BLyS promotes proliferation of WM cells. (A) CD19⁺CD138⁺ cells (0.1 × 10⁶ cells/well) from WM patients (n = 3) were cultured in 96-well round-bottom plates in the presence or absence of 100 ng/mL BLyS or 10 μg/mL anti-Ig Ab, each alone or in combination, for 5 days at 37°C in the presence of 5% CO₂. Values represent the mean of triplicate values ± SD. (B) TACI-Ig fusion protein blocks BLyS-induced proliferation of malignant B cells. A fourth WM patient sample (WM15) was used to show that BLyS-induced proliferation of malignant B cells is inhibited in the presence of TACI-Ig fusion protein.