Prospects of the Use of Cell Therapy to Induce Immune Tolerance

Conditions in which abnormal or excessive immune responses exist, such as autoimmune diseases (ADs), graft-versus-host disease, transplant rejection, and hypersensitivity reactions, are serious hazards to human health and well-being. The traditional immunosuppressive drugs used to treat these conditions can lead to decreased immune function, a higher risk of infection, and increased tumor susceptibility. As an alternative therapeutic approach, cell therapy, in which generally intact and living cells are injected, grafted, or implanted into a patient, has the potential to overcome the limitations of traditional drug treatment and to alleviate the symptoms of many refractory diseases. Cell therapy could be a powerful approach to induce immune tolerance and restore immune homeostasis with a deeper understanding of immune tolerance mechanisms and the development of new techniques. The purpose of this review is to describe the current panoramic scope of cell therapy for immune-mediated disorders, discuss the advantages and disadvantages of different types of cell therapy, and explore novel directions and future prospects for these tolerogenic therapies.

Biodistribution and pharmacokinetic profiles of an altered peptide ligand derived from heat-shock proteins 60 in Lewis rats

Human heat-shock protein 60 (HSP60) is an autoantigen involved in the pathogenesis of rheumatoid arthritis (RA). Epitopes derived from HSP60 can trigger activation of regulatory T cells (Treg). CIGB-814 is an altered peptide ligand (APL) derived from HSP60. In preclinical models, this peptide had anti-inflammatory effects and increased Treg. The results from phase I clinical trial indicated that CIGB-814 was safe and activated mechanisms associated with induction of tolerance. Biodistribution profile for inducers of tolerance is crucial for triggering its effects. The primary goal of this study in Lewis rats was to identify (1) the target organs of CIGB-814 and (2) the pharmacokinetics (PK) profile. 125I-CIGB-814 administered subcutaneously at three dose levels was distributed in the thyroid gland, but also at considerable levels to the stomach and small and large intestines. In addition, concentration of CIGB-814 was increased in lymph nodes (LNs) at 24 h, compared with 4-h post-administration. Small intestine and LNs are excellent sites for induction of tolerance, due to the characteristics of dendritic cells in these tissues. Maximum concentration of CIGB-814 in blood of Lewis rats at 0.5 to 1 h agrees with PK profile determined for patients. Altogether, these results support therapeutic possibilities of CIGB-814 for RA.

Immune Response Regulation by Antigen Receptors' Clone-Specific Nonself Parts

Antigen determinants (epitopes) are recognized by the combining sites (paratopes) of B and T cell antigen receptors (BCR/TCR), which again express clone-specific epitopes (idiotopes) that can be recognized by BCR/TCR not only of genetically different donors but also within the autologous immune system. While xenogeneic and allogeneic anti-idiotypic BCR/TCR are broadly cross-reactive, only autologous anti-idiotypes are truly specific and of functional regulatory relevance within a particular immune system. Autologous BCR/TCR idiotopes are (a) somatically created at the third complementarity-determining regions, (b) through mutations introduced into BCRs during adaptive immune responses, and (c) through the conformational impact of both. As these idiotypic characters have no genomic counterparts they have to be regarded as antigen receptor-intrinsic nonself-portions. Although foreign, however, they are per se non-immunogenic, but in conjunction with immunogenicity- and adjuvanticity-providing antigen-induced immune responses, they induce abating regulatory idiotypic chain reactions. The dualistic nature of antigen receptors of seeing antigens (self and nonself alike) and being nonself at the same time has far reaching consequences for an understanding of the regulation of adaptive immune responses.

Molecular adjuvants that modulate regulatory T cell function in vaccination: A critical appraisal

Adjuvants are substances used to enhance the efficacy of vaccines. They influence the magnitude and alter the quality of the adaptive immune response to vaccine antigens by amplifying or modulating different signals involved in the innate immune response. The majority of known adjuvants have been empirically identified. The limited immunogenicity of new vaccine antigens and the need for safer vaccines have increased the importance of identifying single, well-defined adjuvants with known cellular and molecular mechanisms for rational vaccine design. Depletion or functional inhibition of CD4⁺CD25⁺FoxP3⁺ regulatory T cells (Tregs) by molecular adjuvants has become an emergent approach in this field. Different successful results have been obtained for specific vaccines, but there are still unresolved issues such as the risk of autoimmune disease induction, the involvement of cells other than Tregs and optimization for different conditions. This work provides a comprehensive analysis of current approaches to inhibit Tregs with molecular adjuvants for vaccine improvement, highlights the progress being made, and describes ongoing challenges.

Therapeutic effect of ergotope peptides on CIA by down-regulation of inflammatory and Th1/Th17 responses and induction of regulatory T cells

Rheumatoid arthritis (RA) is a systemic autoimmune disease that results in a chronic and inflammatory disorder. Dynamic balance of helper T cells (Th)1, Th17 and regulatory T cells (Treg) is broken in RA. Since there is no cure for RA at present, it's necessary to find a truly effective and convenient treatment. Several studies intended to induce ergotopic regulation to treat autoimmune diseases. This study was undertaken to find the potential ergotope peptides and investigate its effect in treating the animal model of RA and their underlying regulatory mechanisms. Firstly, we selected the functional ergotope peptides from 25 overlapping peptides derived from interlukin(IL)-2 receptor (IL-2R) α chain, and then used these peptides to treat collagen-induced arthritis (CIA). The study showed ergotope peptides as immunomodulatory factors with great benefits at the clinical and pathologic levels. This effect was associated with the inhibition of type II collagen (CII)-specific proliferation and autoantibody production as well as the induction of anti-ergotypic immune response, the down-regulation of both Th1 and Th17 cells and their related components, and the emergence of Treg cells that had suppressive actions on autoreactive T cells. We also proved that cytotoxic T lymphocyte associated antigen-4 (CTLA-4) and IL-10 are two important mediators which are critical to Treg suppressive function. The inhibition of Th1 and Th17 in established CIA could be attributed to ergotope induced Treg cells. Our findings reveal that ergotope peptides induce regulatory immune responses and restore immune tolerance, suggesting ergotope peptides treatment appears to be a novel approach to the therapy of RA patients and has a good application prospect with cheap, effective, convenient, wide-spectrum features.

APL-2, an altered peptide ligand derived from heat-shock protein 60, induces interleukin-10 in peripheral blood mononuclear cell derived from juvenile idiopathic arthritis patients and downregulates the inflammatory response in collagen-induced arthritis model

Juvenile idiopathic arthritis (JIA) is a heterogeneous group of diseases characterized by autoimmune arthritis of unknown cause with onset before age of 16 years. Methotrexate provides clinical benefits in JIA. For children who do not respond to methotrexate, treatment with anti-tumor necrosis factor (TNF)-α is an option. However, some patients do not respond or are intolerant to anti-TNF therapy. Induction of peripheral tolerance has long been considered a promising approach to the treatment of chronic autoimmune diseases. We aimed to evaluate the potentialities of two altered peptide ligands (APLs) derived from human heat-shock protein 60, an autoantigen involved in the pathogenesis of autoimmune arthritis, in JIA patients. Interferon (IFN)-γ, TNF-α and interleukin (IL)-10 levels were determined in ex vivo assays using peripheral blood mononuclear cells (PBMC) from these patients. Wild-type peptide and one of these APLs increased IFN-γ and TNF-α levels. Unlike, the other APLs (called APL2) increased the IL-10 level without affecting IFN-γ and TNF-α levels. On the other hand, APL2 induces a marked activation of T cells since it transforms cell cycle phase's distribution of CD4+ T cells from these patients. In addition, we evaluated the therapeutic effect of APL2 in collagen-induced arthritis model. Therapy with APL2 reduced arthritis scores and histological lesions in mice. This effect was associated to a decrease in TNF-α and IL-17 levels. These results indicate a therapeutic potentiality of APL2 for JIA.

Mixed lymphocyte reaction induced by multiple alloantigens and the role for IL-10 in proliferation inhibition

The frequency of T cells that can respond to alloantigens is unusually high. It remains unclear how T cells would respond when stimulated by multiple major histocompatibility complex (MHC) disparate alloantigens in the same cultures. In this report, we examined potential interactions of T cell clones that were stimulated simultaneously by two sets of complete MHC disparate alloantigens using mixed lymphocyte reaction (MLR). In this assay, we observed that proliferation of B6 lymphocytes (H-2b) stimulated by both BALB/c (H-2d) and C3H (H-2k) allogeneic cells was not increased but rather reduced as compared to B6 cells stimulated with either BALB/c or C3H allogeneic cells. Interestingly, interleukin (IL)-10 expressions at both protein level and mRNA level was significantly increased in cultures stimulated with the two MHC alloantigens, while IL-2, tumor necrosis factor (TNF)-α, transforming growth factor (TGF)-β1 production did not show any differences. In addition, Foxp3 mRNA expression was comparable amongst all groups. In conclusion, we observed an inhibitory effect in T cell proliferation in response to multiple MHC mismatched alloantigens in MLR, and this effect might be associated with the upregulation of IL-10 expression.

Stress proteins are used by the immune system for cognate interactions with anti-inflammatory regulatory T cells

Since the initial discovery of the protective role of heat shock protein (HSP) 60 in arthritis, T cell recognition of endogenous HSP was found to be one of the possible underlying mechanisms. Recently we have uncovered potent disease-suppressive Tregs (anti-inflammatory immunosuppressive T cells) recognizing HSP70 self-antigens, and enabling selective targeting of such Tregs to inflamed tissues. HSP70 is a major contributor to the major histocompatibility complex (MHC) Class II ligandome and we have shown that a conserved HSP70-epitope (B29) is abundantly present in murine MHC Class II. Upon transfer, B29-induced CD4+CD25+Foxp3+T cells suppressed established proteoglycan-induced arthritis (PGIA) in mice. These self-antigen specific Tregs were activated in vivo and as little as 4.000 cells sufficed to fully inhibit arthritis. Furthermore, in vivo depletion of transferred Tregs abrogated disease suppression. Given that B29 can be presented by most human MHC class II molecules and that B29 inhibited arthritis in HLA-DQ8 (human MHC) transgenic mice, we feel that therapeutic vaccination with selected HSP peptides can be an effective route for induction of anti-inflammatory Tregs as a novel intervention in chronic inflammatory diseases.

Sour cherry seed kernel extract increases heme oxygenase-1 expression and decreases representation of CD3+ TNF-α+ and CD3+IL-8+ subpopulations in peripheral blood leukocyte cultures from type 2 diabetes patients

The present study evaluates a hypothesis that sour cherry (Prunus cerasus) seed extracts (SCE) modulate CD3+ T lymphocyte activity in ways predictive of potential for uses of SCE in management of inflammatory diseases. Peripheral blood mononuclear cells (PBMC) from 12 type 2 diabetes (T2DM) patients and eight healthy control subjects were cultured 24 h with 100 ng/ml lipopolysaccharide (LPS) to increase inflammatory signaling and co-incubated with 0.5-100 µg/ml SCE. Cultures were evaluated by two-color flow cytometry for percent representation of CD3+ IL8+ and CD3+TNF-α cells which express interleukin-8 (IL-8), and tumor necrosis factor-α, (TNF-α+) respectively, and by enzyme-linked immunoassay for lymphocyte-associated heme oxygenase-1 (HO-1, known to be induced by SCE). SCE dosage ranges of 0.5-100 µg/ml in cell cultures significantly suppressed LPS-increased CD3+TNF-α+ and CD3+IL8+ representation from all participants (p < 0.05), with greater pharmacological effect noted in suppression of CD3+TNF-α+ noted in cells from T2DM patients versus healthy control subjects. These effects correlated with increased HO-1 expression in SCE-treated PBMC from all subjects (p < 0.05). Since TNF-α and IL-8 are diagnostic/prognostic biomarkers for many inflammatory syndromes, the capacity of SCE to down-regulate representation of cells that express them suggests potential for therapeutic use of SCE in T2DM and other diseases.

Class II MHC self-antigen presentation in human B and T lymphocytes

Human CD4⁺ T cells process and present functional class II MHC-peptide complexes, but the endogenous peptide repertoire of these non-classical antigen presenting cells remains unknown. We eluted and sequenced HLA-DR-bound self-peptides presented by CD4⁺ T cells in order to compare the T cell-derived peptide repertoire to sequences derived from genetically identical B cells. We identified several novel epitopes derived from the T cell-specific proteome, including fragments of CD4 and IL-2. While these data confirm that T cells can present peptides derived from the T-cell specific proteome, the vast majority of peptides sequenced after elution from MHC were derived from the common proteome. From this pool, we identified several identical peptide epitopes in the T and B cell repertoire derived from common endogenous proteins as well as novel endogenous epitopes with promiscuous binding. These findings indicate that the endogenous HLA-DR-bound peptide repertoire, regardless of APC type and across MHC isotype, is largely derived from the same pool of self-protein.

Immunoproteomic analysis of the antibody response obtained in mouse following vaccination with a T-cell vaccine

T-cell vaccination (TCV), the application of irradiated activated T cells, has been shown to prevent effectively and treat experimental autoimmune diseases. It has been reported that anti-lymphocytic antibodies induced by TCV were capable of strongly inhibiting T-cell proliferation and of ameliorating experimental autoimmune disease. The present study was undertaken to characterize the antigen specificity of these Abs. We used activated mouse ovalbumin (OVA)-specific T cells (OVA-T) as vaccine immunized mice. By combination of 2-DE, 2-D Western blot and Q-TOF mass spectrometry we have identified 11 antigens in activated T cells that were recognized by the anti-T-cell Abs. The resulting antigenic molecules included calreticulin (CRT), ERp57, Vimentin, HSP70-4, tubulin β5 chain, coronin-1A, pyruvate kinase, ATP synthase β chain and transketolase most of which belong to so-called damage-associated molecular pattern molecules (DAMPs). CRT, ERp57 and vementin were further examined by Western blot and cellular ELISA to identify molecular targets which may be involved in the TCV immunotherapy. On the basis of our results, γ-radiation induced the activated T cells "immunogenic apoptosis" and exposed/secreted DAMPs (CRT, ERp57 and Vementin) played an important role in TCV therapy.

TLR1/2 activation during heterologous prime-boost vaccination (DNA-MVA) enhances CD8+ T Cell responses providing protection against Leishmania (Viannia)

BACKGROUND

Leishmania (Viannia) parasites present particular challenges, as human and murine immune responses to infection are distinct from other Leishmania species, indicating a unique interaction with the host. Further, vaccination studies utilizing small animal models indicate that modalities and antigens that prevent infection by other Leishmania species are generally not protective.

METHODOLOGY

Using a newly developed mouse model of chronic L. (Viannia) panamensis infection and the heterologous DNA prime - modified vaccinia virus Ankara (MVA) boost vaccination modality, we examined whether the conserved vaccine candidate antigen tryparedoxin peroxidase (TRYP) could provide protection against infection/disease.

RESULTS

Heterologous prime - boost (DNA/MVA) vaccination utilizing TRYP antigen can provide protection against disease caused by L. (V.) panamensis. However, protection is dependent on modulating the innate immune response using the TLR1/2 agonist Pam3CSK4 during DNA priming. Prime-boost vaccination using DNA alone fails to protect. Prior to infection protectively vaccinated mice exhibit augmented CD4 and CD8 IFNγ and memory responses as well as decreased IL-10 and IL-13 responses. IL-13 and IL-10 have been shown to be independently critical for disease in this model. CD8 T cells have an essential role in mediating host defense, as CD8 depletion reversed protection in the vaccinated mice; vaccinated mice depleted of CD4 T cells remained protected. Hence, vaccine-induced protection is dependent upon TLR1/2 activation instructing the generation of antigen specific CD8 cells and restricting IL-13 and IL-10 responses.

CONCLUSIONS

Given the general effectiveness of prime-boost vaccination, the recalcitrance of Leishmania (Viannia) to vaccine approaches effective against other species of Leishmania is again evident. However, prime-boost vaccination modality can with modulation induce protective responses, indicating that the delivery system is critical. Moreover, these results suggest that CD8 T cells should be targeted for the development of a vaccine against infection caused by Leishmania (Viannia) parasites. Further, TLR1/2 modulation may be useful in vaccines where CD8 T cell responses are critical.

T-cell vaccination leads to suppression of intrapancreatic Th17 cells through Stat3-mediated RORγt inhibition in autoimmune diabetes

Immunization with inactivated autoreactive T cells is an effective therapeutic approach to ameliorating autoimmune diseases, while the underlying mechanisms that regulate autoreactive T cells are not completely understood. This study tested the hypothesis that T-cell vaccination (TCV) inhibits autoimmune diabetes in mice through the suppression of Th17 cells. The results showed that TCV treatment decreased hyperglycemia in type 1 diabetes (T1D) induced by multiple low-dose streptozotocin (MLD-STZ) as compared with the controls, preserved the number of healthy pancreatic islets and increased the production of insulin in the islets. Further study revealed that TCV significantly decreased the production of both interleukin (IL)-17 and IL-23 in intrapancreatic infiltrating lymphocytes (IPL) through marked inhibition of mRNA level of retinoic acid-related orphan receptor γt (RORγt) and signal transducer and activator of transcription 3 (Stat3) phosphorylation. The role of TCV-induced Th17 suppression was further validated in adoptive transfer experiments with polarized Th17 cells in sub-diabetogenic mice, which was similar to the effect of anti-IL-17 antibody treatment. Collectively our study shows that intrapancreatic Th17 cell suppression and healthy islet preservation play an important role in the treatment of T1D by TCV.

An altered peptide ligand corresponding to a novel epitope from heat-shock protein 60 induces regulatory T cells and suppresses pathogenic response in an animal model of adjuvant-induced arthritis

Induction of immune tolerance as therapeutic approach for autoimmune diseases constitutes a current research focal point. In this sense, we aimed to evaluate an altered peptide ligand (APL) for induction of peripheral tolerance in patients with rheumatoid arthritis (RA). A novel T-cell epitope from human heat-shock protein 60 (Hsp60), an autoantigen involved in the pathogenesis of RA, was identified by bioinformatics tools and an APL was design starting from this epitope. We investigated the ability of this APL for inducing regulatory T cells (Treg cells) in mice and evaluated the therapeutic effect of this peptide in an adjuvant-induced arthritis (AA) rat model. Clinical score, TNFα levels and histopathology were monitored, as well as the capacity of this APL for inducing Treg cells. Finally, the potentialities of the APL for inducing Treg cells were evaluated in ex vivo assays using mononuclear cells isolated from peripheral blood (PBMC). The APL induced an increase of the proportions of Treg cells in the draining lymph nodes of the injected site in mice. The APL efficiently inhibited the course of AA, with significant reduction of the clinical and histopathology score. This effect was associated with an increase of the proportions of Treg cells and a decrease of TNFα levels in spleen. Finally, stimulation of PBMCs from RA patients by the APL increases the proportions of the CD4(+)CD25(high)FoxP3(+) Treg cells. These results indicate a therapeutic potentiality of APL and support further investigation of this candidate drug for treatment of RA.

T-cell-based immunotherapy in multiple sclerosis: induction of regulatory immune networks by T-cell vaccination

Multiple sclerosis (MS) is a chronic inflammatory disease of the CNS with presumed autoimmune origin. Pathogenic autoimmune responses in MS are thought to be the result of a breakdown of self tolerance. Several mechanisms account for the natural state of immunological tolerance to self antigens, including clonal deletion of self-reactive T cells in the thymus. However, autoimmune T cells are also part of the normal T-cell repertoire, supporting the existence of peripheral regulatory mechanisms that keep these potentially pathogenic T cells under control. One such mechanism involves active suppression by regulatory T cells. It has been indicated that regulatory T cells do not function properly in autoimmune disease. Immunization with attenuated autoreactive T cells, T-cell vaccination, may enhance or restore the regulatory immune networks to specifically suppress autoreactive T cells, as shown in experimental autoimmune encephalomyelitis, an animal model for MS. In the past decade, T-cell vaccination has been tested for MS in several clinical trials. This review summarizes these clinical trials and updates our current knowledge on the induction of regulatory immune networks by T cell vaccination.

Epitope-specific immunotherapy of rheumatoid arthritis: clinical responsiveness occurs with immune deviation and relies on the expression of a cluster of molecules associated with T cell tolerance in a double-blind, placebo-controlled, pilot phase II trial

OBJECTIVE

Induction of immune tolerance to maintain clinical control with a minimal drug regimen is a current research focus in rheumatoid arthritis (RA). Accordingly, we are developing a tolerization approach to dnaJP1, a peptide part of a pathogenic mechanism that contributes to autoimmune inflammation in RA. We undertook this study to test 2 hypotheses: 1) that mucosal induction of immune tolerance to dnaJP1 would lead to a qualitative change from a proinflammatory phenotype to a more tolerogenic functional phenotype, and 2) that immune deviation of responses to an inflammatory epitope might translate into clinical improvement.

METHODS

One hundred sixty patients with active RA and with immunologic reactivity to dnaJP1 were enrolled in a pilot phase II trial. They received oral doses of 25 mg of dnaJP1 or placebo daily for 6 months.

RESULTS

The dnaJP1 peptide was safe and well-tolerated. In response to treatment with dnaJP1, there was a significant reduction in the percentage of T cells producing tumor necrosis factor alpha and a corresponding trend toward an increased percentage of T cells producing interleukin-10. Coexpression of a cluster of molecules (programmed death 1 and its ligands) associated with T cell regulation was also found to be a prerequisite for successful tolerization in clinical responders. Analysis of the primary efficacy end point (meeting the American College of Rheumatology 20% improvement criteria at least once on day 112, 140, or 168) showed a difference between treatment groups that became significant in post hoc analysis using generalized estimating equations. Differences in clinical responses were also found between treatment groups on day 140 and at followup. Post hoc analysis showed that the combination of dnaJP1 and hydroxychloroquine (HCQ) was superior to the combination of HCQ and placebo.

CONCLUSION

Tolerization to dnaJP1 leads to immune deviation and a trend toward clinical efficacy. Susceptibility to treatment relies on the coexpression of molecules that can down-regulate adaptive immunity.

Hsp70 expression and induction as a readout for detection of immune modulatory components in food

Stress proteins such as heat shock proteins (Hsps) are up-regulated in cells in response to various forms of stress, like thermal and oxidative stress and inflammation. Hsps prevent cellular damage and increase immunoregulation by the activation of anti-inflammatory T-cells. Decreased capacity for stress-induced Hsp expression is associated with immune disorders. Thus, therapeutic boosting Hsp expression might restore or enhance cellular stress resistance and immunoregulation. Especially food- or herb-derived phytonutrients may be attractive compounds to restore optimal Hsp expression in response to stress. In the present study, we explored three readout systems to monitor Hsp70 expression in a manner relevant for the immune system and evaluated novel Hsp co-inducers. First, intracellular staining and analysis by flow cytometry was used to detect stress and/or dietary compound induced Hsp70 expression in multiple rodent cell types efficiently. This system was used to screen a panel of food-derived extracts with potent anti-oxidant capacity. This strategy yielded the identity of several new enhancers of stress-induced Hsp70 expression, among them carvacrol, found in thyme and oregano. Second, CD4(+) T-cell hybridomas were generated that specifically recognized an immunodominant Hsp70 peptide. These hybridomas were used to show that carvacrol enhanced Hsp70 levels increased T-cell activation. Third, we generated a DNAJB1-luc-O23 reporter cell line to show that carvacrol increased the transcriptional activation of a heat shock promoter in the presence of arsenite. These assay systems are generally applicable to identify compounds that affect the Hsp level in cells of the immune system.

[Cellular therapy in autoimmune disease]

In addition to natural thymus-derived regulatory T-cells (Tregs), peripherally-induced Tregs are of central importance in immune homeostasis. Homotypic interactions between activated effector T-cells and resting memory T-cells induced the generation of IL-10 and IFNgamma producing Tregs in vitro. This mechanism in Treg development allows new insights into T-cell vaccination, which has been employed in pilot trials of multiple sclerosis and rheumatoid arthritis with promising results.

The specificity of T cell regulation that enables self-nonself discrimination in the periphery

It was recently shown that perceiving the avidity of T cell activation can be translated into peripheral T cell regulation to control autoimmune disease. This regulation is achieved by CD8(+) T cells that recognize a common surrogate target structure, Qa-1/Hsp60sp, preferentially expressed by activated T cells of intermediate but not high avidity. A truncated self-reactive repertoire, devoid of high-avidity T cells, generated by thymic negative selection, allows selective down-regulation of intermediate-avidity T cells to accomplish self-nonself discrimination in the periphery. Identification of the common surrogate target structure expressed on intermediate-avidity T cells opens up a conceptual theme to understand the relationship between the specificity of peripheral immune regulation and self-nonself discrimination. Here, we investigated peptide vaccination induced cross-protection mediated by CD8(+) T cells in two autoimmune disease models, experimental allergic encephalomyelitis (EAE) and type 1 diabetes (T1D). We show that Qa-1 restricted CD8(+) T cells cross-protect animals from either EAE or T1D without abrogating the immune response to foreign antigens. Cross-protection occurs because potentially pathogenic self-reactive T cells included in the pool of intermediate-avidity T cells are capable of preferentially expressing common surrogate target structures on their surface to render themselves subject to the down-regulation, independent of the specificity of the antigens that they are triggered by. Thus, like in the thymus, the immune system discriminates self from nonself, during adaptive immunity in the periphery, not by recognizing the structural differences between self and foreign antigens, but rather by perceiving the avidity of T cell activation.

How the immune system achieves self-nonself discrimination during adaptive immunity

We propose an "Avidity Model of Self-Nonself Discrimination" in which self-nonself discrimination is achieved by both central thymic selection and peripheral immune regulation. The conceptual framework that links these two events is the understanding that both in the thymus and in the periphery the survival or the fate of T cells is determined by the avidity of the interactions between T cell receptors (TCRs) on T cells, specific to any antigens and MHC/antigen peptides presented by antigen-presenting cells (APCs). We envision that the immune system achieves self-nonself discrimination, during adaptive immunity, not by recognizing the structural differences between self versus foreign antigens, but rather by perceiving the avidity of T cell activation. Intrathymic deletion of high avidity T cell clones responding to the majority of self-antigens generates a truncated peripheral self-reactive repertoire composed of mainly intermediate and low but devoid of high avidity T cells compared with the foreign-reactive repertoire. The existence of intermediate avidity self-reactive T cells in the periphery represents a potential danger of pathogenic autoimmunity inherited in each individual because potentially pathogenic self-reactive T cells are included in the pool of intermediate avidity T cells and can often be functionally activated to elicit autoimmune diseases. The distinct composition of peripheral T cell repertoires to self versus to foreign antigens provides a unique opportunity for the immune system to discriminate self from nonself, in the periphery, by selectively downregulating intermediate avidity T cells to both self and foreign antigens. Selective downregulation of the intermediate avidity T cell populations containing the potentially pathogenic self-reactive T cells enables the immune system to specifically control autoimmune diseases without damaging the effective anti-infection immunity, which is, largely, mediated by high avidity T cells specific to the infectious pathogens. In this regard, it has been recently shown that Qa-1-restricted CD8(+) T cells selectively downregulate intermediate avidity T cells, to both self and foreign antigens, and as a consequence, specifically dampen autoimmunity yet optimize the immune response to foreign antigens. Selective downregulation of intermediate avidity T cells is accomplished via specific recognition, by the Qa-1-restricted CD8(+) T cells, of particular Qa-1/self-peptide complexes, such as Qa-1/Hsp60sp, which function as a common surrogate target structure and preferentially expressed on the activated intermediate avidity T cells. This regulatory pathway thus represents one example of the peripheral mechanisms that the immune system evolved to complete self-nonself discrimination that is achieved, imperfectly, by thymic negative selection, in order to maintain self-tolerance. The conceptual framework of the "Avidity Model" differs from, but contains intellectual wisdom of certain conceptual elements of, the "Tunable Activation Thresholds Hypothesis," the "Danger Model," and the "Ergotypic Regulation Phenomenon." It provides a unified and simple paradigm to explain various seemingly unrelated biomedical problems inherent in immunological disorders that cannot be uniformly interpreted by any currently existing paradigms. The potential impact of the conceptual framework of the "Avidity Model" on our understanding of the development and control of commonly seen autoimmune diseases is also discussed.

HSP60 as a target of anti-ergotypic regulatory T cells

The 60 kDa heat shock protein (HSP60) has been reported to influence T-cell responses in two ways: as a ligand of toll-like receptor 2 signalling and as an antigen. Here we describe a new mechanism of T-cell immuno-regulation focused on HSP60: HSP60 is up-regulated and presented by activated T cells (HSP60 is an ergotope) to regulatory (anti-ergotypic) T cells. Presentation of HSP60 by activated T cells was found to be MHC-restricted and dependent on accessory molecules - CD28, CD80 and CD86. Anti-ergotypic T cells responded to T-cell HSP60 by proliferation and secreted IFNγ and TGFβ1. In vitro, the anti-ergotypic T cells inhibited IFNγ production by their activated T-cell targets. In vivo, adoptive transfer of an anti-ergotypic HSP60-specific T-cell line led to decreased secretion of IFNγ by arthritogenic T cells and ameliorated adjuvant arthritis (AA). Thus, the presentation of HSP60 by activated T cells turns them into targets for anti-ergotypic regulatory T cells specific for HSP60. However, the direct interaction between the anti-ergotypic T regulators (anti-HSP60) and the activated T cells also down-regulated the regulators. Thus, by functioning as an ergotope, HSP60 can control both the effector T cells and the regulatory HSP60-specific T cells that control them.

MHC class II-dependent T-T interactions create a diverse, functional and immunoregulatory reaction circle

Unlike conventional T cells, innate-like T cells such as natural killer (NK) T cells are selected by homotypic T-cell interactions. Recently, a few reports have shown that T-T CD4(+) T cells can be generated in a similar manner to that for NKT cells. These two types of cells share common functional properties such as rapid response to antigenic encounters and the potential for a panoply of cytokine secretion. However, T-T CD4(+) T cells differ from NKT cells in that they are restricted by highly polymorphic major histocompatibility complex (MHC) II molecules and have a diverse T-cell receptor repertoire. Additional example of T-T interactions was recently reported in which peripheral T cells re-circulate to the thymus and participate in the thymocyte selection process. In this review, we dissect the cellular mechanisms underlying the production of T-T CD4(+) and NKT cells, with particular emphasis on the differences between these two T-cell prototypes. Finally, we propose that T-T CD4(+) T cells serve two major functions: one as an acute-phase reactant against viral infection and the other is the generation of anti-ergotypic CD4(+) T cells for regulatory purposes. All of these features make it possible to create a diverse set of functional cells through MHC class II-restricted T-T interactions.

Adoptive transfer of transplantation tolerance mediated by CD4+CD25+ and CD8+CD28- regulatory T cells induced by anti-donor-specific T-cell vaccination

Previous studies have shown that vaccinating rodents with anti-donor-specific T cells significantly prolonged allograft survival; however, the putative mechanism of the tolerance remains unclear. In this study, we used the model of heterotopic heart transplantation between the C57BL/6 donor mice and BALB/c recipient mice vaccinated with anti-donor (C57BL/6) or anti-third party (C3H)-specific T cells to determine whether T cells prolong survival of mouse heart allografts and which cells were involved in induction of allograft tolerance. We observed that the mean survival time (MST) of C57BL/6 heart grafts in BALB/c mice vaccinated with anti-C57BL/6 specific T cells (43.1 +/- 4.7 days) was prolonged from that in untreated BALB/c mice (9.5 +/- 1.1 days) or BALB/c mice receiving anti-C3H-specific T cells (10.4 +/- 1.9 days). These results suggested that alloantigen-specific T-cell vaccination significantly prolonged cardiac allograft survival. The CD4+CD25+ or CD8+CD28- T cells purified from splenocytes of BALB/c mice vaccinated with anti-donor-specific T cells proliferated markedly in response to irradiated anti-C57BL/6-specific T cells in vitro. Adoptive transfer of these CD4+CD25+ or CD8+CD28- T cells to naïve syngenic mice significantly prolonged the survival of heart allografts. These data suggested that anti-donor-specific T-cell vaccination induced development of CD4+CD25+ or CD8+CD28- regulatory T cells, which in turn mediated allogeneic-specific tolerance.

Isolation and characterization of CD8+ regulatory T cells in multiple sclerosis

To investigate CD8+ regulatory T cell influence on multiple sclerosis development, peripheral blood and cerebrospinal fluid (CSF) CD8+ T cell clones (TCCs) recognizing MBP(83-102) and MOG(63-87)-specific CD4+ T cells were isolated from 20 patients during acute exacerbations, 15 in remission and 15 controls. Blood and CSF CD8+ regulatory TCC cloning frequency decreased more during exacerbations than remissions or controls. Target cell pre-activation significantly enhanced CD8+ T granule-mediated cell killing of CD4+ targets, and was restricted by HLA-E. During exacerbations, killer-inhibitory receptor CD94/NKG2A expression was significantly higher in CD8+ TCCs, limiting their cytotoxic activity. Moreover, IL-15 and IFN-gamma significantly increased CD94 and NKG2A expression. These data provide evidence that CD94/NKG2A receptors play an important role in regulating T cell activity during the course of MS.

Real and artificial immune systems: computing the state of the body

Here I present the idea that the immune system uses a computational strategy to carry out its many functions in protecting and maintaining the body. Along the way, I define the concepts of computation, Turing machines and system states. I attempt to show that reframing our view of the immune system in computational terms is worth our while.

Immunization of mice with DNA coding for the variable regions of anti-idiotypic antibody generates antigen-specific response

Understanding the mechanisms of generation and maintenance of immunological memory is crucial for rational vaccine design. A hypothesis known as relay hypothesis was earlier proposed which explains the maintenance of immunological memory through interaction of idiotypic and anti-idiotypic lymphocytes. In the present study, we have shown that immunization with rinderpest virus hemagglutinin protein specific anti-idiotypic antibody (Ab(2)v(beta)) DNAs coding for heavy and light chains generates antigen-specific antibody and T cell responses as well as Ab1 specific T cell response. We further show that boosting with the recombinant Ab(2)-vbeta proteins generates B and T cell memory response specific for antigen in anti-id DNA primed mice. This study provides experimental evidence for perpetuation of immunological memory through idiotypic network interactions.

Idiotypic networks: toward a renaissance?

Idiotypic networks, after being a dominating paradigm for more than a decade, have fallen out of fashion in parallel with the rapid success of molecular immunobiology. Today signs of a possible renaissance in idiotypic network studies are visible. For system biologists and also for physicists, the network idea remains attractive. Herein, a short account of the historical development of the paradigm is given. The necessary technical and conceptual ingredients for a theoretical description of idiotypic networks are briefly reviewed, and previous approaches are discussed. We also describe a minimalistic model developed in our group that allows for understanding the random evolution toward a highly non-trivial complex architecture. In the network, a connected large cluster of idiotype clones and many disconnected ones coexist, thus resembling the notion of central and peripheral parts proposed in the 'second-generation' version of the paradigm. The connected cluster consists of groups of idiotypic clones with clearly distinct statistical properties. The simplicity of the model allows for calculating the size of the groups and the number of inter- and intragroup links, which define the architecture. Aspects of idiotypic interactions in experimental medicine are discussed, along with the challenges to theory and experimentation.

Vaccination against the forkhead family transcription factor Foxp3 enhances tumor immunity

Depletion of CD4+CD25+ regulatory T cells (Treg) by treatment with alphaCD25 antibody synergizes with vaccination protocols to engender protective immunity in mice. The effectiveness of targeting CD25 to eliminate Treg is limited by the fact that CD25, the low-affinity interleukin-2 receptor, is up-regulated on conventional T cells. At present, foxp3 is the only product known to be exclusively expressed in Treg of mice. However, foxp3 is not expressed on the cell surface and hence cannot be targeted with antibodies. In this study, we tested the hypothesis that vaccination of mice against foxp3, a self-antigen expressed also in the thymus, is capable of stimulating foxp3-specific CTL that will cause the depletion of Treg and enhanced antitumor immunity. Vaccination of mice with foxp3 mRNA-transfected dendritic cells elicited a robust foxp3-specific CTL response and potentiated vaccine-induced protective immunity comparably with that of alphaCD25 antibody administration. In contrast to alphaCD25 antibody treatment, repeated foxp3 vaccination did not interfere with vaccine-induced protective immunity. Importantly, foxp3 vaccination led to the preferential depletion of foxp3-expressing Treg in the tumor but not in the periphery, whereas alphaCD25 antibody treatment led to depletion of Treg in both the tumor and the periphery. Targeting foxp3 by vaccination offers a specific and simpler protocol for the prolonged control of Treg that may be associated with reduced risk of autoimmunity, introducing an approach whereby specific depletion of cells is not limited to targeting products expressed on the cell surface.

Vaccines against myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease mediated by antibodies to nicotinic acetylcholine receptor (AChR) interfering with the neuromuscular transmission. Experimental autoimmune MG serves as an excellent animal model to study possible therapeutic modalities for MG. This review will focus on the different ways to turn off the autoimmune response to AChR, which results in suppression of myasthenia. This paper will describe the use of fragments or peptides derived from the AChR, antigen-presenting cells and anti-T cell receptor antibodies, and will discuss the underlying mechanisms of action. Finally, the authors propose new promising therapeutic prospects, including treatment based on the modulation of regulatory T cells, which have recently been found to be functionally defective in MG patients.

Anti-ergotypic Immunoregulation

T-cell vaccination (TCV) controls pathogenic autoimmune T-cell responses via two different regulatory cell populations: anti-idiotypic and anti-ergotypic T cells. Anti-idiotypic T cells recognize clone-specific determinants, like the CDR3 region of the T-cell receptor. Anti-ergotypic T cells recognize antigenic determinants derived from activation markers, which are upregulated by activated T cells, like CD25. In this review, we analyse the different components of the anti-ergotypic response: (1) the target T cells, which can be CD8+ or CD4+ T cells that express TCRalphabeta or TCRgammadelta; (2) the ergotope, which can be a T cell-restricted ergotope not expressed by other cell types or a widely expressed, shared ergotope and (3) the anti-ergotypic T cells, which are detectable in the naive immune system, but whose numbers can be expanded during the induction of an immune response against, or as a result of TCV or specific, anti-ergotypic vaccination. Finally, we discuss possible interactions between anti-ergotypic regulators and other regulatory T cells. We propose that the expression of major histocompatibility complex class II molecules by regulatory CD4+CD25+ T cells may make possible the cross-regulation of anti-ergotypic and CD4+CD25+ regulatory T cells, fine-tuning immunoregulation in the mature immune system.

Translating the concept of suppressor/regulatory T cells to clinical applications

The in vivo expansion of suppressor/regulatory T cells (Tregs) is a desirable event in autoimmunity and transplantation. Here we summarize the general rules involved in antigen recognition by T cells and describe Tregs and their requirements, discussing different levels of immune intervention.

Recombinant idiotypic TCRβ chain immunization in mice generates antigen specific T cell response

Vaccination remains the most cost-effective means of preventing infectious diseases. Success of vaccination depends on generation of effective memory response. Understanding the mechanism of generation and maintenance of immunological memory would help in the design of rational vaccines. T lymphocytes play a central role in the generation of protective immune response against many microbial infections. A hypothesis known as relay hypothesis was earlier proposed, which explains the maintenance of immunological memory through interaction of idiotypic and anti-idiotypic lymphocytes. In the present study, we have shown that immunization with a model antigen, chicken ovalbumin specific T cell receptor beta chain (idiotypic TCR) generates TCR specific antibody and anti-idiotypic T cell responses as well as ovalbumin specific T cell response. We further show that boosting of ovalbumin primed mice with ovalbumin specific idiotypic TCRbeta DNA or TCRbeta protein gives memory response for ovalbumin. This study provides experimental evidence for perpetuation of immunological memory through idiotypic network interactions.

CD4+ regulatory T cell responses induced by T cell vaccination in patients with multiple sclerosis

Immunization with irradiated autologous T cells (T cell vaccination) is shown to induce regulatory T cell responses that are poorly understood. In this study, CD4(+) regulatory T cell lines were generated from patients with multiple sclerosis that received immunization with irradiated autologous myelin basic protein-reactive T cells. The resulting CD4(+) regulatory T cell lines had marked inhibition on autologous myelin basic protein-reactive T cells and displayed two distinctive patterns distinguishable by the expression of transcription factor Foxp3 and cytokine profile. The majority of the T cell lines had high Foxp3 expression and secreted both IFN-gamma and IL-10 as compared with the other pattern characteristic of low Foxp3 expression and predominant production of IL-10 but not IFN-gamma. CD4(+) regulatory T cell lines of both patterns expressed CD25 and reacted with activated autologous T cells but not resting T cells, irrespective of antigen specificity of the target T cells. It was evident that they recognized preferentially a synthetic peptide corresponding to residues 61-73 of the IL-2 receptor alpha chain. T cell vaccination correlated with increased Foxp3 expression and T cell reactivity to peptide 61-73. The findings have important implications in the understanding of the role of CD4(+) regulatory T cell response induced by T cell vaccination.

Achieving antigen-specific tolerance in diabetes: regulating specifically

Autoreactive T cells that escape negative selection in the thymus do not normally cause productive immune responses to self-antigens because of a number of regulatory mechanisms. Studies with anti-CD3 monoclonal antibodies (mAbs) have suggested that immune regulatory mechanisms are induced by drug treatments that are able to stop on-going unwanted immune responses, such as type 1 diabetes, involving induction of regulatory T cells. TGF-beta dependent and independent mechanisms have been described involving CD4(+) as well as CD8(+) T cells. The challenge is now to apply these mechanisms in an antigen-specific manner and so that lasting tolerance to the autoimmune responses can be maintained. We discuss recent data concerning the mechanisms of anti-CD3 mAb treatment and the ways in which our understanding of these mechanisms can be used to develop adoptive immune therapy with regulatory T cells to treat patients with type 1 diabetes or other autoimmune diseases.

Foxp3-transduced polyclonal regulatory T cells protect against chronic renal injury from adriamycin

Chronic proteinuric renal injury is a major cause of ESRD. Adriamycin nephropathy is a murine model of chronic proteinuric renal disease whereby chemical injury is followed by immune and structural changes that mimic human disease. Foxp3 is a gene that induces a regulatory T cell (Treg) phenotype. It was hypothesized that Foxp3-transduced Treg could protect against renal injury in Adriamycin nephropathy. CD4+ T cells were transduced with either a Foxp3-containing retrovirus or a control retrovirus. Foxp3-transduced T cells had a regulatory phenotype by functional and phenotypic assays. Adoptive transfer of Foxp3-transduced T cells protected against renal injury. Urinary protein excretion and serum creatinine were reduced (P<0.05), and there was significantly less glomerulosclerosis, tubular damage, and interstitial infiltrates (P<0.01). It is concluded that Foxp3-transduced Treg cells may have a therapeutic role in protecting against immune injury and disease progression in chronic proteinuric renal disease.

Heat shock proteins as endogenous adjuvants in sterile and septic inflammation

Heat shock proteins (HSPs) have been reported to stimulate the immune system via innate receptors. However, the role of HSPs as endogenous adjuvants has been challenged by reports claiming that pure HSPs are not innate ligands; it is only the bacterial molecules trapped by the HSPs that can signal the innate immune system. In this review, we discuss data suggesting that both views, in essence, are correct; pure HSPs are indeed innate immunostimulators, but HSPs can also function as transducers of pathogen signals. In other words, HSPs perform diverse functions in two alternative modes of inflammation: sterile inflammation, which results from endogenous stimuli and is necessary for body maintenance, and septic inflammation, which protects us from environmental pathogens. Endogenous HSPs are key players in the modulation of these two modes of inflammation, and as such, they are potential targets for new and more efficient therapies for cancer, infections, and autoimmunity.

Tolerogenic immune responses to novel T-cell epitopes from heat-shock protein 60 in juvenile idiopathic arthritis

BACKGROUND

Juvenile idiopathic arthritis is a heterogeneous autoimmune disease characterised by chronic inflammation of one or more joints. In patients with this disease, T-cell reactivity to autologous heat-shock protein 60 (HSP60) is associated with a favourable prognosis. We sought to identify HSP60 T-cell epitopes to find potential targets for HSP60 immunotherapy and to assess whether immune responses to these epitopes contribute to the distinct clinical outcome of this disease.

METHODS

We identified eight potential epitopes using a computer algorithm from both self and microbial HSP60 binding to many HLA-DR molecules. We analysed the pattern of T-cell responses induced by these HSP60 peptides in peripheral-blood mononuclear cells (PBMC) of 57 patients with juvenile idiopathic arthritis, 27 healthy controls, and 20 disease controls. We undertook in-vitro MHC binding studies with the identified peptides, and HLA class II typing of a subset of patients with juvenile idiopathic arthritis.

FINDINGS

Five of the eight peptides identified yielded proliferative T-cell responses in 50-70% of PBMC from patients with juvenile idiopathic arthritis irrespective of MHC genotype, but not in PBMC from healthy or disease controls. Although PBMC from both patients with juvenile idiopathic arthritis and healthy controls produced interferon gamma in response to these peptides, only PBMC from patients with the disease produced interleukin 10.

INTERPRETATION

The recorded T-cell-induction in juvenile idiopathic arthritis is tolerogenic. In patients with oligoarticular disease, the immune responses to the HSP60 epitopes identified could contribute to disease remission.

RELEVANCE TO PRACTICE

The broad recognition of these HSP60 epitopes in a population of patients with polymorphic MHC genotypes opens the way for HSP60-peptide immunotherapy, representing a novel treatment option to specifically modulate the immune system in patients with juvenile idiopathic arthritis.

DNA vaccines coding for heat-shock proteins (HSPs): tools for the activation of HSP-specific regulatory T cells

Heat-shock proteins (HSPs) perform opposing functions in autoimmune arthritis. HSP-specific T cells drive the progression of adjuvant arthritis (AA), an experimental model of autoimmune arthritis. However, HSP-specific T cells can also have a regulatory phenotype, controlling arthritogenic T cells and inhibiting AA progression. This manuscript reviews the use of DNA vaccines coding for HSPs to analyse the role of these proteins in the regulation of arthritis. Recent studies suggest that HSPs participate in the control of pathological autoimmunity. Indeed, DNA vaccines coding for HSPs can be used to activate these HSP-specific built-in regulatory mechanisms. Thus, DNA vaccines coding for HSPs may serve not only as tools for the dissection of immunoregulatory mechanisms, but also as agents for the treatment of autoimmune disorders.

An integrated view of suppressor T cell subsets in immunoregulation

The immune system evolved to protect organisms from a virtually infinite variety of disease-causing agents but to avoid harmful responses to self. Because immune protective mechanisms include the elaboration of potent inflammatory molecules, antibodies, and killer cell activation--which together can not only destroy invading microorganisms, pathogenic autoreactive cells, and tumors, but also mortally injure normal cells--the immune system is inherently a "double-edged sword" and must be tightly regulated. Immune response regulation includes homeostatic mechanisms intrinsic to the activation and differentiation of antigen-triggered immunocompetent cells and extrinsic mechanisms mediated by suppressor cells. This review series will focus on recent advances indicating that distinct subsets of regulatory CD4+ and CD8+ T cells as well as NK T cells control the outgrowth of potentially pathogenic antigen-reactive T cells and will highlight the evidence that these suppressor T cells may play potentially important clinical roles in preventing and treating immune-mediated disease. Here we provide a historical overview of suppressor cells and the experimental basis for the existence of functionally and phenotypically distinct suppressor subsets. Finally, we will speculate on how the distinct suppressor cell subsets may function in concert to regulate immune responses.