Extracellular vesicles from triple negative breast cancer promote pro-inflammatory macrophages associated with better clinical outcome

Tumor associated macrophages (TAMs), which differentiate from circulating monocytes, are pervasive across human cancers and comprise heterogeneous populations. The contribution of tumor-derived signals to TAM heterogeneity is not well understood. In particular, tumors release both soluble factors and extracellular vesicles (EVs), whose respective impact on TAM precursors may be different.

Researchers from INSERM, France show that triple negative breast cancer cells (TNBCs) release EVs and soluble molecules promoting monocyte differentiation toward distinct macrophage fates. EVs specifically promoted proinflammatory macrophages bearing an interferon response signature. The combination in TNBC EVs of surface CSF-1 promoting survival and cargoes promoting cGAS/STING or other activation pathways led to differentiation of this particular macrophage subset. Notably, macrophages expressing the EV-induced signature were found among patients’ TAMs. Furthermore, higher expression of this signature was associated with T cell infiltration and extended patient survival. Together, this data indicates that TNBC-released CSF-1-bearing EVs promote a tumor immune microenvironment associated with a better prognosis in TNBC patients.

TNBC human tumors release EVs containing CSF-1 and their infiltration with macs
containing an EV-R-mo-macs signature confers them better survival probability

(A) Scheme of tissue-explant culture method for EV isolation from paired tumor tissue and juxta-tumor tissue. EVs were isolated from small volumes of prefiltered CM by ultracentrifugation. (B) Absolute CSF-1 pg present in 400 µL of conditioned medium as described in (A) or in EVs obtained from 400 µL of conditioned medium. (C) Heat map of the genes with the strongest up-regulation (log2 fold change >2) in the EV-R-mo-macs when compared to all the other conditions. These 23 genes constitute the EV-R-signature used to analyze RNA from patients’ tumor samples. (D) Expression of EV-R-mo-macs- or EV-P-mo-macs-enriched genes in TNBC tumor-infiltrating HLA-DR⁺CD11c⁺ cells as determined by scRNA-seq. UMAP embedding of single cells as per the original study are shown, with color intensity representing normalized signature expression level. (Right Panel) UMAP map of macrophage and monocytes clusters from the HLA-DR⁺CD11c⁺cells scRNA-seq analysis from all seven TNBC patients with the identified clusters is shown. Each dot represents a cell, colored by clusters. EV-R and EV-P gene signatures (E) EV-R-mo-macs and EV-P-mo-macs signature expression across breast cancer subsets on the METABRIC cohort (Luminal, n = 1,314; Her2, n = 243; TNBC, n = 330). (F) Correlation of the EV-R-signature and the EV-P-signature with established signatures for CD8 cytotoxic, CD8 memory, CD8 exhausted, and CD4 T regulatory cells and NK cells in the METABRIC cohort. (G) Assay for migration of total T cells using xCELLigence. T cells were seeded in the upper chamber, and supernatant from rCSF-1-mo-macs or EV-R-mo-macs or EV-P-mo-macs or rCXCL10 in the lower chamber of CIM-plates. Migration was evaluated for 24 h. (H) Kaplan-Meier curves showing overall survival of TNBC patients from the METABRIC cohort stratified by high (red) and low (blue) expressions of EV-R-mo-macs (Left), EV-P-mo-macs (Middle), or of a canonical IFN signature (Right). Survival curves were compared with the log-rank test (n = 330).