Irradiated pancreatic cancer cells undergo both apoptosis and necrosis, and could be phagocytized by dendritic cells

The interaction of immature dendritic cells (DC) with irradiated pancreatic cancer cells was examined. Flow cytometric analysis using annexin V and propidium iodide revealed that ionizing radiation (25-35 Gy X-ray) induced both apoptosis and necrosis in pancreatic cancer cell lines. After irradiation, PK-1 and Panc-1 cells were likely to undergo necrosis, whereas MIAPaCa-2 cells underwent apoptosis. When DiO-stained immature DCs were co-incubated with DiI-stained irradiated MIAPaCa-2, it was observed under fluorescent microscopy that DCs phagocytized dead tumor cells as early as 4 h after coincubation. The DCs' phagocytosis of irradiated tumor cells was also confirmed by flow cytometry. These results suggest that irradiated pancreatic cancer cells, which undergo both apoptosis and necrosis, could be a good source of tumor-associated antigens for cross-presentation by DCs.