CD8A and COVID-19: Furthermore, the cell proportion of CXCR6+ memory CD8+T cells was significantly higher among both mild and moderate COVID-19 than that among the normal group (P < 0.05), whereas the cell proportion of CXCR6+ memory CD8+T cells among severe COVID-19 was remarkably lower than that among the normal group (P = 0.012, Fig. 5F).