Regulatory T Cells in Tumor Microenvironment: Therapeutic Approaches and Clinical Implications

ABSTRACT Regulatory T cells (Tregs), previously referred to as suppressor T cells, represent a distinct subset of CD4+ T cells that are uniquely specialized for immune suppression. They are characterized by the constitutive expression of the transcription factor FoxP3 in their nuclei, along with CD25 (the IL‐2 receptor α‐chain) and CTLA‐4 on their cell surface. Tregs not only restrict natural killer cell‐mediated cytotoxicity but also inhibit the proliferation of CD4+ and CD8+ T‐cells and suppress interferon‐γ secretion by immune cells, ultimately impairing an effective antitumor immune response. Treg cells are widely recognized as a significant barrier to the effectiveness of tumor immunotherapy in clinical settings. Extensive research has consistently shown that Treg cells play a pivotal role in facilitating tumor initiation and progression. Conversely, the depletion of Treg cells has been linked to a marked delay in tumor growth and development.