Expression of P-gp on drug-selected and retrovirus transduced cell lines. Western blot of cell lysates from drug-selected CEM cell lines CCRF, A7⁺, 2H6, IC10; the T-cell line 12D7 and 12D7 transduced with a retrovirus containing full-length human MDR1 cDNA (12D7-MDR1) were probed with the anti–P-gp MoAb, C219. The position of 170 kD P-gp is indicated by the arrow on the right.