The experiments in pigs have shown more positive results as their organs are comparable to humans.
While a handful of such procedures were performed in the past year, there have been no formal human xenotransplant trials.
Most agency officials and physicians agree that human trials are needed to help answer the most pressing research questions about interspecies transplants, the report said.
Information is also needed on the pig-breed that is best suited for growing transplant organs, and how co-occurring health conditions, such as diabetes, could affect transplantation success.
“Human trials would help to answer a slew of questions, including what is the best cocktail of immunosuppressive drugs to give humans to help their bodies accept a pig organ, and how can physicians manage the risk that transplanted organs might harbour a pig virus,” added Caroline Zeiss, a veterinary specialist at Yale University.
An increasing number of people waiting for organ transplants also push the need for trials. In the US alone, more than 100,000 people are waiting for organ transplants. Researchers have long hoped that xenotransplantation could help to meet demand and, therefore, save lives.
“We have people dying each day waiting for organs,” Jay Fishman, a specialist in transplant infectious disease at Massachusetts General Hospital in Boston who participated in the FDA meeting, was quoted as saying.
In September 2021, a study published in the American Journal of Transplantation, showed a transplantation of a gene-edited pig’s two kidneys onto a brain dead patient. The kidneys functioned normally over the 54 hours of the test and seemed to produce urine.
Again in October, doctors at NYU Langone Health, New York performed a similar surgery.
In January this year, a severely ill man became the first to receive a pig heart in Maryland, US. However, he died two months later because of a porcine virus, a preventable infection that is linked to devastating effects on transplants.
Even though the heart-transplant recipient died, the surgery represents an enormous accomplishment, Allan Kirk, a transplant surgeon at the Duke University in the US, was quoted as saying.
The high-profile transplants have “increased public awareness of the field” and have “made this an optimal time for public conversation” and clinical trials, added Wilson Bryan, director of the FDA’s Office of Tissues and Advanced Therapies in Silver Spring, Maryland, at the meeting.
Companies such as Revivicor in Blacksburg, Virginia, owned by United Therapeutics, have been breeding pigs for use in xenotransplantation.
They have been searching for the right combination of genetic modifications for their pigs to help ensure that humans’ immune systems accept organs from the animals, the report said.
These companies “have been creative making these pigs; hopefully they’ll be creative testing them”, said FDA investigator Deborah Hursh at the meeting.
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