Tu181 - A Humanized Mouse Model Reveals NETosis as a Key Driver of SARS-CoV-2-Induced Lung Pathology

Abstract Text: Neutrophil extracellular trap (NET) formation, or NETosis, is a distinct response of human, but not mouse, neutrophils to SARS-CoV-2 infection. NETosis contributes to lung pathology and represents a potential therapeutic target. Here, we describe a novel humanized mouse model, MICTRG6, generated on the C57Bl/6N background, which enhances human myelopoiesis and supports the development of functional human neutrophils. Using in vitro and in vivo approaches, we demonstrate that NETosis in human neutrophils results from direct SARS-CoV-2 infection rather than phagocytosis and can be suppressed by inhibiting viral replication. Targeting key enzymes involved in histone citrullination or caspase-1 activity effectively blocked NETosis, implicating these pathways in disease progression. To mechanistically dissect the role of citrullination, we engineered humanized mice lacking PADI4, which exhibited significantly reduced NETosis in circulation and lungs during SARS-CoV-2 infection. Furthermore, treatment with Pefabloc, a serine protease inhibitor, effectively diminished NET formation, highlighting a promising therapeutic approach to mitigate lung pathology and inflammation. Notably, NETosis also influenced systemic immunity, as the elevated frequency of immature neutrophils in MICTRG6 mice—resembling clinical observations—was markedly reduced in the absence of NETosis. These findings provide key insights into the systemic impact of NETosis in SARS-CoV-2 infection and establish MICTRG6 as a valuable model for studying human neutrophil-driven pathophysiology.