A new transplant technique has enabled five kidney recipients to survive for several years without taking drugs that suppress their immune systems, scientists reported today.
Doctors produced the groundbreaking result by injecting transplant recipients with blood stem cells taken from their donors’ bone marrow. The stem cells multiplied and protected the transplanted organ from an immune system attack.
Normally, recipients must follow a lifelong regimen of immunosuppressant drugs for their transplanted organs to survive. Those drugs greatly increase the risk of infections, cancer, high blood pressure and other serious medical problems.
Transplant experts expressed excitement over the findings, reported in the New England Journal of Medicine, while calling them “very preliminary.” The results need to be replicated in larger numbers of patients over a longer period of time, they cautioned.
In addition, the new findings don’t mean patients who have already received transplants can stop taking their drugs. Only new patients who receive organs from living donors are eligible for the still-experimental therapies.
But the reports provide evidence that immune tolerance to transplants can be achieved in humans, as it has in animal experiments.
Dr. Suzanne Ildstad, director of the institute for cellular therapeutics at the University of Louisville Health Sciences Center, said she thinks it will be possible within a few years to eliminate immune-suppressing drugs for significant numbers of transplant patients. “It’s achievable,” she said.
In one of the new studies, scientists at Harvard Medical School and Massachusetts General Hospital reported that four people who received kidneys from living donors are alive and well after forgoing the usual medications for two to five years.
The kidneys came from “mismatched” donors, or people whose bodies produce proteins known as antigens that are incompatible with the organ recipient. The vast majority of transplants in the U.S. occur between mismatched pairs.
In the other study, Stanford University scientists have discontinued immune-suppressing therapy for more than two years in a middle-aged man who received a kidney from a brother. This case was an antigen match.
Scientists in both studies first administered powerful antibodies to the recipient to knock out cells that stimulate immune defenses. Then the kidney transplant was carried out, followed by an injection of blood stem cells from the donor. Blood stem cells produce immune cells as well as red and white blood cells.
The procedure was designed to allow the immune systems of the two individuals to mingle and co-exist, so that the recipient’s body would not recognize the donor’s kidney as foreign.
To prevent rejection of the new organ, patients were started on immunosuppressant drugs but gradually weaned off the medications if there was evidence of immune tolerance.
“It’s just a beginning, but it shows that it can work,” said Dr. David Sachs, director of the transplantation biology research center at Massachusetts General. “Clearly, we need to do more patients but it looks very promising.”