Surgeons perform first bioengineered blood vessel transplant in military patient
By Sarah Marshall, Uniformed Services University of the Health Sciences
/ Published May 28, 2019
An Army veteran in danger of losing his leg from vascular disease has become the first patient in the Military Health System to undergo transplantation of a new type of bioengineered blood vessel thanks to surgeons from the Uniformed Services University of the Health Sciences and Walter Reed National Military Medical Center.
Air Force Colonel (Dr.) Todd Rasmussen, professor of Surgery and associate dean for Clinical Research at USU, performed the surgery at Walter Reed-Bethesda this month after getting approval for use of an investigational product called the Human Acellular Vessel, or HAV, developed by Humacyte, Inc.
“Military surgeons have been following and researching this technology for a number of years as potentially a new way to repair blood vessel injury on the battlefield. We are excited to see the product come to fruition, and for our team to gain real-world experience with it in the operating room at Walter Reed. Our ability to use this product to save this patient’s leg is a credit to a partnership that included the military’s medical research program, Humacyte, and a forward-leaning approach by the Food and Drug Administration.”
The rate of vascular injury during the wars in Iraq and Afghanistan was higher than that reported during previous wars, and faced with this challenge, the Department of Defense (DoD) was in search of an off-the-shelf biologic conduit that could be used to save the limbs of service members. Repair of a damaged blood artery would normally involve surgically removing and using an extra vein that runs just under the surface of the length of the patient’s inner leg called the saphenous. However, some patients may not have an adequate sized vein, or they may have had the vein damaged during the original injury; a common situation in blast-injured service members. Using the patient’s own saphenous vein for repair also increases the time of an already complex operation, and requires another surgical incision that has its own risks.
The HAV was created by a team of clinician-scientists from Yale and Duke Universities led by Drs. Laura Niklason and Jeff Lawson, respectively, and has only recently been used in hundreds of civilian patients in the U.S. and around the world, mostly on a research basis. In 2011, amidst several deployments and while serving as the deputy commander of the U.S. Army Institute of Surgical Research, Rasmussen had an opportunity to see how the HAV worked and was able to study it himself in an animal model of vascular injury. For nearly a decade, Rasmussen has led collaborative efforts to help bring this innovative technique into the Military Health System. Because the HAV does not yet have full FDA clearance, Rasmussen worked with members of the FDA to get his own approval to use the investigational device at Walter Reed. Rasmussen believes this procedure could soon be the new way to help save limbs on the battlefield.
“I think this product could be a game changer for the management of vascular injury and vascular disease – it could eliminate the need for saphenous vein harvest or use of plastic vascular conduits. We’ve been enthused by its potential use on the battlefield, studied it in our military labs and supported its research in civilian centers, and it’s great to see it now diffuse into real-world practice,” Rasmussen said. “Injury to major blood vessels of the body is the most common cause of death and disability in combat and we need new technologies such as this to improve our ability to save lives and limbs. Because this product is made of neutral biologic material, it has the potential to be resistant to infection and become incorporated or adopted by the recipient patient. The fact that it can be bio-manufactured to a specific size and available for immediate, off-the-shelf use is also revolutionary.”
Development of the HAV starts by taking living cells from a human blood vessel and placing them onto a tube-shaped frame. Just as cells would normally grow inside a petri dish, these vascular cells are kept alive in an organ chamber and allowed grow around the tube-shaped lattice. As the cells are maintained in the chamber they secrete the strong structural substances that make up a blood vessel. During the process, the chamber generates a pulsating rhythm through the tube-shaped frame, mimicking a heartbeat and giving the new vessel the sensation of blood pressure as it is forming. Over the course of weeks, the cells and the strong framework they form begin to “think and behave” like a real blood vessel, Rasmussen said. Over time, the lattice that was used to seed the original vascular cells dissolves, and scientists remove the original cells so the new vessel doesn’t cause an immune response when it’s implanted. What is left is a solid, tubular structure made of human vascular material, which looks and performs like a blood vessel – thus, the bio-engineered and newly grown blood vessel, or HAV.
The HAV is then removed from the organ chamber, packaged in sterile preservative fluid, and stored ready for surgical implantation into a patient with an injured or blocked blood vessel. When sewn in place in the operating room, the HAV reroutes and restores blood flow around the vascular blockage or injury.
Since the finished framework that makes up the HAV is immune-neutral, Rasmussen noted, patients do not have problems “taking” the transplanted vessel, meaning the recipient’s body does not reject the HAV that it might otherwise not recognize because it’s a biologic originating from someone else’s vascular cells. Also, because the vascular framework can conform to any tube-shaped lattice, these vessels could potentially be made into various shapes and sizes to meet an individual patient’s needs, he said.
“Once the HAV is implanted, the patient’s own cells circulate through and hopefully make themselves at home to ‘redecorate’ the new vessel as their own” Rasmussen said. “Although further research needs to be performed to understand the long-term durability and features of this product, the hope is that as the HAV functions in the recipient patient, it will become that patient’s own ‘living’ vessel and last indefinitely.
“Having this innovative product reach the point of clinical use and study is a great example of the synergies that exist between university-based innovation, private industry, the DoD-medical research program and the FDA. It’s another example of how priorities and the lessons learned from war propel advances in medicine and the biomedical sciences – hopefully to the betterment of military and civilian patients.”