MTT assays on cell lines treated with the demethylating agent 5-Aza-2′-deoxycytidine (decitabine) show preferential cytotoxicity in MLL-r cell lines. ALL cell lines were treated with decitabine at 0-, 0.5-, 1-, 2-, and 4-μM concentrations over 72 hours. Cell lines with an MLL-r (A-C) showed robust dose- and time-dependent cell kill. However, the MLL-wt cell lines (D-F) showed no response to decitabine. A summary graph representing the 72-hour time point for all cell lines treated is presented as panel G.