COMMON EXPRESSION OF THE MULTIDRUG-RESISTANCE MARKER P-GLYCOPROTEIN IN B-CELL CHRONIC LYMPHOCYTIC-LEUKEMIA AND CORRELATION WITH IN-VITRO DRUG-RESISTANCE

The expression of P-glycoprotein (Pgp), which is associated with multi drug resistance (MDR), was investigated in 20 B-cell chronic lymphocyt ic leukaemia (B-CLL) patients by flow cytometry using two Pgp-specific monoclonal antibodies (mAb), MRK-16 which recognizes an extra-cellula r epitope, and JSB-1 which recognizes an intracellular epitope. Sixtee n (80%) patients were positive with MRK-16 whereas all patients were p ositive with JSB-1. The proportion of Pgp-positive lymphocytes from ea ch patient sample varied from 2-94% for MRK-16 and 20-93% for JSB-1. T here was no correlation between the level of positivity and disease st age or treatment history. In vitro drug resistance to vincristine (VCR ) and doxorubicin (DOX) was determined by the colorimetric MTT assay. All patients were resistant to one or both drugs being consistent with the expression of Pgp. There was no correlation beween the level of r esistance and disease stage or drug treatment. We investigated the exp ression of Pgp in the normal counterpart of the B-CLL cells, CD5+CD19 B-lymphocytes. A minor subpopulation (3%) of CD5+CD19+ lymphocytes is olated from normal controls expressed Pgp suggesting that these cells may be the potential precursors to the B-CLL cell. We conclude that Pg p expression and drug resistance are inherent characteristics of the B -CLL lymphocyte.