Single-cell and spatial transcriptome profiling identifies cellular heterogeneity and immunosuppressive tumor microenvironment in inflammatory breast cancer

Inflammatory breast cancer (IBC) is a highly aggressive subtype of breast cancer associated with a poor prognosis. A better understanding of IBC's pathological and molecular basis is crucial for developing precision medicine strategies. This study aimed to profile IBC at both the single-cell and spatial levels to examine immune cell populations, signaling pathways, and identify potential therapeutic targets for treating IBC. Single-cell RNA sequencing (scRNA-seq) was employed to identify immune-related differences between IBC and non-IBC samples. qRT-PCR and fluorescence staining were utilized to validate the findings from scRNA-seq, while spatial analysis using the NanoString GeoMx Digital Spatial Profiler was conducted to evaluate immune cell infiltration. Tumor-immune cell co-culture assays were conducted to assess the cytotoxic role of CXCL13. In vivo studies were performed to assess the effect of CXCL13 on the efficacy of immunotherapy. Furthermore, a screening of natural products was performed to identify potential immunomodulatory agents for the treatment of IBC. scRNA-seq revealed a significant reduction in CXCL13 expression in T cells within the IBC tumor microenvironment, a finding that correlated with poorer patient outcomes. Additionally, immune-related gene sets were notably downregulated, and cell-cell interactions were diminished, indicating a state of immune suppression within IBC. Spatial analysis further demonstrated a reduced presence of CD45-positive immune cells within IBC tumor tissues, highlighting the compromised immune infiltration characteristic of this aggressive cancer subtype. Most importantly, overexpression of CXCL13 in tumor cells, under co-culture with immune cells, significantly promoted tumor cell death. CXCL13 can also enhance the efficacy of anti-PD-1 therapy in vivo. Furthermore, screening of natural products identified sanguinarine and α-mangostin as potential immunomodulatory compounds, offering promising therapeutic avenues for modulating the immune response in IBC and improving treatment outcomes. Our findings reveal inherent heterogeneity within the "cold" tumor microenvironment of IBC. These factors collectively contribute to the immune suppression characteristic of IBC. Additionally, natural product screening identified sanguinarine and α-mangostin as promising immunomodulatory agents, offering potential therapeutic strategies to improve treatment outcomes.