Comparison of cytotoxic activity against tumor and normal cells at various time points during expansion. (A) Cytotoxicity of day-0 (all patients), day-5 (patients 2, 3, and 5), and day-20 (all patients) cells against the K562 cell line as measured by the standard ⁵¹Cr release assay, and (B) against autologous MM cells and non-MM cells from the BM as measured by the flow cytometry–based assay. (C) Representative data (patient 5) for the flow cytometry–based cytotoxicity assay showing the gating strategy used during analysis. Target cells were identified as the TFL4⁺ events. Further gating on CD38⁺ CD138⁺ cells was used for the analysis of MM cells within the BM samples. The percentage of live/dead cells was evaluated using 7-AAD. (D) Cytotoxicity of day-20 cells against autologous CD34⁺ cells (patients 1, 3, and 5), autologous PHA blasts (patients 1 and 5), and the RPMI8226 myeloma cell line (patients 1, 3, and 5).