Background/Objectives: The prevalence of food allergy (FA) in children is increasing. Dysbiosis of the microbiome has been linked to FA but needs to be better understood. We aimed to characterize the gut and skin microbiome of young food-allergic children over time and within different types of immunoglobulin E (IgE)-mediated FA. Methods: We studied 23 patients, as a pilot study of an ongoing prospective multicenter cohort study including children < 2y with newly diagnosed IgE-mediated FA. Samples (feces/skin swabs) were collected at enrollment and at 1-year follow-up and sequenced for the bacterial 16S rRNA gene (hypervariable v1–v2 region). Results: Gut and skin bacterial diversity was significantly higher in patients compared with controls and increased over time (beta test, Shannon diversity, p < 0.01). Within different types of IgE-mediated FA, bacterial diversity was similar. Community composition differed significantly over time and within IgE-mediated FA types (PERMANOVA: p < 0.01). Several significantly different genus abundances were revealed. We observed a positive correlation between high total IgE and a high abundance of the genus Collinsella in patients with a higher number of allergies/sensitizations (≥3), and patients with tree nut and/or peanut allergy. Conclusions: This study revealed an increased bacterial diversity in children with FA compared with non-atopic children. Importantly, the gut and skin microbiome differed in their composition over time and within different types of IgE-mediated FA. These findings contribute to the understanding of microbiome changes in children with FA and indicate the potential of the genus Collinsella as a biomarker for tree nut and/or peanut allergy and possibly for allergy persistence.

AIM OF THE STUDY: Oral immunotherapy (OIT) is increasingly used for the treatment of childhood food allergies, with limited data available on cashew nut OIT. This real-life study investigated the safety and feasibility of cashew nut OIT, comparing it with peanut OIT, with a focus on the up-dosing process. METHODS: We analysed cashew nut (n = 24) and peanut (n = 38) OIT cases with treatment initiated between 2018 and 2022 at the University Childrenʼs Hospital Basel. All patients who commenced therapy within this time frame were enrolled without prior selection. Two different starting protocols were used. Within the up-dosing protocol, the nut intake was incrementally increased by 20–30% every 2 weeks until reaching a maintenance dose of 1 g of nut protein. After consuming the maintenance dose regularly for 18–24 months, a second oral food challenge was performed. Patients who passed this challenge were considered desensitised. The safety of the therapy was evaluated based on the severity of adverse reactions during the up-dosing phase. Symptom severity was evaluated using the validated ordinal food allergy severity scale (o-FASS-5). RESULTS: Over the study period, 33% of cashew nut-allergic and 63% of peanut-allergic patients experienced mild to moderate allergic reactions. Severe allergic reactions occurred in five peanut-allergic children with high baseline allergen-specific IgE levels. Six patients with peanut, and none with cashew nut OIT, discontinued the therapy due to adverse reactions. The mean duration to reach the maintenance phase was longer for children with asthma or another food allergy. Among children who already underwent the second oral food challenge, desensitisation was achieved in 91% (11 out of 12) of cashew nut- and 73% (11 out of 15) of peanut-allergic patients. CONCLUSION: Cashew nut OIT had a low severity of adverse reactions and was generally well-tolerated. However, patient characteristics influenced side effect risk and treatment duration, emphasising the need for individualised OIT strategies.