Evaluation of Tumor Specificity and Immunity of Thymidine Kinase-Deleted Vaccinia Virus Guang9 Strain

PURPOSE: Oncolytic viruses are emerging as promising options for clinical cancer treatment due to their inherent ability of tumor tropism and oncolytic property. Aside from tumor lysis, oncolytic viruses can induce host immune responses against tumor cells and may thus be viewed as a form of immunotherapy. METHODS: The attenuated vaccinia VG9-Luc, which originated from Chinese vaccinia Tian Tan strain, was constructed to express firefly luciferase for bioluminescence imaging and to disrupt the thymidine kinase gene for promoting tumor specificity. An in vivo bioluminescence imaging was performed to observe the virus distribution in live mice. The titers of neutralizing antiviral and antitumor antibodies in plasma were determined by time-resolved fluoroimmunoassay. RESULTS: Except BALB/c mice treated with intravenous virus injection, all immunocompromised and immunocompetent mice showed obvious tumor targeting ability of vaccinia VG9-Luc. Besides, host immune response activated by vaccinia VG9-Luc showed the production of antiviral and antitumor antibodies, the process of which was similar between intravenous and intratumoral viral delivery systems. The results indicated that virus infection promoted tumor-specific immunity by increasing the production of antitumor antibodies. Moreover, virus reinjection was performed and a more rapid viral clearance was observed in immunocompetent mice compared with first virus infection. CONCLUSION: The thymidine kinase-deleted vaccinia Guang9 strain, which has the properties of tumor specificity and antitumor immunity, is a promising candidate vector for cancer therapy.