Abstract Background: Interstitial lung disease (ILD) is a serious and unpredictable toxicity associated with antibody-drug conjugates (ADCs) such as trastuzumab deruxtecan (T-DXd). However, the cellular origins, age-specific susceptibility, and actionable biomarkers of ADC-induced ILD remain undefined. Here, we combined animal modeling, single-cell transcriptomics, functional assays, and clinical validation to elucidate the mechanistic basis of ILD susceptibility and identify circulating biomarkers predictive of ADC-induced ILD. Methods: Age-stratified mouse models (postnatal, adolescent, adult) were treated with T-DXd, followed by lung pathology evaluation and pulmonary function analysis. Single-cell RNA sequencing profiled the lung microenvironment across age groups. Functional assays assessed the maturity and phagocytic capacity of alveolar macrophages. Endothelial injury was evaluated by immunohistochemistry, TEM, and analysis of hyaluronidase expression. Plasma hyaluronic acid (HA) levels were quantified, correlated with ILD severity, and tested in a clinical validation cohort consisting of 20 ADC-induced ILD patients and non-ILD controls. Results: ILD susceptibility was strongly age-dependent, with only adult mice developing interstitial thickening, inflammatory infiltration, and impaired lung function, whereas postnatal and adolescent mice remained protected. Single-cell profiling revealed an adult-specific inflammatory ecosystem with expansion of ILD-associated immune populations absent in immature lungs. Postnatal mice were protected by immature alveolar macrophages with low phagocytic activity and reduced inflammatory signaling, contrasting with the mature, pro-inflammatory macrophages in adults that facilitated ILD onset. Endothelial cells emerged as the earliest and most vulnerable targets of T-DXd, showing the greatest transcriptional perturbation and induction of HYAL2/TMEM2, supported by protein-level and ultrastructural evidence of injury. HYAL2/TMEM2 activation drove excessive HA release into circulation, and plasma HA correlated with ILD severity across mouse models. Importantly, clinical validation in 10 ILD patients showed significantly elevated HA levels compared with 10 ADC-treated controls, with ROC analysis confirming HA as a predictive biomarker consistent with preclinical findings. Conclusions: Using age-stratified models and single-cell resolution, we identify endothelial injury and hyaluronidase upregulation as early, age-dependent drivers of ADC-induced ILD. We further show that circulating HA is a clinically validated biomarker capable of predicting ILD risk. This integrated preclinical-clinical study provides a new understanding of ILD susceptibility and establishes serum HA as a promising biomarker for early ILD detection and risk stratification in ADC therapy. Citation Format: Liming Jin, Ye Lu, Qing Wei, Peng Guo, Liu Yang, Dawei He. Age-dependent lung vulnerability identifies serum hyaluronic acid as a predictive biomarker of ADC-induced interstitial lung disease abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 6760.
Jin et al. (Fri,) studied this question.