PDCD1 and cancer: Immune infiltrating cells include cancer-related fibroblasts (CAF), bone marrow-derived suppressor cells (MDSC), tumor-associated macrophages (TAMs) and Tregs; tumor-related mediators include CTLA-4, PD-1/PD-L1, TGF beta, and adenosine, which directly or indirectly lead to the failure of CAR-T treatment.