To test whether Lin28b is required to impede AML initiation prior to birth, we crossed a previously described Tet-OFF MLL::ENL model (Vav1-Cre; Rosa26LoxP-STOP-LoxP-rtTA; Col1a1TetO_MLL::ENL) to Lin28flox mice to generate Tet-OFF MLL::ENL; Lin28bΔ/Δ offspring [5, 12, 13]. This evidence concerns the gene VAV1 and acute myeloid leukemia.