Paper Summary – Week 6
Sutherland et al. (2005 Circulation) “From Stem Cells to Viable Autologous Semilunar Heart Valve.”

Results of heart valve replacement surgery are complicated by the morbidity associated with lifelong anticoagulation of mechanical valves and the limited durability of bioprostheses. This problem may be addressed by providing living, autologous biological structures which do not require anticoagulation, yet retain the capacity to remodel and repair, obviating the need for late valve replacement.
Mesenchymal stem cells (MSCs) were isolated from ovine bone marrow and characterized by their morphology and antigen expression through immunocytochemistry (using the avidinbiotin-peroxidase method with monoclonal anti-vimentin, anti-α-SMA, and anti-von Willebrand factor primary antibodies), flow cytometry, and capacity to differentiate into multiple cell lineages. Adipocytes were stained with oil-red O, and the mineral was stained with silver by the method of von Kossa. A biodegradable scaffold was developed and characterized by its tensile strength and stiffness as a function of time in cell-conditioned medium, and was evaluated by using needle punching. Autologous semilunar heart valves were created in vitro using MSCs and the biodegradable scaffold and were implanted into the pulmonary position of sheep on cardiopulmonary bypass, and were evaluated by echocardiography at implantation and after 4 months in vivo, explanted (at 4 and 8 months), and examined by histology and immunohistochemistry.
Ovine MSCs expressed β1 integrin CD29 but failed to express the thymocyte and lymphocyte marker CD4, endothelial antigen CD31, and von Willebrand factor. At 24 weeks, tensile strength was ~30% of the initial strength of the scaffold, whereas the estimated burst strength was still 270 mm Hg for a 21-mm-diameter conduit. Valves displayed a maximum instantaneous gradient of 17.2±1.33 mm Hg, a mean gradient of 9.7±1.3 mm Hg, an effective orifice area of 1.35±0.17 cm2, and trivial or mild regurgitation at implantation. Histology showed disposition of extracellular matrix and distribution of cell phenotypes in the engineered valves reminiscent of that in native pulmonary valves.
Stem-cell tissue-engineered heart valves can be created from MSCs in combination with a biodegradable scaffold and function satisfactorily in vivo for periods of >4 months. Although the long-term durability of the valves depends on many factors, such valves can undergo extensive remodeling in vivo to resemble native heart valves.