Bone marrow is the soft, sponge-like material found inside bones.
It contains immature cells called stem cells that produce blood cells. Umbilical cord blood also contains stem cells. Stem cells can divide to form more stem cells, or they can mature into white blood cells, red blood cells, or platelets. In autologous transplants , patients receive their own stem cells. In syngeneic transplants , patients receive stem cells from their identical twin.