DLL4 and acute lymphoblastic leukemia: To demonstrate that spleen is specifically required for DLL4-driven T-ALL development, we used a Notch Intracellular Domain (NICD)-driven T-ALL mouse model (i.e. EF1a-N1IC R26-Cre ER mice) in which Notch1 NICD is preceded by Flox/STOP/Flox 16.