Early IL-10 producing B-cells and coinciding Th/Tr17 shifts during three year grass-pollen AIT

Background: Allergen-specific immunotherapy (AIT) is a causative treatment in allergic airway disease, comprising long-term allergen administration and requiring three years of treatment. Mechanisms and biomarkers that translate into clinical efficacy remain urgently needed. Methods: In an exploratory observational allergy cohort we phenotyped 32 grass-pollen allergic patients with hayfever undergoing AIT for over three years and controls using local and systemic samples for ex vivo FACS, nasal transcriptomes and in vitro phleum-stimulation at critical time windows six hours after therapeutic allergen administration and during peak-season responses. Findings: The up-dosing phase is marked by increased IL-10 ⁺ B-cells with allergen-specific PD-L1 up-regulation, while effector Th1/Th17 cells and CCR6 ⁺ IL-17 ⁺ FoxP3 ⁺ T-cells decrease. The conversion phase exhibits Th17 recovery in the absence of Th2 cells. The tolerance-mounting phase after three years of treatment is characterized by induction of Tregs while Th2 and phleum-specific Th17 responses decrease. Notably, high ratios of circulating Breg/Th17 following initial AIT correlate significantly with clinical improvement after three years. Interpretation: Our exploratory data hypothezise differential shifts in the hierarchy of tolerance in three distinct phases of AIT characterized by conversion of regulatory against pro-inflammatory mechanisms, of which the Breg/Th17 ratio after initial treatment emerges as potential early prediction of AIT efficacy. Fund: This study was partially funded by Allergopharma GmbH & Co. KG, intramural funding and the German Center for Lung Research (DZL).