A study of human T-cell lines generated from multiple sclerosis patients and controls by stimulation with peptides of myelin basic protein

Predicting HLA CD4 Immunogenicity in Human Populations

Background

Prediction of T cell immunogenicity is a topic of considerable interest, both in terms of basic understanding of the mechanisms of T cells responses and in terms of practical applications. HLA binding affinity is often used to predict T cell epitopes, since HLA binding affinity is a key requisite for human T cell immunogenicity. However, immunogenicity at the population it is complicated by the high level of variability of HLA molecules, potential other factors beyond HLA as well as the frequent lack of HLA typing data. To overcome those issues, we explored an alternative approach to identify the common characteristics able to distinguish immunogenic peptides from non-recognized peptides.

Methods

Sets of dominant epitopes derived from peer-reviewed published papers were used in conjunction with negative peptides from the same experiments/donors to train neural networks and generate an “immunogenicity score.” We also compared the performance of the immunogenicity score with previously described method for immunogenicity prediction based on HLA class II binding at the population level.

Results

The immunogenicity score was validated on a series of independent datasets derived from the published literature, representing 57 independent studies where immunogenicity in human populations was assessed by testing overlapping peptides spanning different antigens. Overall, these testing datasets corresponded to over 2,000 peptides and tested in over 1,600 different human donors. The 7-allele method prediction and the immunogenicity score were associated with similar performance [average area under the ROC curve (AUC) values of 0.703 and 0.702, respectively] while the combined methods reached an average AUC of 0.725. This increase in average AUC value is significant compared with the immunogenicity score (p = 0.0135) and a strong trend toward significance is observed when compared to the 7-allele method (p = 0.0938). The new immunogenicity score method is now freely available using CD4 T cell immunogenicity prediction tool on the Immune Epitope Database website (http://tools.iedb.org/CD4episcore).

Conclusion

The new immunogenicity score predicts CD4 T cell immunogenicity at the population level starting from protein sequences and with no need for HLA typing. Its efficacy has been validated in the context of different antigen sources, ethnicities, and disparate techniques for epitope identification.

Characterisation of tissue transglutaminase-reactive T cells from patients with coeliac disease and healthy controls

Previous studies have shown evidence for T lymphocytes specific for tissue transglutaminase (tTG) in the periphery of coeliac disease (CD) patients. These cells could play a role in disease pathogenesis and may be involved in providing help for the production of anti-tTG autoantibodies. The objective of this study was to further investigate the presence of tTG-specific T cells in patients with treated and untreated CD, and normal controls. Positive proliferative responses to three different commercial tTG antigens were detected in all groups tested, occurring more frequently and at higher levels in untreated CD patients. The addition of antibodies to HLA-DQ and HLA-DR caused a significant reduction in the proliferative response to tTG. T cell lines specific for tTG and composed predominantly of CD4-positive T cells were generated from responsive CD and control individuals, and were found to produce large amounts of interferon-γ, as well as interleukins 10, 17A, and 21.

Bladder dysfunction in multiple sclerosis

Multiple sclerosis (MS) is a relatively common disease of young adults. Patients with MS can have a wide range of symptoms and may develop significant disability. The cause of MS is unknown, but immunological mechanisms are important. In MS, the pathological features include prominent demyelination and inflammation, but there is also evidence of neurodegeneration. Bladder symptoms are common in MS. The bladder is under neural control, and bladder disturbance is usually attributed to demyelination or loss of axons from the neural pathways, particularly those in the spinal cord, that control the bladder. However, as with other symptoms in MS, the presence of bladder disturbance does not always correlate well with MRI lesions. We speculate that other possible causes of bladder dysfunction in MS might include the effects of circulating toxic factors. Urgency of micturition is prominent in MS, and better understanding of the receptors involved in bladder sensation suggests possible treatment strategies through inhibiting these receptors.

Immune activation in the peripheral blood of patients with acute ischemic stroke

Lymphocytes, neutrophils and macrophages are found in the brain in areas of acute ischaemic stroke. There is also evidence of modulation of systemic immune function after stroke, with post-stroke immunosuppression being observed. Because lymphocytes are activated in the peripheral immune compartment, before entry to the target organ, we reasoned that activated lymphocytes would be present in the circulation, prior to entering the brain, in patients after stroke. Because immune responses are controlled by regulatory mechanisms, we also reasoned that the post-stroke immunosuppression would involve T regulatory cells. The aim of the study was to look for evidence of immune activation and alterations in regulatory T cells in the peripheral blood of patients after acute ischaemic stroke, in comparison to age-matched healthy controls and patients with other neurological diseases (OND), and to determine the phenotype of the activated cells. The percentages of total and activated T cells, B cells, monocyte/ macrophages, and NK/NK-T cells were determined by labelling peripheral blood leukocytes with specific cell surface markers and analysis with 4-colour flow cytometry. The percentages of activated T cells and regulatory T cells were significantly increased in patients with ischemic stroke compared to healthy subjects and patients with OND. There was also an increase in the percentage of CCR7+ T cells. There were no significant differences in the activation of other cell types. In conclusion, there is evidence of immune activation and Treg cells in acute ischaemic stroke.

Multiple sclerosis and hepatitis B vaccination: Could minute contamination of the vaccine by partial Hepatitis B virus polymerase play a role through molecular mimicry?

Reports of multiple sclerosis developing after hepatitis B vaccination have led to the concern that this vaccine might be a cause of multiple sclerosis in previously healthy subjects. Some articles evidenced that minor Hepatitis B virus (HBV) polymerase proteins could be produced by alternative transcriptional or translational strategies. Their detection is very difficult because they are in minute concentration and probably enzymatically inactive, however, it was shown that they could be exposed on the outside of the virus particles and also be immunogenic. In addition, HBV polymerase shares significant amino acid similarities with the human myelin basic protein. We hypothesise that some of the apparent adverse reactions to the vaccine could be due to a process called of molecular mimicry, the HBV polymerase, which could be a contaminant in the recombinant or plasma-derived vaccines, could act as autoantigens and induce autoimmune demyelinating diseases such as multiple sclerosis.

Effect of gender on T-cell proliferative responses to myelin proteolipid protein antigens in patients with multiple sclerosis and controls

Multiple sclerosis (MS) is an inflammatory demyelinating disorder of the central nervous system. Gender influences both susceptibility to MS, with the disease being more common in women, and the clinical course of disease, with an increased proportion of males developing the primary progressive form of the disease. The basis for these differences may include genetic and immunological factors, and the immunological differences between men and women may be influenced by the effects of the sex hormones. Over several years we have collected blood from MS patients and controls, and measured T-cell responses to myelin proteolipid protein (PLP) and myelin basic protein (MBP) and have shown increased responses to PLP in MS patients compared to healthy controls and patients with other neurological diseases. In the present study we analyzed data from over 500 individuals, to determine whether there are differences between males and females in their responses to PLP and MBP. We found that there was higher frequency of increased T-cell reactivity to immunodominant PLP peptides in women than in men, particularly in non-MS individuals. We suggest that this may be relevant to the higher prevalence of MS in women.

Comprehensive mapping of HLA-A0201-restricted CD8 T-cell epitopes on PDC-E2 in primary biliary cirrhosis

Growing evidence has implicated the involvement of autoreactive T lymphocytes in the pathogenesis of primary biliary cirrhosis (PBC). We have recently taken advantage of motif prediction analysis of HLA-A*0201 and identified the first major histocompatibility complex (MHC) class I restricted epitope, amino acids 159 to 167 on E2 components of pyruvate dehydrogenase complexes (PDC-E2), the major mitochondrial antigens in PBC. The mechanisms involved in the selection of epitope peptide(s) that comprise the PDC-E2-specific autoreactive cytotoxic T lymphocytes (CTLs) are unknown and likely involve other epitopes on PDC-E2 restricted by MHC class I molecules. To address this issue, a comprehensive mapping of the CTL epitope repertoire on the PDC-E2 molecule that binds HLA-A*0201 was performed to provide further clues regarding the role of CTLs. We used the T2 cell line to screen 79 overlapping 15mer peptides, spanning the entire PDC-E2 molecule. Six of the 79 peptides exhibited significantly higher binding activity to HLA-A*0201 than the other 15mer peptides. Two of these 6 peptides induced CTL lines from patients with PBC. Fine mapping with N-terminus or C-terminus truncated peptides identified 10mer peptide, PDC-E2 amino acids 165 to 174, which is a novel CD8 epitope restricted by HLA-A*0201. In conclusion, using a combination of the 15mer peptide library screening with the T2 binding assay and also the induction of CTL lines with candidate peptides, we have defined a novel HLA-A*0201-restricted epitope PDC-E2 165 to 174 in patients with PBC. These data will become important in the development of altered peptide ligands to modulate disease activity.

The human T cell response to myelin oligodendrocyte glycoprotein: a multiple sclerosis family-based study

Myelin oligodendrocyte glycoprotein (MOG) is an encephalitogenic myelin protein and a likely autoantigen in human multiple sclerosis (MS). In this work, we describe the fine specificity and cytokine profile of T cell clones (TCC) directed against MOG in three nuclear families, comprised of four individuals affected with MS and their HLA-identical siblings. TCC were generated from PBMC by limiting dilution against a mixture of eleven 20-mer overlapping peptides corresponding to the encephalitogenic extracellular domain of human MOG (aa 1-120). The frequency of MOG peptide-reactive T cells was surprisingly high (range, 1:400 to 1:3,000) and, unexpectedly, cloning efficiencies were highest at low seeding densities of 10(2) or 10(3) PBMC per well. A total of 235 MOG peptide-reactive TCC were produced, all of which were CD4(+)CD8(-)TCRalphabeta(+)TCRgammadelta(-). All 11 MOG peptides were recognized by the TCC, and different epitopes of MOG appeared to be immunodominant in the HLA-identical siblings. The patterns of cytokine secretion by TCC from single individuals were generally similar. The healthy individuals exhibited Th2-, Th0-, and T regulatory cell 1-like cytokine profiles, whereas TCC from one sibling with MS had a striking Th1-like phenotype, producing high levels of IFN-gamma and TNF-alpha, and low IL-4 levels. Thus, MOG-reactive T cells appear to constitute an important part of the natural T cell repertoire, a finding that could contribute to the development of autoimmunity to this protein.

Quantitative and functional analysis of PDC-E2-specific autoreactive cytotoxic T lymphocytes in primary biliary cirrhosis

While the pathologic mechanisms responsible for organ-specific tissue damage in primary biliary cirrhosis (PBC) remain an enigma, it has been suggested that the pathology is mediated by autoreactive T cells infiltrating the intrahepatic bile ducts. Previously, we have documented that there is 100-fold enrichment in the frequency of CD4(+) autoreactive T cells in the liver that are specific for peptides encoded by the E2 components of the pyruvate dehydrogenase complexes (PDC-E2). We have also recently characterized the first MHC class I-restricted epitope for PDC-E2, namely amino acid 159-167, a region very similar to the epitope recognized by MHC class II-restricted CD4(+) cells and by autoantibodies. The effector functions of these PDC-E2(159-167)-specific CD8(+) cytotoxic T lymphocytes (CTLs) are not well understood. We have taken advantage of tetramer technology and report herein that there is tenfold increase in the frequency of PDC-E2(159-167)-specific CTLs in the liver as compared with the blood in PBC. In addition, the precursor frequency of the CTLs in blood was significantly higher in early-stage PBC. Of interest was the fact that, upon stimulation with the peptide, the response of PDC-E2(159-167) tetramer-positive cells is heterogeneous with respect to IFN-gamma synthesis. These data, we believe for the first time, document the enrichment of autoantigen-specific CD8(+) T cells in the PBC liver, suggesting that CD8(+) T cells play a significant role in the immunopathogenesis of PBC.

Subtle effects on myelin basic protein-specific T cell responses can lead to a major reduction in disease susceptibility in experimental allergic encephalomyelitis

The presence of potentially autoreactive T cells is a necessary, but not sufficient, condition for the development of autoimmune disease. However, the relationship between T cell response and susceptibility to disease is not straightforward. In this report, we use experimental allergic encephalomyelitis as a model to demonstrate that subtle alterations of the T cell response to an encephalitogenic epitope are sufficient to cause a dramatic decrease in disease susceptibility. Transgenic expression of a fusion protein of hen egg lysozyme and an encephalitogenic peptide of myelin basic protein (MBP) residues 84-105, coexpressed with MHC class II, causes profound tolerance to hen egg lysozyme, while maintaining a near normal response to MBP. Detailed analysis of the T cell repertoire of transgenic animals using a panel of T cell hybridomas revealed a highly selective loss of one minor component of the response to the MBP84-104 region. Despite this, transgenic animals were highly resistant to experimental allergic encephalomyelitis induction with the MBP peptide, indicating that minor changes to the T cell repertoire may result in major alterations in disease susceptibility. Possible reasons for this are discussed.

Recommendations for physical activity in patients with multiple sclerosis

For many years, patients with multiple sclerosis (MS), an inflammatory demyelinating disease of the central nervous system, have been advised to avoid exercise. MS is believed to be autoimmune in origin, mediated by activated T cells which penetrate the blood-brain barrier and attack myelin. The pathophysiology, with respect to function is an impairment of saltatory conduction, specifically, slowing of conduction speed and/or conduction block. Symptoms can temporarily worsen on exposure to heat or during physical exercise. Exercise programmes must be designed to activate working muscles but avoid overload that results in conduction block. Fatigue, often severe, affects about 85% of MS patients and, along with motor and sensory symptoms, results in decreased mobility and reduced quality of life. Physical activity and recreation are reduced in patients with MS. Before developing recommendations, physical activity patterns and the physical effects of MS should be assessed in individual patients. Patients may then be functionally classified. Physical activity can also be classified in a pyramid structure, with the most basic functions forming the base and the most integrated functions on top. The muscular fitness pyramid progresses through passive range of motion, active resistive, specific strengthening and integrated strength exercises Overall physical activity may be increased according to functional level by performing activities of daily living, incorporating inefficiencies into daily living, pursuing more active recreation and eventually developing a structured exercise programme. The importance of the proper exercise environment, balance and coordination issues and factors related to adherence are discussed.

Differential recognition of MBP epitopes in BALB/c mice determines the site of inflammatory disease induction

Although myelin basic protein (MBP)-recognizing T cells are not readily obtained after immunization of BALB/c mice with MBP (reflecting the BALB/c resistance to actively induced experimental autoimmune encephalomyelitis (EAE)), they can be expanded and cloned after several rounds of in vitro culture. The majority of BALB/c-derived clones recognize an epitope defined by MBP peptide 59-76. When transferred to naive BALB/c recipients, these clones cause classical EAE, with characteristic inflammation and demyelination of the central nervous system (CNS). We previously showed that two related clones recognizing a minor epitope, defined by MBP peptide 151-168, cause inflammation and demyelination preferentially of the peripheral nervous system (PNS). Because MBP has alternatively spliced isoforms, residues 151-168 are not present contiguously in all MBP isoforms. In order to determine whether induction of PNS disease is idiosyncratic to these sister clones, or related to their properties of epitope recognition, an independent T-cell line with similar recognition properties was studied. Clone 116F, derived from a BALB/c shiverer mouse, expresses a different T-cell receptor (TCR), with distinct TCR contact residues, but like the previously described T cells, this clone requires residues from both exons 6 and 7 for optimal stimulation. When adoptively transferred to BALB/c recipients, this clone preferentially induces disease of the PNS. A control BALB/c shiverer-derived MBP 59-76-recognizing clone, in contrast, induces CNS disease. These data strongly suggest that the site of disease initiation may correlate with epitope recognition, particularly when alternative isoforms are involved.