de Duve Institute, Université catholique de Louvain, Brussels, Belgium.
Int J Cancer. 2012 Apr 15;130(8):1960-6. doi: 10.1002/ijc.26198. Epub 2011 Aug 2.
The human suppressive T cells that stably express transcription factor FOXP3, or regulatory T cells (Tregs), are thought to suppress antitumor immune responses. The most specific marker for human Tregs is the demethylation of CpG dinucleotides located in the first intron of FOXP3 (FOXP3i1). FOXP3i1 is completely methylated in other hematopoietic cells, including nonsuppressive T cells that transiently express FOXP3 after activation. Previously, we and others reported estimations of the frequency of Tregs in the blood of melanoma patients using a FOXP3i1 methylation-specific qPCR assay. Here, we attempted to quantify Tregs inside tumor samples using this assay. However, we found demethylated FOXP3i1 sequences in the melanoma cells themselves. This demethylation was not associated with substantial FOXP3 mRNA or protein expression, even though the demethylation extended to the promoter and terminal regions of the gene in some melanoma cells. Our results imply that analyzing Treg frequencies by quantification of demethylated FOXP3i1 will require that tumor-infiltrating T cells be separated from melanoma cells.
稳定表达转录因子 FOXP3 的人抑制性 T 细胞，或调节性 T 细胞（Tregs），被认为可以抑制抗肿瘤免疫反应。人类 Tregs 最特异的标志物是位于 FOXP3 第一内含子中的 CpG 二核苷酸的去甲基化（FOXP3i1）。在其他造血细胞中，包括在激活后短暂表达 FOXP3 的非抑制性 T 细胞中，FOXP3i1 完全甲基化。以前，我们和其他人使用 FOXP3i1 甲基化特异性 qPCR 检测法报告了黑色素瘤患者血液中 Tregs 的频率估计值。在这里，我们试图使用该检测法来定量肿瘤样本中的 Tregs。然而，我们在黑色素瘤细胞本身中发现了去甲基化的 FOXP3i1 序列。这种去甲基化与大量的 FOXP3 mRNA 或蛋白质表达无关，尽管在一些黑色素瘤细胞中，去甲基化延伸到了基因的启动子和末端区域。我们的结果表明，通过定量分析去甲基化的 FOXP3i1 来分析 Treg 频率，需要将肿瘤浸润性 T 细胞与黑色素瘤细胞分离。
