CTLA4 and COVID-19: Subsequent single-cell RNA sequencing (scRNA-seq) revealed that T cells in patients with COVID-19 have exhaustion characteristics, including the expression of tissue-resident and memory phenotype (ZNF683+ and ITGAE+); high expression of inhibitory molecules PD-1, TIM-3, HAVCR2, LAG3, and CTLA-4; high expression of proinflammatory factors CD70, COTL, and HMGB1; and stress-related molecules HSPD1, HSP90AA1, and BIRC5 (48).