CD8A and cancer: Short-term assays, such as 24-h activation induced marker assays described in the previous reports11,13,15, are useful for the detection of effector CD8+ T cells, whereas in-vitro expansion assays can be used to detect pre-existing CD8+ T cells against cancer or cross-reactive CD8+ T cells to SARS-CoV-2, even at low levels14,25–28.