Neutrophils have long been treated as immunological foot soldiers: short-lived, rapidly deployed phagocytes whose job is to engulf bacteria and fungi. In cancer biology, however, they have acquired a far more sinister reputation. Tumors can co-opt neutrophils and reprogram them into suppressive cells that dampen antitumor T-cell responses, promote angiogenesis, and facilitate metastasis. Circulating neutrophils are conventionally divided by density into normal-density and high-density fractions, and high-density neutrophils constitute the predominant population in the peripheral blood. Previous work has linked an expansion of these cells to poor prognosis in lung cancer, but the field has lacked a granular understanding of whether high-density neutrophils are a uniform entity or a heterogeneous collection of functionally distinct subsets, and whether that diversity might track with clinical outcomes during checkpoint blockade.

The Korean team set out to interrogate that question directly. In an exploratory study, they collected peripheral blood samples from 17 patients with advanced lung cancer at two time points: immediately before the initiation of immune checkpoint inhibitor therapy, and again on Day 7 after treatment began. This paired sampling design is critical, because it allowed the investigators to distinguish between baseline biological features that might predispose a patient to respond or resist therapy, and dynamic changes triggered by the treatment itself. From each sample, the researchers isolated circulating neutrophils and used flow cytometry, a technique that tags cells with fluorescently labeled antibodies and reads their surface markers one cell at a time, to characterize subsets of high-density neutrophils with differing states of maturation and activation.

The first key finding concerned treatment response. At baseline, before any immunotherapy had been given, the proportion of immature high-density neutrophils differed across the response groups. Patients who went on to respond to checkpoint blockade had the lowest fractions of these immature cells, whereas non-responders carried a heavier burden of them. This is consistent with a growing body of evidence that immature neutrophils, sometimes described in the literature as granulocytic myeloid-derived suppressor-like cells, are enriched in settings of tumor-driven inflammation and can suppress T-cell activity, the very mechanism that checkpoint inhibitors rely upon to unleash antitumor immunity. In other words, the cellular backdrop against which immunotherapy is delivered may partly determine whether that therapy can succeed.

To go deeper than surface markers, the investigators performed RNA sequencing on purified high-density neutrophils, profiling the full complement of genes actively transcribed in these cells. The transcriptomic results mirrored the flow cytometric observations. Neutrophils from responders, which contained fewer immature cells, displayed gene-expression programs enriched for ribosomal and mitochondrial activity, hallmarks of cells engaged in active protein synthesis and energetic metabolism, but showed reduced expression of antigen-presentation pathways. That latter detail is intriguing: antigen presentation is the process by which immune cells display fragments of tumor or foreign proteins to T cells, and its baseline suppression in the neutrophils of responders may reflect a different inflammatory equilibrium in these patients rather than a simple measure of immune readiness. The finding underscores how little is still understood about the functional repertoire of neutrophils in human cancer and how transcriptional profiling can reveal dimensions invisible to conventional flow cytometry panels.

The second major strand of the study concerned toxicity. Immune-related adverse events are the flip side of checkpoint inhibitor efficacy: the same unleashing of immune activity that attacks tumors can also attack healthy tissues, producing inflammation of the lungs, colon, liver, endocrine organs, skin, or virtually any organ system. These events can be serious and occasionally fatal, and they frequently force interruption or discontinuation of otherwise effective therapy. Predicting who will develop them has proved as elusive as predicting response. The new study offers a candidate signal. Patients who went on to develop immune-related adverse events exhibited an increase in immature high-density neutrophils selectively in their post-treatment samples, that is, on Day 7 after starting therapy, rather than at baseline. The emergence of these cells during the earliest phase of treatment suggests a treatment-induced shift in myeloid cell dynamics that may foreshadow the loss of immune self-tolerance.

The transcriptomic data reinforced this interpretation. RNA sequencing revealed enhanced tumor necrosis factor, or TNF, signaling in high-density neutrophils, together with upregulation of inflammatory mediators including IRAK2 and ATF3, changes that were particularly pronounced in post-treatment samples. TNF is a master inflammatory cytokine capable of driving both antitumor immunity and tissue-damaging inflammation, while IRAK2 is an adaptor molecule central to signaling downstream of Toll-like receptors and other innate immune sensors, and ATF3 is a stress-responsive transcription factor induced by cellular alarm signals. The coordinated activation of this inflammatory circuitry within neutrophils shortly after checkpoint blockade points to a systemic, treatment-associated inflammatory response that varies from patient to patient, and the authors suggest that this variation may connect to the later development of immune-related toxicity.

The authors are careful to frame their conclusions as exploratory. With 17 patients, the study is small, and associations of this kind require validation in much larger, independent cohorts before they can inform clinical decision-making. The study was conducted in accordance with the Declaration of Helsinki, approved by the Institutional Review Board of Chungnam National University Hospital, and carried out with written informed consent from all participants. The work was funded by the National Research Foundation of Korea, with support from the Korean Ministry of Science and ICT and Chungnam National University, and the authors declared no conflicts of interest. Despite the modest sample size, the paired before-and-after design and the convergence of flow cytometric and transcriptomic evidence give the findings a coherence that invites follow-up.

The broader significance of the work lies in its reframing of neutrophils in cancer immunotherapy. For years, the field’s predictive biomarker efforts have concentrated on T cells: tumor mutational burden, PD-L1 expression on tumor cells, T-cell clonality, and gene-expression signatures of cytotoxic lymphocytes. Neutrophils, despite their abundance and their increasingly recognized role in shaping the immune microenvironment, have been largely absent from the biomarker conversation, partly because they are fragile cells that are difficult to handle in the laboratory and historically undervalued as mere terminal effectors of innate immunity. This study adds to a growing movement that treats neutrophil heterogeneity as a genuine axis of cancer immunology, one that could carry independent prognostic and predictive information.

If the findings hold up in larger studies, the clinical implications could be substantial. A simple blood test measuring immature high-density neutrophil fractions before and during the first week of immunotherapy could, in principle, offer clinicians an early readout on two fronts simultaneously: a baseline signal of likely treatment resistance, and an early warning of incipient immune-related adverse events. Such a test would not dictate therapy on its own, but it could help stratify patients for closer monitoring, adjunctive interventions, or alternative treatment strategies. The researchers themselves emphasize that the phenotypic and transcriptomic features they identified support further investigation of high-density neutrophil heterogeneity in larger cohorts. For now, the message is one of cautious optimism: the answer to one of immunotherapy’s hardest questions may already be flowing through a routine blood draw, waiting to be read.

Subject of Research: High-density neutrophil phenotypes associated with immunotherapy response and toxicity in lung cancer

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

Article References: Distinct high-density neutrophil phenotypes are associated with treatment resistance and immune-related adverse events in lung cancer immunotherapy. (n.d.). https://doi.org/10.1007/s00262-026-04568-9

Image Credits: AI Generated

DOI: 10.1007/s00262-026-04568-9

Keywords: high-density neutrophils, lung cancer, immune checkpoint inhibitors, immunotherapy, treatment resistance, immune-related adverse events, flow cytometry, RNA sequencing, TNF signaling, biomarkers, myeloid cells, Cancer Immunology Immunotherapy