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Abstract Human Cytomegalovirus (HCMV) infection has emerged as a noteworthy factor in breast cancer patients, particularly those experiencing brain metastasis. Despite being prevalent and often asymptomatic, HCMV's contribution to tumor progression remains enigmatic. Notably, a high proportion of breast cancer patients with brain metastasis exhibit HCMV positivity in both primary tumors and metastatic lesions. This study aims to elucidate the influence of HCMV infection on brain metastasis by investigating its impact on the tumor microenvironment. Our findings reveal a distinctive immune suppressive tumor microenvironment in HCMV-positive breast cancer patients. This environment is characterized by impaired NK cell function and an elevated accumulation of TH2 cells. To comprehend the role of HCMV in promoting brain metastasis, we have developed a murine breast tumor model using MCMV, enabling us to mirror the clinical trajectory of tumor progression and metastasis. The integration of a GFP reporter gene into the MCMV genome facilitates the tracking of infected cancer cells. Within this model, we observe a significant increase in brain metastasis coupled with reduced survival rates. Single-cell sequencing analysis uncovers diminished NK cell presence and activation, along with heightened TH2 cell accumulation within the tumor microenvironment—results that parallel the clinical observations in breast cancer patients. GSEA analysis underscores the secretion of inhibitory cytokines by MCMV-infected cancer cells, contrasting with their non-infected counterparts. Collectively, our study reveals that CMV infection contributes to brain metastasis in breast cancer by generating inhibitory cytokines. This hampers the recruitment and proliferation of immune cells within the tumor microenvironment and concurrently impairs the cytotoxic capabilities of NK cells. These insights shed light on the intricate interplay between viral infection and tumor progression, offering potential avenues for therapeutic exploration. Citation Format: Wenjuan Dong, Xin Wang, Kun Han, Akshjot Puri, Amna Irfan, Wei Qian, Liliana Guzman, Roberto Rosato, Jianting Sheng, Hong Zhao, Jenny Chang, Stephen Wong. The Role of HCMV Infection in Facilitating Brain Metastasis through the Creation of a Suppressive Tumor Microenvironment in Breast Cancer Patients abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-27-07.
Dong et al. (Thu,) studied this question.