Nicholas J. Hamilton

Rapid Expansion of Human Epithelial Stem Cells Suitable for Airway Tissue Engineering

RATIONALE Stem cell-based tracheal replacement represents an emerging therapeutic option for patients with otherwise untreatable airway diseases including long-segment congenital tracheal stenosis and upper airway tumors. Clinical experience demonstrates that restoration of mucociliary clearance in the lungs after transplantation of tissue-engineered grafts is critical, with preclinical studies showing that seeding scaffolds with autologous mucosa improves regeneration. High epithelial cell-seeding densities are required in regenerative medicine, and existing techniques are inadequate to achieve coverage of clinically suitable grafts. OBJECTIVES To define a scalable cell culture system to deliver airway epithelium to clinical grafts. METHODS Human respiratory epithelial cells derived from endobronchial biopsies were cultured using a combination of mitotically inactivated fibroblasts and Rho-associated protein kinase (ROCK) inhibition using Y-27632 (3T3+Y). Cells were analyzed by immunofluorescence, quantitative polymerase chain reaction, and flow cytometry to assess airway stem cell marker expression. Karyotyping and multiplex ligation-dependent probe amplification were performed to assess cell safety. Differentiation capacity was tested in three-dimensional tracheospheres, organotypic cultures, air-liquid interface cultures, and an in vivo tracheal xenograft model. Ciliary function was assessed in air-liquid interface cultures. MEASUREMENTS AND MAIN RESULTS 3T3-J2 feeder cells and ROCK inhibition allowed rapid expansion of airway basal cells. These cells were capable of multipotent differentiation in vitro, generating both ciliated and goblet cell lineages. Cilia were functional with normal beat frequency and pattern. Cultured cells repopulated tracheal scaffolds in a heterotopic transplantation xenograft model. CONCLUSIONS Our method generates large numbers of functional airway basal epithelial cells with the efficiency demanded by clinical transplantation, suggesting its suitability for use in tracheal reconstruction.

Tissue engineering airway mucosa: A systematic review

Effective treatments for hollow organ stenosis, scarring, or agenesis are suboptimal or lacking. Tissue‐engineered implants may provide a solution, but those performed to date are limited by poor mucosalization after transplantation. We aimed to perform a systematic review of the literature on tissue‐engineered airway mucosa. Our objectives were to assess the success of this technology and its potential application to airway regenerative medicine and to determine the direction of future research to maximize its therapeutic and commercial potential.

LRIG1 regulates cadherin‐dependent contact inhibition directing epithelial homeostasis and pre‐invasive squamous cell carcinoma development

Epidermal growth factor receptor (EGFR) pathway activation is a frequent event in human carcinomas. Mutations in EGFR itself are, however, rare, and the mechanisms regulating EGFR activation remain elusive. Leucine‐rich immunoglobulin repeats‐1 (LRIG1), an inhibitor of EGFR activity, is one of four genes identified that predict patient survival across solid tumour types including breast, lung, melanoma, glioma, and bladder. We show that deletion of Lrig1 is sufficient to promote murine airway hyperplasia through loss of contact inhibition and that re‐expression of LRIG1 in human lung cancer cells inhibits tumourigenesis. LRIG1 regulation of contact inhibition occurs via ternary complex formation with EGFR and E‐cadherin with downstream modulation of EGFR activity. We find that LRIG1 LOH is frequent across cancers and its loss is an early event in the development of human squamous carcinomas. Our findings imply that the early stages of squamous carcinoma development are driven by a change in amplitude of EGFR signalling governed by the loss of contact inhibition.

Vacuum-assisted decellularization: an accelerated protocol to generate tissue-engineered human tracheal scaffolds

Patients with large tracheal lesions unsuitable for conventional endoscopic or open operations may require a tracheal replacement but there is no present consensus of how this may be achieved. Tissue engineering using decellularized or synthetic tracheal scaffolds offers a new avenue for airway reconstruction. Decellularized human donor tracheal scaffolds have been applied in compassionate-use clinical cases but naturally derived extracellular matrix (ECM) scaffolds demand lengthy preparation times. Here, we compare a clinically applied detergent-enzymatic method (DEM) with an accelerated vacuum-assisted decellularization (VAD) protocol. We examined the histological appearance, DNA content and extracellular matrix composition of human donor tracheae decellularized using these techniques. Further, we performed scanning electron microscopy (SEM) and biomechanical testing to analyze decellularization performance. To assess the biocompatibility of scaffolds generated using VAD, we seeded scaffolds with primary human airway epithelial cells in vitro and performed in vivo chick chorioallantoic membrane (CAM) and subcutaneous implantation assays. Both DEM and VAD protocols produced well-decellularized tracheal scaffolds with no adverse mechanical effects and scaffolds retained the capacity for in vitro and in vivo cellular integration. We conclude that the substantial reduction in time required to produce scaffolds using VAD compared to DEM (approximately 9 days vs. 3–8 weeks) does not compromise the quality of human tracheal scaffold generated. These findings might inform clinical decellularization techniques as VAD offers accelerated scaffold production and reduces the associated costs.

A comparison of tracheal scaffold strategies for pediatric transplantation in a rabbit model

Despite surgical advances, childhood tracheal stenosis is associated with high morbidity and mortality. Various tracheal scaffold strategies have been developed as the basis for bioengineered substitutes, but there is no consensus on which may be superior in vivo. We hypothesized that there would be no difference in morbidity and mortality between three competing scaffold strategies in rabbits.

Use of a single channel dedicated to conveying enhanced temporal periodicity cues in cochlear implants: Effects on prosodic perception and vowel identification

The continuous interleaved sampling (CIS) strategy for cochlear implants has well-established limitations for the perception of pitch changes in speech. This study investigated a modification of CIS in which one channel was dedicated to the transmission of a temporal encoding of fundamental frequency (F0). Normal hearing subjects listening to noise-excited vocoders, and implantees were tested on labelling the pitch movement of diphthongal glides, on using intonation information to identify sentences as question or statement, and on vowel recognition. There were no significant differences between modified processing and CIS in vowel recognition. However, while there was limited evidence of improved pitch perception relative to CIS with simplified F0 modulation applied to the most basal channel, in general it appears that for most implant users, restricting F0-related modulation to one channel does not provide significantly enhanced pitch information.

Tracheal Replacement Therapy with a Stem Cell‐Seeded Graft: Lessons from Compassionate Use Application of a GMP‐Compliant Tissue‐Engineered Medicine

Tracheal replacement for the treatment of end‐stage airway disease remains an elusive goal. The use of tissue‐engineered tracheae in compassionate use cases suggests that such an approach is a viable option. Here, a stem cell‐seeded, decellularized tissue‐engineered tracheal graft was used on a compassionate basis for a girl with critical tracheal stenosis after conventional reconstructive techniques failed. The graft represents the first cell‐seeded tracheal graft manufactured to full good manufacturing practice (GMP) standards. We report important preclinical and clinical data from the case, which ended in the death of the recipient. Early results were encouraging, but an acute event, hypothesized to be an intrathoracic bleed, caused sudden airway obstruction 3 weeks post‐transplantation, resulting in her death. We detail the clinical events and identify areas of priority to improve future grafts. In particular, we advocate the use of stents during the first few months post‐implantation. The negative outcome of this case highlights the inherent difficulties in clinical translation where preclinical in vivo models cannot replicate complex clinical scenarios that are encountered. The practical difficulties in delivering GMP grafts underscore the need to refine protocols for phase I clinical trials. Stem Cells Translational Medicine 2017;6:1458–1464

Reply to: “Recent Advances in Circumferential Tracheal Replacement and Transplantation”

We would like to thank Wurtz and colleagues for their comments on our article documenting the 4-year follow-up of the first tissue-engineered total tracheal replacement in a child (1). Although the fate of the tracheal allograft cannot be determined with certainty, serial endoscopy and computed tomography indicated that the graft embedded within the stent and remodeled over time, with growth occurring at the proximal and distal nonstented areas (Figure 1). Despite the loss of mechanical integrity when using a decellularized method, this case remains the most successful circumferential total tracheal replacement reported, albeit after several months of intensive treatment and the need for stenting. We look forward to reading the outlined large animal investigation using a cryopreserved allograft and hope to see biomechanical data to compare with our decellularized method. An omental-flap wrap is a useful technique prior to transplantation, as has been reported in bladder, bowel, and esophageal replacement (2–4); however, because of the emergent nature of our case, prevascularization was not possible. Instead, part of the omentum was transposed at the point of transplantation (5).

Co-culture-expanded human basal epithelial stem cells for application in tracheal tissue engineering

Abstract Background Stem-cell-based tracheal replacement has been used to treat patients with end-stage airway disease in compassionate cases. Clinical experience suggests that restoration of an epithelial barrier is a priority to improve outcomes, but recent data suggest that a substantial number of autologous epithelial cells are required for effective engraftment. Existing cell culture methods fail to expand the airway epithelial progenitor pool, presenting a considerable hurdle for progression to clinical trials. We aimed to assess feeder layers and a Rho-associated kinase inhibitor as a method to expand human respiratory epithlieum for airway bioengineering. Methods Human epithelial cells from endobronchial biopsy samples were cultured on mouse 3T3-J2 fibroblast feeder layers in medium containing Y-27632, a Rho-associated kinase inhibitor (3T3+Y). Air-liquid interface and tracheosphere assays were done to determine differentiation capacity, and high-speed video microscopy to observe ciliary behaviour. Telomerase expression was measured with immunofluorescence and western blotting and telomere length with real-time PCR. Cells were karyotyped and engraftment potential tested in ex-vivo and in-vivo xenograft models. Findings 3T3+Y allowed for rapid and sustained expansion of airway epithelial basal cells. Population doublings demonstrated that cultures derived from donor biopsy samples could provide sufficient cell numbers to recellularise human tracheal scaffolds. At clinically applicable passages, cells were capable of airway differentiation in vitro, forming both ciliated and goblet lineages. Ciliary beat frequency and beat pattern were within normal range. Cells were karyotypically normal despite extensive expansion. Protein expression of telomerase was increased in 3T3+Y compared with that in conventional growth medium, and telomere length appeared to stabilise. Cultured cells repopulated a decellularised tracheal scaffold ex vivo and restored a differentiated epithelium in an in-vivo tracheal transplantation xenograft model. Interpretation The findings show that 3T3+Y generates large numbers of airway basal epithelial stem cells that retain qualities desirable for clinical transplantation. These data have important implications for personalised autologous airway epithelial cell therapy because cells could be obtained rapidly and in an appropriate number. Preclinical and clinical validation is required. Funding Wellcome Trust.

Use of a decellularised dermis scaffold and human bronchial epithelial cells to tissue engineer airway mucosa suitable for tracheal transplantation

Abstract Background Tracheal reconstruction relies on the use of a split skin graft to re-epithelialise the mucosal layer. Since split skin grafts are made up of a keratinising stratified epithelial layer, sloughing occurs within the airway with mucus retention and subsequent airway obstruction. The delivery of a graft with the same mucociliary function as the native airway would overcome these limitations and greatly improve the safety and effectiveness of this type of surgery. We aimed to generate a transplantable tissue-engineered respiratory epithelial graft with mucociliary function. Methods Cadaveric human skin was decellularised and the epidermal layer removed. Human bronchial epithelial cells were seeded with human respiratory fibroblasts onto the dermis at densities of 1 × 10 6 per cm 2 and 1 × 10 4 per cm 2 , respectively, and cultured at air–liquid interface in a transwell system. At 3 weeks, the constructs were transplanted onto a decellularised trachea that had been prevascularised within a muscle wrap in an immunosuppressed New Zealand White rabbit. Findings After 3 weeks of air–liquid interface culture, high-speed video microscopy showed beating cilia on the surface of the dermis, and the epithelial layer stained positively for the ciliated cell marker acetylated α-tubulin, the secretory cell marker MUC5AC, and the epithelial cell marker pan-cytokeratin on top-down whole-mount confocal microscopy. Staining with haematoxylin and eosin (H&E) demonstrated a pseudostratified mucociliary layer along the length of the dermis. 24 h after transplantation, a pseudostratified, ciliated layer could be observed on H&E staining of sections of trachea. At 5 days, the respiratory epithelial layer consisted of a single layer of cytokeratin 5-positive epithelial cells. Interpretation This study is the first, to our knowledge, to report the delivery of a transplantable tissue-engineered respiratory epithelial graft with mucociliary function. 24 h after transplantation the mucociliary layer was preserved although only a basal layer was demonstrated by 5 days, possibly due to the loss of the air–liquid interface within the muscle wrap. Funding Medical Research Council.