As expected, no differences were observed in phenotypic and functional exhaustion of EBV BMLF-1280–288-specific CD8+ T cells across the six groups of COVID-19 patients with various disease severities (Supplementary Figure 3B), suggesting that the exhaustion of CD4+ and CD8+ T cells in severely ill COVID-19 patients and to patients with fatal COVID-19 outcomes was specific to CCCs/SARS-CoV-2 cross-reactive epitopes. Here, CD4 is linked to COVID-19.