Aberrant expression of immune checkpoints (ICs) in cancer creates an immunosuppressive microenvironment, which supports immune evasion of tumor cells. We have recently reported that epigenetic modifications are critical for ICs expression in the tumor microenvironment (TME) of primary breast cancer (PBC) and colorectal cancer (CRC). Herein, we investigated transcriptomic expression of ICs (PD-1, CTLA-4, LAG-3, TIM-3, TIGIT) and PD-L1 in peripheral blood of PBC and CRC patients, compared to healthy donors (HD). We found that expressions of TIM-3, TIGIT, PD-L1 were significantly upregulated, while LAG-3 expression was downregulated in peripheral blood of PBC and CRC patients. Demethylation enzymes TET2 and TET3 were also upregulated. In addition, promoter DNA methylation status of PD-1 was significantly hypermethylated, while PD-L1 was hypomethylated in PBC and CRC patients. Furthermore, TIGIT was significantly hypomethylated only in CRC patients. Remarkably, promoter methylation status of LAG-3, TIGIT and PD-L1 was in concordance with transcriptomic expression in CRC: the more the hypomethylation, the higher the expression. In comparison, we found that CTLA-4, TIM-3, TIGIT and PD-L1 in PBC, and CTLA-4 in CRC patients were significantly upregulated in peripheral blood, compared with tumor tissues of the same patients. However, demethylation status of all ICs was higher in TT, except for TIGIT in PBC, and CTLA-4 in CRC patients. These data indicate that the underlying mechanisms behind peripheral upregulation of PD-L1 and TIGIT in cancer patients could be due to aberrant promoter methylation profile. Moreover, demethylation inhibitors together with anti-PD-L1/anti-TIGIT could be a more efficient therapeutic strategy in cancer patients.

中文翻译：

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乳腺癌和结直肠癌患者外周血中免疫检查点的DNA甲基化。

免疫检查点（IC）在癌症中的异常表达产生了免疫抑制性微环境，可支持肿瘤细胞的免疫逃逸。最近，我们报道表观遗传修饰对于原发性乳腺癌（PBC）和结直肠癌（CRC）的肿瘤微环境（TME）中的IC表达至关重要。在这里，我们调查了与健康供体（HD）相比，PBC和CRC患者外周血中ICs（PD-1，CTLA-4，LAG-3，TIM-3，TIGIT）和PD-L1的转录组表达。我们发现，PBC和CRC患者外周血中TIM-3，TIGIT，PD-L1的表达显着上调，而LAG-3的表达下调。去甲基化酶TET2和TET3也被上调。此外，PD-1的启动子DNA甲基化状态显着超甲基化，而PD-L1在PBC和CRC患者中被低甲基化。此外，TIGIT仅在CRC患者中显着低甲基化。值得注意的是，LAG-3，TIGIT和PD-L1的启动子甲基化状态与CRC中的转录组表达一致：低甲基化程度越高，表达就越高。相比之下，我们发现与相同患者的肿瘤组织相比，CRC患者的PBC中的CTLA-4，TIM-3，TIIGIT和PD-L1以及CRC患者的CTLA-4明显上调。但是，TT中所有IC的去甲基状态均较高，PBC中的TIGIT和CRC患者中的CTLA-4除外。这些数据表明癌症患者中PD-L1和TIGIT周围上调的潜在机制可能是由于启动子甲基化异常引起的。此外，