Epithelial stem cell-mediated development of the human respiratory mucosa in SCID mice

We have developed an in vivo assay for progenitor cells of the human trache obronchial epithelium relying on the transplantation of human prenatal resp iratory tissues into severe combined immunodeficiency mice. Engrafted embry onic or fetal open tracheobronchial rudiments are rapidly closed at each en d by a neoformed membrane that we named the operculum, After 2-4 weeks, dif ferentiated human respiratory epithelium covers both the native airway matr ix and the new operculum. Human epithelial cells dissociated from either em erging embryonic lung primordia or mature xenografts were seeded in host hu man airway grafts, of which native epithelium had been eliminated by severa l cycles of freezing and thawing. All grafts seeded with donor epithelial c ells and implanted back into SCID mice recovered a surface mucociliary epit helium expressing expected markers and secreting mucus. Spontaneous epithel ium regrowth was never observed in control unseeded, denuded grafts. In som e experiments, donor epithelial cells and host denuded airway were sex-mism atched and the donor origin of newly formed epithelial structures was confi rmed by sex chromosome detection, After two rounds of seeding and reimplant ation, a normal epithelium was observed to line the 3rd generation operculu m. These observations substantiate a functional assay for human candidate a irway epithelium stem cells.