Abstract B111: Vaccination against TAP downregulation-induced neoantigens to prevent future tumor development in the setting of recurrence or premalignancy

Development of therapeutic strategies to prevent recurrence in cancer patients, or tumor progression in individuals at high risk of developing cancer, has been challenging given the long and often unpredictable time to the emergence of the malignant tumors. Mutation-generated neoantigens represent the most potent antigens to induce antitumor immunity, yet the ability to predict which neoantigens will be expressed in future tumors is at present not an option.To overcome the limitations of targeting mutated neoantigens, we have developed a simple and broadly applicable approach to induce neoantigens in tumor cells in situ by reducing the expression of peptide transporter TAP, whereby a TAP-specific siRNA is targeted to tumor cells in mice by conjugation to a broad-range nucleolin-binding aptamer. Nucleolin, normally expressed in the cytoplasm and nucleolus of all somatic cells, is translocated to the cell surface of most murine and human tumors and hence could serve as an almost universal target to deliver therapeutics to tumors in vivo. Previous results have demonstrated that genetic ablation of TAPnot only inhibits the canonical antigen processingpathway but also upregulates alternative pathways presenting new epitopes, essentially neoantigens, that can be recognized by the immune system to elicit effective CD8+ T-cell responses. Such epitopes are shared among all (tumor) cells in which TAPis downregulated, corresponding to the functional equivalent of clonal mutation-generated neoantigens. Our study shows that transiently increasing the neoantigen burden of tumor cells in situ by targeted downregulation of TAPrepresent a potent way of generating antitumor immunity in the absence of measurable toxicity.Exploiting the ability to induce neoantigens in situ, we are developing a novel vaccination strategy targeting potent neoantigens to control the growth of the future tumors—whereby mice in remission or with premalignant lesionsare first vaccinated against TAPdownregulation-induced neoantigens, and when or if tumor develops the same antigens are induced in the tumor, termed prorapeutic vaccination (prophylactic + therapeutic). To induce an immune response against TAPdownregulation-induced neoantigens, mice were vaccinated with TAPsiRNAs that are targeted to DC in situ by conjugation to a short CpG oligonucleotide leading to the downregulation of TAP, expression of neoantigens, as well as activation of the DC, and thereby priming of a potent T-cell response. To induce neoantigens in the future tumors, the TAPsiRNA is targeted to the developing tumor lesion by conjugation to the nucleolin(Nucl) aptamer. Both Nucl and CpG targeted siRNA are administered systemically via intraperitoneal injection to reach the disseminated tumor lesions and resident DC present throughout the body. In murine models of recurrence and premalignant disease, prorapeutic vaccination elicited an adaptive and innate antitumor immune response and inhibited tumor growth. The prorapeutic vaccination approach was more effective than vaccinating against prototypic mutated neoantigens, and did not elicit measurable autoimmune toxicity, in stark contrast to a comparatively therapeutic dose of CTLA-4.The ability to vaccinate against experimentally induced neoantigens using a broadly applicable procedure with two chemically synthesized reagents, introduces a new paradigm in cancer immunotherapyof vaccinating against neoantigens induced in future tumors, to prevent recurrence in patients in remission or preventing tumor development in individuals at high risk of developing cancer. Citation Format: Greta Garrido Hidalgo, Brett Schrand, Ailem Rabasa, AgataLevay, Tal Gefen, Giri Bhuwan Bhuwan, Anthony R. Ferrantella, Vikas Dudeja, Koen Marijt, Thorbald T. van Hall, Eli Gilboa. Vaccination against TAPdownregulation-induced neoantigens to prevent future tumor development in the setting of recurrence or premalignancy [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer ImmunotherapyConference: Translating Scienceinto Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B111.