CTLA4 and neoplasm: Because its ligands PD-L1 (also known as CD274 or B7-H1) and PD-L2 (also known as CD273 or B7-CD) are mainly expressed on the surface of tumor cells and tumor infiltrating leukocytes (TILs), it has been demonstrated that tumor escaped from immune surveillance by expressing PD-L1/L2, thereby suppressing TILs via PD-1/PD-L1,2 interactions, so anti-PD-1 strategy is viewed as predominately play role in TME.