Indomethacin reverses MSC-mediated cell death protection in BCP-ALL. (A) iMSC#3 cells were grown to confluency before growth medium was changed from MEMα to RPMI with or without Indomethacin as indicated. After 24 h, ALL5 cells were cocultured with the iMSC#3 monolayer for 2 h before removal for irradiation with 2 Gy. BCP-ALL blasts were reintroduced to the iMSC#3 monolayer immediately after irradiation and cocultured for 20 h prior to cell death analysis of the CD19+ cell fraction by CD19-FITC/PI co-staining as described in Materials and Methods. The histogram shows mean values of five independent experiments with error bars indicating SEM values. (B) ALL blasts were cocultured, treated with Indomethacin, and analysed as described in 4A. Left panel: The scatter plot represents absolute cell death values from 13 independent experiments (ALL5: n = 5; ALL6: n = 1, ALL16: n = 4, ALL17: n = 1, ALL19: n = 1, ALL20: n = 1), with horizontal bars indicating median values. *P < 0.01 by Wilcoxon matched pairs signed rank test. Right panel: The relative reversal of iMSC#3 effect in irradiated (IR) cells by Indomethacin (Indo) was calculated according to the following formula: ([“+IR, +MSC, +Indo” − “+IR, +MSC, −Indo”] / [“+IR, −MSC, −Indo” − “+IR, +MSC, −Indo”]) × 100% . The values are displayed as a scatter plot with the horizontal bar representing the median value.