Distinct high-density neutrophil phenotypes are associated with treatment resistance and immune-related adverse events in lung cancer immunotherapy

High-density neutrophils (HDNs) constitute the predominant circulating neutrophil population and have been linked to poor prognosis in lung cancer. However, little is known about the phenotypic diversity of HDNs and its association with response and toxicity during immune checkpoint inhibitors (ICIs) therapy. In this exploratory study, peripheral blood samples were collected from 17 patients with advanced lung cancer before treatment initiation and on Day 7 after ICI therapy. Flow cytometric analyses were performed to characterize circulating HDN subsets. RNA sequencing of purified HDNs was conducted to investigate transcriptional programs associated with treatment outcomes and immune-related adverse events (irAEs). Baseline immature HDN proportions differed across response groups, being lowest in responders, accompanied by transcriptomic profiles enriched for ribosomal and mitochondrial activity but reduced antigen-presentation pathways. Patients who developed irAEs exhibited an increase in immature HDNs selectively in post-treatment samples. Transcriptomic analyses further revealed enhanced TNF signaling and upregulation of inflammatory mediators, including IRAK2 and ATF3, particularly in post-treatment samples, suggesting treatment-associated inflammatory changes in HDNs. Distinct phenotypic and transcriptomic features of circulating HDNs were associated with treatment resistance and immune-related adverse events in lung cancer immunotherapy. These exploratory findings support further investigation of HDN heterogeneity in larger cohorts.