PROJECT SUMMARY Food allergies (FAs) are a world-wide problem, and allergies to multiple foods are particularly problematic. In the U.S., ingestion of offending food allergens is the most common cause of anaphylaxis seen in hospital emergency departments (EDs), and it is estimated that ~30,000 food-induced anaphylactic events are seen in U.S. EDs each year; sadly, ~200 of these events prove fatal. Peanuts or tree nuts cause the majority of these deaths, and a recent survey in the U.S. found that 1.4% of the population is allergic to peanuts or tree nuts and ~30% of patients with FAs have allergies to multiple foods. In peanut allergy (PA), landmark studies by A. Wesley Burks and colleagues have shown that children can be desensitized to peanut via an oral immunotherapy (OIT) protocol. We have replicated these results in adults and children, and also have carried out a pilot study showing that FA patients can be desensitized to multiple food allergens simultaneously (i.e., multi-OIT). Moreover, we found that there were fewer adverse events in the build-up phase of multi-OIT if patients received the anti-IgE antibody, omalizumab, concomitantly with multi-OIT. In an effort to improve understanding of the systemic and local (i.e., GI) immune responses that underlie PA and therapeutic responses to OIT, we are currently conducting a placebo-controlled, randomized, phase 2 clinical trial of OIT in 120 children and adults with PA (the POISED trial), and are applying state-of-the-art human immune monitoring methods to analyze blood and GI tissue specimens of participants in that study. In this AADCRC U19 renewal application, we propose to conduct a pilot, placebo-controlled, randomized, phase 2 clinical trial of OIT with or without omalizumab or the anti-IL-4Rα antibody, dupilumab, in children and adults with multiple FAs (multi-FAs). We propose to measure a broad range of blood and GI biopsy cellular findings, as well as serologic and clinical findings, in longitudinal samples from multi-FA participants undergoing the trial, as well as from appropriate control participants (i.e., multi-FA participants who are not treated, healthy controls, and atopic controls without FA). We will use these data to define how key systemic or GI tissue immune parameters change during multi-OIT, and which are most predictive of the nature and durability of patient responses to this therapy. Specifically, we will evaluate whether there are blood- or GI tissue-derived biomarkers that predict therapeutic responses to individual allergens, or to all allergens, in multi-OIT. In addition, we will seek to identify immune monitoring parameters, including findings derived from analyses of basophil phenotype and function that can be rapidly performed in a clinical laboratory using small amounts of blood, that could be used to predict the clinical reactivity to offending allergens in multi-FA subjects, to improve the safety and efficacy of OIT protocols, and...