CCR1 and COVID-19: Based on the specificity algorithm used in MAGMA [63], we noticed that the top specific cell type of CCR1 was CD16+monocytes, CXCR6 was most specifically expressed in memory CD8+T cells, and ABO was specific to megakaryocytes (Additional file 3: Fig. S21A), recalling that CXCR6, CCR1, and ABO were prioritized to be candidate causal genes for severe COVID-19 based on the V2G score in above genetics-based analysis.