Regulation of ROS in myeloid-derived suppressor cells through targeting fatty acid transport protein 2 enhanced anti-PD-L1 tumor immunotherapy.

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 MDSC's suppressive role on T- cells thereby enhanced T-cell's ability for the production of IFN-γ. These findings indicate that FATP2 plays a key role in modulating lipid accumulation-induced ROS in MDSCs and targeting FATP2 in MDSCs provides a novel therapeutic approach to enhance anti-PD-L1 cancer immunotherapy.

Lipidomics data showing the effect of lipofermata on myeloid-derived suppressor cells in the spleens of tumor-bearing mice.

The regulation of myeloid-derived suppressor cells (MDSCs) function is key for effective tumor immunotherapy. Recent lipidomics data revealed that MDSCs accumulate lipid species thereby promote their immunosuppressive activity on T cells. However, genetic manipulation of fatty acid transport protein 2 in mice reduced lipid accumulation in polymorphonuclear MDSCs. Herein we present for the first time lipidome of splenic MDSCs from B16F10 melanoma-bearing mice treated with FATP2 inhibitor - lipofermata compared to the control group. B16F10 were subcutaneously injected into the left flank of wild-type C57BL/6 mice, either lipofermata or vehicle was administered to the mice every day starting from day 7 post-tumor injection for 2 weeks. CD11b+Gr1+ cells from the spleen referred to as MDSCs were sorted on a flow cytometer machine for lipid extraction. Lipid was extracted using methyl­tert­butyl ether as previously described with slight modification, followed by liquid chromatography-mass spectrophotometry lipid profiling using a Q-Exactive instrument coupled with HPLC. The raw scans were identified and quantified with LipidSearch while raw data for various lipid species available on the Mendeley Data repository [1]. The lipid profiles reveal change in lipid species following blockade of FATP2 expression in MDSCs compared to the control. These data were collected in connection to a co-submitted paper [2].