Tumor cell-derived IFN spatially reprograms osteopontin-enriched macrophage niches to promote PARP inhibitor resistance

Poly (ADP-ribose) polymerase inhibitors (PARPi) benefit homologous recombination-deficient (HRD) malignancies, yet resistance remains a major challenge. Leveraging specimens from a prospective neoadjuvant niraparib monotherapy trial in treatment-naïve high-grade serous ovarian cancer, we integrated PhenoCycler-Fusion spatial profiling, scRNA-seq, and multiplex immunohistochemistry to identify two therapeutic-modulated cellular neighborhoods: an IFN+ tumor cell-enriched niche that expands in resistant lesions and a tumor-associated macrophage (TAM)-enriched niche that persists but acquires enhanced immunosuppressive features. Mechanistically, sustained tumor cell-derived IFN induced osteopontin (SPP1) expression in TAMs via STAT signaling, creating immunosuppressive niches enriched in Tregs and myofibroblastic cancer-associated fibroblasts with intensified cell-cell interactions. SPP1 directly suppressed T cell signaling and effector function. High baseline SPP1+ cells predicted lower response rate (30.0% vs 76.2%, P = 0.021) and shorter progression-free survival (median 13.5 vs 28.3 months, P = 0.0006). In HRD mouse models, SPP1 blockade restored PARPi sensitivity, reversed acquired resistance, and enhanced T cell cytotoxicity-effects abrogated in immunodeficient mice, confirming immune dependence. These data establish a spatial IFN-SPP1 axis whereby persistent tumor cell IFN reprograms TAMs to promote PARPi resistance, position SPP1 as a key therapeutic target and prognostic biomarker for this therapy, and underscore therapeutic potential of microenvironment-targeted strategies to overcome PARPi resistance.