Abstract 2617: Inducing neoantigens in therapeutic and prophylactic cancer immunotherapy
Authors: Hidalgo Greta Garrido , Levay Agata , Berezhnoy Alexey , Schrand Brett , Gilboa Eli 
Published: July 2017

Abstract
Correlation between clonal neoantigen burden (neoantigens generated early in tumorigenesis and therefore represented at high frequency in all tumor lesions) and responsiveness to checkpoint blockade has underscored the relevance of neoantigens in promoting tumor immunogenicity. Yet, the most of patients do not express, or express low numbers of, clonal neoantigens, and consequently will be less likely to benefit from checkpoint blockade. We describe strategies to generate de novo neoantigens in the patient’ disseminated tumors and show that in mouse tumor models they potentiate checkpoint blockade. We previously showed that tumor inhibition of the Nonsense-mediated mRNA decay (NMD) results in the neoantigens’ induction and reduces tumor growth (Pastor et al., 2010). We now demonstrate that tumor-targeted NMD inhibition potentiates PD-1 blockade. A general concern and potential limitation of this approach is that a significant proportion of the induced neoepitopes come from mutated products and hence will not be shared by all tumor lesions. To that end, we are exploring alternative strategies by targeting key components of antigen presentation pathways, specifically the TAP transporter, ERAAP peptidase, and Invariant chain. Studies show that downregulation of these products, not only reduces the canonical antigenic presentation but also upregulates alternative pathways that present new, otherwise silent or subdominant, epitopes. Since such epitopes are not generated by random events they are more likely to represent clonal neoepitopes. We are developing approaches to inhibit the aforementioned mediators using corresponding siRNAs targeted to tumor cells by conjugation to a nucleolin-binding aptamer. Nucleolin, a nucleolar product, is translocated to the surface the majority of tumors and thereby serves as a broad target to deliver therapeutic cargo to the disseminated tumors. We show that nucleolin aptamer-targeted downregulation of TAP, ERAAP or Invariant chain inhibits tumor growth and potentiates PD-1 blockade. Recent studies suggest that tumor neoantigen-specific T cells are dysfunctional due to constant antigenic exposure. Transiently expressed siRNA inhibition-induced neoantigens are not expected to be defective. Ongoing studies explore the combinatorial use of neoantigen induction methods with others immune potentiating strategies. Prophylactic cancer vaccination obviates the limitations of therapeutic vaccination. A major barrier for developing this modality is the choice of antigens that will appear in the future cancer. The ability to induce tumor neoantigens can serve the basis for developing a new approach to prophylactic, though not preventative, cancer vaccination whereby neoantigens are induced in the healthy individual (at risk for cancer), and if or when a cancer develops induce the same antigens in the patient’ tumor by the methods described above. Preliminary studies in mice show that the approach has merit.
Citation Format: Greta Garrido Hidalgo, Agata Levay, Alexey Berezhnoy, Brett Schrand, Eli Gilboa. Inducing neoantigens in therapeutic and prophylactic cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2617. doi:10.1158/1538-7445.AM2017-2617