A single amino acid change in a myelin basic protein peptide confers the capacity to prevent rather than induce experimental autoimmune encephalomyelitis

Autoantigen and IL-2 activated CD4+CD25+T regulatory cells are induced to express CD8 and are autoantigen specific in inhibiting experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) induced by immunization with myelin basic protein (MBP) is a self-limiting disease model of multiple sclerosis. CD4+CD25+Foxp3+T cells play a role in limiting autoimmune disease but treatment with antigen naïve CD4+CD25+ cells does not reduce EAE. This study examined if in vitro activation by MBP and rIL-2 induced CD4+CD25+Foxp3+ cells that could inhibit EAE. Culture of CD4+CD8-CD25+cells from naïve rats with MBP and rIL-2 induced activated Treg that reduced the severity of clinical EAE and infiltration of CD8+T cells and macrophage into brain stem. CD4+CD25+T cells activated by an irrelevant autoantigen and rIL-2 did not suppress EAE. Resting CD4+CD25+T cells activated by autoantigen and rIL-2 have mRNA for Infgr, Il12rb2, Il5 but not Tbet, Gata3, Ilr5ra or Ifng. These changes in mRNA expression are the markers of Ts1 cells. A proportion of CD4+CD8-CD25+ cells activated by MBP/rIL-2 were induced to express CD8α, CD8β and CD62L. Depletion of CD4+CD8α+CD25+ cells removed the capacity of MBP and rIL-2 activated CD4+CD25+T cells to suppress EAE. This study demonstrated that in vitro activation of CD4+CD8-CD25+ cells by MBP/rIL-2 induced relevant antigen-specific Treg within days, which expressed CD8α, CD8β and CD62L with a Ts1 phenotype and that had greater potency than freshly isolated antigen naive CD4+CD25+Treg in suppressing clinical severity of EAE and immune inflammation in CNS. These findings may guide development of antigen-specific Treg for therapy.

Evolving understanding of autoimmune mechanisms and new therapeutic strategies of autoimmune disorders

Autoimmune disorders are characterized by aberrant T cell and B cell reactivity to the body's own components, resulting in tissue destruction and organ dysfunction. Autoimmune diseases affect a wide range of people in many parts of the world and have become one of the major concerns in public health. In recent years, there have been substantial progress in our understanding of the epidemiology, risk factors, pathogenesis and mechanisms of autoimmune diseases. Current approved therapeutic interventions for autoimmune diseases are mainly non-specific immunomodulators and may cause broad immunosuppression that leads to serious adverse effects. To overcome the limitations of immunosuppressive drugs in treating autoimmune diseases, precise and target-specific strategies are urgently needed. To date, significant advances have been made in our understanding of the mechanisms of immune tolerance, offering a new avenue for developing antigen-specific immunotherapies for autoimmune diseases. These antigen-specific approaches have shown great potential in various preclinical animal models and recently been evaluated in clinical trials. This review describes the common epidemiology, clinical manifestation and mechanisms of autoimmune diseases, with a focus on typical autoimmune diseases including multiple sclerosis, type 1 diabetes, rheumatoid arthritis, systemic lupus erythematosus, and sjögren's syndrome. We discuss the current therapeutics developed in this field, highlight the recent advances in the use of nanomaterials and mRNA vaccine techniques to induce antigen-specific immune tolerance.

A novel combination approach to effectively reduce inflammation and neurodegeneration in multiple sclerosis models

Multiple sclerosis (MS) is an autoimmune disease characterized by immune-mediated attacks on the central nervous system (CNS), resulting in demyelination and recurring T-cell responses. Unfortunately, there is no cure for it. Current therapies that target immunomodulation and/or immunosuppression show only modest beneficial effects, have many side effects, and do not block neurodegeneration or progression of the disease. Since neurodegeneration and in particular axonal degeneration is implicated in disability in progressive MS, development of novel therapeutic strategies to attenuate the neurodegenerative processes is imperative. This study aims to develop new safe and efficacious treatments that address both the inflammatory and neurodegenerative aspects of MS using its animal model, experimental allergic encephalomyelitis (EAE). In EAE, the cysteine protease calpain is upregulated in CNS tissue, and its activity correlates with neurodegeneration. Our immunologic studies on MS have indicated that increased calpain activity promotes pro-inflammatory T helper (Th)1 cells and the severity of the disease in EAE, suggesting that calpain inhibition could be a novel target to combat neurodegeneration in MS/EAE. While calpain inhibition by SNJ1945 reduced disease severity, treatment of EAE animals with a novel protease-resistant altered small peptide ligand (3aza-APL) that mimic myelin basic protein (MBP), also decreased the incidence of EAE, disease severity, infiltration of inflammatory cells, and protected myelin. A reduction in inflammatory T-cells with an increase in Tregs and myeloid suppressor cells is also found in EAE mice treated with SNJ1945 and 3aza-APL. Thus, a novel combination strategy was tested in chronic EAE mouse model in B10 mice which showed multiple pathological mechanisms could be addressed by simultaneous treatment with calpain inhibitor SNJ1945 and protease-resistant 3aza-APL to achieve a stronger therapeutic effect.

Small Extracellular Vesicles Derived from Altered Peptide Ligand-Loaded Dendritic Cell Act as A Therapeutic Vaccine for Spinal Cord Injury Through Eliciting CD4+ T cell-Mediated Neuroprotective Immunity

The balance among different CD4+ T cell subsets is crucial for repairing the injured spinal cord. Dendritic cell (DC)-derived small extracellular vesicles (DsEVs) effectively activate T-cell immunity. Altered peptide ligands (APLs), derived from myelin basic protein (MBP), have been shown to affect CD4+ T cell subsets and reduce neuroinflammation levels. However, the application of APLs is challenging because of their poor stability and associated side effects. Herein, it is demonstrate that DsEVs can act as carriers for APL MBP87-99 A91 (A91-DsEVs) to induce the activation of 2 helper T (Th2) and regulatory T (Treg) cells for spinal cord injury (SCI) in mice. These stimulated CD4+ T cells can efficiently "home" to the lesion area and establish a beneficial microenvironment through inducing the activation of M2 macrophages/microglia, inhibiting the expression of inflammatory cytokines, and increasing the release of neurotrophic factors. The microenvironment mediated by A91-DsEVs may enhance axon regrowth, protect neurons, and promote remyelination, which may support the recovery of motor function in the SCI model mice. In conclusion, using A91-DsEVs as a therapeutic vaccine may help induce neuroprotective immunity in the treatment of SCI.

Antigen-Specific Treatment Modalities in MS: The Past, the Present, and the Future

Antigen-specific therapy for multiple sclerosis may lead to a more effective therapy by induction of tolerance to a wide range of myelin-derived antigens without hampering the normal surveillance and effector function of the immune system. Numerous attempts to restore tolerance toward myelin-derived antigens have been made over the past decades, both in animal models of multiple sclerosis and in clinical trials for multiple sclerosis patients. In this review, we will give an overview of the current approaches for antigen-specific therapy that are in clinical development for multiple sclerosis as well provide an insight into the challenges for future antigen-specific treatment strategies for multiple sclerosis.

Systemic immunization with altered myelin basic protein peptide produces sustained antidepressant-like effects

Immune dysregulation, specifically of inflammatory processes, has been linked to behavioral symptoms of depression in both human and rodent studies. Here, we evaluated the antidepressant effects of immunization with altered peptide ligands of myelin basic protein (MBP)-MBP_87-99[A⁹¹, A⁹⁶], MBP_87-99[A⁹¹], and MBP_87-99[R⁹¹, A⁹⁶]-in different models of depression and examined the mechanism by which these peptides protect against stress-induced depression. We found that a single dose of subcutaneously administered MBP_87-99[A⁹¹, A⁹⁶] produced antidepressant-like effects by decreasing immobility in the forced swim test and by reducing the escape latency and escape failures in the learned helplessness paradigm. Moreover, immunization with MBP_87-99[A⁹¹, A⁹⁶] prevented and reversed depressive-like and anxiety-like behaviors that were induced by chronic unpredictable stress (CUS). However, MBP_87-99[R⁹¹, A⁹⁶] tended to aggravate CUS-induced anxiety-like behavior. Chronic stress increased the production of peripheral and central proinflammatory cytokines and induced the activation of microglia in the prelimbic cortex (PrL), which was blocked by MBP_87-99[A⁹¹, A⁹⁶]. Immunization with MBP-derived altered peptide ligands also rescued chronic stress-induced deficits in p11, phosphorylated cyclic adenosine monophosphate response element binding protein, and brain-derived neurotrophic factor expression. Moreover, microinjections of recombinant proinflammatory cytokines and the knockdown of p11 in the PrL blunted the antidepressant-like behavioral response to MBP_87-99[A⁹¹, A⁹⁶]. Altogether, these findings indicate that immunization with altered MBP peptide produces prolonged antidepressant-like effects in rats, and the behavioral response is mediated by inflammatory factors (particularly interleukin-6), and p11 signaling in the PrL. Immune-neural interactions may impact central nervous system function and alter an individual's response to stress.

A Modified Peptide Derived from Goodpasture Autoantigen Arrested and Attenuated Kidney Injuries in a Rat Model of Anti-GBM Glomerulonephritis

BACKGROUND

In Goodpasture disease, the noncollagenous domain 1 of the α3 chain (α3NC1) of type IV collagen is the main target antigen of antibodies against glomerular basement membrane (GBM). We previously identified a nephritogenic epitope, P14 (α3_127-148), that could induce crescentic nephritis in WKY rats, and defined its core motif. Designing a modified peptide, replacing critical pathogenic residues with nonpathogenic ones (on the basis of homologous regions in α1NC1 chain of type IV collagen, known to be nonpathogenic), might provide a therapeutic option for anti-GBM GN.

METHODS

We synthesized a modified peptide, replacing a single amino acid, and injected it into α3-P14-immunized rats from day 0 (the early-treatment group) or a later-treatment group (from days 17 to 21). A scrambled peptide administrated with the same protocol served as a control.

RESULTS

The modified peptide, but not the scrambled peptide, attenuated anti-GBM GN in both treatment groups, and halted further crescent formation even after disease onset. Kidneys from the modified peptide-treated rats exhibited reductions in IgG deposits, complement activation, and infiltration by T cells and macrophages. Treatment also resulted in an anti-inflammatory cytokine profile versus a proinflammatory profile for animals not receiving the modified peptide; it also reduced α3-P14-specific T cell activation, modulated T cell differentiation by decreasing Th17 cells and enhancing the ratio of Treg/Th17 cells, and inhibited binding of α3-P14 to antibodies and MHC II molecules.

CONCLUSIONS

A modified peptide involving alteration of a critical motif in a nephritogenic T cell epitope alleviated anti-GBM GN in a rat model. Our findings may provide insights into an immunotherapeutic approach for autoimmune kidney disorders such as Goodpasture disease.

A Novel Aza-MBP Altered Peptide Ligand for the Treatment of Experimental Autoimmune Encephalomyelitis

Myelin basic protein (MBP) is a major target of T cells in lesions of multiple sclerosis (MS) patients and its animal model, experimental autoimmune encephalomyelitis (EAE). Interactions between the major histocompatibility complex II containing antigenic peptides and the T cell receptor activate CD4+ T cells that perpetuate EAE and MS. Previously reported data has shown that treating with an altered peptide ligand (APL) in which the normal antigenic peptide sequence of MBP has been slightly changed at T cell contact positions is helpful in reducing disease in both rodents and humans. The use of natural peptides, which are susceptible to protease degradation, requires high concentrations that can create hypersensitivity reactions. Our hypothesis is that APL containing aza substitutions, CH(R)-N- > N(R)N, could lead to improved protease resistance, reduced clinical disease scores, and a shift in T cell profile. In this study, several aza-APLs and control peptides were synthesized and screened for the best aza-APL candidate (3aza-APL) based on dissociation half time from major histocompatibility complex (MHC) class II, induction of IL-2 response, and resistance to degradation by proteases. The efficacy was then tested in vivo. Results indicate that 3aza-APL is superior to currently available APLs in terms of protease resistance and disease suppression in EAE mice. The 3aza-APL induced anti-inflammatory immune responses by altering key transcription factors and cytokine genes which regulate T cell subpopulations. These data suggest that the novel 3aza-APL has increased protease resistance property and is effective in reducing clinical and physiological signs of disease in EAE animals.

Comparison of antibody responses against Mycobacterium tuberculosis antigen Rv0679c in tuberculosis patients from the endemic and non-endemic regions of the Beijing genotype: a case control study

Background

Strains of the Beijing genotype of Mycobacterium tuberculosis (MTB) are reportedly associated with the virulence of tuberculosis (TB) infection, unfavorable outcomes of anti-TB treatment, and the global TB pandemic. Rv0679c, a hypothetical membrane protein related to host cell invasion, has a Beijing genotype-specific mutation at residue 142 (Asn142Lys). Antigenicity differences between Rv0679c-Asn142 (N-type) and Rv0679c-Lys142 (K-type) have been previously observed in mice antigen-antibody responses. However, the immune response to Rv0679c in humans remains unknown. Therefore, we aimed to investigate the anti-Rv0679c immune response in TB patients from the endemic and non-endemic regions of the Beijing MTB genotype.

Methods

We analyzed the Rv0679c-specific antibody responses in 84 subjects from the endemic region of the Beijing genotype MTB in China, including 45 pulmonary TB patients (C-PTB) and 39 healthy controls (C-HC), and 81 subjects from the Philippines (the endemic region of the non-Beijing genotype), including 51 pulmonary TB patients (P-PTB) and 30 healthy controls (P-HC). Anti-tuberculous-glycolipid (TBGL) antigen was used as the control antibody.

Results

TBGL IgG titers were higher in both C-PTB and P-PTB than those in their corresponding HC (C-PTB median 4.2, P-PTB median 11.2; C-PTB vs. P-PTB, p > 0.05), suggesting immune response comparability in PTB from two different countries. C-PTB showed a higher response compared to C-HC for anti-K-type IgG (53.3%) than anti-N-type IgG (6.67%); this response was not observed in P-PTB (both N-type and K-type 9.80%).

Conclusion

Dimorphic antigen Rv0679c was found to be associated with distinct immune response patterns, indicating the role of Beijing/non-Beijing genotype of MTB in stimulating specific responses in TB patients from the endemic region of Beijing MTB. Meanwhile, reactions to Rv0679c in patients and HC from non-endemic regions of the Beijing MTB may be caused by the response to the common epitope of Rv0679c N/K-type.

Citrullination only infrequently impacts peptide binding to HLA class II MHC

It has been hypothesized that HLA class II alleles associated with rheumatoid arthritis (RA) preferentially present self-antigens altered by post-translational modification, such as citrullination. To understand the role of citrullination we tested four RA-associated citrullinated epitopes and their corresponding wild-type version for binding to 28 common HLA class II. Binding patterns were variable, and no consistent impact of citrullination was identified. Indeed, in one case citrullination significantly increased binding compared to the WT peptide, in another citrullination was associated with a reduction in promiscuity by 40%. For a more comprehensive analysis, we tested over 200 citrullinated peptides derived from vimentin and collagen II for their capacity to bind the RA-associated shared epitope alleles DRB1*01:01 and DRB1*04:01. The overall effect of citrullination on binding was found to be relatively minor, and only rarely associated with 3-fold increases or decreases in affinity. Previous studies have suggested that citrullination of MHC anchor residues, in particular P4, is associated with generation of novel RA-associated epitopes. However, analysis of the predicted MHC-binding cores of all peptides tested found that in modified peptides with increased binding affinity the citrullinated residue was predicted to occupy an anchor position in only a minority of cases. Finally, we also show that identification of citrullinated peptide binders could be facilitated by using the NetMHCIIpan 3.1 algorithm, representing citrullination as a wildcard. Our studies identify a total of 117 citrullinated peptides that bound RA-associated alleles with an affinity of 1000 nM or better.

Roles of regulatory T cells and IL-10 in virus-induced demyelination

Neurotropic viruses are important causes of morbidity and mortality in human populations. Some of these viruses preferentially infect oligodendrocytes in the white matter, causing either direct lysis of infected cells, or more commonly myelin damage as a consequence of the host immune response to the virus. Virus-induced demyelination has similarities to the human disease multiple sclerosis. To study this disease process in experimental animals, mice are infected, most commonly, with neurotropic strains of mouse hepatitis virus, a coronavirus or Theiler's murine encephalomyelitis, a picornavirus. While the diseases caused by these two viruses differ in some aspects, in both cases demyelination is a major consequence of the infection. As in autoimmune disease, therapeutic interventions that diminish an overactive immune response would be useful. However, unlike autoimmune disease, complete suppression would result in unchecked virus replication, generally leading to more severe disease. Here we discuss two approaches that dampen but do not fully suppress the host immune response. Regulatory T cells, especially those that are specific for antigens recognized by pathogenic T cells, and IL-10 are two anti-inflammatory/pro-resolution factors that demonstrate efficacy in experimental models of virus-induced demyelination and may be useful in patients infected with viruses that cause demyelination.

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MHV and TMEV are common causes of virus-induced demyelination in mice

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Virus-induced demyelination is often host cell-mediated.

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Virus-specific Treg dampen pathogenic T cells responding to cognate epitope

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IL-10 expressed by Tregs and Tr1 cells dampens pathogenic T cell responses

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Tregs and IL-10 suppress pathogenic T cells without broad immunosuppression

T cells in the control of organ-specific autoimmunity

Immune tolerance is critical to the avoidance of unwarranted immune responses against self antigens. Multiple, non-redundant checkpoints are in place to prevent such potentially deleterious autoimmune responses while preserving immunity integral to the fight against foreign pathogens. Nevertheless, a large and growing segment of the population is developing autoimmune diseases. Deciphering cellular and molecular pathways of immune tolerance is an important goal, with the expectation that understanding these pathways will lead to new clinical advances in the treatment of these devastating diseases. The vast majority of autoimmune diseases develop as a consequence of complex mechanisms that depend on genetic, epigenetic, molecular, cellular, and environmental elements and result in alterations in many different checkpoints of tolerance and ultimately in the breakdown of immune tolerance. The manifestations of this breakdown are harmful inflammatory responses in peripheral tissues driven by innate immunity and self antigen-specific pathogenic T and B cells. T cells play a central role in the regulation and initiation of these responses. In this Review we summarize our current understanding of the mechanisms involved in these fundamental checkpoints, the pathways that are defective in autoimmune diseases, and the therapeutic strategies being developed with the goal of restoring immune tolerance.

Restoring the balance: immunotherapeutic combinations for autoimmune disease

Autoimmunity occurs when T cells, B cells or both are inappropriately activated, resulting in damage to one or more organ systems. Normally, high-affinity self-reactive T and B cells are eliminated in the thymus and bone marrow through a process known as central immune tolerance. However, low-affinity self-reactive T and B cells escape central tolerance and enter the blood and tissues, where they are kept in check by complex and non-redundant peripheral tolerance mechanisms. Dysfunction or imbalance of the immune system can lead to autoimmunity, and thus elucidation of normal tolerance mechanisms has led to identification of therapeutic targets for treating autoimmune disease. In the past 15 years, a number of disease-modifying monoclonal antibodies and genetically engineered biologic agents targeting the immune system have been approved, notably for the treatment of rheumatoid arthritis, inflammatory bowel disease and psoriasis. Although these agents represent a major advance, effective therapy for other autoimmune conditions, such as type 1 diabetes, remain elusive and will likely require intervention aimed at multiple components of the immune system. To this end, approaches that manipulate cells ex vivo and harness their complex behaviors are being tested in preclinical and clinical settings. In addition, approved biologic agents are being examined in combination with one another and with cell-based therapies. Substantial development and regulatory hurdles must be overcome in order to successfully combine immunotherapeutic biologic agents. Nevertheless, such combinations might ultimately be necessary to control autoimmune disease manifestations and restore the tolerant state.

A modified superantigen rescues Ly6G- CD11b+ blood monocyte suppressor function and suppresses antigen-specific inflammation in EAE

In a previous study, we showed that the Ly6G(-)CD11b(+) blood monocytes residing in naïve mice are intrinsically immunosuppressive and that loss of this suppressive function may contribute to the development of autoimmunity in experimental autoimmune encephalomyelitis (EAE), a murine model of human multiple sclerosis. Here we report that mice treated with a modified superantigen coupled to myelin oligodendrocyte glycoprotein 35-55 (MOG(35-55)) peptide (DM-MOG(35-55)) suppressed the development of EAE. The treatment was associated with impaired MOG(35-55)-specific T cell proliferation and a decrease in IL-17 and IFNγ production in the draining lymph nodes. Analysis of circulating blood immune cells showed that the suppressor function of Ly6G(-)CD11b(+) blood monocytes was reduced in EAE mice, but was restored in mice treated with DM-MOG(35-55). Importantly, adoptive transfer of blood CD11b(+)Ly6G(-) cells isolated from DM-MOG(35-55)-treated mice protected recipient mice from developing EAE. Together, these results show that DM coupled to the auto-antigen MOG(35-55): 1) suppresses EAE via antigen-specific suppression of T cell responses, and 2) re-establishes suppressor function of Ly6G(-)CD11b(+) blood monocytes. Auto-antigens coupled to DM could therefore represent a new therapeutic approach for controlling inappropriate inflammation in autoimmune diseases such as multiple sclerosis by inducing antigen-specific T cell suppression.

Do Natural T Regulatory Cells become Activated to Antigen Specific T Regulatory Cells in Transplantation and in Autoimmunity?

Antigen specific T regulatory cells (T_reg) are often CD4⁺CD25⁺FoxP3⁺ T cells, with a phenotype similar to natural T_reg (nT_reg). It is assumed that nT_reg cannot develop into an antigen specific T_reg as repeated culture with IL-2 and a specific antigen does not increase the capacity or potency of nT_reg to promote immune tolerance or suppress in vitro. This has led to an assumption that antigen specific T_reg mainly develop from CD4⁺CD25⁻FoxP3⁻ T cells, by activation with antigen and TGF-β in the absence of inflammatory cytokines such as IL-6 and IL-1β. Our studies on antigen specific CD4⁺CD25⁺ T cells from animals with tolerance to an allograft, identified that the antigen specific and T_reg are dividing, and need continuous stimulation with specific antigen T cell derived cytokines. We identified that a variety of cytokines, especially IL-5 and IFN-γ but not IL-2 or IL-4 promoted survival of antigen specific CD4⁺CD25⁺FoxP3⁺ T_reg. To examine if nT_reg could be activated to antigen specific T_reg, we activated nT_reg in culture with either IL-2 or IL-4. Within 3 days, antigen specific T_reg are activated and there is induction of new cytokine receptors on these cells. Specifically nT_reg activated by IL-2 and antigen express the interferon-γ receptor (IFNGR) and IL-12p70 (IL-12Rβ2) receptor but not the IL-5 receptor (IL-5Rα). These cells were responsive to IFN-γ or IL-12p70. nT_reg activated by IL-4 and alloantigen express IL-5Rα not IFNGR or IL-12p70Rβ2 and become responsive to IL-5. These early activated antigen specific T_reg, were respectively named Ts1 and Ts2 cells, as they depend on Th1 or Th2 responses. Further culture of Ts1 cells with IL-12p70 induced Th1-like T_reg, expressing IFN-γ, and T-bet as well as FoxP3. Our studies suggest that activation of nT_reg with Th1 or Th2 responses induced separate lineages of antigen specific T_reg, that are dependent on late Th1 and Th2 cytokines, not the early cytokines IL-2 and IL-4.

The Involvement of Calpain in CD4+ T Helper Cell Bias in Multple Sclerosis

The pathogenesis of multiple sclerosis (MS) is mediated by massive infiltration of myelin-specific T cells into the central nervous system (CNS). Self-reactive CD4⁺ T helper (Th) cells, specifically Th1 and Th17 cells, are hallmarks of active disease in progression, whereas Th2 cells are predominately in remission stages. Calpain has been shown to be upregulated in the CNS of MS patients and inhibition of calpain has been shown previously to decrease disease in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. We investigated calpain involvement in Thcell bias. Here, we show that calpain inhibition in primary myelin basic protein (MBP) Ac1-11-specific T cells and MBP-specific T cell line cultures increase Th2 proliferation, cytokine profile, and transcription and signaling molecules. We also show a relative decrease in Th1 inflammatory factors in these same categories and a relative decrease in Th17 proliferation. These studies provide insight into the various roles that calpain plays in Th cell bias and proliferation and increases our understanding of the role that T cells play in the pathophysiology of EAE and MS. Results also indicate the mechanisms involved by which calpain inhibitor decreases the disease signs of EAE, suggesting that calpain inhibitor can be a possible therapeutic agent for the treatment of EAE and MS.

Homology, similarity, and identity in peptide epitope immunodefinition

The tendency to use the terms homology, similarity, and identity interchangeably persists in comparative biology. When translated to immunology, overlapping the concepts of homology, similarity, and identity complicates the exact definition of the self-nonself dichotomy and, in particular, affects immunopeptidomics, an emerging field aimed at cataloging and distinguishing immunoreactive peptide epitopes from silent nonreactive amino acid sequences. The definition of similar/dissimilar peptides in immunology is discussed with special attention to the analysis of immunological (dis)similarity between two or more protein sequences that equates to measuring sequence similarity with the use of a proper measurement unit such as a length determinant.

IL-5 promotes induction of antigen-specific CD4+CD25+ T regulatory cells that suppress autoimmunity

Immune responses to foreign and self-Ags can be controlled by regulatory T cells (Tregs) expressing CD4 and IL-2Rα chain (CD25). Defects in Tregs lead to autoimmunity, whereas induction of Ag-specific CD4+CD25+ Tregs restores tolerance. Ag-specific CD4+CD25+ FOXP3+Tregs activated by the T helper type 2 (Th2) cytokine, IL-4, and specific alloantigen promote allograft tolerance. These Tregs expressed the specific IL-5Rα and in the presence of IL-5 proliferate to specific but not third-party Ag. These findings suggest that recombinant IL-5 (rIL-5) therapy may promote Ag-specific Tregs to mediate tolerance. This study showed normal CD4+CD25+ Tregs cultured with IL-4 and an autoantigen expressed Il-5rα. Treatment of experimental autoimmune neuritis with rIL-5 markedly reduced clinical paralysis, weight loss, demyelination, and infiltration of CD4+ (Th1 and Th17) CD8+ T cells and macrophages in nerves. Clinical improvement was associated with expansion of CD4+CD25+FOXP3+ Tregs that expressed Il-5rα and proliferated only to specific autoantigen that was enhanced by rIL-5. Depletion of CD25+ Tregs or blocking of IL-4 abolished the benefits of rIL-5. Thus, rIL-5 promoted Ag-specific Tregs, activated by autoantigen and IL-4, to control autoimmunity. These findings may explain how Th2 responses, especially to parasitic infestation, induce immune tolerance. rIL-5 therapy may be able to induce Ag-specific tolerance in autoimmunity.

Altered differentiation, diminished pathogenicity, and regulatory activity of myelin-specific T cells expressing an enhanced affinity TCR

Whereas increased affinity enhances T cell competitiveness after immunization, the role of affinity in modulating the pathogenicity of self-reactive T cells is less established. To assess this, we generated two myelin-specific, class II MHC-restricted TCR that differ only in a buried hydroxymethyl that forms a common TCR β-chain V region variant. The variation, predicted to increase TCR stability, resulted in a ~3log(10) difference in TCR sensitivity with preserved fine specificity. The high-affinity TCR markedly diminished T cell pathogenicity. T cells were not deleted, did not upregulate Foxp3, and barring disease induction were predominantly naive. However, high-affinity CD4(+) T cells showed an altered cytokine profile characterized by the production of protective cytokines prior to experimental allergic encephalomyelitis induction and decreased effector cytokines after. Further, the high-affinity TCR promoted the development of CD4(-)CD8(-) and CD8(+) T cells that possessed low intrinsic pathogenicity, were protective even in small numbers when transferred into wild-type mice and in mixed chimeras, and outcompete CD4(+) T cells during disease development. Therefore, TCR affinities exceeding an upper affinity threshold may impede the development of autoimmunity through altered development and functional maturation of T cells, including diminished intrinsic CD4(+) T cell pathogenicity and the development of CD4(-)Foxp3(-) regulatory populations.

(E)-alkene and ethylene isosteres substantially alter the hydrogen-bonding network in class II MHC A(q)/glycopeptide complexes and affect T-cell recognition

The structural basis for antigen presentation by class II major histocompatibility complex (MHC) proteins to CD4(+) T-cells is important for understanding and possibly treating autoimmune diseases. In the work described in this paper, (E)-alkene and ethylene amide-bond isosteres were used to investigate the effect of removing hydrogen-bonding possibilities from the CII259-270 glycopeptide, which is bound by the arthritis-associated murine A(q) class II MHC protein. The isostere-modified glycopeptides showed varying and unexpectedly large losses of A(q) binding that could be linked to the dynamics of the system. Molecular dynamics (MD) simulations revealed that the backbone of CII259-270 and the A(q) protein are able to form up to 11 hydrogen bonds, but fewer than this number are present at any one time. Most of the strong hydrogen-bond interactions were formed by the N-terminal part of the glycopeptide, i.e., in the region where the isosteric replacements were made. The structural dynamics also revealed that hydrogen bonds were strongly coupled to each other; the loss of one hydrogen-bond interaction had a profound effect on the entire hydrogen-bonding network. The A(q) binding data revealed that an ethylene isostere glycopeptide unexpectedly bound more strongly to A(q) than the corresponding (E)-alkene, which is in contrast to the trend observed for the other isosteres. Analysis of the MD trajectories revealed that the complex conformation of this ethylene isostere was structurally different and had an altered molecular interaction pattern compared to the other A(q)/glycopeptide complexes. The introduced amide-bond isosteres also affected the interactions of the glycopeptide/A(q) complexes with T-cell receptors. The dynamic variation of the patterns and strengths of the hydrogen-bond interactions in the class II MHC system is of critical importance for the class II MHC/peptide/TCR signaling system.

A comparative approach linking molecular dynamics of altered peptide ligands and MHC with in vivo immune responses

BACKGROUND

The recognition of peptide in the context of MHC by T lymphocytes is a critical step in the initiation of an adaptive immune response. However, the molecular nature of the interaction between peptide and MHC and how it influences T cell responsiveness is not fully understood.

RESULTS

We analyzed the immunological consequences of the interaction of MHC class II (I-Au) restricted 11-mer peptides of myelin basic protein with amino acid substitutions at position 4. These mutant peptides differ in MHC binding affinity, CD4+ T cell priming, and alter the severity of peptide-induced experimental allergic encephalomyelitis. Using molecular dynamics, a computational method of quantifying intrinsic movements of proteins at high resolution, we investigated conformational changes in MHC upon peptide binding. We found that irrespective of peptide binding affinity, MHC deformation appears to influence costimulation, which then leads to effective T cell priming and disease induction. Although this study compares in vivo and molecular dynamics results for three altered peptide ligands, further investigation with similar complexes is essential to determine whether spatial rearrangement of peptide-MHC and costimulatory complexes is an additional level of T cell regulation.

Manipulating antigenic ligand strength to selectively target myelin-reactive CD4+ T cells in EAE

The development of antigen-specific therapies for the selective tolerization of autoreactive T cells remains the Holy Grail for the treatment of T-cell-mediated autoimmune diseases such as multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). This quest remains elusive, however, as the numerous antigen-specific strategies targeting myelin-specific T cells over the years have failed to result in clinical success. In this review, we revisit the antigen-based therapies used in the treatment of myelin-specific CD4+ T cells in the context of the functional avidity and the strength of signal of the encephalitogenic CD4+ T cell repertoire. In light of differences in activation thresholds, we propose that autoreactive T cells are not all equal, and therefore tolerance induction strategies must incorporate ligand strength in order to be successful in treating EAE and ultimately the human disease MS.

The good, the bad and the ugly: how altered peptide ligands modulate immunity

BACKGROUND

The basis of T cell immune responses is the specific recognition of an immunogenic peptide epitope by a T cell receptor. Peptide alterations of such T cell epitopes with single or few amino acid variations can have drastic effects on the outcome of this recognition. These altered peptide ligands can act as modulators of immune responses as they are capable of downregulating or upregulating responses.

OBJECTIVE/METHODS

We review how altered peptide ligands can have 'good' 'bad' and 'ugly' outcomes in treating diseases.

RESULTS/CONCLUSION

Altered peptide ligands have been used as immunotherapeutics in autoimmune (and allergic) diseases, infectious diseases and cancer. In the next five years we anticipate seeing a number of altered peptide ligands in clinical trials, progressing from contradictory classifications of good, bad or ugly, to the exciting outcome of 'useful'.

A double mutation of MBP(83-99) peptide induces IL-4 responses and antagonizes IFN-gamma responses

A number of treatment options are available to multiple sclerosis patients, however this needs to be improved. Herein, we designed and synthesized a number of peptides by mutating principal TCR contact residues based on MBP(83-99) peptide epitope. Immunization of SJL/J mice with MBP(83-99) and mutant [A(91)]MBP(83-99), [E(91)]MBP(83-99), [F(91)]MBP(83-99), [Y(91)]MBP(83-99), and [R(91), A(96)]MBP(83-99) peptides, induced IFN-gamma, and only [R(91), A(96)]MBP(83-99) mutant peptide was able to induce IL-4 secretion by T cells. T cells against the native MBP(83-99) peptide cross-reacted with all peptides except [Y(91)]MBP(83-99) and [R(91),A(96)]MBP(83-99). The double mutant [R(91), A(96)]MBP(83-99) was able to antagonize IFN-gamma production in vitro by T cells against the native MBP(83-99) peptide. Antibodies generated to [R(91), A(96)]MBP(83-99) did not cross-react with whole MBP protein. Molecular modeling between peptide analogs and H2 I-A(s) demonstrated novel interactions. The [R(91), A(96)]MBP(83-99) double mutant peptide analog is the most promising for further therapeutic studies.

Death, adaptation and regulation: The three pillars of immune tolerance restrict the risk of autoimmune disease caused by molecular mimicry

Extensive cross-reactivity in T cell receptor (TCR) recognition of peptide-MHC (pMHC) complexes seems to be essential to give sufficient immune surveillance against invading pathogens. This carries with it an inherent risk that T cells activated during a response to clear an infection can, perhaps years later, respond to a self pMHC of sufficient similarity. This lies at the heart of the molecular mimicry theory. Here we discuss our studies on the disease-causing potential of altered peptide ligands (APL) based on the sequence of a single autoantigenic epitope, the Ac1-9 peptide of myelin basic protein that induces experimental autoimmune encephalomyelitis in mice. These show that the window of similarity to self for induction of disease by cross-reactive non-self peptides is actually quite restricted. We show that each of the three pillars of immune tolerance (death, anergy/adaptation and regulation) has a role in limiting the risk of molecular mimicry by maintaining a threshold for harm.

Analysis of antigen reactive T-cells

Because antigen-specific cells are the central coordinators of the immune response to infectious organisms, and the principal effector cells in autoimmune disease, there are many circumstances in which investigators may wish to examine the T-cell responses to particular antigens. This chapter outlines techniques for assessing the responses of polyclonal populations of T-lymphocytes by measuring a variety of outputs each of which gives different kinds of information about the response. The outputs discussed are proliferation and cytokine production, with methods for measuring cytokine secretion by the whole population together with techniques for making an estimate of the numbers of cells producing a cytokine in response to antigen, and examining the phenotype of the responsive cells. In many cases detailed information about responses to particular antigens requires the isolation and characterization of antigen-responsive T-cell clones, and this is also described together with methods of identifying unknown antigens by screening recombinant expression libraries. Lastly, because the techniques differ in many respects, methods for isolating antigen-specific CD8+ T-cells, particularly those which recognize bacteria, are also included.

[Update on pathophysiologic and immunotherapeutic approaches for the treatment of multiple sclerosis]

Multiple sclerosis (MS) is a chronic disabling disease with significant implications for patients and society. The individual disease course is difficult to predict due to the heterogeneity of clinical presentation and of radiologic and pathologic findings. Although its etiology still remains unknown, the last decade has brought considerable understanding of the underlying pathophysiology of MS. In addition to its acceptance as a prototypic inflammatory autoimmune disorder, recent data reveal the importance of primary and secondary neurodegenerative mechanisms such as oligodendrocyte death, axonal loss, and ion channel dysfunction. The deepened understanding of its immunopathogenesis and the limited effectiveness of currently approved disease-modifying therapies have led to a tremendous number of trials investigating potential new drugs. Emerging treatments take into account the different immunopathological mechanisms and strategies, to protect against axonal damage and promote remyelination. This review provides a compilation of novel immunotherapeutic strategies and recently uncovered aspects of known immunotherapeutic agents. The pathogenetic rationale of these novel drugs for the treatment of MS and accompanying preclinical and clinical data are highlighted.

Monomeric DR2/MOG-35-55 recombinant TCR ligand treats relapses of experimental encephalomyelitis in DR2 transgenic mice

Treatment of human autoimmune diseases such as multiple sclerosis (MS) will likely require agents that can prevent or reverse the inflammatory process that results in clinical relapses and disease progression. We evaluated the ability of a newly designed monomeric recombinant TCR ligand (RTL342M) containing HLA-DR2 peptide-binding domains covalently linked to MOG-35-55 peptide to prevent and treat both the initial episode and subsequent relapses of experimental autoimmune encephalomyelitis (EAE) in HLA-DR2 transgenic mice. Single doses of RTL342M given either i.v. or s.c. to HLA-DR2 mice produced a rapid (within 24 h) and dose-dependent reversal of clinical signs of paralytic EAE, and even a single dose < or = 2 microg could produce a significant treatment effect. Multiple daily doses were even more effective than the same total amount of RTL given as a single dose. By establishing the minimal effective dose, we determined that RTLs may be 50 times more potent than molar equivalent doses of myelin peptide alone. RTL342M given prior to induction of EAE prevented disease in most mice, and the remainder could be successfully retreated with RTL. Most important for clinical application, RTL342M was highly effective for treating EAE relapses when given periodically prior to the relapse or even after relapses had occurred. These data demonstrate the rapid and potent clinical effects of RTL342M at disease onset and during relapses in EAE and establish important principles governing the application of this novel approach as a possible therapy for patients with MS.

Comparison of Proposed Putative Active Conformations of Myelin Basic Protein Epitope 87−99 Linear Altered Peptide Ligands by Spectroscopic and Modelling Studies: The Role of Positions 91 and 96 in T-Cell Receptor Activation

This work proposes a structural motif for the inhibition of experimental autoimmune encephalomyelitis (EAE) by the linear altered peptide ligands (APLs) [Ala91,96] MBP87-99 and [Arg91,Ala96] MBP87-99 of myelin basic protein. Molecular dynamics was applied to reveal distinct populations of EAE antagonist [Ala91,96] MBP87-99 in solution, in agreement with NOE data. The combination of the theoretical and experimental results led to the identification of a putative active conformation. This approach is of value as no crystallographic data is available for the APL-receptor complex. TCR contact residue Phe89 has an altered topology in the putative bioactive conformations of both APLs with respect to the native peptide, as found via crystallography; it is no longer prominent and solvent exposed. It is proposed that the antagonistic activity of the APLs is due to their binding to MHC, preventing the binding of self-myelin epitopes, with the absence of an immunologic response as the loss of some interactions with the TCR hinders activation of T-cells.

A putative bioactive conformation for the altered peptide ligand of myelin basic protein and inhibitor of experimental autoimmune encephalomyelitis [Arg91, Ala96] MBP87–99

[Arg(91), Ala(96)] MBP(87-99) is an altered peptide ligand (APL) of myelin basic protein (MBP), shown to actively inhibit experimental autoimmune encephalomyelitis (EAE), which is studied as a model of multiple sclerosis (MS). The APL has been rationally designed by substituting two of the critical residues for recognition by the T-cell receptor. A conformational analysis of the APL has been sought using a combination of 2D NOESY nuclear magnetic resonance (NMR) experiments and detailed molecular dynamics (MD) calculations, in order to comprehend the stereoelectronic requirements for antagonistic activity, and to propose a putative bioactive conformation based on spatial proximities of the native peptide in the crystal structure. The proposed structure presents backbone similarity with the native peptide especially at the N-terminus, which is important for major histocompatibility complex (MHC) binding. Primary (Val(87), Phe(90)) and secondary (Asn(92), Ile(93), Thr(95)) MHC anchors occupy the same region in space, whereas T-cell receptor (TCR) contacts (His(88), Phe(89)) have different orientation between the two structures. A possible explanation, thus, of the antagonistic activity of the APL is that it binds to MHC, preventing the binding of myelin epitopes, but it fails to activate the TCR and hence to trigger the immunologic response. NMR experiments coupled with theoretical calculations are found to be in agreement with X-ray crystallography data and open an avenue for the design and synthesis of novel peptide restricted analogues as well as peptide mimetics that rises as an ultimate goal.

Antigen-specific therapies in multiple sclerosis: going beyond proteins and peptides

Multiple sclerosis (MS) is a complex immune-mediated disease resulting largely from an autoimmune attack against components of central nervous system myelin, including several proteins and lipids. Knowledge about the details of this anomalous immune response has come mostly from studies in the animal model experimental autoimmune encephalomyelitis (EAE). In this model, it has been possible to prevent and effectively treat established disease through several antigen-specific therapeutic strategies, which have included administration of whole myelin or myelin proteins by various routes, random copolymers consisting of the main major histocompatability complex (MHC) and T-cell receptor (TCR) contact amino acid residues, altered peptide ligands of dominant myelin epitopes in which one or more residues are selectively substituted, and lately DNA vaccination encoding self-myelin antigens. However, there have been difficulties in making successful transitions from animal models to human clinical trials, due either to lack of efficacy or unforeseen complications. Despite these problems, antigen-specific therapies have retained their attraction for clinicians and scientists alike, and hopefully the upcoming generation of agents--including altered peptide ligands and DNA vaccines--will benefit from the increasing knowledge about this disease and surmount existing difficulties to make an impact in the treatment of multiple sclerosis.

A live diarrheal vaccine imprints a Th2 cell bias and acts as an anti-inflammatory vaccine

An experimental vaccine for enterotoxigenic Escherichia coli (ETEC) composed of a live, attenuated Salmonella vector-expressing enterotoxigenic E. coli fimbriae, colonization factor Ag I (CFA/I), stimulated a biphasic Th cell response when given orally and suppressed the normally produced proinflammatory response. Such suppression was also evident upon the Salmonella-CFA/I infection of macrophages resulting in diminished TNF-alpha, IL-1, and IL-6 production and suggesting that the CFA/I fimbrial expression by Salmonella may protect against a proinflammatory disease. To test this hypothesis, SJL/J mice were vaccinated with Salmonella-CFA/I construct 1 or 4 wk before induction of experimental autoimmune encephalomyelitis using an encephalitogenic proteolipid protein peptide, PLP(139-151). Mice receiving Salmonella-CFA/I vaccine recovered completely from mild acute clinical disease and showed only mild inflammatory infiltrates in the spinal cord white and gray matter. This protective effect was accompanied by a loss of encephalitogenic IFN-gamma-secreting Th cells and was replaced with an increase in IL-4, IL-10, and IL-13 secretion. Collectively, these data suggested that Salmonella-CFA/I is an anti-inflammatory vaccine that down-regulates proinflammatory cells and confers protection against a proinflammatory disease, experimental autoimmune encephalomyelitis, via immune deviation.

MHC Class II tetramers and the pursuit of antigen-specific T cells: define, deviate, delete

Selective expansion and activation of a very small number of antigen-specific CD4(+) T cells is a remarkable and essential property of the adaptive immune response. Antigen-specific T cells were until recently identified only indirectly by functional assays, such as antigen-induced cytokine secretion and proliferation. The advent of MHC Class II tetramers has added a pivotal tool to our research armamentarium, allowing the definition of allo- and autoimmune responses in deeper detail. Rare antigen-specific CD4(+) cells can now be selectively identified, isolated and characterized. The same tetramer reagents also provide a new mean of stimulating T cells, more closely reproducing the MHC-peptide/TCR interaction. This property allows the use of tetramers to direct T cells toward the more desirable outcome, that is, activation (in malignancies and infectious diseases) or Th2/T regulatory cell deviation, anergy and deletion (in autoimmune diseases). These experimental approaches hold promise for diagnostic, prognostic and therapeutic applications.

Therapeutic approaches in multiple sclerosis: lessons from failed and interrupted treatment trials

The therapy for multiple sclerosis (MS) has changed dramatically over the past decade. Recent immunobiological findings and current pathophysiological concepts together with advances in biotechnology, improvements in clinical trial design and development of magnetic resonance imaging have led to a variety of evaluable therapeutic approaches in MS. However, in contrast to the successfully introduced and established immunomodulatory therapies (e.g. interferon-beta and glatiramer acetate), there have been a remarkable number of therapeutic failures as well. Despite convincing immunological concepts, impressive data from animal models and promising results from phase I/II studies, the drugs and strategies investigated showed no benefit or even turned out to have unexpectedly severe adverse effects. Although to date there is no uniformly accepted model for MS, there is agreement on the significance of inflammatory events mediated by autoreactive T cells in the CNS. These can be modified therapeutically at the individual steps of a hypothetical pathogenetic cascade. Crucial corners like: the prevalence and peripheral activation of CNS-autoreactive T cells in the periphery;adhesion and penetration of T cells into the CNS;local activation and proliferation and;de- and remyelination processes can be targeted through their putative mediators. Like a 'specificity pyramid', therapeutic approaches therefore cover from general immunosuppression up to specific targeting of T-cell receptor peptide major histocompatibility (MHC) complex. We discuss in detail clinical MS trials that failed or were discontinued for other reasons. These trials include cytokine modulators [tumour necrosis factor (TNF)-alpha antagonists, interleukin-10, interleukin-4, transforming growth factor-beta2], immunosuppressive agents (roquinimex, gusperimus, sulfasalazine, cladribine), inducers of remyelination [intravenous immunoglobulins (IVIg)], antigen-derived therapies [oral tolerance, altered peptide ligands (APL), MHC-Peptide blockade], T cell and T-cell receptor directed therapies (T cell vaccination, T-cell receptor peptide vaccination), monoclonal antibodies against leucocyte differentiation molecules (anti-CD3, anti-CD4), and inactivation of circulating T cells (extracorporeal photopheresis). The main conclusions that can be drawn from these 'negative' experiences are as follows. Theoretically promising agents may paradoxically increase disease activity (lenercept, infliximab), be associated with unforeseen adverse effects (e.g. roquinimex) or short-term favourable trends may reverse with prolonged follow-up (e.g. sulfasalzine). One should not be too enthusiastic about successful trials in animal models (TNFalpha blockers; oral tolerance; remyelinating effect of IVIg) nor be irritated by non-scientific media hype (deoxyspergualine; bone marrow transplantation). More selectivity can imply less efficacy (APL, superselective interventions like T-cell receptor vaccination) and antigen-related therapies can stimulate rather than inhibit encephalitogenic cells. Failed strategies are of high importance for a critical revision of assumed immunopathological mechanisms, their neuroimaging correlates, and for future trial design. Since failed trials add to our growing understanding of multiple sclerosis, 'misses' are nearly as important to the scientific process as the 'hits'.

Selection and fine-tuning of the autoimmune T-cell repertoire

The immune system must avoid aggressive T-cell responses against self-antigens. But, paradoxically, exposure to self-peptides seems to have an important role in positive selection in the thymus and the maintenance of a broad T-cell repertoire in the periphery. Recent experiments have highlighted situations that allow high-avidity self-reactive T cells to avoid negative selection in the thymus. Accumulating evidence indicates that other, non-deleting mechanisms control the avidity with which T cells recognize self-antigens--a phenomenon that is known as 'tuning'. This might maximize the peripheral T-cell repertoire by allowing the survival of T cells that can respond to self, but only at concentrations that are not normally reached in vivo.

Binding interactions between peptides and proteins of the class II major histocompatibility complex

The activation of helper T cells by peptides bound to proteins of the class II Major Histocompatibility Complex (MHC II) is pivotal to the initiation of an immune response. The primary functional requirement imposed on MHC II proteins is the ability to efficiently bind thousands of different peptides. Structurally, this is reflected in a unique architecture of binding interactions. The peptide is bound in an extended conformation within a groove on the membrane distal surface of the protein that is lined with several pockets that can accommodate peptide side-chains. Conserved MHC II protein residues also form hydrogen bonds along the length of the peptide main-chain. Here we review recent advances in the study of peptide-MHC II protein reactions that have led to an enhanced understanding of binding energetics. These results demonstrate that peptide-MHC II protein complexes achieve high affinity binding from the array of hydrogen bonds that are energetically segregated from the pocket interactions, which can then add to an intrinsic hydrogen bond-mediated affinity. Thus, MHC II proteins are unlike antibodies, which utilize cooperativity among binding interactions to achieve high affinity and specificity. The significance of these observations is discussed within the context of possible mechanisms for the HLA-DM protein that regulates peptide presentation in vivo and the design of non-peptide molecules that can bind MHC II proteins and act as vaccines or immune modulators.

Characterization of the dominant autoreactive T-cell epitope in spontaneous autoimmune haemolytic anaemia of the NZB mouse

NZB mice spontaneously develop autoimmune haemolytic anaemia (AIHA) due to a T helper-dependent autoantibody response against the erythrocyte anion channel protein, Band 3. Here, we characterize the recognition of the Band 3 sequence 861-874, which carries the dominant, I-E(d)-restricted T cell epitope. The ability of N and C-terminal truncated versions of peptide 861-874 to elicit NZB splenic T-cell proliferation indicated that the core epitope spans residues 862-870. Next, a set of alanine substitution analogues was tested to determine which residues functioned either as MHC anchor or TCR contact residues. A combination of proliferation and MHC:peptide binding assays identified residues 862(L), 864(V), 865(L), and 869(K) as I-E(d) anchor residues, and 868(V) as the only TCR contact residue. The ability of the wild-type sequence 861-874 to compete with a high affinity reference peptide for binding to I-E(d) indicates that the escape of pathogenic NZB T cells from purging of the autoreactive repertoire cannot be attributed to ineffective presentation of peptide 861-874 by its restricting element. It will now be possible to design altered peptide ligands of Band 3 861-874, in order to further dissect the mechanisms responsible for the maintenance and loss of T cell tolerance to RBC autoantigens, and to modulate the immune response in AIHA.

Utility of azapeptides as major histocompatibility complex class II protein ligands for T-cell activation

Major histocompatibility complex class II (MHC II) protein binding and antigen specific activation of CD4+ "helper" T cells are demonstrated with peptides composed of the antigenic hen egg ovalbumin 325-339 peptide (OVA) substituted with azaamino acids. AzaAla and azaGly substitutions were made at 10 sequential peptide positions (326Ala-335Asn) that lie in the binding groove. The peptide positions substituted with azaamino acids encompass almost the entire binding groove, including positions where the identity of the amino acid side chain is known to have the most significant effect on MHC binding and the least effect on T-cell recognition. In addition, the T-cell contact 333Glu was substituted with azaGlu to generate a partial agonist ligand for the 3DO-54.8 T-cell hybridoma. Binding to MHC II protein was assayed by measuring the kinetic stability of complexes formed between detergent-solubilized MHC II I-A(d) protein and fluorescein-labeled OVA peptides using a fluorescence-HPLC assay. T-cell activation was also evaluated for aza-substituted peptides with azaamino acid substitutions at the peptide positions known to interact with the MHC II protein. All aza-substituted peptides showed detectable MHC binding, and some were found to show T-cell activation potency equal to the native peptide. Several of these were also found to be weak or partial agonists. Our results demonstrate that azaamino acids substituted into an antigenic peptide cause a subtle, global effect on peptide conformation that can be used to design altered peptide ligands (APL) as T-cell partial agonists. These may have potential as T-cell epitopes for synthetic vaccines and therapeutic agents for autoimmune diseases.

Posttraumatic therapeutic vaccination with modified myelin self-antigen prevents complete paralysis while avoiding autoimmune disease

Spinal cord injury results in a massive loss of neurons, and thus of function. We recently reported that passive transfer of autoimmune T cells directed against myelin-associated antigens provides acutely damaged spinal cords with effective neuroprotection. The therapeutic time window for the passive transfer of T cells was found to be at least 1 week. Here we show that posttraumatic T cell-based active vaccination is also neuroprotective. Immunization with myelin-associated antigens such as myelin basic protein (MBP) significantly promoted recovery after spinal cord contusion injury in the rat model. To reduce the risk of autoimmune disease while retaining the benefit of the immunization, we vaccinated the rats immediately after severe incomplete spinal cord injury with MBP-derived altered peptide ligands. Immunization with these peptides resulted in significant protection from neuronal loss and thus in a reduced extent of paralysis, assessed by an open-field behavioral test. Retrograde labeling of the rubrospinal tracts and magnetic resonance imaging supported the behavioral results. Further optimization of nonpathogenic myelin-derived peptides can be expected to lead the way to the development of an effective therapeutic vaccination protocol as a strategy for the prevention of total paralysis after incomplete spinal cord injury.

Tolerance induction by acylated peptides: suppression of EAE in the mouse with palmitoylated PLP peptides

Treatment of SJL mice either before or after challenge with palmitoylated PLP139-151 (PAL139-151) completely suppressed or considerably reduced both acute and relapsing stages of EAE induced with PLP139-151. In the presence of Pertussis toxin, treatment with PAL139-151 was less effective, but treatment with a mixture of PAL139-151 and PAL178-191, the palmitoylated PLP epitope to which T cell recognition spreads, resulted in almost complete protection. Proliferation of lymphocytes from treated mice were sharply reduced, and adoptive transfer of lymph node lymphocytes from treated mice to naive recipients resulted in the reduction of the acute phase of EAE and in delayed relapses following challenge. The results suggest that treatment with PAL139-151 leads to both anergy and the generation of regulatory cells.

Negative selection during the peripheral immune response to antigen

Thymic selection depends on positive and negative selective mechanisms based on the avidity of T cell interaction with antigen-major histocompatibility complex complexes. However, peripheral mechanisms for the recruitment and clonal expansion of the responding T cell repertoire remain obscure. Here we provide evidence for an avidity-based model of peripheral T cell clonal expansion in response to antigenic challenge. We have used the encephalitogenic, H-2 A(u)-restricted, acetylated NH(2)-terminal nonameric peptide (Ac1-9) epitope from myelin basic protein as our model antigen. Peptide analogues were generated that varied in antigenic strength (as assessed by in vitro assay) based on differences in their binding affinity for A(u). In vivo, these analogues elicited distinct repertoires of T cells that displayed marked differences in antigen sensitivity. Immunization with the weakest (wild-type) antigen expanded the high affinity T cells required to induce encephalomyelitis. In contrast, immunization with strongly antigenic analogues led to the elimination of T cells bearing high affinity T cell receptors by apoptosis, thereby preventing disease development. Moreover, the T cell repertoire was consistently tuned to respond to the immunizing antigen with the same activation threshold. This tuning mechanism provides a peripheral control against the expansion of autoreactive T cells and has implications for immunotherapy and vaccine design.

Identification of alloreactive T-cell epitopes on the Rhesus D protein

Although considerable effort has been devoted to characterizing alloantibodies specific for the Rhesus D (RhD) blood group antigen, virtually nothing is known about the helper response that drives their production. Therefore, the aim of this study was to map alloreactive T-cell epitopes on the RhD protein. Peripheral blood mononuclear cells (PBMCs) were obtained from 22 RhD-negative volunteers in whom anti-D alloantibodies had developed after deliberate immunization or RhD-incompatible pregnancy. The PBMCs were stimulated with a panel of up to 68 overlapping synthetic 15-mer peptides spanning the complete sequence of the RhD protein. One or more peptides elicited proliferative responses by PBMCs from all 22 of the alloimmune volunteers but from only 2 of 8 alloantibody-negative control donors. Proliferation of PBMCs from the alloimmune donors was mediated by major histocompatibility complex class II–restricted T cells expressing the CD45RO marker of previous activation or memory. The number of peptides that induced proliferative responses was unrelated to either the frequency of, or time since, exposure to RhD-positive red blood cells, but it correlated strongly (Rs = 0.75;P &lt; .003) with the level of anti-D antibodies in deliberately immunized donors. The patterns of stimulatory peptides varied among alloimmune volunteers, but particular sequences were commonly recognized, with 4 peptides each eliciting a response in more than 50% of these donors. Identification of such peptides containing dominant alloreactive helper epitopes is the first step in the development of improved or new approaches to preventing hemolytic disease of the newborn that are based on modulating the T-cell response to the RhD protein.

Identification of alloreactive T-cell epitopes on the Rhesus D protein

Although considerable effort has been devoted to characterizing alloantibodies specific for the Rhesus D (RhD) blood group antigen, virtually nothing is known about the helper response that drives their production. Therefore, the aim of this study was to map alloreactive T-cell epitopes on the RhD protein. Peripheral blood mononuclear cells (PBMCs) were obtained from 22 RhD-negative volunteers in whom anti-D alloantibodies had developed after deliberate immunization or RhD-incompatible pregnancy. The PBMCs were stimulated with a panel of up to 68 overlapping synthetic 15-mer peptides spanning the complete sequence of the RhD protein. One or more peptides elicited proliferative responses by PBMCs from all 22 of the alloimmune volunteers but from only 2 of 8 alloantibody-negative control donors. Proliferation of PBMCs from the alloimmune donors was mediated by major histocompatibility complex class II–restricted T cells expressing the CD45RO marker of previous activation or memory. The number of peptides that induced proliferative responses was unrelated to either the frequency of, or time since, exposure to RhD-positive red blood cells, but it correlated strongly (Rs = 0.75;P < .003) with the level of anti-D antibodies in deliberately immunized donors. The patterns of stimulatory peptides varied among alloimmune volunteers, but particular sequences were commonly recognized, with 4 peptides each eliciting a response in more than 50% of these donors. Identification of such peptides containing dominant alloreactive helper epitopes is the first step in the development of improved or new approaches to preventing hemolytic disease of the newborn that are based on modulating the T-cell response to the RhD protein.

Prevention of experimental autoimmune encephalomyelitis by encephalitogenic epitope sequence simplified derivatives

The encephalitogenic epitope P81-100 from mouse myelin basic protein was used to generate two simplified derivatives with glycine substitutions in alternating positions which were tested for their biological activity in a murine model of multiple sclerosis, experimental autoimmune encephalomyelitis. While both derivatives were unable to induce in mice the disease at the same parent peptide P81-100 dosage, T cell proliferation assays demonstrated their ability to compete with the parental peptide in a dose related manner. Experiments of cell surface binding and T cell tolerance revealed a different behavior of the two derivatives, suggesting different roles in the MHC blockade or T cell tolerance. On induction of encephalomyelitis in animals by P81-100 treatment, one variant proved in vivo to be very effective in protecting from the disease.

Modulation of experimental autoimmune encephalomyelitis: effect of altered peptide ligand on chemokine and chemokine receptor expression

Experimental autoimmune encephalomyelitis (EAE) is a T helper 1 (Th1) cell mediated demyelinating disease and the principal animal model for multiple sclerosis. Spinal cords from SJL mice primed with proteolipid protein peptide 139-151 (pPLP) expressed the chemokines RANTES, MCP-1, MIP-2, KC, MIP-1alpha, MIP-1beta, Mig, and fractalkine. We also identified IP-10 in these samples and described a sequence polymorphism in this transcript. Chemokine expression was specific for tissues of the central nervous system. MCP-1, IP-10, and MIP-2 RNA expression significantly correlated with clinical score. Chemokine receptor expression generally correlated with ligand expression. pPLP-primed mice expressed the Th1-associated markers CCR5 and CXCR3 on mononuclear cells. In addition, cells expressing CCR1, CCR2, CCR3, CCR4, CCR8, and CXCR2 were detected. Here we demonstrate that altered peptide ligand (APL)-induced protection from EAE was accompanied by modulation of chemokine and chemokine receptor expression. Spinal cord tissue sections from APL-protected mice showed greatly reduced levels of all chemokines and of CCR1, CCR5, CCR8, CXCR2 and CXCR3. The Th2-associated chemokine receptors CCR3 and CCR4 were found in protected mice, supporting the hypothesis that Th1 but not Th2 cells are down-regulated by APL treatment. This report concludes that chemokines and chemokine receptors can be useful tools to follow modulation of autoimmune disease.

Peptide analogues as a strategy to induce tolerance in T cells with indirect allospecificity

BACKGROUND

It has been demonstrated that indirect recognition of allogeneic MHC molecules might play an important role in provoking graft rejection. Although direct recognition of allogeneic molecules on antigen presenting cells of the graft may induce a state of tolerance, the continuous presentation of processed alloantigens by specialized antigen presenting cells does not allow the same phenomenon to occur. Tolerance to interleukin-2 secreting T cells can be achieved in different ways, among these is the exposure to mutants of the wild type allopeptide. We have investigated whether peptide analogues of the allopeptide can induce tolerance in T cells with indirect allospecificity.

METHODS

T cell clones with indirect anti-HLA-A2-specificity generated from a HLA-A2-DRB1*1502+ patient who chronically rejected a HLA-A2-expressing kidney allograft were used for this study. Nine peptide analogues of HLA-A2 (residues: 103-120) were produced with single amino acid substitutions at the putative T cell receptor for antigen contact positions. Their effect on the proliferation of a panel of T cell clones was evaluated.

RESULTS

Peptide analogues and wild type peptide had similar capacity to bind to the restriction molecule HLA-DRB1*1502. Co-presentation of the peptide analogues 111R/A, H, K and 114H/K, with the wild type peptide inhibited T cell responses, indicative of antagonism. In addition, one analogue 112G/S induced unresponsiveness in the T cells to subsequent culture with the wild type peptide.

CONCLUSIONS

The data presented here suggest that using reagents such as altered peptides may represent a strategy to prevent the activation of T cells with indirect alloreactivity and allograft rejection in vivo.