Umbilical cord blood is an acceptable source of stem cells for transplant in adult leukemia patients when a suitable bone marrow donor is unavailable, according to 2 new studies.

The findings, reported by US and European research groups in the New England Journal of Medicine (Vol. 351, No. 22: 2265-2275 and 2276-2285), offer a promising alternative to thousands of leukemia patients in need of treatment.

Leukemia is a type of cancer that begins in the bone marrow. It strikes both adults and children; about 33,440 people will develop the disease in 2004, according to American Cancer Society estimates. Radiation, chemotherapy, and other drugs can be used to treat the 4 different types of leukemia, but many patients also need a bone marrow transplant. In this procedure, stem cells are removed from a donor's bone marrow and transplanted into the patient.

Transplants are most successful when the stem cells come from a donor whose cells are similar to the patient's -- usually a brother or sister or other relative. But only about 20% of leukemia patients who need a bone marrow transplant have a relative who is a match. The rest have to look for donors in national and international databases.

"As many as 16,000 leukemia patients diagnosed each year require a bone marrow transplant but have no matched relative or can't find a match in the national bone marrow registry," Mary J. Laughlin, MD, associate professor of medicine at Case Western Reserve University School of Medicine and lead researcher of one of the studies, said in a statement. "Umbilical cords that are normally discarded after birth could provide real hope for these patients."

Laughlin and her colleagues compared 600 leukemia patients who had received either a bone marrow transplant from a completely matched, but unrelated, donor, a bone marrow transplant from an imperfectly matched (and unrelated) donor, or a cord blood transplant.

Patients who had a matched marrow donor fared best. Three years after treatment, 33% of them were still disease-free. But there were few differences between patients who had a mismatched marrow donor and those who received a cord blood transplant. About 22% of patients in each of those groups were still disease-free 3 years after the transplant.

The chances of survival were also similar between cord blood recipients and mismatched bone marrow recipients, but significantly higher for people who had a matched marrow donor.

The European study, led by Vanderson Rocha, MD, PhD, of the Hopital Saint-Louis in Paris, saw even better results from cord blood transplants. In that study, which included 682 adults who received either a matched bone marrow transplant or a cord blood transplant, the researchers found no significant differences in disease-free survival, relapse, or transplant-related deaths.

Cord blood transplants have been used successfully in children with leukemia, but the technique has some limitations when used in adults and until recently was not commonly performed. One of the greatest obstacles, said Ralph Vogler, MD, scientific program director at the American Cancer Society, is getting enough stem cells from the cord blood to successfully treat an adult. Typically, cord blood contains about 1/10 the number of useable cells that bone marrow does. The new research shows, however, that progress has been made in expanding the number of cells obtained from cord blood, he said.

Another problem with cord blood transplants is the time it takes for levels of blood platelets and white blood cells to return to normal after the procedure. This process is much slower after a cord blood transplant, and until it is complete, the patient is vulnerable to infections that can be deadly. In Laughlin's study, infection as a cause of death in the first 100 days following transplant was significantly higher in the cord blood group (45% of deaths) than in either of the bone marrow groups (21% for matched marrow, 24% for mismatched marrow). White blood cell recovery in cord blood recipients was also significantly delayed in Rocha's study, but deaths from infection occurred at the same rate in both groups.

But progress has been made in that arena, too, Vogler said. "Now what's being done is, after the transplant they're giving growth factors to stimulate white cell production, and there is a growth factor that can stimulate platelet production," he said. Platelets can also be transfused, he added.

Despite such problems, there are also some advantages to cord blood transplants over bone marrow transplants. There is no danger to the donor, since the blood is collected after birth before the placenta and umbilical cord are discarded. Once a suitable donor is identified through a matching service, the cord blood, which has already been frozen and stored, can be made available more rapidly than bone marrow.

However, storage is expensive, so there are not enough units of cord blood stored to find matches for most patients. Public cord blood banks do not charge the donor for collection or storage, but the recipient must pay $15,000-$25,000 to get the blood. That cost is usually covered by health insurance, according to Robert Steinbrook, MD, who wrote an editorial accompanying the studies.

In addition, Vogler said, stem cells from cord blood are less likely to cause graft-versus-host disease (GVHD), a potentially fatal condition in which the immune cells from the donor attack the recipient's cells.

Overall transplant results are still best when a matched bone marrow donor is available, and neither group of researchers recommends cord blood as a substitute for a matched marrow donor. But having alternatives is important because of the poor survival rate in adult leukemia.

"The cure rate from chemotherapy alone is only around 30% in adults," said Vogler, "so 70% of your patients are going to relapse and die unless you can do something further."

Laughlin also emphasized the need for new therapies. "These are very high risk patients who undergo cord blood transplants only as a last resort effort to stay alive," she said. "Even with a cord blood transplant these patients often suffer from life-threatening infections, but the fact is, without attempting this innovative therapy, none of them would survive."