IRF4 and acute lymphoblastic leukemia: Of note, a forced overexpression of IRF4 in an IRF4-negative human T-ALL cell line (HPB-ALL), which exhibits DP stage immunophenotype, significantly inhibited cell growth and induced apoptosis (Supplementary Fig. 6C, D), suggesting that IRF4 overexpression at this stage of thymocytes is potentially lethal and thus IRF4-positive DP cells cannot expand.