Extracellular vesicle microRNAs as predictors of response to omalizumab in chronic spontaneous urticaria

To the Editor, Despite the marked efficacy for omalizumab in patients with H1antihistamine–resistant chronic spontaneous urticaria (CSU), some patients fail to respond, and there is no available biomarker to predict response outcome.1 Extracellular vesicle (EV)–associated microRNAs are novel response biomarkers.2,3 In this IRB-approved observational study (Figure S1), CSU patients received 300 mg omalizumab on Days 0 (baseline), 30, and 60 and their clinical response was assessed using weekly urticaria activity score (UAS7) for a 12-week period.4 Blood samples for eosinophil and basophil count and EV microRNA extraction were collected at baseline (before omalizumab administration). Blood was also collected at Day 90 for EV microRNA analysis. Participants were classified as complete responders (CR), partial responders (PR), or non-responders (NR) by their area under the curve (AUC) for UAS7 scores (Table S1, Figure S1). Detailed methods including statistics are in Data S1. Study outcomes were identification of (a)