ABSTRACT
In the present study, TNF-alpha gene-transduced B78 melanoma cells (B78/TNF) were used as a vaccine and combined with interleukin (IL)-12 in the treatment of B78 melanoma-bearing mice. The combined administration of genetically modified melanoma cells and IL-12 induced specific protective antitumor immunity resulting in a decreased rate of the tumor take following a rechallenge with parental B78 cells. When used therapeutically, intratumoral injections of irradiated B78/TNF melanoma cells and IL-12 exerted strong antitumor effects and led to complete regression of established tumors in 50% of mice. Injections of irradiated B78/TNF cells alone did not influence tumor development and IL-12 itself significantly delayed tumor growth but without curative effect. FACS analysis of parental B78 melanoma cells and its B78/TNF genetically modified variant showed that a proportion of cells of both cell lines expressed 87-1 (CD80) costimulatory molecule and that the expression of this molecule was increased during incubation with IFN-gamma. Moreover, IFN-gamma markedly augmented expression of major histocompatibility class (MHC) class I and II molecules on B78/TNF cells that were primarily MHC class I and II negative with no substantial effect on MHC-negative parental B78 melanoma. IFN-gamma also synergized in cytostatic/cytotoxic effects with TNF-alpha against B78 melanoma in vitro. Lymphocyte depletion studies in vivo showed reduction of the antitumor response in mice treated with anti - NK monoclonal antibodies (mAbs) as well as in mice treated with anti-CD4+ anti-CD8 mAbs. The results suggest that, when used therapeutically, IL-12 and a vaccine containing TNF-alpha gene-transduced tumor cells may reciprocally augment their overall antitumor effectiveness by facilitating development of systemic antitumor immunity and by stimulating local effector mechanisms of the tumor destruction.
