As for NKp44, until recently its best-characterized ligand was an inhibitory molecule, proliferating cell nuclear antigen, that is commonly expressed by tumor cells, and strongly inhibited by NK cell cytotoxicity and IFN-γ production, likely via the inhibitory ITIM motif atypically present in the intracellular domain of NKp44 (69). This evidence concerns the gene IFNG and neoplasm.