The co-expression of multiple inhibitory receptors was associated with higher exhaustion levels of CD8 T cells and more severe infection during viral infection.39 This severe exhausted CD8 T cell type has not been reported by previous studies.13,26 Because severe exhausted T cells displayed accumulation of mitochondria,40 the low mitochondrial gene percentage parameter setting in the single-cell quality control led to the removal of these cells in previous studies. This evidence concerns the gene CD8A and infection.