Immunological and pathological characteristics of brain parenchymal and leptomeningeal metastases from non-small cell lung cancer

Brain parenchymal metastases (BM) and leptomeningeal metastases (LM) represent distinct subtypes of central nervous system metastases (CNSm) from lung cancer, posing significant clinical challenges. The local immune landscape of LM remains elusive. Herein, we utilized single-cell RNA sequencing to build a cell atlas of LM, and systematically examine the immune profiling and cell heterogeneity between BM and LM. Our analysis reveals that BM has more CXCL9⁺ macrophages, CXCL13⁺CD4⁺ T cells and B cells than LM, exhibiting the presence of tertiary lymphoid (TLS) structures, which is associated with a favorable response to tyrosine kinase inhibitors (TKI). Conversely, a remarkably immunosuppressive tumor microenvironment (TME) is detected in LM, characterized by lymphocyte depletion and a concurrent enrichment of SPP1⁺ macrophages, compared to BM. Furthermore, we identified significant blood-brain barrier (BBB) cell discrepancies between BM and LM, and substantial phenotypic reprogramming of BBB cells in CNSm. This reprogramming encompassed alterations in transporter gene expression, extracellular matrix production and dysregulated cell-cell interactions, potentially contributing to the metastatic process. In summary, this study highlights the divergent cellular and molecular landscapes of BM vs LM, offering critical insights into potential therapeutic targets and informing the development of improved treatment strategies for non-small cell lung cancer patients with CSNm.