

Anti-CD2/CD4 antibody-coated, but not noncoated, NPs encapsulating IL-2 and TGFβ induced CD4+ and CD8+ FoxP3+ Treg cells in vitro. The optimal dosing regimen of NPs for expansion of CD4+ and CD8+ Treg cells was determined in in vivo studies in mice without lupus and then tested in BDF1 mice with lupus. The administration of anti-CD2/CD4 antibody-coated NPs encapsulating IL-2 and TGFβ resulted in the expansion of CD4+ and CD8+ Treg cells, a marked suppression of anti-DNA antibody production, and reduced renal disease.

CONCLUSION

This study shows for the first time that T cell-targeted PLGA NPs encapsulating IL-2 and TGFβ can expand both CD4+ and CD8+ Treg cells in vivo and suppress murine lupus. This approach, which enables the expansion of Treg cells in vivo and inhibits pathogenic immune responses in SLE, could represent a potential new therapeutic modality in autoimmune conditions characterized by impaired Treg cell function associated with IL-2 deficiency.

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.

Bim regulates the survival and suppressive capability of CD8+ FOXP3+ regulatory T cells during murine GVHD

CD8⁺ Foxp3⁺ T cells (Tregs) are a potent regulatory population whose functional and ontological similarities to CD4⁺ Fox3⁺ T cells have not been well delineated. Using an experimental model of graft-versus-host disease (GVHD), we observed that CD8⁺ Tregs were significantly less potent than CD4⁺ Tregs for the suppression of GVHD. To define the mechanistic basis for this observation, we examined the T-cell repertoire and the transcriptional profile of in vivo-derived CD4⁺ and CD8⁺ Tregs that emerged early during this disease. Polyclonal and alloantigen-induced CD8⁺ Tregs had repertoire diversity that was similar to that of conventional CD8⁺ T cells, indicating that a restricted repertoire was not the proximate cause of decreased suppression. Transcriptional profiling revealed that CD8⁺ Tregs possessed a canonical Treg transcriptional signature that was similar to that observed in CD4⁺ Tregs, yet distinct from conventional CD8⁺ T cells. Pathway analysis, however, demonstrated that CD8⁺ Tregs had differential gene expression in pathways involved in cell death and survival. This was further confirmed by detailed mRNA sequence analysis and protein expression studies, which demonstrated that CD8⁺ Tregs had increased expression of Bim and reduced expression of Mcl-1. Transplantation with CD8⁺ Foxp3⁺ Bim^-/- Tregs resulted in prolonged Treg survival and reduced GVHD lethality compared with wild-type CD8⁺ Tregs, providing functional confirmation that increased expression of Bim was responsible for reduced in vivo efficacy. Thus, Bim regulates the survival and suppressive capability of CD8⁺ Tregs, which may have implications for their use in regulatory T-cell therapy.

Overview of the immune system

The immune system is designed to execute rapid, specific, and protective responses against foreign pathogens. To protect against the potentially harmful effects of autoreactive escapees that might arise during the course of the immune response, multiple tolerance checkpoints exist in both the primary and secondary lymphoid organs. Regardless, autoantibodies targeting neural antigens exist in multiple neurologic diseases. The goal of this introductory chapter is to provide a foundation of the major principles and components of the immune system as a framework to understanding autoimmunity and autoimmune neurologic disorders. A broad overview of: (1) innate mechanisms of immunity and their contribution in demyelinating diseases; (2) B and T lymphocytes as effector arms of the adaptive immune response and their contribution to the pathophysiology of neurologic diseases; and (3) emerging therapeutic modalities for treatment of autoimmune disease is provided.

Regulatory T Cells Are Critical for Clearing Influenza A Virus in Neonatal Mice

We previously reported that neonatal mice infected with influenza A virus (IAV) develop interstitial pneumonia characterized by reduced lung cytokine and chemokine responses. The failure of T cells to infiltrate the airways of neonates correlated with delayed clearance of sublethal IAV infections compared to adults. We hypothesized that negative regulators in the neonatal lungs such as cytokines or T regulatory (Treg) cells are responsible for these differences. Neonates either deficient in interleukin-10 (IL-10) or with T cells unresponsive to transforming growth factor-β signaling due to absence of SMAD family member 4 (Smad4) had similar IAV clearance kinetics to wild-type pups and no difference in T-cell responses. In contrast, functional depletion of Treg cells with anti-CD25 monoclonal antibody resulted in increased proportions of activated CD4(+) T cells in the lungs, but failure to clear IAV. Similarly, scurfy pups (mutation in forkhead box P3 [Foxp3] rendering them deficient in Treg cells) had increased proportions of activated T cells in the lungs compared to littermate controls. Scurfy pups also had increased proportions of IL-13-producing CD4(+) T cells. Interestingly, like anti-CD25-treated pups, scurfy pups had significantly elevated viral loads compared to controls. Based on these data, we conclude that Tregs are critical for clearance of IAV in neonatal mice.

Human and Mouse CD8(+)CD25(+)FOXP3(+) Regulatory T Cells at Steady State and during Interleukin-2 Therapy

In addition to CD4⁺ regulatory T cells (Tregs), CD8⁺ suppressor T cells are emerging as an important subset of regulatory T cells. Diverse populations of CD8⁺ T cells with suppressive activities have been described. Among them, a small population of CD8⁺CD25⁺FOXP3⁺ T cells is found both in mice and humans. In contrast to thymic-derived CD4⁺CD25⁺FOXP3⁺ Tregs, their origin and their role in the pathophysiology of autoimmune diseases (AIDs) are less understood. We report here the number, phenotype, and function of CD8⁺ Tregs cells in mice and humans, at the steady state and in response to low-dose interleukin-2 (IL-2). CD8⁺ Tregs represent approximately 0.4 and 0.1% of peripheral blood T cells in healthy humans and mice, respectively. In mice, their frequencies are quite similar in lymph nodes (LNs) and the spleen, but two to threefold higher in Peyer patches and mesenteric LNs. CD8⁺ Tregs express low levels of CD127. CD8⁺ Tregs express more activation or proliferation markers such as CTLA-4, ICOS, and Ki-67 than other CD8⁺ T cells. In vitro, they suppress effector T cell proliferation as well as or even better than CD4⁺ Tregs. Owing to constitutive expression of CD25, CD8⁺ Tregs are 20- to 40-fold more sensitive to in vitro IL-2 stimulation than CD8⁺ effector T cells, but 2–4 times less than CD4⁺ Tregs. Nevertheless, low-dose IL-2 dramatically expands and activates CD8⁺ Tregs even more than CD4⁺ Tregs, in mice and humans. Further studies are warranted to fully appreciate the clinical relevance of CD8⁺ Tregs in AIDs and the efficacy of IL-2 treatment.

Mislocalization of the interferon inducible protein IFI16 by environmental insults: implications in autoimmunity

The nuclear DNA sensor IFI16, a member of PYHIN family of proteins, was previously studied for its role in cell cycle regulation, tumor suppression, apoptosis and DNA damage signaling. Autoantibodies against IFI16 are prevalent in the sera of patients with systemic autoimmunity, thus depicting physiological significance as an autoantigen. At present, the nuclear IFI16 protein has been thoroughly investigated for its role as an innate immune sensor involved in inflammasome signaling and viral restriction. While the sub-cellular localization of IFI16 during such events has been known, very little knowledge about its presence and significance in the extracellular space is available. Recently our group has discovered the presence of circulating IFI16 in the sera from systemic autoimmune patients indicating that in this setting it may be mislocalized form its nuclear site and secreted in the extracellular milieu. In this review, we will discuss the leakage of endogenous IFI16 that has been experimentally proved using in vivo and in vitro models. Also we will comment on the significance of mislocalized inflammasome components in the extracellular space and how it can be responsible for chronic inflammation.

The mouse idd2 locus is linked to the proportion of immunoregulatory double-negative T cells, a trait associated with autoimmune diabetes resistance

Autoimmune diseases result from a break in immune tolerance. Various mechanisms of peripheral tolerance can protect against autoimmunity, including immunoregulatory CD4(-)CD8(-) double-negative (DN) T cells. Indeed, we have previously shown that diabetes-prone mouse strains exhibit a low proportion of DN T cells relative to that of diabetes-resistant mice, and that a single autologous transfer of DN T cells can impede autoimmune diabetes development, at least in the 3A9 TCR transgenic setting. In this study, we aim to understand the genetic basis for the difference in DN T cell proportion between diabetes-resistant and diabetes-prone mice. We thus perform an unbiased linkage analysis in 3A9 TCR F2 (NOD.H2(k) × B10.BR) mice and reveal that a locus on chromosome 9, which coincides with Idd2, is linked to the proportion of DN T cells in the lymph nodes. We generate two NOD.H2(k).B10-Chr9 congenic mouse strains and validate the role of this genetic interval in defining the proportion of DN T cells. Moreover, we find that the increased proportion of DN T cells in lymphoid organs is associated with a decrease in both diabetes incidence and serum IgG Ab levels. Together, the data suggest that Idd2 is linked to DN T cell proportion and that a physiological increase in DN T cell number may be sufficient to confer resistance to autoimmune diabetes. Altogether, these findings could help identify new candidate genes for the development of therapeutic avenues aimed at modulating DN T cell number for the prevention of autoimmune diseases.

CD4+CD25(high), CD8+CD28- cells and thyroid autoantibodies in breast cancer patients

Aim of the study

To investigate the percentage of CD4+CD25^high cells (including Treg cells) and CD8+CD28– cells in breast cancer patients with and without high levels of autoimmune thyroid antibodies.

Material and methods

Thirty-five women with breast cancer (9 of them having high thyroid antibodies) and fourteen healthy subjects were enrolled in this study. Flow cytometry was used to count CD4+CD25^high cells and CD8+CD28– suppressive cells (CD8 cell subtypes).

Results

In the patient group, the percentage of CD28– cells in CD8+ lymphocytes were higher [67.50% (55.1180.33) vs. 51.56% (42.5766.38); p = 0.021] and the percentage of CD28+CD45RO– cells (memory cells) in CD8+ lymphocytes were lower than in the control group. CD4+CD25^high cell percentage in CD4+ lymphocytes was elevated in the patient group [6.44% (4.528.74) vs. 2.97% (1.724.34); p < 0.001]. When the cytometric parameters were compared between patients (with high vs. normal thyroid antibodies), the distribution of CD8+ cell subgroups was also similar. CD4+CD25^high cells among CD4+ lymphocytes were decreased in patients with high levels of thyroid antibodies [5.19% (3.426.17) vs. 6.99% (4.829.95); p = 0.043].

Conclusions

CD4+CD25^high cells may play a role in autoimmunity of breast cancer patients, and may be a predictive marker. Advanced studies which evaluate the possible links between regulatory cells and autoimmunity should be established in cancer patients.

Experimental model for studying the involvement of regulatory cytotoxic T cells in bone resorption

T cells may affect the activity of osteoclasts, the bone resorbing cells. In particular, recently authors focalize their attention on CD8(+) T cells, demonstrating that murine pre-osteoclasts can recruit naïve CD8(+) T cells and induce them to differentiate in regulatory cytotoxic T cells (TcREG), which in turn may suppress osteoclast formation and activity. Thus, here we describe the methodological approach needed to obtain TcREG and to evaluate TcREG effects on murine osteoclast activity and formation in an in vitro experimental model.

Blockade of programmed death-1 in young (New Zealand Black x New Zealand White)F1 mice promotes the suppressive capacity of CD4+ regulatory T cells protecting from lupus-like disease

Programmed death-1 (PD-1) usually acts as a negative signal for T cell activation, and its expression on CD8(+)Foxp3(+) T cells is required for their suppressive capacity. In this study, we show that PD-1 signaling is required for the maintenance of functional regulatory CD4(+)CD25(+)Foxp3(+) regulatory T cells (CD4(+) T(reg)) that can control autoimmunity in (New Zealand Black × New Zealand White)F1 lupus mice. PD-1 signaling induced resistance to apoptosis and prolonged the survival of CD4(+) T(reg). In vivo, the blockade of PD-1 with a neutralizing Ab reduced PD-1 expression on CD4(+) T(reg) (PD1(lo)CD4(+) T(reg)). PD1(lo)CD4(+) T(reg) had an increased ability to promote B cell apoptosis and to suppress CD4(+) Th as compared with CD4(+) T(reg) with elevated PD-1 expression (PD1(hi)CD4(+) T(reg)). When PD-1 expression on CD4(+) T(reg) was blocked in vitro, PD1(lo)CD4(+) T(reg) suppressed B cell production of IgG and anti-dsDNA Ab. Finally, in vitro studies showed that the suppressive capacity of CD4(+) T(reg) depended on PD-1 expression and that a fine-tuning of the expression of this molecule directly affected cell survival and immune suppression. These results indicate that PD-1 expression has multiple effects on different immune cells that directly contribute to a modulation of autoimmune responses.

Eye-mediated induction of specific immune tolerance to encephalitogenic antigens

AIMS

Administration of antigens into the anterior chamber (AC) of the eye induces a form of antigen-specific immune tolerance termed anterior chamber-associated immune deviation (ACAID). This immune tolerance effectively impairs host delayed-type hypersensitivity (DTH) responses. We hypothesized that ACAID could be generated in BALB/c mice following AC inoculation of the encephalitogenic antigens myelin oligodendrocyte glycoprotein (MOG) and myelin basic protein (MBP).

METHODS

We used DTH assays and local adoptive transfer (LAT) assays to test whether MOG/MBP-induced ACAID following their administration into the AC, whether they elicited this immune tolerance via CD8(+) T cells, and whether their AC coadministration (MOG/MBP) induced specific immune tolerance to one or both antigens.

RESULTS

We showed that MOG/MBP-induced AC-mediated specific immune tolerance, as evident from impaired DTH responses. This antigen-driven DTH suppression was solely mediated via splenic CD8(+) T cells as confirmed by LAT assays. Finally, a single AC injection with both antigens was sufficient to induce specific immune tolerance to these antigens, as evident from DTH and LAT assays.

CONCLUSION

ACAID T-cell regulation could be used as a therapeutic tool in the treatment of complicated autoimmune diseases that involve multiple antigens such as multiple sclerosis.

Lactobacillus reuteri DSM 17938 changes the frequency of Foxp3+ regulatory T cells in the intestine and mesenteric lymph node in experimental necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is an inflammatory disease of the intestine in premature infants. Lactobacillus reuteri DSM 17938 improves survival and reduces the incidence and severity of NEC in a rodent model. Foxp3⁺ regulatory T cells (Tregs) maintain intestinal homeostasis by controlling inflammation and inducing tolerance. To determine whether there are insufficient numbers of Tregs to control inflammation in NEC and to determine if LR17938 increases the frequency of Tregs, we studied selected groups of newborn Sprague-Dawley rats according to feeding plan: dam±LR17938, formula±LR17938, and NEC±LR17938. NEC was induced by gavage feeding with special formula and exposure to hypoxic conditions. Lymphocytes isolated from ileum, mesenteric lymph nodes (MLN), spleen and thymus were labeled for T cell surface markers (CD3, CD4, CD8) and intracellular Foxp3; and labeled cells were analyzed by flow cytometry. The percentage of CD3⁺ T cells and Foxp3⁺ Tregs in the ileum significantly decreased in pups with NEC, compared to normal controls. Feeding LR17938 to neonatal rats with NEC increased the % of Foxp3⁺ T cells in the ileum while decreasing the percentage of cells in the MLN. Administration of LR17938 to dam-fed rats significantly increased Foxp3⁺Tregs in the ileum as early as day of life (DOL)1 but did not produce an increase in Tregs in formula-fed rats on DOL1. These results suggest that factors in breast milk may enhance the early immunomodulatory effects of LR17938. An anti-inflammatory effect of LR17938 in NEC was associated with the modulation of immune responses and induction and what appears to be migration of Foxp3⁺ Tregs to the diseased gut. Probiotic-facilitated development of Tregs might play an important role in the prevention of NEC.

Type II collagen induces peripheral tolerance in BALB/c mice via the generation of CD8+ T regulatory cells

Antigens introduced into the anterior chamber (AC) of the eye induce a potent form of antigen-specific peripheral immune tolerance termed AC-associated immune deviation (ACAID), which prevents inflammatory immune responses and is characterized by impaired delayed-type hypersensitivity (DTH) responses. Type-II collagen (CII) is a fibrillar protein expressed exclusively in cartilage tissues. Although of its clinical relevance to Rheumatoid arthritis, aging, and osteoarthritis, there have been no studies to date to test if CII has the ability to induce ACAID. We hypothesized that ACAID could be generated via AC injection of CII in BALB/c mice. Using a DTH assay, the hypothesis was supported and led to another hypothesis that CII is capable of inducing specific immune tolerance via CD8(+) T regulatory cells (Tregs). Thus, we performed functional local adoptive transfer (LAT) assays to examine the regulatory roles of spleen cells, T cells, and CD8(+) T cells in the specific immune regulation induced by CII injection into the AC. Results indicated that CII induced ACAID when injected into the AC. Spleen cells of mice injected with CII in the AC significantly suppressed DTH responses. The T cell compartment of the spleen was capable of expressing this suppression. CD8(+) Tregs could solely express this CII-driven suppression and even exerted more noticeable suppression than spleen cells or splenic T cells. This study suggests a crucial role for CD8(+) Tregs in mediating CII-driven ACAID-mediated immune tolerance. This could have therapeutic implications in Rheumatoid arthritis, aging, osteoarthritis, and other diseases in which CII is involved.

A comprehensive review of the phenotype and function of antigen-specific immunoregulatory double negative T cells

Double negative T cells that lack the expression of both CD4 and CD8 T cell co-receptors exhibit a most unique antigen-specific immunoregulatory potential first described over a decade ago. Due to their immunoregulatory function, this rare T cell population has been studied in both mice and humans for their contribution to peripheral tolerance and disease prevention. Consequently, double negative cells are gaining interest as a potential cellular therapeutic. Herein, we review the phenotype and function of double negative T cells with emphasis on their capacity to induce antigen-specific immune tolerance. While the phenotypic and functional similarities between double negative T cells identified in mouse and humans are highlighted, we also call attention to the need for a specific marker of double negative T cells, which will facilitate future studies in humans. Altogether, due to their unique properties, double negative T cells present a promising therapeutic potential in the context of various disease settings.

Chronic exposure to staphylococcal superantigen elicits a systemic inflammatory disease mimicking lupus

Chronic nasal and skin colonization with superantigen (SAg)-producing Staphylococcus aureus is well documented in humans. Given that trans-mucosal and trans-cutaneous absorption of SAgs can occur, we determined whether chronic exposure to small amounts of SAg per se could activate autoreactive CD4(+) and CD8(+) T cells and precipitate any autoimmune disease without further external autoantigenic stimulation. Because HLA class II molecules present SAg more efficiently than do mouse MHC class II molecules, HLA-DQ8 transgenic mice were implanted s.c. with mini-osmotic pumps capable of continuously delivering the SAg, staphylococcal enterotoxin B (total of 10 μg/mouse), or PBS over 4 wk. Chronic exposure to staphylococcal enterotoxin B resulted in a multisystem autoimmune inflammatory disease with features similar to systemic lupus erythematosus. The disease was characterized by mononuclear cell infiltration of lungs, liver, and kidneys, accompanied by the production of anti-nuclear Abs and deposition of immune complexes in the renal glomeruli. The inflammatory infiltrates in various organs predominantly consisted of CD4(+) T cells bearing TCR Vβ8. The extent of immunopathology was markedly reduced in mice lacking CD4(+) T cells and CD28, indicating that the disease is CD4(+) T cell mediated and CD28 dependent. The absence of disease in STAT4-deficient, as well as IFN-γ-deficient, HLA-DQ8 mice suggested the pathogenic role of Th1-type cytokines, IL-12 and IFN-γ. In conclusion, our study suggests that chronic exposure to extremely small amounts of bacterial SAg could be an etiological factor for systemic lupus erythematosus.

Peptide-based approaches to treat lupus and other autoimmune diseases

After a long period where the potential of therapeutic peptides was let into oblivion and even dismissed, there is a revival of interest in peptides as potential drug candidates. Novel strategies for limiting metabolism and improve their bioavailability, and alternative routes of administration have emerged. This resulted in a large number of peptide-based drugs that are now being marketed in different indications. Regarding autoimmunity, successful data have been reported in numerous mouse models of autoimmune inflammation, yet relatively few clinical trials based on synthetic peptides are currently underway. This review reports on peptides that show much promises in appropriate mouse models of autoimmunity and describes in more detail clinical trials based on peptides for treating autoimmune patients. A particular emphasis is given to the 21-mer peptide P140/Lupuzor that has completed successfully phase I, phase IIa and phase IIb clinical trials for systemic lupus erythematosus.

Osteoclast activated FoxP3+ CD8+ T-cells suppress bone resorption in vitro

Background

Osteoclasts are the body’s sole bone resorbing cells. Cytokines produced by pro-inflammatory effector T-cells (T_EFF) increase bone resorption by osteoclasts. Prolonged exposure to the T_EFF produced cytokines leads to bone erosion diseases such as osteoporosis and rheumatoid arthritis. The crosstalk between T-cells and osteoclasts has been termed osteoimmunology. We have previously shown that under non-inflammatory conditions, murine osteoclasts can recruit naïve CD8 T-cells and activate these T-cells to induce CD25 and FoxP3 (Tc_REG). The activation of CD8 T-cells by osteoclasts also induced the cytokines IL-2, IL-6, IL-10 and IFN-γ. Individually, these cytokines can activate or suppress osteoclast resorption.

Principal Findings

To determine the net effect of Tc_REG on osteoclast activity we used a number of in vitro assays. We found that Tc_REG can potently and directly suppress bone resorption by osteoclasts. Tc_REG could suppress osteoclast differentiation and resorption by mature osteoclasts, but did not affect their survival. Additionally, we showed that Tc_REG suppress cytoskeletal reorganization in mature osteoclasts. Whereas induction of Tc_REG by osteoclasts is antigen-dependent, suppression of osteoclasts by Tc_REG does not require antigen or re-stimulation. We demonstrated that antibody blockade of IL-6, IL-10 or IFN-γ relieved suppression. The suppression did not require direct contact between the Tc_REG and osteoclasts.

Significance

We have determined that osteoclast-induced Tc_REG can suppress osteoclast activity, forming a negative feedback system. As the CD8 T-cells are activated in the absence of inflammatory signals, these observations suggest that this regulatory loop may play a role in regulating skeletal homeostasis. Our results provide the first documentation of suppression of osteoclast activity by CD8 regulatory T-cells and thus, extend the purview of osteoimmunology.

CD8(+) Tregs in autoimmunity: learning "self"-control from experience

Autoreactive CD8(+) regulatory T cells (Tregs) play important roles as modulators of immune responses against self, and numerical and functional defects in CD8(+) Tregs have been linked to autoimmunity. Several subsets of CD8(+) Tregs have been described. However, the origin of these T cells and how they participate in the natural progression of autoimmunity remain poorly defined. We discuss several lines of evidence suggesting that the autoimmune process itself promotes the development of autoregulatory CD8(+) T cells. We posit that chronic autoantigenic exposure fosters the differentiation of non-pathogenic autoreactive CD8(+) T cells into antigen-experienced, memory-like autoregulatory T cells, to generate a "negative feedback" regulatory loop capable of countering pathogenic autoreactive effectors. This hypothesis predicts that approaches capable of boosting autoregulatory T cell memory will be able to blunt autoimmunity without compromising systemic immunity.

Genes, tolerance and systemic autoimmunity

The characterization of functional CD8(+) inhibitory or regulatory T cells and their gene regulation remains a critical challenge in the field of tolerance and autoimmunity. Investigating the genes induced in regulatory cells and the regulatory networks and pathways that underlie mechanisms of immune resistance and prevent apoptosis in the CD8(+) T cell compartment are crucial to understanding tolerance mechanisms in systemic autoimmunity. Little is currently known about the genetic control that governs the ability of CD8(+) Ti or regulatory cells to suppress anti-DNA Ab production in B cells. Silencing genes with siRNA or shRNA and overexpression of genes with lentiviral cDNA transduction are established approaches to identifying and understanding the function of candidate genes in tolerance and immunity. Elucidation of interactions between genes and proteins, and their synergistic effects in establishing cell-cell cross talk, including receptor modulation/antagonism, are essential for delineating the roles of these cells. In this review, we will examine recent reports which describe the modulation of cells from lupus prone mice or lupus patients to confer anti-inflammatory and protective gene expression and novel associated phenotypes. We will highlight recent findings on the role of selected genes induced by peptide tolerance in CD8(+) Ti.

Regulatory T cells in systemic lupus erythematosus (SLE); role of peptide tolerance

Regulatory T cells play an important role in the maintenance and regulation of immune tolerance and in the prevention of autoimmunity. Recent studies have demonstrated a deficiency in number and function of regulatory T cells in lupus and other autoimmune diseases. This may contribute to immune dysregulations and a defect in self-tolerance mechanisms. How to balance and "reset" the immune response from harmful pro-inflammatory to beneficial anti-inflammatory is the current strategy of the research. In this regard, several studies have been performed with various peptides, drugs, steroids and epigenetic agents to induce or modify regulatory cells and some measure of success has been achieved in the animal model of SLE and with lupus patient cells. Challenges ahead include the heterogeneous nature, phenotype and function of regulatory cells and the difficulties in manipulation of regulatory function in healthy versus diseased states. In this review, we will provide some recent findings indicating challenges and potential benefits of targeting of regulatory T cells in lupus.

In vitro induced CD8+ regulatory T cells inhibit skin inflammation

CD8(+) regulatory T cells appear impaired in number and/or function in some autoimmune diseases. However, the role of CD8(+) regulatory T cells in the pathogenesis of skin inflammation and psoriasis remains unknown. In this study, we set out to analyze the capability of CD8(+) regulatory T cells to inhibit skin inflammation in a murine model and to determine the frequency of CD8(+) regulatory T cells in patients with psoriasis. We demonstrate that murine fully competent CD8(+) regulatory T cells can be induced by stimulating naïve CD8(+) T cells in the presence of TGF-β and retinoic acid (RA). Importantly, in vitro induced CD8(+) regulatory T cells significantly suppressed skin inflammation in vivo. Furthermore, we found that the frequency of regulatory CD8(+)CD25(+)Foxp3(+) T cells is decreased in peripheral blood but increased in lesional psoriatic skin of patients with psoriasis. Thus, our study suggests a previously unappreciated role of CD8(+)CD25(+)Foxp3(+) T cells in skin disorders, and induction of these cells in vitro may be an effective immunotherapy for skin inflammation.

Generation and function of immunosuppressive human and murine CD8+ T cells by transforming growth factor-β and retinoic acid

The intestinal immune system is constantly challenged by foreign antigens and commensal bacteria. Therefore, proper control of the intestinal microenvironment is required. One important arm of this regulatory network consists of regulatory T cells. In contrast to CD4(+) Foxp3(+) regulatory T cells, which have been well characterized, immunomodulatory CD8(+) T cells that express Foxp3 are less well defined in terms of their generation and function. Failures of these regulatory mechanisms contribute to the development of inflammatory bowel disease. In this study we demonstrate that the frequency of CD8(+) Foxp3(+) T cells is reduced in the peripheral blood of patients with ulcerative colitis. As these cells might play a currently underestimated role in the maintenance of intestinal homeostasis, we have investigated human and murine CD8(+) Foxp3(+) T cells generated by stimulating naive CD8(+) T cells in the presence of transforming growth factor-β and retinoic acid, mediators that are abundantly produced in the intestinal mucosa. These CD8(+) Foxp3(+) fully competent regulatory T cells show strong expression of regulatory molecules CD25, Gpr83 and CTLA-4 and exhibit cell-cell contact-dependent immunosuppressive activity in vitro. Our study illustrates a previously unappreciated critical role of CD8(+) Foxp3(+) T cells in controlling potentially dangerous T cells and in the maintenance of intestinal homeostasis.

Oral administration of different forms of a tolerogenic peptide to define the preparations and doses that delay anti-DNA antibody production and nephritis and prolong survival in SLE-prone mice

Therapeutic agents currently in use to treat systemic lupus erythematosus (SLE) are predominantly immunosuppressive agents with limited specificities. Multiple groups, including ours, have illustrated that inducing tolerance in SLE animal models ameliorates disease symptoms and increases survival. We examined if oral administration of a tolerogenic peptide could affect SLE disease progression. The pConsensus (pCons) peptide, based on protein sequences of anti-double stranded (anti-ds)DNA antibodies, induces tolerance through upregulation of regulatory T cells when administered intravenously. Six different forms of pCons, including multiple antigenic peptides (MAP) and cyclic peptides made up of L- and D-amino acids, at three different concentrations, were fed to BWF1 SLE-susceptible mice for 30 weeks. Mice fed 100 µg of L-MAP or D-MAP had less cumulative proteinuria and serum anti-dsDNA antibody levels than controls. In addition, animals in these groups also survived significantly longer than controls with a corresponding increase in serum transforming growth factor beta (TGFβ, implying a protective role for pCons-induced regulatory T cells. Oral administration of a tolerogenic peptide is a safe, effective method for ameliorating SLE disease manifestations and prolonging survival in SLE-prone mice. Induction of oral tolerance using modified pCons peptides could lead to a novel targeted therapy for human SLE.

Interferon-inducible gene 202b controls CD8(+) T cell-mediated suppression in anti-DNA Ig peptide-treated (NZB × NZW) F1 lupus mice

Administration of an artificial peptide (pConsensus) based on anti-DNA IgG sequences that contain major histocompatibility complex class I and class II T-cell determinants, induces immune tolerance in NZB/NZW F1 female (BWF1) mice. To understand the molecular basis of CD8⁺ Ti-mediated suppression, we previously performed microarray analysis to identify genes that were differentially expressed following tolerance induction with pCons. CD8⁺ T cells from mice tolerized with pCons showed more than two-fold increase in Ifi202b mRNA, an interferon inducible gene, versus cells from untolerized mice. Ifi202b expression increased through weeks 1–4 after tolerization and then decreased, reapproaching baseline levels at 6 weeks. In vitro polyclonal activation of tolerized CD8⁺ T cells significantly increased Ifi202b mRNA expression. Importantly, silencing of Ifi202b abrogated the suppressive capacity of CD8⁺ Ti cells. This was associated with decreased expression of Foxp3, and decreased gene and protein expression of transforming growth factor (TGF)β and interleukin-2 (IL-2), but not of interferon (IFN)-γ, IL-10, or IL-17. Silencing of another IFN-induced gene upregulated in tolerized CD8⁺ T cells, IFNAR1, had no effect on the ability of CD8⁺ T cells to suppress autoantibody production. Our findings indicate a potential role for Ifi202b in the suppressive capacity of peptide-induced regulatory CD8⁺ Ti cells through effects on the expression of Foxp3 and the synthesis of TGFβ.

Harnessing regulatory T cells for the therapy of lupus and other autoimmune diseases

Regulatory T cells (Tregs) maintain immunological homeostasis and prevent autoimmunity. The depletion or functional alteration of Tregs may lead to the development of autoimmune diseases. Tregs consist of different subpopulations of cells, of which CD4(+)CD25(+)Foxp3(+) cells are the most well characterized. However, CD8 Tregs also constitute a major cell population that has been shown to play an important role in autoimmune diseases. This review will discuss the role of Tregs in autoimmune diseases in general and specifically in systemic lupus erythematosus (SLE). SLE is a multisystem autoimmune disease characterized by the production of autoantibodies against nuclear components and by the deposition of immune complexes in the kidneys as well as in other organs. Abnormalities in Tregs were reported in SLE patients and in animal models of the disease. Current treatment of SLE is based on immunosuppressive drugs that are nonspecific and may cause adverse effects. Therefore, the development of novel, specific, side effect-free therapeutic means that will induce functional Tregs is a most desirable goal. Our group and others have designed and utilized tolerogenic peptides that ameliorate SLE manifestations in murine models. Here, we demonstrate the role of CD4 and CD8 Tregs, as well as the interaction between the two subsets of cells and the mechanism of action of the tolerogenic peptides. We also discuss their therapeutic potential for the treatment of SLE.

Characterization of protective human CD4CD25 FOXP3 regulatory T cells generated with IL-2, TGF-β and retinoic acid

BACKGROUND

Protective CD4+CD25+ regulatory T cells bearing the Forkhead Foxp3 transcription factor can now be divided into three subsets: Endogenous thymus-derived cells, those induced in the periphery, and another subset induced ex-vivo with pharmacological amounts of IL-2 and TGF-β. Unfortunately, endogenous CD4+CD25+ regulatory T cells are unstable and can be converted to effector cells by pro-inflammatory cytokines. Although protective Foxp3+CD4+CD25+ cells resistant to proinflammatory cytokines have been generated in mice, in humans this result has been elusive. Our objective, therefore, was to induce human naïve CD4+ cells to become stable, functional CD25+ Foxp3+ regulatory cells that were also resistant to the inhibitory effects of proinflammatory cytokines.

METHODOLOGY/PRINCIPAL FINDINGS

The addition of the vitamin A metabolite, all-trans retinoic acid (atRA) to human naïve CD4+ cells suboptimally activated with IL-2 and TGF-β enhanced and stabilized FOXP3 expression, and accelerated their maturation to protective regulatory T cells. AtRA, by itself, accelerated conversion of naïve to mature cells but did not induce FOXP3 or suppressive activity. The combination of atRA and TGF-β enabled CD4+CD45RA+ cells to express a phenotype and trafficking receptors similar to natural Tregs. AtRA/TGF-β-induced CD4+ regs were anergic and low producers of IL-2. They had potent in vitro suppressive activity and protected immunodeficient mice from a human-anti-mouse GVHD as well as expanded endogenous Tregs. However, treatment of endogenous Tregs with IL-1β and IL-6 decreased FOXP3 expression and diminished their protective effects in vivo while atRA-induced iTregs were resistant to these inhibitory effects.

CONCLUSIONS/SIGNIFICANCE

We have developed a methodology that induces human CD4(+) cells to rapidly become stable, fully functional suppressor cells that are also resistant to proinflammatory cytokines. This methodology offers a practical novel strategy to treat human autoimmune diseases and prevent allograft rejection without the use of agents that kill cells or interfere with signaling pathways.

Blockade of programmed death-1 in young (New Zealand black x New Zealand white)F1 mice promotes the activity of suppressive CD8+ T cells that protect from lupus-like disease

The programmed death-1 (PD-1)/programmed death-1 ligand 1 (PD-L1) pathway regulates both stimulatory and inhibitory signals. In some conditions, PD-1/PD-L1 inhibits T and B cell activation, induces anergy, and reduces cytotoxicity in CD8(+) T cells. In other conditions, PD-l/PD-L1 has costimulatory effects on T cells. We recently showed that induction of suppressive CD8(+)Foxp3(+) T cells by immune tolerance of lupus-prone (New Zealand black × New Zealand white)F(1) (BWF(1)) mice with the anti-DNA Ig-based peptide pConsensus (pCons) is associated with significantly reduced PD-1 expression on those cells. In this study, we tested directly the role of PD-1 by administering in vivo neutralizing Ab to PD-1 to premorbid BWF(1) and healthy control mice. Anti-PD-1-treated mice were protected from the onset of lupus nephritis for 10 wk, with significantly improved survival. Although the numbers of T cells declined in aging control mice, they were maintained in anti-PD-1-treated mice, including CD8(+)Foxp3(+) T cells that suppressed syngeneic CD4(+)CD25(-) T cell proliferation and IFN-γ production, reduced production of IgG and anti-dsDNA IgG, induced apoptosis in syngeneic B cells, and increased IL-2 and TGF-β production. The administration of anti-PD-1 Ab to BWF(1) mice after induction of tolerance with pCons abrogated tolerance; mice developed autoantibodies and nephritis at the same time as control mice, being unable to induce CD8(+)Foxp3(+) T suppressor cells. These data suggest that tightly regulated PD-1 expression is essential for the maintenance of immune tolerance mediated by those CD8(+)Foxp3(+) T cells that suppress both T(h) cells and pathogenic B cells. PD-1 regulation could represent a target to preserve tolerance and prevent autoimmunity.