Thoracic Surgery Directors Association Award. Bone marrow as a cell source for tissue engineering heart valves

BACKGROUND: This study was designed to assess the feasibility of using ovine bone marrow-derived mesenchymal stem cells to develop a trileaflet heart valve using a tissue engineering approach. METHODS: Bone marrow was aspirated from the sternum of adult sheep. Cells were isolated using a Ficoll gradient, cultured, and characterized based on immunofluorescent staining and the ability to differentiate down a specific cell lineage. Two million cells per centimeter squared were delivered onto a polyglycolic acid (PGA), poly-4-hydroxybutyrate (P4HB) composite scaffold and cultured for 1 week before being transferred to a pulse duplicator for an additional 2 weeks. The tissue-engineered valves were assessed by histology, scanning electron microscopy, and biomechanical flexure testing. RESULTS: Cells expressed SH2, a marker for mesenchymal stem cells, as well as specific markers of smooth muscle cell lineage including alpha-smooth muscle actin, desmin, and calponin. These cells could be induced to differentiate down an adipocyte lineage confirming they had not fully committed to a specific cell lineage. Preliminary histologic examination showed patchy surface confluency confirmed by scanning electron microscopy, and deep cellular material. Biomechanical flexure testing of the leaflets showed an effective stiffness comparable to normal valve leaflets. CONCLUSIONS: Mesenchymal stem cells can be isolated noninvasively from the sternum of sheep and can adhere to and populate a PGA/P4HB composite scaffold to form "tissue" that has biomechanical properties similar to native heart valve leaflets. Thus, bone marrow may be a potential source of cells for tissue engineering trileaflet heart valves, particularly in children with congenital heart disease.