But the hospital added in a statement that they have no reason to believe his death was the result of the transplant.

Richard Slayman, 62, received the transplant in March in a four-hour surgery that the hospital at the time called "a major milestone in the quest to provide more readily available organs to patients."

The kidney came from a pig that had been genetically altered to remove genes harmful to a human recipient and add certain human genes to improve compatibility, according to the hospital.

Mr. Slayman had received a transplant of a human kidney in 2018 after seven years on dialysis, but that organ failed after five years and he had resumed dialysis treatments.