New research shows that genetically modified pig kidneys have survived long after being transplanted into baboons, and experts are banking on this to pave the way for animal-to-human organ transplants.
According to a report, the pigs used in the experiment were engineered to have
human-friendly organs in 2002. They lack a key sugar molecule that normally prompts the human and monkey immune system to launch an aggressive and fatal attack on foreign tissues.
David Sachs at the Massachusetts General Hospital in Cambridge along with his team, transplanted kidneys from the genetically modified pigs into eight baboons. The new organs enabled the animals to survive for up to 81 days, compared with around 30 days for non-transgenic kidneys.
The results show that the genetically engineered pig organs bypass the fierce rejection response and will perhaps escape attack in the human body too.
"It is evidence that rejection can be overcome and with extra work, the likelihood is that we'll be able to go much further," Kathryn Wood, immunologist of the University of Oxford, said.
Experts say that the genetically modified pigs may be the most promising development on the long road towards animal-to-human transplants, or xenotransplants. They hope that animal organs could one day make up for the massive shortfall in available human organs such as hearts and kidneys.
The pigs lack a gene called alpha-1,3-galactosyltransferase, or GGTA1, which adds alpha-1,3-galactose sugar molecules to its cells. Monkeys and humans harbour a pool of ready-made antibodies that instantly recognize this sugar, prompting a rapid and violent rejection, sometimes within minutes.
Researchers have made genetically modified pigs for transplants before, but these animals carried extra genes that suppress this immune response, rather than avoiding it altogether. The animals that Sachs' team used are also miniature pigs, so their organs are roughly the same size as human ones.
However experts have to overcome other rounds of attack by the immune system, such as the tiny blood clots that killed some of Sachs' baboons. The team used other tricks to quell organ rejection in the baboons, including drugs that quieten the immune system. Along with the kidney, the researchers also transplanted pieces of pig thymus, which pump out immune cells that do not attack pig tissues.