Tracheal regeneration: Myth or fact?

Replacement of the esophagus with fascial flap-wrapped allogenic aorta

BACKGROUND

Segmental replacement of the esophagus (SRE) is challenging. Allogenic aorta (AA) has shown promising remodeling abilities when used as an esophageal substitute. The aim of this study was to evaluate the feasibility and results of esophageal replacement with fascial flap-wrapped AA segments in a novel rabbit model.

MATERIALS AND METHODS

Seven Geant des Flandres rabbits and one New Zealand rabbit served as thoracic aorta donors, and 25 New Zealand rabbits were used as recipients. One to 3 wk before esophageal replacement either cryopreserved or fresh thoracic aortic segments were wrapped in thoracic wall fascia to generate revascularization. In an attempt to optimize the model, step-by-step modifications concerning perioperative and postoperative management of the recipients were made as results accumulated. Microscopic evaluation was focused on the viability of aortic segments and neoangiogenesis originating from the fascia.

RESULTS

Survival after SRE was poor. Most recipients died within 1 wk, mainly from upper digestive tract hypomotility. Microscopically, AAs were severely necrosed. In one recipient sacrificed on day 16, the edges of the graft became evanescent. In these areas, esophageal reepithelialization directly covered the fascia, in which unexpected smooth muscle cells were found, suggestive of the first stages of esophageal remodeling of the graft.

CONCLUSIONS

Results for SRE using fascial-wrapped AAs in rabbits were disappointing. The transposition of this approach to larger animals might result in longer survival, increasing the possibility for more complete graft remodeling.

Immune tolerance of epithelium-denuded-cryopreserved tracheal allograft

OBJECTIVES

Animal and clinical studies have demonstrated the feasibility of tracheal allograft transplantation after a revascularization period in heterotopy, thus requiring immunosuppressive therapy. Given the key role of the respiratory epithelium in the immune rejection, we investigated the consequence of both epithelium denudation and cryopreservation in immune tolerance of tracheal allograft in a novel rabbit model.

METHODS

Five adult female New Zealand rabbits served as donors of tracheas that were denuded of their epithelium and then cryopreserved, and 13 males were used as recipients. Following graft wrap using a lateral thoracic fascial flap, allograft segments 20 mm in length with (n = 9) or without (n = 4) insertion of an endoluminal tube were implanted under the skin of the chest wall. The animals did not receive any immunosuppressive drugs. Sacrifices were scheduled up to 91 days. Macroscopic and microscopic examinations and detection of apoptotic cells by immunohistochemical staining (Apostain) were used to study the morphology, stiffness, viability and immune rejection of allografts.

RESULTS

There were no postoperative complications. Grafted composite allografts displayed satisfactory tubular morphology provided that an endoluminal tube was inserted. All rabbits were found to have an effective revascularization of their allograft and a mild non-specific inflammatory infiltrate with no significant lymphocyte infiltration. Cartilage rings showed early central calcification deposit, which increased over time, ensuring graft stiffness. Apoptosis events observed into the allograft cells were suggestive of minimal chronic rejection.

CONCLUSIONS

Our results demonstrated that the epithelium-denuded-cryopreserved tracheal allograft implanted in heterotopy displayed satisfactory morphology, stiffness and immune tolerance despite the absence of immunosuppressive drugs. This allograft with a fascial flap transferable to the neck should be investigated in the setting of tracheal replacement in rabbits. Similar studies need to be conducted in bigger mammals before considering clinical applications.