Flow cytometric analysis with patient serum. (A) Flow cytometric analysis of BCMA-293 (blue filled histogram), vector-293 (red open histogram), and nontransfected 293 cells (black open histogram) with control anti–BCMA antibody. BCMA-293 (red filled histograms) and vector-293 cells (black open histograms) incubated with pre-BMT (Bef. BMT), pre-DLI (Bef. DLI), and 4 months post-DLI serum (4 mo). PE indicates phycoerythrin. (B) Mean fluorescence intensity (MFI) of serial patient samples tested for reactivity against BCMA-293 (—) and vector-293 control cells (–). ♦ indicates patient 1; ▪, patient 2.