Vitamin C (VitC) presents excellent anti-tumor effect for long time. Recently, high dose VitC achieved by intravenous administration manifests superior anti-tumor effect. However, the functions and detailed mechanisms of high dose VitC's role in cancer immunity are not fully understood. This study investigates the effect of high dose VitC on PD-L1 expression in triple negative breast cancer (TNBC) and the potential mechanism. Results showed VitC inhibited PD-L1 expression in breast cancer cell lines and enhanced anti-tumor effects of T cells. Furthermore, we found VitC inhibited PD-L1 transcription through ROS-pSTAT3 signal pathways. Consistent with in vitro results, in vivo study showed VitC suppressed tumor growth in immunocompetent mice and enhanced CD8+ T cells infiltration and function in tumor microenvironment. Our findings identify the effects of high dose VitC on PD-L1 expression and provide a rationale for the use of high dose VitC as immunomodulator for cancer therapy.
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