Further investigation using MLL1-AF4 and AFF4 with deletion of various AF4/AFF4 domains showed that only the CHD domain of AFF4/AF4 is required for leukemic transformation, while other AF4/AFF4′s interacting domains with P-TEFb, ELL and AF9/ENL are dispensable for MLL1-AF4/AFF4 leukemia [39]. This evidence concerns the gene AFF1 and leukemia.