G6PD functions as a metabolic checkpoint to regulate granzyme B expression in tumor-specific cytotoxic T lymphocytes.

BACKGROUND

Granzyme B is a key effector of cytotoxic T lymphocytes (CTLs), and its expression level positively correlates with the response of patients with mesothelioma to immune checkpoint inhibitor immunotherapy. Whether metabolic pathways regulate expression in CTLs is incompletely understood.

METHODS

A tumor-specific CTL and tumor coculture model and a tumor-bearing mouse model were used to determine the role of glucose-6-phosphate dehydrogenase (G6PD) in CTL function and tumor immune evasion. A link between granzyme B expression and patient survival was analyzed in human patients with epithelioid mesothelioma.

RESULTS

Mesothelioma cells alone are sufficient to activate tumor-specific CTLs and to enhance aerobic glycolysis to induce a PD-1 Gzmb CTL phenotype. However, inhibition of lactate dehydrogenase A, the key enzyme of the aerobic glycolysis pathway, has no significant effect on tumor-induced CTL activation. Tumor cells induce H3K9me3 deposition at the promoter of , the gene that encodes the rate-limiting enzyme G6PD in the pentose phosphate pathway, to downregulate expression in tumor-specific CTLs. G6PD activation increases acetyl-coenzyme A (CoA) production to increase H3K9ac deposition at the promoter and to increase expression in tumor-specific CTLs converting them from a Gzmb to a Gzmb phenotype, thus increasing CTL tumor lytic activity. Activation of G6PD increases Gzmb tumor-specific CTLs and suppresses tumor growth in tumor-bearing mice. Consistent with these findings, expression level was found to correlate with increased survival in patients with epithelioid mesothelioma.

CONCLUSION

G6PD is a metabolic checkpoint in tumor-activated CTLs. The H3K9me3/G6PD/acetyl-CoA/H3K9ac/Gzmb pathway is particularly important in CTL activation and immune evasion in epithelioid mesothelioma.