Bone marrow failure due to acute myeloid leukemia (AML) is a significant factor behind the disease’s high rate of morbidity and mortality. Previous studies in mice suggest that AML cells inhibit healthy hematopoietic (blood) stem and progenitor cells (HSPC). A study released in STEM CELLS adds to this extent of knowledge by showing how secreted cell factors, in particular a protein called transforming growth factor beta 1 (TGFβ1), leads to a breakdown in the production of healthy blood cells (a process called hematopoiesis) in humans.