Molecular and Cellular Immunology/Immune Regulation, DFG-Center for Regenerative Therapies Dresden (CRTD), Center for Molecular and Cellular Bioengineering (CMCB), Technische Universität Dresden, Dresden, Germany.
Osteoimmunology, DFG-Center for Regenerative Therapies Dresden (CRTD), Center for Molecular and Cellular Bioengineering (CMCB), Technische Universität Dresden, Dresden, Germany.
Front Immunol. 2018 Feb 2;9:125. doi: 10.3389/fimmu.2018.00125. eCollection 2018.
Under physiological conditions, CD4 regulatory T (Treg) cells expressing the transcription factor Foxp3 are generated in the thymus [thymus-derived Foxp3 Treg (tTregs) cells] and extrathymically at peripheral sites [peripherally induced Foxp3 Treg (pTreg) cell], and both developmental subsets play non-redundant roles in maintaining self-tolerance throughout life. In addition, a variety of experimental and modalities can extrathymically elicit a Foxp3 Treg cell phenotype in peripheral CD4Foxp3 T cells, which has attracted much interest as an approach toward cell-based therapy in clinical settings of undesired immune responses. A particularly notable example is the induction of Foxp3 expression and Treg cell activity (iTreg cells) in initially naive CD4Foxp3 T cells through T cell receptor (TCR) and IL-2R ligation, in the presence of exogenous TGF-β. Clinical application of Foxp3 iTreg cells has been hampered by the fact that TGF-β-driven Foxp3 induction is not sufficient to fully recapitulate the epigenetic and transcriptional signature of induced Foxp3 tTreg and pTreg cells, which includes the failure to imprint iTreg cells with stable Foxp3 expression. This hurdle can be potentially overcome by pharmacological interference with DNA methyltransferase activity and CpG methylation [e.g., by the cytosine nucleoside analog 5-aza-2'-deoxycytidine (5-aza-dC)] to stabilize TGF-β-induced Foxp3 expression and to promote a Foxp3 iTreg cell phenotype even in the absence of added TGF-β. However, the molecular mechanisms of 5-aza-dC-mediated Foxp3 iTreg cell generation have remained incompletely understood. Here, we show that in the absence of exogenously added TGF-β and IL-2, efficient 5-aza-dC-mediated Foxp3 iTreg cell generation from TCR-stimulated CD4Foxp3 T cells is critically dependent on TGF-βR and IL-2R signaling and that this process is driven by TGF-β and IL-2, which could either be FCS derived or produced by T cells on TCR stimulation. Overall, these findings contribute to our understanding of the molecular mechanisms underlying the process of Foxp3 induction and may provide a rational basis for generating phenotypically and functionally stable iTreg cells.
在生理条件下，CD4 调节性 T（Treg）细胞表达转录因子 Foxp3 在胸腺中产生[胸腺来源的 Foxp3 Treg（tTreg）细胞]和外周部位[外周诱导的 Foxp3 Treg（pTreg）细胞]，这两个发育亚群在维持终生的自身耐受中发挥非冗余作用。此外，各种实验和治疗方法可以在外周 CD4Foxp3 T 细胞中诱导产生 Foxp3 Treg 细胞表型，这作为临床治疗中治疗不需要的免疫反应的一种方法引起了广泛关注。一个特别值得注意的例子是通过 T 细胞受体（TCR）和 IL-2R 交联，在存在外源性 TGF-β的情况下，诱导初始幼稚 CD4Foxp3 T 细胞中 Foxp3 的表达和 Treg 细胞活性（iTreg 细胞）。Foxp3 iTreg 细胞的临床应用受到限制，因为 TGF-β 驱动的 Foxp3 诱导不足以完全重现诱导的 Foxp3 tTreg 和 pTreg 细胞的表观遗传和转录特征，包括不能将 iTreg 细胞印记为稳定的 Foxp3 表达。通过药物干扰 DNA 甲基转移酶活性和 CpG 甲基化[例如，通过胞嘧啶核苷类似物 5-氮杂-2'-脱氧胞苷（5-aza-dC）]可以潜在地克服这一障碍，以稳定 TGF-β诱导的 Foxp3 表达，并促进 Foxp3 iTreg 细胞表型的形成，即使在没有添加 TGF-β的情况下也是如此。然而，5-aza-dC 介导的 Foxp3 iTreg 细胞生成的分子机制仍不完全清楚。在这里，我们表明，在没有外加 TGF-β和 IL-2 的情况下，从 TCR 刺激的 CD4Foxp3 T 细胞中高效生成 5-aza-dC 介导的 Foxp3 iTreg 细胞，严重依赖于 TGF-βR 和 IL-2R 信号，并且该过程由 TGF-β和 IL-2 驱动，这些 TGF-β和 IL-2 可以来自 FCS 或 TCR 刺激的 T 细胞产生。总的来说，这些发现有助于我们理解 Foxp3 诱导过程的分子机制，并为生成表型和功能稳定的 iTreg 细胞提供合理的基础。
