Induction and suppression of an autoimmune disease by oligomerized T cell epitopes: enhanced in vivo potency of encephalitogenic peptides

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

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

Understanding the link between neurotropic viruses, BBB permeability, and MS pathogenesis

Neurotropic viruses can infiltrate the CNS by crossing the blood-brain barrier (BBB) through various mechanisms including paracellular, transcellular, and "Trojan horse" mechanisms during leukocyte diapedesis. These viruses belong to several families, including retroviruses; human immunodeficiency virus type 1 (HIV-1), flaviviruses; Japanese encephalitis (JEV); and herpesviruses; herpes simplex virus type 1 (HSV-1), Epstein-Barr virus (EBV), and mouse adenovirus 1 (MAV-1). For entering the brain, viral proteins act upon the tight junctions (TJs) between the brain microvascular endothelial cells (BMECs). For instance, HIV-1 proteins, such as glycoprotein 120, Nef, Vpr, and Tat, disrupt the BBB and generate a neurotoxic effect. Recombinant-Tat triggers amendments in the BBB by decreasing expression of the TJ proteins such as claudin-1, claudin-5, and zona occludens-1 (ZO-1). Thus, the breaching of BBB has been reported in myriad of neurological diseases including multiple sclerosis (MS). Neurotropic viruses also exhibit molecular mimicry with several myelin sheath proteins, i.e., antibodies against EBV nuclear antigen 1 (EBNA1) aa411-426 cross-react with MBP and EBNA1 aa385-420 was found to be associated with MS risk haplotype HLA-DRB1*150. Notably, myelin protein epitopes (PLP139-151, MOG35-55, and MBP87-99) are being used to generate model systems for MS such as experimental autoimmune encephalomyelitis (EAE) to understand the disease mechanism and therapeutics. Viruses like Theiler's murine encephalomyelitis virus (TMEV) are also commonly used to generate EAE. Altogether, this review provide insights into the viruses' association with BBB leakiness and MS along with possible mechanistic details which could potentially use for therapeutics.

Identification and protective role of CD34+ stromal cells/telocytes in experimental autoimmune encephalomyelitis (EAE) mouse spleen

Experimental autoimmune encephalomyelitis (EAE) is a classical animal model of human multiple sclerosis (MS) that is most commonly used to study the neuropathology and therapeutic effects of the disease. Telocytes (TCs) are a specialized type of interstitial or mesenchymal cell first identified by Popescu in various tissues and organs. However, the existence, distribution and role of CD34⁺ stromal cells (SCs)/TCs in the EAE-induced mouse spleen remain to be elucidated. We conducted immunohistochemistry, immunofluorescence (double staining for CD34 and c-kit, vimentin, F4/80, CD163, Nanog, Sca-1, CD31 or tryptase) and transmission electron microscopy experiments to investigate the existence, distribution and role of CD34⁺ SCs/TCs in the EAE-induced mouse spleen. Interestingly, immunohistochemistry, double-immunofluorescence, and transmission electron microscopy results revealed that CD34⁺ SCs/TCs were significantly upregulated in the EAE mouse spleen. Immunohistochemical or double-immunofluorescence staining of CD34⁺ SCs/TCs showed positive expression for CD34, c-kit, vimentin, CD34/vimentin, c-kit/vimentin and CD34/c-kit, and negative expression for CD31 and tryptase. Transmission electron microscopy (TEM) results demonstrated that CD34⁺ SCs/TCs established close connections with lymphocytes, reticular cells, macrophages, endothelial cells and erythrocytes. Furthermore, we also found that M1 (F4/80) or M2 (CD163) macrophages, and haematopoietic, pluripotent stem cells were markedly increased in EAE mice. Our results suggest that CD34⁺ SCs/TCs are abundant and may play a contributing role in modulating the immune response, recruiting macrophages and proliferation of haematopoietic and pluripotent stem cells following injury to promote tissue repair and regeneration in EAE mouse spleens. This suggests that their transplantation combined with stem cells might represent a promising therapeutic target for the treatment and prevention of multiple autoimmune and chronic inflammatory disorders.

Synthetic Cationic Autoantigen Mimics Glatiramer Acetate Persistence at the Site of Injection and Is Efficacious Against Experimental Autoimmune Encephalomyelitis

A synthetic peptide, K-PLP, consisting of 11-unit poly-lysine (K11) linked via polyethylene glycol (PEG) to proteolipid protein epitope (PLP) was synthesized, characterized, and evaluated for efficacy in ameliorating experimental autoimmune encephalomyelitis (EAE) induced by PLP. K-PLP was designed to mimic the cationic nature of the relapsing-remitting multiple sclerosis treatment, glatiramer acetate (GA). With a pI of ~10, GA is able to form visible aggregates at the site of injection via electrostatic interactions with the anionic extracellular matrix. Aggregation further facilitates the retention of GA at the site of injection and draining lymph nodes, which may contribute to its mechanism of action. K-PLP with a pI of ~11, was found to form visible aggregates in the presence of glycosaminoglycans and persist at the injection site and draining lymph nodes in vivo, similar to GA. Additionally, EAE mice treated with K-PLP showed significant inhibition of clinical symptoms compared to free poly-lysine and to PLP, which are the components of K-PLP. The ability of the poly-lysine motif to retain PLP at the injection site, which increased the local exposure of PLP to immune cells may be an important factor affecting drug efficacy.

Changes of B cell subsets in central pathological process of autoimmune encephalomyelitis in mice

Background

Multiple sclerosis is a demyelinating and autoimmune disease and its immune response is not fully elucidated. This study was conducted to examine the pathological changes and B cell subsets in experimental autoimmune encephalomyelitis (EAE) mice, and analyze the expression of triosephosphate isomerase (TPI) and GADPH to define the role of B cell subsets in the disease.

Results

Female C57BL/6 mice were randomly divided into EAE group (n = 18) and control (n = 18). During the experiments, the weight and nerve function scores were determined. The proportions of B cell subsets in the peripheral blood were measured by flow cytometry. Seven, 18 and 30 days after immunization, the brain and spinal cord tissues were examined for the infiltration of inflammatory cells using hematoxylin-eosin (HE) HE staining and the demyelination using Luxol fast blue staining. The expression of B cell-related proteins was detected immunohistochemistrially and the expression of antigenic TPI and GADPH was analyzed using enzyme-linked immunosorbent assay (ELISA). HE staining showed that mice had more severe EAE 18 d than 7 d after modelling, while the symptoms were significantly relieved at 30 d. The results were consistent with the weight measurements and neural function scores. Immunohistochemistry studies showed that B cells aggregated in the spinal cord, but not much in the brain. Flow cytometry studies showed that there were more B cells in control than in EAE models from day 7 and the difference was narrowed at day 30. The level of plasma cells increased continuously, reached the top at day 21 and obviously declined at day 30. On other hand, the numbers of memory B cells increased gradually over the experimental period. The numbers of plasma and memory B cells were similar between the control and EAE mice. ELISA data revealed that the brain contents of TPI and GAPDH were higher in EAE mice than in control at day 7, while at day 18, the levels were reversed.

Conclusions

In the central pathological process of EAE mice, B cells exert role through the mechanism other than producing antibodies and the levels of brain TPI and GADPH are related to the severity of autoimmune induced-damage.

Oxidative damage and chemokine production dominate days before immune cell infiltration and EAE disease debut

Background

Multiple sclerosis is widely accepted as an inflammatory disease. However, studies indicate that degenerative processes in the CNS occur prior to inflammation. In the widely used animal model experimental autoimmune encephalomyelitis (EAE), we investigated the significance of degenerative processes from mitochondrial membrane potentials, reactive oxidative species, cell death markers, chemokines, and inflammatory cell types in brain, spinal cord, and optic nerve tissue during the effector phase of the disease, before clinical disease was evident.

Methods

Sixty-two rats were placed in eight groups, n = 6 to 10. Four groups were immunized with spinal cord homogenate emulsified in complete Freund’s adjuvant (one served as EAE group), three groups were immunized with complete Freund’s adjuvant only, and a control group was injected with phosphate buffered saline only. Groups were sacrificed 3, 5, 7, or 12–13 days after the intervention and analyzed for early signs of CNS degeneration.

Results

Loss of mitochondrial membrane potential and oxidative changes was observed days before clinical disease debut at day 9.75 ± 0.89. The early mitochondrial changes were not associated with cytochrome C release, cleavage of caspases 9 (38/40 kDa) and 3 (17/19 kDa), and cleavage of PARP (89 kDa) or spectrin (120/150 kDa), and apoptosis was not initiated. Axonal degeneration was only present at disease onset. Increases in a range of cytokines and chemokines were observed systemically as a consequence of immunization with complete Freund’s adjuvant, whereas the encephalitogenic emulsion induced an upregulation of the chemokines Ccl2, Ccl20, and Cxcl1, specifically in brain tissue, 7 days after immunization.

Conclusion

Five to seven days after immunization, subtle decreases in the mitochondrial membrane potential and an increased reactive oxygen species burden in brain tissue were observed. No cell death was detected at these time-points, but a specific expression pattern of chemokines indicates activity in the CNS, several days before clinical disease debut.

Immune Modulation and Prevention of Autoimmune Disease by Repeated Sequences from Parasites Linked to Self Antigens

Parasite proteins containing repeats are essential invasion ligands, important for their ability to evade the host immune system and to induce immunosuppression. Here, the intrinsic suppressive potential of repetitive structures within parasite proteins was exploited to induce immunomodulation in order to establish self-tolerance in an animal model of autoimmune neurological disease. We tested the tolerogenic potential of fusion proteins containing repeat sequences of parasites linked to self-antigens. The fusion constructs consist of a recombinant protein containing repeat sequences derived from the S-antigen protein (SAg) of Plasmodium falciparum linked to a CD4 T cell epitope of myelin. They were tested for their efficacy to control the development of experimental autoimmune encephalomyelitis (EAE), In addition, we used the DO11.10 transgenic mouse model to study the immune mechanisms involved in tolerance induced by SAg fusion proteins. We found that repeated sequences of P. falciparum SAg protein linked to self-epitopes markedly protected mice from EAE. These fusion constructs were powerful tolerizing agents not only in a preventive setting but also in the treatment of ongoing disease. The tolerogenic effect was shown to be antigen-specific and strongly dependent on the physical linkage of the T cell epitope to the parasite structure and on the action of anti-inflammatory cytokines like IL-10 and TGF-β. Other mechanisms include down-regulation of TNF-α accompanied by increased numbers of FoxP3⁺ cells. This study describes the use of repetitive structures from parasites linked to defined T cell epitopes as an effective method to induce antigen-specific tolerance with potential applicability for the treatment and prevention of autoimmune diseases.

Targeting T cells responsive to the priming epitope prevent the relapsing phase of experimental autoimmune encephalomyelitis

Upon recovery from the initial episode of experimental autoimmune encephalomyelitis (EAE), virtually all SJL mice develop relapsing/remitting episodes of disease. These relapses may occur due to the reactivation of memory T cells initially stimulated as part of the disease-inducing protocol or naïve T-cell populations stimulated by distinct encephalitogens derived from the inflammatory disease process (epitope spread). We have used encephalitogen-specific non-linear peptide octamers to modify the course of relapsing EAE (rEAE) in SJL mice immunized with an oliogodendrocyte-specific protein peptide (OSP 55-71). Our studies show that the peptide-octamers, which target the T cells stimulated by the priming encephalitogen, but not other candidate encephalitogens, prevent rEAE.

Active suppression induced by repetitive self-epitopes protects against EAE development

BACKGROUND

Autoimmune diseases result from a breakdown in self-tolerance to autoantigens. Self-tolerance is induced and sustained by central and peripheral mechanisms intended to deviate harmful immune responses and to maintain homeostasis, where regulatory T cells play a crucial role. The use of self-antigens in the study and treatment of a range of autoimmune diseases has been widely described; however, the mechanisms underlying the induced protection by these means are unclear. This study shows that protection of experimental autoimmune disease induced by T cell self-epitopes in a multimerized form (oligomers) is mediated by the induction of active suppression.

PRINCIPAL FINDINGS

The experimental autoimmune encephalomyelitis (EAE) animal model for multiple sclerosis was used to study the mechanisms of protection induced by the treatment of oligomerized T cell epitope of myelin proteolipid protein (PLP139-151). Disease protection attained by the administration of oligomers was shown to be antigen specific and effective in both prevention and treatment of ongoing EAE. Oligomer mediated tolerance was actively transferred by cells from treated mice into adoptive hosts. The induction of active suppression was correlated with the recruitment of cells in the periphery associated with increased production of IL-10 and reduction of the pro-inflammatory cytokine TNF-α. The role of suppressive cytokines was demonstrated by the reversion of oligomer-induced protection after in vivo blocking of either IL-10 or TGF-β cytokines.

CONCLUSIONS

This study strongly supports an immunosuppressive role of repeat auto-antigens to control the development of EAE with potential applications in vaccination and antigen specific treatment of autoimmune diseases.

I-domain-antigen conjugate (IDAC) for delivering antigenic peptides to APC: synthesis, characterization, and in vivo EAE suppression

The objectives of this work are to characterize the identity of I-domain-antigen conjugate (IDAC) and to evaluate the in vivo efficacy of IDAC in suppressing experimental autoimmune encephalomyelitis (EAE) in mouse model. The hypothesis is that the I-domain delivers PLP(139-151) peptides to antigen-presenting cells (APC) and alters the immune system by simultaneously binding to ICAM-1 and MHC-II, blocking immunological synapse formation. IDAC was synthesized by derivatizing the lysine residues with maleimide groups followed by conjugation with PLP-Cys-OH peptide. Conjugation with PLP peptide does not alter the secondary structure of the protein as determined by CD. IDAC suppresses the progression of EAE, while I-domain and GMB-I-domain could only delay the onset of EAE. As a positive control, Ac-PLP-BPI-NH(2)-2 can effectively suppress the progress of EAE. The number of conjugation sites and the sites of conjugations in IDAC were determined using tryptic digest followed by LC-MS analysis. In conclusion, conjugation of I-domain with an antigenic peptide (PLP) resulted in an active molecule to suppress EAE in vivo.

Genetics of experimental allergic encephalomyelitis supports the role of T helper cells in multiple sclerosis pathogenesis

OBJECTIVE

The major histocompatibility complex (MHC) is the primary genetic contributor to multiple sclerosis (MS) and experimental allergic encephalomyelitis (EAE), but multiple additional interacting loci are required for genetic susceptibility. The identity of most of these non-MHC genes is unknown. In this report, we identify genes within evolutionarily conserved genetic pathways leading to MS and EAE.

METHODS

To identify non-MHC binary and quantitative trait loci (BTL/QTL) important in the pathogenesis of EAE, we generated phenotype-selected congenic mice using EAE-resistant B10.S and EAE-susceptible SJL mice. We hypothesized that genes linked to EAE BTL/QTL and MS-GWAS can be identified if they belong to common evolutionarily conserved pathways, which can be identified with a bioinformatic approach using Ingenuity software.

RESULTS

Many known BTL/QTL were retained and linked to susceptibility during phenotype selection, the most significant being a region on chromosome 17 distal to H2 (Eae5). We show in pathway analysis that T helper (T(H))-cell differentiation genes are critical for both diseases. Bioinformatic analyses predicted that Eae5 is important in CD4 T-effector and/or Foxp3(+) T-regulatory cells (Tregs), and we found that B10.S-Eae5(SJL) congenic mice have significantly greater numbers of lymph node CD4 and Tregs than B10.S mice.

INTERPRETATION

These results support the polygenic model of MS/EAE, whereby MHC and multiple minor loci are required for full susceptibility, and confirm a critical genetic dependence on CD4 T(H)-cell differentiation and function in the pathogenesis of both diseases.

Enhancing tumor vaccines: catalyzing MHC class II peptide exchange

Peptide vaccination strategies aimed at inducing CD4(+) T-cell responses may be hampered due to the poorly receptive nature of MHC class II molecules to exogenous antigen. It has recently been reported that the small organic molecule adamantane ethanol, when included as an adjuvant in peptide vaccination, is capable of enhancing ligand exchange and markedly augmenting the subsequent antigen-specific CD4(+) T-cell response. These results highlight a novel adjuvant strategy tested in vivo, which opens a further doorway to improving the efficacy of peptide vaccination and continuing the push towards clinical trials.

Immune response to controlled release of immunomodulating peptides in a murine experimental autoimmune encephalomyelitis (EAE) model

The effects of controlled release on immune response to an immunomodulating peptide were evaluated in a murine experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis (MS). The peptide, Ac-PLP-BPI-NH(2)-2 (Ac-HSLGKWLGHPDKF-(AcpGAcpGAcp)(2)-ITDGEATDSG-NH(2); Ac = acetyl, Acp = epsilon aminocaproic acid) was designed to suppress T-cell activation in response to PLP(139-151), an antigenic peptide in MS. Poly-lactide-co-glycolide (PLGA) microparticles containing Ac-PLP-BPI-NH(2)-2 (8+/-4 microm, 1.4+/-0.2% (w/w)) were prepared by a powder-in oil-in water emulsion-solvent evaporation method, sterilized and administered subcutaneously (s.c.) to SJL/J (H-2(s)) mice in which EAE had been induced by immunization with PLP(139-151). Treatment groups received Ac-PLP-BPI-NH(2)-2: (i) in solution by repeated i.v. or s.c. injection, (ii) in solution co-administered with blank PLGA microparticles, (iii) in solution co-administered with Ac-PLP-BPI-NH(2)-2 loaded microparticles, and (iv) as Ac-PLP-BPI-NH(2)-2 loaded microparticles. Administration of Ac-PLP-BPI-NH(2)-2 as an s.c. solution produced clinical scores and maintenance of body weight comparable to i.v. solution, but with reduced overall survival, presumably due to anaphylaxis. Administration as s.c. microparticles provided a somewhat less effective reduction in symptoms but with no toxicity during treatment. Thus, the results suggest that s.c. administration of Ac-PLP-BPI-NH(2)-2 microparticles can provide pharmacological efficacy and reduction in dosing frequency without increased toxicity.

Prophylactic and therapeutic suppression of experimental autoimmune encephalomyelitis by a novel bifunctional peptide inhibitor

The objective was to optimize and evaluate the in vivo activities of our novel bifunctional peptide inhibitor (BPI), which alters immune response in autoimmune diseases by modulating the immunological synapse formation. Previously, we have designed PLP-BPI and GAD-BPI by conjugating myelin proteolipid protein (PLP)(139-151) and glutamic acid decarboxylase (GAD)(208-217), respectively, with CD11a(237-246) via a spacer peptide. PLP-BPI and GAD-BPI suppressed the disease progression in experimental autoimmune encephalomyelitis (EAE) and in type-1 diabetes, respectively. In this study, various PLP-BPI derivatives were synthesized and evaluated in the EAE model. Intravenous injections of PLP-BPI derivatives prevented the disease progression more efficiently than did unmodified PLP-BPI. Production of IL-17, a potent proinflammatory cytokine found commonly among MS patients, was significantly low in Ac-PLP-BPI-NH(2)-2-treated mice. Treatment given after the disease onset could dramatically ameliorate the disease. BPI induced anaphylactic responses at a lower incidence than PLP(139-151). In conclusion, PLP-BPI derivatives can effectively suppress the disease severity and morbidity of EAE by post-onset therapeutic treatment as well as prophylactic use.

The diminishment of experimental autoimmune encephalomyelitis (EAE) by neuropeptide alpha-melanocyte stimulating hormone (alpha-MSH) therapy

The neuropeptide alpha-melanocyte stimulating hormone (alpha-MSH) plays an important role in immune privilege by its suppression of inflammation, and its induction of regulatory T cells. This finding led us to test the possibility that we can use alpha-MSH to suppress autoimmune diseases, and promote re-establishment of immune tolerance to autoantigens. To test this possibility, SJL mice with experimental autoimmune encephalomyelitis (EAE) were injected with alpha-MSH at the first signs of paralysis. The alpha-MSH-treated mice in comparison with untreated EAE mice had a profound diminishment in the severity and tempo of EAE. The spleen cells in alpha-MSH-treated EAE produced TGF-beta in response to PLP-antigen stimulation in contrast to untreated mice spleen cells that produced IFN-gamma. When the alpha-MSH-treated EAE mice were reimmunized there was a delay of a week before the second episode of EAE. Although this delay maybe because of the induction of TGF-beta-producing spleen cells by the alpha-MSH-treatment, it was not adequate to suppress IFN-gamma-production by PLP-antigen stimulated spleen cells from untreated mice, nor able to suppress the eventual second episode of EAE. Therefore, the injection of alpha-MSH at the onset of paralysis is extremely effective in diminishing the severity and tempo of EAE, and the subsequent induction of potential PLP-specific Treg cells suggests that an alpha-MSH therapy could be attempted as part of a therapeutic regiment to impose immunoregulation and immunosuppression on an autoimmune disease of the central nervous system.

Multimerized T cell epitopes protect from experimental autoimmune diabetes by inducing dominant tolerance

Immunotherapy by using multimerized self-peptides has demonstrated a clear protective effect on experimental models of autoimmune diseases. However, the mechanisms involved remain ill-defined. Here we have evaluated the therapeutic efficacy of multimerized self-peptides at the effector phase of autoimmune diabetes and examined their mechanisms of action. Diabetes was induced in rat insulin promoter-hemagglutinin (HA) mice expressing HA in pancreatic beta-cells by adoptive transfer of HA(110-119)-specific T helper 1 cells. Complete protection was provided by low doses of the HA 4-mer consisting of four covalently linked linear HA(107-119) peptides. In vivo, the 4-mer appeared to act directly on the pathogenic HA-specific T helper 1 cells and indirectly by activation/recruitment of lymphocytes with regulatory properties so that mice became resistant to a second transfer of diabetogenic T cells. This effect was associated with a recruitment of Foxp3(+) CD4 T cells around islets. Moreover, we show that dominant protection from autoimmunity was transferable by spleen cells, and that development of this regulatory population was crucially dependent on the lymphocytes from treated rat insulin promoter-HA mice. Thus, immunotherapy using multimerized epitopes emerges as a promising strategy in view of the current identification of self-epitopes that are major targets of the pathogenic CD4 T cell response in autoimmune diseases.

Antigen-specific suppression of experimental autoimmune encephalomyelitis by a novel bifunctional peptide inhibitor

The objective of this study is to evaluate the activity of a novel peptide, i.e., bifunctional peptide inhibitor (BPI), which targets the immunological synapse and inhibits autoimmune responses in an antigen-specific manner. Proteolipid protein (PLP)-BPI was designed by conjugating two peptides, an encephalitogenic epitope of proteolipid protein (PLP(139-151)) and an intercellular adhesion molecule-1-binding peptide derived from alpha(L) integrin (CD11a(237-246)), via a spacer peptide. The therapeutic effect of PLP-BPI was studied in experimental autoimmune encephalomyelitis (EAE) in female SJL/J mice as a model for human multiple sclerosis. Mice that received i.v. injections of PLP-BPI showed significantly lower EAE disease scores and incidence than those treated with vehicle, PLP(139-151) peptide only, CD11a(237-246) peptide only, unlinked mixture of PLP(139-151), and CD11a(237-246) peptides, or other control peptides. Multiple injections of antigenic peptide can produce anaphylactic responses; interestingly, PLP-BPI-treated animals have significantly lower anaphylactic response than do the PLP(139-151)-treated group. Therefore, PLP-BPI can effectively inhibit the disease severity and incidence of EAE with a lower possibility of inducing fatal anaphylaxis. These results suggest that BPI-type molecules can be used to treat different autoimmune diseases in which antigenic epitopes have been identified.

Differential induction of IgE-mediated anaphylaxis after soluble vs. cell-bound tolerogenic peptide therapy of autoimmune encephalomyelitis

The ability of different forms of myelin peptides to induce tolerance for the treatment of preestablished murine experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis, was evaluated. i.v. administration of myelin peptide-pulsed, ethylene carbodiimide-fixed syngeneic splenocytes, but not soluble myelin peptide monomers or oligomers, proved exceedingly effective at treating preestablished EAE, resulting in amelioration of disease progression. In addition to the lack of therapeutic efficacy of soluble peptide and peptide oligomer, administering them i.v. after the onset of clinical symptoms in many but not all peptide-induced EAE models led to a rapid-onset anaphylactic reaction characterized by respiratory distress, erythema, decreased body temperature, unresponsiveness, and, often, death. By using anti-IgE antibody treatments and mice with targeted mutations of the FcgammaRIII alpha-chain or the common gamma-chain of FcepsilonRI and FcgammaRI/III, we demonstrate that IgE crosslinking of FcepsilonRI appears to be necessary and sufficient for myelin peptide-induced anaphylaxis. The implications of these findings to myelin peptide/protein tolerance strategies for the treatment of multiple sclerosis are discussed.

Pathogenesis of collagen-induced arthritis: modulation of disease by arthritogenic T-cell epitope location

Collagen-induced arthritis (CIA) is an animal model of human rheumatoid arthritis that can be induced in susceptible mice by immunization with type II collagen (CII) or with collagen fragments, including cyanogen bromide (CB) peptides. One susceptible mouse strain, B10.RIII (I-Ar), has previously been found to respond to two major T-cell determinants, namely CII 610-618 (GPAGTAGAR) within CB10 and CII 445-453 (GPAGPAGER) within CB8. Although CB10 contains the immunodominant determinant, it is not arthritogenic. Using recombinant techniques, the determinant within CB10 was mutated to rCB10(T614P,A617E), generating a recombinant CB10 that in effect contained the arthritogenic epitope. When used for immunization, rCB10(T614P,A617E) was arthritogenic. This suggested that the arthritogenic property was intrinsic to the epitope and unrelated to its position within the CII molecule. To test this hypothesis, additional mutants were generated. The wild-type T-cell epitope of CB10 was deleted from its natural position, and the 'arthritogenic' GPAGPAGER T-cell epitope was inserted into the C-terminal portion of the CB10 peptide. The resulting peptide induced arthritis in B10.RIII mice. Adding a second copy of the T-cell determinant to other sites within CB10, however, had varying results. A second T-cell epitope located at the C-terminus of rCB10 significantly increased the incidence and severity of arthritis, while determinants placed in other positions had little effect. These data indicate that the T-cell epitope has intrinsic arthritogenic properties, but there are positional and structural constraints that affect its arthritogenicity. Enhanced arthritis was associated with an increased T-cell proliferation to the peptides, an increase in the level of inflammatory cytokines, and higher levels of anti-CII immunoglobulin. These data suggest that the position and copy number of T-cell determinants also affect the overall immune T-cell responses.

“Chemical Analogues” of HLA-DM Can Induce a Peptide-receptive State in HLA-DR Molecules

We had recently identified small molecular compounds that are able to accelerate the ligand exchange reactions of HLA-DR molecules. Here we show that this acceleration is due to the induction of a "peptide-receptive" state. Dissociation experiments of soluble HLA-DR2.CLIP (class II-associated invariant chain peptide) complex and peptide-binding studies with "nonreceptive" empty HLA-DR1 and -DR2 molecules revealed that the presence of a small phenolic compound carrying an H-bond donor group (-OH) results in the drastic increase of both off- and on-rates. The rate-limiting step for ligand exchange, the transition of the major histocompatibility complex molecule from a nonreceptive into the receptive state, is normally mediated by interaction with the chaperone HLA-DM. In this respect, the effect of small molecules resembles that of the natural catalyst, except that they are still active at neutral pH. These "chemical analogues" of HLA-DM can therefore modulate the response of CD4+ T cells by editing the antigen composition of surface-bound class II major histocompatibility complex on living antigen-presenting cells.

MHC Class II Isotype- and Allele-Specific Attenuation of Experimental Autoimmune Encephalomyelitis

Most autoimmune diseases are associated with certain MHC class II haplotypes. Autoantigen-based specific immune therapy can lead either to beneficial or, in the context of inflammatory conditions, detrimental outcomes. Therefore, we designed a platform of peptides by combinatorial chemistry selected in a nonbiased Ag-independent approach for strong binding to the rat MHC class II isotype RT1.D(n) allelic product of the RT1(n) haplotype that is presenting autoantigen in myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis in LEW.1N rats. Peptide p17 (Ac-FWFLDNAPL-NH(2)) was capable of suppressing the induction of and also ameliorated established experimental autoimmune encephalomyelitis. MHC class II isotype and allele specificity of the therapeutic principle were demonstrated in myelin basic protein-induced experimental autoimmune encephalomyelitis in LEW rats bearing the RT1(l) haplotype. A general immunosuppressive effect of the treatment was excluded by allogeneic heart transplantation studies. In vitro studies demonstrated the blocking effect of p17 on autoantigenic T cell responses. We thus demonstrate a rational design of strong MHC class II-binding peptides with absolute isotype and allele specificity able to compete for autoantigenic sequences presented on disease-associated MHC class II molecules.

Structural basis for gluten intolerance in celiac sprue

Celiac Sprue, a widely prevalent autoimmune disease of the small intestine, is induced in genetically susceptible individuals by exposure to dietary gluten. A 33-mer peptide was identified that has several characteristics suggesting it is the primary initiator of the inflammatory response to gluten in Celiac Sprue patients. In vitro and in vivo studies in rats and humans demonstrated that it is stable toward breakdown by all gastric, pancreatic, and intestinal brush-border membrane proteases. The peptide reacted with tissue transglutaminase, the major autoantigen in Celiac Sprue, with substantially greater selectivity than known natural substrates of this extracellular enzyme. It was a potent inducer of gut-derived human T cell lines from 14 of 14 Celiac Sprue patients. Homologs of this peptide were found in all food grains that are toxic to Celiac Sprue patients but are absent from all nontoxic food grains. The peptide could be detoxified in in vitro and in vivo assays by exposure to a bacterial prolyl endopeptidase, suggesting a strategy for oral peptidase supplement therapy for Celiac Sprue.

Novel synthetic amino acid copolymers that inhibit autoantigen-specific T cell responses and suppress experimental autoimmune encephalomyelitis

Copolymer 1 (Cop 1, Copaxone [Teva Marion Partners, Kansas City, Missouri, USA]), a random amino acid copolymer of tyrosine (Y), glutamic acid (E), alanine (A), and lysine (K), reduces the frequency of relapses by 30% in relapsing-remitting multiple sclerosis (MS) patients. In the present study, novel random four-amino acid copolymers, whose design was based on the nature of the anchor residues of the immunodominant epitope of myelin basic protein (MBP) 85-99 and of the binding pockets of MS-associated HLA-DR2 (DRB1*1501), have been synthesized by solid-phase chemistry. Poly (Y, F, A, K) (YFAK) inhibited binding of the biotinylated MBP 86-100 epitope to HLA-DR2 molecules more efficiently than did either unlabeled MBP 85-99 or any other copolymer including Cop 1. Moreover, YFAK and poly (F, A, K) (FAK) were much more effective than Cop 1 in inhibition of MBP 85-99-specific HLA-DR2-restricted T cell clones. Most importantly, these novel copolymers suppressed experimental autoimmune encephalomyelitis, induced in the susceptible SJL/J (H-2(s)) strain of mice with the encephalitogenic epitope PLP 139-151, more efficiently than did Cop 1. Thus, random synthetic copolymers designed according to the binding motif of the human immunodominant epitope MBP 85-99 and the binding pockets of HLA-DR2 might be more beneficial than Cop 1 in treatment of MS.

Ligand exchange of major histocompatibility complex class II proteins is triggered by H-bond donor groups of small molecules

Hydrogen bonds (H-bonds) are crucial for the stability of the peptide-major histocompatibility complex (MHC) complex. In particular, the H-bonds formed between the peptide ligand and the MHC class II binding site appear to have a great influence on the half-life of the complex. Here we show that functional groups with the capacity to disrupt hydrogen bonds (e.g. -OH) can efficiently catalyze ligand exchange reactions on HLA-DR molecules. In conjunction with simple carrier molecules (such as propyl or benzyl residues), they trigger the release of low affinity ligands, which permits the rapid binding of peptides with higher affinity. Similar to HLA-DM, these compounds are able to influence the MHC class II ligand repertoire. In contrast to HLA-DM, however, these simple small molecules are still active at neutral pH. Under physiological conditions, they increase the number of "peptide-receptive" MHC class II molecules and facilitate exogenous peptide loading of dendritic cells. The drastic acceleration of the ligand exchange on these antigen presenting cells suggests that, in general, availability of H-bond donors in the extracellular milieu controls the rate of MHC class II ligand exchange reactions on the cell surface. These molecules may therefore be extremely useful for the loading of antigens onto dendritic cells for therapeutic purposes.

Vaccination, prevention, and treatment of experimental autoimmune neuritis (EAN) by an oligomerized T cell epitope

Using a polypeptide oligomer harboring 16 repeats of the neuritogenic epitope (aa 58-73) of myelin P2 protein separated by spacers, enhancement of the immune response to the P2 protein, an important neuritogenic autoantigen in experimental autoimmune neuritis (EAN), was attempted. In contrast to a previous study with PLP-16-mer antigen-specific response of T cells was attenuated at all doses examined to a variable degree. Treatment of Lewis rats with the P2-16-mer up to 2 months before immunization with P2(53-78) (vaccination) or after immunization but before appearance of disease (prevention) had a strong tolerizing effect against the induction of EAN on immunization with P2(53-78). Moreover, rats injected with 200 microg of the P2-16-mer i.v. on day 11 after disease induction, at which time the initial signs of disease had appeared, were almost completely protected against progression of clinical disease, whereas animals treated with the same amount of monomeric control peptide developed severe disease (treatment). Similar results were obtained by i.v. treatment of adoptive-transfer EAN with the P2-16-mer. The lack of clinical signs of disease after 16-mer therapy could be correlated with a reduced proliferative response of P2(53-78)-specific lymph node cells. The frequency of apoptotic T cells in sciatic nerve or in lymph node cells, however, was not increased by the 16-mer treatment, suggesting that induction of anergy or other forms of peripheral tolerance may be responsible for the effect. Thus, the oligomerized P2 peptide antigen was highly effective in all three treatment modalities examined in this specific autoreactive T cell-mediated immune response.

Specific treatment of autoimmunity with recombinant invariant chains in which CLIP is replaced by self-epitopes

The invariant chain (Ii) binds to newly synthesized MHC class II molecules with the CLIP region of Ii occupying the peptide-binding groove. Here we demonstrate that recombinant Ii proteins with the CLIP region replaced by antigenic self-epitopes are highly efficient in activating and silencing specific T cells in vitro and in vivo. The Ii proteins require endogenous processing by antigen-presenting cells for efficient T cell activation. An Ii protein encompassing the epitope myelin basic protein amino acids 84-96 (Ii-MBP84-96) induced the model autoimmune disease experimental allergic encephalomyelitis (EAE) with a higher severity and earlier onset than the peptide. When applied in a tolerogenic manner, Ii-MBP84-96 abolished antigen-specific T cell proliferation and suppressed peptide-induced EAE more effectively than peptide alone. Importantly, i.v. administration of Ii proteins after EAE induction completely abrogated the disease, whereas peptides only marginally suppressed disease symptoms. Ii fusion proteins are thus more efficient than peptide in modulating CD4(+) T cell-mediated autoimmunity, documenting their superior qualities for therapeutic antigen delivery in vivo.

Immunomodulation of experimental autoimmune encephalomyelitis with ordered peptides based on MHC-TCR binding motifs

T cell-mediated destruction of the myelin sheath causes inflammatory damage of the CNS in multiple sclerosis (MS). The major T and B cell responses in MS patients who are HLA-DR2 (about two-thirds of MS patients) react to a region between residues 84 and 103 of myelin basic protein (1 ). The crystal structure of HLA-DR2 complexed with myelin basic protein(84-102) confirmed that Lys(91) is the major TCR contact site, whereas Phe(90) is a major anchor to MHC and binds the hydrophobic P4 pocket (2 ). We have tested peptides containing repetitive 4-aa sequences designed to bind critical MHC pockets and to interfere with T cell activation. One such sequence, EYYKEYYKEYYK, ameliorates experimental autoimmune encephalomyelitis in Lewis rats, an animal model of MS.

Tetramer-guided epitope mapping: rapid identification and characterization of immunodominant CD4+ T cell epitopes from complex antigens

T cell responses to Ags involve recognition of selected peptide epitopes contained within the antigenic protein. In this report, we describe a new approach for direct identification of CD4+ T cell epitopes of complex Ags that uses human class II tetramers to identify reactive cells. With a panel of 60 overlapping peptides covering the entire sequence of the VP16 protein, a major Ag for HSV-2, we generated a panel of class II MHC tetramers loaded with peptide pools that were used to stain peripheral lymphocytes of an HSV-2 infected individual. With this approach, we identified four new DRA1*0101/DRB1*0401- and two DRA1*0101/DRB1*0404-restricted, VP16-specific epitopes. By using tetramers to sort individual cells, we easily obtained a large number of clones specific to these epitopes. Although DRA1*0101/DRB1*0401 and DRA1*0101/DRB1*0404 are structurally very similar, nonoverlapping VP16 epitopes were identified, illustrating high selectivity of individual allele polymorphisms within common MHC variants. This rapid approach to detecting CD4+ T cell epitopes from complex Ags can be applied to any known Ag that gives a T cell response.

Competitive inhibition in vivo and skewing of the T cell repertoire of antigen-specific CTL priming by an anti-peptide-MHC monoclonal antibody

We have recently described a mAb, KP15, directed against the MHC-I/peptide molecular complex consisting of H-2D(d) and a decamer peptide corresponding to residues 311-320 of the HIV IIIB envelope glycoprotein gp160. When administered at the time of primary immunization with a vaccinia virus vector encoding gp160, the mAb blocks the subsequent appearance of CD8(+) CTL with specificity for the immunodominant Ag, P18-I10, presented by H-2D(d). This inhibition is specific for this particular peptide Ag; another H-2D(d)-restricted gp160 encoded epitope from a different HIV strain is not affected, and an H-2L(d)-restricted epitope encoded by the viral vector is also not affected. Using functional assays and specific immunofluorescent staining with multivalent, labeled H-2D(d)/P18-I10 complexes (tetramers), we have enumerated the effects of blocking of priming on the subsequent appearance, avidity, and TCR Vbeta usage of Ag-specific CTL. Ab blocking skews the proportion of high avidity cells emerging from immunization. Surprisingly, Vbeta7-bearing Ag-specific TCR are predominantly inhibited, while TCR of several other families studied are not affected. The ability of a specific MHC/peptide mAb to inhibit and divert the CD8(+) T cell response holds implications for vaccine design and approaches to modulate the immune response in autoimmunity.

Antigen-specific elimination of T cells induced by oligomerized hemagglutinin (HA) 306-318

In a previous study we reported that oligomerized T cell epitopes "superactivated" CD4+ T cells. These oligomers, consisting of 12-16 copies of a peptide epitope derived from the hemagglutinin protein of influenza virus (HA306-318), induced a specific T cell response in amounts as little as 5 pg/ml. We now show that the improved antigenicity of these multimerized epitopes can also be utilized to induce "high zone tolerance". Tolerization, similar to activation, occurred at about 3 logs lower concentration of oligomer than of peptide. HA306-318-specific T cell cultures became nonresponsive to stimulation with peptide after incubation with 0.5-5 microg/ml HA306-318 12-mer. The nonresponsiveness was accompanied by a drastic down-regulation of the TCR and by T cell elimination by apoptotic cell death. In contrast, stimulation with peptide even at 50 microg/ml led to temporary induction of anergy. Consequently, induction of tolerance with the oligomer was permanent and no recovery of the cultures was seen in recall experiments 12-14 days after high zone exposure to the 12-mer.

Peptide dose, MHC affinity, and target self-antigen expression are critical for effective immunotherapy of nonobese diabetic mouse prediabetes

Cross-reactive T cells that recognize both Tep69 (dominant nonobese diabetic (NOD) T cell epitope in ICA69 (islet cell autoantigen of 69 kDa)) and ABBOS (dominant NOD T cell epitope in BSA) are routinely generated during human and NOD mouse prediabetes. Here we analyzed how systemic administration of these mimicry peptides affects progressive autoimmunity in adoptively transferred and cyclophosphamide-accelerated NOD mouse diabetes. These models were chosen to approximate mid to late stage prediabetes, the typical status of probands in human intervention trials. Unexpectedly, high dose (100 microg) i.v. ABBOS prevented, while Tep69 exacerbated, disease in both study models. Peptide effects required cognate recognition of endogenous self-Ag, because both treatments were ineffective in ICA69null NOD congenic mice adoptively transferred with wild-type, diabetic splenocytes. The affinity of ABBOS for NOD I-A(g7) was orders of magnitude higher than that of Tep69. This explained 1) the expansion of the mimicry T cell pool following i.v. Tep69, 2) the long-term unresponsiveness of these cells after i.v. ABBOS, and 3) precipitation of the disease after low dose i.v. ABBOS. Disease precipitation and prevention in mid to late stage prediabetes are thus governed by affinity profiles and doses of therapeutic peptides. ABBOS or ABBOS analogues with even higher MHC affinity may be candidates for experimental intervention strategies in human prediabetes, but the dose translation from NOD mice to humans requires caution.