Stem-cell-based, tissue engineered tracheal replacement in a child: a 2-year follow-up study

Abstract

Background: Stem-cell-based, tissue engineered transplants might offer new therapeutic options for patients, including children, with failing organs. The reported replacement of an adult airway using stem cells on a biological scaffold with good results at 6 months supports this view. We describe the case of a child who received a stem-cell-based tracheal replacement and report findings after 2 years of follow-up.

Methods: A 12-year-old boy was born with long-segment congenital tracheal stenosis and pulmonary sling. His airway had been maintained by metal stents, but, after failure, a cadaveric donor tracheal scaffold was decellularised. After a short course of granulocyte colony stimulating factor, bone marrow mesenchymal stem cells were retrieved preoperatively and seeded onto the scaffold, with patches of autologous epithelium. Topical human recombinant erythropoietin was applied to encourage angiogenesis, and transforming growth factor β to support chondrogenesis. Intravenous human recombinant erythropoietin was continued postoperatively. Outcomes were survival, morbidity, endoscopic appearance, cytology and proteomics of brushings, and peripheral blood counts.

Findings: The graft revascularised within 1 week after surgery. A strong neutrophil response was noted locally for the first 8 weeks after surgery, which generated luminal DNA neutrophil extracellular traps. Cytological evidence of restoration of the epithelium was not evident until 1 year. The graft did not have biomechanical strength focally until 18 months, but the patient has not needed any medical intervention since then. 18 months after surgery, he had a normal chest CT scan and ventilation-perfusion scan and had grown 11 cm in height since the operation. At 2 years follow-up, he had a functional airway and had returned to school.

Interpretation: Follow-up of the first paediatric, stem-cell-based, tissue-engineered transplant shows potential for this technology but also highlights the need for further research.

Funding: Great Ormond Street Hospital NHS Trust, The Royal Free Hampstead NHS Trust, University College Hospital NHS Foundation Trust, and Region of Tuscany.

Figure 1. Surgical procedure

(A) During surgery the airway was found to be severely stenotic with multiple stents including one entering the ascending aorta. (B and C) The old homograft trachea was removed and replaced by the engineered graft. (C) The aortic defect was closed with a bovine pericardial patch and air leaks sealed. (D) Transforming growth factor β was injected into tracheal rings in the operating theatre before (E) implantation of the recellularised graft. (F) Before closing, an omental wrap was brought up to cover the graft. The graft sits in the anatomical position to the right of the ascending aorta.

Figure 2. Bronchoscopic appearances

(A) Microlaryngobronchoscopy 15 days after the transplant showing a dense web covering the stent and partially occluding the lumen (A), which was cleared by regular bronchoscopies and DNAase. (B) Image at 6 months, showing that reabsorption of the stent (white areas) caused so-called cobblestones of granulation tissue with little normal epithelium. (C) At 15 months after surgery, the graft seemed to be patent, with healthy mucosa.

Figure 3. Identification of protein in the tracheal exudate

Proteins in the tracheal exudate identified in the early weeks (sampled postoperative week 2) were separated using SDS-PAGE and stained with colloidal Coomassie Blue (A). Destained gel slices were digested with trypsin (Promega, Southampton, UK), fractionated by high-performance liquid chromatography (NanoAcquity, Waters, Manchester, UK), and analysed using an in-line Q-TOF mass spectrometer (Waters). (B) The table shows the proteins identified from at least two peptides and with a PLGS score greater than 10. PLGS=Protein Lynx Global Server.

Figure 4. Findings on cytology

Haematoxylin and eosin staining of (A) normal trachea compared with (B) the patient’s previous tracheal homograft removed at the time of surgery, which shows an epithelialised lining but atypical gland formation. (C) A sample of the decellularised tracheal graft used in this study shows loss of cells but preservation of normal architecture. (D) Bronchial brushing taken from the middle of the graft 1 year after surgery shows a cluster of ciliated cells.

Figure 5. Follow-up scans

(A) CT axial scan and (B) coronal scan done 12 months after surgery show the tracheal graft (arrows) surrounded by omental fat (*). The lumen of the graft is narrow (6 mm) and its wall is thick (3-4 mm). Growth in length of the graft was not seen on serial images, possibly because growth in height of the child was not matched by lengthening of the chest. (C) A lung scan (ventilation-perfusion) at 18 months showed normal bilateral ventilation (the left lung is contributing 45% to the total ventilation and the right lung 55%). There is a slight reduction in perfusion in the left lung (receiving 37% of the right heart output) compared with the right lung (63%).