Abstract 6388: The effect of oncolytic virus therapy on neoantigen specific immune responses

Abstract Background: Patients with malignant brain tumor, glioblastoma (GBM), do not benefit from promising immunotherapies that use checkpoint inhibitors, such as PD-1 and CTLA-4 blockade antibodies. Several reasons may underlie this clinical result, particularly because of immunogenically cold nature of the GBM microenvironment, which is characterized by the low level of infiltrating cytotoxic CD8+ T cells and by an enriched myeloid suppressor cell population. We and other groups hypothesize that oncolytic virus (OVs)-based treatments can overcome this problem. Our preclinical GBM models and an ongoing clinical trial with oncolytic herpes simplex virus-1 (oHSV-1) at our institution (NCT03152318) demonstrated that OV treatment leads to an increase in the influx of CD8+ and CD4+ T cells into TME. However, it remained unknown whether these T cells are specific to the tumor. Here, we evaluated T-cell responses against newly identified neoantigens from murine syngeneic glioma line in response to the intratumoral OV treatments. Results: To evaluate the effect of oHSV-1 treatment on neoantigen-specific responses, we first performed whole-exome and RNA sequencing of murine GBM for the identification of tumor-specific mutations. Putative MHC I antigens were predicted with netMHCpan V4 and immunogenicity of candidates, that were selected based on affinity to MHC I molecules, were checked by IFN-gamma enzyme-linked immunospot (ELISpot) assay. With our workflow, 91 H2-Db-restricted and 77 H2-Kb-restricted peptides were identified. From this group, 8 Db- and 9 Kb-restricted peptides were selected based on their highest MHC affinity. We then asked which of these neoantigens would show enhanced presentation upon oHSV infection in vivo. To determine that we first implanted GBM tumors in the brains of syngeneic mice. At Day7 post-tumor implantation, the oHSV-1 (or vehicle control), was in situ stereotactically administered. Seven days later, splenocytes, PBMCs, and TILs were harvested to be screened. TILs from the oHSV-1 treated mice, but not those from the control group reacted to the putative neoantigens, and this activation was similar in magnitude to the response to the immunodominant HSV peptide. We are currently performing immunopeptidome analyses to confirm the binding of these neoepitopes to MHC upon oHSV treatment and in vivo studies to determine how T cells specific to these MHC-I restricted neoepitopes contribute to the anti-tumor effect. Conclusion: Our data with the preclinical model of GBM show for the first time that infection with an oHSV-1 does indeed lead to novel TIL activation against tumor neoantigens that were not presented without OV infection. Thus, oncolytic viruses may offer an in-situ vaccination approach to stimulate neoantigen-specific immune responses. Citation Format: Raziye Piranlioglu, Junfeng Liu, Anan Islam, Alex Ling, Naoyuki Shono, William F. Goins, Hiroshi Nakashima, E. Antonio Chiocca. The effect of oncolytic virus therapy on neoantigen specific immune responses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6388.