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

Our plain-English summary of G6PD functions as a metabolic checkpoint to regulate granzyme B expression in tumor-specific cytotoxic T lymphocytes, by C. Lu, D. Yang, J.D. Klement, et al (Journal for Immunotherapy of Cancer, 2022).

The study

• Authors: C. Lu, D. Yang, J.D. Klement, Y.L. Colson, N.H. Oberlies, C.J. Pearce, A.H. Colby, M.W. Grinstaff, H.F. Ding, H. Shi, K. Liu
• Journal: Journal for Immunotherapy of Cancer
• Published: 2022;10(1)
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

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 Gzmb 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-1hi Gzmblo 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 G6pd, the gene that encodes the rate-limiting enzyme G6PD in the pentose phosphate pathway, to downregulate G6pd expression in tumor-specific CTLs. G6PD activation increases acetyl-coenzyme A (CoA) production to increase H3K9ac deposition at the Gzmb promoter and to increase Gzmb expression in tumor-specific CTLs converting them from a Gzmblo to a Gzmbhi 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, GZMB 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.

© Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

In plain English

This was a laboratory study, mostly in mouse cells and mice. It did not study asbestos. The authors asked how mesothelioma cells weaken tumor-killing immune cells called cytotoxic T lymphocytes (CTLs). In dishes, mouse mesothelioma cells raised CTL lactate production and the protein PD-1 and lowered granzyme B, a killing protein; the authors called this pattern CTL dysfunction. Blocking the lactate-making enzyme LDHA did not significantly change the levels of CTLs carrying PD-1 or granzyme B. The authors reported that tumor cells reduced CTL expression of the gene for an enzyme, G6PD. The G6PD-activating drug AG1 raised granzyme B in tumor-exposed CTLs and increased their tumor killing. In mice with tumors, AG1 slowed tumor growth. The authors analyzed gene-expression data from 58 human epithelioid mesothelioma samples. Higher granzyme B levels were linked to longer survival, but CTL levels in tumors were not. The authors concluded that G6PD may act as a 'metabolic checkpoint.' They noted that AG1 lowered total CTL numbers in tumors. They also noted that estimating immune cell types from bulk tumor data may have limited value in mesothelioma.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory study using cultured mesothelioma cells and tumor-specific T cells, mouse tumor experiments, and an analysis of existing human tumor gene-expression data (TCGA)
• Who was studied: Mouse mesothelioma AB1 cells and a mouse tumor-specific CTL line (2/20 CTLs); female BALB/c mice; human mesothelioma cell lines NCI-H226 (epithelioid) and MSTO-211H (biphasic); and 58 human epithelioid mesothelioma specimens from the TCGA database
• Exposure: No asbestos exposure was studied. The experimental treatments were the G6PD activator AG1, verticillin A (an inhibitor of the H3K9me3 histone methyltransferase), and an LDHA inhibitor, applied to tumor cells and CTLs in culture; AG1 was also given to tumor-bearing mice
• Main results:
  • Compared with CTLs activated by peptide antigen, CTLs cultured with mouse mesothelioma (AB1) cells had significantly lower granzyme B (Gzmb) expression and higher PD-1 expression; the authors described this as a PD-1-high, Gzmb-low dysfunction phenotype
  • Inhibiting LDHA, the key enzyme of aerobic glycolysis, had no significant effect on the levels of PD-1+ and Gzmb+ tumor-specific CTLs, though it slightly decreased CTL numbers
  • In tumor cell and CTL cocultures, verticillin A reduced H3K9me3 at the G6pd gene promoter and increased G6pd expression in the CTLs
  • In CTLs cultured with tumor cells, AG1 increased acetyl-CoA levels in a dose-dependent manner
  • In tumor-bearing mice, AG1 significantly decreased total tumor-infiltrating CD8+ T cells but significantly increased activated tumor-specific CTLs (Gzmb+ gp70 tetramer+ CD8+)
  • AG1 increased CTL killing of AB1 tumor cells in culture; AG1 also killed AB1 tumor cells directly
  • In mice with tumors under the skin, AG1 slowed tumor growth and significantly decreased tumor cell proliferation
  • Among 58 human epithelioid mesothelioma specimens, higher GZMB expression was significantly correlated with longer overall survival; CTL infiltration level was not correlated with survival (no survival figures are given in the text)
• The authors' conclusion: The authors concluded that G6PD may act as a 'metabolic checkpoint' in tumor-activated CTLs. In their view, activating G6PD is potentially an approach for epithelioid mesothelioma immunotherapy.
• Limitations the authors state:
  • The authors noted that G6PD activation lowered total CTL levels in tumors in mice, which is a challenge for use in human treatment
  • The authors noted that characterizing immune cell subsets from bulk genomic datasets may have limited value in malignant pleural mesothelioma, which varies within tumors and has few T cells

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, checkpoint inhibitors, Immunotherapy, Epithelioid, Lactate Dehydrogenase (LDH), Deposition.

Related studies

• H3K9me3 represses G6PD expression to suppress the pentose phosphate pathway and ROS production to promote human mesothelioma growth — C. Lu, D. Yang, et al. (2022)
• Effect of asbestos exposure on differentiation and function of cytotoxic T lymphocytes — N. Kumagai-Takei, Y. Nishimura, et al. (2020)
• The Suppressed Induction of Human Mature Cytotoxic T Lymphocytes Caused by Asbestos Is Not due to Interleukin-2 Insufficiency — N. Kumagai-Takei, Y. Nishimura, et al. (2016)
• Functional Alteration of Natural Killer Cells and Cytotoxic T Lymphocytes upon Asbestos Exposure and in Malignant Mesothelioma Patients — Y. Nishimura, N. Kumagai-Takei, et al. (2015)
• Microenvironment-Dependent Gradient of CTL Exhaustion in the AE17sOVA Murine Mesothelioma Tumor Model — J.L. Hope, P.I. Spantidea, et al. (2019)
• Targeting the inhibitory receptor CTLA-4 on T cells increased abscopal effects in murine mesothelioma model — L. Wu, M.O. Wu, et al. (2015)

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