Abstract A023: Inducing neoantigens in disseminated tumor lesions to enhance their susceptibility to PD-1 blockade therapy

Correlation between “clonal” neoantigen burden (neoantigens generated early during cancer development and therefore represented at high frequency in all tumor lesions) and responsiveness to checkpoint blockade therapy has underscored the importance of neoantigens in promoting tumor immunogenicity, and has spurred a broad effort to develop methods to identify neoantigens for use in vaccination protocols. Yet, the majority of patients do not express, or express low numbers of, clonal neoantigens, and consequently will be less likely to benefit from checkpoint blockade and other forms of immune potentiating therapies. Here we describe several strategies to generate de novo neoantigens in the patient9 disseminated tumor lesions and show that in murine tumor models they potentiate checkpoint blockade therapy. We have previously shown that oligonucleotide aptamer-targeted siRNA inhibition of the Nonsense-mediated mRNA (NMD) process in tumor cells in situ results in the induction of neoatigens and inhibition of tumor growth (Pastor et al., Nature, 2010, 465:227). We now demonstrate that tumor-targeted NMD inhibition potentiates PD-1 blockade therapy. A general concern and potential limitation of the NMD approach is that a significant proportion of NMD inhibition-induced neoantigens are generated as a result of random mutations or aberrant splicing and hence will not be represented at high frequency in all the tumor lesions of the patient. To that end, we are exploring alternative strategies to generate clonal neoantigens by targeting key components of antigen presentation pathways, specifically the TAP transporter, ERAAP peptidase, and Invariant chain, the latter to generate class II-restricted neoantigens. Studies have shown that downregulation of these products, using genetic means or antisense RNA, not only inhibits the canonical antigen presentation pathway but also upregulates alternative pathways that present new, otherwise silent or subdominant, epitopes. Since such epitopes are not generated as a result of random mutations they are more likely to represent “clonal” neoepitopes generated in every cell in which the target was downregulated. Here we are developing clinically feasible broadly applicable approaches to inhibit the aforementioned mediators of antigen presentation using corresponding siRNAs targeted to tumor cells in situ by conjugation to a nucleolin-binding aptamer. Nucleolin, a nucleolar product, is translocated to the surface the majority of tumor cells of both human and murine origin and thereby serves as a broad, if not universal, target to deliver therapeutic cargo to the disseminated tumor cells of the patient. We show that nucleolin aptamer-targeted downregulation of ERAAP or Invariant chain in tumor-bearing mice inhibits tumor growth and potentiates PD-1 blockade therapy. Ongoing studies explore the combinatorial use of neoantigen induction methods and combination of neoantigen induction with immune potentiating strategies including but not limited to checkpoint blockade. Citation Format: Greta Garrido Hidalgo, Agata Levay, Alexey Berezhnoy, Brett Schrand, Eli Gilboa. Inducing neoantigens in disseminated tumor lesions to enhance their susceptibility to PD-1 blockade 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 A023.