Effect of cryopreservation on the presence of endothelial cells on human valve allografts.

Cryopreserved human allograft valves are useful in a variety of cardiac operations. The presence or absence of endothelial cells on allografts may be important in determining immunogenicity and ultimate graft longevity. The purpose of this study was to determine whether endothelial cells are present on cryopreserved human allografts. Portions of cryopreserved allografts (35 valve leaflets, 96 pieces of arterial wall) not used at operation were studied. For comparison, untreated tissues (44 valve leaflets, 46 pieces of arterial wall) were obtained from structurally normal hearts and lungs removed or inserted at the time of transplantation and from pathologic tissues obtained during operations for congenital heart defects. A monolayer of cells from the luminal surface of each specimen was harvested by means of a Hautchen preparation. The monolayer was stained with fluorescein isothiocyanate-labeled Ulex europaeus I, a lectin with strong affinity for human endothelium. Positive staining with fluorescein was considered to be evidence for the presence of human endothelium. Endothelial cells were observed on 21 of 131 (16%) cryopreserved allograft specimens and on 70 of 90 (78%) untreated tissues (p < 0.001). These results show that cryopreservation typically results in the loss of endothelium from aortic and pulmonary valve allografts. These findings may have important implications for the immunologic response of the host to allograft implantation.