Pathophysiological and Molecular Features of DXd ADC-Related Interstitial Pneumonitis in Cynomolgus Monkeys.

Interstitial lung disease (ILD) is an important adverse event related to deruxtecan-based antibody-drug conjugates (DXd ADCs). Understanding mechanisms and translationally relevant preclinical models remain incompletely defined. Here, we established a reproducible cynomolgus monkey model of DXd ADC-related ILD and performed the first integration of bronchoalveolar lavage fluid (BALF) extracellular vesicle (EV) proteomics with lung single-cell RNA sequencing (scRNA-seq). Weekly intravenous administration of a target-nonbinding human IgG1 DXd ADC to cynomolgus monkeys for 12 weeks consistently induced interstitial pneumonitis in all animals, with radiologic abnormalities emerging by Week 6 and progressing thereafter. Longitudinal SomaScan-based proteomic analyses revealed a pronounced and selective increase in differentially expressed proteins (DEPs) in BALF-derived EVs from Week 6 onward, exceeding changes observed in plasma or bulk BALF. Gene Ontology analysis showed enrichment of inflammatory, wound repair/regeneration, and extracellular matrix remodeling pathways within the BALF EV compartment. Integration of BALF EV proteomics with lung scRNA-seq demonstrated strong concordance between EV-associated signatures and transcriptional programs in alveolar epithelial, mesenchymal, and immune cell populations. Core injury-associated genes, including FN1, TIMP1, and COL3A1, were broadly upregulated across cell types, along with cell-type-restricted signatures including AT1 cells (BMP4, HMOX2), AT2 cells (CXCL2, SIRPA), fibroblasts (TNC, IGF1), endothelial cells (LCP1, CXCL12), neutrophils (ADAM17), and macrophages (CD84, HAVCR2, CXCL10). Together, this study defines a robust cynomolgus monkey model of DXd ADC-related ILD and identifies BALF EVs as a sensitive, lung-localized molecular readout and a promising translational source of mechanistic insights.