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

Background. The presence of viable cells may contribute to increased homogr aft valve durability. These cells may be of infiltrating recipient or persi sting 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 we re acquired from patients whose graft had been explanted at reoperation or at autopsy. The period of implantation varied from 14 days to 70 months. Fr ozen sections were made and alternately examined with hematoxylin and eosin staining and in situ hybridization. Male cells were distinguished from fem ale using a biotinylated Y-chromosome-specific deoxyribonucleic acid probe. Results. No endothelial cells were found. Thirty percent of the leaflets sh owed large acellular zones and 30% were completely acellular. The homograft arterial wall was occupied by a vast majority of penetrating host fibrobla sts in 80% of the studied specimens. Donor and recipient cells were coexist ent 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 h omograft pathology. The technique of in situ hybridization may provide an i ndispensable contribution in further homograft research. (C) 1998 by The So ciety of Thoracic Surgeons.