Abstract LB-B001: Recognition of senescent breast tumor antigen by CD4+ T cells causes IFNγ release leading to target gene expression

Abstract Chemotherapy induces senescence rather than apoptosis in breast cancer cells that have wild type p53, leading to relapse and worse patient outcomes. Senescent tumor cells evade immune-mediated cell death by upregulating several hundred interferon gamma (IFNγ)-dependent genes that suppress T cell activity, including Cd274 (PD-L1), but also sensitize to immune checkpoint inhibitors through expression of antigen presentation and MHC-I/II genes. The expression of IFNγ in the residual disease of treated tumors is entirely dependent on tiny, potent population of CD4+ T cells. Syngeneic mammary tumors transplanted orthotopically into Cd4-KO mice have no expression of IFNγ or associated target genes during senescence, while tumors in Cd8-KO mice have an intermediate phenotype. To investigate the mechanism of IFNγ expression by the CD4+ T cells in the residual disease of chemotherapy-treated, senescent tumors, we first examined the role of T cell receptor (TCR) engagement. We transplanted MMTV-Wnt1 and MMTV-PyMT tumor models into WT or SMARTA1 mice that have a specific CD4+ TCR that recognizes the LCMV GP61-80 epitope. After treatment, we found that isolated tumor cells from SMARTA1 mice expressed p53 target genes, such as Cdkn1a, but failed to express IFNγ target genes despite having an abundant CD4+ T cell population. To determine if tumor cell expression of the LCMV GP61-80 epitope could rescue IFNγ-dependent gene expression induced by CD4+ cells in SMARTA1 mice, we transduced our two tumor models with a vector containing mCherry or mCherry-LCMV GP61-80. Following transplant and treatment, we found that senescent tumor cells expressing mCherry-LCMV GP61-80 from treated SMARTA1 host mice fully restored expression of IFNγ-dependent genes to comparable levels observed in WT hosts. Senescent tumor cells expressing mCherry alone in SMARTA1 hosts, however, were dramatically diminished in expression of IFNγ target genes. Flow cytometry on isolated CD45+ cells from treated and untreated tumors showed that immune populations remained relatively stable between host genotypes. In sum, our data demonstrate that, in the residual disease of treated tumors, the IFNγ that induces tumor expression of critically important immune modulatory and antigen presentation genes is derived entirely from CD4+ TCRs that recognize specific tumor antigens. Citation Format: Calvin WT. Adam, Raegan M. Kvadas, Fang-Yen Chiu, David A. Gervasio, Timothy Kayes, Dorota D. Wyczechowska, James G. Jackson. Recognition of senescent breast tumor antigen by CD4+ T cells causes IFNγ release leading to target gene expression [abstract]. In: Proceedings of the AACR Immuno-Oncology Conference (AACR IO): Discovery and Innovation in Cancer Immunology: Revolutionizing Treatment through Immunotherapy; 2026 Feb 18-21; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Immunol Res 2026;14(2 Suppl):Abstract nr LB-B001.