To determine the effects of cell–cell contact between NK cells and tumor cells on differentiation and resistance of tumor cells to NK cell-mediated cytotoxicity, we cultured purified NK cells untreated or treated with IL-2 + anti-CD16mAb + sAJ2 in the presence or absence of anti-TNF-α and anti-IFN-γ antibodies. This evidence concerns the gene IFNG and neoplasm.