The targeting vector was designed with tetO (TRE) promoter, upstream of human KMT2A/MLLT3 (MLL-AF9) cDNA followed by an IRES-deltaNGFR cassette. The KMT2A/MLLT3 translocation T(9:11) contains the AT hook and DNA methyltransferase from KMT2A (1444 amino acids) at the N terminal fused to the 192 C-term amino acids from MLLT3 (breakpoints are variable). MLL-AF9 expression is monitored by the co-expressed deltaNGFR on the cell surface. This construct was inserted into a cassette exchange locus upstream of the hypoxanthine guanine phosphoribosyl transferase (Hprt) gene on the X chromosome using Inducible Cassette Exchange (ICE) recombination. (J:282726)