Bone marrow transplants, already used to treat some children with sickle cell disease, also may cure some adults with this deadly genetic defect that causes red blood cells to contort, U.S. scientists said on Wednesday.
Nine of 10 adult patients given an experimental bone marrow transplant treatment were cured of sickle cell disease, researchers at the U.S. government's National Institutes of Health reported in the New England Journal of Medicine.
If the early results hold, the treatment could be ideal for patients with severe sickle cell disease, Dr. Miguel Abboud of American University of Beirut Medical Center in Lebanon said in an editorial accompanying the study.
Such transplants already are used to cure children with the disease who have a compatible donor who provides bone marrow. Bone marrow gives rise to blood cells.
Destroying a patient's bone marrow and replacing it with healthy marrow from a donor, often a sibling, is considered too risky for adults.
In conventional bone marrow transplants, doctors try to destroy all of a patient's own bone marrow. Using the new technique, adults are given a lower dose of radiation, only partially destroying the patient's bone marrow.
This approach leaves enough space inside the patient's bones for the donated marrow to find a home and produce enough healthy red blood cells to compensate for the defective ones.
In sickle cell disease, an inherited disorder, blood cells become stiff and sickle-shaped, causing them to block blood vessels and starve tissues of oxygen.
It had been thought that by the time people with sickle cell disease become adults, they had have suffered too much kidney, lung and liver damage to allow for a safe transplant.
All of these organs are essential for getting through a bone marrow transplant, Dr. John Tisdale of the NIH's National Heart, Lung and Blood Institute, who led the study, said in a telephone interview.
Tisdale and his team used about one quarter of the conventional dose of radiation, which was enough to wipe out part of the marrow. They also eliminated chemotherapy normally given to suppress the immune system.
As a result, each patient's bone marrow was a mix of cells from the patient and the donor.
But that was enough to cure nine out of the 10 patients who underwent a transplant and keep them well for an average of 2-1/2 years. The ages of the patients in the study ranged from 16 to 45 at the time of their transplants.
The healthy disc-shaped red blood cells produced by the donated marrow overwhelmed the diseased sickle-shaped cells generated by the patient's remaining marrow.
Because sickle red blood cells only live about six or seven days and normal red blood cells live 120 days, if you can get a little bit of the donor cells in there, the donor cells take over, Tisdale said.
Abboud cautioned that the technique's applicability is still limited by the small number of available siblings of patients with matching bone marrow types. Only 24 of the 112 eligible patients in this study had a compatible donor.
Tisdale estimated that of the 70,000 sickle cell patients in the United States, about 10 percent would be adults with a compatible donor and thus be eligible for the treatment.