Enumeration of cytoplasmic μ immunoglobulin positive acute lymphoblastic leukemia cells by flow cytometry: Comparison with fluorescence microscopy

The pre-B phenotype of childhood acute lymphoblastic leukemia, in which the mu immunoglobulin molecule is expressed in the cytoplasm of the blast cells, has been shown to have independent prognostic significance. Patients with this phenotype of the disease tend to have a poorer outcome on contemporary treatment regimens than do those with the other B-precursor phenotypes. For these clinical studies, the detection of the pre-B phenotype has depended upon fluorescent-microscope based techniques. A flow-cytometry based technique for the detection of the cytoplasmic mu immunoglobulin molecule is presented here and the results compared in detail with those of fluorescent microscopy. The results show that the two techniques are equivalent. The flow cytometry method has the advantage of a standardized control, is less labor intensive, and is observer-independent.