Flow-cytometric analysis of bone marrow aspirate obtained before transplantation shows CD19+ cells outside the dominant CD38+CD45− multiple myeloma plasma-cell population characterized in Figure 3. Before this analysis, gating was performed to exclude doublets, debris, T cells, monocytes, and dead cells (not shown). CD45+ cells (top row, left plot) were found to contain the following CD19+ populations: polyclonal CD19+CD20+ B cells (top row, middle and right plots); a minor population of plasma cells (BCMA+CD38+), a subset of which is CD19+ and all of which are kappa-restricted (shaded inset), indicating that they are a component of the multiple myeloma clone; and a small population of CD45+CD38(dim)+CD20−CD19+ cells without immunoglobulin light-chain expression, most likely representing pro-B cells or early pre-B cells (third row, left and middle plots). BCMA denotes B-cell maturation antigen.