PDCD1 and cancer: Several aptamers have been developed for immunological checkpoints associated with immunosuppression in cancer patients, including T-cell immunoglobulin-3 (TIM-3), cytotoxic T lymphocyte-associated protein 4 (CTLA4), and programmed death receptor I (PD-1) or its ligand, programmed death ligand I (PD-L1) [268,269,270].