AFF1 and acute lymphoblastic leukemia: In line with previous findings [17, 20, 27, 41], we identified MLL-AF4 binding at the promoter and spreading into the gene body of PROM1 in CD133+ ALL cell lines (SEM and RS4;11; see Fig. 1a) and in MLL-AF4 blasts from a CD133+ ALL patient primograft [17] (Fig. 2a and Supplementary Fig. 3a).