There are many different therapies available for treating cancer. Inside the body, tumor is composed of tumor cells that are surrounded by the tumor microenvironment, which is made up of diverse cells and has a significant effect on tumor development. The tumor microenvironment contributes to the metastasis ability and participates in the immune system's ability to recognize or hide the tumor. Using the multispectral immunofluorescence staining method, we label several different cell types on the same tissue slice. In the experimental part of the thesis, we labeled veins, proliferation sites, macrophages, cytotoxic T lymphocytes, and helper T cells. We stained two different mouse tumor models, namely, mouse melanoma cells (B16F10) and colon and rectal cancer cells (CT26). Most macrophages were located around the tumor after interleukin-12 gene transfer therapy. The veins stained well in all tumors, while the only traces of T lymphocytes were observed in the CT26 tumor. Staining was better performed on CT26 tumor slices stored at -20 ° C and thawed. The sizes of all tumors decreased or necrosis occurred after the therapies. Based on the results, we can conclude that frozen tissue slices are more suitable for multispectral immunofluorescent imaging. In both tumor models, increased amounts of macrophages have been demonstrated around and inside the tumors after all therapies involving interleukin-12 gene transfer.