Lawrence Faucette, the 58-year-old patient with terminal heart disease who was the second person to receive a genetically engineered pig heart, died on October 30, according to a statement from the University of Maryland Medical Center in Baltimore, where the transplant was performed.

Faucette received the transplant on September 20 and lived for six weeks—less time than the first recipient, despite extra precautions by the Maryland team. Initially, Faucette made progress following his surgery. He was doing physical therapy, spending time with family members, and playing cards with his wife, according to the university. But in the days leading up to his death, his heart began to show signs of organ rejection; in other words, his immune system recognized the pig heart as foreign and attacked it. Rejection is also the biggest challenge with traditional transplants involving human organs.

At the University of Maryland Medical Center and elsewhere, researchers have been studying the possibility of transplanting animal organs into people—known as xenotransplantation—as a way to ease the human organ shortage. In the United States, more than 103,000 people are on the national transplant waiting list, and 17 people die each day waiting for an organ. Because donor organs are a scarce resource, doctors want to select patients for transplants who are likely to survive the transplant and go on to do well after surgery.

Faucette was in end-stage heart failure when he first came to the University of Maryland Medical Center on September 14. His heart stopped, and he required resuscitation, but he was deemed ineligible for a traditional heart transplant because he was too sick. A day later, the US Food and Drug Administration granted an emergency authorization for him to receive a genetically engineered pig heart in the hope of extending his life. Faucette consented to the procedure after being fully informed of the risks, according to the university.

During the first month of Faucette’s recovery, the pig heart performed well without any initial evidence of rejection. Faucette was even working toward regaining his ability to walk.

“We intend to conduct an extensive analysis to identify factors that can be prevented in future transplants,” said Muhammad Mohiuddin, who oversees the university’s xenotransplantation program, in the statement.

The first person to receive a genetically engineered pig heart, David Bennett, survived for two months after undergoing the groundbreaking procedure in January 2022. He died of sudden heart failure. The Maryland team concluded that Bennett’s poor health before the transplant and a pig virus found in his transplant heart may have contributed to his death.

When speaking with WIRED in December, Bartley Griffith, the surgeon who conducted both transplants, said, “We believe we can avoid some of the pitfalls that we had with David because he did so well for so very long.”

The donor pigs used in both surgeries were bred with 10 genetic edits to make their organs more compatible with the human body. Three genes involved in immune rejection were knocked out, while six human genes responsible for immune acceptance were added. The last edit involved removing a gene to prevent excessive growth of the pig heart tissue.

With Faucette’s surgery, the Maryland team was taking new steps to screen the donor pig heart for viruses. They were also using a novel antibody therapy, along with conventional anti-rejection drugs, to prevent Faucette’s body from damaging or rejecting the organ. Transplant experts who were not involved with Faucette’s surgery told WIRED in September that they were optimistic about his outcome.

This year, researchers at New York University and the University of Alabama at Birmingham have carried out short-term experiments involving genetically engineered pig organs in brain-dead people. The groups hope to launch trials in living patients soon, but Faucette’s death may be a setback for the prospect of xenotransplantation.