Significant immunosuppressive therapy is still needed to reduce other types of host immune reaction against the pig pancreatic cells. But Reisner claims that this is at the level typically seen in transplant medicine--even though the researchers report that both animals died from infections and drug toxicity a year after their transplants. He adds that there is scope for further reducing the amount of therapy required. "We're fine-tuning things to reduce the levels of toxicity," he says. "The important thing is that we set out to show that a pancreas could be grown this way, and that it could correct the uncontrolled glucose levels caused by diabetes, which is what we've done."

Reisner believes that the technique could eventually help humans with the same condition. Human-to-human pancreatic transplants have been shown to be effective, but a lack of donors severely limits the number of such treatments available. "The purpose of this study was to show that we could potentially have a method of providing an unlimited source of transplantation for treating diabetes."

However, Reisner, who is a scientific consultant and holds equity with Tissera, which supported the research, says that much work needs to be done before the xenotransplantation method can be used clinically.

Gordon Weir, head of the Islet Transplantation and Cell Biology Center, at Harvard Medical School's Joslin Diabetes Center, says that it is too soon to write off sources other than 42-day-old embryonic tissue for growing new islets. "I'm not necessarily convinced by the 42-day number," he says. "Some people have had good results with neonatal tissue." He adds that even mature pancreatic transplant tissue can become infiltrated to some extent by host blood vessels.

Other approaches to reversing type 1 diabetes are also emerging. Of particular interest are methods that seek to reprogram a patient's immune system to stop it from attacking the pancreas. Recently, it was reported that destroying pancreas-killing immune cells and replacing them with a patient's own stem cells can help her gain control over blood-sugar levels.

A more extreme approach is to completely wipe out a diabetic's immune system and rebuild it using his bone-marrow stem cells--a strategy that has raised some safety concerns.
"This is an interesting approach that seeks to avoid transplants," says Reisner. "It could work if used early on in the disease, while the patient still has some pancreatic tissue. But later on, when all the beta cells are destroyed, an alternative approach like ours might have to be used."

Weir adds that "terrific progress" has been made in harvesting stem cells to make new pancreatic tissue and that he is hopeful that before long this will translate into major clinical breakthroughs.