Why is high-dose cyclophosphamide used to treat aplastic anemia?

Current treatments for aplastic anemia include high doses of the chemotherapy drug cyclophosphamide, which can lead to long-lasting, complete remission in some patients. This type of therapy rids the body of the cells that cause aplastic anemia without destroying key blood and bone marrow-forming stem cells. Stem cells contain high levels of an enzyme called aldehyde dehydrogenase, which makes them resistant to the toxic effects of cyclophosphamide.