Neutrophil depletion dampens inflammation and enhances CD8+ T cell effect on tumor control but undermines anti-PD-1 therapy.

Background: Lung cancer remains a leading cause of cancer-related mortality, with poor survival outcomes. Despite the widespread use of programmed cell death protein 1 (PD-1) blockade therapy, more than 70% of patients fail to benefit and might even develop adverse inflammatory responses. Clinical observations have shown that patients with high neutrophil levels experience worse outcomes following PD-1 blockade. However, the underlying mechanism remains elusive. This study aimed to investigate the impact of neutrophils on anti-PD-1 therapy in lung cancer. Methods: Clinical cohort analysis revealed that peripheral neutrophil levels correlated with survival and metastasis in non-small cell lung cancer (NSCLC) patients treated with PD-1 blockade. In this study, we established a subcutaneous Lewis lung carcinoma (LLC) mouse model, and depleted neutrophils by anti-Ly6G antibody with or without PD-1 blockade. Dynamic changes of peripheral immune cells (CD4+T cells, CD8+ T cells, macrophages, neutrophils, and myeloid-derived cells) in mice were examined by Flow cytometry during treatment, and cytokine levels were measured using Luminex multiplex assays. Results: Clinically, patients with high neutrophil counts exhibited significantly shorter progression-free survival (PFS) and overall survival (OS), and were more prone to distant organ metastases. In the mouse model, neutrophil depletion enhanced CD8+ T cell infiltration in tumor tissues and suppressed neutrophil-mediated interleukin (IL)-5, IL-6 and IL-17A inflammation, resulting in the inhibition of tumor growth. However, the combination of neutrophil depletion with PD-1 blockade paradoxically restored inflammatory cytokine production and increased myeloid-derived suppressor cell (MDSCs) infiltration, thereby compromising tumor suppression. Conclusions: Our observation shows that high neutrophil levels in cancer patients are associated with poorer prognosis and increased risk of distant metastasis. Depletion of neutrophils reshapes the tumor immune microenvironment, wherein excessive inflammatory cytokines drive resistance to PD-1 antibody therapy.