Researchers successfully transplanted genetically modified pig hearts into two recently deceased people connected to ventilators, the New York University team announced today. The surgeries are the latest step forward in the field of animal-to-human transplants, or xenotransplantation, which has seen a flurry of successes so far this year — raising hopes for a new, steady supply of organs to ease shortages.

The only thing different about these heart transplants from a normal human-to-human heart transplant was the organ itself, the research team said in a statement. “Our goal is to integrate the practices used in a typical, everyday heart transplant, only with a nonhuman organ that will function normally without additional aid from untested devices or medicines,” said Nader Moazami, director of heart transplantation at the NYU Langone Transplant Institute.

The team performed the transplants on June 19th and July 9th, and each recipient was monitored for three days. In that time, the hearts functioned normally, and there weren’t signs of rejection from the recipients, who were connected to ventilators to keep their body processes functioning semi-regularly, even after death. The two recipients were not able to be organ donors but were able to participate in whole-body donation for this type of research.

The two pig hearts came from biotechnology company Revivicor, which produces genetically modified pigs (and also funded the research). The pigs had 10 genetic modifications — four to block pig genes and prevent rejection and six to add human genes.

A living person was successfully given a pig heart, also produced by Revivicor, in early January. David Bennett Sr, who had severe heart disease, initially responded well to the transplant but died in March of heart failure. The specific cause is still unknown, but infection with a pig virus may have contributed to his death. The pig hearts are supposed to be free of viruses, but experts say they can be hard to detect.

The NYU team said it introduced additional virus screening protocols for its transplants. It also dedicated an operating room to xenotransplantation — that room won’t be used for any other surgical procedures.

Brain-dead patients have also been used at NYU to test kidney xenotransplantation. This fall, NYU announced that it successfully attached a pig kidney to the leg of a patient on a ventilator. The patient’s body did not reject the organ, and it functioned normally through 54 hours of observation.

Research on deceased whole-body donors is a step toward full clinical trials of xenotransplantation. Revivicor said in April that it’s hoping to start clinical trials in the next year or two. There’s still a lot to learn about xenotransplantation and a lot to figure out about the ethical implications of animal-to-human procedures. But if they work, they could offer a new option to the thousands of people on wait lists for organs.

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