B cell receptor repertoire sequencing to characterise antibody subclass expression and somatic hypermutation in severe eosinophilic asthma and EGPA

Abstract

Introduction Severe eosinophilic asthma (SEA), eosinophilic granulomatosis with polyangiitis (EGPA) and nasal polyposis (NP) are immune-mediated diseases characterised by eosinophilic inflammation. However, there is also increasing interest in the potential pathological roles of auto-antibodies in these diseases. Objectives Understanding the antibody repertoire in these conditions may provide valuable insights into disease mechanisms, and contribute to our understanding of potential roles of targeted biologic therapies. Methods We conducted B cell receptor repertoire sequencing using peripheral blood from 43 patients, comprising SEA with nasal polyps (SEA+NP), SEA without nasal polyps (SEA-NP), and EGPA, along with 16 healthy controls (HCs). Results Compared to HCs, patients with EGPA exhibited increased relative proportions of IgA1, IgG1, IgG2, and IgG4 subclasses. Similarly, SEA-NP patients demonstrated a significantly higher proportion of IgG2 compared to HCs. Notably, the IgG4 subclass was significantly elevated across all patient groups compared to HCs. Patients receiving anti-IL-5/5R biologic treatments showed increased relative proportions of IgA2, IgG2, and IgG3 subclasses compared to untreated patients. Conversely, the proportions of IgE and IgM were decreased in patients on anti-IL-5/5R biologic therapies. Variation across participant groups in mean somatic hypermutation was evident with an increased mutation frequency in IgG3 in SEA-NP patients and decreased mutation frequency in IgA2 in SEA+NP and EGPA patients. No differences were evident in mutation frequencies between those patients on and not on anti-IL-5/5R biologics, except for IgM. Conclusions Our preliminary data is consistent with a pattern of a more mature B cell component in the periphery and with the T2 inflammatory response observed in SEA and EGPA. Analysis of patterns of somatic hypermutation among clonally expanded sequences may be necessary to determine whether the IgE and IgG4 compartments in the peripheral blood are subject to antigen-driven clonal expansion.