Xenotransplantation: No Longer Science Fiction

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Pig Heart via Shutterstock Pig Heart via Shutterstock

Once deemed a freak experiment, summoning imagery of Frankenstein's monster, animal-to-human organ transplantation has made a huge leap forward.

A research team reports keeping baboons alive using pig hearts for over 900 days. One heart kept a baboon healthy for nearly three years. According to government organ donor data, 22 people in the U.S. die needing transplants each day, due to the short supply of human organs available for transplant.

Such xenotransplantation itself is not new. In 1984, Baby Fae, an American infant born with a life-threatening heart defect, received the heart of a baboon. She died 21 days later due to rejection of the transplant, which has always been a concern in transplants. The future road map is to grow organs from a patient's own stem cells, avoiding waiting lists and immunosuppressive drugs, but until then this sort of "bridge transplant" using animal organs could be ideal.

What happened between 1984 and 2016? As noted, a rough move of an organ from one species to another would cause severe and quick damage to the host's immune system. A pig's heart is the best option for humans, since our organs are about the same size, but researchers found that pigs carry a gene known as gal that would cause blood clots in humans. In 2001, scientists used a genetically engineered pig without the gal gene. After this, pig organs started thriving in primate bodies for months. These baboons and other primates must still take a number of drugs to protect from the foreign organs. But the drugs also suppress their immune systems.

The search was on for more effective drugs that would both protect animals during transplants but do less damage to the immune system. They tested such drugs as antibodies, as well as the blood-thinning drug heparin to prevent blood clotting in heart-transplanted baboons.

Those worked, until the drugs stopped.

As soon as the team began cutting down on the drugs, the baboons started rejecting the hearts and some died. The authors believe that keeping the drugs to a lower dosage might work best, but that would also mean a lifetime of suppressed immune systems and increased infection risk.

So it might not be a permanent solution but as bridge transplants, until a matching donor comes up on a waiting list, it could save lives -- and this breakthrough certainly advances science in the process.