JMML subpopulations differentially express NK cell ligands. Subpopulations (CD34^–CD3^–CD19^– bulk, CD34⁺CD38^– stem, and CD34⁺CD38⁺ progenitor cell populations) from 3 samples from patients with JMML were analyzed for surface expression of ligands for various NK cell–activating and –inhibitory receptors by mass cytometry. Results are plotted as average normalized expression of MMI (A) or percent positive cells (B) with error bars representing standard deviation and statistically significant differences represented by asterisks for ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001. PDL1, Programmed Death-Ligand 1.