CD11b⁺ B cells coexpress CD34, which identifies the clonotypic subset. (A) PBMC from 3 different MM patients were stained with CD11b-PE and CD34-FITC. The box indicates the set of cells for which multidrug transporter function has been analyzed in Figs 1, 3, and 6 and Table 1. (B) In situ RT-PCR amplifies clonotypic transcripts from sorted CD19⁺ 11B⁺ MM B cells but not from normal B cells. The left column of panels show in situ RT-PCR on CD19⁺11B⁺ B cells from (A) patient no. 11, (B) patient no. 6, and (C) patient no. 13. The right column shows patient-specific in situ RT-PCR on CD19⁺ B cells from healthy donors. Row (A) used primers specific for patient no. 11, row (B) primers specific for patient no. 6 and (C) primers specific for patient no. 13.