CD4 and COVID-19: Interestingly, plasmacytoid dendritic cell cluster DC_c4 − LILRA4, T_CD4_c04 − ANXA2, T_c14_gdT-TRDV2 (γδ T cells), T_CD8_c09-SLC4A10, and T_CD8_c08-IL2RB clusters were decreased in the progression stage of severe COVID-19 patients (Fig. 1a).