CD8A and COVID-19: On the other hand, the proportion of the cluster expressing high levels of genes encoding cytokines, including IFNG, TNF, CCL3, CCL4, XCL1, and XCL2, was lower in SARS-CoV-2-reactive CD8+ T cells from COVID-19 patients than in IAV- and RSV-reactive CD8+ T cells from healthy donors [111], suggesting that SARS-CoV-2-reactive CD8+ T cells have a reduced capacity to secrete effector cytokines.