A 17-YEAR-OLD girl with diabetes has not needed to take insulin or any other drugs for more than a year after being given cells from newborn pigs, claims the Mexican team that performed the transplant. If confirmed, it represents a rare success for animal-to-human xenotransplantation.
However, five other teenagers given the cells have only had their insulin requirements reduced by half, and another six didn鈥檛 benefit at all. Sceptical researchers have pointed out that young people with diabetes sometimes start producing insulin again, and that the Mexican team has yet to prove that the insulin is coming from the pig cells. 鈥淚 am not convinced,鈥� says Camillo Ricordi of the University of Miami, former president of the International Pancreas and Islet Cell Transplantation Association.
Hundreds of millions of people worldwide have insulin-dependent or type I diabetes, caused by the death of the insulin-producing islet cells in the pancreas. There have been many attempts to cure it by transplanting pancreases or islet cells. In the past three years, up to 80 per cent of people given human islet cells taken from corpses have still been making enough insulin in their own bodies a year later.
Advertisement
But there is a severe shortage of human islet cells suitable for transplantation. Worse, all those who have received transplants will have to take immunosuppressive drugs, with all their nasty side effects, for the rest of their lives.
To get around the need for immunosuppressive drugs, Rafael Vald茅s of the Children鈥檚 Hospital of Mexico transplanted Sertoli cells from the testes of newborn pigs along with pig islet cells. Previous studies have shown that Sertoli cells have a special marker on their surface that makes attacking immune cells commit suicide.
First, Vald茅s implanted two 3-centimetre-long stainless steel tubes just below the skin. Two months later, when tissue had grown around and into the tubes to provide an ample blood supply to the area, the Sertoli cells and around a million islet cells from week-old piglets were inserted. No immune-suppressing drugs were used.
The patients lost a large number of the cells early on due to rejection, but the immune response lessened over time, says David White of the Robarts Research Institute in Canada, who collaborated with Vald茅s. The findings were presented this week at a meeting of the Transplantation Society in Miami.
The trial did spark concern about 鈥渞ogue鈥� transplanters operating in 鈥渦nregulated鈥� countries, says transplant surgeon David Cooper of Harvard Medical School. But Cooper says he inspected the facilities of Diatranz, the New Zealand company that supplied the pig islet cells, and found them to be excellent. Although the Food and Drug Administration has no jurisdiction in Mexico, Cooper would like Vald茅s to apply for FDA approval for the new trials he plans. 鈥淚f he did that, everyone would be happy,鈥� he says.
There are also worries that xenotransplantation could allow porcine endogenous retroviruses (PERVs), which lurk in the pig genome, to leap to humans. But Ricordi says there鈥檚 no evidence of this in the hundreds of patients worldwide who have been (unsuccessfully) treated with pig islet cells so far.
One of the major hurdles with xenotransplantation is that the immune system attacks animal cells even more vigorously than cells from non-compatible people. But PPL Therapeutics of Edinburgh announced last week that it had removed both copies of the gene responsible for provoking the most severe immune attack from pigs (see 快猫短视频, 12 January, p 7). Transplants from these pigs should have a better chance of surviving.