Tracheal allotransplantation maintaining cartilage viability with long-term cryopreserved allografts

Background. Cartilage viability of a cryopreserved tracheal allograft seems to affect graft function and durability. We previously reported the influence of warm ischemia and cryopreservation on cartilage viability of tracheal allografts. For the clinical application of tracheal allotransplantation, it is essential to preserve grafts for a long time. In this study, we assessed cartilage viability of tracheal allografts after long-term cryopreservation in transplantation models. Methods. The tracheas were harvested from Lewis rats. The grafts were frozen to −80°C in a programmable freezer immediately after being harvested and were then stored in liquid nitrogen (−196°C) for different lengths of preservation (1, 2, 6, 9, 12, 18, and 24 months; n for each GROUP = 8). Cartilage viability was evaluated by estimating proteoglycan synthesis. After harvest or thawing of the tracheas, the cartilage was labeled with 4 μCi/mL of Na235SO4. Specimens were then hydrolyzed in 0.5 mol/L NaOH, and a solution of the extracts was then counted by a liquid scintillation counter. 35Sulfur incorporation before and after cryopreservation was examined in each group. Tracheal allotransplantation was performed using Lewis rats as donors and Brown Norway rats as recipients. Results. The average 35S incorporation in the cartilage before cryopreservation was 224 ± 17 disintegrations per minute per milligram of tissue protein. The average 35S incorporation in the cartilage after cryopreservation decreased to 67% to 76% compared with that before cryopreservation. There were no significant differences among the groups in 35S incorporations after cryopreservation. Histologic examination after transplantation revealed normal tracheal cartilage in all groups. Conclusions. The viability of tracheal cartilage after cryopreservation decreased to 67% to 76%. There were no significant differences in viability of cartilage among the tracheas after different lengths of cryopreservation. Tracheal allotransplantation after long-term cryopreservation can be safely performed in the rat model.