Adult HSC compartment responds to multiple cytokine stimuli and expresses cytokine receptors. (A) Representative flow cytometric plot of phosphorylation responses [Stat3(pY705), Stat5(pY694)] after 15-minute stimulation with the indicated cytokines in healthy adult BM HSCs. HSCs are CD34⁺CD38⁻CD90⁺CD45RA⁻. The percentage of cells responding via each node is indicated in each quadrant and is calculated relative to the unstimulated control for each sample. Stimuli used were G-CSF (20 ng/mL), GM-CSF (20 ng/mL), FLT3 ligand (FL; 100 ng/mL), SCF (100 ng/mL), thrombopoietin (Tpo; 50 ng/mL), IL-3 (20 ng/mL), IL-6 (20 ng/mL), and a combination of FL, SCF, Tpo, IL-3, and IL-6 (referred to as FST36). Gray arrows represent directionality of response, but in the case where multiple nodes are activated, not necessarily the sequence of activation. (B) Heatmap of the average percentage of cells responding in each stem and progenitor compartment in normal adult BM after 15-minute cytokine stimulation. MPPs are CD34⁺CD38⁻CD90⁻CD45RA⁻, CMPs are CD34⁺CD38⁺CD123⁺CD45RA⁻, GMPs are CD34⁺CD38⁺CD123⁺CD45RA⁺, and MEPs are CD34⁺CD38⁺CD123^lo/−CD45RA⁻. Measurements were obtained from 2-4 distinct biologic samples. Epo is erythropoietin, and 3 units/mL was used to stimulate cells. (C) Representative flow cytometric analyses of cytokine receptor expression on adult marrow HSCs. Red histogram is isotype control, blue histogram is cytokine receptor. Median fluorescence intensity (MFI) is indicated with isotype control on top. Measurements were taken on 3 distinct biologic samples.