FOXP3 (forkhead box P3) is a transcription factor that serves as the master regulator of regulatory T cells (Tregs), which are essential for immune homeostasis and self-tolerance 1. FOXP3 functions as both a transcriptional activator and repressor, controlling the suppressive capacity of Tregs by activating genes like CTLA4 and TNFRSF18 while repressing pro-inflammatory cytokines including IL-2 and interferon-gamma 1. The protein operates through interactions with various transcription factors and chrX-modifying enzymes to coordinate immune suppression programs. Mutations in FOXP3 cause IPEX syndrome (Immunodeficiency, Polyendocrinopathy, Enteropathy, X-linked), a fatal disorder characterized by immune dysregulation, autoimmune enteropathy, and endocrinopathy 23. In cancer contexts, FOXP3 expression is complex and context-dependent, being found in both tumor-infiltrating Tregs that suppress anti-tumor immunity and in some tumor cells themselves, where its role varies across different cancer types 456. However, in humans, FOXP3 expression alone is insufficient to definitively identify regulatory T cells, as activated conventional T cells can transiently express FOXP3 without acquiring regulatory function 7.