Inhibition of 3-mercaptopyruvate sulfurtransferase enhances CD8⁺ T-cell antitumor immunity

Abstract Hydrogen sulfide (H₂S) is a redox-active gasotransmitter implicated in tumor progression and immune regulation. The enzyme 3-mercaptopyruvate sulfurtransferase (3-MST) is a key contributor to endogenous H₂S and polysulfide production, but its role in tumor–immune interactions remains poorly defined. Here, we show that 3-MST is the most abundantly expressed H₂S-synthesizing enzyme in human renal cell carcinoma cells (RCC) and that high 3-MST expression correlates with reduced patient survival. Pharmacological inhibition of 3-MST lowered intracellular H₂S levels in Renca renal carcinoma cells, suppressed proliferation, induced apoptosis, and increased surface expression of the immunogenic markers CD70, CD86, and PD-L1. In immune cells, partial inhibition of 3-MST promoted T cell activation, as evidenced by increased CD69 expression on both CD4⁺ helper and CD8⁺ cytotoxic T cells. In contrast, complete inhibition of 3-MST, achieved by high concentrations of the inhibitor, modestly reduced CD8⁺ T cell proliferation. Functionally, 3-MST inhibition potentiated antigen-specific CD8⁺ T cell-mediated killing of tumor cells, an effect further amplified by PD-L1 blockade. These results establish 3-MST as a redox-sensitive metabolic driver of tumor growth and immune evasion in RCC and demonstrate that its inhibition can boost antitumor immune responses, offering a potential avenue for combination immunotherapy.