Early CAs in MS-5 coculture are mediated by the Flt3-ITD. Transduced CB-CD34⁺ cells expressing the MIGR1 control, W51 Flt3-ITD, and a constitutively activated Stat5 mutant (Stat5A1*6) were plated in triplicate MS-5 cocultures, with weekly evaluation of nonadherent cell expansion in control cultures (A) and in cultures supplemented with 10 μM AG1295 (Flt3-RTK inhibitor) every 48 hours. Day-10 CAs were enumerated for each set of cultures (B). Parallel MS-5 coculture experiments were also performed with W51 Flt3-ITD cells in the presence of 10 μMof the c-kit RTK specific inhibitor, PD16, demonstrating no effect on early CAs (C). TNC indicates total nucleated cell.