TCR peptide-reactive T cells and peripheral tolerance to myelin basic protein

Insulin-dependent diabetes loci Idd5 and Idd9 increase sensitivity to experimental autoimmune encephalomyelitis

The spontaneous development of autoimmune diabetes in NOD mice suggests that they are unable to establish and maintain immunologic self-tolerance. Congenic NOD mice expressing B10-derived alleles are protected from pancreatic beta cell destruction and autoimmune diabetes. To determine if the B10 alleles in loci Idd5 and Idd9 could influence susceptibility to autoimmunity in other organs, we compared MOG35-55-induced EAE in NOD mice to that of diabetes-resistant NOD.B10.Idd5 and NOD.B10.Idd9 mice. Surprisingly, the severity and chronicity of EAE were enhanced in the diabetes-resistant congenic mice. Our findings indicate that some alleles may influence susceptibility to immune-mediated damage in an organ or tissue-specific fashion, and highlight the necessity of disease-specific investigations.

Homeostatic control of immunity by TCR peptide-specific Tregs

Regulation of the immune response is a multifaceted process involving lymphocytes that function to maintain both self tolerance as well as homeostasis following productive immunity against microbes. There are 2 broad categories of Tregs that function in different immunological settings depending upon the context of antigen exposure and the nature of the inflammatory response. During massive inflammatory conditions such as microbial exposure in the gut or tissue transplantation, regulatory CD4+CD25+ Tregs broadly suppress priming and/or expansion of polyclonal autoreactive responses nonspecifically. In other immune settings where initially a limited repertoire of antigen-reactive T cells is activated and expanded, TCR-specific negative feedback mechanisms are able to achieve a fine homeostatic balance. Here I will describe experimental evidence for the existence of a Treg population specific for determinants that are derived from the TCR and are expressed by expanding myelin basic protein-reactive T cells mediating experimental autoimmune encephalomyelitis, an animal prototype for multiple sclerosis. These mechanisms ensure induction of effective but appropriately limited responses against foreign antigens while preventing autoreactivity from inflicting escalating damage. In contrast to CD25+ Tregs, which are most efficient at suppressing priming or activation, these specific Tregs are most efficient in controlling T cells following their activation.

Regulatory T cells control autoimmunity in vivo by inducing apoptotic depletion of activated pathogenic lymphocytes

Clinical autoimmunity requires both activation of self-reactive T cells as well as a failure of peripheral tolerance mechanisms. We previously identified one such mechanism that involves regulatory T cells recognizing TCR V beta 8.2 chain-derived peptides in the context of MHC. How this regulation affects the fate of target V beta 8.2(+) T lymphocytes in vivo that mediate experimental autoimmune encephalomyelitis has remained unknown. The present study using immunoscope and CFSE-labeling analysis demonstrates that the expansion of regulatory CD4 and CD8 T cells in vivo results in apoptotic depletion of the dominant, myelin basic protein-reactive V beta 8.2(+) T cells, but not subdominant V beta 13(+) T cells. The elimination of only activated T cells by this negative feedback mechanism preserves the remainder of the naive V beta 8.2(+) T cell repertoire and at the same time results in protection from disease. These studies are the first in clearly elucidating the fate of myelin basic protein-specific encephalitogenic T cells in vivo following regulation.

Activation of natural killer T cells potentiates or prevents experimental autoimmune encephalomyelitis

Natural killer (NK) T cells recognize lipid antigens in the context of the major histocompatibility complex (MHC) class 1-like molecule CD1 and rapidly secrete large amounts of the cytokines interferon (IFN)-gamma and interleukin (IL)-4 upon T cell receptor (TCR) engagement. We have asked whether NK T cell activation influences adaptive T cell responses to myelin antigens and their ability to cause experimental autoimmune encephalomyelitis (EAE), a model for multiple sclerosis. While simultaneous activation of NK T cells with the glycolipid alpha-galactosylceramide (alpha-GalCer) and myelin-reactive T cells potentiates EAE in B10.PL mice, prior activation of NK T cells protects against disease. Exacerbation of EAE is mediated by an enhanced T helper type 1 (Th1) response to myelin basic protein and is lost in mice deficient in IFN-gamma. Protection is mediated by immune deviation of the anti-myelin basic protein (MBP) response and is dependent upon the secretion of IL-4. The modulatory effect of alpha-GalCer requires the CD1d antigen presentation pathway and is dependent upon the nature of the NK T cell response in B10.PL or C57BL/6 mice. Because CD1 molecules are nonpolymorphic and remarkably conserved among different species, modulation of NK T cell activation represents a target for intervention in T cell-mediated autoimmune diseases.

Induction of a type 1 regulatory CD4 T cell response following Vβ8.2 DNA vaccination results in immune deviation and protection from experimental autoimmune encephalomyelitis

DNA vaccination has been used to generate effective cellular as well as humoral immunity against target antigens. Here we have investigated the induction and involvement of regulatory T cell (T(reg)) responses in mediating prevention of experimental autoimmune encephalomyelitis (EAE), following vaccination with plasmid DNA encoding the TCR V(beta)8.2 chain predominantly displayed on disease-causing lymphocytes. Vaccination with DNA encoding the wild-type TCR results in priming of type 1 CD4 T(reg) and skewing of the global response to myelin basic protein in a T(h)2 direction, leading to significant protection from disease. In contrast, vaccination with mutant DNA encoding altered residues critically involved in recognition by the T(reg) results in priming of a type 2 regulatory response which fails to mediate immune deviation or protection from EAE. Control mice immunized with DNA, encoding TCR with changes at an irrelevant site, were protected from antigen-induced disease. Furthermore, protection can be transferred into naive recipients with CD4 T(reg) from wild-type DNA-immunized mice but not from animals vaccinated with the mutant DNA. These data suggest that vaccination with plasmid DNA encoding one or multiple V(beta) genes can be exploited to enhance natural regulatory responses for intervention in autoimmune conditions.

Cellular and humoral immune responses against autoreactive T cells in multiple sclerosis patients after T cell vaccination

Myelin basic protein (MBP)-reactive T cells may play an important role in the autoimmune pathogenesis of multiple sclerosis (MS). MBP-reactive T cells can be specifically targeted by T cell vaccination, a procedure whereby MS patients are immunized with attenuated autologous MBP reactive T cells. T cell vaccination induces immune responses to the vaccine cells together with a depletion of MBP reactive T cells. Forty-nine MS patients were treated with T cell vaccination in an extended phase I trial to study the safety, immune responses and clinical effects of T cell vaccination. In the present paper the immune responses towards the vaccine cells were characterized. Substantial long-term in vitro proliferative responses were observed in all treated patients. Some patients, immunized with different clones, displayed distinct proliferative reactivity against the various vaccine clones, suggesting unequal immunogenic properties of these clones. Reactive TCRalphabeta(+), CD8(+)and CD4(+)T cells, and to a lesser extent, gammadelta T cells and NK cells were observed to in vitro stimulation with the vaccine cells. A small fraction only of CD8(+)T cells expressed cytolytic and inhibitory anti-clonotypic reactivity against the vaccine cells. Stimulation with the vaccine clones predominantly induced expression of pro-inflammatory cytokines in these mixed cultures, although one vaccine clone consistently induced production of IL-4. CD4(+)T cells are the major cytokine-producing cells in these anti-vaccine lines. We could not detect upregulated antibody responses to the vaccine cells in most patients, although a temporary antibody response was observed in one patient. In conclusion, immunization with attenuated autoreactive T cells induces a complex cellular response specifically targeted at the vaccine cells, but no antibody responses. These data provide further insights into the mechanisms of T cell vaccination and improve our understanding of the complex regulatory networks of autoreactive T cells.