Characterization of CTLs induced by stimulation with mature DCs cocultured with apoptotic MM cells. (A) CTLs induced by stimulations with DCs cocultured with apoptotic U266 bodies showed significantly higher cytotoxicity (*, P = .02) against U266 cells (▪) than against RPMI 8226 cells (□) or K562 cells (▦), assessed with ⁵¹Cr-release assay at indicated effector-to-target (E/T) ratios for 4 hours at 37°C. Spontaneous release of target cells was less than 15%. Results shown are mean ± SD of triplicate wells and representative of 3 experiments. (B) HLA restriction of CTLs was examined using target blocking ⁵¹Cr-release assay. CTLs stimulated with apoptotic U266 body–pulsed DCs were cocultured with ⁵¹Cr-labeled U266 after incubation with blocking antibody against HLA class I (□), HLA class II (▨), control antibody (▦), or without antibody (▪). Cytotoxicity was significantly inhibited by anti–HLA class I Abs (*, P = .02). Spontaneous release of target cells was less than 15%. Results shown are mean ± SD of triplicate wells and representative of 2 experiments. (C) Cell surface phenotype of CTLs was analyzed by flow cytometry using FITC- or PE-conjugated Abs against CD3, CD8, CD4, and CD56 (filled histogram). Percentages positive are calculated relative to an isotype-matched control Ab (open histogram).