Persistent viral activity, cytokine storm and lung fibrosis in severe COVID-19

Severe COVID-19 may progress into acute respiratory distress syndrome (ARDS) with high mortality risk. Its exact pathological mechanism, therapeutic obstacles and the clinical sequelae are critical and unresolved issues. Here, we reported a representative COVID-19 induced ARDS case experienced initially stable, then suddenly deteriorating up to final respiratory failure courses, until his death despite of lung transplantation. His lung pathology showed necrosis of parenchymal tissues, extensive immune cell infiltration and lung fibrosis. Single-cell RNA sequencing revealed various immune cell populations were largely expanded in his lung, and manifested inflammatory/activated functions. We also showed that cell-crosstalk between lung macrophages and fibroblasts promoted pulmonary fibrosis through IL-1B and TGF-? signaling pathways. Although SARS-CoV-2 RNA remained undetectable in his respiratory tract specimens including BALF at the later stage of his disease, the presence of SARS-CoV-2 was definitely confirmed in his lung tissues. Thus, this case indicates the pathological mechanism of severe COVID-19 includes pulmonary SARS-CoV-2 persistence, deranged inflammation and the extensive lung fibrosis which set the barriers for effective treatments and indicate potential health complications for severe COVID-19 patients. Overall design: Using 10x genomics to measure single-cell RNA sequence (scRNA-seq) to comprehensively characterize the lung microenvironment in 4 lung tissues from the same COVID-19 severe patient.