Stromal cells support survival of CLL cells in long- and short-term cocultures. PBMCs from 3 patients with CLL (> 94% CD19⁺/CD5⁺/CD23⁺) were monocyte depleted by plastic adhesion and then incubated either with BMSCs, SSCs, and LNSCs in a long-term coculture experiment (4 weeks). (A) Cell viability was consistently greater than 80% in parallel to a moderate increase in cell number (20%-30%) compared with the input cell number (B). (C) Phase contrast microscopy shows the nonadherent (i) and adherent cellular compartment including islands of closely adherent cells and cells which migrate beneath the stromal cells (ii). The supportive effect of BMSCs was validated in short-term cultures (4 days) with the use of CLL cells from 44 patients. A representative experiment is showing cell viability with AO/EtBr staining (Di-ii) where green fluorescence of the nuclei indicates viable cells, whereas nuclear red fluorescence indicates cell death and by FACS analysis (Diii-iv). The overall supportive effect of BMSCs in cocultures compared with suspension cultures as measured by FACS analysis in samples (n = 44) is shown in panel E (P < .01). FITC indicates fluorescein isothiocyanate.