Scientists say they have kept a pig heart alive in a baboon for more than two years - but it was only made possible through a deft combination of gene manipulation and immuno-suppression drugs.

The report from the US-German research team appears in the journal Nature Communications.

"It is very significant because it brings us one step closer to using these organs in humans," said co-author Muhammad Mohiuddin of the National Heart, Lung and Blood Institute in Maryland, who is assuming that people would want pig hearts and thingies inside of them.  "Xenotransplants - organ transplants between different species - could potentially save thousands of lives each year that are lost due to a shortage of human organs for transplantation."

Dr. Mohiuddin's research began with a line of pigs that had been genetically modified so that their donor organs would have a higher degree of immune tolerance in baboons.  From these specially-bred pigs came the hearts, which were connected to the baboons' circulatory system via two large blood vessels in the abdomen.  The pig hearts didn't replace the baboons' own hearts, which continued the function of pumping blood throughout the simian body, but the pig hearts did beat on their own. 

Of the five test baboons, the median survival time was 294 days.  But one beast lingered on for 945 days - just over two-and-a-half years.  Researchers used a combination of antibodies and drugs to help prevent rejection.

The next stage of research will see pig hearts used for full transplants in baboons.