BCMA and TACI expression on primary myeloma cells. (A) Fresh BM MNCs were stained with CD138 APC and 1 of BCMA PE, TACI PE (blue) or isotype control (red). Antigen densities of BCMA and TACI on CD138⁺ tumor cells (gated) were then quantified using QuantiBRITE beads and subtracting ABC of isotype control. FACS plots from 4 representative patient samples with antigen densities (ABC) are shown. (B) Stacked plot of BCMA and TACI expression on CD138⁺ cells. Each bar represents a separate myeloma patient. (C) Distribution of BCMA and TACI expression on primary CD138⁺ myeloma cells (n = 50; medians shown. BCMA range: 105-8323, mean: 1623; TACI range: 0-21 301, mean: 853).