Couzin's "Wanted: pig transplants that work" 2002

From Biol557

• We look to pigs because we don't have enough human donors.
• In 1960, Reemtsa transplanted some chimpanzee kidneys into humans; one patient lived for 9 more months and we thought we had an unending supply of organs.
• Because of many failures over the last 4 decades, many industrialized nations have stopped working on whole-organ transplants and are focusing on tissue and cell transplants.
• We've switched from chimps to pigs because pigs have very similar organs in size and shape.
• We routinely do pig heart valve transplants and don't even regulate them as a xenotransplant because the valve is treated chemically (thus killing any living cells) before implantation.
• We've made pigs heterozygous for alpha-gal (short for 1,3 alpha-galactotransferase which puts a certain carbohydrate on the endothelial cells of pig tissue, thus making it an easy target for the human immune system). From these, we hope to generate homozygous knockouts.
  • However, there are lots of opinions about whether removal of this enzyme will be enough.
• Because cell and tissue transplants are considered easier, and because vasculature and other endothelial tissues from pigs are the part that cause immune rejection issues, one company is tranplanting procine neurons into stroke patients.
  • While they have shown that the cells live for long periods of time, they have been set back by several seizures which may or may not be caused by the transplant.
• Some companies have been formed around the idea of using xenobiotic material but not transplanting it.
  • One company has extended the life of liver failure patients by running their blood through a machine that uses porcine liver tissue to filter the blood.
• We are also very concerned about transmission of viruses from pigs to humans. Though, a study of 160 transplant recipients has not shown any of the virus.
• The FDA approves xenotransplant studies on a case-by-case basis and requires a rather intimidating consent form that includes that the patient consent to life-long monitoring (though the FDA cannot enforce this).
• Though the FDA is strict, European governments--if not fully banning xenotransplants--highly discourage them with ultra-strict rules and extremely difficult application review.
• Though xenotransplantation work continues, much hope is focused on bioengineering and the emerging field of stem cell therapy.