Flow cytometric detection of cytoplasmic antigens in acute leukemias: implications for lineage assignment

This study aimed at optimizing the conditions for flow cytometric detection of myeloperoxidase (MPO), cytoplasmic CD3 (cCD3), and cytoplasmic CD22 (cCD22), which seem to be more reliable lineage-associated markers in acute leukemia than surface antigens. Fixation methods employing saponin as detergent resulted in accurate detection of MPO and cCD3, whereas cCD22 was detectable only after buffered-formaldehyde-acetone fixation. MPO was detected in 16/17 AML, but only in 1/6 ALL, the MPO positive ALL being also CD13 positive. MPO was detectable in 3/4 AML with T-lymphoid features; a case of myeloid antigen-positive T-ALL, however, was MPO-negative. cCD3 was expressed only in T-ALL, and five cases of lymphoid antigen-positive AML were cCD3-negative. We suggest that these flow cytometric assays are useful for the lineage assignment of poorly differentiated leukemias and contribute to the identification of truly biphenotypic acute leukemias.