t(8;21)–positive AML cells express MPL and respond to THPO induction. (A) Expression Correlation View (2856 probe sets) of 285 human AML samples, adapted from Valk et al.²⁶  The 16 clusters identified on the basis of the Correlation View are shown by different colors alongside the Correlation View (1-16). Clusters 9 and 13, aggregating all AML cells with inv(16) and t(8;21), respectively, are indicated by horizontal lines. Expression of MPL (detected by 3 independent probe sets 207550_at, 211903_s_at, 216825_s_at) is plotted in the latter 3 columns in which the bars are proportional to the MPL expression level. (B) Relative proliferation levels of 86 human AML cells in response to THPO as single cytokine. Samples were incubated with THPO or PBS for 3 days, and proliferation was tested by ³H-thymidine incorporation. The fold increase in proliferation with THPO was normalized to that without cytokine and ordered by increasing response. Samples carrying t(8;21) translocation (black bar) and inv(16) rearrangement (“v” mark) are shown. (C) MPL transcript levels determined by quantitative RT-PCR in human AML samples that were subjected to proliferation assays. The MPL levels are the average of duplicate values and relative to the average value of 6 healthy CD34⁺ BM samples (REL). Correlation between MPL expression and THPO response was performed by R statistics (R = 0.572, P < .001).