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In adoptive immunotherapy, in vivo trafficking of adoptively transferred cells, including their accumulation at tumor sites, remains to be further investigated. Tracking of these cells by visualization is useful to clarify antitumor mechanisms and develop new modalities to enhance antitumor capacities. In the present study, an in vivo tracking study was performed using an adoptive transfer model of lymphokine-activated killer (LAK) cells induced from green mice into C57/BL6 mice with B16 melanoma metastases. Green mice are green fluorescent protein (GFP) transgenic mice originating from C57/BL6 mice. All of the tissues, except for erythrocytes and hair, express green fluorescence under excitation light. Although LAK cells in combination with IL-2 potently suppressed pulmonary metastases with survival prolongation, very few LAK cells accumulated in tumor tissues compared to those localized in the spleen, as visualized by fluorescent microscopy and quantitated by flow cytometry. The present method using transfer of green mice-derived cells into parental tumor-bearing mice is simple because there is no need for in vitro labeling and is feasible for the in vivo tracking of effector cells in an adoptive immunotherapy model.

The use of gene-modified dendritic cells (DC) is a powerful tool to enhance antitumor immune responses stimulated by these cells in cancer immunotherapy. Cationized gelatin is preferably incorporated via phagocytosis and is gradually degraded by proteolysis while buffering lysosomal activity. This may be appropriate for gene transfer into phagocytic cells, such as immature DC. In the present study, successful transfection into monocyte-derived immature DC was demonstrated using cationized gelatin and plasmid DNA complexes. A high transfection efficiency, approaching 16%, was obtained upon transfection of the enhanced green fluorescent protein (EGFP) gene as evaluated by flow cytometry. Transgene expression of EGFP and murine interleukin 12 were also detected by RT-PCR. The antigen-presenting capacity of the transfected DC was equal to that of untransfected DC as evaluated by the allogeneic mixed lymphocyte reaction. Cationized gelatin has the potential to be a unique non-viral vector for gene transfer into DC.

Milky spots (MS), peritoneal lymphoid tissues, expose the extracellular matrix (ECM) due to a defect of mesothelial cells on their surface, which may explain why peritoneal implantation of cancer cells preferentially takes place at MS. We recently reported that adenovirus vector-mediated intraperitoneal production of NK4 strongly suppressed MS-selective implantation of cancer cells and subsequent peritoneal dissemination, without histological evidence of angiogenesis inhibition. The present study was conducted to clarify the mechanisms underlying the suppressive effects of NK4 on peritoneal implantation. In mice intraperitoneally injected with CT26 cells that were genetically modified to produce NK4 (CT26-NK4), peritoneal dissemination was significantly suppressed with survival prolongation. A decreased cell implantation to omental MS was also detected and evaluated by green fluorescence protein (GFP) imaging. In an in vitro adhesion assay, hepatocyte growth factor-stimulated adhesion to ECM components, such as fibronectin and collagen, was inhibited in CT26-NK4 compared to control cells. These results strongly suggest an inhibition of cancer cell adhesion to the ECM in the suppression of peritoneal implantation by NK4.