(A) Expression of CD80 on AML cells transfected with pCDNA-B7 plasmid vector. CD80 expression was determined by FACS 48 hours after transfection of the cells. I, pCDNA-B7- transfected cells + no MoAb; II, untransfected cells + anti-CD80; III, mock-transfected cells + anti-CD80; IV, pCDNA-B7– transfected cells + anti-CD80. (B) HLA mismatched and HLA identical MLR reactions induced by cytokine-treated or CD80-transfected AML cells. Control stimulator cells are AML cells transfected with empty plasmid (mock transfection), AML cells electroporated without DNA, and untreated AML cells. Results are expressed as the mean cpm of triplicate cultures. The SEM did not exceed 15%.