|Ph.D Student||Rony Dahan|
|Subject||Antibodies against Auto Reactive T cell Epitopes: Study of|
Autoimmune-Associated Antigens Presented by MHC
Class II Molecules
|Department||Department of Biology||Supervisor||Full Professor Reiter Yoram|
|Full Thesis text|
Antigen presenting cell-associated four-domain MHC class-II molecules play a central role in activating specific CD4 T-cells involved in autoimmune diseases, including Multiple Sclerosis (MS) and Type 1 Diabetes (T1D). In contrast, two domain MHC class II structures with the same covalently attached self peptide (RTLs = Recombinant T-cell receptor Ligands) can regulate pathogenic CD4 T cells and reverse clinical signs of experimental autoimmune disease in animal models. We isolated and characterized novel antibodies against autoreactive T-cell epitopes associated with T1D and MS autoimmunity. Our antibodies mimic the specificity of the CD4 autoreactive T-Cell receptor, while binding MHC class II/peptide complexes in an autoantigen peptide specific, MHC restricted manner. We isolated TCR-Like (TCRL) Abs directed to the minimal Diabetes-associated DR4/GAD-555-567 T-cell epitope. These Abs were found to be of high significance for two major research directions: for translational-clinical applications and for basic studies of autoantigen presentation during T1D. Our TCRL Abs enabled the detection of APCs presenting the DR4/GAD-555-567 epitope in islets of Langerhans of the pancreas of RIP-B7/DR4 diabetic mice. Such APCs were detected in infiltrated islets of young pre-diabetic mice as well as in islets of diabetic mice, demonstrating the important role of this epitope both in the initiation and early stages as well as in the later progression stage of T1D. For clinical studies, G3H8 capable of significantly inhibit GAD-555-567 specific, HLA-DR4 restricted T-cell response. Thus, we demonstrated a proof of concept for the utility of our TCRL Abs as Ag-specific therapeutic agents that can regulate pathogenic CD4 T-cells. To evaluate opposing biological effects of the DR2/MOG-35-55 idiotope present in native vs. RTL structures, we generated TCRL Abs against RTL constructs. Different high-affinity Abs were isolated that bound to and neutralized activity of the two-domain idiotopes present in RTLs, but none of these Abs recognized the cognate four-domain idiotope present in native MHC. These results demonstrate for the first time distinct conformational determinants characteristic of activating vs. tolerogenic idiotopes involved respectively in induction vs. regulation of human autoimmune diseases. Moreover, detection of native two-domain HLA-DR structures in human plasma implicated naturally-occurring regulatory idiotopes. This finding implies that the distinct shape of class II idiotopes formed by truncated two-domain structures may provide a natural tolerogen for regulating inflammatory T cells. TCR-like Abs represent a valuable tool for studying Ag presentation during autoimmune inflammation, and may constitute novel therapeutic agents for treating human diseases involving excessive or deficient immune reactivity.