[Multidrug resistance in acute leukemia].

We examined the multidrug resistance (MDR) P-glycoprotein (P-gp) on normal bone marrow (BM) cells and acute myeloid leukaemia (AML) cells, using newly devised flow cytometric multi-parameter analysis with CD33, CD34 and MRK16 monoclonal antibodies. With biotinylated MRK16 and a Streptavidin-RED670 (SA-RED670) conjugate, we succeeded in the detection of a small amount of P-gp on these cells. In normal bone marrow cells, the percentage of P-gp positive CD34+CD33-, CD34+CD33+ and CD34-CD33+ cells were 12.2 (2.2% (mean +/- standard deviation), 6.3 +/- 3.1% and 1.4 +/- 0.9%, respectively. By the more precise list-mode analysis, myeloid lineage cells showed continuously regressing P-gp expression as they maturated from CD34+CD33- to CD34-CD33+ cells. In AML cells at diagnosis, CD34+ CD33- cells expressed P-gp strongly, CD34+CD33+ cells moderately, and CD34-CD33+ cells weakly, showing the same tendency as observed in normal BM cells. Blast cells from acute promyelocytic leukemia (APL), which mainly expressed CD34-CD33+ but no detectable CD34+CD33- at diagnosis, expressed less amount of P-gp than the other subtypes of AML. P-gp expression on these three phenotypes increased in relapsed cases, especially on the CD34+CD33- subpopulation.