Neutrophil myeloperoxidase as a functional biomarker for RSV severity: implications for in vitro therapeutic...

Respiratory syncytial virus (RSV) is a leading cause of severe lower respiratory tract infections in infants, yet therapeutics are lacking. The aim of this study was to develop a pre‑clinical model that recapitulates key clinical outcomes in infants with RSV bronchiolitis, such as neutrophil activation and migration into the airways. Peripheral blood neutrophils from infants with severe RSV disease admitted to the Paediatric Intensive Care Unit showed elevated myeloperoxidase (MPO) in children with RSV, compared to age-matched controls. To mechanistically model this response, we established an air-liquid interface (ALI) system incorporating paediatric airway epithelial cells, endothelial cells and neutrophils from adults, to recapitulate the blood-airway barrier. Following RSV infection, with and without treatment with antivirals remdesivir or RSV604, neutrophil migration and activation were assessed using flow cytometry. While both drugs reduced viral load, only RSV604 attenuated MPO expression. This model suggests that MPO could be useful as a readout of therapeutic efficacy. Targeting neutrophil-driven inflammatory pathways may be critical for reducing pathology in infant RSV infection.