Surgeons Transplanted Living Pig Skin Onto Humans for the First Time

Genetically engineered pigs could be the solution to the world’s organ transplant shortage

Credit: Minipigs/Wikimedia Commons

In a pathogen-free facility in Grafton, Massachusetts, a small town about 40 miles west of Boston, genetically engineered miniature pigs are being bred to donate their skin to humans.

Their skin, which looks remarkably similar to the human variety and is referred to as Xeno-Skin, will be transplanted by surgeons at Massachusetts General Hospital to a small group of burn victims in an attempt to speed up the healing process. It’s the first experiment approved by the U.S. Food and Drug Administration to use genetically engineered animal tissue in humans, a necessary step toward someday transferring entire organs grown in animals to people who need them — a process known as xenotransplantation.

The need for such organs is dire. Each day, 20 people die waiting for an organ transplant. More than 113,000 people in the United States are currently waiting for one, while only 36,528 transplants were performed in 2018, according to government data. Every year, the waiting list grows, greatly outpacing the number of available organs. For decades, researchers looked to animal donors as a way to ease this chronic shortage, but transplants from animals have often failed.

“As humans, we’re just a bag of fluids and our skin is the plastic bag.”

Xeno-Skin, developed by Boston-based biotech company XenoTherapeutics, shows promise. So far, one patient has received the genetically engineered pig skin graft, and five more burn victims are slated to receive it. The grafts are meant to be temporary and will be removed once the patients’ own skin has grown back. Doctors involved in the trial say the donor tissue appears to be healing as well as a human skin graft, which was transplanted next to the pig skin for side-by-side comparison. The process also hasn’t caused negative reactions like provoking an immune response or transmitting animal viruses, two major issues in xenotransplantation. “We’re trying to replicate exactly the same mechanisms that are used in the standard of care, or the gold standard treatment, for severe and extensive burns,” Paul Holzer, CEO of XenoTherapeutics, tells OneZero.

Typically, severe second- and third-degree burns are treated with allografts, or skin from human cadavers. Allografts help protect wounds from infection, prevent fluid loss from the body, and stabilize patients while their own skin grows back. “The skin is a really important barrier to all the things in the world,” says Dr. Curtis Cetrulo, a plastic and reconstructive surgeon at Massachusetts General Hospital who previously served as president of XenoTherapeutics’ board of directors. “As humans, we’re just a bag of fluids, and our skin is the plastic bag.”

Skin stays alive for some time after death, which is why it can be preserved from both humans and pigs. But like other organs, cadaver skin is expensive and can be difficult to acquire from national skin banks because there aren’t enough donors. Skin banks have strict criteria and can’t accept skin from donors with cancer or viral infections like HIV and hepatitis because of the potential to transmit those diseases to graft recipients. Some banks also have age restrictions on skin donors.

Pig skin could be an alternative when cadaver skin is scarce, especially on the battlefield and in developing countries, says Holzer. Skin from pigs and other animals is already used for wound dressings, but these are first treated with chemicals or radiation and essentially dried out so their cells are no longer alive. “It’s basically a piece of leather,” says Cetrulo. “It’s dead, processed tissue.”

Pig heart valves have also been used in people for decades, but the tissue is “fixed” using chemicals so that the cells are no longer alive.

Xeno-Skin is made of living tissue and is intended to promote blood flow, or vascularization, a key step in the healing process that helps fight off infections. The first patient received a five-by-five-centimeter piece of Xeno-Skin, but subsequent patients will receive larger grafts. Five days after the first patient’s transplant, surgeons removed both the pig and cadaver grafts, replacing them with permanent grafts taken from the patient’s thigh. The patient is healing and is expected to return to work soon.

Temporarily grafting pig skin onto burns is much less complicated than transplanting pig organs into humans for the long term, but Dr. Abbas Ardehali, a heart and lung transplant surgeon at the University of California, Los Angeles, who is not involved in the Xeno-Skin trial, says trying it transiently makes sense from a safety perspective. “I think the benefit of that approach is that if worst comes to worst, the pig skin fails and you’re back to square one. It’s not like you’ve undergone a major operation like a heart or lung transplant to find that the patient dies as a result.”