hMSCs inhibit B-cell proliferation. (A) B cells purified from PB of healthy donors were cocultured for 3 days with allogeneic hMSC suspensions at 1:1 and 1:2 ratios in the presence of CpG 2006, rCD40L, anti-immunoglobulin antibodies, IL-2, and IL-4. Cell proliferation was assessed by [³H]-thymidine incorporation. Median counts per minute, maximum and minimum values, from 9 independent experiments are shown. ^**P = .008; ^*P = .036. (B) B-cell-enriched populations cultured for 3 days with or without hMSCs at a 1:1 ratio in the presence of stimuli were double-stained with CD19 mAb and annexin V and analyzed by flow cytometry. Results are median percent CD19, annexin V⁺ cells, and maximum and minimum values from 3 independent experiments. (C) B-cell-enriched populations cocultured with (right panel) or without (left panel) hMSCs at a 1:1 ratio in the presence of stimuli were fixed, permeabilized, and stained with CD19 and anti-Ki67 mAb. A representative experiment is shown. Gated CD19⁺ B cells were stained with anti-Ki67 mAb (black histograms) or its isotypic control (white histograms). Results are shown as percentage of positive cells. The differences between the histograms of left and right panels are likely related to changes in B-cell shape caused by their coculture with hMSCs.