Infants receiving heart transplants from donors with a different blood type can learn to tolerate the foreign tissue, possibly expanding the pool of organs available to babies who might otherwise die on the waiting list, researchers say.
"We discovered that the immune system of these infants is able to reprogram itself" to accept transplants from donors of different blood types, said Dr. Lori West, principal investigator of the study being published in the November issue of the journal Nature Medicine.
West, of the Hospital for Sick Children in Toronto, targeted ABO-incompatibility. That's an acute response in which organs from someone with a different blood type causes a rapid rejection that can lead death to in the first week. It is why doctors doing transplants seek to match the blood types of donors and recipients.
But in infants, the immune system is not fully developed and they can learn to tolerate the incompatible organs, West reported in a paper made available online Sunday.
Other immune responses can occur and, the infants, like adult organ recipients, still need drugs to suppress their immune systems.
But the discovery that they can learn to tolerate ABO-incompatible organs opens a much larger pool of organs for possible use.
Many organs are thrown away because there is not an appropriate recipient, "so if you can match organs to be thrown away to infants that are at death's door, you're going to improve survival," said Dr. Stephen G. Pophal of Northwestern University and Children's Memorial Hospital in Chicago.
Steven A. Webber, a professor at the University of Pittsburgh School of Medicine, said about one-fourth of babies who need heart transplants die while on the waiting list.
"For the dying child this is an important advance. For the child who is stable, the jury's still out," he said.
Dr. Nancy D. Bridges, chief of clinical transplantation at the National Institute of Allergy and Infections Disease, agreed that the finding seems unlikely to affect older transplant recipients.
"It's very likely that this will allow timely transplants for some babies who would otherwise not be that fortunate, who would die before a heart because available," she said.
Pophal, Webber and Bridges were not part of the research team.
Some of the infants with transplants remained healthy eight years after their operation.
"Isn't it exciting," West said in a telephone interview.
The next step, she said, is to see if it is possible to develop a way to intentionally induce immune system tolerance so incompatible heart transplants will be possible in older patients. She said the infants involved were mostly under six months old, although one was 14 months old.
West said the hospital began doing the transplants involving donors and recipients of different blood types because of a shortage of compatible donor hearts. So far 20 such transplants have been done at the Toronto hospital and 48 worldwide.
When an organ is transplanted into another person, an immune reaction can cause rejection. That happens with the host's immune system recognizes chemicals from the new organ as being foreign. It then produces antibodies that attack the newcomer.
West's research was funded by the Canadian Institutes for Health Research, the Heart and Stroke Foundation of Ontario and the Research Training Competition at the Hospital for Sick Children.
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Nature Medicine: http://www.nature.com/naturemedicine
