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

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, disrupted cellular metabolism, and increased expression of immune-related genes and proteins. In immune cells, partial inhibition of 3-MST promoted T cell activation, as evidenced by increased CD69 expression on CD3+, CD4+, and CD8+ 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.