The combination of dexamethasone and lenalidomide has an additive effect on increasing the production of erythroid cells from CD34⁺ cells expressing RPS19 or RPS14 shRNAs. The effects of combination treatment with dexamethasone (Dex) and lenalidomide (Len) and control on cells infected with a RPS19 shRNA are shown in panel A and with a RPS14 shRNA in panel B. The absolute number of erythroid cells after 10 days in liquid culture was determined by multiplying the number of cells counted per well by the percentage of cells expressing any erythroid markers (CD71, glycophorin A) as assayed by flow cytometry. Data are presented as relative number to eliminate differences caused by cell number and infection rate. The expected number of erythroid cells was calculated as follows: expected number of cells = (absolute number of erythroid cells with Dex treatment alone − control) + (absolute number of erythroid cells with Len treatment alone − control) + control. The experiments were performed in triplicate and the entire experiment was repeated with similar results with an independent shRNA (supplemental Figure 6). ANOVA was used and the statistical findings are discussed in the text.