BCMA is specifically and highly expressed on the cell membrane of patient MM cells. (A) BCMA mRNA was quantitated by real-time qRT-PCR in CD138⁺ cells from 5 MM patients and 3 normal donors (NPC). 18S is an internal control for normalization. P < .04 (B) BCMA mRNA was measured in paired CD138⁺ and pDCs from MM patients and normal donors (N1-3) (left and middle panel), as well as matched CD138⁺ cells, pDCs, and CD138-negative (CD138⁻) cells from 3 MM patients (MM1-3, right panel). (C) MM cell lines were immunostained with a novel humanized anti-BCMA J6M0 mAb (solid line) or isotype control human IgG (dashed line). (D) Dual staining by J6M0-PerCP-Cy5.5 and CD38-PE Cy7 was done in MM1S and CD138⁺ patient MM cells. Immunostaining with J6M0 mAb (solid line) or isotype control human IgG (iso IgG1, dashed line) was performed in CD138⁺ cells from additional MM patients (E), as well as paired CD138⁺ cells and pDCs from a MM patient (F). qRT-PCR, quantitative RT-PCR.