Detection of myeloperoxidase by flow cytometry in acute leukemia

The value of flow cytometric detection of myeloperoxidase (MPO) in the differential diagnosis of acute leukemia was evaluated in 57 cases of acute leukemia and in 9 leukemia cell lines. Cells were fixed and permeabilized with Fix & Perm cell permeabilization kit at room temperature for 15 min each, and stained with anti-MPO monoclonal antibody (MPO-7) by direct immunofluorescence. One myeloid cell line, HL-60, was MPO-positive, while the other myeloid cell lines (KG-1, K-562, and MEG-01) as well as lymphoid cell lines (KM-3, NALM-6, Raji, REH, and T-ALL-1) were MPO-negative as previously described. Among acute leukemias, MPO was detected in 23 of 26 cases of acute myeloid leukemia (AML), 7 of 23 cases of B-lineage acute lymphoblastic leukemia (ALL), 1 of 6 cases of T-lineage ALL (T-ALL), and 1 of 2 cases of acute unclassified leukemia (AUL). The intensity of MPO expression in 6 of 7 B-lineage ALL cases was weak compared with AML labeling. There was no detectable cytochemical MPO in the cells of ALL, AUL, or AML that stained negative for anti-MPO. No relationship between the expression of MPO and myeloid lineage surface antigens was observed in ALL. Three cases of MPO-positive ALL and AUL could be reclassified as biphenotypic leukemia according to the revised Catovsky scoring system. These results indicate that anti-MPO is an excellent marker for the diagnosis and classification of acute leukemia and can be reliably detected by flow cytometry. This rapid technique should be a valuable addition to routine immunophenotyping of acute leukemia.