AFF1 and acute lymphoblastic leukemia: To examine the fetal and postnatal gene expression programs that are key to determining the age-related differences between MLL-AF4 ALLs, we used the 139 genes up- or downregulated in both FL (compared to ABM) and MLL-AF4 infant-ALL (compared to MLL-AF4 childhood-ALL) (Supplementary Data 2).