Interferon-induced senescent CD8⁺ T cells reduce anti-PD1 immunotherapy efficacy in early triple-negative breast cancer

Triple-negative breast cancers (TNBCs) lack predictive biomarkers to guide immunotherapy, especially during early-stage disease. To address this issue, we used single-cell RNA sequencing, bulk transcriptomics, and pathology assays on samples from 171 patients with early-stage TNBC receiving chemotherapy with or without immunotherapy. Our investigation identified an enriched subset of interferon (IFN)-induced CD8⁺ T cells in early TNBC samples, which predict immunotherapy nonresponsiveness. Mechanistically, IFN produced by HLA-DR⁺ monocytes triggered cellular senescence in CD8⁺ T cells, which was marked by excessive NAD⁺ consumption, reduced cytotoxicity, and immunotherapy nonresponsiveness. Nicotinamide mononucleotide treatment restored the function of IFN-induced senescent CD8⁺ T cells and enhanced immunotherapy efficacy in patient-derived organoid-T cell coculture and in mouse models. Overall, our study identifies IFN-induced T cell senescence as a driver of immunotherapy nonresponsiveness in early TNBC and provides a strategy to restore CD8⁺ T cell function for immunotherapeutic benefit.