Regulation of lipid accumulation-induced ROS in myeloid-derived suppressor cells via targeting fatty-acid transport protein 2 enhanced anti-PD-L1 tumor immunotherapy

Abstract

Despite the remarkable success and efficacy of immune checkpoint blockade (ICB) therapy against the PD-1/PD-L1 axis, it induces sustained responses in a sizeable minority of cancer patients due to the activation of immunosuppressive factors such as myeloid-derived suppressor cells (MDSCs). Inhibiting the immunosuppressive function of MDSCs is critical for successful cancer ICB therapy. Interestingly, lipid metabolism is a crucial factor in modulating MDSCs function. Fatty acid transport protein 2 (FATP2) conferred the function of PMN-MDSCs in cancer via the upregulation of arachidonic acid metabolism. However, whether regulating lipid accumulation in MDSCs by targeting FATP2 could block MDSCs reactive oxygen species (ROS) production and enhance PD-L1 blockade-mediated tumor immunotherapy remains unexplored. Here we report that FATP2 regulated lipid accumulation, ROS, and immunosuppressive function of MDSCs in tumor-bearing mice. Tumor cells-derived granulocyte macrophage-colony stimulating factor (GM-CSF) induced FATP2 expression in MDSCs by activation of STAT3 signaling pathway. Pharmaceutical blockade of FATP2 expression in MDSCs by lipofermata decreased lipid accumulation, reduced ROS, blocked immunosuppressive activity, and consequently inhibited tumor growth. More importantly, lipofermata inhibition of FATP2 in MDSCs enhanced anti-PD-L1 tumor immunotherapy via the upregulation of CD107a and reduced PD-L1 expression on tumor-infiltrating CD8+ T-cells. Furthermore, the combination therapy blocked MDSCs suppressive role on T-cells thereby enhanced T-cells ability for the production of IFN-{gamma}. These findings indicate that FATP2 plays a key role in modulating lipid-induced ROS in MDSCs and targeting FATP2 in MDSCs provides a novel therapeutic approach to enhance anti-PD-L1 cancer immunotherapy. Research highlightsO_LIFATP2 inhibition in MDSCs blocked ROS-mediated immunosuppressive function and promoted MDSCs differentiation to immune-stimulatory phenotype. C_LIO_LIGM-CSF mediated FATP2 expression via activation of STAT3 signaling leading to lipid accumulation-induced ROS in MDSCs. C_LIO_LIFATP2 inhibition enhanced anti-PD-L1 tumor immunotherapy by reducing MDSCs immunosuppressive activity in blocking T-cells ability to produce IFN-{gamma}. C_LIO_LICombination of anti-PD-L1 antibody and FATP2 inhibitor decreased MDSCs accumulation and PD-L1 surface expression in the spleens of LLC-bearing mice. C_LIO_LICombined treatment of FATP2 inhibitor and PD-L1 blockade-mediated tumor immunotherapy enhanced tumor-infiltrating CD8+ T cells activation via increased CD107a and reduced PD-L1 surface expression. C_LI