P-Glycoprotein Expression in Drug-Resistant Chronic Lymphoproliferative Disorder.

Peripheral blood lymphocytes from 60 patients with drug-resistant chronic lymphoproliferative disorders (LPD) were examined for expression of P-glycoprotein (P-gp) by direct immunofluorescence (IF) test using monoclonal antibody (MoAb) C219. Four of the 15 patients with prolymphocytic leukaemia (PLL), and both patients with Adult T cell leukaemialymphoma (ATLL) expressed P-gp. However, none of the 3 hairy cell leukaemia (HCL) patients expressed P-gp. Two of the 14 patients with anthracycline resistant chronic lymphocytic leukaemia (CLL) expressed P-gp but none of the 26 CLL patients resistant only to chlorambucil expressed it. The percentage of cells expressing P-gp varied considerably between different groups as well as different individuals (20-100%). Activation of peripheral blood lymphocytes from non-resistant CLL patients with phorbol myristic acetate (PMA) did not induce P-gp expression. It appears that multidrug resistance in ATLL is most likely mediated by over-expression of P-gp and this may also be an important mechanism in multidrug resistance in some PLL and CLL patients.