A pig kidney is still functioning correctly more than six weeks after surgeons at NYU Langone Health in New York City transplanted the genetically engineered organ into the body of a 57-year-old man, who had been declared brain-dead.

This marks the longest period a pig kidney has functioned in a human being, according to a press release from the hospital.

After he was "declared dead by neurologic criteria," the man was placed on supportive measures to keep his heart beating, the release stated. His family agreed to donate his body because his organs were not suitable for transplant.

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"All signs are pointing in a positive direction with the kidney’s ability to function just as a normal human kidney would," Dr. Philip Sommer, a critical care anesthesiologist and system director for organ donation at NYU Langone's Transplant Institute, told Fox News Digital.

The hope is that animal kidneys will one day be viable alternatives for transplant into live humans.

"Too many people are dying because of the lack of available organs, and I strongly believe xenotransplantation is a viable way to change that," Dr. Robert Montgomery, M.D., who is the director of the NYU Langone Transplant Institute and led the NYU Langone Health surgical team, said in the news release.

Montgomery’s team removed the man’s kidneys on July 14 and replaced them with the genetically engineered pig kidney to ensure that the animal organs were performing the expected functions without assistance. 

While keeping the man alive on a ventilator, the intensive care clinical staff has been monitoring the pig kidney’s performance and taking weekly biopsies.

The kidney’s creatinine levels, which are indicators of function, have been in the optimal range during the length of the study. The biopsies have shown no evidence of rejection, according to the release.

"From what we are seeing, this kidney is doing all the jobs that a normal human kidney would do," Sommers told Fox News Digital. "We have not had to intervene to correct its function."

He added, "We are studying its ability to clear and metabolize certain medications during the study, and it appears that it is doing that job very well, too."

To prevent a "hyper-acute rejection" of the pig kidney, the surgeons said they "knocked out" the gene that is responsible for the human body’s immune response to reject an animal organ. 

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This rejection usually occurs within minutes when an animal organ is connected to a human circulatory system, the researchers explained in the release. 

In the past, researchers performing genetically engineered pig organ transplants have incorporated up to 10 genetic modifications, but this approach involved only one gene.

"We’ve now gathered more evidence to show that, at least in kidneys, just eliminating the gene that triggers a hyper-acute rejection, along with clinically approved immunosuppressive drugs, may be enough to successfully manage the transplant in a human for optimal performance — potentially in the long-term," Montgomery said in the news release.

Besides knocking out the gene, Montgomery’s team also embedded the pig’s thymus gland in the outer layer of the kidney. This gland teaches the immune system how to guard against delayed immune responses.

The team also used standard transplant immunosuppression medications and screened for certain viruses that have been shown to trigger organ failure.

"This information we are gathering is going to help move so many aspects of xenotransplant forward," Sommers told Fox News Digital. "We are getting data on the function of the kidney, immunosuppression, clearance of medications and safety from disease spreading," 

The NYU team will continue to monitor the organ in the recipient's body until mid-September.

"We think using a pig already deemed safe by the FDA, in combination with what we have found in our xenotransplantation research so far, gets us closer to the clinical trial phase," Montgomery said in the release.

"We know this has the potential to save thousands of lives, but we want to ensure the utmost safety and care as we move forward."

The success of this study suggests that this may be a viable long-term transplant option, Sommers told Fox News Digital.

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"Before this, we only knew that there would be no immediate rejection. We have now moved toward being able to define this as a safe and viable mechanism for transplant," he said.

Testing the pig kidney in a brain-dead patient is seen as "the best and safest way to perfect this technology prior to it entering clinical trials," Sommers noted.

"Our goal is to mimic exactly what would be happening in a living human, so when things do occur, we’ll know how to treat them safely and won’t be experimenting on living beings," he said.

While the number of organ donors has remained steady through the years, the need for organ donations has increased, leading researchers to explore non-conventional solutions to save patients’ lives.

"We are not meeting the needs with the current system and supply we have, so we have to look to other ways to meet the need and help society," Sommers told Fox News Digital. 

"Xenotransplant has been studied for a very long time, and the use of pig tissue has been used for heart valves for a long time as well."

More than 100,000 people in the United States are currently awaiting an organ transplant, according to the United Network for Organ Sharing in Richmond, Virginia.

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Dr. David Klassen, the network’s chief medical officer, told Fox News Digital that this study is a critical step toward clinical trials in living people, as it allows the investigators to study the physiological function of the animal organ over an extended period.

Another non-conventional method being explored is the potential of 3D printing, Klassen noted. 

"Xenotransplantation is likely to start formal clinical trials relatively soon, while 3-D printed organs is further off," he said. "There are lots of resources being applied to the printing of transplantable organs."

Some private industries are focused on printing lungs for transplantation, he added.

Dr. Ron Shapiro, surgical director of the Kidney and Pancreas Transplant Program at Mount Sinai's Recanati/Miller Transplantation Institute in New York City, was not part of the NYU Langone study but commented on it to Fox News Digital. 

"This study is substantial further progress on the road to the implementation of xenotransplantation into clinical practice," he said. 

"These results are extremely encouraging and suggest that clinical xenotransplantation will be feasible and successful."