Jeffrey Stern, MD, left, and Robert Montgomery, MD, DPhil, prepare to implant a genetically engineered pig kidney into the recipient's abdomen.
CNN  — 

A pig kidney successfully functioned in a human body for about two months, marking the longest documented case of a xenotransplant of its kind.

In July, researchers at NYU Langone Health transplanted a genetically modified pig kidney into the body of a 58-year-old man named Maurice Miller, known as Mo, who had a brain tumor and was experiencing brain death. The organ was removed on Wednesday, a predetermined date, after 61 days of study.

Now, the researchers will analyze their findings from this pre-clinical human research to assess the body’s response to the procedure and help prepare for clinical trials in living humans.

For example, tissue collected during the study showed some “novel cellular changes” that required additional immunosuppression medication to reverse a mild rejection, NYU Langone Health shared in a news release. But overall, the kidney was found to perform “optimally.”

“We have learned a great deal throughout these past two months of close observation and analysis, and there is great reason to be hopeful for the future,” said Dr. Robert Montgomery, director of the NYU Langone Transplant Institute and chair of the surgery department, who led the research.

“None of this would have been possible without the incredible support we received from the family of our deceased recipient. Thanks to them, we have been able to gain critical insight into xenotransplantation as a hopeful solution to the national organ shortage.”

In August, another research team published peer-reviewed research on new advancements in transplanting pig kidneys to humans.

Researchers at the University of Alabama at Birmingham Heersink School of Medicine found that transplanted kidneys not only produced urine; they provided the “life-sustaining kidney function” of filtering waste, according to a research letter published in the medical journal JAMA Surgery.

Both research teams used genetically modified pig kidneys that were transplanted into recipients experiencing brain death in what is considered pre-clinical human research. The NYU Langone team used just one genetic modification to “knockout” the alpha-gal biomolecule, which has been found to lead to rapid rejection of pig organs by humans. The pig’s thymus was also transplanted to help protect the kidneys from being attacked by the human immune system.

Researchers say that more work is needed, including studies in living human recipients, to establish whether pig kidney transplants could be a bridge or destination therapy for people with end-stage kidney disease, but they are hopeful about the progress being made.

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“We’re gaining critical evidence about how well pig kidneys work in the human environment,” said Dr. Adam Griesemer, surgical director of the NYU Langone Pediatric Liver Transplant Program and the Living Donor Transplant Program, said at a news conference last month.

“Over the last 20 years, we’ve gained a lot of information about how pig kidneys work to replace the functions in primates. But the critical question – ‘Will those data be translated exactly to the human recipients?’ – was unknown. And for the first time, we’re being able to supply that information. So hopefully this also give some assurance to the FDA regarding the safety of initiating phase one clinical trials.”

The vast majority of people waiting for an organ transplant need a kidney. About 89,000 people are on the waiting list, according to data from the US Department of Health and Human Services’ Organ Procurement and Transplantation Network.