MLLT1 and acute myeloid leukemia: One of the reasons arguing against the contact first hypothesis was that 3D-FISH analysis indicated closer spatial proximity of MLL and ENL genes in interphase nuclei of myeloid (AML-193, PLB-985) and lymphoid cells (Nalm-6, IM-9) as compared with MLL and AF4 genes, even though AF4 represents the most frequent partner in MLL translocations (Gué et al., 2006).