Tracheal Replacement with Fresh and Cryopreserved Aortic Allograft in Adult Dog

A Multimodal Approach to Quantify Chondrocyte Viability for Airway Tissue Engineering

OBJECTIVES/HYPOTHESIS

Partially decellularized tracheal scaffolds have emerged as a potential solution for long-segment tracheal defects. These grafts have exhibited regenerative capacity and the preservation of native mechanical properties resulting from the elimination of all highly immunogenic cell types while sparing weakly immunogenic cartilage. With partial decellularization, new considerations must be made about the viability of preserved chondrocytes. In this study, we propose a multimodal approach for quantifying chondrocyte viability for airway tissue engineering.

METHODS

Tracheal segments (5 mm) were harvested from C57BL/6 mice, and immediately stored in phosphate-buffered saline at -20°C (PBS-20) or biobanked via cryopreservation. Stored and control (fresh) tracheal grafts were implanted as syngeneic tracheal grafts (STG) for 3 months. STG was scanned with micro-computed tomography (μCT) in vivo. STG subjected to different conditions (fresh, PBS-20, or biobanked) were characterized with live/dead assay, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), and von Kossa staining.

RESULTS

Live/dead assay detected higher chondrocyte viability in biobanked conditions compared to PBS-20. TUNEL staining indicated that storage conditions did not alter the proportion of apoptotic cells. Biobanking exhibited a lower calcification area than PBS-20 in 3-month post-implanted grafts. Higher radiographic density (Hounsfield units) measured by μCT correlated with more calcification within the tracheal cartilage.

CONCLUSIONS

We propose a strategy to assess chondrocyte viability that integrates with vivo imaging and histologic techniques, leveraging their respective strengths and weaknesses. These techniques will support the rational design of partially decellularized tracheal scaffolds.

LEVEL OF EVIDENCE

N/A Laryngoscope, 133:512-520, 2023.

Replacement of a 5-cm intrathoracic trachea with a tissue-engineered prosthesis in a canine model

BACKGROUND

Critical obstacles must be addressed before clinical application of artificial tracheas. The major complications of long tracheal replacement include anastomotic dehiscence and stenosis owing to poor vascularity and incomplete re-epithelialization. The objective of this report was to clarify whether pre-incubation of the prosthesis in the omentum could be applicable for reconstruction of a long segment of the intrathoracic trachea in a canine model.

METHODS

The framework of an artificial trachea was fabricated from a polypropylene mesh tube and coated with 1% neutral atelocollagen inside and outside the lumen. The prosthesis was placed in the omentum of nine healthy male beagle dogs for 3 weeks. Then, the pedicled prosthesis was used to replace a 50 mm long section of intrathoracic trachea. Results were evaluated bronchoscopically, macroscopically, and histologically.

RESULTS

After 3 weeks of abdominal incubation, the prostheses were incorporated into the host tissue. None of the dogs showed dehiscence of the anastomosis or infection of the prostheses during the postoperative period. Seven of the nine dogs survived for more than 1 year. One dog died of a bowel obstruction resulting from a diaphragmatic hernia 3 months after replacement, and another died due to reasons unrelated to the prosthesis at 6 months. Bronchoscopic examination revealed no stenosis or dehiscence, and microscopic examination of all dogs showed that the luminal surface was covered by newly regenerated connective tissue and respiratory epithelium.

CONCLUSIONS

Pedicled omentum-prosthesis complexes may allow successful reconstruction of a long segment of the intrathoracic trachea.

Experimental Tracheal Replacement Using 3-dimensional Bioprinted Artificial Trachea with Autologous Epithelial Cells and Chondrocytes

Various treatment methods for tracheal defects have been attempted, such as artificial implants, allografts, autogenous grafts, and tissue engineering; however, no perfect method has been established. We attempted to create an effective artificial trachea via a tissue engineering method using 3D bio-printing. A multi-layered scaffold was fabricated using a 3D printer. Polycaprolactone (PCL) and hydrogel were used with nasal epithelial and auricular cartilage cells in the printing process. An artificial trachea was transplanted into 15 rabbits and a PCL scaffold without the addition of cells was transplanted into 6 rabbits (controls). All animals were followed up with radiography, CT, and endoscopy at 3, 6, and 12 months. In the control group, 3 out of 6 rabbits died from respiratory symptoms. Surviving rabbits in control group had narrowed tracheas due to the formation of granulation tissue and absence of epithelium regeneration. In the experimental group, 13 of 15 animals survived, and the histologic examination confirmed the regeneration of epithelial cells. Neonatal cartilage was also confirmed at 6 and 12 months. Our artificial trachea was effective in the regeneration of respiratory epithelium, but not in cartilage regeneration. Additional studies are needed to promote cartilage regeneration and improve implant stability.

Aortic allografts: final destination?-a summary of clinical tracheal substitutes

The patient population in desperate need for an airway substitute are individuals with long segment tracheal defects that are considered, technically, inoperable. Regardless of the underlying etiology, benign or malignant growing processes, this patient category enters a palliative setting or require tracheal transplantation. Different airway substitutes have been categorized by Grillo as follows; tracheal transplantation, autogenous tissue, non-viable tissue, tissue-engineering and foreign materials. These fields have been explored in the past in animal models and in clinical patients. Research on airway replacement has been exposed to a level of controversies in the past years. The field has been turbulent and apocryphal. In particular, the area of tissue-engineering using stem cells has suffered from a major set-back leaving scientists, clinicians and ethical committees skeptical. Recently, a hopeful study emerged using aortic allografts as tracheal substitutes in patients with airway defects. The initial results seem promising and reliable. The developments of the field at this point seem striking and hopeful. The focus of this review is to shed light on developments in the field of aortic allografts as substitute for tracheal replacement.

Serial Analysis of Tracheal Restenosis After 3D-Printed Scaffold Implantation: Recruited Inflammatory Cells and Associated Tissue Changes

Tracheal restenosis is a major obstacle to successful tracheal replacement, and remains the greatest challenge in tracheal regeneration. However, there have been no detailed investigations of restenosis. The present study was performed to analyze the serial changes in recruited inflammatory cells and associated histological changes after tracheal scaffold implantation. Asymmetrically porous scaffolds, which successfully prevented tracheal stenosis in a partial trachea defect model, designed with a tubular shape by electrospinning and reinforced by 3D-printing to reconstruct 2-cm circumferential tracheal defect. Serial rigid bronchoscopy, micro-computed tomography, and histology [H&E, Masson's Trichrome, IHC against α-smooth muscle actin (α-SMA)] were performed 1, 4, and 8 weeks after transplantation. Progressive stenosis developed especially at the site of anastomosis. Neutrophils were the main inflammatory cells recruited in the early stage, while macrophage infiltration increased with time. Recruitment of fibroblasts peaked at 4 weeks and deposition of α-SMA increased from 4 weeks and was maintained through 8 weeks. During the first 8 weeks post-transplantation, neutrophils and macrophages played significant roles in restenosis of the trachea. Antagonists to these would be ideal targets to reduce restenosis and thus play a pivotal role in successful tracheal regeneration.

Current Solutions for Long-Segment Tracheal Reconstruction

This article is a continuation of previous reviews about the appropriate method for long-segment tracheal reconstruction. We attempted to cover the most recent, successful and promising results of the different solutions for reconstruction that are rather innovative and suitable for imminent clinical application. Latest efforts to minimize the limitations associated with each method have been covered as well. In summary, autologous and allogenic tissue reconstruction of the trachea have been successful methods for reconstruction experimentally and clinically. Autologous tissues were best utilized clinically to enhance revascularization, whether as a definitive airway or as an adjunct to allografts or tissue-engineered trachea (TET). Allogenic tissue transplantation is, currently, the most suitable for clinical application, especially after elimination of the need for immunosuppressive therapy with unlimited supply of tissues. Similar results have been reported in many studies that used TET. However, clinical application of this method was limited to use as a salvage treatment in a few studies with promising results. These results still need to be solidified by further clinical and long-term follow-up reports. Combining different methods of reconstruction was often required to establish a physiological rather than an anatomical trachea and have shown superior outcomes.

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.

Aortic squamous metaplasia in a patient with aortoesophageal fistula secondary to thoracic aortic aneurysm: an autopsy case

Aortoesophageal fistula (AEF) is highly lethal. A 74-year-old man presented with hematemesis and consciousness loss. He had a long-term history of hypertension and gout. Computed tomography revealed an aneurysm of the distal descending thoracic aorta, which was treated by insertion of an aortic stent graft. After 24 days of stenting, endoscopic examination revealed an AEF. After 6 months of stenting, he died owing to mediastinitis. On autopsy, macroscopically, we found a 4 × 2.5-cm, oval, well-circumscribed AEF. We identified squamous epithelium in the area surrounding the AEF that covered the thoracic aorta inner cavity. Immunohistochemical analysis revealed that the squamous epithelium in the thoracic aorta was positive for p63 and 34βE12. In conclusion, we encountered a long-term AEF case with aortic squamous metaplasia. To the best of our knowledge, human aortic metaplasia has never been reported. In the present case, aortic squamous metaplasia retained continuity with the esophageal squamous epithelium; therefore, the migration of the squamous epithelium through the AEF may have been induced by aortic erosion.

Successful tracheal replacement in humans using autologous tissues: an 8-year experience

BACKGROUND

Fifty years of surgical research using synthetic materials and heterologous tissues failed to find a good, durable replacement for the trachea. We investigated autologous tracheal substitution (ATS) without synthetic material or immunosuppression.

METHODS

For ATS, we used a single-stage operation to construct a tube from a forearm free fasciocutaneous flap vascularized by radial vessels that was reanastomosed to internal mammary vessels and reinforced by rib cartilages interposed transversally in the subcutaneous tissue. Tracheal resections 7 to 12 cm long (mean, 11 cm) were done to treat 8 primary tracheal neoplasms, including 5 adenoid cystic carcinomas (ACC) and 3 squamous cell carcinomas (SCC); 3 secondary tracheal neoplasms, including 1 thyroid carcinomas and 2 lymphomas; and 1 postintubation tracheal destruction after a long history of stenting. Transitory tracheotomy was associated to the absence of mucociliary clearance.

RESULTS

ATS has been performed in 12 patients since 2004, with additional resections in 4 patients, comprising 1 carinal resection alone, 1 associated with lobectomy, and 2 pharyngolaryngectomies. All patients were extubated on postoperative day 1. Eight patients are alive at a mean of 36 months (range, 2 to 94 months) postoperatively, with no respiratory distress. The 2 patients with ATS and carinal resections died of pulmonary infection. No airway collapse has been detected by endoscopy, dynamic computed tomography scan, or spirometry. Two patients still have a tracheotomy because the procedure was performed too low at the level of the proximal anastomosis. One patient with a chronic severe respiratory insufficiency recently required a distal, short stent.

CONCLUSIONS

ATS is a good, durable, tracheal substitution that resists respiratory pressure variations because of transverse rigidity, without any immunosuppression.

Autologous tracheal replacement: from research to clinical practice

BACKGROUND

Despite numerous attempts, synthetic materials and heterologous tissues failed to replace durably the trachea. Autologous tracheal substitution (ATS) without synthetic material or immunosuppression was investigated to replace extended tracheal defect. We present our experience regards to this innovative challenge.

METHOD

After a previous research study, we developed a novel reconstruction technique for extended tracheal defects on animals. Through a single stage operation, a tube from a forearm free fascio-cutaneous flap vascularized by radial vessels is re-anastomosed to cervical vessels. This flap is reinforced by rib cartilages interposed transversally in the subcutaneous tissue. It provides also a reliable ATS. Twelve patients benefits from an extended tracheal resections, 7-12 centimeter (mean 11 cm) long. Indications were eight Primary tracheal Neoplasms (including 5 adenoid cystic carcinoma [ACC] and 3 squamous cell carcinoma [SCC]), three secondary tracheal neoplasms (including 1 thyroid carcinoma and 2 lymphoma) and one post-intubation tracheal destruction after long history of stenting. Daily bronchoscopy and transitory tracheotomy was associated due to absence of mucociliary clearance.

RESULTS

The research work leads to present the first described animal model for tracheal resection and replacement with an autologous conduit. It was constructed from costal cartilages and a pediculed cervical skin flap. From 2004 to 2012, 12 patients have had ATS with associated resections in four cases. All patients were extubated on the first postoperative days; eight patients are alive at 2 to 94 months (mean=36) postoperatively, with no respiratory distress. The two patients with ATS after resection extended to the carina died due to pulmonary infection. No airway collapse has been detectable, either by endoscopy, dynamic CT scan or spirometry. Two patients still have a tracheotomy because performed too low at the level of the proximal anastomosis. One patient with a chronic severe respiratory insufficiency required recently a distal and short stent.

CONCLUSION

ATS is actually a good, durable tracheal substitute that can resist respiratory pressure variations because of their transverse rigidity without any immunosuppression. The limits of this technique are probably, chronic respiratory insufficiency and cartilage calcifications. Research to develop a method for lining the neo-trachea with ciliated respiratory epithelium is needed.