In a noteworthy step towards the goal of eventually using animal organs in medically necessary transplants, a doctor and his team successfully surgically attached a pig's kidney to a human on a temporary basis, National Public Radio (NPR) reports.

On September 25, a New York transplant surgeon named Robert Montgomery and a team at NYU Langone Health conducted a successful surgery that transplanted a pig's kidney into a brain-dead human.

In recent years, swine have been frequently used for studies developed to address the organ shortage.

But as such studies have been carried out, a sugar called 'alpha-gal,' which is found within pig cells, presented a major hurdle.

Because alpha-gal is foreign to humans, when a human candidate receives an organ transplant from a pig, the presence of the sugar triggers an organ rejection in the human patient.

Dr. Montgomery and a team of researchers believe they've now discovered a way around the alpha-gal dilemma.

To successfully carry out last month's operation, Montgomery sourced the kidney from a pig that was gene-edited so as to eliminate alpha-gal, thereby significantly reducing the possibility of an immune system attack.

Montgomery surgically attached the kidney to two large blood vessel's outside of the brain-dead recipient's body, and then observed it for two days. 

After the observation period, doctors concluded that the kidney worked properly in filtering waste and producing urine without inciting an immune system attack.

"It had absolutely normal function," said Montgomery. "It didn't have this immediate rejection that we have worried about."

The body used during the surgery belonged to a woman who, prior to her death, expressed a desire to be an organ donor. Her family agreed to the experiment on the grounds that, "there was a possibility that some good could come from this gift," Montgomery said.

Revivicor, a subsidiary of United Therapeutics, is the company that engineered the pig used in the surgery.

In December, the Food and Drug Administration (FDA) approved the gene alteration in Revivicor's pigs, declaring it safe for human food consumption and medicine.

But the FDA also said more information is needed before pig organs can be transplanted into living humans.

Incidentally, Montgomery is a transplant patient himself. Three years ago, he had a human heart transplant.

In looking back on that time in his life, Montgomery said, "I was one of those people lying in an ICU waiting and not knowing whether an organ was going to come in time."

The transplant surgery he conducted last month was funded by a $3.2 million grant from United Therapeutics, a biotechnology company based in Silver Spring, Maryland, involved in treatments for lung disease.

According to the Living Kidney Donor's Network, there are currently over 93,000 people on the transplant kidney waiting list.