Primary human T-ALL cells are GSI sensitive regardless of PTEN status. In vitro proliferation and cell size analysis of primary human T-ALL samples maintained briefly (up to 6 days) on either MS5/MS5-DL1 murine stromal feeder cells (A,C) or immobilized Delta1 ligand (Delta1^ext-IgG; B), and then treated with GSI (1μM compound E or 10μM DAPT) versus DMSO vehicle for 4 days. At the end of the treatment period, cultures were pulsed with BrdU and assayed by flow cytometry. Human T-ALL cells were discriminated from murine cells by costaining with hCD45. Each plotted data point in panels A and C represents a different primary human sample. Results are summarized from individual data plots presented in supplemental Figure 7. FSC indicates forward light scatter; ns, nonsignificant (Student t test).