On Wednesday, the University of Maryland Medical Center announced that David Bennett, the first human to receive a pig heart transplant, died on Tuesday, March 8. His death comes roughly two months after the transplant; the cause of death wasn't specified.

The university's statement is short on details, and those will be critical for understanding the prospects for future transplants of this sort. Bennett was in very poor health at the time of the transplant, with his heart requiring mechanical assistance to keep him alive, so there are many potential explanations for his death that have nothing to do with the transplant. All the university is revealing is that the organ was not immediately rejected by Bennett's immune system and that his health had started declining several days prior to his death.

Understanding the causes of his death is critical because Bennett will not be the last human to receive a pig organ. Shortly after his transplant, a different group published results from an early clinical trial using hearts from the same genetically engineered pigs. In this case, the hearts were transplanted into brain-dead individuals rather than being used to keep someone alive, but the trial clearly represented a step toward normal transplants.

It's likely that there will be a publication describing the course of the transplant in the coming months. But most research journals discourage publicizing results while they're still in peer review, so we're unlikely to get any details until the paper is published.