Bone Marrow Transplants.

In bone marrow transplantation, all blood-forming cells in the body, both normal and malignant, are totally destroyed and then replaced with bone marrow cells taken from a donor. Experience in bone marrow transplantation technique has grown rapidly over the last several years and is strongly encouraging. In the opinion of some investigators, this drastic treatment may eventually offer the best chance of cure. Transplants are now reserved for patients with disease that is resistant to standard therapy. They are performed at only four or five institutions across the United States, and have in some instances reversed an otherwise hopeless situation.

Much more study is required, however, before transplantation will be regarded as the initial treatment of choice for leukemia patients. There has not yet been a rigorous statistical study comparing the results of transplantation with intensive chemotherapy continued after complete remission. The available data, when compared on a less than rigorous basis, do not show a significant difference between the two treatment paths. In any case, transplantation is a realistic therapeutic option for only about one third of patients, since careful genetic matching with a close relative, such as a brother or sister, is necessary and only patients under forty without other disabling medical problems are considered.

In preparation for a bone marrow transplant, the patient is given ultra-high doses of radiation and chemotherapy to destroy all blood-forming cells. Careful immunological tissue testing is carried out to choose the best donor from among the patient's close relatives. The donor's cells are injected into the recipient's bloodstream to reseed the marrow with healthy cells. The leukemia patient is kept in isolation to diminish the chance of infection and is given transfusions and antibiotics as needed.

Two fundamental problems can occur after injection of the donor marrow. The recipient's (host's) immune system can reject the marrow transplant or, the donor's marrow, in its immunologically foreign environment, can reject the host. The latter, a "graft versus host" reaction, can be very serious. Strong suppression of the immune cells in the donor marrow or in the recipient can often control these problems, but fatalities have been caused by either response. For this reason, the closer the genetic match (HLA correspondence) between donor and host, the better the chance of the transplant's "taking." Ways to reduce the graft versus host reaction such as using highly specific monoclonal antibodies to remove the cells that mediate immunologic function in the donor marrow before it is given to the recipient are being explored at several research institutions.