The immune system mediates powerful effector mechanisms to protect against a diversity of pathogens and equally as important regulatory functions, to limit collateral damage of inflammation, prevent misguided immune responses to “self”, and promote tissue repair. Inadequate regulatory control can lead to a variety of inflammatory disorders including autoimmunity, metabolic syndrome, allergies, and progression of malignancies. Cancers evolve complex mechanisms to thwart immune eradication including coopting normal host regulatory processes. This is most evident in the analysis of tumor infiltrating lymphocytes (TILs), where a preponderance of immunosuppressive immune cells, such as regulatory T (Treg) cells are found. Treg cells express the X-chromosome linked transcription factor Foxp3 and play a crucial role in maintaining immune homeostasis by suppressing inflammatory responses in diverse biological settings. Treg cells in the tumor microenvironment promote tumor development and progression by dampening anti-tumor immune responses, directly supporting the survival of transformed cells through elaboration of growth factors, and interacting with accessory cells in tumors such as fibroblasts and endothelial cells. Current insights into the phenotype and function of tumor associated Treg cells have opened up opportunities for their selective targeting in cancer with the goal of alleviating their suppression of anti-tumor immune responses while maintaining overall immune homeostasis. Here, we review Treg cell biology in the context of the tumor microenvironment (TME), and the important role they play in cancer immunotherapy.

免疫系统介导强大的效应机制以保护免受多种病原体的侵害，并具有同样重要的调节功能，以限制炎症的附带损害，防止对“自我”的错误免疫反应，并促进组织修复。监管控制不足会导致多种炎症性疾病，包括自身免疫、代谢综合征、过敏和恶性肿瘤的进展。癌症进化出复杂的机制来阻止免疫根除，包括采用正常的宿主调节过程。这在肿瘤浸润淋巴细胞 (TIL) 的分析中最为明显，其中发现了免疫抑制性免疫细胞的优势，例如调节性 T (Treg) 细胞。Treg 细胞表达与 X 染色体相关的转录因子 Foxp3，并通过抑制不同生物环境中的炎症反应，在维持免疫稳态中发挥关键作用。肿瘤微环境中的 Treg 细胞通过抑制抗肿瘤免疫反应来促进肿瘤的发展和进展，通过精细化生长因子直接支持转化细胞的存活，并与肿瘤中的辅助细胞（如成纤维细胞和内皮细胞）相互作用。目前对肿瘤相关 Treg 细胞的表型和功能的见解为它们在癌症中的选择性靶向提供了机会，目的是减轻它们对抗肿瘤免疫反应的抑制，同时保持整体免疫稳态。这里，