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Background TIGIT is an immune checkpoint under investigation as therapeutic target. Understanding the regulation of TIGIT on an epigenetic level might support the development of companion biomarkers. Methods We correlated  TIGIT  DNA methylation of single CpG sites with gene expression, signatures of immune infiltrates and interferon-γ, and survival in melanoma. We further analyzed methylation levels in immune cell subsets, melanocyte and melanoma cell lines.  TIGIT  expression patterns within components of the melanoma microenvironment were analyzed by single cell sequencing. We used quantitative methylation-specific PCR, flow cytometry, and immunohistochemistry for correlations between expression and methylation and to assess the effect of pharmacological demethylation of melanoma cells treated with 5‐aza‐2‐deoxycytidine (decitabine). Finally, we investigated the association of patients’ survival with  TIGIT  mRNA and methylation. Results Depending on the sequence context of the analyzed CpG site, we found a cell type-specific  TIGIT  gene locus methylation pattern and significant correlations of  TIGIT  methylation with mRNA expression, an interferon γ signature, and distinct immune cell infiltrates, including TIGIT +  lymphocytes. We detected a melanoma cell-intrinsic TIGIT protein expression. Pharmacological demethylation of the A375 melanoma cell line led to a constitutive  TIGIT  expression. Low promoter flank methylation and high mRNA expression was associated with patients’ prognosis and predicted progression-free survival in patients treated with anti-PD-1 immunotherapy. A high TIGIT +  lymphocyte score was associated with better progression-free survival under anti-PD-1 immunotherapy. Conclusions Our data demonstrate an epigenetic regulation of  TIGIT  expression via DNA methylation within the melanoma microenvironment.  TIGIT  DNA methylation and expression may serve as predictive biomarkers in the context of immunotherapies in melanoma.

clinical epigenetics

DNA methylation regulates TIGIT expression within the melanoma microenvironment, is prognostic for overall survival, and predicts progression-free survival in patients treated with anti-PD-1 immunotherapy