Mesenchymal Stem Cell Grafting to Treat Cutaneous Radiation Syndrome: Developement of a New Minipig Model.

Abstract 4574

Cutaneous radiation syndrome (CRS) is the delayed consequence of localized skin exposure to high doses of ionizing radiations. Recent grafting of 3 burned patients has suggested the benefit of local injection of bone marrow multipotent mesenchymal stem cells to favour wound healing. However, further studies are required to standardize recommendations. The aim of this study was to set up a pig model of severe CRS in order to clarify some of these points. Göttingen minipigs were locally irradiated (20 cm x 3 cm area at the back) using a ⁶⁰Co gamma source. This model corresponds to a 50-60 Gy entrance and a 15-25 Gy exit dose delivery. Skin damage was associated to deeper lesions especially muscular. Experimental groups were as followed: ungrafted 50 Gy (n=2) and 60 Gy (n=1); grafted 50 Gy (minipig GM5) and 60 Gy (minipig GM4). Humeral bone marrow collected before irradiation was put into culture in minimal essential medium with 10% Fetal Calf Serum and Fibroblast Growth Factor (2ng/ml) at 37° in air with 5% CO₂. Pig GM5 was intradermally injected at days 48, 69 and 96 for a total amount of 128.5 ×10⁶ MSC, pig GM4 at days 48 and 69 for a total amount of 99 ×10⁶ MSC (range 2 to 3×10⁶ MSC per point). All animals exhibited an early erythema on day 1 and a hair loss marked within 28 days. Minipig GM4, grafted after the onset of macroscopic damage (day 40), exhibited a similar evolution to controls. In minipig GM5, local inflammation and macroscopic damages were delayed in entrance area when compared with ungrafted 50 Gy animals (thermal camera signal at day 96 versus day 53; no macroscopic damage in entrance area until day 222 euthanasia versus day 85).

Immunolabellings showed severe late skin damages in all animals (reduced keratinisation, deep ingrowth of epidermis, small cavities and apoptotic cells). Finally this study establishes a new minipig model close to human for the improvement of cell therapy strategies to treat high local irradiations. Work is going on to document the homing of injected cells (eGFP labelled MSC) and the molecular response of grafted tissues in order to optimize graft efficacy.