Tracheal Replacement by Allogenic Aorta in the Pig: Discussion

Tracheal Replacement by Allogenic Aorta in the Pig: DiscussionRecently, Martinod et al’ and Seguin et al showed, in sheep, that heterotopic transplantation of fresh aortic homo, but also allografts, produced a respiratory conduit sharing fundamental elements of the trachea. No acute or chronic graft rejection was observed, a finding consistent with the experience of orthotopic aortic transplantation, in which only discrete immunologic reactions were noted despite the absence of any IT.> More intriguing was the development of cartilage and of a posterior membrane. Spots of immature cartilage and newly formed cartilage, as well as regular cartilaginous rings, were seen after 1, 3, and 6 months, respectively. After 6 months, the neotrachea was stiff enough to prevent airway collapse and allow stent withdrawal. In contrast to successful grafting, the biological process described by Marti-nod et al involves guided tissue regeneration, since the transplanted tissue completely disappeared and was progressively replaced by recipient cells that generated functional tissue. They hypothesized that environmental factors may have triggered recipient cell differentiation. These results were questioned with respect to early observations that foreshortening of a grafted aortic segment may be so substantial that proximal and distal marginal native rings may be pulled in contact.
The present study attempted to confirm that the biological process observed in sheep is applicable to other mammals. The unexpectedly high stent migration rate was the major shortcoming of the study. Hence, only a small number of animals made it to a meaningful follow-up period. This short follow-up period still enabled us to study the fate of AA in terms of ischemia of rejection: indeed, since two thirds of the animals could be followed up for > 3 months, we were able to study epithelial ingrowths and cartilage formation. The high stent migration rate in pigs was unexpected, since none of the sheep had stent migration Anatomic features may account for this finding. First, the biomechanical properties of sheep and pig trachea certainly differ. In vivo, the trachea in adult sheep is approximately 35 cm in length, consisting of a total of 50 rings, and > 60% of this is extrathoracic. Adult minipigs, in contrast, have tracheas measuring approximately 15 cm, with a total of 29 to 30 rings, and > 60% is intrathoracic. Also, tracheal replacement in sheep never exceeded 30% of the tracheal length, whereas in our study at least seven pigs had more than half of their trachea replaced.

This entry was posted in Allogenic Aorta and tagged airway, lung cancer, transplants.