Delineation of the minimal encephalitogenic epitope within the immunodominant region of myelin oligodendrocyte glycoprotein: diverse V beta gene usage by T cells recognizing the core epitope encephalitogenic for T cell receptor V beta b and T cell receptor V beta a H-2b mice

Presentation of Human Neural Stem Cell Antigens Drives Regulatory T Cell Induction

Transplantation of human neural stem cells (hNSCs) is a promising regenerative therapy to promote remyelination in patients with multiple sclerosis (MS). Transplantation of hNSCs has been shown to increase the number of CD4+CD25+Foxp3+ T regulatory cells (Tregs) in the spinal cords of murine models of MS, which is correlated with a strong localized remyelination response. However, the mechanisms by which hNSC transplantation leads to an increase in Tregs in the CNS remains unclear. We report that hNSCs drive the conversion of T conventional (Tconv) cells into Tregs in vitro. Conversion of Tconv cells is Ag driven and fails to occur in the absence of TCR stimulation by cognate antigenic self-peptides. Furthermore, CNS Ags are sufficient to drive this conversion in the absence of hNSCs in vitro and in vivo. Importantly, only Ags presented in the thymus during T cell selection drive this Treg response. In this study, we investigate the mechanisms by which hNSC Ags drive the conversion of Tconv cells into Tregs and may provide key insight needed for the development of MS therapies.

LAG3 ectodomain structure reveals functional interfaces for ligand and antibody recognition

The immune checkpoint receptor lymphocyte activation gene 3 protein (LAG3) inhibits T cell function upon binding to major histocompatibility complex class II (MHC class II) or fibrinogen-like protein 1 (FGL1). Despite the emergence of LAG3 as a target for next-generation immunotherapies, we have little information describing the molecular structure of the LAG3 protein or how it engages cellular ligands. Here we determined the structures of human and murine LAG3 ectodomains, revealing a dimeric assembly mediated by Ig domain 2. Epitope mapping indicates that a potent LAG3 antagonist antibody blocks interactions with MHC class II and FGL1 by binding to a flexible 'loop 2' region in LAG3 domain 1. We also defined the LAG3-FGL1 interface by mapping mutations onto structures of LAG3 and FGL1 and established that FGL1 cross-linking induces the formation of higher-order LAG3 oligomers. These insights can guide LAG3-based drug development and implicate ligand-mediated LAG3 clustering as a mechanism for disrupting T cell activation.

A Journey to the Conformational Analysis of T-Cell Epitope Peptides Involved in Multiple Sclerosis

Multiple sclerosis (MS) is a serious central nervous system (CNS) disease responsible for disability problems and deterioration of the quality of life. Several approaches have been applied to medications entering the market to treat this disease. However, no effective therapy currently exists, and the available drugs simply ameliorate the destructive disability effects of the disease. In this review article, we report on the efforts that have been conducted towards establishing the conformational properties of wild-type myelin basic protein (MBP), myelin proteolipid protein (PLP), myelin oligodendrocyte glycoprotein (MOG) epitopes or altered peptide ligands (ALPs). These efforts have led to the aim of discovering some non-peptide mimetics possessing considerable activity against the disease. These efforts have contributed also to unveiling the molecular basis of the molecular interactions implicated in the trimolecular complex, T-cell receptor (TCR)–peptide–major histocompatibility complex (MHC) or human leucocyte antigen (HLA).

Pregnancy Enables Expansion of Disease-Specific Regulatory T Cells in an Animal Model of Multiple Sclerosis

Disease activity of autoimmune disorders such as multiple sclerosis and its mouse model experimental autoimmune encephalomyelitis (EAE) is temporarily suppressed by pregnancy. However, whether disease amelioration is due to nonspecific immunomodulation or mediated by Ag-specific regulation of disease-causing conventional T cells (Tcon) and immunosuppressive regulatory T cells (Tregs) remains elusive. In the current study, we systematically analyzed changes of the TCRβ repertoire driven by EAE and pregnancy using TCR sequencing. We demonstrate that EAE, but not pregnancy, robustly increased TCR repertoire clonality in both peripheral Tcon and Treg. Notably, pregnancy was required for the expansion of Treg harboring the dominant EAE-associated TRBV13-2 chain and increased the frequency of EAE-associated clonotypes within the Treg compartment. Our findings indicate that pregnancy supports the expansion of Treg clonotypes that are equipped to recognize EAE-associated Ags. These Treg are thereby particularly suited to control corresponding encephalitogenic Tcon responses and likely contribute to pregnancy-associated protection in autoimmunity.

Experimental Autoimmune Encephalomyelitis (EAE) as Animal Models of Multiple Sclerosis (MS)

Multiple sclerosis (MS) is a multifocal demyelinating disease of the central nervous system (CNS) leading to the progressive destruction of the myelin sheath surrounding axons. It can present with variable clinical and pathological manifestations, which might reflect the involvement of distinct pathogenic processes. Although the mechanisms leading to the development of the disease are not fully understood, numerous evidences indicate that MS is an autoimmune disease, the initiation and progression of which are dependent on an autoimmune response against myelin antigens. In addition, genetic susceptibility and environmental triggers likely contribute to the initiation of the disease. At this time, there is no cure for MS, but several disease-modifying therapies (DMTs) are available to control and slow down disease progression. A good number of these DMTs were identified and tested using animal models of MS referred to as experimental autoimmune encephalomyelitis (EAE). In this review, we will recapitulate the characteristics of EAE models and discuss how they help shed light on MS pathogenesis and help test new treatments for MS patients.

Thymus-specific serine protease, a protease that shapes the CD4 T cell repertoire

The lifespan of T cells is determined by continuous interactions of their T cell receptors (TCR) with self-peptide-MHC (self-pMHC) complexes presented by different subsets of antigen-presenting cells (APC). In the thymus, developing thymocytes are positively selected through recognition of self-pMHC presented by cortical thymic epithelial cells (cTEC). They are subsequently negatively selected by medullary thymic epithelial cells (mTEC) or thymic dendritic cells (DC) presenting self-pMHC complexes. In the periphery, the homeostasis of mature T cells is likewise controlled by the interaction of their TCR with self-pMHC complexes presented by lymph node stromal cells while they may be tolerized by DC presenting tissue-derived self-antigens. To perform these tasks, the different subsets of APC are equipped with distinct combination of antigen processing enzymes and consequently present specific repertoire of self-peptides. Here, we discuss one such antigen processing enzyme, the thymus-specific serine protease (TSSP), which is predominantly expressed by thymic stromal cells. In thymic DC and TEC, TSSP edits the repertoire of peptide presented by class II molecules and thus shapes the CD4 T cell repertoire.

Prenatal Administration of Betamethasone Causes Changes in the T Cell Receptor Repertoire Influencing Development of Autoimmunity

Prenatal glucocorticoids are routinely administered to pregnant women at risk of preterm delivery in order to improve survival of the newborn. However, in half of the cases, birth occurs outside the beneficial period for lung development. Glucocorticoids are potent immune modulators and cause apoptotic death of immature T cells, and we have previously shown that prenatal betamethasone treatment at doses eliciting lung maturation induce profound thymocyte apoptosis in the offspring. Here, we asked if there are long-term consequences on the offspring’s immunity after this treatment. In the non-obese diabetic mouse model, prenatal betamethasone clearly decreased the frequency of pathogenic T cells and the incidence of type 1 diabetes (T1D). In contrast, in the lupus-prone MRL/lpr strain, prenatal glucocorticoids induced changes in the T cell repertoire that resulted in more autoreactive cells. Even though glucocorticoids transiently enhanced regulatory T cell (Treg) development, these cells did not have a protective effect in a model for multiple sclerosis which relies on a limited repertoire of pathogenic T cells for disease induction that were not affected by prenatal betamethasone. We conclude that prenatal steroid treatment, by inducing changes in the T cell receptor repertoire, has unforeseeable consequences on development of autoimmune disease. Our data should encourage further research to fully understand the consequences of this widely used treatment.

Thymic-Specific Serine Protease Limits Central Tolerance and Exacerbates Experimental Autoimmune Encephalomyelitis

The genetic predisposition to multiple sclerosis (MS) is most strongly conveyed by MHC class II haplotypes, possibly by shaping the autoimmune CD4 T cell repertoire. Whether Ag-processing enzymes contribute to MS susceptibility by editing the peptide repertoire presented by these MHC haplotypes is unclear. Thymus-specific serine protease (TSSP) is expressed by thymic epithelial cells and thymic dendritic cells (DCs) and, in these two stromal compartments, TSSP edits the peptide repertoire presented by class II molecules. We show in this article that TSSP increases experimental autoimmune encephalomyelitis severity by limiting central tolerance to myelin oligodendrocyte glycoprotein. The effect on experimental autoimmune encephalomyelitis severity was MHC class II allele dependent, because the lack of TSSP expression conferred protection in NOD mice but not in C57BL/6 mice. Importantly, although human thymic DCs express TSSP, individuals segregate into two groups having a high or 10-fold lower level of expression. Therefore, the level of TSSP expression by thymic DCs may modify the risk factors for MS conferred by some MHC class II haplotypes.

Myelin oligodendrocyte glycoprotein induces incomplete tolerance of CD4(+) T cells specific for both a myelin and a neuronal self-antigen in mice

T-cell polyspecificity, predicting that individual T cells recognize a continuum of related ligands, implies that multiple antigens can tolerize T cells specific for a given self-antigen. We previously showed in C57BL/6 mice that part of the CD4(+) T-cell repertoire specific for myelin oligodendrocyte glycoprotein (MOG) 35-55 also recognizes the neuronal antigen neurofilament medium (NF-M) 15-35. Such bi-specific CD4(+) T cells are frequent and produce inflammatory cytokines after stimulation. Since T cells recognizing two self-antigens would be expected to be tolerized more efficiently, this finding prompted us to study how polyspecificity impacts tolerance. We found that similar to MOG, NF-M is expressed in the thymus by medullary thymic epithelial cells, a tolerogenic population. Nevertheless, the frequency, phenotype, and capacity to transfer experimental autoimmune encephalomyelitis (EAE) of MOG35-55 -reactive CD4(+) T cells were increased in MOG-deficient but not in NF-M-deficient mice. We found that presentation of NF-M15-35 by I-A(b) on dendritic cells is of short duration, suggesting unstable MHC class II binding. Consistently, introducing an MHC-anchoring residue into NF-M15-35 (NF-M15-35 T20Y) increased its immunogenicity, activating a repertoire able to induce EAE. Our results show that in C57BL/6 mice bi-specific encephalitogenic T cells manage to escape tolerization due to inefficient exposure to two self-antigens.

Preferential Use of Public TCR during Autoimmune Encephalomyelitis

How the TCR repertoire, in concert with risk-associated MHC, imposes susceptibility for autoimmune diseases is incompletely resolved. Due largely to recombinatorial biases, a small fraction of TCRα or β-chains are shared by most individuals, or public. If public TCR chains modulate a TCRαβ heterodimer's likelihood of productively engaging autoantigen, because they are pervasive and often high frequency, they could also broadly influence disease risk and progression. Prior data, using low-resolution techniques, have identified the heavy use of select public TCR in some autoimmune models. In this study, we assess public repertoire representation in mice with experimental autoimmune encephalomyelitis at high resolution. Saturation sequencing was used to identify >18 × 10(6) TCRβ sequences from the CNSs, periphery, and thymi of mice at different stages of autoimmune encephalomyelitis and healthy controls. Analyses indicated the prominent representation of a highly diverse public TCRβ repertoire in the disease response. Preferential formation of public TCR implicated in autoimmunity was identified in preselection thymocytes, and, consistently, public, disease-associated TCRβ were observed to be commonly oligoclonal. Increased TCR sharing and a focusing of the public TCR response was seen with disease progression. Critically, comparisons of peripheral and CNS repertoires and repertoires from preimmune and diseased mice demonstrated that public TCR were preferentially deployed relative to nonshared, or private, sequences. Our findings implicate public TCR in skewing repertoire response during autoimmunity and suggest that subsets of public TCR sequences may serve as disease-specific biomarkers or influence disease susceptibility or progression.

Bi-Allelic TCRα or β Recombination Enhances T Cell Development but Is Dispensable for Antigen Responses and Experimental Autoimmune Encephalomyelitis

Dual TCRα-expressing T cells outnumber dual TCRβ-expressing cells by ~10:1. As a result, efforts to understand how dual TCR T cells impact immunity have focused on dual TCRα expression; dual TCRβ expression remains understudied. We recently demonstrated, however, that dual TCRβ expression accelerated disease in a TCR transgenic model of autoimmune arthritis through enhanced positive selection efficiency, indicating that dual TCRβ expression, though rare, can impact thymic selection. Here we generated mice hemizygous for TCRα, TCRβ, or both on the C57BL/6 background to investigate the impact bi-allelic TCR chain recombination has on T cell development, repertoire diversity, and autoimmunity. Lack of bi-allelic TCRα or TCRβ recombination reduced αβ thymocyte development efficiency, and the absence of bi-allelic TCRβ recombination promoted γδ T cell development. However, we observed no differences in the numbers of naïve and expanded antigen-specific T cells between TCRα^+/-β^+/- and wildtype mice, and TCR repertoire analysis revealed only subtle differences in Vβ gene usage. Finally, the absence of dual TCR T cells did not impact induced experimental autoimmune encephalomyelitis pathogenesis. Thus, despite more stringent allelic exclusion of TCRβ relative to TCRα, bi-allelic TCRβ expression can measurably impact thymocyte development and is necessary for maintaining normal αβ/γδ T cell proportions.

Autoregulatory CD8 T cells depend on cognate antigen recognition and CD4/CD8 myelin determinants

Objective:

To determine the antigenic determinants and specific molecular requirements for the generation of autoregulatory neuroantigen-specific CD8⁺ T cells in models of multiple sclerosis (MS).

Methods:

We have previously shown that MOG35-55-specific CD8⁺ T cells suppress experimental autoimmune encephalomyelitis (EAE) in the C57BL/6 model. In this study, we utilized multiple models of EAE to assess the ability to generate autoregulatory CD8⁺ T cells.

Results:

We demonstrate that alternative myelin peptides (PLP178-191) and other susceptible mouse strains (SJL) generated myelin-specific CD8⁺ T cells, which were fully capable of suppressing disease. The disease-ameliorating function of these cells was dependent on the specific cognate myelin antigen. Generation of these autoregulatory CD8⁺ T cells was not affected by thymic selection, but was dependent on the presence of both CD4⁺ and CD8⁺ T-cell epitopes in the immunizing encephalitogenic antigen.

Conclusions:

These studies show that the generation of autoregulatory CD8⁺ T cells is a more generalized, antigen-specific phenomenon across multiple neuroantigens and mouse strains, with significant implications in understanding disease regulation.

DQB1*06:02-Associated Pathogenic Anti-Myelin Autoimmunity in Multiple Sclerosis-Like Disease: Potential Function of DQB1*06:02 as a Disease-Predisposing Allele

Susceptibility to multiple sclerosis (MS) has been linked mainly to the HLA-DRB1 locus, with the HLA-DR15 haplotype (DRB1*1501-DQA1*0102-DQB1*0602-DRB5*0101) dominating MS risk in Caucasians. Although genes in the HLA-II region, particularly DRB1*1501, DQA1*0102-DQB1*0602, are in tight linkage disequilibrium, genome-wide-association, and gene candidate studies identified the DRB1*15:01 allele as the primary risk factor in MS. Many genetic and immune-functional studies have indicated DRB1*15:01 as a primary risk factor in MS, while only some functional studies suggested a disease-modifying role for the DRB5*01 or DQB1*06 alleles. In this respect, the susceptibility of DRB1*15:01-transgenic (Tg) mice to myelin basic protein- or myelin oligodendrocyte glycoprotein-induced MS-like disease is consistent with primary contribution of DRB1*15:01 to HLA-DR15+ MS. The studies summarized here show that susceptibility to MS-like disease, induced in HLA-“humanized” mice by myelin oligodendrocytic basic protein or by the proteolipid protein, one of the most prominent encephalitogenic target antigens implicated in human MS, is determined by DQB1*06:02, rather than by the DRB1*15:01 allele. These findings not only offer a rationale for a potential role for DQB1*06:02 in predisposing susceptibility to MS, but also suggest a more complex and differential functional role for HLA-DR15 alleles, depending on the primary target myelin antigen. However, the conflict between these findings in HLA-Tg mice and the extensive genome-wide-association studies, which could not detect any significant effect from the DQB1*06:02 allele on MS risk, is rather puzzling. Functional analysis of MS PBLs for DQB1*06:02-associated anti-myelin autoimmunity may indicate whether or not DQB1*06:02 is associated with MS pathogenesis.

Single β³-amino acid substitutions to MOG peptides suppress the development of experimental autoimmune encephalomyelitis

CD4(+) T-cells play a key role in the pathogenesis of multiple sclerosis (MS). Altered peptide ligands capable of modulating T-cell autoreactivity are considered a promising strategy for development of antigen-specific therapies for MS. Since peptides are inherently unstable, the current study explored single β-amino acid substitution as a means of stabilizing an epitope of myelin oligodendrocyte glycoprotein. β-Amino acid substitution at position 44, the major T-cell receptor contact residue, increased the half-life of active metabolites. Vaccination with one altered peptide, MOG44βF, conferred protection from EAE, decreased T-cell autoreactivity and pro-inflammatory cytokine production. Additional studies using MOG44βF in an oral treatment regimen, administered after EAE induction, also attenuated disease severity. Thus, altered peptides such as those reported here may lead to the development of novel and more specific treatments for MS.

From classic to spontaneous and humanized models of multiple sclerosis: impact on understanding pathogenesis and drug development

Multiple sclerosis (MS), a demyelinating disease of the central nervous system (CNS), presents as a complex disease with variable clinical and pathological manifestations, involving different pathogenic pathways. Animal models, particularly experimental autoimmune encephalomyelitis (EAE), have been key to deciphering the pathophysiology of MS, although no single model can recapitulate the complexity and diversity of MS, or can, to date, integrate the diverse pathogenic pathways. Since the first EAE model was introduced decades ago, multiple classic (induced), spontaneous, and humanized EAE models have been developed, each recapitulating particular aspects of MS pathogenesis. The advances in technologies of genetic ablation and transgenesis in mice of C57BL/6J background and the development of myelin-oligodendrocyte glycoprotein (MOG)-induced EAE in C57BL/6J mice yielded several spontaneous and humanized EAE models, and resulted in a plethora of EAE models in which the role of specific genes or cell populations could be precisely interrogated, towards modeling specific pathways of MS pathogenesis/regulation in MS. Collectively, the numerous studies on the different EAE models contributed immensely to our basic understanding of cellular and molecular pathways in MS pathogenesis as well as to the development of therapeutic agents: several drugs available today as disease modifying treatments were developed from direct studies on EAE models, and many others were tested or validated in EAE. In this review, we discuss the contribution of major classic, spontaneous, and humanized EAE models to our understanding of MS pathophysiology and to insights leading to devising current and future therapies for this disease.

The effect of vitamin A supplementation on stimulated T-cell proliferation with myelin oligodendrocyte glycoprotein in patients with multiple sclerosis

Background:

Multiple sclerosis (MS) is an autoimmune disease whereby myelin sheath of the central nervous system is destroyed. Vitamin A is known to play a role in the immune system. It has been recognized that some metabolites of vitamin A can be used effectively to treat experimental autoimmune encephalomyelitis (EAE).

Aims:

The effect of vitamin A as retinyl palmitate on T-cell proliferation in MS patients.

Setting and Design:

This study is a double blind clinical trial of two test groups over a period of 6 months.

Materials and Methods:

Thirty five multiple sclerosis (MS) patients were divided into two groups. One group received 25,000 IU/day vitamin A (as retinyl palmitate) and the other group were administered a placebo. The peripheral blood mononuclear cells (PBMCs) were separated and stimulated with myelin oligodendrocyte glycoprotein (MOG) and phytohemagglutinin (PHA) before and after the trial period. BrdU calorimetric assay was performed to measure cell proliferation.

Statistical Analysis:

Analysis of covariance (ANCOVA) and paired t-test were used to analyze the data.

Results:

Observations showed statistical significant differences in the reduction of cell proliferation in the presence of MOG and fetal calf serum (FCS) in the culture medium, between patients receiving vitamin A and the placebo (P = 0.046). Although, this difference was not significant between the two vitamin A and placebo groups in MOG treatment with human serum, a decrease was observed in the group of patients taking vitamin A supplements (P = 0.019). Phytohemagglutinin did not cause any change in cell proliferation between the two groups.

Conclusion:

The results suggest supplementation with retinyl palmitate in patients with MS reduce MOG stimulatory effects on T-cells.

Increased synapse formation obtained by T cell epitopes containing a CxxC motif in flanking residues convert CD4+ T cells into cytolytic effectors

The nature of MHC class II-binding epitopes not only determines the specificity of T cell responses, but may also alter effector cell functions. Cytolytic CD4+ T cells have been observed primarily in anti-viral responses, but very little is known about the conditions under which they can be elicited. Their potential as regulators of immune responses, however, deserves investigations. We describe here that inclusion of a thiol-disulfide oxidoreductase motif within flanking residues of class II-restricted epitopes results, both in vitro and in vivo, in elicitation of antigen-specific cytolytic CD4+ T cells through increased synapse formation. We show that both naïve and polarized CD4+ T cells, including Th17 cells, can be converted by cognate recognition of such modified epitopes. Cytolytic CD4+ T cells induce apoptosis on APCs by Fas-FasL interaction. These findings potentially open the way towards a novel form of antigen-specific immunosuppression.

Unravelling the T-cell-mediated autoimmune attack on CNS myelin in a new primate EAE model induced with MOG34-56 peptide in incomplete adjuvant

Induction of experimental autoimmune encephalomyelitis (EAE) has been documented in common marmosets using peptide 34-56 from human myelin/oligodendrocyte glycoprotein (MOG(34-56) ) in incomplete Freund's adjuvant (IFA). Here, we report that this EAE model is associated with widespread demyelination of grey and white matter. We performed an in-depth analysis of the specificity, MHC restriction and functions of the activated T cells in the model, which likely cause EAE in an autoantibody-independent manner. T-cell lines isolated from blood and lymphoid organs of animals immunized with MOG(34-56) displayed high production of IL-17A and specific lysis of MOG(34-56) -pulsed EBV B-lymphoblastoid cells as typical hallmarks. Cytotoxicity was directed at the epitope MOG(40-48) presented by the non-classical MHC class Ib allele Caja-E, which is orthologue to HLA-E and is expressed in non-inflamed brain. In vivo activated T cells identified by flow cytometry in cultures with MOG(34-56,) comprised CD4(+) CD56(+) and CD4(+) CD8(+) CD56(+) T cells. Furthermore, phenotypical analysis showed that CD4(+) CD8(+) CD56(+) T cells also expressed CD27, but CD16, CD45RO, CD28 and CCR7 were absent. These results show that, in the MOG34-56/IFA marmoset EAE model, a Caja-E-restricted population of autoreactive cytotoxic T cells plays a key role in the process of demyelination in the grey and white matter.

'Multi-epitope-targeted' immune-specific therapy for a multiple sclerosis-like disease via engineered multi-epitope protein is superior to peptides

Antigen-induced peripheral tolerance is potentially one of the most efficient and specific therapeutic approaches for autoimmune diseases. Although highly effective in animal models, antigen-based strategies have not yet been translated into practicable human therapy, and several clinical trials using a single antigen or peptidic-epitope in multiple sclerosis (MS) yielded disappointing results. In these clinical trials, however, the apparent complexity and dynamics of the pathogenic autoimmunity associated with MS, which result from the multiplicity of potential target antigens and “epitope spread”, have not been sufficiently considered. Thus, targeting pathogenic T-cells reactive against a single antigen/epitope is unlikely to be sufficient; to be effective, immunospecific therapy to MS should logically neutralize concomitantly T-cells reactive against as many major target antigens/epitopes as possible. We investigated such “multi-epitope-targeting” approach in murine experimental autoimmune encephalomyelitis (EAE) associated with a single (“classical”) or multiple (“complex”) anti-myelin autoreactivities, using cocktail of different encephalitogenic peptides vis-a-vis artificial multi-epitope-protein (designated Y-MSPc) encompassing rationally selected MS-relevant epitopes of five major myelin antigens, as “multi-epitope-targeting” agents. Y-MSPc was superior to peptide(s) in concomitantly downregulating pathogenic T-cells reactive against multiple myelin antigens/epitopes, via inducing more effective, longer lasting peripheral regulatory mechanisms (cytokine shift, anergy, and Foxp3+ CTLA4+ regulatory T-cells). Y-MSPc was also consistently more effective than the disease-inducing single peptide or peptide cocktail, not only in suppressing the development of “classical” or “complex EAE” or ameliorating ongoing disease, but most importantly, in reversing chronic EAE. Overall, our data emphasize that a “multi-epitope-targeting” strategy is required for effective immune-specific therapy of organ-specific autoimmune diseases associated with complex and dynamic pathogenic autoimmunity, such as MS; our data further demonstrate that the “multi-epitope-targeting” approach to therapy is optimized through specifically designed multi-epitope-proteins, rather than myelin peptide cocktails, as “multi-epitope-targeting” agents. Such artificial multi-epitope proteins can be tailored to other organ-specific autoimmune diseases.

Regulatory T cells play a role in T-cell receptor CDR2 peptide regulation of experimental autoimmune encephalomyelitis

Eliciting T-cell receptor (TCR) -specific responsiveness has been known to provide an effective autoregulatory mechanism for limiting inflammation mediated by T effector cells. Our previous use of TCR peptides derived from the CDR3 regions of a pathogenic TCR effectively reversed ongoing experimental autoimmune encephalomyelitis (EAE) in a humanized TCR transgenic model. In this study, we use the TCR BV8S2 CDR2 peptide in the non-transgenic C57BL/6 EAE model to down-regulate the heterogeneous TCR BV8S2(+)  MOG-35-55-specific pathogenic T-cell population and demonstrate successful treatment of EAE after disease onset. Suppression of disease was associated with reduced MOG-35-55-specific and non-specific T-cell production of interleukin-17a and interferon-γ in the central nervous system, as well as reduced numbers of CD4(+) and Foxp3(+) T cells in the central nervous system. With the use of Foxp3-GFP and Foxp3 conditional knockout mice, we demonstrate that the TCR CDR2 peptide treatment effect is dependent on the presence of Foxp3(+) regulatory T cells and that regulatory T cell numbers are significantly expanded in the periphery of treated mice. Hence, TCR CDR2 peptide therapy is effective in regulating heterogeneous, pathogenic T-cell populations through the activity of the Foxp3(+) regulatory T cell population.

Recognition of a high affinity MHC class I-restricted epitope of myelin oligodendrocyte glycoprotein by CD8⁺ T cells derived from autoantigen-deficient mice

CD4⁺ T cells have a well-defined pathogenic role in experimental autoimmune encephalomyelitis, the rodent model of multiple sclerosis (MS), yet CD8⁺ T cells are commonly found in MS lesions. To determine whether immunological tolerance might impact differently on CD4⁺ versus CD8⁺ T cells, we studied T cell responses in mice genetically deficient for the central nervous system (CNS) autoantigen myelin oligodendrocyte glycoprotein (MOG) versus wild type (WT) C57BL/6 mice. We show that MOG(-/-) mice have enhanced sensitivity to immunization with the immunodominant peptide of MOG (35-55), as evidenced by increased expansion of both CD4⁺ and CD8⁺ T cell subsets. Most strikingly, CD8⁺ T cells from MOG(-/-) mice responded to a novel T cell epitope which binds to MHC class I with high affinity. Despite this, MOG-responsive CD8⁺ T cells sourced from either WT or MOG(-/-) mice failed to initiate CNS inflammation upon transfer to MOG-sufficient mice. In our hands, this capacity was only found in CD4⁺ T cells. However, MOG(-/-) CD4⁺ cells did not show greater pathogenic activity than their WT counterparts. Our data indicate that, in the presence of endogenous MOG, CD8⁺ T cells capable of responding to a MHC class I-restricted epitope that can be stably expressed are subject to rigorous control through central and/or peripheral tolerance.

Rational design of T cell receptors with enhanced sensitivity for antigen

Enhancing the affinity of therapeutic T cell receptors (TCR) without altering their specificity is a significant challenge for adoptive immunotherapy. Current efforts have primarily relied on empirical approaches. Here, we used structural analyses to identify a glycine-serine variation in the TCR that modulates antigen sensitivity. A G at position 107 within the CDR3β stalk is encoded within a single mouse and human TCR, TRBV13-2 and TRBV12-5 respectively. Most TCR bear a S107. The S hydroxymethyl side chain intercalates into the core of the CDR3β loop, stabilizing it. G107 TRBV possess a gap in their CDR3β where this S hydroxymethyl moiety would fit. We predicted based on modeling and molecular dynamics simulations that a G107S substitution would increase CDR3β stability and thereby augment receptor sensitivity. Experimentally, a G107S replacement led to an ∼10–1000 fold enhanced antigen sensitivity in 3 of 4 TRBV13-2⁺ TCR tested. Analysis of fine specificity indicated a preserved binding orientation. These results support the feasibility of developing high affinity antigen specific TCR for therapeutic purposes through the identification and manipulation of critical framework residues. They further indicate that amino acid variations within TRBV not directly involved in ligand contact can program TCR sensitivity, and suggest a role for CDR3 stability in this programming.

High prevalence of low affinity peptide-MHC II tetramer-negative effectors during polyclonal CD4+ T cell responses

Two-dimensional analysis reveals that peptide–MHC class II tetramers underestimate the frequency of cytokine-producing antigen-specific CD4⁺ T cells in polyclonal responses.

T cell affinity for antigen initiates adaptive immunity. However, the contribution of low affinity cells to a response is unknown as it has not been possible to assess the entire affinity range of a polyclonal T cell repertoire. In this study, we used a highly sensitive two-dimensional binding assay to identify low affinity cells in polyclonal autoreactive and pathogen-reactive CD4⁺ T cell populations specific for myelin oligodendrocyte glycoprotein (MOG) and lymphocytic choriomeningitis virus (LCMV) antigens, respectively. Low affinity CD4⁺ T cells, below detection with peptide–major histocompatibility complex class II tetramers, were at least as frequent as high affinity responders and contributed significant effector cytokines in both primary antigen–specific responses. We further demonstrated that MOG- and LCMV-specific CD4⁺ T cells possessed similarly broad ranges in their affinities (>100-fold wide), only differing in the frequencies of low and high affinity cells. Thus, low as well as high affinity CD4⁺ T cells are critical effectors in autoimmune and pathogen-specific responses.

Discrete TCR repertoires and CDR3 features distinguish effector and Foxp3+ regulatory T lymphocytes in myelin oligodendrocyte glycoprotein-induced experimental allergic encephalomyelitis

Regulatory T lymphocytes (Tregs) expressing the Foxp3 transcription factor are critical modulators of autoimmunity. Foxp3(+) Tregs may develop in the thymus as a population distinct from conventional Foxp3(-) αβ T cells (Tconvs). Alternatively, plasticity in Foxp3 expression may allow for the interconversion of mature Tregs and Tconvs. We examined >160,000 TCR sequences from Foxp3(+) or Foxp3(-) populations in the spleens or CNS of wild-type mice with experimental allergic encephalomyelitis to determine their relatedness and identify distinguishing TCR features. Our results indicate that the CNS-infiltrating Tregs and Tconvs arise predominantly from distinct sources. The repertoires of CNS Treg or Tconv TCRs showed limited overlap with heterologous populations in both the CNS and the spleen, indicating that they are largely unrelated. Indeed, Treg and Tconv TCRs in the CNS were significantly less related than those populations in the spleen. In contrast, CNS Treg and Tconv repertoires strongly intersected those of the homologous cell type in the spleen. High-frequency sequences more likely to be disease associated showed similar results, and some public TCRs demonstrated Treg- or Tconv-specific motifs. Different charge characteristics and amino acid use preferences were identified in the CDR3β of Tregs and Tconvs infiltrating the CNS, further indicating that their repertoires are qualitatively distinct. Therefore, discrete populations of Tregs and Tconvs that do not substantially interconvert respond during experimental allergic encephalomyelitis. Differences in sequence and physical characteristics distinguish Treg and Tconv TCRs and imply dissimilar Ag recognition properties.

Immunological basis for the development of tissue inflammation and organ-specific autoimmunity in animal models of multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is an animal model for multiple sclerosis (MS) that has shaped our understanding of autoimmune tissue inflammation in the central nervous system (CNS). Major therapeutic approaches to MS have been first validated in EAE. Nevertheless, EAE in all its modifications is not able to recapitulate the full range of clinical and histopathogenic aspects of MS. Furthermore, autoimmune reactions in EAE-prone rodent strains and MS patients may differ in terms of the relative involvement of various subsets of immune cells. However, the role of specific molecules that play a role in skewing the immune response towards pathogenic autoreactivity is very similar in mice and humans. Thus, in this chapter, we will focus on the identification of a novel subset of inflammatory T cells, called Th17 cells, in EAE and their interplay with other immune cells including protective regulatory T cells (T-regs). It is likely that the discovery of Th17 cells and their relationship with T-regs will change our understanding of organ-specific autoimmune diseases in the years to come.

T cell receptor CDR3 sequence but not recognition characteristics distinguish autoreactive effector and Foxp3(+) regulatory T cells

The source, specificity, and plasticity of the forkhead box transcription factor 3 (Foxp3)(+) regulatory T (Treg) and conventional T (Tconv) cell populations active at sites of autoimmune pathology are not well characterized. To evaluate this, we combined global repertoire analyses and functional assessments of isolated T cell receptors (TCR) from TCRalpha retrogenic mice with autoimmune encephalomyelitis. Treg and Tconv cell TCR repertoires were distinct, and autoantigen-specific Treg and Tconv cells were enriched in diseased tissue. Autoantigen sensitivity and fine specificity of these cells intersected, implying that differences in responsiveness were not responsible for lineage specification. Notably, autoreactive Treg and Tconv cells could be fully distinguished by an acidic versus aliphatic variation at a single TCR CDR3 residue. Our results imply that ontogenically distinct Treg and Tconv cell repertoires with convergent specificities for autoantigen respond during autoimmunity and argue against more than limited plasticity between Treg and Tconv cells during autoimmune inflammation.

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.

Pathogenic MOG-reactive CD8+ T cells require MOG-reactive CD4+ T cells for sustained CNS inflammation during chronic EAE

XIncreasing evidence supports a role for CD8+ T cells in multiple sclerosis. In an attempt to isolate the contribution of CD8+ T cells in a murine model of MS, we immunized mice with a dominant CD8 epitope MOG37-46, a truncated version of MOG35-55. The data presented here show mild disease induced with MOG37-46, characterized by lower clinical scores, a decrease in CNS infiltration and a decrease in microglial activation. CD8+ T cells reactive to MOG37-46 are pro-inflammatory and traffic to the CNS; however, the presence of CD4+ T cells elicits more severe disease and sustained inflammation of the CNS.

A heat shock protein gene (Hsp70.1) is critically involved in the generation of the immune response to myelin antigen

Protracted inflammation has been associated with the generation of autoimmune responses. In this respect, increase in the chaperonin, heat shock protein 70 (hsp70) is an outcome of prolonged inflammatory stress. Previous experiments have shown that overexpression of inducible hsp70 in vitro enhanced myelin autoantigen recognition. To prove the role of hsp70 in myelin-directed responses in vivo, we applied a mouse deficient in the major gene encoding inducible hsp70, hsp70.1. Hsp70.1(-/-) mice sensitized for experimental autoimmune encephalomyelitis (EAE) with myelin oligodendrocyte glycoprotein (MOG) peptide 35-55, displayed almost complete resistance to the disease. This correlated with the loss of T cell proliferation and IFN-gamma production in response to MOG(35-55). T cell transfer experiments as well as antigen presentation assays in vitro demonstrated that hsp70 deficiency was associated with dysfunction in the activation of autoreactive T cells. Moreover, T cell responses to ovalbumin (OVA) peptide 323-339 were altered and CD4(+) T cells were more prone to TCR-induced apoptosis, suggesting broader spectrum of T cell defect in hsp70.1(-/-) mice. These results provide compelling evidence for generalized effect mediated by inducible hsp70 in the recognition of myelin self and non-self antigens that influences the cytokine profile of the immune response affecting autoimmune demyelination.

In vivo regulation of experimental autoimmune encephalomyelitis by NK cells: alteration of primary adaptive responses

Innate immune responses provide the host with its first line of defense against infections. Signals generated by subsets of lymphocytes, including NK cells, NKT cells, and APC during this early host response determine the nature of downstream adaptive immune responses. In the present study, we have examined the role of innate NK cells in an autoimmune model through the use of primary immunization with the myelin oligodendrocyte glycoprotein peptide to induce experimental autoimmune encephalomyelitis (EAE). Our studies have shown that in vivo depletion of NK cells can affect the adaptive immune responses, because NK cells were found to regulate the degree of clinical paralysis and to alter immune adaptive responses to the myelin oligodendrocyte glycoprotein peptide. The requirement for NK cells was reflected by changes in the T cell responses and diminished clinical disease seen in mice treated with anti-NK1.1, anti-asialo GM1, and selected Ly49 subtype-depleted mice. In addition to alteration in T cell responses, the maturational status of dendritic cells in lymph nodes was altered both quantitatively and qualitatively. Finally, examination of TCR Vbeta usage of the brain lymphocytes from EAE mice indicated a spectra-type change in receptor expression in NK- depleted mice as compared with non-NK-depleted EAE mice. These findings further establish a recently postulated link between NK cells and the generation of autoreactive T cells.

Loss of IFN-gamma enables the expansion of autoreactive CD4+ T cells to induce experimental autoimmune encephalomyelitis by a nonencephalitogenic myelin variant antigen

MHC variant peptides are analogues of immunogenic peptides involving alterations of the MHC-binding residues, thereby altering the affinity of the peptide for the MHC molecule. Recently, our laboratory demonstrated that immunization of WT B6 mice with 45D, a low-affinity MHC variant peptide of MOG(35-55), results in significantly attenuated experimental autoimmune encephalomyelitis (EAE), yet IFN-gamma production is comparable to myelin oligodendrocyte glycoprotein (MOG)(35-55)-immunized mice. In light of these findings, we asked whether IFN-gamma was required for the reduced encephalitogenicity of the weak ligand 45D in EAE. In this study, we report that immunization of mice deficient in IFN-gamma or its receptor with 45D exhibit significant EAE signs compared with 45D-immunized wild-type B6 mice. Moreover, 45D-immunized IFN-gamma(-/-) and IFN-gammaR(-/-) mice demonstrate MOG tetramer-positive CD4(+) T cells within the CNS and display substantial numbers of MOG-specific CD4(+) T cells in the periphery. In contrast, wild-type mice immunized with 45D exhibit reduced numbers of MOG-specific CD4(+) T cells in the periphery and lack MOG tetramer- positive CD4(+) T cells in the CNS. Importantly, the increased encephalitogenicity of 45D in mice lacking IFN-gamma or IFN-gammaR was not due to deviation toward an enhanced IL-17-secreting phenotype. These findings demonstrate that IFN-gamma significantly attenuates the encephalitogenicity of 45D and are the first to highlight the importance of IFN-gamma signaling in setting the threshold level of responsiveness of autoreactive CD4(+) T cells to weak ligands.

Peptide-based immunotherapy of experimental autoimmune encephalomyelitis without anaphylaxis

Administration of peptide antigens in tolerogenic form holds promise as a specific treatment for autoimmune and allergic disorders. However, experiments in rodent autoimmune models have highlighted the risk of anaphylaxis in response to systemic peptide application once the aberrant immune response is underway. Thus, mice with clinical signs of experimental autoimmune encephalomyelitis (EAE) or diabetes have been reported to suffer fatal anaphylaxis upon administration of native autoantigenic peptides. Clearly, this might represent a significant barrier to the use of synthetic peptides in the treatment of ongoing human autoimmune conditions. Here we describe the development of an altered peptide ligand (APL) engineered to prevent anaphylaxis (no antibody binding) whilst retaining the ability to silence pathogenic myelin-reactive T lymphocytes. Administration of the APL to mice with an ongoing anti-myelin immune response did not cause anaphylaxis, but led to complete protection from the subsequent induction of EAE and, when given during ongoing EAE, led to a rapid remission of clinical signs. The approach of removing antibody recognition whilst maintaining the desired functional effect (in this case T cell tolerance) may be of value in other situations in which there is a risk of triggering anaphylaxis with peptide-based drugs.

Active induction of experimental allergic encephalomyelitis

This protocol details a method to actively induce experimental allergic encephalomyelitis (EAE), a widely used animal model for studies of multiple sclerosis. EAE is induced by stimulating T-cell-mediated immunity to myelin antigens. Active induction of EAE is accomplished by immunization with myelin antigens emulsified in adjuvant. This protocol focuses on induction of EAE in mice; however, the same principles apply to EAE induction in other species. EAE in rodents is manifested typically as ascending flaccid paralysis with inflammation targeting the spinal cord. However, more diverse clinical signs can occur in certain strain/antigen combinations in rodents and in other species, reflecting increased inflammation in the brain.

Central nervous system and non-central nervous system antigen vaccines exacerbate neuropathology caused by nerve injury

Previously, we showed that autoimmune (central nervous system myelin-reactive) T cells exacerbate tissue damage and impair neurological recovery after spinal cord injury. Conversely, independent studies have shown T cell-mediated neuroprotection after spinal cord injury or facial nerve axotomy (FNAx). The antigen specificity of the neuroprotective T cells has not been investigated after FNAx. Here, we compared the neuroprotective capacity of autoimmune and non-autoimmune lymphocytes after FNAx. Prior to axotomy, C57BL/6 mice were immunized with myelin basic protein, myelin oligodendrocyte glycoprotein (MOG) or ovalbumin (a non-self antigen) emulsified in complete Freund's adjuvant (CFA). FNAx mice receiving injections of phosphate-buffered saline (PBS) only (unimmunized) or PBS/CFA emulsions served as controls. At 4 weeks after axotomy, bilateral facial motor neuron counts were obtained throughout the facial motor nucleus using unbiased stereology (optical fractionator). The data show that neuroantigen immunizations and 'generic' lymphocyte activation (e.g. PBS/CFA or ovalbumin/CFA immunizations) exacerbated neuron loss above that caused by FNAx alone. We also found that nerve injury potentiated the effector potential of autoimmune lymphocytes. Indeed, prominent forelimb and hindlimb motor deficits were accompanied by disseminated neuroinflammation and demyelination in FNAx mice receiving subencephalitogenic immunization with MOG. FNAx or neuroantigen (MOG or myelin basic protein) immunization alone did not cause these pathological changes. Thus, irrespective of the antigens used to trigger an immune response, neuropathology was enhanced when the immune system was primed in parallel with nerve injury. These data have important implications for therapeutic vaccination in clinical neurotrauma and neurodegeneration.

Epitope specificity of autoreactive T and B cells associated with experimental autoimmune encephalomyelitis and optic neuritis induced by oligodendrocyte-specific protein in SJL/J mice

The encephalitogenic potential of oligodendrocyte-specific protein (OSP) in mice, its specific localization in the intralamellar tight junctions in CNS myelin, and the detection of autoreactivity against OSP in multiple sclerosis (MS) strongly suggest the relevance of autoreactivity against OSP in the pathogenesis of MS. In this study, we have characterized the autoimmune T and B cells that are associated with clinicopathological manifestations of OSP-induced MS-like disease in mice by using recombinant soluble mouse OSP (smOSP) and synthetic overlapping peptides spanning smOSP. SJL/J mice immunized with smOSP developed chronic relapsing clinical experimental autoimmune encephalomyelitis accompanied with intense perivascular and parenchymal inflammatory infiltrates, widespread demyelination, axonal loss, and remarkable optic neuritis. The smOSP-primed lymph node cells reacted predominantly against OSP55-80 and to a lesser extent also to OSP22-46 and OSP179-207. Unexpectedly, in vitro selection with smOSP resulted in pathogenic smOSP-specific CD4+ T cells that reacted equally well against OSP55-80, OSP22-46, OSP45-66, and OSP179-207. Fine analysis of the anti-OSP autoimmunity revealed that the disease is primarily associated with CD4+ T cells directed against the major (OSP55-80) and the minor (OSP179-207) encephalitogenic regions that were further delineated, both in vitro and in vivo, to OSP55-66 and OSP194-207, respectively. In contrast, the OSP-induced Abs were predominantly directed against OSP22-46; these Abs were mostly of IgG1 isotype, but high levels of IgG2a and IgG2b and significant levels of IgE were also observed. The reactivity of pathogenic T cells to two encephalitogenic regions, OSP55-80 and OSP179-207, and their diverse TCRVbeta gene repertoire may impose difficulties for epitope-directed or TCR-targeting approaches to immune-specific modulation of OSP-related pathogenesis.

Distinct T cell recognition of naturally processed and cryptic epitopes within the immunodominant 35-55 region of myelin oligodendrocyte glycoprotein

We have assessed the complexity in T cell recognition of the immunodominant 35-55 region of myelin oligodendrocyte glycoprotein (MOG) in C57BL/6 mice. Immunization with the p35-55 peptide generated two types of T cell, recognizing either a cryptic, or a naturally-processed epitope. Clear differences in the recognition of residues within a core sequence of 40-48 were observed. The majority of the p35-55-reactive repertoire in vivo appeared responsive to the intact autoantigen, supporting the notion of a failure of central tolerance to this region of MOG. Our data also provide a basis for exploring the requirements for antigen processing of MOG.

A Pathogenic Role for CD8+ T Cells in a Spontaneous Model of Demyelinating Disease

Transgenic (Tg) mice that overexpress the costimulatory ligand B7.2/CD86 on microglia spontaneously develop a T cell-mediated demyelinating disease. Characterization of the inflammatory infiltrates in the nervous tissue revealed a predominance of CD8+ T cells, suggesting a prominent role of this T cell subset in the pathology. In this study, we show that the same neurological disease occurred in Tg mice deficient in the generation of CD4+ T cells, with an earlier time of onset. Analysis of the CD8+ T cell repertoire at early stage of disease revealed the presence of selected clonal expansions in the CNS but not in peripheral lymphoid organs. We further show that Tg animals deficient in IFN-gamma receptor expression were completely resistant to disease development. Microglia activation that is an early event in disease development is IFN-gamma dependent and thus appears as a key element in disease pathogenesis. Collectively, our data indicate that the spontaneous demyelinating disease in this animal model occurs as a consequence of an inflammatory response initiated through the activation of CNS-specific CD8+ T cells by Tg expression of B7.2 within the target organ. Thus, autoreactive CD8+ T cells can contribute directly to the pathogenesis of neuroinflammatory diseases such as multiple sclerosis.

MBP-PLP fusion protein-induced EAE in C57BL/6 mice

Gene knock-out and knock-in mice are becoming increasingly indispensable for mechanism-oriented studies of EAE. Most gene-modified mice are on the C57BL/6 background, for which presently there are only two EAE models available, the MOG peptide 35-55 and the PLP 178-191 peptide induced disease. However, because MS is not a single pathogenic entity, different EAE models are required to reproduce and study its various features. Here we are introducing MBP-PLP fusion protein (MP4)-induced EAE for C57BL/6 mice. B cell- and CD8+ T cell-dependence, as well as multi-determinant recognition are among the unique features of this demyelinating EAE.

Molecular mimicry revisited: gut bacteria and multiple sclerosis

Molecular mimicry is a possible explanation for autoimmune side effects of microorganism infections. Protein sequences from a particular microorganism are compared to known autoimmune immunogens. For diseases such as multiple sclerosis (MS), where the infectious agent is unknown, guesses to its identity are made. Mimics are assumed to be rare. This study takes a radically different approach. Reported sequences from all known human bacterial and viral agents were searched for autoimmune immunogen mimics. Three encephalitogenic peptides, whose autoimmune requirements have been studied extensively, were selected for comparison. Mimics were seen in a wide variety of organisms. For each immunogen, the mimics were found predominantly in nonpathogenic gut bacteria. Since the three immunogens used in this study are related to MS, it is suggested that a microorganism responsible for autoimmune activity in MS could be a normally occurring gut bacterium. This would explain many of the peculiar MS epidemiological data and why no infective agent has been identified for MS and supports recently found MS gut metabolism abnormalities.

Anatomy of T cell autoimmunity to myelin oligodendrocyte glycoprotein (MOG): Prime role of MOG44F in selection and control of MOG-reactive T cells in H-2b mice

Myelin oligodendrocyte glycoprotein (MOG) is an important myelin target antigen, and MOG-induced EAE is now a widely used model for multiple sclerosis. Clonal dissection revealed that MOG-induced EAE in H-2(b) mice is associated with activation of an unexpectedly large number of T cell clones reactive against the encephalitogenic epitope MOG35-55. These clones expressed extremely diverse TCR with no obvious CDR3alpha/CDR3beta motif(s). Despite extensive TCR diversity, the cells required MOG40-48 as their common core epitope and shared MOG44F as their major TCR contact. Fine epitope-specificity analysis with progressively truncated peptides suggested that the extensive TCR heterogeneity is mostly related to differential recognition of multiple overlapping epitopes nested within MOG37-52, each comprised of a MOG40-48 core flanked at the N- and/or the C-terminus by a variable number of residues important for interaction with different TCR. Abrogation of both the encephalitogenic potential of MOG and T cell reactivity against MOG by a single mutation (MOG44F/MOG44A), together with effective down-regulation of MOG-induced EAE by MOG37-44A-52, confirmed in vivo the primary role for MOG44F in the selection/activation of MOG-reactive T cells. We suggest that such a highly focused T cell autoreactivity could be a selective force that offsets the extensive TCR diversity to facilitate a more "centralized control" of pathogenic MOG-related T cell autoimmunity.

Pathogenic myelin oligodendrocyte glycoprotein antibodies recognize glycosylated epitopes and perturb oligodendrocyte physiology

Antibodies to myelin components are routinely detected in multiple sclerosis patients. However, their presence in some control subjects has made it difficult to determine their contribution to disease pathogenesis. Immunization of C57BL/6 mice with either rat or human myelin oligodendrocyte glycoprotein (MOG) leads to experimental autoimmune encephalomyelitis (EAE) and comparable titers of anti-MOG antibodies as detected by ELISA. However, only immunization with human (but not rat) MOG results in a B cell-dependent EAE. In this study, we demonstrate that these pathogenic and nonpathogenic anti-MOG antibodies have a consistent array of differences in their recognition of antigenic determinants and biological effects. Specifically, substituting proline at position 42 with serine in human MOG (as in rat MOG) eliminates the B cell requirement for EAE. All MOG proteins analyzed induced high titers of anti-MOG (tested by ELISA), but only antisera from mice immunized with unmodified human MOG were encephalitogenic in primed B cell-deficient mice. Nonpathogenic IgGs bound recombinant mouse MOG and deglycosylated MOG in myelin (tested by Western blot), but only pathogenic IgGs bound glycosylated MOG. Only purified IgG to human MOG bound to live rodent oligodendrocytes in culture and, after cross-linking, induced repartitioning of MOG into lipid rafts, followed by dramatic changes in cell morphology. The data provide a strong link between in vivo and in vitro observations regarding demyelinating disease, further indicate a biochemical mechanism for anti-MOG-induced demyelination, and suggest in vitro tools for determining autoimmune antibody pathogenicity in multiple sclerosis patients.

Autoreactive CD8+ T cells in multiple sclerosis: a new target for therapy?

Multiple sclerosis afflicts more than 1 million individuals worldwide and is widely considered to be an autoimmune disease. Traditionally, CD4(+) T helper cells have almost exclusively been held responsible for its immunopathogenesis, partly because certain MHC class II alleles clearly predispose for developing multiple sclerosis and also, because of their importance in inducing experimental autoimmune encephalomyelitis (EAE), the animal model for multiple sclerosis. However, several strategies that target CD4(+) T cells beneficially in EAE have failed to ameliorate disease activity in multiple sclerosis, and some have even triggered exacerbations. Recently, the potential importance of CD8(+) T cells has begun to emerge. Physiologically, CD8(+) T cells are essential for detecting and eliminating abnormal cells, whether infected or neoplastic. In multiple sclerosis, genetic associations with MHC class I alleles have now been established, and CD8(+) as well as CD4(+) T cells have been found to invade and clonally expand in inflammatory central nervous system plaques. Recent animal models induced by CD8(+) T cells show interesting similarities to multiple sclerosis, in particular, in lesion distribution (more inflammation in the brain relative to the spinal cord), although not all of the features of the human disease are recapitulated. Here we outline the arguments for a possible role for CD8(+) T cells, a lymphocyte subset that has long been underrated in multiple sclerosis and should now be considered in new therapeutic approaches.

Asparagine Endopeptidase Is Not Essential for Class II MHC Antigen Presentation but Is Required for Processing of Cathepsin L in Mice

Class II MHC molecules survey the endocytic compartments of APCs and present antigenic peptides to CD4 T cells. In this context, lysosomal proteases are essential not only for the generation of antigenic peptides but also for proteolysis of the invariant chain to allow the maturation of class II MHC molecules. Recent studies with protease inhibitors have implicated the asparagine endopeptidase (AEP) in class II MHC-restricted Ag presentation. We now report that AEP-deficient mice show no differences in processing of the invariant chain or maturation of class II MHC products compared with wild-type mice. In the absence of AEP, presentation to primary T cells of OVA and myelin oligodendrocyte glycoprotein, two Ags that contain asparagine residues within or in proximity to the relevant epitopes was unimpaired. Cathepsin (Cat) L, a lysosomal cysteine protease essential for the development to CD4 and NK T cells, fails to be processed into its mature two-chain form in AEP-deficient cells. Despite this, the numbers of CD4 and NK T cells are normal, showing that the single-chain form of Cat L is sufficient for its function in vivo. We conclude that AEP is essential for processing of Cat L but not for class II MHC-restricted Ag presentation.

Specificity, magnitude, and kinetics of MOG-specific CD8+ T?cell responses during experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) has traditionally been thought to be almost exclusively mediated by CD4(+) effector T cells. Here, we provide evidence for the existence of mouse CD8(+) T cells that are specific for an epitope of the myelin oligodendrocyte glycoprotein (MOG). Using a panel of truncated MOG peptides, we have identified the minimal epitope recognized by these T cells as MOG 37-46. This peptide, while possessing relatively low affinity for H-2D(b), efficiently stimulates IFN-gamma production from MOG-specific CD8(+) T cell lines in vitro and induces EAE in vivo. To further characterize the magnitude and kinetics of expansion of the MOG-specific CD8(+) T cell population in vivo, we used MOG 37-50/H-2D(b) MHC tetramers to visualize MOG-specific CD8(+) effectors in the peripheral lymphoid organs and central nervous system during the course of EAE induction and progression. Our results identify MOG-specific CD8(+) T cells in the central nervous system prior to and after the onset of disease, suggesting that CD8(+) T cells are a possible target for therapeutic intervention during EAE.

The magnitude and encephalogenic potential of autoimmune response to MOG is enhanced in MOG deficient mice

Myelin oligodendrocyte glycoprotein (MOG) is a minor component of central nervous system myelin presumably implicated in the pathogenesis of Multiple Sclerosis (MS). Immunization with MOG leads to the development of Experimental Autoimmune Encephalomyelitis (EAE), the experimental model of MS. It has been suggested that its encephalitogenic potential may be due to the lack of MOG self-immune tolerance. To clarify this, we have generated a MOG deficient mouse (MOG(-/-)) strain. Surprisingly, MOG(35-55)specific proliferation and Th1-type cytokine production were markedly enhanced in MOG(-/-)mice compared to wild type control. Furthermore, adoptive transfer of MOG(35-55)specific T cells, isolated from MOG deficient mice, into wild-type recipients resulted in the development of a more severe disease, indicating a high capacity of MOG(-/-)T cells to initiate effector responses. Interestingly, T cell reactivity to overlapping MOG peptides in MOG(-/-)mice did not reveal new potential immunodominant epitopes in H-2(b)mice. Taken together, our data suggests that MOG self-tolerance modulates the encephalitogenic potential of autoreactive MOG T cells in the periphery.

The Myelin-Associated Oligodendrocytic Basic Protein Region MOBP15–36 Encompasses the Immunodominant Major Encephalitogenic Epitope(s) for SJL/J Mice and Predicted Epitope(s) for Multiple Sclerosis-Associated HLA-DRB1*1501

Autoimmune response to the myelin-associated oligodendrocytic basic protein (MOBP), a CNS-specific myelin constituent, was recently suggested to play a role in the pathogenesis of multiple sclerosis (MS). The pathogenic autoimmune response to MOBP and the associated pathology in the CNS have not yet been fully investigated. In this study, we have characterized the clinical manifestations, pathology, T cell epitope-specificity, and TCRs associated with experimental autoimmune encephalomyelitis (EAE) induced in SJL/J mice with recombinant mouse MOBP (long isoform, 170 aa). Analysis of encephalitogenic MOBP-reactive T cells for reactivity to overlapping MOBP peptides defined MOBP15-36 as their major immunodominant epitope. Accordingly, MOBP15-36 was demonstrated to be the major encephalitogenic MOBP epitope for SJL/J mice, inducing severe/chronic clinical EAE associated with intense perivascular and parenchymal infiltrations, widespread demyelination, axonal loss, and remarkable optic neuritis. Molecular modeling of the interaction of I-A(s) with MOBP15-36, together with analysis of the MOBP15-36-specific T cell response to truncated peptides, suggests MOBP20-28 as the core sequence for I-A(s)-restricted recognition of the encephalitogenic region MOBP15-36. Although highly focused in their epitope specificity, the encephalitogenic MOBP-reactive T cells displayed a widespread usage of TCR Vbeta genes. These results would therefore favor epitope-directed, rather than TCR-targeted, approaches to therapy of MOBP-associated pathogenic autoimmunity. Localization by molecular modeling of a potential HLA-DRB1*1501-associated MOBP epitope within the encephalitogenic MOBP15-36 sequence suggests the potential relevance of T cell reactivity against MOBP15-36 to MS. The reactivity to MOBP15-36 detected in MS shown here and in another study further emphasizes the potential significance of this epitope for MS.

Regulation of polyclonal T cell responses by an MHC anchor-substituted variant of myelin oligodendrocyte glycoprotein 35-55

Analogs of immunogenic peptides containing substitutions at TCR contact residues (altered peptide ligands (APLs)) have been used to manipulate Ag-specific T cell responses in models of autoimmunity, including experimental autoimmune encephalomyelitis. However, recent clinical trials with APL of a myelin basic protein epitope revealed limitations of this therapy. In this study, we demonstrate that individual myelin oligodendrocyte glycoprotein (MOG) 35-55-specific T cell clones responded differentially to a MOG 35-55 APL, raising questions about the ability of peptide analogs containing amino acid substitutions at TCR contact residues to control polyclonal populations of T cells. In contrast, we found that a variant peptide containing a substitution at an MHC anchor residue uniformly affected multiple MOG 35-55-specific clones and polyclonal lines. Stimulation of polyclonal MOG 35-55-specific T cells with an MHC variant peptide resulted in the induction of anergy, as defined by a dramatic reduction in proliferation and IL-2 production upon challenge with wild-type peptide. Furthermore, treatment of T cell lines with this peptide in vitro resulted in a significant reduction in their encephalitogenicity upon adoptive transfer. These results indicate that the use of MHC anchor-substituted peptides may be efficacious in the regulation of polyclonal T cell responses such as those found in EAE.

Rat and human myelin oligodendrocyte glycoproteins induce experimental autoimmune encephalomyelitis by different mechanisms in C57BL/6 mice

C57BL/6 mice immunized with the extracellular Ig-like domain of rat myelin oligodendrocyte glycoprotein (MOG) developed experimental autoimmune encephalomyelitis (EAE) resembling that induced by rodent MOG 35-55 in its B cell independence and predominantly mononuclear CNS infiltrate. In contrast, human MOG protein-induced EAE was B cell dependent with polymorphonuclear leukocytes. Human MOG differs from rat MOG at several residues, including a proline for serine substitution at position 42. Human MOG 35-55 was only weakly encephalitogenic, and a proline substitution in rat MOG at position 42 severely attenuated its encephalitogenicity. However, human MOG 35-55 was immunogenic, inducing proliferation and IFN-gamma and IL-13 to human, but not rodent MOG 35-55 [corrected]. The B cell dependence of EAE induced by human MOG protein was not due to a requirement for Ag presentation by B cells, because spleen cells from B cell-deficient mice processed and presented human and rat MOG proteins to T cells. The different pathogenic mechanisms of human and rat MOG proteins might result from different Abs induced by these proteins. However, rat and human MOG proteins induced Abs to mouse MOG that were equivalent in titer and IgG subclass. These data demonstrate that EAE can be induced in C57BL/6 mice by two mechanisms, depending on the nature of the immunogen: an encephalitogenic T cell response to rat MOG or rodent MOG 35-55, or an encephalitogenic B cell response to epitopes on human MOG protein that most likely cross-react with mouse determinants.