IDO1 and COVID-19: Meanwhile, we verified the existence of CCR7+CCL22/IDO1+ DCs, CD160+CD8+ T cells, and TNFRSF4+CD4+ T cells in public scRNA-seq datasets of normal human lung tissues29 and bronchoalveolar lavage fluid (BALF) of COVID-19 patients in COVID-19 Cell Atlas (Fig. 4f), suggesting the potential role of these cell types in lung immune surveillance and response to SARS-CoV-2 pulmonary infection.