The human airway epithelium is regenerated by basal cells. Thus, basal cell therapy has the potential to cure cystic fibrosis (CF) lung disease. We previously reported that the human basal cells repopulated the mouse airway epithelium after transplantation, and we estimated that 60 million cells would be needed to treat a human patient. To further develop cell therapy, we compared the proliferation potential of non‐CF and CF tissue‐derived bronchial basal cells. Three methods were used: regenerative cell frequency, burst size, and cell division frequency. Second, we used a serial passage strategy to determine if CF basal cells could be amplified to the estimated therapeutic dose. These studies evaluated that tissue‐derived bronchial basal cells and the basal cells that were recovered by brushing bronchial airways or the nasal respiratory epithelium. Finally, we used the limiting dilution method to isolate non‐CF and CF basal cell clones. The proliferation assays and the air‐liquid‐interface differentiation method were used to determine if cell amplification altered the proliferation and/or differentiation potential of clonal isolates. We demonstrate that: (a) non‐CF and CF basal cell proliferation is similar, (b) CF basal cells can be amplified to a therapeutic cell dose, and (c) amplified non‐CF and CF basal cell clones differentiate normally. Despite these encouraging findings, we also find that the cell amplification process depletes the regenerative basal cell pool. Analysis of basal cell clones indicates that serial passage selects for long‐lived basal cells and raise the possibility that prospective isolation of these stem‐like cells will improve the efficacy of cell replacement therapy. Stem Cells Translational Medicine 2019;8:225&235

Objectives Humans receiving tissue-engineered tracheal grafts have experienced poor outcomes ultimately resulting in death or the need for graft explantation. We assessed the performance of the synthetic scaffolds used in humans with an ovine model of orthotopic tracheal replacement, applying standard postsurgical surveillance and interventions to define the factors that contributed to the complications seen at the bedside. Study Design Large animal model. Setting Pediatric academic research institute. Subjects and Methods Human scaffolds were manufactured with an electrospun blend of polyethylene terephthalate and polyurethane reinforced with polycarbonate rings. They were seeded with autologous bone marrow–derived mononuclear cells and implanted in sheep. Animals were evaluated with routine bronchoscopy and fluoroscopy. Endoscopic dilation and stenting were performed to manage graft stenosis for up to a 4-month time point. Grafts and adjacent native airway were sectioned and evaluated with histology and immunohistochemistry. Results All animals had signs of graft stenosis. Three of 5 animals (60%) designated for long-term surveillance survived until the 4-month time point. Graft dilation and stent placement resolved respiratory symptoms and prolonged survival. Necropsy demonstrated evidence of infection and graft encapsulation. Granulation tissue with signs of neovascularization was seen at the anastomoses, but epithelialization was never observed. Acute and chronic inflammation of the native airway epithelium was observed at all time points. Architectural changes of the scaffold included posterior wall infolding and scaffold delamination. Conclusions In our ovine model, clinically applied synthetic tissue-engineered tracheas demonstrated infectious, inflammatory, and mechanical failures with a lack of epithelialization and neovascularization.

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