High-risk comutations induce opposing myeloid lineage outcomes. (A) Differentiation efficiency of SF3B1-mutant 5F-HPCs CRISPR-edited for RUNX1 (S-R), STAG2 (S-S), or AAVS1 (S-A). Representative flow plot (left); S-R compared with S-A (center); S-S compared with S-A (right); same control group for both comparisons. Percent erythroid, myeloid, and Lin^– precursors of mCherry⁺DAPI^– lentivirus–transduced edited cells. Data are presented as mean ± SD from 5 independent experiments, each with S-A, S-R, and S-S groups; ratio paired t test. (B) Outline of the experimental approach used to introduce SF3B1 K700E knockin mutation with high-risk RUNX1 (S-R) or STAG2 (S-S) comutations, or AAVS1 control (S-A) into CB- or PB-derived CD34⁺ HSPCs. (C) Differentiation efficiency of CB CD34⁺ HSPCs gene edited for SF3B1 K700E and RUNX1 (S-R), STAG2 (S-S), or AAVS1 (S-A). Representative flow plot (left); S-R compared with S-A (center); S-S compared with S-A (right); the same control group was used for both comparisons. Percent erythroid, myeloid, and Lin^– precursors of total BFP⁺ cells is shown. Data are presented as mean ± SD from 3 independent experiments, each with S-A, S-R, and S-S groups; ratio paired t test. (D) Granulocytic maturation in BM samples of SF3B1-mutant patients. Representative flow plot with gating strategy (left) and quantification of immature CD13⁺CD16^– granulocytes (center) and mature CD16⁺ cells (right). Data are shown as mean with interval; 1-way analysis of variance (ANOVA). BFP, blue fluorescent protein; DAPI, 4′,6-diamidino-2-phenylindole; Lin^–, lineage-negative; ns, not significant.