In the past year, doctors have performed history-making transplants, placing genetically modified pig kidneys and pig hearts into patients. Now, a group of doctors and scientists in China report they have done the same with a pig liver.

In a study published in Nature, the group describes transplanting a gene-edited pig liver into a brain-dead patient. At the request of the patient’s family, the study was terminated after 10 days and the pig liver was removed. The patient’s original liver was not removed, so the experiment served as a way to test whether a pig liver could supplement the function of failing livers for patients waiting for a transplant.

“The transplanted pig liver successfully secreted bile and produced liver-derived albumin, and we think that is a great achievement,” said Dr. Lin Wang, a surgeon at Xijing Hospital, Fourth Military Medical University and one of the senior authors of the paper, during a briefing. “It means the pig liver could survive together with the original liver in a human being—and would give additional support to an injured liver, maybe, in the future.”

Pigs are promising sources of organs, but the human immune system rejects transplanted pig tissue. Scientists have been getting around this by genetically modifying the pigs that provide the organs. The donor liver in this case came from a pig that had received six modifications to certain genes in order to remove major pig proteins that would have led to rejection; the editing technique also added genes that made the liver appear more human to immune cells.