Expansion of Cytotoxic CD4+ T Cells in the Lungs in Severe COVID-19

The contributions of T cells infiltrating the lungs to SARS-CoV-2 clearance and disease progression are poorly understood.  Although studies of CD8+ T cells in bronchoalveolar lavage and blood have suggested that these cells are exhausted in severe COVID-19, CD4+ T cells have not been systematically interrogated within the lung parenchyma. We establish here that cytotoxic CD4+ T cells (CD4+CTLs) are prominently expanded in the COVID-19 lung...