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Single cell characterization of the immune microenvironment of melanoma brain and leptomeningeal metastases

ABSTRACT: Melanoma brain metastases (MBM) and leptomeningeal metastases (LMM) are two manifestations of melanoma CNS metastasis with vastly different survival outcomes. Using single cell RNA-Seq analysis we uncovered a unique, immune-suppressed T-cell landscape in the LMM microenvironment distinct from that of brain and skin metastases. An LMM patient with an unusually long survival demonstrated an immune repertoire that was distinct from those of poor survivors and more similar to CSF from non-LMM patients. Upon response to PD-1 therapy, this extreme responder showed increased levels of T-cells and dendritic cells in their CSF, whereas poor survivors showed little improvement in their T-cell responses. In MBM patients, systemic therapy was associated with increased immune infiltrate, with similar T-cell transcriptional diversity noted between skin metastases and MBM - suggestive of immune cell trafficking into the brain. A correlation analysis across the entire immune landscape identified the presence of a rare population of dendritic cells (DC3s) that correlated with increased overall survival and positively regulated the immune environment through modulation of activated T-cells and MHC expression. Our study provides the first atlas of two distinct sites of melanoma CNS metastases and identifies rare populations of cells that underlie the biology of this devastating disease.

ORGANISM(S): Homo sapiens

PROVIDER: GSE174401 | GEO | 2021/05/14

REPOSITORIES: GEO

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Project description:Brain metastases (BrMs) are a devastating complication of solid tumors with challenging clinical management. In this study, immunogenomic and digital spatial analyses were applied to interrogate the peripheral blood and tumor specimens derived from 53 unique patients with metastatic brain tumors originating from different solid tumors including melanoma, breast cancer, lung cancer and renal cell carcinoma. In the peripheral blood, lower levels of neutrophil -lymphocytes ratio (NLR) were detected at time of craniotomy in patients with melanoma-derived brain metastasis (MBM) vs. non-melanoma- derived brain metastasis (non-MBM). Independently from the primary tumor of derivation, patients with BrMs and increased NLR levels were characterized by shorter overall survival (OS) following craniotomy. In the tumor microenvironment (TME), molecular evaluations performed on FFPEs revealed higher expression of genes and mRNA signatures identifying NK cells, CD8 cells and B cells in MBM (n=13) vs. non-MBM brain metastasis (n=41). Focusing on CD8 cells, higher infiltration of CD8+ cells were observed in patients with MBM with longer OS following craniotomy. Spatial proteomic analysis further highlighted the infiltration of CD8+ cells, antigen presenting cells- (HLA-DR+, CD11c+, B2M+), agonists of T cell activity (CD137+, CD40+) and B cells (CD20+) enriched in MBM vs non-MBM. On the contrary, an increased expression of genes associated with neuro-development, cell- cell adhesion, neutrophil enrichment together with the increased infiltrations of cells promoting neuro-differentiation (Neun+, S100+), immune regulatory functions (CD25+, CD127+), and granulocytes aggregation (CD66b+) were observed in non-MBM vs. MBM. These findings highlight that the TME of BrMs plays a pivotal role in the pathogenesis and therapeutic resistance of BrMs derived from different solid tumors. Our results also suggest that distinct neuro-immune interplay may contribute to treatment resistance in BrMs.

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Single cell characterization of the immune microenvironment of melanoma brain and leptomeningeal metastases

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