B-cell expression of costimulatory molecules is unaffected by incubation with hMSCs. Purified B cells were cultured for 24 hours with or without hMSCs at a 1:1 ratio, in the presence of CpG 2006, rCD40L, anti-immunoglobulin antibodies, IL-2, and IL-4. After culture, B cells were stained with anti-HLA-DR, anti-CD40, anti-CD86, and anti-CD80 mAbs in combination with CD19 mAb and analyzed by flow cytometry. Results are expressed as median percent positive cells, maximum and minimum values obtained from 7 different experiments.