Objective:To explore the effect and mechanism of dendritic cell derived exosomes (Dexs) loading ubiquitinated (Ub) hepatitis D antigen (HDAg) on activating specific cytotoxic T lymphocytes (CTL).Methods:Ub-S-HDAg-Dexs were co-cultured with dendritic cells (DC) which were from the femora of C57BL/6 mice for 48 h, then flow cytometry was used to detect the maturity of DC (CD86, CD80 and major histocompatibility complex (MHC) Ⅱ). The spleen-derived T lymphocytes from C57BL/6 mice were added in vitro to activate DC and co-cultivated for 72 h. The T cells were divided into Ub-S-HDAg-Dexs group (add 50 μg/mL Ub-S-HDAg-Dexs), Blank-Dexs group (add 50 μg/mL DC derived exosomes without plasmid transfection), Con-Dexs group (add 50 μg/mL DC derived exosomes transfected by cantrol plasmid), PBS group (add 50 μL/mL phosphate buffered saline), and Ub-S-HDAg-Dexs+ AG490 group (add 50 μg/mL Ub-S-HDAg-Dexs, DC and T lymphocytes stimulated by exosomes, and 50 μmol/L AG490 was also added to the cell mix). Flow cytometry was used to detect CD8 + T cells secreting interferon-gamma, non-radioactive lactate dehydrogenase release test to detect the killing activity of specific CTL. Real-time quantitative polymerase chain reaction (PCR) and Western blotting were used to detect the mRNA and protein expressions of JAK kinase (JAK) 2, GATA-binding protein 3 (GATA3), T-bet, signal transduction and activator of transcription (STAT) 1 and STAT4. Independent sample t test were used for statistical analysis. Results:The positive rates of the surface molecules CD80, CD86, MHCⅡof DC stimulated by Ub-S-HDAg-Dexs were 83.850%±0.219%、68.910%±0.134%、84.320%±0.445%, respectively.In the Ub-S-HDAg-Dexs group, the rate of CD8 + T cells secreting interferon-gamma was 6.420%±0.028%, which was higher than those of other groups, including PBS group, Blank-Dexs group, Con-Dexs group and Ub-S-HDAg-Dexs+ AG490 group ( t=90.78, 30.32, 63.06 and 85.42, respectively, all P<0.001). The cytotoxicity of T cells in the Ub-S-HDAg-Dexs group was 82.4%±3.9%, which was higher than those of other groups ( t=17.28, 9.74, 3.95 and 15.89, respectively, all P<0.050). The relative mRNA expressions of JAK2, T-bet, STAT1, STAT4 in Ub-S-HDAg-Dexs group were higher than those in other groups, including Con-Dexs group ( t=10.74, 32.34, 13.00 and 16.28, respectively, all P<0.001), Blank-Dexs group ( t=15.05, 21.51, 6.46 and 13.12, respectively, all P<0.050), PBS group ( t=21.83, 41.42, 7.30 and 17.50, respectively, all P<0.050), Ub-S-HDAg-Dexs+ AG490 group ( t=35.75, 20.69, 17.02 and 17.07, respectively, all P<0.001), and the differences were all statistically significant. The protein expressions of T-bet, STAT1, STAT4 in Ub-S-HDAg-Dexs group increased compared with those in PBS group ( t=346.70, 57.54 and 55.81, respectively, all P<0.001), with statistical significance. In the presence of AG490, the protein expressions of T-bet, STAT1 and STAT4 decreased compared with those in Ub-S-HDAg-Dexs group, and the differences were statistically significant ( t=355.40, 52.79 and 126.10, respectively, all P<0.001). Conclusions:Ubiquitinated HDAg transported by exosomes could effectively promote DC maturation, induce T lymphocyte differentiation, and generate specific CTL responses, which provides a new idea for the treatment of hepatitis D.