LSD1 Promotes Immune Exclusion and Suppresses IFN-γ-Associated Transcriptional Programs in Triple-Negative Breast Cancer

Background: Triple-negative breast cancer (TNBC) exhibits aggressive biology and heterogeneous immune infiltration. Lysine-specific demethylase 1 (LSD1/KDM1A) is an epigenetic regulator implicated in oncogenic transcriptional programs, but its role in immune exclusion remains incompletely defined. Methods: LSD1 expression was evaluated by immunohistochemistry in TNBC specimens and correlated with survival. Functional effects of LSD1 depletion or pharmacological inhibition were assessed in TNBC cell lines and patient-derived xenograft organoids (PDXOs). Transcriptomic, ChIP-seq, multiplex immunofluorescence, and GeoMX digital spatial profiling analyses were integrated to characterize LSD1-associated transcriptional, chromatin, and immune programs. PBMC-PDXO co-cultures evaluated the effects of LSD1 inhibition on tumor growth and immune cell infiltration. Results: High LSD1 expression was associated with inferior overall survival, hypoxia-associated programs and suppressed immune pathways. LSD1-high tumors exhibited reduced infiltration of T cells, B cells, NKT-like cells, and macrophages. Spatial profiling revealed suppressed innate immune responses and type I interferon signaling within B-cell and T-cell compartments, respectively. ChIP-seq demonstrated preferential LSD1 occupancy at AP-1 motif-enriched regions, while co-immunoprecipitation supported association with AP-1 complexes. Integration of LSD1 chromatin occupancy sites with transcriptomics data identified SPPL2A and NCOA3 as candidate LSD1-regulated genes associated with interferon-γ response pathways. LSD1 depletion increased SPPL2A, NCOA3, MHC-I and PD-L1 expression. LSD1 inhibition reduced PDXO growth and increased immune cell infiltration. Conclusions: LSD1 is associated with a poor clinical outcome and immune exclusion in TNBC. These findings support a role for LSD1 in AP-1-associated chromatin regulation and interferon-γ-related transcriptional response; they warrant further investigation into LSD1 inhibition as a therapeutic strategy for immune-cold TNBCs.