Noëlle Mathieu

Mesenchymal stem cell therapy stimulates endogenous host progenitor cells to improve colonic epithelial regeneration.

Patients who undergo pelvic radiotherapy may develop severe and chronic complications resulting from gastrointestinal alterations. The lack of curative treatment highlights the importance of novel and effective therapeutic strategies. We thus tested the therapeutic benefit of mesenchymal stem cells (MSC) treatment and proposed molecular mechanisms of action. MSC efficacy was tested in an experimental model of radiation-induced severe colonic ulceration histologically similar to that observed in patients. In this model, MSC from bone marrow were administered intravenously, immediately or three weeks (established lesions) after irradiation. MSC therapy reduces radiation-induced colonic ulceration and increases animal survival. MSC treatment induces therapeutic efficacy whatever the time of cell infusion. Infused-MSC engraft in the colon but also increase endogenous MSC mobilization in blood that have lasting benefits over time. In vitro analysis demonstrates that the MSC effect is mediated by paracrine mechanisms through the non-canonical WNT (Wingless integration site) pathway. In irradiated rat colons, MSC treatment increases the expression of the non-canonical WNT4 ligand by epithelial cells. The epithelial regenerative process is improved after MSC injection by stimulation of colonic epithelial cells positive for SOX9 (SRY-box containing gene 9) progenitor/stem cell markers. This study demonstrates that MSC treatment induces stimulation of endogenous host progenitor cells to improve the regenerative process and constitutes an initial approach to arguing in favor of the use of MSC to limit/reduce colorectal damage induced by radiation.

Characterization and Histological Localization of Multipotent Mesenchymal Stromal Cells in the Human Postnatal Thymus

The aim of this work was to characterize multipotent mesenchymal stromal cells (MSCs) in the postnatal human thymus and to localize these MSCs in the organ. Adherent cells isolated from thymus samples were characterized by cell-surface antigen expression. This showed that adherent cells have a MSC profile as assessed by the expression of CD73 and CD105 markers and the lack of CD45 expression. These cells are able to differentiate in vitro into adipocytes, osteoblasts, and chondrocytes and to inhibit mixed lymphocyte reaction. This indicates that isolated cells have all of the characteristics of MSC. The fibroblast colony-forming unit (CFU-F) assay was used to determine their frequency in the postnatal thymus. This frequency was 60.9 +/- 14.8 CFU-F per 1 x 10(5) freshly isolated mononuclear cells. Moreover, taking advantage of CD34 and CD105 expression, immunohistological staining allowed us to localize MSC within interlobular trabeculae in close contact with the outer cortex. Polymerase chain reaction experiments indicated that thymic MSC expressed interleukin-7 and stromal cell-derived factor-1 messenger RNA. Overall, these results confirm previous findings of the presence in the adult human thymus of multipotent MSCs with a phenotype similar to adipose-derived adult stem cells. These results also show for the first time a histological localization of MSC in an organ. This suggests a possible role of thymic MSC in intrathymic differentiation.

TH17 predominant T-cell responses in radiation-induced bowel disease are modulated by treatment with adipose-derived mesenchymal stromal cells.

Radiation proctitis is an insidious disease associated with substantial morbidity and mortality. It may develop following the treatment of several cancers by radiotherapy when normal colorectal tissues are present in the irradiation field. There is no unified approach for the assessment and treatment of this disease, partly due to insufficient knowledge about the mechanism involved in the development of radiation proctitis. However, unresolved inflammation is hypothesized to have an important role in late side effects. This study aimed to analyse the involvement of specific immunity in colorectal damage developing after localized irradiation, and evaluate the benefit of immunomodulatory mesenchymal stromal cells isolated from adipose tissue (Ad‐MSCs) for reduction of late side effects. Our experimental model of colorectal irradiation induced severe colonic mucosal damage and fibrosis that was associated with T‐cell infiltration. Immune cell activation was investigated; adoptive transfer of T cells in nude rats showed stronger colonization by T cells isolated from irradiated rats. The predominant role of T cells in late radiation‐induced damage and regeneration processes was highlighted by in vivo depletion experiments. Treatments using Ad‐MSCs reduced T‐cell infiltration in the colon and reduced established colonic damage as measured by histological score, functional circular muscle contractibility, and collagen deposition. Here, we have demonstrated for the first time the predominance of the TH17 population compared to TH1 and TH2 in radiation‐induced bowel disease, and that this is reduced after Ad‐MSC treatment. Additionally, we demonstrated in vitro that IL17 acts directly on colonic smooth muscle cells to induce expression of pro‐inflammatory genes that could participate in the development of radiation‐induced injury. Our data demonstrate that the TH17 population is specifically induced during development of radiation‐induced side effects in the colon. Moreover, Ad‐MSC treatment modulates the TH17 population and reduces the extracellular matrix remodelling process induced following irradiation. Copyright

Bowel Radiation Injury: Complexity of the pathophysiology and promises of cell and tissue engineering.

Ionizing radiation is effective to treat malignant pelvic cancers, but the toxicity to surrounding healthy tissue remains a substantial limitation. Early and late side effects not only limit the escalation of the radiation dose to the tumor but may also be life-threatening in some patients. Numerous preclinical studies determined specific mechanisms induced after irradiation in different compartments of the intestine. This review outlines the complexity of the pathogenesis, highlighting the roles of the epithelial barrier in the vascular network, and the inflammatory microenvironment, which together lead to chronic fibrosis. Despite the large number of pharmacological molecules available, the studies presented in this review provide encouraging proof of concept regarding the use of mesenchymal stromal cell (MSC) therapy to treat radiation-induced intestinal damage. The therapeutic efficacy of MSCs has been demonstrated in animal models and in patients, but an enormous number of cells and multiple injections are needed due to their poor engraftment capacity. Moreover, it has been observed that although MSCs have pleiotropic effects, some intestinal compartments are less restored after a high dose of irradiation. Future research should seek to optimize the efficacy of the injected cells, particularly with regard to extending their life span in the irradiated tissue. Moreover, improving the host microenvironment, combining MSCs with other specific regenerative cells, or introducing new tissue engineering strategies could be tested as methods to treat the severe side effects of pelvic radiotherapy.

Development of mandibular osteoradionecrosis in rats: Importance of dental extraction

OBJECTIVES To develop an animal model of mandibular osteoradionecrosis (ORN) using a high-energy radiation source (as used in human therapeutics) and to assess the role of tooth extraction on ORN development. MATERIALS AND METHODS (STUDY DESIGN) Ten animals were irradiated with a single 35- or 50-Gy dose. Three weeks later, the second left mandibular molar was extracted from three animals in each group. Nine weeks after irradiation, the animals were euthanized, with an injection of contrast agent in the bloodstream to highlight vascularization. Mandibles were harvested and studied using micro-CT, histology, tartrate-resistant acid phosphatase activity and scanning electron microscopy. RESULTS This study demonstrates that a single 50-Gy dose associated with molar extraction is necessary for ORN development. In these conditions, absence of healing of the mucosa and bone, dental effects, fibrosis, an increase in osteoclast activity and a decrease in vascularization were observed. We also determined that molar extraction increases the impact of the cellular effects of radiation. CONCLUSION The mandibular ORN animal model was validated after 50-Gy irradiation and molar extraction. The results of this study therefore support an animal ORN model and tissue engineering strategies will now be developed to regenerate bone for patients with head and neck cancer.

Adipose-Derived Mesenchymal Stromal Cells Improve the Healing of Colonic Anastomoses Following High Dose of Irradiation Through Anti-Inflammatory and Angiogenic Processes:

Cancer patients treated with radiotherapy (RT) could develop severe late side effects that affect their quality of life. Long-term bowel complications after RT are mainly characterized by a transmural fibrosis that could lead to intestinal obstruction. Today, surgical resection is the only effective treatment. However, preoperative RT increases the risk of anastomotic leakage. In this study, we attempted to use mesenchymal stromal cells from adipose tissue (Ad-MSCs) to improve colonic anastomosis after high-dose irradiation. MSCs were isolated from the subcutaneous fat of rats, amplified in vitro, and characterized by flow cytometry. An animal model of late radiation side effects was induced by local irradiation of the colon. Colonic anastomosis was performed 4 wk after irradiation. It was analyzed another 4 wk later (i.e., 8 wk after irradiation). The Ad-MSC-treated group received injections several times before and after the surgical procedure. The therapeutic benefit of the Ad-MSC treatment was determined by colonoscopy and histology. The inflammatory process was investigated using Fluorine-182-Fluoro-2-Deoxy-d-Glucose Positron Emission Tomography and Computed Tomography (18F-FDG-PET/CT) imaging and macrophage infiltrate analyses. Vascular density was assessed using immunohistochemistry. Results show that Ad-MSC treatment reduces ulcer size, increases mucosal vascular density, and limits hemorrhage. We also determined that 1 Ad-MSC injection limits the inflammatory process, as evaluated through 18F-FDG-PET-CT (at 4 wk), with a greater proportion of type 2 macrophages after iterative cell injections (8 wk). In conclusion, Ad-MSC injections promote anastomotic healing in an irradiated colon through enhanced vessel formation and reduced inflammation. This study also determined parameters that could be improved in further investigations.