Tissue Engineering of Pulmonary Heart Valves on Allogenic Acellular Matrix Conduits : In Vivo Restoration of Valve Tissue

TLDR

Tissue engineering with autologous vascular wall cells offers a novel approach to biological heart valve replacement. The study investigates a new method for preparing allogenic acellular pulmonary valve scaffolds and seeding them with autologous cells in a sheep model. The authors acellularized valves with trypsin/EDTA, then reseeded the upper surface with autologous myofibroblasts for six days followed by endothelial cells for two days, and evaluated the constructs in sheep orthotopic pulmonary valve transplants. The tissue‑engineered valves achieved complete histological restitution, confluent endothelial coverage, and normal function in 5 of 6 sheep, whereas unseeded controls showed partial degeneration, demonstrating that the acellular scaffold with autologous reseeding restores viable valve tissue in vivo.

Abstract

Tissue engineering using in vitro-cultivated autologous vascular wall cells is a new approach to biological heart valve replacement. In the present study, we analyzed a new concept to process allogenic acellular matrix scaffolds of pulmonary heart valves after in vitro seeding with the use of autologous cells in a sheep model.Allogenic heart valve conduits were acellularized by a 48-hour trypsin/EDTA incubation to extract endothelial cells and myofibroblasts. The acellularization procedure resulted in an almost complete removal of cells. After that procedure, a static reseeding of the upper surface of the valve was performed sequentially with autologous myofibroblasts for 6 days and endothelial cells for 2 days, resulting in a patchy cellular restitution on the valve surface. The in vivo function was tested in a sheep model of orthotopic pulmonary valve conduit transplantation. Three of 4 unseeded control valves and 5 of 6 tissue-engineered valves showed normal function up to 3 months. Unseeded allogenic acellular control valves showed partial degeneration (2 of 4 valves) and no interstitial valve tissue reconstitution. Tissue-engineered valves showed complete histological restitution of valve tissue and confluent endothelial surface coverage in all cases. Immunohistological analysis revealed cellular reconstitution of endothelial cells (von Willebrand factor), myofibroblasts (alpha-actin), and matrix synthesis (procollagen I). There were histological signs of inflammatory reactions to subvalvar muscle leading to calcifications, but these were not found in valve and pulmonary artery tissue.The in vitro tissue-engineering approach using acellular matrix conduits leads to the in vivo reconstitution of viable heart valve tissue.