PDCD1 and neoplasm: Since the discovery of cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) and programmed cell death protein 1 (PD-1) as immune checkpoints by James P. Allison and Tasuku Honjo, respectively, multiple immunoglobulins (Igs) and their modified extensions have been developed to optimize anti-tumor response with both immunological and non-immunological pathways.8