Fig 1: MSC enhanced the therapeuti efficacy of RT by remodulating tumor microenvironment in vivo.A About 4 × 105 CT26shSTING cells were subcutaneously inoculated into the left leg of BALB/c mice for 10 days (n = 5). About 1 × 106 MSC were intraperitoneally injected into tumor-bearing BALB/c mice on days 10, 15, and 21. Local radiotherapy (5 Gy) was given on days 11, 16, and 21. Tumor volume was measured every 3 days. *p < 0.05 and **p < 0.01. B Tumors were harvested on day 26 for immunohistochemistry. The representative result of cleaved caspase-3 and apoptotic cells was shown. Scale bar: 20 μm. C The TUNEL+ apoptotic cells were evaluated (mean ± SEM, n = 3). *p < 0.05 and **p < 0.01. D The cleaved caspase-3 cells were evaluated (mean ± SEM, n = 3). **p < 0.01 and ***p < 0.001. E The level of cleaved caspase-3 was analyzed. F The quantification of cleaved caspase-3 cells was shown (mean ± SEM, n = 3). ***p < 0.001. G The level of PD-L1 (CD274) was evaluated by qRT-PCR (mean ± SEM, n = 3). ***p < 0.001. H The tumor-infiltrating cytotoxic CD8+, Granzyme B+, and Foxp3+ Treg cells was evaluated by immunofluorescent analysis. Scale bar: 20 μm. I The quantification of cytotoxic CD8+GzmB+ cells was shown (mean ± SEM, n = 3). *p < 0.05. J The quantification of cytotoxic Foxp3+ Treg was shown (mean ± SEM, n = 3).