Circulating epithelial cell as viral infection and tissue origin marker in patients with severe COVID-19.

Liquid biopsy (LB) is a minimally invasive procedure that detects biomarkers in body fluids for real-time monitoring of patients. This study developed a new LB approach to analyze Circulating Epithelial Cells (CECs) in Intensive Care Unit (ICU) patients with severe COVID-19 and High-Exposure Negative Population to COVID-19 (HENPC) as the control group. The CECs were characterized by multispectral imaging flow cytometry, and an anti-SARS-CoV-2 Spike S1 protein (ProtS) antibody was used to detect infection. The results showed that CECs were present in most ICU patients (p = 0.0412), and their median number was significantly higher (p = 0.0004) than in controls. CEC clusters were only identified in patients, and high positive ProtS expression was observed in CECs from ICU patients compared to negative controls. In conclusion, LB could be a minimally invasive tool for detecting tissue damage caused by infectious agents and could provide real-time biological information about disease status and evolution. However, further validation in a larger population of patients is needed.