Regulatory T cells (Tregs), a population of T cells, are essential for maintaining immune balance and their dysfunction could lead to critical immunological disorders. Tregs are classified as either thymus-derived natural Tregs (nTregs) or adaptive Tregs that are triggered in the periphery in the presence of certain cytokines such as IL-10, and transforming growth factor-β (TGF- β). Treg cells are recognized by expression of FOXP3, a forkhead/winged helix transcription factor 3, and high expression levels of CD25 (the α-chain of the IL-2 receptor). CD8+ T cells represent a major constituent of adaptive immunity. Although CD8+ Tregs with a suppressive function have been identified, the regulatory properties of these cells are still not fully characterized. CD8+CD25+ Treg cells can suppress CD4+CD25− T cells in a manner dependent on their membrane-bound TGFβ and CTLA-4. Moreover, they can secrete certain immunosuppressive cytokines such as TGF-β and IL10.