CD45 phenotype and LI of myeloma and bone marrow PCs. PC phenotype analysis was performed in 2 steps. In the first step, 15 000 total events were acquired to draw a PC gate in the side scatter (SSC)/CD38⁺⁺ dot-plot (R1). In the second step, an acquisition of 15 000 PCs (at least 1000 PCs for very low plasmacytoses) was performed through the R1 live-gate. PCs were identified by coexpression of CD38 and CD138 (gate R2). A third region was set on the light scatter of the cells satisfying both R1 and R2 to exclude debris or apoptotic PCs with a low CD138 expression and a characteristic light-scatter distribution.¹²  The lack of Apo 2.7 staining in the gated population confirmed that cells were not apoptotic.¹⁵  Then 2 PC subpopulations were identified on the CD45 versus SSC dot plot: R3 was set around PC with a large SSC expressing a high level of CD45, while R4 was set around PC with low SSC and negative or weak CD45 expression. The analyses of the phenotype and the LI were performed in these 2 PC subpopulations, separately and simultaneously. The percentage of BrdU⁺ PCs within the population incubated with BrdU (BrdU⁺) or without (control, BrdU^-) were indicated within the cytograms. For example, in patient MM1 the global LI was 1.7% (3.1%-1.4%) but 8.5% (9.1%-0.6%) in R3 and 1.4% (1.5%-0.1%) in R4. Overlay histograms represent the immunofluorescence of Bcl-2 (thick line) over the control (thin line). r indicates the ratio of MFI.