MODELING THE PATHOGENESIS OF RUNX1 DEFICIENCY IN INHERITED AML PREDISPOSITION SYNDROMES IN PRIMARY CELLS

Germline mutations in RUNX1 cause an autosomal dominant disorder characterized by lifelong thrombocytopenia and increased risk of progression to acute myeloid leukemia. Yet, the mechanisms by which these individuals progress to leukemia remains unclear. This project investigates the cell autonomous and non-autonomous drivers of disease. To determine the cell-autonomous effects of RUNX1 deficiency, we knocked out RUNX1 in cord blood HSPCs. Cell-context disruption of RUNX1 in CD34+CD38- early progenitors and CD34+CD38+ mature progenitors indicates that RUNX1 knockout (KO) in early progenitors causes erythroid and CD15+ granulocytic differentiation defects, whereas RUNX1 KO in mature progenitors causes megakaryocytic maturation defects and increases CD14+ monocytic differentiation. Further, RUNX1 KO HSPCs have a stem and proliferative defect. In addition, the type of RUNX1 mutation and location of the mutation are thought to affect the severity of disease. To explore this, we introduced the putative loss-of-function point mutation RUNX1R201Q or the putative dominant negative truncating mutation RUNX1R204X into the endogenous RUNX1 locus in HSPCs, and compared the differentiation and stem potential of these cells to RUNX1 KO HSPCs or to HSPCs expressing only the native dominant negative RUNX1 isoform, RUNX1A. As expected, cells expressing RUNX1R201Q phenocopied RUNX1 KO defects. Surprisingly, while cells expressing RUNX1R204X had greater stem and proliferative capacity compared to RUNX1 KO, they did not gain the proliferative profile seen in RUNX1A-expressing cells. Ongoing work is focused on determining the mechanism of how wildtype and mutant RUNX1 determines cell fate, and parallel efforts are exploring how commonly co-occurring mutations and RUNX1 deficient stroma are interacting with RUNX1 deficiency to drive disease progression.