Detection of minimal residual disease in unselected patients with acute myeloid leukemia using multiparameter flow cytometry for definition of leukemia-associated immunophenotypes and determination of their frequencies in normal bone marrow.

BACKGROUND AND OBJECTIVES: Detection of minimal residual disease (MRD) by multiparameter flow cytometry is an emerging prognostic factor in patients with acute myeloid leukemia (AML). The present analysis aimed at improving the applicability of this approach to more patients with AML. DESIGN AND METHODS: Bone marrow samples from unselected patients with AML at diagnosis and from healthy volunteers were immunophenotyped applying triple-stainings of 31 antigens. Leukemia-associated immunophenotypes were defined by gating on populations displaying an aberrant or infrequent immunophenotype and by applying Boolean algebra. The combination of gates obtained was applied to list mode data files containing measurements of normal bone marrow samples. Dilution experiments of AML samples in normal bone marrow were performed to test the linearity of measurements.
RESULTS: At least one aberrant/infrequent immunophenotype was identified (median, 2; range, 1-5) in all of 68 analyzed AML patients. The median frequencies of cells displaying an aberrant/infrequent immunophenotype within normal bone marrow ranged from 0.00% to 1.20% (median, 0.07%). Limiting this analysis to only the most sensitive aberrant/infrequent immunophenotype per patient resulted in frequencies of cells displaying an aberrant/infrequent immunophenotype within normal bone marrow ranging from 0.00% to 0.43% (median, 0.05%). Serial dilution experiments confirmed the linearity of measurements (R>0.90 in all cases analyzed). INTERPRETATION AND
CONCLUSIONS: The application of multiparameter flow cytometry to identify cells displaying an aberrant/infrequent immunophenotype and to quantify MRD is feasible in unselected patients with AML.