Stromal cells promote colony formation without altering the effects of dexamethasone and lenalidomide. After 3 days of treatment with the compounds in liquid culture, hematopoietic cells were separated from GFP⁺ OP9 cells by flow sorting, and the hematopoietic cells were plated in methylcellulose without drugs. Data are presented as the number of colonies per 3200 cells plated. The effects of dexamethasone (Dex) and lenalidomide (Len) on CFU-E colony formation are shown in panel A. The effects of Dex and Len on BFU-E colony formation are shown in panel B. The experiments were performed in triplicate and the entire experiment was repeated on HS5 stromal cells with similar results. ANOVA was used and the statistical findings are discussed in the text.