Antigenicity of human melanoma cells transfected to express the B7-1 co-stimulatory molecule (CD80) varies with the level of B7-1 expression

The aim of this study was to compare the antigenicity of human melanoma cel ls molecularly modified by particle-mediated gene transfer to have transien t or stable expression of the B7-1 co-stimulatory molecule (CD80). The unmo dified melanoma cells (me15, m21) had no constitutive expression of B7-1, b ut 22%-28% of cells had transient B7-1 expression 24 h following transfecti on with cDNA for B7-1 (me15-B7, m21-B7). In addition, 85%-90% of cells had stable B7-1 expression following transfection with cDNA for B7-1 and in vit ro culture under selection conditions (me15-B7neo, m21-B7neo). Allogeneic H LA-unmatched normal donor peripheral blood mononuclear cells (PBMC) secrete d greater amounts of granulocyte/macrophage-colony-stimulating factor (GM-C SF) when incubated for 3 days with m21-B7neo than did PBMC incubated with m 21-B7, which, in turn, secreted greater amount of GM-CSF than PBMC incubate d with m21. Similarly, cell-mediated cytotoxicity against unmodified melano ma cells by PBMC co-cultured for 5 days with the modified or unmodified mel anoma cells was proportional to the level of B7-1 expression on the stimula ting cells. This cytolytic activity had both an HLA-class-I-restricted and an HLA-class-I-unrestricted component. Following 5 days of co-culture, PBMC expression of CD28, the ligand for B7-1, was down-regulated in proportion to the level of B7-1 expression on the stimulating melanoma cells. Thus, pa rticle-mediated gene delivery of cDNA for B7-1 into human melanoma cells in creased expression of functional B7-1 and enhanced the antigenicity of the gene-modified cells in proportion to their level of B7-1 expression.