Tetramer analysis of human autoreactive CD4-positive T cells

Analysis of self-antigen specificity of islet-infiltrating T cells from human donors with type 1 diabetes

A major therapeutic goal for type 1 diabetes (T1D) is to induce autoantigen-specific tolerance of T cells. This could suppress autoimmunity in those at risk for the development of T1D, as well as in those with established disease who receive islet replacement or regeneration therapy. Because functional studies of human autoreactive T cell responses have been limited largely to peripheral blood-derived T cells, it is unclear how representative the peripheral T cell repertoire is of T cells infiltrating the islets. Our knowledge of the insulitic T cell repertoire is derived from histological and immunohistochemical analyses of insulitis, the identification of autoreactive CD8⁺ T cells in situ, in islets of human leukocyte antigen (HLA)-A2⁺ donors and isolation and identification of DQ8 and DQ2-DQ8 heterodimer-restricted, proinsulin-reactive CD4⁺ T cells grown from islets of a single donor with T1D. Here we present an analysis of 50 of a total of 236 CD4⁺ and CD8⁺ T cell lines grown from individual handpicked islets or clones directly sorted from handpicked, dispersed islets from nine donors with T1D. Seventeen of these T cell lines and clones reacted to a broad range of studied native islet antigens and to post-translationally modified peptides. These studies demonstrate the existence of a variety of islet-infiltrating, islet-autoantigen reactive T cells in individuals with T1D, and these data have implications for the design of successful immunotherapies.

Gut commensalism, cytokines, and central nervous system demyelination

There is increasing support for the importance of risk factors such as genetic makeup, obesity, smoking, vitamin D insufficiency, and antibiotic exposure contributing to the development of autoimmune diseases, including human multiple sclerosis (MS). Perhaps the greatest environmental risk factor associated with the development of immune-mediated conditions is the gut microbiome. Microbial and helminthic agents are active participants in shaping the immune systems of their hosts. This concept is continually reinforced by studies in the burgeoning area of commensal-mediated immunomodulation. The clinical importance of these findings for MS is suggested by both their participation in disease and, perhaps of greater clinical importance, attenuation of disease severity. Observations made in murine models of central nervous system demyelinating disease and a limited number of small studies in human MS suggest that immune homeostasis within the gut microbiome may be of paramount importance in maintaining a disease-free state. This review describes three immunological factors associated with the gut microbiome that are central to cytokine network activities in MS pathogenesis: T helper cell polarization, T regulatory cell function, and B cell activity. Comparisons are drawn between the regulatory mechanisms attributed to first-line therapies and those described in commensal-mediated amelioration of central nervous system demyelination.

Tetramers reveal IL-17-secreting CD4+ T cells that are specific for U1-70 in lupus and mixed connective tissue disease

Antigen-specific CD4(+) T cells are implicated in the autoimmune disease systemic lupus erythematosus (SLE), but little is known about the peptide antigens that they recognize and their precise function in disease. We generated a series of MHC class II tetramers of I-E(k)-containing peptides from the spliceosomal protein U1-70 that specifically stain distinct CD4(+) T-cell populations in MRL/lpr mice. The T-cell populations recognize an epitope differing only by the presence or absence of a single phosphate residue at position serine(140). The frequency of CD4(+) T cells specific for U1-70(131-150):I-E(k) (without phosphorylation) correlates with disease severity and anti-U1-70 autoantibody production. These T cells also express RORγt and produce IL-17A. Furthermore, the U1-70-specific CD4(+) T cells that produce IL-17A are detected in a subset of patients with SLE and are significantly increased in patients with mixed connective tissue disease. These studies provide tools for studying antigen-specific CD4(+) T cells in lupus, and demonstrate an antigen-specific source of IL-17A in autoimmune disease.

Update on islet transplantation

Clinical islet transplantation has progressed considerably over the past 12 years, and >750 patients with type 1 diabetes have received islet transplants internationally over this time. Many countries are beginning to accept the transition from research to accepted and funded clinical care, especially for patients with brittle control that cannot be stabilized by more conventional means. Major challenges remain, including the need for more than one donor, and the requirement for potent, chronic immunosuppression. Combining immunological tolerance both to allo- and autoantigens, and a limitless expandable source of stem cell- or xenograft-derived insulin-secreting cells represent remaining hurdles in moving this effective treatment to a potential cure for all those with type 1 or 2 diabetes.

Antigen microarrays for the study of autoimmune diseases

BACKGROUND

The immune response involves the activation of heterogeneous populations of T cells and B cells that show different degrees of affinity and specificity for target antigens. Although several techniques have been developed to study the molecular pathways that control immunity, there is a need for high-throughput assays to monitor the specificity of the immune response.

CONTENT

Antigen microarrays provide a new tool to study the immune response. We reviewed the literature on antigen microarrays and their advantages and limitations, and we evaluated their use for the study of autoimmune diseases. Antigen arrays have been successfully used for several purposes in the investigation of autoimmune disorders: for disease diagnosis, to monitor disease progression and response to therapy, to discover mechanisms of pathogenesis, and to tailor antigen-specific therapies to the autoimmune response of individual patients. In this review we discuss the use of antigen microarrays for the study of 4 common autoimmune diseases and their animal models: type 1 diabetes, systemic lupus erythematosus, rheumatoid arthritis, and multiple sclerosis.

CONCLUSIONS

Antigen microarrays constitute a new tool for the investigation of the immune response in autoimmune disorders and also in other conditions such as tumors and allergies. Once current limitations are overcome, antigen microarrays have the potential to revolutionize the investigation and management of autoimmune diseases.

Molecular basis for T cell response induced by altered peptide ligand of type II collagen

Mounting evidence from animal models has demonstrated that alterations in peptide-MHC interactions with the T cell receptor (TCR) can lead to dramatically different T cell outcomes. We have developed an altered peptide ligand of type II collagen, referred to as A9, which differentially regulates TCR signaling in murine T cells leading to suppression of arthritis in the experimental model of collagen-induced arthritis. This study delineates the T cell signaling pathway used by T cells stimulated by the A9·I-A(q) complex. We have found that T cells activated by A9 bypass the requirement for Zap-70 and CD3-ζ and signal via FcRγ and Syk. Using collagen-specific T cell hybridomas engineered to overexpress either Syk, Zap-70, TCR-FcRγ, or CD3-ζ, we demonstrate that A9·I-A(q) preferentially activates FcRγ/Syk but not CD3-ζ/Zap-70. Moreover, a genetic absence of Syk or FcRγ significantly reduces the altered peptide ligand induction of the nuclear factor GATA3. By dissecting the molecular mechanism of A9-induced T cell signaling we have defined a new alternate pathway that is dependent upon FcRγ and Syk to secrete immunoregulatory cytokines. Given the interest in using Syk inhibitors to treat patients with rheumatoid arthritis, understanding this pathway may be critical for the proper application of this therapy.

Uveitis-associated epitopes of retinal antigens are pathogenic in the humanized mouse model of uveitis and identify autoaggressive T cells

Noninfectious uveitis is a leading cause of blindness and thought to involve autoimmune T cell responses to retinal proteins (e.g., retinal arrestin [soluble-Ag (S-Ag)]). There are no known biomarkers for the disease. Susceptibility is associated with HLA, but little is known about susceptible class II alleles or the potentially pathogenic epitopes that they present. Using a humanized HLA-transgenic mouse model of S-Ag-induced autoimmune uveitis, we identified several susceptible and resistant alleles of HLA-DR and -DQ genes and defined pathogenic epitopes of S-Ag presented by the susceptible alleles. The sequences of these epitopes overlap with some previously identified peptides of S-Ag ("M" and "N"), known to elicit memory responses in lymphocytes of uveitis patients. HLA-DR-restricted, S-Ag-specific CD4(+) T cells could be detected in blood and draining lymph nodes of uveitic mice with HLA class II tetramers and transferred the disease to healthy mice. Importantly, tetramer-positive cells were detected in peripheral blood of a uveitis patient. To our knowledge, these findings provide the first tangible evidence that an autoimmune response to retina is causally involved in pathogenesis of human uveitis, demonstrating the feasibility of identifying and isolating retinal Ag-specific T cells from uveitis patients and may facilitate their development as biomarkers for the disease.

Increased frequencies of myelin oligodendrocyte glycoprotein/MHC class II-binding CD4 cells in patients with multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease characterized by infiltration of pathogenic immune cells in the CNS resulting in destruction of the myelin sheath and surrounding axons. We and others have previously measured the frequency of human myelin-reactive T cells in peripheral blood. Using T cell cloning techniques, a modest increase in the frequency of myelin-reactive T cells in patients as compared with control subjects was observed. In this study, we investigated whether myelin oligodendrocyte glycoprotein (MOG)-specific T cells could be detected and their frequency was measured using DRB1*0401/MOG(97-109(107E-S)) tetramers in MS subjects and healthy controls expressing HLA class II DRB1*0401. We defined the optimal culture conditions for expansion of MOG-reactive T cells upon MOG peptide stimulation of PMBCs. MOG(97-109)-reactive CD4(+) T cells, isolated with DRB1*0401/MOG(97-109) tetramers, and after a short-term culture of PMBCs with MOG(97-109) peptides, were detected more frequently from patients with MS as compared with healthy controls. T cell clones from single cell cloning of DRB1*0401/MOG(97-109(107E-S)) tetramer(+) cells confirmed that these T cell clones were responsive to both the native and the substituted MOG peptide. These data indicate that autoantigen-specific T cells can be detected and enumerated from the blood of subjects using class II tetramers, and the frequency of MOG(97-109)-reactive T cells is greater in patients with MS as compared with healthy controls.

T cell receptor signaling induced by an analog peptide of type II collagen requires activation of Syk

We have previously described an analog peptide of type II collagen (CII) that can suppress collagen-induced arthritis (CIA). This analog peptide represents CII(245-270), the immunodominant epitope of CII, but with substitutions at 260, 261, and 263 - CII(245-270) (A(260), B(261), and N(263)) (A9). To elucidate the mechanisms responsible for suppression, we used mice transgenic for a collagen-specific T cell receptor (TCR). When we found that APCs pulsed with A9 failed to induce T cell phosphorylation of TCR-zeta and ZAP-70, we explored alternative signaling pathways. We determined that A9 instead induced phosphorylation of spleen tyrosine kinase (Syk). The importance of Syk was confirmed by the use of chemical Syk inhibitors, which blocked both cytokine secretion and activation of GATA-3 mediated by peptide A9. In summary, T cells use an alternative pathway in response to A9 that involves Syk. This novel T cell pathway may represent an important means for altering T cell phenotypes.

Progress in the development of immune-based therapies for type 1 diabetes mellitus

Between ten and twenty million people worldwide have type 1 diabetes mellitus (T1DM), which has previously been called juvenile diabetes, childhood diabetes, and insulin-dependent diabetes mellitus. T1DM is undoubtedly a multifactorial disease affecting predisposed individuals with genetic susceptibilities; it is also associated with environmental factors leading to unbalanced immune responses. This chronic disorder is caused by auto-aggressive T lymphocytes entering the pancreatic islets of Langerhans where they destroy the insulin-producing beta-cells. A wide variety of immuno-interventions cure T1DM effectively in different animal models when given early in disease development. However, few of these interventions are efficacious in humans at a later stage of the disease. Indeed, only three immunotherapeutic compounds have demonstrated both safety and efficacy in phase II/III clinical trials. Although much time and resources have been spent on generating potent immune therapies, none of the patients enrolled in these trials have achieved normoglycemia in the absence of insulin injections. Many reasons can account for such a disappointing conclusion. Firstly, the dynamics of disease pathogenesis differs significantly from patient to patient, which directly impacts the therapeutic efficacy. Also, at trial entry, the percentage of remaining pancreatic beta-cells in T1DM patients often reflects the odds of responding positively to treatment. Based on the knowledge we have gained from preclinical studies and clinical trials, several steps have been made in the development of safer and more efficient immune-based therapies. There are, however, a number of concerns that should be addressed in order to improve future therapeutic strategies.

High-content T-cell and B-cell analysis

Immune responses are orchestrated by B- and T-cells endowed with a diverse repertoire of antigen receptors. Comprehensive profiling of the humoral and cellular immune responses, including molecular composition, the specificity of the response, the cellular activation, differentiation, and homing status, will aid to improve diagnosis, classification, monitoring, and prognostication of immune disorders driven by antigen-specific B- and T-lymphocytes.

Analog peptides of type II collagen can suppress arthritis in HLA-DR4 (DRB1*0401) transgenic mice

Rheumatoid arthritis (RA) is an autoimmune disease associated with the recognition of self proteins secluded in diarthrodial joints. We have previously established that mice transgenic for the human DR genes associated with RA are susceptible to collagen-induced arthritis (CIA) and we have identified a determinant of type II collagen (CII(263-270)) that triggers T-cell immune responses in these mice. We have also determined that an analog of CII(263-270) would suppress disease in DR1 transgenic mice. Because the immunodominant determinant is the same for both DR1 transgenic and DR4 transgenic mice, we attempted to determine whether the analog peptide that was suppressive in DR1 transgenic mice would also be effective in suppressing CIA in DR4 transgenic mice. We treated DR4 transgenic mice with two analog peptides of CII that contained substitutions in the core of the immunodominant determinant: CII(256-276) (F263N, E266D) and CII(256-270) (F263N, E266A). Mice were observed for CIA, and T-cell proliferative responses were determined. Either peptide administered at the time of immunization with CII significantly downregulated arthritis. Binding studies demonstrated that replacement of the phenylalanine residue in position 263 of the CII peptide with asparagine significantly decreased the affinity of the peptide for the DR4 molecule. In contrast, replacement of the glutamic acid residue in position 266 with aspartic acid or with alanine had differing results. Aspartic acid reduced the affinity (35-fold) whereas alanine did not. Both peptides were capable of suppressing CIA. With the use of either peptide, CII(256-276) (F263N, E266D) or CII(256-270) (F263N, E266A), the modulation of CIA was associated with an increase in T-cell secretion of IL-4 together with a decrease in IFN-gamma. We have identified two analog peptides that are potent suppressors of CIA in DR4 transgenic mice. These experiments represent the first description of an analog peptide of CII recognized by T cells in the context of HLA-DR4 that can suppress autoimmune arthritis.

The human T cell response to melanoma antigens

The cornerstone of the concept of immunosurveillance in cancer should be the experimental demonstration of immune responses able to alter the course of in vivo spontaneous tumor progression. Elegant genetic manipulation of the mouse immune system has proved this tenet. In parallel, progress in understanding human T cell mediated immunity has allowed to document the existence in cancer patients of naturally acquired T cell responses to molecularly defined tumor antigens. Various attributes of cutaneous melanoma tumors, notably their adaptability to in vitro tissue culture conditions, have contributed to convert this tumor in the prototype for studies of human antitumor immune responses. As a consequence, the first human cytolytic T lymphocyte (CTL)-defined tumor antigen and numerous others have been identified using lymphocyte material from patients bearing this tumor, detailed analyses of specific T cell responses have been reported and a relatively large number of clinical trials of vaccination have been performed in the last 15 years. Thus, the "melanoma model" continues to provide valuable insights to guide the development of clinically effective cancer therapies based on the recruitment of the immune system. This chapter reviews recent knowledge on human CD8 and CD4 T cell responses to melanoma antigens.