FAS and neoplasm: The onset of CAR-T exhaustion is linked suppressive immune cells, including regulatory T-cells (Treg), myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs), cancer-associated fibroblasts (CAFs), tumor-associated neutrophils, and mast cells and to external inhibitory signals (such as TGF-β, IL-10, PGE2, soluble FAS, adenosine, ROS) [121].