Department of Medical Biology, Faculty of Medicine, Gaziantep University, Turkey.
J Immunother. 2019 Jan;42(1):11-22. doi: 10.1097/CJI.0000000000000247.
Regulatory T cells (Treg cells), a subgroup of CD4 lymphocytes, play a crucial role in serving as an immune suppressor and in maintaining peripheral tolerance. As the accumulation of Treg cells in the tumor microenvironment is significantly associated with a decreased survival time of patients, they are considered as an important therapeutic target in the immunotherapy of human cancers. These cells are either derived from the thymus, which are called (CD4CD25CD127) natural Treg cells (nTreg cells), or they are generated from CD4CD25 naive T cells by transforming growth factor-beta 1 and interleukin 2 (IL-2) in the periphery, which are called induced Treg cells (iTreg cells). Although iTreg cells are unstable, nTreg cells stably express forkhead box P3 (FOXP3) protein. Moreover, nTreg cells can be classified as memory (CD45RA) and naive (CD45RA) Treg cells, and this classification is based on the expression of CD45RA. FOXP3, which is a master regulator transcription factor, is essential for the functions of Treg cells, and it is mainly controlled by epigenetic mechanisms. The cyclooxygenase 2 (COX2)/prostaglandin E2 (PGE2) pathway is also reported to contribute to the regulatory functions of tumor-infiltrating Treg cells. As a new approach, we investigated whether S-adenosylmethionine (SAM), a substrate of DNA methyltransferase, attenuates the immune-suppressive capacity of the naive subtype of nTreg cells (CD4CD25CD127CD45RA). Moreover, we examined the effects of PGE2/COX2 pathway blockers on the suppressive capacity of Treg cells. We found that SAM diminished the suppression competency of Treg cells by decreasing the FOXP3 mRNA and protein levels in a dose-dependent manner. SAM increased the DNA methylation of FOXP3 at the first intron site. In addition, SAM decreased the mRNA and protein levels of the IL-10 cytokine, which has suppressive roles in the immune system. Moreover, mRNA levels of interferon gamma (IFNG) were found to be increased. COX2 inhibition and blockage of PGE2 receptors also reduced the protein and mRNA levels of IL-10, but they did not exhibit any significant effect on Treg cells' suppression in the coculture system. Our results show that SAM might be considered and investigated as a promising agent for immunotherapy in the future.
调节性 T 细胞（Treg 细胞）是 CD4 淋巴细胞的一个亚群，作为免疫抑制剂在维持外周耐受方面发挥着关键作用。由于肿瘤微环境中 Treg 细胞的积累与患者生存时间的缩短显著相关，因此它们被认为是人类癌症免疫治疗的一个重要治疗靶点。这些细胞要么来自胸腺，称为（CD4CD25CD127）天然 Treg 细胞（nTreg 细胞），要么在周围环境中由转化生长因子-β 1 和白细胞介素 2（IL-2）从 CD4CD25 幼稚 T 细胞中产生，称为诱导性 Treg 细胞（iTreg 细胞）。虽然 iTreg 细胞不稳定，但 nTreg 细胞稳定表达叉头框 P3（FOXP3）蛋白。此外，nTreg 细胞可分为记忆（CD45RA）和幼稚（CD45RA）Treg 细胞，这种分类是基于 CD45RA 的表达。FOXP3 是一种主要的调控转录因子，对 Treg 细胞的功能至关重要，主要受表观遗传机制的控制。环氧化酶 2（COX2）/前列腺素 E2（PGE2）途径也被报道有助于肿瘤浸润性 Treg 细胞的调节功能。作为一种新方法，我们研究了 S-腺苷甲硫氨酸（SAM），一种 DNA 甲基转移酶的底物，是否能减弱幼稚型 nTreg 细胞（CD4CD25CD127CD45RA）的免疫抑制能力。此外，我们还研究了 PGE2/COX2 途径抑制剂对 Treg 细胞抑制能力的影响。结果发现，SAM 以剂量依赖的方式降低 FOXP3 mRNA 和蛋白水平，从而减弱 Treg 细胞的抑制能力。SAM 增加了 FOXP3 内含子 1 位点的 DNA 甲基化。此外，SAM 降低了 IL-10 细胞因子的 mRNA 和蛋白水平，IL-10 在免疫系统中具有抑制作用。此外，IFNG 的 mRNA 水平也升高。COX2 抑制和 PGE2 受体阻断也降低了 IL-10 的蛋白和 mRNA 水平，但它们在共培养系统中对 Treg 细胞的抑制作用没有显著影响。我们的结果表明，SAM 可能被认为是未来免疫治疗的一种有前途的药物。
