In particular, studies on peripheral blood mononuclear cells (PBMCs) have revealed reduced IFN-gamma production (1), expansion of highly cytotoxic effector T cell subsets (2), and increased expression of the exhaustion markers programmed cell death protein 1 and Tim-3 on CD8+ T cells in the severe COVID-19 patients (3). Here, HAVCR2 is linked to COVID-19.