Abstract 1732: Gp96-Ig/costimulator combination platform improves T cell priming and enhances immunity, memory, and tumor elimination

Abstract In this study, we report that addition of checkpoint inhibition and T cell costimulators into the Heat Biologics gp96-Ig-based vaccine platform elicits stronger antigen-specific CD8+ T cell activation and expansion, stimulates memory precursor cell activation, and enhances rejection of murine tumors. Despite the dramatic successes of checkpoint inhibitors in limited populations of cancer patients, 60-90% of patients are still failing to respond to these therapies. It is widely believed that approaches such as ours that target multiple facets of the immune system, including combinations with checkpoint inhibition and costimulator agonism, will be required to improve patient outcomes. Heat Biologics' first-generation ImPACT vaccine is a cell-based therapy that utilizes representative tumor cell lines expressing the antigen chaperone, gp96-Ig, to efficiently prime antigen-specific CD8+ T cells. Heat recently developed a next generation vaccine called ComPACT (COMbination Pan-Antigen Cytotoxic Therapy) that incorporates expression of a T cell costimulator (OX40L-Ig) and gp96-Ig within a single vaccine cell line. In multiple murine tumor and tumor-naive models, ComPACT elicits more potent activation of antigen-specific T cells as well as expansion of CD127+KLRG1- memory precursor cells, leading to a detectable memory response. Furthermore, ComPACT lacks the toxic systemic inflammatory cytokine production and proliferation of non-specific CD4+ T cells and Tregs observed with systemic administration of OX40 agonist antibodies. ComPACT also leads to high frequencies of IFNγ+, TNFα+, granzyme B+ and IL-2+ antigen-specific CD8+ T cells in mice at both priming and boosting, which increases rejection of established murine melanoma (B16.F10) and colon cancer (CT26) tumors and increased overall survival. Here, we have further assessed ImPACT and ComPACT-OX40L in combination with the anti-PD1 checkpoint inhibitor and with expression of an additional cell-secreted T cell costimulator, TL1A-Ig. In various murine models we show that these treatments synergize effectively to amplify antigen-specific T cells, program a functional memory response, and eliminate tumors. The combination of ComPACT-OX40L/TL1A with αPD1 or αPD-L1 may therefore translate into an efficacious approach to treat human cancers. Citation Format: Louise Giffin, Louis Gonzalez, Jason Rose, Jeff Hutchins. Gp96-Ig/costimulator combination platform improves T cell priming and enhances immunity, memory, and tumor elimination [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1732.