Considering that TIGIT and CD226 compete for the same ligand CD155 on APCs and binding of CD226 to this ligand promotes cytotoxicity in CD8+ T cells the simultaneous increase of CD226 and decrease of TIGIT expression could benefit CD8+ T cells to maintain cytotoxic effector functions in COVID-19 (40, 68). The gene discussed is PVR; the disease is COVID-19.