From hearts and lungs to livers and kidneys, over 100,000 U.S. men, women and children currently await an organ transplant, while 17 people die each day when their need is not met, according to the Health Resources and Services Administration.
Over the past few decades, pigs have played a vital role in medical research to “fill the gap” in available organs.
In late 2021, a pig kidney was transplanted into a human without triggering immediate rejection for the first time. For three days, the new kidney was attached to a brain-dead patient exhibiting signs of kidney dysfunction. During the trial, the recipient’s symptoms showed improvement.
Only a few months later, a 57-year-old Maryland man, David Bennett, received the first heart from a genetically modified pig. Though a breakthrough in medical history, Bennett’s story ended two months later. This proved to be the longest a recipient has survived after experimental xenotransplantation.
With thousands of pigs born every year in the U.S., it might seem disappointing that more medical advancements have not been made.
However, it’s not nearly as simple as taking any pig from a farm and harvesting its organs for transplant. The preparation and care begin long before the pig is born.
First, future donor pigs receive the gene-editing tool CRISPR to “humanize” their organs as a number of genes are added or deleted.
After genetic modifications, the pig embryos are transferred to a surrogate sow inside a designated pathogen-free (DPF) facility, including filtered air, UV-treated water, concrete surroundings and sterile tools and equipment.
The risk of disease and other pathogens, such as porcine cytomegalovirus (pCMV), remains a priority when delivering the piglets. Therefore, a few days before expected delivery, surgeons perform a caesarian section. The piglets are then taken directly from the womb to a bath of disinfectant and are raised in isolation boxes, away from their mothers.
Pigs are fed a milk replacement by technicians in full biosecurity suits and are checked regularly for viruses. Those testing positive are killed.
After around six months of age, when pigs have reached adult human size, the organs are ready to be harvested and transplanted.
Despite all of the biosecurity precautions, Bennett’s fate proved disease is still possible when he contracted pCMV. The donor pig was screened four separate times before transplantation via nasal swab and polymerase chain reaction (PCR), testing negative every time. Bennett’s surgeon Bartley Griffith believes the pig was carrying a dormant pCMV infection that reactivated in Bennett’s immunosuppressed body. Though the medical team successfully treated the infection, the virus had likely already done too much damage to Bennett’s heart, a Slate article reports.
The ability to ensure a “clean pig” continues to be a challenge moving forward in finding the solution for organ transplant needs across the country.
Through Bennett’s unfortunate ending, Dr. Griffith told the New York Times, “Knowing it was there, we’ll probably be able to avoid it in future.”
