GM-CSF Promotes Neutrophil PD-L1 Expression Through the VEGFR-2/STAT6/CSF2 Signaling Axis in Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) remains a highly aggressive malignancy with limited responsiveness to anti-PD-1 immunotherapy. Recent neoadjuvant studies combining VEGFR-2 inhibition (VEGFR2i) with anti-PD-1 (aPD-1) have yielded markedly improved pathological responses, suggesting a VEGFR-2-dependent immunoregulatory mechanism. Here, we identify a PD-L1-expressing CD66b⁺ neutrophil-enriched tumor-associated population as a critical immunosuppressive population enriched in VEGFR-2-high OSCC tumors and associated with increased metastatic propensity and inferior patient outcomes. Using multiplex immunohistochemistry, scRNA-seq, and flow cytometry, we demonstrate that VEGFR-2-overexpressing OSCC cells drive robust GM-CSF secretion, which in turn induces PD-L1 upregulation in neutrophils. Mechanistically, VEGFR-2 activation promotes STAT6 phosphorylation and nuclear translocation, enabling direct transcriptional activation of CSF2. GM-CSF subsequently activates STAT5 and mTOR/S6K signaling in neutrophils, thereby enhancing PD-L1 protein synthesis. Functionally, these PD-L1⁺ TANs suppress CD8⁺ T-cell proliferation, augment T-cell exhaustion, and diminish cytotoxicity. Importantly, VEGFR-2 inhibition or GM-CSF neutralization restored CD8⁺ T-cell function and improved responsiveness to anti-PD-1 therapy in vivo, whereas exogenous GM-CSF impaired VEGFR2i/aPD-1 efficacy. Collectively, our findings reveal a previously unrecognized VEGFR-2/STAT6/CSF2 axis that licenses neutrophil-mediated immune suppression in OSCC. These data provide mechanistic rationale and preclinical support for targeting the VEGFR-2/GM-CSF-neutrophil axis to improve the efficacy of PD-1 blockade in OSCC.