The peripheral blood mononuclear cells (PBMCs) of each individual were isolated from the whole blood, and a scRNA-seq analysis of the PBMCs was performed on the 10X genomics platform with Chromium Next GEM Single-Cell V(D)J Reagent Kits v1.1(Fig. 1a).18 After quality control, in the first-round analysis, we obtained 241,292 PBMC cells, 131,391 TCR clones, and 23,674 BCR clones from the 19 samples of 19 individuals, including 16 patients with COVID-19 and three controls. Here, BCR is linked to COVID-19.