Hematopoietic stem cells (HSCs) are rare, self-renewing progenitors that give rise to all lineages of blood cells. HSCs can be found in all hematopoietic organs, from the para-aortic mesoderm (1),(2) and yolk sac (3),(4) in fetuses to the bone marrow (reviewed in ref. 5), blood and spleens of adults.
