More than 50 years of experience studying blood-forming stem cells called hematopoietic stem cells, scientists have developed sufficient understanding to actually use them as a therapy.Hematopoietic stem cell transplants are now routinely used to treat patients with cancers and other disorders of the blood and immune systems.Recently,researchers have observed in animal studies that hematopoietic stem cells appear to be able to form other kinds of cells ,such as muscle ,blood vessels,and bone. If this can be applied to human cells, it may eventually be possible to use hematopoietic stem cells to replace a wider array of cells and tissues than once thought.