Abstract A007: Intratumoral delivery of inactivated vaccinia virus is more efficacious than live oncolytic vaccinia virus in murine bilateral tumor implantation models

Poxviruses are large cytoplasmic DNA viruses that have potentials as vaccine vectors and oncolytic agents. Although almost all of the oncolytic vaccinia viruses that are being investigated in clinical trials are replication competent, it is still unclear how these viruses exert antitumor immunologic effects, and whether viral replication is even necessary to achieve systemic antitumor efficacy. In this study, we compared therapeutic efficacy of the intratumoral delivery of the live, attenuated, replication competent oncolytic vaccinia virus expressing mGM-CSF (VC-TK − -mGM-CSF)vs. its heat-inactivated counterpart (iVC-TK − -mGM-CSF) in two bilateral tumor implantation models- B16-F10 murine melanoma and MC38 colon adenocarcinoma. We found that intratumoral injection of inactivated virus exerted stronger systemic antitumor effects than the live virus. FACS analyses of tumor infiltrating immune cells revealed that intratumoral injection of iVC-TK − -mGM-CSF lead to increased percentages and numbers of activating effector CD8 + and CD4 + T cells and reduced percentages and numbers of CD4 + Foxp3 + regulatory T cells in the non-injected tumors compared with intratumoral delivery of the live virus. Infection of bone marrow-derived dendritic cells (DCs) with iVC-TK − -mGM-CSF induced type I IFN and proinflammatory cytokine and chemokine production and DC maturation, whereas the live virus did not. Taken together, our results demonstrate that intratumoral delivery of inactivated vaccina virus is safer and more efficacious than live oncolytic vaccinia virus expressing mGM-CSF in two murine bilateral tumor implantation models. Our findings have important implications for the design of poxviral-based immunotherapeutics for patients with metastatic cancers. Note: This abstract was not presented at the conference. Citation Format: Weiyi Wang, Peihong Dai, Ning Yang, Stewart Shuman, Taha Merghoub, Jedd D. Wolchok, Liang Deng. Intratumoral delivery of inactivated vaccinia virus is more efficacious than live oncolytic vaccinia virus in murine bilateral tumor implantation models [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A007.