Alexandra Sémont

Local irradiation not only induces homing of human mesenchymal stem cells at exposed sites but promotes their widespread engraftment to multiple organs : A study of their quantitative distribution after irradiation damage

Mesenchymal stem cells (MSCs) have been shown to migrate to various tissues. There is little information on the fate and potential therapeutic efficacy of the reinfusion of MSCs following total body irradiation (TBI). We addressed this question using human MSC (hMSCs) infused to nonobese diabetic/ severe combined immunodeficient (NOD/SCID) mice submitted to TBI. Further, we tested the impact of additional local irradiation (ALI) superimposed to TBI, as a model of accidental irradiation. NOD/SCID mice were transplanted with hM‐SCs. Group 1 was not irradiated before receiving hMSC infusion. Group 2 received only TBI at a dose of 3.5 Gy, group 3 received local irradiation to the abdomen at a dose of 4.5 Gy in addition to TBI, and group 4 received local irradiation to the leg at 26.5 Gy in addition to TBI. Fifteen days after irradiation, quantitative and spatial distribution of the hMSCs were studied. Histological analysis of mouse tissues confirmed the presence of radio‐induced lesions in the irradiated fields. Following their infusion into nonirradiated animals, hMSCs homed at a very low level to various tissues (lung, bone marrow, and muscles) and no significant engraftment was found in other organs. TBI induced an increase of engraftment levels of hMSCs in the brain, heart, bone marrow, and muscles. Abdominal irradiation (AI) as compared with leg irradiation (LI) increased hMSC engraftment in the exposed area (the gut, liver, and spleen). Hind LI as compared with AI increased hMSC engraftment in the exposed area (skin, quadriceps, and muscles). An increase of hMSC engraftment in organs outside the fields of the ALI was also observed. Conversely, following LI, hMSC engraftment was increased in the brain as compared with AI. This study shows that engraftment of hMSCs in NOD/ SCID mice with significantly increased in response to tissue injuries following TBI with or without ALI. ALI induced an increase of the level of engraftment at sites outside the local irradiation field, thus suggesting a distant (abscopal) effect of radiation damage. This work supports the use of MSCs to repair damaged normal tissues following accidental irradiation and possibly in patients submitted to radiotherapy.

Mesenchymal Stem Cells Increase Self-Renewal of Small Intestinal Epithelium and Accelerate Structural Recovery after Radiation Injury

Patients who undergo pelvic or abdominal radiotherapy may develop side effects that can be life threatening. Tissue complications caused by radiation-induced stem cell depletion may result in structural and functional alterations of the gastrointestinal (GI) tract. Stem cell therapy using mesenchymal stem cells (MSC) is a promising approach for replenishment of the depleted stem cell compartment during radiotherapy. There is little information on the therapeutic potential of MSC in injured-GI tract following radiation exposure. In this study, we addressed the ability of MSC to support the structural regeneration of the small intestine after abdominal irradiation. We isolated MSC from human bone marrow and human mesenchymal stem cells (hMSC) were transplanted into immunotolerent NOD/SCID mice with a dose of 5.10(6) cells via the systemic route. Using a model of radiation-induced intestinal injury, we studied the link between damage, hMSC engraftment and the capacity of hMSC to sustain structural recovery. Tissue injury was assessed by histological analysis. hMSC engraftment in tissues was quantified by PCR assay. Following abdominal irradiation, the histological analysis of small intestinal structure confirms the presence of partial and transient (three days) mucosal atrophy. PCR analysis evidences a low but significant hMSC implantation in small intestine (0.17%) but also at all the sites of local irradiation (kidney, stomach and spleen). Finally, in presence of hMSC, the small intestinal structure is already recovered at three days after abdominal radiation exposure. We show a structural recovery accompanied by an increase of small intestinal villus height, three and fifteen days following abdominal radiation exposure. In this study, we show that radiation-induced small intestinal injury may play a role in the recruitment of MSC for the improvement of tissue recovery. This work supports, the use of MSC infusion to repair damaged GI tract in patients subjected to radiotherapy. MSC therapy to avoid extended intestinal crypt sterilization is a promising approach to diminish healthy tissue alterations during the course of pelvic radiotherapy.

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.

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.

Human Mesenchymal Stem Cells (MSC) Indirectly Preserve Liver of Irradiation Damage

The present work was initiated in an effort to evaluate the potential therapeutic contribution of the infusion of MSC for the correction of liver injuries. We subjected NOD-SCID mice to a 10.5 Gy abdominal irradiation and we tested the biological and histological markers of liver injury in the absence and after infusion of expanded human MSC. Irradiation alone induced a significant elevation of transaminases (ALT and AST). Apoptosis in the endothelial layer of vessels was observed. When MSC were infused in mice, a significant decrease of transaminases was measured, and a total disappearance of apoptotic cells. MSC were not found in liver. To explain the protection of liver without MSC en- graftment, we hypothesize an indirect action of MSC on the liver via the intestinal tract. Pelvic or total body irradiation induces intestinal absorption defects leading to an alteration of the enterohepatic recirculation of bile acids. This alteration induces an increase in Deoxy Cholic Acid (DCA) which is hepatoxic. In the present study, we confirm these results. DCA concentration increased approximately 2-fold after irradiation but stayed to the baseline level after MSC injection. We propose from our observations that, following irradiation, MSC infusion indirectly corrected liver dysfunction by preventing gut damage. This explanation would be consistent with the absence of MSC engraftment in liver. These results evidenced that MSC treatment of a target organ may have an effect on distant tissues. This observation comes in support to the interest for the use of MSC for cellular therapy in multiple pathologies proposed in the recent years.