CD8⁺CD45RA⁺CCR7⁺FOXP3⁺ T cells with immunosuppressive properties: A novel subset of inducible human regulatory T cells

CD8 T cells stimulated with a suboptimal dose of anti-CD3 Abs (100 pg/ml) in the presence of IL-15 retain a naive phenotype with expression of CD45RA, CD28, CD27, and CCR7 but acquire new functions and differentiate into immunosuppressive T cells. CD8⁺ CCR7⁺ regulatory T cells (Tregs) express FOXP3 and prevent CD4 T cells from responding to TCR stimulation and entering the cell cycle. Naive CD4 T cells are more susceptible to inhibition than memory cells. The suppressive activity of CD8 ⁺CCR7⁺ Tregs is not mediated by IL-10, TGF-β, CTLA-4, CCL4, or adenosine and relies on interference with very early steps of the TCR signaling cascade. Specifically, CD8⁺CCR7⁺ Tregs prevent TCR-induced phosphorylation of ZAP70 and dampen the rise of intracellular calcium in CD4 T cells. The inducibility of CD8⁺CCR7⁺ Tregs is correlated with the age of the individual with PBLs of donors older than 60 y yielding low numbers of FOXP3^low CD8 Tregs. Loss of CD8⁺CCR7⁺ Tregs in the elderly host may be of relevance in the aging immune system as immunosenescence is associated with a state of chronic smoldering inflammation.