Abstract A075: Preclinical analysis of combinatorial glioblastoma therapy with the prodrug mediated gene therapy vector AdV TK and immune checkpoint inhibition in GBM therapy
While the brain has traditionally been considered to be an immune privileged site, evidence supporting the use of immunotherapeutics has been rapidly accumulating. Given that virus based cancer therapies can be immunostimulatory and immune checkpoint inhibitors block tumor induced T cell exhaustion, the combination of these two approaches offers a potentially synergistic interaction. One of the molecular underpinnings of T cell exhaustion is the expression of Programmed Death 1 (PD1) on T cells that recognizes its ligand PD L1. AdV tk is an immunostimulatory virus based approach, known as Gene Mediated Cytotoxic Immunotherapy (GMCI) that involves the intra tumoral delivery of a non replicating adenoviral vector carrying the Herpes virus thymidine kinase gene(TK) followed by administration of an anti herpetic prodrug(ganciclovir GCV) and recently showed encouraging results in a Phase II trial in glioblastoma(Wheeler et al.,2016) To provide a rationale for this therapeutic combination we investigated PD L1 expression during GMCI therapy in human and mouse glioma cells in vitro and found that there was a consistent increase in cell surface PD L1 levels. Interestingly, this was not associated with an increase of mRNA or protein. We also show that GMCI induces a type I interferon response, and that the release of IFNb is at least partially responsible for autocrine/paracrine PD L1 up regulation. In vivo studies using an intracranial GL261 model showed high levels of long term survivors in the GMCI/PD1 combination (11/14) compared with GMCI (6/16) anti PD1 (5/12) and controls (0/11) In addition, tumor infiltrating lymphocytes after GMCI showed an increase in CD8+ CD8+/GranzymeB+ and CD8+/IFNg+/TNFa+cells suggestive of cytotoxic T cell activation. However, there was also a significant increase in CD4+ CD4+/FoxP3+ and IL 10 indicating a significant infiltration by Tregs, releasing immunosuppressive cytokines. Additionally, there was a significant increase in PD1+/TIM3+ T cells, indicative of an immunosuppressive microenvironment. Overall, our data show that GMCI/anti PD1 combinatorial therapy is effective in a syngeneic tumor model, and strongly support clinical trials of GMCI/checkpoint inhibitor combinations in glioblastoma patients. Citation Format: Maria Carmela Speranza, Kazue Kasai, Franz Ricklefs, Sarah R. Klein, Carmela Passaro, Hiroshi Nakashima, Johanna Kaufmann, Agnieszka Bronisz, Estuardo Aguilar Cordova, Brian W. Guzik, Gordon J. Freeman, David A. Reardon, Patrick Wen, E. Antonio Chiocca, Sean E. Lawler. Preclinical analysis of combinatorial glioblastoma therapy with the prodrug mediated gene therapy vector AdV TK and immune checkpoint inhibition in GBM therapy [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 A075.