Detection of residual disease in pediatric B-cell precursor acute lymphoblastic leukemia by comparative phenotype mapping: A study of five cases controlled by genetic methods

We recently investigated samples of pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL) and normal bone marrow (BM). We found that leukemic blasts, compared to their physiologic counterpart cells, frequently display aberrant phenotypes with respect to levels of expression of certain antigens. Using multiparameter flow cytometry, these differences enabled us to trace leukemic cells admixed to normal BM, which suggested that this approach might be a useful strategy for minimal residual disease detection. In the present study, we used the same multiparameter approach (“comparative phenotype mapping”) to prove that such quantitative phenotypic differences really exist between malignant and normal BCP when simultaneously present in the BM. We demonstrate this by five exemplary follow-up BM samples from patients with BCP-ALL, all of which showed phenotypically aberrant cells according to levels of expression of CD10, CD11a, CD19, CD34, CD44, or CD45RA, as well as according to altered orthogonal light scattering properties. We confirmed the leukemic nature of these cells by polymerase chain reaction-based detection of bcr1/abl transcripts, and of leukemia clone-specific immunoglobulin heavy chain rearrangements in only the suspicious cells when sorted by flow cytometry, but not in normal BCP or non-B cells. Comparative phenotype mapping thus allows one to distinguish between normal and leukemic cells, and we show that it may enable rapid, specific, and quantitative detection of residual/resurgent leukemia in BCP-ALL.