||A significant number of patients treated for B-lymphoblastic leukemia (B-ALL) relapse despite achieving clinical remission after induction therapy. One of the proposed mechanisms of relapse is the presence of minimal residual disease (MRD) where there is persistence of leukemic blasts below the level of detection by morphologic evaluation (less than 5% blasts). Multiple studies showed that detection of MRD at levels greater than 0.01% of mononuclear cells during and/or after induction therapy correlates with increased risk of relapse and poorer outcome in both adults and children.
Currently MRD assessment is performed via multicolor flow cytometry assays, real-time quantitative polymerase chain reaction assays, and next-generation sequencing base assays to detection fusion genes (e.g. BCR-ABL1), clonal rearrangement in immunoglobulin heavy chain genes, and/or T-cell receptor genes. While the sensitivity of MRD detection varies among different assays, the concordance rate between different methods is high.
This assay utilizes “Difference from Normal” technique to discriminate immunophenotypically abnormal leukemic blasts from normal B cell populations via multicolor flow cytometry. The assay is certified by the Children’s Oncology Group (COG) and performed on peripheral blood (Day 8) or bone marrow (Day29 or later). The peripheral blood panel consists of a single 5-color tube that allows for detection of abnormal CD19+ blasts. The bone marrow assay utilizes a panel of three 6-color tubes, where two tubes are designed to detect abnormal antigen expression in B lineage cells (defined as CD19+ events) and the third tube allows for quantification of CD19+ events from mononuclear cells. Because we analyze at least 1x106 events, the analytic sensitivity of this assay is approximately 0.01% of mononuclear cells.