NEW YORK (GenomeWeb) – Adult humans have between 50,000 and 200,000 hematopoietic stem cells that are actively making blood cells in their bodies, a new study has found. This estimate — which is based on the number of somatic mutations researchers found — is about 10 times higher than previous approximations.

Hematopoietic stem cells differentiate into myeloid, T, and B cells to replenish the body's blood cells. But despite the use of hematopoietic stem cells as a therapy for diseases such as leukemia, their exact number and dynamics have been unclear.