MDR expression. (A) P-glycoprotein expression on tumoral cells in the three cases according to MRK16 staining. Vertical solid lines show the limits of the isotype control IgG2a. (B) Efflux of Rh123 in dual fluorescence assay with PE-labeled CD56 MoAb (vertical axis). After rhodamine uptake cells were incubated in a dye-free medium at 37°C with (first graph) or without verapamil (second graph). Green rhodamine fluorescence (horizontal axis) is diminished at 37°C without verapamil in cases no. 1 and 3. (C) MDR1 mRNA is analyzed using RT-PCR with 31 cycles. Lane 1, sensitive K562 c-DNA; lane 2, resistant K562 R7 c-DNA; lanes 3, 4, and 5 refer to patient nos. 1, 2, and 3, respectively. β-μG, β2-microglobulin.