A recent single-cell RNA sequencing study identified key hub genes such as class I–restricted T cell–associated molecule (CRTAM; encoded by CRTAM), C-type lectin domain–containing 2D (CLEC2D; encoded by CLEC2D), and killer cell lectin-like receptor subfamily B member 1 (KLRB1; encoded by KLRB1) that are characteristic of exhausted CD8+ T cell states in breast cancer. The gene discussed is KLRB1; the disease is breast cancer.