Newcastle disease virus mediates pancreatic tumor rejection via NK cell activation and prevents cancer relapse by prompting adaptive immunity

Pancreatic cancer is the 8th most common cause of cancer‐related deaths worldwide and the tumor with the poorest prognosis of all solid malignancies. In 1957, it was discovered that Newcastle disease virus (NDV) has oncolytic properties on tumor cells. To study the oncolytic properties of NDV in pancreatic cancer a single dose was administered intravenously in a syngeneic orthotopic tumor model using two different murine pancreatic adenocarcinoma cell lines (DT6606PDA, Panc02). Tumor growth was monitored and immune response was analyzed. A single treatment with NDV inhibited DT6606PDA tumor growth in mice and prevented recurrence for a period of three months. Tumor infiltration and systemic activation of NK cells, cytotoxic and helper T‐cells was enhanced. NDV‐induced melting of Panc02 tumors until d7 pi, but they recurred displaying unrestricted tumor growth, low immunogenicity and inhibition of tumor‐specific immune response. Arrest of DT6606PDA tumor growth and rejection was mediated by activation of NK cells and a specific antitumor immune response via T‐cells. Panc02 tumors rapidly decreased until d7 pi, but henceforth tumors characterized by the ability to perform immune‐regulatory functions reappeared. Our results demonstrated that NDV‐activated immune cells are able to reject tumors provided that an adaptive antitumor immune response can be initiated. However, activated NK cells that are abundant in Panc02 tumors lead to outgrowth of nonimmunogenic tumor cells with inhibitory properties. Our study emphasizes the importance of an adaptive immune response, which is initiated by NDV to mediate long‐term tumor surveillance in addition to direct oncolysis. What's new? The dismal prognosis of pancreatic cancer has prompted investigation of alternative therapeutic avenues, one of which is the use of oncolytic viruses, which target cancer cells, proliferating specifically within them. Here, orthotopic implantation of two different pancreatic cancer cell lines (DT6606PDA and Panc02) in mice was used to evaluate immune activation following infection with Newcastle disease virus (NDV). While NDV successfully prompted an antitumor immune response in DT6606PDA tumors, initial tumor shrinkage in Panc02 mice was overtaken by relapse. The findings in DT6606PDA tumors suggest that direct oncolysis is followed by an adaptive immune response critical for long‐term tumor rejection.