Uncovering Immune Evasion in EGFR-mutant and Treatment Resistant NSCLC: Insights from a Novel Mouse Model

Lung cancer remains one of the most prevalent and deadly malignancies globally, with non-small cell lung cancer (NSCLC) comprising approximately 84% of all cases. Despite advances in treatment, the overall 5-year survival rate for NSCLC remains at 15%. Among NSCLC cases, 15-20% are driven by activating mutations (such as L858R) in the epidermal growth factor receptor (EGFR), which are treated with EGFR tyrosine kinase inhibitors (TKIs). Although three generations of TKIs have been developed, a number of genetic mutations (T790M and C797S) have been shown to evolve that confer resistance in most patients. This has spurred interest in combination therapies, particularly with PD-1 and PD-L1 immune checkpoint inhibitors (ICIs), however, these have limited efficacy in patients with EGFR-mutant NSCLC. Therefore, understanding the immune landscape of these tumors is critical. We developed a mouse model of EGFR-mutant lung cancer using a transgenic mouse model expressing an EGFR carrying L858R activating, as well as T790M and C797S resistance mutations. We demonstrate the expression of this gene after intranasal delivery of an adenovirus carrying GFP-Cre (Ad-GFP-Cre) from a CAG promoter, along with expression of Td-tomato and Luciferase to allow for tumor tracking and visualization. In a time-course experiment, we monitored tumor progression and immune infiltration. By 4-6 weeks post-Ad-GFP-Cre injection, we observed consistent and palpable tumor growth, establishing a critical window for therapeutic intervention. At 2 weeks post-injection, lung tissues showed robust infiltration of CD8+ T cells, highlighting a strong initial immune response. However, levels of regulatory T cells (Tregs) increased significantly over time. This accumulation of Tregs coincided with tumor growth and suppression of cytotoxic T cell activity, suggesting a shift toward an immunosuppressive microenvironment. CD4+ T cells remained relatively constant, underscoring the specific role of Tregs in facilitating immune evasion. Systemic adaptive immunity against EGFR was detected in all tumor bearing mice, demonstrating the potency of local immune suppression in EGFR+ tumor evolution. To evaluate the therapeutic relevance of these findings, we treated mice with a PD-1 inhibitor starting at 4 weeks post-injection. Tumor response was minimal, mirroring clinical observations of limited efficacy for ICIs in EGFR-mutant NSCLC. The early wave of cytotoxic immune activity followed by Treg-mediated suppression offers insights into potential therapeutic targets. This will be a useful model to study the impact of different EGFR TKIs, as well as the combination of these agents with different immunotherapeutic modalities to identify strategies to optimize combination therapies. This work has the potential to inform innovative approaches for treating EGFR-mutant NSCLC and improving patient outcomes. Anchit Bhagat, Cong-Xiao Liu, Xiao Yang, Melissa Gajda, Jason McBane, Herbert K. Lyerly, Zachary C. Hartman. Uncovering immune evasion in EGFR-mutant and treatment resistant NSCLC: insights from a novel mouse model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2197.