Celiac Sprue is an inheritable autoimmune disorder of the small intestine that is triggered in patients upon exposure to dietary gluten from common food sources such as wheat, rye and barley. Notwithstanding 50 years of active research into this disease, there is no therapeutic alternative to a strict lifelong gluten-free diet. The long-term goal of this project is the development of inhibitors for the Class II MHC-mediated immunopathogenic response to gluten in Celiac Sprue patients. Several studies have implicated a causative role for HLA-DQ2, the class II MHC allele present in >90% of Celiac Sprue patients. More recently, epitopes have been identified in gluten that induces proliferation of CD4+ inflammatory T-helper cells in a DQ2 restricted manner. Therefore, the specific aims of this exploratory project are two-fold: (i) To solve the X-ray crystal structure of HLA-DQ2 bound to a high-affinity gluten epitope; and (ii) To identify synthetic peptides that bind tightly to HLA-DQ2, but inhibit HLA-DQ2 mediated proliferation of disease-specific T cells derived from Celiac Sprue patients. In support of these aims, we have (i) identified a proteolytically resistant gluten peptide that contains a high affinity HLA-DQ2 binding sequence; (ii) developed a homology model for the binding of this epitope to the HLA-DQ2 active site based on the recent crystal structure of the closely related HLA-DQ8 heterodimer; (iii) used this model to predict which residues in the epitope are likely to influence DQ2 binding and T cell receptor binding; (iv) developed an expression system and purification procedure for a soluble form of HLADQ2; and (v) identified conditions for reproducible growth of birefringent crystals of soluble HLA-DQ2. If successful, the project will provide a strong starting point for the eventual identification of an oral prophylactic drug candidate for Celiac Sprue therapy. More generally, it provides a unique opportunity to validate class II MHC proteins as attractive therapeutic targets for autoimmune disorders.
