TNFRSF9 and COVID-19: To explore this further, CD4+ and CD8+ T cells in controls, patients who recovered from COVID-19, and household members were gated by their expressions of eight functional markers (i.e., CD154, OX40, CD137, CD69, CD38, Fas, LAG-3, and TIGIT) after stimulation with SARS-CoV-2 peptides.