Bypassing immune rejection of pig pancreas cells

Scientists have discovered a clever trick that might help to treat insulin-dependent diabetes.

Diabetes occurs when so-called beta cells in the pancreas fail to produce insulin, leading to high blood glucose levels, which sufferers manage by injecting additional insulin through the skin. A better option would be the replacement of the insulin-secreting cells themselves, since this would render blood sugar testing and insulin injection unnecessary. Doctors have achieved this in a limitd number of cases by carrying out pancreas transplants, but the number of diabetics far outstrips the supply of donor organs. Consequently scientists have looked to animals as potential sources of donor organs and especially pigs, which are close physiological matches for humans.

However, attempts to 'xenograft' pig organs into other animals usually results in the destruction of the donor tissue through a process called hyperacute rejection - the recipient immune system attacks the blood vessels supplying the organ, destroying it.

To combat this problem, writing in PNAS a group of scientists in Israel led by Weizmann Institute researcher Yair Reisner have been exploring the use of donor foetal cells rather than whole organs. Using diabetic non-human primates, the team implanted pancreatic cells collected from developmental day 42 pig embryos. Cells from this time point were chosen because they have been shown to have a low risk of producing tumours. When the grafts were carried out the cells grew, multiplied and began to secrete insulin, curing the recipient primate's diabetes. And because the cells were ultimately supplied by blood vessels derived from the recipient rather than their own blood vessels there was no risk of hyperacute rejection. One of the four recipient animals survived for almost one year after the transplant was carried out.

The researchers are cautious in drawing conclusions at this stage, particularly given the small number of subjects, and admittedly the recipients required immunosuppression to prevent their immune systems from attacking the donor cells, but they point out that this is undoubtedly an intriguing alternative to whole-organ transplants.