Abstract 4098: A citrullinated-ENO1 peptide vaccine delayed tumor growth and markedly improved overall survival in a mouse model of triple-negative breast cancer

Abstract Purpose: To evaluate the impact of a novel citrullinated-enolase 1 (cit-ENO1) peptide-based vaccine on the immune response, tumor growth and overall survival in a mouse model of triple-negative breast cancer (TNBC). Background: Cancer vaccines have consisted primarily of mutated or overexpressed proteins in cancer. We have uncovered dysregulated protein citrullination by peptidyl arginine deiminases (PADI) as a feature of triple negative breast cancer inducing immunogenicity to citrullinated proteins. On the basis of these findings, we investigated a novel vaccine based on cancer-selective cit-ENO1 peptides that we identified from mass spectrometry analysis of the surfaceome and immunopeptidome in TNBC. We assessed the extent to which the vaccine elicited an immune response and delayed tumor growth and improved overall survival in a syngeneic mouse model of TNBC. Experimental Design: We immunized female B6129SF1/J mice with cit-ENO1 peptides or corresponding unmodified ENO1 (unm-ENO1) peptides as antigens, together with the TLR3 agonist poly I:C as an adjuvant, once a week, for three weeks. PBS or poly I:C alone were used as controls. One week post the last round of immunization, draining lymph nodes (LN) and immunized skin were harvested, and T cell phenotypes evaluated using flow cytometry. To assess anti-cancer efficacy, mice were immunized with cit-ENO1 or unm-ENO1 peptides, followed by orthotopic implantation with murine BRCA1co/co; MMTV-Cre; p53+/- TNBC cells. Tumor growth and overall survival were assessed. Results: Cit-ENO1 peptide vaccination induced a statistically significantly greater percentage of activated CD8+ PD-1+ effector T cells as well as CD8+ CD44+ CD62L- effector memory T cells in the LNs compared with either the control groups or the unm-ENO1 peptide. CD8+ PD-1+ T-cells were also significantly elevated in immunized skin of cit-ENO1 vaccinated mice. Both cit-ENO1 and unm-ENO1 vaccine increased CD4+ PD-1+ T cells from the LNs and immunized skin. Remarkably, the cit-ENO1 vaccine but not the um-ENO1 vaccine significantly delayed tumor growth and markedly improved overall survival compared to respective controls. Conclusion: Cancer-selective cit-ENO1 peptides induced a potent anti-cancer immune response and significantly delayed tumor initiation and progression in a preclinical, immune competent mouse model of TNBC. Citation Format: Ricardo A. Leon Letelier, Hiroyuki Katayama, Yihui Chen, Yinning Cai, Fuchung Hsiao, Banu Arun, Samir Hanash. A citrullinated-ENO1 peptide vaccine delayed tumor growth and markedly improved overall survival in a mouse model of triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4098.