Transplant surgery can go wrong

In pregnancy it seems to ensure the developing foetus is not rejected by its mother by keeping key immune system cells quiet.

Researchers from the Medical College of Georgia hope it can be used to improve transplant success without putting patients at risk of infection.

At present, patients must take potent drugs to cut the risk of rejection.

The patient needs to fight infection and, in this case, the immune system will be ready to do that and be tolerant of the transplant only Dr Anatolij Horuzsko

The molecule, HLA-G, works by toning down the activity of dendritic cells, which effectively play the role of air-traffic controllers for the immune system, directing its efforts towards attacking invaders.

It is vital these cells are muted during the early stages of pregnancy because the foetus is made up of genetic material from both parents - and therefore could potentially be seen as a foreign invader by the immune system.

Many patients who undergo a transplant do not reject their new organ.

However, at present it is not possible to predict those who will have problems.

Therefore, all transplant patients receive potent immunosuppressant drugs, whether they need them or not, increasing their vulnerability to infection.

And although rejection rates of transplanted organs have dramatically dropped over the last 20 years, many organs still fail over time.

Skin grafts

The researchers found skin grafts on mice genetically modified to produce HLA-G lasted about a month longer than those on normal mice.

The researchers are hopeful of success

The human equivalent would be likely to be much longer since a day in a mouse's life translates to about a month for a human.

Next they plan to test the theory by transplanting pancreatic cells into rats whose dendritic cells have been modified by HLA-G.

Lead researcher Dr Anatolij Horuzsko said the eventual aim would be to inject a few cells into a person undergoing a transplant with a view to reducing the risk of rejection without compromising the ability to fight infection generally.

He said: "This is a goal because the patient needs to fight infection and, in this case, the immune system will be ready to do that and be tolerant of the transplant only."

Transplant surgeon Dr Oscar Grandas said at present doctors tried to minimise the threat of rejection by using bone marrow transplants in conjunction with organ transplants - effectively replacing the components of the immune system.

He said: "We think Dr Horusko's approach is a step ahead because you will infuse only a particular subset of cells that have the function we want regulated."

Potential flaws

Mr Murat Aqyol, a consultant transplant surgeon at the Scottish Liver Transplant Unit in Edinburgh, told BBC News Online: "If we could induce tolerance - where the immune system does not react against a specific thing, but otherwise is still intact to fight infection - that would be very desirable."

However, he said previous attempts to achieve this had failed in humans, despite promising results in animals.

He also warned HLA-G had a very specific action in pregnancy, and that for it to work for transplant patients the treatment would have to be geared to deal with the specific immune response stimulated by a donor organ.

"To tolerise a patient, you would potentially need to know what type of donor organ was to be used months in advance," he said.

"For that reason this approach would be unlikely to work for organs taken from dead people.

"However, it might potentially be useful for kidney transplants where the donor organ is taken from a family member."