ERG LOF variants fail to drive megakaryocytic differentiation and cytokine independence. (A) In vitro differentiation of FLCs that overexpress WT ERG and variants. Immature stem or progenitor cell population with megakaryocytic features were stained using antibodies against cKIT⁺ and CD41⁺ with the percentage of double positive cells measured by flow cytometry (6 independent experiments). Pairwise comparisons are shown (∗∗∗∗P < .001 in comparison with WT). In all comparisons, a Student t test was used. (B) Example of gating strategy for cKIT⁺ and CD41⁺ expression on ERG WT– or variant-transduced FLCs. Cells were first gated for viability and mCherry expression. (C) Cell viability of FLC culture after cytokine removal measured over time.