SPP1 and COVID-19: We identified that enrichment of transcriptional signature of SPP1-driven CD274+ (PD-L1+) neutrophils was significantly higher in Neutrophil_2 phenotype than any other cell population (Figure 6, E and F) in COVID-19 patients and that this phenotype was uniquely increased in severe disease, suggesting that SPP1 might be responsible for the pathogenic activation of neutrophils in severe COVID-19.