CTLA4 and neoplasm: Tumor cells can overexpress some specific molecules such as PD-L1 and CTLA-4 to silence the immune response and these molecules are collectively termed as “immune checkpoints.” Programmed cell death (PD) pathway is the first and most characterized “immune checkpoints.” PD-1, a co-inhibitory receptor, is highly expressed on activated T cells, B lymphocytes, natural killer cells, and MDSCs.