The therapeutic effect of oncolytic virotherapy is mediated largely by two mechanisms; direct oncolysis due to tumor-selective viral replication and the simultaneous activation of innate and adaptive immune responses with the potential of long-lasting tumor remissions. The chimeric vesicular stomatitis virus pseudotyped with LCMV glycoprotein (VSV-GP) has been previously reported to have both a rapid lytic cycle and a broad tumor tropism. In this study, we demonstrate its therapeutic potential in the syngeneic lung cancer model LLC1.
To address the effect of IFN sensitivity of LLC1 cells to VSV-GP mediated oncolysis, we generated interferon receptor deficient cells (LLC1-IFNAR1-/-) using TALENs. Therapeutic efficacy of VSV-GP was assessed in vivo in syngeneic C57BL/6 mice and athymic nude mice bearing subcutaneous tumors. The mechanisms of VSV-GP treatment effect were investigated using bio-luminescent imaging (BLI), immunohistochemistry, multiplex ELISA and Nanostring® technology.
The ability of VSV-GP to infect and lyse LLC1 cancer cell-lines in vitro was abrogated by exogenously applied interferon (IFN) type I indicating a dependence of the oncolytic effect on defects in the IFN response of cancer cells. Interferon resistance of LLC1-IFNAR1-/- cells correlated with prolonged intratumoral viral replication and improved therapeutic outcome in vivo, as demonstrated by using a matched pair of LLC1 wildtype and LLC1-IFNAR-/- tumors. Additionally, BLI revealed successful tumor-to-tumor spread of viral progeny in bilateral tumor models. VSV-GP therapy was associated with enhanced T cell infiltration and upregulation of various immune-associated genes. Interestingly, the efficacy of VSV-GP therapy in treating LLC1-IFNAR-/- tumors was not diminished by the absence of CD8+ T cells and cured mice were not immune to tumor rechallenge indicating a predominant lytic effect.
The treatment effect of VSV-GP in LLC1-IFNAR-/- lung cancer model is primarily lytic with negligible contribution of adaptive immunity despite strong activation of both innate and adaptive immune signatures.
Medical University of Innsbruck.
ViraTherapeutics GmbH, Innsbruck, Austria.
G. Wollmann: Scientific advisor: Boehringer Ingelheim GmbH & Co. KG. B. Spiesschaert: Part time employment: ViraTherapeutics GmbH; Part of Christian Doppler Laboratory. F. Heinemann, B. Stierstorfer, P. Müller: Employment: Boehringer Ingelheim GmbH & Co. KG. M. Petersson, P. Erlmann: Employment: ViraTherapeutics GmbH. D. von Laer: Inventor of VSV-GP; Minority shares: ViraTherapeutics GmbH (which holds the intellectual property rights for VSV-GP); Scientific advisor: Boehringer Ingelheim. All other authors have declared no conflicts of interest.