Naturally occurring thymus-derived CD4+ CD25+ Foxp3+ regulatory T cells (nTregs) are critical regulators of immune tolerance. Foxp3+ Tregs can also be induced from CD25− na�ve CD4 T cells in vivo and ex vivo. This conversion process requires cytokines such as IL2 and TGFβ as well as suboptimal TCR stimulation, thus is regulated by the co-stimulatory status of antigen-presenting cells (i.e., dendritic cells). Although mature dendritic cells (DCs) are potent initiators of adaptive immune response, immature steady-state DCs contribute to immune tolerance. In this chapter, we summarize methods that use ex vivo splenic DCs to induce the conversion of na�ve CD4+ T cells to adaptive Foxp3+ CD4+ regulatory T cells (aTreg) in the presence of TGFβ.
