A pig’s heart can now live inside a baboon—and the breakthrough could prove vital for humans needing organ transplants

Thousands die every year waiting for an organ transplant.

There are, of course, a lot more humans dying than there are humans needing an organ. However, for human-to-human transplantation to work, the potential organ donor has to be declared braindead (or assumed to have no other way to recover) while their body is kept on a ventilator. This happens far less than there is demand for those organs.

One way to satisfy demand for organs is xenotransplantation, where humans are given organs from another animal. Pigs are ideal because some of their organs are of a similar size to humans. Now, in a step in that direction, scientists at the US National Institutes for Health have for the first time kept a pig’s heart alive in a baboon for nearly three years.

To achieve the feat, scientists genetically modified pigs so that their heart cells would be more compatible with those of baboons and humans. They then transplanted those hearts inside five baboons’ abdomen connected to their circulatory system. In effect, the baboons had two beating hearts.

Next, as they would in any organ transplantation, they fed the baboons a special cocktail of drugs that suppressed the immune system. Without the drugs, the body would have rejected the organ by unleashing an immune attack, just as it would on disease-causing microbes.

This combination of genetic engineering and drugs, they report in Nature Communications, kept the pig’s heart alive in three out five baboons for more than 300 days, including in one case for 945 days.

The heart could have survived longer, but scientists wanted to test whether the baboons had developed tolerance for the organs, so they stopped giving the baboons the drug cocktail. That, however, triggered the organ rejection process to start. To save the baboons, the scientists then removed the pig hearts.

Successfully keeping the heart alive for so long inside a baboon is a big deal. This is only the first time it’s been done, even though scientists have been working on xenotransplantation for more than 50 years.

The next step for this research would be to replace a baboon’s heart with a pig’s. If successful, it would be the most significant step towards pig-to-human transplantations—and it could help approve human trials for the treatment.

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