Experimental tracheal transplantation using a cryopreserved aortic allograft

Reconstruction of the trachea and carina: Surgical reconstruction, autologous tissue transplantation, allograft transplantation, and bioengineering

There have been significant advancements in medical techniques in the present epoch, with the emergence of some novel operative substitutes. However, the treatment of tracheal defects still faces tremendous challenges and there is, as yet, no consensus on tracheal and carinal reconstruction. In addition, surgical outcomes vary in different individuals, which results in an ambiguous future for tracheal surgery. Although transplantation was once an effective and promising method, it is limited by a shortage of donors and immune rejection. The development of bioengineering has provided an alternative for the treatment of tracheal defects, but this discipline is full of ethical controversy and hindered by limited cognition in this area. Meanwhile, progression of this technique is blocked by a deficiency in ideal materials. The trachea together with the carina is still the last unpaired organ in thoracic surgery and propososal of a favorable scheme to remove this dilemma is urgently required. In this review, four main tracheal reconstruction methods, especially surgical techniques, are evaluated, and a thorough interpretation conducted.

Airway transplantation

No definitive solution has been discovered for replacing long segments or the entire trachea in humans. Most of this challenge stems from the specific function and mechanics that are almost impossible to replicate except in the setting of an allotransplantation, which requires lifelong immunosuppressive medication. Recently, tissue engineering provided significant evidence concerning the next promising therapeutic alternative for tracheal replacement. Underlying mechanism and pathways of cell-surface interactions, cell migration, and differentiation are essential to understand the complexity of tracheal tissue regeneration. Tracheal replacement remains challenging but initial steps toward an ideal therapeutic concept have been made.

An animal model study for repair of tracheal defects with autologous stem cells and differentiated chondrocytes from adipose-derived stem cells

BACKGROUND

Stenosis of trachea with mucosal and cartilage lesions is a challenging problem in tracheal surgery. Owing to ease of harvest and abundance, adipose-derived stem cells (ADSCs) are attractive and increasingly used in tissue engineering. The aim of this study was to evaluate the repair of trachea with autologous stem cells and differentiated chondrocytes from adipose-derived stem cells in an animal model.

METHODS AND MATERIAL

Six canine ADSCs were isolated and proliferated in monolayer culture and CD44; CD90 markers were investigated by flow cytometry. ADSCs were seeded in alginate beads and were differentiated into chondrocytes by TGF-β3. Cartilage-specific markers with reverse transcriptase polymerase chain reaction were demonstrated in differentiated cells. These differentiated cells and stem cells in alginate scaffold were separately transferred to a defect created in canine's trachea. After 8 weeks, the healing and cartilage formation in the trachea was evaluated by histological methods.

RESULTS

We identified formed cartilage pieces and chondrocytes with lacuna and extracellular matrix in defects implanted with differentiated cells, but in other groups, staining of the sections did not show the presence of cartilage in the engineered tracheal wall.

CONCLUSION

We showed that cartilage- engineered from differentiated adipose-derived stem cells in alginate biodegradable scaffold could repair tracheal cartilage defects.

Tracheal reconstruction with a composite graft: fascial flap-wrapped allogenic aorta with external cartilage-ring support

OBJECTIVES

Animal and clinical studies have demonstrated the feasibility of tracheal replacement by silicone-stented allogenic aortas. In clinical trials, however, this graft did not show mature cartilage regeneration into the grafts as was observed in animal models. To solve this issue, we investigated tracheal replacement with a composite graft based on a fascial flap-wrapped allogenic aorta with external cartilage-ring support in a rabbit model.

METHODS

Seven male 'Géant des Flandres' and 'New Zealand' rabbits served as donors of aortas and cartilage rings, respectively. Nineteen female 'New Zealand' rabbits were used as recipients. First, in nine animals, neoangiogenesis of the composite graft following a wrap using a pedicled lateral thoracic fascial flap and implantation under the skin of the chest wall was investigated. Animal sacrifice was scheduled at regular intervals up to 38 days. Second, 10 animals underwent tracheal replacement with the composite graft after a 7-to-9 day revascularization period, and were followed-up to death. Macroscopic and microscopic examinations were used to study the morphology, stiffness and viability of the construct.

RESULTS

There was one operative death after tracheal replacement. The first group of animals was found to have a satisfactory tubular morphology and stiffness of their construct associated with preserved histological structure of cartilages and moderate to severe aortic ischaemic lesions. In the group of rabbits having undergone tracheal replacement, the anatomical results were characterized by a discrepancy between the severity of ischaemic lesions involving both allogenic aorta and cartilage rings and the satisfactory biomechanical characteristics of the graft in 7 of 10 animals, probably due to cartilage calcification deposits associated with inflammatory scar tissue ensuring the stiffness of the construct.

CONCLUSIONS

Our investigations demonstrate the feasibility of the replacement of circumferential tracheal defects using our composite graft. Future experiments using therapeutic bronchoscopy tools are required to draw conclusions regarding the effectiveness of this tracheal substitute in the long-term.

Cryopreservation of the tracheal grafts: Review and perspective

Transplantation of the trachea may become the preferred method for the reconstruction of extensive tracheal defects, however, several unresolved problems must be addressed, such as immunosuppression, preservation and donor shortage. In this manuscript, the cryopreservation of tracheal grafts is reviewed, which potentially is associated with a lessened immunological response. Cryopreservation may be used clinically for long-term preservation and may solve the donor shortage. It is very important to confirm the immunomodulatory effect of cryopreservation on tracheal allografts in order to expand the potential clinical application of tracheal transplantation in the future. The cartilage as well as the epithelium and lamina propria serve as targets for rejection. However, the effect of cryopreservation on chondrocytes could be associated with reduced allogenicity of the trachea. The long-term cryopreservation of cartilage must be investigated in basic research models of chondrocyte viability. Growth of cryopreserved tracheal allografts is less well understood. Further studies are needed to elucidate the mechanism of synergistic effects of both cryopreservation and adequate immunosuppression for tracheal xenografts.

Construction of a tube-shaped tracheal substitute using fascial flap-wrapped revascularized allogenic aorta

OBJECTIVES

Animal studies have demonstrated the feasibility of tracheal replacement by silicone-stented allogenic aortas (AAs), showing mature cartilage regeneration into the grafts. In clinical trials, this graft did not prove stiff enough to allow long-term stent withdrawal. This graft insufficiency could be due to ischaemic phase prior to neoangiogenesis. To solve this issue, we investigated both the efficacy of the rabbit lateral thoracic fascial flap as a vehicle for revascularization of the AA and construction of a tube-shaped graft with transferable vascular pedicle, for more efficient replacement of the trachea.

METHODS

Thirty-four New Zealand rabbits were used. After harvesting of donors 'thoracic aortas', the fresh aortic allografts were transplanted within 1 h, and the others were cryopreserved. Fifteen male and four female rabbits were used as recipients for fresh (n = 9) or cryopreserved (n = 10) aortic allografts that were implanted under the skin of the chest wall, after graft wrap using a pedicled lateral thoracic fascial flap. Animal sacrifice was scheduled at regular intervals up to 61 days. Macroscopic and microscopic examinations and fluorescence in situ hybridization (FISH) were used to study the morphology, revascularization process and viability of the construct.

RESULTS

There was no operative death. Animals showed no graft rejection, despite the absence of immunosuppressive therapy. They all had a satisfactory tubular morphology of their construct. Of the 19 rabbits, 15 were found to have a generally preserved histological structure of the aorta and satisfactory neoangiogenesis. In the last four, a severe wound complication was associated with necrosis of the aortic graft. FISH on three aortic grafts with satisfactory neoangiogenesis showed migration of recipient cells into the aortic graft, decreasing from the adventitial to the luminal side, associated with the persistence of cells from the donor.

CONCLUSIONS

Our results showed that the chimeric construct transformed into a well-vascularized tube-shaped organ with transferable pedicle and some degree of stiffness. Persistence of donor's cells of normal morphology into the aortic graft was suggestive of minimal ischaemia during the initial phase of revascularization. This construct might be investigated in the setting of tracheal replacement in the rabbit model.

Tracheal replacement with cryopreserved allogenic aorta

BACKGROUND

Radical resection of primary tracheal tumors may be challenging when more than one-half of the tracheal length is concerned. The present study evaluated the use of cryopreserved aortic allografts (CAAs) to replace long tracheal segments.

METHODS

Sixteen adult minipigs underwent tracheal replacement with a CAA. A silicone stent was used to splint the CAA for the first 12 months. Animals were followed-up using bronchoscopic evaluation and killed at predetermined times, for a period up to 18 months long.

RESULTS

Intense inflammation and progressive disappearance of typical histologic structures of the aorta were seen within the first 3 months. All animals studied for more than 3 months showed progressive transformation of the graft into a chimerical conduit sharing aortic and tracheal histologic patterns (eg, islands of disorganized elastic fibers/mature respiratory ciliated epithelium, respiratory glands, islets of cartilage). Stent removal was attempted after 12 months in 10 animals, and critical tracheal stenosis was found in six animals and moderate asymptomatic stenosis in four. Clinical course in these latter animals was uneventful until they were killed at 15 to 18 months. In situ hybridization showed that collagen2a1 mRNA was expressed in the cartilage islets at 1 year. Polymerase chain reaction analysis of the SRY gene demonstrated that the newly formed cartilage cells derived from the host.

CONCLUSIONS

CAA may be considered as a valuable tracheal substitute for patients with extensive tracheal tumors. Prolonged stenting will be probably mandatory for the clinical application of the procedure in humans.

Carinal Replacement With an Aortic Allograft

BACKGROUND

Carinal replacement after extensive resection remains a tremendous challenge in thoracic surgery. In previous studies, we demonstrated that an aortic graft could be a valuable tracheal substitute. The goal of this new study was to evaluate the reconstruction of the carina using a stent supported bifurcated aortic allograft.

METHODS

In 15 sheep the replacement of the tracheobronchial bifurcation with an aortic allograft was performed under cardiopulmonary bypass. A temporary stent prevented airway collapse. No immunosuppression was used. Aortic segments were retrieved at regular intervals up to 24 months after implantation.

RESULTS

All animals survived the initial aortic allograft operation. Six animals died postoperatively (1 of graft necrosis, 2 of pneumonia, and 3 of bronchial fistula). The remaining 9 animals were in good condition until they were euthanized. Stent removal was tolerated after 9 months in 3 animals. Progressive transformation of the arterial graft initially into extensive inflammatory tissue, and after 3 to 6 months into a tracheal tissue comprising a well-differentiated epithelium and cartilage was confirmed by histology.

CONCLUSIONS

This study showed that regeneration of a functional tissue can be obtained after replacement of the carina with an aortic allograft. The origin and mechanisms of this regenerative process remains to be discovered. These results represent an important hope for the reconstruction of the carina after extensive resection, especially for cancer lesions. In human application, the systemic use of omentoplasty or myoplasty should further reduce its risk of complication.

Tracheal regeneration following tracheal replacement with an allogenic aorta

BACKGROUND

Tracheal replacement remains an unsolved surgical problem. Attempts to use tracheal substitutes have failed to achieve reliable results. In this study, tracheal regeneration was obtained after tracheal replacement with an allogenic aorta.

METHODS

Twenty female sheep underwent a 8-cm tracheal replacement with a fresh aortic allograft. In the six last animals, aortic grafts came from male sheep. A stent prevented airway collapse. No immunosuppressive therapy was used. Aortic segments were retrieved at regular intervals up to 16 months. A polymerase chain reaction for the SRY gene was performed in specimens with aortic grafts from male sheep.

RESULTS

All animals but one survived the operation without complications. Clearly identified between the suture lines, the aortic segments were completely transformed into a tracheal structure. Histology showed initially an inflammatory reaction with proliferation of a squamous epithelium followed by mucociliary epithelium and newly formed cartilage rings. SRY gene was not found in newly formed cartilage rings showing that the regeneration originated from recipient cells.

CONCLUSIONS

This study presents a new type of tissue regeneration and brings hopes to the treatment of extensive tracheal lesions.

Liposomal entrapment of cefoxitin to improve cellular viability and function in human saphenous veins

Liposomal cefoxitin was prepared and applied to the pretreatment of human saphenous vein (HSV) for implantation. The possible use of liposomal cefoxitin to improve cellular viability and function and to maintain its potential sterilization effect was investigated. Entrapment efficiency and size distribution of liposomal cefoxitin were 75.7% and 652 +/- 75.7 nm, respectively. The weight ratio between cefoxitin and liposome was calculated at 1 : 40.6. When cefoxitin was entrapped with liposome, the released amount of cefoxitin was not affected by temperature conditions (37 degrees C, 25 degrees C, and 4 degrees C). The amount of free cefoxitin present in HSV reached 59% at 0.5 h and gradually decreased with time, while liposomal cefoxitin showed a maximum amount (63%) at 1.5 h, indicating that liposomal cefoxitin seemed to control the initial amount of cefoxitin present in HSV. Liposomal cefoxitin showed better viabilities of whole cells and endothelial cells dissociated from HSV than free cefoxitin and remarkably superior function of endothelial cells, as determined by Griffonia simplicifolia agglutinins-fluorescein isothiocyanate/propidium iodide double-staining methods combined with flow cytometry and endothelial nitric oxide synthase assay, respectively. In terms of sterilization effect, there was no significant difference between liposomal cefoxitin and free cefoxitin. These results suggest that liposomal entrapment of cefoxitin could improve cellular viability and functions and maintain the original sterilization effect.

Long-term evaluation of the replacement of the trachea with an autologous aortic graft

BACKGROUND

Tracheal reconstruction after extensive resection remains a challenge in thoracic surgery. The goal of this experimental study was to analyze the long-term evolution of tracheal replacement using an autologous aortic graft.

METHODS

In 21 sheep, a 5-cm segment of the cervical trachea was replaced by a segment of the descending thoracic aorta that was reconstructed to a prosthetic graft. Because of the airway collapse reported in a previous series, a permanent (n = 13) or temporary (n = 8) stent was systematically placed in the lumen of the graft. Clinical, bronchoscopic, and histologic examinations were performed up to 3 years after implantation.

RESULTS

All animals survived the operation with no paraplegia. In the group with a permanent stent, three complications occurred: one stent displacement, one laryngeal edema, and one infection. Stent removal was tolerated after 6 months in the group with a temporary stent. Histologic examination showed a progressive transformation of the arterial segment into first extensive inflammatory tissue with a squamous epithelium, and after 6 to 36 months well-differentiated tracheal tissue including a continuous mucociliary epithelium and regular rings of newly formed cartilage.

CONCLUSIONS

An autologous aortic graft used as a substitute for extensive tracheal replacement in sheep remained functional for periods up to 3 years. The progressive transformation of the graft into a structure resembling tracheal tissue seems to be a key factor in long-term patency. The mechanism of this regenerative process and the possibility of using arterial homografts, which would make clinical application easier, remain to be evaluated.

Failure of airway healing in an ovine autotransplantation model that includes basic fibroblast growth factor

OBJECTIVE

Basic fibroblast growth factor is among the most potent promoters of angiogenesis. Its ability to enhance the blood supply to ischemic airways or nonvascularized tracheal autograft has been demonstrated. Its cumulative effect with muscular wrapping and its efficacy in a noncanine large animal model remain unknown. Treatment with basic fibroblast growth factor and muscular wrapping were compared with no special treatment and with muscular wrapping alone in an ovine tracheal autotransplantation model.

METHODS

All sheep underwent orthotopic tracheal transplantation with 5 to 8 ring autografts in the cervical trachea. Fifteen sheep were classified randomly into the following three groups: no treatment (group A, n = 5), muscular wrapping with the right sternomastoid muscle (group B, n = 5), and topical administration of fibrin glue enriched with 2 microg/cm(2) basic fibroblast growth factor (group C, n = 5).

RESULTS

Devascularized tracheal autografts were unable to maintain their structural integrity without other treatment (group A). However, the grafts were surrounded by well-vascularized connective tissue. In the muscular wrapping group (group B), infections occurred around the grafts, and the muscular wrapping was subject to necrosis. No neovascularization of the grafts occurred. Therapy with basic fibroblast growth factor (group C) led to improved muscular wrapping circulation and to adherence to the tracheal stumps. However, no success was achieved in validating the circulation in the grafts.

CONCLUSIONS

In contrast to the results achieved by other authors with canine models, the neovascularization of tracheal autografts was not achieved in sheep with the topical administration of basic fibroblast growth factor. Cranially pediculated muscular wrapping led to poorer circulation in the tissue around the graft than did no therapy at all.

The characterisation of human respiratory epithelial cells cultured on resorbable scaffolds: first steps towards a tissue engineered tracheal replacement

In this study we have used lectin histochemistry and scanning electron microscopy (SEM) to assess the growth and characterise the differentiation of human respiratory epithelial cells (REC) cultured on two biomaterial scaffolds. The first scaffold, based on a hyaluronic acid derivative, was observed to be non-adhesive for REC. This lack of adhesion was found to be unrelated to the presence of the hyaluronic acid binding domain on the surface of isolated REC. The other scaffold, consisting of equine collagen. was observed to encourage REC spreading and adhesion. Positive Ulex Europaeus agglutinin (UEA) lectin staining of this preparation indicated the presence of ciliated REC on the scaffold surface. However, the marked decrease in peanut agglutinin (PNA) positive staining, relative to that of control cultures and native tissue, indicates a dedifferentiation of the secretory cells of the REC monolayer. SEM analysis of REC cultured on the collagen scaffold confirmed the presence of ciliated cells thereby validating the UEA positive staining. The presence of both established and developing cilia was also verified. This study indicates that collagen biomaterials are appropriate for the tissue engineering of REC. Furthermore, that UEA and PNA staining is a useful tool in the characterisation of cells cultured on biomaterials, therefore helpful in identifying biomaterials that are suitable for specific tissue engineering purposes.