EPHA3 IS DISPENSABLE FOR NUP98-HOXD13-DRIVEN ACUTE MYELOID LEUKAEMIA BUT CRITICAL FOR NORMAL HAEMATOPOIETIC STEM CELL FUNCTION

Abstract

EphA3, a receptor tyrosine kinase which mediates cell-cell interactions, is a potential therapeutic target for haematopoietic malignancies because of overexpression of EphA3 in patients with these diseases, along with negligible expression in healthy mice or humans. The NUP98-HOXD13 (NHD13) mouse is a well-established model of myelodysplasia and AML. NHD13 is a fusion gene which drives an abnormal gene expression program including overexpression of HoxA9. These mice also overexpress EphA3, and we sought to discover whether EphA3 contributed to the disease phenotype. We followed NHD13 EphA3 +/+ and NHD13 EphA3 -/- mice through their disease course. Overall survival was significantly better in the NHD13 EphA3 -/- mice (p=0.0436; EphA3+/+ n=30, EphA3-/- n=25). This difference was attributable to mice that developed T cell lymphoblastic leukaemia (T-ALL) in each cohort (EphA3+/+ n=9, EphA3-/- n=4). Survival of mice that developed AML was not impacted by the loss of EphA3. We also sought to discover whether there might be a functional role for EphA3 in normal haematopoiesis. To investigate a potential role in stem cell function, a competitive transplant was performed. CD45.1 B6 recipients were lethally irradiated and transplanted with whole bone marrow cells from either wild type CD45.2 mice or EphA3−/− CD45.2 mice, together with whole bone marrow cells from CD45.1 B6 mice. Primary transplants revealed no differences in blood or bone marrow reconstitution between groups. Secondary transplants revealed that both myeloid and lymphoid lineage reconstitution in the blood and bone marrow were dramatically decreased in the EphA3−/− recipients versus the wild type recipients, demonstrating a defect in stem cell repopulating ability in the absence of EphA3. This study provides the first evidence that EphA3 has a role in normal haematopoietic stem cell function.