Peptide-induced T cell regulation of experimental autoimmune encephalomyelitis: a role for IL-10

Autoimmune susceptible HLA class II motifs facilitate the presentation of modified neoepitopes to potentially autoreactive T cells

Rheumatoid arthritis (RA), multiple sclerosis (MS), type 1 diabetes (T1D), and celiac disease (CD), are strongly associated with susceptible HLA class II haplotypes. The peptide-binding pockets of these molecules are polymorphic, thus each HLA class II protein presents a distinct set of peptides to CD4⁺ T cells. Peptide diversity is increased through post-translational modifications, generating non-templated sequences that enhance HLA binding and/or T cell recognition. The high-risk HLA-DR alleles that confer susceptibility to RA are notable for their ability to accommodate citrulline, promoting responses to citrullinated self-antigens. Likewise, HLA-DQ alleles associated with T1D and CD favor the binding of deamidated peptides. In this review, we discuss structural features that promote modified self-epitope presentation, provide evidence supporting the relevance of T cell recognition of such antigens in disease processes, and make a case that interrupting the pathways that generate such epitopes and reprogramming neoepitope-specific T cells are key strategies for effective therapeutic intervention.

Induction of Tolerance to Therapeutic Proteins With Antigen-Processing Independent T Cell Epitopes: Controlling Immune Responses to Biologics

The immune response to exogenous proteins can overcome the therapeutic benefits of immunotherapies and hamper the treatment of protein replacement therapies. One clear example of this is haemophilia A resulting from deleterious mutations in the FVIII gene. Replacement with serum derived or recombinant FVIII protein can cause anti-drug antibodies in 20-50% of individuals treated. The resulting inhibitor antibodies override the benefit of treatment and, at best, make life unpredictable for those treated. The only way to overcome the inhibitor issue is to reinstate immunological tolerance to the administered protein. Here we compare the various approaches that have been tested and focus on the use of antigen-processing independent T cell epitopes (apitopes) for tolerance induction. Apitopes are readily designed from any protein whether this is derived from a clotting factor, enzyme replacement therapy, gene therapy or therapeutic antibody.

Peptide allergen-specific immunotherapy for allergic airway diseases-State of the art

Allergen-specific immunotherapy (AIT) is the only means of altering the natural immunological course of allergic diseases and achieving long-term remission. Pharmacological measures are able to suppress the immune response and/or ameliorate the symptoms but there is a risk of relapse soon after these measures are withdrawn. Current AIT approaches depend on the administration of intact allergens, often comprising crude extracts of the allergen. We propose that the challenges arising from current approaches, including the risk of serious side-effects, burdensome duration of treatment, poor compliance and high cost, are overcome by application of peptides based on CD4⁺ T cell epitopes rather than whole allergens. Here we describe evolving approaches, summarize clinical trials involving peptide AIT in allergic rhinitis and asthma, discuss the putative mechanisms involved in their action, address gaps in evidence and propose future directions for research and clinical development.

Advancement of antigen-specific immunotherapy: knowledge transfer between allergy and autoimmunity

Targeted restoration of immunological tolerance to self-antigens or innocuous environmental allergens represents the ultimate aim of treatment options in autoimmune and allergic disease. Antigen-specific immunotherapy (ASI) is the only intervention that has proven disease-modifying efficacy as evidenced by induction of long-term remission in a number of allergic conditions. Mounting evidence is now indicating that specific targeting of pathogenic T cells in autoinflammatory and autoimmune settings enables effective restoration of immune homeostasis between effector and regulatory cells and alters the immunological course of disease. Here, we discuss the key lessons learned during the development of antigen-specific immunotherapies and how these can be applied to inform future interventions. Armed with this knowledge and current high-throughput technology to track immune cell phenotype and function, it may no longer be a matter of ‘if’ but ‘when’ this ultimate aim of targeted tolerance restoration is realised.

Chromatin Priming Renders T Cell Tolerance-Associated Genes Sensitive to Activation below the Signaling Threshold for Immune Response Genes

Immunological homeostasis in T cells is maintained by a tightly regulated signaling and transcriptional network. Full engagement of effector T cells occurs only when signaling exceeds a critical threshold that enables induction of immune response genes carrying an epigenetic memory of prior activation. Here we investigate the underlying mechanisms causing the suppression of normal immune responses when T cells are rendered anergic by tolerance induction. By performing an integrated analysis of signaling, epigenetic modifications, and gene expression, we demonstrate that immunological tolerance is established when both signaling to and chromatin priming of immune response genes are weakened. In parallel, chromatin priming of immune-repressive genes becomes boosted, rendering them sensitive to low levels of signaling below the threshold needed to activate immune response genes. Our study reveals how repeated exposure to antigens causes an altered epigenetic state leading to T cell anergy and tolerance, representing a basis for treating auto-immune diseases.

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Activation of immune response genes is suppressed in tolerant T cells

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Epigenetic priming of repressive genes is boosted when tolerance is established

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Inhibitory receptor genes have a lower threshold of activation in tolerant cells

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Induction of tolerance by peptides points toward a therapy for multiple sclerosis

The Mechanism of Action of Antigen Processing Independent T Cell Epitopes Designed for Immunotherapy of Autoimmune Diseases

Immunotherapy with antigen-processing independent T cell epitopes (apitopes) targeting autoreactive CD4⁺ T cells has translated to the clinic and been shown to modulate progression of both Graves’ disease and multiple sclerosis. The model apitope (Ac1-9[4Y]) renders antigen-specific T cells anergic while repeated administration induces both Tr1 and Foxp3⁺ regulatory cells. Here we address why CD4⁺ T cell epitopes should be designed as apitopes to induce tolerance and define the antigen presenting cells that they target in vivo. Furthermore, we reveal the impact of treatment with apitopes on CD4⁺ T cell signaling, the generation of IL-10-secreting regulatory cells and the systemic migration of these cells. Taken together these findings reveal how apitopes induce tolerance and thereby mediate antigen-specific immunotherapy of autoimmune diseases.

Non-Genetically Encoded Epitopes Are Relevant Targets in Autoimmune Diabetes

Islet antigen reactive T cells play a key role in promoting beta cell destruction in type 1 diabetes (T1D). Self-reactive T cells are typically deleted through negative selection in the thymus or deviated to a regulatory phenotype. Nevertheless, those processes are imperfect such that even healthy individuals have a reservoir of potentially autoreactive T cells. What remains less clear is how tolerance is lost to insulin and other beta cell specific antigens. Islet autoantibodies, the best predictor of disease risk, are known to recognize classical antigens such as proinsulin, GAD65, IA-2, and ZnT8. These antibodies are thought to be supported by the expansion of autoreactive CD4⁺ T cells that recognize these same antigenic targets. However, recent studies have identified new classes of non-genetically encoded epitopes that may reflect crucial gaps in central and peripheral tolerance. Notably, some of these specificities, including epitopes from enzymatically post-translationally modified antigens and hybrid insulin peptides, are present at relatively high frequencies in the peripheral blood of patients with T1D. We conclude that CD4⁺ T cells that recognize non-genetically encoded epitopes are likely to make an important contribution to the progression of islet autoimmunity in T1D. We further propose that these classes of neo-epitopes should be considered as possible targets for strategies to induce antigen specific tolerance.

Antigen-Specific Immunotherapy for Treatment of Autoimmune Liver Diseases

The liver is a critical organ in controlling immune tolerance. In particular, it is now clear that targeting antigens for presentation by antigen presenting cells in the liver can induce immune tolerance to either autoantigens from the liver itself or tissues outside of the liver. Here we review immune mechanisms active within the liver that contribute both to the control of infectious diseases and tolerance to self-antigens. Despite its extraordinary capacity for tolerance induction, the liver remains a target organ for autoimmune diseases. In this review, we compare and contrast known autoimmune diseases of the liver. Currently patients tend to receive strong immunosuppressive treatments and, in many cases, these treatments are associated with deleterious side effects, including a significantly higher risk of infection and associated health complications. We propose that, in future, antigen-specific immunotherapies are adopted for treatment of liver autoimmune diseases in order to avoid such adverse effects. We describe various therapeutic approaches that either are in or close to the clinic, highlight their mechanism of action and assess their suitability for treatment of autoimmune liver diseases.

Mucosal Administration of E-selectin Limits Disability in Models of Multiple Sclerosis

E-selectin plays an important role in mediating the rolling of leukocytes along and thus, the subsequent extravasation across activated endothelial cells comprising the microvasculature of the blood brain barrier (BBB). In multiple sclerosis (MS) and other inflammatory disorders of the central nervous system (CNS), the microvasculature is altered and immune cells infiltrate the brain and spinal cord contributing to damage, demyelination and ultimately disability. While mucosal administration is typically used to affect lymphocyte hyporesponsiveness or tolerance to suspect autoantigens, intranasal administration to E-selectin has previously been shown to protect against CNS inflammatory insults. We characterized the potential for mucosal administration of E-selectin to modulate CNS autoimmunity in the experimental autoimmune encephalomyelitis (EAE) model of MS. Intranasally administered E-selectin reduced swelling by as much as 50% in delayed-type hypersensitivity reactions compared to ovalbumin-tolerized controls. Intranasal E-selectin delivery prior to disease induction with myelin oligodendrocyte glycoprotein (MOG)_35-55 reduced disease severity and total disease burden by more than 50% compared to PBS-tolerized animals; this protection was not associated with differences in the magnitude of the autoimmune response. Examination after the onset of disease showed that protection was associated with significant reductions in inflammatory infiltrates throughout the spinal cord. Tolerization to E-selectin did not influence encephalitogenic characteristics of autoreactive T cells such as IFN-gamma or IL-17 production. Clinical disease was also significantly reduced when E-selectin was first delivered after the onset of clinical symptoms. Splenic and lymph node (LN) populations from E-selectin-tolerized animals showed E-selectin-specific T cell responses and production of the immunomodulatory cytokine IL-10. Transfer of enriched CD4+ T cells from E-selectin tolerized mice limited disability in the passive SJL model of relapsing remitting MS. These results suggest a role for influencing E-selectin specific responses to limit neuroinflammation that warrants further exploration and characterization to better understand its potential to mitigate neurodegeneration in disorders such as MS.

Antigen-specific therapeutic approaches for autoimmunity

The main function of the immune system in health is to protect the host from infection by microbes and parasites. Because immune responses to nonself bear the risk of unleashing accidental immunity against self, evolution has endowed the immune system with central and peripheral mechanisms of tolerance, including regulatory T and B cells. Although the past two decades have witnessed the successful clinical translation of a whole host of novel therapies for the treatment of chronic inflammation, the development of antigen-based approaches capable of selectively blunting autoimmune inflammation without impairing normal immunity has remained elusive. Earlier autoantigen-specific approaches employing peptides or whole antigens have evolved into strategies that seek to preferentially deliver these molecules to autoreactive T cells either indirectly, via antigen-presenting cells, or directly, via major histocompatibility complex molecules, in ways intended to promote clonal deletion and/or immunoregulation. The disease specificity, mechanistic underpinnings, developability and translational potential of many of these strategies remain unclear.

Antigen-specific regulatory T-cell responses against aeroantigens and their role in allergy

The mucosal immune system of the respiratory tract is specialized to continuously monitor the external environment and to protect against invading pathogens, while maintaining tolerance to innocuous inhaled particles. Allergies result from a loss of tolerance against harmless antigens characterized by formation of allergen-specific Th2 cells and IgE. Tolerance is often described as a balance between harmful Th2 cells and various types of protective "regulatory" T cells. However, the identity of the protective T cells in healthy vs. allergic individuals or following successful allergen-specific therapy is controversially discussed. Recent technological progress enabling the identification of antigen-specific effector and regulatory T cells has significantly contributed to our understanding of tolerance. Here we discuss the experimental evidence for the various tolerance mechanisms described. We try to integrate the partially contradictory data into a new model proposing different mechanism of tolerance depending on the quality and quantity of the antigens as well as the way of antigen exposure. Understanding the basis of tolerance is essential for the rational design of novel and more efficient immunotherapies.

Immunotherapy With Apitopes Blocks the Immune Response to TSH Receptor in HLA-DR Transgenic Mice

We have combined major histocompatibility complex-binding assays with immunization and tolerance induction experiments in HLA-DR3 transgenic mice to design apitopes (antigen-processing independent epitopes) derived from thyrotropin receptor (TSHR) for treatment of patients with Graves' disease (GD). A challenge model was created by using an adenovirus-expressing part of the extracellular domain of the thyrotropin receptor (TSHR289). This model was used to test whether current drug treatments for GD would have an impact on effective antigen-specific immunotherapy using the apitope approach. Furthermore, selected peptides were assessed for their antigenicity using peripheral blood mononuclear cell samples from patients with GD. A mixture of two immunodominant apitopes was sufficient to suppress both the T-cell and antibody response to TSHR when administered in soluble form to HLA-DR transgenic mice. Tolerance induction was not disrupted by current drug treatments. These results demonstrate that antigen-specific immunotherapy with apitopes from TSHR is a suitable approach for treatment of GD.

ATX-MS-1467 Induces Long-Term Tolerance to Myelin Basic Protein in (DR2 × Ob1)F1 Mice by Induction of IL-10-Secreting iTregs

INTRODUCTION

Antigen-specific immunotherapy could provide a targeted approach for the treatment of multiple sclerosis that removes the need for broad-acting immunomodulatory drugs. ATX-MS-1467 is a mixture of four peptides identified as the main immune-dominant disease-associated T-cell epitopes in myelin basic protein (MBP), an autoimmune target for activated autoreactive T cells in multiple sclerosis. Previous animal studies have shown that ATX-MS-1467 treatment prevented the worsening of signs of disease in experimental autoimmune encephalitis (EAE) in the humanized (DR2 × Ob1)F1 mouse in a dose-dependent fashion.

METHODS AND RESULTS

Our study extends these observations to show that subcutaneous treatment with 100 µg of ATX-MS-1467 after induction of EAE in the same mouse model reversed established clinical disability (p < 0.0001) and histological markers of inflammation and demyelination (p < 0.001) compared with vehicle-treated animals; furthermore, in longitudinal magnetic resonance imaging analyses, disruption of blood-brain barrier integrity was reversed, compared with vehicle-treated animals (p < 0.05). Chronic treatment with ATX-MS-1467 was associated with an enduring shift from a pro-inflammatory to a tolerogenic state in the periphery, as shown by an increase in interleukin 10 secretion, relative to interleukin 2, interleukin 17 and interferon γ, a decrease in splenocyte proliferation and an increase in interleukin 10+ Foxp3- T cells in the spleen.

CONCLUSION

Our results suggest that ATX-MS-1467 can induce splenic iTregs and long-term tolerance to MBP with the potential to partially reverse the pathology of multiple sclerosis, particularly during the early stages of the disease.

FUNDING

EMD Serono, Inc., a business of Merck KGaA.

Dysfunctional immunoregulation in human liver allograft rejection associated with compromised galectin-1/CD7 pathway function

Regulatory T cells in rejected allograft patients display an inability to control responder T cells. Galectin-1 (Gal1) inhibits responder T cells through binding CD7. We investigated whether the dysfunctional immunoregulation in liver allograft rejection patients results from reduced regulatory T-cell Gal1 expression and/or responder T-cell CD7 expression. Circulating regulatory T cells and responder T cells were profiled from 31 acute rejection transplant patients, 85 transplant patients in remission, and 40 healthy controls. CD7+ and CD7− responder T cells were co-cultured with regulatory T cells to assess regulatory T-cell suppressor function. Gal1-small interfering RNA was used to silence regulatory T-cell Gal1. The CD7+ cell percentage was inversely correlated with AST, ALT, and GGT levels. The proportions of CD7+ responder T cells and Gal1+ regulatory T cells were higher in healthy controls than in transplant patients in remission and lowest in acute rejection transplant patients. Notably, CD7+ responder T-cell susceptibility to Gal1+ regulatory T-cell control was ranked in the same manner. Silencing Gal1 expression in regulatory T cells reduced their ability to suppress CD7+ (but not CD7−) responder T cells. Additionally, the proportions of CD43+ and CD45+ responder T cells were higher in healthy controls than in acute rejection transplant patients. CD43 co-expression (but not CD45 co-expression) on CD7+ responder T cells promoted their apoptosis in a Gal1-dependent manner. In sum, dysfunctional immunoregulation in liver allograft rejection patients can be partly attributed to reduced regulatory T-cell Gal1 expression and reduced responder T-cell CD7 expression. Responder T-cell CD43 downregulation in acute rejection patients may further contribute to reduced responder T-cell responsiveness to regulatory T-cell control.

IL-4 enhances IL-10 production in Th1 cells: implications for Th1 and Th2 regulation

IL-10 is an immunomodulatory cytokine with a critical role in limiting inflammation in immune-mediated pathologies. The mechanisms leading to IL-10 expression by CD4⁺ T cells are being elucidated, with several cytokines implicated. We explored the effect of IL-4 on the natural phenomenon of IL-10 production by a chronically stimulated antigen-specific population of differentiated Th1 cells. In vitro, IL-4 blockade inhibited while addition of exogenous IL-4 to Th1 cultures enhanced IL-10 production. In the in vivo setting of peptide immunotherapy leading to a chronically stimulated Th1 phenotype, lack of IL-4Rα inhibited the induction of IL-10. Exploring the interplay of Th1 and Th2 cells through co-culture, Th2-derived IL-4 promoted IL-10 expression by Th1 cultures, reducing their pathogenicity in vivo. Co-culture led to upregulated c-Maf expression with no decrease in the proportion of T-bet⁺ cells in these cultures. Addition of IL-4 also reduced the encephalitogenic capacity of Th1 cultures. These data demonstrate that IL-4 contributes to IL-10 production and that Th2 cells modulate Th1 cultures towards a self-regulatory phenotype, contributing to the cross-regulation of Th1 and Th2 cells. These findings are important in the context of Th1 driven diseases since they reveal how the Th1 phenotype and function can be modulated by IL-4.

Induction of IL-10 cytokine and the suppression of T cell proliferation by specific peptides from red cell band 3 and in vivo effects of these peptides on autoimmune hemolytic anemia in NZB mice

PURPOSE

The anion channel protein band 3 is the main target of the pathogenic red blood cells (RBC) autoantibodies in New Zealand black (NZB) mice. CD4 T cells from NZB mice with autoimmune hemolytic anemia respond to band 3. Previously, we have shown that IL-10 and peptides containing a dominant T cell epitope from red cell band 3 modulate autoimmune hemolytic anemia in NZB mice. Because of the immunoregulatory role of IL-10 in autoimmune diseases, we aim to identify individual band 3 peptides that induce high IL-10 production and simultaneously suppress CD4 T cell proliferation and to investigate the effect intranasal administration of IL-10 producing band 3 peptides on autoantibody responses of NZB mice.

METHODS

Splenic CD4 T cells of NZB mice were isolated and stimulated by co-culture of T cells with individual band 3 peptides. IL-10 production was measured by enzyme-linked immunosorbent assay and proliferative response of CD4 T cells was estimated by incorporation of [³H] thymidine assay. NZB mice were given either PBS, or peptides 25 (241-251) and 29 (282-296) or both peptides intranasally on three occasions at 2-day intervals. The mice were bled at 6, 10 and 18 weeks after peptide inhalation, and the number of RBC auto-antibodies was measured by DELAT and hematocrit values were assessed.

RESULTS

Peptides 25 (241-251) and 29 (282-296) induced the highest IL-10 production by CD4 T cells. These peptides also inhibited the peak T cell proliferative response. 6 and 10 weeks after peptide inhalation, the total IgG, IgG1 and IgG2a in mice treated with both peptides 241-251 and 282-296 were significantly higher than control (P < 0.05). However, no significant difference in the mean hematocrit between of the peptide-treated mice and the control group was found.

CONCLUSIONS

Although band 3 peptides 241-251 and 282-296 induced to the highest IL-10 production by CD4 T cells in vitro but fail to reverse the RBC autoantibody response in vivo. Modifications to improve solubility these peptides might help to modulate the immune response toward a T helper-2 profile and decrease the severity of anemia.

Protein kinase C theta is required for efficient induction of IL-10-secreting T cells

Secretion of interleukin-10 (IL-10) by CD4+ T cells is an essential immunoregulatory mechanism. The work presented here assesses the role of the signaling molecule protein kinase C theta (PKCθ) in the induction of IL-10 expression in CD4+ T cells. Using wildtype and PKCθ-deficient Tg4 T cell receptor transgenic mice, we implemented a well-described protocol of repeated doses of myelin basic protein (MBP)Ac1-9[4Y] antigen to induce Tr1-like IL-10+ T cells. We find that PKCθ is required for the efficient induction of IL-10 following antigen administration. Both serum concentrations of IL-10 and the proportion of IL-10+ T cells were reduced in PKCθ-deficient mice relative to wildtype mice following [4Y] treatment. We further characterized the T cells of [4Y] treated PKCθ-deficient Tg4 mice and found reduced expression of the transcription factors cMaf, Nfil3 and FoxP3 and the surface receptors PD-1 and Tim3, all of which have been associated with the differentiation or function of IL-10+ T cells. Finally, we demonstrated that, unlike [4Y] treated wildtype Tg4 T cells, cells from PKCθ-deficient mice were unable to suppress the priming of naïve T cells in vitro and in vivo. In summary, we present data demonstrating a role for PKCθ in the induction of suppressive, IL-10-secreting T cells induced in TCR-transgenic mice following chronic antigen administration. This should be considered when contemplating PKCθ as a suitable drug target for inducing immune suppression and graft tolerance.

Selection of epitopes from self-antigens for eliciting Th2 or Th1 activity in the treatment of autoimmune disease or cancer

Vaccines have been valuable tools in the prevention of infectious diseases, and the rapid development of new vectors against constantly mutating foreign antigens in viruses such as influenza has become a regular, seasonal exercise. Harnessing the immune response against self-antigens is not necessarily analogous or as achievable by iterative processes, and since the desired outcome includes leaving the targeted organism intact, requires some precision engineering. In vaccine-based treatment of autoimmunity and cancer, the proper selection of antigens and generation of the desired antigen-specific therapeutic immunity has been challenging. Both cases involve a threshold of existing, undesired immunity that must be overcome, and despite considerable academic and industry efforts, this challenge has proven to be largely refractory to vaccine approaches leveraging enhanced vectors, adjuvants, and administration strategies. There are in silico approaches in development for predicting the immunogenicity of self-antigen epitopes, which are being validated slowly. One simple approach showing promise is the functional screening of self-antigen epitopes for selective Th1 antitumor immunogenicity, or inversely, selective Th2 immunogenicity for treatment of autoimmune inflammation. The approach reveals the importance of confirming both Th1 and Th2 components of a vaccine immunogen; the two can confound one another if not parsed but may be used individually to modulate antigen-specific inflammation in autoimmune disease or cancer.

Preclinical development and first-in-human study of ATX-MS-1467 for immunotherapy of MS

OBJECTIVE

The study was designed to test the efficacy of ATX-MS-1467 in a relevant preclinical model and to assess its safety for the treatment of patients with secondary progressive multiple sclerosis (SPMS).

METHODS

ATX-MS-1467 was tested for its ability to suppress experimental autoimmune encephalomyelitis (EAE) in the (Ob x DR2)F1 mouse both before and after disease onset. Safety was assessed by clinical assessment, MRI analysis, and the measurement of immune responses to self- and nonself-antigens in patients with SPMS.

RESULTS

ATX-MS-1467 displayed a dose-dependent inhibition of EAE and was more effective than glatiramer acetate in the treatment of ongoing disease in humanized mice. A phase 1 open-label dose-escalating study demonstrated that ATX-MS-1467 was safe and well-tolerated in a group of 6 patients with SPMS, up to a dose of 800 µg.

CONCLUSIONS

The results of this study support further development of ATX-MS-1467 in a clinical trial powered to investigate the immunologic and clinical benefits of treatment in relapsing-remitting MS.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that ATX-MS-1467 is safe and tolerated in a group of 6 patients with SPMS.

Vitamin D Actions on CD4(+) T Cells in Autoimmune Disease

This review summarizes and integrates research on vitamin D and CD4⁺ T-lymphocyte biology to develop new mechanistic insights into the molecular etiology of autoimmune disease. A deep understanding of molecular mechanisms relevant to gene–environment interactions is needed to deliver etiology-based autoimmune disease prevention and treatment strategies. Evidence linking sunlight, vitamin D, and the risk of multiple sclerosis and type 1 diabetes is summarized to develop the thesis that vitamin D is the environmental factor that most strongly influences autoimmune disease development. Evidence for CD4⁺ T-cell involvement in autoimmune disease pathogenesis and for paracrine calcitriol signaling to CD4⁺ T lymphocytes is summarized to support the thesis that calcitriol is sunlight’s main protective signal transducer in autoimmune disease risk. Animal modeling and human mechanistic data are summarized to support the view that vitamin D probably influences thymic negative selection, effector Th1 and Th17 pathogenesis and responsiveness to extrinsic cell death signals, FoxP3⁺CD4⁺ T-regulatory cell and CD4⁺ T-regulatory cell type 1 (Tr1) cell functions, and a Th1–Tr1 switch. The proposed Th1–Tr1 switch appears to bridge two stable, self-reinforcing immune states, pro- and anti-inflammatory, each with a characteristic gene regulatory network. The bi-stable switch would enable T cells to integrate signals from pathogens, hormones, cell–cell interactions, and soluble mediators and respond in a biologically appropriate manner. Finally, unanswered questions and potentially informative future research directions are highlighted to speed delivery of etiology-based strategies to reduce autoimmune disease.

Epigenetic modification of the PD-1 (Pdcd1) promoter in effector CD4(+) T cells tolerized by peptide immunotherapy

Clinically effective antigen-based immunotherapy must silence antigen-experienced effector T cells (Teff) driving ongoing immune pathology. Using CD4⁺ autoimmune Teff cells, we demonstrate that peptide immunotherapy (PIT) is strictly dependent upon sustained T cell expression of the co-inhibitory molecule PD-1. We found high levels of 5-hydroxymethylcytosine (5hmC) at the PD-1 (Pdcd1) promoter of non-tolerant T cells. 5hmC was lost in response to PIT, with DNA hypomethylation of the promoter. We identified dynamic changes in expression of the genes encoding the Ten-Eleven-Translocation (TET) proteins that are associated with the oxidative conversion 5-methylcytosine and 5hmC, during cytosine demethylation. We describe a model whereby promoter demethylation requires the co-incident expression of permissive histone modifications at the Pdcd1 promoter together with TET availability. This combination was only seen in tolerant Teff cells following PIT, but not in Teff that transiently express PD-1. Epigenetic changes at the Pdcd1 locus therefore determine the tolerizing potential of TCR-ligation.

DOI:http://dx.doi.org/10.7554/eLife.03416.001

The immune system protects the body from dangerous microbes and removes damaged cells. However, in some cases, the immune system can malfunction and attack healthy tissues, which can lead to type-1 diabetes, multiple sclerosis, and other autoimmune diseases. Many of the current treatments for these disorders suppress the immune system, which can make the individuals more susceptible to infections.

It may be possible to treat autoimmune diseases using small pieces of protein—called peptides—that are based on proteins found on the cells that the immune system attacks by mistake. This strategy would target the specific immune cells that are malfunctioning, but allow the rest of the immune system to continue to work as normal. Peptide-based therapies for autoimmune diseases are currently being tested in clinical trials, and although the results look promising, it is not known precisely how they work.

McPherson et al. used mice that develop a disease similar to multiple sclerosis because some of their immune cells, known as effector T cells, attack a protein found in the mouse brain called MBP. The mice were treated with a peptide based on part of MBP, which prevented them from developing the autoimmune disease. The success of the peptide therapy depended on the T cells producing large amounts of a protein called PD-1. This protein stops the T-cells from activating immune responses when they detect the MBP protein.

The gene that makes PD-1 can have a methyl-tag—a chemical modification to DNA—which alters how much PD-1 is made in the T cells. When the gene has this methyl-tag, it can only be switched on for a short time to make a small amount of PD-1, which helps to control the immune responses activated by the T cell. However, when the methyl-tag was removed as a result of the peptide therapy the gene could be switched on for much longer, so that much more PD-1 was produced.

This work helps us to understand how peptide therapy works and should improve the chances of using this therapy to successfully treat patients with autoimmune diseases.

DOI:http://dx.doi.org/10.7554/eLife.03416.002

Mannan-conjugated myelin peptides prime non-pathogenic Th1 and Th17 cells and ameliorate experimental autoimmune encephalomyelitis

Antigen presenting cells (APC) are critical for regulating immune responses. We tested mannan-peptide conjugates for targeting myelin peptides to APC to induce T cell tolerance and resistance to experimental autoimmune encephalomyelitis (EAE). Myelin peptides conjugated to mannan in oxidized (OM) or reduced (RM) forms protected mice against EAE in prophylactic and therapeutic protocols, with OM-conjugated peptides giving best results. Protection was peptide-specific and associated with reduced antigen-specific T cell proliferation, but not alterations in Th1, Th17 and Treg cell differentiation or T cell apoptosis compared to EAE controls. Bone marrow-derived dendritic cells (DC) loaded with OM-MOG showed up-regulated expression of co-stimulatory molecules, reduced PD-L1 expression and enhanced CD40-inducible IL-12 and IL-23 production compared to MOG DC, features consistent with immunogenic DC. OM-MOG induced active T cell tolerance because i.d. administration or passive transfer of OM-MOG DC suppressed ongoing EAE, while OM-MOG-vaccinated mice did not reduce the proliferation of transferred MOG-specific T cells. As in vivo, MOG-specific T cells cultured with OM-MOG DC showed reduced proliferation and equal Th1 and Th17 cell differentiation compared to those with MOG DC, but surprisingly cytokine production was unresponsive to CD40 engagement. Impaired effector T cell function was further evidenced in spinal cord sections from OM-MOG-vaccinated EAE mice, where markedly reduced numbers of CD3(+) T cells were present, restricted to leptomeninges and exceptional parenchymal lesions. Our results show that mannan-conjugated myelin peptides protect mice against EAE through the expansion of antigen-specific Th1 and Th17 cells with impaired proliferation responses and APC-induced co-stimulatory signals that are required for licensing them to become fully pathogenic T cells.

Effects of Preinfection With Bovine Viral Diarrhea Virus on Immune Cells From the Lungs of Calves Inoculated With Bovine Herpesvirus 1.1

The aim of this work was to study the interstitial aggregates of immune cells observed in pulmonary parenchyma of calves preinfected with bovine viral diarrhea virus and challenged later with bovine herpesvirus 1. In addition, the intent of this research was to clarify the role of bovine viral diarrhea virus in local cell-mediated immunity and potentially in predisposing animals to bovine respiratory disease complex. Twelve Friesian calves, aged 8 to 9 months, were inoculated with noncytopathic bovine viral diarrhea virus genotype 1. Ten were subsequently challenged with bovine herpesvirus 1 and euthanized at 1, 2, 4, 7, or 14 days postinoculation. The other 2 calves were euthanized prior to the second inoculation. Another cohort of 10 calves was inoculated only with bovine herpesvirus 1 and then were euthanized at the same time points. Two calves were not inoculated with any agent and were used as negative controls. Pulmonary lesions were evaluated in all animals, while quantitative and biosynthetic changes in immune cells were concurrently examined immunohistochemically to compare coinfected calves and calves challenged only with bovine herpesvirus 1. Calves preinfected with bovine viral diarrhea virus demonstrated moderate respiratory clinical signs and histopathologic evidence of interstitial pneumonia with aggregates of mononuclear cells, which predominated at 4 days postinoculation. Furthermore, this group of animals was noted to have a suppression of interleukin-10 and associated alterations in the Th1-driven cytokine response in the lungs, as well as inhibition of the response of CD8+ and CD4+ T lymphocytes against bovine herpesvirus 1. These findings suggest that bovine viral diarrhea virus preinfection could affect the regulation of the immune response as modulated by regulatory T cells, as well as impair local cell-mediated immunity to secondary respiratory pathogens.

Sequential transcriptional changes dictate safe and effective antigen-specific immunotherapy

Antigen-specific immunotherapy combats autoimmunity or allergy by reinstating immunological tolerance to target antigens without compromising immune function. Optimization of dosing strategy is critical for effective modulation of pathogenic CD4⁺ T-cell activity. Here we report that dose escalation is imperative for safe, subcutaneous delivery of the high self-antigen doses required for effective tolerance induction and elicits anergic, interleukin (IL)-10-secreting regulatory CD4⁺ T cells. Analysis of the CD4⁺ T-cell transcriptome, at consecutive stages of escalating dose immunotherapy, reveals progressive suppression of transcripts positively regulating inflammatory effector function and repression of cell cycle pathways. We identify transcription factors, c-Maf and NFIL3, and negative co-stimulatory molecules, LAG-3, TIGIT, PD-1 and TIM-3, which characterize this regulatory CD4⁺ T-cell population and whose expression correlates with the immunoregulatory cytokine IL-10. These results provide a rationale for dose escalation in T-cell-directed immunotherapy and reveal novel immunological and transcriptional signatures as surrogate markers of successful immunotherapy.

Dose escalation in antigen-specific therapies is recognized as safe and effective, but the underlying effects of dosing variables on the immune system are not understood. Here, the authors demonstrate that dose escalation causes sequential modulation of gene expression among antigen-specific lymphocytes.

Amelioration of ovalbumin-induced allergic airway disease following Der p 1 peptide immunotherapy is not associated with induction of IL-35

In the present study, we show therapeutic amelioration of established ovalbumin (OVA)-induced allergic airway disease following house dust mite (HDM) peptide therapy. Mice were sensitized and challenged with OVA and HDM protein extract (Dermatophagoides species) to induce dual allergen sensitization and allergic airway disease. Treatment of allergic mice with peptides derived from the major allergen Der p 1 suppressed OVA-induced airway hyperresponsiveness, tissue eosinophilia, and goblet cell hyperplasia upon rechallenge with allergen. Peptide treatment also suppressed OVA-specific T-cell proliferation. Resolution of airway pathophysiology was associated with a reduction in recruitment, proliferation, and effector function of T(H)2 cells and decreased interleukin (IL)-17⁺ T cells. Furthermore, peptide immunotherapy induced the regulatory cytokine IL-10 and increased the proportion of Fox p3⁺ cells among those expressing IL-10. Tolerance to OVA was not associated with increased IL-35. In conclusion, our results provide in vivo evidence for the creation of a tolerogenic environment following HDM peptide immunotherapy, leading to the therapeutic amelioration of established OVA-induced allergic airway disease.

Global Inhibition of DC Priming Capacity in the Spleen of Self-Antigen Vaccinated Mice Requires IL-10

Dendritic cells (DC) in the spleen are highly activated following intravenous vaccination with a foreign-antigen, promoting expansion of effector T cells, but remain phenotypically and functionally immature after vaccination with a self-antigen. Up-regulation or suppression of expression of a cohort of pancreatic enzymes 24–72 h post-vaccination can be used as a biomarker of stimulatory versus tolerogenic DC, respectively. Here we show, using MUC1 transgenic mice and a vaccine based on the MUC1 peptide, which these mice perceive as a self-antigen, that the difference in enzyme expression that predicts whether DC will promote immune response or immune tolerance is seen as early as 4–8 h following vaccination. We also identify early production of IL-10 as a predominant factor that both correlates with this early-time point and controls DC function. Pre-treating mice with an antibody against the IL-10 receptor prior to vaccination results in DC that up-regulate CD40, CD80, and CD86 and promote stronger IFNγ+ T cell responses. This study suggests that transient inhibition of IL-10 prior to vaccination could improve responses to cancer vaccines that utilize self-tumor antigens.

Effector and central memory T helper 2 cells respond differently to peptide immunotherapy

Peptide immunotherapy (PIT) offers realistic prospects for the treatment of allergic diseases, including allergic asthma. Much is understood of the behavior of naive T cells in response to PIT. However, treatment of patients with ongoing allergic disease requires detailed understanding of the responses of allergen-experienced T cells. CD62L expression by allergen-experienced T cells corresponds to effector/effector memory (CD62L(lo)) and central memory (CD62L(hi)) subsets, which vary with allergen exposure (e.g., during, or out with, pollen season). The efficacy of PIT on different T helper 2 (Th2) cell memory populations is unknown. We developed a murine model of PIT in allergic airway inflammation (AAI) driven by adoptively transferred, traceable ovalbumin-experienced Th2 cells. PIT effectively suppressed AAI driven by unfractionated Th2 cells. Selective transfer of CD62L(hi) and CD62L(lo) Th2 cells revealed that these two populations behaved differently from one another and from previously characterized (early deletional) responses of naive CD4(+) T cells to PIT. Most notably, allergen-reactive CD62L(lo) Th2 cells were long-lived within the lung after PIT, before allergen challenge, in contrast to CD62L(hi) Th2 cells. Despite this, PIT was most potent against CD62L(lo) Th2 cells in protecting from AAI, impairing their ability to produce Th2 cytokines, whereas this capacity was heightened in PIT-treated CD62L(hi) Th2 cells. We conclude that Th2 cells do not undergo an early deletional form of tolerance after PIT. Moreover, memory Th2 subsets respond differently to PIT. These findings have implications for the clinical translation of PIT in different allergic scenarios.

Combination peptide immunotherapy suppresses antibody and helper T-cell responses to the RhD protein in HLA-transgenic mice

The offspring from pregnancies of women who have developed anti-D blood group antibodies are at risk of hemolytic disease of the newborn. We have previously mapped four peptides containing immunodominant T-helper cell epitopes from the RhD protein and the purpose of the work was to develop these into a product for suppression of established anti-D responses. A panel of each of the four immunodominant RhD peptides was synthesized with modifications to improve manufacturability and solubility, and screened for retention of recognition by human T-helper cells. A selected version of each sequence was combined in a mixture (RhDPmix), which was tested for suppressive ability in a humanized murine model of established immune responses to RhD protein. After HLA-DR15 transgenic mice had been immunized with RhD protein, a single dose of RhDPmix, given either intranasally (P=0.008, Mann-Whitney rank sum test) or subcutaneously (P=0.043), rapidly and significantly suppressed the ongoing antibody response. This was accompanied by reduced T-helper cell responsiveness, although this change was less marked for subcutaneous RhDPmix delivery, and by the recruitment of cells with a regulatory T-cell phenotype. The results support human trials of RhDPmix peptide immunotherapy in women with established antibody responses to the RhD blood group.

Peptide-based immunotherapy: a novel strategy for allergic disease

The T-cell component of the antigen-specific immune response is the target of various novel interventions to modify chronic immunologic disorders, such as allergic diseases. Recent clinical trials have evaluated the safety and efficacy of therapeutic vaccines consisting of short, synthetic, allergen-derived peptides, corresponding to T-cell epitopes from the eliciting antigen. The main advantage of such an approach is the reduction in systemic, immunoglobulin E-mediated adverse events compared with existing whole allergen immunotherapy, often referred to as 'allergy shots'. T-cell peptide epitopes, although capable of inducing immunologic tolerance, are short linear structures that have reduced ability to cross-link mast cell- and basophil-bound immunoglobulin E. The precise mechanism of tolerance induction remains incompletely defined. However, recent data indicate that peptide therapy induces/expands a population of antigen-specific regulatory T-cells. A novel form of treatment combining efficacy with a substantially decreased occurrence of adverse events is likely to have a major impact on the management and prevalence of allergic diseases. Furthermore, the principles of epitope-specific therapy hold promise for the development of therapeutic vaccines for the treatment of autoimmune diseases.

Antigen-specific induced T regulatory cells impair dendritic cell function via an IL-10/MARCH1-dependent mechanism

Foxp3(+) T regulatory cells (Tregs) are critically important for the maintenance of immunological tolerance, immune homeostasis, and prevention of autoimmunity. Dendritic cells (DCs) are one of the major targets of Treg-mediated suppression. Some studies have suggested that Treg-mediated suppression of DC function is mediated by the interaction of CTLA-4 on Tregs with CD80/CD86 on the DCs resulting in downregulation of CD80/CD86 expression and a decrease in costimulation. We have re-examined the effects of Tregs on mouse DC function in a model in which Ag-specific, induced Tregs (iTregs) are cocultured with DCs in the absence of T effector cells. iTreg-treated DCs are markedly defective in their capacity to activate naive T cells. iTregs from CTLA-4-deficient mice failed to induce downregulation of CD80/CD86, but DCs treated with CTLA-4-deficient iTregs still exhibited impaired capacity to activate naive T cells. The iTreg-induced defect in DC function could be completely reversed by anti-IL-10, and IL-10-deficient iTregs failed to downregulate DC function. iTreg-treated DCs expressed high levels of MARCH1, an E3 ubiquitin ligase, recently found to degrade CD86 and MHC class II on the DCs and expressed lower levels of CD83, a molecule involved in neutralizing the function of MARCH1. Both the enhanced expression of MARCH1 and the decreased expression of CD83 were mediated by IL-10 produced by the iTregs. Taken together, these studies demonstrate that a major suppressive mechanism of DC function by iTregs is secondary to the effects of IL-10 on MARCH1 and CD83 expression.

Regulation of adaptive immunity; the role of interleukin-10

Since the discovery of interleukin-10 (IL-10) in the 1980s, a large body of work has led to its recognition as a pleiotropic immunomodulatory cytokine that affects both the innate and adaptive immune systems. IL-10 is produced by a wide range of cell types, but for the purposes of this review we shall focus on IL-10 secreted by CD4(+) T cells. Here we describe the importance of IL-10 as a mediator of suppression used by both FoxP3(+) and FoxP3(-) T regulatory cells. Moreover, we discuss the molecular events leading to the induction of IL-10 secretion in T helper cell subsets, where it acts as a pivotal negative feedback mechanism. Finally we discuss how a greater understanding of this principle has allowed for the design of more efficient, antigen-specific immunotherapy strategies to exploit this natural phenomenon clinically.

Drainage of cells and soluble antigen from the CNS to regional lymph nodes

Despite the absence of conventional lymphatics, there is efficient drainage of both cerebrospinal fluid (CSF) and interstitial fluid (ISF) from the CNS to regional lymph nodes. CSF drains from the subarachnoid space by channels that pass through the cribriform plate of the ethmoid bone to the nasal mucosa and cervical lymph nodes in animals and in humans; antigen presenting cells (APC) migrate along this pathway to lymph nodes. ISF and solutes drain from the brain parenchyma to cervical lymph nodes by a separate route along 100–150 nm wide basement membranes in the walls of cerebral capillaries and arteries. This pathway is too narrow for the migration of APC so it is unlikely that APC traffic directly from brain parenchyma to lymph nodes by this route. We present a model for the pivotal involvement of regional lymph nodes in immunological reactions of the CNS. The role of regional lymph nodes in immune reactions of the CNS in virus infections, the remote influence of the gut microbiota, multiple sclerosis and stroke are discussed. Evidence is presented for the role of cervical lymph nodes in the induction of tolerance and its influence on neuroimmunological reactions. We look to the future by examining how nanoparticle technology will enhance our understanding of CNS-lymph node connections and by reviewing the implications of lymphatic drainage of the brain for diagnosis and therapy of diseases of the CNS ranging from neuroimmunological disorders to dementias. Finally, we review the challenges and opportunities for progress in CNS-lymph node interactions and their involvement in disease processes.

Adaptive immune responses in CNS autoimmune disease: mechanisms and therapeutic opportunities

The processes underlying autoimmune CNS inflammation are complex, but key roles for autoimmune lymphocytes seem inevitable, based on clinical investigations in multiple sclerosis (MS) and related diseases such as neuromyelitis optica, together with the known pathogenic activity of T cells in experimental autoimmune encephalomyelitis (EAE) models. Despite intense investigation, the details of etiopathology in these diseases have been elusive. Here we describe recent advances in the rodent models that begin to allow a map of pathogenic and protective immunity to be drawn. This map might illuminate previous successful and unsuccessful therapeutic strategies targeting particular pathways, whilst also providing better opportunities for the future, leading to tailored intervention based on understanding the quality of each individual's autoimmune response.

Combination peptide immunotherapy based on T-cell epitope mapping reduces allergen-specific IgE and eosinophilia in allergic airway inflammation

Peptide immunotherapy using soluble peptides containing allergen-derived immunodominant T-cell epitopes holds therapeutic promise for allergic asthma. Previous studies in BALB/c mice using the immunodominant peptide epitope of chicken ovalbumin (p323-339) have been unable to demonstrate therapeutic effects in ovalbumin-induced allergic airway inflammation. We have previously shown that intravenous application of p323-339 can effectively tolerise p323-339-reactive T cells in a non-allergic model in C57BL/6 mice. This study aimed to assess the effects of using p323-339 immunotherapy in a C57BL/6 model of ovalbumin-induced allergic airway inflammation, identify any additional epitopes recognized by the ovalbumin-responsive T-cell repertoire in C57BL/6 mice and assess the effects of combination peptide immunotherapy in this model. Ovalbumin-reactive T-cell lines were generated from ovalbumin-immunized C57BL/6 mice and proliferative responses to a panel of overlapping peptides covering the ovalbumin sequence were assessed. Soluble peptides (singly or combined) were administered intravenously to C57BL/6 mice before the induction of ovalbumin-induced allergic airway inflammation. Peptide immunotherapy using the 323-339 peptide alone did not reduce the severity of allergic airway inflammation. An additional immunodominant T-cell epitope in ovalbumin was identified within the 263-278 sequence. Combination peptide immunotherapy, using the 323-339 and 263-278 peptides together, reduced eosinophilia in the bronchoalveolar lavage and ovalbumin-specific IgE, with apparent reductions in interleukin-5 and interleukin-13. Characterization of the T-cell response to a model allergen has allowed the development of combination peptide immunotherapy with improved efficacy in allergic airway inflammation. This model holds important potential for future mechanistic studies using peptide immunotherapy in allergy.

Carbon monoxide-treated dendritic cells decrease β1-integrin induction on CD8⁺ T cells and protect from type 1 diabetes

Carbon monoxide (CO) treatment improves pathogenic outcome of autoimmune diseases by promoting tolerance. However, the mechanism behind this protective tolerance is not yet defined. Here, we show in a transgenic mouse model for autoimmune diabetes that ex vivo gaseous CO (gCO)-treated DCs loaded with pancreatic β-cell peptides protect mice from disease. This protection is peptide-restricted, independent of IL-10 secretion by DCs and of CD4(+) T cells. Although no differences were observed in autoreactive CD8(+) T-cell function from gCO-treated versus untreated DC-immunized groups, gCO-treated DCs strongly inhibited accumulation of autoreactive CD8(+) T cells in the pancreas. Interestingly, induction of β1-integrin was curtailed when CD8(+) T cells were primed with gCO-treated DCs, and the capacity of these CD8(+) T cells to lyse isolated islet was dramatically impaired. Thus, immunotherapy using CO-treated DCs appears to be an original strategy to control autoimmune disease.

Antigen-specific blocking of CD4-specific immunological synapse formation using BPI and current therapies for autoimmune diseases

In this review, we discuss T-cell activation, etiology, and the current therapies of autoimmune diseases (i.e., MS, T1D, and RA). T-cells are activated upon interaction with antigen-presenting cells (APC) followed by a "bull's eye"-like formation of the immunological synapse (IS) at the T-cell-APC interface. Although the various disease-modifying therapies developed so far have been shown to modulate the IS and thus help in the management of these diseases, they are also known to present some undesirable side effects. In this study, we describe a novel and selective way to suppress autoimmunity by using a bifunctional peptide inhibitor (BPI). BPI uses an intercellular adhesion molecule-1 (ICAM-1)-binding peptide to target antigenic peptides (e.g., proteolipid peptide, glutamic acid decarboxylase, and type II collagen) to the APC and therefore modulate the immune response. The central hypothesis is that BPI blocks the IS formation by simultaneously binding to major histocompatibility complex-II and ICAM-1 on the APC and selectively alters the activation of T cells from T(H)1 to T(reg) and/or T(H)2 phenotypes, leading to tolerance.

Identification, immunomodulatory activity, and immunogenicity of the major helper T-cell epitope on the K blood group antigen

The K blood group remains an important target in hemolytic disease of the newborn (HDN), with no immune prophylaxis available. The aim was to characterize the Th response to K as a key step in designing specific immunotherapy and understanding the immunogenicity of the Ag. PBMCs from K-negative women who had anti-K Abs after incompatible pregnancy, and PBMCs from unimmunized controls, were screened for proliferative responses to peptide panels spanning the K or k single amino acid polymorphism. A dominant K peptide with the polymorphism at the C terminus elicited proliferation in 90% of alloimmunized women, and it was confirmed that responding cells expressed helper CD3(+)CD4(+) and "memory" CD45RO(+) phenotypes, and were MHC class II restricted. A relatively high prevalence of background peptide responses independent of alloimmunization may contribute to K immunogenicity. First, cross-reactive environmental Ag(s) pre-prime Kell-reactive Th cells, and, second, the K substitution disrupts an N-glycosylation motif, allowing the exposed amino acid chain to stimulate a Th repertoire that is unconstrained by self-tolerance in K-negative individuals. The dominant K peptide was effective in inducing linked suppression in HLA-transgenic mice and can now be taken forward for immunotherapy to prevent HDN because of anti-K responses.

Age-related accumulation of T cells with markers of relatively stronger autoreactivity leads to functional erosion of T cells

Background

Thymic involution is a prominent characteristic of an aging immune system. When thymic function is reduced/absent, the peripheral T cell pool is subject to the laws of peripheral T cell homeostasis that favor survival/expansion of T cell receptors with relatively higher functional avidity for self-peptide/MHC complexes. Due to difficulties in assessing the TCR avidity in polyclonal population of T cells, it is currently not known whether high avidity T cells preferentially survive in aging individuals, and what impact this might have on the function of the immune system and development of autoimmune diseases.

Results

The phenotype of T cells from aged mice (18-24 months) indicating functional TCR avidity (CD3 and CD5 expression) correlates with the level of preserved thymic function. In mice with moderate thymic output (> 30% of peripheral CD62L^hi T cells), T cells displayed CD3^lowCD5^hi phenotype characteristic for high functional avidity. In old mice with drastically low numbers of CD62L^hi T cells reduced CD5 levels were found. After adult thymectomy, T cells of young mice developed CD3^lowCD5^hi phenotype, followed by a CD3^lowCD5^low phenotype. Spleens of old mice with the CD3^low/CD5^hi T cell phenotype displayed increased levels of IL-10 mRNA, and their T cells could be induced to secrete IL-10 in vitro. In contrast, downmodulation of CD5 was accompanied with reduced IL-10 expression and impaired anti-CD3 induced proliferation. Irrespective of the CD3/CD5 phenotype, reduced severity of experimental allergic myelitis occurred in old mice. In MTB TCRβ transgenic mice that display globally elevated TCR avidity for self peptide/MHC, identical change patterns occurred, only at an accelerated pace.

Conclusions

These findings suggest that age-associated dysfunctions of the immune system could in part be due to functional erosion of T cells devised to protect the hosts from the prolonged exposure to T cells with high-avidity for self.

Role of dendritic cell maturity/costimulation for generation, homeostasis, and suppressive activity of regulatory T cells

Tolerogenicity of dendritic cells (DCs) has initially been attributed exclusively to immature/resting stages, while mature/activated DCs were considered strictly immunogenic. Later, all different subsets among the myeloid/conventional DCs and plasmacytoid DCs have been shown to bear tolerogenic potential, so that tolerogenicity could not be attributed to a specific subset. Immunosuppressive treatments of immature DC subsets could prevent re-programming into mature DCs or upregulated inhibitory surface markers or cytokines. Furthermore, the different T cell tolerance mechanisms anergy, deletion, immune deviation, and suppression require different quantities and qualities of costimulation by DCs. Since expansion of regulatory T cells (Tregs) has been shown to be promoted best by fully mature DCs the role of CD80/B7-1 and CD86/B7-2 as major costimulatory molecules for Treg biology is under debate. In this review, we discuss the role of these and other costimulatory molecules on myeloid DCs and their ligands CD28 and CD152/CTLA-4 on Tregs for peripheral conversion from naive CD4⁺ T cells into the major subsets of Foxp3⁺ Tregs and Foxp3⁻ IL-10⁺ regulatory type-1 T cells (Tr1) or Tr1-like cells and their role for peripheral maintenance in the steady state and after activation.

IL-9 is important for T-cell activation and differentiation in autoimmune inflammation of the central nervous system

Experimental autoimmune encephalomyelitis (EAE) is generally believed to be an autoimmune disease of the central nervous system (CNS) caused by myelin-specific Th1 and/or Th17 effector cells. The underlying cellular and molecular mechanisms, however, are not fully understood. Using mice deficient in IL-9 (IL-9(-/-) ), we showed that IL-9 plays a critical role in EAE. Specifically, IL-9(-/-) mice developed significantly less severe EAE than their WT counterparts following both immunization with myelin proteolipid protein (PLP)(180-199) peptide in the presence of Complete Freund's Adjuvant (CFA), and adoptive transfer of PLP(180-199) peptide-specific effector T cells from WT littermates. EAE-resistant IL-9(-/-) mice exhibited considerably fewer infiltrating immune cells in the CNS, with lower levels of IL-17 and IFN-γ expression, than their WT littermates. Further studies revealed that null mutation of the IL-9 gene resulted in significantly lower levels of PLP(180-199) peptide-specific IL-17 and IFN-γ production. Moreover, IL-9(-/-) memory/activated T cells exhibited decreased C-C chemokine receptors (CCR)2, CCR5, and CCR6 expression. Interestingly, IL-10 was significantly increased in IL-9(-/-) mice compared with WT littermates. Importantly, we found that IL-9-mediated Th17-cell differentiation triggers complex STAT signaling pathways.

Immunotherapy with peptides

Specific allergen immunotherapy is clinically effective and disease modifying. It has a duration of effect that exceeds the treatment period and prevents both the progression of allergic rhinitis to asthma and the acquisition of new allergic sensitizations. However, immunotherapy is associated with a high frequency of adverse events related to the allergenicity of vaccines. Allergenicity is conferred by the presence of intact B-cell epitopes that crosslink allergen-specific IgE on effector cells. The use of linear peptide sequences representing fragments of the native allergen is one approach to reduce allergenicity. Preclinical models of peptide immunotherapy have demonstrated efficacy in both autoimmunity and allergy. Translation of this technology into the clinic has gained momentum in recent years based on encouraging results from early clinical trials. To date, efforts have focused on two major allergens, but vaccines to a broader range of molecules are currently in clinical development. Mechanistically, peptide immunotherapy appears to work through the induction of adaptive, allergen-specific regulatory T cells that secrete the immunoregulatory cytokine IL-10. There is also evidence that peptide immunotherapy targeting allergen-specific T cells can indirectly modulate allergen-specific B-cell responses. Peptide immunotherapy may provide a safe and efficacious alternative to conventional subcutaneous and/or sublingual approaches using native allergen preparations.

T cell epitope-based allergy vaccines

Specific immunotherapy (SIT) with extracts containing intact allergen molecules is clinically efficacious, but associated with frequent adverse events related to the allergic sensitization of the patient. As a result, treatment is initiated in an incremental dose fashion which ultimately achieves a plateau (maintenance dose) that may be continued for several years. Reduction of allergic adverse events may allow safer and more rapid treatment Thus, many groups have developed and evaluated strategies to reduce allergenicity whilst maintaining immunogenicity, the latter being required to achieve specific modulation of the immune response. Peptide immunotherapy can be used to target T and/or B cells in an antigen-specific manner. To date, only approaches that target T cells have been clinically evaluated. Short, synthetic peptides representing immunodominant T cell epitopes of major allergens are able to modulate allergen-specific T cell responses in the absence of IgE cross linking and activation of effector cells. Here we review clinical and mechanistic studies associated with peptide immunotherapy targeting allergy to cats or to bee venom. 

Immune regulation of multiple sclerosis by transdermally applied myelin peptides

OBJECTIVE

Antigen-specific therapy targeting selective inhibition of autoreactive responses holds promise for controlling multiple sclerosis (MS) without disturbing homeostasis of the whole immune system. Key autoantigens in MS include myelin proteins, such as myelin basic protein (MBP), proteolipid protein (PLP), and myelin oligodendrocyte glycoprotein (MOG). In this study, we examined the effect of transdermal therapy with myelin peptides on immune responses in the skin, lymph nodes, and peripheral blood immune cells of MS patients.

METHODS

In a 1-year placebo-controlled study, 30 patients with relapsing-remitting MS were treated transdermally with a mixture of 3 myelin peptides: MBP85-99, PLP139-151, and MOG35-55, or placebo. The phenotype of immune cells in the skin was assessed using immunohistochemistry. Cell populations in lymph nodes were analyzed using flow cytometry. In peripheral blood immune cells, cytokine production was measured by enzyme-linked immunosorbent assay, and myelin-specific proliferation was examined by carboxyfluorescein succinimidyl ester-based assay.

RESULTS

We found that myelin peptides applied transdermally to MS patients activated dendritic Langerhans cells in the skin at the site of immunization and induced a unique population of granular dendritic cells in local lymph nodes. In the periphery, transdermal immunization with myelin peptides resulted in the generation of type 1, interleukin-10-producing regulatory T cells, suppression of specific autoreactive proliferative responses, and suppression of interferon-γ and transforming growth factor-β production.

INTERPRETATION

We demonstrate for the first time the immunoregulatory potential of transdermal immunization with myelin peptides in MS patients.

T-cell based immunotherapy in experimental autoimmune encephalomyelitis and multiple sclerosis

One of the reasons multiple sclerosis (MS) has been considered a T-cell mediated autoimmune disease is that a similar experimental disease can be induced in certain rodents and primates by immunization with myelin antigens, leading to T-cell-mediated inflammatory demyelination in the CNS. In addition, most if not all pharmacological treatments available for MS are biologically active on T cells. In this article we review the principles of T-cell-based immunotherapies and the specific actions of current and novel treatments on T-cell functions, when these are known. For both licensed and innovative agents, we also discuss biological actions on other immune cell types. Finally, we offer a brief perspective on expected changes in the use of MS immunotherapies in the near future.

Reduced lymphocyte infiltration during cytomegalovirus brain infection of interleukin-10-deficient mice

Interleukin (IL)-10 deficiency results in highly elevated levels of interferon (IFN)-gamma, as well as the IFN-gamma-inducible chemokines CXCL9 and CXCL10 within murine cytomegalovirus (MCMV)-infected brains. To test the hypothesis that these elevated chemokine levels would result in enhanced brain infiltration, we compared immune cell infiltration in response to MCMV brain infection between wild-type and IL-10 knockout (KO) mice. Longitudinal analysis following adoptive transfer of cells from beta-actin-luciferase transgenic wild-type mice showed maximal brain infiltration by peripheral immune cells occurred at 5 days post infection. Although the overall percentage of CD45(hi) cells infiltrating the brain was not altered by IL-10 deficiency, paradoxically, despite elevated chemokine levels, reduced T lymphocyte (CD8+) and natural killer (NK) (CD49b+) cell infiltration into the brain was observed in IL-10-deficient animals. This decreased lymphocyte infiltration was associated with elevated levels of the lymph node homing receptor L-selectin/CD62L on CD8+ T cells. Lymph node cells obtained from MCMV-infected mice deficient in IL-10 also displayed reduced migration towards CXCL10 when compared to wild-type animals. Taken together, these data show that despite elevated chemokine levels, absence of IL-10 results in reduced lymphocyte infiltration into MCMV-infected brains.

Antigenic strength controls the generation of antigen-specific IL-10-secreting T regulatory cells

Administration of peptides i.n. induces peripheral tolerance in Tg4 myelin basic protein-specific TCR-Tg mice. This is characterized by the generation of anergic, IL-10-secreting CD4+ T cells with regulatory function (IL-10 Treg). Myelin basic protein Ac1-9 peptide analogs, displaying a hierarchy of affinities for H-2 A(u) (Ac1-9[4K]<<[4A]<[4Y]), were used to investigate the mechanisms of tolerance induction, focusing on IL-10 Treg generation. Repeated i.n. administration of the highest affinity peptide, Ac1-9[4Y], provided complete protection against EAE, while i.n. Ac1-9[4A] and Ac1-9[4K] treatment resulted in only partial protection. Ac1-9[4Y] was also the most potent stimulus for IL-10 Treg generation. Although i.n. treatment with Ac1-9[4A] gave rise to IL-10-secreting CD4+ T cells, the population as a whole was also capable of secreting IFN-gamma after an in vitro recall response to Ac1-9[4A] or [4Y]. In addition to IL-10 production, other facets of tolerance, namely, anergy and suppression (both in vitro and in vivo), were affinity dependent, with i.n. Ac1-9[4Y]-, [4A]- or [4K]-treated CD4+ T cells being the most, intermediate and least anergic/suppressive, respectively. These findings demonstrate that the generation of IL-10 Treg in vivo is driven by high signal strength.

The cytokine milieu in the interplay of pathogenic Th1/Th17 cells and regulatory T cells in autoimmune disease

The propagation and regulation of an immune response is driven by a network of effector and regulatory T (Treg) cells. The interplay of effector T and Treg cells determines the direction of the immune response towards inflammation or its resolution in an autoimmune disease setting. In autoimmune diseases, this interplay shifts the balance in favor of the development of autoreactive effector T cells, resulting in inflammatory pathology. The objective of an effective therapeutic approach for autoimmune disease is to restore this balance. In this review, we describe the characteristics and development of pathogenic T helper 1 (Th1) and Th17 cells and the beneficial Treg cells in autoimmune diseases and the crucial roles of the cytokine milieu in influencing the balance of these T-cell subsets. Given the importance of cytokines, we discuss current immunotherapeutic strategies using cytokine or cytokine receptor antibodies for the treatment of autoimmune diseases.