Achievement could aid dialysis and might be replicated for heart disease, scientists say,,,,
THURSDAY, April 23 (HealthDay News) -- The successful use of a patient's own skin cells to grow tissue-engineered shunts for dialysis could portend a revolution in kidney care, researchers say.
The problem right now is that about half of all dialysis patients have their blood filtered three times a week via a plastic tube that creates a shunt -- a connection between the patient's arteries and veins. These plastic tubes fail more often than shunts made from the patient's own vein, but only about half of patients have veins that are suitable for creating a shunt.
The new technology, outlined in the April 25 issue of The Lancet, may offer a solution for those patients.
"This was the first demonstration that a tissue-engineered vascular graft that did not have any sort of synthetic support could provide the strength and durability for long-term implant," said lead researcher Todd N. McAllister, from Cytograft Tissue Engineering in Novato, Calif., the creators of the new shunts.
"The tissue-engineered vascular graft actually appeared slightly better" than using either a plastic tube or the patient's vein, he added.
McAllister's team used the engineered tissue shunts in 10 patients undergoing dialysis for end-stage kidney disease. All the patients either had an earlier graft fail or were going to need a plastic tube graft to continue treatment.
The researchers first took cells from the back of the patient's hand. These were then grown in a lab, producing a tissue-engineered sheet of cells. This sheet was then formed into a vessel and implanted in the patient, in much the same way a plastic shunt would be.
The procedure does not use any synthetic material such as plastics, which have been used in other attempts to create engineered tissue.
The researchers tracked the safety and stability of the shunts over three months. They also evaluated the effectiveness of the shunts once dialysis was started.
Three shunts failed during the safety phase of the study, which is a normal failure rate seen in these high-risk patients, the researchers noted. In addition, one patient withdrew from the trial and one patient died of causes unrelated to the shunt.
Of the five remaining patients, the grafts were used for dialysis for six to 20 months. Only one patient needed surgical correction to keep the shunt open. In all, seven patients used the shunt for one month, and five used the shunt for six months. That's close to the standard performance of all shunts, the researchers noted.
The average life expectancy for a patient on dialysis is about six years, McAllister said. These patients go through one to two vein grafts made from their own veins, and after that they will need to have plastic tubes implanted. Plastic tubes fail on average every 12 months, he said.
In contrast, the new tissue-engineered graft should last from one to five years, McAllister said. In addition, since the patient's cells are banked, another graft can be grown and implanted as needed, he said.
This process of creating grafts is expensive, McAllister noted. However, he expects the process to become cost-effective given the amount of time the graft lasts, and further cost reductions should emerge as the process is streamlined and becomes more common.
This therapy won't be available to patients for three to four years, McAllister predicted. The company is also working on creating other vessels to repair heart and other vascular damage, he said.
Dr. Vladimir Mironov, director of the Shared Tissue Engineering Lab at the Medical University of South Carolina and author of an accompanying editorial in the journal, called the technique a milestone in tissue engineering.
"We have the first commercial clinically tested, completely biological tissue-engineered vascular graft. It is a historic milestone," Mironov said. "Clinical vascular tissue engineering is a reality -- the always-promising field of tissue engineering finally delivered its promises."
In the future, the same techniques could be used for engineered heart valves and cardiac tissue, Mironov believes. "But whether tissue engineering products are cost-effective is another question," he said.
Dr. Ajay Singh, clinical chief of the renal division and director of dialysis at Brigham and Women's Hospital in Boston, and an associate professor of medicine at Harvard Medical School, noted that many shunts fail in dialysis patients and this new method, if it proves itself, could aid many patients.
"The ability to use a blood vessel grown in the laboratory is really quite remarkable," Singh said. "This could become a very important alternative to what is done presently."
One other expert wasn't so sure, however.
"This is very preliminary," said Dr. Jonathan Bromberg, a professor of surgery at Mount Sinai School of Medicine and director of the Transplantation Institute at Mount Sinai Medical Center in New York City.
"It looks like a reasonable approach, it looks like a promising approach, but it needs a tremendous amount of more study," he said. "It's very far from being widely applicable and it is also not clear that this is any better than what we already have with our current technology."
For more on kidney disease and dialysis, visit the U.S. National Institute of Diabetes and Digestive and Kidney Diseases.
SOURCES: Todd N. McAllister, Ph.D., Cytograft Tissue Engineering, Novato, Calif.; Ajay Singh, M.D., clinical chief, renal division, director, dialysis, Brigham and Women's Hospital, associate professor of medicine, Harvard Medical School, Boston; Jonathan Bromberg, M.D., Ph.D., professor of surgery, Mount Sinai School of Medicine and director, Transplantation Institute, Mount Sinai Medical Center, New York City; Vladimir Mironov, M.D., Ph.D., director, Shared Tissue Engineering Lab, Medical University of South Carolina, Charleston; April 25, 2009, The Lancet
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