FL + IL-7–stimulated CD19⁻ cells expand in the absence and presence of IL-10. A total of 500 Lin⁻Sca-1⁺c-kit⁺ cells was cultured in the presence of FL + IL-7 for 12 days. The resulting cells were counted and CD19⁻ cells sorted as described in the Materials and Methods. Subsequently, 23,000 CD19⁻ cells (mean of five experiments) were cultured in FL + IL-7 or FL + IL-7 + IL-10. Based on the total number of cells generated and analysis of CD19 expression, the number of CD19⁺ (▪) and CD19⁻ (□) cells was calculated. Data represent absolute cell numbers (mean ± SEM) of five separate experiments.