Peptide-induced T-cell tolerance to prevent autoimmune diabetes in a transgenic mouse model

Tissue-resident memory CD8+ T cells cooperate with CD4+ T cells to drive compartmentalized immunopathology in the CNS

In chronic inflammatory diseases of the central nervous system (CNS), immune cells persisting behind the blood-brain barrier are supposed to promulgate local tissue destruction. The drivers of such compartmentalized inflammation remain unclear, but tissue-resident memory T cells (T_RM) represent a potentially important cellular player in this process. Here, we investigated whether resting CD8⁺ T_RM persisting after cleared infection with attenuated lymphocytic choriomeningitis virus (LCMV) can initiate immune responses directed against cognate self-antigen in the CNS. We demonstrated that time-delayed conditional expression of the LCMV glycoprotein as neo-self-antigen by glia cells reactivated CD8⁺ T_RM. Subsequently, CD8⁺ T_RM expanded and initiated CNS inflammation and immunopathology in an organ-autonomous manner independently of circulating CD8⁺ T cells. However, in the absence of CD4⁺ T cells, TCF-1⁺ CD8⁺ T_RM failed to expand and differentiate into terminal effectors. Similarly, in human demyelinating CNS autoimmune lesions, we found CD8⁺ T cells expressing TCF-1 that predominantly exhibited a T_RM-like phenotype. Together, our study provides evidence for CD8⁺ T_RM-driven CNS immunopathology and sheds light on why inflammatory processes may evade current immunomodulatory treatments in chronic autoimmune CNS conditions.

CD4+ T cell activation and concomitant mTOR metabolic inhibition can ablate microbiota-specific memory cells and prevent colitis

Microbiota-reactive CD4⁺ T memory (T_M) cells are generated during intestinal infections and inflammation, and can revert to pathogenic CD4⁺ T effector (T_E) cells, resulting in chronicity of inflammatory bowel disease (IBD). Unlike T_E cells, T_M cells have a low rate of metabolism unless they are activated by reencountering cognate antigen. Here, we show that the combination of cell activation and metabolic checkpoint inhibition (CAMCI), by targeting key metabolic regulators mTORC and AMPK, resulted in cell death and anergy, but enhanced the induction of the regulatory subset. Parenteral application of this treatment with a synthetic peptide containing multiple flagellin T cell epitopes (MEP1) and metabolic inhibition successfully prevented the development of CD4⁺ T cell-driven colitis. Microbiota-specific CD4⁺ T cells, especially the pathogenic T_E subsets, were decreased 10-fold in the intestinal lamina propria. Furthermore, using the CAMCI strategy, we were able to prevent antigen-specific T_M cell formation upon initial antigen encounter, and ablate existing T_M cells upon reactivation in mice, leading to an altered transcriptome in the remaining CD4⁺ T cells after ablation. Microbiota flagellin-specific CD4⁺ T cells from patients with Crohn's disease were ablated in a similar manner after CAMCI in vitro, with half of the antigen-specific T cells undergoing cell death. These results indicate that parenteral activation of microbiota-specific CD4⁺ T cells with concomitant metabolic inhibition is an effective way to ablate pathogenic CD4⁺ T_M cells and to induce T regulatory (T_reg) cells that provide antigen-specific and bystander suppression, supporting a potential immunotherapy to prevent or ameliorate IBD.

Viral Infections and Autoimmune Disease: Roles of LCMV in Delineating Mechanisms of Immune Tolerance

Viral infections are a natural part of our existence. They can affect us in many ways that are the result of the interaction between the viral pathogen and our immune system. Most times, the resulting immune response is beneficial for the host. The pathogen is cleared, thus protecting our vital organs with no other consequences. Conversely, the reaction of our immune system against the pathogen can cause organ damage (immunopathology) or lead to autoimmune disease. To date, there are several mechanisms for virus-induced autoimmune disease, including molecular mimicry and bystander activation, in support of the “fertile field” hypothesis (terms defined in our review). In contrast, viral infections have been associated with protection from autoimmunity through mechanisms that include Treg invigoration and immune deviation, in support of the “hygiene hypothesis”, also defined here. Infection with lymphocytic choriomeningitis virus (LCMV) is one of the prototypes showing that the interaction of our immune system with viruses can either accelerate or prevent autoimmunity. Studies using mouse models of LCMV have helped conceive and establish several concepts that we now know and use to explain how viruses can lead to autoimmune activation or induce tolerance. Some of the most important mechanisms established during the course of LCMV infection are described in this short review.

Naturally presented HLA class I-restricted epitopes from the neurotrophic factor S100-β are targets of the autoimmune response in type 1 diabetes

Type 1 diabetes (T1D) results from the destruction of pancreatic β-cells by the immune system, and CD8⁺ T lymphocytes are critical actors in this autoimmune response. Pancreatic islets are surrounded by a mesh of nervous cells, the peri-insular Schwann cells, which are also targeted by autoreactive T lymphocytes and express specific antigens, such as the neurotrophic factor S100-β. Previous work has shown increased proliferative responses to whole S100-β in both human T1D patients and the nonobese diabetic (NOD) mouse model. We describe for the first time naturally processed and presented epitopes (NPPEs) presented by class I human leukocyte antigen–A*02:01 (A2.1) molecules derived from S100-β. These NPPEs triggered IFN-γ responses more frequently in both newly diagnosed and long-term T1D patients compared with healthy donors. Furthermore, the same NPPEs are recognized during the autoimmune response leading to diabetes in A2.1-transgenic NOD mice as early as 4 wk of age. Interestingly, when these NPPEs are used to prevent diabetes in this animal model, an acceleration of the disease is observed together with an exacerbation in insulitis and an increase in S100-β–specific cytotoxicity in vaccinated animals. Whether these can be used in diabetes prevention needs to be carefully evaluated in animal models before use in future clinical assays.—Calviño-Sampedro, C., Gomez-Tourino, I., Cordero, O. J., Reche, P. A., Gómez-Perosanz, M., Sánchez-Trincado, J. L., Rodríguez, M. Á., Sueiro, A. M., Viñuela, J. E., Calviño, R. V. Naturally presented HLA class I–restricted epitopes from the neurotrophic factor S100-β are targets of the autoimmune response in type 1 diabetes.

Engineered erythrocytes covalently linked to antigenic peptides can protect against autoimmune disease

Current therapies for autoimmune diseases rely on traditional immunosuppressive medications that expose patients to an increased risk of opportunistic infections and other complications. Immunoregulatory interventions that act prophylactically or therapeutically to induce antigen-specific tolerance might overcome these obstacles. Here we use the transpeptidase sortase to covalently attach disease-associated autoantigens to genetically engineered and to unmodified red blood cells as a means of inducing antigen-specific tolerance. This approach blunts the contribution to immunity of major subsets of immune effector cells (B cells, CD4⁺ and CD8⁺ T cells) in an antigen-specific manner. Transfusion of red blood cells expressing self-antigen epitopes can alleviate and even prevent signs of disease in experimental autoimmune encephalomyelitis, as well as maintain normoglycemia in a mouse model of type 1 diabetes.

Coherent somatic mutation in autoimmune disease

BACKGROUND

Many aspects of autoimmune disease are not well understood, including the specificities of autoimmune targets, and patterns of co-morbidity and cross-heritability across diseases. Prior work has provided evidence that somatic mutation caused by gene conversion and deletion at segmentally duplicated loci is relevant to several diseases. Simple tandem repeat (STR) sequence is highly mutable, both somatically and in the germ-line, and somatic STR mutations are observed under inflammation.

RESULTS

Protein-coding genes spanning STRs having markers of mutability, including germ-line variability, high total length, repeat count and/or repeat similarity, are evaluated in the context of autoimmunity. For the initiation of autoimmune disease, antigens whose autoantibodies are the first observed in a disease, termed primary autoantigens, are informative. Three primary autoantigens, thyroid peroxidase (TPO), phogrin (PTPRN2) and filaggrin (FLG), include STRs that are among the eleven longest STRs spanned by protein-coding genes. This association of primary autoantigens with long STR sequence is highly significant (p<3.0x10(-7)). Long STRs occur within twenty genes that are associated with sixteen common autoimmune diseases and atherosclerosis. The repeat within the TTC34 gene is an outlier in terms of length and a link with systemic lupus erythematosus is proposed.

CONCLUSIONS

The results support the hypothesis that many autoimmune diseases are triggered by immune responses to proteins whose DNA sequence mutates somatically in a coherent, consistent fashion. Other autoimmune diseases may be caused by coherent somatic mutations in immune cells. The coherent somatic mutation hypothesis has the potential to be a comprehensive explanation for the initiation of many autoimmune diseases.

Autoimmune responses in T1DM: quantitative methods to understand onset, progression, and prevention of disease

Understanding the physiological processes that underlie autoimmune disorders and identifying biomarkers to predict their onset are two pressing issues that need to be thoroughly sorted out by careful thought when analyzing these diseases. Type 1 diabetes (T1D) is a typical example of such diseases. It is mediated by autoreactive cytotoxic CD4⁺ and CD8⁺ T-cells that infiltrate the pancreatic islets of Langerhans and destroy insulin-secreting β-cells, leading to abnormal levels of glucose in affected individuals. The disease is also associated with a series of islet-specific autoantibodies that appear in high-risk subjects (HRS) several years prior to the onset of diabetes-related symptoms. It has been suggested that T1D is relapsing-remitting in nature and that islet-specific autoantibodies released by lymphocytic B-cells are detectable at different stages of the disease, depending on their binding affinity (the higher, the earlier they appear). The multifaceted nature of this disease and its intrinsic complexity make this disease very difficult to analyze experimentally as a whole. The use of quantitative methods, in the form of mathematical models and computational tools, to examine the disease has been a very powerful tool in providing predictions and insights about the underlying mechanism(s) regulating its onset and development. Furthermore, the models developed may have prognostic implications by aiding in the enrollment of HRS into trials for T1D prevention. In this review, we summarize recent advances made in determining T- and B-cell involvement in T1D using these quantitative approaches and delineate areas where mathematical modeling can make further contributions in unraveling certain aspect of this disease.

Quantifying the importance of pMHC valency, total pMHC dose and frequency on nanoparticle therapeutic efficacy

Nanoparticles (NPs) coated with β-cell-specific peptide major histocompatibility complex (pMHC) class I molecules can effectively restore normoglycemia in spontaneously diabetic nonobese diabetic mice. They do so by expanding pools of cognate memory autoreactive regulatory CD8+ T cells that arise from naive low-avidity T-cell precursors to therapeutic levels. Here we develop our previously constructed mathematical model to explore the effects of compound design parameters (NP dose and pMHC valency) on therapeutic efficacy with the underlying hypothesis that the functional correlates of the therapeutic response (expansion of autoregulatory T cells and deletion of autoantigen-loaded antigen-presenting cells by these T cells) are biphasic. We show, using bifurcation analysis, that the model exhibits a 'resonance'-like behavior for a given range of NP dose in which bistability between the healthy state (possessing zero level of effector T-cell population) and autoimmune state (possessing elevated level of the same population) disappears. A heterogeneous population of model mice subjected to several treatment protocols under these new conditions is conducted to quantify both the average percentage of autoregulatory T cells in responsive and nonresponsive model mice, and the average valency-dependent minimal optimal dose needed for effective therapy. Our results reveal that a moderate increase (≥1.6-fold) in the NP-dependent expansion rate of autoregulatory T-cell population leads to a significant increase in the efficacy and the area corresponding to the effective treatment regimen, provided that NP dose ≥8 μg. We expect the model developed here to generalize to other autoimmune diseases and serve as a computational tool to understand and optimize pMHC-NP-based therapies.

Viruses and cytotoxic T lymphocytes in type 1 diabetes

Histopathological studies on pancreas tissues from individuals with recent-onset type 1 diabetes (T1D) consistently find that CD8 T cells substantially contribute to the formation of islet lesions. CD8 T cells reactive against islet-associated antigens can also be found in blood samples from T1D patients. Mechanistic studies on the pathogenic role of this T cell subset have mostly focused on two animal models, i.e., the non-obese diabetic mouse and the virally induced rat insulin promoter-lymphocytic choriomeningitis virus model. Data were obtained in support of a role for viral infection in expanding a population of diabetogenic cytotoxic T lymphocytes. In view of the theorized association of viral infection with initiation of islet autoimmunity and progression to clinically overt disease, CD8 T cells thus represent an attractive target for immunotherapy. We will review here arguments in favor of a pivotal role for CD8 T cells in driving T1D development and speculate on etiologic agents that may provoke their aberrant activation.

Acute and chronic animal models for the evaluation of anti-diabetic agents

Diabetes mellitus is a potentially morbid condition with high prevalence worldwide thus being a major medical concern. Experimental induction of diabetes mellitus in animal models is essential for the advancement of our knowledge and understanding of the various aspects of its pathogenesis and ultimately finding new therapies and cure. Experimental diabetes mellitus is generally induced in laboratory animals by several methods that include: chemical, surgical and genetic (immunological) manipulations. Most of the experiments in diabetes are carried out in rodents, although some studies are still performed in larger animals. The present review highlights the various methods of inducing diabetes in experimental animals in order to test the newer drugs for their anti-diabetic potential.

In situ induction of dendritic cell-based T cell tolerance in humanized mice and nonhuman primates

Administration of an ICAM-1–specific antibody arrests dendritic cells in a semi-immature state and facilitates antigen-specific T cell tolerance to islet allografts in humanized mice and Rhesus monkeys.

Induction of antigen-specific T cell tolerance would aid treatment of diverse immunological disorders and help prevent allograft rejection and graft versus host disease. In this study, we establish a method of inducing antigen-specific T cell tolerance in situ in diabetic humanized mice and Rhesus monkeys receiving porcine islet xenografts. Antigen-specific T cell tolerance is induced by administration of an antibody ligating a particular epitope on ICAM-1 (intercellular adhesion molecule 1). Antibody-mediated ligation of ICAM-1 on dendritic cells (DCs) led to the arrest of DCs in a semimature stage in vitro and in vivo. Ablation of DCs from mice completely abrogated anti–ICAM-1–induced antigen-specific T cell tolerance. T cell responses to unrelated antigens remained unaffected. In situ induction of DC-mediated T cell tolerance using this method may represent a potent therapeutic tool for preventing graft rejection.

Induction of insert-specific immune response in mice by hamster polyomavirus VP1 derived virus-like particles carrying LCMV GP33 CTL epitope

Hamster polyomavirus (HaPyV) major capsid protein VP1 based chimeric virus-like particles (VLPs) carrying model GP33 CTL epitope derived from Lymphocytic choriomeningitis virus (LCMV) were generated in yeast and examined for their capability to induce CTL response in mice. Chimeric VP1-GP33 VLPs were effectively processed in antigen presenting cells in vitro and in vivo and induced antigen-specific CD8+ T cell proliferation. Mice immunized only once with VP1-GP33 VLPs without adjuvant developed an effective GP33-specific memory T cell response: 70% were fully and 30% partially protected from LCMV infection. Moreover, aggressive growth of tumors expressing GP33 was significantly delayed in these mice in vivo. Therefore, HaPyV VP1-derived VLP harboring CTL epitopes are attractive vaccine candidates for the induction of insert-specific CTL immune response.

Immunological perspective of self versus tumor antigens: insights from the RIP-gp model

Self-reactive T cells in the body are controlled by mechanisms of peripheral tolerance that limit their activation and induction of immune pathology. Our understanding of these mechanisms has been advanced by the use of tissue-specific promoters to express neo-self-antigens. Here, we present findings using the RIP-gp (rat insulin promoter-glycoprotein) transgenic mouse, which expresses the lymphocytic choriomeningitis virus glycoprotein (LCMV-gp) specifically in the pancreatic β islet cells. T cells responsive to this antigen remain ignorant of the LCMV-gp expressed by the islets, and breaking tolerance is dependent upon the maturation status of antigen-presenting cells, the avidity of the T-cell receptor ligation, and the level of major histocompatibility complex expression in the pancreas. Furthermore, decreased activity of Casitas B-lineage lymphoma b, a negative regulator of T-cell receptor signaling, can allow recognition and destruction of the pancreatic islets. This review discusses the roles of these factors in the context of anti-tissue responses, both in the setting of autoimmunity and in anti-tumor immunity.

Peptide-MHC-based nanovaccines for the treatment of autoimmunity: a "one size fits all" approach?

Nanotechnology offers enormous potential in drug delivery and in vivo imaging. Nanoparticles (NPs), for example, are being extensively tested as scaffolds to deliver anti-cancer therapeutics or imaging tags. Our recent work, discussed herein, indicates that an opportunity exists to use NPs to deliver ligands for, and trigger, cognate receptors on T lymphocytes as a way to induce therapeutic immune responses in vivo. Specifically, systemic delivery of NPs coated with Type 1 diabetes (T1D)-relevant peptide-major histocompatibility complex molecules triggered the expansion of cognate memory autoregulatory (disease-suppressing) T cells, suppressed the progression of autoimmune attack against insulin-producing beta cells, and restored glucose homeostasis. This therapeutic avenue exploits a new paradigm in the progression of chronic autoimmune responses that enables the rational design of disease-specific "nanovaccines" capable of blunting autoimmunity without impairing systemic immunity, a long sought-after goal in the therapy of these disorders. Here, we discuss the research paths that led to the discovery of this therapeutic avenue and highlight the features that make it an attractive approach for the treatment, in an antigen-specific manner, of a whole host of autoimmune diseases.

On how monospecific memory-like autoregulatory CD8+ T cells can blunt diabetogenic autoimmunity: a computational approach

We have recently shown that during progression to autoimmune diabetes in NOD mice, memory autoreactive regulatory CD8(+) T cells arising from low-avidity precursors can be expanded to therapeutic levels using nanoparticles coated with disease-relevant peptide-major histocompatibility complexes (pMHCs). Here we examine the dynamics of memory autoregulatory CD8(+) T cells specific for islet-specific glucose-6-phosphatase catalytic subunit-related protein(206-214), a prevalent β cell autoantigen; their high-avidity counterparts (dominant effectors); and all other autoreactive non-islet-specific glucose-6-phosphatase catalytic subunit-related protein(206-214)-specific CD8(+) T cell specificities (subdominant effectors) in response to pMHC-coated nanoparticle (pMHC-nanoparticle) therapy. We combine experimental data with mathematical modeling to investigate the clonal competition dynamics of these T cell pools. To mimic the response diversity observed in NOD mice, we simulated many individual mice, using a wide range of parameters, and averaged the results as done experimentally. We find that under certain circumstances, pMHC-nanoparticle-induced expansion of autoregulatory CD8(+) T cells can effectively suppress the expansion of dominant and subdominant effectors simultaneously but, in some few cases, can lead to the substitution (or switching) of one effector population by another. The model supports the idea that disease suppression is based on the elimination of autoantigen-loaded APCs by the expanded autoregulatory CD8(+) T cells. The model also predicts that treatment strategies that operate by selectively inhibiting autoantigen-loaded APCs, such as the pMHC-nanoparticle approach, have the highest promise to blunt polyclonal, multiantigen-specific autoimmune responses in vivo without impairing systemic immunity.

TRAIL-expressing CD8+ T cells mediate tolerance following soluble peptide-induced peripheral T cell deletion

Peripheral tolerance controls the action of self-reactive T cells that escape thymic deletion. We showed previously that deletion of Ag-specific CD4+ T cells induced a CD8+ T(reg) population that maintained tolerance by deleting T cells with the same Ag specificity. The present study explored the mechanism of action of these CD8+ T(reg). Following OT-II T cell deletion by soluble OVA₃₂₃₋₃₃₉, B6 mice were unresponsive to challenge after CFA/OVA immunization, and Trail⁻/⁻ or Dr5⁻/⁻ mice were immune, although all strains displayed similar OT-II peripheral deletion. Interestingly, B6 mice remained tolerant to OVA even after a second infusion of OT-II T cells. Tolerance could be transferred to naïve recipients using CD8+ T cells from B6 or Dr5⁻/⁻ mice that experienced peptide-induced peripheral OT-II deletion but not from Trail⁻/⁻ mice. Subsequent investigation found that the mechanism of action of the CD8+ T(reg) was TRAIL-mediated OT-II T cell deletion in a TCR-specific manner. Furthermore, the tolerance was transient, as it was established by 14 days after peptide injection but lost by Day 56. Together, these data provide evidence to suggest that the mechanism behind transient peripheral tolerance induced following T cell deletion is the cytotoxic activity of TRAIL-expressing CD8+ T(reg).

The use of mouse models to better understand mechanisms of autoimmunity and tolerance

A major emphasis of our studies has been on developing a better understanding of how and why the skin serves as a target for immune reactions as well as how the skin evades becoming a target for destruction. For these studies we developed transgenic mice that express a membrane-tethered form of a model self antigen, chicken ovalbumin (mOVA), under the control of a keratin 14 (K14) promoter. K14-mOVA transgenic mice that express OVA mRNA and protein in the epithelia have been assessed for their immune responsiveness to OVA and are being used as targets for T cells obtained from OT-1 transgenic mice whose CD8+ T cells carry a Vα2/Vβ5-transgenic T cell receptor with specificity for the OVA(257-264)-peptides (OVAp) in association with class I MHC antigens. Some of the K14-mOVA transgenic mice develop a graft-versus-host-like disease (GvHD) when the OT-1 cells are injected while others appear to be tolerant to the OT-1 cells. We found that γc cytokines, especially IL-15, determine whether autoimmunity or tolerance ensues in K14-mOVA Tg mice. We also developed transgenic mice that express soluble OVA under the control of a K14 promoter (K14-sOVA) that die within 5-8 days after adoptive transfer of OT-1 cells and identified these mice as a model for more acute GvHD-like reactions. Spontaneous autoimmunity occurs when these K14-sOVA mice are crossed with the OT-I mice. In contrast, we found that preventive or therapeutic OVAp injections induced a dose-dependent increase in survival. In this review the characterization of 5 strains of K14-OVATg mice and underlying mechanisms involved in autoimmune reactions in these Tg mice are discussed. We also describe a strategy to break tolerance and describe how the autoimmunity can be obviated using OVAp. Finally, a historical overview of using transgenic mice to assess the mechanisms of tolerance is also provided.

CTL induction by cross-priming is restricted to immunodominant epitopes

CTL are induced by two pathways, i.e. direct priming, where tumor cells present tumor antigens to naïve specific CTL, and cross-priming, where professional APC cross-present captured tumor antigens to CTL. Here, we examined direct priming versus cross-priming after immunizing (H-2(b) x H-2(d)) F1 mice with either H-2(b) or H-2(d) positive tumor cells transfected with the GP or nucleoprotein (NP) of lymphocytic choriomeningitis virus (LCMV). Cross-priming was observed for the immunodominant epitopes LCMV-gp33 and -np118, although direct induction resulted in higher CTL frequencies. In contrast, CTL specific for the subdominant epitopes LCMV-gp283 or -np396 were induced only if epitopes were presented directly on MHC class I molecules of the immunizing cell. The broader repertoire and the higher CTL frequencies induced after vaccination with haplotype-matched tumor cells resulted in more efficient anti-tumor and antiviral protection. Firstly, our results indicate that certain virus and tumor antigens may not be detected by CD8(+) T cells because of impaired cross-priming. Secondly, efficient cross-priming contributes to the immunodominant nature of a tumor-specific CTL epitope. Thirdly, vaccine strategies using autologous or syngenic antigen-expressing cells induce a broader repertoire of tumor-specific CTL and higher CTL frequencies.

Antigen controls IL-7R alpha expression levels on CD8 T cells during full activation or tolerance induction

The high-affinity chain of the IL-7 receptor, IL-7Ralpha (CD127), is expressed by effector CD8 T cells that have the capacity to become memory cells. IL-7Ralpha expression is uniformly high on naive CD8 T cells, and the majority of these cells down-regulate expression upon antigenic challenge. At the peak of expansion, the fraction of effectors expressing high IL-7Ralpha varies depending on the response examined. The signals that a CD8 T cell receives during a response to Ag that lead to altered expression of IL-7Ralpha have not been fully defined. In vitro experiments demonstrated that Ag alone is sufficient to down-regulate IL-7Ralpha on all cells and most of the cells rapidly re-express the receptor upon removal from Ag. Expression was not altered by the B7.1 costimulatory ligand or when IL-12 was present to provide the signal needed for development of effector functions, indicating that TCR engagement is sufficient to regulate IL-7Ralpha expression. Consistent with this, in vivo priming with peptide Ag resulted in IL-7Ralpha expression that inversely correlated with Ag levels, and expression levels were not changed when IL-12 or adjuvant were administered with Ag. A large fraction of the cells present at the peak of expansion had re-expressed IL-7Ralpha, but most of these cells failed to survive; those that did survive expressed high IL-7Ralpha levels. Thus, Ag-dependent signals regulate IL-7Ralpha levels on responding CD8 T cells, and this occurs whether the responding cells become fully activated or are rendered tolerant by administration of peptide Ag alone.

CD8+ CTL priming by exact peptide epitopes in incomplete Freund's adjuvant induces a vanishing CTL response, whereas long peptides induce sustained CTL reactivity

Therapeutic vaccination trials, in which patients with cancer were vaccinated with minimal CTL peptide in oil-in-water formulations, have met with limited success. Many of these studies were based on the promising data of mice studies, showing that vaccination with a short synthetic peptide in IFA results in protective CD8(+) T cell immunity. By use of the highly immunogenic OVA CTL peptide in IFA as a model peptide-based vaccine, we investigated why minimal CTL peptide vaccines in IFA performed so inadequately to allow full optimization of peptide vaccination. Injection of the minimal MHC class I-binding OVA(257-264) peptide in IFA transiently activated CD8(+) effector T cells, which eventually failed to undergo secondary expansion or to kill target cells, as a result of a sustained and systemic presentation of the CTL peptides gradually leaking out of the IFA depot without systemic danger signals. Complementation of this vaccine with the MHC class II-binding Th peptide (OVA(323-339)) restored both secondary expansion and in vivo effector functions of CD8(+) T cells. Simply extending the CTL peptide to a length of 30 aa also preserved these CD8(+) T cell functions, independent of T cell help, because the longer CTL peptide was predominantly presented in the locally inflamed draining lymph node. Importantly, these functional differences were reproduced in two additional model Ag systems. Our data clearly show why priming of CTL with minimal peptide epitopes in IFA is suboptimal, and demonstrate that the use of longer versions of these CTL peptide epitopes ensures the induction of sustained effector CD8(+) T cell reactivity in vivo.

Molecular basis for checkpoints in the CD8 T cell response: tolerance versus activation

CD8 T cells specific for self-antigens are present in the peripheral lymphoid system and can contribute to autoimmunity or transplant rejection. Whether recognition of Ag leads to full activation, or to induction of tolerance, depends upon availability of cytokine at critical stages of the response. Signals provided by IL-12 and/or IFN-alpha/beta are required for activation of naïve CD8 T cells, and IL-2 is needed to sustain and further expand the effector cells if Ag persists. These critical signaling requirements provide new insights into the factors that regulate the CD8 T cell contributions to development of autoimmunity or rejection of transplants.

"Viral déjà vu" elicits organ-specific immune disease independent of reactivity to self

Autoimmune diseases are often precipitated by viral infections. Yet our current understanding fails to explain how viruses trigger organ-specific autoimmunity despite thymic tolerance extending to many non-lymphohematopoietic self antigens. Additionally, a key epidemiological finding needs to be explained: In genetically susceptible individuals, early childhood infections seem to predispose them to multiple sclerosis (MS) or type 1 diabetes years or even decades before clinical onset. In the present work, we show that the innate immune system of neonatal mice was sufficient to eliminate an attenuated lymphocytic choriomeningitis virus (LCMV) from most tissues except for the CNS, where the virus persisted in neurons (predisposing virus). Virus-specific cytotoxic T cells (CTLs) were neither deleted nor sufficiently primed to cause disease, but they were efficiently triggered in adulthood upon WT LCMV infection (precipitating virus). This defined sequence of viral infections caused severe CNS inflammation that was histomorphologically reminiscent of rasmussen encephalitis, a fatal human autoimmune disease. Yet disease in mice was mediated by antiviral CTLs targeting an epitope shared by the precipitating virus and the predisposing virus persisting in neurons (déjà vu). Thus the concept of "viral déjà vu" demonstrates how 2 related but independently encountered viral infections can cause organ-specific immune disease without molecular mimicry of self and without breaking self tolerance.

Tissue-resident memory CD8+ T cells can be deleted by soluble, but not cross-presented antigen

Under noninflammatory conditions, both naive and central memory CD8 T cells can be eliminated in the periphery with either soluble peptide or cross-presented Ag. Here, we assess the tolerance susceptibility of tissue-resident memory CD8 T cells in mice to these two forms of tolerogen. Soluble peptide specifically eliminated the majority of memory CD8 cells present in both lymphoid and extralymphoid tissues including lung and liver, but was unable to reduce the number present in the CNS. In contrast, systemic cross-presentation of Ag by dendritic cells resulted in successful elimination of memory cells only from the spleen, with no significant reduction in the numbers of tissue-resident memory cells in the lung. The fact that tissue-resident memory cells were unable to access cross-presented Ag suggests that either the memory cells in the lung do not freely circulate out of the tissue, or that they circulate through a region in the spleen devoid of cross-presented Ag. Thus, although tissue-resident memory cells are highly susceptible to tolerance induction, both the form of tolerogen and location of the T cells can determine their accessibility to tolerogen and the degree to which they are successfully deleted from specific tissues.

Prevention of diabetes by manipulation of anti-IGRP autoimmunity: high efficiency of a low-affinity peptide

Antigen therapy may hold great promise for the prevention of autoimmunity; however, most clinical trials have failed, suggesting that the principles guiding the choice of treatment remain ill defined. Here, we examine the antidiabetogenic properties of altered peptide ligands of CD8+ T cells recognizing an epitope of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP206-214), a prevalent population of autoreactive T cells in autoimmune diabetes. We show that islet-associated CD8+ T cells in nonobese diabetic mice recognize numerous IGRP epitopes, and that these cells have a role in the outcome of protocols designed to induce IGRP206-214-specific tolerance. Ligands targeting IGRP206-214-reactive T cells prevented disease, but only at doses that spared low-avidity clonotypes. Notably, near complete depletion of the IGRP206-214-reactive T-cell pool enhanced the recruitment of subdominant specificities and did not blunt diabetogenesis. Thus, peptide therapy in autoimmunity is most effective under conditions that foster occupation of the target organ lymphocyte niche by nonpathogenic, low-avidity clonotypes.

Among CXCR3 chemokines, IFN-gamma-inducible protein of 10 kDa (CXC chemokine ligand (CXCL) 10) but not monokine induced by IFN-gamma (CXCL9) imprints a pattern for the subsequent development of autoimmune disease

Infection of the pancreas with lymphocytic choriomeningitis virus results in rapid and differential expression among CXCR3 chemokines. IFN-gamma-inducible protein of 10 kDa (IP-10), in contrast with monokine induced by IFN-gamma and IFN-inducible T cell-alpha chemoattractant, is strongly expressed within 24 h postinfection. Blocking of IP-10, but not monokine induced by IFN-gamma, aborts severity of Ag-specific injury of pancreatic beta cells and abrogates type 1 diabetes. Mechanistically, IP-10 blockade impedes the expansion of peripheral Ag-specific T cells and hinders their migration into the pancreas. IP-10 expression was restricted to viruses infecting the pancreas and that are capable of causing diabetes. Hence, virus-induced organ-specific autoimmune diseases may be dependent on virus tropism and its ability to alter the local milieu by selectively inducing chemokines that prepare the infected tissue for the subsequent destruction by the adaptive immune response.

An Altered Self-Peptide with Superagonist Activity Blocks a CD8-Mediated Mouse Model of Type 1 Diabetes

T cell tolerance can be experimentally induced through administration of self-peptides with single amino acid substitution (altered peptide ligands or APLs). However, little is known about the effects of APLs on already differentiated autoreactive CD8+ T cells that play a pivotal role in the pathogenesis of autoimmune diabetes. We generated a panel of APLs derived from an influenza virus hemagglutinin peptide exhibiting in vitro functions ranging from antagonism to superagonism on specific CD8+ T cells. A superagonist APL was further characterized for its therapeutic activity in a transgenic mouse model of type 1 diabetes. When injected i.v. 1 day after the transfer of diabetogenic hemagglutinin-specific CD8+ T cells into insulin promoter-hemagglutinin transgenic mice, the superagonist APL proved more effective than the native hemagglutinin peptide in blocking diabetes. This protective effect was associated with an inhibition of CD8+ T cell cytotoxicity in vivo and with a decreased accumulation of these cells in the pancreas, leading to a marked reduction of intrainsulitis. In conclusion, a superagonist "self-peptide" APL was more effective than the native peptide in treating a CD8+ T cell-mediated diabetes model.

Tolerogenic dendritic cells

Dendritic cells (DCs) have several functions in innate and adaptive immunity. In addition, there is increasing evidence that DCs in situ induce antigen-specific unresponsiveness or tolerance in central lymphoid organs and in the periphery. In the thymus DCs generate tolerance by deleting self-reactive T cells. In peripheral lymphoid organs DCs also induce tolerance to antigens captured by receptors that mediate efficient uptake of proteins and dying cells. Uptake by these receptors leads to the constitutive presentation of antigens on major histocompatibility complex (MHC) class I and II products. In the steady state the targeting of DC antigen capture receptors with low doses of antigens leads to deletion of the corresponding T cells and unresponsiveness to antigenic rechallenge with strong adjuvants. In contrast, if a stimulus for DC maturation is coadministered with the antigen, the mice develop immunity, including interferon-gamma-secreting effector T cells and memory T cells. There is also new evidence that DCs can contribute to the expansion and differentiation of T cells that regulate or suppress other immune T cells. One possibility is that distinct developmental stages and subsets of DCs and T cells can account for the different pathways to peripheral tolerance, such as deletion or suppression. We suggest that several clinical situations, including autoimmunity and certain infectious diseases, can be influenced by the antigen-specific tolerogenic role of DCs.

Tumor growth enhances cross-presentation leading to limited T cell activation without tolerance

Using a tumor model of spontaneously arising insulinomas expressing a defined tumor-associated antigen, we investigated whether tumor growth promotes cross-presentation and tolerance of tumor-specific T cells. We found that an advanced tumor burden enhanced cross-presentation of tumor-associated antigens to high avidity tumor-specific T cells, inducing T cell proliferation and limited effector function in vivo. However, contrary to other models, tumor-specific T cells were not tolerized despite a high tumor burden. In fact, in tumor-bearing mice, persistence and responsiveness of adoptively transferred tumor-specific T cells were enhanced. Accordingly, a potent T cell-mediated antitumor response could be elicited by intravenous administration of tumor-derived peptide and agonistic anti-CD40 antibody or viral immunization and reimmunization. Thus, in this model, tumor growth promotes activation of high avidity tumor-specific T cells instead of tolerance. Therefore, the host remains responsive to T cell immunotherapy.

Myelin-specific tolerance attenuates the progression of a virus-induced demyelinating disease: implications for the treatment of MS

Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD), a multiple sclerosis (MS) model, is a central nervous system (CNS) demyelinating disease characterized by early peripheral T cell responses to virus epitopes which spreads to myelin epitopes during chronic disease. We show that CD4(+) T cells isolated from the spinal cords of chronically infected SJL mice proliferate and secrete pro-inflammatory cytokines upon in vitro challenge with both TMEV epitopes and proteolipid protein (PLP(139-151)). Importantly, myelin-specific tolerance induced by intravenous administration of MP4, a fusion of the myelin proteins myelin basic protein (MBP) and PLP, to SJL mice with ongoing TMEV-IDD attenuated disease progression and resulted in significantly less demyelination and decreased inflammatory cell infiltration in the CNS. Paradoxically, peptide-specific splenic T cell proliferative and IFN-gamma responses were enhanced in the tolerized mice. Collectively, these results indicate that myelin-specific T cell responses contribute to chronic disease progression in this virus-induced model of MS, and suggest caution in the use of antigen-specific tolerance for treatment of ongoing autoimmune disease.

Viruses and autoimmune disease--two sides of the same coin?

Some viruses have the ability to modulate the development of autoimmune diseases. Virus infections have long been associated with the exacerbation of autoimmune disease, however, there is also evidence that viruses can actually protect against autoimmune disease. Several experimental models have been developed to investigate how some virus infections can prime for and trigger autoimmunity whereas others ameliorate the pathway leading to clinical disease. It is possible that the type I interferons, via interleukin 12, provide the link between viruses and autoimmunity.

Tolerance induction with agonist peptides recognized by autoaggressive lymphocytes is transient: therapeutic potential for type 1 diabetes is limited and depends on time-point of administration, choice of epitope and adjuvant

Immunization with agonist peptides recognized by autoaggressive lymphocytes has been used successfully in several animal models for type 1 diabetes (T1D) or multiple sclerosis (MS) to prevent disease. Depending on the timing of immunization, use of adjuvant and route of administration either elimination of autoaggressive T cells or induction of regulation reflected by cytokine shifts were described. Since it was also reported that such agonist peptides could enhance autoimmunity by activating aggressive lymphocytes, our goal was to re-evaluate their efficacy in an antigen-specific model of virally-induced T1D that allowed us to precisely track the autoaggressive response. We find that rather than the route of administration (oral versus sc) the precise timing is important for inducing tolerance to self-antigens. Tolerance is transient and only immunization during a susceptible phase 10 to 20 days prior to the induction of disease but not in prediabetic mice resulted in protection. Further, use of a stronger adjuvant (CFA) compared to IFA enhanced the protective effect. Mechanistically, a transient loss of autoaggressive T cells was responsible for preventing disease, the effect was quantitative and no regulatory lymphocytes or cytokine shifts were induced by any of our treatments. Thus, MHC class I-restricted agonist peptides might only find a limited use in treating autoimmune disorders, because tolerance induction is transient and treatment has to be given very early, ideally prior to activation of the aggressive response.

Biological and clinical developments in melanoma vaccines

The identification of antigens recognised on human tumours by autologous T-lymphocytes has opened the way for vaccination strategies involving defined tumour antigens. These vaccinations are therapeutic, i.e. they involve patients with detectable disease. Tumour regressions have been observed in a minority of melanoma patients in Phase I/II trials. Some of these regressions have been complete and long lasting. Improving the efficacy of therapeutic vaccines will critically depend on their capacity to trigger a robust immune response, on the development of appropriate methods to monitor these antitumour immune responses to vaccination and on a better understanding of the mechanisms used by tumours to escape immune attack. Finally, the initiation of large randomised Phase III trials will determine the impact of these vaccines on melanoma treatment.

Interleukin-4 acts at the locus of the antigen-presenting dendritic cell to counter-regulate cytotoxic CD8+ T-cell responses

The mechanism underlying suppression of immune responses by interleukin-4 (IL-4) has remained unexplained. Here we show that the antigen-presenting dendritic cell is central to counter-regulation of autoimmune disease by IL-4. IL-4 acts at the locus of the dendritic cell to decrease the cytolytic T-cell response, preventing autoimmunity. Stimulation of cytotoxic precursors by antigen pulsed dendritic cells induces their differentiation but the process is blocked by IL-4. IL-4-influenced DC produce distinct effects on CD8+ T cells depending on their state of activation. The molecular basis for this regulation is the alteration of the expression ratio of the costimulatory ligands B7.1/B7.2 on dendritic cells. Our findings demonstrate that B7.2 induces expansion of CD8+ T cells and B7.1 governs their acquisition of cytolytic activity. IL-4 influences the dendritic cell to elicit qualitative differences in T-cell responses, providing the basis for counter-regulation mediated by IL-4.

Autoantigen-specific CD4+CD28low T cell subset prevents autoimmune exocrinopathy in murine Sjögren's syndrome

Organ-specific autoimmune exocrinopathy resembling Sjögren's syndrome (SS) that spontaneously develops in NFS/sld mutant mice thymectomized 3 day after birth is dependent on Th1-type CD4+ T cells. We previously reported that a cleavage product of 120-kDa alpha-fodrin may be an important autoantigen in the pathogenesis of SS in both an animal model and the patients. We demonstrate that in an animal model of SS with overt exocrinopathy, a unique CD4+ T cell subset expressing CD28low is dramatically increased in spleen cells before the disease onset, but that the CD4+ T cells of diseased mice were virtually all CD28high. We found that the spleen cells in these mice before the disease onset showed a significant increase in autoantigen-specific T cell proliferation. Analysis of in vitro cytokine production by spleen cells indicated, before the disease onset, severely impaired production of IL-2 and IFN-gamma in the animal model, whereas high levels of IL-4 were observed. Expression of cytokine genes, including IL-4, IL-10, and TGF-beta, was detected in FACS-sorted CD4+CD28low T cells by RT-PCR analysis. Transfer of CD4+CD28low T cells into the animal model actually prevented the development of autoimmune lesions including autoantibody production. These results suggest that a CD4+CD28low T cell subset that is continuously activated by an organ-specific autoantigen may play a regulatory role in the development of organ-specific autoimmune disease in an animal model of SS.

Systemic administration of agonist peptide blocks the progression of spontaneous CD8-mediated autoimmune diabetes in transgenic mice without bystander damage

Insulin-dependent diabetes is an autoimmune disease targeting pancreatic beta-islet cells. Recent data suggest that autoreactive CD8+ T cells are involved in both the early events leading to insulitis and the late destructive phase resulting in diabetes. Although therapeutic injection of protein and synthetic peptides corresponding to CD4+ T cell epitopes has been shown to prevent or block autoimmune disease in several models, down-regulation of an ongoing CD8+ T cell-mediated autoimmune response using this approach has not yet been reported. Using CL4-TCR single transgenic mice, in which most CD8+ T cells express a TCR specific for the influenza virus hemagglutinin HA512-520 peptide:Kd complex, we first show that i.v. injection of soluble HA512-520 peptide induces transient activation followed by apoptosis of Tc1-like CD8+ T cells. We next tested a similar tolerance induction strategy in (CL4-TCR x Ins-HA)F1 double transgenic mice that also express HA in the beta-islet cells and, as a result, spontaneously develop a juvenile onset and lethal diabetes. Soluble HA512-520 peptide treatment, at a time when pathogenic CD8+ T cells have already infiltrated the pancreas, very significantly prolongs survival of the double transgenic pups. In addition, we found that Ag administration eliminates CD8+ T cell infiltrates from the pancreas without histological evidence of bystander damage. Our data indicate that agonist peptide can down-regulate an autoimmune reaction mediated by CD8+ T cells in vivo and block disease progression. Thus, in addition to autoreactive CD4+ T cells, CD8+ T cells may constitute targets for Ag-specific therapy in autoimmune diseases.

Review: Age-related cataract: immunity and lens epithelium-derived growth factor (LEDGF)

This short review summarizes our recent work and relevant publications on autoimmunity and cataract. A complete review of this subject is beyond the scope of this paper. Age-related cataract (ARC) is the leading cause of world blindness. In spite of more than fifty years of basic and clinical research, there is no nonsurgical intervention to prevent or treat ARC, but there is a better understanding of the manifold complexities of this age-related condition. ARC is a multifactorial condition in which incidence and progress are modified by factors such as age, sex, radiation [visible, ultraviolet (UV), and X-ray], oxidation, physical trauma, diet, and medications. The lens contains at least three different cell types: central epithelial cells, dividing germinative epithelial cells, and fiber cells. The central epithelial cells covering the anterior axial part of the lens do not divide but survive throughout life. The bulk of the lens comprises anucleate fiber cells, differentiated germinative epithelial cells, which have undergone an apoptosis-like change "diffoptosis" to become elongated, crystallin-rich, organelle-deficient, cells. The epithelial cells and their active transport mechanisms maintain lens homeostasis and clarity. The survival mechanisms of the central lens epithelial cells (LECs) are unknown. In other cells, growth or survival factors, when present, enhance survival and, when absent or deficient, induce programmed cell death "apoptosis". Many developing mammalian cells produce signal proteins, or require signal proteins from other cells, to avoid apoptosis. Although much is known about the role of growth factors in the lens, less is known about how such signals are involved in the survival and death of LECs. We have hypothesized that LECs, like other mammalian cells, use signal proteins to regulate growth, survival, and apoptosis, and we have begun a search for such molecules. Furthermore, we have hypothesized that such factors, if found, may also be involved in the death of LECs, the consequent alteration of lens homeostasis and, eventually, certain types of ARC.

Adjuvant Effect of IL-12: Conversion of Peptide Antigen Administration from Tolerizing to Immunizing for CD8+ T Cells In Vivo

CD8+ T cells from TCR transgenic 2C mice, specific for SIYRYYGL peptide bound to H-2Kb, were adoptively transferred into C57BL/6 recipients to allow monitoring of their location, numbers, and phenotype upon peptide challenge. Recipients were primed by s.c. injection of SIYRYYGL alone or with CFA or IL-12, and the transferred cells then tracked by flow cytometry using the 1B2 mAb specific for the 2C TCR. Peptide alone induced a transient and weak expansion of 1B2+ cells in the draining lymph nodes (DLN) by day 3, but these cells were tolerant to secondary peptide challenge. In contrast, priming with CFA/peptide resulted in a large clonal expansion of 1B2+ cells in DLN by day 3, and the cells exhibited a CD25highCD44high phenotype, blast transformation, and lytic effector function. By day 5, 1B2+ cell numbers decreased in the DLN and increased in the spleen and blood. 1B2+ cells with a memory phenotype persisted through day 60 in the DLN, spleen, and blood and responded to secondary peptide challenge. Immunization with peptide, along with IL-12, mimicked the adjuvant effects of CFA with respect to phenotype, clonal expansion, effector function, and establishment of memory. IL-12 was not unique in providing this adjuvant effect however, since CFA/peptide immunization of IL-12-deficient recipient mice also resulted in 1B2+ T cell activation and clonal expansion. Thus, CFA or IL-12 can enhance Ag-specific CD8+ T cell responses to peptide, demonstrating that an inflammatory cytokine(s) can support activation and prevent tolerance induction.

Intravenous or intranasal administration of gliadin is able to down-regulate the specific immune response in mice

The mucosal lesion in coeliac disease (CD) represents an immunologically mediated injury triggered by gliadin and is restricted by a particular assortment of major histocompatibility complex (MHC) class II genes. Therefore, immunomodulatory strategies to tolerize gliadin-specific, class II-restricted T-cell responses could represent an alternative to current treatments of CD, which are based on a gluten-free diet. In this study, BALB/c mice derived from a gluten-free diet colony were tolerized by either intranasal (i.n.) or intravenous (i.v.) administration of single or multiple doses of gliadin. While a single dose failed to induce tolerance, a significant decrease in gliadin-specific T-cell proliferation was detected (P < 0.001) after multiple i.n. or i.v. administrations. No significant difference in antibody titre was detected for antigen-specific immunoglobulin G (IgG) or the IgG1 subclass, but a lower IgG2a-specific titre was observed. Both interferon-gamma (IFN-gamma) and interleukin (IL)-2 expression, measured by enzyme-linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR), were reduced on antigen administration, both i.v. and i.n. Neither regimen showed a regulatory effect on IL-4 production. As T helper 1 (Th1) cytokines seem to be important in the pathogenesis of CD, our data therefore highlight the potential of i.n. and i.v. routes for the design of useful immunomodulatory strategies for CD.