FTY720 sensitizes MCL cell lines and primary patient tumor cells to milatuzumab-mediated cytotoxicity. (A) Four MCL cell lines and primary cells from 6 patients were treated with FTY720 and/or milatuzumab plus cross-linking Abs at indicated the concentrations. (B) Patient characteristics. (C) Individual patient responses. (D) Representative histograms summarizing patient responses. Cell death was determined by annexin V/propidium iodide staining and flow cytometry at 24 hours. Data are shown as the percentage of annexin V⁻/propidium iodide⁻ cells (live cells) and are normalized to untreated controls. Combination treatment resulted in a statistically significant enhanced induction of cell death compared with either agent alone in MCL cell lines and primary cells (P < .01). Combination treatment resulted in synergistic cell death in blastic variant–derived cell lines (Jeko-1, UPN-1, and Z-138), and was additive in a classic variant–derived cell line (Mino) and in primary MCL cells.