The congress, being held at the Westin Diplomat Resort and Spa in Hollywood, Fla., began on Sunday and concludes this Friday.
Xenotransplantation, or cross-species transplantation, is viewed as one answer to the critical shortage of human organs for transplantation. Because the immune system barriers are so great between humans and animals, the field has been dominated by small and incremental developments. But last week's news of the world's first cloned double "knockout" pigs represents a major boost to the field.
"This could well prove the biggest advance in xenotransplantation research to date," remarked Dr. David K.C. Cooper, associate professor of surgery at Harvard Medical School and head, Xenotransplantation Group, Transplantation Biology Research Center, Massachusetts General Hospital. "It is likely, however, that this will not provide the entire answer, and that further gene 'knockout' procedures may be necessary. Nevertheless, a big step forward at this stage would be greatly encouraging to researchers, and would indicate that the organ shortage will be resolved by the use of pig organs within the foreseeable future."
Somatic nuclear transfer, or cloning, of pigs offers "the most radical and promising strategy" for creating pigs that lack the enzyme responsible for hyper-acute rejection, reported Dr. Alan Colman, one of the creators of Dolly, the first animal cloned from an adult cell, at today's congress. Formerly with PPL Therapeutics, PLC, where the work with the pigs was performed, Dr. Colman is now with ES Cell International, Pte., Ltd. in Singapore.
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:
Held every two years, the International Congress of The Transplantation Society is recognized as the field's most important international scientific meeting. More than 1,600 abstracts covering basic and clinical science are being presented, and more than 3,000 surgeons, physicians and researchers from 71 countries are in attendance. Co-chairs of the congress are Drs. Camillo Ricordi of the Diabetes Research Institute at the University of Miami School of Medicine and Domingo Casadei of the Instituto de Nefrologia in Buenos Aires. The president of the society is Dr. Carl Groth of the Karolinska Institute in Stockholm.
Transplantation