Vaccination with irradiated tumor cells genetically modified to secrete granulocyte-macrophage colony-stimulating factor (GM-CSF tumor vaccine) induces a potent systemic antitumor immunity. To develop a protocol for cancer therapy to further augment the host immune response, we examined the effects of the GM-CSF tumor vaccines simultaneously producing additional cytokines. We prepared cancer vaccines expressing double cytokines by sequential recombinant retrovirus-mediated genetic transductions. We then used a murine intracerebral tumor model in which the GM-CSF tumor vaccine was less effective in immunopotentiation and evaluated tumor vaccines producing various cytokines in conjunction with GM-CSF. The cytokine combination of GM-CSF and interleukin 4 induced more potent antitumor immunity than GM-CSF alone. An in vivo depletion test showed that CD4+, CD8+, and asaloGM1+ cells were required for the optimum function of the GM-CSF plus interleukin 4 tumor vaccine. Histological examinations revealed infiltration of inflammatory cells at the site of tumor cell challenge as well as at the site of vaccination, indicating the induction of a systemic antitumor immune response which reached the central nervous system. Our findings suggest the feasibility of applying the intensified vaccination strategy to treat human cancers including malignant brain tumors.
This work was supported in part by a grant from the Ministry of Education, Science, and Culture, Japan and by a grant from the Vehicle Racing Commemorative Foundation.