One of the triumphs of modern medicine was the development of organ transplantation in the 1950s and 1960s. But there’s always been one big problem—the supply of human organs is limited. According to The United Network for Organ Sharing, 22 people per day die waiting for a transplant. One of the suggested solutions is xenotransplantation, or putting organs from other species into humans.
Immune system reactions and organ rejection have made that a challenging endeavor. But against the odds, researchers announced this week that they’ve taken a huge step forward in that quest by keeping a genetically modified pig’s heart alive in a baboon for over two and half years.
Researchers at the National Institutes of Health placed pig hearts in the abdomens of five baboons, connecting them to the circulatory system but keeping the baboons’ original hearts intact, according to the study published in Nature Communications. The hearts came from pigs with three genetic modifications that allow the baboons’ immune systems to tolerate them better. The primates also received a cocktail of new immunosuppressant drugs during the trial.
The median survival rate for the hearts was 298 days, while one of the hearts lived 945 days, beating the previous record of 500 days. “People used to think that this was just some wild experiment and it has no implications,” Muhammad Mohiuddin, the cardiac transplant surgeon at National Heart, Lung, and Blood Institute who led the study, tells Kelly Servick at Science. “I think now we’re all learning that [xenotransplantation in humans] can actually happen.”
When researchers weaned the baboons off their immunosuppressants it led to rejection of the organs, which were removed from four of the baboons (the fifth died of an infection). “These hearts could have gone even longer, but we wanted to test to see if the animals had developed some kind of tolerance to the organs,” Mohiuddin tells Arielle Duhaime-Ross of The Verge.
The hope is that in the future the genetically-modified pigs will lead a steady supply of livers, kidneys and hearts for human patients. While primates like chimpanzees and baboons may seem like more logical choices for donor organs, the BBC points out that ethical questions, low supply and the potential for interspecies disease transmission makes primates less suitable. Pigs, on the other hand, mature quickly and have hearts anatomically similar to humans.
Despite the recent success, reliable xenotransplantation in humans is still along way off. Though the hearts were "alive" inside the baboons, they didn't actually pump blood. Transplant immunologist Daniel Salomon of Scripps Research Institute tells Servick that keeping the heart alive doesn’t mean it will function well in another species. “Having to actually do the pump work to keep the animals alive…is a big deal,” he says. “Just contracting in the abdomen and doing nothing physiological is much easier.”
Mohiuddin and his team are gearing up for true heart replacement surgeries in a new group of baboons.