Abstract： Objective To investigate the protective effect and mechanism of glutathione peroxidase 3-(GPx3)modified mesenchymal stem cells(MSC)against radiation-induced lung injury(RILI).Methods GPx3-modified MSCs were injected into the tail vein of mice whose lungs were irradiated with 20 Gy.Lung tissues were collected and sections were stained to observe pathological changes.The expression levels of inflammation-related factors were detected by real time quantitative PCR(qPCR),while the levels of malondialdehyde(MDA),H2O2,and 8-hydroxyguanine(8-OHG)were detected via biochemical experiments.Additionally,RNA damage was assessed by reverse transcription blocking combining with double primer PCR.Results GPx3-modified MSCs significantly improved the pathological damage in post-radiation lung tissues and inhibited the fibrosis process and inflammatory response.GPx3-modified MSCs were able to scavenge reactive oxygen species(ROS)more effectively,resulting in a reduction of lipid peroxidation products such as MDA and oxidative damage to RNA formation of 8-OHG.Conclusion By decreasing ROS accumulation,GPx3-modified MSCs can potentially reduce oxidative damage and attenuate RILI.GPx3-modified MSCs can improve the therapeutic efficacy against RILI.