Effect of CD4+PD-1+CXCR6+ T cells on the response of immune checkpoint inhibitor therapy in brain metastases of NSCLC.

2028 Background: Brain metastases (BrM) in non-small cell lung cancer (NSCLC) presented a significant challenge due to poor prognosis. While immune checkpoint inhibitors (ICIs) have been standard treatments for NSCLC, their efficacy in BrM is variable, emphasizing the urgent need for predictive biomarkers and fundamental mechanisms. Methods: We prospectively collected 20 cerebrospinal fluid (CSF) and 4 BrM tumors from 18 NSCLC patients with BrM undergoing ICI therapy for single-cell RNA sequencing (scRNA-seq), complemented by integrating data from multiple published datasets. Three independent cohorts (8 and 25 CSF, and 31 BrM tumors) underwent flow cytometry, proteomics, and multiplex immunohistochemistry for validation, respectively. Results: Our study provided a high-resolution atlas of cellular dynamics in the CSF and BrM during ICI therapy in NSCLC patients with BrM. Notably, we identified a key immune cell subset, CD4 + PD-1 + CXCR6 + T cells, as a positive predictor of ICI intracranial tumor responses, which presented highly functional and transcriptomic similarities in both CSF and BrM tumor environment. Moreover, CXCR6 could serve as a specific marker for CD4 + PD-1 + T cells linked to ICI response. Further, we revealed that the novel cluster of CD4 + PD-1 + CXCR6 + T cells was closely associated with lymphocyte activation and aggregation in CSF and BrM of ICI responders, and cDCs of ICI responders interacted with CD4 + PD-1 + CXCR6 + T cells for enhanced antigen presentation and inflammatory activation. Conclusions: Our findings revealed critical insights into the immune landscape of NSCLC BrM under ICI therapy, highlighting CD4 + PD-1 + CXCR6 + T cells in CSF as a promising biomarker and illuminating fundamental mechanisms underlying ICI efficacy.