A new blood system isn’t created from scratch—just something close to it. A single type of stem cell, a new study demonstrates, can fully repopulate the bone marrow and give rise to all the cell lineages that constitute a complete blood system.

This blood-forming stem cell is distinguished by three cell-surface markers—or rather the presence of two markers and the absence of a third. By heeding these markers, scientists may improve transplantation procedures, as well develop better gene therapy and gene-editing approaches.