Pig-to-Human Heart Transplants One Step Closer

( Farm Journal )

Hearts taken from genetically engineered pigs can support the life of recipient baboons for up to 195 days, reported Nature on Wednesday. The study, in which four baboons lived in good health for several months after surgery, brings xenotransplantation, the process of transplanting organs or tissues between members of different species, one step closer to the clinic.

Heart failure claims the lives of hundreds of thousands of people in the U.S. every year. Current medications manage the symptoms—such as reducing blood pressure—but the only cure at this time is to receive a new donor heart. However, the demand for human hearts outweighs the supply. 

“There are many patients who would benefit from a transplant, but who are never going to get one,” says Guerard Byrne, a xenotransplantation researcher at the University of Alabama at Birmingham, who did not participate in the study. These are the people who might one day benefit from xenotransplantation, he adds.

For years, researchers have studied pigs as potential donor species, genetically engineering them to remove their most immunogenic antigens. Until now, when the pigs’ organs have been transplanted into primates and the recipients take immunosuppressive drugs, the maximum survival of a baboon has been 57 days until that animal finally experienced an antibody-mediated rejection of the organ, said Byrne, who was involved with past research.

Bruno Reichart of the University of Munich and colleagues have adopted immunosuppression methods and optimized the xenotransplantation procedure to carry out pig-to-baboon heart replacements that support the recipients’ lives for longer.

Specifically, they improved preservation of the donor heart and restricted heart growth within the primates. Pigs are larger than baboons and because they used hearts from young pigs, the hearts grew accordingly. To stop this, the team reduced the baboons’ blood pressure to avoid enlargement and gave the animals a drug to prevent proliferation and growth of cells.

In humans, however, heart growth may not be an issue because adult humans are a closer size-match to pigs.

“I’m not saying that we’re ready to go into the clinic tomorrow,” says Byrne, but “the field can be stuck optimizing for nonhuman primates and get nowhere, when what we really need to do is to begin optimizing in humans.”

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