Nature Communications | 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

This study systematically reveals the immunosuppressive mechanisms underlying CD8+ T cell exclusion and the absence of tertiary lymphoid structures (TLS) in non-small cell lung cancer (NSCLC) brain metastases, providing direct evidence for designing combination therapeutic strategies to enhance anti-tumor immunity in the central nervous system. It offers critical guidance for optimizing treatment approaches in NSCLC and for overcoming resistance to immune checkpoint inhibitors.

 

Literature Overview

This article, '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,' published in Nature Communications, systematically investigates the deep mechanisms underlying resistance to immune checkpoint inhibitors in non-small cell lung cancer (NSCLC) brain metastases (BrMs). By integrating clinical data analysis, paired patient sample assessments, and mouse model validation, the study reveals that brain metastatic lesions exhibit a pronounced immune-excluded phenotype, characterized by reduced CD8+ T cell infiltration and defective tertiary lymphoid structure (TLS) formation. Further findings demonstrate that combined anti-PD-1 and anti-CTLA-4 therapy can remodel the brain metastatic microenvironment, enhance CD8+ T cell effector functions, and induce TLS-like structure formation, thereby overcoming the limitations of monotherapy. This work provides a solid mechanistic foundation for improving immunotherapy response rates in patients with brain metastases.

Background Knowledge

Brain metastasis is a major cause of mortality and reduced quality of life in NSCLC patients, with treatment responses typically inferior to those of primary tumors, particularly showing low response rates to PD-1 monoclonal antibody therapy. Current understanding of the mechanisms driving the immunosuppressive microenvironment in BrMs remains insufficient, especially regarding the regulation of T cell infiltration barriers and defects in lymphoid-like structures. Emerging evidence suggests that TLS play a critical role in anti-tumor immunity, yet their status and regulatory mechanisms in BrMs remain unclear. This study focuses on systematically dissecting the immunological differences between NSCLC brain metastases and primary tumors, specifically CD8+ T cell exclusion and TLS deficiency, and explores whether combination immunotherapy can reverse this phenotype. The research further employs a syngeneic mouse model to validate therapeutic mechanisms, bridging the translational gap between clinical observations and preclinical research. Using single-cell RNA sequencing (scRNA-seq) and multiplex immunofluorescence, the authors deeply analyze dynamic changes in T cell subsets, revealing the potential role of Tfh cells in TLS formation, thereby opening new avenues for future interventions targeting immune exclusion.

 

 

Research Methods and Experiments

The study employs a multidimensional strategy to validate its hypotheses. First, a retrospective analysis of NSCLC patient cohorts treated with nivolumab alone or in combination with ipilimumab was conducted to assess intracranial disease control rates and survival differences. Second, public transcriptomic datasets and in-house paired clinical samples were analyzed using bulk RNA-seq and immunohistochemistry to compare immune microenvironment characteristics between BrMs and primary tumors. Subsequently, a syngeneic BrM mouse model based on intracarotid artery injection was established to simulate hematogenous metastasis and evaluate the in vivo efficacy of different immunotherapies. Tumor burden was monitored via bioluminescence imaging (BLI), with treatment efficacy confirmed through survival analysis. To dissect underlying mechanisms, scRNA-seq was performed on intracranial immune cells to reveal changes in T cell subsets. Finally, CD8+ T cell infiltration, effector phenotypes, and TLS-like structure formation were validated using flow cytometry and immunofluorescence. Key evidence includes: combination therapy significantly prolonged survival and increased CD8+ T cell infiltration; scRNA-seq revealed an increased proportion of effector memory T cells; Tfh-like cells expanded in the combination group; and TLS-like aggregates formed in treatment-responsive mice.

Key Conclusions and Perspectives

• NSCLC brain metastases exhibit an immune-excluded phenotype, characterized by reduced infiltration of CD8+ T cells and Tregs and decreased TLS density, indicating a microenvironment that suppresses T cell homing and organization — providing a clear direction for developing interventions targeting chemokines such as CCL19/CCL21
• Combination anti-PD-1 and anti-CTLA-4 therapy significantly improves intracranial disease control, extends patient survival, and reduces the risk of new brain metastases — supporting the prioritization of combination immunotherapy in BrM patients
• In mouse models, combination therapy significantly suppresses brain metastatic growth and prolongs survival, whereas monotherapy shows limited efficacy — validating clinical observations and establishing a reliable preclinical model for further mechanistic studies
• scRNA-seq and flow cytometry show that combination therapy increases the proportion of CD8+ T cells and enhances their GzmB expression and effector functions — indicating enhanced CTL activity as a core mechanism of treatment response
• CD8+ T cell depletion experiments completely abolish the therapeutic efficacy of combination treatment — confirming CD8+ T cells as essential effector cells and emphasizing their central role in immune surveillance
• Combination therapy promotes the expansion of Tfh-like CD4+ T cells and induces TLS-like structure formation in responsive mice — revealing that CTLA-4 blockade may remodel lymphoid tissue microenvironments via the Tfh-B cell axis, offering a new pathway to enhance durable anti-tumor immunity

Research Significance and Prospects

This study represents a mechanistic breakthrough in immunotherapy for NSCLC brain metastases. It not only explains the limited efficacy of PD-1 monotherapy but also proposes that dual blockade of PD-1 and CTLA-4 can achieve stronger central anti-tumor immunity through two mechanisms: enhancing CD8+ T cell infiltration and function, and promoting TLS formation. This finding has important implications for drug development, suggesting future exploration of combination strategies targeting CCL19/CCL21 or LTβR pathways to promote TLS generation. From a clinical monitoring perspective, TLS or Tfh density may serve as potential biomarkers to predict immunotherapy response. Additionally, this work underscores the importance of using humanized immune system models or syngeneic models for brain metastasis research, providing a standardized paradigm for disease modeling.

 

 

Conclusion

This study systematically uncovers the core mechanisms of immune exclusion in non-small cell lung cancer brain metastases—specifically, restricted CD8+ T cell infiltration and defective TLS formation—that lead to poor responses to PD-1 monotherapy. Through clinical cohort analysis and mouse model validation, the research demonstrates that combined anti-PD-1 and anti-CTLA-4 therapy can effectively reverse this phenotype, significantly enhancing intracranial anti-tumor immunity. Mechanistically, the combination therapy not only boosts CD8+ T cell effector functions but also promotes the formation of TLS-like structures by expanding Tfh-like cells, thereby establishing local immune-active hubs. This dual-action model offers a novel perspective for overcoming immune tolerance in brain metastases. From bench to bedside, these findings support prioritizing combination immunotherapy in NSCLC patients with brain metastases and lay the foundation for developing next-generation therapies targeting immune exclusion. Future research may focus on how to specifically enhance TLS formation without increasing toxicity, aiming for more durable treatment responses. This work marks a critical step toward precise regulation of the central immune microenvironment and holds promise for significantly improving long-term survival and quality of life for patients with NSCLC brain metastases.

 

Kazutaka Hosoya, Hiroaki Ozasa, Takahiro Tsuji, Hiroaki Wake, and Toyohiro Hirai. 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. Nature Communications.