PDCD1 and neoplasm: However, objective response rates in checkpoint blockade therapy targeting programmed cell death 1 (PD-1), cytotoxic T lymphocyte-associated protein-4 (CTLA4) or programmed cell death ligand 1 (PD-L1) remain at ~10–40% owing to multiple immunosuppressive factors, such as T-cell exclusion, immunosuppressive cells, deprivation of tumour-infiltrating lymphocytes and neoantigens, and negatively regulating markers and cytokines1–5.