785P The predictive role of circulating exosomal PD-L1 in cervical cancer immunotherapy

The purpose of this study is to investigate the effect of radiotherapy on programmed death ligand 1 (PD-L1) expression and explore the predictive role of exosomal PD-L1 (ExoPD-L1) in immunotherapy for cervical cancer. The consecutive tumor sample of 40 primarily diagnosed CC patients who accepted radical radiotherapy (RT) were collected before and during RT. Blood samples of 37 advanced CC patients who accepted ICIs combination therapy were collected from each participant before and during treatment. Exosomes were identified by Western blot (CD9/TSG101/Calnexin), transmission electron microscope and nanoparticle tracking analysis. ExoPD-L1 detection was conducted by ELISA. The knockout of PD-L1 was conducted via CRISPR/Cas9 assay and the overexpress of PD-L1 was conducted by lentiviral transfection. Lymphocyte were detected by multicolor flow cytometry. The consecutive detection of PD-L1 showed a dynamic change during RT. Compared with the level before RT, PD-L1 expression elevated in most patients (87.5%) after RT. And the responders (n=18) had elevated ExoPD-L1 level at the first two circles in the ICIs combination therapy (P<0.001). The median follow-up time was 14.13m. The mPFS in increased vs. decreased group: NR vs.11.02m (P=0.025). Continuous blood sampling of mice models also found that effective therapeutic intervention could increase ExoPD-L1 in the early stage. The combination of exosome inhibitor GW4869 and anti-PD-1 further inhibited tumor growth. Mice were injected with external ExoPD-L1OEand ExoPD-L1KO. The results showed that ExoPD-L1OE suppressed body immunity and promoted tumor growth. The results of flow cytometry showed that ExoPD-L1OE inhibited CD8+T cells from releasing interferon-γand granzyme B. And ExoPD-L1OE also suppressed the CD8+T cells proliferation in spleen. The coculture of CD8+T cells and exosomes in vitro also confirmed the above conclusion. Compared with unstable tumoral PD-L1, ExoPD-L1 can better predict the efficacy of immunotherapy in CC, which was with easy accessibility and continuation. Exosome PD-L1 played an immunosuppressive role by inhibiting the proliferation and functional factor release of CD8+T cell.