Lipid-rich ascites reprograms the T cell lipid metabolic transcriptome to drive dysfunction

Malignant ascites is a lipid-rich, immunosuppressive environment that has recently emerged as a target for locoregional bispecific T-cell engager (BiTE) therapy. However, the mechanisms by which ascites, particularly its lipid components, suppress antitumour immunity and limit therapeutic efficacy remain poorly understood. Here, we investigated the impact of ascites lipids on T-cell immunosuppression and assessed whether lipid modulation could enhance the efficacy of BiTE therapy. Transcriptomic profiling of T cells exposed to acellular ascites fluid revealed an enriched signature associated with cholesterol efflux and incomplete fatty acid oxidation, which are metabolic features often found in exhausted T cells. These alterations converged on a metabolically imbalanced state linked to impaired plasma membrane signalling. Meanwhile, anti-CD3/CD28-stimulated T cells showed marked lipid accumulation in ascites, which was attenuated by lipid depletion. Functionally, lipid removal was associated with enhanced TCR-associated signalling, as demonstrated by increased ZAP70 phosphorylation, and restored CD137 expression while leaving CD25 unchanged. To determine whether ascites lipids also affected BiTE efficacy, T cells were cocultured with ovarian cancer cells and an EpCAM-targeting BiTE in untreated or lipid-depleted ascites. Ascites suppressed BiTE-mediated T-cell activation and abolished tumour cell killing, whereas lipid depletion contributed to the restoration of T-cell activation, IFN-γ production and BiTE-mediated cytotoxicity. Together, these findings suggest that lipids contribute to T-cell dysfunction in ovarian cancer ascites and demonstrate that lipid depletion is associated with restored antitumour T-cell activity. Targeting this metabolic barrier may therefore provide a combination strategy to potentiate BiTE therapy in malignant ascites.