Cell-free vascular grafts: immunological response and vascular regeneration

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ABSTRACT Cardiovascular disease is the leading cause of death in the United States. In particular, coronary artery disease is the most common disorder, with over 350,000 bypass grafting procedures performed every year and an estimated total cost of $26 billion annually, according to the AHA. Tissue engineering approaches using native or synthetic scaffolds and even scaffold-free strategies have developed functional and implantable vascular grafts that have been tested in small and large animal models, as well as in human clinical trials 1-12. In recent years, the field has focused on engineering acellular (A)-TEVs as a potential alternative approach that may provide off-the-shelf grafts for treatment of cardiovascular disease. Recently, we reported successful development of A-TEV based on small intestinal submucosa (SIS) that was functionalized sequentially with heparin and vascular endothelial growth factor (VEGF-165, denoted as VEGF) 13,14. This A-TEV was implanted successfully into the arterial circulation of small (mice) 15 and large (sheep) animal models 13, demonstrating patency, endothelialization and regeneration of contractile vascular wall. Interestingly, VEGF-decorated grafts were populated by anti-inflammatory, M2 macrophages, while vascular grafts containing heparin alone contained mostly M1 type macrophages 15. What is more, VEGF containing grafts had an architecture that was similar to native arteries, in contract to grafts without VEGF (heparin alone), which appeared disorganized and lacked well- defined endothelium and vascular wall. This prompted us to hypothesize that successful regeneration of A-TEV in vivo may depend on generating an anti-inflammatory and pro-regenerative environment, which may be modulated (at least in part) by the immobilized VEGF (iVEGF) decorating the surface of the grafts. In this proposal, we seek to investigate this hypothesis in three specific aims. In Aim 1, we will explore the mechanism through which VEGF modulates the inflammatory response. In Aim 2, we will employ novel transgenic mouse models to monitor monocyte infiltration into the grafts and study the role of VEGF signaling on inflammation and graft regeneration. Finally, in Aim 3 we will explore the long-term patency and remodeling of A-TEV in a large, pre-clinical animal model (ovine) to assess the clinical potential of these grafts. This is a highly innovative proposal that seeks to investigate how regulating the inflammatory response may affect the patency and regeneration of vascular grafts. We also seek to determine the clinical potential of these VEGF-based A-TEVs in a large, pre-clinical animal model. Given the importance of the inflammatory response for tissue regeneration, our work may have broader implications for regenerative medicine. Our productivity during the last funding cycle (35 publications), the promising discoveries including mechanistic and translational studies that originated from our laboratory, and the excellent team of investigators that we assembled inspires confidence that the work can be carried out successfully in our laboratories.