Guidelines for the flow cytometric minimal residual disease monitoring in B-lineage acute lymphoblastic leukemia after CD19-directed immunotherapy

   Multicolor flow cytometry is now routinely used in laboratory practice for the minimal residual disease (MRD) monitoring in B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Wide application of CD19-directed immunotherapy leads to frequent loss of CD19 expression, that hampers significantly the flow cytometric MRD detection methodology. We developed an antibody panel and data analysis algorithm for multicolor flow cytometry, which is a reliable method for MRD detection in patients with BCP-ALL treated with CD19-directed therapy. We recommend a single-tube 11-color panel for MRD detection, which is adapted for the case of possible CD19 loss. Based on patterns of antigen expression changes and the relative expansion of normal CD19-negative BCPs, guidelines for multicolored flow cytometry data analysis and interpretation are established. The recommended approach is reliable tool for therapy response monitoring displaying the same effectiveness with the more laborious and costly molecular techniques.