Niklason’s grafts would be less likely to form clots because they would “recreate the environment that the blood normally sees,” says Langer.
Another experimental approach is to grow blood vessels on demand using individual patients’ own cells as the starting material. Researchers at Cytograft, based in California, proved that they could create vascular grafts with this strategy, and they have used it successfully to treat a small number of dialysis patients outside the United States, according to data published in October in the New England Journal of Medicine. (Dialysis patients are often given vascular grafts to facilitate blood flow to the dialysis machine during the procedure.)
These vessels from Cytograft promise very high compatibility with a patient’s body since they are made from his or her own cells. But they currently take between six and nine months to grow and may turn out to be prohibitively expensive and difficult to apply in less specialized settings. “To reach the wide patient population that is in need, we can’t simply talk about doing this in major academic medical centers,” Nerem says. “It has to be out there in community hospitals, in the whole health-care system. And for that to happen, these products will need to be available off the shelf.”
If successful, Niklason’s product would offer a more efficient, less expensive alternative to growing vessels from scratch for individual patients, says Langer. (Cytograft says that it is also pursuing an approach that would use donor cells to create an off-the-shelf product.)
So far, Niklason and her team have mainly tested their approach in dogs. Using canine smooth muscle cells, they created a dog version of the grafts and implanted them in nine surgical procedures: two coronary grafts, three arterial patches, and four carotid-bypass grafts. In one of the dogs, a clot formed, and the graft was removed after roughly a week. In the other dogs, the new vessels did not cause complications and appeared to remain viable for up to a year, according to data presented this week at a meeting of the American Heart Association.
Niklason says that her team has also created vascular grafts from human cells and implanted them into several baboons, although that work is not yet public.
Going forward, she and her team will need to test the human-derived vessels in larger animals for longer periods of time. The goal is to win FDA approval and begin further tests in humans, perhaps within the next two years, Niklason says.
Another major challenge would be to scale up the manufacturing processes so that the grafts can be produced more efficiently in greater quantities.
“We’ll just have to see how this plays out,” says Nerem. Niklason and her team “still have a lot of work to do.”