Pii: S1010-7940(99)00145-1

Objectives: The purpose of this study was to determine the appropriate cryopreservation period of tracheal allografts based on morphological and immunological ®ndings and to test the possibility of tracheal transplantation in rats using cryopreserved allografts without immunosuppression. Methods: Morphological and immunological studies were performed to compare the differences between non-cryopreserved grafts and cryopreserved grafts. Orthotopic tracheal transplantation using cryopreserved allografts, non-cryopreserved allografts, and non-cryopreserved autografts was performed and the rejection score of each group was evaluated. Results: Epithelial cells were lost when the grafts were cryopreserved for more than 20 days. Immunohistochemical staining of the trachea revealed that the MHC classII antigen was expressed on normal epithelium. These ®ndings suggest that cryopreservation for more than 20 days decreased the antigeneicity of allografts because of epithelial desquamation. All rats that received allografts cryopreserved for more than 20 days survived until the scheduled sacri®ce day. Microscopically, cryopreserved allografts that had been preserved for more than 20 days had a signi®cantly lower rejection score than that of non-cryopreserved allografts (P , 0:05). Conclusions: We conclude that the appropriate period for cryopreservation of allografts would be 20 days or more, because cryopreservation for more than 20 days depleted epithelium, which possessed the MHC classII antigen. Therefore, a longer period of cryopreservation decreases the antigeneicity of allografts. Rat tracheal transplantations using cryopreserved allografts is possible without immunosuppression when the grafts have been cryopreserved for more than 20 days. q 1999 Elsevier Science B.V. All rights reserved.