Airway transplantation using aortic allografts: a 'hot topic'

We read with great interest the article published by Wurtz et al. [1]. As airway transplantation remains a ‘hot topic’ in the field of thoracic surgery, some key points in the manuscript should be clarified by the authors. In the discussion, they wrote: ‘Our results showed that the composite construct, juxtaposition of recipient's fascial vascular carrier as an outer layer and donor's aorta as an inner layer, had transformed into a chimeric tube-shaped organ including a unique transferable vascular pedicle, with early neoangiogenesis of the aortic component’. With respect to the authors' work, the short follow-up should make any conclusion very questionable. Indeed, the follow-up was inferior to 25 days for the majority (18/19) of animals. In addition, 42% (8/19) of the recipient rabbits experienced early complications, thus obscuring the issue. On the other hand, the term ‘chimeric’ seems to be inappropriate compared with the study by Delaere et al. [2] where chimerism occurred after the recipient buccal mucosa was introduced into the tracheal allograft placed in a heterotopic position. In contrast, the aortic graft could be considered as a perfect tracheal matrix that allows the colonization by recipient cells prefiguring the regeneration of a mature tracheal tissue. This type of regenerative mechanism can be observed within the graft only if it is situated in a ‘tracheal environment’. ‘The grafts, however, showed no biomechanical properties allowing a potential tracheal replacement without the need for postoperative silicone stenting’. How did the authors investigate the biomechanical properties of the aortic grafts? This is not made clear in the ‘Materials and methods’ section. Did the authors believe that it was possible to obtain a rigid structure with regenerated cartilage after only 5–24 days of follow-up in 18/19 animals? ‘In the present investigation, using FISH analysis for both X and Y chromosome identification, we demonstrated that the migrating cells present in the aortic component of the construct were derived from the recipient’. As this outcome has been well established on a sheep model since 2005, did the authors suppose that it could be different in another animal species [3]? ‘Future issues of particular interest will be to investigate whether the efficient neoangiogenesis, with no significant ischaemia during the initial phase of revascularization, that we observed: (i) prevents the graft from axial contraction and (ii) facilitates both regeneration of the epithelium and the mature cartilage regeneration into the graft, which was previously observed in other mammals’. Contrary to the authors' assertion, we believe that the axial contraction of aortic allografts could be considered as a favourable phenomenon. Indeed, we have theorized that tracheal healing after replacement with biological scaffolds (like aortic allografts) was the consequence of a mixed phenomenon associating a tracheal approximation and a tracheal regeneration [4]. Finally, a muscle flap could be a better option than a fascial flap in order to promote revascularization. This has been clearly demonstrated in our experimental and clinical phases of airway transplantation using aortic allografts [5, 6].