Abstract
Hematopoietic stem cells (HSCs) in the bone marrow (BM) form mature blood cells of all lineages through expansion of lineage-biased progenitors. In a recent issue of Nature, Hérault et al. (2017) uncover a unique spatiotemporal mechanism of granulocyte-macrophage progenitors (GMPs) employed in emergency hematopoiesis that is also hijacked in leukemia.