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

PurposeBispecific T cell engagers (BiTEs) have recently been approved as a locoregional immunotherapy for malignant ascites. Although ascites is recognised as a lipid-rich, immunosuppressive environment, the mechanisms by which ascites, particularly its lipid components, suppress antitumour immunity remain poorly understood. Here, we investigated the impact of ascites-associated lipids on T cell immunosuppression and assessed whether lipid modulation could enhance the efficacy of BiTE therapy. Experimental DesignTranscriptomic profiling was performed on T cells treated with acellular ascites fluid to identify gene expression signatures associated with ascites exposure. Functional assays were conducted to evaluate the effects of ascites-associated lipids on T cell activation and cytotoxicity. In parallel, T cells were cocultured with ovarian cancer cells and EpCAM-targeting BiTEs in the presence or absence of a lipid-removal agent to assess how lipid depletion affected BiTE efficacy. ResultsT cells exposed to acellular ascites fluid exhibited an enriched transcriptomic 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. Lipid removal from ascites selectively rescued CD137 expression but not CD25, and restored BiTE-mediated cytotoxicity, suggesting a differential impact of lipid metabolism on TCR complex-dependent versus cytokine-driven activation pathways. ConclusionsThese findings identified lipid as a driver for T cell dysfunction in ovarian cancer ascites. Removal of ascites lipids restored T cell activation and augmented BiTE-mediated cytotoxicity, supporting a combination approach to potentiate BiTE therapy in malignant ascites. Translational RelevanceMalignant ascites represents a lipid-rich, immunosuppressive tumour microenvironment that is increasingly targeted by emerging T cell-based therapies. Although EpCAM-targeting bispecific T cell engagers (BiTEs) have recently been approved for malignant ascites and multiple similar BiTEs are in clinical development, the mechanisms by which ascites impairs T cell function and potentially limits therapeutic efficacy remain poorly understood. Using patient-derived ascites throughout, this study demonstrated that lipid metabolic reprogramming, rather than immune checkpoint upregulation, was a driver of T cell dysfunction. Importantly, we demonstrated that lipid removal from ascites rescued T cell function and restored BiTE efficacy, identifying a targetable metabolic barrier to immunotherapy. While EpCAM was used as a proof-of-concept target, we anticipate the metabolic insights and therapeutic strategies identified here will be equally applicable to other BiTE and CAR-T platforms, supporting a new combination approach for the treatment of malignant ascites.