SCD1 inhibition enhances the effector functions of CD8⁺ T cells via ACAT1-dependent reduction of esterified cholesterol

We previously reported that the inhibition of stearoyl-CoA desaturase 1 (SCD1) enhances the antitumor function of CD8⁺ T cells indirectly via restoring production of DC recruiting chemokines by cancer cells and subsequent induction of antitumor CD8⁺ T cells. In this study, we investigated the molecular mechanism of direct enhancing effects of SCD1 inhibitors on CD8⁺ T cells. In vitro treatment of CD8⁺ T cells with SCD1 inhibitors enhanced IFN-γ production and cytotoxic activity of T cells along with decreased oleic acid and esterified cholesterol, which is generated by cholesterol esterase, acetyl-CoA acetyltransferase 1 (ACAT1), in CD8⁺ T cells. The addition of oleic acid or cholesteryl oleate reversed the enhanced functions of CD8⁺ T cells treated with SCD1 inhibitors. Systemic administration of SCD1 inhibitor to MCA205 tumor-bearing mice enhanced IFN-γ production of tumor-infiltrating CD8⁺ T cells, in which oleic acid and esterified cholesterol, but not cholesterol, were decreased. These results indicated that SCD1 suppressed effector functions of CD8⁺ T cells through the increased esterified cholesterol in an ACAT1-dependent manner, and SCD1 inhibition enhanced T cell activity directly through decreased esterified cholesterol. Finally, SCD1 inhibitors or ACAT1 inhibitors synergistically enhanced the antitumor effects of anti-PD-1 antibody therapy or CAR-T cell therapy in mouse tumor models. Therefore, the SCD1–ACAT1 axis is regulating effector functions of CD8⁺ T cells, and SCD1 inhibitors, and ACAT1 inhibitors are attractive drugs for cancer immunotherapy.