Objective:To investigate the role and mechanism of human umbilical cord mesenchymal stem cell exosomes (hUCMSC-ex) in wounds with escharectomy and skin grafting in scalded rats.Methods:The study was an experimental study. Twelve male Sprague-Dawley (SD) rats aged 6-8 weeks were divided into combined treatment group, fixed+allogeneic skin group, autologous skin+allogeneic skin group, and allogeneic skin group by random number table method (the same grouping method hereinafter), with 3 rats in each group. The four groups of rats were inflicted with scalded wounds on the back and performed with escharectomy, and then the wounds of rats in combined treatment group were fixed with a metal ring (the same fixing method hereinafter) and transplanted with autologous skin grafts and allogeneic skin grafts, and the other three groups of rats were fixed and/or transplanted with skin grafts corresponding to the group name. At 14, 21, and 28 d after surgery, the wound healing area in the four groups of rats was measured. Another 15 male SD rats aged 6-8 weeks were divided into normal group with no treatment, high exosome group, low exosome group, supernatant group, and phosphate buffer solution (PBS) group, with 3 rats in each group. The last 4 groups of rats were treated as that in the above-mentioned combined treatment group, and then were injected around the wounds with 200 μL of PBS containing 100 μg of hUCMSC-ex, 200 μL of PBS containing 50 μg of hUCMSC-ex, 200 μL of supernatant with no hUCMSC-ex, and 200 μL of PBS at 0 (immediately), 7, 14, and 21 d after surgery, respectively. At 14, 21, and 28 d after surgery, the wound healing area in the four groups of rats was measured. The wound neo-epithelial tissue of rats in high exosome group and PBS group at 28 d after surgery and the normal skin tissue of rats in normal group at the same time point were taken, and the differentially expressed proteins were screened by label-free quantitative proteomics method; the two up-regulated and differentially expressed proteins, the immunoglobulin G1 heavy chain constant region (IGHG1) and cystatin A (CSTA) with the largest and second largest fold changes in comparison between high exosome group and PBS group were selected, and their protein expressions were detected by Western blotting. The number of samples in all experiments was 3.Results:At 14, 21, and 28 d after surgery, the wound healing area in combined treatment group, autologous skin+allogeneic skin group, and allogeneic skin group of rats was significantly larger than that in fixed+allogeneic skin group ( P<0.05), the wound healing area in autologous skin+allogeneic skin group of rats at 21 d after surgery and that in allogeneic skin group of rats at 14 and 21 d after surgery was significantly larger than that in combined treatment group ( P<0.05), and the wound healing area in allogeneic skin group of rats at 14 d after surgery was significantly larger than that in autologous skin+allogeneic skin group ( P<0.05). The wound healing area of rats in high exosome group and low exosome group at 14, 21, and 28 d after surgery and in supernatant group at 14 and 28 d after surgery was significantly larger than that in PBS group ( P<0.05); the wound healing area in high exosome group of rats at 14 and 21 d after surgery was significantly larger than that in supernatant group ( P<0.05), and the wound healing area at 14 d after surgery was significantly larger than that in low exosome group ( P<0.05); the wound healing area in low exosome group of rats at 14 d after surgery was significantly larger than that in supernatant group ( P<0.05). Compared with that in PBS group, 332 proteins were differentially expressed in the neo-epithelial tissue of the wounds in high exosome group of rats at 28 d after surgery ( P<0.05), among which the protein expressions of IGHG1 and CSTA were significantly up-regulated (with fold change of 12.60 and 2.27, respectively, P<0.05). Compared with those of normal skin tissue in normal group, 1 400 and 1 057 proteins were differentially expressed in the neo-epithelial tissue of the wounds in high exosome group and PBS group of rats at 28 d after surgery, respectively. The protein expressions of IGHG1 and CSTA in the wound neo-epithelial tissue in high exosome group of rats at 28 d after surgery were significantly larger than those in normal skin tissue of rats in normal group ( P<0.05) and those in PBS group ( P<0.05). Conclusions:hUCMSC-ex may accelerate the repair process of wounds with escharectomy and skin grafting and improve the quality of wound healing in scalded rats by regulating the protein expressions of IGHG1 and CSTA.