Lung cancer is the leading cause of cancer-related deaths. ICB response prediction remains challenging, with 70% of patients non-responsive. TLS, containing B and T cells, predict ICB response in LUAD, but causal relationships are unestablished. TLS feature GC-like structures where B cells mature antibodies with T follicular helper (TFH) cells, dependent on the CXCL13-CXCR5 axis. Anti-tumour antibodies target tumour-associated antigens (TAAs), including ERVs, which are immunogenic due to upregulation in cancer. We explored the role of TLS, B cells, and anti-tumour antibodies in LUAD.

Results

B Cell Responses in a Mouse LUAD Model

The KPAR mouse LUAD model (KrasLSL-G12D/+Trp53f/f background) forms TLS with segregated T/B cell areas and active GCs, unlike non-immunogenic KPB6 tumours. KPAR tumours induce GC B cells and TFH cells, with class-switched (IgG/IgA) tumour-binding antibodies. Serum from KPAR-challenged mice prolongs recipient survival, associated with increased tumour-infiltrating NK cells mediating antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC).

Anti-ERV Antibodies in Mouse LUAD

KPAR serum targets ERV envelope glycoproteins (e.g., KPAR-associated retrovirus, KARV). Blocking ERV envelope glycoproteins abrogates serum tumour binding. Therapeutic anti-ERV antibody (83A25) extends survival, and ERV-deficient (KPAR.eMLV−/−) tumours grow faster with reduced GC/TFH responses. PD-L1 blockade expands GC/TFH cells, increases anti-ERV antibody titres/avidity, and serum from anti-PD-L1-treated mice enhances recipient survival. A dominant anti-ERV monoclonal antibody (J1KK) mediates anti-tumour effects via NK cells.

B Cell Responses in Targeted Therapies

KRAS(G12C) inhibitor (G12Ci) upregulates B cell/GC-related genes and TLS formation in KPARG12C tumours, enhancing anti-tumour antibodies. MEK inhibitor (MEKi) impairs GC/TFH responses, reducing antibody avidity. B cell depletion increases G12Ci-treated tumour relapse, suggesting B cells contribute to durable responses.

CXCL13 Therapy Synergizes with ICB

CXCL13 is upregulated in KPAR tumours. CXCL13 blockade diminishes lung GC responses and negates ICB efficacy, while CD20 depletion abrogates systemic GC/antibody responses. Intranasal CXCL13 delivery increases GC responses and survival, synergizing with anti-PD-L1 for enhanced therapeutic effect.

B Cell Responses in LUAD Patients

TLS/B cell signatures are elevated in LUAD vs. lung squamous cell carcinoma (LUSC), correlating with better survival. CXCL13 expression predicts ICB response in TLS-associated cancers. ERVK-7 (HERV-K(HML-2)) is highly expressed in LUAD, with chromosome 1q22 amplification driving its upregulation. 45% of TRACERx LUAD patients have anti-HERV-K(HML-2) antibodies, which mediate ADCC against tumour cells. ICB boosts anti-HERV-K titres, and pre-treatment ERVK-7 expression predicts ICB response/survival in LUAD patients.

Discussion

Our study identifies ERV envelope glycoproteins as key targets of anti-tumour B cell responses in LUAD. TLS formation (CXCL13-dependent) and ERV-targeting antibodies are amplified by ICB and KRAS(G12C) inhibition, contributing to anti-tumour immunity. ERV expression and anti-ERV antibodies may serve as biomarkers for ICB response, while CXCL13 therapy offers a strategy to enhance immunotherapy efficacy. These findings advance understanding of TLS function and humoral immunity in lung cancer, opening avenues for improved treatment strategies

Conclusion

This study delineates a critical mechanistic link between tertiary lymphoid structures (TLS), B cell responses targeting endogenous retroviruses (ERVs), and improved outcomes of lung adenocarcinoma (LUAD) immunotherapy. In both murine models and human LUAD cohorts, ERV envelope glycoproteins emerge as dominant targets of tumour-reactive antibodies, with these humoral responses amplified by immune checkpoint blockade (ICB) and KRAS(G12C) inhibition. The anti-tumour activity of ERV-reactive antibodies, mediated via natural killer (NK) cell-dependent mechanisms, underscores their functional relevance in restricting tumour growth. Notably, effective ICB relies on CXCL13-dependent TLS formation, and therapeutic CXCL13 delivery synergizes with ICB to enhance anti-tumour immunity, offering a translatable strategy to boost treatment efficacy. In human LUAD, ERVK-7 (HERV-K(HML-2)) expression—driven by chromosomal amplification—correlates with anti-ERV antibody titres and predicts ICB response, highlighting ERV-related signatures as potential biomarkers for patient stratification. Collectively, these findings establish ERV-targeting B cell responses as a key mediator of TLS-associated immunotherapy success, providing a rationale for developing ERV-directed agents and CXCL13-based combinations to improve LUAD treatment outcomes.