Tissue engineering of pulmonary heart valves on allogenic acellular matrixconduits - In vivo restoration of valve tissue

Background-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 ma trix scaffolds of pulmonary heart valves after in vitro seeding with the us e of autologous cells in a sheep model. Methods non Results-Allogenic heart valve conduits were acellularized by a 48-hour trypsin/EDTA incubation to extract endothelial cells and myofibrobl asts. 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 resti tution on the valve surface. The in vivo function was tested in a sheep mod el of orthotopic pulmonary valve conduit transplantation. Three of 4 unseed ed control valves and 5 of 6 tissue-engineered valves showed normal functio n up to 3 months. Unseeded allogenic acellular control valves showed pal-ti al degeneration (2 of 4 valves) and no interstitial valve tissue reconstitu tion. Tissue-engineered valves showed complete histological restitution of valve tissue and confluent endothelial surface coverage in all cases. Immun ohistological analysis revealed cellular reconstitution of endothelial cell s (von Willebrand factor), myofibroblasts (alpha -actin), and matrix synthe sis (procollagen I). There were histological signs of inflammatory reaction s to subvalvar muscle leading to calcifications, but these were not found i n valve and pulmonary artery tissue. Conclusions-The in vitro tissue-engineering approach using acellular matrix conduits lends to the in vivo reconstitution of viable heart valve tissue.