Two Cord Blood Transplants May Be Better Than One

December 11, 2002

Jane Salodof MacNeil

Dec. 11, 2002 (Philadelphia) — An experiment at the University of Minnesota has come up with a potential solution for the problem of mismatched bone marrow donors mismatched umbilical cord blood donations.

Juliet Barker, MD, of the University of Minnesota in Minneapolis gave pairs of umbilical cord blood units from different donors to 23 high-risk patients with hematological malignances. The hope was that together the units would provide a sufficiently large pool of stem cells for the patients to become engrafted.

Instead, the units appear to have done battle with each other. After 21 days, traces of only one blood cord unit could be found in two-thirds of the patients. By 60 days, all evidence of the losing unit had disappeared in 16 of the 18 patients who had been successfully engrafted.

Despite each unit having a smaller number of cells than is desirable for transplants, the engraftment rate was 92%. It was "better than what we would have expected based on that cell dose of the winning unit," Dr. Barker said at a press conference during the American Society of Hematology annual meeting.

Why did the struggle between the two mismatched cord blood units not defeat the experiment? Dr. Barker has no explanation for why the interaction enabled the patients to be engrafted. It's a mystery that will, undoubtedly, be pursued.

"Two cords are in there, but one cord wins," she said, proposing that the next big question is how to predict which cord unit would predominate. Researchers in the blood and marrow transplant program could not find a clear-cut pattern when they looked at the victors in the small pilot study, she said. The winners were not consistently the larger dose, nor were they an HLA match with the recipient.

Dr. Barker said her group attempted the experiment because cord blood transplants have become a promising alternative to bone marrow transplantation in children. The big obstacle to using them in adults, she said, was that adults are bigger; one unit of cord blood would not typically provide enough cells.

Among the potential advantages of cord blood compared with bone marrow is that it is far easier to obtain donors and harvest stem cells. Because neonatal cells are less mature, they are also less likely to bring on an immune response. Even so, Dr. Barker said, "We would have expected a higher incidence of graft vs. host failure than we saw."

The implications were immediately apparent to John Wagner, MD, also of the University of Minnesota, who reported on a large trial of graft vs. host prophylaxis at the meeting. He suggested that the Bone Marrow Donor Program consider coordinating a central cord blood bank. "Lots of women are having babies every day," he said.

A major limitation of bone marrow donation has been the lack of donations that can be matched to patients who are not of white European descent. "The majority of ethnic minorities will not have a donor," Dr. Barker told Medscape.

In another presentation at the meeting, Karen Ballen, MD, director of the program at Massachusetts General Hospital in Boston, reported that samples from black, Asian, and Hispanic Americans are available in the American Red Cross's cord blood program.

Although two-thirds of donors are identified as Caucasian, she reported that 13% are African American, 12% Hispanic, 5% Asian, and 2% Native American. About half the donated cord blood passes muster for storage, according to Dr. Ballen, and the minority representation varies with location. In Detroit, for example, she reported that 78% of donors are African American.

The Red Cross has accumulated 8,500 cord blood units at 10 different collection sites, said Dr. Ballen, who is a consultant for the organization. So far it has provided 98 units of cord blood for transplants worldwide, she said.

"There are enough cord blood units," she told Medscape, adding that convincing new mothers to sign consent forms so that their placentas can be used is usually not a problem when the program is explained.

How big is the demand? "It depends on who you ask and which transplantation institute you are talking to," she said. "At the University of Minnesota we have emphasized cord blood."

ASH 44th Annual Meeting: Abstract 142. Presented Dec. 8, 2002.

Reviewed by Gary D. Vogin, MD

Jane Salodof MacNeil is a freelance writer for Medscape.

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