Abstract 776: Therapeutic immunity against melanoma by IL-12 cDNA electroporation: a possible therapeutic mechanism

Abstract

Abstract We observed that large-established melanoma was eradicated by intratumoral (IT)-electroporation (EP) of IL-12 cDNA in an animal model. In this study, we explored the mechanism(s) as to how this tumor eradication is mediated in vivo and evaluated if long-term memory responses to parental tumor cell re-challenge can be induced. Melanoma (B16) cells were subcutaneously inoculated. When tumor reached 6-8 mm in mean diameter, 50 μg of IL-12 cDNA was intratumorally injected and electroporated using Cellectra® of VGXI at 0.2A for 4 sec. To further determine the antitumor mechanism(s), IT-EP was performed in tumor-bearing wild type, IFN-γ knockout (KO), and perforin KO animals. Furthermore, immune cell infiltration was measured by histological analysis. In vitro and in vivo immune cell subset depletion assay was also performed to see an involvement of T and NK cell populations in tumor Ag-specific IFN-γ production and tumor control. IT-EP of IL-12 cDNA resulted in eradicating tumors established on the skin without any significant levels of long-term antitumor memory immunity. This effect required mainly CD8+ and to a lesser degree CD4+ T cells, but not NK cells. Both IFN-γ KO animal studies and IT-EP assay of IFN-γ cDNA confirmed that IFN-γ was indirectly involved in melanoma control. Furthermore, perforin was found to be essential for the tumor-eradicating activity. However, B16 melanoma cells expressed Fas, but failed to exhibit Fas-mediated cell lysis, suggesting that perforin/granzyme B-mediated killing pathway is associated with CD8+ T cell-mediated melanoma control. Taken together, these studies show that IT-EP of IL-12 cDNA is an important approach to control melanoma on the skin and this antitumor effect is mediated mainly by CD8+ T cells (as a killer T cell) through perforin/granzyme B-mediated killing pathway. This study also suggests that additional approaches are needed to induce long-term antitumor memory responses. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 776. doi:10.1158/1538-7445.AM2011-776