Overexpression of Bmi1, Meis1, and Pbx1 in JAK2-mutant HSCs enhance MPN-like phenotype in vivo. (A) Schematic of candidate gene overexpression transplants. Bulk CD45⁺Lin⁻CD48⁻CD150⁺ (HSPC) cells (300-800 per mouse) were sorted from WT and JAK HOM mice and infected with lentivirus carrying no gene (empty vector) or lentivirus carrying genes to overexpress Bmi1, Pbx1, Runx1, or Meis1 (2 independent experiments). Three days after infection, GFP⁺ cells (300-2000) were isolated and transplanted into recipient mice. Serial analysis of peripheral blood was performed to assess chimerism (B-C, n = 4-5 recipients) and blood cell parameters (D-E). Hematocrit (Hct) and hemoglobin (Hgb) at 20 weeks posttransplantation for JAK HOM cells overexpressing each gene compared with WT cells transduced with the same construct (D-E). Successfully repopulated JAK HOM cells overexpressing either of Meis1 or Bmi1 display an erythrocytic phenotype compared with JAK HOM cells transduced with the empty vector. *P < .05. A dark circle indicates a mouse that died before the 20-week point (unrelated to transplantation in the mouse receiving Runx1-transduced cells or the mouse receiving nonrepopulating Pbx1-transduced cells).