Scientists have grown a ready-made supply of blood vessels to transplant into patients undergoing heart surgery and kidney dialysis. So far, it works in baboons and dogs.
“Not only are bioengineered veins available at the time of patient need, but the ability to generate a significant number of grafts from a cell bank will allow for a reduction in the final production costs, as compared to other regenerative medicine strategies,” says lead author Shannon Dahl, co-founder of Humacyte, Inc.
These grafts are the first to be engineered from human tissue that are also fit for storage. And, according to the study, they can be grown from donor cells and transplanted into unrelated patients without infection, clogging, or triggering immune responses.
To create readily available blood vessels that retain their strength and elasticity during long-term storage:
1. They cultured smooth muscle cells from human tissue on biodegradable polymer scaffolds shaped like tubes.
2. The smooth muscle cells produced collagen and other molecules that formed an extracellular matrix covering the scaffold.
3. When the scaffold degraded, fully formed blood vessels were left behind.
4. Then, they used detergent to scrub off the donor muscle cells from the blood vessels. This helps make sure immune responses won’t be elicited once transplanted.
5. Stored in a simple salt solution in the fridge for a year, the grafts retained their efficacy and remained unclogged.
The researchers tested their grafts in the arms of 8 baboons. The vessels remained open and strong for up to 6 months, and the vessel walls didn’t thicken. They also made smaller vessels and transplanted those into 5 dogs. These stayed blockage-free for up to a year.
In both models, Science explains, the new vessels were soon populated by several types of cells present in normal blood vessels, suggesting that the animals' bodies were tolerating the transplants.
On the need for this kind of alternative, Nature reports:
Patients with coronary artery disease or peripheral arterial disease are often treated with bypass surgeries – in which the blood vessel that has narrowed as a consequence of the illness is closed off and circumvented by the implantation of an unrestricted 'conduit'. To avoid complications, surgeons prefer to use vessels taken from a patient's own body – harvesting a portion of vein from the leg, for example. But alternatives are often necessary for patients who have had to go under the knife many times, or who merely lack enough robust blood vessels.
One particularly promising option has been the development of tissue-engineered vascular grafts, which are made using a patient's own cells – limiting the likelihood of rejection. However, these types of patient-specific grafts take up to 9 months to grow and can cost more than $15,000 per vessel.
According to the new study, scientists could use cell banks to make as many as 37 large or 74 smaller blood vessels per donor, and cell banks put together from multiple donors could hold even more.
Dahl says they're now "laying the groundwork" for how they might safely begin to test the vessels in human patients. Although the animal results are preliminary, they're encouraging enough that "it is worth our energy to evaluate the technology in the clinic."
In 2007, over 400,000 coronary bypass procedures were performed in the US, according to the American Heart Association. And each year, 110,000 new patients develop kidney failure and need dialysis, according to the National Kidney Foundation.
The study, "Readily Available Tissue-Engineered Vascular Grafts," was published in Science Translational Medicine today.
Image: 6-mm-diameter tissue-engineered vascular graft before implant / Science/AAAS