Immobilized rituximab and milatuzumab treatment-induced cell death in MCL cells. The 6 MCL cell lines (A), patient characteristics (B), and primary cells from 7 patients (C-D) were treated with rituximab (10 μg/mL) and/or milatuzumab (5 μg/mL), in the presence of a cross-linking antibody. Cell death was determined by annexin V–PI staining and flow cytometry at 8, 24, and 48 hours for the 6 cell lines and at 24 hours for MCL primary cells. Data are shown as the percentage of annexin V−PI cells (live cells) and are normalized to untreated control. Individual patient responses (C) and representative histograms summarizing patient responses (D) are shown. Combination treatment resulted in statistically significant enhanced induction of MCL cell death compared with either agent alone (P < .01).