PD-1 is transiently upregulated on γδ T cells on stimulation,28 29 and PD-1 expression has been described on γδ T cells residing at the tumor site.30, 33 In vitro studies demonstrated a diminished cytotoxic function of Vδ2 T cells in the presence of PD-L1, which could be reversed by an anti-PD-L1 monoclonal antibody (mAb), suggesting the presence of a functional PD-1/PD-L1 system in these cells.34 This evidence concerns the gene PDCD1 and neoplasm.