Flow cytometric histograms of Pgp expression in representative AML cases.

Leukemia blasts enriched over density gradients were assessed for Pgp expression using the fluorescence-conjugated Pgp-specific monoclonal antibody MRK16. MRK16 fluorescence, and that of appropriately matched isotype controls, were detected using highly sensitive flow cytometric assays. MRK16 expression was quantitated with the Kolmogorov-Smirnov statistic D. Representative histograms for AML cases in the present study are shown for (A) case considered “Pgp⁺ high” (defined as D > 0.3) with a D value of 0.45 relative to the isotype control; (B) case considered “Pgp⁻”(defined as D < 0.2) with a D value of 0.10; (C) “PgP⁺ low” AML (defined as 0.2 < D < 0.3) with a D value of 0.25 relative to the isotype control; and (D) the Pgp⁺ DOX 6 cell line used as a positive control for MRK16 staining, with a D value of 0.42 relative to the isotype control.