PO:37:258 | Neutrophil and eosinophil extracellular traps in eosinophilic granulomatosis with polyangiitis: phenotype-based characterization and response to mepolizumab

Michele Moretti¹, Francesco Ferro², Francesco Pisani¹, Elisa Ferrigno¹, Gaetano La Rocca¹, Federica Di Cianni³, Rosaria Talarico², Marta Mosca¹, Chiara Baldini¹, Ilaria Puxeddu¹. | ¹University of Pisa - Department of Clinical and Experimental Medicine, Pisa, Italy; ²Azienda Ospedaliero Universitaria Pisana - Rheumatology Unit, Pisa, Italy; ³University of Siena, Siena, Italy.

Background. EGPA presents eosinophil (EOS)-related and vasculitic features. Introduction of mepolizumab (MEP) revolutionized the treatment of EOS manifestations. However, efficacy of MEP also in vasculitic phenotypes suggests direct interactions between EOS and neutrophilic inflammation in EGPA. Neutrophil extracellular traps (NETs) are an important innate immune response involved in ANCA-associated vasculitis pathogenesis. Similarly, EOS produce extracellular traps (EETs), recently detected in EGPA patients. Our study aims to analyse NETs and EETs in different disease phenotypes and in response to MEP therapy.

Materials and Methods. EGPA patients classified according to MIRRA trial and/or ACR/EULAR 2022 criteria and eligible for MEP therapy were consecutively enrolled. Clinical and routine blood chemistry data were collected before (T0) and after 6 (T1) and 12 (T2) months of treatment with MEP 300mg/4weeks. Oral steroid was tapered according to clinical judgement. Therapy with immunosuppressant, if taken, was unchanged during the study. In parallel, we evaluated NETs and EETs on peripheral blood by immunofluorescence staining (Petretto et al.,2019). NETs and EETs were expressed as percentage of total area of cells in the fields. Patients were stratified by disease phenotype according to presence/absence of MPO-ANCA, asthma, nasal polyposis (CRSwNP) and organ involvement.

Results. 17 patients were enrolled (53% female (9/17)). MPO-ANCA were detected in 29.4% of patients (5/17). 88% (15/17) were asthmatic, 60% had severe asthma. 53% (9/17) were atopic and 82% had CRSwNP. At T0 94% (16/17) were administered oral prednisone (5.83±4.18mg, mean dose). Figure 1 reports distribution of organ involvement. Following MEP introduction, EOS blood count reduced from T0 to T1 (p=0.036) but not from T1 to T2, while neutrophils did not vary in any period. Steroid dosage was reduced to 1.04±2.59mg at T2 (p=0.003). 10 patients (58.8%) were steroid-free. No relapse was observed. At T0, NETs and EETs levels did not vary by ANCA status, organ involvement, EOS peak count, asthma or CRSwNP presence/severity. NETs levels were negatively correlated to total IgE titre (r=-0.52, p=0.05). EETs values are higher in atopic patients (p=0.017) regardless of steroid dosage and EOS blood count. In response to MEP, NETs and EETs decreased at T1 (respectively p=0.001, p=0.014) but were stable between T1 and T2 in the overall group (Figure 2). After stratification by ANCA status, NETs significantly decreased only in ANCA positive patients at T1 (p=0.01), whereas EETs only in ANCA negative patients at T1 (p=0.025), with no differences observed between T1 and T2. No difference was found according to asthma and CRSwNP presence.

Conclusions. In a representative cohort of EGPA patients, NETs and EETs vary by atopic status but not by ANCA status or organ involvement. After 6 months of therapy, MEP influences NETs and EETs formation according to ANCA profile, suggesting utility of NETs and EETs assessment in disease phenotyping.