Chinese Academy of Sciences Jul 7 2025 CD8⁺ T cells are the immune system's frontline warriors, charged with detecting and eliminating cancer cells. But in the hostile and chronic environment of tumors, these cells often falter. Prolonged exposure to antigens, lack of co-stimulatory signals, and a barrage of suppressive molecules push them into an exhausted state. Like batteries drained of power, they stop proliferating, reduce cytokine production, and overexpress inhibitory receptors like PD-1,