Expression of BCMA, TACI, and BAFF-R in myeloma cells and normal plasmablasts. (A) Expression of BCMA, TACI, and BAFF-R mRNA was analyzed by RT-PCR in 13 HMCLs, in CD138⁺ purified primary myeloma cells from 6 patients with intramedullary MM (patients 1-6), and 5 patients with plasma cell leukemia (patients 7-11), and in 5 normal in vitro–generated polyclonal plasmablastic cells (PPCs). B cells and dendritic cells (DCs) were used as positive and negative controls, respectively. (B) Cell-surface expression of receptors for BAFF by HMCLs was determined by flow cytometry using a biotinylated human BAFF–murine CD8 fusion protein and phycoerythrin-conjugated streptavidin. (C) Cell-surface expression of receptors for BAFF by primary myeloma cells and PPCs was determined by flow cytometry using a biotinylated human BAFF–murine CD8 fusion protein and phycoerythrin-conjugated streptavidin. Broken lines indicate Ig control; and solid lines, BAFF-mu CD8.