MLLT1 and acute myeloid leukemia: Comparable results on L-GMPs and AML development have been obtained when MLL-AF9-GFP-transduced and MLL-ENL-YFP-transduced Il21R+/− and Il21R−/− LSKs were transplanted into Il21R+/− control mice (Il21R+/− AML and Il21R−/− AML, respectively) (Figures 1J–1N, S1I–S1L, and S2A–S2E), indicating that IL-21/IL-21R signaling on AML cells regulates leukemogenesis.