Background Cytomegalovirus (CMV) stands as a member of the herpesvirus family, characterized by its linear double-stranded DNA genome, boasting a length of about 230 kbp and harboring over 200 potential open reading frames.¹ Widespread in its occurrence, CMV infects 70–90% of the global population, adopting a latent state following primary infection, and later resurges to trigger severe illnesses among immunocompromised individuals.² CMV’s involvement has been reported in various primary cancers and metastasis, encompassing breast cancer,³ brain cancer,⁴ and colorectal malignancies,⁵ and also found in brain metastasis.⁶

Methods We used single cell sequencing and spatial transcriptome analysis to characterize the immune environment of the brain metastasize from breast cancer patients as well as MCMV breast tumor mouse models. We then applied the computational tool CCCExplorer for modeling crosstalk interactions among tumor, immune, and stroma cells. Furthermore, we used COMPASS as a metabolic analysis tool to identify metabolic pathways and changes in immune cells, advancing our understanding of the interplay between metabolism and immunity in the tumor-immune microenvironment of the brain.

Results Our study unveils a distinct immune-suppressive tumor microenvironment in CMV+ breast cancer patients, characterized by compromised NK cell function and elevated TH2 cell accumulation. To understand how CMV promotes brain metastasis, we developed a breast tumor model using Murine CMV (MCMV) to mirror tumor progression and metastasis by integrating a GFP reporter gene into MCMV genome to track infected cancer and immune cells. We observed a significant increase in brain metastasis and reduced survival rates in MCMV+ tumor models. Single-cell analysis unveils viral-induced inhibition of NK cell proliferation and activation, with distinct molecular changes in secretomes, transcriptomes, metabolomes, and interactomes. Spatial transcriptomic and proteomic analysis identified a marked accumulation of TH2 cells and dysfunctional NK cells in proximity to MCMV-positive tumor cells.

Conclusions Our study shows CMV infection contributes to breast cancer brain metastasis by creating an immune-suppressive microenvironment, hampering immune cell proliferation and activation, impairing cytotoxic capabilities of NK cells, and recruiting TH2 cells, which further exacerbates immune suppression. These insights highlight the intricate interplay between viral infection and cancer progression, opening new vistas for potential therapeutic interventions of this devastating disease.

References

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