Bioengineered human blood vessels Niklason, Laura E.; Lawson, Jeffrey H.
Science (American Association for the Advancement of Science),
10/2020, Volume:
370, Issue:
6513
Journal Article
Peer reviewed
Evolution of bioengineered blood vessels
Biotechnology approaches to repair and replace arteries have been under development for more than a century. Early synthetic approaches used rubber-based ...replacements, which then evolved into the use of polymer fabrics and, more recently, into biological approaches that permit the growth of blood vessels in the laboratory. Niklason and Lawson review the scientific and technological advances that allow the regeneration of a patient's own blood vessels. The authors discuss how blood vessel cells, when combined with suitable substrates for tissue growth under conditions that mimic human physiology, can produce functional bioengineered arteries. These biological approaches pave the way to advancing how vascular disease is managed and treated in the future.
Science
, this issue p.
eaaw8682
BACKGROUND
Vascular replacement and repair for the treatment of atherosclerotic disease, infection, and traumatic injury are some of the most commonly performed surgical procedures in the Western world. In the United States alone, hundreds of thousands of coronary and peripheral arteries are repaired, replaced, or bypassed every year. But despite the enormity of the clinical need for engineered arterial replacements, the equally enormous simultaneous challenges of immune acceptance, requisite tissue mechanics, low thrombogenicity, and immediate availability have made the broad clinical application of engineered arteries quite difficult to achieve. In this regard, recent years have seen the fusion of cell biology, physiology, and engineering to now allow for the creation of human tissues that can truly function in the setting of vascular repair and replacement.
ADVANCES
For a biological engineered artery to function successfully without requiring immunosuppression, the following objectives should be met: (i) The engineered artery should have an extracellular matrix of sufficient quality to provide suitable tensile, suture retention, and rupture strength properties. A focus on production of suitable amounts of high-quality cross-linked vascular collagens type I and III is probably necessary for any biological engineered artery to be successful. (ii) To minimize risks of inflammation, foreign-body response, and immune recognition, the vascular tissue matrix should be of human origin and without substantial synthetic material additives or artificial covalent cross-linking. (iii) If the engineered artery is cellular, even if the cells are nonviable, those cells should be autologous to prevent immune recognition, degradation, and aneurysm formation in the implanted vessels. (iv) Once implanted, the engineered arteries should have the potential to be remodeled, repopulated, and rejuvenated by the host. (v) For small-caliber or low-flow arterial bypass applications, it is likely that a suitable nonthrombogenic luminal surface is required. This surface may be either cellular or biochemical, but it should prevent blood coagulation contact activation, platelet adhesion and activation, and thrombosis in the arterial system.
OUTLOOK
Guided by the design criteria above, engineered blood vessels have been developed by several groups that have progressed to clinical trials. Recent clinical studies have demonstrated the feasibility of using human tissue–engineered blood vessels in the settings of vascular trauma, peripheral arterial disease, and vascular access for hemodialysis. Engineered arteries reaching the clinical domain have been composed of autologous cells or allogeneic cells, or have been engineered from allogeneic cells or tissues and then decellularized. Vascular functionality in patients has been demonstrated in both low-pressure environments (pediatric cardiac surgery) and high-pressure environments (peripheral arterial surgery in adults).
Autologous cell approaches have shown some promise, particularly in clinical settings of venous reconstruction and low pressure and in pediatric populations. However, scaling production of engineered arteries to tens of thousands of vessels per year, as would be needed to treat arterial atherosclerosis at large scale, presents enormous logistical challenges if autologous cell sources are used. Hence, it is likely that future successes of engineered arteries will employ allogeneic human cells or cell banks to generate tissues at clinically relevant scales, and suitable strategies will be required to prevent adaptive immunity and rejection of these vessels. Furthermore, next-generation techniques such as three-dimensional bioprinting of both cells and matrix may one day allow vessel production at accelerated speeds, possibly producing usable tissues in hours or days, rather than weeks or months. Microvascular and cardiac tissue engineering are also making important strides, pointing toward a future that could enable revascularization of solid organs. The evolution of scientific thinking and approaches that have brought us to this point is summarized in this review.
An engineered human artery cultured from human vascular cells and implanted into a patient.
Immunostaining for smooth muscle (red), progenitor cells (green), and cell nuclei (blue) shows extensive cellular repopulation of the engineered vessel. Engineered cells were implanted into the patient for 4 years. The layer of red-staining cells at the bottom of the image shows the repopulated engineered vessel wall. Blue staining at the top shows the nuclei of skin cells.
Since the advent of the vascular anastomosis by Alexis Carrel in the early 20th century, the repair and replacement of blood vessels have been key to treating acute injuries, as well as chronic atherosclerotic disease. Arteries serve diverse mechanical and biological functions, such as conducting blood to tissues, interacting with the coagulation system, and modulating resistance to blood flow. Early approaches for arterial replacement used artificial materials, which were supplanted by polymer fabrics in recent decades. With recent advances in the engineering of connective tissues, including arteries, we are on the cusp of seeing engineered human arteries become mainstays of surgical therapy for vascular disease. Progress in our understanding of physiology, cell biology, and biomanufacturing over the past several decades has made these advances possible.
Arterial tissue-engineering techniques that have been reported previously typically involve long waiting times of several months while cells from the recipient are cultured to create the engineered ...vessel. In this study, we developed a different approach to arterial tissue engineering that can substantially reduce the waiting time for a graft. Tissue-engineered vessels (TEVs) were grown from banked porcine smooth muscle cells that were allogeneic to the intended recipient, using a biomimetic perfusion system. The engineered vessels were then decellularized, leaving behind the mechanically robust extracellular matrix of the graft wall. The acellular grafts were then seeded with cells that were derived from the intended recipient—either endothelial progenitor cells (EPC) or endothelial cell (EC)—on the graft lumen. TEV were then implanted as end-to-side grafts in the porcine carotid artery, which is a rigorous testbed due to its tendency for graft occlusion. The EPC- and EC-seeded TEV all remained patent for 30 d in this study, whereas the contralateral control vein grafts were patent in only 3/8 implants. Going along with the improved patency, the cell-seeded TEV demonstrated less neointimal hyperplasia and fewer proliferating cells than did the vein grafts. Proteins in the mammalian target of rapamycin signaling pathway tended to be decreased in TEV compared with vein grafts, implicating this pathway in the TEV's resistance to occlusion from intimal hyperplasia. These results indicate that a readily available, decellularized tissue-engineered vessel can be seeded with autologous endothelial progenitor cells to provide a biological vascular graft that resists both clotting and intimal hyperplasia. In addition, these results show that engineered connective tissues can be grown from banked cells, rendered acellular, and then used for tissue regeneration in vivo.
Summary Background For patients with end-stage renal disease who are not candidates for fistula, dialysis access grafts are the best option for chronic haemodialysis. However, polytetrafluoroethylene ...arteriovenous grafts are prone to thrombosis, infection, and intimal hyperplasia at the venous anastomosis. We developed and tested a bioengineered human acellular vessel as a potential solution to these limitations in dialysis access. Methods We did two single-arm phase 2 trials at six centres in the USA and Poland. We enrolled adults with end-stage renal disease. A novel bioengineered human acellular vessel was implanted into the arms of patients for haemodialysis access. Primary endpoints were safety (freedom from immune response or infection, aneurysm, or mechanical failure, and incidence of adverse events), and efficacy as assessed by primary, primary assisted, and secondary patencies at 6 months. All patients were followed up for at least 1 year, or had a censoring event. These trials are registered with ClinicalTrials.gov , NCT01744418 and NCT01840956. Findings Human acellular vessels were implanted into 60 patients. Mean follow-up was 16 months (SD 7·6). One vessel became infected during 82 patient-years of follow-up. The vessels had no dilatation and rarely had post-cannulation bleeding. At 6 months, 63% (95% CI 47–72) of patients had primary patency, 73% (57–81) had primary assisted patency, and 97% (85–98) had secondary patency, with most loss of primary patency because of thrombosis. At 12 months, 28% (17–40) had primary patency, 38% (26–51) had primary assisted patency, and 89% (74–93) had secondary patency. Interpretation Bioengineered human acellular vessels seem to provide safe and functional haemodialysis access, and warrant further study in randomised controlled trials. Funding Humacyte and US National Institutes of Health.
Traditional vascular grafts constructed from synthetic polymers or cadaveric human or animal tissues support the clinical need for readily available blood vessels, but often come with associated ...risks. Histopathological evaluation of these materials has shown adverse host cellular reactions and/or mechanical degradation due to insufficient or inappropriate matrix remodeling. We developed an investigational bioengineered human acellular vessel (HAV), which is currently being studied as a hemodialysis conduit in patients with end-stage renal disease. In rare cases, small samples of HAV were recovered during routine surgical interventions and used to examine the temporal and spatial pattern of the host cell response to the HAV after implantation, from 16 to 200 weeks. We observed a substantial influx of alpha smooth muscle actin (αSMA)-expressing cells into the HAV that progressively matured and circumferentially aligned in the HAV wall. These cells were supported by microvasculature initially formed by CD34
/CD31
cells in the neoadventitia and later maintained by CD34
/CD31
endothelial cells in the media and lumen of the HAV. Nestin
progenitor cells differentiated into either αSMA
or CD31
cells and may contribute to early recellularization and self-repair of the HAV. A mesenchymal stem cell-like CD90
progenitor cell population increased in number with duration of implantation. Our results suggest that host myogenic, endothelial, and progenitor cell repopulation of HAVs transforms these previously acellular vessels into functional multilayered living tissues that maintain blood transport and exhibit self-healing after cannulation injury, effectively rendering these vessels like the patient's own blood vessel.
Advances in standards of care have extended the life expectancy of patients with kidney failure. However, options for chronic vascular access for haemodialysis - an essential part of kidney ...replacement therapy - have remained unchanged for decades. The high morbidity and mortality associated with current vascular access complications highlights an unmet clinical need for novel techniques in vascular access and is driving innovation in vascular access care. The development of devices, biological approaches and novel access techniques has led to new approaches to controlling fistula geometry and manipulating the underlying cellular and molecular pathways of the vascular endothelium, and influencing fistula maturation and formation through the use of external mechanical methods. Innovations in arteriovenous graft materials range from small modifications to the graft lumen to the creation of completely novel bioengineered grafts. Steps have even been taken to create new devices for the treatment of patients with central vein stenosis. However, these emerging therapies face difficult hurdles, and truly creative approaches to vascular access need resources that include well-designed clinical trials, frequent interaction with regulators, interventionalist education and sufficient funding. In addition, the heterogeneity of patients with kidney failure suggests it is unlikely that a 'one-size-fits-all' approach for effective vascular access will be feasible in the current environment.
Autologous or synthetic vascular grafts are used routinely for providing access in hemodialysis or for arterial bypass in patients with cardiovascular disease. However, some patients either lack ...suitable autologous tissue or cannot receive synthetic grafts. Such patients could benefit from a vascular graft produced by tissue engineering. Here, we engineer vascular grafts using human allogeneic or canine smooth muscle cells grown on a tubular polyglycolic acid scaffold. Cellular material was removed with detergents to render the grafts nonimmunogenic. Mechanical properties of the human vascular grafts were similar to native human blood vessels, and the grafts could withstand long-term storage at 4 °C. Human engineered grafts were tested in a baboon model of arteriovenous access for hemodialysis. Canine grafts were tested in a dog model of peripheral and coronary artery bypass. Grafts demonstrated excellent patency and resisted dilatation, calcification, and intimal hyperplasia. Such tissue-engineered vascular grafts may provide a readily available option for patients without suitable autologous tissue or for those who are not candidates for synthetic grafts.
Abstract Objective The Kidney Disease Outcome Quality Initiative and Fistula First Breakthrough Initiative call for the indiscriminate creation of arteriovenous fistulas (AVFs) over arteriovenous ...grafts (AVGs) without providing patient-specific criteria for vascular access selection. Although the U.S. AVF rate has increased dramatically, several reports have found that this singular focus on increasing AVFs has resulted in increased AVF nonmaturation/early failure and a high prevalence of catheter dependence. The objective of this study was to determine the appropriateness of vascular access procedures in clinical scenarios constructed with combinations of relevant factors potentially influencing outcomes. Methods The RAND/UCLA Appropriateness Method was used. Accordingly, a comprehensive literature search was performed and a synthesis of results compiled. The RAND/UCLA Appropriateness Method was applied to 2088 AVF and 1728 AVG clinical scenarios with varying patient characteristics. Eleven international vascular access experts rated the appropriateness of each scenario in two rounds. On the basis of the distribution of the panelists' scores, each scenario was determined to be appropriate, inappropriate, or indeterminate. Results Panelists achieved agreement in 2964 (77.7%) scenarios; 860 (41%) AVF and 588 (34%) AVG scenarios were scored appropriate, 686 (33%) AVF and 480 (28%) AVG scenarios were scored inappropriate, and 542 (26%) AVF and 660 (38%) AVG scenarios were indeterminate. Younger age, larger outflow vein diameter, normal or obese body mass index (vs morbidly obese), larger inflow artery diameter, and higher patient functional status were associated with appropriateness of AVF creation. Older age, dialysis dependence, and smaller vein size were associated with appropriateness of AVG creation. Gender, diabetes, and coronary artery disease were not associated with AVF or AVG appropriateness. Dialysis status was not associated with AVF appropriateness. Body mass index and functional status were not associated with AVG appropriateness. To simulate the surgeon's decision-making, scenarios were combined to create situations with the same patient characteristics and both AVF and AVG options for access. Of these 864 clinical situations, 311 (36%) were rated appropriate for AVG but inappropriate or indeterminate for AVF. Conclusions The results of this study indicate that patient-specific situations exist wherein AVG is as appropriate as or more appropriate than AVF. These results provide patient-specific recommendations for clinicians to optimize vascular access selection criteria, to standardize care, and to inform payers and policy. Indeterminate scenarios will guide future research.
Vascular conduit is essential for arterial reconstruction for a number of conditions, including trauma and atherosclerotic occlusive disease. We have developed a tissue-engineered human acellular ...vessel (HAV) that can be manufactured, stored on site at hospitals, and be immediately available for arterial vascular reconstruction. Although the HAV is acellular when implanted, extensive preclinical and clinical testing has demonstrated that the HAV subsequently repopulates with the recipient's own vascular cells. We report a first-in-man clinical experience using the HAV for arterial reconstruction in patients with symptomatic peripheral arterial disease.
HAVs were manufactured using human vascular smooth muscle cells grown on a biodegradable scaffold. After the establishment of adequate cell growth and extracellular matrix deposition, the vessels were decellularized to remove human cellular antigens. Manufactured vessels were implanted in 20 patients with symptomatic peripheral arterial disease as above-knee, femoral-to-popliteal arterial bypass conduits. After HAV implantation, all patients were assessed for safety, HAV durability, freedom from conduit infection, and bypass patency for 2 years.
Twenty HAVs were placed in the arterial, above-knee, femoral-to-popliteal position in patients with rest pain (n = 3) or symptomatic claudication (n = 17). All HAVs functioned as intended and had no evidence of structural failure or rejection by the recipient. No acute HAV infections were reported, but three surgical site infections were documented during the study period. Three non-HAV-related deaths were reported. One vessel developed a pseudoaneurysm after suspected iatrogenic injury during a balloon thrombectomy. No amputations of the HAV implanted limb occurred over the 2-year period, and no HAV infections were reported in approximately 34 patient-years of continuous patient follow-up.
Human tissue engineered blood vessels can be manufactured and readily available for peripheral arterial bypass surgery. Early clinical experience with these vessels, in the arterial position, suggest that they are safe, have acceptable patency, a low incidence of infection, and do not require the harvest of autologous vein or any cells from the recipient. Histologic examination of tissue biopsies revealed vascular remodeling and repopulation by host cells. This first-in-man arterial bypass study supports the continued development of human tissue engineered blood vessels for arterial reconstruction, and potential future expansion to clinical indications including vascular trauma and repair of other size-appropriate peripheral arteries.
Display omitted
Since ancient times we have attempted to facilitate hemostasis by application of topical agents. In the last decade, the number of different effective hemostatic agents has increased drastically. In ...order for the modern surgeon to successfully choose the right agent at the right time, it is essential to understand the mechanism of action, efficacy and possible adverse events as they relate to each agent. In this article we provide a comprehensive review of the most commonly used hemostatic agents, subcategorized as physical agents, absorbable agents, biologic agents, and synthetic agents. We also evaluate novel hemostatic dressings and their application in the current era. Furthermore, wholesale acquisition prices for hospitals in the United States are provided to aid in cost analysis. We conclude with an expert opinion on which agent to use under different scenarios.
Thrombin is a naturally derived enzyme that has been widely characterized for its roles in hemostasis, inflammation, and cell signaling. Thrombin has been purified from numerous sources and used as a ...clinical aid for topical hemostasis for more than 60 years. Due to both its ease of use and apparent effectiveness, thrombin has become used routinely as an aid for topical hemostasis in nearly all types of surgical procedures, including but not limited to cardiovascular, orthopedic, neurologic, general, gynecologic, and dental procedures. Due to the widespread acceptance of thrombin in the surgical setting, it is conservatively estimated that at least 1 million patients in the United States are treated with topical applications of thrombin each year. Although the U.S. Food and Drug Administration (FDA) has approved a wide array of topical and biologic products to stop surgical bleeding, the only thrombin that is currently FDA approved as a stand-alone hemostatic product in the United States is derived from bovine sources. Bovine-derived thrombin has potent biologic activity in its ability to convert fibrinogen to fibrin, activate platelets, and induce vascular contraction. However, it has also been shown to induce a robust immune response following human exposure. Numerous reports have documented an array of clinical events that follow bovine thrombin exposure, which include the development of antibodies against thrombin, prothrombin, factor V, and cardiolipin. In some well-described cases, these antibodies have led to clinical syndromes that range from severe postoperative bleeding to high rates of vascular bypass graft thrombosis. Furthermore, experimental applications of bovine thrombin to various strains of mice have induced a postexposure autoimmune syndrome that was pathologically identical to lupus. Thrombin-derived products are well accepted by the surgical community for use as an aid for hemostasis, but the bovine-derived products have an unacceptably high and unnecessary association with immunologic side effects. If a nonimmunologic and effective thrombin were developed, one would expect it to be rapidly adopted by the clinical community.
PDF
