TIGIT and COVID-19: Interestingly, we detected a small population of exhausted CD8+ T cells (TEX) characterized by expression of TIGIT, CTLA4, CD279 (PD-1) and HAVCR2 (Tim-3) that was exclusive to the severe COVID-19 group (Figures 1B, G), a finding which has been reported by others before (49, 50).