LEF1 (lymphoid enhancer binding factor 1) is a transcription factor that functions primarily as a nuclear mediator of Wnt/β-catenin signaling, with roles spanning developmental, immunological, and oncological contexts. LEF1 transcriptionally activates target genes including fibronectin and hair growth-related factors like ALP and VCAN 1, while also repressing E-cadherin expression [UniProt]. In vascular development, LEF1 overexpression increases brain vasculature specificity in human blood vessel organoids 2. Within immune cells, LEF1 co-expression with TCF7 identifies multipotent T helper 2 progenitor cells capable of self-renewal and differentiation into diverse effector and regulatory populations in chr4 allergic disease 3. LEF1 drives central memory programs in natural killer T cells, enhancing antitumor activity and limiting exhaustion 4. In hepatoblastoma, divergent LEF1 expression patterns distinguish fetal versus embryonal tumor subtypes with different Wnt signaling dependencies 5, while in hepatocellular carcinoma, XBP1s transactivates LEF1 to enhance classical Wnt signaling 6. Clinically, LEF1 haploinsufficiency causes ectodermal dysplasia-17, characterized by oligodontia, hypotrichosis, and hypohidrosis, reflecting LEF1's essential role in ectoderm-derived structure development 7. In T-cell acute lymphoblastic leukemia, LEF1 positively regulates tumor suppressor genes like DHRS2, indicating context-dependent oncogenic versus tumor-suppressive roles 8.