Specific immunotherapeutic strategy for myasthenia gravis: targeted antigen-presenting cells

The pathogenesis of myasthenia gravis (MG) involves a T cell-dependent antibody-mediated autoimmune response directed against acetylcholine receptors (AChR). Inactivation of AChR-specific T cells should interrupt the immune response, resulting in therapeutic benefit. Since each individual's repertoire of T cells responds to a heterogeneous and unique spectrum of AChR epitopes presented in association with self-major histocompatibility complex (MHC) class II, an individualized approach is required to target all relevant AChR-specific T cells. The individual's own antigen-presenting cells (APC) can be used for this purpose, since they process and present the antigen appropriately, and express the correct MHC class II. A novel method of binding AChR to surface immunoglobulin with a heterobifunctional antibody conjugate allows us to use all B cells as APC. Conjugate-plus-AChR-treated B cells (AChR-APC) effectively targeted AChR-specific T cells, stimulating vigorous proliferative responses in a rat cell culture system. If APCs are 'fixed' with cross-linking reagents, they induce long-lasting or permanent 'anergy' of the specific T cells. We prepared AChR-APC, allowed them to process AChR in vitro, and fixed them with paraformaldehyde. Pre-culture of these fixed AChR-APC with AChR-specific T cells induced anergy: when restimulated with fresh AChR-APC, the T cells exhibited markedly reduced proliferative responses and IL-2 production, compared with responses of T cells pre-cultured with control fixed B cells. Implications for the design of antigen-specific therapeutic strategies for MG and other immune disorders will be discussed.