CD274 and cancer: Cancer stem cells also successfully escape immune surveillance via the upregulation of programmed cell death ligand-1 (PD-L1) that is a negative regulator of T cells and, thus, suppresses activation of T lymphocytes; the downregulation of the natural killer (NK) activator molecule natural killer group 2D (NKG2D) ligand via tumour hypoxia, resulting in the loss of NK lymphocyte-mediated reactions against CSCs; and defects in the major histocompatibility complex MHC I, which affects the antigen presentation to T cells [12].