Antigen-specific tolerance as a therapy for experimental autoimmune encephalomyelitis

Harnessing autoimmunity with dominant self-peptide: Modulating the sustainability of tissue-preferential antigen-specific Tregs by governing the binding stability via peptide flanking residues

Sensitization to self-peptides induces various immunological responses, from autoimmunity to tumor immunity, depending on the peptide sequence; however, the underlying mechanisms remain unclear, and thus, curative therapeutic options considering immunity balance are limited. Herein, two overlapping dominant peptides of myelin proteolipid protein, PLP136-150 and PLP139-151, which induce different forms of experimental autoimmune encephalomyelitis (EAE), monophasic and relapsing EAE, respectively, were investigated. Mice with monophasic EAE exhibited highly resistant to EAE re-induction with any encephalitogenic peptides, whereas mice with relapsing EAE were susceptible, and progressed, to EAE re-induction. This resistance to relapse and re-induction in monophasic EAE mice was associated with the maintenance of potent CD69+CD103+CD4+CD25high regulatory T-cells (Tregs) enriched with antigen specificity, which expanded preferentially in the central nervous system with sustained suppressive activity. This tissue-preferential sustainability of potent antigen-specific Tregs was correlated with the antigenicity of PLP136-150, depending on its flanking residues. That is, the flanking residues of PLP136-150 enable to form pivotally arranged strong hydrogen bonds that secured its binding stability to MHC-class II. These potent Tregs acting tissue-preferentially were induced only by sensitization of PLP136-150, not by its tolerance induction, independent of EAE development. These findings suggest that, for optimal therapy, "benign autoimmunity" can be critically achieved through inverse vaccination with self-peptides by manipulating their flanking residues.

Recent advancements in nanoparticle-mediated approaches for restoration of multiple sclerosis

Multiple Sclerosis (MS) is an autoimmune disease with complicated immunopathology which necessitates considering multifactorial aspects for its management. Nano-sized pharmaceutical carriers named nanoparticles (NPs) can support impressive management of disease not only in early detection and prognosis level but also in a therapeutic manner. The most prominent initiator of MS is the domination of cellular immunity to humoral immunity and increment of inflammatory cytokines. The administration of several platforms of NPs for MS management holds great promise so far. The efforts for MS management through in vitro and in vivo (experimental animal models) evaluations, pave a new way to a highly efficient therapeutic means and aiding its translation to the clinic in the near future.

An insight into the role of liposomal therapeutics in the reversion of Multiple Sclerosis

INTRODUCTION

Multiple Sclerosis (MS), as an autoimmune disease, has complicated immunopathology, which makes its management relevant to various factors. Novel pharmaceutical vehicles, especially liposomes, can support efficacious handling of this disease both in early detection and prognosis and also in a therapeutic manner. The most well-known trigger of MS onset is the predominance of cellular to humoral immunity and enhancement of inflammatory cytokines level. The installation of liposomes as nanoparticles to control this disease holds great promise up to now.

AREAS COVERED

Various types of liposomes with different properties and purposes have been formulated and targeted immune cells with their surface manipulations. They may be encapsulated with anti-inflammatory, MS-related therapeutics, or immunodominant myelin-specific peptides for attaining a higher therapeutic efficacy of the drugs or tolerance induction. Cationic liposomes are also highly applicable for gene delivery of the anti-inflammatory cytokines or silencing the inflammatory cytokines. Liposomes have also been used as biotools for comprehending MS pathomechanisms or as diagnostic agents.

EXPERT OPINION

The efforts to manage MS through nanomedicine, especially liposomal therapeutics, pave a new avenue to a high-throughput medication of this autoimmune disease and their translation to the clinic in the future for overcoming the challenges that MS patients confront.

Approaches to inducing antigen-specific immune tolerance in allergy and autoimmunity: Focus on antigen-presenting cells and extracellular vesicles

Increasing prevalence of allergic and autoimmune diseases urges clinicians and researchers to search for new and efficient treatments. Strategies that activate antigen-specific immune tolerance and simultaneously maintain immune reactivity to all other antigens deserve special attention. Accordingly, antigen-presenting cells (APCs) seem to be the best suited for orchestrating these mechanisms by directing T cell immune responses towards a tolerant subtype. Recent advances in understanding cell-to-cell communication via extracellular vesicles (EVs) make the latter promising candidates for reprogramming APCs towards a tolerant phenotype, and for mediating tolerogenic APC function. Thus, comprehensive studies have been undertaken to describe the interactions of APCs and EVs naturally occurring during immune tolerance induction, as well as to develop EV-based manoeuvres enabling the induction of immune tolerance in an antigen-specific manner. In this review, we summarize the findings of relevant studies, with a special emphasis on future perspectives on their translation to clinical practice.

Nanoparticle-based autoimmune disease therapy

The goal of immunotherapy against autoimmunity is to block pathogenic inflammation without impairing immunity against infections and tumours. Regulatory T-cells (Tregs) play a central role in maintaining immune homeostasis, and autoimmune inflammation is frequently associated with decreased numbers and/or function of these T-cells. Therapies harnessing Tregs to treat autoimmune inflammation remain under-developed with caveats ranging from the lack of antigenic and disease specificity to the potential phenotypic and functional instability of in vitro-expanded Treg cells in vivo. Here, we review nanotechnology-based approaches designed to promote immune tolerance through various mechanisms, ranging from systemic or local suppression of antigen-presenting cells and deletion of antigen-specific T-cells, to the systemic expansion of antigen- and disease-specific Treg cells in vivo.

Antigen-Specific Therapies in Multiple Sclerosis

During recent years, many new therapies for human autoimmune diseases such as multiple sclerosis (MS) have been considered based on promising in vitro data or animal experiments. A number of them have proceeded to early clinical testing. However, very few finally advanced to approval by the regulatory agencies and are currently available to patients. The main reasons for failure were either lack of efficacy in humans and/or unexpected and untolerable adverse events. Although previous attempts toward antigen-specific immunomodulation have often been disappointing, these difficulties have led to renewed interest in therapies that aim at reestablishing tolerance to autoantigens at the level of either T cell-mediated or antibody-mediated immune responses or both. Such antigen-specific immunotherapies offer the prospect of correcting pathological immune reactivity against autoantigens in a highly specific and effective manner and also achievement of this goal with relatively little side effects. Here we will review the various approaches that are currently being considered for antigen-specific immunotherapies in MS.

Molecular mechanisms of T-cell receptor and costimulatory molecule ligation/blockade in autoimmune disease therapy

SUMMARY

Pro-inflammatory CD4(+) T-cell-mediated autoimmune diseases, such as multiple sclerosis and type 1 diabetes, are hypothesized to be initiated and maintained by activated antigen-presenting cells presenting self antigen to self-reactive interferon-gamma and interleukin-17-producing CD4(+) T-helper (Th) type 1/Th17 cells. To date, the majority of Food and Drug Administration-approved therapies for autoimmune disease primarily focus on the global inhibition of immune inflammatory activity. The goal of ongoing research in this field is to develop both therapies that inhibit/eliminate activated autoreactive cells as well as antigen-specific treatments, which allow for the directed blockade of the deleterious effects of self-reactive immune cell function. According to the two-signal hypothesis, activation of a naive antigen-specific CD4(+) T cell requires both stimulation of the T-cell receptor (TCR) (signal 1) and stimulation of costimulatory molecules (signal 2). There also exists a balance between pro-inflammatory and anti-inflammatory immune cell activity, which is regulated by the type and strength of the activating signal as well as the local cytokine milieu in which the naive CD4(+) T cell is activated. To this end, the majority of ongoing research is focused on the delivery of suboptimal TCR stimulation in the absence of costimulatory molecule stimulation, or potential blockade of stimulatory accessory molecules. Therefore, the signaling pathways involved in the induction of CD4(+) T-cell anergy, as apposed to activation, are topics of intense interest.

Prospects for antigen-specific tolerance based therapies for the treatment of multiple sclerosis

A primary focus in autoimmunity is the breakdown of central and peripheral tolerance resulting in the survival and eventual activation of autoreactive T cells. As CD4(+) T cells are key contributors to the underlying pathogenic mechanisms responsible for onset and progression of most autoimmune diseases, they are a logical target for therapeutic strategies. One method for restoring self-tolerance is to exploit the endogenous regulatory mechanisms that govern CD4(+) T cell activation. In this review, we discuss tolerance strategies with the common goal of inducing antigen (Ag)-specific tolerance. Emphasis is given to the use of peptide-specific tolerance strategies, focusing on ethylene carbodiimide (ECDI)-peptide-coupled cells (Ag-SP) and nonmitogenic anti-CD3, which specifically target the T cell receptor (TCR) in the absence of costimulatory signals. These approaches induce a TCR signal of insufficient strength to cause CD4(+) T cell activation and instead lead to functional T cell anergy/deletion and activation of Ag-specific induced regulatory T cells (iTregs) while avoiding generalized long-term immunosuppression.

Intrinsic and induced regulation of the age-associated onset of spontaneous experimental autoimmune encephalomyelitis

Multiple sclerosis is characterized by perivascular CNS infiltration of myelin-specific CD4(+) T cells and activated mononuclear cells. TCR transgenic mice on the SJL background specific for proteolipid protein (PLP)(139-151) develop a high incidence of spontaneous experimental autoimmune encephalomyelitis (sEAE). We examined the intrinsic mechanisms regulating onset and severity of sEAE. CD4(+) T cells isolated from the cervical lymph nodes, but not spleens, of diseased 5B6 transgenic mice are hyperactivated when compared with age-matched healthy mice and produce both IFN-gamma and IL-17, indicating that the cervical lymph node is the initial peripheral activation site. The age-associated development of sEAE correlates with a decline in both the functional capacity of natural regulatory T cells (nTregs) and in PLP(139-151)-induced IL-10 production and a concomitant increase in IL-17 production. Anti-CD25-induced inactivation of nTregs increased the incidence and severity of sEAE. Conversely, induction of peripheral tolerance via the i.v. injection of PLP(139-151)-pulsed, ethylcarbodiimide-fixed APCs (PLP(139-151)-SP) inhibited the development of clinical disease concomitant with increased production of IL-10 and conversion of Foxp3(+) Tregs from CD4(+)CD25(-) progenitors. These data indicate that heterogeneous populations of Tregs regulate onset of sEAE, and that induction of peripheral tolerance can be exploited to prevent/treat spontaneous autoimmune disease.

Therapeutic blockade of T-cell antigen receptor signal transduction and costimulation in autoimmune disease

CD4+ T-cell-mediated autoimmune diseases are initiated and maintained by the presentation of self-antigen by antigen-presenting cells (APCs) to self-reactive CD4+ T-cells. According to the two-signal hypothesis, activation of a naive antigen-specific CD4+ T-cell requires stimulation of both the T-cell antigen receptor (signal 1) and costimulatory molecules such as CD28 (signal 2). To date, the majority of therapies for autoimmune diseases approved by the Food and Drug Administration primarily focus on the global inhibition of immune inflammatory activity. The goal of ongoing research in this field is to develop antigen-specific treatments which block the deleterious effects of self-reactive immune cell function while maintaining the ability of the immune system to clear nonself antigens. To this end, the signaling pathways involved in the induction of CD4+ T-cell anergy, as apposed to activation, are a topic of intense interest. This chapter discusses components of the CD4+ T-cell activation pathway that may serve as therapeutic targets for the treatment of autoimmune disease.

Antigen-specific tolerance strategies for the prevention and treatment of autoimmune disease

The development of safe and effective antigen-specific therapies is needed to treat patients with autoimmune diseases. These therapies must allow for the specific tolerization of self-reactive immune cells without altering host immunity to infectious insults. Experimental models and clinical trials for the treatment of autoimmune disease have identified putative mechanisms by which antigen-specific therapies induce tolerance. Although advances have been made in the development of efficient antigen-specific therapies, translating these therapies from bench to bedside has remained difficult. Here, we discuss the recent advances in our understanding of antigen-specific therapies for the treatment of autoimmune diseases.

Peripheral tolerance induction using ethylenecarbodiimide-fixed APCs uses both direct and indirect mechanisms of antigen presentation for prevention of experimental autoimmune encephalomyelitis

MHC class II (MHC II)-restricted T cell responses are a common driving force of autoimmune disease. Accordingly, numerous therapeutic strategies target CD4(+) T cells with the hope of attenuating autoimmune responses and restoring self-tolerance. We have previously reported that i.v. treatment with Ag-pulsed, ethylenecarbodiimide (ECDI)-fixed splenocytes (Ag-SPs) is an efficient protocol to induce Ag-specific tolerance for prevention and treatment of experimental autoimmune encephalomyelitis (EAE). Ag-SPs coupled with peptide can directly present peptide:MHC II complexes to target CD4(+) T cells in the absence of costimulation to induce anergy. However, Ag-SPs coupled with whole protein also efficiently attenuates Ag-specific T cell responses suggesting the potential contribution of alternative indirect mechanisms/interactions between the Ag-SPs and target CD4(+) T cells. Thus, we investigated whether MHC II compatibility was essential to the underlying mechanisms by which Ag-SP induces tolerance during autoimmune disease. Using MHC-deficient, allogeneic, and/or syngeneic donor Ag-SPs, we show that MHC compatibility between the Ag-SP donor and the host is not required for tolerance induction. Interestingly, we found that ECDI treatment induces apoptosis of the donor cell population which promotes uptake and reprocessing of donor cell peptides by host APCs resulting in the apparent MHC II-independent induction of tolerance. However, syngeneic donor cells are more efficient at inducing tolerance, suggesting that Ag-SPs induce functional Ag-SP tolerance via both direct and indirect (cross-tolerance) mechanisms leading to prevention and effective treatment of autoimmune disease.

Longitudinal single-cell cytokine responses reveal recurrent autoimmune myelin reactivity in relapsing--remitting multiple sclerosis patients

The relationship between multiple sclerosis (MS) disease activity and myelin protein-induced cytokine responses over time is not elucidated. We addressed this relationship by examining longitudinal cytokine responses to myelin proteins every three months for one year, in the context of gadolinium (gad)-enhancing brain lesions and of clinical relapses. The ELISPOT assay was used to determine the ex vivo cytokine production in response to nine amino acid long peptides spanning the entire proteolipid protein (PLP) and myelin basic protein (MBP) molecules in relapsing-remitting (RR) MS patients and matched healthy controls. We identified three longitudinal levels of myelin-induced cytokine secretion by adding up the positive responses for all PLP or MBP peptides obtained for five timepoints, at three-month intervals: low reactivity (< 200 cumulative cytokine-secreting cells), isolated peptide reactivity (201-450 cumulative cytokine-secreting cells) and recurrent protein-wide bursts of cytokine reactivity (> 451 cumulative cytokine-secreting cells). The majority of MS patients showed recurrent bursts to PLP and MBP. In contrast, controls showed a more even distribution between all levels of cytokine reactivity. The majority of patients with gad-enhancing lesions showed PLP/IFN gamma and MBP/IFN gamma recurrent burst responses. This is the first longitudinal study on MS patients in which nine amino acid long myelin peptides are used to reveal the broad range of PLP- and MBP-peptide cytokine reactivity across the whole molecule of these two major myelin proteins. This study also reveals the extremely dynamic nature of the immune reactivity to numerous regions of myelin, which can fluctuate dramatically over time. Such fluctuation could hamper the efficacy of antigen-based therapies for MS.

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.

Adherent dendritic cells expressing high levels of interleukin-10 and low levels of interleukin-12 induce antigen-specific tolerance to experimental autoimmune encephalomyelitis

We have previously shown that tolerance can be induced against acute experimental autoimmune encephalomyelitis (EAE) in Lewis rats by bone marrow-derived dendritic cells (DC) that have been pulsed in vitro with encephalitogenic myelin basic protein peptide 68-86 (MBP 68-86), and injected subcutaneously into healthy rats prior to immunization with MBP 68-86 plus complete Freund's adjuvant. To elucidate better the properties of tolerogenic DC, we here compared plastic-adherent DC with floating, non-adherent DC, which were cultured for 7 days in the presence of granulocyte-macrophage colony-stimulating factor plus interleukin-4 (IL-4). Adherent DC expressed high levels of IL-10 mRNA and protein, and low levels of IL-12 mRNA and showed high expression of CD54 compared with floating DC. Proliferation, nitrite concentration and capacity for antigen presentation were lower in adherent DC than in floating DC. There were no differences between adherent and floating DC regarding expression of CD11c, OX62, major histocompatibility complex class II, CD80, or CD86. Most importantly, we observed that adherent DC induced tolerance to EAE in vivo when injected subcutaneously into Lewis rats prior to immunization, while floating DC did not. Adherent DC-mediated tolerance to EAE was associated with augmented proliferation, nitric oxide production and frequency of apoptotic cells as well as with up-regulation of transforming growth factor-beta (TGF-beta) -expressing cells in T-cell areas of lymph nodes. Tolerance induction by adherent DC seems to be related to a nitric oxide-apoptosis pathway and to up-regulation of TGF-beta-expressing cells.

Mechanisms of suppression of experimental autoimmune encephalomyelitis by intravenous administration of myelin basic protein: role of regulatory spleen cells

Experimental allergic encephalomyelitis (EAE) can be downregulated by intravenous (iv) administration of myelin basic protein (MBP). In this report we show that downregulation of EAE by two 500-microgram doses of MBP administered iv before immunization was associated with reduced encephalitogenicity of both spleen and lymph node cells (day 12 postimmunization) in adoptive transfer studies. However, efficient downregulation of EAE by two 500-microgram iv doses of MBP on days 10 and 11 after active immunization (at the time of disease onset) was associated with no significant change in the encephalitogenicity of lymph node cells, but a complete abrogation of the ability of spleen cells (both at day 12 postimmunization) to transfer EAE compared to controls. Furthermore, coculture of spleen cells from rats tolerized by iv MBP on days 10 and 11 after active immunization with MBP with MBP-reactive T cells resulted in a decreased ability of the spleen T cells to transfer EAE compared to effector cells in monoculture. In contrast, coculture of MBP-reactive T cells with spleen cells from rats tolerized by iv MBP on days 14 and 7 before active immunization resulted in increased disease in recipient rats. These results suggest that reversal of clinical EAE by iv injection of MBP at the time of disease onset is due at least in part to a T cell control mechanism located in the spleen and suggest the presence of splenocyte regulatory cells that can suppress the ability of encephalitogenic T cells to induce EAE.

Tolerance induction by acylated peptides: effect on encephalitogenic T cell lines

We reported previously that acylation of an encephalitogenic peptide of myelin basic protein (MBP68-86) by attachment of palmitoyl chloride (PAL68-86) converted this peptide into a powerful tolerogen for EAE in the Lewis rat. In this study we show that T cell lines derived from a PAL68-86-protected rat proliferated poorly to MBP68-86 in vitro, even after repeated passages in this peptide and IL-2. Conversely, T cell lines derived from untreated rats that were challenged with MBP68-86 or PAL68-86 in CFA responded vigorously to MBP68-86 when propagated for many passages in this peptide but became gradually unresponsive after being propagated in the presence of PAL68-86. The modulation of the T cell lines by PAL68-86 in vitro was reflected by a significant reduction in their ability to transfer EAE to recipients. A high percentage of cells stained with an anti-Vbeta8.2 antibody, regardless of whether they were propagated in the presence of unmodified or acylated peptide. The results are consistent with the notion that tolerance induced by PAL68-86 operates by functional inactivation and provide the basis for the use of acylated peptides in the antigen-specific treatment of autoimmune diseases.

Targeting the B7/CD28:CTLA-4 costimulatory system in CNS autoimmune disease

The B7/CD28:CTLA-4 costimulatory pathway plays a critical role in determining the fate of immune responses (activation vs. down-regulation) and is a highly promising therapeutic target for treating autoimmune diseases. In this review, we highlight the mechanisms by which this costimulatory pathway operates emphasizing the role of the different components in the pathogenesis of relapsing experimental autoimmune encephalomyelitis, a CD4 T cell-mediated autoimmune model of multiple sclerosis. The separate and distinct roles of B7-1, B7-2 and CTLA-4 in positive and negative regulation of autoimmune pathogenesis are considered and a working model is proposed.

Effect of Disease Stage on Clinical Outcome After Syngeneic Bone Marrow Transplantation for Relapsing Experimental Autoimmune Encephalomyelitis

Relapsing experimental autoimmune encephalomyelitis (R-EAE) is an immune-mediated demyelinating central nervous system (CNS) disease. Myeloablation and syngeneic bone marrow transplantation (SBMT), when performed at the peak of acute disease (day 14), prevented glial scarring and ameliorated the disease severity. In contrast, when syngeneic BMT was performed late in chronic phase (day 78), significant glial scarring remained and the clinical severity did not differ significantly from that of the controls. After SBMT in either the acute or chronic phase of disease, the posttransplant immune system remained responsive to myelin epitopes as determined by in vitro proliferation and interferon-γ (IFN-γ) production. However, in mice undergoing SBMT, in vivo delayed-type hypersensitivity (DTH) responses were significantly decreased while IFN-γ RNA levels and inflammatory infiltrates within the CNS were slightly improved. We conclude that failure of SBMT to improve the clinical disease when performed in chronic phase may be due to preexisting glial scarring. We also conclude that in the absence of glial scarring and irreversible neuronal injury, in vivo DTH responses and histology are better predictors of clinical improvement than in vitro proliferation or IFN-γ cytokine production.

Effect of Disease Stage on Clinical Outcome After Syngeneic Bone Marrow Transplantation for Relapsing Experimental Autoimmune Encephalomyelitis

Relapsing experimental autoimmune encephalomyelitis (R-EAE) is an immune-mediated demyelinating central nervous system (CNS) disease. Myeloablation and syngeneic bone marrow transplantation (SBMT), when performed at the peak of acute disease (day 14), prevented glial scarring and ameliorated the disease severity. In contrast, when syngeneic BMT was performed late in chronic phase (day 78), significant glial scarring remained and the clinical severity did not differ significantly from that of the controls. After SBMT in either the acute or chronic phase of disease, the posttransplant immune system remained responsive to myelin epitopes as determined by in vitro proliferation and interferon-γ (IFN-γ) production. However, in mice undergoing SBMT, in vivo delayed-type hypersensitivity (DTH) responses were significantly decreased while IFN-γ RNA levels and inflammatory infiltrates within the CNS were slightly improved. We conclude that failure of SBMT to improve the clinical disease when performed in chronic phase may be due to preexisting glial scarring. We also conclude that in the absence of glial scarring and irreversible neuronal injury, in vivo DTH responses and histology are better predictors of clinical improvement than in vitro proliferation or IFN-γ cytokine production.

Regulation of the effector stages of experimental autoimmune encephalomyelitis via neuroantigen-specific tolerance induction. III. A role for anergy/deletion

Our previous work has shown that specific peripheral immune tolerance induced by the intravenous administration of ECDI-fixed, antigen-coupled syngeneic splenocytes is an extremely efficient method for prevention and treatment of chronic relapsing experimental autoimmune encephalomyelitis (R-EAE) in susceptible SJL/J mice. The current study examined the mechanisms by which unresponsiveness is induced in primed encephalitogenic T cells. The results indicate that the inhibition of MBP-specific T cells by the i.v. injection of MBP-coupled splenocytes is not due to the induction of antigen-specific regulatory T cells, but rather to the induction of anergy/deletion of the effector cells. This conclusion is supported by the findings that spleen or lymph node cells isolated from MBP-tolerant mice fail to inhibit the adoptive transfer of R-EAE in cotransfer assays, and that tolerance is not inhibited by prior thymectomy or prior treatment with cyclophosphamide or anti-CD8 monoclonal antibody. In contrast, we demonstrate that splenocytes from MBP-tolerized, asymptomatic mice have a significantly reduced ability to serially transfer R-EAE to naive secondary recipients following antigen re-activation in vitro, in the first several weeks following tolerization, but that the ability to serially transfer R-EAE returns to sham tolerant control levels within 1-2 months. We also demonstrate a significantly reduced precursor frequency of MBP-specific, IL-2-producing T cells in the MBP-tolerant within three days of treatment. Collectively, the data most closely support a model wherein inhibition of MBP-specific encephalitogenic CD4+ effector T cells by i.v. injected MBP-coupled splenocytes is due to the direct induction of anergy/deletion from which they can recover over time.

Approaches to the treatment of central nervous system autoimmune disease using specific neuroantigen

The ultimate aim in the treatment of autoimmune disease is to restore self-tolerance to the autoantigen(s) in question. In lieu of this ideal result, the conversion of a destructive or pathogenic autoimmune response into one of benign autoimmunity would also be highly desirable. In either case the use of the antigenic epitope, which is the target of the destructive immune response, would ideally be employed so as to give specificity to the protection without the need for long-term immunosuppression. This review describes a number of different approaches using various forms, doses, and routes of injection of specific neuroantigen to inhibit the different clinical varieties of autoimmune encephalomyelitis in a number of animal models; all done with the view to translating the findings into the clinic for the treatment of multiple sclerosis. We conclude that any treatment strategy for multiple sclerosis (MS) must have a number of features: it must be clinically acceptable, specific, long-lasting, require only short-term treatment, able to shunt off ongoing disease, and have the potential to prevent or deal with epitope spreading. Few of the approaches we describe fulfill all of these criteria. We suggest that investigations of new adjunctive agents to be used with a specific antigen be pursued, and that currently the use of chimeric proteins or DNA vaccination with or without the new adjunctives may hold the most hope for the future.

Degenerate antigen recognition by CD4+ effector T cells in experimental autoimmune encephalomyelitis

Peptide-specific tolerance with PLP139-151 peptide analogs was used to compare the fine antigen-specificity requirements at both the inductive and effector phases of relapsing EAE (R-EAE). A PLP139-151 analog peptide containing a single substitution at the primary T cell receptor (TcR) contact residue (A144) did not induce proliferation in PLP139-151-primed CD4+ T cells. In addition, tolerance induced with ECDI-treated. A144-coupled splenocytes failed to prevent the inductive phase of PLP139-151-induced R-EAE or to inhibit the induction of peptide-specific DTH indicating that naive PLP139-151-specific T cells do not react with the A144 peptide analog. In contrast, A144-coupled splenocytes did prevent the expression of the effector phase of R-EAE and inhibited the elicitation of peptide-specific DTH responses upon administration to mice seven days after immunization with PLP139-151. The results provide in vivo evidence that "antigen-experienced' T cells recognize a broader repertoire of antigens than do naive T cells and have important implications for the regulation of immune responses and for advancing our understanding of the pathogenesis and treatment of autoimmune disease.

Suppression of experimental allergic encephalomyelitis in the Lewis rat, by administration of an acylated synthetic peptide of myelin basic protein

A Myelin Basic Protein (MBP) epitope encephalitogenic for the Lewis rat (amino acid residues 68-86) was synthesized and acylated by the attachment of a palmitoyl residue. Lewis rats treated intravenously (i.v.) with the palmitoylated peptide alone were better protected against clinical manifestations of experimental allergic encephalomyelitis (EAE) than rats treated with the peptide inserted into liposomes or with the native peptide at similar doses. The administration of the acylated peptide (PAL68 86) conferred excellent protection against a challenge with the encephalitogenic peptide (p68-86) or with the intact MBP molecule, both before and after induction of active disease, and also when administered to recipients after the transfer of lymphocytes from MBP-challenged donors. Histological manifestations were also reduced to a statistically significant degree. Treatment with a palmitoylated peptide from a non-encephalitogenic region of the MBP molecule (PAL44-62) or with a palmitoylated unrelated peptide were ineffective. In vitro Ag-specific proliferative responses as well as the ability to transfer disease to syngeneic recipients, by lymph node lymphocytes from PAL68-86-treated donors, were considerably reduced. Addition of IL-2 to these cultures failed to restore either Ag-specific responsiveness or the ability of the cells to transfer disease. The results suggest that the administration of acylated peptides induces a profound state of unresponsiveness, and thus may provide an effective means for treating T cell-mediated autoimmune inflammatory disorders.

Allogeneic hematolymphoid microchimerism and prevention of autoimmune disease in the rat. A relationship between allo- and autoimmunity

Conventional allogeneic bone marrow transplantation after myeloablation can prevent experimental autoimmunity and has been proposed as treatment for humans. However, trace populations of donor hematolymphoid cells persisting in solid organ allograft recipients have been associated in some circumstances with therapeutic effects similar to replacement of the entire bone marrow. We therefore examined whether inducing hematolymphoid microchimerism without myeloablation could confer the ability to resist mercuric chloride (HgCl2)-induced autoimmunity. Brown-Norway (BN) rats were pretreated with a syngeneic or allogeneic bone marrow infusion under transient FK506 immunosuppression before receiving HgCl2. They were compared with BN rats receiving either no pretreatment (naive) or FK506 alone. Administration of HgCl2 to naive BN rats induced marked autoantibody production, systemic vasculitis and lymphocytic infiltration of the kidneys, liver and skin in all of the animals and a 47% mortality. In contrast, BN rats pretreated with HgCl2-resistant allogeneic Lewis bone marrow and transient FK506 showed less clinical disease and were completely protected from mortality. More specifically, IgG anti-laminin autoantibody production was decreased by 40% (P < 0.05), and there was less histopathological tissue injury (P < 0.005), less in vitro autoreactivity (P < 0.05), less of an increase in class II MHC expression on B cells (P < 0.01), and 22% less weight loss (P < 0.01), compared with controls. Protection from the experimental autoimmunity was associated with signs of low grade activation of the BN immune system, which included: increased numbers of circulating B and activated T cells before administration of HgCl2, and less autoreactivity and spontaneous proliferation in vitro after HgCl2.

Two models of multiple sclerosis: experimental allergic encephalomyelitis (EAE) and Theiler's murine encephalomyelitis virus (TMEV) infection. A pathological and immunological comparison

Theiler's murine encephalomyelitis virus (TMEV) infection and experimental allergic encephalomyelitis (EAE) are considered among the best models of human multiple sclerosis (MS). In both models, clinical disease is characterized by paralysis, while pathological changes consist of inflammatory demyelination. In both models there is a genetic influence on susceptibility/resistance to the development of disease. This has been thoroughly studied in TMEV infection, and it has been found to depend on both major histocompatibility complex (MHC) and non-MHC genes. At least four genes have been so far identified. Because of this genetic influence, some strains of mice are more susceptible to both clinical and pathological changes than others, and susceptibility appears to best correlate with the ability of a certain murine strain to develop a delayed-type hypersensitivity (DTH) response to viral antigens. We have also observed that even among mice which are equally susceptible clinically, striking differences may be seen under pathological examination. These consist of different gradients of severity of inflammation, particularly in regards to the macrophage component. There is an inverse relationship between the number of macrophages, and their length of stay in the CNS, and the ability of mice to remyelinate their lesions. The most severe lesions are in SJL/J mice, and remyelination in this strain is extremely poor. The least severe lesions in terms of macrophage invasion are in strains such as NZW and RIIIS/J, and these are able to remyelinate lesions very successfully. Murine chronic relapsing EAE (CR-EAE) shows pathological changes in many ways similar to those in TMEV-infected SJL/J mice, although less severe in terms of degrees of macrophage infiltration and tissue destruction. Mice with CR-EAE have a correspondingly limited ability to remyelinate their lesions. In both models the pathology appears to be mediated through a DTH response. However, while in EAE the DTH response is clearly against neuroantigens, the response in TMEV infection is against the virus itself. The end result in both models would be that of myelin destruction through a lymphotoxin-cytokine-mediated mechanism. The importance of the DTH response in both models is well illustrated by the effects of tolerance induction in EAE and TMEV infection to neuroantigens and virus, respectively. These are important models of human MS, since the current hypothesis is that a viral infection early in life, on the appropriate genetic background, may trigger a secondary misdirected immune response which could be directed either against myelin antigens and/or possible persistent virus(es).

Functional evidence for epitope spreading in the relapsing pathology of experimental autoimmune encephalomyelitis

The role of epitope spreading in the pathology of relapsing-remitting experimental autoimmune encephalomyelitis (R-EAE) was examined. Using peripherally induced immunologic tolerance as a probe to analyze the neuropathologic T cell repertoire, we show that the majority of the immunopathologic reactivity during the acute phase of R-EAE in SJL/J mice induced by active immunization with the intact proteolipid (PLP) molecule is directed at the PLP139-151 epitope and that responses to secondary encephalitogenic PLP epitopes may contribute to the later relapsing phases of disease. Intermolecular epitope spreading was demonstrated by showing the development of T cell responses to PLP139-151 after acute disease in mice in which R-EAE was initiated by the transfer of T cells specific for the non-cross-reactive MBP84-104 determinant. Intramolecular epitope spreading was demonstrated by showing that endogenous host T cells specific for a secondary encephalitogenic PLP epitope (PLP178-191) are demonstrable by both splenic T cell proliferative and in vivo delayed-type hypersensitivity responses in mice in which acute central nervous system damage was initiated by T cells reactive with the immunodominant, non-cross-reactive PLP139-151 sequence. The PLP178-191-specific responses are activated as a result of and correlate with the degree of acute tissue damage, since they do not develop in mice tolerized to the initiating epitope before expression of acute disease. Most importantly, we show that the PLP178-191-specific responses are capable of mediating R-EAE upon adoptive secondary transfer to naive recipient mice. Furthermore, induction of tolerance to intact PLP (which inhibits responses to both the initiating PLP139-151 epitope and to the PLP178-191 epitope) after the acute disease episode is sufficient to prevent relapsing disease. These results strongly support a contributory role of T cell responses to epitopes released as a result of acute tissue damage to the immunopathogenesis of relapsing clinical episodes and have important implications for the design of antigen-specific immunotherapies for the treatment of chronic autoimmune disorders in humans.

Syngeneic bone marrow transplantation eliminates V beta 8.2 T lymphocytes from the spinal cord of Lewis rats with experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE), an animal model for multiple sclerosis (MS), is a paralytic disease of the central nervous system (CNS) mediated by T-lymphocytes reactive to myelin basic protein (MBP). Lewis rats actively immunized with fragment 68 to 82 of guinea pig MBP develop a monophasic disease with spontaneous recovery. Lymphocyte recognition of the primary encephalitogenic sequence of MBP (fragment 68 to 82) is V beta 8.2 T cell receptor (TCR) skewed [1-3]. Lewis rats in clinical remission at 1 month and 3 months after spontaneous resolution of EAE retain V beta 8.2 T-lymphocytes in the CNS when analyzed by reverse transcriptase polymerase chain reaction or in situ hybridization. In contrast, 1 and 3 months after clinical remission from syngeneic bone marrow transplantation, V beta 8.2 T lymphocytes are absent from the CNS. During clinically active EAE and inflammatory breakdown of the blood-brain barrier, immune ablation and reconstitution with syngeneic bone marrow results in clinical tolerance of the new immune system to myelin.

Tolerogenic forms of auto-antigens and cytokines in the induction of resistance to experimental allergic encephalomyelitis

Resistance to experimental allergic encephalomyelitis (EAE) induction by homogenized myelin (MSCH) in complete Freund's adjuvant (CFA) and pertussigen (P) in SJL mice was seen 1 week after intravenous injection of PLP 139-151 coupled to spleen cells (PLP-ECDI-SP). Although this resistance could be transferred by spleen cells enriched for CD8+ T cells and thus had a component of immunoregulatory T cells, it was primarily due to anergy, as it was reversible by four daily injections of interleukin (II)-2 starting 3 days after the PLP-ECDI-SP. Earlier treatment with IL-2 did not reverse the tolerance. In view of the known higher sensitivity to anergy induction of Th1 than of Th2 cells, a change in the cytokine balance in the response to MSCH+CFA after anergy induction might be responsible for the resistance to EAE induction. The effect of treatment with cytokines alone on induction of EAE was therefore also determined. Short-term (1-2 weeks) daily pretreatment with IL-2 (4000 U) or TGF-beta 2 (1 micrograms) somewhat decreased the susceptibility to subsequent EAE induction, but IL-4 (5 ng), IL-10 (5 micrograms) or IL-12 (50-200 ng) had no effect under those conditions, even if low doses of PLP were injected simultaneously. Daily injections of IL-4 over an 8-week period prior to immunization, however, significantly lowered the incidence of EAE. Simultaneous injections of IFN-gamma (2000 U/day) completely abolished this effect of IL-4. The effect of these cytokines administered immediately after the immunization with MSCH + CFA + P was also examined. As shown earlier, TGF-beta 2 (100-1000 ng/day) caused a marked protection when it was given intraperitoneally on days 5-9 after injection of MSCH + CFA. IL-4 (5 ng/day), in contrast, was very protective when administered on days 0-4 and less so when given on days 5-9 or even on days 0-12. IL-10 (1 microgram/day) was not protective under these conditions and IL-12 (50 ng/day) significantly increased the severity and mortality of EAE when given on days 0-4 after MSCH + CFA.

Evolution of the T-cell repertoire during the course of experimental immune-mediated demyelinating diseases

Fig. 6 depicts a model for epitope spreading in T cell-mediated demyelination. The acute phase of disease is due to T cells specific for the initiating epitope, which can be either a determinant on the CNS target organ of the autoimmune response or a determinant on a persisting, CNS-tropic virus. The primary T cell response is responsible for the initial tissue damage by the production of proinflammatory Th1 cytokines which can affect myelination directly (Selmaj et al. 1991) and indirectly by their ability to recruit and activate macrophages to phagocytize myelin (Cammer et al. 1978). As a result of myelin damage and opening of the blood-brain-barrier during acute disease, T cells specific for endogenous epitopes on the same and/or different myelin proteins are primed and expand either in the periphery or locally in the CNS. These secondary T cells initiate an additional round of myelin destruction, leading to a clinical relapse by production of additional pro-inflammatory cytokines, similar to the bystander demyelination operative during acute disease. It will be of great interest to determine the relative contributions of local and systemic immune responses to these endogenous neuroepitopes. It is possible that local CNS presentation of endogenous neuroepitopes following acute CNS damage could be mediated by infiltrating inflammatory macrophages, activated microglial cells, endothelial cells and/or astrocytes. These tissue resident antigen presenting cells have been shown to upregulate expression of MHC class II (Sakai et al. 1986, Traugott & Lebon 1988), certain adhesion molecules (Cannella et al. 1990), and B7 costimulatory molecules (K. M. Nikcevich, J. A. Bluestone, and S. D. Miller, in preparation) in response to pro-inflammatory cytokines. The data on epitope spreading provided by the murine demyelinating disease models clearly illustrate the dynamic nature of the T cell repertoire during chronic inflammation in a specific target organ. The contribution of epitope spreading to chronic CNS demyelination could be considered to be a special case since tolerance to myelin epitopes would be expected to be inefficient due to their sequestration behind the blood-brain-barrier. However, the recent description of epitope spreading in response to pancreatic antigens in spontaneous diabetes in the NOD mouse may indicate that this phenomenon is operative in a variety of organ-specific experimental and spontaneous autoimmune diseases.(ABSTRACT TRUNCATED AT 400 WORDS)

Fine specificity of CD4+ T cell responses to the dominant encephalitogenic PLP 139-151 peptide in SJL/J mice

PLP 139-151(S) is the major encephalitogenic epitope of PLP in the SJL/J mouse. CD4+ T cells specific for PLP 139-151(S) induce a relapsing-remitting form of EAE which is similar to the human demyelinating disease MS in both clinical course and histopathology. We are interested in events involved in activation of autoreactive T cells and how to specifically regulate these immune response to both prevent and treat ongoing demyelinating disease. In the current study, we examined the effect of both amino acid substitutions and deletions in the native PLP 139-151(S) peptide to identify which residues are critical for immunogenicity and encephalitogenicity. Conservative and nonconservative substitutions at position 145 diminished or completely destroyed the encephalitogenic potential of the peptide without affecting the ability to recall a proliferative response in lymph node T cells primed with the native PLP 139-151(S) peptide indicating an interesting dichotomy between ability to induce T cell proliferation and ability to induce active clinical disease. In addition, tryptophan at position 144 was identified as a critical TCR contact site as a peptide containing an alanine for tryptophan at this position (A144) primed a unique population of T cells which did not cross react with the native PLP 139-151(S). In addition, A144 was unable to stimulate PLP 139-151(S)-specific T cells in vitro or to induce active relapsing EAE in vivo. The significance of these results to the potential development of new strategies for preventing and treating T cell-mediated autoimmune diseases is discussed.

The immunopathogenesis and regulation of T-cell-mediated demyelinating diseases

A variety of experimental approaches are currently being evaluated for controlling CD4+ T helper 1 (Th1)-mediated autoimmune pathology. Here, Stephen Miller and William Karpus compare and contrast the efficacies of various antigen-specific regulatory strategies. Particular emphasis is placed on the mechanisms of peripheral immune tolerance and how this may be used in the treatment and analysis of the pathologic T-cell repertoire in autoimmune and virus-induced demyelinating diseases.

T cell deletion in high antigen dose therapy of autoimmune encephalomyelitis

Encounters with antigen can stimulate T cells to become activated and proliferate, become nonresponsive to antigen, or to die. T cell death was shown to be a physiological response to interleukin-2-stimulated cell cycling and T cell receptor reengagement at high antigen doses. This feedback regulatory mechanism attenuates the immune response by deleting a portion of newly dividing, antigen-reactive T cells. This mechanism deleted autoreactive T cells and abrogated the clinical and pathological signs of autoimmune encephalomyelitis in mice after repetitive administration of myelin basic protein.

Determinant spreading and the dynamics of the autoimmune T-cell repertoire

In this article the authors propose a dynamic model of autoimmunity with T-cell recruitment and selection leading to changes in the specificity of the anti-self response during the course of disease. They argue that these changes are due to alterations in self-antigen presentation that lead to the display of previously cryptic self-determinants. Mechanisms that could underlie this differential self-presentation are proposed.