In the present study, to evaluate whether LOS cooperates with t(8;21) in leukemogenesis, we first used a retroviral transduction/transplantation model to express RUNX1-ETO in hematopoietic cells from XO mice.     ///    "To determine whether GM-CSF signaling affects RUNX1-ETO leukemogenesis, hematopoietic stem/progenitor cells that lack GM-CSF signaling were used to express RUNX1-ETO and transplanted into lethally irradiated mice, and a high penetrance of AML was observed in recipients. "    ///    These results suggest a possible tumor-suppressor role of GM-CSF in RUNX1-ETO leukemia.     ///    The RUNX1-ETO fusion protein that is expressed by this translocation is poorly leukemogenic and requires additional mutations for transformation. 