[The immunoregulatory functions of exosome derived from mesenchymal stem cells that are genetically modified by adeno-associated virus].

Objectives: To verify the effects and mechanisms of natural MSC-exosome in treating acute GVHD in mice, explore and establish a method for targeted modification of MSC-exosome, and verify the functions of the modified MSC-exosome. Methods: In different doses of MSC-exosome groups and MSC group, weight loss in acute GVHD mice was observed; then the proliferation levels of activated T cells were measured through T cell activation experiment in vitro and OVA antigen-specific T cell activation experiment in vivo. AAV2YF3 mutants carrying PD-L1 and PD-L1-ITGB1 were obtained after the construction of recombinant expression vectors and were then applied to infect human MSC to modify their exosome. The immunoregulatory functions of the modified MSC-exosome were measured with the abovementioned methods. Results: ①Mouse MSC-exosome (300 µg×3 times) and MSC (1×10(6)×3 times) effectively alleviated the weight loss in acute GVHD mice. ②Compared with IL-2, 10, 25 and 50 µg human MSC-exosome inhibited the proliferation of activated T cells in vitro, respectively, 86.0% (IL-2) , 40.0%, 39.6%, and 42.8%; compared with PBS, 50, 100 and 200 µg mouse MSC-exosome inhibited the proliferation of antigen-specific activated OT-1 cells in vivo, respectively, 42.6%, 33.1%, 14.2%, and 10.6%. ③After the infection of AAV2YF3 mutant carrying PD-L1 or PD-L1-ITGB1, the positive proportion of MSC-exosome exceeds 40% and 60%, respectively. ④Compared with the natural state, MSC-exosome modified by PD-L1 or PD-L1-ITGB1 showed better proliferation inhibitory effect in vivo and increased the proportion of Treg cells in vitro. Conclusions: MSC-exosome exhibited similar immunomodulatory effects with MSC. MSC-exosome after PD-L1 and PD-L1-ITGB1-targeted modification effectively inhibited the proliferation of activated T cells and increased the proportion of Treg cells.