CD69 and COVID-19: When whole blood was stimulated with Cytostim, which acts as a superantigen by crosslinking the T-cell receptor (TCR) (regardless of TCR variable β gene usage) and major histocompatibility complex (MHC), there was a statistically significant difference in the percent of CD25+OX40+CD4+ T-cells and CD69+CD137+CD8+ T-cells in COVID-19 patients 1–3 months post-symptom onset (Figure 3a,b).