Airway transplantation: a challenge for regenerative medicine.

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.

Tracheal regeneration: evidence of bone marrow mesenchymal stem cell involvement.

OBJECTIVES: Recent advances in airway transplantation have shown the ability of ex vivo or in vivo tracheal regeneration with bioengineered conduits or biological substitutes, respectively. Previously, we established a process of in vivo-guided tracheal regeneration using vascular allografts as a biological scaffold. We theorized that tracheal healing was the consequence of a mixed phenomenon associating tracheal contraction and regeneration. The aim of the present study was to determine the role that bone marrow stem cells play in that regenerative process. METHODS: Three groups of 12 rabbits underwent a gender-mismatched aortic graft transplantation after tracheal resection. The first group received no cells (control group), the second group had previously received autologous green fluorescent protein-labeled mesenchymal stem cell transplantation, and the third group received 3 labeled mesenchymal stem cell injections on postoperative days 0, 10, and 21. RESULTS: The clinical results were impaired by stent complications (obstruction or migration), but no anastomotic leakage, dehiscence, or stenosis was observed. The rabbits were killed, and the trachea was excised for analysis at 1 to 18 months after tracheal replacement. In all 3 groups, microscopic examination showed an integrated aortic graft lined by metaplastic epithelium. By 12 months, immature cartilage was detected among disorganized elastic fibers. Positive SRY gene detection served as evidence for engraftment of cells derived from the male recipient. EF-green fluorescent protein detection showed bone marrow-derived mesenchymal stem cell involvement. CONCLUSIONS: The results of the present study imply a role for bone marrow stem cells in tracheal regeneration after aortic allografting. Studies are necessary to identify the local and systemic factors stimulating that regenerative process.

Human transplantation of a biologic airway substitute in conservative lung cancer surgery.

BACKGROUND: Pneumonectomies for lung cancer are associated with a high postoperative mortality, especially when right-sided, after neoadjuvant radiochemotherapy, and in patients over 70 years of age. Preliminary studies in our laboratory have shown that aortic grafts could be valuable airway substitutes. We report the first human bronchial transplantation of a cryopreserved aortic allograft used as a biologic airway substitute to prevent a pneumonectomy for lung cancer. METHODS: The procedure was performed in a high-risk 78-year old patient with an extensive right bronchopulmonary malignant tumor pretreated with chemotherapy. After a complete resection of the lung cancer using an upper bilobectomy with lymph node removal, mobilization procedures did not allow for a primary end-to-end bronchial anastomosis. A stent-supported cryopreserved aortic allograft from a certified tissue bank was interposed to restore the bronchial continuity with sparing of the lower lobe. RESULTS: The postoperative course was eventful for a supraventricular arrhythmia leading to mild pulmonary edema that resolved using standard medical therapy, and a right lower lobe atelectasis with bacterial colonization that required fiberoptic bronchoscopies in addition to antibiotic treatment. A 1-year postoperative evaluation found a well-functioning reimplanted lower lobe with no complications related to the cryopreserved aortic allograft or the stent. The patient recovered to his baseline activity with a satisfying health-related quality of life. CONCLUSIONS: We demonstrate the feasibility of this surgical innovation to prevent the high-risk procedure of pneumonectomy in a single case. If confirmed in larger series of selected patients, it could bring new perspectives in conservative lung cancer surgery.

[The lung]. / Le poumon.

Lung transplantation is still the only curative treatment for end-stage pulmonary diseases. The results remain poor, however, because of the limited availability of lung donors, chronic rejection, and complications related to immunosuppressive therapy. The use of a bioartificial lung generated from autologous cells could offer a solution. We have demonstrated that in vivo epithelial and cartilage regeneration of the airways is feasible with the use of an aortic tissue matrix. Other studies show that in vitro and in vivo airway regeneration, respectively, can be obtained by using bio-engineering and heterotopic allograft implantation. A more complex challenge is the creation of an artificial lung Indeed, this would require the use of an elastic matrix that can promote regeneration of the different lung components (airways, alveoli, vessels) over a large surface area, thus allowing ventilation, blood perfusion and gas exchanges. Recent studies have demonstrated the possibility of in vitro and in vivo regeneration of lung tissue from autologous cells, and especially stem cells. This emerging research field is currently dominated by the use of decellularized lung matrices and autologous epithelial and endothelial cells. Implantation of such a recellularized matrix in animals has proved the feasibility of a functional bio-artificial lung. The first human transplantation of a bio-artificial lung should be possible within 10-20 years.

Bronchial replacement with arterial allografts.

BACKGROUND: Pneumonectomy is well known for a high risk of postoperative death. The alternative, sleeve lobectomy, is sometimes technically inaccessible, and is associated with locoregional recurrence. In certain situations, the use of a bronchial substitute would allow longer bronchial resections with better security margins. Previous experiments demonstrated that aortic grafts are valuable tracheal and carinal substitutes. The present study evaluated bronchial replacement with arterial allografts. METHODS: Fifteen female sheep underwent a left bilobectomy with replacement of the bronchus intermedius with arterial allografts: 5 received a fresh graft (group 1) and 10 received cryopreserved (group 2). A bronchial silicone stent was used to confer rigidity. Evaluation was conducted on clinical and histologic criteria at regular intervals up to 18 months. RESULTS: There were no perioperative deaths. Atelectasis, the only early postoperative complication (n = 2), was successfully treated by fiberscopic aspiration. The late postoperative period was uneventful in 12 sheep. Complications included 1 bronchopneumonia, 1 pulmonary abscess, and 1 distortion of the bronchial stent. Fiberscopic examination revealed 3 sheep with granuloma formation. The bronchial stent was removed in 3 sheep, 1 at 9 months and 2 at 12 months, without clinical complications or stenosis of the graft. Histologic analysis showed regeneration of new bronchial tissue, comprising epithelium and cartilage. CONCLUSIONS: This study confirmed that an arterial allograft could be a valuable bronchial substitute. The use of a bronchial substitute offers new perspectives in surgical resection of lung cancer because it would avoid pneumonectomy in some patients.

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.

Tracheal replacement with cryopreserved, decellularized, or glutaraldehyde-treated aortic allografts.

BACKGROUND: Seven years of experimental research provided a valuable tracheal substitute, the aortic allograft, which can promote the regeneration of epithelium and cartilage. In human application, both fresh and preserved aortic allografts could be used. The optimal method of aortic allograft preservation remains to be evaluated. This study assessed the use of cryopreserved, decellularized, or glutaraldehyde-treated aortic allografts as tracheal substitutes. METHODS: Twenty-two sheep underwent tracheal replacement using cryopreserved (n = 10), decellularized (n = 7) or glutaraldehyde-treated (n = 5) allografts, supported by a temporary stent to prevent airway collapse. Aortic segments were retrieved at regular intervals up to 12 months after implantation to analyze the regenerative process. RESULTS: All animals survived the operation. Major complications such as infection, stent migration, or obstruction were predominantly encountered in the decellularized group. The lack of major inflammatory response within the aortic graft observed in the glutaraldehyde group was associated with the absence of tracheal regeneration. Histologic examinations showed a progressive transformation of the aorta into a tracheal tissue comprising respiratory epithelium and cartilage only in the cryopreserved group. CONCLUSIONS: This study demonstrated that regeneration of a functional tissue could be obtained after tracheal replacement with a cryopreserved aortic allograft. The regenerative process followed the same pattern as previously described for fresh allografts. Cryopreserved aortic allografts present major advantages: availability in tissue banks, permanent storage, and no need for immunosuppression. This offers a new field of perspectives for clinical application in patients with extensive tracheal cancer.

Intracardiac renal cell carcinoma metastasis.

Cardiac involvement by intravascular protruding renal cell carcinoma is a well-recognised phenomenon. It most commonly occurs through inferior vena cava extension. Here, we report a case of a lower lobar lung metastasis from renal cell carcinoma involving the left atrium via the inferior pulmonary vein in a patient presenting with von Hippel-Lindau disease. Complete surgical resection was achieved under cardiopulmonary bypass.

Postoperative pneumonia after major pulmonary resections: an unsolved problem in thoracic surgery.

BACKGROUND: Antibiotics currently recommended for prophylaxis in thoracic surgery are first-generation and second-generation cephalosporins. Despite this prophylaxis, postoperative pneumonia after major pulmonary resections remains frequent and severe. However, in the medical literature, the origin of these infections is poorly documented. METHODS: To evaluate the efficiency of current prophylactic regimens, we retrospectively analyzed 312 consecutive cases of major pulmonary resection, performed between January 2000 and December 2004. For patients who experienced postoperative pulmonary infection, the microbiologic agents and their antibiotic susceptibility were studied. RESULTS: A postoperative pneumonia was diagnosed in 76 patients (24.4% +/- 0.43%). Sixty patients (78.9%) experienced the infection in the first 5 postoperative days. A microbiologic documentation was obtained in 44 cases (57.9%) with 56 microorganisms involved. Pathogens responsible for the infections were Staphylococcus aureus (n = 10), Streptococcus pneumoniae (n = 8), group B Streptococcus organisms (n = 1), nongroupable Streptococcus organisms (n = 2), Enterococcus faecalis (n = 1), Haemophilus spp. (n = 9), Branhamella catarrhalis (n = 2), Enterobacteriaceae (n = 15), Pseudomonas aeruginosa (n = 3), Acinetobacter baumannii (n = 1), and Candida spp. (n = 4). According to the antibiotic susceptibility testings, the prophylactic regimen by cefazolin proved ineffective for 84% of the microbiologically documented cases. CONCLUSIONS: This study confirmed the inefficiency of current prophylaxis against pathogens involved in postoperative pneumonia after major lung resections. Evaluation of new and more-adapted approaches of antibiotic prophylaxis should be the subject of prospective multicenter trials.

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.

Early and long-term results of lung resection for non-small-cell lung cancer in patients with severe ventilatory impairment.

OBJECTIVE: To study clinical characteristics, surgical treatment modalities, early and long-term outcome of patients with severe ventilatory impairment undergoing lung resection for NSCLC. METHODS: We performed a retrospective review of clinical records of all patients with severe chronic ventilatory impairment (FEV1 and/or FVC< or =50% of predicted values) operated on for NSCLC in a 21-year period (1983-2003). RESULTS: One hundred and six patients were operated on. Mean FEV1 and FVC were 40% (range 23-50%) and 69% (17-117%), respectively. An obstructive pattern was observed in 87 cases (82%). Extent of maximal exeresis was based on the assessment of predicted post-operative FEV1 (ppoFEV1). Major resections were contraindicated if ppoFEV1 was lower than 30%. Sixteen pneumonectomies, 73 lobectomies and 17 sublobar resections were carried out. Pathologic stages were I, II, IIIA and IIIB in 58, 26, 18 and 4 cases, respectively. Resection was complete in 104 patients. Operative mortality and morbidity were 8.5% (n=9) and 70% (n=74), respectively. Twenty-two patients needed prolonged (>48 h) mechanical ventilation. Overall mean ppoFEV1 loss was 9.1% (0-34%). If ppoFEV1 loss was >15%, the morbidity rate was 100%. Mean PaCO2 and ppoFEV1 loss were higher among patients who died (41 mmHg versus 37 mmHg, P=0.02 and 13.2% versus 8.5%, P=0.025, respectively) as compared with operative survivors. Among patients with PaCO2>39 mmHg and ppoFEV1 loss>15% (n=9), mortality rate was 33%. Overall 1-year and 5-year survival rates were 82 and 33%, respectively. Respiratory failure was the cause of late death in 2 patients. Among patients available at follow-up (n=85), respiratory function was considered subjectively improved, stable and worsened in 6 (7%), 62 (73%) and 17 (20%) cases, respectively. Eleven patients needed continuous oxygen therapy. CONCLUSIONS: Lung resection should not be denied a priori in patients with severe ventilatory impairment. Evaluation of predicted post-operative function often allows major resections, which are functionally economic, at the price of a high operative morbidity. Operative mortality, long-term survival and respiratory function are acceptable in the absence of a valid therapeutic alternative.

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.

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.