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Oncolytic viruses (OVs) are an emerging therapeutic approach for the treatment of cancer. Clinical benefit has been demonstrated for intratumoral administration, but the therapeutic effectiveness of intravenous delivery has been limited by neutralizing antibody responses against the virus. To circumvent this limitation, we developed Synthetic RNA viruses, a novel approach for intravenous and repeated administration of OVs, consisting of a viral RNA genome (vRNA) formulated within lipid nanoparticles. For two Synthetic RNA virus drug candidates, Seneca Valley virus (SVV) and Coxsackievirus A21 (CVA21), we demonstrate vRNA delivery, viral replication, spread, and lysis of tumor cells leading to potent anti-tumor efficacy, even in the presence of OV neutralizing antibodies in the bloodstream. Synthetic-SVV replication in tumors promoted immune cell infiltration and enhanced anti-tumor activity in combination with anti-PD-1 checkpoint inhibitor. Altogether, the Synthetic RNA virus platform provides an innovative approach that enables repeat intravenous administration of viral immunotherapy.

Oncolytic viruses (OVs) are an emerging therapeutic approach for the treatment of cancer. Clinical benefit has been demonstrated for intratumoral administration. Still, the therapeutic effectiveness of intravenous delivery has been limited by neutralizing antibody responses against the virus. To circumvent this limitation, we developed Synthetic RNA viruses, a novel approach for intravenous and repeated administration of OVs, consisting of a viral RNA genome (vRNA) formulated within lipid nanoparticles. Systemic administration of ONCR-788, the Synthetic RNA virus drug candidate encoding the vRNA of Seneca Valley virus (SVV), led to potent anti-tumor efficacy, even in the presence of OV neutralizing antibodies in the bloodstream. After a single intravenous administration of ONCR-788, we demonstrated vRNA delivery, viral replication, spread, and lysis of tumor cells. Robust anti-tumor efficacy was observed across diverse neuroendocrine tumor models, including tumor CDX and PDX xenografts, lung orthotopic, and GEMM-derived models. In a syngeneic model, ONCR-788 stimulated both tumor lysis and modulation of the tumor microenvironment. Enhanced T cell recruitment and activation, increased expression of PD-L1 on tumor cells and myeloid cells, and M2 to M1 macrophage conversion were observed. Combination of ONCR-788 with anti-PD-1 resulted in improved anti-tumor activity versus the monotherapy arms. Altogether, ONCR-788 provides an innovative approach that enables repeat intravenous administration of viral immunotherapy. Citation Format: Edward M. Kennedy, Agnieszka Denslow, Jacqueline Hewett, Lingxin Kong, Ana De Almeida, Jeffrey Bryant, Jennifer S. Lee, Judy Jacques, Sonia Feau, Hayes Hayes, Elizabeth L. McMichael, Daniel Wambua, Sanmit Adhikari, Jessica Deterling, Matthew Scott, Brian H. Haines, Mitchel H. Finer, Ted Ashburn, Christophe Quéva, Lorena Lerner. Development of ONCR-788, a synthetic oncolytic virus based on Seneca Valley virus for the treatment of neuroendocrine tumors [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 3299.

Identification of neoantigens that can elicit strong anti-tumor responses has become critical to vaccine design for cancer immunotherapy. Conventional methods for in silico neoantigen identification have yielded poor predictive value, highlighting the need for methods that identify bona fide neoantigen targets. The Genocea ATLAS™ platform uses autologous antigen presenting cells and T cells to identify pre-existing CD4+ and/or CD8+ T cell responses to patient-specific mutations and therefore selects confirmed neoantigens that can be used for vaccines and cell therapies. Screened neoantigens are characterized as stimulatory or inhibitory based on up- or downregulation of inflammatory cytokine secretion compared to baseline controls. In the mouse B16F10 melanoma model, therapeutic immunization with stimulatory neoantigen peptides arrested tumor growth whereas in contrast, inhibitory antigen immunization (henceforth referred to as inhibigens) resulted in accelerated tumor progression. The presence of an inhibigen in an otherwise protective vaccine formulation completely abolished protection. Global IFNγ responses to neoantigens were abrogated in these mice as measured by ELISpot suggesting that inhibigen pro-tumor responses can be immunodominant. Analysis of tumor-infiltrating lymphocytes (TILs) from mice immunized with ATLAS-identified neoantigen ± inhibigen peptide vaccines revealed significant alterations in the tumor microenvironment. Inclusion of inhibigens resulted in low T cell infiltration into tumors and increased expression of TIL inhibitory surface markers (e.g. PD-1, LAG-3). Immunological mechanisms of the inhibitory phenomenon are currently being explored. These data promote rational methods for neoantigen identification and highlight the potential advantages of excluding deleterious inhibigens from cancer vaccines and immunotherapies. GEN-009, a personalized cancer vaccine filtered for inclusion of only ATLAS-identified neoantigens (excluding inhibigens) is currently being evaluated in a Phase 1/2a clinical trial (NCT03633110). Citation Format: Victoria L. DeVault, Hanna Starobinets, Sanmit Adhikari, Simran Singh, Stephanie Rinaldi, Brendan Classon, Jessica B. Flechtner, Hubert Lam. Inclusion of inhibitory neoantigens can abolish efficacy of otherwise protective therapeutic anti-tumor vaccines [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6680.

Therapeutic cancer vaccine efficacy is reliant on tumor-specific neoantigens. Empirical methods to identify relevant neoantigens may overcome poor predictive values of current in silico approaches. The ATLAS™ platform is a personalized bioassay that uses high-throughput screening of autologous APCs and T cells against a patient’s mutanome to identify neoantigens that are characterized as stimulatory or inhibitory (inhibigens) based on changes in T cell cytokine secretion. In a B16F10 murine model, therapeutic vaccination with ATLAS-identified neoantigens resulted in arrested tumor growth with durable immune responses that protected mice from re-challenge. Mice that were vaccinated with an inhibigen and neoantigen combination had significantly abrogated tumor protection relative to controls. IFNγ ELISpot analysis revealed that inhibigen vaccination suppressed all antigen-specific immune responses, suggesting that inhibigens can be immunodominant. Inhibigen vaccinated mice had multiple tumor microenvironment changes including reduced T cell infiltration, altered CD8+/CD4+ T cell ratios and increased inhibitory marker expression relative to controls. These results indicate that the presence of inhibigens in an otherwise protective vaccine can alter the tumor microenvironment and abolish T cell-mediated protection. Epitope mapping of neoantigens and inhibigens and tetramer design for differential gene signature analysis of inhibigen-specific T cells is being performed. These data suggest that identification and exclusion of inhibigens from cancer vaccines is critical to prevent unintended pro-tumor responses.