A myeloid and lymphoid infiltrate in murine pancreatic tumors exposed to plasma-treated medium

Metastatic pancreatic cancer often is fatal in patients. Palliation can include disseminating large amounts of chemotherapeutic liquid in the peritoneal cavity to slow tumor growth. We have previously demonstrated that repeated application of plasma-treated medium performed well in decreasing peritoneal tumor burden in mice and prolonging animal survival. We here extend on this study by detailed immune-related analysis of cryo-conserved tumor nodes of mice that had received either cell culture medium alone or plasma-treated cell culture medium. Animals of the treatment group had significantly fewer lesions, which were characterized by an increased influx of macrophages. The staining intensity of CD206, a murine M2 macrophage marker associated with tumor promotion, was decreased in tissue sections, while iNOS (M1 marker associated with inflammatory macrophages) was not changed. In the infiltrate, other myeloid cells such as neutrophils and dendritic cells were in tendency increased and decreased, respectively. Further, we observed a significant increase in T cells and calreticulin staining, suggesting an involvement of immunogenic cancer cell death in plasma-treated medium therapy of pancreatic tumor lesions. In summary, exposure to plasma-treated medium not only decelerates tumor growth but also serves as immunomodulatory agent with a possible relevance for therapeutic outcome.