Age-determined expression of priming protease TMPRSS2 and localization of SARS-CoV-2 infection in the lung epithelium.

The SARS-CoV-2 novel coronavirus global pandemic (COVID-19) has led to millions of cases and hundreds of thousands of deaths around the globe. While the elderly appear at high risk for severe disease, hospitalizations and deaths due to SARS-CoV-2 among children have been relatively rare. Integrating single-cell RNA sequencing (scRNA-seq) of the developing mouse lung with temporally-resolved RNA-in-situ hybridization (ISH) in mouse and human lung tissue, we found that expression of SARS-CoV-2 Spike protein primer was highest in ciliated cells and type I alveolar epithelial cells (AT1), and expression was increased with aging in mice and humans. Analysis of autopsy tissue from fatal COVID-19 cases revealed SARS-CoV-2 RNA was detected most frequently in ciliated and secretory cells in the airway epithelium and AT1 cells in the peripheral lung. SARS-CoV-2 RNA was highly colocalized in cells expressing . Together, these data demonstrate the cellular spectrum infected by SARS-CoV-2 in the lung epithelium, and suggest that developmental regulation of may underlie the relative protection of infants and children from severe respiratory illness.