Combining DC-mediated immunotherapy with oncolytic virotherapy in the treatment of HGG

Abstract

Oncolytic viruses (OV) are either naturally selective for neoplastic cells or are engineered to be so. Whereas conservative therapies use the unspecific genome vulnerability of highly proliferating cells to target malignancies, OV have the advantage of often being extremely specific in infecting tumor cells. This (intrinsic) selectivity combined with the demonstrated safety and lack of host toxicity in phase I clinical studies make OV very appealing as novel cancer therapeutics. Recently, Alkassar et al. have shown in vitro and in vivo that naturally occurring Reovirus, Parvovirus and Newcastle disease virus (NDV) strains mediate strong anti-tumoral effects on glioblastoma. We hypothesize that upon combining a systemic immunotherapy approach with preceding oncolytic virotherapy (OVT), as a means of lowering the tumor viability and volume and altering the local micro environment within the tumor, a better immune control can be induced. In the immunotherapy field, it is known that the immunosuppressive microenvironment induced by the tumor can profoundly suppress the antitumor immunity and therefore inhibit vaccine efficacy. Viral presence within the tumor does the opposite; acting as a danger signal to alert and activate the immune system, it can reduce or eliminate the tumor induced immune suppression. Furthermore, the direct tumor cell killing effects of OV can lower tumor burden prior to immunotherapy. Both active specific immunotherapy and OVT have shown promising results in preclinical and clinical studies but the possible additive or synergistic effects of these treatment strategies have not been studied. We aim to combine OVT with dendritic cell (DC)-mediated immunotherapy in a preclinical murine glioma model to demonstrate additive or synergistic effects. Our initial results show good susceptibility of the murine GL261 glioma cell line to cytotoxic killing by oncolytic Reovirus, Parvovirus and NDV in vitro. The strains were also combined to exploit the synergism recently demonstrated by Alkassar et al. Results indicate increased cytotoxic effects when Reovirus was combined with NDV or when Reovirus was combined with Parvovirus. GL261 cell infection capacity of the viruses was quantified by immunofluorescence imaging. In vivo, intracranial injection of Reovirus, Parvovirus, NDV or combinations of two viruses in healthy mice led to signs of inflammation in the brain, as visualized by MR imaging. Infiltration of inflammatory cells will be confirmed by histology. In tumor-bearing mice, prolonged survival and induction of long term survival was seen when mice were treated intra tumorally with Reovirus, Parvovirus or a combination of both. Similar results were found when tumor-bearing mice were treated with NDV and/or Reovirus. Toxicity of the viruses will be analyzed by histological analysis of brain and other vital organs.