London, January 24 : People receiving organ transplants may not have to remain dependent on immuno-suppressant drugs in future, as scientists have found that transplanting part of the immune system along with an organ can help prevent rejection.
That the immune system can be trained to tolerate transplanted organs has been shown by three independent research teams, though they adopted different procedures.
Patients' dependence over immuno-suppressant medicines to prevent rejection may sometimes prove dangerous, a major reason why the new finding attains significance, reports Nature magazine.
Thousands of kidney transplantations are performed every year. However, the transplant recipients often need to take immunosuppressant drugs for the rest of their lives to ward off organ rejection, even when the donor is a close relative. esides being very pricey, such medicines also increase the risk of infection.
In previous studies, it was found that mice and monkeys receiving organ transplant coupled with an infusion of blood stem cells - which are made by bone marrow and give rise to white blood cells, including the B cells that produce antibodies, and T cells that are important in distinguishing host from donor - could sometimes be weaned off the immuno-suppressant drugs.
They showed that transplanting blood stem cells into the host created a hybrid immune system, and that the transplanted organ was then no longer recognized as foreign.
Michael Stormon of the Children's Hospital at Westmead in Sydney, Australia and his colleagues performed a liver transplantation in a nine-year-old girl with hepatitis. The stem cells brought in by the donated liver almost completely replaced her immune cells.
The girl was able to discontinue her immuno-suppressant regime a year after the procedure, and has not experienced any complications in the four years since.
In another case, a patient received a kidney and an infusion of blood that had been enriched for blood-producing stem cells, both from his brother, at Stanford University in California.
Genetic tests revealed the presence of the brother's immune cells still circulating in the host's blood more than two years after the procedure. The patient stopped taking immuno-suppressant drugs with no signs of rejection.
Finally, David Sachs of Massachusetts General Hospital in Boston and his colleagues performed transplantations of kidneys and bone marrow in five patients whose donors were not related to them, making rejection more difficult to avoid.
The antibodies of one of the first three patients to undergo the procedure rejected the organ in the first attempt, though the second attempt was successful. Because of this, the researchers added an extra drug to their protocol to destroy the host's antibody-producing B cells in the following two patients.
All four of the patients with successful initial transplants were able to discontinue their immuno-suppressants in less than a year after the procedure.
What is surprising is that these patients did not continue to produce donor immune cells. The researchers still do not know precisely why they did not reject their new kidneys.
The researchers are preparing to continue the study in more patients.
The findings, reported in the New England Journal of Medicine, are preliminary and involve only a few patients. If replicated in a larger population, they might eliminate the need to continue taking sometimes-dangerous immuno-suppressant drugs.