The study investigates the Foxp3-dependent program of regulatory T-cell (T_R) differentiation, focusing on the molecular and functional features that Foxp3 imparts to T_R precursor cells. Key findings include: 1. **Foxp3-independent Features**: Foxp3 expression is required for the survival and anergic state of T_R precursors, but the anergic phenotype and dependence on paracrine IL-2 are established before Foxp3 expression. 2. **T_R Cell Characteristics**: Foxp3 amplifies and fixes pre-established features of T_R cells, such as anergy and IL-2 dependence, through modifications in cell surface and signaling molecules. 3. **Lineage Stability**: Foxp3 solidifies T_R cell lineage stability by adapting them to signals required for their induction and maintenance, including repression of cyclic nucleotide phosphodiesterase 3B (PDE3B), which affects genes responsible for T_R cell homeostasis. 4. **T_R Suppressor Activity**: Foxp3 is essential for T_R cell suppressor activity, which is crucial for controlling autoimmune diseases. In males, Foxp3 deficiency leads to fatal early-onset systemic autoimmune disease. 5. **Gene Expression Profiling**: Global gene expression profiling revealed that Foxp3-dependent genes are enriched for cell surface and extracellular proteins, and cell-cycle-associated genes, indicating Foxp3's role in adapting developing T_H cells to environmental cues. 6. **PDE3B Repression**: PDE3B repression is a central component of Foxp3-dependent T_H cell maintenance, as its re-expression results in reduced biosynthetic processes, attenuation of proliferative fitness, and loss of some Foxp3-dependent gene expression. Overall, the study highlights how Foxp3 integrates and amplifies pre-existing features of T_R cells, ensuring their suppressive function and lineage stability.The study investigates the Foxp3-dependent program of regulatory T-cell (T_R) differentiation, focusing on the molecular and functional features that Foxp3 imparts to T_R precursor cells. Key findings include: 1. **Foxp3-independent Features**: Foxp3 expression is required for the survival and anergic state of T_R precursors, but the anergic phenotype and dependence on paracrine IL-2 are established before Foxp3 expression. 2. **T_R Cell Characteristics**: Foxp3 amplifies and fixes pre-established features of T_R cells, such as anergy and IL-2 dependence, through modifications in cell surface and signaling molecules. 3. **Lineage Stability**: Foxp3 solidifies T_R cell lineage stability by adapting them to signals required for their induction and maintenance, including repression of cyclic nucleotide phosphodiesterase 3B (PDE3B), which affects genes responsible for T_R cell homeostasis. 4. **T_R Suppressor Activity**: Foxp3 is essential for T_R cell suppressor activity, which is crucial for controlling autoimmune diseases. In males, Foxp3 deficiency leads to fatal early-onset systemic autoimmune disease. 5. **Gene Expression Profiling**: Global gene expression profiling revealed that Foxp3-dependent genes are enriched for cell surface and extracellular proteins, and cell-cycle-associated genes, indicating Foxp3's role in adapting developing T_H cells to environmental cues. 6. **PDE3B Repression**: PDE3B repression is a central component of Foxp3-dependent T_H cell maintenance, as its re-expression results in reduced biosynthetic processes, attenuation of proliferative fitness, and loss of some Foxp3-dependent gene expression. Overall, the study highlights how Foxp3 integrates and amplifies pre-existing features of T_R cells, ensuring their suppressive function and lineage stability.