AML induces an inflammatory response in the human bone marrow niche linked to an activation of JAK/STAT signaling. (A) Cytokine concentrations in the extracellular bone marrow fluid of AML patients (n = 19; mean age, 62.1 years ± standard deviation [SD] 12.1) and controls (n = 19; mean age, 58.2 years ± 15.7) quantified by Magnetic Luminex Performance Assay. Corresponding P values are given for each cytokine tested. (B) Median fluorescence intensity (MFI) of pSTAT3 and pSTAT5 in unstimulated peripheral blood mononuclear cells (PBMCs) from AML patients (n = 8) and controls (n = 7) assessed by BD Phosflow technology. (C) Representative flow cytometry plots showing fluorescence intensity of pSTAT3 (left) and pSTAT5 (right) of 1 AML patient sample under indicated conditions. (D) MFI of pSTAT3 (left) and pSTAT5 (right) in PBMCs from AML patients and controls after incubation with either IL-6 at the indicated concentrations or in combination with 2 µM ruxolitinib (Ruxo) for 15 minutes. MFI is given in relation to the unstimulated control condition; linked dots represent 1 patient sample under indicated conditions. (E) Primary human AML cells and controls were cocultured with HS-5 cells and treated with 2 µM ruxolitinib. Left, representative fluorescence intensity of 1 AML patient sample after mono- and coculture compared with fluorescence minus one (FMO) control. Right, MFI of pSTAT3 and pSTAT5 (normalized to monocultured control [n = 4-6]; each primary sample was tested in duplicate). DMSO, dimethyl sulfoxide. Data are shown as mean ± standard error of the mean (SEM). See also supplemental Figure 1. *P < .05; **P < .01; ***P < .001; ****P < .0001 as determined by Mann-Whitney U test or Wilcoxon signed-rank test.