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Encapsulated Islet Cell Transplants Avoid Rejection

Jun 21, 2005

Encapsulating islets cells with polyethylene glycol — may soon obviate the need for immunosuppression in islet cell transplantation. Dr. David Scharp, lead presenter stated that the technology that has been under development for several years. The net result will be effective control of blood glucose levels in patients with insulin-dependent diabetes without the danger of hypoglycemia or graft rejection. Dr. Scharp is chief scientific officer and executive vice president of research and development at Novocell, Inc. in Irvine California.

By coating cells with polyethylene glycol, "immune cells cannot contact the graft and graft cells cannot contact the host, but they’re wide open for exchange of insulin and glucose," he explained.

His group’s research was conducted in diabetic baboons in which coated islet cells were injected subcutaneously. The only immunosuppression provided was a low dose of cyclosporine for 30 days.

In a group of 16 baboons, 15 showed significant reductions in hemoglobin A1c, average and fasting blood glucose, glycemic excursions and insulin requirements. Five of eight recipients were insulin-independent at 3 months after transplantation, as were two of eight recipients in a second group tested at 6 months.

So far, three treated animals have achieved insulin independence for 14 to 20 months before they were sacrificed.

Histological examination of the subcutaneous implant sites revealed little immune reactivity and increased capillaries. "We know that islets cells can’t live indefinitely outside of the pancreas and have to be replaced," Dr. Scharp said. "The coating is biodegradable so that about the time the islets would be failing in the patient the coating will be broken down and cleared in the kidney."

The investigators have also shown that the animals can be re-treated safely after the initial graft has failed. "So we should be able to do multiple implants safely without immunosuppressive drugs and eliminate diabetes altogether or come close to that," the researcher added.

Current limitations imposed by the restricted number of available cadaver donors means that only a fraction of eligible patients could be treated with this technique. For that reason, Novocell is working with a partner company to develop PEG-coated islet cells from embryonic stem cells, Dr. Scharp noted, which potentially could provide transplantable islets for any suitable candidate.

He expects a phase I/II safety and efficacy clinical trial to be started within the next several months.

Presentation at the American Diabetes Association’s 65th Annual Scientific Sessions in San Diego, California.


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