NOTCH1 and acute lymphoblastic leukemia: First, we generated NOTCH1-induced T-ALL based on the transformation of Klf4fl/fl;Vav-iCre (Klf4∆/∆) hematopoietic cells with retrovirus carrying either gain-of-function mutant NOTCH1L1601P-∆P (leukemic) or empty retrovirus (non-leukemic) as the control followed by transplantation into cytoablated hosts [9, 30, 31].