Abstract 6696: A senescent whole-cell vaccine platform derived from conditionally reprogrammed primary tumor cells primes potent T-cell immunity and overcomes ICI resistance in murine breast cancer models

Abstract Background: Aggressive cancers, including breast cancer, face challenges of therapeutic resistance and recurrence. Autologous cancer vaccines are limited by difficulties in obtaining sufficient primary tumor material. Our lab uses the Conditional Reprogramming Cell (CRC) method to enable long-term in vitro expansion of primary tumor cells. We are developing a novel vaccine strategy based on cellular senescence, a highly immunogenic state. We hypothesize that irradiated, senescent whole-tumor cells (SWCs) generated via CRC will function as potent, poly-antigenic vaccines to prime robust anti-tumor T-cell responses, synergize with immune checkpoint inhibitors (ICIs), and establish long-term immune memory. Experimental method: Senescence was induced in murine breast cancer lines by γ-irradiation. Immune priming was assessed by injecting SWCs into naïve syngeneic mice, quantifying systemic T-cell activation (CD4+, CD8+, CD69+, PD-1+) in spleens and lymph nodes via flow cytometry. Therapeutic efficacy will be evaluated in orthotopic, tumor-bearing mice treated with SWC vaccine + CpG adjuvant, +/- dual ICI blockade (anti-PD-L1/anti-CTLA-4). Endpoints include tumor regression and survival. Vaccine efficacy will also be tested in prophylactic and post-surgical anti-recurrence models (simulating R1/R2 residual disease). Summary of new data: In vivo immune-priming experiments (four weekly injections) demonstrated that senescent tumor cells elicited a robust, systemic adaptive immune response. Compared to controls, SWC-treated mice showed a marked expansion of both CD8α+ and CD4+ T-cell populations in spleens and lymph nodes. Flow cytometry revealed an activated effector phenotype with elevated CD69 and cytotoxic markers in CD8+ T cells. These findings confirm SWCs are highly immunogenic and induce systemic T-cell activation. Conclusion: Senescent whole-tumor cells derived via the CRC method are a feasible and potent poly-antigenic vaccine platform. Our preliminary data demonstrate that this strategy breaks immune tolerance, inducing robust T-cell activation. This provides a strong rationale for advancing this personalized, autologous vaccine to overcome immune resistance and prevent recurrence in aggressive solid tumors. Citation Format: Sara Rasouli, Chongwen Cao, Weiyi Gong, Haichang Li, Bei Liu, Anna Vilgelm, Jenny Li, Xuefeng Liu. A senescent whole-cell vaccine platform derived from conditionally reprogrammed primary tumor cells primes potent T-cell immunity and overcomes ICI resistance in murine breast cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 6696.