Moreover, other ligands expressed by malignant cells which act to stimulate NK cell activity include CD155 and CD112 which bind to the activating receptor DNAX Accessory Molecule-1 (DNAM-1), with CD155 in particular being overexpressed in both solid and hematological malignancies (16–18), and ligands to the natural cytotoxicity receptors, NKp30, NKp44, and NKp46 that have been shown important for NK cell targeting of several tumor types (18–20). This evidence concerns the gene PVR and neoplasm.