Effect of cryopreservation period on rat tracheal allografts

Background: The effect of cryopreservation on tracheal allogenicity is still unclear. Therefore, in this study, we assessed the effect of cryopreservation period on tracheal allografts in 62 rats. Methods: Each transplant consisted of a 3-ring segment of the trachea harvested from 8 Lewis rats, immersed in preservation solution, and cryopreserved and stored in a Bicell biofreezing vessel in a deep freezer at -80 degreesC. Six tracheal grafts without cryopreservation that underwent a heterotopically syngeneic transplantation into the omentum served as controls. Forty-eight tracheal segments were randomly assigned to 8 groups according to period of cryopreservation, which ranged from 0 to 12 months (0, 0.5 [2 weeks], 1, 2, 3, 6, 9 and 12 months). The cryopreserved grafts were then thawed and heterotopically implanted into the omentum of recipient Brown-Norway rats. After 28 days, the tracheal segments were then evaluated histologically. Results: All isografts in Group 1 were intact, whereas the allografts undergoing a particularly shorter period of cryopreservation showed a more stenotic lumen. Prolonged periods of cryopreservation tended to show decreasing tendencies of viability of chondrocytes, mononuclear cell infiltration and sub-epithelial thickness, whereas all allografts showed a uniformly denuded epithelium, irrespective of the length of cryopreservation. Conclusions: A longer period of cryopreservation may help to maintain a better patency of tracheal allografts by preventing an allogeneic response. Reduced tracheal allogenicity may be associated with a decreased viability of chondrocytes by cryopreservation.