High-level MCL-1 expression is associated with in vivo prednisone resistance in MLL-rearranged infant ALL. (A) On the basis of a 7-day window of prednisone monotherapy, patients with MLL-rearranged infant ALL are classified as prednisone good responders (PGRs; < 1000 leukemic blasts/μL) or PPRs (≥ 1000 leukemic blasts/μL). The graph shows the relative MCL-1 expression as determined by quantitative real-time RT-PCR (TaqMan) in both patient groups. (B) The differences in relative MCL-1 expression in patients with infant ALL who are PGRs and are sensitive to prednisolone in vitro, compared with patients who are resistant either in vivo (PPRs) or in vitro. Dots represent individual patients; lines indicate the median MCL-1 expression level in each group. The difference between patient groups was statistically analyzed using the Mann-Whitney U test.