Spleen migrating dendritic cells primed with CC531 colon cancer antigen and LPS - is it a method to compromise liver metastases?

The anti-tumor vaccination is burdened by low recruitment rate of intravenously administered in vitro primed DC in liver metastases and lack of supplying them continuously in large numbers. Therefore, it seemed rational to create a model of in vivo vaccination with specifically primed splenic DC and cytotoxic T lymphocytes being continuously supplied to the liver vascular bed. The question we raised was whether anti-tumor immunized splenic DC flowing to liver metastases could adhere to and be cytotoxic to tumor cells. We immunized rats with CC531 tumor cells and stimulated them with Escherichia coli LPS. Subsequently, spleen DC-enriched population was isolated, its activation by LPS, adherence to CC531 cells and cytotoxicity were measured. Spleen cells home to the liver reaching it via splenic vein. These cells can be retrieved by simple washout of liver sinusoids (liver sinusoidal washout cells - LSWC). Their adherence to and cytotoxicity against CC531 cells were evaluated. Moreover, in vitro adherence of splenic DC-enriched cells and LSWC to CC531 liver tumor sections was measured. We found that in vivo immunization of splenic population containing DC, NK cells and lymphocytes with CC531 cells and stimulation with LPS activated these cells but did not significantly increase the cytotoxicity against CC531 cells. There was also no increase in cytotoxicity of LSWC. Adhesion of splenic DC and LWSC to liver CC531 metastases on cryosections was higher than to the adjacent liver tissue. However, it was more expressed on tumor stromal than neoplastic cells. The level of splenic Treg cells down-regulating immune response was found only slightly increased after immunization. Taken together, in the model of in vivo immunization against CC531 cells, low level of spleen DC and spleen-derived LSWC cytotoxicity as well as adherence rate to tumor cells were observed. More effective methods of immunizing splenic DC overcoming the suppressive mechanisms should be looked for.