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Abstract Oncolytic viruses (OVs) are potent cancer therapeutics that can selectively kill tumor cells and promote anti-tumor immunity. mSJ-650 (Wyeth, K2L-, TK-, murine GM-CSF, human CD55) is the Wyeth strain of vaccinia virus with human complement regulatory protein CD55 incorporated on the intracellular mature virion membrane to evade complement-mediated attack during circulation. The virus also expresses mGM-CSF in replace of thymidine kinase to increase tumor selectivity and enhance immunogenicity. We previously reported that a single dose of mSJ-650 effectively evades complement and shows prominent anti-tumor efficacy in A549 and HCT116 xenograft model. Here, we further investigated the capability of mSJ-650 in promoting anti-tumor response after multiple systemic administration in immunocompetent breast cancer mouse model. In an orthotopic EMT6 breast cancer model, mSJ-650 or control mSJ-612 devoid of CD55 was intravenously injected at low dose (1x106 pfu) and high dose (3x106 pfu), twice weekly. mSJ-650 treatment dose-dependently suppressed tumor growth, showing superior antitumor efficacy compared to treatment of control mSJ-612. Moreover, multiple systemic administration of mSJ-650 was well-tolerated with no apparent signs of toxicity in serum tested via AST and ALT assay. To further elucidate whether mSJ-650 can evade neutralization by antibody and maintain its antitumor potency in vivo, we designed two experimental models. Firstly, endogenous vaccinia virus specific neutralizing antibody was generated by intravenous injection of mSJ-650 prior to tumor cell inoculation in tumor-bearing mouse, followed by systemic administration of mSJ-650 twice weekly. Second, serum containing vaccinia virus specific neutralizing antibody was intravenously injected 24 hours prior to mSJ-650 administration in tumor-bearing mouse. In both experimental models, mSJ-650 treated group significantly inhibited tumor growth despite the presence of neutralizing antibody, while control mSJ-612 treated group failed to suppress tumor growth. These results imply that mSJ-650 is capable of evading neutralization and maintaining its antitumor efficacy. Moreover, we performed multi-color flow cytometry analysis of tumor-infiltrating leukocytes to evaluate immunogenicity of mSJ-650. As a result, we observed a significant increase in recruitment of activated CD4+ and CD8+ T cells by 2-fold and high expression level of cytotoxic molecules (perforin, TNF-α, IFN-γ) in tumor-infiltrating T cells. In summary, multiple systemic administration of mSJ-650 markedly evaded neutralization and suppressed tumor growth by promoting anti-tumor response in immunocompetent breast cancer mouse model, thus implying that mSJ-650 is a promising candidate for cancer immunotherapy. Citation Format: Yeonsoo Yang, Solchan Won, Namhee Lee, Eunhye Kim, Songyi Lee, Mi-Ju Park, Byung-Jin Jung, Yun-Kyoung Hong, Hang-Rae Kim, Dong-Sup Lee, Keunhee Oh. A novel oncolytic vaccinia virus with intravenous compatibility evaded complement- and neutralizing antibody-mediated inhibition and provided superior anti-tumor activity to intra-tumoral administration in immunocompetent mice abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr LB354.
Yang et al. (Fri,) studied this question.