A combined local treatment with anti-PD-1 antibody and bone marrow derived dendritic cells after x-ray irradiation to subcutaneous melanoma in a murine model.

Abstract

e14541 Background: In situ dying and just died tumor cells after irradiation give danger signals and release tumor-specific antigens which are supposed to be incorporated into dendritic cells (DCs), and sequentially rendering T-cells activated and proliferated. However, it has been clarified that activated T-cells are killed by PD-L1 ligands on tumor cells which bind to PD-1 receptors on T-cells, consequently suppressing systemic cellular immunological response. To improve local control and prevent metastases after localized radiotherapy, we examined whether the combination of anti-PD-1 antibody and bone marrow derived DCs (BM-DCs) can enhance both the local and systemic antitumor immunoreactions after localized X-ray irradiation in a murine melanoma model. Methods: BM-DCs were induced by using GM-CSF and IL-4 from bone marrow cells taken from the femur and tibia of C57BL/6 mice. Syngeneic B16 melanoma cells implanted subcutaneously at the left thighs of C57BL/6 mice were irradiated with X-ray (8 Gy) 5 days after inoculation. After 1, 3, 5, 7 days from irradiation, induced DCs were injected directly to the tumor site, similarly, after 1, 3, 5 days from irradiation, anti-PD-1 antibody were injected intraperitoneally. To examine the systemic immunoreaction, B16 cells were also inoculated to the right side 4 days after the left side inoculation, and treated with the same protocols only on the left side. The size of tumors was monitored and survival analyses were performed. Results: The induced DCs showed the ability to incorporate antigens and to prime and proliferate T-cells in vitro. The combination treatment of anti-PD-1 antibody, BM-DCs and X-ray irradiation showed a significant delay of tumor growth compared to single or double combination treatments in vivo. In addition, this triple combination treatment significantly inhibited the tumor growth on the other side compared to other treatments. Conclusions: DCs and anti-PD-1 antibody significantly enhanced the antitumor effect of X-ray irradiation and prolonged the survival time. This combination also can induce a strong systemic antitumor immunoreaction which could treat metastatic tumors.