Divergent Effects of H-2K and H-2D Genes on Sensitivity of BL6 Melanoma Cells to NK Cells or TNF-Mediated Cytotoxicity

Transfection of BL6-8 (H-2Kb-, H-2Db+) and BL6-2 (H-2Kb-, H-2Db-) melanoma clones with H-2Kb or H-2Kd gene resulted in a stable augmentation of their sensitivity to lysis by NK cells or TNF-α that was associated with alterations of various phenotypic properties such as loss of endogenous A- and C-type retrovirus production and expression of melanoma-associated antigen and appearance of cell surface carbohydrates reacting with soybean agglutinin (SBA) and Grifonia simplicifolia I-B4 (GSIB4) lectins. In contrast, transfection of the same clones with H-2Dd or H-2Ld gene did not reverse their resistance to NK cell- and TNF-mediated cytotoxicity and did not affect the phenotype of melanoma cells. These data suggest that the effect of H-2K gene on NK/TNF sensitivity of BL6 cells is indirect and it is closely associated with H-2K-induced phenotypic changes in these cells. To examine the possible role or the observed alterations of cell surface carbohydrates in augmentation of sensitivity of BL6 melanoma cells to lysis by NK cells or TNF, BL6-8 melanoma cells were transfected with cDNA encoding α1,3-galactosyltransferase (α1,,3GT). Although the α1.3GT gene-transfected cells expressed α-galactosyl epitopes reacting with GSIB4 lectin and reduced sialylation of cell membrane with unmasking SBA lectin-binding carbohydrates, they did not show an increase in tumor cell sensitivity to lysis by NK cells or TNF, indicating that H-2K gene-induced alterations in cell surface carbohydrate expression are not accountable for the observed increase in NK/TNF sensitivity or BL6 melanoma cells. It is possible that the H-2K gene-induced elimination of the endogenous retroviruses might be responsible for the observed increased sensitivity of BL6 melanoma cells to NK cell- and TNF-mediated cytotoxicity.