Hematopoietic Stem Cell Expansion and Distinct Myeloid Developmental Abnormalities in a Murine Model of the AML1-ETO Translocation

Abstract

The t(8;21)(q22;q22) translocation, which fuses the ETO gene on human chromosome 8 with the AML1 gene on chromosome 21 (AML1-ETO), is one of the most frequent cytogenetic abnormalities associated with acute myelogenous leukemia (AML). It is seen in approximately 12 to 15% of AML cases and is present in about 40% of AML cases with a French-American-British classified M2 phenotype. We have generated a murine model of the t(8;21) translocation by retroviral expression of AML1-ETO in purified hematopoietic stem cells (HSC). Animals reconstituted with AML1-ETO-expressing cells recapitulate the hematopoietic developmental abnormalities seen in the bone marrow of human patients with the t(8;21) translocation. Primitive myeloblasts were increased to approximately 10% of bone marrow by 10 months posttransplant. Consistent with this observation was a 50-fold increase in myeloid colony-forming cells in vitro. Accumulation of late-stage metamyelocytes was also observed in bone marrow along with an increase in immature eosinophilic myelocytes that showed abnormal basophilic granulation. HSC numbers in the bone marrow of 10-month-posttransplant animals were 29-fold greater than in transplant-matched control mice, suggesting that AML1-ETO expression overrides the normal genetic control of HSC pool size. In summary, AMLI-ETO-expressing animals recapitulate many (and perhaps all) of the developmental abnormalities seen in human patients with the t(8;21) translocation, although the animals do not develop leukemia or disseminated disease in peripheral tissues like the liver or spleen. This suggests that the principal contribution of AML1-ETO to acute myeloid leukemia is the inhibition of multiple developmental pathways.

We thank John Kearney for help with the fluorescent microscope; Dan Tenen for the C/EBPα probe; Raymond Davidson for animal care; and Hyung Kim, C. Scott Swindle, and Claudiu Cotta for helping in retroviral transduction and transplantation. We also thank Tom Ryan, Trent Schoeb, Max Cooper, and the Division of Developmental and Clinical Immunology for valuable discussions and support.

This work was supported by a Howard Hughes faculty development award to C.A.K. (53000281) and a Molecular and Viral Oncology Predoctoral Fellowship grant (5T32CA09467) to C.D.G. A.J.W. holds an MRC Senior Clinical Fellowship through the Department of Haematology, University of Cambridge.