Dnmt3a loss of function and an Idh2 neomorphic mutant interacted to promote myeloid malignancies. (A) Kaplan-Meier survival curves for mice receiving different genetically modified stem cells. P value by log-rank test. (B-E) Blood cell counts in the transplant-recipient groups shown in panel A at 180 to 220 days after transplantation. White blood cells (B), red blood cells (C), monocytes (D), and platelets (E). **P < .01; ***P < .001, by 1-way ANOVA and post hoc Bonferroni test. (F-I) Bone marrow Giemsa stain showing multilineage dysplastic features of Dnmt3a^–/–;Idh2^R140Q (3aKO-140) mice that developed MDS/myeloproliferative neoplasms (5/8 animals) and MDS (1/8 examined animals). (F) Dysmegakaryopoiesis; yellow arrowheads indicate dysplastic multinucleated and monolobular megakaryocytes. (G) Dysgranulopoiesis; yellow arrowhead indicates pseudo-Pelger-Hüet neutrophils. (H) Dyserythropoiesis; yellow arrowhead indicates a binucleated erythroid progenitor. (I) AML blast in bone marrow of 3aKO-140 recipient (2/8 examined animals developed AML). (F) Bar represents 20 μm. (J) Mass spectrometry measurements of 2-HG in the serum of genetically manipulated mice relative to WT controls. Mean ± standard deviation (n = 3 per group); *P < .05; ***P < .001. (K) Loss of KSL stem cell pool in GFP⁺ bone marrow cells of recipient mice in the 3aKO-140 group (n = 3 for each genotype, representative flow plots are shown for each genotype). (L-M) Venn diagrams of genes upregulated (L) and downregulated (M) in 3aKO-140 MEP-like HSPCs, Dnmt3aKO MEP+GMPs, and WT-140 MEP+GMPs, relative to WT MEP+GMPs. Examples of overlapping differentially expressed genes from 2 different genotypes are labeled. (N) Stem cell gene and megakaryocyte progenitor gene signatures were enriched in overexpressed transcripts in 3aKO-140 MEP-like HSPCs relative to WT-140 MEP+GMPs; late progenitor genes were depleted in 3aKO-140 MEP-like HSPCs. n.s., not significant.