Objective::Pancreatic cancer (PC) is a highly lethal malignancy with an immunosuppressive environment. Yet, current immune checkpoint inhibitor monotherapies have shown limited efficacy in PC, prompting the need for combination therapies. Herein, we hypothesized that combinations of Notch signaling inhibitor and anti-ligand programmed death-ligand 1 (PD-L1) antibody immunotherapy would show synergistic efficacy.Methods::The baseline expression of PD-L1 and HES1 was measured in PC cell lines, single-cell RNA-seq data of PC (GSA: CRA001160), and cBioPortal databases. In an in vitro study, MIA PaCa2 and SW1990 were used to explore the mechanism between Notch signaling and PD-L1. To study the effects in vivo, a subcutaneous tumor model was established using Pan02 cells treated with either anti-PD-L1 monoclonal antibody and/or Notch inhibitor DAPT. The study performed involving human samples was approved by the Ethics Committee of Peking Union Medical College Hospital (approval No. S-K460, approval date: April 23, 2018). Animal studies were approved by the Animal Research Ethics Committee of Peking Union Medical College Hospital (approval No. XHDW-2019-049, approval date: November 28, 2019).Results::The Notch signaling inhibitor upregulated PD-L1 expression in PC tumor cells both in vitro and in vivo. Notch effector HES1 knockdown produced PD-L1 upregulation in both MIA PaCa2 and SW1990 cells. Combined DAPT and anti-PD-L1 antibody treatment of Pan02 subcutaneous tumor model resulted in significantly reduced tumor weights compared to that with monotherapy, as well as significantly reduced Ki67 than that in the monotherapy group and control group. Flow cytometry analysis revealed significantly increased CD8n + T cell infiltration in tumors of the combination group compared with those of the monotherapy group.n Conclusion::Notch signaling blockade might enhance the antitumor effect of anti-PD-L1 therapy in PC.“,”Objective::Pancreatic cancer (PC) is a highly lethal malignancy with an immunosuppressive environment. Yet, current immune checkpoint inhibitor monotherapies have shown limited efficacy in PC, prompting the need for combination therapies. Herein, we hypothesized that combinations of Notch signaling inhibitor and anti-ligand programmed death-ligand 1 (PD-L1) antibody immunotherapy would show synergistic efficacy.Methods::The baseline expression of PD-L1 and HES1 was measured in PC cell lines, single-cell RNA-seq data of PC (GSA: CRA001160), and cBioPortal databases. In an in vitro study, MIA PaCa2 and SW1990 were used to explore the mechanism between Notch signaling and PD-L1. To study the effects in vivo, a subcutaneous tumor model was established using Pan02 cells treated with either anti-PD-L1 monoclonal antibody and/or Notch inhibitor DAPT. The study performed involving human samples was approved by the Ethics Committee of Peking Union Medical College Hospital (approval No. S-K460, approval date: April 23, 2018). Animal studies were approved by the Animal Research Ethics Committee of Peking Union Medical College Hospital (approval No. XHDW-2019-049, approval date: November 28, 2019).Results::The Notch signaling inhibitor upregulated PD-L1 expression in PC tumor cells both in vitro and in vivo. Notch effector HES1 knockdown produced PD-L1 upregulation in both MIA PaCa2 and SW1990 cells. Combined DAPT and anti-PD-L1 antibody treatment of Pan02 subcutaneous tumor model resulted in significantly reduced tumor weights compared to that with monotherapy, as well as significantly reduced Ki67 than that in the monotherapy group and control group. Flow cytometry analysis revealed significantly increased CD8n + T cell infiltration in tumors of the combination group compared with those of the monotherapy group.n Conclusion::Notch signaling blockade might enhance the antitumor effect of anti-PD-L1 therapy in PC.