More than 330,000 Americans with end-stage renal disease (ESRD) currently rely on regular dialysis treatment to replace many of the normal duties their failing kidneys are no longer able to perform. The procedure is straightforward: two needles are inserted into an access point in the arm, leg, or sometimes in the neck, one on the artery side and one on the vein side. Blood drains into the dialysis machine, where it is cleansed of potentially toxic waste, salt and extra water and is then returned to the body. The best access for most patients is called a fistula; an artery joined to a vein under the skin to make a larger vessel. If no vessels are suitable for a fistula, the doctor might use a synthetic tube or a graft to join an artery and vein. A graft made from a segment of the patient’s own vein typically works best but many times, the person doesn’t have a suitable vein segment. However, stem cells may soon provide a solution.
In what experts have hailed a “revolutionary milestone,” researchers at Cytograft Tissue Engineering of California have developed grafts made entirely of a patient’s own cells. To make the graft, tissue is taken from the back of the patient’s hand, from which two cell types are extracted—fibroblasts that provide the structural backbone of the vein, and endothelial cells that form the lining of the vein. The cells are grown into a sheet, then rolled into a tube and allowed to fuse at the seam. The process takes about six to nine months and, unlike other vein grafts that have been developed using a patient’s own cells, contains no plastic scaffolding to give the vein strength. “What we have done is provide something that has no foreign material, therefore minimizing or eliminating the foreign body (rejection) response so the body doesn’t degrade the tissue,” said Dr. Todd McAllister, chief executive of Cytograft. “The fact that there is no synthetic material makes this novel.”
The grafts were then tested for strength and stability in ten seriously ill patients undergoing kidney dialysis. All the patients either had an earlier graft fail or were going to need a plastic tube graft in order to continue treatment. During the initial phase of the trial, three of the grafts failed, which the researchers say is a normal failure rate for such a high-risk group. One patient withdrew because of severe stomach bleeding, and one died of unrelated causes. The five remaining patients used the grafts for dialysis for six to twenty months, and needed fewer interventions including surgeries, to maintain the vessels than regular dialysis patients. “We had extremely good long-term performance,” McAllister said. “The tissue-engineered vascular graft actually appeared slightly better” than using either a plastic tube or the patient’s vein, he added.
In an editorial accompanying the study findings, Dr. Vladimir Mironov, director of the Shared Tissue Engineering lab at the Medical University of South Carolina, 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,” he said. “Clinical vascular tissue engineering is a reality—the always-promising field of tissue engineering finally delivered its promises.” However, Mironov worries that the vessels, which cost between $15,000 and $20,000, compared to the $3,000 conventional product made using plastic, might not be cost effective enough to be used widely.
“The ability to use a blood vessel grown in the laboratory is really quite remarkable,” 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. “This could become a very important alternative to what is done presently.”
McAllister said Cytograft wants to study the graft in a much larger trial and hopes to have a product on the U.S. market in about three years. They are also working on replacement veins to repair heart damage and to replace diseased veins in patients that would otherwise need an amputation.
Studies estimate there are between 1.5 and 2.0 million people around the world receiving dialysis and many more are in need of treatment. Today, 20 million Americans have been diagnosed with chronic kidney disease (CKD), while another 20 million more are at risk for kidney disease but are unaware of their condition. In 2006, the number of people receiving dialysis treatments in the U.S. increased by nearly 95,000.
The study is published in the medical journal The Lancet.
No comments:
Post a Comment