Michael Helyer is a diabetic with a difference. Ten years ago he was implanted with pancreatic cells from pigs in the hope that they would restore his insulin production, so helping to control his blood glucose levels. Now, to the surprise of researchers who carried out the trial, not only are those pig cells still alive, but a few continue to produce insulin.
The finding is rekindling hopes that âxenotransplantsâ of tissue from pigs into humans may help combat diabetes and other human diseases. At present surgeons treating diabetes use insulin-producing human cells derived from dead donors, for which demand hugely outstrips supply. Pig cells could rapidly overcome the shortage.
ÂThe finding is rekindling hopes that âxenotransplantsâ of tissue from pigs into humans may help combat diabetesÂ
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Though Helyer still has to inject himself with insulin, the amount he needed fell by up to a third in the year following the transplant. This effect then faded, but Helyer, who lives in Auckland, New Zealand, says his diabetes remains under better control â a claim supported by data showing that his blood glucose is more stable than before treatment.
âItâs not dramatic, but the proof of principle is there,â says Bob Elliott, chief scientist and founder of Living Cell Technologies (LCT), the Auckland-based company that pioneered the treatment.
In 1996, LCT injected 1.3 million capsules of alginate, a resin derived from seaweed, into Helyerâs peritoneal cavity. Each capsule contained about 500 insulin-producing islet cells isolated from the pancreases of newly born piglets. âThe alginate lets insulin out of the capsule and nutrients in, to keep the cells alive,â explains Elliott. Importantly, it also hides the âalienâ pig cells from the human immune system.
Recent samples taken from the capsules suggest that many of the cells are still alive, and a few were found to still produce insulin when exposed to glucose in the lab. Chemical analysis also showed that traces of pig insulin appeared in Helyerâs blood shortly after he ate a large amount of glucose (Xenotransplantation, vol 14, p 157).
It is not certain, however, that the reported improvement in Helyerâs condition is down to the pig cells. âSelf-reported insulin requirements might be determined by other factors such as carbohydrate intake and physical activity,â says Bernhard Hering, who heads the islet transplant team at The Transplant Center of the University of Minnesota, Minneapolis.
The study also shows that Helyer has suffered no illness or infection from the pig cells. One objection to xenotransplantation is that pig cells contain so-called porcine endogenous retroviruses (PERVs), which are dormant in pigs but could conceivably trigger disease in humans.
âThere has never been a report of PERV transmission in any relevant animal model or in hundreds of human patients who have received various pig tissues over the past two decades,â says David Ayares, chief scientist at Revivicor, a company in Blacksburg, Virginia, that develops genetically engineered pigs to supply hearts, kidneys and livers for transplant. LCTâs results support this experience, he says.
To minimise the chances of PERV infection, the piglets used by LCT are taken from an island in the Antarctic where the population has remained isolated for more than 200 years.
LCT now plans two follow-up trials in around three monthsâ time in which 14 people will receive islet cell transplants from pigs. Elliott says the capsules have improved dramatically since 1996, and this time he will investigate whether a second dose of cells helps to sustain their effect.
