Pre-B ALL primary cells and SD-1 cells show increased growth in the presence of IL-15. (A) Six different primary pre-B ALL samples were grown in optimized 3-cytokine mix with or without the addition of IL-15 (25 ng/mL). Numbers of viable blast cells were measured at weeks 1, 2, and 3 by flow cytometry. Each sample is shown individually, and then results from all 6 experiments are pooled (bottom panel; data represent mean ± standard error of the mean). (B) Fold change in cell numbers compared with baseline (starting cell count at initiation of the experiment) was calculated for the 2 experimental conditions in each of the 6 primary samples. Data were analyzed using a Wilcoxon matched-pairs sign rank test, and bars display mean ± standard error of the mean. (C) Growth of SD-1, Sup-B15, REH, and SEM cells following treatment with 1, 5, or 25 ng/mL IL-15 for up to 96 hours. (D) Growth of SD-1 and SupB-15 cells following treatment with media alone, 6 μg/mL isotype control antibody, or 6 μg/ml IL-15Rα nAb. Viable cells were determined using trypan blue. Data represent mean ± standard error of the mean. Data were analyzed using an unpaired Student t test (*P < .05) and are representative of 3 independent experiments carried out per cell line.