"Our work at the U of A and Emory, along with recent work at the University of Minnesota, is very exciting and shows that xenotransplantation in humans may soon be possible, thus solving the islet supply problem," says one of the study authors Ray Rajotte, a professor of Surgery at the University of Alberta.
The paper appeared in an advanced on-line publication of Nature Medicine, February 26, entitled "Long-term survival of neonatal porcine islets in non-human primates by targeting co-stimulation pathways." The work follows on the heels of similar work published last week by University of Minnesota researchers; those researchers used islets isolated from adult pig pancreases.
Neonatal islets were produced in Edmonton using a procedure Drs. Greg Korbutt and Rajotte developed in 1995. The pig islets were sent to the Yerkes Research Center for transplantation into diabetic rhesus macaques using an anti-rejection protocol developed by Drs. Christian Larsen and Kenneth Cardona of the Yerkes Research Center and the Emory Transplant Center. The isolation method developed by the U of A researchers is simple and reproducible with the neonatal pig islets having some growth potential post-transplant, considered a major advantage over adult pig islets.
The diabetic animals were treated with a CD28/CD154 co-stimulation blockade-based immunosuppressive regimen, and achieved sustained insulin independence (median survival >140 days with one animal now at 300 days) without evidence of porcine endogenous retrovirus (PERV) dissemination. "This represents a major step for ward and proves neonatal porcine islets can correct diabetes long-term in primates," said Drs. Korbutt and Rajotte.
"To meet the needs of the millions suffering from type 1 diabetes, we must find new donor sources to allow large-scale application of islet cell transplantation in humans," said Dr. Larsen. "While there is much work to be done these studies suggest that the rejection response to porcine islets can be surmounted."
"The next step is to prove that these neonatal porcine islet cells could become a source for human transplantation," said Dr. Rajotte. "It's hoped that within the next three to five years, we will be transplanting patients with pig islets once we prove that it is safe."
Using a relatively simple and reproducible method of obtaining large numbers of islets from neonatal pig pancreata developed at the U of A, the researchers then transplanted islets comprised of endocrine and endocrine precursor cells into the monkeys. In vivo, these cells have been shown to proliferate, differentiate and reverse hyperglycemia in immunodeficient diabetic mice and allogeneic out-bred pigs.
However, humans and Old World primates have naturally occurring antibodies that are directed against antigens that can cause hyperacute or acute humoral rejection. To combat that, the researchers administered an anti-IL-2 receptor and anti-CD154 (H106) antibody, while maintaining immunosuppression using sirolimus and belatacept (a second-generation high affinity derivative of CTLA4-Ig)9-11 on diabetic rhesus macaques transplanted with neonatal porcine islets.