The operation room at the Massachusetts General Hospital erupted in cheers in March when a 62-year-old man urinated just 15 minutes after receiving a pig kidney — a sign that the organ was functioning properly in a human body.

But the euphoria — marking the success of the world's first transplant of a genetically modified pig kidney into a living person — didn’t last long. Two months later, the man died abruptly, highlighting the still-high hurdles for cross-species transplants.

Despite this, Tatsuo Kawai, a Japan-born doctor and one of the surgeons who performed the procedure, remains hopeful about using pig organs in humans. He said the transplant itself was a success, noting that the patient's preexisting heart condition likely contributed to his death.