MRD analysis using 6-color flow cytometry assay. A representative analysis of a peripheral blood sample is shown, in which the presence of an obvious MRD population can be seen. Analysis was performed after gating cells based on the expression of CD19 (A) and the side/forward scatter profile (B) in both test tubes (see text). Leukemic cells are shown in red in panels C-H. For the first test tube, the CD19/CD3 combination (C) is used to calculate the number of CD3⁺ events in the B-cell gate and the combination of 3 gates based on CD5, CD20, CD79b, and CD38 expression (D-F) is used for the calculation of events with a CLL-like phenotype. For the second test tube, MRD events are identified through 3 gates based on the expression of CD5, CD20, CD22, CD43, and CD81 (G-I).