Osteoprogenitor-GMP crosstalk underpins solid tumor-induced systemic immunosuppression and persists after tumor removal.

Remote tumors disrupt the bone marrow (BM) ecosystem (BME), eliciting the overproduction of BM-derived immunosuppressive cells. However, the underlying mechanisms remain poorly understood. Herein, we characterized breast and lung cancer-induced BME shifts pre- and post-tumor removal. Remote tumors progressively lead to osteoprogenitor (OP) expansion, hematopoietic stem cell dislocation, and CD41- granulocyte-monocyte progenitor (GMP) aggregation. The tumor-entrained BME is characterized by co-localization between CD41- GMPs and OPs. OP ablation abolishes this effect and diminishes abnormal myeloid overproduction. Mechanistically, HTRA1 carried by tumor-derived small extracellular vesicles upregulates MMP-13 in OPs, which in turn induces the alterations in the hematopoietic program. Importantly, these effects persist post-surgery and continue to impair anti-tumor immunity. Conditional knockout or inhibition of MMP-13 accelerates immune reinstatement and restores the efficacies of immunotherapies. Therefore, tumor-induced systemic effects are initiated by OP-GMP crosstalk that outlasts tumor burden, and additional treatment is required to reverse these effects for optimal therapeutic efficacy.

Resistance to natural killer cell immunosurveillance confers a selective advantage to polyclonal metastasis.

Polyclonal metastases frequently arise from clusters of circulating tumor cells (CTCs). CTC clusters metastasize better than single CTCs, but the underlying molecular mechanisms are poorly understood. Here, we show that polyclonal metastatic seeds exhibit higher resistance to natural killer (NK) cell killing. Using breast cancer models, we observed higher proportions of polyclonal lung metastasis in immunocompetent mice compared with mice lacking NK cells. Depleting NK cells selectively increased monoclonal but not polyclonal metastases, suggesting that CTC clusters are less sensitive to NK-mediated suppression. Transcriptional analyses revealed that clusters have elevated expression of cell-cell adhesion and epithelial genes, which is associated with decreased expression of NK cell activating ligands. Furthermore, perturbing tumor cell epithelial status altered NK ligand expression and sensitivity to NK-mediated killing. Collectively, our findings show that NK cells can determine the fate of CTCs of different epithelial and mesenchymal states, and impact metastatic clonal evolution by favoring polyclonal seeding.