Immune Aging Within the Tumor Microenvironment Predicts Survival in Lung Adenocarcinoma

Background/Objectives: Immune aging has been associated with survival outcomes in patients with lung adenocarcinoma (LUAD), but its relevance within the tumor microenvironment (TME) remains unclear. Methods: Clinical, RNA-sequencing, and somatic mutation data from the TCGA LUAD cohort were analyzed. Immune aging score within the TME was quantified using a predefined blood-driven 121-gene immune aging signature (IAS-121), and patients were categorized into the lowest versus the highest IAS-121 tertiles. Immune cell composition in the TME was inferred using xCell. Overall survival (OS) was evaluated using Kaplan-Meier analysis, Cox proportional hazards models adjusted for age, sex, tumor stage, smoking status, and EGFR mutation status, and restricted cubic spline analysis to examine the dose-response relationship between IAS-121 and mortality risk. Sensitivity analyses comparing the highest versus lowest quartiles or higher than median versus lower than median of IAS-121 were performed. Two independent LUAD cohorts (GSE68465 and GSE50081) were employed for validation. Results: A total of 518 patients with LUAD from the TCGA cohort were analyzed. Restricted cubic spline analysis showed a linear association between IAS-121 and OS. Patients in the highest IAS-121 tertile showed significantly better survival than those in the lowest tertile in both the TCGA cohort (p < 0.001) and the external validation cohorts (p = 0.003). In multivariable-adjusted Cox models, the lowest IAS-121 tertile was associated with worse survival in TCGA (adjusted HR 1.87, 95% CI 1.20-2.92) and in the pooled external cohorts (adjusted HR 1.57, 95% CI 1.02-2.43). Subgroup analyses showed generally consistent associations across clinical strata. Tumors with higher IAS-121 exhibited lower CD8⁺ and CD4⁺ naïve T-cell enrichment but higher neutrophil infiltration. Conclusions: Immune aging within TME is associated with poorer survival in LUAD. Given this study is hypothesis-generating, further investigations integrating tissue- and blood-based measures of immune aging are warranted to clarify its clinical and biological implications.