Efficient Therapeutic Function and Mechanisms of Human Polyclonal [CD8.sup.+][CD103.sup.+][Foxp3.sup.+] Regulatory T Cells on Collagen-Induced Arthritis in Mice

Objective. To investigate the potential therapeutic effect in a rheumatoid arthritis model of stable human [CD8.sup.+] regulatory T cells ([hCD8.sup.+]Tregs) induced by TGF-[beta]1 and rapamycin (RAPA) in vitro. Methods. Human [CD8.sup.+]T cells were isolated from human peripheral blood mononuclear cells and induced/expanded with TGF-[beta]1 and RAPA along with anti-CD3/28 beads and IL-2 in vitro and harvested as [hCD8.sup.+]Tregs. The phenotypes, suppressive characteristics, and stability of the [hCD8.sup.+]Tregs in an inflammatory microenvironment were examined in vitro. Human [CD8.sup.+]Tregs were transfused into an acollagen-induced arthritis (CIA) mouse model, and their therapeutic effects and related mechanisms were investigated. Results. Human [CD8.sup.+]Tregs induced by TGF-[beta]1/RAPA showed high expression of Foxp3 and CD103, exhibited vigorous suppression ability, and were stable in inflammatory microenvironments. In CIA mice, the clinical scores, levels of anti-collagen IgG antibody, and cartilage destruction were significantly reduced after adoptive transfusion with [hCD8.sup.+]Tregs. Moreover, [hCD8.sup.+]Treg treatment significantly reduced the number of Th17 cells, increased the number of [CD4.sup.+][IFN-[gamma].sup.+]T cells, and produced self [CD4.sup.+][Foxp3.sup.+]Tregs in vivo. In an in vitro cell coculture assay, [hCD8.sup.+]Tregs significantly inhibited mouse [CD4.sup.+] effector T cell proliferation, induced mouse [CD4.sup.+][Foxp3.sup.+]Treg and [CD4.sup.+][IFN-[gamma].sup.+]Th1 cell production, reduced Th17 cell development, and downregulated CD80/86 expression on mature DCs (mDCs). Conclusion. TGF-[beta]1/RAPA can induce [hCD8.sup.+]Tregs with stable suppressive characteristics, which could significantly alleviate the severity of CIA based on their stable suppressive ability in an inflammatory microenvironment and further influence the function of other downstream cell subtypes. Human [CD8.sup.+]Tregs might be a therapeutic strategy for rheumatoid arthritis.