Transplantation of the cryopreserved tracheal allograft in growing rabbits: effect of immunosuppressant

Transplantation of a cryopreserved tracheal allograft is considered to be a useful strategy in treating congenital tracheal stenosis. Recent reports of tracheal transplant experiments have shown that the antigenicity of the trachea is decreased by cryopreservation, making transplantation of the trachea possible. However, we reported that cryopreserved tracheal allografts exhibited favorable patency, but no significant growth in an animal model. In this study, we hypothesize that an immune reaction may play a role in the failure of an allograft’s growth. Each allograft was harvested from 90- to 120-day-old Japanese rabbits, immersed in preservation solution, stored in a programmable freezer until it reached −80˚C, and then kept for 1 month. Orthotopic tracheal transplantation of four tracheal rings in an end-to-end fashion was performed in age-matched young rabbits. Ten recipients were classified into three groups: a group provided with tacrolimus (FK-506) as an immunosuppressant (n = 6), a group receiving a graft irradiated before transplantation (n = 2), and a control group (n = 2). All grafts were evaluated 4–8 weeks after transplantation (tacrolimus group: 3–13 weeks). Body weight gain of the tacrolimus group was less than that of the other two groups. All grafts were well incorporated with the recipients macroscopically, but the grafts showed no growth in diameter. Microscopic examination showed inflammation in the tacrolimus and control groups temporarily. The irradiated allografts had marked fibrosis in the subepithelium. Although calcification of the tracheal cartilage was present in all transplanted allografts, the difference between groups was not significant. Patency of the cryopreserved tracheal allografts was favorable but no growth occurred even with an immunosuppressant. Further studies are required to address the growth of the tracheal allograft.