Tissue chimerism in human cryopreserved homograft valve explants demonstrated by in situ hybridization

Background. The presence of viable cells may contribute to increased homograft valve durability. These cells may be of infiltrating recipient or persisting donor origin. In this study, in situ hybridization was used to assess the origin of cells in cryopreserved homograft valve explants. Methods. A total of 10 homografts with a donor–recipient gender mismatch were acquired from patients whose graft had been explanted at reoperation or at autopsy. The period of implantation varied from 14 days to 70 months. Frozen sections were made and alternately examined with hematoxylin and eosin staining and in situ hybridization. Male cells were distinguished from female using a biotinylated Y–chromosome-specific deoxyribonucleic acid probe. Results. No endothelial cells were found. Thirty percent of the leaflets showed large acellular zones and 30% were completely acellular. The homograft arterial wall was occupied by a vast majority of penetrating host fibroblasts in 80% of the studied specimens. Donor and recipient cells were coexistent in the wall in 60% of the studied specimens and in 50% of the leaflets. In 30% only host cells could be identified. Conclusions. This finding of tissue chimerism may lead to new insights in homograft pathology. The technique of in situ hybridization may provide an indispensable contribution in further homograft research.