Disclosures: The following people have nothing to disclose: Roberto Scirpo, Romina Fiorotto, Ambra Villani, Luca Fabris, Mario Strazzabosco Background: Various types of immunosuppressive networks exist in the microenvironment of hepatocelluar carcinoma (HCC). Recently, it has been reported

that myeloid-derived suppressor cells (MDSCs) suppress the function of NK cells and tumor-specific T cells in the tumor-bearing host. In patients with HCC, MDSCs are described as CD33+HLA-DRlowCD11b+CD14+ cells. We showed that MDSCs express surface ALK inhibitor cancer PD-L1 molecules in peripheral blood mononuclear cells (PBMCs) from patients with HCC. The aim of this study is to determine PD-L1+ MDSCs are likely to become a

new biomarker in hepatocellular carcinoma patients. Material and method: Patients: Permission for the study was obtained from the Ethics Committee at our University. (i) We collected blood samples from 30 healthy donors and 120 patients with various stages of HCC who were hospitalized Ulixertinib mouse in our institute and subjected them to multicolor flow cytometric analysis (FACS) for PD-L1+ MDSCs percentages. (ii) We used a transwell coculture system with PBMCs and several different liver cancer cell lines such as HepG2, Huh7, Hep3B, Li7, PLC. After 72 hours coincubation, multicolor FACS analysis was performed. RNA from these cell lines was extracted, and PCR amplification was done using primers for human CSF-1, CSF-2, CSF-3, IL-1β, IL-6, CCL2, VEGFA, S100A8 and S100A9. Results: (i) PBMCs from HCC patients contained significantly higher percentages of PD-L1+ MDSCs in comparison to those from healthy subjects (p < 0.001). PBMCs from TNM IV HCC patients had significantly higher percentages of PD-L1+ MDSCs in comparison to those of TNM I, II and III patients (p < 0.001). However, this increase was not correlated with the Child-Pugh grade, serum concentrations

of cancer biomarkers (AFP and PIVKA-II). The percentages of PD-L1+ MDSCs were reduced by treatment for HCC. (ii) After 72 hours coincubation with the liver cell lines, the percentages of PD-L1+ MDSCs MCE were significantly increased compared with control. By cocultured with Hep3B, Li7 and PLC, the percentages of PD-L1+ MDSCs were higher than in those cocultured with other cell lines (Hep-G2:p<0.05, Huh7:p<0.005, Hep3B, Li7, PLC: p<0.001). The expression of CSF-1 and VEGFA was higher in the cell lines that strongly induced PD-L1+ MDSCs. Conclusion: The differentiation of PD-L1+ MDSCs was induced by soluble factors from hepatocellular carcinoma, and peripheral blood from HCC patients had significantly higher percentages of PD-L1+ MDSCs in comparison to those of healthy subjects. The percentages of PD-L1+ MDSCs were reduced by HCC treatment, suggesting that we might use PD-L1+ MDSCs as a new biomarker and a new target of treatment in hepatocellular carcinoma.