Structural and functional characterization of protective antibodies induced in peanut oral immunotherapy

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Food allergy affects up to 10% of the US population, and peanut is one of the most common food allergens, often leading to persistent IgE-mediated food allergy. Only a subset of patients with food allergy develop clinical tolerance after oral immunotherapy (OIT), while most only have transient benefit. We and others have shown that serum IgG antibodies to peanut allergens suppress basophil activation, which is a biomarker of tolerance in OIT. In order to elucidate the mechanisms of long-term tolerance in OIT, we still need to understand how these peanut-specific IgG antibodies contribute to clinical protection on a clonal level. Our long-term goal to develop new antibody-based treatments for IgE-mediated food allergies depend on elucidating the underlying antibody-mediated mechanism of long-term tolerance induced by OIT. During OIT, peanut-specific IgG antibodies are induced and can inhibit effector cells, such as mast cells or basophils. in vitro, these IgG antibodies can prevent allergen effector cell activation by both blocking IgE from being cross-linked by allergen and binding to inhibitory receptors. Our previous work focused on Ara h 2, which is the most immunodominant and clinically relevant peanut allergen. In that study, suppression of Ara h 2 stimulated basophils was a biomarker of tolerance while the concentration of Ara h 2 specific IgG, was not. Therefore, we hypothesize that tolerance after OIT results from the induction of uniquely protective IgG clones rather than the general increase in allergen-specific IgG. These protective antibodies effectively prevent IgE-mediated reactions. Based on these findings, we hypothesize that protective antibodies share unique structural characteristics that allow them to bind to critical epitopes of Ara h 2 with competitive fitness and that epitope- specific protective antibodies can functionally suppress allergen-specific IgE from a diverse set of patients. Our approach involves using recombinant antibodies cloned from single antigen-specific B cells isolated from individuals with or without tolerance after OIT. We are uniquely positioned to conduct this study in that we have expertise in affinity-selection of antigen-specific B cells, recombinant antibody cloning, and antibody characterization from a unique patient cohort. We will address our hypothesis in the following specific aims: (1) Define Ara h 2 binding characteristics of protective allergen-specific IgG antibodies in tolerance; and (2) Identify functionally suppressive allergen-specific IgG antibodies in tolerance. We anticipate that the proposed studies will elucidate the connection between long-lasting clinical efficacy of OIT on a clonal level with protective antibodies, highlighting the critical role of specific clones in conferring long-term tolerance in food allergy. This work will lead to new strategies for the treatment of food allergies.