When one cell is enough

For many years, the hematopoietic stem cell (HSC) has been well characterized in mice as a cell that can singly reconstitute the whole hematopoietic system of primary recipient animals as well as that of secondary hosts. That clinical bone marrow transplantation is a successful treatment strategy is indirect evidence that such a cell exists in humans. To date, similar criteria have not been applied to human HSCs. However, using a humanized mouse model of xenotransplantation, a recent paper shows that single human cells can fully reconstitute the lymphomyeloid system of primary recipient animals and, in some cases, that of secondary hosts.