Litjen Tan

Antigen-specific tolerance as a therapy for experimental autoimmune encephalomyelitis

The effects of neuroantigen-specific tolerance on the induction and effector stages of EAE were examined. Tolerance induced by the i.v. injection of syngeneic splenocytes coupled with purified neuroantigens or encephalitogenic peptides of MBP and PLP using ethylene carbodiimide was extremely effective in both prevention and treatment of acute and relapsing forms of EAE in Lewis rats and SJL/J mice. The unresponsiveness is rapidly-induced, dose-dependent, long-lasting, efficient, MHC class II-restricted, and exquisitely antigen-specific. This procedure targets only effector cells bearing clonotypic receptors specific for the autoantigen/autoepitope and thus does not depend upon the autoimmune response being dominated by a restricted T cell repertoire. Moreover, it does not require that the response to the autoantigen be dominated by recognition of a specific epitope(s) within a particular autoantigen, or even the identification of the specific autoantigen. The results also demonstrate the usefulness of peripheral tolerance induced by antigen-coupled syngeneic splenocytes for identifying the fine specificity of autoimmune T cell responses which appear to change during the progression of relapsing EAE. Thus, this technique offers major advantages over many other currently employed immunoregulatory strategies and is therefore relevant for establishment of therapeutic protocols for the antigen-specific treatment of human T cell-dependent autoimmune disorders.

CTLA-4 Regulates Expansion and Differentiation of Th1 Cells Following Induction of Peripheral T Cell Tolerance

Intravenous treatment with Ag (peptide)-coupled, ethylene carbodiimide-fixed syngeneic splenocytes (Ag-SP) is a powerful method to induce anergy in vitro and peripheral T cell tolerance in vivo. In this study, we examined the effects of Ag-SP administration on T cell activity ex vivo and in vivo using OVA-specific DO11.10 TCR transgenic T cells. Although treatment with OVA323–339-SP resulted in a strong inhibition of peptide-specific T cell recall responses in vitro, examination of the immediate effects of Ag-SP treatment on T cells in vivo demonstrated that tolerogen injection resulted in rapid T cell activation and proliferation. Although there was an increase in the number of OVA-specific DO11.10 T cells detected in the lymphoid organs, these previously tolerized T cells were strongly inhibited in mounting proliferative or inflammatory responses upon rechallenge in vivo with peptide in CFA. This unresponsiveness was reversible by treatment with anti-CTLA-4 mAb. These results are consistent with the hypothesis that Ag-SP injection induces a state of T cell anergy that is maintained by CTLA-4 engagement.

Specific Immunoregulation of the Induction and Effector Stages of Relapsing EAE via Neuroantigen-Specific Tolerance Induction

The effects of neuroantigen-specific tolerance on the induction and effector stages of relapsing experimental autoimmune encephalomyelitis (R-EAE) were examined. The incidence of clinical and histologic signs of active MSCH-induced R-EAE, and accompanying neuroantigen-specific DTH responses, were dramatically reduced in SJL/J mice tolerized via the i.v. injection of syngeneic splenocytes coupled with MSCH, PLP, or encephalitogenic PLP peptides 7-14 days before priming. MBP-specific tolerance was not effective in preventing active R-EAE. In contrast to MSCH-induced active R-EAE, treatment of recipient mice with splenocytes coupled with MBP and the encephalitogenic MBP 84-104 peptide, but not with PLP, suppressed of clinical signs of adoptive R-EAE mediated by MBP-specific effector T cells in a dose-dependent manner. Neuroantigen-coupled splenocytes were also efficient in treating established disease as tolerization of SJL/J mice after the first incidence of clinical disease significantly reduced the incidence and severity of subsequent paralytic relapses. Antigen-specific tolerance thus provides a powerful approach for the prevention and/or treatment of autoimmune disease.

Successful treatment of adoptive relapsing EAE in SJL/J mice via neuroantigen-specific tolerance induction

REGULATION OF ENCEPHALITOGENIC T CELLS WITH T CELL RECEPTOR PEPTIDES Arthur A. Vandenbark, George Hashim, and Halina Offner, Veterans Affairs Medical Center, Portland, OR. Immunization of Lewis rats with basic protein in adjuvant induces eneephalitogenic T cells specific for the immunodominant 72-89 epitop6, :rid for a secondary epitope, residues 8799. Evaluation of T coil receptor genes utilized by these T cells revealed that the 72-89 specific clones isolated from lymph nodes and spinal cord predominantly utilized V[38.2, whereas the 87-99 specific clones from both organs predominae.tly utilized VI56. These data indicate that the same T cell specificities recovered from the circulation actually penetrate the CNS compartment during induction of EAE. The expression of common V genes allowed the use of TCR peptides for the induction of autoregulatory T cells and antibodies. Injection of the CDR2 peptide corresponding to V~8.2 residues 39-59 or 44-54 not only prevented EAE, but also was eff~ctive as treatment, halting disease progression and speeding recovery from EAE. The rapid offect of TCR peptide therapy suggested triggering of a regulatory recall response to the TCR peptide, resulting in decreased activity of encephalitoganic specificities. In direct support of this idea, TCR peptide treated rats had increased frequencies of TCR peptide specific T cells and decreased frequencies of encephalitogenic T cells in the lymph node, blood, and spinal cords compared to untreated paralyzed rats. These data demonstrate that TCR peptides can induce selective autoregulation of pathogenic T cells, with potential therapeutic application to human autoimmune diseases.