SPTLC2-driven sphingolipid reprogramming of neutrophils impairs anti-tumour immunity and drives liver cancer progression.

Liver cancer exhibits limited and heterogeneous responses to immune checkpoint blockade, underscoring the need to elucidate tumour microenvironmental mechanisms sustaining immune dysfunction. Here, we integrated single-cell transcriptomic annotation with BayesPrism deconvolution across multiple bulk cohorts and combined these analyses with in vivo liver cancer models, functional assays, and mechanistic investigations to define tumour-associated neutrophil (TAN) programmes linked to clinical outcome. We identified a neutrophil subset characterized by elevated sphingolipid metabolism as the predominant poor-prognosis signature, with SPTLC2 serving as the key molecular marker. High SPTLC2 expression defining this sphingolipid metabolism-high neutrophil population correlated significantly with advanced disease stage, inferior overall survival, and increased tumour infiltration. Tumour cell co-culture induced SPTLC2 upregulation and enhanced sphingolipid metabolic activity in neutrophils. Functional assays verified that myriocin, an SPTLC2 inhibitor, suppressed the proliferation and metastasis of Liver cancer cells and remodelled the antitumour immune function of neutrophils. Myriocin attenuated neutrophil sphingolipid metabolism and restored ROS production and neutrophil extracellular trap (NETosis) formation, revealing a critical regulatory role for sphingolipid metabolism in neutrophil-mediated innate immunity, as corroborated by single-cell analyses showing impaired innate immune function in sphingolipid metabolism-high neutrophils. Mechanistically, we uncovered an SPTLC2-dependent sphingolipid-lipid raft checkpoint that remodels plasma membrane microdomains to constrain neutrophil anti-tumour effector functions. Specifically, myriocin restored NOX2-dependent ROS generation by reducing ceramide accumulation in lipid rafts, thereby facilitating p47