Translation of non-tissue engineering (TE) and TE approaches for tracheal restoration and regeneration in human clinical trials

Patient(s) detailsTechnologyMaterial(s)CellsProcedure detailsOutcomeRef.
Non-TE approaches
 43-year-old femaleAutograftForearm freeflap supported with an Ultraflex stentNAA freeflap was harvested and wrapped around a stent after implantation in a 6 cm tracheal defect arising for a carcinoma.Died 16 months after the procedure from pre-existing conditions.[131]
 63-year-old femaleAutograftForearm freeflap with an external mesh supportNARadial forearm fasciocutaneous flap with a Hemashield vascular graft and PolyMax resorbable mesh.Patient remains symptom-free at 6 months and has returned to normal activities. Bronchoscopy at 6 months showed slight migration but healed flap with no obstruction.[132]
 16 patients (37–68 years)AutograftCartilage rib and fascial skin padNASegments of the patient's own cartilage were inserted within a skinpad harvested from the forearm. Construct was wrapped around silicone tube for suturing and implanted within the defect.Three deaths following surgical procedure due to lung infections, acute respiratory distress syndrome and myocardial infarction. Long-term follow-up showed a 65% survival rate.[129, 133]
 21-year-old maleAllotransplantationDonor cadaveric tracheaNA or autologous patient cellsPatient suffering from extensive tracheal stenosis. A cadaveric trachea with intact blood supply was implanted heterotopically into the sternocleidomastoid muscle for 3 weeks. It was then implanted orthopically into the trachea defect with a vascularised muscular section of the sternocleidomastoid.Integration of the trachea graft and proper function for 9 weeks without evidence of rejection, ischaemia or infection.[124]
 24-year-old femaleAllotransplantationDonor cadaveric tracheaNAPatient suffering from tracheal stenosis and third stage respiratory insufficiency. The allograft was implanted and wrapped with omentum and the patient was placed on immunosuppressive therapy.Uneventful postoperative course with signs of graft rejection, necrosis, bacterial and viral infection which lead to the need of silicon endoprosthesis. Signs for rejection reduced and 1-year follow-up suggested patient was still alive with a restored tracheal lumen.[125]
 Four patients (17–64 years; three males, one female)AllotransplantationHuman cadaveric tracheaRecipient's buccal mucosa and/or ingrown recipient cellsPatients suffering from tracheal stenosis or tracheal chondrosarcoma. Decellularised tracheas were implanted in the forearm and grafted with buccal mucosa or wrapped in forearm fascia to improve vascularisation.Tracheal necrosis after withdrawal of immunosuppression and poor vascularisation around the grafts leading to partial loss of the allotransplant in three patients while additional approaches for recipient cell repopulation of the construct in one patient allowed a vascularised allotransplant and normal airways 6 months after transplantation.[128]
 68-year-old maleStent-supported aortic autograftAorta autograft and silicone Dumon stentNAPatient presenting tracheal squamous cell carcinoma. A 7 cm abdominal aorta autograft was harvested and replaced with a Dracon graft. The aortic graft was implanted coupled with a silicone Dumon stent to avoid aortic wall injury.Granulation tissue formation led to acute respiratory distress syndrome which was treated by introduction of an additional tracheal stent. Stent was removed due to migration albeit no airway collapse was detected. Pneumonia, respiratory distress and pneumothorax lead to death of patient due to septic shock.[120]
 Six patients (17–52 years; five males, one female)Stent-supported aortic allograftFresh or cryopreserved aortic grafts and silicone stentNAPatients suffering from mucoepidermoid and adenoid cystic carcinoma. Aortic allografts were wrapped with well vascularised pectoral muscle or thymopericardial fat flaps and implanted using a silicone stent.Complete resection achieved in 83% of patients. Major morbidity, fistulas and uneventful outcomes. All grafts showed adequate vascularisation and four patients are disease-free.[122]
 78-year-old maleStent-supported aortic allograftCryopreserved aortic graft and custom-made nitinol stentNAPatient suffering from extensive bronchopulmonary malignant tumour pre-treated with chemotherapy. Lung cancer was resected, and a stent-supported graft was implanted.Well-functioning re-implanted lobe found 1 year post procedure. Patient recovered baseline activity with satisfying health quality of life.[121]
 20 patients (24–79 years; 13 males, seven females)Stent-supported aortic allograftCryopreserved aortic graft and custom-made nitinol stentNAPatients presenting proximal lung tumours and malignant or benign lesions of the trachea and bronchi. Radial tumour resections were performed and the stent-supported graft was implanted and covered circumferentially with a local muscle flap.Patient follow-up of 90 days detecting a 5% mortality rate. No adverse effect of the surgical technique used showing a 76.5% survival at a median follow-up of 3 years and 11 months. Regeneration of cartilage and respiratory epithelium observed.[123]
TE approaches
 26-year-old maleDecellularisationDecellularised porcine jejunum containing autologous cell populationRecipient's mvECs and skMCsPatient suffering from extensive tracheal and oesophageal defect. Porcine cell-free vascularised scaffolds were obtained through a decellularisation process and seeded to ensure re-endothelialisation with recipient's cell prior to implantation into the 5×2 cm defect. The construct was characterised prior to implantation to ensure safety and maximum performance.The postoperative period was uneventful and the transplanted bioengineered construct was fully integrated presenting a fully functional respiratory epithelium on the lining of the airway without tissue scar formation or tissue dedifferentiation.[134]
 12-year-old maleDecellularisationHuman decellularised trachea containing autologous stem-cell populationsRecipient's CD34 or CD45wk haematopoietic stem cells and CD73+, CD90+, CD105+, CD117+ or CD45+ MSCsPatient born with long-segmental tracheal stenosis and pulmonary sling. A decellularised cadaveric trachea was saturated with the recipient's stem cell suspension and implanted coupled with a PDO stent. The construct was saturated with hrEPO, G-CSF and TGF-β.The graft was vascularised 1 week following surgery, but epithelium restoration was not seen until 1 year post-implantation. Biomechanical strength was not appropriate until 18 months. Functional airway found at 2 years follow-up. Patient free from medical intervention in a 4-year follow-up study.[135, 136]
 15-year-old femaleDecellularisationHuman decellularised trachea containing autologous stem-cell populationsRecipient's BM-MSCs and nasal-derived epithelial cellsPatient presenting critical tracheal stenosis. A decellularised cadaveric trachea was pre-seeded in vitro in a custom-made bioreactor before implantation.Patency of the graft and intact anastomoses following implantation. Tracheal graft narrowing was observed 13 days after surgery leading to ventilator compromise and respiratory arrest, which finally resulted in cerebral hypoxic injury and oedema.[137]
 78-year-old femaleTE scaffoldMarlex mesh tube covered with a collagen type I and III (porcine dermal atelocollagen) spongeNAPatient showing right lobe thyroid gland tumour and consequent tracheal invasion. The construct was implanted and injected with autologous venous blood for air-tightness, water-tightness and endogenous factors release.The bioengineered construct supported the epithelial growth 2 months after surgery, proper epithelialisation was observed 7 months later and was completely covered with respiratory epithelium 20 months after surgery. Epithelialisation continued to cover the trachea for 2 years showing no complication.[138]
 Four patients (59–78 years; two male, two female)TE scaffoldMarlex mesh tube covered with a collagen type I and III (porcine dermal atelocollagen) spongeNAPatients with history of tracheotomy, stenosis and thyroid cancer. The construct was implanted and injected with autologous venous blood.Observation period of 8–34 months showed sufficient epithelialisation of the construct without obstructions.[139]
 Three patients (39–71 years; one male, two female)TE scaffoldMarlex (PP) mesh tube covered with a collagen type I and III (porcine dermal atelocollagen) spongeNAPatients suffering from stenosis of the trachea and/or cricoids caused by endotracheal intubations. Two-stage operation for the resection of the stenotic regions and implantation of the construct followed by delivery of venous blood and b-FGF to the cartilage defect.All patients were able to breath after implantation and showed no discomfort in daily activities. Enough air space in the trachea was observed 6 months after implantation.[140]
 Infant (2 months old)3DPPCLNAPatient suffering from TBM. A custom-designed and custom-fabricated resorbable 3DP airway splint was implanted and predicted to be fully resorbed within 3 years.21 days after the procedure ventilator support was ended and patient was discharged. 1 year after surgery a patent left mainstem bronchus was observed and no unforeseen problems related to the splint arose.[141]
 Three infants (3–16 months; three males)3DPPCLNAPatients suffering from TBM. 3DP splints were customised for each patients needs using CT imaging and CAD modelling software.At the time of publication, all patients did not show signs of airway disease showing continued growth of the primary airways.[78]
 46-year-old female3DPPCLNAPatient with TBM. 3DP splint designed using CT imaging and modelling software was implanted wrapped in an artificial pleural patch.2 weeks after surgery the patient was discharged from hospital with increased tracheal inner diameter and cross-sectional area. Breathing and physical strength improvement in a 3-month follow-up. No adverse reaction or toxicity was found.[142]
 Young female3DPPEKKNAPatient suffering from acquired TBM. A PEKK splint was design using CT imaging and modelling software. PEKK was chosen over PCL for its superior properties and suitability for manufacturing.Restoration of tracheal patency and patient remains asymptomatic, no further complications or hospitalisations were recorded.[143]
 15 patients (3–25 months; six male, nine female)3DPPCLNAPatients suffering from TBM and airway erosion. 3DP split designed using CT imaging and modelling software. A total of 29 splints (10 tracheal, 12 left bronchus and seven right bronchus) were implanted with the help of PP sutures.No patients required splint removal or re-operation. Three mortalities were recorded. At 8.5-month follow-up, 11 patients were living at home.[77]

NA: not applicable; mvEC: microvascular endothelial cell; skMC: skeletal muscle cell; MSC: mesenchymal stem cells; PDO: polydioxanone; hrEPO: human recombinant erythropoietin; G-CSF: granulocyte-colony stimulating factor; TGF-β: transforming growth factor-β; BM-MNC: bone marrow mononuclear cell; PP: polypropylene; b-FGF: basic fibroblast growth factor; PCL: polycaprolactone; TBM: tracheobronchomalacia; 3DP: 3D printing-2; CT: computed tomography: CAD: computer-aided design; PEKK: polyetherketoneketone.