A 62-year-old Pittsburgh man who received a baboon liver in a Sunday evening operation was groggy but in good condition Monday, his surgeons said.
The unidentified man, who before the 13-hour operation had only an estimated 30 days to live because of a fatal liver disease, is the second human to receive a baboon liver. He could not be given a human liver because of an active hepatitis B infection, which would infect and destroy a transplanted human liver.
The operation was performed by a University of Pittsburgh team that did the first such operation in June on a 35-year-old man. He died 70 days later from an apparent overdose of anti-rejection drugs.
In a Monday press conference, members of the transplant team said that the liver appeared to be functioning normally. "Overall, the liver seems to be behaving as if it were a liver from a human donor," said Dr. Andreas Tzakis.
"There is a reasonable chance that the patient should survive at least as long as the first one," said Dr. John Fung.
The surgery brings to about 35 the number of cases in which organs from baboons, chimpanzees and pigs have been implanted into humans since 1963. The June baboon-liver transplant patient lived the longest of any recipient.
Physicians are turning to such cross-species transplants, called xenotransplants, largely because of the growing shortage of suitable human donor organs. An estimated 2,500 people now die each year while awaiting organ transplants, primarily hearts and livers, according to the United Network for Organ Sharing, which helps match donors and recipients.
The shortage of donor organs means that none are available for people who would receive only short-term benefit. Hepatitis victims thus cannot get a human organ because if would be quickly destroyed by the continuing infection.
Such patients' only hope is a xenotransplant, said Dr. Thomas Starzl, the head of the Pittsburgh team and a transplant pioneer. Pig and baboon livers are thought not to be susceptible to hepatitis infection.
The increasing use of xenotransplants is also made possible by the continuing development of improved drugs that block the body's efforts to reject a foreign organ without harming the recipient. The Pittsburgh team's recent successes in transplants of both human and animal organs have been made possible primarily by the development there of an anti-rejection drug called FK-506.
The liver is a key organ for filtering toxic byproducts of metabolism from the bloodstream. In its absence, those toxins quickly poison the brain, producing swelling, coma and ultimately death. The liver also produces bile, which aids in digestion, and performs as many as 500 other metabolic functions. None of those functions can be performed artificially, as is the case with kidney dialysis, for example.
Dr. Leonard Makowka and his colleagues at Cedars-Sinai Medical Center attempted in October to use a pig liver to revive 26-year-old Susan Fowler, who was also dying of a liver ailment. But the disease had already progressed too far before the transplant, Makowka said, and Fowler died 30 hours later.
Sunday's operation came, coincidentally, only a day after the team reported in the British medical journal The Lancet on their analysis of the death of the first baboon liver recipient. The team concluded that, because of their fear that the liver would be rejected, they overdosed the patient with anti-rejection drugs, particularly one called cyclophosphamide.
That overdose led to a fungal infection that ultimately produced a fatal stroke. The baboon liver itself appeared to have functioned normally in the patient, they said, and had grown substantially, until it was about the size of a normal human liver.
Starzl and his colleagues said Monday that they will use less cyclophosphamide with the new patient. They also said that they are using an unusual new technique to try to reduce rejection of the baboon organ. Shortly before the surgery, the team removed and purified white blood cells from the baboon's bone marrow. During the course of the operation, these white blood cells were infused into the organ recipient.
"The introduction of the donor's immune system cells to the recipient's own immune system promotes a state of acceptance," Fung said. The cells "should protect the transplanted liver by preventing the recipient's immune system cells from launching an attack."