PDCD1 and non-small cell lung carcinoma: Cytotoxic T lymphocyte associated antigen-4 (CTLA-4) and programmed cell death protein-1 (PD-1) are the representatives of immune checkpoints in NSCLC, which act as inhibitors in the activation of T cells.14 CTLA-4 is presented on T cells and its interaction with B7 on APCs reduces IL-2 production and T cell proliferation in lymphoid organs.