A pig’s kidney transplanted by surgeons into a brain-dead man has continued to function normally for more than a month, which constitutes a critical step toward carrying out similar operations on living patients, the New York team hopes.

The latest experiment, announced on Wednesday by New York University Langone Health, marks the longest a pig kidney has functioned in a person, although deceased. For a second month, researchers will continue to monitor the kidney's functionality.

"Is this organ really going to work like a human organ? So far it’s looking like it is," Dr. Robert Montgomery, director of NYU Langone’s transplant institute, informed the Associated Press.

"It looks even better than a human kidney," Montgomery remarked in July as he replaced a dead man's own kidneys with a single kidney from a genetically altered pig and saw how it started making pee right away.

The family of 57-year-old Maurice "Mo" Miller from upstate New York was convinced to donate his corpse for the experiment driven by the possibility that pig kidneys might one day help ease a dire shortage of transplantable organs.

"I struggled with it," Mary Miller-Duffy, his sister, told the AP. But since he liked helping people, she believed, "This is what my brother would want. So I offered my brother to them." She added that he will be in medical books and will live on forever.

Since the immune systems of the recipients attacked the foreign tissue, attempts at animal-to-human transplants have been ineffective for decades. Now, scientists are utilizing pigs that have had their organs genetically altered to better match human bodies.

In a last-ditch effort to save a dying man last year, the University of Maryland surgeons transplanted a gene-edited pig heart with special approval from authorities. He lived for just two months until eventually, the organ failed for unknown causes, but those circumstances can be used as lessons for future attempts.

Read: Man gets heart transplant from genetically modified pig heart

The Food and Drug Administration is currently debating whether to approve some modest but thorough investigations of pig heart or kidney transplants in willing individuals.

Dr. Jayme Locke of UAB, a transplant surgeon, published laboratory testing demonstrating the effectiveness of the gene-modified pig organs in the journal Jama Surgery. She said that the seven-day test showed they could "provide life-sustaining kidney function."

According to Montgomery, the NYU kidney transplant surgeon who previously underwent a heart transplant and is keenly aware of the need for a new source of organs, these tests are essential to addressing additional unanswered concerns "in a setting where we're not putting someone's life in jeopardy."

It took meticulous timing for the procedure. Drs. Adam Griesemer and Jeffrey Stern, two medical professionals, flew hundreds of miles early that morning to a facility housing genetically modified pigs owned by Virginia-based Revivicor Inc. They removed kidneys lacking a gene that would cause the human immune system to immediately destroy them.

Montgomery was taking both kidneys from the donor body as they hurried back to NYU so that it would be clear whether the next pig version was effective. One kidney from a pig was transplanted, and the other was kept for comparison purposes after the procedure.

Dr. Muhammad Mohiuddin of the University of Maryland warns that it is unclear how closely a dead body will resemble a live patient's reactions to a pig organ; however, this research teaches the public about xenotransplantation so "people will not be shocked" when it's time to try again in the living.