Expression of MDR1 gene in acute leukemia cells: Association with CD7⁺ acute myeloblastic leukemia/acute lymphoblastic leukemia

MDR1 gene expression was examined in acute leukemia cells from 75 Japanese patients at diagnosis (50 with acute myeloblastic leukemia [AML]: 10 M1, 18 M2, 5 M3, 8 M4, 9 M5; 25 with acute lymphoblastic leukemia [ALL]: 13 B- precursor, 12 T-lineage). The results of MDR1 mRNA expression by reverse transcriptase polymerase chain reaction were confirmed by immunostaining using the anti-P-glycoprotein monoclonal antibody UIC2 and by a functional study using the rhodamine efflux test. Morphologically, AML M1 cases had the highest incidence of MDR1 gene expression (6 of 10 patients). Phenotypically, CD7 and CD34 were the only surface markers that were significantly associated with MDR1 gene expression (P < .01). In CD7⁺CD4^-CD8^- ALL, which is thought to originate from the lymphohematopoietic stem cell, expressed the MDR1 gene with a high incidence (six of eight patients), whereas three surface CD3⁺ and one CD4⁺CD8⁺ T-cell ALL (T-ALL) did not have detectable MDR1 transcripts. Only two cases of 13 B-precursor ALL had MDR1 mRNA, one of which had the Philadelphia (Ph¹) chromosome. No association was observed between MDR1 gene expression and CD34 positivity in ALL. Our results that MDR1 mRNA was frequently expressed in CD7⁺ AML and CD7⁺CD4^-CD8^- ALL, together with the previous reports indicating clinical similarities between these leukemias, provides a clue to clarify a relationship between CD7⁺ AML and CD7⁺CD4^-CD8^- ALL. In addition, MDR1 expression in CD7⁺ AML/ALL might be responsible for the poor response to conventional chemotherapies of these types of leukemia.