In contrast to AML gene rearrangements, ectopic expression of either MLL/AF9 or MLL/ENL alone confers human CD34+ cell expansion and results in myeloid or lymphoid leukemia development in a NOD/SCID transplantation mouse model (Barabe et al., 2007; Wei et al., 2008). Here, CD34 is linked to acute myeloid leukemia.