Search

Accumulating evidence indicates that multiple sclerosis, a chronic inflammatory disease of the central nervous system, has an autoimmune origin. Since T cells reactive to myelin basic protein (MBP) are thought to play an important role in the pathogenesis of this disease, it was assumed that inactivation or depletion of this pathogenic T cell subset may have therapeutic effects in multiple sclerosis. We have recently reported that T cell vaccination, i.e. immunisation with attenuated autologous MBP-reactive T cell clones, leads to the depletion of the MBP-reactive T cells. Furthermore, this approach induced favourable clinical effects in the treated patients, encouraging further studies of T cell vaccination in multiple sclerosis.

Suppressor T cell (Ts) lines specific for myelin basic protein (MBP)-reactive helper T cell (Th) clones were generated from two patients with multiple sclerosis (MS) following a primary culture of peripheral blood mononuclear cells (PBMC) with MBP and cyclosporine A (CsA). These suppressor T cell lines were maintained in culture by alternate stimulation with MBP and antigen-presenting cells (APC). The Ts lines expressed preferentially the CD4 phenotype (5/6 Ts lines tested) and exhibited potent antigen-specific suppressor activity on the proliferation of MBP-specific Th clones and not on the T cell lines with other antigen specificity. For some Ts lines, a Ts-to-Th ratio of 1 was sufficient to inhibit the proliferation of MBP-specific T cells by 90%. The suppressor T cells obtained were weakly responsive to MBP and required the presence of the autologous PBMC for proliferation. Furthermore, proliferation of these suppressor T cell lines was restricted by HLA-DR molecules (for CD4+ Ts lines) and HLA class I (for a CD8+ Ts line). The suppressor T cell lines generated and the techniques described in this study may be helpful in our understanding of the events involved in the immune regulation in MS and other autoimmune diseases.

A panel of 17 myelin basic protein (MBP)-specific T lymphocyte clones were generated from four multiple sclerosis (MS) patients. All T cell clones expressed CD4 phenotype and 14 clones exhibited substantial cytotoxic activity on MBP-coated target cells. T cell recognition sites of the clones on human MBP were identified by using MBP fragments and synthetic peptides. Despite the fact that at least three epitopes were defined, these T cell clones displayed a striking bias to the C-terminal peptide 149–171 independent of differences in HLA-DR and DQ expression. In addition, the T cell responses of the clones appeared to be restricted by HLA-DR molecules irrespective of peptide specificities. The present study suggests an immunodominant property of the C-terminal peptide for HLA-DR-restricted T cell responses to MBP. However, its association with encephalitogenicity in humans and its potential pathologic importance in MS await further clarification.

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS) characterised by focal areas of demyelination in the CNS (Ffrench-Constant 1994). Autoimmune processes involving myelin-reactive T cells are considered to play an essential role in the pathogenesis of MS (for a review, see Stinissen et al. 1997). In vivo activated T cells reactive to myelin basic protein (MBP) are clonally expanded in the blood of MS patients and may persist for many years in some patients (Goebels et al. 2000). The activation of MBP-reactive T cells via molecular mimicry could be a common process, as suggested by the high level of cross-reactivity of MBP-reactive T cells to various microbial ligands, even in the absence of any sequence homology (Wucherpfennig et al. 1995,Hemmer et al. 1998). Accidentally stimulated autoreactive T cells however may not automatically lead to autoimmunity. Indeed, several observations support the existence of a peripheral regulatory network that prevents activation or expansion of pathogenic T cells (Cohen et al. 1992). However, an imbalanced regulatory network may lead to sub-optimal suppression of activated pathogenic T cells and give rise to autoimmunity. Administration of attenuated autoreactive T cells as a vaccine (T cell vaccination, TCV) may enhance the regulatory networks to specifically suppress the eliciting autoreactive T cells as shown in experimental autoimmune encephalomyelitis (EAE), an animal model of MS (Ben-Nun et al. 1981,Lider et al. 1988). We have performed a pilot study of TCV with MBP-reactive T cells in a small number of MS patients (Zhang et al. 1993,Medaer et al. 1995). The patients were immunised three times with autologous irradiated MBP-reactive T cell clones (see Figure 1).

In multiple sclerosis (MS), T-cells are considered to be critical in coordinating an immunopathological cascade that results in myelin damage. We investigated whether clinical disease activity or brain inflammatory activity as measured by magnetic resonance imaging (MRI) was associated with changes in autoreactive T-cell reactivities in MS patients. To this end, a longitudinal study was performed in which T-cell-related immune parameters and clinical parameters (including MRI) were monitored in seven relapsing-remitting (RR) MS patients and two healthy controls with bimonthly intervals over a period of 18 months. The serial evaluation of antimyelin (MBP, PLP, MOG) T-cell responses revealed highly dynamic shifts and fluctuations from one pattern to another in a patient-dependent manner. In some of the patients, changes in T-cell-related immune variables were found to concur with MRI activity and generally preceded clinical relapses. These alterations include: increased number of myelin-reactive IFN-gamma secreting T-cells, detection of clonally expanded myelin-reactive T-cells, elevated proinflammatory and decreased antiinflammatory cytokine production, upregulation of ICAM-1 membrane expression and highly increased serum levels of soluble VCAM-1. However, not all exacerbations and MRI changes were associated with changes in antimyelin reactivity. Some of the observed immune alterations were also detected in the healthy controls, indicating that additional regulatory mechanisms-which may be defective in MS-play a role in the downregulation of potentially pathological T-cell responses. In conclusion, this study provides further support for an important role of myelin-reactive T-cells in the pathogenesis of MS. In addition, the observed dynamic changes in the antimyelin T-cell reactivity pattern may be a major obstacle for the development of antigen-specific immunotherapies.

Myelin proteins, including myelin basic protein (MBP), proteolipid protein (PLP) and myelin oligodendrocyte glycoprotein (MOG) are candidate autoantigens in MS. It is not clear whether MS patients show a predominant reactivity to one or several myelin antigens. We evaluated the IFN-gamma production induced by MBP and MOG and selected MBP-, MOG- and PLP-peptides in MS patients and healthy controls using the IFN-gamma ELISPOT assay. Most MS patients and healthy controls showed a heterogeneous anti-myelin T-cell reactivity. Interestingly in MS patients a positive correlation was found between the anti-MOG and anti-MBP T-cell responses. No myelin peptide was preferentially recognized among the peptides tested (MBP 84-102, 143-168, MOG 1-22, 34-56, 64-86, 74-96, PLP 41-58, 184-199, 190-209). In addition the frequency of IL2R+ MBP reactive T-cells was significantly increased in blood of MS patients as compared with healthy subjects, indicating that MBP reactive T-cells exist in an in vivo activated state in MS patients. Most of the anti-MBP T-cells were of the Th1-type because reactivity was observed in IFN-gamma but not in IL-4 ELISPOT-assays. Using Th1 (IL-12) and Th2 (IL-4) promoting conditions we observed that the cytokine secretion pattern of anti-MBP T-cells still is susceptible to alteration. Our data further indicate that precursor frequency analysis of myelin reactive T-cells by proliferation-based assays may underestimate the true frequency of myelin specific T-cells significantly.

Although the etiology and pathogenesis of Multiple Sclerosis (MS) remain elusive, accumulating evidence indicates that MS is a chronic inflammatory disease with an autoimmune component, mediated by autoreactive T lymphocytes specific for myelin antigens. The triggering T cell autoantigen has not been identified yet, but recent immunological studies in MS and parallel experiments in experimental allergic encephalomyelitis (EAE), the animal model of MS, have indicated that myelin basic protein (MBP) can be considered as one of the major candidate autoantigens in the pathogenesis of the disease. Based on these observations, several therapeutic strategies have been developed aimed at the specific elimination or inactivation of MBP reactive T cells in MS. One of these approaches involves the immunization of MS patients with autologous attenuated autoreactive T cells to induce an immune response specifically targeted at these autoreactive T cells. This method, termed T cell vaccination, has been shown to prevent and treat EAE. We have recently conducted a pilot trial of T cell vaccination in a limited group of MS patients to evaluate the immunological responses to the injected cells. The data obtained indicate that this type of vaccination induces an effective anti-clonotypic T cell response leading to a specific depletion of circulating MBP reactive T cells. Preliminary data on the clinical effects are promising, encouraging further clinical trials.

A panel of 90 myelin basic protein (MBP)-specific T-cell lines were derived from peripheral blood of eight patients with multiple sclerosis and four normal subjects. The precursor frequency of MBP-reactive T cells in peripheral blood mononuclear cells ranged from 10(-7) to 9 x 10(-7) (mean, 6.7 x 10(-7)) in the group of patients with multiple sclerosis and from 0.5 x 10(-7) to 9.8 x 10(-7) (mean, 5.6 x 10(-7)) in the control subjects. This difference between the two groups was not statistically significant (p greater than 0.1). These T-cell lines expressed exclusively CD3+CD4+CD8- phenotypes and were restricted predominantly by HLA-DR molecules. When tested with fragments and synthetic peptides of human MBP, these MBP-specific T-cell lines (45 lines for each group) displayed a limited heterogeneous pattern with a biased recognition to peptide 84-102 and the C-terminal peptide 149-171. The reactivity to the 84-102 region of MBP was associated with the HLA-DR2, DRw15 (DRw15,2) haplotype, whereas the recognition to peptide 149-171 did not correlate with a particular HLA-DR allele(s). Furthermore, the majority of T-cell lines (greater than 75%) were found to exhibit substantial cytotoxic activity against MBP-coated target cells, but showing no significant difference between these two groups. This MBP-dependent cytotoxicity was not associated with epitope specificities of the T-cell lines tested.