Epigenetic Regulation of Immune Checkpoints and T Cell Exhaustion Markers in Tumor-Infiltrating T Cells of Colorectal Cancer Patients

Abstract

Aim: To elucidate the epigenetic alterations behind the upregulation of immune checkpoints and T cell exhaustion markers in colorectal cancer (CRC) patients. Materials&methods: mRNA expressions of different immune checkpoint/exhaustion markers were analyzed by quantitative real-time reverse transcriptase PCR and epigenetic investigations were performed using bisulfite sequencing and chromatin immunoprecipitation quantitative PCR. Results: mRNA expressions of PD-1, TIM-3, CTLA-4, PD-L1 and TOX2 were significantly upregulated in CD4⁺ and CD8⁺ tumor-infiltrating lymphocytes and bulk CRC tumor tissues. Histone 3 lysine 9 trimethylation was downregulated and histone 3 lysine 4 trimethylation was upregulated in PD-L1 and TOX2 promoters in tumor tissues, suggesting that PD-L1 and TOX2 upregulation in CRC tumors could be mediated by activating histone 3 lysine 4 trimethylation. Conclusion: Epigenetic modifications in promoters of immune checkpoint and T cell exhaustion genes could induce their upregulation, and potentially implicate the use of epigenetic modifiers to enhance antitumor immunity in CRC patients.

Keywords::

• colorectal cancer
• DNA methylation
• epigenetics
• histone modifications
• immune checkpoints

Supplementary data

To view the supplementary data that accompany this paper please visit the journal website at: www.tandfonline.com/doi/suppl/10.2217/epi-2020-0267

Acknowledgments

We would like to thank the staff of the Genomics Core at Qatar Biomedical Research Institute for performing Sanger sequencing. We extend our gratitude to Ms Eleonor Dela Cruz Belita and Mr Mark Edison Baladad from Hamad Medical Corporation for assisting in collecting patient samples, and all patients for donating their samples.

Financial&competing interests disclosure

This work was supported by a start-up grant (VR04) for Professor Eyad Elkord from Qatar Biomedical Research Institute, Qatar Foundation. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Ethical conduct of research

The authors state that they have obtained appropriate institutional review board approval or have followed the principles outlined in the Declaration of Helsinki for all human or animal experimental investigations. In addition, for investigations involving human subjects, informed consent has been obtained from the participants involved.

Additional information

Funding

This work was supported by a start-up grant (VR04) for Professor Eyad Elkord from Qatar Biomedical Research Institute, Qatar Foundation. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. No writing assistance was utilized in the production of this manuscript.