Transfection of COS-7 cells with the AC133 gene confers expression of AC133 antigen. COS-7 cells were transfected with AC133 antigen cDNA or with irrelevant CD8 cDNA and stained with AC133-PE after 48 hours of culture. (A), AC133 antigen–transfected COS stained with irrelevant isotype control; (B), CD8-transfected COS stained with AC133-PE; (C), AC133 antigen–transfected COS stained with AC133-PE. COS cells transfected with the irrelevant CD8 cDNA were nonreactive with AC133-PE, and AC133 antigen–transfected cells were nonreactive with a PE-conjugated isotype control.