PDCD1 and neoplasm: Tumours can display, amongst others, increased programmed death ligand 1 (PDL1) and HLA class I histocompatibility antigen alpha chain E (HLA-E), which bind programmed cell death protein 1 (PD1) and CD94/NK group 2 member A (NKG2A) to dampen T-cell and natural killer (NK) cell responses respectively (48).