Anti-PD-1 plus anti-CTLA-4 blockade overcomes immune exclusion in NSCLC brain metastases by enhancing CD8+ T cell responses and promoting tertiary lymphoid structure formation

Abstract

Abstract Brain metastases (BrMs) in non-small cell lung cancer (NSCLC) respond poorly to anti-PD-1 monotherapy, but the underlying immune resistance remains incompletely defined. Here we integrate clinical outcome analyses, paired human tissue profiling and syngeneic mouse models to characterize the BrM immune microenvironment. Clinical analyses suggest improved intracranial disease control with nivolumab plus ipilimumab compared with nivolumab alone. Paired human specimens show that BrMs contain fewer cytotoxic T lymphocytes (CTLs) and tertiary lymphoid structures (TLSs) than primary tumors, defining an immune-excluded phenotype. A syngeneic BrM model recapitulates this phenotype and resists anti-PD-1 monotherapy, whereas combined anti-PD-1 and anti-CTLA-4 blockade suppresses tumor growth and prolongs survival. Single-cell RNA sequencing, flow cytometry and immunofluorescence show increased CTL infiltration and effector function after combination therapy. CD8 + T cell depletion abrogates therapeutic benefit, and combination therapy expands T follicular helper-like cells and induces TLS-like structures. These findings manifest increased adaptive immune response of dual checkpoint blockade in NSCLC BrMs.