Leukemia is a cancer of white blood cells, or leukocytes. Like other blood cells, leukocytes develop from somatic stem cells. Mature leukocytes are released into the bloodstream, where they work to fight off infections in our bodies. Leukemia results when leukocytes begin to grow and function abnormally, becoming cancerous. These abnormal cells cannot fight off infection, and they interfere with the functions of other organs. Successful treatment for leukemia depends on getting rid of all the abnormal leukocytes in the patient, and allowing healthy cells to grow in their place. One way to do this is through chemotherapy, which uses drugs to target and kill abnormal cells. When chemotherapy alone is not successful, physicians sometimes turn to bone marrow transplants.
A bone marrow transplant includes several steps. Order these steps for a successful transplant to cure leukemia.

A. donor match located
B. a sample of donor bone marrow containing healthy stem cells is introduced into the patient's bloodstream
C. patient's existing bone marrow and abnormal leukocytes are killed using a combination of chemotherapy and radiation
D. donor stem cells will migrate to patient's bone marrow and begin producing healthy leukocytes