Isabelle M.A. Lombaert

Head and neck cancer is the fifth most common malignancy and accounts for 3% of all new cancer cases each year. Despite relatively high survival rates, the quality of life of these patients is severely compromised because of radiation-induced impairment of salivary gland function and consequential xerostomia (dry mouth syndrome). In this study, a clinically applicable method for the restoration of radiation-impaired salivary gland function using salivary gland stem cell transplantation was developed. Salivary gland cells were isolated from murine submandibular glands and cultured in vitro as salispheres, which contained cells expressing the stem cell markers Sca-1, c-Kit and Musashi-1. In vitro, the cells differentiated into salivary gland duct cells and mucin and amylase producing acinar cells. Stem cell enrichment was performed by flow cytrometric selection using c-Kit as a marker. In vitro, the cells differentiated into amylase producing acinar cells. In vivo, intra-glandular transplantation of a small number of c-Kit(+) cells resulted in long-term restoration of salivary gland morphology and function. Moreover, donor-derived stem cells could be isolated from primary recipients, cultured as secondary spheres and after re-transplantation ameliorate radiation damage. Our approach is the first proof for the potential use of stem cell transplantation to functionally rescue salivary gland deficiency.

The maintenance of a progenitor cell population as a reservoir of undifferentiated cells is required for organ development and regeneration. However, the mechanisms by which epithelial progenitor cells are maintained during organogenesis are poorly understood. We report that removal of the parasympathetic ganglion in mouse explant organ culture decreased the number and morphogenesis of keratin 5-positive epithelial progenitor cells. These effects were rescued with an acetylcholine analog. We demonstrate that acetylcholine signaling, via the muscarinic M1 receptor and epidermal growth factor receptor, increased epithelial morphogenesis and proliferation of the keratin 5-positive progenitor cells. Parasympathetic innervation maintained the epithelial progenitor cell population in an undifferentiated state, which was required for organogenesis. This mechanism for epithelial progenitor cell maintenance may be targeted for organ repair or regeneration.

PURPOSE: One of the major reasons for failure of radiotherapeutic cancer treatment is the limitation in dose that can be applied to the tumor because of coirradiation of the normal healthy tissue. Late radiation-induced damage reduces the quality of life of the patient and may even be life threatening. Replacement of the radiation-sterilized stem cells with unirradiated autologous stem cells may restore the tissue function. Here, we assessed the potential of granulocyte colony-stimulating factor (G-CSF)-mobilized bone marrow-derived cells (BMC) to regenerate and functionally restore irradiated salivary glands used as a model for normal tissue damage. EXPERIMENTAL DESIGN: Male-eGFP+ bone marrow chimeric female C57BL/6 mice were treated with G-CSF, 10 to 60 days after local salivary gland irradiation. Four months after irradiation, salivary gland morphology and flow rate were assessed. RESULTS: G-CSF treatment induced homing of large number of labeled BMCs to the submandibular glands after irradiation. These animals showed significant increased gland weight, number of acinar cells, and salivary flow rates. Donor cells expressed surface markers specific for hematopoietic or endothelial/mesenchymal cells. However, salivary gland acinar cells neither express the G-CSF receptor nor contained the GFP/Y chromosome donor cell label. CONCLUSIONS: The results show that BMCs home to damaged salivary glands after mobilization and induce repair processes, which improve function and morphology. This process does not involve transdifferentiation of BMCs to salivary gland cells. Mobilization of BMCs could become a promising modality to ameliorate radiation-induced complications after radiotherapy.