841. Anti-Tumor Effect of Tumor Specific Replicating Adenovirus Expressing IL-12 and IL-18

Abstract

Cancer immunotherapy denotes a strategy for activating a host's immune response for the treatment of malignancy. Although cancer cells are less immunogenic, immune system is capable of recognizing and eliminating cancer cells. Oncolytic adenoviral vectors are currently being developed as biologic anti-tumor agents, and coupling the lytic function of an oncolytic adenovirus with its ability as a transgene delivery system represents a powerful extension of this methodology. IL-12 is reported to exhibit potent anti-tumor effect by promoting NK cell and cytotoxic T cell activities. IL-18 is also have shown that augments cytotoxicity of NK cells and proliferation of T cells. It stimulates Th1 cells to produce IL-2 and IFN-γ. This effect augmented in a synergistic manner IL-12. To increase the potential anti-tumor effect of the oncolytic adenovirus, we have generated an E1B deleted and E1A mutated oncolytic adenoviruses, Ad-ΔB7-IL12, Ad-ΔB7-IL18, or Ad-ΔB7/IL12-IL18 that expresses IL-12, IL-18, or IL-12 plus IL-18, respectively. The therapeutic efficacy of these oncolytic adenoviruses was then evaluated in immunocompetent C57BL/6 mice bearing murine melanoma B16- F10 tumor. The results showed significant inhibition of tumor growth following Ad-ΔB7/IL12-IL18 treatment compared to Ad-ΔB7, Ad- ΔB7-IL18, or Ad-ΔB7-IL12 treated tumors. Moreover, the oncolytic adenovirus expressing both IL-12 and IL-18 demonstrated enhanced anti-tumor effect and higher incidences of complete tumor regression compared to Ad-ΔB7, Ad-ΔB7-IL18, or Ad-ΔB7-IL12. To establish that the observed anti-tumor effect is associated with the generation of a tumor-specific immune response, we examined the cytolytic activity by IFN-γ ELISpot assay and CTL assay. We observed that Ad-ΔB7/IL12-IL18 induced significantly higher T cell-mediated anti- tumor effect than its cognate controls, Ad-ΔB7, Ad-ΔB7-IL12, and Ad-ΔB7-IL18. Furthermore, immunohistochemical studies demonstrated robust CD4+ and CD8+ T-cell infiltration in these mice compared to the Ad-ΔB7, Ad-ΔB7-IL18, or Ad-ΔB7-IL12- treated subjects. These data indicate that oncolytic adenovirus-mediated IL-12 and IL-18 gene transfer provides a potential therapeutic strategy for the management of neoplasia. Cancer immunotherapy denotes a strategy for activating a host's immune response for the treatment of malignancy. Although cancer cells are less immunogenic, immune system is capable of recognizing and eliminating cancer cells. Oncolytic adenoviral vectors are currently being developed as biologic anti-tumor agents, and coupling the lytic function of an oncolytic adenovirus with its ability as a transgene delivery system represents a powerful extension of this methodology. IL-12 is reported to exhibit potent anti-tumor effect by promoting NK cell and cytotoxic T cell activities. IL-18 is also have shown that augments cytotoxicity of NK cells and proliferation of T cells. It stimulates Th1 cells to produce IL-2 and IFN-γ. This effect augmented in a synergistic manner IL-12. To increase the potential anti-tumor effect of the oncolytic adenovirus, we have generated an E1B deleted and E1A mutated oncolytic adenoviruses, Ad-ΔB7-IL12, Ad-ΔB7-IL18, or Ad-ΔB7/IL12-IL18 that expresses IL-12, IL-18, or IL-12 plus IL-18, respectively. The therapeutic efficacy of these oncolytic adenoviruses was then evaluated in immunocompetent C57BL/6 mice bearing murine melanoma B16- F10 tumor. The results showed significant inhibition of tumor growth following Ad-ΔB7/IL12-IL18 treatment compared to Ad-ΔB7, Ad- ΔB7-IL18, or Ad-ΔB7-IL12 treated tumors. Moreover, the oncolytic adenovirus expressing both IL-12 and IL-18 demonstrated enhanced anti-tumor effect and higher incidences of complete tumor regression compared to Ad-ΔB7, Ad-ΔB7-IL18, or Ad-ΔB7-IL12. To establish that the observed anti-tumor effect is associated with the generation of a tumor-specific immune response, we examined the cytolytic activity by IFN-γ ELISpot assay and CTL assay. We observed that Ad-ΔB7/IL12-IL18 induced significantly higher T cell-mediated anti- tumor effect than its cognate controls, Ad-ΔB7, Ad-ΔB7-IL12, and Ad-ΔB7-IL18. Furthermore, immunohistochemical studies demonstrated robust CD4+ and CD8+ T-cell infiltration in these mice compared to the Ad-ΔB7, Ad-ΔB7-IL18, or Ad-ΔB7-IL12- treated subjects. These data indicate that oncolytic adenovirus-mediated IL-12 and IL-18 gene transfer provides a potential therapeutic strategy for the management of neoplasia.