With any luck, future patients in need of transplants will find a plentiful supply of organs at the University. The catch, however, is that the organs to be transplanted might not come from human donors, but from pigs.
The transplantation of virtually every major pig organ into humans may be a “consistently accepted and successful practice” within 10 to 15 years, said Dr. R. Morton Bolman, chief of cardiovascular and thoracic surgery in the University Medical School.
Under the leadership of Bolman, University researchers are experimenting with cross-species transplantations. Bolman’s research, thus far, has involved transplanting pig hearts into baboons and studying the rejection response of pig organs to human blood.
Dr. Christopher Salerno, a fifth-year surgical resident in charge of the day-to-day operation of Bolman’s study, said three pig-to-baboon heart transplants have been done at the University in the last year. The last transplant, which occurred in the spring, was successful, he said. The baboon lived for 10 days before succumbing to what Salerno thinks was a rejection of the pig heart by the primate’s immune system.
Because of their genetic similarity to humans, baboons might seem like the most logical source of organs for transplant into people. But there are several reasons primates are not actually the best choice for potential organs, Bolman said.
First of all, he said, “using primates for human transplantation would never be feasible and acceptable to society.” Many animal-rights activists believe it is morally wrong to take the life of a baboon to save that of a human.
Second, primates sometimes harbor infectious diseases that could prove fatal to humans. And third, it would be impossible to breed primates fast enough to meet the needs of the many people who need transplants, Bolman said.
Pig organs are not currently transplanted into humans because the organs are rejected by the human immune system. Salerno said pig and human organs work in basically the same way, but differ on a cellular level.
Those differences cause the rejection of pig organs by human blood, Bolman said. This rejection is the biggest impairment to moving forward with transplanting pig organs into humans.
To counteract this rejection response, Bolman is studying antirejection drugs and ways to remove the human antibodies that cause organ rejection. Bolman and Salerno, as well as researchers at Duke University, Columbia University and several other schools, are learning more about why pig organs are rejected. By circulating human blood through hearts removed from pigs, “you can begin to understand what the mechanisms of rejection of the heart are and begin to modify them,” Bolman said.
Researchers are working to find more suitable pig organs by genetically modifying them. Bolman said he is experimenting on pigs genetically engineered to incorporate human characteristics into their blood vessels. These characteristics, he said, can keep the human body from recognizing the pig organs as foreign.
Cross-species transplantation was first attempted in the 1950s, Bolman said, when several chimpanzee kidneys were transplanted into humans with modest success. In some cases, Bolman said, the patients lived as long as six months. Experiments in transplanting baboon livers have been attempted as well, but those organs were only used temporarily and patients later received human organs.
The most famous case of cross-species transplant was that of Baby Faye in 1984. The infant girl received a baboon heart but died 21 days later after her immune system rejected the organ.
Bolman’s research is funded by Alexion Pharmaceuticals and the University. Salerno said he hopes to continue the study if funding can be found for next year.