2 pig hearts were successfully transplanted into brain-dead human patients

Doctors recently transplanted pig hearts into two deceased patients, raising hopes that animal transplants could one day be used to save human lives.

Led by Dr. Nader Moazami, a cardiac surgeon at NYU Langone Health medical center in New York City, the surgeries took place in June and July, according to the Associated Press. Earlier this year, a different group of doctors from the University of Maryland Medical Center transplanted a pig heart into another patient, who died two months after the operation, Live Science reported in March.

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For the two recent surgeries, Moazami and his team transplanted the hearts of two genetically modified pigs into two recently deceased patients who were on ventilator support: 72-year-old Lawrence Kelly and 64-year-old Alva Capuano. 

Both patients had long histories of heart disease, according to CNN. After the transplants, the patients received standard post-transplant medications. Physicians monitored the patients' heart functions for three days but detected no signs of early organ rejection. No additional mechanical support equipment was used after the surgeries, representatives from NYU Langone Health said in a statement. 

Operating on the deceased as opposed to living patients "allowed more in-depth study of how well the recipients' bodies tolerated the pig hearts," Dr. Robert Montgomery, director of the NYU Langone Transplant Institute, told CNN. "We can do much more frequent monitoring and really sort of understand the biology and fill in all of the unknowns."

The first transplant of an animal organ into a person was a corneal transplant from a pig that took place in 1838, according to the National Library of Medicine. Since then, such efforts have been largely unsuccessful, as the human immune system typically attacks and rejects a transplanted animal organ as a foreign body. In recent years, researchers have circumvented this rejection by genetically modifying pigs to make their organs more closely resemble those of humans, the Associated Press reported. They "fool" the immune system by modulating the organ’s growth and reducing the chance that the recipient’s immune system would reject it. 

According to the United Network for Organ Sharing (UNOS), a non-profit that serves as the nation’s organ transplant system, there are more than 105,000 Americans on waiting lists for organ transplants. The Food and Drug Administration (FDA) is considering trials that would transplant genetically modified pig hearts or kidneys  into volunteer patients, Nature reported. The success of the two recent surgeries will help researchers get one step closer to making this a reality, according to NYU Langone Health.

Originally published on Live Science.