By David N. Leff
What with organ transplantation, a Type 1 diabetic patient confronts a double whammy from his or her immune system. The injury to which it adds insult is the autoimmune cause of the disease, in which misguided antibodies and T cells destroy their insulin-producing cells. The added insult is that attempts to transplant donor Islets of Langerhans - the pancreatic cellular source of insulin - come up against the prospect of a lifetime on immunosuppressive drugs to prevent annihilation of the alien islets by that same immune system. But stay tuned.
"In the past," observed biomedical engineer Ray Rajotte, at the University of Alberta in Edmonton, "from 1989 to 1998 - that's ten years - there were 267 islet transplants. And to the disappointment of all of us," he continued, "the number of these diabetics who achieved insulin independence for one year was only eight percent. Their donor islets came in combination with a kidney transplant, and always the problem was the immunosuppressive steroids they used in those days. We've known for years that islets don't like steroids."
Rajotte, who directs the university's Islet Research Group, is co-senior author of a paper in the New England Journal of Medicine, (NEJM), due to appear July 27, 2000. Its title: "Islet transplantation in seven patients with Type 1 diabetes mellitus using a glucocorticoid-free immunosuppressive regimen." Its first co-senior author is transplant surgeon James Shapiro, who heads the university's Clinical Islet Transplant Program.
Rajotte recounted to BioWorld Today why on June 6 NEJM released this article from its normal embargo date. "With the journal's permission, Dr. Shapiro presented its data to the American Transplantation Society meeting in Chicago last month. However, a press reporter leaked it somehow, which caught all of us off guard."
Now the number of patients who received these donor islets at Edmonton has climbed from seven to 10, Rajotte said, "and all of them have become insulin-independent - the goal of our program." He detailed the innovative procedure - now known as "the Edmonton protocol" - which achieved this 100 percent success rate.
Multi-Innovations Mark 'Edmonton Protocol'
The first step was isolating the individual islets, of which a million or so are scattered, like raisins in a cake, throughout the banana-size adult pancreas:
¿ "We started by putting some cannulas, or tubes, into the pancreatic duct, and perfused the enzyme collagenase to the organ. This specifically releases the islets from the sticky matrix.
¿ "Then, we chopped up the pancreas into several pieces, and transferred them over to a rotating, shaking rinsing chamber. As the islets recirculated the collagenase through the chamber, we took samples.
¿ "Once we were seeing free islets, we had to get them out of the system quickly, collect them, and inactivate the collagenase quickly.
¿ "After this step, we had 50 to 60 cubic centimeters of tissue, probably 95 percent unwanted pancreatic tissue, and five percent pure isolated islets.
¿ "So then we had to purify them, using a modified cell washer - another recent innovation. This was a three- to four-hour process that ended up with 50 cc to maybe 5 cc of pure islets."
¿ "Now that we'd got the islets isolated, another thing we did differently was to immediately transplant them into the patient. In the past we'd put them in culture for 24 to 48 hours. Now we get them into the recipient right away.
"A single islet is about 300 micrometers in diameter," Rajotte pointed out, "like a little speck of sand - barely visible to the eye. It contains not only the insulin-producing beta cells, but also the glucagon-producing alpha cells. If the body's blood glucose level goes too high, the beta cells sense that and secrete insulin. If the glucose goes too low, the alpha cells sense that and secrete the glucagon."
Perhaps the single most significant departure from prior transplant practice was to replace the standard, steroid-based anti-rejection cyclosporin with a three-drug, steroid-free regimen. "So Shapiro came up with rapamycin, tacrolimus and Zenapax," Rajotte related. "To replace the steroids, we did induction therapy with this Roche product, Zenapax, which is an anti-interleukin-2 antibody. It suppressed the immune system right at the time of transplant. Then we put the patients on low-dose, oral tacrolimus and tapered doses of rapamycin.
"Because on average we can isolate from 400,000 to 500,000 islets per donor pancreas," Rajotte went on, "our transplant patients always got, initially, 4,000 to 5,000 islets per kilogram of body weight. Then we watched to see what happened. It turned out that in these patients, their insulin requirement was reduced quite low. They had no episodes of hypoglycemia. However, they still needed a little bit of insulin.
"To produce insulin-independence, we wanted to see just how many islets they needed. So we waited for two or three weeks, then gave them a second transplant. And it turned out that they needed 10,000 to 11,000 islets per kg. Receiving that aliquot, all 10 patients became insulin-independent, and have remained that way - the longest for 14 months.
The actual transplantation has proved a simple outpatient procedure, as Rajotte related:
"The patients are on pagers. We just tell them to come up to the X-ray department when we've isolated a full dose of islets. The radiologist - not a surgeon - goes in. With the patient totally awake, a small needle goes through the skin and liver, and finds the portal vein, into which a little catheter is threaded. Then we bring the islets over from the isolation lab. Dr. Shapiro injects them up into the liver, while the patient's talking to us. The catheter is pulled out, the recipient gets up off the table - and that's it."
Biotech Getting Into The Act
Shapiro made the point that "if islet transplantation can get glucose in the body into the normal range, then we are likely to prevent or slow down the progression of diabetic complications - blindness, amputation and kidney failure
"Obviously," he told BioWorld Today, "though we don't have enough of these islets to treat every Type I diabetic right now, what we do have is the huge potential of this treatment. So if we can carry the transplant out without needing drugs - that's called tolerance - that's going to be a huge breakthrough for the biotechnology industry, which is trying to develop new antibodies, costimulatory blockers and other treatments that will allow tolerance to happen."