Nasal mucus-derived KLK13 restricts SARS-CoV-2 infection via proteolytic cleavage of spike

Epithelial cilia directly come into contact with inhaled pathogens. The nasal mucus functions as a formidable barrier against penetration of viral particles. KLK13 is secreted into nasal mucus and efficiently cleaves the spike proteins across different coronavirus species. KLK13-mediated cleavage of spike inhibits SARS-CoV-2 entry and syncytium formation. Intranasally delivered KLK13 also restricts SARS-CoV-2 infection <i>in vivo</i>. The finding that KLK13 acts as a scissor of viral spike in nasal mucus paves the way for the development of new antivirals against respiratory viruses.