Lack of toxic and apoptotic effect on BM cells cocultured with HMCLs. Viability of BM-adherent cells in long-term cocultures with HMCLs (OPM2, XG-6, RPMI-8226, XG-1) was assessed after 21 days of coculture as described in “Patients, materials, and methods.” Graphs represent the percent mean ± SD of viable cells of 6 replicate wells. (A) MG63 cells treated with FAS (anti-CD95 mAb) were used as positive control for death cells. The presence of both death and apoptotic PreOBs has been investigated by flow cytometry after 48-hour coculture with XG-6 or OPM2 either in the presence or absence of a transwell insert using 7-amino-actinomycin D (7AAD) gating on all (B) CD138^- cells and (C) Apo 2.7 mAb gating on viable CD138^- cells. Any significant difference in the number of death or apoptotic PreOBs was not observed in the control and coculture condition.