(453h) Implantation of Vascular Grafts Made From Small Intestinal Sub-Mucosa and Hair Follicle Stem Cells in an Ovine Animal Model

Introduction: Cardiovascular disease is the leading cause of mortality worldwide. Regarded as the therapeutic gold standard, treatment by autologous vein grafting has several technical and patient-related risks.  Alternatively, engineered grafts have shown to be one promising solution. Synthetic grafts have complications with compatibility, whereas natural, cell-seeded biomaterial scaffolds have been proven to perform better at the blood-material-interface.  In this study, we aim to engineer fully functional and implantable arterial grafts made from human hair follicle derived smooth muscle cells (HF-SMC), ovine pulmonary artery endothelial cells, and small intestine submucosa (SIS). 

Materials and Methods: Tubular tissues constructs were prepared from SIS and HF-SMC were incorporated in the vessel wall using fibrin glue.  In order to promote living tissue development and improve the function of our TEVs, we mechanically stimulated the HF-SMCs within the construct using biomechanical forces and the stimulatory effects of TGFβ-1, insulin, and ascorbic acid. Using a customized bioreactor, arterial shear stress was achieved within our constructs. Prior to implantation, we investigated in vivo effects on parameters sustaining long-term patency of our grafts with the use of an arterio-venous shunt bypass model that we developed in our laboratory.  Long-term patency of SIS grafts was evaluated when implanted as an interpositional graft in an ovine model, and followed for up to 12 weeks.

Results and Discussion: The grafts exhibited high burst pressure (1123327 mmHg, n=5) and similar compliance as compared to the native artery within physiological range (SIS=8.42+/-4.51, n=7; artery=8.62+/-2.99%, n=4, P>0.05, 0-120mmHg).  Under dynamic strain, HF-SMC aligned circumferentially and showed collagen and elastin synthesis, as evidenced by histological examination. As expected, application of shear stress induced alignment of endothelial cells in the lumen in the direction of flow. The implanted tissues were monitored biweekly using Doppler ultrasound to document patency and measure blood flow rates through the grafts. At 4 and 12 weeks we also performed angiography to examine patency and measure blood flow rates through the grafts. After angiography the tissues were explanted and processed for histology and immunostaining. We found that all implants remained patent, contained a uniform endothelial monolayer and a robust vascular wall with numerous smooth muscle cells. Explanted grafts showed infiltration of host cells, robust ECM remodeling and vascular contractility similar to that of ovine arteries, demonstrating that our strategy was successful in engineering implantable arterial substitutes.

Conclusions: Our results demonstrate that SIS based vascular grafts with SMC from human HF-derived mesenchymal stem cells can be implanted in the arterial system of a large animal model. The patency of the grafts and their capacity for remodeling and development of vascular function suggest that this approach is very promising and may be of clinical significance.