CD8A and COVID-19: On the other hand, as differentiated by PD-1 expression level within the naïve CD8+ T cells,18 approximately 1% of them might belong to the so-called stem-like memory T cells (TSCM) (Supplementary information, Fig. S3b), and we found that the frequency of CD8+ TSCM within CD8+ T cells was similarly decreased in the presymptomatic and moderate COVID-19 groups but not in the asymptomatic and mild COVID-19 groups, as compared to the healthy controls (Fig. 2l).