Four cloned double "knockout" pigs were born at PPL Therapeutics, Inc., in Blacksburg, Va., on July 25. Each lacked both copies of the gene responsible for making the enzyme alpha1, 3 galactosyl transferase, a feat that could bring in the next generation of organ donors, making animal-to-human transplantation feasible. Without the enzyme, which adds a sugar to the surface of cells that the human immune system immediately recognizes as being foreign, hyper-acute rejection is unlikely.
Given the current pace of research, when can human trials be anticipated? Australian researcher Dr. Anthony J.F. d'Apice of St. Vincent's Hospital in Fitzroy, Australia, and president-elect of the International Xenotransplantation Association (IXA), commented that when "knockout" pigs of both sexes are generated that are viable and normal, and survival of grafts extend beyond the current barrier of six to 12 weeks, "human clinical trials would be justified."
Added Dr. Cooper, immediate past president of IXA, a section of The Transplantation Society, after cellular xenotransplantation, "It is likely that the first clinical trials will be of pig islet transplantation in patients with diabetes. The first organs transplanted will likely be the kidney or the heart since we have evidence that these organs will function well in the human body environment. Because of the role of the liver in the manufacture of hundreds of different proteins, many of which are likely to be slightly different in the pig than in the human, trials of pig liver transplantation are likely to be delayed."
In the areas of drug development and transplant tolerance, some of the predictions for future developments discussed in the "What's Hot" session were: