Cartilaginous injury limits cryopreservation of tracheal isograft

Histological recovery of tracheal grafts after cryopreservation was investigated using a rat heterotopic tracheal transplant model in order to evaluate the clinical applicability of tracheal cryopreservation.

Heterotopic syngeneic tracheal transplantation was performed between F344 rats. Recipient animals received either a non-cryopreserved or a cryopreserved tracheal graft for direct comparison with regard to the effect of cryo-injury. In the non-cryopreserved group (CP(-)), tracheal segments were transplanted syngeneically between F344 rats immediately after harvest. Grafts were implanted into the abdominal space and wrapped with the greater omentum. In the cryopreserved group (CP(+)), grafts were implanted after cryopreservation for 7 days at -85 degrees C. Recipient rats were killed on days 7, 14, 21, 28, and at 2 months after surgery. Epithelial regeneration and cartilage changes were evaluated using a semiquantitative four grade scoring system.

Squamous epithelium without ciliated structure was observed on day 7 in both groups. Bronchial epithelium was then regenerated gradually and normally ciliated epithelium was observed on day 28 in both groups. The condition of the epithelium was still well maintained in the CP(-) group at 2 months post-transplantation; however, a severe epithelial defect was observed in the CP(+) group. Bronchial cartilage showed a normal shape and mostly viable chondrocytes with proliferative cell nuclear antigen (PCNA) positive staining at all time points in the CP(-) group until 2 months after surgery. However, in the CP(+) group, a massive loss of viable chondrocytes was observed at 2 months post-transplantation. Macroscopically, CP(+) grafts showed a diminished structure without satisfactory airway lumen at 2 months.

The epithelium of a tracheal graft can be temporarily recovered after implantation followed by 7 days cryopreservation. However, bronchial cartilage may be severely damaged by freezing, which results in late destruction with loss of viable chondrocytes. It is suggested here that establishing a method of safe cryopreservation for tracheal cartilage will be imperative to making tracheal cryopreservation possible.