Limits...
Airway transplantation: a challenge for regenerative medicine.

Martinod E, Seguin A, Radu DM, Boddaert G, Chouahnia K, Fialaire-Legendre A, Dutau H, Vénissac N, Marquette CH, Baillard C, Valeyre D, Carpentier A, FREnch Group for Airway Transplantation (FREGA - Eur. J. Med. Res. (2013)

Bottom Line: In 1997, we proposed a novel approach: the use of aortic grafts as a biological matrix for extensive airway reconstruction.In vivo regeneration of epithelium and cartilage were demonstrated in animal models.Favorable results obtained in pioneering cases have to be confirmed in larger series of patients with extensive tracheobronchial diseases.

View Article: PubMed Central - HTML - PubMed

Affiliation: Assistance Publique-Hôpitaux de Paris, Hôpitaux Universitaires Paris-Seine-Saint-Denis, Avicenne Hospital, Department of Thoracic and Vascular Surgery, Paris 13 University, Sorbonne Paris Cité, Faculty of Medicine SMBH, Bobigny, France. emmanuel.martinod@avc.aphp.fr.

ABSTRACT
After more than 50 years of research, airway transplantation remains a major challenge in the fields of thoracic surgery and regenerative medicine. Five principal types of tracheobronchial substitutes, including synthetic prostheses, bioprostheses, allografts, autografts and bioengineered conduits have been evaluated experimentally in numerous studies. However, none of these works have provided a standardized technique for the replacement of the airways. More recently, few clinical attempts have offered encouraging results with ex vivo or stem cell-based engineered airways and tracheal allografts implanted after heterotopic revascularization. In 1997, we proposed a novel approach: the use of aortic grafts as a biological matrix for extensive airway reconstruction. In vivo regeneration of epithelium and cartilage were demonstrated in animal models. This led to the first human applications using cryopreserved aortic allografts that present key advantages because they are available in tissue banks and do not require immunosuppressive therapy. Favorable results obtained in pioneering cases have to be confirmed in larger series of patients with extensive tracheobronchial diseases.

Show MeSH
Histologic examination of cryopreserved aortic allograft at 2 months (sheep model) showing regenerated cartilage (hematoxylin and eosin staining; original magnification ×10).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3750833&req=5

Figure 2: Histologic examination of cryopreserved aortic allograft at 2 months (sheep model) showing regenerated cartilage (hematoxylin and eosin staining; original magnification ×10).

Mentions: The complex approach of ex vivo tissue engineering has been unable to recreate functional regenerated tissues or organs in most attempts. Thus, some investigators have proposed the use of the human body as a natural bioreactor to achieve in vivo tissue engineering [18]. In 1997, we proposed a different approach to airway transplantation. During our preliminary work on tracheal replacement, we noticed that one structure had been ignored: the aorta. This biological structure has major advantages; it is a tubular conduit with a diameter similar to the trachea’s. Moreover, it is well-known for its solidity, elasticity and resistance to infection. On the other hand, it has a major disadvantage: the risk of collapse. However, this can be avoided by the use of a stent. Our work has been performed in successive steps using as tracheal substitutes aortic autografts, then fresh and cryopreserved allografts [19-25]. No complications occurred in the majority of animals during a maximum follow-up of 3 years. The macroscopic evaluation was very surprising. First, there was no stenosis in cases where a stent was inserted into the graft. Second, there was an unexpected tracheal regeneration, including epithelium and cartilage (Figures 1 and 2). This regenerative process was also observed after replacement of the carina. At the beginning of our experiments, we used a nitinol stent. Facing the regeneration of cartilage, we decided to remove the stent. It was impossible, however, because of major adhesions following the use of this type of stent. As a result, we placed a silicone stent into the graft. Removal was easy, and there were no clinical consequences. This showed that the regenerated cartilage was functional. Histological examinations showed a progressive regeneration of epithelium from an inflammatory tissue to a squamous, mixed and mucociliary epithelium. The phenomenon we observed was similar to that seen in the repair described by others after epithelium destruction. This is a well-documented process arising from basal and mucosal cells of the native trachea. At all intervals, we found residual elastic fibers from the aortic tissue. The inflammatory process was associated with reconstruction by fibroblasts secreting collagen. To discover whether cartilage came from aortic cells or from recipient cells, we decided in the six last animals in the allograft study to implant aorta from male sheep to trachea of female sheep and to search for SRY genes in the newly formed cartilage. Using a type 2 collagen marker, we demonstrated that newly formed structures within the aortic graft were indeed cartilage. PCR studies showed SRY amplification for male specimens but no amplification for female specimens or the newly formed cartilage. This clearly showed that newly formed cartilage originated not from aortic cells but from recipient cells. Today we know that this process did not come from aortic cells. Furthermore, chondrocytes cannot migrate, and newly formed cartilage was distant from the native trachea. These two points evidently refute the possibility of regeneration from the native cartilage. The last hypothesis is that regeneration came from mesenchymal cells, local cells or, most probably, circulating stem cells from bone marrow, as this has been demonstrated for the repair of other organs. This was recently confirmed by our group in a rabbit model [26]. Cryopreserved aortic allograft seems to be the better option in the view of human applications because of availability in tissue banks, permanent storage and no need for immunosuppression. We demonstrated that regeneration of a functional tissue could also be obtained after tracheal replacement with cryopreserved aortic allografts, in contrast to decellularized or glutaraldehyde-treated aortic grafts [25]. The regenerative process followed the same pattern as previously described for fresh allografts. These results were confirmed in a pig model as discussed by others [27-29]. We also demonstrated that an arterial allograft could be a valuable bronchial substitute with results similar to those obtained after tracheal replacement [30]. We theorized that airway healing after replacement with biological scaffolds was the consequence of a mixed phenomenon associating airway approximation and regeneration [31].


Airway transplantation: a challenge for regenerative medicine.

Martinod E, Seguin A, Radu DM, Boddaert G, Chouahnia K, Fialaire-Legendre A, Dutau H, Vénissac N, Marquette CH, Baillard C, Valeyre D, Carpentier A, FREnch Group for Airway Transplantation (FREGA - Eur. J. Med. Res. (2013)

Histologic examination of cryopreserved aortic allograft at 2 months (sheep model) showing regenerated cartilage (hematoxylin and eosin staining; original magnification ×10).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3750833&req=5

Figure 2: Histologic examination of cryopreserved aortic allograft at 2 months (sheep model) showing regenerated cartilage (hematoxylin and eosin staining; original magnification ×10).
Mentions: The complex approach of ex vivo tissue engineering has been unable to recreate functional regenerated tissues or organs in most attempts. Thus, some investigators have proposed the use of the human body as a natural bioreactor to achieve in vivo tissue engineering [18]. In 1997, we proposed a different approach to airway transplantation. During our preliminary work on tracheal replacement, we noticed that one structure had been ignored: the aorta. This biological structure has major advantages; it is a tubular conduit with a diameter similar to the trachea’s. Moreover, it is well-known for its solidity, elasticity and resistance to infection. On the other hand, it has a major disadvantage: the risk of collapse. However, this can be avoided by the use of a stent. Our work has been performed in successive steps using as tracheal substitutes aortic autografts, then fresh and cryopreserved allografts [19-25]. No complications occurred in the majority of animals during a maximum follow-up of 3 years. The macroscopic evaluation was very surprising. First, there was no stenosis in cases where a stent was inserted into the graft. Second, there was an unexpected tracheal regeneration, including epithelium and cartilage (Figures 1 and 2). This regenerative process was also observed after replacement of the carina. At the beginning of our experiments, we used a nitinol stent. Facing the regeneration of cartilage, we decided to remove the stent. It was impossible, however, because of major adhesions following the use of this type of stent. As a result, we placed a silicone stent into the graft. Removal was easy, and there were no clinical consequences. This showed that the regenerated cartilage was functional. Histological examinations showed a progressive regeneration of epithelium from an inflammatory tissue to a squamous, mixed and mucociliary epithelium. The phenomenon we observed was similar to that seen in the repair described by others after epithelium destruction. This is a well-documented process arising from basal and mucosal cells of the native trachea. At all intervals, we found residual elastic fibers from the aortic tissue. The inflammatory process was associated with reconstruction by fibroblasts secreting collagen. To discover whether cartilage came from aortic cells or from recipient cells, we decided in the six last animals in the allograft study to implant aorta from male sheep to trachea of female sheep and to search for SRY genes in the newly formed cartilage. Using a type 2 collagen marker, we demonstrated that newly formed structures within the aortic graft were indeed cartilage. PCR studies showed SRY amplification for male specimens but no amplification for female specimens or the newly formed cartilage. This clearly showed that newly formed cartilage originated not from aortic cells but from recipient cells. Today we know that this process did not come from aortic cells. Furthermore, chondrocytes cannot migrate, and newly formed cartilage was distant from the native trachea. These two points evidently refute the possibility of regeneration from the native cartilage. The last hypothesis is that regeneration came from mesenchymal cells, local cells or, most probably, circulating stem cells from bone marrow, as this has been demonstrated for the repair of other organs. This was recently confirmed by our group in a rabbit model [26]. Cryopreserved aortic allograft seems to be the better option in the view of human applications because of availability in tissue banks, permanent storage and no need for immunosuppression. We demonstrated that regeneration of a functional tissue could also be obtained after tracheal replacement with cryopreserved aortic allografts, in contrast to decellularized or glutaraldehyde-treated aortic grafts [25]. The regenerative process followed the same pattern as previously described for fresh allografts. These results were confirmed in a pig model as discussed by others [27-29]. We also demonstrated that an arterial allograft could be a valuable bronchial substitute with results similar to those obtained after tracheal replacement [30]. We theorized that airway healing after replacement with biological scaffolds was the consequence of a mixed phenomenon associating airway approximation and regeneration [31].

Bottom Line: In 1997, we proposed a novel approach: the use of aortic grafts as a biological matrix for extensive airway reconstruction.In vivo regeneration of epithelium and cartilage were demonstrated in animal models.Favorable results obtained in pioneering cases have to be confirmed in larger series of patients with extensive tracheobronchial diseases.

View Article: PubMed Central - HTML - PubMed

Affiliation: Assistance Publique-Hôpitaux de Paris, Hôpitaux Universitaires Paris-Seine-Saint-Denis, Avicenne Hospital, Department of Thoracic and Vascular Surgery, Paris 13 University, Sorbonne Paris Cité, Faculty of Medicine SMBH, Bobigny, France. emmanuel.martinod@avc.aphp.fr.

ABSTRACT
After more than 50 years of research, airway transplantation remains a major challenge in the fields of thoracic surgery and regenerative medicine. Five principal types of tracheobronchial substitutes, including synthetic prostheses, bioprostheses, allografts, autografts and bioengineered conduits have been evaluated experimentally in numerous studies. However, none of these works have provided a standardized technique for the replacement of the airways. More recently, few clinical attempts have offered encouraging results with ex vivo or stem cell-based engineered airways and tracheal allografts implanted after heterotopic revascularization. In 1997, we proposed a novel approach: the use of aortic grafts as a biological matrix for extensive airway reconstruction. In vivo regeneration of epithelium and cartilage were demonstrated in animal models. This led to the first human applications using cryopreserved aortic allografts that present key advantages because they are available in tissue banks and do not require immunosuppressive therapy. Favorable results obtained in pioneering cases have to be confirmed in larger series of patients with extensive tracheobronchial diseases.

Show MeSH