JAK inhibition blocks cytokine rescue. (A) Immunoblot of MV4;11 cells treated with crenolanib 10 nM, ruxolitinib 1 μM, or both for 2 hours, then stimulated with GM-CSF for 15 minutes. Colony-forming assay in cytokine-rich methylcellulose treated with crenolanib, ruxolitinib, or both for MV4;11 cells (B; n = 3) or primary human FLT3-ITD AML (C). (D) Adenosine triphosphate–based survival assay of primary human FLT3-ITD AML treated with crenolanib, ruxolitinib, and IL-3. Supplemental Table 1 provides characteristics of patient samples. Dashed line represents DMSO-treated control (n = 5). (E) Colony-forming assay in cytokine-rich methylcellulose treated with crenolanib, ruxolitinib, PIM inhibitor, or combinations for normal human adult BM CD34⁺ cells. Error bars represent SEM. *P < .05; **P < .01; ***P < .001; ****P < .0001. Rux, ruxolitinib 0.1 or 1 μM.