Peripheral immune tolerance is a natural defense mechanism that helps the body control immune reactions outside the thymus. It prevents the immune system from attacking normal body cells and maintains immune balance. Tregs are synthesized in bone marrow and mature in the thymus. The main cells involved regulatory T cells (Tregs), which depend on the FOXP3 gene for their proper function. When this gene is disturbed then it cause immune disorders and uncontrolled inflammation can occur. Recent scientific progress, recognized by the 2025 Nobel Prize in Medicine, has explained how peripheral tolerance is controlled at the molecular level. Studies using Scurfy mouse model have shown that defects in FOXP3 lead to autoimmune diseases. Current research focuses on developing therapies that can strengthen or restore tolerance, which may help in treating autoimmune disorders and some types of cancer. This project aims to study the mechanism, role, and clinical applications of peripheral immune tolerance, highlighting its importance in drug development and disease management. The study also discusses new findings and future possibilities in immunotherapy based on tolerance regulation.