RUNX1T1 and leukemia: This was confirmed in vivo as Mga(±) and Mga(−/−) HSPCs expressing RUNX1::RUNX1T1 9 A rapidly expanded and developed into leukemias characterized by immature GFP+, cKit+ myeloid progenitor-like cells when transplanted into lethally irradiated recipient mice (Fig. 5C and Supplementary Fig. 5D, E, H).