Latest research holds promise for reversing the most severe form of diabetes
To the million or so Americans with type 1 diabetes, the notion of one day being disease-free seems too good to be true. But, says David Sutherland, M.D., Ph.D., it could become a reality in the foreseeable future.
Sutherland directs the Diabetes Institute for Immunology and Transplantation, the University of Minnesota’s focal point for research aimed at advancing the transplantation of insulin-producing islet cells to cure diabetes. Since it was founded in 1994, the institute has made great strides in refining whole-organ pancreas transplants and islet transplants to more effectively treat type 1 diabetes. This past winter, associate director Bernhard Hering, M.D. announced the results of a landmark study that moves them closer than ever to a possible cure: They successfully reversed diabetes in 12 monkeys by transplanting islet cells from pigs.
Brian Flanagan, Ph.D., acting director of the Juvenile Diabetes Research Foundation’s islet biology and transplantation program, calls the report—along with one from an Emory University team also looking at pig islets—“milestones.”
“We were very encouraged by those papers,” Flanagan says. “It is a significant step forward. But we’re certainly not at the end yet.”
Diabetes actually comprises several disorders. Their common thread is an inability to properly control the amount of glucose circulating in the blood.
Normally, when the digestive tract releases energy in the form of glucose into the body, beta cells—found in the pancreas in cell clusters called islets—release insulin. Just as a subway token admits riders through a turnstile, insulin ushers glucose into body cells, where it is used or stored for future energy needs.
In type 1 diabetes, the kind that most commonly appears in childhood, a person’s immune system mysteriously destroys his or her beta cells. Traditional treatment involves painstaking daily insulin shots, or infusion. Even with the best of care, many with type 1 diabetes suffer devastating and sometimes deadly side effects, including kidney disease, circulatory problems, and blindness.
Why not replace the destroyed islets with ones that work? In 1966 University of Minnesota surgeons Richard C. Lillehei, M.D., and William D. Kelly, M.D., did just that when they performed the world’s first pancreas transplant. Sutherland took the concept one step further in 1974 when he transplanted islets from a deceased donor into a patient with diabetes.
But there are hefty obstacles to overcome before islet transplantation can be considered a viable cure. A major one is improving the effectiveness and reducing the adverse effects of the immunosuppressive drugs used to prevent the recipient’s body from rejecting the foreign cells. Another is figuring out how to provide enough islets to meet the demand. Each year about 30,000 Americans are diagnosed with type 1 diabetes, while only about 6,000 donor pancreases become available.
When Sutherland and colleagues established the Diabetes Institute for Immunology and Transplantation in 1994, it was to initiate a full-court press against these obstacles. Two years later they were joined by Hering, a worldwide leader in islet transplant therapy.
“We need to have this mindset that diabetes is a curable disease, and we should not accept anything else that will not get us there; anything else will be a compromise,” says Hering, who holds the Eunice L. Dwan Diabetes Research Chair. “I know it is possible.”
In the years since then, the institute has made substantial progress. By developing, testing, and refining various approaches to harvesting and handling islets and preventing rejection, institute staff have been able in clinical trials to reverse diabetes in some islet recipients for years.
Institute staff has stretched the islet supply as well. Last year Hering reported success using islets from a single donor, rather than the two or more normally required. But the availability of islets still remains a serious limiting factor.
“The real advantage of islets is to come in the future, when we can get islets from another source,” Sutherland says.
Breaking new ground
In February 2006 Hering, Sutherland, and colleagues at the University of Minnesota announced a major step forward in efforts to overcome the islet supply issue. In a paper published in the scientific journal Nature Medicine, the researchers reported they had reversed diabetes in monkeys using islets harvested from pigs.
“People thought it was impossible,” Hering says. “This is really breaking new ground.”
Xenotransplantation—or transplanting tissue from one species into another—generally causes a hyperacute rejection that is dramatically more severe than immune responses to transplants within a species. Hering and colleagues discovered that, unlike other pig tissue, most pig islets don’t carry the protein that stimulates this hyperacute reaction. As a result, they were able to successfully implant the islets into monkeys using immunosuppression regimens similar to those used in human organ transplants. All 12 monkeys in the study produced enough insulin to control their blood sugar after the transplant. Although some of the monkeys had trouble with blood clots, islets were still functioning in some animals 100 days after the transplant.
One step away
Having successfully transplanted pig islets into monkeys, the researchers are eager to develop a safe, effective protocol for doing the same in humans.
“There’s a lot of momentum to position us to expedite and lead the development of pig islets to potentially benefit people with diabetes,” Hering says. “This is one step away for us. The question is, How long will that step be?”
Before pig islet transplantation can enter clinical trials, the researchers must conduct additional studies—based on what they’ve learned about how the monkeys’ immune systems reacted to the pig islets—to identify an antirejection strategy for humans. They also must find a way to raise pigs under the stringent conditions required by the U.S. Food and Drug Administration for producing tissue for use in humans.
“We have both initiatives well under way,” Hering says. The institute has recruited several additional researchers to carry the antirejection work forward. It is also looking at novel approaches, such as placing islets and antirejection drugs together under the skin or in abdominal fat to avoid the adverse effects of full-body immune suppression.
While researchers continue their work, a separate nonprofit organization, Spring Point Project, is working to fund and build a facility for raising the pigs needed to produce islets. The researchers hope to receive FDA approval to start the clinical trial phase in three years, with the first pig islets implanted in humans within about five years.
“At some point in the hopefully not-too-distant future, people with diabetes will have better options available to them,” Hering says. “They will be able to get a pig islet transplant without toxic immune suppression and enjoy the beauty of life free of diabetes.”
As he looks forward to further advances, Hering also expresses gratitude to the donors who made it all possible by investing in exploratory research.
“They positioned us to do the initial work to show proof of
principle,” he says. “If we had gone with the initial idea to major
funding organizations, they would have said, ‘Now you have gone
completely insane.’ That’s why you need philanthropic donations.”
By Mary Hoff