Defective Interferon Gamma Production by Tumor-Specific CD8 + T Cells Is Associated With 5'Methylcytosine-Guanine Hypermethylation of Interferon Gamma Promoter.

Interferon gamma (IFN gamma) supports effector responses of CD8(+) cytotoxic T lymphocytes (CTLs) and is a surrogate marker for detection of antigen-specific T cells. Here, we show that tumor-specific CTL clones have impaired IFN gamma expression and production upon activation. Assessment of the relationship between IFN gamma production and the 5 ' methylcytosine-guanine (CpG) dinucleotide methylation of the IFN gamma promoter using bisulfite treatment has shown that IFN gamma(-) CTL clones accumulates CpG hypermethylation within the promoter at key transcription factor binding sites (-186 and -54), known to be vital for transcription. We confirmed these findings using ex vivo isolated and short-term expanded bulk tumor-specific CTL lines from four cancer patients and demonstrated that IFN gamma methylation inversely correlates with transcription, protein level, and cytotoxicity. Altogether, we propose that a sizeable portion of human tumor-specific CTLs are deficient in IFN gamma response, contributed by CpG hypermethylation of the IFN gamma promoter. Our findings have important implications for immunotherapy strategies and for methods to detect human antigen-specific T cells.