The study demonstrates that endothelial progenitor cells (EPCs) can be isolated from peripheral blood, expanded ex vivo, and used to seed decellularized vascular grafts, resulting in functional neovessels with long-term patency. EPCs were isolated from sheep, expanded in culture, and seeded onto decellularized porcine iliac vessels. These grafts were then preconditioned with varying shear stresses to optimize endothelial cell retention. When implanted into sheep, EPC-seeded grafts remained patent for up to 130 days, while non-seeded grafts occluded within 15 days. The EPC-seeded grafts exhibited contractile activity and nitric oxide (NO)-mediated vascular relaxation similar to native carotid arteries, which has not been previously reported for tissue-engineered small diameter grafts. These results suggest that EPCs can function similarly to arterial endothelial cells, providing a non-thrombogenic luminal surface that enhances vascular graft survival. The study also shows that EPCs can maintain their endothelial phenotype for up to 20 passages, indicating their stability and feasibility for clinical application. Additionally, EPCs may have broader applications in tissue engineering and vascular disease treatment due to their unique properties. The study highlights the importance of endothelializing vascular grafts for long-term patency and suggests that EPCs could replace autologous endothelial cells in grafts, eliminating the need for vessel sacrifice. The results indicate that EPC-seeded grafts have vasomotor properties similar to native carotid arteries, potentially leading to long-term patency. The study also explores the potential sources of smooth muscle cells in the neo-intima of the graft, including migration from adjacent arteries and transdifferentiation of EPCs. Overall, the study demonstrates the feasibility of using EPCs to create functional neovessels with long-term patency, offering a promising approach for tissue engineering small diameter blood vessels.The study demonstrates that endothelial progenitor cells (EPCs) can be isolated from peripheral blood, expanded ex vivo, and used to seed decellularized vascular grafts, resulting in functional neovessels with long-term patency. EPCs were isolated from sheep, expanded in culture, and seeded onto decellularized porcine iliac vessels. These grafts were then preconditioned with varying shear stresses to optimize endothelial cell retention. When implanted into sheep, EPC-seeded grafts remained patent for up to 130 days, while non-seeded grafts occluded within 15 days. The EPC-seeded grafts exhibited contractile activity and nitric oxide (NO)-mediated vascular relaxation similar to native carotid arteries, which has not been previously reported for tissue-engineered small diameter grafts. These results suggest that EPCs can function similarly to arterial endothelial cells, providing a non-thrombogenic luminal surface that enhances vascular graft survival. The study also shows that EPCs can maintain their endothelial phenotype for up to 20 passages, indicating their stability and feasibility for clinical application. Additionally, EPCs may have broader applications in tissue engineering and vascular disease treatment due to their unique properties. The study highlights the importance of endothelializing vascular grafts for long-term patency and suggests that EPCs could replace autologous endothelial cells in grafts, eliminating the need for vessel sacrifice. The results indicate that EPC-seeded grafts have vasomotor properties similar to native carotid arteries, potentially leading to long-term patency. The study also explores the potential sources of smooth muscle cells in the neo-intima of the graft, including migration from adjacent arteries and transdifferentiation of EPCs. Overall, the study demonstrates the feasibility of using EPCs to create functional neovessels with long-term patency, offering a promising approach for tissue engineering small diameter blood vessels.