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Single-Cell Map of Diverse Immune Phenotypes in the Metastatic Brain Tumor Microenvironment of Non Small Cell Lung Cancer (lung cancer)

Cancer immunotherapies have shown sustained clinical success in treating primary non-small-cell lung cancer (NSCLC). However, patients with brain metastasis are excluded from the trials because the brain is viewed traditionally as an immune-privileged organ. The composition and properties of tumor-infiltrating myeloid cells in metastatic brain tumors are mostly unknown. To depict the baseline landscape of the composition, gene signature, and functional states of these immune cells, we performed - single-cell RNA sequencing (scRNAseq) for 12,196cellsafter data preprocessing, including 2,241 immunecells from three surgically removed brain lesions of treatment-naïve NSCLC patients. We found a lack of T lymphocyte infiltration and activation, as well as the vast expansion of tumor-associated macrophage(TAM) in the brain lesions of NSCLC patients. By comparing our scRNAseq dataset with published data from early and late-stage primary NSCLC tumors, we showed that this compromised T cell response is unique to brain lesions. We identified a unique alternative activation (M2) gene expression pattern of the TAM in the brain metastasis and a lack of known T cell co-stimulator expression. Accumulation of M2 polarized TAM may, therefore, cause the comprised anti-tumor T cell response in metastatic brain lesions. These findings can contribute to the design of new immunotherapy strategies for NSCLC patients with brain metastasis.